Ericsson UMTS Feature Guidelines
FSC Performance Engineering
Document Initiated
Revision Number
Revision Date
July 17, 2007
0.6
December 5, 2007
© Copyright 2007 T-Mobile USA, Inc. All rights reserved.
Confidential and proprietary information of T-Mobile USA, Inc. Not for distribution outside T-Mobile.
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Document Information
The information in these materials is confidential and proprietary to T-Mobile USA, Inc. These materials are authorized for the use of TMobile USA service providers and their employees and agents, solely for the purposes of the agreement under which these materials are
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Acknowledgements
The following individuals are responsible for contribution to the specifications, design and
implementations represented in the various revisions:
Alejandro Aguirre
Changbo Wen
Dinesh Arcotkumar
Pankaj Chopra
Ryan Kolln
Shubhankar Saha
Sireesha Panchagnula
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Revision Code
The revision number will reflect the modifications by following the format Rev. x, y, where
X is the first digit, incremented for changes of substance, i.e. technical/procedural issues.
Y is the second digit, incremented when editorial only changes have been incorporated.
All draft/preliminary versions are 0.n; the first final version is Revision 1.0.
Revision History
Rev.
Date
0.1
07/17/2007
T-Mobile USA, INC. Confidential
Author
Information
Alejandro Aguirre and
Sireesha Panchagnula
Initial document for Ericsson UMTS features covering
Neighbor List, Soft Handover, 3G to 3G cell Reselection and
Location and Routing Area.
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0.2
8/07/07
Sireesha Panchagnula
0.21
0.3
8/09/07
8/28/07
0.4
9/26/07
Sireesha Panchagnula
Ryan
Kolln,
Sireesha
Panchagnula
Alejandro Aguirre and
Sireesha Panchagnula
0.5
11/26/07
Sireesha Panchagnula
0.6
12/5/07
Alejandro Aguirre, Dinesh
Arcotkumar and Sireesha
Panchagnula
T-Mobile USA, INC. Confidential
Updates made to original content in IRAT Guideline and
transferred to this document for Ericsson 3G.
Same content as V 0.2. V0.21 has tracking disabled.
Power Control Section added to the document.
Added sections Call setup, Random Access Procedure and
Paging. Additional content to section 10.7. based on
feedback form south region.
Added sections Capacity Management Overview, Admission
Control and Congestion Control
Added content on UE States, PS data services and Channel
switching
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Table of Contents
1.
2.
1.1.
1.2.
2.1.
2.1.1.
2.1.2.
2.1.3.
2.1.4.
2.2.
3.
3.1.
3.2.
3.3.
3.4.
4.
4.1.
4.1.1.
4.1.2.
4.1.3.
4.1.4.
4.2.
4.3.
4.3.1.
4.3.2.
4.3.3.
4.4.
4.5.
4.5.1.
4.5.2.
4.5.3.
4.6.
4.7.
4.7.1.
4.7.2.
4.7.3.
4.7.4.
4.7.5.
5.
5.1.
5.1.1.
5.1.2.
5.1.3.
5.1.4.
5.1.5.
5.2.
5.2.1.
5.2.2.
5.2.3.
5.2.4.
5.2.5.
Introduction ....................................................................................................................... 9
Purpose & Scope ...........................................................................................................................9
Definitions for this Document .........................................................................................................9
Neighbor List .................................................................................................................... 12
Monitored Set Creation ................................................................................................................ 12
Neighbor Cell Priority................................................................................................................... 13
IAF Monitored Subset Creation..................................................................................................... 13
Field example of Monitored set creation ....................................................................................... 15
IEF and GSM Monitored Subset Creation ...................................................................................... 15
Neighbor List Creation and Priority ............................................................................................... 15
3G to 2G Neighbor List Generation .................................................................................. 18
UMTS to GSM 1:1 overlay with matched azimuths ......................................................................... 18
UMTS to GSM 1:1 overlay with mis-matched azimuths .................................................................. 19
UMTS site without overlay ........................................................................................................... 19
New GSM site added to the 2G Network ....................................................................................... 20
Idle Mode Process, Algorithms and Parameters .............................................................. 21
PLMN Selection ........................................................................................................................... 22
PLMN Selection at UE switch on ................................................................................................... 22
PLMN selection in Automatic Mode ............................................................................................... 22
PLMN Selection in Manual Mode ................................................................................................... 24
PLMN Selection while Roaming .................................................................................................... 24
Cell Selection Procedure in UTRAN state ....................................................................................... 24
Cell Reselection Parameters from 3G to 3G ................................................................................... 26
Measurements ............................................................................................................................ 26
Eligibility ..................................................................................................................................... 26
Ranking ...................................................................................................................................... 27
Recommended Values for 3G to 3G Selection and Reselection parameters ...................................... 28
Cell Reselection Parameters from 3G to 2G ................................................................................... 29
Measurements ............................................................................................................................ 29
Eligibility ..................................................................................................................................... 30
Ranking ...................................................................................................................................... 30
Recommended Values for 3G to 2G Reselection parameters .......................................................... 32
Location and Routing Area Registration and Updating ................................................................... 33
Terminology ............................................................................................................................... 33
Normal LA and RA Updating ........................................................................................................ 34
Periodic LA and RA Updating ....................................................................................................... 34
IMSI Attach/Detach ..................................................................................................................... 35
Recommended Values for LA and RA update parameters ............................................................... 36
Call Setup Procedure ........................................................................................................ 37
Circuit Switched Call Setup .......................................................................................................... 37
RRC Setup Phase, CS Voice ......................................................................................................... 37
Pre-RAB Phase, CS Voice ............................................................................................................. 38
RAB Setup Phase, CS Voice ......................................................................................................... 41
Counters Related to CS Voice Call Setup ....................................................................................... 43
Circuit Switched Voice Accessibility KPI ......................................................................................... 47
Packet Switched Call Setup .......................................................................................................... 48
RRC Setup Phase, PS Setup ......................................................................................................... 48
Pre-RAB Phase, PS Setup............................................................................................................. 49
RAB Setup Phase, PS Setup ......................................................................................................... 51
Counters Related to PS Setup ...................................................................................................... 53
Packet Switched Accessibility KPI ................................................................................................. 55
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6.
Random Access Procedure ............................................................................................... 56
6.1.
Random Access Overview ............................................................................................................ 56
6.1.1.
Random Access Channels ............................................................................................................ 56
6.1.2.
Open Loop Power Control ............................................................................................................ 57
6.1.3.
Physical Layer Random Access Procedure ..................................................................................... 58
6.1.4.
MAC Monitoring and Control of Random Access Transmissions ....................................................... 60
6.1.5.
RRC Control or Random Access Transmissions .............................................................................. 61
6.1.6.
Interaction of RRC, MAC and Physical Layer Random Access Procedures ........................................ 62
6.1.7.
RACH Sub-Channels .................................................................................................................... 63
6.1.8.
Access Class and Access Service Class .......................................................................................... 64
6.2.
Ericsson Specific Parameter for Random Access ............................................................................ 66
6.3.
Random Access Parameter Optimization and Troubleshooting ........................................................ 66
7.
Paging Procedures............................................................................................................ 69
7.1.
Paging Types .............................................................................................................................. 70
7.1.1.
Paging Type 1............................................................................................................................. 70
7.1.2.
Paging Type 2............................................................................................................................. 71
7.2.
Paging Channels ......................................................................................................................... 72
7.2.1.
Paging Indication Channel ........................................................................................................... 72
7.3.
DRX Procedure ........................................................................................................................... 73
7.4.
Paging Repetition ........................................................................................................................ 75
7.5.
Ericsson Specific Parameter and Counters for Paging .................................................................... 75
7.5.1.
Ericsson Paging Control Parameters ............................................................................................. 75
7.5.2.
Ericsson Paging Counters ............................................................................................................ 75
8.
Soft/Softer Handover Feature .......................................................................................... 78
8.1.
Soft/Softer Handover Procedure and Parameters .......................................................................... 78
8.1.1.
Event 1a Evaluation .................................................................................................................... 80
8.1.2.
Event 1b Evaluation .................................................................................................................... 81
8.1.3.
Event 1c Evaluation ..................................................................................................................... 82
8.1.4.
Event 1d Evaluation .................................................................................................................... 83
8.1.5.
Event Triggered Periodical Measurement Reporting ....................................................................... 85
8.1.6.
Buffering and Queuing ................................................................................................................ 85
8.1.7.
Soft/Softer Handover Execution ................................................................................................... 85
8.1.8.
Soft/Soft Handover Signaling ....................................................................................................... 86
8.1.9.
ReleaseConnOffset setting ........................................................................................................... 88
8.2.
Recommended Values for Soft/Softer handover parameters .......................................................... 88
9.
Compressed Mode Operation ........................................................................................... 90
9.1.
Halving the Spreading factor (SF/2) Method ................................................................................. 90
9.2.
Higher Layered Scheduling (HLS) Method: .................................................................................... 91
9.3.
Compressed Mode Pattern ........................................................................................................... 91
9.4.
Limitations on number of mobiles in Compressed Mode ................................................................. 92
10.
3G to 2G Handover and Cell Change Procedure and Parameters .................................... 93
10.1.
T-Mobile Strategy for IRAT .......................................................................................................... 93
10.2.
Feature Activation ....................................................................................................................... 93
10.3.
IRAT Interaction with Inter-Frequency Handover .......................................................................... 94
10.4.
3G to 2G IRAT Handover/Cell Change Procedure .......................................................................... 94
10.4.1. Event based Connection quality monitoring .................................................................................. 94
10.4.2. Event based GSM measurements reporting ................................................................................... 98
10.4.3. Identification of target GSM cell for Handover/Cell Change .......................................................... 100
10.4.4. 3G to 2G IRAT Handover/Cell Change Execution ......................................................................... 100
10.5.
Scenarios for 3G to 2G IRAT Handover / Cell Change .................................................................. 105
10.5.1. Edge Thresholds ....................................................................................................................... 106
10.5.2. Core Thresholds ........................................................................................................................ 106
10.6.
Parameter recommendations for IRAT Scenarios ......................................................................... 106
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10.6.1. Edge Thresholds ....................................................................................................................... 107
10.6.2. Core Thresholds ........................................................................................................................ 107
10.7.
3G to 2G IRAT Handover/Cell Change Optimization Strategy ....................................................... 108
11.
Emergency Call treatment .............................................................................................. 110
12.
2G to 3G IRAT Cell Reselection ...................................................................................... 112
12.1.
Ericsson 2G to Ericsson 3G Reselection ....................................................................................... 112
12.1.1. Measurements on WCDMA neighbors in idle mode ...................................................................... 113
12.1.2. Cell Reselection to UMTS for mobiles that don’t support RSCP evaluation ..................................... 113
12.1.3. Cell Reselection to UMTS for mobiles that support RSCP evaluation.............................................. 115
12.2.
Nokia 2G to Ericsson 3G Reselection .......................................................................................... 115
12.2.1. UTRAN Neighbor Definitions and System Information .................................................................. 116
12.2.2. Measurements on WCDMA neighbors in idle mode ...................................................................... 116
12.2.3. Cell Reselection to UMTS for mobiles that don’t support RSCP evaluation ..................................... 117
12.2.4. Cell Reselection to UMTS for mobiles that support RSCP evaluation .............................................. 118
12.3.
Nortel 2G to Ericsson 3G Reselection .......................................................................................... 119
12.3.1. Measurements on WCDMA neighbors in idle mode ...................................................................... 120
12.3.2. Cell Reselection to UMTS for mobiles that don’t support RSCP evaluation ..................................... 120
12.3.3. Cell Reselection to UMTS for mobiles that support RSCP evaluation .............................................. 121
13.
Capacity Management Overview .................................................................................... 123
13.1.
Overview of UMTS Resources .................................................................................................... 124
13.1.1. DL Power ................................................................................................................................. 124
13.1.2. Received Total Wideband Power ................................................................................................ 125
13.1.3. OVSF Codes .............................................................................................................................. 125
13.1.4. RBS Channel Elements .............................................................................................................. 126
13.2.
Common Resource Utilization..................................................................................................... 127
13.2.1. Overhead and Common Channels .............................................................................................. 127
13.2.2. Maximum Downlink Transmission Power .................................................................................... 129
13.2.3. HSDPA Resources ..................................................................................................................... 129
13.3.
Dedicated Monitor Resource Handling ........................................................................................ 130
13.3.1. Downlink Channelization Code Monitor ....................................................................................... 130
13.3.2. Histogram Monitor .................................................................................................................... 130
13.3.3. Downlink Transmitted Carrier Power .......................................................................................... 131
13.3.4. ASE Monitor .............................................................................................................................. 132
13.3.5. RTWP Monitor .......................................................................................................................... 133
13.3.6. RBS Hardware Monitor .............................................................................................................. 133
13.4.
Services Class and Setup Type ................................................................................................... 133
13.4.1. Service Class ............................................................................................................................ 133
13.4.2. Setup Type ............................................................................................................................... 134
14.
Admission Control .......................................................................................................... 135
14.1.
Enhanced Soft Congestion ......................................................................................................... 135
14.2.
Downlink OVSF Code Usage Admission ....................................................................................... 136
14.3.
Histogram Admission ................................................................................................................. 137
14.3.1. Downlink OVSF Code Admission ................................................................................................. 137
14.3.2. Uplink OVSF Code Admission ..................................................................................................... 138
14.3.3. HSDPA Admission ..................................................................................................................... 138
14.3.4. Compressed Mode Admission ..................................................................................................... 139
14.4.
Transmitted Downlink Carrier Power Admission........................................................................... 139
14.5.
Air Interface Speech Equivalents Admission ................................................................................ 141
14.5.1. Uplink ASE Admission ................................................................................................................ 141
14.5.2. Downlink ASE Admission ........................................................................................................... 143
14.6.
Node B Hardware Admission ...................................................................................................... 145
14.6.1. Uplink Channel Element Admission ............................................................................................. 145
14.6.2. Downlink Channel Element Admission ........................................................................................ 147
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14.7.
Admission Control Parameters ................................................................................................... 149
14.8.
Counters Related to Admission Control ....................................................................................... 149
15.
Congestion Control ......................................................................................................... 153
15.1.
Downlink Cell Congestion .......................................................................................................... 153
15.2.
Uplink Cell Congestion ............................................................................................................... 155
15.3.
Resolution of Congestion ........................................................................................................... 156
15.4.
Congestion Control Parameters .................................................................................................. 158
15.5.
Counters Related to Congestion Control ..................................................................................... 158
16.
Power Control ................................................................................................................. 164
16.1.
Importance of Power Control ..................................................................................................... 164
16.2.
Overall Power Control Procedure ................................................................................................ 164
16.3.
Power Control of downlink common channels ............................................................................. 165
16.4.
Open Loop Power Control (Power Control of uplink common channels) ........................................ 166
16.5.
Power Control of Dedicated channels ......................................................................................... 168
16.5.1. Initial Downlink Power Setting ................................................................................................... 169
16.5.2. Downlink Power Limits .............................................................................................................. 171
16.5.3. Initial Uplink Power Setting ........................................................................................................ 173
16.5.4. Initial Uplink SIR Target Setting ................................................................................................. 174
16.5.5. Uplink Outer Loop Power Control ............................................................................................... 175
16.5.6. Downlink Outer Loop Power Control ........................................................................................... 177
16.5.7. Downlink Inner Loop Power Control ........................................................................................... 177
16.5.8. Uplink Inner Loop Power Control ................................................................................................ 177
16.6.
Power Control during Soft Handover .......................................................................................... 178
16.6.1. Uplink power control during SHO ............................................................................................... 178
16.6.2. Downlink power control during Soft Handover ............................................................................ 179
16.7.
Power Control during Compressed Mode .................................................................................... 182
16.7.1. Uplink Power Control in Compressed Mode ................................................................................. 182
16.7.2. Downlink Power Control in Compressed Mode ............................................................................. 182
16.8.
Power Control Scenarios ............................................................................................................ 183
16.8.1. Power Control steps for Radio Link Setup Procedure ................................................................... 183
16.8.2. Power Control steps for RAB Establishment ................................................................................ 183
16.8.3. Power Control steps for Soft Handover ....................................................................................... 184
16.9.
Example of Power Control Procedure .......................................................................................... 184
17.
UE States ........................................................................................................................ 186
17.1.
Cell_DCH .................................................................................................................................. 186
17.1.1. CELL_DCH to CELL_FACH state .................................................................................................. 187
17.2.
Cell_FACH ................................................................................................................................ 187
17.2.1. CELL_FACH to CELL_DCH .......................................................................................................... 187
17.2.2. CELL_FACH to URA_PCH ........................................................................................................... 188
17.3.
URA_PCH ................................................................................................................................. 188
17.3.1. URA_PCH to CELL_FACH ........................................................................................................... 189
17.3.2. URA_PCH to IDLE ..................................................................................................................... 189
18.
Introduction to R99 PS data services............................................................................. 190
18.1.
Radio bearer QoS ...................................................................................................................... 190
18.2.
Differentiation between traffic classes ........................................................................................ 190
18.3.
Radio Resource Management for packet data services ................................................................. 191
18.4.
Active Queue Management feature ............................................................................................ 191
18.5.
Channel Switching Feature ........................................................................................................ 192
18.6.
Channel Switching Triggers ....................................................................................................... 192
18.7.
Triggers for Dedicated to Dedicated channel switching ................................................................ 193
18.7.1. Throughput-triggered Upswitch ................................................................................................. 193
18.7.2. Throughput-triggered Downswitch ............................................................................................. 193
18.7.3. Coverage-triggered downswitch ................................................................................................. 193
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18.8.
Multi RAB State Transitions ........................................................................................................ 194
18.8.1. Speech + Interactive ................................................................................................................. 194
18.8.2. 2xInteractive ............................................................................................................................ 194
18.8.3. Speech + 2xInteractive ............................................................................................................. 194
19.
Channel Switching Algorithms ....................................................................................... 195
19.1.
Common to Dedicated Evaluation ............................................................................................... 195
19.2.
Dedicated to Common Evaluation ............................................................................................... 196
19.3.
Common to URA Evaluation ....................................................................................................... 197
19.4.
URA to Idle Evaluation .............................................................................................................. 197
19.5.
Coverage Triggered Downswitch Evaluation ................................................................................ 197
19.6.
Dedicated to Dedicated Upswitch Evaluation ............................................................................... 198
19.7.
Throughput Based Dedicated to Dedicated Downswitch Evaluation .............................................. 200
19.8.
Multi RAB Downswitch Evaluation .............................................................................................. 200
19.9.
Multi RAB Upswitch Evaluation ................................................................................................... 200
19.10.
Channel Switching Parameter Optimization ................................................................................. 201
20.
Appendix A: Weighting Factor Analysis for Soft Handover Algorithm ........................... 202
20.1.
Event 1a evaluation................................................................................................................... 202
20.2.
Event 1b evaluation .................................................................................................................. 203
20.3.
Tradeoff due to weighting factor ................................................................................................ 203
21.
Appendix B: Monitored Set Creation Field Example ....................................................... 205
21.1.
Description ............................................................................................................................... 205
21.2.
Execution ................................................................................................................................. 205
21.3.
Neighbor Lists ........................................................................................................................... 205
21.4.
Results ..................................................................................................................................... 205
22.
Appendix C: Parameter Recommendations for 3G to 2G Reselection ........................... 209
23.
Appendix D: Parameter Recommendations for 3G to 2G Handover/Cell Change ......... 210
24.
Appendix E: Parameter Recommendations for 2G to 3G Reselection ............................ 212
24.1.
Ericsson BSS ............................................................................................................................. 212
24.2.
Nokia BSS ................................................................................................................................. 212
24.3.
Nortel BSS ................................................................................................................................ 212
25.
Appendix F: Parameter Recommendations for Channel Switching ............................... 213
26.
Reference ....................................................................................................................... 214
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1. Introduction
1.1. Purpose & Scope
The intent of this document is to introduce the important UMTS features of the Ericsson
Radio Access Network (RAN), and provide detailed algorithms and parameters related to
these features. Wherever applicable, recommended values for these parameters are also
provided. In the initial phases these recommended values are based on vendor
recommendations and prior UMTS experience. Once UMTS networks are available for
testing, these parameters will be tested and updated with new recommended values. The
recommended values per feature are listed at the end of each section or in the Appendix for
quick and easy access.
The parameters and algorithms described here are applicable to the P5 release.
This document is not all inclusive and merely provides a quick reference to some of the
various UMTS features available in the Ericsson UMTS RAN. For any information not covered
here, the relevant Ericsson product documentation should be referenced.
1.2. Definitions for this Document
Term or Acronym
3GPP
Definition
Third Generation Partnership Project
AS
Active Set
BSIC
Base Station Identity Code
BTS
Base Transceiver Station
CN
Core Network
CPICH
Common Pilot Channel
DCH
Dedicated Channel
DL
DownLink
DPCCH
Dedicated Physical Control Channel
DPCH
Dedicated Physical Channel
DRNC
Drift Radio Network Controller
FACH
Forward Access Channel
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FIFO
First In First Out
GERAN
GSM EDGE RAN
GSM
Global System for Mobile Communications
HCS
Hierarchical Cell Structure
IAF
Intra Frequency
IE
Information Element
IEF
Inter Frequency
IFHO
Inter Frequency HandOver
Inter-RAT
Inter Radio Access Technology
IRAT
Inter Radio Access Technology
Iur
Interface between two RNCs
KPI
Key Parameter Indicator
LA
Location Area
LAI
Location Area Indicator
NBAP
Node B
Node B Application Part
Logical node responsible for radio
transmission and reception in one or
several cells
OCNS
Orthogonal Channel Noise Simulator
PLMN
Public Land Mobile Network
RA
Routing Area
RAB
Radio Access Bearer
RAI
Routing Area Indicator
RAN
Radio Access Network
RAT
Radio Access Technology
RB
Radio Bearer
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RBS
Radio Base Station – another name for the
Node B
RF
Radio Frequency
RL
Radio Link
RNC
Radio Network Controller
RRC
Radio Resource Control
RSCP
Received Signal Code Power
RSSI
Received Signal Strength Indicator
SIB
System Information Block
SIR
Signal to Interference Ratio
TRX
Transceiver
TX
Transmit
UE
User Equipment
UL
UMTS
UpLink
Universal
Services
UTRAN
UMTS Terrestrial Radio Access Network
WCDMA
Wideband Code Division Multiple Access
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2. Neighbor List
Neighbor List creation is crucial to the proper operation of a WCDMA network. When the UE
is in connected mode, the RNC follows it on cell level. Once it knows in which cell the UE is
located, the RNC checks information about all the neighboring cells and transmits the data
back to the UE. The RNC updates continuously the neighbor cell lists in order to reflect the
changing neighborhood of a moving mobile station in connected mode. By relaying
information about neighbor cells to the UE, the RNC is effectively telling it what to look for,
and the RNC knows what the available options are if the load in the serving cell increases.
Neighbor cell definitions also speed up cell re-selection procedures, as the UE does not have
to decode the scrambling codes of other cells.
The cells in a WCDMA RAN, from the UE’s point of view are divided into the following sets
as per 3GPP 25.331 [4].

Active Set: The cells involved in Soft/Softer Handover and measured by the UE.

Virtual Active Set: The Active set associated with a non-used frequency for support
of Inter-Frequency evaluation.

Monitored Set: The cells measured by the UE but not part of the Active Set. The
monitored set is further divided into intra-frequency monitored subset, interfrequency monitored subset and GSM monitored subset.

Detected Set: The intra frequency cells (P-CPICH scrambling codes) detected by
the UE but not part of the Monitored Set.
The number of Intra-frequency cells in the Monitored Set + the Active Set cells is limited to
32 as per [4]. The number of Inter-Frequency cells in the Monitored set is limited to 32. The
number of Inter-RAT cells in the Monitored set is limited to 32.
2.1. Monitored Set Creation
The maximum number of cells that a UE is required to measure according to [4] is 32 of
each type - Intra-Frequency, Inter-Frequency and GSM cells. For IEF cells, the number may
be divided between a maximum of two frequencies. The IAF monitored subset always
includes the cells in the active set.
The IAF Monitored Subset is obtained by performing Monitored Subset Reduction with
MaxMonSubset=MaxIafMonSubset = C_MaxSohoListSubset(32) –PresActiveSet, where
PresActiveSet is the number of cells in the present Active Set. It is equal to 1 when the
connection is set up on CELL_DCH. The cells in the Reduced IAF neighbor Cell Lists that are
not included in the IAF Monitored Subset shall be retained in the IAF Unmonitored Subset.
The IAF Unmonitored Subset is used to check if a reported cell, belonging to the Detected
Set, is a valid cell.
The IEF Monitored Subset is obtained by performing Monitored Subset Reduction with
MaxMonSubset=MaxIefMonSubset = maxIefMonSubset(32). A maximum of two unused
frequencies are included in the IEF Monitored Set, if a third frequency is found during the
filtering process then all “third-frequency” inter frequency neighbor cells are discarded.
The GSM Monitored subset is obtained by performing Monitored Subset reduction with
MaxMonSubset=MaxGSMMonSubset = maxGsmMonSubset(32).
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Recommended Values: The parameters maxIefMonSubset and maxGsmMonSubset are
recommended to be set to a value of 32. The parameter C_MaxSohoListSubset is a constant
hard coded value and is set to 32 by Ericsson.
The listed set sent to the UE contains the Active Set cells, plus the monitored set cells. The
monitored set is created from the neighbor cell lists of all the cells in the Active Set, and if
the resulting Monitored subset contained in the listed set becomes larger than
MaxMonSubset, some of the neighbor cells will be removed and stored in the unmonitored
set.
2.1.1.
Neighbor Cell Priority
The neighbor cell priority defined by selectionPriority is used when building the monitored
set, so that neighbor cells with higher priority are included before low priority neighbors, for
each cell in the active set. The neighbor priorities are not compared between different cells
in the active set, priorities only apply among defined neighbors out from the same cell. If
several neighbors are given the same priority, the order between them is not defined. The
highest priority is 1, which should be given to the most important neighbors.
If no value or a value of zero is entered when a neighbor is defined, the system will
automatically set it to the currently highest used value of selectionPriority + 1, that is, to
the currently lowest priority definition for the source cell and for the relation type (Intra /
Inter / GSM).This priority can be set separately for IAF, IEF and GSM neighbors.
Refer to section “Neighbor List Creation and Priority” for the procedure to assign the
Neighbor Cell priority for different neighbors of a serving cell.
2.1.2.
IAF Monitored Subset Creation
If possible, a specific cell’s position in the listed set sent to the UE is retained in consecutive
measurement control messages. Cells that are removed from the IAF Monitored subset and
not sent to the UE, are retained in the IAF Unmonitored subset.
If there is only one cell (A) in the Active Set, a monitored set containing the first 31
neighbors of this cell is created in priority order (based on the setting of parameter
selectionPriority). When a second cell (B) is added to the Active Set, and assuming that Cell
(A) is reported as the strongest cell in the 1a event triggered measurement report, the
monitored set is created in the following manner.
Add both the active cells (A) and (B) to the listed set in the same position as they existed
previously.
Take the neighbor cell with the highest priority for the best active set cell, cell (A), and if it
already exists in the old listed set, add it to the new listed set in the same position. If it
does not exist in the old listed set, then the position does not matter; therefore store it for
addition later in a temporary array.
Take the neighbor cell with the highest priority for the second best active set cell (B), and if
it already exists in the old listed set, add it to the new listed set in the same position. If it
does not exist in the old listed set, then the position does not matter and it can be stored in
a temporary array for addition later. Store the neighboring cell only if it does not already
exist in the temporary array to avoid duplications. If it is already stored in the temporary
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array, take the next neighboring cell in priority order from the next cell in the Active Set, cell
(A) applying the same rules.
Repeat until all neighbor cells have been processed or until MaxIafMonSubset number of
neighboring cells have been selected for the listed set.
Take the cells that have been selected to be included in the new listed set that are stored in
the temporary array and add them to the listed set by filling the empty spaces. The
neighboring cells are picked from the temporary array in the order they were stored (FIFO).
This makes sure that neighboring cells stored early in the temporary array will be the first to
fill out the spaces in the listed set.
If the listed set gets full (reaches a value of C_MaxSohoListSubset), remaining unprocessed
neighbor cells or cells in the temporary array shall instead be stored in the unmonitored set,
without duplicates.
If the Active Set contains more than 2 cells, the above algorithm can be expanded to
include the neighboring cells of all the active set cells. Below is an illustration of the
combined monitored set, when the Active set has 3 cells.
The following figure shows the individual neighbor lists for the 3 cells in the active set.
Assume that Cell A is the strongest cell and Cell C is the weakest cell. The combined
monitored set when the active set contains all 3 cells is shown below.
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2.1.3.
Field example of Monitored set creation
Refer to Appendix B for a field example of the monitored set creation for event 1a when
there is initially 1 cell in the Active set.
2.1.4.
IEF and GSM Monitored Subset Creation
The IEF and GSM Monitored sets don’t contain any Active set cells, and there is no
unmonitored set in these cases. The maximum number of cells in the monitored subsets is
maxIefMonSubset and maxGsmMonSubset respectively. Otherwise, the same approach as
described in the previous section is used when creating the IEF and GSM monitored subsets.
2.2. Neighbor List Creation and Priority
A good cell plan and correctly defined neighbor cell list is the foundation for good handover
behavior. Due to the restriction in the number of neighbors that is possible to monitor as
per [4], superfluous neighbors should not be defined. On the other hand, it is important for
all true neighbor cells to be defined. A UE will approach an undefined neighbor cell without
adding it to the Active Set, and will therefore not be power controlled by the cell. If the UE
comes close to an undefined neighbor, it will cause destructive interference that in the
worst case leads to dropped calls.
By defining a large number of neighbors per each cell, there is a risk that the combined
neighbor list would exceed the maximum limit of 32 cells when the Active Set contains more
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than 1 cell. Hence it is important to define only the required neighbors. In addition to this
risk, for Ericsson networks, there is an additional disadvantage of defining a large number of
neighbors, which is covered below.
Recommended Value: It is recommended not to exceed 16 neighbor definitions per each
serving cell for the Intra Frequency case. This recommendation is based partly on vendor
recommendations. This number will be updated in the future based on network
performance and needs. This section will be updated with recommendations for IEF
neighbors in the future when more than one WCDMA carrier is deployed in T-Mobile
networks. Refer to the next section for the recommendations on neighbor list size for the
GSM neighbor case.
Though the recommended maximum neighbor list size is 16 neighbors, it is foreseen that in
most cases depending on the network plan, a much smaller number of neighbor definitions
will be needed for most serving cells. There may also be a few cases, where due to cell site
locations issues caused by zoning, a neighbor list greater than 16 may been needed.
However these cases should be limited to a minimum number and used only when
absolutely required.
Since the priority of neighbors per each serving cell plays a huge part in the creation of the
unmonitored set, it is very important to plan the neighbor list with the correct priorities for
each neighbor.
One property of the Monitored set reduction algorithm in Ericsson RAN is that if cells in the
active set have a large difference in number of neighbors, all of equal importance; for
example, cell A = 32 and Cell B = 10, then assuming that these cells have a very small
number of common neighbors, Cell A with the most neighbors will be penalized relative to
cell B by the monitored set reduction algorithm, since cell B will get all its neighbors into the
monitored set, but only a subset of Cell A’s neighbors may be included. This can be
controlled to a certain extent by assigning the correct priorities to the neighbors, such that
the more important neighbors of Cell A will be selected into the combined neighbor list.
The following are some options that can be used for constructing the priorities of the IAF
neighbor list. Refer to the next section for the GSM neighbor list creation. The IEF neighbor
list creation will be covered in future updates when a second WCDMA carrier is planned to
be deployed.

Option 1: Visualization of the cell proximities to assign higher priorities for
neighbors that are closer to the serving cell, with lower priorities as we radiate
farther away form the server. This option while being a very basic and practical
approach might take longer to implement.

Option 2: The neighbors of the underlying GSM cell of any serving WCDMA cell can
be ordered based on the number of handover attempts obtained from GSM
statistics, with the highest priority for neighbors with the most handover attempts.
This ordered GSM neighbor list can then be translated in to an ordered UMTS
neighbor list by replacing each of the GSM neighbors with the corresponding
overlay UMTS cell. This option results in the most automated way to create a
neighbor list as long as the UMTS site has the same sector configurations as the
collocated GSM site, but would need manual work otherwise.
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
Option 3: Scanner data if available can be processed to create an ordered IAF
neighbor list. This can only be used if the entire network has scanner data
available.

Option 4: For areas with weak coverage, which are covered by far away cells, it
might be advisable to make sure these cells are defined as higher priority
neighbors, even if they have lesser number of handover attempts, so as to keep a
call alive in these poor coverage areas.
The options provided here should be treated only as a starting point, and should be further
verified with planning tools and visual checks.
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3. 3G to 2G Neighbor List Generation
GSM neighbor definitions are required for 3G to 2G handovers and 3G to 2G Reselection to
work. It is recommended to define GSM neighbors for all UMTS cells in the network,
irrespective of their location with respect to the edge of the coverage, and then use relevant
parameters to disable IRAT handovers and reselection for UMTS cells that are well within
the 3G coverage area. This would allow rescue handovers to work from 3G to 2G in case
there is ever a service disruption on the UMTS network due to any reason.
For Ericsson RAN, a UMTS cell can have up to 32 GSM cells defined as neighbors. However
it is recommended to keep the GSM neighbor list to an optimum number as the time it takes
for a UE to find a candidate GSM cell generally increases with longer neighbor lists. Keeping
the neighbor list short would generally lead to less time in compressed mode and better
retainability. More information on compressed mode and its effects are covered in a
subsequent section. If the UMTS coverage falls quickly, the probability of quickly finding a
suitable GSM candidate cell will increase, if there are fewer GSM cells to measure on.
The following strategy for the creation of GSM neighbor lists for UMTS cells depends on the
overlay configuration and utilizes existing neighbor lists on the GERAN network where
possible. Planning tools can be used to run validation checks on neighbor lists created
through this procedure.
The following is the neighbor list creation strategy for all the possible overlay configurations.
It should be noted that the intent of the following neighbor list tuning strategy is to create
the initial GSM neighbor list for UMTS cells. Once the UMTS cell is integrated and enabled,
scanner data from cluster drives, wherever available should be utilized to tune the UMTS GSM neighbor list. Ultimately, the UMTS neighbor lists should be based on the signal
strength of the best server, not just the geographical proximity of the UMTS and GSM cells.
Neighbor list tuning techniques are outside the scope of this document.
In the Ericsson 3G network, neighbor priorities play an important role in the creation of a
monitored set. Hence the following procedure addresses recommendations to assign
priorities among neighbors for a particular UMTS cell.
For any other cases that are not covered here, the GSM neighbor list should be planned
using visual checks and planning tools as necessary.
3.1. UMTS to GSM 1:1 overlay with matched azimuths
This scenario refers to the case where the UMTS site is co-located with the GSM site, and
the UMTS cell azimuths are within +/- 15 degrees of the GSM azimuths. In addition, the
UMTS antennas are required to have a horizontal beam width of 65 or 90 degrees.
The recommended size of the GSM neighbor list for this configuration is 11 neighbors, with
8 neighbors generated from the following procedure and 3 neighbors reserved for any
missing GSM cells found after validation checks.
Procedure to generate GSM neighbors
Identify the corresponding sector of the co-located GSM site for the UMTS cell.
Add this GSM cell to the top of the neighbor list with highest priority.
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Add the other sectors of the co-located GSM site to this list starting with priority 2.
Using the 2G network statistics, order the remaining 2G neighbors of the GSM cell as per
number of handover attempts. Choose the top 5 neighbors and add them to the bottom of
the above created list.
Validate the list using visual checks or planning tools to make sure none of the obvious
neighbors are missing.
Make sure that all required in-building GSM cells are included, otherwise add them as
necessary.
Extend the neighbor list beyond 11, only if necessary to accommodate any missing 2G
neighbors found after validation checks.
3.2. UMTS to GSM 1:1 overlay with mis-matched azimuths
This scenario refers to the case where the UMTS site is co-located with the GSM site, but
the UMTS sector azimuths are more than +/- 15 degrees different from the GSM azimuths.
This solution can also be used for co-located sites with matched azimuths (within +/- 15
degrees of GSM), but with narrow horizontal beam widths (less than 65 degrees).
The recommended size of the GSM neighbor list for this configuration is 14 neighbors with
11 neighbors generated from the following procedure and 3 neighbors reserved for any
missing GSM cells found after validation checks.
Procedure to generate GSM neighbors
Add all sectors of the co-located GSM site to the top of the 3G -> 2G neighbor list with the
highest priorities.
Identify the two closest co-located GSM sectors for the UMTS cell.
Using GSM statistics, order the combined 2G neighbor list of these 2 GSM sectors as per
number of handover attempts. Choose the top 8 neighbors and add them to the bottom of
the above created list with the next highest priorities.
Validate the list using visual checks or planning tools to make sure none of the obvious
neighbors are missing.
Make sure that all required in-building GSM cells are included, otherwise add them as
necessary.
Extend the number of neighbors beyond 14, only if necessary to accommodate any missing
2G neighbors found after validation checks.
3.3. UMTS site without overlay
This scenario refers to a new UMTS site without a co-located GSM site. In this case the GSM
neighbors will have to be created using planning tools. The recommended size of the GSM
neighbor list for this scenario is 11 neighbors. The neighbor list size should be extended
beyond 11, only if required, to accommodate missing 2G neighbors after validation checks.
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3.4. New GSM site added to the 2G Network
When a new GSM site is added to the 2G network, since GSM handover statistics would not
available as soon as the new site is added, visual checks and planning tools will have to be
used to ensure that the new GSM site is correctly configured as a neighbor to the relevant
UMTS cells.
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4. Idle Mode Process, Algorithms and Parameters
The idle mode tasks are divided into the following 3 processes:

PLMN Selection

Cell Selection & Reselection

Location and Routing Areas Registration
The relationship between these 3 processes is shown in the figure below.
Camping on a cell is necessary for the UE to get access to some services in the network.
The following three types of services are defined for the UE in Idle mode:

Limited service, which allows the UE to make emergency calls only on an
acceptable cell.

Normal service, for public use on a suitable cell

Operator-related services, which allow the operator to test newly deployed cells
without being disturbed by normal traffic.
An "acceptable cell" is a cell on which the UE may camp to obtain limited services (originate
emergency calls). Such a cell fulfils the following requirements, which is the minimum set of
requirements to initiate an emergency call in a UTRAN network:

The cell is not barred.

The cell selection criteria are fulfilled.
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A "suitable cell" is a cell on which the UE may camp on to obtain normal service. Such a cell
fulfils all the following requirements.

The cell is part of the selected PLMN or, of the registered PLMN or, of a PLMN
considered as equivalent by the UE according to the information provided by the
NAS.

The cell is not barred.

The cell is not part of the list of "forbidden LAs for roaming".

The cell selection criteria are fulfilled.
A “barred cell” is a cell that is restricted (barred) to camp on for all access classes. This is
indicated on SIB 3.
A “reserved cell” is a cell that has been reserved for operator use where only UEs with USIM
access class 11 or 15 can camp on. This is indicated on SIB 3.
4.1. PLMN Selection
The PLMN selection for the various modes are detailed below.
4.1.1.
PLMN Selection at UE switch on
Whenever a UE is switched on or enters an area with acceptable coverage after coverage
loss, it attempts to camp on the last registered PLMN or equivalent PLMN, if available. To
speed up the PLMN selection procedure, the UE uses information about the last registered
PLMN, such as carrier frequencies or the list of neighboring cells stored in the USIM before
the UE was switched off. On each stored carrier frequency, the UE searches first for the cell
with strongest signal and reads its system information to verify the PLMN to which the cell
belongs. It also reads the system information for PLMN identity, which consists of MCC and
MNC. Then the UE decides whether the chosen cell is acceptable or whether at least one
acceptable cell belonging to that PLMN exists. Finally, the UE attempts registration if the
PLMN is allowed. If the last registered PLMN is not available, a registration attempt fails. If
there is no registered PLMN stored in the USIM, the UE selects and attempts registration on
other PLMNs using either the Automatic mode or the Manual mode.
4.1.2.
PLMN selection in Automatic Mode
In Automatic mode, if no last registered PLMN exists or is available, the UE will select a
PLMN that is available and allowed, in the following order:

Home PLMN (HPLMN), if not previously selected, according to the Radio Access
Technologies (RATs) supported by the UE.

Each PLMN in the user-controlled PLMN list in the USIM, if present, in order of
priority, according to the RATs supported by the UE

Each PLMN in the operator-controlled PLMN list in the USIM, in order of priority,
according to the RATs supported by the UE.

Other PLMNs, according to the high-quality criterion, in random order.

Other PLMNs that do not fulfill high-quality criterion, in order of decreasing signal
strength (SS).
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PLMNs are considered high quality if the Received CPICH RSCP fulfills the high-quality
criterion. The high-quality criterion is fulfilled when CPICH RSCP level is greater than or
equal to –95 dBm. For GSM cells the high-quality criterion is fulfilled when the signal level is
above –85 dBm. A PLMN with at least one acceptable cell is considered available. If that
PLMN is allowed, the UE tries to register on it. If registration is successful, the UE displays
the selected PLMN. When the UE cannot register on any PLMN in the user and operator
lists, it attempts to register on other PLMNs according to the high-quality criterion.
If the UE cannot register on any PLMN, it selects an available PLMN and enters a limited
service state. If it does not find an available PLMN, the UE enters the non-service state, and
waits until a new PLMN is available and allowed.
The following figure shows the PLMN selection procedure using the Automatic mode.
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4.1.3.
PLMN Selection in Manual Mode
The Manual mode allows the user to select a PLMN among those indicated by the UE. The
UE displays all PLMNs that it finds by scanning all frequency carriers. The UE displays those
PLMNs that are allowed as well as those that are not allowed. The user makes a manual
selection, according to the available RAT for the chosen PLMN, and the UE attempts
registration on this PLMN, ignoring the contents of the forbidden Location Area Identities
(LAIs) and PLMN lists. If the user selects an available PLMN in the forbidden PLMN list, the
UE attempts to register and may receive a positive acknowledgement from the CN. In this
case, the PLMN is removed from the forbidden list.
If the user does not select a PLMN, the selected PLMN is the one that was selected before
the PLMN selection procedure started. If this PLMN is no longer available, the UE attempts
to camp on an acceptable cell at any PLMN and enters the limited service state. The UE
remains in that state until it is switched off or the user makes a manual PLMN reselection.
4.1.4.
PLMN Selection while Roaming
Roaming is a service through which a UE is able to obtain services from another PLMN in
the same country (national roaming area) or another country (international roaming area).
The behaviour that the UE must follow is specified by agreements among the network
operators. A UE in automatic mode, having selected and registered on a Visited PLMN
(VPLMN) in its home country, periodically attempts to return to its Home PLMN (HPLMN).
The time interval between consecutive attempts is stored in the USIM and is managed by
the network operator using a timer. The timer may have a value of between 6 minutes and
8 hours, with a step size of 6 minutes. In the absence of a fixed value, a default value of 60
minutes shall be used by the UE as per 3GPP 22.011. This timer is not a radio or core
network parameter; it is stored in the USIM when provisioned. T-Mobile is setting this timer
to 6 minutes.
4.2. Cell Selection Procedure in UTRAN state
The cell selection and reselection process allows the UE to look for a suitable cell in the
selected PLMN and to camp on it. The UE then camps on the suitable cell in a “camped
normally’ state. In this state, the UE monitors paging and system information, performs
periodical radio measurements, and evaluates cell reselection criteria. If the UE finds a
better cell, that cell is selected by the cell reselection process. The change of cell may imply
a change of the RAT.
The purpose of camping on a cell in idle mode is the following:

It enables the UE to receive system information from the PLMN.

When registered and if the UE wishes to establish an RRC connection, it can do this
by initially accessing the network on the control channel of the cell on which it is
camped.

If the PLMN receives a call for the registered UE, it knows the registration area of
the cell in which the UE is camped. It can then send a "paging" message for the UE
on control channels of all the cells in the registration area. The UE will then receive
the paging message because it is tuned to the control channel of a cell in that
registration area and the UE can respond on that control channel.
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
It enables the UE to receive cell broadcast services.
The UE attempts cell selection in the following cases:

When a UE is switched on

When a UE in idle mode has had a number of failed RRC connection requests

When a UE returns to idle mode from connected mode on common channels
(CELL_FACH state) after a number of failed cell update attempts.

When a UE moves from dedicated mode to idle mode. The candidate cells for cell
selection are the ones used immediately before leaving connected mode. If no
suitable cell is found, the UE can use stored information cell selection procedure to
find a suitable cell.

When a UE returns to idle mode after an emergency call on any PLMN. The UE
selects an acceptable cell on which to camp. In this case, candidate cells for cell
selection are the ones used immediately before leaving the connected mode. If no
acceptable cell on that PLMN is found, the UE continues to search for an acceptable
cell on any PLMN.

When a UE moves from dedicated mode to state CELL_FACH or URA_PCH.
The UE uses one of the following cell selection procedures:

Initial Cell Selection: This procedure requires no prior knowledge of which RF
channels are UTRA carriers. The UE shall scan all RF channels in the UTRA bands
according to its capabilities to find a suitable cell of the selected PLMN. On each
carrier, the UE only needs to search for the strongest cell. Once a suitable cell is
found this cell is selected.

Stored Information Cell Selection: This procedure requires stored information of
carrier frequencies and optionally also information on cell parameters, e.g.
scrambling codes, from previously received measurement control information
elements. Once the UE has found a suitable cell for the selected PLMN the UE
selects it. If no suitable cell of the selected PLMN is found, the Initial cell selection
procedure is started.
The cell selection criterion S is fulfilled when the following is true.
Squal > 0 and Srxlev > 0
The quantities Squal and Srxlev are defined as
Squal = Qqualmeas - qQualMin and
Srxlev = Qrxlevmeas - qRxLevMin – Pcompensation
Qqualmeas is the quality of the received signal expressed as CPICH Ec/No and Qrxlevmeas
is the received signal strength expressed as CPICH RSCP.
The parameter qQualMin in object UtranCell indicates the minimum required quality value in
the cell while the UtranCell parameter qRxLevMin indicates the minimum required signal
strength in the cell. These values are sent in SIB 3 for the serving cell.
Pcompensation = max (maxTxPowerUl - P, 0)
Pcompensation is introduced for UEs that cannot transmit at maximum power on the RACH
in the cell. The cell range decreases for those UEs. P is the output power of the UE
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according to its class. The parameter maxTxPowerUl in the object UtranCell is the maximum
allowed transmission power when the UE accesses the system on RACH. It is broadcast in
SIB 3.
4.3. Cell Reselection Parameters from 3G to 3G
The UE performs the cell reselection procedure in the following cases:

When the cell on which it is camping is no longer suitable.

When the UE, in “camped normally” state, has found a neighboring cell better than
the cell on which it is camping.

When the UE is in “limited service” state on an acceptable cell.
The cell reselection process is divided into 3 steps – Measurements, Eligibility and Ranking.
The parameters for each of these phases are detailed below. For more details on the value
ranges, please refer to the Parameter Guidelines document.
4.3.1.
Measurements
A UE makes measurements on intra frequency neighbors when Squal <= sIntraSearch. The
quantity Squal is defined as Squal = QqualMeas – qQualMin. Qqualmeas is the quality of the
received signal in the serving cell, expressed as CPICH Ec/No.
Hence
If CPich_Ec/Nomeas > qQualMin + sIntraSearch , then no intra frequency measurements.
If CPich_Ec/Nomeas <= qQualMin + sIntraSearch, then UE makes intra frequency
measurements.
If the parameter sIntraSearch is not sent for the serving cell (this is accomplished by setting
the value of sIntraSearch = 0), the UE always performs intra frequency measurements.
The parameters qQualMin and sIntraSearch are cell based parameters are found in the
object UtranCell.
4.3.2.
Eligibility
The eligibility of the intra frequency neighbors for reselection is verified using the cell
selection criteria (S criteria). The cell selection criterion S is fulfilled when Squal > 0 and
Srxlev > 0
The quantities Squal and Srxlev are defined as
Squal = Qqualmeas - qQualMin and
Srxlev = Qrxlevmeas - qRxLevMin – Pcompensation
Pcompensation = max (maxTxPowerUl - P, 0)
As per the Ericsson implementation, the parameters qQualMin, qRxLevMin and
maxTxPowerUl are the same as the ones found in the object UtranCell, and are not defined
separately for the intra frequency neighboring cells.
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4.3.3.
Ranking
The cells that satisfy the Selection criteria are then selected to be ranked as per the
following procedure. The cells are ranked according to the R criteria.
R(serving) = Qmeas(s) + qHyst(s)
R(neighbor) = Qmeas(n) - qOffset(s,n)
Qmeas is the quality value of the received signal, which is derived from the average CPICH
Ec/No or CPICH RSCP level for WCDMA cells and from the average received signal for GSM
cells. (s) and (n) refer to the serving cell and neighboring cell values respectively. The
ranking of GSM neighbors is always made using the measurement quantity CPICH RSCP.
The ranking of WCDMA cells can be done using CPICH RSCP or CPICH Ec/No based on the
value of the parameter qualMeasQuantity. The recommended setting is qualMeasQuantity =
2 which corresponds to CPICH Ec/No.
The quantity qHyst(s) is the hysteresis value of the serving cell and is configured by the
parameter qHyst1 when the ranking is based on CPICH RSCP and by parameter qHyst2
when the ranking is based on CPICH Ec/No. The quantity qOffset(s,n) is the offset between
the serving and neighbor cell and can be used to move the border between the two cells. It
can be configured using the parameter qoffset1sn when the ranking is based on CPICH
RSCP and by qoffset2sn when the ranking is based on CPICH Ec/No.
For cells that fulfill the selection criteria, a first ranking is done using CPICH RSCP.
R(serving) = CPICH RSCP(s) + qHyst1
RWCDMA(neighbor) = CPICH RSCP(n) – qoffset1sn(s,n)
RGSM(neighbor) = RxLev(n) – qoffset1sn(s,n)
If a GSM cell is the best ranked cell after the first ranking, it is selected for the 3G to 2G
reselection. The UE reselects to the new cell, if it is better ranked than the serving cell for a
time equal to treSelection.
A second ranking is only performed if the best ranked cell resulting from the first ranking is
a WCDMA neighbor and the parameter qualMeasQuantity is set to CPICH Ec/No.
The second ranking is performed as per CPICH Ec/No as follows.
R(serving) = CPICH Ec/No(s) + qHyst2
RWCDMA(neighbor) = CPICH Ec/No(n) – qoffset2sn(s,n)
After the second ranking the UE reselects to the best ranked neighbor, as long as this
neighbor is better ranked than the serving cell for at least a time equal to a value defined by
the parameter treSelection.
The parameters qHyst1, qHyst2 qualMeasQuantity and treselection are defined per 3G cell
and are set in the object UtranCell. The parameter qoffset1sn is defined per 3G – 3G
neighbor pair (configured in object UtranRelation) and per 3G – 2G neighbor pair
(configured in object GsmRelation). The parameter qoffset2sn is defined per 3G – 3G
neighbor pair and is configured in the object UtranRelation.
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4.4. Recommended Values for 3G to 3G Selection and Reselection
parameters
The camping strategy places an important role in determining the recommended values of
Reselection parameters. T-Mobile’s camping strategy is to camp on UMTS, whenever UMTS
coverage is available, and reselect to GSM at the boundaries of UMTS coverage. Since UMTS
is being launched with only 1 WCDMA carrier, the setting of sInterSearch is not considered
here. Hence, in order to adhere to this camping strategy, the values of sIntraSearch and
sRatSearch should be set such that the UE is making measurements only on 3G neighbors
as long as it is in the UMTS coverage area, and tries to make measurements on GSM
neighbors only when at the edge of the 3G coverage area.
A constant value of -18 dB is recommended for qQualMin and a constant value of -115 dBm
for the qRxLevMin, so that all cells are selected at the same thresholds. The other
reselection parameters should be used to optimize the idle mode cell size.
Recommended value for sIntraSearch: With qQualMin set to a constant value, a small
value of sIntraSearch would reduce the number of measurements on intra frequency
neighbors, while a large value of sIntraSearch would increase the number of times the UE
measures on intra frequency cells. A large number of measurements would decrease the
battery life in the UE. On the other hand, less frequent measurements may result in the UE
camping on a non-optimum cell, thus increasing the call setup time when the UE tries to
place a call. An optimum value for this parameter should achieve a balance between good
battery life and lower call setup time. It should be noted that the battery life impacted
would be the idle mode battery life which is not as critical as the connected mode battery
life.
The vendor recommended value of 0 for sIntraSearch would result in the UE always
measuring on all available intra frequency cells, thus reducing the call setup time. However
this may result in a lower UE battery life while compared to a different setting. Again the
battery life reduction would be only in the idle mode, which is not as critical as the
connected mode battery life. Further testing will be done to optimize this parameter value.
The table below shows the recommended values for some intra frequency reselection
related parameters. For details on the complete parameter set, refer to the Parameter
Guidelines document.
Parameter
Name
Object Name
Recommended
Value
maxTxPowerUl
UtranCell
24 dBm
qHyst1
UtranCell
4 dB
qHyst2
UtranCell
4 dB
qQualMin
UtranCell
-18 dB
qRxLevMin
UtranCell
-115 dBm
qoffset1sn
UtranRelation
0 dB
qualMeasQuantity
UtranCell
CPICH_EC_NO
sIntraSearch
UtranCell
0 dB
treselection
UtranCell
2s
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4.5. Cell Reselection Parameters from 3G to 2G
The following are the parameters involved in the inter RAT reselection of a 3G cell on the
Ericsson RAN to a 2G cell of any vendor’s BSS.
The cell reselection process is divided into 3 steps – Measurements, Eligibility and Ranking.
4.5.1.
Measurements
For a 3G cell that has GSM neighbors defined, the decision about when the GSM
measurements are performed is based on the parameter sRatSearch in relation to Squal.
The parameter Squal is defined as QqualMeas – qQualMin. If the Squal value is larger than
the parameter sRatSearch, the UE does not perform measurements on GSM cells. If the
Squal value is less than or equal to the parameter sRatSearch, the UE performs
measurements on the GSM neighbors. If the value of sRatSearch is not sent for the
serving cell (by setting sRatSearch = 0), the UE always performs measurements on GSM
cells.
Squal = QqualMeas – qQualMin = CPich_Ec/Nomeas – qQualMin
As illustrated in the example below, qQualMin = -18 dB and sRatSearch = 4 dB. As the
Ec/Io of the pilot drops below -14 dB, the UE will begin measuring GSM candidates
assuming they are provided as neighbors in SIB 11/12. If the Ec/Io of the current pilot
improves and exceeds -14 dB, the UE will cease measuring GSM candidates.
The parameters qQualMin and sRatSearch are cell based parameters and are found in the
UtranCell object.
In order to trigger GSM measurements based on RSCP measurements relative to
qRxLevMin, the sHcsRat parameter is used. The behavior of these measurements is
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similar to the Ec/Io case. Assuming qRxLevMin = -115 dBm and sHcsRat = 3 dB, the UE
will begin measuring GSM candidates when the current pilot’s RSCP drops below -112 dBm.
If the RSCP of the current pilot improves and exceeds -112 dB, the UE will cease measuring
GSM candidates. The default value for this parameter is -105 dB, which deactivates the
parameter and only allows the UE to trigger GSM measurements based on Ec/Io. Because
Ec/Io measurements are not indicative of quality, especially at the UMTS network edge, it is
recommended that sHcsRat parameter be enabled. The recommended value of
sHcsRat is 3 dB, which would allow measurements on GSM when the serving cell’s RSCP
falls below -112 dBm.
The parameter fachMeasOccaCycLenCoeff is used to control the inter frequency and IRAT
cell reselection measurements of a UE in CELL_FACH state. A UE in CELL_FACH state is
allowed to make inter frequency and/or IRAT measurements only when this parameter
fachMeasOccaCycLenCoeff > 0. If there are only GSM neighbors or inter-frequency
neighbors defined for a cell, then fachMeasOccaCycLenCoeff should be set to 4 so that the
UE will leave the FACH channel every 16th frame to perform measurements on these
neighbors. If a cell has both GSM and Inter-frequency neighbors, then this parameter
should be set to a value of 3, so that the UE will leave the FACH channel every 8th frame to
perform measurements on the inter-frequency and GSM neighbors.
Since T-Mobile networks will have only 1 WCDMA carrier to start with, for cells that have
GSM neighbors defined, this parameter is recommended to be set to 4. For any cell with no
IRAT neighbors or Inter frequency neighbors, fachMeasOccaCycLenCoeff should be set to 0.
4.5.2.
Eligibility
The eligibility of the neighboring GSM cells for reselection is verified using the selection
criteria (S criteria). The selection criteria are fulfilled when Srxlev > 0 for the neighboring
GSM cells. The parameter Srxlev is defined as
Srxlev = Qrxlevmeas - qRxLevMin - Pcompensation
Where
Qrxlevmeas is the quality value of the received signal and is derived from the average
received signal level for a GSM cell.
qRxlevMin is the minimum received signal strength for a specific GSM cell.
Pcompensation = max (maxTxPowerUl - P, 0)
where
P is the output power of the UE according to its class
maxTxPowerUl is the maximum allowed transmission power when the UE accesses the
system on RACH
The parameters qRxLevMin and maxTxPowerUl are defined per GSM cell and can be set in
the ExternalGsmCell Object.
4.5.3.
Ranking
Only GSM cells that satisfy the selection criteria are chosen for ranking. The cells are ranked
according to the R criteria.
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R(serving) = Qmeas(s) + qHyst(s)
R(neighbor) = Qmeas(n) - qOffset(s,n)
Qmeas is the quality value of the received signal, which is derived from the average CPICH
Ec/No or CPICH RSCP level for WCDMA cells and from the average received signal for GSM
cells. (s) and (n) refer to the serving cell and neighboring cell values respectively.
The ranking of GSM neighbors is always made using the measurement quantity CPICH
RSCP. The ranking of WCDMA cells can be done using CPICH RSCP or CPICH Ec/No based
on the value of the parameter qualMeasQuantity. The quantity qHyst(s) is the hysteresis
value of the serving cell and is configured by the parameter qHyst1 when the ranking is
based on CPICH RSCP and by parameter qHyst2 when the ranking is based on CPICH
Ec/No. The quantity qOffset(s,n) is the offset between the serving and neighbor cell and can
be used to move the border between the two cells. It can be configured using the
parameter qoffset1sn when the ranking is based on CPICH RSCP and by qoffset2sn when
the ranking is based on CPICH Ec/No.
For cells that fulfill the selection criteria, a first ranking is done using CPICH RSCP.
R(serving) = CPICH RSCP(s) + qHyst1
RWCDMA(neighbor) = CPICH RSCP(n) – qoffset1sn(s,n)
RGSM(neighbor) = RxLev(n) – qoffset1sn(s,n)
If a GSM cell is the best ranked cell after the first ranking, it is selected for the 3G to 2G
reselection. The UE reselects to the new cell, if it is better ranked than the serving cell for a
time equal to treSelection.
A second ranking is only performed if the best ranked cell resulting from the first ranking is
a WCDMA neighbor and the parameter qualMeasQuantity is set to CPICH Ec/No. In this case
a 3G to 3G reselection will be performed.
Simply put, the evaluation of a GSM candidate for reselection is based on the following
parameters qHyst1, qOffset1sn, and treSelection. qHyst1 is a hysteresis added to the
CPICH RSCP of the serving UMTS cell. The parameter qOffset1sn is offset subtracted from
the candidate GSM RSSI. This offset can be used to appropriately compare a GSM RSSI to
a UMTS RSCP value. Two examples are illustrated below.

In the first example, qOffset1sn = 0 dB, and qHyst1 = 4 dB. In this case,
reselection will occur if the target GSM cell’s RSSI is 4 dB stronger than the serving
CPICH RSCP, for period of treSelection seconds.

In the second example, qOffset1sn = 7 dB, and qHyst1 = 4 dB. In this case,
reselection will occur if the target GSM cell’s RSSI is 11 dB stronger than the
serving CPICH RSCP, for period of treSelection seconds
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The parameters qHyst1, qualMeasQuantity and treSelection are defined per 3G cell
and are set in the object UtranCell. The parameter qoffset1sn is defined per 3G – 3G
neighbor pair (configured in object UtranRelation) and per 3G – 2G neighbor pair
(configured in object GsmRelation).
4.6. Recommended Values for 3G to 2G Reselection parameters
T-Mobile camping strategy is to keep the UE on UMTS coverage as far as possible with good
quality. The following are the recommended values for the 3G to 2G reselection parameters.
Measurements: The parameters qQualMin and sRatSearch found in the UtranCell object to
trigger measurements on 2G neighbors should be set to -18 dB and 4 dB respectively, so
that the UE can make GSM measurements when the CPICH Ec/No of the serving UMTS cell
is less than or equal to -14 dB. The threshold of -14 dB is consistent with the Planning
Guidelines as well as the 2G to 3G reselection threshold of -12 dB, avoiding ping pong
between 3G and 2G networks. The parameters qRxlevMin and sHcsRat are recommended to
be set to -115 dBm and 3 dB. It is recommended to keep the same parameter value for all
cells so as to trigger the 2G measurements at the same threshold. The parameter qQualMin
also influences the start of measurements on 3G neighbors. If this value is changed, then
the sRatSearch parameter should be changed accordingly to keep the mobile measuring on
GSM cells when the CPICH Ec/No falls below or is equal to -14 dB.
Eligibility: The parameters qRxLevMin and maxTxPowerUl defined per GSM cell in the
ExternalGsmCell Object should be set to -105 dBm and 24 dBm respectively. The value of
qRxLevMin chosen is the minimum receive signal level required for a GSM call. It is
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recommended to keep the same parameter value for all cells. With these values, a GSM cell
would be eligible for reselection to Class 3 UEs as long as the Rxlev in that cell is greater
than -105 dBm. For Class 4 UEs, with a maximum transmit power of 21 dBm, the
Pcompensation factor would be equal to 3 dB. This would result in the GSM cell to be
eligible to Class 4 UEs, only when the Rxlev is greater than -102 dBm.
Ranking: The recommended value for the parameter qHyst1 in UtranCell is 4 dB. The
parameter qHyst1 is used to avoid ping pong between the serving cell and the neighbor
cells. The parameter qoffset1 can be used to move the borders between cells. From the 3G
to 3G reselection, it can be seen that the recommended value of qOffset1 in UtranRelation
is 0 dB. From various testing it had been shown that the WCDMA RSCP is related to GSM
RSSI as WCDMA RSCP + 7dB ~ GSM RSSI. Hence in order to keep RSSI and RSCP
comparable, the parameter qOffset1 in GsmRelation should be set to 7 dB. This implies that
a neighboring 3G cell needs to be greater than 4dB of the serving cell in order to be ranked
higher, and a neighboring GSM cell needs to be greater than 11 dB of the serving cell in
order to be ranked higher than the serving cell. This would ensure that a WCDMA cell is first
checked for reselection before choosing a GSM cell for reselection.
If for any reason, if we choose to prefer reselection to GSM above WCDMA, this can be
accomplished by reducing the value of qOffset1 in object GsmRelation for the corresponding
GSM neighbor.
Recommended value for treSelection: The setting for the parameter treSelection is a
compromise between a too low value, triggering too many reselections in the fading radio
environment, and a too high value, that slows down the process. The recommended value
for the parameter treselection is set to 2 seconds. This value would avoid too many
reselections between cells and hence too many LA/RA updates when crossing LA/RA
borders. Thus there would be less signaling and less call failures at LA/RA borders due to
LA/RA update.
It is recommended to keep the same values for these parameters for all cells and all
neighbor relations for network launch, and only change on as needed basis afterwards.
The recommended values for all 3G to 2G reselection parameters for the Ericsson 3G RAN
are tabulated in Appendix C.
4.7. Location and Routing Area Registration and Updating
After a UE has found a suitable cell and can access services requiring registration, it tries to
register on the selected PLMN. If the Location Area Identity (LAI) or Routing Area Identity
(RAI), read on SIB 1, is different from the one stored on the USIM before switch-off, the UE
performs a LA or RA registration update. When a UE in idle mode moves into a new cell in a
new LA or RA or into a new PLMN, it performs a registration area update. The LA or RA
update procedure is managed by the CN and is transparent to the WCDMA RAN.
There are three types of registration update procedures: normal, periodic and IMSI
attach/detach.
4.7.1.
Terminology
Location Area (LA) is an area to which the core network (CN) sends a paging message for
circuit switch services. The LA may consist of cells belonging to one or more RNCs, which
are connected to the same CN.
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Location Area Identity (LAI) is formed by a PLMN Identity and a Location Area Code (LAC)
sent in SIB 1.
Routing Area (RA) is an area to which the CN sends a paging message for packet switch
services. The RA may consist of cells belonging to one or more RNCs, which are connected
to the same CN.
Routing Area Identity (RAI) is formed by a PLMN Identity and a Routing Area Code (RAC)
sent in the SIB 1.
4.7.2.
Normal LA and RA Updating
A UE executes a normal registration update when, in a cell belonging to a new LA or RA, it
is switched on or leaves the Connected mode. Normal registration update is also performed
when the UE, in Idle mode, moves in a cell belonging to a new LA or RA, or when the UE is
unknown to the CN. The UE reads the LAI and the RAI in the system information and
detects that one or both of the received area identities differ from the ones stored on the
USIM. If the LAI received is not in the forbidden LAIs list, an LA and/or RA update request is
sent by the UE to the WCDMA RAN. If the LAI is forbidden, the UE tries to select another
cell belonging to a permitted LAI or another PLMN.
4.7.3.
Periodic LA and RA Updating
Periodic LA or RA updating is used to notify the network of the UEs availability, and to avoid
unnecessary paging attempts for a UE that has lost coverage and is not able to inform the
CN that it is inactive.
The periodic LA update procedure is controlled by a timer, t3212, which gives the time
interval between two consecutive periodic location updates. The value is sent by the
WCDMA RAN to UEs on the SIB 1.
The periodic RA update procedure is controlled by a timer, t3312, which gives the time
interval between two consecutive periodic routing updates. The value of this timer is sent by
the CN to the UE in the IMSI attached or in the routing area update message accept.
The following figure shows an Example of a SIB1 and Attach Accept messages showing the
periodic LA and RA update timer values, respectively.
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4.7.4.
IMSI Attach/Detach
A location registration request indicating IMSI attach is made when the UE is activated in
the same LA in which it was deactivated, and the system information indicates that IMSI
attach/detach is used (SIB 1). The IMSI attach/detach procedure allows the UE to avoid
unnecessary paging attempts from the CN. If IMSI attach/detach is used the UE sends an
“attach” or “detach” message to the CN when is powered on or off indicating whether the
UE is active or inactive in the network.
The CN avoids performing paging attempts when the IMSI detach is applied and the UE is
switched off. When the UE is switched on and the IMSI attach/detach procedure is applied
the UE performs a location registration request, indicating IMSI attach, if it is in the same LA
or RA in which it was switched off. If the registration area is changed, a normal LA update is
performed by the UE.
Ericsson has a parameter called “att” to indicate if IMSI attach/detach is used.
The following figure depicts an example of an IMSI detach message sent by UE when
powered off.
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4.7.5.
Recommended Values for LA and RA update parameters
Parameter Name
Object
Name
Recommended Value
Att
LocationArea
TRUE
t3212
LocationArea
54 minutes
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5. Call Setup Procedure
The fundamental steps required in the accessing the T-Mobile UMTS network is similar for
both CS and PS services. In both cases the UE utilizes the same random access procedure
to request establishment of a RRC Connection with the RNC. If dedicated resources are
available to setup this radio link, an RRC Connection will be established with the RNC. Once
an RRC Connection is established with the RNC, the Core Network (CN) is signaled to
establish an Iu connection between the CN and RNC. At this time core network may initiate
security procedures such as Authentication and Ciphering. After the security procedures are
complete, the UE requests services from the Core Network. At this point the CN requests
the establishment of a Radio Access Bearer (RAB) with the RNC to support the requested
services. If this RAB is established, the RNC will acknowledge the CN request and a
successful access will have occurred. Alternatively, if any of these steps fail, an access
failure will occur.
The procedure described above only summarizes the steps required to successfully access
the UMTS network. In the following sections, the details for both the CS and PS setup
procedure are described. Understanding these setup procedures is required to successfully
troubleshoot and optimize the Accessibility metric of the UMTS network.
5.1. Circuit Switched Call Setup
Figure 1 illustrates the call flow diagram for a typical CS call establishment. The setup is
divided into three phases:
5.1.1.

The RRC Setup Phase

The Pre-RAB Phase

The RAB Setup Phase
RRC Setup Phase, CS Voice
In order to setup a call, the UE must establish an RRC Connection with the UTRAN. Once
the UE has completed the Random Access Procedure, a RRC Connection Request
message is sent to the SRNC. Embedded in this message is the establishment cause, or the
reason the UE is requesting a RRC connection. For the case of mobile originating CS Call,
the establishment cause would be “Originating Conversational Call”. If the UE is
responding to a page, or a mobile terminating call, the establishment cause would be
“Terminating Conversational Call”.
Upon reception of the RRC Connection Request, the UE is assigned UMTS Radio Network
Temporary Identifier (U-RNTI). This identifier is unique to the PLMN and is derived from
the SRNC identity and a unique SRNC RNTI (S-RNTI). In this manner the U-RNTI is unique
to the UE.
After a RRC Connection Request message is received, the Admission Control algorithm is
invoked to confirm the required dedicated resources are available to establish a signaling
connection. These resources include codes, power, and channel elements. If admission
can not be granted, an RRC Connection Reject message is sent, and the counter
pmNoReqDeniedAdm is pegged. If admission is granted, a Radio Link Setup request is
sent to the Node B requesting dedicated resources be reserved. Once resources are
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reserved, the Node B responds with a Radio Link Setup Response message, and
activates its Radio Link Set Supervision algorithm for this Radio Link.
At this time, the RRC Connection Setup is sent to the UE with a RRC state indicator
ordering the UE to go to CELL_DCH. Embedded in this message is all the information the
UE needs to construct a dedicated channel. This includes all the logical, transport, and
physical layer information required to build the 13.6 kbps SRB. For Ericsson, the SRB is
identified by Transport Channel 31, and uses third rate convolution coding. The transport
channel DL BLER target for outer loop power control, as well as the Rate Matching for the
SRB is also transmitted to the UE at this time. At the physical layer, this SRB utilizes a 128
bit spreading factor.
After the RRC Connection Setup message is sent, the Node B begins transmitting the DL
DPCH to enable L1 synchronization. Once synchronization has occurred, the UE sends an
RRC Connection Setup Complete message to the SRNC. Within this message are all the
UE radio access capabilities for the RLC, Transport Channel, and Physical Channel. At this
point, an RRC connection has been established between the UE and the SRNC.
At this point in the call setup, the UE has reached a major milestone. Not only has it
successfully completed the Random Access procedure, it has also setup a dedicated radio
bearer with the RNC. This allows the UE to utilize fast power control, and soft handover to
overcome adverse RF conditions. Prior to this, the UE was highly susceptible to interference
and coverage issues.
The UE is now known by the UTRAN and has been assigned an ID: U-RNTI. It has signaling
resources assigned to it, but has no bearer resources. The CN, however, has no visibility
about this UE at this point. That is where the next phase (Pre-RAB Phase) comes in.
5.1.2.
Pre-RAB Phase, CS Voice
Once the RRC connection has been established, the next phase of the call setup procedure
is the Pre-RAB or Signaling phase. This is initiated by the UE transmitting the Non-Access
Stratum (NAS) message, CM Service Request, to the CN. This initial NAS message will
trigger the creation of an Iu Signaling Connection between the SRNC and the MSC. At this
point, the core network initiates the security procedures like Authentication and Ciphering.
During the Authentication process, the Authentication Center (AuC) uses an IMSI specific
Authentication Key (K) and a randomly generated number (RAND) to generate five security
parameters, known as the Quintet. Once these security parameters are generated, the CN
sends the NAS message, Authentication Request, to the UE. Embedded in this message
is the RAND used to generate the Quintet, as well as an Authentication Token (AUTN),
which is derived from two of the Quintet parameters. Because the Authentication Key is
also stored on the UE’s SIM card, the UE can use this RAND to generate the same Quintet
that was generated by the AUC. In this manner, the UE can compare its locally generated
AUTN to the version sent in the Authentication Request message. If these versions match,
the UE has successfully authenticated the sender of the message, thus eliminating
fraudulent access to UE specific information. This network authentication step is new for
UMTS and was not available in GSM. Once this is complete, the UE responds with a NAS
Authentication Response message, which contains one of the Quintet parameters, know
as the Response (RES). The CN compares this RES with is locally generated Expected
Response (XRES) to authenticate the UE. This method of bi-directional authentication
between the UE and the CN is known as Mutual Authentication.
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Once Mutual Authentication is complete, the Integrity and Ciphering security features can
be initiated. Integrity insures that L3 messaging can not be altered in an unauthorized
manner and that the sender of the signaling is the appropriate sender (i.e. Integrity protects
the UE from the “man in the middle attack”). Ciphering encrypts the signaling and user
data sent between the UE and the SRNC. Integrity and Ciphering procedures are initiated
by the MSC by sending the RANAP message Security Mode Command. This message
contains the Integrity Key (IK) and the Ciphering Key (CK), which are two of the five
security parameters (Quintet). The RNC uses these keys to perform the Integrity and
Ciphering security features. Because the UE can generate the same Quintet that was
generated by the AUC, the IK and CK are known to the UE as well. The RRC message
Security Mode Command is sent by the SRNC to instruct the UE to start the Integrity and
Ciphering procedures. The Security Mode Control procedure is finalized by sending the RRC
Security Mode Complete message from the UE to the SRNC. This message is also
forwarded to the MSC using the RANAP Security Mode Complete message.
Once the security functions are enabled, the NAS message Setup is sent from the UE to the
MSC. This message contains the dialed digits, as well as some Bearer and Call Control
capabilities of the UE. The MSC confirms the call setup request has been received and is in
progress with a Call Proceeding message.
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Figure 1 - Circuit Switched Call Setup Flow Diagram
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5.1.3.
RAB Setup Phase, CS Voice
Now that the RRC Connection is established, and the UE authentication and encryption is
enabled, the UE can request the setup it requires for this call and the MSC can start
negotiating the call with the UE. Upon a successful negotiation, the MSC triggers the setup
of resources for the User Plane by means of the “RAB Assignment” procedure. Since the
QoS parameters indicate that the Traffic Class for this call is “Conversational”, the RRC state
for the Radio Bearer to be set up is “Cell_DCH.” Having set up the resources for the User
Plane, the call can be completed by means of some further NAS messages to notify the user
that the call has been accepted. The voice traffic can now be sent over the resources in the
User Plane.
Once the service request has been initiated, the MSC requests the UTRAN to allocate the
necessary radio resources via the RANAP message RAB Assignment Request. The RAB
Assignment is the mechanism for the CN to notify the UTRAN of the appropriate Quality of
Service (QoS) and attributes required to deliver the service. Examples of these attributes
include, but are not limited to:

Maximum Bit Rate
o
o

UL = 12.2 kbps
DL = 12.2 kbps
Guaranteed Bit Rate:
o
o

UL = 4.75, 5.9, 7.95, 12.2 kbps
DL = 4.75, 5.9, 7.95, 12.2 kbps
Maximum SDU Size:
o

244 (bits)
Sub-flow SDU Size (bits)
o
o
o
Sub-flow 1: 42, 55, 75, 81, 39
Sub-flow 2: 53, 63, 84, 103, 0
Sub-flow 3: 0, 0, 0, 60, 0
Because this is requesting dedicated resources, the Admission Control Algorithm is again
invoked. If admission is granted, a Radio Link Setup Request message is sent from the
RNC to the Node B via Node B Application Part (NBAP) signaling. If the Node B responds
positively with a Radio Link Setup Response, and Bearer Synchronization is established,
a RRC Radio Bearer Setup message is sent from the RNC to the UE. Embedded in this
message is all the information the UE needs to construct a dedicated channel to support the
CS voice call (e.g. AMR 12.2 kbps codec plus SRB). The AMR trans-coder within the MSC
divides speech into 3 classes (A, B, and C) where A is the highest priority, B is next, C is
lowest priority. Since each of these classes has unique RAB attributes, they are mapped to
their own logical and transport channel within the radio bearer. For Ericsson, the AMR A bit
sub-flow is identified by Transport Channel 8, and uses third rate convolutional coding. The
transport channel DL BLER target for outer loop power control, as well as the Rate Matching
attribute the for this Transport Channel are also transmitted to the UE at this time. Because
the successful transmission of the B and C sub-flows (Transport Channels 9 and 10
respectfully) are not monitored by the outer loop power control, transport channel DL BLER
targets are not required. The AMR B sub-flow transport channel uses third rate
convolutional coding, while the AMR C sub-flow uses half rate convolutional coding. Table
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1 lists some of the Transport Channel attributes for each of the sub-flows used for AMR
Speech.
Ericsson
TrCh ID
AMR
Sub-flow
Coding
8
9
10
A
B
C
1/3
1/3
1/2
CRC
12 bits
None
None
Physical
Frame
Size
20 ms
20 ms
20 ms
Table 1 - Transport Channel Attributes AMR Speech
In addition to configuring the transport channels for the AMR speech sub-flows, Transport
Channel 31 is reconfigured from 13.6 kbps to a 3.4 kbps SRB. All four of these transport
channels (8, 9, 10, and 31) are multiplexed into a single Coded Composite Transport
Channel (CcTrCh), and mapped to a physical channel with a 64 bit spreading factor for the
UL, and a 128 bit spreading factor for the DL (assuming AMR 12.2 kbps). Once this Radio
Bearer has been configured and synchronized in the DL, the UE sends the SRNC a RRC
Radio Bearer Setup Complete message. Upon receiving this message, the SRNC
responds to the MSC with a RANAP RAB Assignment Response message. At this point,
the call has been successfully setup, and moves into the Retainability phase of the call.
The remaining NAS messages are used to provide the UE with the status of the call. The
NAS Alerting message indicates to the UE that the other end has been notified of an
incoming call. At this time, the UE typically generates ringing tones to alert the caller that
progress is being made. Once the called party answers the call, the MSC sends NAS
message Connect to the UE. At this point the UE and MSC activate their respective voice
coders, and the UE sends the NAS message Connect Acknowledgement to the MSC.
Figure 2 illustrates the actual L3 messaging of a call setup, collected by UE logging tool, in a
market with an Ericsson UTRAN.
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Figure 2 - L3 Messaging sample
5.1.4.
Counters Related to CS Voice Call Setup
In this section, the counters associated with a CS Voice call setup are discussed.
Understanding which counters are affected, and under what circumstances they are
incremented during the call flow, is essential to successfully monitor and troubleshoot the
performance of the network.
Figure 3 illustrates the counters associated with a RRC Connection establishment based a CS
establishment cause. These counters include, but are not limited to the following:

pmTotNoRrcConnectReq

pmTotNoRrcConnectReqSucc

pmTotNoRrcConnectReqCs

pmTotNoRrcConnectReqSuccCs

pmNoRejRrcConnMpLoadC
Refer to [14] for details on these counters.
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Figure 3 - Flowchart for Ericsson Counters, RRC Connection Setup, CS
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Figure 4 and Figure 5 illustrate the counters associated with a RAB Establishment Attempt
and Success respectively. These counters related to a CS Call Setup include, but are not
limited to the following:

pmNoRabEstablishAttempts

pmNoRabEstablishAttemptSpeech

pmpmNoRabEstablishSuccess

pmpmNoRabEstablishSuccessSpeech

pmNoRabEstablishFailureUeCapability

pmNoFailedRabEstAttemptExceedConnLimit

pmNoFailedRabEstAttemptLackDlAse

pmNoFailedRabEstAttemptLackUlAse

pmNoFailedRabEstAttemptLackDlChnlCode

pmNoFailedRabEstAttemptLackDlPwr
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Figure 4 - Flowchart for Ericsson Counters, RAB Setup
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Figure 5 - Flowchart for Ericsson Counters, Successful RAB Setup
5.1.5.
Circuit Switched Voice Accessibility KPI
Equation 1 provides the KPI equation for CSV Access failure rate.
  pmTotNoRrc ConnectReq CsSucc(Utr anCell) pmNoRabEst ablishSucc essSpeech( UtranCell)
100 * 1  
*
pmNoRabEst ablishAtte mptSpeech( UtranCell)
  pmTotNoRrc ConnectReq Cs(UtranCe ll)



Equation 1 - CSV Access Failure Rate
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5.2. Packet Switched Call Setup
Figure 6 illustrates call flow diagram for the typical establishment of a Packet Switched call.
Similar to the CS call setup, the PS setup is also divided into three phases:
5.2.1.

The RRC Setup Phase

The Pre-RAB Phase

The RAB Setup Phase
RRC Setup Phase, PS Setup
In order to setup a call, the UE must establish an RRC Connection with the UTRAN. Once
the UE has completed the Random Access Procedure, a RRC Connection Request
Message is sent to the SRNC. Embedded in this message is the establishment cause, or
the reason the UE is requesting a RRC connection. For the case mobile originating PS Call,
the establishment cause could be “Originating Interactive Call”, or “Originating Background
Call”. If the UE is responding to a page, or a mobile terminating PS call, the establishment
cause could be “Terminating Interactive Call”, or “Terminating Background Call”.
Upon reception of the RRC Connection Request, the UE is assigned UMTS Radio Network
Temporary Identifier (U-RNTI). This identifier is unique to the PLMN and is derived from
the SRNC identity and a unique SRNC RNTI (S-RNTI). In this manner the U-RNTI is unique
to the UE.
After a RRC Connection Request message is received, the Admission Control algorithm is
invoked to confirm the required dedicated resources are available to establish a signaling
connection. These resources include codes, power, and channel elements. If admission
can not be granted, an RRC Connection Reject message is sent, and the counter
pmNoReqDeniedAdm is pegged. If admission is granted, a Radio Link Setup request is
sent to the Node B requesting dedicated resources be reserved. Once resources are
reserved, the Node B responds with a Radio Link Setup Response message, and
activates its Radio Link Set Supervision algorithm for this Radio Link.
At this time, the RRC Connection Setup is sent to the UE with a RRC state indicator
ordering the UE to go to CELL_DCH. Embedded in this message is all the information the
UE needs to construct a dedicated channel. This includes all the logical, transport, and
physical layer information required to build the 13.6 kbps SRB. For Ericsson, the SRB is
identified by Transport Channel 31, and uses third rate convolution coding. The transport
channel DL BLER target for outer loop power control, as well as the Rate Matching for the
SRB is also transmitted to the UE at this time. At the physical layer, this SRB utilizes a 128
bit spreading factor.
After the RRC Connection Setup message is sent, the Node B begins transmitting the DL
DPCH to enable L1 synchronization. Once synchronization has occurred, the UE sends an
RRC Connection Setup Complete message to the SRNC. Within this message are all the
UE radio access capabilities for the RLC, Transport Channel, and Physical Channel. At this
point, an RRC connection has been established between the UE and the SRNC.
At this point in the PS call setup, the UE has reached a major milestone. Not only has it
successfully completed the Random Access procedure, it has also setup a dedicated radio
bearer with the RNC. This allows the UE to utilize fast power control, and soft handover to
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overcome adverse RF conditions. Prior to this, the UE was highly susceptible to interference
and coverage issues.
The UE is now known by the UTRAN and has been assigned an ID: U-RNTI. It has signaling
resources assigned to it, but has no bearer resources. The CN, however, has no visibility
about this UE at this point. That is where the next phase (Pre-RAB Phase) comes in.
5.2.2.
Pre-RAB Phase, PS Setup
Once the RRC connection has been established, the next phase of the PS call setup
procedure is the Pre-RAB or Signaling phase. This is initiated by the UE transmitting the
Non-Access Stratum (NAS) message, Service Request, to the CN. This initial NAS message
will trigger the creation of an Iu Signaling Connection between the SRNC and the SGSN. At
this point, the core network initiates the security procedures like Authentication and
Ciphering.
During the Authentication process, the Authentication Center (AuC) uses an IMSI specific
Authentication Key (K) and a randomly generated number (RAND) to generate five security
parameters, known as the Quintet. Once these security parameters are generated, the CN
sends the NAS message, Authentication Request, to the UE. Embedded in this message
is the RAND used to generate the Quintet, as well as an Authentication Token (AUTN),
which is derived from two of the Quintet parameters. Because the Authentication Key is
also stored on the UE’s SIM card, the UE can use this RAND to generate the same Quintet
that was generated by the AUC. In this manner, the UE can compare its locally generated
AUTN to the version sent in the Authentication Request message. If these versions
match, the UE has successfully authenticated the sender of the message, thus eliminating
fraudulent access to UE specific information. This network authentication step is brand new
in UMTS and was not available in GSM. Once this is complete, the UE responds with a NAS
Authentication Response message, which contains one of the Quintet parameters, know
as the Response (RES). The CN compares this RES with its locally generated Expected
Response (XRES) to authenticate the UE. This method of bi-directional authentication
between the UE and the CN is known as Mutual Authentication.
Once Mutual Authentication is complete, the Integrity and Ciphering security features can
be initiated. Integrity insures that L3 messaging can not be altered in an unauthorized
manner and that the sender of the signaling is the appropriate sender (i.e. Integrity protects
the UE from the “man in the middle attack”). Ciphering encrypts the signaling and user
data sent between the UE and the SRNC. Integrity and Ciphering procedures are initiated
by the SGSN by sending the RANAP message Security Mode Command. This message
contains the Integrity Key (IK) and the Ciphering Key (CK), which are two of the five
security parameters (Quintet). The RNC uses these keys to perform the Integrity and
Ciphering security features. Because the UE can generate the same Quintet that was
generated by the AUC, the IK and CK are known to the UE as well. The RRC message
Security Mode Command is sent by the SRNC to instruct the UE to start the Integrity and
Ciphering procedures. The Security Mode Control procedure is finalized by sending the RRC
Security Mode Complete message from the UE to the SRNC. This message is also
forwarded to the SGSN using the RANAP Security Mode Complete message.
Once the security functions are enabled, the NAS message PDP Context Activation
Request is sent from the UE to the CN. This message is basically requesting a connection
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to the Public Packet Data Network via the SGSN and GGSN, using the Packet Data Protocol
(PDP).
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Figure 6 - Packet Switched Call Flow Diagram
5.2.3.
RAB Setup Phase, PS Setup
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Now that the RRC Connection is established, and the UE authentication and encryption
enabled, the UE can request the setup it requires for this call and the SGNS can start
negotiating the setup with the UE. Upon a successful negotiation, the SGSN triggers the
setup of resources for the User Plane by means of the “RAB Assignment” procedure. Since
the QoS parameters indicate that the Traffic Class for this call is “Interactive”, the RRC state
for the Radio Bearer to be set up is “Cell_DCH.”
Once the service request has been initiated, the SGSN requests the UTRAN to allocate the
necessary radio resources via the RANAP message RAB Assignment Request. The RAB
Assignment is the mechanism for the CN to notify the UTRAN of the appropriate Quality of
Service (QoS) and attributes required to deliver the service. Examples of these attributes
include, but are not limited to:

Maximum Bit Rate
o
o

UL = 12.2 kbps
DL = 12.2 kbps
Guaranteed Bit Rate:
o
o

UL = 8, 64, 128, 384 and HSPA
DL = 8, 64, 128, 384 and HSPA
Maximum SDU Size:
o
12016 (bits)
Because this is requesting dedicated resources, the Admission Control Algorithm is again
invoked. If admission is granted, a Radio Link Setup Request message is sent from the
RNC to the Node B via Node B Application Part (NBAP) signaling. If the Node B responds
positively with a Radio Link Setup Response, and Bearer Synchronization is established,
a RRC Radio Bearer Setup message is sent from the RNC to the UE. Embedded in this
message is all the information the UE needs to construct a Radio Bearer to support the PS
session. At this point, the PS session may be setup utilizing dedicated channels, (i.e. 64
kbps UL/64 kbps DL), the High Speed Downlink Shared Channel (HS-DSCH) and an UL
dedicated channel (i.e. 64 kbps UL/HS-DSCH), or the HS-DSCH and Enhanced Uplink (EUL)
(i.e. EUL/HS-DSCH). Setup for these three scenarios is dependant on UE capabilities (as
communicated in the RRC Connection Setup Complete message), and the capabilities of
the serving cell. For this discussion, it is assumed that the PS session is setup using
dedicated channels (i.e. 64k/64k).
Since this bearer has unique RAB attributes, it is mapped to its own logical, transport and
physical channel within the radio bearer. For Ericsson, Transport Channel 24 is used for PS,
and utilizes Turbo coding for forward error correction. The transport channel DL BLER
target for outer loop power control as well as the Rate Matching attribute for this transport
channel is also transmitted to the UE at this time.
In addition to configuring the transport channel for the PS Session, Transport Channel 31 is
reconfigured from 13.6 kbps to a 3.4 kbps SRB. Both of these transport channels (24 and
31) are multiplexed into a single Coded Composite Transport Channel (CcTrCh), and
mapped to a physical channel with a 16 bit spreading factor for the UL, and a 32 bit
spreading factor for the DL (assuming 64k/64k RAB). Once this Radio Bearer has been
configured and synchronized in the DL, the UE sends the SRNC a RRC Radio Bearer Setup
Complete message. Upon receiving this message, the SRNC responds to the SGSN with a
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RANAP RAB Assignment Response message. At this point, the session has been
successfully setup, and moves into the Retainability phase of the call. The NAS Activate
PDP Context Accept message indicates to the UE that an IP address has been assigned
and the PS session may begin. Figure 7 illustrates the actual L3 messaging of a PS session
setup, collected by UE logging tool, in a market with an Ericsson UTRAN.
Figure 7 - L3 Messaging for PS Setup
5.2.4.
Counters Related to PS Setup
In this section, the counters associated with a PS session setup are discussed.
Understanding which counters are affected, and under what circumstances they are
incremented during the call flow, is essential to successfully monitor and troubleshoot the
performance of the network.
Figure 8 illustrates the counters associated with a RRC Connection establishment based a PS
establishment cause. These counters include, but are not limited to the following:

pmTotNoRrcConnectReq

pmTotNoRrcConnectReqSucc

pmTotNoRrcConnectReqPs

pmTotNoRrcConnectReqSuccPs

pmTotNoUtranRejRrcConnReq

pmNoRejRrcConnMpLoadC
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Figure 8 - Flowchart for Ericsson Counters, RRC Connection Setup, PS
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Figure 4 and Figure 5 illustrate flowchart for the counters associated with a RAB
Establishment Attempt and Success respectively. The counters related to a PS Session
Setup include, but are not limited to the following:
5.2.5.

pmNoRabEstablishAttempts

pmNoRabEstablishAttemptPacketInteractive

pmpmNoRabEstablishSuccessPacketInteractive

pmNoRabEstablishAttemptPacketInteractiveHs

pmNoRabEstablishSuccessPacketInteractiveHs

pmNoRabEstablishFailureUeCapability

pmNoFailedRabEstAttemptExceedConnLimit

pmNoFailedRabEstAttemptLackDlAse

pmNoFailedRabEstAttemptLackUlAse

pmNoFailedRabEstAttemptLackDlChnlCode

pmNoFailedRabEstAttemptLackDlPwr
Packet Switched Accessibility KPI
Equation 2 provides the KPI equation for PSD Access failure rate (refer to the Ericsson
UMTS Network KPI document for details regarding this equation).
  pmTotNoRrc ConnectReq PsSucc(Utr anCell)

100 * 1  
* 0.9993 * R99 InteractiveRABEstabl ishSuccess Rate 
pmTotNoRrc
ConnectReq
Ps(UtranCe
ll)

 
Equation 2 - PSD Access Failure Rate
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6. Random Access Procedure
The Random Access Procedure is utilized by the UE to access the UTRAN network from an
Idle, or Cell_FACH state. Since this is a critical step in the CS or PS call setup process,
understanding this procedure is essential to successfully maintain and operate the UMTS
network. In addition to being familiar with the Random Access Procedure, it is important to
understand the configurable parameters utilized by the algorithm, and the affects of
modifying these parameters. It is quite possible to aggressively configure the Random
Access parameters to improve the likelihood of accessing the network, at the cost of
capacity. Alternatively, it is also possible to be overly concerned about capacity at the cost
of successfully accessing the network.
The UMTS Random Access Procedure is based on a slotted ALOHA approach, which is
commonly utilized by modern wireless communication systems. Developed at the University
of Hawaii in the early 1970’s, this access algorithm allows any terminal to transmit on the
shared uplink channel without considering if the channel is being utilized by another
terminal. The term “slotted” implies that these transmissions occur at predefined time slots.
If the transmission is received by the Node B correctly, an acknowledgement will be sent to
the UE. If no acknowledgement is received by the UE, it assumes the previous transmission
was lost and retransmits after waiting a random amount of time. An overview of the 3GPP
implementation of this Random Access Procedure, and the configurable parameters utilized
by Ericsson, are discussed in the following section.
6.1. Random Access Overview
When accessing the UMTS network, several factors must be considered. The channel which
is utilized, the Random Access Channel (RACH), is a shared channel. Because of this, the
possibility of collisions from multiple user access attempts is possible. In addition, all uplink
transmissions result in co-channel interference and therefore require stringent power control
to minimize this interference. However, since the RACH does not use closed loop power
control, the UE must estimate the power required to transmit the RACH message. The goal
of the Random Access Procedure is to minimize the chance of collisions, and to estimate the
UE transmit power so that interference to other UEs is minimized. However, these goals
must be achieved while minimizing system access time.
6.1.1.
Random Access Channels
To achieve these goals, the UE initially sends test messages (i.e. preambles) on the Physical
Random Access Channel (PRACH), prior to sending the RACH message (e.g. the RRC
Connection Request message). The preamble messages are sent in predefined slots
known as Access Slots. The PRACH Access Slot format, and its relation to the Acquisition
Indication Channel (AICH) slots, is illustrated in Figure 9 (ref. 3GPP TS 25.214). There are
15 defined Access slots, divided into two access slot sets, every 20 ms. There are 8 access
slots (0-7) in access slot set 1, and 7 access slots (8-14) in access slot set 2. In addition,
there are 15 corresponding AICH slots which are time offset by p-a. The AICH only exists
on the physical layer and is used solely to acknowledge preambles sent on PRACH Access
Slots.
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Figure 9- PRACH access slot and downlink AICH relation
p-a is the preamble to Acquisition Indication (AI) distance
p-p is the preamble to preamble distance
p-m is the preamble to message distance
The AICH Transmission Timing (p-a) can be set by a configurable parameter called
aichTransmissionTiming and can be either equal to 0 or 1 in the Ericsson
implementation. This parameter is interpreted as follows (Reference 3GPP TS 25.211).
If aichTransmissionTiming = 0



p-p, min = 15360 chips ( 3 access slots)
p-a = 7680 chips
p-m = 15360 chips (3 access slots)
If aichTransmissionTiming = 1



p-p, min = 20480 chips ( 4 access slots)
p-a = 12800 chips
p-m = 20480 chips (4 access slots)
The AICH Transmission Timing parameter is broadcast in SIB 5.
6.1.2.
Open Loop Power Control
As previously stated, the initial preamble power (P_PRACH) must be conservatively
calculated to insure that uplink interference to other UEs is minimized. To achieve this, the
initial preamble power (P_PRACH) is calculated by the following equation:
P_PRACH  L_PCPICH  RTWP  constantVa lueCprach 
Equation 3 - Initial Preamble Transmit Power
Where:
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
L_PCPICH = the estimated downlink path loss of the Pilot Channel (CPICH)

RTWP = the Received Total Wideband Power (i.e. Uplink Interference) measured
by the Node B

constantValueCprach = is a configurable parameter used to offset the equation’s
result
The downlink path loss of the Pilot Channel (L_CPICH) is estimated by subtracting the
CPICH RSCP (measured by the UE) from the primaryCPICH-TX-Power, which is broadcast in
System Information Block 5 (SIB 5). In addition, the parameter constantValueCprach is
also broadcast in SIB 5. The uplink interference (RTWP) measured by the Node B is
broadcast in SIB 7. The purpose of the configurable parameter constantValueCprach, is
to account for the processing gain of the preamble, which is equivalent to 10log(256) = 24
dB. Ericsson’s default value for constantValueCprach is equal to -27 dB, which results in
a -3 dB offset to the initial preamble transmit power. This negative offset yields a
conservative estimate for the transmit power of the initial preamble, thus reducing the
potential of causing unnecessary uplink interference.
6.1.3.
Physical Layer Random Access Procedure
Once the initial preamble transmit power is determined, the physical layer random access
procedure shall be performed as follows (reference 3GPP TS 25.214, Section 6):
1. An access slot is randomly selected from the group of available access slots in the next
full access slot set (e.g. Access Slot set 1). If there are no available access slots in the
selected set, randomly select an available access slot in the next access slot set (e.g.
Access Slot set 2). The term “available access slots” is used because some of the access
slots may be reserved for a higher priority Access Class (AC), such as emergency
personnel.
2. Once an access slot has been selected, the UE randomly selects a Preamble Signature
from the set of available signatures. As specified in 3GPP TS 25.213, Section 4.3.3, the
set of Preamble Signatures consist of 16 Hadamard codes, each 16 bits long. The
selected 16 bit code is repeated 256 times and combined with a preamble scrambling
code, to form the transmitted preamble code. The preamble scrambling code selected is
one of 16 associated with the CPICH Scrambling code of the cell being accessed. In this
manner, the Node B can identify preambles targeted for it, and ignore preambles
intended for other Node Bs. Similar to the access slot scenario, the term “available
signatures” is used because some of the signatures may be reserved for a higher priority
Access Class (AC), such as emergency personnel.
3. At this point, the UE transmits the selected preamble code, using the selected slot; at an
initial preamble transmit power (P_PRACH), which was calculated using Equation 3. If
the calculated transmit power exceeds the maximum allowed UE transmit power (as
broadcast on SIB 3), the preamble will be transmitted at the maximum allowed power.
4. After the preamble is sent, the UE monitors the AICH for an acknowledgement on the
corresponding AICH access slot (refer to Figure 9). The UE is able to differentiate AICH
acknowledgements targeted for it, and ignore those intended for other UEs, because the
16 specified 32 bit AICH signature patterns used by the AICH are related to the 16
preamble signatures previously described. Refer to 3GPP TS 25.211, Section 5.3.3.7 for
information regarding the AICH.
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5. If no acknowledgement (positive or negative) is detected on the corresponding AICH
access slot, the UE utilizes the next available access slot, randomly picks an available
preamble signature, and increases the preamble transmit power by a value equal to the
configurable parameter powerOffsetP0 (broadcast in SIB 5/6). If this newly adjusted
power is not greater than the maximum allowed UE transmit power by 6 dB, the
preamble is transmitted at the calculated power or the maximum UE transmit power,
whichever is minimum.
6. Assuming no acknowledgement is detected, the power ramping process will continue (as
described in step 5), unless one or both of the following events occur:
a. The number of preambles transmitted equals the configurable parameter
preambleRetransMax (broadcast in SIB 5/6).
b. The newly calculated preamble transmit power exceeds the maximum allowed UE
transmit power by 6 dB, after applying the powerOffsetP0 offset.
7. If step 6a or 6b occur, the UE will exit the physical random access process and inform
the MAC layer that “No Ack on AICH” was detected.
8. If the preamble is detected, and the Node B responds with a positive acknowledgement,
the UE will transmit the Layer 3 message three or four access slots after the last
preamble transmitted. The control part of this message will be transmitted at a power
equal to the power of the last preamble sent, plus the value of the configurable
parameter powerOffsetPpm (not to exceed the maximum allowed UE transmit power).
The data part of this Layer 3 message is transmitted based on the gain factors for
PRACH, which are also broadcast in SIB 5.
9. If the preamble is detected, and the Node B responds with a negative acknowledgement
the UE will exit the physical random access process and inform the MAC layer that a
“Nack on AICH recieved”.
Figure 10 illustrates the major aspects of the physical random access procedure. The first
preamble is transmitted at the calculated initial preamble transmit power. If no
acknowledgement is received on the AICH, the next preamble is transmitted with a power
that is increased by powerOffsetP0. Once the preamble is positively acknowledged, the
message is sent with a power that is increased by powerOffsetPpm, relative to the last
preamble power.
Figure 10 - Random Access Power Ramping on PRACH
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The time between preamble transmissions is dependant on the availability of access slots,
and the AICH Transmission Timing parameter described earlier. The minimum time interval
is based on the AICH Transmission Timing parameter as specified earlier. The maximum
time between preambles is dependant on the availability of access slots. If access slots are
reserved for a higher priority Service Class (SC), the time between preambles may increase
as a function of the number of sub channels used.
6.1.4.
MAC Monitoring and Control of Random Access Transmissions
The physical layer random access procedure described is only part of the overall Random
Access procedure. In addition to initiating the physical random access procedure, the
Medium Access Control (MAC) also monitors and reinitiates RACH transmission based on
parameters provided by higher layers. Figure 11 is a flowchart illustrating the MAC’s control
for RACH transmissions. Once it is determined that there is a message to send on RACH,
the MAC obtains required parameters from higher layers and initiates the physical layer
random access procedure, which is described in the previous section. The three possible
responses from Layer 1 are: “Ack”; “Nack”; or “No Ack”

An “Ack” indicates a positive acknowledgement was received during the physical
random access procedure. In this case, the procedure was successful and the RRC
Message was transmitted on RACH. At this point, the MAC ends the RACH
transmission procedure.

A “Nack” indicates that a negative acknowledgement was received during the
physical random access procedure, possible due to contention. In this case, the UE
needs to reinitiate the random access procedure after time delay. As shown in
Figure 11, the MAC inserts a fixed T2 =10 ms delay, plus an additional back off
timer TBO1 = (NBO1 * 10 ms), where NBO1 is an integer randomly selected within the
range of parameters NBO1 (max) and NBO1 (min), which are broadcast in SIB 5. The
purpose of this random back off timer is to reduce the probability of repeated
collisions on the PRACH. Once this timer has expired, the MAC checks the number
of initiated preamble transmissions to the configurable parameter
maxPreambleCycle. This parameter basically limits the number of physical
random access procedures that can be initiated by the MAC, per request from
higher layers. If the maxPreambleCycle limit has been exceeded, the MAC ends
the RACH transmission procedure and the higher layer (RRC) is notified that the
transmit status was “unsuccessful”. If the maxPreambleCycle limit has not been
exceeded, the MAC performs a persistency check. A persistency check is basically
another way to insert a random delay (in increments of 10 ms) into the algorithm.
Once this delay is completed, the command is sent to the physical layer to
reinitiate the physical random access procedure.

A “No Ack” indicates that neither a negative or positive acknowledgement was
received during the physical random access procedure. In this case, the UE needs
to reinitiate the random access procedure after a time delay. As shown in Figure
11, the process used for this scenario is similar to the “Nack” scenario, except the
back off timer TBO1 is not utilized.
Simply put, the MAC will reinitiate the physical layer random access procedure (described in
Section 6.1.3) repeatedly until either a positive acknowledgement is received, or the
maxPreambleCycle limit has been exceeded.
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In the Ericsson implementation, NBO1 (max) = NBO1 (min) = 0, which means the backoff
timer TBO1 is not used. Also the persistence value selected is 1, so that the delay due to
persistence check is not implemented either.
Start
NOTE: MAC-c/sh receives
RACH tx control parameters from
RRC with CMAC-CONFIG-Req
primitive whenever one of the
parameters is updated
Get RACH tx control parameters
from RRC:
M max , N BO1min ,
N BO1max , set of ASC parameters
N
Any data to be
transmitted ?
Y
ASC selection:
(PRACH partition i, P i)
M := 0
Increment preamble transmission
counter M
M  M max ?
Indicate to higher layer
that maximum number of
preamble cycles have been
reached (TX status
"unsuccessful")
N
Y
End
Set and wait expiry
timer T BO1 (N BO1 *10 ms)
Update RACH tx control
parameters
Wait expiry
Timer T 2 (10 ms)
Wait expiry
Timer T 2 (10 ms)
Set Timer T 2 (10 ms)
Wait expiry
timer T 2 (10 ms)
Draw random number 0  Ri 1
N
R  Pi ?
Y
Send PHY-ACCESS-REQ
(start of L1 PRACH transmission
procedure)
No Ack
L1 access info
N ack
?
Ack
Send PHY-DATA-REQ,
indicate TX status to higher
layer
(PRACH message part transmitted)
End
Figure 11 – MAC Flowchart of RACH Transmission Control
6.1.5.
RRC Control or Random Access Transmissions
The Radio Resource Control (RRC) initiates the MAC RACH transmission control algorithm
whenever a message needs to be sent on the RACH. In addition, the RRC monitors the
results of these transmissions and has the ability to resend messages that were not
successfully transmitted. For the specific case of the RRC Connection Request message,
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these retransmissions are controlled by the N300 and T300 parameters, which are
broadcast in SIB 1.
When it is determined that an Idle UE requires an RRC Connection, RRC will initiate the RRC
Connection procedure. At the onset of this procedure, an internal counter, V300 is set to 1
and the RRC Connection Request message is submitted to the lower layers (MAC and L1)
for transmission on RACH. When the MAC indicates either success or failure in sending this
RRC message, timer T300 is started. If this transmission does not result in the reception of
a RRC Connection Setup message before T300 expires, the RRC checks the value of
counter V300. If V300 is less than or equal to N300, the RRC Connection Request
message is resubmitted to the MAC for transmission on the RACH. This process is
continued until either an RRC Connection Setup message is received by the UE, or the
V300 counter exceeds the parameter N300. If the latter occurs, the UE enters idle mode
and RRC Connection procedure is considered to be unsuccessful. (Reference 3GPP TS
25.331, Section 8.1.3.5)
To summarize, if the transmission of the RRC Connection Request message does not
result in the reception of the RRC Connection Setup message; it will be retransmitted
N300 times with T300 seconds delay between transmissions. Failure to receive the RRC
Connection Setup message may be due to several reasons, which include, but are not
limited to:

The Layer 1 preambles were never detected

The Layer 1 preambles were detected, and a “Nack” was transmitted by the AICH
(preambleRetransMax times)

The Layer 1 preambles were detected, an “Ack” was transmitted by the AICH, and
the RRC Connection Request message was sent, however it was not
successfully detected by the Node B

The RRC Connection Request message was received by the Node B, however
the RRC Connection Setup message was not successfully detected by the UE.
In Ericsson implementation, these parameters are not operator configurable and are
currently set as N300 = 5, and T300 = 2000 ms.
6.1.6.
Interaction of RRC, MAC and Physical Layer Random Access
Procedures
As described before, the Physical, MAC, and RRC layers all play a part in the random access
procedure. In order to clarify the interaction of these layers on random access, an example
will be provided in this section. For this example, the following parameter values will be
assumed:

powerOffsetP0 = 2 dB

preambleRetransMax = 15

maxPreambleCycle = 3

powerOffsetPpm = 2 dB

N300 = 5

T300 = 2000 ms
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Assume that an idle UE is originating CS call, and RRC Connection Request message
needs to be sent. The initial preamble power is determined by Equation 3 to be -25 dBm.
The preamble is sent at this power and no acknowledgement is sent on the AICH. The
second preamble is sent at -23 dBm (due to powerOffsetP0 = 2 dB). Assuming an
acknowledgement is not received on all the following preambles, a total of 15 preambles
(preambleRetransMax = 15) would be sent with the last one transmitting at +3 dBm.
After a delay of 2-15 ms, the MAC would repeat the process up to 2 more times
(maxPreambleCycle = 3). Every time the process is repeated, the initial preamble
transmit power would be recalculated. If the process continued without a received
acknowledgement on all the following preambles, an additional 30 preambles could be
transmitted during the 2nd and 3rd preamble cycle. This would bring the total to 45
preambles for the initial RRC Connection Request (15 * 3 = 45 preambles). After a 2
second delay (T300 = 2000 ms), a second RRC Connection Request message would be
sent to the MAC layer initiating the process to repeat. If this continues without an
acknowledgement being received, it is possible that a total of 270 preambles could be sent
over a 10-11 second period (45 * (5+1) = 270). This is a worst case scenario; however its
occurrence in real world situation is not rare.
As a second example, assume that RF conditions are poor and the initial preamble power is
determined by Equation 3 to be +18 dBm. The second preamble is sent at +20 dBm and a
positive acknowledgement is sent on the AICH. The UE would transmit the RRC
Connection Request message with the control part of the message at +22 dBm
(powerOffsetPpm = 2 dB). Assuming a RRC Connection Setup message is received
within 2 seconds, then no additional preambles will be sent. Figure 12 is an example of a
physical random access logged with TEMS. This mode report lists the initial preamble
transmit power (18 dBm), the number of preambles sent during this cycle (2 preambles)
and the result on the associated AICH slot (Ack received).
Figure 12 – Log file of Physical Layer Random Access
6.1.7.
RACH Sub-Channels
As mentioned previously, some of the PRACH access slots may be reserved for UEs
containing higher priority Access Class (AC) USIMS, such as those for emergency personnel.
This functionality is accomplished by means of RACH sub-channels. By reserving one or
more RACH sub-channels to a specific Access Service Class (ASC), the likelihood of a
successful access can be improved for members of that AC.
A RACH sub-channel is defined as a subset of the PRACH access slots. There are a total of
12 sub-channels with each sub-channel consisting of 5 access slots. Since 15 access slots
span 2 radio frames, the 12 sub-channels repeat every 60 access slots (or 8 radio frames).
Each sub channel consists of 5 access slots which include the access slot corresponding to
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the sub channel number as well as the 12th access slot relative to the sub channel number.
Table 2 defines the PRACH access slot to RACH sub-channel mapping (3GPP TS 25.214,
Section 6.1.1). As shown in the Table 2, Sub-channel 0 consists of 5 access slots: 0 (frame
1), 12 (frame 2), 9 (frame 3), 6 (frame 4), and 3 (frame 6). Here access slot 0
corresponds to the sub channel number 0, and the 12th access slot for this sun channel
would be access slot 12. Sub-channels 1-11 are similarly distributed across the 8 radio
frames.
SFN modulo 8
0
of
corresponding
P-CCPCH frame
0
0
1
12
2
3
4
5
6
7
Sub-channel number
1
2
3
4
5
6
7
1
13
2
14
3
4
5
6
7
0
12
1
13
2
14
3
9
6
10
7
3
4
11
8
5
9
6
10
7
8
9
10
11
8
5
9
6
10
7
11
4
1
13
2
14
3
4
8
5
11
0
12
8
9
10
11
0
12
1
13
2
14
Table 2 – The available uplink access slots for different RACH sub-channels
6.1.8.
Access Class and Access Service Class
16 Access Classes (0-15) are defined for UMTS and GSM users (3GPP TS 22.011). Access
Classes 0 to 9 are equivalent and are randomly allocated to all UEs such that every UE
belong to one of these ten Access Classes. The access class assigned to a user is stored in
their SIM/USIM. In addition to these first 10 Access Classes, UEs may also belong to one
or more of the 5 special Access Classes (11-15). These special Access Classes are allocated
to high priority users as follows:

Class 15: PLMN Staff;

Class 14: Emergency Services;

Class 13: Public Utilities (e.g. water/gas suppliers);

Class 12: Security Services;

Class 11: For PLMN Use
Access Class 10 is used for Emergency Calls. In addition, any number of these Access
Classes may be barred access to the network at any time. For example, Access Classes 015 can be barred access to a site during maintenance, or testing. Alternatively, Access
Classes 0-9 can be barred access to the entire network during a natural disaster (e.g. a
hurricane).
The 16 Access Classes are mapped to 7 Access Service Classes (ref 3GPP 25.331, Section
8.5.13). This mapping is shown in Table 3. At the RRC layer, the set of available signatures
and the set of available RACH sub-channels for each Access Service Class (ASC). In this
manner, specific RACH signatures and RACH sub-channels can be reserved for specific
Access Classes.
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AC
ASC
0–9
1st IE
10
2nd IE
11
3rd IE
12
4th IE
13
5th IE
14
6th IE
15
7th IE
Table 3 – Access Class to Access Service Class Mapping
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6.2. Ericsson Specific Parameter for Random Access
The following list contains the configurable parameters related to Random Access. The
values shown here are vendor defaults and will be updated based on tests in the future.
Parameter Name
constantValueCprach
aichPower
maxPreambleCycle
powerOffsetP0
powerOffsetPpm
preambleRetransMax
Object
Name
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
Recommended
Value
-27 dB
- 6 dB
4 cycles
3 dB
-4 dB
8 preamble
Table 4 – Ericsson Specific Random Access Parameters
The following section details some of the steps that can be considered for optimization of
these parameters based on field testing.
6.3. Random Access Parameter Optimization and Troubleshooting
When optimizing the Random Access parameters, one must consider the tradeoffs between
accessibility, and capacity. As previously stated, it is quite possible to aggressively configure
the Random Access parameters to improve the likelihood of accessing the network, at the
cost of capacity. Alternatively, it is also possible to be overly concerned about capacity at
the cost of successfully accessing the network. Several of the parameters utilized in the
random access process can be configured to achieve one of these extremes. This section
will discuss how the configurations of these parameters will affect accessibility, as well as
capacity.
As previously described, the initial preamble transmit power is calculated at the beginning of
every ramping cycle, using Equation 3. The configurable parameter in this equation is
constantValueCprach, which has a default value of -27 dB. If the maximum value of -10
dB was used, the initial preamble transmit power would likely be excessive, as well as the
power of the subsequent RRC message. Although the chance for successfully sending the
RRC message is increased, the side effect of increased UL interference is unwanted. Note
that if drive testing analysis determines that the estimated transmit power for the initial
preamble is consistently low; adjusting this parameter to a higher value (e.g. – 24 dB) will
improve the accuracy of the estimate. Alternatively, if drive testing analysis determines that
a large percentage of the initial preambles are being acknowledged, then the initial
preamble power is likely to be excessive and constantValueCprach may need to be
reduced.
Once the initial preamble transmit power is calculated, the preamble power is ramped until
an acknowledgement is detected on the AICH. The two parameters related to this
functionality are powerOffsetP0, and preambleRetransMax. The dynamic range of the
power ramping function can be calculated by using Equation 4. Assume that 2 dB and 15
were used for powerOffsetP0, and preambleRetransMax respectively. This would
result in a dynamic range of 28 dB. The dynamic range of the UE (assuming 24 dBm max
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power) is (24 dBm – (-50 dB) = 74 dB. Comparing these two ranges emphasizes the need
for the initial preamble power estimate to be relatively accurate. Under certain conditions
(i.e. very high measure CPICH RSCP), it has been observed in the field that this estimate is
erroneous and yields a value that is too low. The result, in some cases, is that all
preambleRetransMax preambles are transmitted, no acknowledgement was received,
and the UE did not transmit at maximum power (e.g. 24 dBm).
PowerRampDynRange  powerOffse tP0  preambleRe transMax - 1
Equation 4 – Dynamic Range of Preamble Power Ramping Function
An example of this is shown in Figure 13. As the mode report shows, 15 preambles were
transmitted without an acknowledgement received on the AICH. The initial preamble
transmit power is -40 dBm, and the step size is 2 dB (not shown). This equates to a final
preamble transmit power of -12 dBm, which is 36 dB less than the maximum UE transmit
power. The occurrence of this scenario needs to be minimized as it can lead to access
failures and increased call setup time.
Figure 13 - Log File of Failed Preamble Ramping Function
To mitigate the risk of this occurring, the dynamic range of the power ramping function can
be increased. This can be accomplished by increasing either powerOffsetP0 or
preambleRetransMax. If powerOffsetP0 is increased, the potential of overshooting the
required preamble transmit power during a power ramp step is increased. The average
amount of overshoot should be approximately (50% x powerOffsetP0). Therefore,
increasing the step size from 2 to 3 dB would result in the average amount of overshoot
increasing from 1 dB to 1.5 dB. The alternative would be increasing the maximum number
of preamble step with the parameter preambleRetransMax. Although this change would
not result in an increase in the average amount of overshoot, it would potentially increase
the number of preambles transmitted. Although this could result in increased setup time
and rise, the effects should be negligible and should only affect UEs in bad radio condiitons.
Since this scenario has a low percentage of occurrences, increasing the
preambleRetransMax parameter would have the least effect on the network, given the
two options. If drive test analysis determines that this scenario is occurring frequently,
increasing the preambleRetransMax value may be required. Since this is a UtranCell
parameter, only cells effected by this problem can be modified.
The final issue to consider is related to the transmission of the RRC Connection Request
message after a positive acknowledgement has been received on the AICH. The parameter
powerOffsetPpm defines transmit power of the message, relative to the last transmitted
preamble. For example, if the last transmitted preamble was sent at +10 dBm, and
powerOffsetPpm = 2 dB, the control part of the RRC message would be sent at +12
dBm. Since both the preamble signature and the RRC Connection Request message
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have the same processing gain, it is tempting to set the parameter to 0 dB (which would
also reduce UL interference). However one must consider the Node Bs ability to receive and
decode these messages. The preamble signatures are known to the Node B. By using a
matched filter in the channel element, the Node B only has to detect the preamble, not
actually decode the message. On the other hand, the RRC Connection Request message
must be received and correctly decoded by the Node B. Based on this, it is likely that the
transmit power for the RRC Connection Request message should be higher than the
power used on the detected preamble. If test analysis indicates this scenario may be
occurring, it can be validated with RNC logs (e.g. UETR) and powerOffsetPpm parameter
can be optimized.
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7. Paging Procedures
The primary purpose of paging is to set up a Mobile Terminating (MT) call. The idle User
Equipment (UE) is normally paged in a Location Area (LA) or a Routing Area (RA) using a
subscriber-Id (e.g. IMSI or P-TMSI), depending on the Core Network (CN) domain that
originated the page message. The idle UE’s response to the paging message will reveal its
location at the cell level to the network and necessary signaling will continue on common
and/or dedicated channels in order to establish a connection to the UE. The LA and RA
definitions in UMTS are exactly the same as for GERAN. As a vendor feature, the UE may
be paged in a global RNC area corresponding to cells under the control of one RNC.
In UMTS the paging procedure has been enhanced in a number of ways. This is required in
order to deal with the more complicated behavior of the UE in connected mode (“connected
while sleeping”), and the increased responsibilities of the UTRAN in managing radio related
tasks. As an example, unlike GERAN, a paging message in UMTS may be originated
autonomously by the RNC in order to inform the UE about changes in System Information
Blocks (SIB), or trigger the UE to do a Cell Update. As in 2G networks there is a great need
for reducing battery consumption by the UEs. UMTS also utilizes a discontinuous reception
(DRX) mechanism on paging channels which is similar to the paging-groups concept of GSM
but quite different in details due to the radical difference in the air interface between GSM
and UMTS. This is discussed in the following sections.
In addition to paging in LA and RA, UMTS defines a new paging area known as UTRAN
Registration Area (URA). The URAs are known only within the UTRAN and are generally
independent of LAs and RAs. A UE is paged in a URA only when it is in the RRC URA_PCH
mode (i.e. it has an active RRC connection towards a Serving RNC). A single cell can
belong to more than one URA, thus allowing for overlapping URAs. SIB 2 indicates a list of
URAs the cell belongs to, and a UE can be assigned more than one URA-id. Careful URAplanning involves considerations regarding a balance between the paging load and UE
initiated URA-updates, similar to LA/RA planning.
The chart below shows the possible scenarios related to paging in terms of the UE states,
the resources used, the originating node for pages and the paging area. Further details on
Paging in UTRAN can be found in [19].
In Ericsson, CELL_PCH state is not implemented.
UE State
RRC
Connected
Paging Type Resources
Used
Originating
Node
Paging
Reason
Paging Area
Idle
No
Type 1
PICH &
SCCPCH
(carrying
PCH)
CN
Terminating
service
LA/RA
UTRAN
System
Information
updates
DPCCH
(carrying
CN
Terminating
service from
CELL_DCH
Yes
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DCH)
a CN that
UE is not
connected
to
CELL_FACH
Yes
Type 2
SCCPCH
(carrying
FACH) and
PRACH
(carrying
RACH)
CN
Terminating
service from
a CN that
UE is not
connected
to
Specific UE
CELL_PCH
Yes
Type 1
PICH &
SCCPCH
(carrying
PCH)
CN
CS
terminating
service
Last known
cell
UTRAN
System
Information
updates,
allow UE to
trigger cell
update
PICH &
SCCPCH
(carrying
PCH)
CN
CS
terminating
service
UTRAN
System
Information
updates,
allow UE to
trigger cell
update
URA_PCH
Yes
Type 1
Last known
URA
7.1. Paging Types
The paging procedure is normally initiated by CN using the RANAP procedure called
PAGING. Once the PAGING message has been received by the RNC, it will use one of the
two types of RRC paging messages depending on the state of the UE.
7.1.1.
Paging Type 1
For a UE in RRC Idle state, an RRC: PAGING TYPE 1 is sent from the RNC to the UE. Two
parameters in Paging Type 1 are the CN domain-Id and the IMSI/(P)TMSI of the paged UE.
If the UE has already an RRC connection, then the RNC may convert the IMSI/(P)TMSI to a
UTRAN Radio Network Temporary Id (U-RNTI). The reception of the PAGING TYPE 1
message typically results in the establishment of an RRC Connection which is initiated by the
UE after the page message is received.
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Another use of the Paging Type 1 message is when the UE has an RRC connection but no
radio resources are allocated to it. In this case the UE is either in Cell_PCH or URA_PCH
mode. As indicated by the name of these RRC states, the UE’s position is known to the
serving RNC at cell and URA levels respectively and the UE is monitoring the paging channel
based on certain criteria that can be set differently from the idle mode criteria for
monitoring paging channels.
Figure 14 - Signaling for Paging Type 1
7.1.2.
Paging Type 2
For a UE that is already in the RRC Connected mode and has dedicated (Cell-DCH) or
common channels (Cell_FACH) assigned to it, the paging procedure uses the RRC PAGING
TYPE 2 message. This is especially useful in a scenario where the other CN domain that
does not already have an active connection with the UE wants to establish a new signaling
connection. PAGING TYPE 2 is sometimes referred to as “Dedicated Paging”. From the
radio access point of view this is just like any other signaling message carried on dedicated
channels.
Figure 15 – Signaling for Paging Type 2
Note that the RANAP PAGING message is similar in both cases. It is the RNC that decides
to initiate the correct paging type based on UE-id and the current state of the paged UE.
The UE’s response to these paging messages also depends on the current RRC state of the
UE. In RRC Idle mode, the UE sends an RRC Connection Request message with
establishment cause set to “paging response”. In RRC connected mode the paging can
trigger the UE to change RRC state from Cell_PCH or URA_PCH to Cell_FACH by doing a Cell
Update procedure, with cause value set to “paging response”. Alternatively the UE will
directly send a Paging Response if it is already in Cell_DCH/FACH mode. An autonomous
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Paging Type 1 message can be initiated from the RNC when new downlink data or signaling
messages need to be sent to the UE. This causes the UE to transition to Cell_FACH and
subsequently do a Cell Update.
Figure 16 - State Changes due to Paging
7.2. Paging Channels
The paging message is carried in the downlink on the Logical channel Paging Control
Channel (PCCH). The logical channel is mapped to the transport channel Paging Channel
(PCH) at the MAC layer. This channel in turn is coded and carried over the air using the
Secondary Common Control Physical Channel (S-CCPCH). A paging message type 2 is
associated with the Dedicated Control Channel DCCH, which may be mapped to FACH or
DCH transport channels. A cell may be configured with more than one S-CCPCH depending
for example on the cell load and the expected paging volume. The S-CCPCH spreading
factor (SF) may be chosen from any valid SF from 4 to 256.
Figure 17 - Logical, Transport, and Physical Channels Associated with Paging
7.2.1.
Paging Indication Channel
The Paging Indicator Channel (PICH) has fixed spreading factor of 256 and carries the
Paging Indicator. The paging indicator indicates the presence of a page message on the
PCH for the UEs using Paging Indicator (PI) bits. Each PICH is associated with a S-CCPCH
which carries the transport channel PCH (see Figure 17). Of the 300 available bits in a
10ms PICH frame, 288 are used to carry paging indicators, while the remaining 12 bits are
not used. Each PICH frame can carry Np paging indicators, where Np = 18, 36, 72 or 144,
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corresponding to 16, 8, 4 or 2 bits per Paging Indicator. The PICH frame timing is fixed in
relation to the associated S-CCPCH. The PICH transmission power is given in relation to the
CPICH power level and depends on the number of PIs configured in PICH.
For higher Np values, more power is needed on the PICH. This follows from the fact that
for higher Np values there will be fewer bits for each PI. In order to maintain an acceptable
bit error probability, more power per bit will be required. The PICH power offset is
broadcasted in SIB 5/6. On the other hand, a higher Np value can decrease the probability
of false paging indications. A false paging indication occurs when a UE sees positive paging
indication on PICH but does not see a paging message on S-CCPCH for itself (IMSI/TMSI or
RNTI).
In Ericsson implementation, the value of Np is hard coded to 18.
Figure 18 – PICH and PCH Frame Synchronization
7.3. DRX Procedure
A UE in idle mode (or RRC Cell_PCH/URA_PCH) has to continuously monitor PCH so that it
will not miss any incoming calls or RRC messages. This can be very demanding on the UE’s
battery power consumption. For this reason, discontinuous reception (DRX) mechanism is
used in UMTS as in many other wireless systems. The PICH is used to indicate to the UE
when it should read the S-CCPCH which carries the true paging message. If a UE that is
monitoring the PICH does not see an indication that it is paged, it will ignore the following
S-CCPCH. If the UE does see an indication then it will decode the S-CCPCH which occurs
2ms after the PICH frame. This may be a false indication as described above. In that case
the S-CCPCH will carry a paging message for another UE that happens to share the same
PI.
Although the PICH carries a simple “yes-no” message, listening to PICH on every frame is
not a very effective power saving feature. Further enhancement to power saving can be
achieved if the UE only wakes up and listens to certain PICH frames. This frequency of
wake-up is called the Paging Occasion (PO) and is determined by important DRX cycle
length parameter.
Each UE will calculate a PO which simply corresponds to the frame number that the UE must
read the PICH on. The PO is a function of the IMSI, the DRX cycle length, and the number
of S-CCPCH in the cell and the System Frame Number (SFN). In Ericsson’s current
implementation, only 1 SCCPCH can be configured per cell. Hence the paging occasions for
a specific UE are calculated as
(IMSI mod DRX cycle length) + n * DRX cycle length where n = 0, 1, 2 …
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Using the Np value and the IMSI, the UE can also calculate its own Paging Indicator to know
where in the PICH to look for paging indicators. The paging indicator for a particular UE can
be calculated based on its IMSI as
PI = (IMSI div 8192) mod Np
Figure 19 - Paging Occasions
The DRX cycle length is defined by Equation 5, where k is the DRX cycle coefficient and
ranges from 3 to 9. The possible DRX values are then from 80ms to a little more than 5
seconds of sleeping time. If this value is set too low, the UE is more active in monitoring the
PICH, thus decreasing the UE stand-by time. On the other hand, large values of this
parameter will increase mobile-terminating call set-up times, since the UE will take longer
periods of time to read the PICH. The DRX Cycle Length value can be set separately for
each Core Network domain type. If a UE is connected to both the PS and CS Core networks
simultaneously, then the shorter of the two values will always be used by the UE. For UEs
in connected mode (URA_PCH and Cell_PCH) a separate k value is defined as in the table
below. It is generally considered beneficial to decrease the DRX cycle length for connected
mode UEs since transitions to Cell_FACH need to occur faster in comparison to those
between idle mode and connected mode.
DRX_CYCLE_ LENGTH  2 k  10 msec
Equation 5 - DRX Cycle Length
A useful rule-of-thumb used by Ericsson when dealing with the DRX_Cycle_Length
parameter, is the fact that an increase in the DRX_Cycle_Length will generally increase the
call set-up time by half of the increased amount. For example, changing the value from 640
ms to 1280 ms (k is changed from 6 to 7) will increase the call set-up time by (1280-640)
ms/2 = 320 ms on average.
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7.4. Paging Repetition
Paging repetition in Ericsson UTRAN depends on the UE state and on where the page was
originated.

A page that is initiated by the CN is repeated by the UTRAN
“noOfPagingRecordTransm” subsequent times, irrespective of the response to
the first paging attempt.

A UTRAN originated page for a UE in URA_PCH state is time supervised. An RNC
timer is started when a page is sent and stopped when the UE answers. If the
timer expires the paging is repeated once. On a second expiry of this timer, the PS
connection of the UE is released. The RNC timer is hard coded to a value of (10
ms * 2k * noOfPagingRecordTransm) + 1000 ms, where k =
utranDrxCycleLength.

When the UTRAN has to inform a UE about updates to system information, it sends
a number of consecutive Paging Type 1 messages to the UE using the maximum
possible DRX cycle length to ensure that the UE receives this at least once. The
number of times a page indicating updates to the same system information is sent
to the UE is set with a configurable RNC parameter “noOfMaxDrxCycles”.
7.5. Ericsson Specific Parameter and Counters for Paging
7.5.1.
Ericsson Paging Control Parameters
The following list contains the configurable parameters related to Random Paging.
Parameter Name
Object
Name
Recommended
Value
noOfPagingRecordTransm
RNC
2
cnDrxCycleLengthCs
RNC
640 ms
cnDrxCycleLengthPs
RNC
1280 ms
utranDrxCycleLength
noOfMaxDrxCycles
RNC
RNC
320 ms
1
Table 5 – Ericsson Specific Paging Parameters
7.5.2.
Ericsson Paging Counters
Figure 19 illustrates the counters associated with the Ericsson Paging Process. These
counters include, but are not limited to the following:

pmNoPagingAttemptCnInitDcch

pmCnInitPagingToIdleLa

pmNoPageDiscardCmpLoadC

pmCnInitPagingToIdleRa

pmCnInitPagingToIdleUe
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
pmNoPagingAttemptUtranRejected

pmCnInitPagingToUraUe

pmUtranInitPagingToUraUe

pmNoPagingType1Attempt

pmNoPagingType1AttemptPS

pmNoPagingType1AttemptCS
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Figure 20 Flowchart for Ericsson Counters, Paging
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8. Soft/Softer Handover Feature
Soft/Softer Handover implies that a UE is connected to more than one WCDMA BTS at the
same time. For a UE moving from the coverage area of one WCDMA cell to another,
Soft/Softer handover allows the UE to start communicating with the new cell before it stops
communicating with the old cell. In Soft Handover, the UE is connected to at least 2 cells
belonging to different Node B’s, and the uplink signals from the different cells are combined
in the RNC. When the UE is connected to at least 2 cells belonging to the same Node B, the
handover is called Softer Handover, and in this case, the uplink signals from the different
cells are combined in the Node B.
The following are the advantages of Soft/Softer handover.

Seamless Handover without disconnection of the radio access bearer.

Fast closed loop power control is possible since the UE is always linked to the
strongest cell.

Sufficient reception level for communication at cell edge by combining reception
signals from different cells.

The macro diversity gain achieved by combining reception signals improves the
uplink signal quality and decreases the required transmission power of the UE,
reducing uplink interference and increasing system capacity.
Despite the above advantages of Soft/Softer Handover, there is a trade-off between soft
handover and system capacity. A UE involved in Soft/Softer Handover uses several radio
links, more DL channelization codes, more DL power and more channel elements than a
single link connection. However, as long as the number of radio links involved in Soft
Handover is optimized, the capacity advantage offered due to Soft Handover from
interference reduction is larger and hence system capacity is actually improved.
8.1. Soft/Softer Handover Procedure and Parameters
The Soft/Softer handover Algorithm can be split into the following 3 parts.

Algorithm for handling cell sets, subsets and Lists to determine the subset of cells
to be measured on by the UE based on the cells present in the active set and their
configured neighboring cells. This has been detailed in the previous 2 sections.

Soft/Softer Handover Evaluation for determining which cells should be proposed to
be added, removed, or replaced in the Active Set. The algorithm bases its decision
on quality measures of the P-CPICH done in the UE. An evaluation that results in a
revised Active Set proposes it to the execution part of Soft/Softer handover.

Soft/Softer Handover Execution covers the actual addition and/or removal of radio
links proposed by the Soft/Softer Handover Evaluation algorithm.
Soft/Softer Handover evaluation is enabled for a UE entering the CELL_DCH state.
Soft/Softer Handover evaluation is performed based on the UE’s intra frequency
measurement report. Before the first MEASUREMENT CONTROL message has been sent
from the RNC, any MEASUREMENT REPORT message received from the UE is evaluated
based on intra-frequency measurement reporting criteria broadcasted by system information
(SIB11/SIB12).
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Soft/Softer Handover is controlled by the events 1a, 1b, 1c and 1d. The following is the
description of these four events.

Event 1a: A new candidate for the active set enters the reporting range.

Event 1b: A cell in the active set leaves the reporting range.

Event 1c: A cell not in the active set becomes stronger than a cell in the active set
when the active set is at its maximum size.

Event 1d: Any cell becomes better than the best cell in the active set.
When a UE enters CELL_DCH state, intra frequency measurements are set up by sending a
MEASUREMENT CONTROL message with IE MEASUREMENT REPORT MODE set to “setup”
for event 1a, 1b, 1c and 1d. This first MEASUREMENT CONTROL message is used to setup
the UE reporting mode as well as send the very first Intra-frequency Monitored Subset.
After an Active Set update, a MEASUREMENT CONTROL message with IE “MEASUREMENT
REPORT MODE” set to “modify” for event 1a, 1b, 1c and 1d is sent to the UE, telling it
which cells will be added to and deleted from the Monitored Subset. The measurement
criteria don’t change during a connection lifetime.
The UE is configured to check event criteria for the different events as follows:

Event 1a: IAF Monitored Subset and Detected set cells.

Event 1b: Active set cells

Event 1c: Any cell that is not included in the active set.

Event 1d: Any cell that is not the best cell.
In addition to the 3GPP cell sets, Ericsson 3G network uses the following additional
classification.
Valid Cell: A cell that is part of the Active Set, Monitored set or the Unmonitored set, so
that the SRNC is able to translate information about reported P-CPICH scrambling code to a
configured cell by using the configured neighbor cell lists.
Invalid Cell: A cell that is not part of the Active Set, Monitored set or the Unmonitored set,
so the SRNC does not have information for P-CPICH scrambling code translation to a
configured neighboring cell.
The UE is configured to base event evaluation as per the setting of the parameter
measQuantity1. The measured values are filtered by the UE before comparing the resulting
values with the event report criteria.
Recommended Value: The recommended value for measQuantity1 is CPICH_EC_NO. This
configures the UE to base event evaluation on CPICH Ec/No.
A MEASUREMENT REPORT sent by the UE for event 1a, 1b, 1c and 1d contains the following
messages:

Quality of cells in the active set.

List of cells that fulfill the event criteria.

Quality of cells that fulfill the event criteria.

Synchronization information for the cells that fulfill the event criteria.
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8.1.1.
Event 1a Evaluation
Reporting event 1a is used to add cells into the active set. The UE sends event 1a triggered
measurement report when a cell enters the reporting range defined by the following formula
for at least a time equal to timeToTrigger1a.
 NA

10  LogM
 individualoffset  w1a  10  Log   M   (1  w1a)  10  LogM  (reportingRange1a  hystere
New
New
best
 i 1 i 


The following are the definitions of the parameters used.
MNew: measurement result of the cell entering the reporting range
individualoffsetNew: offset of the neighbor cell entering the reporting range.
w1a: weighting factor for event 1a.
Mi: measurement result of a cell in the active set.
NA: number of cells in the current active set.
Mbest: measurement result of the strongest cell in the active set.
reportingRange1a: relative threshold referenced to the CPICH of the best cell in the active
set.
hysteresis1a: Hysteresis used in event evaluation for event 1a to avoid ping pong effects.
timeToTrigger1a: Minimum time during which a candidate cell should stay within reporting
range of event 1a before the UE can send event 1a triggered measurement report to the
RNC.
filterCoefficient1: The measured values are filtered by the UE using the filter coefficient
value before comparing with event criteria.
Since the parameter measQuantity1 is recommended to be set to CPICH_EC_NO, the
measurement result in the above equation refers to the CPICH Ec/No of the relevant cell.
Recommended Value: The recommended value for w1a is 0 for network launch, so that
the event evaluation is only done with respect to the best cell in the active set. Refer to the
Appendix A for more information on the weighting factor. The recommended value for
parameter individualoffset is 0 for initial network launch. These parameters should be reevaluated based on network statistics and changed to a non-zero value only as needed for
specific scenarios.
When an event 1a triggered MEASUREMENT REPORT is received, the Soft/Softer Handover
Evaluation Algorithm at the RNC processes the report and evaluates if the proposed
candidate can be added to the Active set. Only the best cell that fulfilled the reporting
criteria is retained, and all other cells from the MEASUREMENT REPORT are discarded. If the
retained cell already belongs to the Active set, the RNC updates the Active Set with the
Ec/No value from the measurement report and the evaluation process terminates with no
other actions. If the retained cell is not in the active set, the following 3 scenarios are
possible based on the validity of the retained cell.
Invalid Retained Cell: If the retained cell is invalid and the quality measure (Ec/No) of
this invalid cell is not included in the MEASUREMENT REPORT, then the Soft Handover
evaluation process is terminated. If the retained cell is an invalid cell and its quality measure
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exceeds the quality measure of the best cell in the Active set by an amount defined by the
parameter releaseConnoffset, then the connection is terminated. The reason for terminating
this connection is to avoid UL interference caused by the UE entering a new cell area
without being power controlled by that cell. If the retained cell is invalid, but the quality
measure of the cell doesn’t exceed the quality measure of the best cell in the Active set by
the amount of releaseConnoffset, then the Soft handover Evaluation procedure updates the
ordered Active Set List with the quality measure reported in the received measurement
report, and the evaluation process terminates with no other action.
Valid retained Cell missing synchronization information: If the retained cell is a valid
cell but is missing synchronization information, the Soft handover procedure can’t be
executed, since the synchronization information is necessary to perform soft handover.
Hence the Soft Handover Evaluation Procedure updates the quality measures in the ordered
Active Set List with the values received in the Measurement report, and the evaluation
process terminates with no other actions.
Valid retained Cell with synchronization information: If the retained cell is valid with
synchronization information available, and the number of cells in the current active set is
less than the amount defined by the parameter maxActiveSet, the Soft handover Evaluation
Algorithm creates a new Active Set by adding the retained cell to the Active set. If the
retained cell is valid with synchronization information available, but the number of cells in
the current active set is equal to the maximum possible valued defined by the parameter
maxActiveSet, and the quality of the retained cell is better than that of the worst cell in the
Active set, the Soft Handover Evaluation Algorithm creates a new Active set by replacing the
worst cell in the previous Active set with the retained cell.
Recommended Value: The recommended value for the parameter maxActiveSet is 3. This
would limit the number of soft handover links, thus optimizing network capacity.
8.1.2.
Event 1b Evaluation
Reporting event 1b is used to delete cells from the Active set. The UE sends event 1b
triggered measurement report when a cell leaves the reporting range defined by the
following formula for at least a time equal to timeToTrigger1b.
 NA

 w1b  10  Log   M   (1  w1b)  10  LogM  (reportingRange1b  hysteresis
Old
Old
best
 i 1 i 


The following are the definitions of the parameters used.
10  LogM
 individualoffset
MOld: measurement result of the cell leaving the reporting range
individualoffsetOld: offset of the neighbor cell leaving the reporting range.
w1b: weighting factor for event 1b.
Mi: measurement result of a cell in the active set.
NA: number of cells in the current active set.
Mbest: measurement result of the strongest cell in the active set.
reportingRange1b: relative threshold referenced to the CPICH of the best cell in the active
set.
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hysteresis1b: Hysteresis used in event evaluation for event 1b to avoid ping pong effects.
timeToTrigger1b: Minimum time during which a candidate cell should stay within reporting
range of event 1b before the UE can send event 1b triggered measurement report to the
RNC.
filterCoefficient1: The measured values are filtered by the UE using the filter coefficient
value before comparing with event criteria.
Since the parameter measQuantity1 is recommended to be set to CPICH_EC_NO, the
measurement result in the above equation refers to the CPICH Ec/No of the relevant cell.
Recommended Value: The recommended value for w1a is 0 for network launch, so that
the event evaluation is only done with respect to the best cell in the active set. Refer to the
Appendix A for more information on the weighting factor. The recommended value for
parameter individualoffset is 0 for initial network launch. These parameters should be reevaluated based on network statistics and changed to a non-zero value only as needed for
specific scenarios.
When an event 1b triggered MEASUREMENT REPORT is received, the Soft Handover
Evaluation Algorithm at the RNC processes the report and evaluates if the proposed
candidate can be removed from the Active set. If the event 1b triggered MEASUREMENT
REPORT includes more than 1 cell, then all the cells fulfilling the reporting criteria are stored
in a Remove List. The Soft Handover Evaluation Algorithm retains the first cell in the
Remove List and deletes it from the list. If this retained cell is not in the Active set, then the
next cell on the Remove List is processed. When the current retained cell is in the Active
Set, the Soft handover Evaluation Algorithm creates a new proposed Active set by removing
the retained cell from the Active set. The new Active Set is forwarded to the Soft Handover
Execution Algorithm. This process is repeated as long as there is at least 1 cell remaining in
the Remove List. When the Remove List is empty, the evaluation process terminates for that
particular MEASUREMENT REPORT.
8.1.3.
Event 1c Evaluation
Reporting event 1c is used for replacing cells in the Active Set. A UE sends the event 1c
triggered MEASUREMENT REPORT when the number of cells in the Active set is equal to the
value defined by parameter maxActiveSet, and a cell that is not included in the Active Set
becomes better than a cell in the Active set as defined by the following formula for at least
a time equal to timeToTrigger1c.
10  LogM New  individualoffset New  10  LogM InAS  individualoffset InAS  hysteresis1c / 2
The following are the definitions of the parameters used.
MNew: measurement result of the cell not included in the Active set.
individualoffsetNew: offset of the neighbor cell not included in the Active set.
MInAS: measurement result of a cell in the active set with the least measurement value
among active set cells.
IndividualoffsetInAS: offset of the cell in the Active set.
hysteresis1c: Hysteresis used in event evaluation for event 1c to avoid ping pong effects.
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timeToTrigger1c: Minimum time during which a candidate cell should stay stronger than a
cell in the Active set before the UE can send event 1c triggered measurement report to the
RNC.
filterCoefficient1: The measured values are filtered by the UE using the filter coefficient
value before comparing with event criteria.
Since the parameter measQuantity1 is recommended to be set to CPICH_EC_NO, the
measurement result in the above equation refers to the CPICH Ec/No of the relevant cell.
The evaluation of an event 1c triggered MEASUREMENT REPORT is the same as of an event
1a triggered report. When an event 1a triggered MEASUREMENT REPORT is received, the
Soft Handover Evaluation Algorithm at the RNC processes the report and evaluates if the
proposed candidate can be added to the Active set. Only the best cell that fulfilled the
reporting criteria is retained, and all other cells from the MEASUREMENT REPORT are
discarded. If the retained cell already belongs to the Active set, the RNC updates the Active
Set with the Ec/No value from the measurement report and the evaluation process
terminates with no other actions. If the retained cell is not in the active set, the following 3
scenarios are possible based on the validity of the retained cell.
Invalid Retained Cell: If the retained cell is invalid and the quality measure (Ec/No) of
this invalid cell is not included in the MEASUREMENT REPORT, then the Soft Handover
evaluation process is terminated. If the retained cell is an invalid cell and its quality measure
exceeds the quality measure of the best cell in the Active set by an amount defined by the
parameter releaseConnoffset, then the connection is terminated. The reason for terminating
this connection is to avoid UL interference caused by the UE entering a new cell area
without being power controlled by that cell. If the retained cell is invalid, but the quality
measure of the cell doesn’t exceed the quality measure of the best cell in the Active set by
the amount of releaseConnoffset, then the Soft handover Evaluation procedure updates the
ordered Active Set List with the quality measure reported in the received measurement
report, and the evaluation process terminates with no other action.
Valid retained Cell missing synchronization information: If the retained cell is a valid
cell but is missing synchronization information, the Soft handover procedure can’t be
executed, since the synchronization information is necessary to perform soft handover.
Hence the Soft Handover Evaluation Procedure updates the quality measures in the ordered
Active Set List with the values received in the Measurement report, and the evaluation
process terminates with no other actions.
Valid retained Cell with synchronization information: If the retained cell is valid with
synchronization information available, but the number of cells in the current active set is
equal to the maximum possible valued defined by the parameter maxActiveSet, and the
quality of the retained cell is better than that of the worst cell in the Active set, the Soft
Handover Evaluation Algorithm creates a new Active set by replacing the worst cell in the
previous Active set with the retained cell.
8.1.4.
Event 1d Evaluation
Reporting event 1d is used to change the best cell in an Active set. A UE send the event 1d
triggered MEASUREMENT REPORT when a cell in the Active set, Monitored set or Detected
set becomes stronger than the best cell in the Active set as defined by the following formula
for at least a time equal to timeToTrigger1d.
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10  LogM NotBest  10  LogM Best  hysteresis1d / 2
The following are the definitions of the parameters used
MNotBest: measurement result of a cell that is currently not the best cell.
MBest: measurement result of the best cell in the active set.
hysteresis1d: Hysteresis used in event evaluation for event 1d to avoid ping pong effects.
timeToTrigger1d: Minimum time during which a candidate cell should stay stronger than the
best cell in the Active set before the UE can send event 1d triggered measurement report to
the RNC.
filterCoefficient1: The measured values are filtered by the UE using the filter coefficient
value before comparing with event criteria.
Since the parameter measQuantity1 is recommended to be set to CPICH_EC_NO, the
measurement result in the above equation refers to the CPICH Ec/No of the relevant cell.
When an event 1d triggered MEASUREMENT REPORT is received, the Soft Handover
Evaluation Algorithm at the RNC processes the report and evaluates if the proposed
candidate can be added to the Active set. If the retained cell already belongs to the Active
set, the RNC updates the Active Set with the Ec/No value from the measurement report and
the evaluation process terminates with no other actions. If the retained cell is not in the
active set, the following 3 scenarios are possible based on the validity of the retained cell.
Invalid Retained Cell: If the retained cell is invalid then the Soft Handover evaluation
process is terminated with no other actions.
Valid retained Cell missing synchronization information: If the retained cell is a valid
cell but is missing synchronization information, the Soft handover procedure can’t be
executed, since the synchronization information is necessary to perform soft handover.
Hence the Soft Handover Evaluation Procedure updates the quality measures in the ordered
Active Set List with the values received in the Measurement report, and the evaluation
process terminates with no other actions.
Valid retained Cell with synchronization information: If the retained cell is valid with
synchronization information available, and the number of cells in the current active set is
less than the amount defined by the parameter maxActiveSet, the Soft handover Evaluation
Algorithm creates a new Active Set by adding the retained cell to the Active set. If the
retained cell is valid with synchronization information available, but the number of cells in
the current active set is equal to the maximum possible valued defined by the parameter
maxActiveSet, then the Soft Handover Evaluation Algorithm creates a new Active set by
replacing the worst cell in the previous Active set with the retained cell.
In most cases event 1d is triggered when a cell already in the active set becomes stronger
than the best cell. Hence these reports will not lead to a proposed Active Set. The ordered
Active Set List is updated with the Ec/No values reported in the Measurements section of
the received report and the evaluation process terminates with no other actions.
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8.1.5.
Event Triggered Periodical Measurement Reporting
When a cell enters the reporting range and triggers event 1a or 1c, the UE transmits a
measurement report to the RNC in order to update the Active Set. The RNC maybe unable
to add the reported cell to the Active set due to various reasons, one of which is capacity
shortage on the target cell. If the UE doesn’t receive an Active Set Update message from
the RNC, it continues the measurement reporting by changing to periodical reporting mode.
During periodical reporting, the UE transmits measurement reports to the RNC at predefined intervals. If an event 1a triggered measurement report doesn’t result in an Active
Set Update message received, the UE transmits the same event every interval defined by
the parameter reportingInterval1a. If an event 1c triggered measurement report didn’t
result in an Active Set Update message, then the UE transmits this event every interval
defined by the parameter reportingInterval1c.
The event triggered periodic reporting is applicable only for valid retained cells that weren’t
added to the Active set. An invalid cell will not be considered by the RNC to be part of the
Active set to begin with.
Event-triggered periodic measurement reporting is terminated either when there are no
more monitored cells within the reporting range or when the RNC has updated the active
set so that it includes the optimal cells
8.1.6.
Buffering and Queuing
There are 3 buffers for event 1x measurement reports. There is 1 combined buffer for event
1a and event 1c, a separate buffer for event 1b and another for event 1d. The 1a/1c
reporting buffer is used to hold reports triggered on event 1a and event 1c, and also the
event triggered periodic reports based on these events. This buffer holds only the last
received report, so a new received report overwrites a report already in the buffer.
The 1b reporting buffer is used to hold reports triggered on event 1b, and the 1d reporting
buffer is used to hold reports triggered on event 1d. These 2 buffers can hold up to 10
reports each. The reports in these 2 buffers are queued in order of arrival with the oldest
report first and the newest report last in the queue. If the 1b or 1d reporting buffer is full
when a new event 1b or event 1d report is received, an indication is forwarded to Soft
Handover Execution Algorithm to release the connection.
When the Soft Handover Evaluation Algorithm is ready to process a new report, the buffers
are searched in the following order – 1d reporting buffer, then the 1a/1c reporting buffer
followed by the 1b reporting buffer. A report is removed from the buffer when its processing
begins.
8.1.7.
Soft/Softer Handover Execution
Once a proposed new Active Set is created by the Soft/Softer Handover Evaluation
Algorithm, Soft/Softer Handover Execution is started and the result of this is one of the
following.

Radio Link Addition

Radio Link Removal

Radio Link Replacement
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
Proposed Active set Rejection

RRC Connection Release
The Active set always includes at least 1 radio link and hence the Soft Handover Algorithm
would never remove the last existing radio link from the Active set. There is no information
loss or interruption of data flow during a Soft handover procedure. Soft Handover Algorithm
interacts with the Capacity Management Algorithm to request admission before adding radio
links and also informs the Capacity Management Algorithm about successful changes to the
Active set.
8.1.8.
Soft/Soft Handover Signaling
The Soft/Softer Handover Signaling for the following processes is covered below.

Radio Link Addition

Radio Link Deletion

Radio Link Replacement
Radio Link Addition
Radio link addition is normally triggered by event 1a, event 1c or event 1d reports from the
UE. During execution of addition, the Admission Control algorithm in the SRNC is asked if
the new RL setup can be allowed in the cell. After access has been granted, the Code
Control algorithms in the SRNC allocate DL channelization code, and the Power Control
algorithms in the SRNC set the initial DL transmission power, UL SIR Target, and DL power
range. The SRNC then contacts the Node B, which allocates resources, starts reception, and
tries to synchronize the UE on the uplink. The SRNC sends the Active Set UPDATE message
to the UE, which allocates reception resources, synchronizes to the new radio link on the
downlink. The UE responds with an Active Set UPDATE COMPLETE message. Other
Evaluation algorithms and interacting functions are informed about the new Active Set.
In case of Inter-RNC Radio Link Addition, the SRNC establishes signaling connections to the
DRNC over the Iur interface. Once the Iur connection exits, Node B resources are
demanded by the SRNC and if resources are available, the new radio link is setup.
Radio Link Removal
Radio Link removal is triggered by the reception of an event 1b report from the UE. The
Soft/Softer Handover Evaluation algorithm sends an Active Set proposal to the Execution
part in the SRNC to remove the reported cells from the Active Set of the UE. During
execution of the removal, the SRNC sends an Active Set UPDATE message to the UE, which
releases the resources for that radio link and responds with an Active Set UPDATE
COMPLETE message. Other Evaluation algorithms and interacting functions are informed
about the new Active Set.
In case of Inter-RNC Radio Link Removal, the DRNC stays involved in the connection
provided that at least one radio link uses an RBS belonging to the DRNC. If not, the Iur
connection will be released.
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Radio Link Replacement
Combined radio link addition and removal replaces one radio link with another in the Active
Set. Radio link replacement is normally triggered by an event 1c report or an event 1d
report from the UE. The new Node B is contacted by the SRNC. The new Node B allocates
resources, starts reception, and tries to synchronize the UE on the uplink. During
replacement execution, power is determined for the radio link to be added. The SRNC sends
an Active Set UPDATE message to the UE indicating which radio link to add and which radio
link to remove. The UE allocates resources for the new radio link and releases
corresponding resources for the old radio link. The UE responds with an ACTIVE SET
UPDATE COMPLETE message. Node B and SRNC resources are then released for the
removed radio link, and Evaluation algorithms and interacting functions are informed about
the new Active Set.
The RRC messages between the UE and the RNC for the Radio Link Addition and removal
procedures are shown in the following figure.
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If a Radio Link Addition is denied by the Admission Control Algorithm, then the UE will
normally repeat the 1a or 1c event reports. Capacity Management might perform best-effort
cleanup actions in the target cell and downgrade actions for the current connection, so that
the repeated RL add requests might be admitted.
RRC Connection Release
The current RRC connection can be released due to any of the following reasons.
A Detected Set report is received where the invalid cell is more than releaseConnOffset
stronger than the strongest cell in the active set.
A failed RL add/replace attempt, where the proposed cell is more than releaseConnOffset
stronger than the strongest cell in the active set.
A Measurement Control message failure for a 1x event.
An Active set update failure, in which the UE does not respond to the Active Set UPDATE
message and the timer <RRC> T-ASU expires. The timer <RRC> T-ASU is started when an
Active Set UPDATE message is sent and stopped when the Active Set UPDATE COMPLETE or
Active Set UPDATE FAILURE is received and is a hard-coded value set to 5 s.
8.1.9.
ReleaseConnOffset setting
The vendor recommended value for this parameter is set at 12 dB, which would imply that
the a call is released only when a cell that is 12 dB stronger than the best cell in the Active
set is not being added to the Active set. This value would make the dropped calls due to
this feature less likely. This is the recommended value for network launch. A value smaller
than 12 dB can be used during optimization to find problems related to missing neighbors
which would result in drop calls. The parameter should be put back to 12 dB after
optimization to ensure that the drop call rate is not affected.
8.2. Recommended Values for Soft/Softer handover parameters
As before, the intent of the soft handover guidelines here is not to provide parameter
recommendations, but to offer methods to analyze the change of certain specific soft
handover parameters on overall network performance.
The parameter values provided here are vendor recommended values, and will be updated
as and when more information is available. All Ericsson 3G parameters related to Soft/Softer
handover are listed here.
Parameter Name
Object Name
Recommended
Value
filterCoefficient1
UeMeasControl
2
hysteresis1a
UeMeasControl
0
hysteresis1b
UeMeasControl
0
hysteresis1c
UeMeasControl
1 dB
hysteresis1d
UeMeasControl
7.5 dB
individualOffset
ExternalUtranCell
0
individualOffset
UtranCell
0
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maxActiveSet
Handover
3
measQuantity1
UeMeasControl
CPICH_EC_NO
releaseConnOffset
Handover
12 dB
reportingInterval1a
UeMeasControl
1s
reportingInterval1c
UeMeasControl
1s
reportingRange1a
UeMeasControl
3 dB
reportingRange1b
UeMeasControl
5 dB
timeToTrigger1a
UeMeasControl
320 ms
timeToTrigger1b
UeMeasControl
640 ms
timeToTrigger1c
UeMeasControl
320 ms
timeToTrigger1d
UeMeasControl
2560 ms
T-ASU
Hardcoded
5s
w1a
UeMeasControl
0
w1b
UeMeasControl
0
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9. Compressed Mode Operation
Compressed mode is a physical layer function that allows the UE to temporarily tune to
another frequency, and measure the RF environment of another UMTS frequency (e.g.
IFHO) or another technology (e.g. IRAT), while maintaining an existing dedicated channel.
Unlike TDMA type air interfaces, the WCDMA physical frame does not contain any idle or
unused slots to make measurements on other frequencies. This is not an issue if a UE has
a dual Transceiver, which would allow the second receivers to make measurements while
the first receiver is processing the 10 millisecond frames. However, most UEs do not
contain dual transceivers (at this time), thus requiring an alternate means for a single
transceiver UE to make measurements on other frequencies
In the case of Ericsson, compressed mode may take one of two forms depending on the
radio bearer combination at the measurements on other frequencies are taken. If the radio
bearer contains any delay sensitive services (e.g. circuit switched voice), then SF/2 is
utilized. If it is not critical to delay the data flow (e.g. interactive or background packet
switched data) then Higher Layered Scheduling (HLS) is used.
9.1. Halving the Spreading factor (SF/2) Method
If SF/2 is required, the spreading factor (or OVSF) is reduced to half of its typical value. For
example, a radio bearer containing an AMR 12.2k utilizes a 128 OVSF code. When
compressed mode is enabled, the spreading factor will be reduced to a 64 bit OVSF. This
allows a transmission gap of up to seven slots (of the fifteen slots per frame) to be available
for measurements on other frequency. However this 50% reduction in the spreading factor
has many side effects. To maintain the appropriate Bit Error Rate (BER), and counter the
reduced processing gain, the power of the compressed frame will have to be increased by
approximately 3 dB. This is illustrated in the following figure of a compressed mode
transmission from 3GPP TS 25.212. In addition to downlink power utilization, compressed
mode will also affect capacity by consuming more codes in the downlink, increasing channel
element usage, and increasing uplink noise rise due to increased UE transmit power.
Because of these side effects, care must be taken to ensure that UEs do not unnecessarily
trigger compressed mode. In addition, the time spent in compressed mode should be
minimized.
One frame
(10 ms)
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inter-frequency measurements
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9.2. Higher Layered Scheduling (HLS) Method:
In the case of HLS, the transmission gap is generated by simply reducing the user
throughput in the higher layers. This is achieved in Layer 2 where the MAC utilizes a subset
of the available transport format combinations (TFC) within the transport format
combination set (TFCS). For example, the transport block set size for a PS 64 kbps
transport channel may contain 0, 1, 2, 3 or 4 transport blocks of 336 bits within every 20 ms
transport time interval (TTI). By only utilizing 0, 1, or 2 transport blocks every TTI, a
transmission gap of up to 7 slots can be generated, while maintaining a maximum
throughput of 50% of the original transport channel. Unlike the SF/2 method, HLS does not
require additional power, code usage, channel element usage, or UE transmit power to
achieve compressed mode operation.
9.3. Compressed Mode Pattern
When the UE reports that event 2d or 6d has occurred, the RNC sends a Physical Channel
Reconfiguration Message to the UE which contains the Compressed Mode parameters.
These parameters include the following (which are illustrated below in the figure from 3GPP
TS 25.215):

TGPSI (Transmission Gap Pattern Sequence Indicator): This defines a unique
transmission gap pattern sequence. Multiple transmission gap pattern sequence
may be configured in a single Physical Reconfiguration Message;

TGPRC (Transmission Gap Pattern Repetition Count): This is the number of
repeated transmission gap patterns within the transmission gap pattern sequence;

TGSN (Transmission Gap Starting Slot Number): This is the slot number of the first
transmission gap slot within the first radio frame of the transmission gap pattern;

TGL1 (Transmission Gap Length 1): This is the number of slots in the first
transmission gap;

TGL2 (Transmission Gap Length 2): This is the number of slots in the second
transmission gap;

TGD (Transmission Gap start Distance): This is the number of slots between the
first and second transmission gap within a transmission gap pattern;

TGPL1 (Transmission Gap Pattern Length): This is the number of frames within a
transmission gap pattern.
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#1
#2
#3
#4
#5
#TGPRC
TG pattern 1
TG pattern 1
TG pattern 1
TG pattern 1
TG pattern 1
TG pattern 1
TG pattern 1
Transmission
Transmission
gap 1
gap 2
TGL1
TGL2
TGSN
TGD
TGPL1
9.4. Limitations on number of mobiles in Compressed Mode
To minimize the impact of compressed mode on coverage, capacity and call quality, it is
possible to limit the number of UEs in compressed mode on a cell basis using the UtranCell
parameter compModeAdm. It is recommended to keep the value of this parameter equal to
the vendor default value of 15. In case the number of UEs in compressed mode for a cell
reaches this number, Admission control blocks a new radio link in being setup for this cell.
This is the only configurable parameter with regard to Compressed Mode for Ericsson 3G
RAN. The actual implementation of the Compressed Mode implementation is hard coded in
the Ericsson 3G RAN. Power control parameters related to Compressed Mode will be dealt
with in the Power Control section of this document.
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10. 3G to 2G Handover and Cell Change Procedure and
Parameters
This section details the 3G to 2G handover algorithm and the relevant parameters for
Ericsson 3G network.
10.1. T-Mobile Strategy for IRAT
T-Mobile deployment of UMTS in the U.S. will be carried out in several phases. In order to
maintain contiguous coverage to customers, it is important to transition them to the GERAN
network at the edge of UMTS coverage, without service disruption. This can be
accomplished by configuring 3G to 2G handover in the connected mode and 3G to 2G
reselection in the idle mode.
The following is the current T-Mobile strategy for IRAT transition:

Allow 3G to 2G handover in poor UMTS coverage areas.

Allow 3G to 2G cell change in poor UMTS coverage areas.

Allow 3G to 2G Reselection in poor UMTS coverage areas.

Allow 2G to 3G Reselection even in good GSM coverage as long as UMTS coverage
is available.

Do not allow 2G to 3G handovers in connected mode.
The objectives of the IRAT feature as described here are:

Offload the CS traffic on GSM networks by maximizing the use of UMTS networks,
where available to carry speech traffic. This will be done through the use of 2G to
3G reselection even in areas of good GSM signal strength, as long as there is UMTS
coverage available.

Keep UMTS capable UEs on UMTS coverage as long as possible with an acceptable
call quality.

Move 3G UEs to GSM using handover or reselection while leaving UMTS coverage
areas before call quality degradation.
10.2. Feature Activation
The IRAT feature in the Ericsson 3G RAN can be activated using the following parameters.
C_GsmHoAllowed: IRAT handover is only attempted if this parameter is set to Allowed for
the current UeRc state. This is a constant hard coded value and is currently set to Allowed
by Ericsson.
FddGsmHoSupp: This parameter at the RNC level should be set to TRUE to enable IRAT
functionality.
hoType: This cell parameter controls if IRAT Handover or Inter-Frequency HO or None shall
be evaluated in case both Inter RAT and Inter-Frequency neighboring cells have been
configured. The detailed working of this parameter is covered in the following section.
defaultHoType: This parameter set per DRNC indicates the hoType for cells in the
neighboring RNC. If not datafilled, IRAT handover is preferred.
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10.3. IRAT Interaction with Inter-Frequency Handover
For 3G cells that have both GSM and Inter frequency neighbors configured, the cell
parameter hoType controls which type of handover is actually carried out.
If all cells in the active set have hoType = None, then neither IRAT nor Inter-Frequency
Handover is attempted. If at least one cell in the active set has hoType = IF-Preferred, then
Inter-Frequency handover is attempted. If at least one cell in the active set has hoType =
GSM-Preferred and no cell has hoType = IF-Preferred, then IRAT handover will be
attempted.
Recommendation: For network launch, when only one WCDMA carrier is available, hoType
should be set to GSM-Preferred for all cells in the network. When there is more than one
WCDMA carrier available, this parameter would be re-evaluated and this guideline would be
updated accordingly.
10.4. 3G to 2G IRAT Handover/Cell Change Procedure
When a UE is on a CS call, 3G to 2G IRAT Handover is used to transition the mobile to GSM
at the edge of UMTS coverage area allowing service continuation on dedicated channels.
When the UE is on a PS call at the edge of the 3G network, IRAT Cell Change procedure is
used to transition the mobile to GPRS. The IRAT Cell Change procedure on dedicated
channels involves a network initiated cell reselection from UMTS to GSM, after which the UE
is responsible to continue the existing PS connection through the GPRS network. One
important difference in the Cell Change and IRAT handover procedures is that there are no
resources allocated in the target system in the case of the Cell Change procedure.
The 3G to 2G Handover procedure for Ericsson RAN can be grouped into the following 4
steps.

Connection quality monitoring based on event triggers.

Event based GSM measurements reporting.

Identification of target GSM cell for Handover/Cell Change.

3G to 2G IRAT Handover/Cell Change execution.
10.4.1.
Event based Connection quality monitoring
Three connection qualities are monitored and used to trigger IRAT handover process. The
downlink is monitored using CPICH RSCP and CPICH Ec/No, and the uplink is monitored
using UE TX power. If any of these three monitored connections qualities reach a
predefined threshold, indicating poor RF conditions, the IRAT handover process is triggered
(i.e. GSM candidate cells will be measured).
If RF conditions improve, and all three monitored connection qualities meet predefined
thresholds indicating minimum RF conditions are met, the IRAT handover attempt will be
aborted.
Filtering Concept
The measurement values are filtered by the UE before comparison with the event criteria.
The filtering is performed as per 3GPP recommendations according to the following formula.
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Fn = (1–a) Fn-1 + a Mn
where
Fn is the updated filtered measurement result
Fn-1 is the old filtered measurement result
Mn is the latest received measurement result from physical layer measurements
a = ½^(k/2), where k is the parameter received in the IE "Filter coefficient", and refers to
the filter coefficient parameter available in the Ericsson network for the various features.
A high value of this parameter emphasizes an old filtered measurement result (for example,
with k = 9, the weight of an old filtered measurement is 96% and the weight of a new
measurement is 5%). A low value of this parameter emphasizes a new measurement result
(for example, with k = 1, the weight of a new measurement result is 71%). With k = 0, old
measurements are not considered.
The details of the Ericsson implementation of the filtering period from the filter coefficient
are out of the scope of this document.
The recommended values in Appendix D for the different filter coefficients related to the
IRAT feature are the same as the Ericsson default values and will be changed as required in
the future.
Weighting Concept
A weighting factor is used to include active cells other than the best cell in the evaluation
criteria for reporting events. The measured value after weighting will be
 NA

W  10  Log   M i   (1  W )  10  LogM Best
 i 1

where
Mi is a measurement result of a cell in the active set
NA is the number of cells in the current active set
MBest is the measurement result of the cell in the active set with the
highest measurement result
W is the weighting factor
Recommendation: The recommended value for the weighting factors is 0. This would enable
the evaluation criteria for the reporting events to be based completely on the best cell’s
measurement.
Event 2d and 2f for CPICH RSCP and CPICH Ec/No monitoring
Events 2d and 2f are typically used to trigger and suspend compressed mode operations,
respectively. The Threshold, Hysteresis and Time-to-trigger parameters are delivered to the
IRAT capable UE via Measurement Control messages. The Measurement Quantity for the
Threshold can be CPICH RSCP, or CPICH Ec/No.
If a Measurement Quantity drops below the Event 2d threshold level, for the specified Time
to trigger, a Measurement Report indicating Event 2d has occurred will be sent to the RNC.
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This will typically result in compressed mode being triggered to enable the UE to measure
GSM neighbors. The actual Event 2d threshold is defined by the parameters
(usedFreqThresh2dEcno - hysteresis2d/2), for the Measurement Quantity CPICH Ec/No; and
(usedFreqThresh2dRscp - hysteresis2d/2), for the Measurement Quantity CPICH RSCP. The
time to trigger is defined by the parameters timeToTrigger2dEcno and timeToTrigger2dRscp
for Measurement Quantities CPICH Ec/No and CPICH RSCP respectively.
If a Measurement Quantity improves and goes above the Event 2f threshold level, for the
specified Time-to-trigger, a Measurement Report indicating Event 2f has occurred will be
sent to the RNC. This will typically result in compressed mode being suspended, and the
measurement of GSM neighbors ending. The actual Event 2f threshold is defined by the
parameters (usedFreqThresh2dEcno + usedFreqRelThresh2fEcno + hysteresis2f/2), for the
Measurement Quantity CPICH Ec/No; and (usedFreqThresh2dRscp +
usedFreqRelThresh2fRscp + hysteresis2f/2), for the Measurement Quantity CPICH RSCP.
The time to trigger is defined by the parameters timeToTrigger2fEcno and
timeToTrigger2fRscp for Measurement Quantities CPICH Ec/No and CPICH RSCP
respectively.
The following figure shows the concept of events 2d and 2f for CPICH Ec/No monitoring.
The following are the definitions of parameters used for events 2d and 2f. Refer to Appendix
D for the recommended values for these parameters as well as the object where these
parameters reside. For details on the ranges of these parameters, refer to the Parameter
Guidelines document [3].

usedFreqThresh2dEcno: indicates threshold to trigger event 2d for Ec/No.

usedFreqThresh2dRscp: indicates threshold to trigger event 2d for RSCP.

usedFreqThresh2dEcnoDrnc: indicates the threshold to trigger event 2d for Ec/No
when the best cell in the active set belongs to a DRNC.
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
usedFreqThresh2dRscpDrnc: indicates the threshold to trigger event 2d for RSCP
when the best cell in the active set belongs to a DRNC.

hysteresis2d: Hysteresis used for event 2d.

timeToTrigger2dEcno: Minimum interval of time the Measurement Quantity Ec/No
must be below the Event 2d threshold level before event 2d is triggered, and a
measurement report is sent.

timeToTrigger2dRscp: Minimum interval of time the Measurement Quantity RSCP
must be below the Event 2d threshold level before event 2d is triggered, and a
measurement report is sent.

usedFreqRelThresh2fEcno: Relative threshold for event 2f for Ec/No referenced to
the parameter usedFreqThresh2dEcno.

usedFreqRelThresh2fRscp: Relative threshold for event 2f for RSCP referenced to
the parameter usedFreqThresh2dRscp.

hysteresis2f: Hysteresis used for event 2f.

timeToTrigger2fEcno: Minimum interval of time the Measurement Quantity Ec/No
must be above the Event 2f threshold level before event 2f is triggered, and a
measurement report is sent.

timeToTrigger2fRscp: Minimum interval of time the Measurement Quantity RSCP
must be above the Event 2f threshold level before event 2f is triggered, and a
measurement report is sent.

filtercoefficient2: coefficient used to filter measured values before comparing to
event criteria. This is set to a value of 2, so that there is equal weight given to an
old filtered measurement result as well as to the new measurement result.

usedFreqW2d: weighting factor for event 2d.

usedFreqW2f: weighting factor for event 2f.
If the value of 2d threshold changes as a result of an Active Set update for the Ec/No or the
RSCP measurement, due to different settings of the cell parameter usedFreqThresh2dEcno
or usedFreqThresh2dRscp, the corresponding measurements using event 2d and event 2f
must be modified with the new thresholds.
If the best cell of the active set belongs to a neighboring RNC, then the parameters
usedFreqThresh2dEcnoDrnc and usedFreqThresh2dRscpDrnc are used to evaluate the event
2d. The parameters usedFreqThresh2dEcnoDrnc and usedFreqThresh2dRscpDrnc are RNC
based parameters. These can’t be modified on a cell level, however, with the current
implementation of soft handovers at the IuR boundary, there will be minimal IRAT
handovers, if any at RNC borders. Hence the absence of flexibility in tuning these
parameters on a cell level should not pose a big disadvantage to network optimization.
Finally, the parameters usedFreqThresh2dEcno and usedFreqThresh2dRscp can be uniquely
configured at the cell level. This allows the event 2d threshold for individual cells to be
tuned to meet desired network conditions (e.g. a cell in the UMTS core may have more
stringent conditions to trigger event 2d as opposed to a site on the UMTS network border).
All other IRAT (as well as handover) parameters are global RNC parameters.
Event 6d and 6b for UE TX Power monitoring
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Event 6d is used to evaluate if the TX power of the UE increases above the maximum
transmit power of the UE class. There is no pre-defined threshold to trigger event 6d. The
transmit power of the UE is compared to its maximum transmit power, P_max in order to
trigger event 6d, which typically results in IRAT measurements. Event 6b is used to evaluate
when the TX power goes below a pre-defined threshold, typically ending GSM
measurements. There is no support for hysteresis for events 6d and 6b. Also since the
comparison is done on the UE (and not on a specific cell in the active set), there is no
requirement of a weighting factor.
The following are the definitions of parameters used for events 6d and 6b. Refer to
Appendix D for the recommended values for these parameters as well as the object where
these parameters reside. For details on the ranges of these parameters, refer to the
Parameter Guidelines document [3].
txPowerConnQualMonEnabled: Enables or disables the connection quality monitoring based
on UE Tx power.
ueTxPowerThresh6b: The threshold used to trigger event 6b when UE Transmit power
becomes less than an absolute threshold.
timeToTrigger6d: Minimum interval of time the UE transmit power must be above the Event
6d threshold level before event 6d is triggered, and a measurement report is sent.
timeTrigg6b: Minimum interval of time the UE transmit power must be below the Event 6b
threshold level before event 6b is triggered, and a measurement report is sent.
filterCoeff6: Coefficient for layer 3 filtering before UE internal measurement reporting
evaluation. This is set to a value of 3, so that there is more weight given to an old filtered
measurement result (65%) and less weight given to the new measurement result (35%).
10.4.2.
Event based GSM measurements reporting
Once the UE receives the compressed mode parameters and responds with a Physical
Channel Reconfiguration Complete message, the RNC delivers a Measurement Control
message to the UE which contains the following:
The GSM monitored subset, built from the GSM neighbors of the active set cells. This is a
list of the candidate cells to measure (i.e. GSM cells). In the case of IRAT, the BCCH
ARFCN, and BSIC are also provided
The event 3a parameters, including the following:

The UMTS event 3a threshold trigger

The weighting factor, used to include measurements from the cells in the active set

The hysteresis applied to the UMTS event 3a threshold

The time to trigger

The GSM event 3a threshold trigger

The connection frame number (CFN) indicating which frame each TGPSI begins.
Note that the Measurement Quantity used for the UMTS event 3a threshold trigger is
dependant on the original event 2d or event 6d trigger. If event 2d was triggered based on
Ec/No, then the event 3a threshold trigger will be based on Ec/No. If event 2d was
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triggered based on RSCP, or an event 6d was the trigger, then the event 3a threshold
trigger will be based on RSCP.

If the connection quality trigger is CPICH Ec/No, event 3a is triggered when the
(estimated quality < usedFreqThresh2dEcno + utranRelThresh3aEcno hysteresis3a/2) and the (GSM carrier RSSI > gsmThresh3a), for at least
TimeToTrigger3a.

If the connection quality is CPICH RSCP, event 3a is triggered when the (estimated
quality < usedFreqThresh2dRscp + utranRelThresh3aRscp - hysteresis3a/2) and
the (GSM carrier RSSI > gsmThresh3a), for at least TimeToTrigger3a.

If the connection quality is UE Tx power, event 3a is triggered when the (estimated
quality < usedFreqThresh2dRscp + utranRelThresh3aRscp + utranRelThreshRscp hysteresis3a/2 and the (GSM carrier RSSI > gsmThresh3a), for at least
TimeToTrigger3a. In the case of UE Tx power, the event 3a is always evaluated
only on CPICH RSCP and not on CPICH Ec/No.
The following figure shows the concept of event 3a when the trigger is CPICH Ec/No.
The following are the definitions of the parameters used for event 3a. Refer to Appendix D
for the recommended values for these parameters as well as the object where these
parameters reside. For details on the ranges of these parameters, refer to the Parameter
Guidelines document [3].
utranRelThresh3aEcno: Relative threshold for event 3a versus event 2d when the 2d
measurement quantity is CPICH Ec/No.
utranRelThresh3aRscp: Relative threshold for event 3a versus event 2d when the 2d
measurement quantity is CPICH RSCP.
utranRelThreshRscp: This is used to compute the absolute RSCP threshold for event 3a
when bad connection quality has been triggered in the UL.
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timeToTrigger3a: Minimum interval of time that both the UMTS and GSM event 3a
thresholds are met, before event 3a is triggered, and a measurement report is sent.
Hysteresis3a: Hysteresis used for event 3a.
gsmThresh3a: Threshold for event 3a (the estimated quality of the currently used UTRAN
RAN frequency is below a certain threshold and the estimated quality of the GSM system is
above a certain threshold for GSM).
individualOffset: The offset is added to the measured quantity before the UE evaluates
whether an event has occurred. This parameter is found in the object ExternalGSMCell.
Improper use of non-default values may result in instability and unequal cell borders.
Recommended value is 0 for network launch.
maxGsmMonSubset: Maximum number of GSM cells that the UE will measure on. It is
recommended to keep this value to the default = 32.
utranFilterCoefficient3: Coefficient for layer 3 filtering of UTRAN quality before IRAT
reporting evaluation. This is set to a value of 2, so that there is equal weight given to an old
filtered measurement result as well as to the new measurement result.
utranW3a: Weighting factor for event 3a for UTRAN.
If the RNC receives a second event 3a MEASUREMENT REPORT while it is already
processing one, the new report is buffered. The buffer holds only the last received report so
a new received report overwrites a report already in the buffer.
10.4.3.
Identification of target GSM cell for Handover/Cell Change
The RNC uses the measurement report from event 3a and orders the GSM cells according to
their GSM quality measure. While doing this, RNC discards all GSM cells that are not BSIC
verified and cells whose GSM carrier RSSI is less than gsmThresh3a. RNC then chooses the
target GSM cell as the cell which has the best carrier RSSI and starts an IRAT handover
attempt towards this cell.
10.4.4.
3G to 2G IRAT Handover/Cell Change Execution
Once the evaluation carried by the IRAT Handover Evaluation algorithm has lead to a target
GSM/GPRS cell, IRAT Handover Execution starts. The result of the execution part is one of
the following:

Hand over the UE connection to a GSM/GPRS cell. That is, the UE is finally
connected to the GSM/GPRS cell and WCDMA RAN resources related to the UE
connection are released.

The UE connection remains on the WCDMA RAN due to a handover to GSM/GPRS
failure.
IRAT Handover Execution requests resources in the GSM/GPRS system, according to the
proposal received from the IRAT Handover Evaluation algorithm. If the attempt succeeds,
the actions necessary to fulfill the handover proposal are executed. If execution fails,
exception handling is performed to get back to stable situation and keep the UE connection
on the WCDMA RAN.
3G to 2G IRAT Handover Execution for CS services
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IRAT Handover function can only be executed for connections in CELL_DCH state and only
for UEs connected towards a Circuit-Switched service. The Circuit-Switched service can be
either voice or data. The following ladder diagram (reference 3GPP TS 25.931) illustrates
the signaling required between the UMTS and GSM network to perform a handover for CS
services.
UE
Node B
RNC
Serving
RANAP
CN
1. Relocation
Required
MSC
BSC
BTS
RANAP
MAP/E
2. Prepare
Handover
MAP/E
BSSMAP
3. Handover
Request
BSSMAP
4. Handover
Request Ack
BSSMAP
MAP/E
5. Prepare
Handover
Response
BSSMAP
MAP/E
6. Relocation
Command
RANAP
RANAP
7. DCCH : Handover from UTRAN
Command
RRC
RRC
8. Handover
Detect
BSSMAP
BSSMAP
9. Handover Complete
RR
RR
10. Handover
Complete
BSSMAP
MAP/E
RANAP
12. Iu Release
Command
11. Send End
Signal
Request
BSSMAP
MAP/E
RANAP
13. Iu Release
Complete
RANAP
RANAP
14. Send End
Signal Response
MAP/E
MAP/E
Once a target GSM neighbor is selected for handover, the RNC sends the RANAP message
RELOCATION REQUIRED to the 3G MSC, and the timer T_RELOC_prep is started. The
RELOCATION REQUIRED message contains information regarding the target GSM cell, and
this is forwarded on to the 2G MSC and BSC via MAP/E and BSSMAP signaling respectively.
If resources are allocated by the GSM target system, a RELOCATION COMMAND message is
received by the SRNC. At this point, the SRNC sends HANDOVER FROM UTRAN COMMAND
message to the UE to initiate the handover. The GSM/GPRS message HANDOVER
COMMAND is included in the handover message. The resources on WCDMA RAN side are
kept to allow the UE return to the old channels in case of handover failure. When the target
GSM BSS detects the UE and the handover is completed, the RR message HANDOVER
COMPLETE is sent by the UE to the BSC. At this point, the successful IRAT handover is
reported to the 3G Core Network, and a RANAP IU RELEASE COMMAND message is sent to
the RNC. At the reception of this message, the SRNC de-allocates all resources related to
the UE connection and responds to the 3G MSC with an IU RELEASE COMPLETE message.
The RRC and RANAP messages between the UE, UTRAN, and 3G MSC, for the IRAT
Handover execution are shown in the figure below. Actual UE traces showing IRAT message
flow will be included once available.
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Exception Handling of Failed 3G to 2G IRAT Handover
As stated in the previous section, the hard coded timer T_RELOC_prep, is started at the
transmission of the RELOCATION REQUIRED message and stopped at the reception of the
RELOCATION COMMAND. If this timer expires prior to receiving a response to the
RELOCATION REQUIRED message (either positive or negative), a RELOCATION CANCEL
message is sent to the 3G CS core network. The current 3G connection is maintained if
possible.
If a MEASUREMENT CONTROL failure occurs for event 3a, the SRNC cancels the IRAT
Handover procedure and the connection is released. If the RELOCATION PREPARATION
FAILURE message is received at SRNC from the Core Network, IRAT Handover is canceled,
and the connection is kept, if possible. If the cause of the message is “No resource
available”, the IRAT Handover Evaluation algorithm is informed that the allocation failed due
to lack of resources in the target system. If it is not possible to fulfill the RELOCATION
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COMMAND message for any reason, the function is cancelled and the RELOCATION CANCEL
message is sent from the SRNC to Core Network. The connection is kept, if possible.
If the UE fails to access the GSM cell and returns to the old channel, then a RADIO LINK
RESTORE INDICATION message is sent from RBS to the SRNC to indicate that the UE has
returned to the old channel. When the UE comes back to the old channel, a HANDOVER
FROM UTRAN FAILURE message is sent to the SRNC by the UE. The SRNC informs the Core
Network that IRAT Handover has failed so GSM resources can be de-allocated. The IRAT
Handover Execution informs the IRAT Handover Evaluation algorithm that the handover has
failed.
If the IRAT handover to the target cell fails, and if there are soft handover reports buffered,
RNC uses these to perform soft handover evaluation before returning to the IRAT handover
evaluation. If the IRAT handover fails, and there is a buffered 3a measurement report, RNC
terminates the existing event 3a handling, and processes the buffered event 3a report to
find a new GSM target for handover.
If the IRAT handover fails due to RELOCATION PREPARATION FAILURE (which is the failed
response to the RELOCATION REQUIRED message) or HANDOVER FROM UTRAN FAILURE,
then the RNC makes multiple attempts to the same GSM cell. If there is more than one
GSM cell in the 3a measurement report, repeated handover attempts shall be made to these
cells in quality order. The following are the parameters that influence repeated attempts to
handover. Refer to Appendix D for the recommended values for these parameters as well as
the object where these parameters reside. For details on the ranges of these parameters,
refer to the Parameter Guidelines document [3].
gsmAmountPropRepeat: Maximum number of repeated attempts (not including the first
attempt) of GSM cells for handover based on the same measurement report.
gsmPropRepeatInterval: Minimum time interval between handover attempts to the same
GSM cell based on the same measurement report.
gsmFilterCoefficient3: Coefficient for layer 3 filtering of GSM quality before IRAT reporting
evaluation. This is set to a value of 1, so that there is less weight given to an old filtered
measurement result (29%) and more weight given to the new measurement result (71%).
If the IRAT handover failure cause is “Other”, then the IRAT algorithm will be terminated
and the UE stays on UMTS.
3G to 2G IRAT Cell Change Execution for PS services
IRAT Cell Change is used to transition a UE connected to PS on a dedicated channel to the
GSM system. A network-initiated cell reselection is used to transition the UE to GPRS. The
following ladder diagram (reference 3GPP TS 25.931) illustrates the signaling required
between the UMTS and GSM network to perform a network initiated cell change for PS
services.
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UE
Serving
RNC
CN
1. Cell Change Order from
UTRAN
RRC
RRC
RANAP
RANAP
2. Iu Release Command
3. Iu Release Complete
RANAP
RANAP
Once a target GSM cell is selected for a UE connected to the PS network (via HLS
compressed mode), the SRNC initiates the IRAT Cell Change in the UE by sending the CELL
CHANGE ORDER FROM UTRAN message to UE. The message includes information of the
RAB to hand over and a target cell description. The UE synchronizes to the GPRS system
and sends a ROUTING AREA UPDATE message. Then, the PS Core Network sends a SRNS
CONTEXT REQUEST message that includes the RAB id for which the context must be
transferred. At this moment the DL transmission is stopped. The SRNC sends an SRNS
CONTEXT RESPONSE message. The PS Core Network initiates the release of the Iu
connection by sending the IU RELEASE COMMAND message. When this message is received
by the SRNC, the Iu bearers are released. The SRNC terminates the Iu release by sending
an IU RELEASE COMPLETE message to the PS Core Network.
The RRC connection messages between the UE and the UTRAN for the IRAT Cell Change
Execution are shown in the figure below. Actual UE traces showing IRAT message flow will
be included once available.
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Exception Handling of Failed 3G to 2G IRAT Cell Change
If the UE sends a MEASUREMENT CONTROL FAILURE message, the SRNC will cancel the
IRAT Cell Change Execution procedure and the connection is released. If the UE fails to
access the GPRS cell, it returns to the old channel. A RADIO LINK RESTORE INDICATION is
sent from the Node B to the SRNC to indicate that the UE has returned to the old channel.
The UE then sends a CELL CHANGE ORDER FROM UTRAN FAILURE message to the SRNC.
The IRAT Handover Evaluation is informed about the failure. If there is an invalid RAB id in
the SRNS CONTEXT TRANSFER, the SRNC will respond with SRNS CONTEXT RESPONSE
using the indicator that “RABs Context Failed to Transfer”, due to invalid RAB id.
3G to 2G IRAT Handover Execution for CS and PS Multi-service
In cases where the UE is connected to both the CS and PS networks simultaneously, the
transition to 2G is handled by the IRAT Handover Execution procedure for CS.
10.5. Scenarios for 3G to 2G IRAT Handover / Cell Change
The primary purpose of 3G to 2G IRAT handover in the T-Mobile USA network is to
transition mobile users from the UMTS network to the GSM network while leaving the UMTS
coverage areas. A UE might leave the UMTS coverage area in the following 4 cases.
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
At the edge of the defined UMTS network – As the UMTS network is scheduled to
be deployed in phases across the country, there are bound to be gaps in UMTS
coverage area. Hence while leaving the UMTS network; the users would be able to
maintain a call through handover to 2G.

In-building areas without dedicated UMTS sites – In the initial phase of 3G network
planning, outdoor UMTS sites will be used to cover in-building areas. The 2G
network would then provide better in-building coverage in these areas, and hence
a 3G to 2G handover might be useful to maintain the call in indoor locations.

Missing Sites – During initial deployment, it is possible that one or more planned
UMTS sites in a cluster may be built later than the rest of the cluster. In these
cases as well, it would be beneficial to use 3G to 2G handover to maintain a call
while transitioning between sites.

Coverage Holes – To address any unplanned coverage holes resulting from site
related failures. 2G handover can be used maintain a call in this scenario as well.
The following are the 2 scenarios chosen for 3G to 2G IRAT handover optimization.
10.5.1.
Edge Thresholds
The Edge thresholds can be used when the intent of the 3G to 2G handover is to transition
the UE to GSM at fairly stronger values of RSCP and Ec/No. The intent is to compromise on
the extent of the UMTS coverage area, by enabling mobiles to handover to GSM well within
the 3G coverage. This would help in making the handover more reliable and minimize the
number of drop calls. Since this set of values for RSCP and Ec/No triggers would reduce the
3G coverage area, this should be used only as required for a limited number of sites. The
details on the actual RSCP and Ec/No values are available in the next chapter.
10.5.2.
Core Thresholds
The Core thresholds should be used when the intent of 3G to 2G handover is to allow
transition from UMTS to GSM at relatively weaker values of RSCP and Ec/No when
compared to the Edge case. The intent of these lower thresholds is to maximize the UMTS
coverage area, especially in areas where a temporary fade in the RF environment may
otherwise trigger unwanted handovers to 2G when higher values are used for the trigger
points. In the core of the network, there may be areas where the signal strength may start
falling due to temporary fade conditions, but the UE maybe able to recover fairly quickly
from these temporary fade conditions, making handover to GSM unnecessary. By not setting
the thresholds to stronger values, the UE is given enough time to recover from these
temporary fade conditions. This is the recommended starting configuration for most sites in
the UMTS network, thus maximizing the UMTS coverage area.
10.6. Parameter recommendations for IRAT Scenarios
This section details the recommended values for parameters that influence IRAT 3G to 2G
handover for the two scenarios discussed in the previous section. The following are the
recommended values for each of the two scenarios.
Core Thresholds: For the core of the network, the recommended settings for IRAT handover
are based on UMTS outdoor design thresholds. As per [2], the UMTS design threshold for
AMR 12.2 Voice is an RSCP of -105 dBm and an Ec/No of -14 dB. The intent of the IRAT
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feature is to maximize the UMTS coverage area; hence a UE on UMTS should handover to
GSM when the RSCP reaches a value of -105 dBm or when the Ec/No reaches a value of -14
dB. Since there is a delay between triggering compressed mode and the actual IRAT
handover to GSM, the thresholds to trigger compressed mode should be set higher than the
above mentioned thresholds. Hence the thresholds to trigger compressed mode are
recommended to be set at an RSCP of -102 dBm and an Ec/No of -13 dBm, giving a margin
for IRAT handover before UMTS coverage loss.
Edge Thresholds: The Edge thresholds are recommended to be set higher than the Core
values so as to handover a UE to GSM with minimum drop calls. An RSCP of -98 dBm and
an Ec/No of -12 dB is recommended as the trigger to start compressed mode measurements
on GSM neighbors.
In the following subsections, the above thresholds for 3G to 2G handover are translated into
specific parameter values from an Ericsson RNC perspective.
For the Ericsson 3G RAN, the parameters usedFreqThresh2dEcno for Ec/No based trigger
and usedFreqThresh2dRscp for RSCP based trigger are configurable on a per-cell basis.
10.6.1.
Edge Thresholds
The recommended values to trigger compressed mode (event 2d) in this case are
usedFreqThresh2dEcno = -12 dB
usedFreqThresh2dRscp = -98 dBm
The recommended values to trigger compressed mode cancellation (event 2f) are obtained
from the event 2d values using a constant (RNC-level) offset of usedFreqRelThresh2fEcno
for Ec/no and usedFreqRelThresh2fRscp for RSCP.
usedFreqRelThresh2fEcno = 3 dB (thus resulting in 2f threshold of -9 dB)
usedFreqRelThresh2fRscp = 3 dBm (thus resulting in 2f threshold of -95 dBm)
The recommended values to trigger IRAT handover (event 3a) are obtained from the event
2d values using a constant (RNC-level) offset of utranRelThresh3aEcno for Ec/No and
utranRelThresh3aRscp for RSCP.
utranRelThresh3aEcno = -1 dB (thus resulting in 3a threshold of -13 dB)
utranRelThresh3aRscp = -3 dBm (thus resulting in 3a threshold of -101 dBm)
The recommended values for the complete set of IRAT related parameters are available in
Appendix D.
10.6.2.
Core Thresholds
The recommended values to trigger compressed mode (event 2d) in this case are
usedFreqThresh2dEcno = -13 dB
usedFreqThresh2dRscp = -102dBm
The recommended values to trigger compressed mode cancellation (event 2f) are obtained
from the event 2d values using a constant (RNC-level) offset of usedFreqRelThresh2fEcno
for Ec/no and usedFreqRelThresh2fRscp for RSCP.
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usedFreqRelThresh2fEcno = 3 dB (thus resulting in 2f threshold of -10 dB)
usedFreqRelThresh2fRscp = 3 dBm (thus resulting in 2f threshold of -99 dBm)
The recommended values to trigger IRAT handover (event 3a) are obtained from the event
2d values using a constant (RNC-level) offset of utranRelThresh3aEcno for Ec/No and
utranRelThresh3aRscp for RSCP.
utranRelThresh3aEcno = -1 dB (thus resulting in 3a threshold of -14 dB)
utranRelThresh3aRscp = -3 dBm (thus resulting in 3a threshold of -105 dBm)
In case the best cell of the active set belongs to a DRNC, then the parameters
usedFreqThresh2dEcnoDrnc and usedFreqThresh2dRscpDrnc are used for IRAT handover to
2G. Since these parameters are set at the RNC level, these have the same value for both
scenarios and are set equal to the Core Thresholds.
The recommended values for the complete set of Ericsson IRAT related parameters are
available in Appendix D.
10.7. 3G to 2G IRAT Handover/Cell Change Optimization Strategy
Initially, it is recommended to use the Core set of values for the RSCP and Ec/No thresholds
for the majority of the UMTS sites in the UMTS network, except for UMTS cells that fall at
the defined edge of a UMTS market. This would ensure that the UMTS coverage area is
maximized in the core of the network, and in any particular case of a UMTS coverage hole
due to a missing site either outdoor or in-building, a UE on UMTS can be transitioned to
GSM before dropping the call.
The strategy outlined here is for the optimization of the Core and Edge thresholds in order
to ensure that the UE is transitioned to 2G only at the edge of the UMTS coverage area
while minimizing the overall 3G plus 2G drop call rate. Since the intent of the Edge
thresholds (as described in the previous sections) is to transition a UE to 2G well within the
3G coverage area, even though the UMTS coverage is slightly reduced, the final Edge
thresholds should still be at higher RSCP and Ec/No values when compared to the Core
thresholds.
The metrics outlined here are only to aid in the optimization strategy of the IRAT
thresholds. The exact counter names are not specified here and can be referenced from the
KPI documents [5] and [6].

3G and 2G Drop Call Rate: The combined drop call rate of 3G and 2G should be
monitored to ensure that the IRAT handover feature doesn’t affect the
performance of the T-Mobile network. The goal of 3G to 2G IRAT handovers is to
transition mobiles to 2G systems at the edge of UMTS network, while minimizing
the drop call rate on 3G as well as 2G. The 3G and 2G drop call percentages should
be monitored on a network level as well as on a cell level for each of the cells that
have IRAT handover enabled. The trend in drop call rate changes for 3G and 2G
corresponding to any IRAT related parameter changes should be monitored to
ensure the success of the new values.

Ratio of 3G to 2G Handover attempts to 3G calls established: This metric when
compared for 2 different sets of IRAT handover triggers, would give an idea as to
which set of values for RSCP and Ec/No threshold might be more suitable. As long
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as the 3G and 2G total drop call rate is not affected, the thresholds for IRAT
handover should be chosen such that the ratio of 3G to 2G handover attempts to
3G calls established is minimized. This would eliminate unnecessary IRAT handover
attempts to 2G.

Ratio of 3G to 2G Handover attempts to Number of Compressed Mode (CM)
attempts: This metric gives a trend of how many compressed mode triggers
actually result in a 3G to 2G handover attempt. This metric in combination with the
combined 3G and 2G drop call rate can be used to pick a suitable value for 2
different sets of RSCP and Ec/No thresholds. As long as the total 3G and 2G drop
call rate is not affected, the set of thresholds which minimize the ratio of IRAT
handover attempts to number of CM attempts should be chosen.

Ratio of 3G to 2G handover attempts to overlay GSM cell to total 3G to 2G
handover attempts: This metric on a WCDMA cell level, helps in finding premature
IRAT handover trigger. A high value shows a lot of IRAT handovers happening in
the core of the cell, and may point to non-optimal compressed mode and IRAT
handover triggers.

IRAT attempts for UMTS cells in the core: A high value for this metric indicates
problems with the UMTS cell.

Ratio of Number of IRAT handovers from a UMTS cell to Number of idle mode 2G3G reselections to the same UMTS cell: A low value can be used to identify ping
pong behavior between in-call mode and idle mode. If the IRAT Handover and idle
mode reselection parameters are set incorrectly, it can happen that a UE camps on
3G in idle mode and when a call is setup it will do an IRAT HO almost immediately
because of aggressive IRAT parameter settings and the call will be completed on
2G. After the call is completed it will reselect back to 3G until the next call and the
process will repeat itself.
This is just a high level strategy for optimization thresholds and further analysis of drive test
data as well as counter data should be performed before actual changes in parameter
values is implemented.
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11. Emergency Call treatment
The Location Technology Systems team has defined in [7] how a E911 call needs to be
treated in order to be reported to the PSAP (Public Safety Answering Point) with the most
accurate latitude and longitude values.
The following is just a very brief explanation of the proposed treatment for an emergency
call. The long term solution is a network based A-GPS system called as stand along SMLC
(Service Mobile Location Center) or SAS based on 3GPP standards. Unfortunately, neither
this system nor the A-GPS capable UEs will be available at launch. Therefore, interim
solutions have been defined for emergency call handling. One interim solution is based on
Service Based Handover (SBHO) and the other is based on emergency RRC Redirection.
The preferred solution is to use SBHO, however this would need the availability of the Lb
interface via LCS conversion. Markets with a Lb interface will be using SBHO for emergency
calls, while markets that don’t have a Lb interface available will be using the emergency
RRC redirection method for handling emergency calls.
SBHO for emergency calls can be enabled by setting parameter “ecCnSbhoRequestIgnore”
to False. The handover from WCDMA to GSM will be performed immediately following the
RAB Assignment request message from the MSC and it will be performed only if the
following is fulfilled: the ServiceHandover IE in the RAB Assignment request need to have
the value "should" and the Priority Level IE in the same RANAP message need to have the
value equal to the configurable parameter ecCnPriorityLevel. Also the parameter
agpsEnabled should be set to False indicating the lack of AGPS support in the 3G network. A
timer, ecSbhoTimer, is started if a handover to GSM is initiated. Before expiration of this
timer, the RNC will not respond to a Location Reporting Control message from the CN. At
expiration of the timer, a Location Report may be sent if the handover to GSM was
unsuccessful, but otherwise no response will be sent. In order for SBHO to be used for
emergency calls,
For emergency RRC redirection, the parameter emergencyCallRedirect is set to ‘On’ to allow
all emergency calls to be redirected to GSM. When a UE requests to establish an RRC
connection and indicates 'Emergency call' as establishment code, the WCDMA RAN will
reject the request by sending the message RRC Connection Reject with the 'Redirection info'
equal to 'Inter-RAT info GSM'. The UE will then perform a cell selection to GSM and attempt
to establish a connection to GSM. This procedure is applied when there is no RRC
connection already setup in WCDMA RAN. If there is an existing RRC connection used for
packet-switched traffic, this RRC connection has to be ended by the user ending its packet
session before dialing an emergency call..
If the cell selection in GSM fails, the UE may do a cell re-selection to UMTS after the time
stated in the 'Wait time' has elapsed. The timer ‘Wait time’ is sent by the RNC to the UE in
the ‘RRC Reject Message’. It is the minimum wait time after which the UE can perform a
reselection back to UMTS after a failed call attempt on GSM following an emergency call
redirection. This timer is hard coded to 1 second. Once the UE returns to UMTS, the RNC
will provide location information to the PSAP based on cell ID (CI).
There is a second UE timer in the RNC, hard coded to 60 seconds, enabling the RNC to
remember the “initial UE identity” for 60 seconds from the time of RRC reject message. If
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this UE makes a second RRC connection attempt within this 60 second time period, then the
RNC will recognize the UE and allow it to make a call on UMTS.
The following are the related parameters to the E911 interim solutions activation. The
proposed settings are to allow the interim solutions to be activated. All other settings are
following vendors default values.
Parameter Name
Object
Name
Recommended Value
emergencyCallRedirect
RncFunction
On
ecCnSbhoRequestIgnore
RncFunction
False
ecLocationAttemptUmts
RncFunction
Off
ecSbhoTimer
RncFunction
6s
ecCnPriorityLevel
RncFunction
7
agpsEnabled
UtranCell
False
uePositioning
RncFunction
enabledPositioningFeatures = Cell_ID_ONLY
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12. 2G to 3G IRAT Cell Reselection
The T-Mobile camping strategy is to allow mobiles to camp on UMTS, wherever UMTS
service is available, so that the users can take advantage of the advanced features available
in the UMTS network, as well as to offload the GSM traffic whenever possible. The 2G to 3G
Cell Reselection feature can be used to transition mobiles in idle mode from GSM to UMTS,
when entering UMTS coverage areas. In order to comply with T-Mobile strategy, the UEs
should be allowed to camp on UMTS, irrespective of the GSM signal strength whenever
UMTS coverage is available.
This section details the reselection algorithms to transition to 3G for the Ericsson BSS, Nokia
BSS and Nortel BSS. In each case the recommended values required to implement the
above mentioned T-Mobile strategy are presented. Since the reselection is carried out from
the 2G side, the target 3G system is immaterial to this discussion. In general, the algorithms
detailed here are applicable for transition to any 3G network including the Ericsson 3G
network.
12.1. Ericsson 2G to Ericsson 3G Reselection
The following discussion is valid for Ericsson BSS version R12. The parameter COEXUMTS is
used to enable the GSM-UMTS Cell Reselection feature. The following are the possible
values for this parameter.

COEXUMTS = 0 (OFF): In this case, none of the GSM – UMTS features is activated.

COEXUMTS = 1 (ON): In this case, the GSM – UMTS Cell Reselection and Handover
features are activated.

COEXUMTS = 2 (ONADDINFO): In this case, the GSM-UMTS Cell Reselection and
Handover, as well as Combined Reselection Triggering GSM to WCDMA (this
feature is detailed in the following sections) are activated.
The recommended value for this parameter is 2 (ONADDINFO).
8.1.1. UTRAN Neighbor Definitions and System Information
The UTRAN cells to be monitored for inter system cell reselection are defined in the 3G
neighboring cell list which is broadcast on BCCH using the System Information Type 2quater
(SI 2quater). If a PBCCH is also configured, the 3G neighboring cell list is also broadcast on
PBCCH using the Packet System Information Type 3quater (PSI 3quater).
The SI 2quater and PSI 3 quarter messages are only broadcast if any UTRAN neighbor cells
exist and if the parameter COEXUMTS is not set to OFF.
In T-Mobile GSM networks, PBCCH is currently not configured. Hence, only the SI 2quater
message will be broadcast.
SI 2quater can be broadcast either on BCCH Normal or BCCH Extended. If all the
information doesn’t fit into a single SI 2quater message, the remaining information will be
sent in other instances of this message.
When SI 2quater is sent, AGBLK is recommended to be set to 1 when SI 2bis and SI 2ter
are sent, when GPRS/EGPRS is active and SI 2bis is sent, and when GPRS/EGPRS is active
and SI 2ter is sent. This is because SI 2quater will share the same resources as SI 13
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and/or SI 2ter on BCCH normal implying longer cycle for the System Information to be
broadcast. This could impact cell selection/reselection performance. When AGBLK = 1,
either SI2quater or SI 13 are placed on BCCH extended in the above cases. However, use of
BCCH extended implies reduction of the paging capacity since BCCH extended shares the
resource with PCH and AGCH.
UTRAN FDD neighboring cells are identified with a frequency and scrambling code
combination. In idle mode, the measurement frequency (MFDDARFCN) and scrambling
code (MSCRCODE) for the neighboring UTRAN cells are defined within the parameter
UMFI. This parameter is also used to define if diversity is applied or not for an UTRAN cell.
Up to 64 UTRAN neighboring cells may be defined per GSM cell.
12.1.1.
Measurements on WCDMA neighbors in idle mode
In addition to measurements on surrounding GSM/GPRS/EGPRS cells, a Multi-RAT mobile
also performs measurements on UTRAN neighboring cells. The parameter QSI can be used
to enable measurements on UTRAN cells in idle mode and packet switched modes. This
parameter is broadcast on BCCH and PBCCH (if PBCCH is enabled).
There are four possible scenarios based on value of QSI for measurements on UTRAN
neighbors.

UTRAN neighbors are measured only when the signal strength of the GSM serving
cell is above the threshold set by QSI.

UTRAN neighbors are measured only when the signal strength of the GSM serving
cell is below the threshold set by QSI.

UTRAN neighboring cells are always measured.

UTRAN neighboring cells are never measured.
Since T-Mobile camping strategy is to have the mobiles camp on the UMTS network,
whenever UMTS coverage is available, this parameter QSI should be set to ‘always’, so that
UTRAN cells are measured even when the GSM signal strength is good.
Recommended Value: The parameter QSI is recommended to be set to 7 (= always).
12.1.2. Cell Reselection to UMTS for mobiles that don’t support RSCP
evaluation
This section is focused on the reselection algorithm used for mobiles that don’t support
RSCP evaluation.
A similar algorithm to the one for GSM reselection is used for the GSM to UMTS cell
reselection. Since the modulation technique used for UMTS is completely different from
GSM, there is a difference in the evaluation of signal quality for GSM and UMTS
measurements. Hence a mapping of UMTS signal strength is performed in such a way that it
can be compared to GSM signal strength values.
The following two criteria have to be fulfilled for a period of 5 seconds for a multi-RAT
mobile to reselect a suitable UTRAN cell.
CPICH Ec/No > FDDQMIN
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and
CPICH RSCP > RLA(s+n) + FDDQOFF
Where
RLA(s+n) refers to the Received Level Average of the serving and neighboring GSM cells.
RLA is the average of the received signal levels measured in dBm for all monitored GSM
frequencies in the BA list.
FDDQMIN is the minimum quality of a UTRAN cell for cell reselection. This parameter
ensures a sufficient quality of the candidate UTRAN cell.
FDDQOFF is the key parameter to control the behavior of inter-system cell reselection. It
defines an offset between the signal strength of UTRAN and GSM cells. Lower values of the
parameter FDDQOFF can be used to off-load the GSM system, while higher values can be
used to keep multi-RAT mobiles in the GSM system. Since the values of GSM signal strength
and UTRAN CPICH RSCP are not of the same kind, the balance between the two should be
set with the offset FDDQOFF.
Cell reselection back to UTRAN will not occur within 5 seconds after a previous cell
reselection from UTRAN. If a cell reselection occurred within the previous 15 seconds, an
additional offset of 5 dB is added to FDDQOFF by the mobile. These conditions prevent
ping-pong for a mobile that has just entered GSM.
To achieve the preferred camping strategy of the mobile camping on UMTS, whenever
UTRAN coverage is available, the value of FDDQOFF should be such that the UTRAN CPICH
RSCP always looks better than the GSM RLA. A negative value of FDDQOFF would achieve
this by making a UTRAN cell always look better than a GSM cell. Since this might sometimes
result in cell reselection to a weak UMTS cell, the value of parameter FDDQMIN should be
set to control this.
A value of FDDQMIN such that FDDQMIN > qQualMin + sRatSearch would prevent the
mobile from making cell reselection to a weak UTRAN cell. This setting would also ensure
that the MS will not start to measure on GSM cells immediately after reselecting a UTRAN
cell. For details on these parameters with respect to the Ericsson RAN, refer to the Chapter
“Cell Reselection Parameters from 3G to 2G”.
The available values for parameter FDDQMIN are one of [-20dBm, -6dBm, -18dBm, -8dBm,
-16dBm, -10dBm, -14dBm, -12dBm]. Since the recommended value for qQualMin = -18 dB
and sRatSearch = 4 dB, the parameter FDDQMIN should be greater than -14 dB. The lowest
value that achieves this condition (-12 dB) should be selected to speed up the reselection of
a UTRAN cell.
Recommended Values: From the above reasoning, the recommended value of FDDQOFF = infinity and FDDQMIN = -12 dB. This would allow the MS to camp on UMTS, whenever
UTRAN coverage is available, irrespective of the signal strength of GSM. These settings
would result in a cell reselection algorithm that is based only on the quality of the UTRAN
cell, since the reselection criterion 2 is always satisfied.
Refer to Appendix E for a quick look at the recommended values for all 2G to 3G reselection
parameters.
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12.1.3.
Cell Reselection to UMTS for mobiles that support RSCP evaluation
For mobiles that support RSCP evaluation for reselection to 3G, an additional criterion is
used to further minimize the number of ping pong cell reselections. This is achieved by
adding a threshold for CPICH RSCP measurements to assure a sufficient downlink signal
strength, which in turn increases the possibility for the mobile to reach the network in the
uplink.
The following three criteria have to be fulfilled for a period of 5 seconds for a multi-RAT
mobile with RSCP evaluation capability to reselect a suitable UTRAN cell.
CPICH RSCP > RLA(s+n) + FDDQOFF
CPICH Ec/No > FDDQMIN – FDDQMINOFF
and
CPICH RSCP > FDDRSCPMIN - min((P_MAX-21), 3dB)
Where
RLA(s+n) refers to the Received Level Average of the serving and neighboring GSM cells.
RLA is the average of the received signal levels measured in dBm for all monitored GSM
frequencies in the BA list.
FDDQMIN is the minimum quality of a UTRAN cell for cell reselection. This parameter
ensures a sufficient quality of the candidate UTRAN cell.
FDDQMINOFF defines an offset to the threshold FDDQMIN.
FDDQOFF defines an offset between the signal strength of UTRAN and GSM cells.
FDDRSCPMIN defines the minimum threshold for the “signal strength” measure CPICH RSCP
for cell reselection to UTRAN.
P_MAX is the maximum RF output power of the MS in UTRAN FDD mode. For a Class 3
mobile, this is equal to 24 dBm.
The recommended values for FDDQMIN and FDDQOFF are equal to -12 dB and –infinity as
explained in the previous section. The recommended value for FDDQMINOFF = 0 dB, which
would keep FDDQMIN – FDDQMINOFF > qQualMin + sRatSearch (= -14 dB).
The absolute minimum CPICH RSCP value to reselect a UTRAN cell is given by the selection
parameter qRxLevMin in UTRAN. A setting of FDDRSCPMIN such that FDDRSCPMIN >
qRxLevMin + hysteresis prevents the multi-RAT mobile to trigger a reselection to a weak
UTRAN cell.
The recommended value for FDDRSCPMIN = -102 dBm, which would result in a Class 3 MS
(P_MAX = 24 dBm) reselecting a 3G cell when the cell’s CPICH RSCP > -105 dBm, and a
Class 4 MS (P_MAX = 21 dBm) reselecting a 3G cell when the CPICH RSCP > -102 dBm.
Refer to Appendix E for a quick look at the recommended values for all 2G to 3G reselection
parameters
12.2. Nokia 2G to Ericsson 3G Reselection
The following discussion is valid for Nokia BSS version S11.5. The ISHO_SUPPORT_IN_BSC
option must be in use to handle, modify and output any of the GSM-WCDMA Inter System
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Handover and Cell Reselection parameters which are not GPRS related. To enable the GPRS
capable mobiles on PBCCH to measure and select an adjacent WCDMA cell the
ISHO_SUPPORT_IN_BSC and BSC_GPRS_PARAM_ENABLED options must be in use.
As per the current T-Mobile implementation there is no PBCCH configured in the GSM
networks, hence the parameter BSC_GPRS_PARAM_ENABLED should be set to False.
12.2.1.
UTRAN Neighbor Definitions and System Information
The UTRAN cells to be monitored for inter system cell reselection are defined in the 3G
neighboring cell list which is broadcast on BCCH using the System Information Type 2quater
(SI 2quater). If a PBCCH is also configured, the 3G neighboring cell list is also broadcast on
PBCCH using the Packet System Information Type 3quater (PSI 3quater).
The SI 2quater and PSI 3 quarter messages are only broadcast if UTRAN neighbor cells are
defined. These messages may contain more than one instance.
The dual mode GSM/WCDMA mobiles are divided into two separate categories according to
the GPRS capabilities: GPRS and non-GPRS capable mobiles. There are both common and
category specific user defined parameters for the adjustment of the mobile functionality in
the idle state, packet idle mode, dedicated state and packet transfer mode.
For the BSC radio network parameter handling, this means that most if the WCDMA related
idle state parameters are applicable foe all mobiles. However, the operator is also able to
define the GPRS capability specific neighbor WCDMA cell measuring and reselection
threshold values for the WCDMA capable mobiles.
The dual mode GSM/WCDMA mobiles are able to find and identify a WCDMA RAN cell by the
information included in the parameters WCDMA downlink carrier frequency (FREQ),
scrambling code SCC), and downlink transmission diversity (DIV).
The maximum number of 3G neighboring cells per serving GSM cell is limited to 32 cells
over 3 frequencies.
If GSM-WCDMA Inter-System Handover is in use, the maximum number of neighbor GSM
cells (ADJC) per a serving cell (or segment) is 31 without Common BCCH Control in BSC or
30 if there is also at least one of the Common BCCH software activated. If GSM-WCDMA
Inter-System Handover is in use, the maximum number of frequencies in a BCCH Allocation
(BA) list is 31 without Common BCCH Control in BSC or 30 if there is also at least one of the
Common BCCH software activated.
A serving GSM cell cannot have two or more neighbor WCDMA RAN cells with the same
UARFCN and scrambling code. A serving GSM cell cannot have two or more neighbor
WCDMA RAN cells which use the same MCC + MNC + RNC id + CI combination and/or
WCDMA RAN cell index value.
12.2.2.
Measurements on WCDMA neighbors in idle mode
In addition to measurements on surrounding GSM/GPRS/EGPRS cells, a Multi-RAT mobile
also performs measurements on UTRAN neighboring cells. The parameter qSearchI for nonGPRS and qSearchP for GPRS capable UEs can be used to enable measurements on UTRAN
cells in idle mode and packet switched modes. This parameter is broadcast on BCCH and
PBCCH (if PBCCH is enabled).
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There are four possible scenarios based on value of qSearchI for non-GPRS capable mobiles
(qSearchP for GPRS capable mobiles) for measurements on UTRAN neighbors.

UTRAN neighbors are measured only when the signal strength of the GSM serving
cell is above the threshold set by qSearchI (qSearchP).

UTRAN neighbors are measured only when the signal strength of the GSM serving
cell is below the threshold set by qSearchI (qSearchP).

UTRAN neighboring cells are always measured.

UTRAN neighboring cells are never measured.
Since T-Mobile camping strategy is to have the mobiles camp on the UMTS network,
whenever UMTS coverage is available, the parameters qSearchI and qSearchP should be set
to ‘always’, so that the UTRAN cells are measured even when the GSM signal strength is
good.
Recommended Value: The parameters qSearchI and qSearchP are recommended to be
set to 7 (= always).
12.2.3. Cell Reselection to UMTS for mobiles that don’t support RSCP
evaluation
A similar algorithm to the one for GSM reselection is used for the GSM to UMTS cell
reselection. Since the modulation technique used for UMTS is completely different from
GSM, there is a difference in the evaluation of signal quality for GSM and UMTS
measurements. Hence a mapping of UMTS signal strength is performed in such a way that it
can be compared to GSM signal strength values.
The following two criteria have to be fulfilled for a period of 5 seconds for a multi-RAT
mobile to reselect a suitable UTRAN cell.
For a Non-GPRS capable UE:
CPICH Ec/No > fddQMin
and
CPICH RSCP > RLA_C + fddQOffset
For a GPRS capable UE:
CPICH Ec/No > gprsFddQMin
and
CPICH RSCP > RLA_C + fddGprsQOffset
Where
RLA_C refers to the Received Level Average of the serving GSM cells. RLA is the average of
the received signal level measured in dBm for the serving GSM.
fddQMin and gprsFddQMin are the minimum quality of a UTRAN cell for cell reselection for
non-GPRS and GPRS capable UEs, respectively. These parameters ensure a sufficient quality
for the candidate UTRAN cell.
fddQOffset and fddGprsQOffset are the key parameters to control the behavior of intersystem cell reselection for non-GPRS and GPRS capable UEs, respectively. They define an
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offset between the signal strength of UTRAN and GSM cells. Lower values of these
parameters can be used to off-load the GSM system, while higher values can be used to
keep multi-RAT mobiles in the GSM system. Since the values of GSM signal strength and
UTRAN CPICH RSCP are not of the same kind, the balance between the two should be set
with the offsets fddQOffset and fddGprsQOffset for non-GPRS and GPRS capable UEs,
respectively.
If more than one WCDMA cell fulfils the above criteria, the cell with the best RSCP is
selected for reselection.
The parameters that are required to determine whether the WCDMA RAN cell is suitable are
broadcast on BCCH of the WCDMA RAN cell. A mobile may start re-selection towards the
WCDMA RAN cell before decoding the BCCH of the WCDMA RAN cell. If the WCDMA RAN
cell is not suitable, this leads to a short interruption of service.
Cell reselection back to UTRAN will not occur within 5 seconds after a previous cell
reselection from UTRAN. If a cell reselection occurred within the previous 15 seconds, the
value of parameters fddQOffset and fddGprsQOffset is increased by 5 dB by the mobile.
These conditions prevent ping-pong for a mobile that has just entered GSM.
To achieve the preferred camping strategy of the mobile camping on UMTS, whenever
UTRAN coverage is available, the value of fddQOffset (fddGprsQOffset) should be such that
the UTRAN CPICH RSCP always looks better than the GSM RLA_C. A negative value of
fddQOffset (fddGprsQOffset) would achieve this by making a UTRAN cell always look better
than a GSM cell. Since this might result sometimes in cell reselection to a weak UMTS cell,
the value of parameter fddQMin (gprsFddQMin) should be set to control this.
A value of fddQMin (gprsFddQMin) such that fddQMin (gprsFddQMin) > qQualMin +
sRatSearch would prevent the mobile from making cell reselection to a weak UTRAN cell.
This setting would also ensure that the MS will not start to measure on GSM cells
immediately after reselecting a UTRAN cell. For details on these parameters qQualMin and
sRatSearch, refer to Chapter “Cell Reselection Parameters from 3G to 2G” for Ericsson 3G
networks.
The available values for parameter fddQMin (gprsFddQMin) are one of [-20dBm, -6dBm, 18dBm, -8dBm, -16dBm, -10dBm, -14dBm, -12dBm]. Since the recommended value for
qQualMin = -18 dB and sRatSearch = 4 dB, the parameter fddQMin (gprsFddQMin) should
be greater than -14 dB. The lowest value that achieves this condition (-12 dB) should be
selected to speed up the reselection of a UTRAN cell.
Recommended Values: From the above reasoning, the recommended value of fddQOffset
(fddGprsQOffset) = -infinity and fddQMin (gprsFddQMin) = -12 dB. This would allow the MS
to camp on UMTS, whenever UTRAN coverage is available, irrespective of the signal
strength of GSM. These settings would result in a call reselection algorithm that is based
only on the quality of the UTRAN cell, since the reselection criterion 2 is always satisfied.
Refer to Appendix E for a quick look at the recommended values for all 2G to 3G reselection
parameters.
12.2.4.
Cell Reselection to UMTS for mobiles that support RSCP evaluation
For mobiles that support RSCP evaluation for reselection to 3G, an additional criterion is
used to further minimize the number of ping pong cell reselections. This is achieved by
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adding a threshold for CPICH RSCP measurements to assure a sufficient downlink signal
strength, which in turn increases the possibility for the mobile to reach the network in the
uplink.
As per 3GPP, the additional criterion is given by
CPICH RSCP > FDD_RSCP_threshold for a period of 5s, where
FDD_RSCP_threshold = FDD_RSCPmin – min((P_MAX – 21 dBm), 3 dB) if FDD_RSCPmin is
broadcast on the serving cell, else Qrxlevmin + Pcompensation + 10 dB, if these parameters
are available, otherwise the default value of FDD_RSCPmin.
Nokia 2G doesn’t support the availability of the parameter FDD_RSCPmin until BSS V13.
Hence for a MS that supports RSCP evaluation, the CPICH RSCP of the 3G cell is compared
to the default value of FDD_RSCPmin, which is equal to -102 dBm minus the value of
min(P_MAX – 21 dBm, 3 dB). Hence for a Class 3 mobile that supports RSCP evaluation for
cell reselection, a 3G cell is reselected when the RSCP > -105 dBm, in addition to the 2
criteria covered in the previous section for a time equal to 5 seconds.
12.3. Nortel 2G to Ericsson 3G Reselection
The following discussion is valid for Nortel BSS version V16. GSM to UMTS Mobility is
provided to UEs in Idle Mode to reselect to the 3G network. This section does not deal with
UEs in connected mode. The parameter “uMTSReselectionARFCN” should be set to a nonnull value in order for the SI2quater message containing the UMTS neighbor cell information
to be broadcast on the BCCH. A null value for this parameter would otherwise disable this
feature and prevent reselection to UMTS.
8.1.2. UTRAN Neighbor Definitions and System Information
The cell reselection does not require any specific algorithm in the GSM-BSS. The intersystem
reselection only requires new piece of information to be broadcast on the BCCH by the
GSMBSS:

new intersystem cell reselection control parameters

neighboring UMTS cell list
The broadcast of parameters required for 2G to 3G reselection is done using the "System
Information 2quater" message. Due to the volume of information, it may happen that the
set of data exceeds the 23 byte limit for "System Information" messages sent on BCCH. In
such a case, the information is segmented into several parts i.e. several instances of the
System Information 2quater message, each of them tagged with an INDEX from 0 to
COUNT, (COUNT + 1) being the number of segments.
When the information is updated (following a change at the OMC-R), the CHANGE MARK bit
is set to a new value.
The System Information 2quater is scheduled either on Normal or Extended BCCH

If sent on Normal BCCH: It shall be sent when TC = 5 if neither of 2bis and 2ter
are used, otherwise it shall be sent at least once within any of 4 consecutive
occurrences of TC = 4.

If sent on BCCH Ext, it is sent at least once within any of 4 consecutive occurrences
of TC = 5.
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As a consequence, System Information 3 message has been updated in order to indicate to
the mobile:

Whether or not SI2quater is broadcast.

If broadcast is done on Normal or Extended BCCH.
The current Nortel implementation doesn’t support UMTS neighbor definitions for the
serving GSM cell. Only the UMTS FDD_ARFCN is defined on a BTS level. Hence the
neighboring cell scrambling codes are not broadcast in the Nortel implementation, only
FDD_ARFCN will be broadcast using SI 2quater.
12.3.1.
Measurements on WCDMA neighbors in idle mode
The parameter “uMTSSearchLevel” can be used to enable measurements on UTRAN cells in
idle mode. This parameter is broadcast on BCCH.
There are four possible scenarios based on value of “uMTSSearchLevel” for measurements
on UTRAN neighbors.

UTRAN neighbors are measured only when the signal strength of the GSM serving
cell is above the threshold set by uMTSSearchLevel.

UTRAN neighbors are measured only when the signal strength of the GSM serving
cell is below the threshold set by uMTSSearchLevel.

UTRAN neighboring cells are always measured.

UTRAN neighboring cells are never measured.
Since T-Mobile camping strategy is to have the mobiles camp on the UMTS network,
whenever UMTS coverage is available, this parameter uMTSSearchLevel should be set to
‘always’, so that the UTRAN cells are measured even when the GSM signal strength is good.
Recommended Value: The parameter uMTSSearchLevel is recommended to be set to 7
(= always).
12.3.2. Cell Reselection to UMTS for mobiles that don’t support RSCP
evaluation
Instead of C2 criterion used in a GSM-only network, the multimode cell reselection uses a
criteria based on RLA_C (Received Level Averages for Circuit services), which is an
unweighted average of the received signal levels measured in dBm.
The UE starts measuring 3G cells based on the serving GSM cell’s RLA_C with respect to the
setting of the parameter uMTSSearchLevel.
The following two criteria have to be fulfilled for a period of 5 seconds for a multi-RAT
mobile to reselect a suitable UTRAN cell.
CPICH Ec/No(n) > uMTSAccessMinLevel
and
CPICH RSCP(n) > RLA_Cserving + uMTSReselectionOffset
The parameter “uMTSAccessMinLevel” is the Nortel implementation of the 3GPP parameter
FDD_Qmin and is the minimum quality of a UTRAN cell for cell reselection. This parameter
ensures a sufficient quality of the candidate UTRAN cell.
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The parameter “uMTSReselectionOffset” is the key parameter to control the behavior of
inter-system cell reselection and is the Nortel implementation of the 3GPP parameter
FDD_Qoffset. It defines an offset between the signal strength of UTRAN and GSM cells.
Lower values of this parameter can be used to off-load the GSM system, while higher values
can be used to keep multi-RAT mobiles in the GSM system. Since the values of GSM signal
strength and UTRAN CPICH RSCP are not of the same kind, the balance between the two
should be set with the offset uMTSReselectionOffset.
To achieve the preferred camping strategy of the mobile camping on UMTS, whenever
UTRAN coverage is available, the value of uMTSReselectionOffset should be such that the
UTRAN CPICH RSCP always looks better than the GSM RLA_C. A negative value of
uMTSReselectionOffset would achieve this by making a UTRAN cell always look better than
a GSM cell. Since this might sometimes result in cell reselection to a weak UMTS cell, the
value of parameter uMTSAccessMinLevel should be set to control this.
A value of uMTSAccessMinLevel such that uMTSAccessMinLevel > qQualMin + sRatSearch
would prevent the mobile from making cell reselection to a weak UTRAN cell. This setting
would also ensure that the MS will not start to measure on GSM cells immediately after
reselecting a UTRAN cell. For details on these parameters with respect to the Ericsson RAN,
refer to the Chapter “Cell Reselection Parameters from 3G to 2G”.
The available values for parameter uMTSAccessMinLevel are one of [-20dB, -6dB, -18dB, 8dB, -16dB, -10dB, -14dB, -12dB]. Since the recommended value for qQualMin = -18 dB
and sRatSearch = 4 dB, the parameter uMTSAccessMinLevel should be greater than -14 dB.
The lowest available value that achieves this condition (-12 dB) should be selected to speed
up the reselection of a UTRAN cell.
Recommended Values: From the above reasoning, the recommended value of
uMTSReselectionOffset = -infinity and uMTSAccessMinLevel = -12 dB. This would allow the
MS to camp on UMTS, whenever UTRAN coverage is available, irrespective of the signal
strength of GSM. These settings would result in a cell reselection algorithm that is based
only on the quality of the UTRAN cell, since the reselection criterion 2 is always satisfied.
Refer to Appendix E for a quick look at the recommended values for all 2G to 3G reselection
parameters.
12.3.3.
Cell Reselection to UMTS for mobiles that support RSCP evaluation
For mobiles that support RSCP evaluation for reselection to 3G, an additional criterion is
used to further minimize the number of ping pong cell reselections. This is achieved by
adding a threshold for CPICH RSCP measurements to assure a sufficient downlink signal
strength, which in turn increases the possibility for the mobile to reach the network in the
uplink.
As per 3GPP, the additional criterion is given by
CPICH RSCP > FDD_RSCP_threshold for a period of 5s, where
FDD_RSCP_threshold = FDD_RSCPmin – min((P_MAX – 21 dBm), 3 dB) if FDD_RSCPmin is
broadcast on the serving cell, else Qrxlevmin + Pcompensation + 10 dB, if these parameters
are available, otherwise the default value of FDD_RSCPmin.
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Nortel 2G doesn’t support the availability of the parameter FDD_RSCPmin until BSS V17.
Hence for a MS that supports RSCP evaluation, the CPICH RSCP of the 3G cell is compared
to the default value of FDD_RSCPmin, which is equal to -102 dBm minus the value of
min(P_MAX – 21 dBm, 3 dB). Hence for a Class 3 mobile that supports RSCP evaluation for
cell reselection, a 3G cell is reselected when the RSCP > -105 dBm, in addition to the two
criteria covered in the previous section for a time equal to 5 seconds.
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13. Capacity Management Overview
The fundamental algorithms associated with capacity management are Admission Control,
and Congestion Control. These algorithms depend on Ericsson’s Dedicated Monitored
Resource Handling function to supervise the utilization of system resources and provide
inputs to the admission and Congestion Control programs. Figure 21 illustrates Ericsson’s
capacity management functions.
Admission Control is invoked whenever new or additional resources are required; such as an
access attempt or a soft handover request. In either of these cases, the Admission Control
algorithm must confirm there are adequate system resources available to support this new
request. Examples of these resources include codes, power and channel elements.
Congestion Control is invoked when the utilization of resources is reaching a critical limit and
this contention needs to be resolved. An example of this would be downlink power nearing
one hundred percent. In this case, resources dedicated to users may be reduced, or in the
extreme case removed, to eliminate congestion.
Both power and orthogonal codes are a limited resource. In general, once a cell’s capacity
demands consume these resources, the only option is to add a new site or a second
frequency in order to offload the cell’s usage. On the other hand, channel elements are
typically limited by license agreements between Ericsson and T-Mobile. Once the user
capacity needs consistently approach a predefined channel element threshold, more channel
elements will have to be licensed.
Before getting into the details of the capacity management algorithms, this section will
discuss resources that are monitored by the capacity management algorithms. Resources
are consumed to support overhead channels (e.g. the Pilot channel), as well as common
user channels (e.g. the FACH or HS-DSCH channels). Additionally resources are obviously
made use of to support dedicated channels. The term dedicated channel (DCH) refers to a
channel which is only used by a single user (e.g. a CS voice call), and consumes resources
that are solely allocated to this user. Every DCH requires the use of orthogonal codes,
channel elements and power. The consumption of these resources is described in the
following sections.
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Figure 21 - Overview of Ericsson Capacity Management Functions
13.1. Overview of UMTS Resources
The resources that are monitored by the capacity management algorithms include power,
orthogonal codes and channel elements. In addition the uplink noise rise is monitored as
well. In this section, some properties of these resources, as well as some of their
configurable parameters (if applicable) will be discussed.
13.1.1.
DL Power
All physical channels require an allocation of downlink power. The power for common
channels is typically fixed and parametrically controlled. On the other hand, dedicated
channels utilize power dynamically depending on RF conditions (i.e. interference) and
distance from the cell (i.e. pathloss). When a dedicated channel is configured, the amount
of downlink power it uses is controlled by closed loop power control. If the transport
channel’s configured Block Error Rate (BLER) is not met, outer loop power control raises the
SIR target, which results in increased DL power. If the maximum power for a given DCH
was not limited by some mechanism, it is possible that a majority of the cell’s power could
be consumed by a single user.
In order to curtail the amount of power that a single user can use, a maximum downlink
transmitted code power is defined. This is defined per cell, by use of the interpolation curve
shown in Figure 22 - Bit Rate (bps) versus Maximum Downlink Transmitted Code Power. As
the figure illustrates, the curve is defined by six parameters: minPwrMax;
minimumRate; interPwrMax; interRate; maxPwrMax; maxRate. In this manner,
the maximum power for a DCH can be limited based on its data rate, and a single user can
not consume an excessive amount of power. For data rates that fall between these
parameter data points, interpolation is used.
As an example, the maximum power a 12.2 kbps voice call can use is less than the
maximum power a 384 kbps PS radio bearer can use. Since these two dedicated channels
use a 128 bit code and an 8 bit code respectively, the processing gain of the PS call is
approximately 12 dB less than the CS call. Therefore it is logical that the PS call will need
more power than the CS call to maintain the same coverage within the cell.
In addition to this power limiting effect described above, soft and softer handover also add
to the consumption of downlink power. Assuming that the average soft handover factor
was 1.8 radio links per user, each user would require power from 1.8 cells, on an average
(excluding the HS-PDSCH).
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Figure 22 - Bit Rate (bps) versus Maximum Downlink Transmitted Code Power
13.1.2.
Received Total Wideband Power
All transmissions in the uplink contribute to the increase in uplink noise, or Received Total
Wideband Power (RTWP). To limit the interference a UE can create, the parameter
maxTxPwrUl is used to control the maximum power the UE can transmit. This parameter
is typically configured to be 24 dBm for a Class 3 UE.
13.1.3.
OVSF Codes
Every dedicated channel that is configured utilizes an orthogonal code, or an Orthogonal
Variable Spreading Factor (OVSF), from the code tree. In addition, some common channels
also consume OVSF codes. Unfortunately, the number of available codes is limited within
each cell. Figure 23 illustrates a portion of the OVSF code tree (reference 3GPP TR 25.292).
As the figure shows, the number of available codes is equal to the number of bits in the
code (e.g. there are two 2 bit codes, four 4 bits codes, etc.). In addition, once a specific
code is allocated, other codes on the same branch of the code tree become unavailable for
use.
For example, if the 4 bit code (1,1,-1,-1) is assigned, all preceding codes on the same
branch, such as (1, 1), are unusable. In addition, all the codes the follow on the same
branch are unusable as well. This would include (1,1,-1,-1, 1,1,-1,-1), (1,1,-1,-1, -1,-1,1,1),
as well as all the 16, 32, 64, 128, and 256 bit codes that are decedents of this 4 bit code.
These codes are unusable because the orthogonal properties of OVSF codes do not exist
between parent codes and their descendants.
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c4,1 = (1,1,1,1)
C8,1
C8,2
c4,2 = (1,1,-1,-1)
C8,3
C8,4
c2,1 = (1,1)
c1,1 = (1)
Unusable
Codes
c4,3 = (1,-1,1,-1)
Allocated
Code
c2,2 = (1,-1)
c4,4 = (1,-1,-1,1)
SF = 1
SF = 2
Unusable
Codes
SF = 4
Figure 23 – OVSF Code Tree
Based on the properties of OVSF codes discussed above, it is apparent why codes can be
consumed so quickly. Table 6 provides a sample of downlink code utilization of
miscellaneous user applications. Because the descendants of codes become unusable, a
user utilizing an 8 bit OVSF for a 384 kbps session reduces the pool of available 128 bit
codes by 16 codes. This has a direct impact on 128 bit code availability for 12.2 kbps AMR
voice calls.
User Application
5.9 AMR CS
12.2 AMR CS
HSDPA Code
DCH 64k PS
DCH 128k PS
DCH 384k PS
DL Code Length
256 bit
128 bit
16 bit
32 bit
16 bit
8 bit
Available Codes
256
128
16
32
16
8
Table 6 - Code Utilization of Misc. User Applications
In addition to this code limiting effect described above, soft and softer handover also add to
the consumption of OVSF codes. Assuming that the average soft handover factor was 1.8
radio links per user, each user would require 1.8 codes on an average (excluding the HSPDSCH).
13.1.4.
RBS Channel Elements
The term channel element (CE) is used to quantify processing power in the Node B chipset.
The number of channel elements available for users is dependant on hardware
configuration, and number of licensed channel elements enabled. In general, channel
elements for the common and overhead channels are included with the Node B, and do not
take from the pool of licensed channel elements.
In the Ericsson Node B, channel elements for uplink are located on the Random Access and
Receiver (RAX) board. The total number of CE available is dependant on the type of RAX
board, as well as the number of RAX boards that are installed in the Node B. As an
example, the high capacity 3206 RBS can contain 8 RAX R2 boards with 128 channel
element each, for a total of 1024 channel elements.
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The channel elements for the downlink are located on the transmitter card. The total
number of CE available is dependant on the number of transmitter boards installed. The
3206 RBS can be configured with 2 transmitter cards with 256 channel elements each, for a
total of 512 channel elements.
The number of channel elements utilized by a UE is dependant on several factors. This
includes the RAB type used, as well as the soft/softer handover state of the UE. Table 7
provides some examples of downlink and uplink CE usage based on RAB type. As the table
shows, RABs with high data rates require additional processing and therefore more channel
elements. When a UE is in soft handover, the CE requirement obviously increases since
multiple Node Bs are involved. However, when a UE is in softer handover, the same CE will
process the multiple radio links within the same Node B.
CS/PS RAB
Speech
64 kbps
128 kbps
384 kbps
Downlink (CE)
1
2
4
8
Uplink (CE)
1
4
8
16
Table 7 - Channel Element Consumption by RAB Type
13.2. Common Resource Utilization
In general, capacity management is typically focused on controlling resources for dedicated
channels. However, common channels also consume resources and affect the pool of
resources available for dedicated channels. In order to better understand how capacity
management operates, this section will review the utilization of common resources.
13.2.1.
Overhead and Common Channels
The term overhead channels refer to the set of channels that are required for the network
to operate, however they are not used to relay user plane data (i.e. a CS call or PS data).
Common channels, such as the Forward Access Channel, do have the capability to deliver
user specific data over a common resource. All of these channels require the use of
orthogonal codes, channel elements, and downlink power. In general, channel elements for
the overhead channels are included with the Node B, and do not take from the pool of
licensed channel elements. The consumption of the downlink power and codes resources,
for each of the overhead and common physical layer channels, is described in the following
sections.
Primary Common Pilot Channel
The Primary Common Pilot Channel (CPICH), also known has the pilot, is an overhead
channel that is constantly broadcast. The CPICH utilizes a 256 bit orthogonal code, and its
power is configured by the parameter primaryCpichPower. Typically the CPICH is set to
approximately 10% of the cell’s output power capability. Because this parameter is set at
the antenna reference point (see figure below), the insertion loss of the feeder lines, and
other miscellaneous coupler losses should be considered when setting this parameter.
As an example, assume the Node B has a 40 watt (i.e. 46 dBm) power amplifier (PA), and
the total insertion loss was 3 dB between the Node B and the antenna reference point. If
the desired CPICH power was 10% of the total PA power, primaryCpichPower would be
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set to 33 dBm. This based on a maximum Node B output of 43 dBm (46 -3 = 43) at the
antenna reference point; and 10 % of 43 dBm is 33 dBm.
Antenna
Reference
Point
Node B
Figure 24: Antenna Reference point
Primary Common Control Physical Channel
The Broadcast Channel (BCH) is used to transmit system and cell specific information to idle
UEs. The BCH is mapped to the Primary Common Control Physical Channel (P-CCPCH). The
P-CCPCH utilizes a 256 bit orthogonal code, and its power is configured relative to the
CPICH by the parameter bchPower.
Secondary Common Control Physical Channel
The Paging Channel (PCH) and the Forward Access Channel (FACH) transport channels are
mapped to the Secondary Common Control Physical Channel (S-CCPCH). It is possible to
map the PCH and the FACH to a single S-CCPCH, or to map each of them to a unique SCCPCH. Typically the S-CCPCH with the FACH mapped to it will have a 64 bit orthogonal
code, while a stand alone PCH mapped S-CCPCH only requires a 128 bit orthogonal code.
The power for the PCH is controlled by the parameter pchPower; and the maximum power
for FACH is configured by maxFach1Power. Both of these parameters are configured
relative to the CPICH power. If a second FACH channel is configured, the power is
configured with the parameter maxFach2Power.
Primary and Secondary Synchronization Channels
The Primary Synchronization Channel (P-SCH) and Primary Synchronization Channel (S-SCH)
are used by the UE to obtain slot and frame synchronization. The P-SCH and S-SCH only
exist at the physical layer, and do not consume orthogonal codes. The power for the PSCH, and the S-SCH are configured relative to the CPICH power by the parameters
primarySchPower, and secondarySchPower respectively.
Paging Indication Channel
The Paging Indication Channel (PICH) is used by the network to instruct the UE to monitor
the Paging Channel for a possible page. The PICH was introduced into the 3GPP standard
to improve UE battery life. This channel only exists at the physical layer and does not
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consume any orthogonal codes. The power for the PICH is configured relative to the pilot
by the parameter pichPower.
Acquisition Indication Channel
The Acquisition Indication Channel (AICH) is used to acknowledge random access
preambles when the UE is attempting to access the network. The AICH only exists at the
physical layer and does not consume any orthogonal codes from the code tree. The power
for the AICH is configured relative to the pilot by the parameter aichPower.
13.2.2.
Maximum Downlink Transmission Power
The maximum downlink power transmitted from a cell can be limited by the configurable
parameter maximumTransmissionPower. As described earlier in the section, the
reference point for this parameter is at the antenna reference point. This parameter allows
limiting the power to a level lower than the actual power available, which is reported by the
Node B as maxDlPowerCapability. This reported power available is derived from the
maximum PA output power, less the insertion losses between the PA and the antenna
reference point. If the parameter maximumTransmissionPower is configured to a value
that differs from the maxDlPowerCapability reported by the Node B, the lesser of the
two values will be utilized.
13.2.3.
HSDPA Resources
High Speed Downlink Packet Access (HSDPA) uses the High Speed Physical Downlink
Shared Channel (HS-PDSCH) to deliver user data to HS capable UEs. This channel utilizes
16 bit orthogonal codes, as well as the remaining unused power in the cell. The number of
orthogonal codes utilized for HS is controlled by multiple parameters, and will be described
below.
The parameter numHsPdschCodes is used to reserve a fixed number of 16 bit orthogonal
codes for use by the HSDPA scheduler. In this manner, HS users are guaranteed codes
regardless of DCH resource requests. However, these reserved codes will be unavailable for
DCH resource requests, even if there are not any HSDPA users in the cell.
It is possible to dynamically allocate more HS-PDSCH codes by enabling the HSDPA Dynamic
Code Allocation algorithm by setting the parameter dynamicHsPdschCodeAdditionOn to
TRUE. This algorithm will periodically assess the use of 16 codes every second. If there are
any unused codes available, they will be temporarily made available to the scheduler.
However, if there is a need for codes to support DCH requests, they will be immediately deallocated from the scheduler (excluding those reserved by the parameter
numHsPdschCodes). The maximum number of simultaneous codes used by the HSPDSCH at any give time is limited by the configurable parameter maxNumHsPdschCodes.
Care should be taken when configuring the parameter numHsPdschCodes. If the value is
set too high, the potential of blocking DCH users (e.g. CS calls), is increased. However,
setting this value too low may starve HS cell throughput if DCH traffic is high. This
parameter is configured at the cell level and therefore can be tuned to meet user
requirements.
In addition to HS-PDSCH, the High Speed Shared Control Channel (HS-SCCH) requires a 128
bit orthogonal code. The parameter numHsScchCodes controls the number of HS-SCCH
broadcast per cell. The number of HS users that can be simultaneously allocated resources
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by the scheduler per 2 ms Transport Time Interval (TTI) is directly related to the number of
HS-SCCH broadcast (maximum is 4). If a cell has a high HS traffic load, and a low DCH
load, it may be beneficial to increase the number of broadcast HS-SCCH. However, if the
overall cell throughput is limited due to power, HS-PDSCH codes or transport limitations,
consuming another 128 bit code to support an additional HS-SCCH is unneeded.
13.3. Dedicated Monitor Resource Handling
The utilization of system resources is constantly changing based on several factors. These
factors include the number of users, the RF conditions each user is experiencing, the
applications they are using, their soft handover state, etc. Because of this dynamic use of
resources, the Ericsson UTRAN monitors the most critical resources. The admission and
Congestion Control algorithms depend on Ericsson’s Dedicated Monitored Resource Handling
function to supervise the utilization of system resources and provide inputs to the admission
and Congestion Control programs.
13.3.1.
Downlink Channelization Code Monitor
The Downlink Channelization Code Monitor tracks the usage of OVSF codes. The fraction of
code tree usage is reported to the capacity management programs. Both common and
dedicated OVSF code usage is accounted for when calculating the fraction of code tree
usage. This monitor is used by Admission Control to reserve OVSF codes for handover
admission requests.
13.3.2.
Histogram Monitor
The Histogram Monitor is used to track specific events that impact resource utilization. This
includes OVSF codes usage, HSDPA users and the number of users in compressed mode.
Enhanced Uplink or HSUPA is not currently addressed in this version of the Feature Guide
and hence E-DCH resources are not covered in this discussion. These specific events are
described in the following sections:
DL Spreading Factor Usage
This function of the histogram monitor tracks the downlink OVSF code use on per spreading
factor (SF) length basis. This is unlike the Downlink Channelization Monitor which tracks the
fraction of code tree usage. The Histogram Monitor reports the usage of SF8, SF16 and
SF32 to Admission Control so that the use of these spreading factors can be limited. As
described before, the descendants of allocated codes become unavailable for use. Because
of this fact, it is apparent that limiting the allocation of these codes may be necessary.
It is important to note that the histogram monitor does not include the number of SF16
OVSF codes reserved for HSDPA by the parameter numHsPdschCodes. Therefore care
should be taken when configuring the Admission Control parameter limiting the number of
SF16 codes.
UL Spreading Factor Usage
This function of the histogram monitor tracks the uplink spreading factor usage of all the
users in the cell. The Histogram Monitor reports the usage of SF4, S8 and SF16 to
Admission Control so that the use of these spreading factors can be limited. The reason for
limiting the use of these codes in the uplink is not because of code usage, rather it is the
additional uplink noise caused by these codes. Because these OVSF codes exhibit a lower
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processing gain, the amount of uplink power required increases resulting in a rise of RTWP.
Because of this fact, it is apparent that limiting the allocation of these codes may be
necessary.
Number of Compressed Mode Radio Links
Compressed Mode (CM) is used to allow a UE to make inter-frequency measurements. In
order to make these measurements, gaps are created in the uplink and downlink physical
frame. For CS users, these gaps are created by dividing the spreading factor by two (i.e.
SF/2). This reduced processing gain due to halving of the spreading factor results in
increased RTWP. Therefore, the number of CM users is monitored and reported to
Admission Control.
Number of HSDPA Users Allocated to the HS-DSCH
The number of HSDPA users allocated to the HS-DSCH is monitored and reported to
Admission Control. If the number of HSDPA users becomes excessive, the HSDPA
Scheduler’s ability to operate efficiently may be impacted.
13.3.3.
Downlink Transmitted Carrier Power
The downlink transmitted carrier power is obviously a limited resource. The use of this
resource must be monitored to provide input to the Admission Control and Congestion
Control algorithms. The amount of power (non-HS) used at any given time is constantly
changing based on the number of users; their radio bearer type (i.e. spreading factor),
distance from site, and RF conditions.
Two mechanisms are used by the Node B to report the total transmitted carrier power of
the cell (non-HS) to the RNC. Periodic reports are used by Admission Control to determine
if admission requests, soft handover requests, and radio link reconfiguration requests will be
granted or denied. In addition, event based measurements are used in extreme cases when
the total downlink power usage exceeds a predefined threshold and Congestion Control
must offload users. Once the carrier power drops below a second predefined threshold,
another event based measurement is sent to indicate that the congestion condition has
been resolved. The details of these two measurement types are provided in the following
sections.
Periodic Measurement Report
When a cell is integrated and enabled in the UTRAN, the controlling RNC utilizes NBAP
messaging to initiate periodic measurement reports for the downlink transmitted carrier
power. These periodic reports are filtered in the RNC, and tracked by the Downlink
Transmitted Carrier Power Monitor. In addition to the reported carrier power, this monitor
also estimates power utilization for pending radio links that have been granted admission,
but may have not had time to be implemented. These estimates decay over time and allow
the Admission Control algorithm to handle new requests while previously admitted radio
links are being set up. Equation below illustrates how the monitor derives the downlink
transmitted carrier power.
P_Monitore d  P_Measure_ Filter  f P_Estimate _RL 
Equation 6 - Monitored Downlink Carrier Power
where:
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power
P_Monitored
Total monitored power
P_Measure_Filter
Filtered periodic measurement of downlink transmitted carrier
f(P_Estimate_RL)
Sum of all decaying estimates of recently admitted radio links
The estimated power for recently admitted radio links is derived by providing a scaling
factor based on the type of radio link; and multiplying it to the maximum transmitted code
power for that type of radio link. This scaling factor is based on characteristics for that
specific type of radio link (i.e. activity factor, discontinuous transmission, etc.). The
derivation of this estimated radio link power is provided in Equation below.
P_Estimate _RL  F * P_Max_RL
Equation 7 - Estimated Radio Link Power
Where:
link
P_ Estimate_RL
Estimated power of the recently admitted radio link
F
Scaling factor for the specific type of radio link
P_Max_RL
Maximum transmitted code power for the specific type of radio
Event Based Measurement Report
Event based measurement reports are also set up by NBAP signaling when a Node B is
integrated into the network. The thresholds for the (downlink transmitted carrier power)
event based measurements are configured by Congestion Control parameters. These
parameters define at what carrier power level congestion is triggered, and at what power
level congestion is resolved. Event based measurement reports are sent to the RNC when
the total downlink power of the cell exceeds the congestion threshold; and an additional
event based measurement report is sent once the carrier power drops below the congestion
resolution threshold. The details regarding these parameters, as well as the Congestion
Control algorithm, will be covered in later sections.
13.3.4.
ASE Monitor
The Air Interface Speech Equivalent (ASE) is an Ericsson specific term used to quantitatively
describe the interference caused by a single 12.2 AMR speech call (excluding the SRB). The
term is used for both the uplink and downlink. As an example, a PS 384 has an ASE equal
to 40.27 in the downlink. This implies that a 384 kbps downlink radio bearer, including its
SRB, contributes 40.27 times the amount of interference in the downlink than a single 12.2
kbps speech call does. Some ASE values for some sample radio connections are provided in
the table below. Note that the values provided below and utilized by the capacity control
algorithm account for the 0.61 ASE load contributed by the 3.4 kbps SRB.
The number of uplink ASEs credited to a cell, from a specific UE, is dependant on the soft
handover state of that UE. The ASE load for a cell is divided by the number of radio links in
the active set. If a UE is in 2 way soft handover, ASE load for each cell will be halved. This
is because of the reduced uplink interference due to soft handover gain.
Radio Connection Type Uplink ASEs Downlink ASEs
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SRB
AMR 12.2
CS64
PS16/64
(Streaming)
2.43
1.61
11.10
4.74
2.43
1.61
11.10
10.59
PS64/384
MultiRAB
(speech+PS64/64)
8.32
9.32
40.27
9.32
PS64/HS
8.32
0.61
Table 8 - ASE Value per Radio link
13.3.5.
RTWP Monitor
All transmissions in the uplink contribute to the increase in uplink noise, or Received Total
Wideband Power (RTWP). The RTWP monitor tracks the noise rise by mean of event based
measurement reports configured via NBAP signaling. The thresholds for the RTWP event
based measurements are configured by Congestion Control parameters. These parameters
define at what uplink noise level congestion is triggered, and at what noise level congestion
is resolved. Event based measurement reports are sent to the RNC when the RTWP of the
cell exceeds the congestion threshold; and an additional event based measurement report is
sent once the RTWP drops below the congestion resolved threshold. The details regarding
these parameters, as well as the Congestion Control algorithm, will be covered in later
sections.
13.3.6.
RBS Hardware Monitor
The RBS Hardware Monitor tracks both uplink and downlink CE utilization. As described
previously, the term channel element (CE) is used to quantify processing power in the Node
B chipset. The number of channel elements available for users is dependant on hardware
configuration and the number of licensed channel elements enabled.
The Node B’s CE consumption is tracked as a percentage, based on the number of
dedicated radio links in the cell, the type of radio link, and the amount of available licensed
channel elements. The admission thresholds for both uplink and downlink CE usage are
configured by Admission Control parameters. The details regarding these parameters, as
well as the Admission Control algorithm, will be covered in the next section.
13.4. Services Class and Setup Type
Service class and setup type of a specific user are used to prioritize the allocation of
dedicated resources, and the retention of resources when the system becomes congested.
13.4.1.
Service Class
The service classes are divided and prioritized into the four specific groups:
1. Guaranteed-emergency: This group includes any calls that are considered to be an
emergency call.
2. Guaranteed: This group includes the “conversational” and “streaming” traffic classes,
as described in 3GPP TS 23.107. Both of these traffic classes are characterized as “real
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time”. Examples of applications that use the “conversational” and “streaming” traffic
classes are voice calls and streaming video respectively.
3. Guaranteed-HS: This group includes the HS configurations that require an associated
dedicated channel (e.g. Signaling Radio Bearer) to be configured. Enhanced Uplink
connections are also included in this service class.
4. Non-guaranteed: This group includes the “background” and “interactive” traffic
classes, as described in 3GPP TS 23.107. Both of these traffic classes are characterized
as “best effort”. Examples of applications that use the “background” and “interactive”
traffic classes are web browsing and email respectively.
It should be obvious that an emergency call will be prioritized over the other three service
classes. In addition, a “real time” traffic class ranks higher that a “best effort” class. The
HS class is third in the list because it can more effectively utilize available resources (e.g.
codes and power) than a full fledged PS dedicated channel.
13.4.2.
Setup Type
The setup type is divided and prioritized into two groups:
1. Handover: This setup type refers to requests for resources when a connection exists,
and an additional radio link is requested to support soft handover.
2. Non-handover: This setup type refers to requests for resources when there is no
existing connection (i.e. a new call setup request).
The thought behind this prioritization is that a user denied admission to setup a new call will
be less “irritated” than a user that drops a call due to a failed handover. In addition, a
denied handover request is likely to result in a degradation of resources in the target cell.
This is due to the additional uplink and downlink interference the target cell will be
subjected to if it can not power control the UE as it enters the target cells coverage area.
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14. Admission Control
Admission Control is invoked whenever new or additional dedicated resources are required;
such as an access attempt, a soft handover request, or a radio bearer reconfiguration
request. In either of these cases, the Admission Control algorithm must confirm there are
adequate system resources available to support this new request. Examples of these
resources include codes, power and channel elements.
In the case of an access attempt, the Admission Control algorithm may be invoked multiple
times. When a RRC Connection Request message is received on the RACH, the
corresponding RRC Connection Setup Complete message typically instructs the UE to setup
a dedicated SRB. Regardless if the request is for CS, PS or simply a reselection, Admission
Control must confirm resources are available to support the requested SRB. In addition, the
algorithm is invoked again once the RNC receives a RAB Assignment Request from the core
network. In the case of CS call, the SRB is reconfigured to include the AMR transport
channels; and resources must be confirmed. If the RAB Assignment Request is for PS
Services, Admission Control must confirm that DCH or HS resources are available. In the
case of an ongoing DCH PS session, a radio bearer reconfiguration may be requested by the
channel switching algorithm to support higher user throughput. Since this reconfiguration
would require additional codes, power, and channel elements, Admission Control would
obviously be triggered.
As mentioned previously, the admission request may also originate from a UE requesting
soft handover. Although these types of requests do take priority over new call setups, the
Admission Control algorithm must confirm the cell can handle the additional load.
In order to assess the resource availability, every admission request must include the
following information:

Setup type (e.g. handover/non-handover)

Service class (e.g. non-guaranteed, guaranteed, guaranteed-hs, or guaranteedemergency)

Additional requested downlink transmitted carrier power

Additional requested uplink and downlink ASEs

Additional requested compressed mode resources
The following sections will describe the different aspects of the Admission Control algorithm,
and the parameters and counters associated with them. In addition, impacts of parameter
changes to system performance will be discussed.
14.1. Enhanced Soft Congestion
Enhanced soft congestion is a feature of Admission Control that reduces the resource
utilization of existing non-guaranteed users, when admission thresholds have been reached.
In this manner other users can be admitted into the cell, by down switching existing nonguaranteed users. Resources requirements that can trigger soft congestion include
downlink transmitted carrier power, downlink OVSF codes, and uplink/downlink channel
elements.
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When soft congestion is triggered by a new admission request, the request is conditionally
blocked. If a non-guaranteed user can be down switched to free the resource under
contention, then the new admission will be granted. If the down switching of the existing
non-guaranteed users does not free up the required resources, the new admission request
will be denied.
When the conditionally blocked access attempt is a guaranteed or guaranteed-HS service
class, the higher rate non-guaranteed connections will be reduced prior to the lower rate
non-guaranteed connections. Therefore, existing 384 kbps connections will be down
switched prior to existing 128 kbps connections being down-switched. Existing 64 kbps
radio links are never down switched as a result of soft congestion.
14.2. Downlink OVSF Code Usage Admission
The Downlink Channelization Code Monitor tracks the percentage of downlink OVSF codes
utilized. In order to reserve some of these codes for soft handover requests, there is a code
blocking threshold for non-handover requests.
As seen in the figure below the admission policy for the DL OVSF code usage is defined as
follows:

The Non-guaranteed, non-handover admission requests can be granted when the
resource usage exceeds the dlCodeAdm – beMarginDlCode level if it is possible to
free resources by downswitching a non-guaranteed user with a lower spreading
factor than the spreading factor being requested in the admission request
otherwise they are blocked when the resource usage exceeds the dlCodeAdm beMarginDlCode level.

Guaranteed, non-handover and guaranteed-hs, non-handover admission requests
can be granted when the resource usage exceeds the dlCodeAdm level if it is
possible to free resources by downswitching a non-guaranteed user, otherwise they
are blocked when the resource usage exceeds the dlCodeAdm level.
It is important to note that the Downlink Channelization Code Monitor does not account for
16 bit OVSF codes utilized by the HS-DSCH. Therefore if codes are statically allocated for
HS, by means of the parameter numHsPdschCodes, the allocation of these 16 bit codes
for HS will not be tracked by the code monitor.
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Figure 25 - Blocking Thresholds for Downlink OVSF Codes
14.3. Histogram Admission
Histogram Monitor tracks OVSF code usage, as well as the number of users utilizing HSDPA,
E-DCH, and compressed mode. This information is used by Admission Control to determine
if these dedicated resources will be allocated or denied.
14.3.1.
Downlink OVSF Code Admission
High data rate PS users utilizing downlink dedicated resources can quite quickly consume
system resources. For example a PS user with a 384k RAB in the downlink requires an 8 bit
OVSF. This is 12.5% of the code tree. In fact, the code usage will exceed 12.5% if the soft
handover factor is taken into account. For this reason, Ericsson’s Admission Control
algorithm allows to parametrically limit the admission of non-guaranteed users based on
downlink code usage. As illustrated in the figure below, the parameters sf8Adm,
sf16Adm, and sf32Adm set the admission limit for these non-guaranteed users based on
8 bit, 16 bit and 32 bit downlink OVSF codes usage respectively. In addition, the downlink
code utilization of high consumption streaming users can be limited with the parameter
sf16gAdm, which sets the admission limit for guaranteed users requesting 16 bit OVSF
codes. However, as previously stated, any 16 bit codes statically allocated to HSDPA by the
parameter numHsPdschCodes will not considered by the Histogram Monitor. Therefore,
the configured value of numHsPdschCodes should be considered when the parameter
sf16Adm and sf16gAdm is determined.
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Figure 26 – Downlink OVSF Admission Limits for Non-guaranteed Users
14.3.2.
Uplink OVSF Code Admission
Unlike the downlink case, uplink OVSF codes are not typically a limited resource because
each UE has the complete OVSF code tree for its disposal. However, since each UE uses a
unique uplink scrambling code, the uplink transmissions of these different UEs lack any
orthogonal properties. Therefore, every UE uplink transmission contributes to uplink noise
rise, or RTWP. This problem is compounded when 4 bit, 8 bit and 16 bit uplink OVSF codes
are utilized by dedicated users. Because these codes have a low processing gain, they can
contribute a higher amount of uplink noise when compared to higher order OVSF codes like
the 64 bit code used for uplink 12.2k AMR. In order to limit this uplink noise rise, the
parameters sf4AdmUl, sf8AdmUl, and sf16AdmUl set the admission limit for nonguaranteed users based on 4 bit, 8 bit and 16 bit uplink OVSF codes usage respectively. For
the guaranteed users requesting high speed streaming services, the admission threshold for
uplink OVSF codes is controlled by the parameter sf8gAdmUl.
14.3.3.
HSDPA Admission
HSDPA utilizes the HS-DSCH, which is a shared resource. Although HSDPA is a highly
efficient means to deliver data to PS users, the number of simultaneous users monitoring
the HS-SCCH should be limited. Excessive users monitoring the same HSDPA cell not only
tax the scheduler’s processing capabilities, they can also impact the end user throughput
and system capacity.
At a first glance, it may seem advantageous to not limit HSDPA users, thus maximizing cell
throughput. However, one must also consider the effect to system capacity. Currently, for
every user that is assigned to a HSDPA serving cell, that user requires a downlink dedicated
physical channel (DPDCH/DPCCH) to support RRC/NAS signaling and power control of the
subsequent UL dedicated channel. This physical channel requires power, and a 256 bit
downlink OVSF code. Although this may seem trivial, one must remember that for every
HSDPA user assigned a 256 bit OVSF code to support this downlink DCH, a 16 bit code
becomes unavailable for use by the HS-DSCH. As users continue to be added to a HSDPA
serving cell, a point of diminishing returns is reached as 16 bit codes for the HS-DSCH
become unavailable. In addition, each HSDPA user is assigned a High Speed Dedicated
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Physical Control Channel (HS-DPCCH) in the uplink. Each of these dedicated uplink
channels contribute to uplink noise rise, thus limiting system capacity. Optimizing the
parameters related to state changes, to efficiently de-allocate HS resources from idle PS
users, is the best way to maximize user access to HSDPA resources.
Admission requests for HSDPA connections are limited by the parameter
maxNumHsdpaUsers. However, this is only applied to admission requests for new
HSDPA connections. If an admission request is originated from an existing HSDPA
connection, as a result of mobility, the request is not blocked based on
maxNumHsdpaUsers. That being the case, the mobility of HSDPA users should be
considered when configuring this parameter.
14.3.4.
Compressed Mode Admission
Compressed mode is used when it becomes necessary for the UE to make inter-frequency
or inter-system measurements when the currently utilized UMTS frequency’s RF coverage
deteriorates. In order to make these measurements, it is necessary to create gaps in the 10
millisecond physical frames. For circuit switched users, this gap is created by reducing the
typically used downlink and uplink spreading factor by half (e.g. SF/2). For example, a 12.2
kbps AMR voice call typically utilizes a 128 bit and 64 bit OVSF code for the downlink and
uplink respectively. To create a gap, these OVSF codes are reduced to 64 bits and 32 bits
for the downlink and uplink. This impacts system capacity because of reduced downlink
code availability, increased downlink power, and increased uplink noise rise. The increased
downlink power and uplink noise rise are a result of the lost processing gain caused when
the downlink and uplink codes are halved. Because of the capacity impacts due to
compressed mode, the number of compressed mode radio links allowed in a cell at any
given time is controlled by the parameter compModeAdm.
14.4. Transmitted Downlink Carrier Power Admission
The transmitted downlink carrier power is limited by power rating of the Node B’s power
amplifier, as well as the various insertion losses between the Node B and the antenna
reference point (e.g. downlink feeder lines, duplexers, diplexers, etc.). The maximum
downlink transmission power of the Node B is defined by the configurable parameter
maximumTransmissionPower; unless the maximum power capability reported by the
Node B (maxDlPowerCapability) is less. This maximum downlink transmission power is
used to define relative thresholds for admission based on transmitted downlink carrier
power as reported by the Histogram Monitor.
The downlink carrier power admission policy is simply defined by three thresholds. These
thresholds are set by the configurable parameters pwrAdm, pwrAdmOffset, and
beMarginDlPwr. Figure below illustrates how these parameters are utilized to define the
three admission thresholds. It should be noted that the values provided in this figure are
the default values. The parameter pwrAdm is defined as a percentage of the maximum
downlink transmission power. On the other hand, parameters pwrAdmOffset and
beMarginDlPwr are percentages relative to pwrAdm.
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DL Transmitted
Carrier Power
maximumTransmissionPower
100 %
Power Reserved for Power Control
pwrAdm + pwrAdmOffset
85 %
Admit: (Guaranteed/Handover) & (All Guaranteed-HS)
75 %
Admit: (All Guaranteed) & (Non-Guaranteed/Handover) & (All Guaranteed-HS)
65 %
pwrAdm
pwrAdm - beMarginDlPwr
Admit: (All Guaranteed) & (All Non-Guaranteed) & (All Guaranteed-HS)
Figure 27 - Admission Thresholds for Downlink Transmitted Carrier Power (default
values)
 The first admission threshold is defined by subtracting beMarginDlPwr from
pwrAdm (i.e. pwrAdm- beMarginDlPwr). This defines the maximum carrier
power allowed to grant admission to new best effort DCH users. If the downlink
carrier power is greater than this threshold, an admission request by a nonguaranteed/non-handover service class user will trigger enhanced soft congestion.

The second admission threshold is defined by the parameter pwrAdm. This
defines the maximum carrier power allowed to grant admission for guaranteed
users requesting a new connection, as well as existing best effort DCH users
requiring soft handover. If the downlink carrier power is greater than the
pwrAdm threshold, an admission request by a guaranteed/non-handover service
class user, or a non-guaranteed/handover service class user, will trigger enhanced
soft congestion.

The final admission threshold is defined by adding pwrAdmOffset to pwrAdm
(i.e. pwrAdmOffset+ PwrAdm). This defines the maximum carrier power
allowed to grant admission for guaranteed users requesting soft handover, as well
as both new and existing HS connections requiring the cell to become the new HS
serving cell. If the downlink carrier power is greater than this threshold, an
admission request by a guaranteed/handover service class user, or a guaranteedHS service class user, will trigger enhanced soft congestion.
The remaining power (i.e. greater than pwrAdmOffset+ PwrAdm) is reserved for power
control, to support existing users served by the cell. Once a user is admitted to the cell,
their mobility, or changing RF conditions, may require additional power to support the
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quality of the connection. If this reserved carrier power did not exist, Congesting Control
would be triggered due to minor fluctuations in user downlink power requirements.
Figure below provides an alternative view of the admission thresholds based on downlink
carrier power usage, as well as the trigger points for enhanced soft congestion. As the
figure illustrates, the applicable threshold is dependant on the user’s service class and setup
type. When soft congestion is triggered by any non-guaranteed service class, only existing
best effort connections with rates greater than the conditionally blocked rate will be
considered for rate reduction. For example, an admission request for a best effort 128 kbps
connection will only impact existing 384 kbps best effort connections when enhanced soft
congestion is triggered.
Figure 28 – Admission Policy for Downlink Transmitted Carrier Power
14.5. Air Interface Speech Equivalents Admission
The Air Interface Speech Equivalent (ASE) is an Ericsson specific term used to quantitatively
describe the interference caused by a single 12.2 AMR speech call (excluding the SRB). The
term is used for both the uplink and downlink. The ASE Monitor reports both uplink and
downlink ASE usage to the Admission Control Algorithm.
14.5.1.
Uplink ASE Admission
Uplink ASE admission thresholds are a mechanism that can be utilized to limit uplink noise
rise, which results in reduced uplink coverage. This dynamic change in uplink coverage is
known as cell breathing. Cell breathing is due to the fact that increased uplink interference
requires the UE to use more of its uplink power to overcome interference, leaving less
power available to overcome uplink path loss.
The uplink ASE admission policy is simply defined by three thresholds. These thresholds are
adjusted by the configurable parameters aseUlAdm, aseUlAdmOffset, and
beMarginAseUl. Figure below illustrates how these parameters are utilized to define the
three admission thresholds. It should be noted that the values provided in this figure are
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the default values. The unit of measure for these three parameters is uplink ASE. In
addition, it should be noted that enhanced soft congestion is not triggered when these
thresholds are exceeded.

The first admission threshold is defined by subtracting beMarginAseUl from
aseUlAdm (i.e. aseUlAdm-beMarginAseUl). This defines the maximum
number of uplink ASEs allowed to grant admission to new best effort DCH users. If
the uplink ASE utilization is greater than this threshold, an admission request by a
non-guaranteed/non-handover service class user will be denied.

The second admission threshold is defined by the parameter aseUlAdm. This
defines the maximum uplink ASEs allowed to grant admission for guaranteed and
HS users requesting a new connection, as well as existing best effort DCH users
requiring soft handover. If the uplink ASE consumption is greater than the
aseUlAdm threshold, an admission request by a guaranteed/non-handover,
guaranteed-HS/non-handover, or a non-guaranteed/handover service class user
will not be allowed.
UL ASE Usage
Maximum Configurable Value
1000
aseUlAdm + aseUlAdmOffset
200
Admit: (Guaranteed/Handover) & (Guaranteed-HS/Handover)
aseUlAdm
160
Admit: (All Guaranteed) & (Non-Guaranteed/Handover) & (All Guaranteed-HS)
aseUlAdm - beMarginAseUl
140
Admit: (All Guaranteed) & (All Non-Guaranteed) & (All Guaranteed-HS)
Figure 29 - Admission Thresholds for Uplink ASE Usage (default values)

The final admission threshold is defined by adding aseUlAdmOffset to
aseUlAdm (i.e. aseUlAdmOffset + aseUlAdm). This defines the maximum
uplink ASEs allowed to grant admission for guaranteed users requesting soft
handover, as well as existing HS connections requiring the cell to become the new
HS serving cell. If the uplink ASE utilization is greater than this threshold, an
admission request by a guaranteed/handover service class user, or a guaranteedHS/handover service class user, will be denied.
Figure below provides a different view of the admission thresholds based on uplink ASE
consumption. As the figure illustrates, the applicable threshold is dependant on the user’s
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service class and setup type. If it is determined that the ASE thresholds are triggering
Admission Control, and uplink cell coverage is not being affected, the parameter aseUlAdm
should be increased.
Figure 30 - Admission Policy for Uplink ASE Usage
It is important to note the side effects of incorrectly configuring these parameters. Since
this admission policy does not trigger soft congestion, UEs requesting admission due to
handover may be denied access to the cell. If a mobile UE with an existing connection is
denied access to the cell, the uplink power from this UE can not be power controlled as it
approaches the new cell. This will result in excessive uplink interference and could result in
cell breathing. To mitigate the potential of this scenario occurring, the parameter
aseUlAdmOffset can be increased to effectively disable the threshold for guaranteed and
HS handover admission requests. To totally disable this feature, aseUlAdm can be set to
its maximum value 500; and beMarginAseUl can be set to zero.
14.5.2.
Downlink ASE Admission
Downlink ASE admission thresholds is another mechanism that can be utilized, along with
downlink carrier power, to control admission for various service classes and access types.
The downlink ASE admission policy is only defined by two thresholds. These thresholds are
adjusted by the configurable parameters aseDlAdm and beMarginAseDl. Figure below
illustrates how these parameters are utilized to define both admission thresholds. It should
be noted that the values provided in this figure are the default values. The unit of measure
for these parameters is downlink ASE. In addition, it should be noted that enhanced soft
congestion is not triggered when these thresholds are exceeded.
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DL ASE Usage
Maximum Configurable Value
1000
aseDlAdm
240
Admit: (All Guaranteed) & (Non-Guaranteed/Handover) & (All Guaranteed-HS)
aseDlAdm - beMarginAseDl
140
Admit: (All Guaranteed) & (All Non-Guaranteed) & (All Guaranteed-HS)
Figure 31 - Admission Thresholds for Downlink ASE Usage (default values)

The first admission threshold is defined by subtracting beMarginAseDl from
aseDlAdm (i.e. aseDlAdm-beMarginAseDl). This defines the maximum
number of downlink ASEs allowed to grant admission to new best effort DCH users.
If the downlink ASE utilization is greater than this threshold, an admission request
by a non-guaranteed/non-handover service class user will be denied.

The second admission threshold is defined by the parameter aseDlAdm. This
defines the maximum downlink ASEs allowed to grant admission for all guaranteed
and HS users, as well as existing best effort DCH users requiring soft handover. If
the downlink ASE consumption is greater than the aseDlAdm threshold, an
admission request by any guaranteed or guaranteed-HS service class user or a
non-guaranteed/handover service class user will not be allowed.
Figure below provides an alternative view of the admission thresholds based on downlink
ASE consumption. As the figure illustrates, the applicable threshold is dependant on the
user’s service class and setup type. Unlike the uplink ASE scenario, which is the only means
to control uplink interference, monitoring downlink ASEs and downlink carrier power can
both achieve similar results. Since most UMTS systems are downlink power limited, the
downlink ASE admission algorithm may prematurely block users if it is not configured
correctly. If it is determined that the ASE thresholds are triggering Admission Control, and
downlink power is not limited, the parameter aseDlAdm should be increased.
Similar to the issue mentioned in the previous section, handover admission requests may be
denied due to this admission policy. This may result in increased uplink interference and
cell breathing. To mitigate the potential of this scenario occurring, the parameter
aseDlAdm can be increased, or disabled. Because the downlink carrier power admission
policy can trigger soft congestion, and it performs a similar job as downlink ASE admission
policy, disabling this feature is a viable option. To disable this feature, aseDlAdm can be
set to its maximum value 500; and beMarginAseDl can be set to zero.
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Figure 32 - Admission Policy for Downlink ASE Usage
14.6. Node B Hardware Admission
Node B hardware usage, or specifically channel element usage, is monitored by the RBS
Hardware Monitor and reported to Admission Control. The term channel element (CE) is
used to quantify processing power in the Node B chipset. The number of channel elements
available for users is dependant on hardware configuration, and number of licensed channel
elements enabled. Channel elements for the common and overhead channels are included
with the Node B, and are not considered by the RBS Hardware Monitor or Admission
Control. Both uplink and downlink channel element usage is monitored and can limit
admission based on parameter setting, user admission class, and user access type.
14.6.1.
Uplink Channel Element Admission
The uplink channel element admission policy is simply defined by three thresholds. These
thresholds are adjusted by the configurable parameters ulHwAdm and beMarginUlHw.
Figure below illustrates how these parameters are utilized to define these admission
thresholds. The unit of measure for these two parameters is percentage of available uplink
CE utilization. In addition, it should be noted that enhanced soft congestion is triggered
when these thresholds are exceeded.
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UL CE Usage
100 %
Admit: (Guaranteed/Handover) & (Non-Guaranteed/Handover)
ulHwAdm
m%
Admit: (All Guaranteed) & (Non-Guaranteed/Handover) & (Guar-HS/Handover)
ulHwAdm - beMarginUlHw
n%
Admit: (All Guaranteed) & (All Non-Guaranteed) & (All Guaranteed-HS)
Figure 33 - Admission Thresholds for Percentage of Uplink Channel Element
Usage
 The first admission threshold is defined by subtracting beMarginUlHw from
ulHwAdm (i.e. ulHwAdm- beMarginUlHw). This defines the maximum
percentage of available uplink channel elements that can be consumed to grant
admission to new best effort DCH users, as well HS users requesting a new
connection. If the uplink CE utilization is greater than this threshold, an admission
request by a non-guaranteed/non-handover, or a guaranteed-HS/non-handover
service class user will trigger enhanced soft congestion.

The second admission threshold is defined by the parameter ulHwAdm. This
defines the maximum percentage of available uplink channel elements that can be
consumed to grant admission for guaranteed users requesting new connections, as
well as existing HS connections requiring the cell to become the new HS serving
cell. If the uplink CE consumption is greater than the ulHwAdm threshold, an
admission request by a guaranteed/non-handover or a guaranteed-HS/handover
service class user will trigger enhanced soft congestion.

The final admission threshold is defined as 100% channel element utilization. This
defines the maximum uplink channel element threshold to grant admission for both
guaranteed and non-guaranteed users requesting soft handover. Only if the
available uplink CE pool is 100% utilized, will an admission request by a
guaranteed/handover service class user, or a non-guaranteed/handover service
class user, be denied.
Figure below provides a different view of the admission thresholds based on uplink CE
consumption. As the figure illustrates, the applicable threshold is dependant on the user’s
service class and setup type. Because of soft congestion, and the threshold for existing
guaranteed and non-guaranteed users requesting handover being fixed at 100%, the risk of
increased uplink interference and cell breathing is inherently reduced for this admission
policy.
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Figure 34 - Admission Policy for Uplink Channel Element Usage
14.6.2.
Downlink Channel Element Admission
The downlink channel element admission policy is defined by three thresholds. These
thresholds are adjusted by the configurable parameters dlHwAdm and beMarginDlHw.
Figure below illustrates how these parameters are utilized to define the admission
thresholds. The unit of measure for these two parameters is percentage of available
downlink CE utilization. In addition, it should be noted that enhanced soft congestion is
triggered when these thresholds are exceeded.
DL CE Usage
100 %
Admit: (Guaranteed/Handover) & (Guaranteed-HS/Handover)
dlHwAdm
m%
Admit: (All Guaranteed) & (Non-Guaranteed/Handover) & (All Guaranteed-HS)
dlHwAdm - beMarginDlHw
n%
Admit: (All Guaranteed) & (All Non-Guaranteed) & (All Guaranteed-HS)
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Figure 35 - Admission Thresholds for Percentage of Downlink Channel Element
Usage
 The first admission threshold is defined by subtracting beMarginDlHw from
dlHwAdm (i.e. dlHwAdm- beMarginDlHw). This defines the maximum
percentage of available downlink channel elements that can be utilized to grant
admission to new best effort DCH users. If the downlink CE utilization is greater
than this threshold, an admission request by a non-guaranteed/non-handover
service class user will trigger enhanced soft congestion.

The second admission threshold is defined by the parameter dlHwAdm. This
defines the maximum percentage of available downlink channel elements that can
be consumed to grant admission for best effort DCH users requesting soft
handover, guaranteed users requesting new connections, as well HS users
requesting a new connection. If the downlink CE consumption is greater than the
dlHwAdm threshold, an admission request by a non-guaranteed/handover,
guaranteed/non-handover, or a guaranteed-HS/non-handover service class user
will trigger enhanced soft congestion.

The final admission threshold is defined as 100% channel element utilization. This
defines the maximum downlink channel element threshold to grant admission for
both existing guaranteed users requesting handover, as well as existing HS
connections requiring the cell to become the new HS serving cell. Only if the
available downlink CE pool is 100% utilized, will an admission request by a
guaranteed/handover service class user, or a non-guaranteed/handover service
class user, be denied.
Figure below provides an alternative view of the admission thresholds based on downlink CE
consumption. As the figure illustrates, the applicable threshold is dependant on the user’s
service class and setup type. Because of soft congestion, as well as the threshold for
existing guaranteed and HS users requesting handover is fixed at 100%, the risk of
increased uplink interference and cell breathing is inherently reduced for this admission
policy.
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Figure 36 - Admission Policy for Downlink Channel Element Usage
14.7. Admission Control Parameters
The following table provides details regarding for the Ericsson parameters for Admission
Control.
Parameter Name
dlCodeAdm
beMarginDlCode
sf8Adm
sf16Adm
sf32Adm
sf16gAdm
sf4AdmUl
sf8AdmUl
sf16AdmUl
sf8gAdmUl
maxNumHsdpaUsers
eulServingCellUsersAdm
eulNonServingCellUsersAdm
compModeAdm
pwrAdm
pwrAdmOffset
beMarginDlPwr
aseUlAdm
aseUlAdmOffset
beMarginAseUl
aseDlAdm
beMarginAseDl
ulHwAdm
beMarginUlHw
dlHwAdm
beMarginDlHw
Object
Name
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
RbsLocalCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
IubLink
IubLink
IubLink
IubLink
Recommended
Value
80 %
5%
8
16
32
16
1000
8
16
8
16
4
100
15
75 %
10 %
10 %
500
0
0
500
0
100
0
100
0
Table 9 – Ericsson Parameters for Admission Control
14.8. Counters Related to Admission Control
Tracking performance statistics or counters allow monitoring and troubleshooting UTRAN
system performance. The counters specifically related to Admission Control can be utilized
to tune parameter settings, or trigger capacity/dimensioning related actions (e.g. channel
element additions). The counters described in this section include some of the more
important counters related to Admission Control. For a complete list of performance
counters, refer to the Ericsson RNC Performance Management documentation [14].
Figures below provide a three part flowchart for the some of the counters related to
Admission Control. The counters illustrated on the right side of Figure 37 include some of
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the level counters used by the Dedicated Monitored Resource Handling function (e.g.
pmLevelAseUl, pmLevelAseDl, and pmLevelCompMode). These counters are
incremented and decremented based on resource utilization and typically do not yield useful
information from a statistical or troubleshooting perspective. On the other hand, the left
side of Figure 37 provides the path for failed admission requests.
If enhanced soft congestion is triggered, the counter pmNoOfSwDownNgAdm is
incremented. The fact that this counter was incremented does not indicate that the down
switch was successful, rather that a down switch was attempted. For more information
related to channel switching counters, refer to the Ericsson RNC Performance Management
documentation [14]. If the down switch fails, the admission request will be denied and the
counter pmNoReqDeniedAdm will be incremented. In addition, this counter is also
incremented for failed admission requests that do not trigger enhanced soft congestion.
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Figure 37 - Ericsson Admission Control Flowchart (1 of 3)
Continuing down the path for failed admission requests, figure below illustrates when nonhandover related counters are incremented based on service type. If the failed admission
attempt is for a new speech connection (non-handover), the counter
pmNoOfNonHoReqDeniedSpeech is incremented. For circuit switched data or circuit
switched streaming admission requests, the counter pmNoOfNonHoReqDeniedCs is
incremented, for non-handover scenarios.
Figure 38 - Ericsson Admission Control Flowchart (2 of 3)
The counter pmNoOfNonHoReqDeniedInteractive is incremented if the failed
admission request is for non-HS interactive packet switch RABs, while the counter
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pmNoOfNonHoReqDeniedPsStreaming is pegged if the request was for a non-HS
streaming packet switched RAB. If the failed streaming PS RAB request was specifically for
a 128 kbps bearer, the counter pmNoOfNonHoReqDeniedPsStr128 would be
incremented, along with pmNoOfNonHoReqDeniedPsStreaming.
High speed admission failures are also counted, as shown in figures 38 and 39. The
performance counter pmNoOfNonHoReqDeniedHs is incremented when non-handover,
failed admission request occurs for HSDPA.
Figure 39 - Ericsson Admission Control Flowchart (3 of 3)
In addition to the circumstances listed above, there are additional counters for handover
related admission requests. When the handover request triggers enhanced soft congestion,
the counter pmNoOfSwDownNgHo is incremented. The fact that this counter was
increased does not indicate that the down switch was successful, rather that a down switch
was attempted. If the handover request is denied due to admission (whether soft
congestion is triggered or not) the counter pmNoRlDeniedAdm is pegged.
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15. Congestion Control
Congestion Control monitors the dynamic utilization of specific cell resources and insures
that overload conditions do not occur. If overload conditions do occur, Congestion Control
will immediately restrict Admission Control from granting additional resources. In addition,
Congestion Control will attempt to resolve the congestion by either down switching, or
terminating existing users. Once the congestion is corrected, the congestion resolution
actions will cease, and Admission Control will be enabled.
The two specific resources monitored are downlink transmitted carrier power, as well as
uplink noise (i.e. RTWP).
The consumption of downlink carrier power is dynamic, and can change after users are
admitted into the cell. As users travel within the cell, or the RF environment changes, their
downlink power requirements can increase and drive the cell into congestion. For the uplink
case, the mobility of users outside of the cell can affect the RTWP, and trigger congestion.
The other resources controlled by Admission Control (e.g. OVSF code usage, or ASEs) will
not dynamically change without the admission criterion being met; therefore there is no
need for Congestion Control to monitor these resources.
The following sections will describe the different aspects of the Congestion Control
algorithm, and the parameters and counters associated with them. In addition, impacts of
parameter changes to system performance will be discussed.
15.1. Downlink Cell Congestion
The detection of downlink cell congestion is solely based on the utilization of downlink
transmitted carrier power. Although the allocation of this resource is controlled by
Admission Control, the mobility of users within the cell is dynamic. As users move away
from the cell, the power required for their dedicated channel is increased by the power
control algorithm. This mobility can result in an overload situation for the downlink
transmitted carrier power and trigger Congestion Control.
The thresholds that define when downlink congestion is triggered, as well as resolved, are
provided in the figure below. Congestion is triggered when the downlink carrier power
exceeds the threshold equivalent to the summation of the parameters pwrAdm,
pwrAdmOffset and pwrOffset (or pwrAdm + pwrAdmOffset + pwrOffset), for a
period of time equal to the parameter pwrHyst. Once congestion is triggered, actions will
be taken to reduce the downlink transmitted carrier power until the congestion is considered
to be resolved. Congestion is resolved when the downlink carrier power drops below the
threshold defined by the summation of the parameters pwrAdm, pwrAdmOffset (or
pwrAdm + pwrAdmOffset), for a hysteresis time equal to the parameter pwrHyst.
Event based measurement reports from the Node B, for the downlink transmitted carrier
power, are set up by NBAP signaling when a Node B is configured. The thresholds for these
event based measurements are defined by the Congestion Control parameters described in
the previous paragraph. Event based measurement reports are triggered when the total
downlink power of the cell exceeds the congestion threshold, for the defined hysteresis
time. Once this event based measurement report is triggered, periodic reports follow until
the carrier power drops below the congestion resolution threshold, for the defined
hysteresis time. At this point, a final measurement report is sent to the RNC indicating that
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the congestion has been resolved. By using event based measurements, the Node B can
quickly report to the RNC when congestion occurs, and when it is resolved.
Figure 40 - Congestion Thresholds for Downlink Transmitter Carrier Power
Figure below provides an alternative view of how these parameters are utilized to define the
two congestion thresholds. It should be noted that all the values provided in this figure are
the default values. In addition to the congestion thresholds, the admission thresholds for
transmitted carrier power are included for comparison. As the figure illustrates, the
congestion threshold is simply derived by adding the parameter pwrOffset to the
admission threshold defined for the highest priority service class/access type. Assuming
that default values are used, congestion would be triggered at 95%; and resolved when the
power dropped below 85%.
DL Transmitted
Carrier Power
Congestion Triggered
Congestion Resolved
maximumTransmissionPower
100 %
pwrAdm + pwrAdmOffset +pwrOffset
90 %
85 %
Power Reserved for Power Control
Admit: (Guaranteed/Handover) & (All Guaranteed-HS)
75 %
Admit: (All Guaranteed) & (Non-Guaranteed/Handover) & (All Guaranteed-HS)
65 %
pwrAdm + pwrAdmOffset
pwrAdm
pwrAdm - beMarginDlPwr
Admit: (All Guaranteed) & (All Non-Guaranteed) & (All Guaranteed-HS)
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Figure 41 – Congestion and Admission Thresholds for Downlink Transmitted Carrier
Power (default values)
15.2. Uplink Cell Congestion
The detection of uplink cell congestion is exclusively based on the utilization of RTWP
measurements. Similar to the downlink scenario, the mobility of users within the network is
dynamic. As “out of cell” users approach the cell, their uplink transmissions may contribute
to the cell’s noise rise prior to soft handover occurring. In addition, Admission Control does
not monitor RTWP when evaluating admission requests for users. Situations may occur
when excessive cell loading occurs as users are admitted. Finally, the uplink transmit power
of users within the cell is dynamic based on mobility, resulting in variable noise rise. The
net result of these various conditions can contribute to high uplink interference and trigger
Congestion Control.
The thresholds that define when uplink congestion is triggered, as well as resolved, are
provided in the figure below. Congestion is triggered when the uplink RTWP exceeds the
threshold equivalent to the summation of the parameters iFCong and iFOffset (or iFCong
+ iFOffset), for a period of time equal to the parameter iFHyst. Once congestion is
triggered, actions will be taken to reduce the uplink noise rise until the congestion is
considered to be resolved. Congestion is resolved when the uplink RTWP drops below the
threshold defined by the parameter iFCong, for a hysteresis time equal to the parameter
iFHyst.
Event based measurement reports from the Node B, for the uplink RTWP, are set up by
NBAP signaling when a Node B is configured. The thresholds for these event based
measurements are defined by the Congestion Control parameters described in the previous
paragraph. Event based measurement reports are triggered when the uplink RTWP of the
cell exceeds the congestion threshold, for the defined hysteresis time. Once this event
based measurement report is triggered, periodic reports follow until the RTWP drops below
the congestion resolution threshold, for the defined hysteresis time. At this point, a final
measurement report is sent to the RNC indicating that the congestion has been resolved.
By using event based measurements, the Node B can quickly report to the RNC when
congestion occurs, and when it is resolved.
Figure 42 - Congestion Thresholds for Uplink RTWP
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Typically, system capacity is not uplink limited and this feature can be disabled. In fact the
default values for the parameters controlling uplink Congestion Control do indeed disable
the feature. By setting the parameter iFCong = -49.9 dBm, and iFOffset to 0 dB; it is
highly unlikely that uplink congestion will ever be triggered. The side effect of disabling this
feature is the increased potential of cell breathing which may, or may not be an issue. If it
is determined that system performance is being impacted by cell breathing, enabling the
uplink congestion algorithm may be required.
When configuring these parameters, the source of uplink noise must be considered. To
begin with, thermal noise (i.e. kTB = -107.5 dBm) defines the best case value of RTWP.
Added to this is the cascaded noise figure for the uplink path. This cascaded noise figure is
based on the individual gain and noise figures of each stage of the uplink path (e.g. TMA,
feeder loss, Node B LNA, etc.). This can be derived from TMA and Node B specifications,
and results for antenna sweeps. Finally, the noise rise due to loading needs to be added.
The target loading factor is typically defined in uplink link budgets, and is a function of the
calculated pole capacity.
Alternatively, another method to tune these parameters would employ the unloaded cell’s
RTWP measurement to define a baseline; and then apply the designed noise rise due to
loading (i.e. loading factor) to define the congestion threshold. The hysteresis iFHyst
should be long enough to ignore short term spikes in RTWP.
15.3. Resolution of Congestion
Once congestion is detected, due to downlink carrier power or uplink RTWP, Congestion
Control takes actions to resolve the congestion. The first action taken is to limit additional
admissions to the cell. If congestion was triggered by downlink transmitted carrier power,
all admissions are blocked until the congestion is resolved. Alternatively, if congestion is
triggered by uplink RTWP, only non-handover admissions are prevented. Admission
requests due to handover are allowed, for the uplink congestion case, because the user is
likely a contributor of the uplink interference and admission to the cell will improve the
situation. Note that blocking the admission of new users is the only action taken by
Congestion Control when uplink congestion is triggered.
When downlink congestion is detected, actions will be taken to resolve the issue.
Congestion Control will achieve this by periodically releasing the amount of resources
utilized by users in the cell. The amount of resources released periodically will be based on
downlink air interface speech equivalents (ASEs). The users targeted will be based on their
service class, as well as their specific resource consumption. Non-guaranteed users are
targeted first, followed by guaranteed-HS users, and finally guaranteed users. Figure below
illustrates how the different parameters are utilized to resolve congestion, based on service
class.
The first step taken to resolve congestion is to target non-guaranteed users. At the
moment congestion is detected, the higher data rate best effort users will be targeted to be
down switched to a lower data rate. The parameter releaseAseDlNg defines how many
ASEs will be released during this initial step (releaseAseDlNg = 0 indicates that no ASEs
will be released). The Congestion Control algorithm will begin with the highest data rate
users first, and then proceed to the lower data rates (i.e. 384k first, then 128k, then 64k).
If the all users have been down switched and releaseAseDlNg ASEs have not been
released, non-guaranteed users’ connections will be switched to common channels until the
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desired number of ASEs have been released. If this first step resolves congestion, the
process is ended. However, if downlink congestion still exists, and there are still nonguaranteed users connected, the process is repeated after a delay defined by the parameter
tmCongActionNg. This periodical release of non-guaranteed users continues until all nonguaranteed users have been released, or congestion is resolved.
If all non-guaranteed users have been released, and congestion still exists, guaranteed-HS
users will be targeted after timer tmCongActionGhs has expired. At this point,
guaranteed-HS user connections will be terminated until releaseAseDlGhs ASEs have been
released (releaseAseDlGhs = 0 indicates that no ASEs will be released). If this step
resolves congestion, the process is ended. If downlink congestion is detected again, and
there are still guaranteed-HS users connected, the process is repeated after a delay defined
by the parameter tmCongActionGhs. If congestion is detected, and the cell does not
originally contain non-guaranteed users, guaranteed-HS users will be initially targeted for
release. In this special case, the initial release of releaseAseDlGhs ASEs can not occur
until the timer, defined by the parameter tmInitialGhs, has expired. This timer is started
when congestion is initially detected. In both scenarios, periodical release of users
continues until all guaranteed-HS users have been released, or congestion is resolved.
The last targeted group is guaranteed users. If all non-guaranteed and guaranteed HS
users have been released, and congestion still exists, guaranteed users will be targeted
after timer tmCongAction has expired. At this point, guaranteed user connections will be
terminated until releaseAseDl ASEs have been released. If this step resolves congestion,
the process is ended. However, if downlink congestion still exists, the process is repeated
after a delay defined by the parameter tmCongAction. If congestion is detected, and the
cell does not originally contain guaranteed-HS users, guaranteed users will be initially
targeted for release. In this special case, the initial release of releaseAseDl ASEs can not
occur until the timer, defined by the parameter tmInitialG, has expired. This timer is
started when congestion is initially detected. In both scenarios, periodical release of users
continues until congestion is resolved.
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Figure 43 - Resolution of Downlink Congestion
The priority of non-guaranteed users released is based on the origination of their
connections. Non-Iur dedicated connections will be targeted first and their connections will
be switched to common channels. Connections originating over Iur will be targeted last and
will result in their connections being terminated. For the guaranteed-HS service class
releases, the priority is based on the origination of the connection, as well as HS serving cell
status of the radio link. The HS connections in which the congested cell is the HS serving
cell will have the highest priority and will be the last link released. For guaranteed CS users,
streaming calls will be terminated prior to speech calls.
In addition, a particular service class can be omitted from the congestion resolution actions
if its “releaseAse” parameter is set to zero. For example, the default value for
releaseAseDlGhs = 0, which indicates that no guaranteed-HS ASEs will be released during
congestion resolution. For the other two service classes, the parameters releaseAseDlNg
and releaseAseDl behave similarly.
15.4. Congestion Control Parameters
The following table provides details regarding for the Ericsson parameters for Congestion
Control.
Parameter Name
pwrOffset
pwrHyst
iFCong
iFOffset
iFHyst
releaseAseDlNg
releaseAseDlGhs
releaseAseDl
tmCongActionNg
tmCongActionGhs
tmCongAction
tmInitialGhs
tmInitialG
Object
Name
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
UtranCell
Recommended
Value
5%
300 ms
-49.9 dBm
0.0 dB
60000 ms
3 ASE
0 ASE
1 ASE
800 ms
300 ms
2000 ms
500 ms
3000 ms
Table 10 - Ericsson Parameters for Congestion Control
15.5. Counters Related to Congestion Control
Tracking performance statistics or counters allow monitoring and troubleshooting UTRAN
system performance. The counters specifically related to Congestion Control can be utilized
to tune parameter settings, or trigger capacity/dimensioning related actions. The counters
described in this section include some of the more important counters related to Congestion
Control. For a complete list of performance counters, refer to the Ericsson RNC
Performance Management documentation [14].
The flowchart for the counters related to the detection of downlink congestion is provided in
the figure below. As the flowchart indicates, the counter pmSumOfTimesMeasOlDl is
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incremented when a NBAP common measurement report is received from Node B indicating
that the downlink transmitted carrier power is above the congestion threshold. Note that
this counter is not incremented by the reception of the periodic measurement reports that
follow the initial congestion report. This counter only pegs once for each downlink
congestion occasion. The total amount of time a cell is downlink congested (in seconds) is
provided by the counter pmTotalTimeDlCellCong. This counter is incremented once
every second the cell remains in the downlink congested state.
Figure 44 – Ericsson Counter Flowchart for DL Congestion Detection
The flowchart for the counters related to the detection of uplink congestion is provided in
the figure below. As the flowchart indicates, the counter pmSumOfTimesMeasOlUl is
incremented when a NBAP common measurement report is received from Node B indicating
that the uplink RTWP is above the congestion threshold. Note that this counter is not
incremented by the reception of the periodic measurement reports that follow the initial
congestion report. This counter only increases once for each uplink congestion occasion.
The total amount of time a cell is uplink congested (in seconds) is provided by the counter
pmTotalTimeUlCellCong. This counter is incremented once every second the cell
remains in the uplink congested state.
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Figure 45 – Ericsson Counter Flowchart for UL Congestion Detection
The actions taken for congestion resolution of non-guaranteed users are illustrated in the
below figure. If non-guaranteed users are down switched to common channels (non-Iur
case) the counter pmNoOfSwDownNgCong is incremented by a number equal to the
number of users affected. On the other hand, non-guaranteed users with an Iur connection
(drift RNC) will increment pmNoOfIurSwDownNgCong accordingly. This figure also
illustrates at what points the timer tmInitialGhs, tmInitialG, and tmCongActionNg are
started.
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Figure 46 - Resolution of Congestion (1 of 2)
Figure below details how guaranteed-HS service class related counters are affected. For
non-Iur HS connections, the counter pmNoOfSwDownHsCong is incremented for each
HSDPA user that is switched to common channels due to congestion. For the Iur scenario,
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the connections are not switched to common channels. Instead, they are terminated and
the counter pmNoOfIurTermHsCong is increased accordingly.
The counters for guaranteed users impacted by congestion are also shown in this figure.
For non-Iur circuit switched connections released due to the Congestion Control algorithm,
the counters pmNoOfTermCsCong and pmNoOfTermSpeechCong are incremented for
CS data and CS speech users respectively. If the circuit switched connection was released
from a congested cell by a drift RNC (Iur), the counters pmNoOfIurTermCsCong and
pmNoOfIurTermSpeechCong are incremented for CS data and CS speech users
respectively.
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Figure 47 - Resolution of Congestion (2 of 2)
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16. Power Control
This section deals with the Power Control algorithms and parameters related to the Ericsson
3G RAN.
16.1. Importance of Power Control
Any WCDMA system is limited by interference and it is important to minimize the
interference level, since the lower the interference, the better the network capacity is. The
intent of Power control is to allow as many users as possible into the WCDMA network,
while keeping the interference caused by these users to a minimum. Power control aims at
using the minimum signal to interference ratio (SIR) required for the quality of the
connection to remain sufficient. Power control provides protection against large changes in
shadowing, immediate response to fast changes in signal and interference levels. It is also
needed to cope with the near-far problem found in WCDMA systems, and to bring the SIR
back close to the target SIR as fast as possible after each transmission gap in compressed
mode.
The two main capabilities of Power Control in a WCDMA system are as follows:

To maintain the quality of connections (including common channels needed, for
example, for call access)

To minimize the transmitted power in both uplink and downlink
Power Control works on a connection basis.
16.2. Overall Power Control Procedure
There are three different types of power control in UMTS
Open Loop: Open Loop power control is used when no feedback mechanism is possible.
An estimate of the required power is made from measurements and system information.
This is used for initial network access and finding initial power settings during dedicated
mode.
Closed Inner Loop: This power control technique uses a fast feedback mechanism to
request an increase or decrease in output power based on the difference between the
target and measured SIR. The feedback is provided via Transmit Power Control (TPC) bits
on the DPCCH channel 1500 times per second. Inner loop power control exists in both
the uplink and downlink.
Closed Outer Loop: Outer loop power control is used to set the target SIR that is used
during inner loop power control. For downlink power control this is set in the UE by an
algorithm that is proprietary to the UE manufacturer. For uplink power control it is set by
the RNC.
The key difference between closed and open loop is the feedback cycle. Closed loop relies
on feedback from the receiving node to adjust the power at the transmitting node. Open
loop has no feedback on the amount to increase or decrease it’s transmit power.
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UMTS
Power Control
Open Loop Power
Control
Closed Loop Power Control
Power control during
initial network access
Inner Loop
Outer Loop
Fast power control for
compensation of
signal fluctuations
Slow power control for
ensuring the desired
signal power level
16.3. Power Control of downlink common channels
This section outlines how the different downlink common channels handle Power Control.
The following downlink common channels are not subject to dynamic Power control as they
are required to cover the entire coverage area of the cell. The transmission powers of these
channels are determined during radio network planning. Refer to [2] for the actual values.
PCPICH: The transmission of the PCPICH determines the actual cell size. Its power
primaryCpichPower is set to an absolute value, and the power level of every other
downlink channel is expressed as an offset relative to it.
PCCPCH: The PCCPCH carries the broadcast channel (BCH), which is broadcast time
multiplexed with the SCH. The last 2304 chips of every slot transmit the PCCPCH. The
parameter bchpower determines the power and is expressed as on offset of the PCPICH
power.
SCH: The SCH consists of a primary SCH (P-SCH) and a secondary SCH (S-SCH), used in
the cell search procedure in the UE. Their powers are set as primarySchPower for P-SCH
and secondarySchPower for S-SCH, and are expressed as offsets of the PCPICH power.
AICH: The AICH carries the acquisition indication (AI), which is the response to the PRACH
preambles. The AICH is not continuously broadcast in the cell. Its power is set by the
parameter aichPower and is expressed as an offset relative to the PCPICH power.
SCCPCH carrying FACH: When the SCCPCH carries the FACH transport channel, one of 2
parameters determines the power depending on the logical channels carried by the FACH. If
the FACH frame carries a logical control channel (BCCH, CCCH, DCCH), the power is set
through parameter maxFach1Power. If the FACH frame carries a logical traffic channel
(DTCH), the power is then set through the parameter maxFach2Power. These are both
expressed as offsets relative to the PCPICH power. The SCCPCH uses discontinuous
transmission (DTX) to halt power transmission when there is no payload. Additional offset
for the TFCI field of the SCCPCH carrying FACH frame can set with the parameter
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pOffset1Fach and for the pilot field can be set as pOffset3Fach, which are relative to the
power on the payload.
SCCPCH carrying PCH: The parameter pchPower sets the power level, expressed as an
offset relative to the PCPICH power. The SCCPCH uses discontinuous transmission (DTX) to
halt power transmission when there is no payload.
PICH: The PICH carries the paging indicators, which tell UEs belonging to specific paging
groups to listen to the paging channel. The PICH power is set by the parameter
pichPower, relative to the PCPICH power.
16.4. Open Loop Power Control (Power Control of uplink common
channels)
Need for Open Loop Power Control: The power control of the uplink control channels is
done using the Open Loop Power control method. Uplink open loop power control is
controlled by the UE. In a UMTS network, the UE always initiates the RRC connection setup
procedure. This is applicable for mobile terminating calls (MTC) also in which case the
network pages the UE, telling it to establish an RRC connection. The UE does this using the
random access procedure. Before it initiates the random access procedure, the UE has to
determine how much power it has to use in the uplink. If a UE uses a fixed power level for
random access, and if it happens to be close to the BTS, then it would block out messages
from the UEs farther away. Therefore the UE must always use the lowest possible
transmission power.
The goal of power control during call setup is for the UE to transmit the minimum amount of
power required to access the network. At this time the UE does not know the power
required to reach the system, so it estimates the initial preamble power (based on broadcast
information and downlink measurements). If there is no acknowledgement from the RBS to
this initial request (via acquisition indication sent by the RBS), the UE will increase its power
based on predefined increments and retransmissions until it is heard. This procedure is
known as ‘Power Ramping’ and because of the limited feedback provided by the network is
termed ‘Open Loop Power Control’.
The UE uses an equation to estimate the initial preamble transmit power on the Physical
Random Access Channel (PRACH), based on CPICH received power and System Information
(broadcast in the cell).
P_PRACH = PCPICH DL Tx Power – CPICH_RSCP+UL Interference
+constantValueCprach
Where
P_PRACH
Power of the first preamble on the PRACH
PCPICH DL Tx Power
Primary CPICH transmit power (sent in SIB5)
CPICH_RSCP
Received CPICH RSCP measured by UE
UL Interference
UL Interference measured by RBS and broadcast by BCH
constantValueCprach
configurable parameter in object Rach used by the UE to
calculate the initial power on the PRACH (SIB5)
(SIB7)
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CPICH >> RSCP
System Info >> BCCH >> P-CCPCH
§
§
§
§
§
UE measures CPICH
RSCP and receives
network parameters in the
System Information (SIB)
messages
CPICH DL Tx Power
UL Interference
Constant Value
Power Ramp Step
Preamble Retrans Max
P_PRACH = CPICH DL Tx Power –
CPICH_RSCP + UL Interference + Constant
Value (+ Power Ramp Step)
UE uses a formula to
calculate the initial
transmit power, and
increases the power
each retry by Power
Ramp Step
Once the first preamble is transmitted the UE monitors the Acquisition Indication Channel
(AICH) to see if an Acquisition Indicator (AI) has been sent. The system will send an
Acquisition Indicator only if the preamble has been received.
If there is no Acquisition Indicator received on the AICH, the UE will transmit another
preamble with an increased power, increasing the transmission power with respect to the
previous preamble power by a parameter powerOffsetP0. It will continue to increase the
preamble power until it is successfully received by the system and an Acquisition Indicator is
received. If the preamble sequence finishes before an Acquisition Indicator is received, the
UE may repeat the preamble sequence. If the preamble is not received by the network and
the entire sequence has been completed, the call setup will be counted as an access failure.
Once the Acquisition Indicator is received, the UE sends the PRACH message part that
contains the internal details about the desired connection to the radio network. The power
of the control part of the PRACH message is determined by the power of the last
transmitted preamble and by an offset configurable by the parameter powerOffsetPpm.
The power of the data part of the PRACH message is determined by the gain factors for
PRACH, which is included in the System information.
Preamble ramping does not go on indefinitely. The maximum number of steps in each
preamble ramping cycle is set by the configurable parameter preambleRetransMax.
When this maximum is reached, a new preamble ramping cycle is attempted. The maximum
number of preamble ramping cycles before the access attempt is aborted is set by the
configurable parameter maxPreambleCycle.
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Once preamble is heard,
increase power for
message
Increase power
until heard
Message
(Control Part)
1st transmitted
preamble
PRACH
UL
Preamble heard
and Acquisition
Indicator sent
Preamble Sequence
AICH
DL
The following are the values of the various parameters involved in the Open Loop Power
control procedure.
Parameter Name
constantValueCprach
Object Name
Rach
Recommended Value
-27 dB
maxPreambleCycle
Rach
4
powerOffsetP0
Rach
3 dB
powerOffsetPpm
Rach
-4 dB
preambleRetransMax
Rach
8
16.5. Power Control of Dedicated channels
The power control of dedicated channels is performed by a combination of the Outer loop
power control and the inner loop power control procedures.
Outer Loop power control adjusts the target SIR in the BTS according to the needs of the
individual radio links and aims at constant quality, defined in terms of a certain block error
rate (BLER). This target SIR is signaled to the inner loop power control, which is then used
to compare against the received SIR by the BTS and the UE.
In the Inner loop power control, the BTS and UE continuously compare the SIR of the
received signal to the target SIR value for a particular connection. Based on this they tell
each other to increase or decrease the transmission power. The inner loop power control
can vary the transmission power from one slot to another. And since a WCDMA frame
consists of 15 slots in a 10 ms duration, the inner loop power control can be performed at a
maximum rate of 1500 times per second. Hence inner loop power control is also called fast
closed loop power control.
The overall power control procedure of dedicated channels is shown in the figure below.
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The following sections detail the different steps involved in the outer loop and inner loop
power control procedures.
16.5.1.
Initial Downlink Power Setting
RNC calculates initial DL power for
dedicated channels (DPDCH/
DPCCH) and sends to RBS
UE
RNC
RBS
An initial transmit power setting for the downlink dedicated channels (DPCCH/DPDCH) is
calculated by the RNC and sent to the RBS utilizing open loop power control. This initial
setting is intended to ensure a reliable radio connection setup while minimizing the impact
on existing connections.
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The following equation is used to determine the initial power setting for the dedicated
physical data channels (DPDCH).
primaryCPI CHPower + (dlInitSirT arg et - PCPICH _ EcNo ) +
P _ DL _ DPDCH =
cBack Off + 10 log
2
SF _ DL _ DPDCH
where
P_DL_DPDCH is the Initial power setting for the Dedicated Physical Data Channel (DPDCH)
primaryCpichPower is the downlink output power used for the PCPICH in the cell where
the connection is set up
PCPICH_EcNo is the measured Ec/No on PCPICH in the cell where the connection is set up,
received from the UE.
dlInitSirTarget is the required initial SIR target for the downlink DPDCH.
SF_DL_DPDCH is the Spreading Factor for the downlink DPDCH.
cBackOff is a configurable parameter to adjust the Open Loop Power Control estimate for
the initial transmit power level on DPDCH. It can either back off the open loop power
control estimate to a more conservative starting point or to increase the initial downlink
power to improve the call setup reliability.
In the case of IRAT handover where there is no measured Ec/No, the system uses a default
setting for Ec/No configured by the parameter ecNoPcpichDefault. This parameter should
be set to a value typically seen at the cell edge. This is recommended to -14 dBm as per [2]
for cell edge coverage value.
The initial power setting for the dedicated control channels (DPCCH) is calculated using the
following equations.
P_DL_DPCCH_TFCI = (P_DL_DPDCH + pO1)
P_DL_DPCCH_TPC = (P_DL_DPDCH + pO2)
P_DL_DPCCH_PILOT = (P_DL_DPDCH + pO3)
where
P_DL_DPCCH_TFCI is the Initial output power for the DPCCH TFCI field.
pO1 is the power offset between the data field and the TFCI field of the downlink DPCCH,
expressed in dB. This offset is constant, regardless of the service.
P_DL_DPCCH_TPC is the initial output power for the DPCCH TPC field.
pO2 is the power offset between the data field and the TPC field of the downlink DPCCH,
expressed in dB. This offset is constant, regardless of the service.
P_DL_DPCCH_PILOT is the initial output power for the DPCCH Pilot field.
pO3 is the power offset between the data field and the Pilot field of the downlink DPCCH,
expressed in dB. This offset is the same regardless of the service.
The values of the parameters discussed above are shown in the table below.
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Parameter Name
Object
Name
Recommended
Value
cBackOff
Power Control
0
dlInitSirTarget
Power Control
4.1 dB
ecNoPcpichDefault
Power Control
-14 dBm
pO1
Power Control
0 dB
pO2
Power Control
3 dB
pO3
Power Control
3 dB
The main reason for recommending a higher offset for pO2 when compared to pO1 and
pO3 is that the TPC commands received from different RBSs are subject to logical
combining in the UE. Consequently, the TPC command from each RBS must be decoded
before being combined, whereas the user data, Pilot bits, and TFCI bits can be combined
before decoding. To allow reliable decoding of TPC commands, it is advisable to increase
their power with respect to the other fields of the DPCCH.
16.5.2.
Downlink Power Limits
RNC calculates max and min DL
power limits and sends to RBS
RNC
RBS
UE
In power control systems there must be maximum and minimum limits for how much power
can be transmitted.
Maximum Downlink Transmitted Code Power: In the downlink, the maximum allowable
transmit power is dependant upon the radio connection type, specifically the maximum data
rate of the radio link. This is set on a per cell basis using a combination of parameters.
minPwrMax & minimumRate This sets the maximum transmit power (relative to CPICH)
for any services requiring minimumRate data transfer rates
or less
interPwrMax & interRate
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This is used to adjust the slope between minPwrMax and
maxPwrMax. Any service that requires data transfer rates
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great than minRate and less than maxRate will be
interpolated on this slope.
maxPwrMax & maxRate
This sets the maximum transmit power (relative to CPICH)
for any services requiring maxRate data transfer rates or
greater
The following table provides the maximum radio link data rate for different services.
Radio Connection Type
Maximum Radio Link Rate
PS384/HS
3700
SRB
14800
AMR 12.2
15900
CS64
67700
PS64/64
70900
MultiRAB (CS64 + PS8/8)
76100
PS64/384
406900
Using the above table and the limits base on radio link data rates, the RNC calculates the
max DL transmit power and sends it to the RBS.
The following graph provides an example of the mapping of these parameters. Ericsson
default parameters have been included in this example.
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Max DL TX Power (dB)
CPICH + maxPwrMax
4.8dB
CPICH + interPwrMax
3.8dB
The max power for services
with RL rate 406.9kbps or
greater is 4.8dB stronger than
CPICH Tx Pwr
CPICH + minPwrMax
0dB
The max power for services
with RL rate 15.9kbps or
less is 0dB stronger than
CPICH Tx Pwr
Min
Rate
15900
(AMR12.2)
Inter
Rate
Max
Rate
Maximum
RL Rate (bps)
406900
(PS384)
77600
Minimum Downlink Transmitted Code Power: If the power of a radio link is very low,
it is very sensitive to the impact from interference changes. To avoid this, the minimum
downlink transmitted code power is set using the configurable parameter minPwrRl which
is relative to the CPICH Tx Power.
16.5.3.
Initial Uplink Power Setting
RNC Calculates
DPCCH_POWER_OFFSET and
sends to UE
DPCCH_POWER_OFFSET
UE
RNC
RBS
UE uses DPCCH_POWER_OFFSET
and CPICH RSCP to determine
initial UL DPCCH Power
The initial uplink power is set in a similar way to setting the initial downlink power by
utilizing open loop power control. The power of the uplink dedicated physical control
channel (DPCCH) is first set using the following equation.
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Power_UL_DPCCH_INIT = DPCCH_POWER_OFFSET - RSCP_PCPICH
Where
RSCP_PCPICH is the Received Signal Code Power (RSCP) measured on the PCPICH
DPCCH_POWER_OFFSET = primaryCpichPower + RTWP + ulInitSirTarget - 10 log
(SF_DPCCH) + cPO
where
primaryCpichPower is the downlink power used for the PCPICH. If the serving RNC is not
aware of the power on the PCPICH when another physical RNC controls the cell, it uses a
configured default value pcpichPowerDefault, which is used only for this calculation.
RTWP is the Received Total Wideband Power (uplink interference) level measured by the
RBS.
ulInitSirTarget is the Initial value for the Uplink SIR Target, defined according to the
minimum Spreading Factor (SF) of the uplink Dedicated Physical Data Channel (DPDCH):
SF_DPCCH is the Spreading Factor for the DPCCH.
cPO is a parameter to set the uplink DPCCH power offset to a conservative level to avoid
excessive UL interference
DPCCH_POWER_OFFSET is calculated in the RNC and sent to the UE via the ul-DPCHPowerControlInfo part of the RRC Connection Setup (DL-CCCH) message.
The initial uplink power in DPDCH is then determined from the initial uplink DPCCH power
according to the relative power offsets between DPCCH and DPDCH (gain factor, as
described in 3GPP TS 25.214). The UTRAN determines and sends to the UE the gain factor
for the reference Transport Format Combination (TFC) only. The UE, in turn computes the
gain factors for other TFCs, based on the reference TFC.
16.5.4.
Initial Uplink SIR Target Setting
Initial Uplink SIR Target is a configurable parameter defined according to the minimum
Spreading Factor (SF) of the uplink Dedicated Physical Data Channel (DPDCH). The
following parameters are used to configure the initial uplink SIR target for different
scenarios.
ulInitSirTargetSrb: Used for stand-alone SRB, i.e. RRC connection setup, Inter-RAT
handover and common to dedicated(SRB) RAB release,
ulInitSirTargetLow: Used for RABs having minimum DPDCH SF equal to or higher than
32.
ulInitSirTargetHigh: Used for RABs having minimum DPDCH SF equal to 16 or 8.
ulInitSirTargetExtraHigh: Used for RABs having minimum DPDCH SF equal to or lower
than 4.
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16.5.5.
Uplink Outer Loop Power Control
DPCCH
DPCCH
RNC Sends new SIR Target to
RBS
UE
RNC
RBS
RNC uses CRC on DPCCH to
determine UL SIR Target
The purpose of outer loop power control in the uplink is to define the SIR target that the UE
will attempt to maintain. By adjusting the SIR target, and consequently the transmission
power levels, the outer loop power control aims at providing the required quality. Too high
quality would waste the system capacity, so the goal is to use as little power as possible.
The RNC uses the quality of the DPCCH to determine if the SIR target needs to be increased
or decreased, and sends the new target to the RBS. Since AMR voice CRCs are received on
20 ms TTI boundaries, the fastest this outer loop power control method can be adjusted is
50 times a second.
The RNC can use two methods to determine the new SIR target:. The parameter
ulOuterLoopRegulator determines whether to use Constant Step Regulator or Jump
Regulator. The default setting is Jump Regulator.
The initial uplink SIR targets are determined by the parameters ulInitSirTargetLow,
ulInitSirTargetHigh or ulInitSirTargetExtraHigh depending on the spreading factor of
the DPDCH. There are limits set for the maximum and minimum SIR targets. These are set
using the parameters sirMax and sirMin.
Constant Step Regulator
Whenever the Cyclic Redundancy Check (CRC) indicates that the reception of a transport
block is erroneous, the uplink SIR target is increased by configurable increment ulSirStep,
expressed in dB. Whenever NBR_OF_CRC_OK consecutive transport blocks are correctly
received, the uplink SIR target is decreased by an equal step. The number of consecutive
correct transport blocks needed to trigger a decrease of the uplink SIR target depends on
the BLER target.
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ulSirStep
NBR_OF_CRC_OK
SIR
Target
CRC
Jump Regulator
The Jump Regulator increases the uplink SIR target by a configurable increment ulSirStep,
expressed in dB, whenever a transport block is erroneously received. When a block is
correctly received, the uplink SIR target is decreased by a fraction of ulSirStep. This
fraction, denoted UP_DOWN_STEP_RATIO, depends on the BLER target.
ulSirStep
UP_DOWN_STEP_RATIO
SIR
Target
ulSirStep
CRC
If several transport blocks are received in one Transmission Time Interval (TTI), the change
in the uplink SIR target will be based on the accumulated change individually caused by
each of the transport blocks. To reduce the variations of the uplink SIR target, the change
of uplink SIR target is always scaled by the number of transport blocks received in the
corresponding TTI, as
SIRtarget_new = SIRtarget + ulSirStep [-X/(Z*UP_DOWN_STEP_RATIO)+Y/Z]
where
Z is the total number of received transport blocks.
X is the number of transport blocks that have a CRC=OK.
Y is the number of transport blocks that have a CRC=NG
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16.5.6.
Downlink Outer Loop Power Control
The downlink outer loop power control is taken care by the UE using its own proprietary
algorithm. The SIR target is set according to an autonomous function in the UE in order to
achieve the same measured quality as the quality target set by the RNC. The quality target
is set as the transport channel BLER value and signaled by the RNC to the UE. This resultant
SIR target is used by the UE as an input to the downlink inner loop power control.
16.5.7.
Downlink Inner Loop Power Control
UE requests power control
adjustment in TPC command
(1500 per second)
RBS monitors TPC
commands sent in
DPCCH and increases
or decreases Tx power
in steps ± 0.5dB
DPCCH/DPDCH sent
with new power
UE
RNC
RBS
UE uses an internal algorithm to
set the SIR target (outer-loop)
The UE power controls the RBS to maintain the call quality in the downlink. Based on the
difference between the actual SIR and the target SIR, the UE will request the RBS to either
increase or decrease its transmit power. The UE requests a power adjustment by sending a
Transmit Power Control (TPC) command in every slot (1500 times per second).
Actual SIR >= Target SIR  UE sends Power Down command
Actual SIR < Target SIR  UE sends Power Up command
As soon as the RBS receives power control commands (TPC bits), it starts regulating the
downlink power of the radio link according to these commands - increasing or decreasing
the power by TPC equal to 0.5 dB (1.0 dB if the link is established over Iur).
16.5.8.
Uplink Inner Loop Power Control
Uplink inner loop power control uses a similar feedback method to downlink inner loop. The
RBS sends power up or power down commands (TPC bits on the DPCCH) based on the
difference between the target SIR and the measured SIR. The UE monitors the TPC bits on
the DPCCH and increases or decreases its transmit power accordingly at the rate of 1500
times per second. The uplink transmit power is adjusted in steps of ±1dB.
Actual SIR >= Target SIR  RBS sends Power Down command
Actual SIR < Target SIR  RBS sends Power Up command
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RBS compares measured
SIR against target SIR
(from UL outer loop PC)
and determines if power
up or power down is
required
RBS requests power control
adjustment in TPC command
(1500 per second)
DPCCH/DPDCH sent
with new power
UE
RNC
RBS
UE monitors TPC commands
sent in DPCCH and
increases or decreases Tx
power in steps ± 1dB
16.6. Power Control during Soft Handover
During soft-handoff the UE has to manage power control to and from multiple RBSs. This is
handled differently in both the uplink and downlink.
16.6.1.
Uplink power control during SHO
During uplink power control, the UE receives TPC bits from the RBS instructing it to either
increase or decrease its transmit power. When the UE is in soft-handover it receives TPC
bits from multiple RBSs at the same time. The received TPC bits from the different RBSs
are independent from each other so there is a good chance that they will be different. The
UE resolves this conflict using a simple rule: if any Node B commands the UE to reduce
power, it will reduce power. This is called OR of the downs. The UE will increase the DPCCH
power by 1 dB, only if all the RBSs in the active set send a power up command.
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TPC1
TPC2
UE
RBS2
RBS1
Rule of the OR of the Down
If any RBS requests the UE to power
down, it will power down
UE Tx
Pwr (dB)
+1
-1
-1
+1
-1
-1
+1
-1
-1
Power Up
TPC1
Power Down
Power Up
TPC2
Power Down
In the event of softer-handover, the UE should receive identical commands from the two
cells. Knowing this, the UE “soft combines” the bits before making a decision on the value of
the bit. Here, there is no OR of the downs. The reason is that if the signal is from two cells
of the same Node B, the signal likely experiences the same general fading environment. The
UE can tell whether two or more radio links are from the same Node B with the help of the
TPC index.
16.6.2.
Downlink power control during Soft Handover
Initial Downlink power in Soft Handover
During soft handover, the aim of power control is to equalize the power transmissions from
the different RBSs, while compensating for differences in PCPICH power so that every signal
is received with the same strength at the cell border. The first step in this process is to set
the initial downlink power of the added radio link.
The power for a radio link added through soft handover is initially set as
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 primaryCPICHPower  dlInitSirT arg et - EcNo _ PCPICH   










P _ DL _ DPDCH 










2

 cSho  10 log 

 SF _ DL _ DPDCH 


where
P_DL_DPDCH is the Initial power setting for the Dedicated Physical Data Channel (DPDCH)
primaryCpichPower is the downlink output power used for the PCPICH in the cell where
the connection is set up
EcNo_PCPICH is the measured Ec/No on PCPICH in the cell where the connection is set up,
received from the UE.
dlInitSirTarget is the required initial SIR target for the downlink DPDCH.
SF_DL_DPDCH is the Spreading Factor for the downlink DPDCH.
cSho is a correction factor that takes into account the handover margin mSho and a
configurable parameter initShoPowerParam
Typically, a new radio link is added when the measured PCPICH Ec/No of the cell to be
added is higher than the best PCPICH Ec/No of cells already having a radio link, lowered by
a handover margin. It is desirable to let the different RBSs transmit the same power, but,
due to handover margin (mSho), the received PCPICH Ec/No is lower in the new cell,
resulting in a higher-than-required initial power. The correction factor cSho is used to
compensate for this effect, ideally allowing every RBS in the active set to transmit the same
downlink power. Its value is determined as a function of mSho, to which the configurable
parameter initShoPowerParam is added. This parameter is mainly useful to help the UE in
getting frame synchronization, in case high input signals are required by the base band
processing.
When entering soft handover, the downlink Inner Loop Power control of the existing branch
is directly applied to the new branch. The initial power setting allows all branches to start
with the correct power levels. Each RBS in the active set listens to the same sequence of
TPC commands from the UE. However, due to the different radio conditions of the different
soft handover links, the different TPC commands may be affected by different errors.
Consequently, the transmitted power at different RBSs will start to drift, eventually leading
to uncoordinated links. The Power Balancing mechanism prevents this power drift by using a
modified type of power control during soft handover.
Power Balancing: RNC calculates a single reference power based on the transmitted code
power measured in each radio link, and periodically sends it to all the RBSs. Each RBS
involved in soft handover makes synchronized adjustments of the downlink power of the
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radio links according to the received reference power. This will result in the convergence of
RBSs power levels and prevents the power drift.
The Power balancing method works in conjunction with the downlink Inner Loop Power
control based on the setting of the parameter dlPcMethod.
If dlPcMethod is set to FIXED, both Power balancing and downlink Inner Loop Power
control are disabled and the downlink power is kept at a constant level set by the parameter
fixedPowerDL during the call.
If dlPcMethod is set to NO BALANCING, downlink Inner Loop Power control is active, but
Power Balancing is disabled.
If dlPcMethod is set to BALANCING, downlink Inner Loop Power control is always active
and Power Balancing runs in parallel with downlink Inner Loop power control when more
than one radio link is involved.
If dlPcMethod is set to FIXED BALANCING, downlink Inner loop power control is active as
long as only one radio link is involved. As soon as an additional radio link is added to the
active set, downlink inner loop power control is disabled, and Power balancing is activated;
the downlink power stays at the configurable parameter fixedRefPower as long as the
active set includes multiple radio links.
The power control mechanism in a soft handover scenario is shown in the figure below.
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16.7. Power Control during Compressed Mode
16.7.1.
Uplink Power Control in Compressed Mode
Power Control in uplink Compressed Mode aims at recovering the SIR target as quickly as
possible after each transmission gap, in order to avoid block errors during and after the
compressed frames. To achieve this recovery, the uplink Inner Loop Power Control
increases the SIR target.
The active set cells estimate the SIR value of the received uplink DPCCH, generate TPC
commands, and transmit them one per slot, except during downlink transmission gaps,
according to the following rule:
If estimated SIR
SIR cm_target, the RBS sends a down command.
If estimated SIR < SIRcm_target, the RBS sends an up command.
SIRcm_target is the target SIR during Compressed Mode, which is increased to compensate for
the interruption in the Power Control due to transmission gaps, as well as for differences in
the number of pilot bits in the uplink DPCCH.
Compressed and non-compressed frames in the uplink DPCCH can have a different number
of pilots per slot. The total number of transmitted slots in compressed frames is decreased,
but the same number of bits as in a non-compressed frame must be sent. To accomplish
this, some of the pilot bits are replaced with TFCI bits. The total pilot energy per slot should
nevertheless be maintained, implying that an additional PILOT needs to be added to the
transmitted uplink power.
PILOT
= 10Log10 (N pilot,prev /N pilot,curr );
where
N pilot,prev and Npilot,curr represent the number of pilot bits in the most recently transmitted slot
and in the current slot respectively.
Thus, the received SIR per slot will increase correspondingly, and so as not to misinterpret
this as improved channel conditions, the SIR target is increased by SIR PILOT:
SIR PILOT = 10Log10 (Npilot,N /N pilot,currframe );
where N pilot,N and Npilot,currframe represent the number of pilot bits per slot in a normal uplink
frame (without transmission gap) and in the current uplink frame respectively.
16.7.2.
Downlink Power Control in Compressed Mode
Power Control in downlink Compressed Mode aims at recovering the SIR target as quickly as
possible after each transmission gap, in order to avoid block errors during and after the
compressed frames. To achieve this recovery, the Power Control increases the downlink
power, and the RRC signaling increases the downlink SIR target used by the Power Control
algorithm in the UE. In compressed frames, the transmission of downlink DPDCH and
DPCCH stops during transmission gaps. Downlink Inner Loop Power Control is not active
during the transmission gap.
In every slot in Compressed Mode, except during downlink transmission gaps, UTRAN
estimates the k-th TPC command and adjusts the current downlink power P(k-1) [dB] to the
new value P(k) [dB], according to the following formula:
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P(k) = P(k - 1) + PTPC(k) + PSIR(k) + P bal(k)
where
PTPC (k) is the k-th power adjustment due to the Inner Loop Power Control
PSIR (k) is the k-th power adjustment due to the downlink SIR target variation
Pbal (k) [dB] is the correction due to the Power Balancing
Due to transmission gaps in uplink compressed frames, uplink TPC commands might be
missing. If none is received, PTPC(k), derived by the Node B, is set to zero. Otherwise,
PTPC(k) is calculated in the same way as in normal mode, but applying a step size STEP
instead of TPC. STEP is set equal to 2 TPC during the slots belonging to the Recovery
Period, after each transmission gap, and to TPC otherwise. The Recovery Period Length
(RPL) is expressed as a number of slots, and is equal to MINIMUM(transmission gap
length, 7). Refer to the ‘Compressed Mode’ section earlier in this document for details on
the compressed mode feature.
In Compressed Mode, the transmitted DPDCH power does not exceed the maximum
transmission power by more than the accumulated effect of P SIR(k).
16.8. Power Control Scenarios
16.8.1.
Power Control steps for Radio Link Setup Procedure
When a dedicated radio link is established, the following power control actions are
performed.

Set Initial Downlink Power

Set Downlink Power Limits

Set Initial Uplink Power

Set Initial Uplink SIR Targets

Start Uplink Outer Loop Power Control

Start Downlink Inner Loop Power Control

Start Uplink Inner Loop Power Control
The details of each of these actions are covered in the previous sections.
16.8.2.
Power Control steps for RAB Establishment
When a RAB is added to the existing connection, the following actions related to Power
Control are taken.

Set Downlink Power Limits

Downlink Inner Loop Power Control is already running and no changes are made as
a result of the addition of the service. Any requirements for increased power is
handled through the regular downlink power updates ordered through the TPC
commands sent on the uplink Dedicated Physical Control Channel (DPCCH).

Set Initial Uplink SIR Target

Start Uplink Outer Loop Power Control
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
16.8.3.
Uplink Inner Loop Power Control is already running, and no changes of the uplink
DPCCH Power are made as a result of the addition of the service. Any requirements
for increased power are handled through the regular uplink power updates ordered
through the TPC commands sent on the downlink DPCCH.
Power Control steps for Soft Handover
When a radio link is added to the active set, the following actions related to Power Control
are taken:

Set Initial Downlink Power

Set Downlink Power Limits

Start Power Balancing
Upon radio link addition, no Power Control actions are initially needed for the uplink, since
the UE is already power controlled by the existing radio links. As soon as the added radio
link obtains uplink synchronization, the RBS issues Power Control commands based on the
SIR estimates for uplink Inner Loop Power Control.
In case of softer handover, the instantaneous power level is copied from the existing to the
new radio link.
When a radio link is removed from the active set, no Power Control actions are taken,
except for stopping Power Balancing when the soft handover ends.
16.9. Example of Power Control Procedure
The following figure shows the steps involved in the power control procedure for the
establishment of a speech call, followed by a soft handover. Each box in the figure
represents NBAP/RRC procedure or power control action described in the above
subsections.
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17. UE States
In UMTS, a UE is said to be in idle mode when it has no RRC connection with the RNC. An
RRC connection is a logical connection between UE and RAN used by two peer entities to
support the upper layer exchange of information flows. A UE can have only one RRC
connection. Several upper layer entities use the same RRC connection.
A UE in RRC connected state can be in one of 4 states – CELL_DCH, CELL_FACH, CELL_PCH
and URA_PCH. In the Ericsson implementation, the CELL_PCH state is not supported and is
not covered in the rest of the document. The remaining 4 states are shown in the figure
below.
Connected Mode
URA_PCH
Cell_DCH
Cell_FACH
Idle Mode
Figure 48: UE States in Ericsson UTRAN
Each of these UE states is covered in detail below.
17.1. Cell_DCH
The CELL_DCH state is characterized by:

A dedicated physical channel is allocated to the UE in uplink and downlink.

The UE is known on cell level according to its current active set.
The CELL_DCH-state is entered from the Idle Mode through the setup of an RRC
connection, or by establishing a dedicated physical channel from the CELL_FACH state. In
this state the UE is allocated a DCH/E-DCH (Dedicated Transport Channel) or HS-DSCH
(Common Transport Channel). The logical channel DCCH (Dedicated Control Channels) is
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used for control signaling and DTCH (Dedicated Traffic Channels) is used for user data
transmission. They are mapped onto the Transport channels and further multiplexed onto
Dedicated Physical Channels.
17.1.1.
CELL_DCH to CELL_FACH state
Switching from a dedicated transport channel to the common transport channels on
RACH/FACH when the traffic volume is low makes better use of dedicated radio resources.
It allows other users to take advantage of the unused resources. This switch is triggered by
inactivity (uplink and downlink combined) and applies to all CELL_DCH rates including
DCH/DCH, DCH/HS and EUL/HS. It is initiated by the S-RNC based on RLC throughput
measurements and is triggered by the Dedicated to Common Evaluation algorithm (covered
in the later section).
17.2. Cell_FACH
The CELL_FACH state is characterized by:

No dedicated physical channel is allocated to the UE.

The UE continuously monitors a FACH in the downlink

The UE is assigned a default common or shared transport channel in the uplink
(e.g. RACH) that it can use anytime according to the access procedure for that
transport channel

The position of the UE is known by UTRAN on cell level according to the cell where
the UE last made a cell update.
Cell Update
In CELL_FACH state, the Cell Update procedure is used to keep the UTRAN informed about
the UEs location on a cell level. Cell Update is initiated in the following cases when a UE is in
the CELL_FACH state:

A UE in state CELL_FACH enters a new cell.

As part of a supervision mechanism, Cell Update is performed periodically by UEs in
state CELL_FACH. The periodicity is controlled by the timer t305.

If a UE in state CELL_FACH re-enters the service area after having been out of
coverage when a periodic Cell Update should have been sent.

UE in state CELL_FACH detects RLC unrecoverable error in an AM RLC entity.
In the CELL_FACH state, the UE is able to transmit control signals and data packets on the
common transport channel RACH in the uplink direction and on the FACH in the downlink
direction. A maximum of 32 kbps is available on downlink for user data transmission.
17.2.1.
CELL_FACH to CELL_DCH
A transition occurs, when a dedicated physical channel is established via explicit signaling.
When the traffic volume of a UE on CELL_FACH state increases, it is switched to the 64/64,
64/HS or EUL/HS state if there are resources available. This is to better serve the needs of
the UE and to keep the common channels available to others that require only small amount
of resources. This switch is triggered by the Common to Dedicated Evaluation algorithm
based on buffer load measurements made in the S-RNC and in the UE.
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17.2.2.
CELL_FACH to URA_PCH
A UE on CELL_FACH is switched down to URA_PCH if it shows no activity for a long period
of time. This time is given by the RNC parameter inactivityTimer. In this way, system
resources are freed and UE power consumption is reduced, since the UE does not have to
monitor the FACH any more. This switch is triggered by the Common to URA_PCH algorithm
based on complete inactivity on both the uplink and the downlink.
17.3. URA_PCH
For a UE in URA_PCH state the service re-activation time is shorter compared to setting up
the connection from idle mode. At the same time the UE requires less signaling and power
consumption when in URA_PCH state compared to when on the common CELL_FACH
channel. Hence, it is possible to keep the UE in URA_PCH state for long time and let the
user benefit from the short service reactivation time.
The URA_PCH state is characterized by:

Neither an uplink nor a downlink dedicated physical channel is allocated to the UE

The UE uses DRX for monitoring a PCH via an allocated PICH.

No uplink activity is possible

The location of the UE is known on UTRAN Registration area (URA) level according
to the URA assigned to the UE during the last URA update in CELL_FACH state.
In this state the UE performs the following actions:

Monitor the paging occasions according to the DRX cycle and receive paging
information on the PCH

Listens to the BCH transport channel of the serving cell for the decoding of system
information messages

Initiates a URA updating procedure on URA change.
The Cell Update procedure in the URA_PCH state is for the following cases:

UE in state URA_PCH has uplink data to transmit

UE in state URA_PCH state is paged by the network. The page can be either
UTRAN or CN initiated.
URA Update
In state URA_PCH, the procedure URA Update is used to keep WCDMA RAN informed about
the UEs location on a URA level. To perform the URA update procedure, UE is moved
temporarily from URA_PCH to CELL_ FACH state. After the URA update is completed, UE
state is changed back to URA _PCH.
URA Update is initiated in the following cases:

A UE in state URA_PCH enters a new cell not belonging to the same URA that the
UE is registered in.

The UE enters a cell that has no URAs defined. This will trigger a release of the
RRC Connection and the UE enters idle mode.
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
As part of a supervision mechanism, URA Update is performed periodically. The
periodicity is controlled by the timer t305.
In the response to the URA Update, WCDMA RAN selects which URA the UE shall be
registered to. Also for periodical URA Updates, where the UE might not have moved, the
selected URA has to be specified by the network. System Information Block Type 2 contains
the URA identities of the URAs configured in the cell. The same cell can belong to a
maximum of 4 different URAs. In the URA_PCH state, the UE is not able to transmit or
receive any control signals or data packets.
17.3.1.
URA_PCH to CELL_FACH
When UE detects request for data activity on uplink it will send a cell-update message which
triggers a switch to CELL_FACH state. When RNC detects need for data transmission on
downlink it will send a URA page to UE which will trigger a cell-update leading to switch to
CELL_FACH. Note that the release of an RRC connection is not possible in the URA_PCH
State. The UE will first move to Cell_FACH state to perform the release signaling.
17.3.2.
URA_PCH to IDLE
Upon extended inactivity on both the uplink and the downlink, a URA_PCH state will be
switched down to IDLE. This is controlled by the RNC parameter inactivityTimerPch timer
which limits the time the connections stays in URA_PCH state. The switch is triggered by the
URA_PCH to idle evaluation algorithm.
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18. Introduction to R99 PS data services
The aim of this section and the subsequent ones is to describe the important features
offered in Ericsson Radio Access Network (RAN) that impact the delivery of R99 Packet
Switch (PS) data services to T-Mobile’s customers. This section explains the different QoS
and Traffic classes related to packet data services as well as the Radio Resource
Management (RRM) functionality. The Channel Switching Algorithm is the main function
inside the RRM that controls PS Data Services, which is covered in the subsequent sections.
18.1. Radio bearer QoS
The Packet Switch data services are defined according to its Quality of Service (QoS)
requirement in order to deliver the service effectively. For example certain applications are
more tolerant to delay (latency) and can therefore be assigned a lower priority.
The three main QoS service considerations that must be taken into account are:

Call quality - mapping of UMTS QoS parameters to the WCDMA transport and
physical channel characteristics,

Priority - bearer admission and scheduling,

Service availability and blocking - perceived QoS in terms of service coverage
and capacity.
18.2. Differentiation between traffic classes
In general, the UMTS traffic classes provide the means for the network to differentiate
between end-to-end user applications according to their required traffic characteristics for
that service. The main differentiation between the traffic classes is based on how sensitive
the service is to delay. Given that radio spectrum is a limited resource, the radio access
bearers (RABs) are limiting factors in terms of the available resources (compared to a fixed
network where additional circuits can be provided with the extension of hardware e.g. fiber
cable,) then traffic must be prioritized and handled according to its service class attributes.
However, it is the performance of both the radio and fixed bearers (Transmission
infrastructure) that determine the overall QoS offered by the network. Table 11 shows the
main characteristics of the QoS classes that are supported in UMTS.
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Table 11: Traffic Classes Characteristics
18.3. Radio Resource Management for packet data services
In addition to the Channel Switching algorithms, Congestion Control, Admission Control and
Handover functions can also trigger switching of a transport channel for an interactive RAB
to one with a lower rate.
Admission Control switches a UE from one dedicated transport channel to another one at
the next lower-rate when the resource is needed to establish a new connection for a UE
with high priority. Congestion Control may switch a UE from a dedicated to a common
transport channel to resolve a congestion situation.
When the Soft Handover algorithm fails to add a radio link due to admission denial and the
current connection has uplink and/or downlink rates higher than 64 kbps, it will switch the
connection down to 64/64 or 64/HS before trying to add the radio link again.
When a UE enters the area of a new RNC, while being in states FACH or URA_PCH, it will be
switched down to IDLE state in order to avoid common transport channel (FACH/RACH)
signaling over the Iur interface.
18.4. Active Queue Management feature
The Active Queue Management for interactive RAB feature introduces an optimized buffer
handling, which minimizes the buffering delays and interacts with the TCP protocol in a
favorable manner, thereby significantly improving the quality of the service experienced by
the end user.
With Active Queue Management, a mechanism to detect link overload before the absolute
limits of the buffer in the RNC have been reached is introduced. Through this, a carefully
selected packet dropping profile is applied to the overloaded buffers in order to avoid
uncontrolled packet losses and high buffering delays when link overload is detected.
Active Queue Management can be turned on and off with the activeQueueMgmt
parameter.
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18.5. Channel Switching Feature
Traffic on the interactive Radio Access Bearer (RAB) causes large variations in offered traffic
over time for a particular user. Consequently, it is not efficient to reserve resources for a
dedicated channel continuously. Channel Switching is a feature that dynamically allocates
resources to a user according to the amount of data that needs to be transmitted in the
uplink and the downlink. This is achieved by switching the interactive RAB of the user
between transport channels of different rates. When an interactive RAB has only a small
amount of data to send and receive, it is switched to common transport channels .This
allows more users to share the radio resources than in a circuit-switched scenario. When the
traffic increases, the user is switched to a dedicated transport channel if there are resources
available
Channel Switching applies only to packet traffic on the interactive RAB, which has little or no
quality of service attributes that apply. It belongs to the interactive and Background Quality
of Service classes, which have no guaranteed bit rates and no packet delay requirements.
When sufficient resources are available, the interactive RAB receives high bit rates but when
the system is heavily loaded and not many resources are available, the bit rates offered may
be low. In a heavily loaded situation, it may not be given any bandwidth at all, since there
are no guarantees on resource allocation for the RAB. Channel Switching switches only
between transport channels. The logical channels are not affected.
The channel switching feature will only affect users that are turned on and in connect mode,
sending or receiving data. The UEs in connected mode can be changed through the
different states to optimize the resources.
The channel switching feature consists of two parts: evaluation and execution. Channel
switching evaluation is responsible for monitoring and reporting the needs of a UE by
measurement reports received from the UE, RBS and RNC. The evaluation part will then
send an execution request to the execution part when the criteria for a channel switch is
fulfilled. Chanel switching execution is responsible for the allocation of resources according
to the UE and cell capabilities and executing the Radio Bearer Reconfiguration procedure for
performing the channel switch.
18.6. Channel Switching Triggers
The Channel Switching Evaluation is based on two criteria

User activity measured in terms of either channel throughput or RLC (Radio Link
Control) buffer load.

Coverage condition measured in terms of downlink code power.
An upswitch is requested when high user activity is detected either on a dedicated channel
(DCH) as high channel throughput close to the maximum capacity of the current transport
channel or on FACH as high buffer load. For a dedicated to dedicated channel upswitch on
the downlink, a test is also made to ensure that there will be sufficient coverage (downlink
code power) after the switch. Upswitch from URA_PCH to FACH is triggered by user activity.
When low or no user activity is detected, a downswitch is requested. When on a dedicated
channel, the detection is based on throughput measurement and the connection will be
switched down either to a lower rate on a dedicated channel or to FACH depending on
throughput level. This happens after periods defined by downswitch timers. When on FACH,
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a switch down request to URA_PCH state will be made based on user data inactivity after
the period specified by an inactivity timer. Also, when on URA_PCH, the measurement is
based on data inactivity and a request to release the connection will be made after the
period specified by an inactivity timer.
When the coverage on downlink of a connection falls below a certain threshold considered
to be insufficient for the current rate, a downswitch to the next lower state will be
requested.
There is no coverage-triggered downswitch for the uplink. Also there is no coverage test for
dedicated to dedicated channel upswitch on the uplink. The UE is expected to perform
transport format reduction to compensate for insufficient uplink coverage.
18.7. Triggers for Dedicated to Dedicated channel switching
18.7.1.
Throughput-triggered Upswitch
This is triggered by high channel utilization in the uplink or the downlink as indicated by a
measured channel throughput that is close to the maximum capacity of the current
transport channel. The UE will be switched to a state with a higher rate in the link that
triggered the switch. The HS-DSCH is the preferred channel for the downlink and E-DCH in
the uplink. A check on the EUL/HS capability or DCH/HS capability of both the UE and the
connected cells is made before the switch. If all are EUL/HS capable, the transition will be to
the EUL/HS state. If both are DCH/HS capable but not EUL/HS capable the transition will be
to 64/HS or 384/HS depending on the need. For an uplink trigger, the UE is switched to a
state with a higher uplink rate without compromising the downlink rate and for downlink
trigger; the UE is switched to a state with a higher downlink rate without compromising the
uplink rate.
A coverage test based on the current DL code power utilization is made to see if the UE has
sufficient code power to switch up to the target state. This is to avoid loss of connection or
immediate coverage triggered downswitch due to insufficient code power. Note that if the
current best cell is not HSDPA enabled but a coverage related cell on another frequency is,
the connection may be redirected to that cell. These transitions are triggered by the
CELL_DCH to CELL_DCH Upswitch Evaluation algorithm.
18.7.2.
Throughput-triggered Downswitch
This is triggered by low channel utilization in the uplink or the downlink as indicated by a
measured channel throughput that is below a certain percentage of the maximum capacity
of the transport channel with the next lower rate. The UE will be switched down to a state
with the next lower rate in the link that triggered the switch.
18.7.3.
Coverage-triggered downswitch
Insufficient downlink coverage is detected in the form of high downlink code power. This
applies only to UE’s that have a DCH transport channel on the downlink. The downlink
channel will be switched to one with the next lower rate, i.e., DCH/384 to DCH/128,
DCH/128 to DCH/64, with DCH equals 64,128 and 384. This is triggered by the CoverageTriggered Downswitch Evaluation algorithm.
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18.8. Multi RAB State Transitions
18.8.1.
Speech + Interactive
Five different types of Channel Switching among the seven states Speech + 0/0, Speech +
64/64, Speech + 64/128, Speech + 64/384, Speech +128/64, Speech + 64/HS, Speech +
384/HS are available.
The Multi-RAB Downswitch Evaluation monitors the states with a non-zero interactive rates
and triggers a switch to the lowest state Speech + 0/0 (SP0) when there is no activity on
the Interactive RAB for an extended period of time. If the state SP0 is not available
(multiRabSp0Available set to 0), a request to release the Interactive RAB is made, instead.
The Multi-RAB Upswitch Evaluation monitors the activity on both the uplink and the
downlink of the SP0 state and switch it up to the Speech + 64/64 or Speech + 64/HS state
if necessary.
The CELL_DCH to CELL_DCH Upswitch Evaluation switching for a downlink trigger:

Speech + 64/64, Speech + 64/128, Speech + 64/384 to Speech + 64/HS

Speech + 128/64 to Speech + 384/HS

Speech + 64/64 and Speech+ 64/128 to Speech + 64/384

Speech +64/64 to Speech + 64/128.
The CELL_DCH to CELL_DCH Upswitch Evaluation switching for an uplink trigger:

Speech + 64/64, Speech + 64/128, Speech + 64/384, Speech + 128/64, Speech +
64/HS to Speech + 384/HS

Speech + 64/64 to Speech + 64/128
The CELL_DCH to CELL_DCH Downswitch Evaluation switching for a downlink trigger:

Speech + 64/384 to Speech + 64/128

Speech + 64/128 to Speech + 64/64.
The CELL_DCH to CELL_DCH Downswitch Evaluation switching for an uplink trigger:

Speech + 128/64 to Speech + 64/64

Speech + 384/HS to Speech + 64/HS.
The Coverage Triggered Downswitch Evaluation switches Speech + 64/384 to Speech + 64
/128 and switches Speech + 64/ 128 to Speech + 64/64.
18.8.2.
2xInteractive
Inactivity monitoring is available on the 2xInteractive multi-RAB. The Multi-RAB Downswitch
Evaluation triggers a request to release one of the interactive RAB's upon a period of
inactivity on both the uplink and the downlink for one of the RAB's.
18.8.3.
Speech + 2xInteractive
Inactivity monitoring is available on the Speech + 2xInteractive multi-RAB. The Multi-RAB
Downswitch Evaluation triggers a request to release one of the interactive RAB’s upon a
period of inactivity on both the uplink and the downlink for that RAB.
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19. Channel Switching Algorithms
The objective of the channel switching algorithms is to determine for each interactive RAB if
there is a need to switch a UE from one transport channel to another and to select a
transport channel with a user bit rate corresponding to the required bandwidth of the data
transmission.
The channel switching algorithms consist of the following sub-algorithms:

Common to Dedicated Evaluation

Dedicated to Common Evaluation

Common to URA Evaluation

URA to Idle Evaluation

Coverage Triggered Downswitch Evaluation

Dedicated to Dedicated Upswitch Evaluation

Throughput based Dedicated to Dedicated Downswitch Evaluation

Multi RAB Downswitch Evaluation

Multi RAB Upswitch Evaluation
The Channel Switching algorithms use buffer load, throughput, and transmitted code power
as input to the algorithms. These terms are defined as follows:

Buffer load is defined as the minimum of the Radio Link Control (RLC)
transmission window and the sum of bytes in the SDU (service data unit) buffers
and retransmission buffers of some of the RLC instances (each interactive RAB
connection consists of five RLC instances).

Uplink throughput is defined as the number of bits transmitted from the MAC
layer to the RLC layer. Downlink throughput is defined as the number of bits
transmitted from the RLC layer to the MAC layer. The RLC instances to be
considered for the buffer load and throughput measure depends on the UE state
and the algorithm using the measure.

Transmitted code power is defined as the downlink power of the pilot bits of the
DPCCH (Dedicated Physical Control Channel) field. For channel switching purposes,
periodic reporting with a 1 second period is used.
The following sections will describe in detail the different channel switching algorithms and
will mention the parameters involved in them. Refer to Appendix F for a quick look at the
recommended values for all Channel Switching parameters.
19.1. Common to Dedicated Evaluation
The Common to Dedicated Evaluation algorithm monitors the amount of user data
waiting to be transmitted (buffered) in the RNC or UE. If the buffer load increases and a
switch from the common transport channels FACH/RACH to a higher bit rate dedicated
transport channel is required, an upswitch request is sent to channel switching execution.
The evaluation algorithm is activated at the entry of the common state, and uses RLC buffer
loads in both the uplink and the downlink as input.
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When the RLC buffer load in the uplink exceeds the threshold value set by the RNC
parameter ulRlcBufUpswitch, a measurement report is sent from the UE and an upswitch
request is issued after the reception of the measurement report. A request is also issued
when the RLC buffer load in the RNC, in the downlink exceeds the threshold value set by
the RNC parameter dlRlcBufUpswitch. Channel switching execution thereafter performs
the upswitch when permission is given from Admission Control.
The common to dedicated switching function always tries to allocate the highest rate
transport channel pair possible. If the highest is not possible it tries with the second highest
and so on (i.e. EUL/HS, 64/HS, 64/384, 64/128).
19.2. Dedicated to Common Evaluation
The Dedicated to Common Evaluation algorithm monitors the transmitted user data. If
user throughput decreases so that a switch from a dedicated transport channel to the
common transport channels FACH/RACH is required, a downswitch request is sent to
channel switching execution.
The evaluation is activated once the dedicated state is entered and it uses throughput
measurements, performed in the S-RNC, in both the uplink and downlink for both control
and user data as input.
When the throughput on both the uplink and downlink is below the threshold value set by
the RNC parameter downswitchThreshold, the timer defined by the RNC parameter
downswitchTimer is started for a DCH/DCH allocation or the timer defined by the RNC
parameter hsdschInactivityTimer is started for a DCH/HS or EUL/HS allocation. If the
throughput increases above a second threshold set by the parameter
downswitchTimerThreshold before the timer expires, the timer is stopped and no switch
is issued. This is done for stability reasons, and could be used to prevent switches back and
forth at momentary dips in throughput.
Figure 49: Dedicated to common channel switching evaluation
The example in the previous figure shows the following:
1. The throughput decreases below the downswitch threshold (downswitchThreshold)
and the timer (downswitchTimer) is started.
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2. The throughput increases and exceeds the upper threshold
(downswitchTimerThreshold) and the timer is stopped.
3. The throughput decreases again and the downswitch threshold
(downswitchThreshold) is crossed, which starts the timer.
4. Finally, the timer expires and a switching request from the dedicated to the common
state is issued.
The evaluation is restarted when the switch request is issued to Channel Switching
execution. This is necessary in order to handle failing downswitches. If the downswitch fails,
a new request is issued when the restarted timer expires.
A value of 0 for the downswitchTimer disables the Dedicated to Common Evaluation
algorithm.
When the UE is ordered to switch to the common state, no target cell is specified. This
means that the UE selects a cell and performs a cell update procedure.
19.3. Common to URA Evaluation
The Common to URA Evaluation releases UEs with no activity in order to free resources. It
also decreases the power consumption of the UE, since the UE does not have to monitor the
FACH for long periods of time.
The algorithm is activated at the entry of the FACH state. Uplink and downlink activity is
monitored and the algorithm requests a switch to URA_PCH state if no uplink or downlink
activity is detected (i.e. no data has been transmitted) during a time defined by the RNC
parameter inactivityTimer.
If the URA_PCH state is not available, the UE is switched down to idle state.
19.4. URA to Idle Evaluation
The URA to Idle Evaluation releases UEs with no activity in order to free resources. The
algorithm is activated at the entry of the URA_PCH state. The algorithm requests a switch to
idle mode if a UE has been allocated to URA_PCH state for a time defined by the RNC
parameter InactivityTimerPch. The request is issued to the Signaling Connection
Handling function. Signaling Connection Handling issues an Iu release request to the Core
Network, which in turn decides whether the connection should be released.
19.5. Coverage Triggered Downswitch Evaluation
The Coverage Triggered Downswitch Evaluation algorithm monitors the code power
utilization on the downlink. If the code power increases so that a switch to a lower rate
dedicated channel on the downlink is required due to coverage reasons, a downswitch
request is sent to the Channel Switching Execution function. The goal is to minimize call
drops due to bad link quality. When downlink transmitted code power increases to a value
too close to its maximum, there is a risk that the link quality cannot be maintained. In this
situation, a user should be switched down to a lower rate to decrease the needed downlink
transmitted code power. This feature is used to prevent a user from using a data rate in an
area where there is risk for no coverage of that particular rate.
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The algorithm monitors the downlink transmitted code power of all legs in the active set and
the code power is then filtered by each Node B in the active set. A downswitch request is
issued when all handover legs use a power above the power alarm threshold defined by the
parameter downswitchPwrMargin below the maximum code power for a period defined
by the parameter coverageTimer. If the transmitted downlink code power falls below the
power alarm threshold by a margin equal to the parameter reportHysteresis while the
timer defined by the parameter coverageTimer is running, the request will be cancelled
and no downswitch is executed. The reason for this hysteresis is to prevent the algorithm
from cancel a downswitch due to small, momentary dips in transmitted downlink code
power.
This evaluation algorithm is started at the entry of the single RAB states DCH/384 and
DCH/128 and Multi RAB states speech + 64/384 , speech + 64/128 and 64/128 + 64/128 .
Figure 50: Coverage Triggered Downswitch
19.6. Dedicated to Dedicated Upswitch Evaluation
The Dedicated to Dedicated Upswitch Evaluation algorithm determines whether a switch to
a higher rate channel should be made. The same algorithm applies both for Single RAB and
for Multi RAB transitions.
The algorithm monitors the uplink and the downlink throughput separately. A channel
switch request to a higher uplink rate Radio Bearer (uplink triggered) or to a higher
downlink rate Radio Bearer (downlink triggered) is issued if all of the following conditions
are fulfilled:

The downlink throughput increases above the threshold specified by the RNC
parameter bandwidthMargin for a period defined by the parameter
upswitchTimer or the uplink throughput increases above the threshold specified
by the RNC parameter bandwidthMarginUl for a period defined by the
parameter upswitchTimerUl.
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
For a trigger on the downlink, the transmitted code power consumption on the
current rate is below the power upswitch threshold defined by the RNC parameter
upswitchPwrMargin for all legs in the active set at the expiry of the timer set by
the parameter upswitchTimer.

The maximum bit rate capability for QoS profiling does not indicate that the current
rate is the maximum bit rate for the user

After a throughput based downswitch, the downlink throughput has fallen below
the threshold specified by dlThroughputAllowUpswitchThreshold or the uplink
throughput has fallen below the threshold specified by
ulThroughputAllowUpswitchThreshold.
The power upswitch threshold is defined from the power alarm threshold through the
parameter upswitchPwrMargin and the estimated power increase, as shown in the figure
below. The estimated power increase is based on the relative rate difference between the
current and a higher rate. For an upswitch from 64 to 128 kbps, the estimated power
increase is 2.9 dB and for the 128 to 384 kbps upswitch, it is 4.7 dB. When evaluating an
upswitch from 64 kbps, rate 384 kbps is targeted as first alternative and rate 128 kbps as
second alternative.
If the bandwidthMargin parameter is set to 0 or the bandwidthMarginUl is set to 0,
the Dedicated to Dedicated Upswitch evaluation is turned off for downlink or uplink
respectively. If the dlThroughputAllowUpswitchThreshold parameter is set to 0 or the
ulThroughputAllowUpswitchThreshold is set to 0, this condition is not used for
downlink or uplink respectively.
As long as the upswitch request cannot be fulfilled, the upswitch request will be repeated.
An adaptive upswitch time is achieved by doubling the time between requests for each new
request sent, where the time between first and second request is determined by
upswitchTimer or by upswitchTimerUl to a maximum of 60 seconds. This decreases the
possibility of immediately ending up in a congestion situation again when a congestion
situation had just been resolved.
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Figure 51: Coverage testing before a downlink upswitch
19.7. Throughput Based Dedicated to Dedicated Downswitch
Evaluation
The Dedicated to Dedicated Downswitch Evaluation algorithm determines whether a switch
to a lower rate channel should be made. The same algorithm applies both for Single RAB
and for Multi RAB transitions.
The uplink and the downlink throughput are monitored separately. A channel switch request
to the next lower uplink rate Radio Bearer (uplink triggered) or to the next lower downlink
rate Radio Bearer (downlink triggered) is issued when the downlink throughput decreases
below the threshold specified by dlDownswitchBandwidthMargin for a period defined
by the parameter dlThroughputDownswitchTimer or the uplink throughput decreases
below the threshold specified by ulDownswitchBandwidthMargin for a period defined
by the parameter ulThroughputDownswitchTimer.
If the dlDownswitchBandwidthMargin parameter is set to 0 or the
ulDownswitchBandwidthMargin parameter is set to 0, the Dedicated to Dedicated
downswitch evaluation is turned off for downlink or uplink respectively.
19.8. Multi RAB Downswitch Evaluation
This algorithm monitors the user data throughput both in the uplink and the downlink. If no
data is transmitted for the duration specified by a downswitch timer, a request is issued to
switch the interactive RAB to state Speech + 0/0 (SP0) in the cases of Speech + interactive
DCH/DCH Multi-RAB or Speech + DCH/HS Interactive Multi-RAB. If the state SP0 is not
available, this would instead result in a request to release the interactive RAB for the
2xinteractive multi-RAB. The downswitch timer for the Speech + interactive DCH/DCH multiRAB is given by the parameter downswitchTimerSp and that for the Speech + Interactive
DCH/HS multi-RAB is given by the parameter hsdschInactivityTimer. The downswitch
timer for the 2xinteractive multi-RAB is given by the parameter
inactivityTimeMultiPsInteractive.
The algorithm receives throughput measurement reports every 500 ms and if the
throughput in both uplink and downlink is equal to zero, the timer is started. The timer is
stopped when the throughput in either UL or DL increase above zero. If the
downswitchTimerSp or downswitchTimerUp parameter is set to 0, the corresponding MultiRAB Downswitch Evaluation is turned off and no downswitches will occur irrespective of how
long the throughput has been zero.
19.9. Multi RAB Upswitch Evaluation
The Multi RAB Upswitch Evaluation algorithm is specific to the Speech + interactive multiRAB. It monitors the RLC buffer load on both the uplink and the downlink of the interactive
part of the Speech + 0/0 state (SP0).
The evaluation algorithm is activated at the entry of the Multi RAB SP0 state, and uses RLC
buffer loads in both the uplink and the downlink as input.
When the buffer load in the uplink exceeds the threshold value set by the parameter
ulRlcBufUpswitchMrab, a measurement report is sent from the UE. An upswitch request
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is issued upon reception of the measurement report. A request is also issued when the RLC
buffer load in the RNC exceeds the threshold value set by the parameter
dlRlcBufUpswitchMrab.
If the dlRlcBufUpswitchMrab parameter is set to 0, the Multi-RAB Upswitch Evaluation
algorithm is turned off, meaning that no upswitches from SP0 will occur, irrespective of the
RLC buffer load.
19.10.
Channel Switching Parameter Optimization
Optimization of channel switching is a trade-off between user throughput and system
capacity. For example, the time a user stays on DCH can be increased so that a short period
without traffic does not lead to a downswitch to FACH. This improves the user throughput
since transmission can be started immediately after the short period without transmission.
However, since the user then also holds the resources associated to a DCH for a longer
time, the system capacity will decrease. When optimizing the parameter setting of channel
switching it is also important to consider the different kinds of traffic and the different kinds
of mobiles in the network since both traffic and mobile behavior can differ significantly.
Optimization of the channel switching from common to dedicated channels depends on the
parameter ulRlCBufUpswitch. A lower value for this parameter might be useful to trigger an
upswitch to a dedicated state when a UE is used for an application like we browsing, but
when used as a modem with a laptop, signaling from other applications might trigger an
unwanted upswitch to a CELL_DCH state.
The above discussion is also applicable to a downswitch from a dedicated to common
channels. The setting of the downswitchThreshold parameter dictates when a UE changes
to a CELL_FACH state from a CELL_DCH state. While a value of 0 kbps for this parameter
would be accurate for a UE doing a FTP download, when used as a modem, the applications
on a laptop may create low level background traffic which would force the UE to stay in a
CELL_DCH state when this parameter is set to 0 kbps.
These are just some initial guidelines for trending of the channel switching parameters and
actual recommended values for all related parameters would have to be evaluated with the
help of network trials.
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20. Appendix A: Weighting Factor Analysis for Soft
Handover Algorithm
A weighting factor is used to include active cells other than the best cell in the evaluation
criteria for reporting events. The measured value after weighting will be
 NA

W  10  Log   M i   (1  W )  10  LogM Best
 i 1

where
Mi is a measurement result of a cell in the active set
NA is the number of cells in the current active set
MBest is the measurement result of the cell in the active set with the highest measurement
result
W is the weighting factor
When W = 0, as can be seen from the above equation, only the best cell’s measured value
is considered for event analysis. Consider the following example of the influence of a nonzero weighting factor on event 1a and event 1b evaluation.
20.1. Event 1a evaluation
When there is only 1 cell in the active set, the value of W doesn’t influence the
measurement result, and hence the example below considers a case where there are 2 cells
in the active set, and a third cell is being considered to trigger either event 1a.
Consider that the active set has only 2 cells, cell A with CPICH Ec/No = -8 dB, and cell B
with CPICH Ec/No = -12 dB. Assume the following values for the different soft handover
related parameters.
reportingrange1a = 3 dB
hysteresis1a = 0
individualoffset = 0
With these values, the Event 1a conditions simplifies to
10  LogM
New
 NA

 w1a  10  Log   M   (1  w1a)  10  LogM
 reportingRange1a
best
 i 1 i 


If W1a = 0, then the right hand part of the above equation equals -11 dB, which means
that Event 1a is satisfied when the neighboring cell’s CPICH Ec/No is greater than or equal
to -11 dB.
If W1a = 0.5, then the right hand part of the above equation equals -9.9, which means
that Event 1a is met when a neighboring cell’s CPICH Ec/No is greater than or equal to -9.9
dB. So in this case, a neighbor cell has to be stronger than the previous case in order to be
added to the active set.
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If W1a = 1, then the right hand part of the above equation equals -8.8, which means that
Event 1a is met when a neighboring cell’s CPICH Ec/No is greater than or equal to -8.8 dB.
So in this case, a neighbor cell has to be even stronger than the previous two cases in order
to be added to the active set.
20.2. Event 1b evaluation
Consider that the active set has only 2 cells, cell A with CPICH Ec/No = -8 dB, and cell B
with CPICH Ec/No = -12 dB. Assume the following values for the different soft handover
related parameters.
reportingrange1b = 5 dB
hysteresis1b = 0
individualoffset = 0
With these values, the Event 1b conditions simplifies to
10  LogM
Old
 NA

 w1b  10  Log   M   (1  w1b)  10  LogM
 reportingRange1b
best
 i 1 i 


If W1b = 0, then the right hand part of the above equation equals -13 dB, which means
that Event 1b is satisfied when the neighboring cell’s CPICH Ec/No is less than or equal to 13 dB.
If W1b = 0.5, then the right hand part of the above equation equals -11.9, which means
that Event 1b is met when a neighboring cell’s CPICH Ec/No is less than or equal to -11.9
dB. So in this case, a neighbor cell has to be stronger than the previous case in order to
remain in the active set.
If W1b = 1, then the right hand part of the above equation equals -10.8, which means
that Event 1b is met when a neighboring cell’s CPICH Ec/No is less than or equal to -10.8
dB. So in this case, a neighbor cell has to be even stronger than the previous two cases in
order to remain in the active set.
20.3. Tradeoff due to weighting factor
From the above two cases it can be inferred that for a non-zero value of the weighting
factor, a neighboring cell has to be stronger than when the weighting factor = 0, for it to be
added to the Active set or retained in the Active set. Hence a non-zero weighting factor
would result in a small reduction in the Active set size. Note that this reduction is only valid
when the Active set size is at least equal to 2.
A larger value of W will result in a reduction in the Active Set size, thus saving network
capacity. However a large value of W would mean that the a possible neighbor is added less
quickly into the Active set, which might impact call quality negatively in some cases. Also
delaying the addition of a neighbor into the Active set would result in larger number of
measurement reports being sent to the RNC for the same candidate cell, thus more
processing would be needed from the RNC to handle this increase in received measurement
reports.
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In networks where capacity is an issue, a larger value of W might be more useful as long as
the reporting ranges are modified for this newer value of W. For initial network launch, a
value of W = 0 is still recommended.
Further tests in the field will be performed to assess the impact of the weighting factor on
Soft Handover performance.
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21. Appendix B: Monitored Set Creation Field Example
21.1. Description
This test will compare a theoretical monitored set against a measured monitored set after
SHO has occurred between 2 cells with a mixture of common and unique neighbors.
21.2. Execution
The following is the list of the test steps that were performed.

Begin a CS voice call on BQU4659C (SC165)

Drive until BQU4841A (SC221) is added to the active set

Record new monitored set from TEMS

Compare against theoretical neighbor list
21.3. Neighbor Lists
Neighbor List - BQU4659C (SC165)
1
2
3
4
5
6
149 157 52
68
323 331
17
18
19
20
21
22
403
7
221
23
8
229
24
9
124
25
10
133
26
11
141
27
12
268
28
13
395
29
14
28
30
15
36
31
16
237
32
Neighbor List - BQU4841A (SC221)
1
2
3
4
5
6
229 237 395 403 165 268
17
18
19
20
21
22
213 125 96
7
323
23
8
331
24
9
68
25
10
141
26
11
28
27
12
149
28
13
157
29
14
181
30
15
155
31
16
236
32
21.4. Results
The following shows the steps in the monitored set creation for this test case.
Original List
1
2
165 149
17
18
237 403
- Serving
3
4
157 52
19
20
Cell = BQU4659C
5
6
7
68 323 331
21 22
23
(SC165)
8
9
221 229
24
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
BQU4841A (SC221) added to Active Set - Calculate New Monitored List
STEP 1 - Add both the active cells (A) and (B) to the listed set in the same position as they
existed previously.
New List
1
2
165
3
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17
18
Old List
1
2
165 149
17
18
237 403
19
20
21
22
23
24
25
26
27
28
29
30
31
32
3
157
19
4
52
20
5
68
21
6
323
22
7
331
23
8
221
24
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
STEP 2 - Take the neighbor cell with the highest priority for the best active set cell, cell(A),
and if it already exists in the old listed set add it to the new listed set in the same position.
If it does not exist in the old listed set, then the position does not matter, therefore store it
for addition later in a temporary array.
New
1
165
17
List
2
149
18
3
4
5
6
7
19
20
21
22
3
157
19
4
52
20
5
68
21
Temporary List
1
2
3
4
17
20
Old List
1
2
165 149
17
18
237 403
18
19
9
10
11
12
13
14
15
16
23
8
221
24
25
26
27
28
29
30
31
32
6
323
22
7
331
23
8
221
24
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
5
6
7
8
9
10
11
12
13
14
15
16
21
22
23
24
25
26
27
28
29
30
31
32
STEP 3 - Take the neighbor cell with the highest priority for the second best active set cell
(B), and if it already exists in the old listed set add it to the new listed set in the same
position. If it does not exist in the old listed set, then the position does not matter and it
can be stored in a temporary array for later addition. Store the neighboring cell only if it
does not already exist in the temporary array (avoid duplicate). If it is already stored in the
temporary array, take the next neighboring cell in priority order from the next cell in the
Active Set, cell (A) applying the same rules.
New
1
165
17
List
2
149
18
3
4
5
6
7
19
20
21
22
23
8
221
24
9
229
25
10
11
12
13
14
15
16
26
27
28
29
30
31
32
Old List
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1
165
17
237
2
149
18
403
4
52
20
5
68
21
6
323
22
7
331
23
8
221
24
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
Temporary List
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
20
21
22
23
24
25
26
27
28
29
30
31
32
18
3
157
19
19
STEP 4 - Repeat until all neighbor cells have been processed or until MaxIafMonSubsetIAF
neighboring cells have been selected for the listed set.
New
1
165
17
237
List
2
149
18
403
3
157
19
4
52
20
5
68
21
6
323
22
7
331
23
8
221
24
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
Old List
1
2
165 149
17
18
237 403
3
157
19
4
52
20
5
68
21
6
323
22
7
331
23
8
221
24
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
Temporary
1
2
149 157
17
18
List
3
181
19
4
155
20
5
236
21
6
213
22
7
125
23
8
96
24
9
10
11
12
13
14
15
16
25
26
27
28
29
30
31
32
STEP 5 - Take the cells that have been selected to be included in the new listed set (stored
in the temporary array) and add them to the listed set by filling the spaces that have not
been filled in step (c), the neighboring cells are picked from the temporary array in the
order they was stored (FIFO). (This makes sure that neighboring cells stored early in the
temporary array will be the first to fill out the spaces in the listed set).
New
1
165
17
237
List
2
149
18
403
Old List
1
2
3
157
19
181
4
52
20
155
5
68
21
236
6
323
22
213
7
331
23
125
8
221
24
96
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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165
17
237
149
18
403
Temporary
1
2
181 155
17
18
157
19
52
20
68
21
323
22
331
23
221
24
229
25
124
26
133
27
141
28
268
29
395
30
28
31
36
32
List
3
236
19
4
213
20
5
125
21
6
96
22
7
8
9
10
11
12
13
14
15
16
23
24
25
26
27
28
29
30
31
32
5
68
21
236
6
323
22
213
7
331
23
125
8
221
24
96
9
229
25
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
5
68
21
155
6
323
22
236
7
331
23
213
8
221
24
125
9
229
25
96
10
124
26
11
133
27
12
141
28
13
268
29
14
395
30
15
28
31
16
36
32
COMPARISON - PASS
Theoretical
1
2
165 149
17
18
237 403
New List
3
4
157 52
19
20
181 155
Measured List
1
2
3
165 149 157
17
18
19
237 403 403
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4
52
20
181
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22. Appendix C: Parameter Recommendations for 3G to 2G
Reselection
Parameter Name
qQualMin
sRatSearch
qRxLevMin
maxTxPowerUl
sHcsRat
qHyst1
qoffset1sn
qoffset1sn
treselection
T-Mobile USA, INC. Confidential
Object
Name
UtranCell
UtranCell
ExternalGsmCell
ExternalGsmCell
UtranCell
UtranCell
UtranRelation
GsmRelation
UtranCell
Rev. 0.6
Recommended
Value
-18 dB
4
-105 dBm
24 dBm
3 dB
4
0
7
2s
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23. Appendix D: Parameter Recommendations for 3G to 2G
Handover/Cell Change
This section lists the recommended values for the IRAT 3G to 2G Handover for an Ericsson
3G RAN. The parameter values presented here are based on Ericsson recommendations.
These values will be updated when more testing is done on the IRAT feature.

Values for parameters independent of handover
scenarios
Parameter Name
Recommended
Value
Object Name
C_GsmHoAllowed
Hard Coded Value
Allowed
defaultHoType
WcdmaCarrier
Gsm-Preferred
FddGsmHoSupp
Handover
True
filterCoeff6
UeMeasControl
3
filtercoefficient2
UeMeasControl
2
gsmAmountPropRepeat
Handover
4
gsmFilterCoefficient3
UeMeasControl
1
gsmPropRepeatInterval
Handover
5
gsmThresh3a
UeMeasControl
-95 dBm
hoType
UtranCell
Gsm-Preferred
hysteresis2d
UeMeasControl
0 dB
hysteresis2f
UeMeasControl
0 dB
hysteresis3a
UeMeasControl
0 dB
individual offset
ExternalGsmCell
0
maxGsmMonSubset
Handover
32
T_RELOC_prep
Hard Coded Value
10 s
timeToTrigger2dEcno
UeMeasControl
320 ms
timeToTrigger2fEcno
UeMeasControl
1280 ms
timeToTrigger2dRscp
UeMeasControl
320 ms
timeToTrigger2fRscp
UeMeasControl
1280 ms
timeToTrigger3a
UeMeasControl
100 ms
timeToTrigger6d
UeMeasControl
320 ms
timeTrigg6b
UeMeasControl
640 ms
txPowerConnQualMonEnabled
UeMeasControl
True
ueTxPowerThresh6b
UeMeasControl
18 dBm
usedFreqRelThresh2fEcno
UeMeasControl
3 dB
usedFreqRelThresh2fRscp
UeMeasControl
3 dB
usedFreqThresh2dEcnoDrnc
UeMeasControl
-13 dB
usedFreqThresh2dRscpDrnc
UeMeasControl
-102 dBm
usedFreqW2d
UeMeasControl
0
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usedFreqW2f
UeMeasControl
0
utranFilterCoefficient3
UeMeasControl
2
utranRelThreshRscp
UeMeasControl
5 dB
utranRelThresh3aEcno
UeMeasControl
-1 dB
utranRelThresh3aRscp
UeMeasControl
-3 dB
utranW3a
UeMeasControl
0

Values for parameters based on handover scenarios
Parameter Name
Object Name
Recommended
Value for Core
Thresholds
Recommended
Value for Edge
Thresholds
usedFreqThresh2dEcno
UtranCell
-13 dB
-12 dB
usedFreqThresh2dRscp
UtranCell
-102 dBm
-98 dBm
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24. Appendix E: Parameter Recommendations for 2G to 3G
Reselection
24.1. Ericsson BSS
Parameter
Name
COEXUMTS
FDDQMIN
FDDQMINOFF
FDDQOFF
FDDRSCPMIN
QSI
Object
Name
Recommended
Value
BSC
BTS
BTS
BTS
BTS
BTS
ON
7 (-12 dB)
0 (0 dB)
0 (-infinity)
6 (-102 dBm)
7 (always)
24.2. Nokia BSS
Parameter
Name
fddQOffset (FDD)
fddQMin (FDM)
fddGprsQOffset
(GFDD)
gprsFddQMin
(GFDM)
qSearchI (QSRI)
qSearchP (QSRP)
Object
Name
Recommended
Value
BTS
BTS
N (-infinity)
-12 dB
BTS
N (-infinity)
BTS
BTS
BTS
-12 dB
7 (always)
7 (always)
24.3. Nortel BSS
Parameter Name
Object
Name
uMTSAccessMinLevel
BTS
uMTSReselectionARFCN
uMTSReselectionOffset
uMTSSearchLevel
BTS
BTS
BTS
T-Mobile USA, INC. Confidential
Rev. 0.6
Recommended
Value
-12 dB
ARFCN of UMTS
carrier
-infinity
7 (always)
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25. Appendix F: Parameter Recommendations for Channel
Switching
Parameter Name
bandwidthMargin
bandwidthMarginUl
coverageTimer
dlDownswitchBandwidthMargin
dlRlcBufUpswitch
dlRlcBufUpswitchMrab
dlThroughputAllowUpswitchThreshold
dlThroughputDownswitchTimer
downswitchPwrMargin
downswitchThreshold
downswitchTimer
downswitchTimerSp
downswitchTimerThreshold
downswitchTimerUp
hsdschInactivityTimer
inactivityTimeMultiPsInteractive
inactivityTimer
inactivityTimerPch
reportHysteresis
ulDownswitchBandwidthMargin
ulRlcBufUpswitch
ulRlcBufUpswitchMrab
ulThroughputAllowUpswitchThreshold
ulThroughputDownswitchTimer
upswitchPwrMargin
upswitchTimer
upswitchTimerUl
activeQueueMgmt
T-Mobile USA, INC. Confidential
Object Name
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
ChannelSwitching
RabHandling
Rev. 0.6
December 5, 2007
Recommended Value
90%
90%
1 sec
80%
500 bytes
500 bytes
0 % (Not used)
2 sec
1 dB
0 kBps
1 sec
10 sec
0 kBps
20 sec
2 sec
5 sec
30 sec
30 min
3 dB
80%
256 bytes
8 bytes
0 % (not used)
2 sec
3 dB
0.5 sec
0.5 sec
0 (OFF)
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26. Reference
1. 3GPP TS 25.331 V 5.19.0 “UMTS Radio Resource Control Protocol Specification”.
2. Allan Orbigo, Christophe Vidal, UMTS RF Planning and Design Guidelines
3. Alejandro Aguirre, Changbo Wen, Sireesha Panchagnula UMTS Parameter Guidelines
4. 3GPP TS 25.304 V 5.9.0 “UMTS UE Procedures in Idle Mode and Procedures for Cell
Reselection in Connected Mode”.
5. UMTS Network KPI, U12 UMTS Network KPI v6.14 080406TMO LR.doc
6. UMTS Network KPI Level 2, UMTS Network KPI Level-2_v1_20070205ERI_Updated.doc
7. UMTS RNC LCS KPI definitions and Formulas, Michael Gebretsadik
8. 3GPP TS 25.331, UMTS RRC protocol specification.
9. 3GPP TS 25.211 V 5.8.0, “UMTS Physical channels and mapping of transport channels
onto physical channels”.
10. 3GPP TS 25.413 V 5.12.0, “UTRAN Iu Interface RANAP Signaling”.
11. 3GPP TS 25.214, ”UMTS Physical Layer Procedures FDD”.
12. Ericsson Product Documentation, EN/LZN 733 0017 R4A.
13. Ericsson Product Documentation, “Guidelines for LA/RA/URA planning”
14. Ericsson Product Documentation 58/1551-AXD 105 03/1 Uen G, “Performance Statistics
RNC 3810”.
15. Nabeel Lughmani, Pradeep Singh, Tim Zhang, “Paging Performance Guidelines”.
16. Sireesha Panchagnula, “UMTS Paging Concepts”.
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