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ERICSSON WCDMA RADIO ACCESS NETWORK
RETAINABILITY &
ACCESSIBILITY
IMPROVEMENTS
 Ericsson AB 2012
The contents of this product are subject to revision without notice due to continued progress in methodology,
design and manufacturing.
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ERICSSON INTERNAL INFORMATION 1(42)
RETAINABILITY & ACCESSIBILITY IMPROVEMENTS
Revision history
Rev
Date
Description
A
2012-06-28
First version
B
2012-08-16
Editorial changes.
New sections:
- Section 3.7 – Increasing maxActiveSet
- Section 3.8 – Tuning time to trigger 1b
- Section 3.9 – Initial power at IFHO
- Section 4.3 – Enable 16 kbps and Flexible
Initial Rate Selection
- Section 4.6 – Tuning of pathloss parameter
for IFLS
- Section 4.7 – Balanced carrier strategy
- Section 5.6 – Downlink initial SIR target
Updated sections:
- Section 3.3 – Recommended power mapping
curve updated
- Section 5.2 – pO2 tuning included
- Section 5.5 – proposed change for
ulInitSirTargetLow updated
Removed section: Minimum downlink power for
R99 RABs – Removed due to very minor
improvement. Trial results are also unreliable.
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Contents
1 Introduction ....................................................................... 4
1.1
1.2
1.3
1.4
1.5
Guideline feedback ...............................................................................4
Purpose and scope ...............................................................................4
Abbreviations ........................................................................................5
Concepts ...............................................................................................6
Conventions ..........................................................................................6
2 Priority order ...................................................................... 6
2.1 Stepwise approach................................................................................6
3 Improvements in general .................................................. 8
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
Overview ...............................................................................................8
Increasing supervision timers – W12B .................................................8
Maximum downlink power for R99 RABs ...........................................12
Increased FACH1 power .....................................................................17
Improved RACH capacity ....................................................................18
Minimum downlink power for R99 RABs ............................................19
Increasing maxActiveSet.....................................................................20
Tuning of event 1b ..............................................................................21
Initial power at IFHO ...........................................................................23
4 Improvements for Multi-RAB .......................................... 24
4.1
4.2
4.3
4.4
4.5
4.6
4.7
Overview .............................................................................................24
Disable high-rate Multi-RABs ..............................................................25
Enable 16 kbps and Flexible Initial Rate Selection .............................25
Tuning of activation time .....................................................................27
Disable CQI repetition .........................................................................29
Tuning of pathloss parameter for IFLS ...............................................30
Balanced carrier strategy ....................................................................32
5 Improving radio environment ......................................... 34
5.1
5.2
5.3
5.4
5.5
5.6
5.7
Overview .............................................................................................34
Power offset ........................................................................................34
Reduce EUL max SIR target ...............................................................35
Increase EUL Transmission Target Error ...........................................36
Uplink initial SIR target ........................................................................37
Downlink initial SIR target ...................................................................38
BLER target interactive .......................................................................39
6 References ....................................................................... 42
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1
Introduction
1.1
Guideline feedback
We value your feedback!
Please rate this guideline and suggest improvements
Please help us to prioritize upcoming guidelines
Check the latest guidelines on the RAN Methods & Guidelines home page
1.2
Purpose and scope
The descriptions and recommendations in this document are valid up to the
Ericsson WCDMA W12B RAN release.
The aim of the document is to give help with parameter tuning that improves
accessibility and retainability KPIs in the network. The suggested parameter
changes are based on live network experience from one or several live networks,
where improvements have been seen after parameter changes.
Although, previous trials show improvements, the proposed parameters should
always be evaluated in the network before deployment on a larger scale. It is
not certain that there will be improvements in all networks. Usually there are
two sides of a parameter change: some aspects of the network improve, while
other aspects may get worse Therefore careful evaluation of all proposed
changes is recommended.
The document includes both parameter and system constant changes.
The network could be tuned in many different ways, depending on traffic profiles,
UE penetration etc. In this guideline it is assumed that the network traffic is
dominated by Smartphone users, i.e. Smartphone type of traffic model, many
HSPA capable UEs, etc.
Before starting to tune parameters it is recommended to make a network audit on
retainability and accessibility. This could provide a lot of valuable information to
what parameter tuning activities to do in the network. Information on how to
make an audit for accessibility and retainability can be found in the Network
Performance Optimization portal [15].
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1.3
Abbreviations
A-DCH
Associated Dedicated Channel
ACK
Acknowledgement
BLER
Block Error Rate
CPICH
Common Pilot Channel
CS
Circuit Switched
CQI
Channel Quality Indicator
DCH
Dedicated Channel
DPDCH
Dedicated Physical Data Channel
DPCCH
Dedicated Physical Control Channel
EUL
Enhanced Uplink
FACH
Forward Access Channel
GGSN
Gateway GPRS Support Node
HSDPA
High Speed Downlink Packet Access
IFHO
Inter Frequency Handover
KPI
Key Performance Indicator
LA
Location Area
NACK
Not Acknowledge
PDU
Packet Data Units
PS
Packet Switched
R99
WCDMA Release 99 (all RABs except EUL and HSDPA)
RAB
Radio Access Bearer
RA
Routing Area
RLC
Radio Link Control
RRC
Radio Resource Control
SHO
Soft Handover
SDU
Service Data Unit
SF
Spreading Factor
SGSN
Serving GPRS Support Node
SIR
Signal to Interference Ratio
SRB
Signaling Access Bearer
TTI
Transmission Time Interval
TPC
Transmit Power Control
UTRAN
Universal Terrestrial Radio Access Network
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1.4
Concepts
In this guideline the following concepts are used.
HSDPA: When only HDSPA is used in the downlink channel.
HSPA: When HSDPA is used in the downlink and EUL is used in the uplink.
1.5
Conventions
In this document, parameters are presented in bold font type and counters in
courier font type, respectively.
dchRcLostT
Timer that is started when all radio links for
a connection are lost. At time-out, the radio
connection is considered lost.
pmNoRrcReqDeniedAdmDlPwr
Number of RRC Connection Requests denied
by admission control due to lack of DL
Power.
2
Priority order
2.1
Stepwise approach
It is suggested that a stepwise approach is used when optimizing accessibility and
retainability parameters, i.e. a parameter is changed and evaluated before moving
on to the next parameter/group of parameters. In some cases it is recommended
that a group of parameters is changed on the same time since there may be
dependencies between the parameters.
Table 1 lists all parameter changes with priority order, where highest priority (1)
is expected to give largest gain in retainability and accessibility.
The parameter changes are divided into three impact areas:
•
General improvements:
this group includes improvements that will have an impact on all RABs.
•
Multi-RAB improvements:
this group includes improvements on Multi-RAB performance.
•
Radio environment:
this group includes changes that improve radio environment, in one way
or another, for example by reducing interference in uplink or downlink.
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The improved radio environment has a positive impact on accessibility
and retainability.
Table 1
Proposed parameter changes, priority and improvement area.
Prio
Impact
Parameter change
Improvement
area
Section
Comments
1
General
Increasing supervision
timers – W12B
Retainability /
Accessibility
3.2
System software is
W12B release
1
General
Maximum downlink power
for R99 RABs
Retainability
3.3
1
General
Increased FACH1 power
Accessibility
3.4
2
General
Improved RACH capacity
Accessibility
3.5
4
General
Minimum downlink power
for R99 RABs
Retainability
3.6
2
General
Increasing maxActiveSet
Retainability
3.7
2
General
Tuning of event 1b
Retainability
3.8
2
General
Initial power at IFHO
Retainability
3.9
3
Multi-RAB
Disable high-rate MultiRABs
Retainability
4.2
2
Multi-RAB
Enable 16 kbps and
Flexible Initial Rate
Selection
Retainability
4.3
3
Multi-RAB
Tuning of activation time
Retainability
4.4
4
Multi-RAB
Disable CQI repetition
Retainability
4.5
2
Multi-RAB
Tuning of pathloss
parameter for IFLS
Retainability /
Accessibility
4.6
1
Multi-RAB
Balanced carrier strategy
Retainability /
Accessibility
4.7
2
Radio
Power offset
Retainability /
Accessibility
5.2
2
Radio
Reduce EUL max SIR
target
Retainability /
Accessibility
5.3
2
Radio
Increase EUL Transmission
Target Error
Retainability /
Accessibility
5.4
2
Radio
Uplink initial SIR target
Retainability /
Accessibility
5.5
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3
Radio
Downlink initial SIR target
Retainability /
Accessibility
5.6
2
Radio
BLER target interactive
Retainability /
Accessibility
5.7
3
Improvements in general
3.1
Overview
This section describes retainability and accessibility improvements that have an
impact on both single- and Multi-RAB connections.
3.2
Increasing supervision timers – W12B
3.2.1
Improvement area
Retainability and Accessibility
3.2.2
Overview
In W12B L1 and L3 timers are operator parameters. The only system constants
that remain are the L2 RLC parameters, which already have improved default
values in W12B, and therefore do not need to be changed.
The parameters dchSynchReconfTime, dchNonSynchReconfTime and
rrcConnSetupTime are new in W12B. They replace the old parameters
tRrcActiveSetUpdate, tRrcEst1, tRrcRABEst, tRrcRABRel tRrcChSwitch3.
The recommendations presented here are valid when the feature Call ReEstablishment is OFF. Information on how to set parameters when Call ReEstablishment is ON can be found in [14].
More information (triggering conditions, use cases and state transitions) about L3
timers is found in [12].
3.2.3
Summary of changes
In Table 2 all proposed parameter changes are presented. More information about
the parameter changes can be found in the referenced sections.
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Table 2
Proposed parameter changes W12B
Target
Improvement
Area
Parameter Name
Level
Default
Value
Modified
Value
Operator/
Ericsson
Section
Retainability
T313
RNC
3s
7s
Operator
3.2.4
Retainability
dchRcLostT
RNC
5s
7s
Operator
3.2.4
Retainability
hsDschRcLostT
RNC
5s
7s
Operator
3.2.4
Retainability
Accessibility
dchSynchReconfTime
RNC
01
10 s
Operator
3.2.5
Retainability
dchNonSynchReconfTi
me
RNC
01
10 s
Operator
3.2.6
Accessibility
rrcConnSetupTime
RNC
5s
9s
Operator
3.2.7
3.2.4
UE/UTRAN Radio Link Failure
Background
Layer 1 timers for Radio Link Failure on UE and RNC side can be increased. That
way more time is allowed for the UE to be in poor radio before the radio
connection is improved again. This way the risk for dropped call is reduced.
The time for UE Radio Link Failure is calculated using parameter N313 and timer
T313. After receiving N313 (default: 100) consecutive "out of sync" indications
from layer 1, the UE starts timer T313. If T313 expires, the UE consider it as a
Radio Link Failure and goes to Idle. The total time for the UE to detect RL failure
is calculated as:
Total time UE = N313 * 10 ms + T313
UTRAN RL failure detection is controlled by the Radio Connection Supervision
(RCS) and Radio Link Set (RLS) Supervision functions. After receiving
nOutSyncInd (default: 10) consecutive frames, UTRAN starts timer rlFailureT
(default: 1s). If rlFailureT expires, the RLS function considers the connection as
out-of-sync and reports RL Failure to SRNC. When RL Failure is received on all
radio links in the connection, the SRNC starts timer dchRcLostT and when it
expires the connection is considered lost by RCS and the call is counted as
dropped. The total time for UTRAN to detect RL failure:
Total time RNC = nOutSyncInd * 10 ms + rlFailureT + dchRcLostT
For a connection that includes HSDPA, the PS part of the connection is
considered lost by the RCS when the RLS that contains the Serving HS-DSCH
cell, has been out-of-sync for a time given by the parameter hsDschRcLostT.
This means that when the hsDschRcLostT timer expires, an Iu Release will be
1 The value 0 is used to select the same behavior as in pre-W12B, in which pre-W12B system constants and hard coded values are
used.
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requested to the PS CN and when the dchRcLostT timer expires, an Iu Release
will be requested to all involved CNs.
The total time for UTRAN to detect RL failure for the serving HS-DSCH radio
link:
Total time RNC, HS = nOutSyncInd * 10 ms + rlFailureT + hsDschRcLostT
Figure 1 shows how uplink and downlink RCS interacts (with default parameters).
When the UE looses sync in the downlink it will turn off its transmitter and only
monitor downlink until in sync again. At that stage it will be the UE only that can
recover the radio link. Since the UE is turning off its transmitter there will be no
in sync detected in the uplink. To recover the radio link the UE must get in sync
on the downlink, and then start to transmit on the uplink again.
dchRcLostT
Uplink_RLS
(last RL)
No receiving in-sync indicator due to UE TX power off
starts
Uplink_RCS
System release
NOutsyncInd rlFailureT (1sec)
(10)
Out of sync Out of sync
5sec
Drop Call
Out of sync
UE goes to idle
Downlink_RCS
N313 (100)
On
T313 (3sec)
If ‘Out of synch’ detected over the last 160ms,
•‘Out of sync’ reporting is started (every frame)
•UE shall shut its transmitter off within 40 ms.
T313 timer expiry
(Dl Radio Link Failure)
UE Tx Pwr
Off
Figure 1 Interaction between uplink timer dchRLostT and downlink timer T313
(with default values).
It is important to align timers on uplink and downlink to detect RL. If for example
dchRcLostT is set to a short value it does not matter setting the timer T313 to a
long value since the call will be released when timer dchRcLostT expires. Also it
is important to set the timer dchRcLostT to longer value than T313, so that the
system does not release the call before the UE goes to idle (at expiry of T313)
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Proposed changes
UE radio link failure
Change T313 from 3 to 7 (3 s  7 s)
Total time UE = N313 * 10ms + T313 = 100 * 0.010 + 7 = 8 s
Timer T313 is a system constant and may only be changed by Ericsson personnel.
RNC radio link failure
Change dchRcLostT from 50 to 70 (5 s  7 s)
Change hsDschRcLostT from 50 to 70 (5 s  7 s)
Total time RNC = nOutSyncInd * 10 ms + rlFailureT + dchRcLostT
= 10 * 0.010 + 1 + 7 = 8.1 s
Total time RNC, HS = nOutSyncInd * 10 ms + rlFailureT + hsDschRcLostT
= 10 * 0.010 + 1 + 7 = 8.1 s
Timer dchRcLostT and timer hsDschRcLostT are operator parameters.
3.2.5
DCH to DCH synchronized configurations
Background
The timer dchSynchReconfTime is a L3 timer for supervision of all CELL_DCH
to CELL_DCH synchronized re-configurations including RAB Establishment,
RAB Release, Channel Switching and HS Serving Cell Change.
Proposed change
Change dchSynchReconfTime from 0 to 10 (use old pre-W12B timers with
default values  use timer dchSynchReconfTime with value 10 s)
3.2.6
DCH to DCH non-synchronized configurations
Background
The timer dchNonSynchReconfTime is a L3 timer for supervision of all
CELL_DCH to CELL_DCH non-synchronized re-configurations including Active
Set Update and RB Reconfiguration.
Proposed change
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Change dchNonSynchReconfTime from 0 to 10 (use old pre-W12B timers
with default values  use timer dchNonSynchReconfTime with value 10 s)
3.2.7
RRC connection setup
Background
The timer rrcConnSetupTime is a L3 timer value for supervision for the RRC
Connection Setup procedure.
Proposed change
Change rrcConnSetupTime from 5 to 9 (5 s  9 s)
3.2.8
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
UL RSSI
•
Mac-HS Throughput
Counter formulas can be found in [7] and [8].
3.3
Maximum downlink power for R99 RABs
3.3.1
Improvement area
Retainability
3.3.2
Background
Improving DL power mapping curve
By using the parameters minimumRate, minPwrMax, interRate,
interPwrMax, maxRate and maxPwrMax the so called DL power mapping
curve is made up. The parameters decide three points on the curve giving the
maximum transmission power (relative CPICH power) for corresponding rate [1].
Between these points the maximum transmission power is interpolated, see Figure
2.
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Relative radio link power
1590
7760
40690
maxPwrMax
48
interPwrMax
38
minPwrMax
0
minimumRate
maxRate
interRate
Figure 2
Maximum RL rate
Downlink power mapping curve with default parameter values.
It has been seen in field trials that the DL power mapping curve can be improved,
both from a Speech retainability and from a DL power consumption point of
view. This is accomplished by increasing Speech power, but decreasing power for
all other R99 RABs. For pedagogical reasons the improvement is described in
four steps (Step 1 – Step 4) below. Please note that the only recommended setting
is the one described in Section 3.3.3. All other solutions are sub-optimized.
Step 1 – increasing Speech power
It has been seen in various field trials that a very efficient way to improve Speech
retainability is to increase minPwrMax. This increases maximum transmission
power for all radio links with a transmission rate up to minimumRate (default
15.9 kbps). More power can be used if the radio link gets poor and the call can be
maintained longer, thus improving retainability. Field trials have been done
increasing minPwrMax from 0 dB up to 3 dB with very good improvements on
Speech retainability, see Figure 3.
Relative radio link power
1590
7760
40690
maxPwrMax
48
interPwrMax
minPwrMax
38
30
20
0
minimumRate
maxRate
interRate
Figure 3
dB).
Maximum RL rate
Downlink power mapping with increased minPwrMax (from 0 dB to 3
Step 2 – bringing back A-DCH power to default
This change, however, is only recommended if the HSDPA traffic is very limited
and if the cells have a lot of capacity left in terms of power, otherwise this change
may result in power blocking. For cells with high HSDPA load (many HSDPA
users) the A-DCH power can constitute of a large part of the used downlink
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power. In these cases it is not wanted to increase minPwrMax, since this will not
only increase the possible power for Speech, but also for A-DCH (radio link rate
= 3.7 kbps) [1]. Instead it is suggested to move the minimumRate point to
3.7 kbps, interRate point to 15.9 kbps and use the interRate point to increase
maximum transmission power for Speech. This way it is possible to use more
power for Speech while A-DCH is kept the same, see Figure 4.
Relative radio link power
1590
370
7760
40690
maxPwrMax
48
interPwrMax
minPwrMax
38
30
0
ADCH power kept at 0 dB
minimumRate
maxRate
interRate
Maximum RL rate
Figure 4 The power control curve is changes by moving the point for
minimumRate and interRate. This way the maximum A-DCH power can be kept
the same.
Step 3 – lowering power for high-rate R99
As seen in Figure 4 the maximum transmission power for interactive R99 RABs is
also somewhat lowered by this change. This is good from a HSDPA performance
view, since this leads to less consumed non-HS power leaving more power for
HSDPA. To further improve HSDPA performance is possible to lower the
maximum transmission power for maxRate from 4.8 dB to 3 dB. This will lead to
even lower non-HS power consumption, see Figure 5. The drawback with this
solution is that DL coverage is reduced for R99 high rate bearers. However, this is
normally not any issue in Smartphone dense networks with a high number of
HSDPA users. In these networks high R99 rates are not really wanted at all since
they are very expensive from a DL power point of view – it is much more
efficient to send data on HSDPA. For high capacity networks it is recommended
to limit the number of high rate R99, or even switched off them completely [3].
Relative radio link power
1590
370
7760
40690
maxPwrMax
48
interPwrMax
minPwrMax
38
30
R99 interactive power lowered for high rates
minimumRate
interRate
maxRate
0
Maximum RL rate
Figure 5 The maximum power for R99 interactive can be further lowered to
improve HSDPA performance.
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Step 4 – lowering power for A-DCH
Another step in further improving the HSDPA performance is to lower the
possible transmission power for A-DCH. Since there can be a large number
HSDPA users in a cell, each one having one A-DCH consuming non-HS power, it
can lead to quite good improvements in available HSDPA power. Field trials have
indicated that it is possible to lower maximum A-DCH power from 0 dB to 1.5 dB without any KPI degradation, see Figure 6.
Relative radio link power
370
40690
1590
48
maxPwrMax
30
interPwrMax
20
0
minPwrMax
ADCH power lowered 1.5dB
minimumRate
interRate
-15
maxRate
Maximum RL rate
Figure 6 A-DCH power consumption can be lowered by changing minPwrMax
from 0 dB to -1.5 dB.
Recommended solution
Finally, the retainability can be improved for lower Speech AMR rates also. This
can be done by using the same power for all Speech AMR rates. The interRate
point is moved from 15.9 kbps (Speech 12.2 kbps) to 8.45 kbps (Speech AMR
4.75 kbps), see Figure 7.
Figure 7 The power control curve is adapted to also give retainability
improvements for Speech AMR 4.75 kbps (and all other higher Speech AMR
rates.
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This will result in improved retainability for all AMR rates.
The change can be done even though no low rate Speech AMR is used in the
network. There are no other RABs with radio link rates between 3.7 kbps (ADCH) and 15.9 kbps (Speech 12.2 kbps), meaning that no extra power is
consumed if no lower AMR rates are used.
The following Radio Link Rates are used by lower rate Speech AMR:
• 8450 bps for Speech AMR 4.75 kbps
• 9600 bps for Speech AMR 5.9 kbps
• 11650 bps for Speech AMR 7.95 kbps
3.3.3
Proposed change
Do following changes:
a) minimumRate from 1590 to 370 (15.9 kbps  3.7 kbps)
b) minPwrMax from 0 to -15 (0 dB  -1.5 dB)
c) interRate from 7760 to 845 (77.6 kbps  8.45 kbps)
d) interPwrMax from 38 to 30 (3.8 dB  3 dB)
e) maxPwrMax from 48 to 30 (4.8 dB  3 dB)
If the network contains many R99 devices and if the operator wants to prioritize
high-rate R99 bearers, it is possible to change above parameter setting with
maxPwrMax = 48 (4.8dB) so that power is not reduced for higher R99 rates.
Please note that the recommended solution is only valid if CPICH power is set
according to recommendations (at least 5% of total power) [6]. If CPICH power is
set lower than this, tuning is needed of the above recommended parameters.
3.3.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
Mac-HS Throughput
Counter formulas can be found in [7] and [8].
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3.4
Increased FACH1 power
3.4.1
Improvement area
Accessibility
3.4.2
Background
FACH1 is used to carry control information (Broadcast Control Channel (BCCH),
Common Control Channel (CCCH) or Dedicated Control Channel (DCCH)) to
the UEs in the cell [6].
It has been seen in field that both PS and CS accessibility can be improved by
increasing FACH1 power from default (1.8 dB relative CPICH). FACH1 power is
changed with the parameter maxFach1Power.
If the UE is in Idle Mode and trying to access the network, the UE sends the
RACH message: “RRC Connection Request” to the RNC to request for a
dedicated channel. The RNC checks available resources with admission control
and sends a “RRC Connection Setup” message on FACH (which carriers logical
control channel). This message gives information about the dedicated channel to
be setup, see Figure 8.
Figure 8
RRC Connection Request/Setup
By increasing the power of FACH1, the UEs will have higher probability to
receive RRC Connection Setup, as an answer to a RRC Connection Request,
especially in low coverage areas. This will lead to better Accessibility KPIs.
3.4.3
Proposed changes
Change maxFach1Power from 18 to 38 (1.8 dB  3.8 dB)
In some networks, maxFach1Power has been set to 5.3 dB relative CPICH power
with even better accessibility results. However, this setting is not recommended
for high capacity cells where downlink power may be a limited resource. It’s
recommended to change the parameter maxFach1Power in smaller steps (e.g.
1 dB steps) and balance improved accessibility against increased downlink power.
Note that FACH1 is power regulated and that the parameter maxFach1Power
only sets the maximum allowed power, i.e. even though the increase of
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maxFach1power is large, the increase in average measured non-HSDPA power
may be quite small. The increase in average non-HSDPA power depends on UE
coverage, but also on the activity on the FACH1 channel.
3.4.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
MAC-HS throughput
•
Non-HS power
•
Failures due to lack of DL power at RRC using
pmNoRrcReqDeniedAdmDlPwr and
pmNoFailedRabEstAttemptLackDlPwr
•
Overall failures at RRC, e.g. pmTotNoRrcConnectReqCs and
pmTotNoRrcConnectReqCsSucc.
•
Failures after admission measured with pmNoFailedAfterAdm.
It is expected that the number of RRC failures after admission is decreased
after increasing FACH1 power. With too low FACH1 power resources get
allocated, but FACH1 cannot complete the setup du to too low power. The
counter pmNoFailedAfterAdm is incremented when a function that has
been granted admission for a UE fails after being admitted due to a problem
in the RRC or RAB Setup procedure.
Counter formulas can be found in [7] and [8].
3.5
Improved RACH capacity
3.5.1
Improvement area
Accessibility
3.5.2
Background
With the increase of new terminals, like Smartphones, the number of PS users will
increase in the network. Due to this, more capacity is needed in CELL_DCH and
CELL_FACH.
The parameter spreadingFactor changes the spreading factor and slot format on
the RACH channel. RACH capacity is improved by changing spreadingFactor
from default 64 to 32. This changes RACH slot format from 20 ms to 10 ms,
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which reduces the risk for RACH collisions and therefore accessibility is
improved.
Value mapping:
•
SF32: TTI = 10 ms.
•
SF64: TTI = 20 ms.
Note that setting spreadingFactor = 32 may reduce RACH coverage. If this is
seen it is recommended to tune parameter powerOffsetPpm, which sets the
power level for the RACH message based on the received pre-amble power [4].
3.5.3
Proposed change
Change spreadingFactor for RACH from 64 to 32
3.5.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
Random access failure messages.
•
UL RSSI
•
MAC HS Cell throughput
•
Latency
Counter formulas can be found in [7] and [8].
3.6
Minimum downlink power for R99 RABs
3.6.1
Improvement area
Retainability
3.6.2
Background
It is recommended to keep the minimum transmitted DL radio link power not
more than 25 dB from maximum transmission power [1]. If minimum DL
transmitted code power is set to a too low level, there is the risk (depending on the
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mobile vendor) that UEs cause a sudden rush in DL power behavior. This can
result in that DL cell congestion is unnecessarily detected. The minimum
downlink power is decided by the parameter minPwrRl and is set relative
CPICH. Some live network tests have shown that this may have an impact on
retainability.
3.6.3
Proposed change
The default value for minPwrRl (-15 dB) assumes that CPICH is set to -10 dB
relative maximum downlink power (i.e. 10% of total downlink power is used for
CPICH). If lower CPICH power is used, for example 5% of total downlink power
(-13 dB), it is recommended that the parameter minPwrRl is adjusted. The
following rule should be used when tuning minPwrRl:
minPwrRl = max DL Tx Power – primaryCpichPower – 25
Example:
The maximum DL TX power is 40 dBm.
a) If primaryCpichPower is set to 30 dBm (10% of total DL Tx power), then
minPwrRl should be set to: 40 – 30 – 25 = -15 dB
b) If primaryCpichPower is set to 27 dBm (5% of total DL Tx power), then
minPwrRl should be set to: 40 – 27 – 25 = -12 dB
3.6.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
Counter formulas can be found in [8].
3.7
Increasing maxActiveSet
3.7.1
Improvement area
Retainability
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3.7.2
Background
The parameter maxActiveSet sets the maximum number of cells in active set. It
has been seen in field trials that increasing this parameter from default 3 to 4 has
had a positive impact on retainability (in particular CS retainability).
When the parameter maxActiveSet is increased it means that the soft handover
overhead increases in the network, resulting in that more resources are used in the
uplink and downlink. Therefore it is important to evaluate resource consumption
before and after the change. In particular the following resources should be
monitored: CE usage, DL code utilization, MP load in RNC and Iub load.
3.7.3
Proposed change
Change parameter maxActiveSet from 3 to 4 (3  4 radio links in active set)
3.7.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
CE usage
•
DL code utilization
•
MP load in RNC
•
Iub blocking
•
Number of 1a, 1b and 1c events
•
SHO overhead
•
Number of radio links in AS
•
Power efficiency (DL non-HS power relative to R99 Traffic)
Counter formulas can be found in [8].
3.8
Tuning of event 1b
3.8.1
Improvement area
Retainability
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3.8.2
Background
The parameter timeToTrigger1b sets the time between detection of event 1b and
sending of the measurement report [9]. When a P-CPICH, included in the Active
Set, leaves reportingRange1b - hysteresis1b/2, and the measured value is
outside reportingRange1b - hysteresis1b/2 during a time at least equal to
timeToTrigger1b, event 1b occurs. The UE sends a MEASUREMENT REPORT
message for event 1b to the SRNC, see [9].
Figure 9
Reporting 1a and 1b concepts.
It has been seen in field trials that slowing down the radio link deletion (event 1b)
may have a positive effect on retainability. If the radio link gets temporarily
shadowed, for example by buildings, it can be better to keep the radio link longer
instead of releasing it, and then adding it back (using event 1a) when the radio
conditions have improved again. When the radio link is released it will act as an
interferer until it is added back to the Active Set. This can cause dropped calls in
situations where the radio link quality changes quickly.
Note that this parameter change should only be done when maxActiveSet is set to
maximum 4. Otherwise the number of 1c events (replace) may increase too much,
see section 3.7.
3.8.3
Proposed change
Change timeToTrigger1b from 12 to 14 (640 ms  2560 ms)
Assure that maxActiveSet is set to 4
The change needs to be carefully evaluated since it may give retainability
improvements in some areas and retainability degradations in others. The
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parameter change can also be performed in smaller steps, e.g. 640 ms  1280 ms
 2560 ms.
Another way to slow down the radio link deletion is to increase the parameter
reportingRange1b (for example from 5 dB to 6 dB).
3.8.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS Call accessibility
•
CS & PS retainability
•
CS drop call reason
•
Number of radio links in AS
Counter formulas can be found in [8].
3.9
Initial power at IFHO
3.9.1
Improvement area
Retainability
3.9.2
Background
The parameter cNbifho is included in the power control algorithm for initial
power setting at inter frequency handover and CN hard handover.
The initial DPDCH power at Inter Frequency Handover is decided by the
following formula [4]:
P_DL_DPDCH = primaryCpichPower + (dlInitSirTarget – Ec/No_PCPICH) +
cNbifho + 10 log(2/SF_DL_DPDCH) [dB]
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where:
primaryCpichpower
is the downlink output power used for the PCPICH
in the target frequency cell.
dlInitSirTarget
is the required initial SIR target for the DL
DPDCH.
Ec/No_PCPICH
is the measured Ec/N0 on PCPICH in the target
frequency cell received in the UE.
SF_DL_DPDCH
is the SF for the DL DPDCH.
cNbifho
is a correction factor that takes the non-blind interfrequency handover margins into account.
Field trials have shown that by setting cNbifho to a higher value than default it is
possible to increase the reliability of the inter-frequency handover, thus reducing
the number of dropped calls caused by unsuccessful inter-frequency attempts.
3.9.3
Proposed change
Change cNbifho from 10 to 15 (1 dB  1.5 dB)
3.9.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS retainability
•
DL power utilization
•
Inter Frequency Handover success ratio
Counter formulas can be found in [7] and [8].
4
Improvements for Multi-RAB
4.1
Overview
This section describes retainability and accessibility improvements that have an
impact mainly on Multi-RAB connections.
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4.2
Disable high-rate Multi-RABs
4.2.1
Improvement area
Retainability
4.2.2
Background
Field trials have shown that Multi-RAB drops constitute a large portion of the
total dropped Speech calls in a network. It has been seen that the drop call rate on
Multi-RAB can be several times larger than a single Speech RAB. The main
reasons for this are:
•
Multi-RABs with low SF on UL are less UL SRB protected, resulting in
higher call drop probability in poor radio conditions.
•
A high number of Multi-RAB states increase the probability of drop call
due to many radio bearer transitions.
The proposed change has shown good retainability improvement in field.
4.2.3
Proposed change
Deactivate all multi-RAB combinations with an uplink rate larger
than 64 kbps
Deactivation is done by disabling corresponding UeRc.
4.2.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
MAC-HS throughput
Counter formulas can be found in [7] and [8].
4.3
Enable 16 kbps and Flexible Initial Rate Selection
4.3.1
Improvement area
Retainability
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4.3.2
Background
As discussed in section 4.2 one reason for increased drop call rate for multi-RAB
is the use of low SF and a high number of transitions between multi-RAB states.
In order to lower SF even more for multi-RABs it is recommended to enable
UeRc 113: Speech + 16/HS. This will increase the UL SRB protection compared
to using Speech + 64/HS due to lower data rate. To reduce the number of
transitions on multi-RAB it is recommended to enable the feature Flexible Initial
Rate Selection, and use 16 kbps as preferred rate for both UL and DL. Typically a
large portion of the Smartphone traffic consists of background traffic, with small
amounts of sent/received data. This means that the UE is often downswitched to
16 kbps if not used as preferred rate, increasing the number of transitions and the
risk for dropped call. In fact, when analyzing the drop call reason for multi-RAB
in some live networks, one of the most common drops due to channel switching is
the reconfiguration from Speech + 64/HS to Speech + 16/HS, most probably short
after RAB establishment. Therefore in these cases Flexible Initial Rate Selection
would allow to establish on Speech + 16/HS directly, removing the channel
switch from 64 kbps to 16 kbps and therefore reducing the drop call rate.
4.3.3
Proposed change
Enable UeRc 113: Speech + 16/HS
Enable feature: Flexible Initial Rate Selection
Change rateSelectionPsInteractive.ulPrefRate from 64 to 16
(64 kbps  16 kbps)
Change rateSelectionPsInteractive.dlPrefRate from 64 to 16
(64 kbps  16 kbps)
Another option is to establish on FACH directly by using the feature Dynamic PS
I/B RAB Establishment. This reduces code and power utilization dramatically, but
increases latency. It is recommended to use initial allocation on FACH only in
extremely busy cells and only on a temporarily basis. RACH is more sensitive to
noise rise than DCH, so PS retainability degrades with high uplink noise rise.
4.3.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
Counter formulas can be found in [8].
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4.4
Tuning of activation time
4.4.1
Improvement area
Retainability
4.4.2
Background
The activation time for a new radio link is decided by a Connection Frame
Number (CFN) and is calculated by the system. The CFN when the
reconfiguration should be done is calculated based on a number of factors, like
message length, RLC retransmissions etc. [2].
When switching between different RAB combinations and setting the activation
time (decided by CFN), it is possible to add an extra margin to the calculated
value by the parameter cfnOffsetMarginSrbDchDl when the SRB is on DCH
DL. The CFN offset (Δ CFN) is then calculated as:
Δ CFN = calculated value + cfnOffsetMarginSrbDchDl
If the CFN offset is not long enough the RBS will change configuration before the
UE and the UE will loose sync and there is a risk for dropped call. On the other
hand setting the CFN offset too long may also cause dropped calls.
Figure 10 shows how the parameter cfnOffsetMarginSrbDchDl is used when
reconfiguring radio link:
•
The RNC informs the RBS that the existing radio link needs to be
reconfigured by sending a Radio Link Reconfigurations Prepare message.
•
The RBS responds with a Radio Link Reconfiguration Ready message, but
waits with changing the radio link.
•
When resources have been allocated in the RNC a Radio Link Commit
Message is sent to the RBS. This message contains the CFN at which the
radio link should be changed. Enough margin must be applied on the
current CFN so that there is time to send the Radio Bearer Setup message to
the UE and for the UE to change radio link configuration. The margin, Δ
CFN is decided by the calculated value + cfnOffsetMarginSrbDchDl.
•
The UE sends a Radio Bearer Setup Complete message to the RNC
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UE
RBS
RNC
Reconf. Prepare
Reconf. Ready
Current CFN
Reconf. Commit
r Setup
Radio Beare
Δ CFN
Activation CFN
Margin so that reconfiguration can be done in UE and RBS
at the same time
Radio Bearer
Set
up Complete
Figure 10 Reconfiguration of a radio link
4.4.3
Proposed change
Change cfnOffsetMarginSrbDchDl from 40 to 80 (40 frames  80 frames)
Field trials have shown good improvement on CS retainability by doing this
change. No other negative KPI impacts have been observed.
One frame equals 10 ms, meaning that the activation time is prolonged 400 ms by
this change.
Please note that this change is not needed in networks with long TN delays, for
example when Iub over satellite is used.
4.4.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
Latency for PS
Counter formulas can be found in [7] and [8].
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4.5
Disable CQI repetition
4.5.1
Improvement area
Retainability
4.5.2
Background
The RBS can initiate updates of the CQI Repetition Factor, CQI Feedback Cycle
and ACK/NACK Repetition Factors, see [4]. The parameter updates are initiated
by the CQI reception performance.
CQI Repetition Factor, CQI Feedback Cycle and ACK/NACK Repetition Factors
are:
•
Increased if the number of consecutive CQI errors > cqiErrors.
•
Reduced if no CQI errors for at least cqiErrorsAbsent consecutive CQI
reports.
The update of CQI Repetition Factor, CQI Feedback cycle and ACK/NACK
repetition factors are timer supervised physical channel reconfiguration
procedures (hardcoded Layer 3 timer). If the timer times out the call is dropped,
which is typical if the UE is in poor radio. This is a reason to disable CQI
repetition.
The RBS triggered updates can be turned off by setting the parameters cqiErrors
and cqiErrorsAbsent to 0.
Note that there is a dependency to the parameters initialCqiRepetitionFactor and
initialAcknackRepetitionFactor, which sets the initial number for CQI and
ACK/NACK repetitions. If CQI repetition is turned OFF, the number of
CQI/ACK/NACK messages will always be the same as set by parameters
initialCqiRepetitionFactor and initialAcknackRepetitionFactor (since the
RBS can not update the values). Normally there is no reason to use initial
repetition. Therefore it is recommended to use default 1 for
initialCqiRepetitionFactor and initialAcknackRepetitionFactor.
4.5.3
Proposed changes
Change cqiErrors from 10 to 0
(10 consecutive CQI errors  RBS triggered updates turned off)
Change cqiErrorsAbsent from 10 to 0
(10 consecutive CQI reports with no errors  RBS triggered updates turned off)
Assure that initialCqiRepetitionFactor and initialAcknackRepetitionFactor
are set to 1 (default value)
Only UeRcs containing HS-DSCH are affected by the change
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The reconfiguration procedure is only triggered if HS-DPCCH performance
becomes bad, meaning that the impact of the parameter change may differ
between cells depending on radio quality.
Field trials have shown quite small improvement from this change.
4.5.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
UL RSSI
•
MAC HS Cell throughput
•
EUL HARQ retransmission rate
•
Latency for PS
Counter formulas can be found in [7] and [8].
4.6
Tuning of pathloss parameter for IFLS
4.6.1
Improvement area
Retainability and Accessibility
4.6.2
Background
When going from single RAB Speech to multi-RAB Speech + HS, the set up of
HSDPA may trigger HSDPA Inter-frequency Load Sharing (IFLS) and change of
serving cell. This may cause dropped calls, especially if the IFLS attempt is made
close to the cell border in mobility situations. It has also turned out that one of the
main reasons for garbled speech is failed IFLS.
To reduce the probability for dropped calls it is recommended to tune pathloss
parameters so that a safety margin is introduced towards making IFLS too close to
cell border. The parameter tuning depends on which system release is used:
•
Pre W12B: tune parameter pathlossThreshold so that IFLS is only
attempted when not close to cell border.
•
W12B: disable IFLS for multi-RAB by setting parameter
hsIflsSpeechMultiRabTrigg to 0 (OFF). The parameter
hsPathlossThreshold is tuned to only do IFLS attempts for single RAB
HS when not close to cell borders. Both above parameters are coming in
W12B.
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Please note that pathlossThreshold and hsPathlossThreshold are only checked
during RAB-establishment, and not during upswitch from FACH and URA. This
means that the impact from pathlossThreshold and hsPathlossThreshold tuning
may be less evident on accessibility and retainability KPIs when URA is enabled,
since there will be fewer transitions to Idle state (which is the only state from
where the path loss is checked when establishing a new connection).
Pre W12B
A path loss check is made against the parameter pathlossThreshold at the
following occasions [10]:
•
HS Cell Selection
•
HSDPA Inter-Frequency Load Sharing
•
Non- HSDPA Inter-Frequency Load Sharing
The path loss measurements are based on CPICH power and UE RSCP
measurements and decide whether a blind IFHO is allowed or not. The intention
with the parameter is to avoid changing cell on calls with poor radio quality, since
it may increase the probability for failed cell change attempts and dropped calls.
The pathlossThreshold is most critical at cell borders in mobility situations when
the UE moves from one cell in to another. A call may be dropped if a blind IFHO
is attempted and during the attempt the UE moves into a neighboring cell. In that
case the UE will try to make a blind IFHO to a cell that is no longer the best from
a radio perspective, resulting in a failed IFHO. When the UE then tries to go back
to the originating cell, best cell have changed and the call is dropped.
Ideally the pathlossThreshold value should be calculated from measured or
estimated cell border RSCP values, CPICH power at TX reference and a safety
margin, S:
pathlossThreshold = PCPICH, TXref – RSCPcellBorder – S
The safety margin S is used to back-off the possibility to make blind IFHO from
the cell border. Recommended value for S is 10 dB.
If for example CPICH power at TX reference point is 30 dBm and RSCP at cell
border is -100 dBm, the value to use for pathlossThreshold is calculated as:
pathlossThreshold = PCPICH, TXref – RSCPcellBorder – S = 30 – (-100) – 10 = 120 dB
If no measured or estimated cell border RSCP values are available,
pathlossThreshold can be lowered to around 120 – 130 dB. This has shown
positive effect on retainability at live field trials.
W12B
In W12B it is possible to deactivate triggering of HS IFLS when a HS connection
is added to a Speech connection. This is done with the parameter
hsIflsSpeechMultiRabTrigg. It is recommended to set
hsIflsSpeechMultiRabTrigg to 0 (OFF) to improve Speech retainability since
from a Speech drop rate perspective it is better to finish the Speech call in one
carrier before considering IFHO for the HS part.
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Even though multi-RAB IFHO is disabled with the parameter
hsIflsSpeechMultiRabTrigg, a tuned path loss check can be used for improving
retainability for single RAB HS, and for improving accessibility for both R99 and
HS (due to larger share of successful IFHO attempts). It is therefore
recommended to do similar tuning as in pre W12B. In W12B the pathloss
threshold can be configured per coverage relation using the parameter
hsPathlossThreshold [11]. It is recommended to lower hsPathlossThreshold
and pathlossThreshold from 170 to around 120 – 130 dB. Note that for a HS
connection the system will limit IFHO to the pathloss decided by the minimum of
parameters hsPathlossThreshold and pathlossThreshold. If pathlossThreshold
is set to a smaller value than hsPathlossThreshold IFHO will never be limited
hsPathlossThreshold.
4.6.3
Proposed change
Pre W12B: change pathlossThreshold from 170 to 120 – 130
(170 dB  120 – 130 dB)
W12B: change hsIflsSpeechMultiRabTrigg from 1 to 0 (ON to OFF)
Change hsPathlossThreshold and pathlossThreshold from 170 to 120 – 130
(170 dB  120 – 130 dB)
4.6.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
IFLS (at RRC) performance
•
HS Cell Selection performance
•
HSDPA IFLS performance
•
Non-HSDPA IFLS performance
Counter formulas can be found in [7], [8] and [10].
4.7
Balanced carrier strategy
4.7.1
Improvement area
Retainability and Accessibility
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4.7.2
Background
It is recommended to use equal idle mode distribution, balanced HSDPA Inter
Frequency Load Sharing and as much as possible have equal capabilities (HS and
EUL) on the carriers [10]. Field trials have shown that this may have a large
impact on multi-RAB retainability.
Balancing the load between the carriers as much as possible, both in idle mode
and connected mode, means less blind Inter Frequency Handovers. This reduces
the risk for dropped calls, especially in cell border areas, see also Section 4.6.
The initial traffic balancing is performed by cell reselection in idle mode, FACH
and URA using qOffset and possibly priority from Hierarchical Cell Structure
(HCS). During RAB establishment, HSDPA IFLS and non-HSDPA IFLS blind
IFHO can be triggered if the load is unbalanced between carriers. The trigger for
HSDPA IFLS is based on UE and carrier capability and number of HSDPA users.
The trigger for non-HSDPA IFLS are R99 downlink power and R99 code
utilization.
4.7.3
Proposed change
Use:
a) Equal idle mode distribution
b) Balanced HSDPA Inter Frequency Load Sharing
c) Equal capabilities on the carriers
4.7.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
IFLS (at RRC) performance
•
HS Cell Selection performance
•
HSDPA IFLS performance
•
Non-HSPA IFLS performance
Counter formulas can be found in [7], [8] and [10].
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5
Improving radio environment
5.1
Overview
This section includes recommendations on how to improve the radio environment.
An improvement of the radio environment (lower interference in uplink and
downlink) is beneficial from a retainability and accessibility perspective.
5.2
Power offset
5.2.1
Improvement area
Retainability and Accessibility
5.2.2
Background
The parameter pO3 sets the power offset between pilot bits and data bits in the
downlink. The parameter pO2 sets the power offset between TPC bits and data
bits in the downlink [4].
It has been seen in previous field trials that tuning these parameter has a very
positive effects on used A-DCH power in the downlink. The A-DCH power can
be substantial in cells with many HSDPA users [3]. The change improves HSDPA
performance since less non-HS power is used in the downlink. The reduced power
consumption also has a positive effect on downlink interference, i.e. downlink
interference is lowered resulting in better retainability and accessibility KPIs, see
Figure 11.
Data bits DPCCH
PO2: Power offset on TPC bits
TPC bits DPCCH
PO3: Power offset on Pilot bits
Pilot bits
PO2
PO3
Default: Slot format 4, PO3 = 3dB
Slot format 4, PO3 = 0dB
PO2 = 1.5dB
Figure 11 A-DCH power is reduced by reducing pO2 and pO3.
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5.2.3
Proposed change
Change pO3 to 0 (0 dB)
Change pO2 from 12 to 6 (3 dB  1.5 dB)
5.2.4
Observability
To evaluate the impact of the changes on parameter pO3, the following should be
monitored:
•
CS & PS accessibility, EUL accessibility
•
CS & PS retainability, EUL retainability
•
Non-HS power
•
HSDPA user- and cell throughput
Counter formulas can be found in [7] and [8].
5.3
Reduce EUL max SIR target
5.3.1
Improvement area
Retainability and Accessibility
5.3.2
Background
The uplink SIR is limited by sirMax for EUL 10 ms users and by sirMaxTti2 for
EUL 2 ms users. It is recommended to tune in particular sirMaxTti2 since it has
been seen in field that the default value is too high and may cause instability
problems and high noise rise peaks. Tuned values will result in lower RSSI,
which in turn will have a positive effect on retainability for all RABs.
Proposed Change
Normal operation: change sirMaxTti2 from 173 to 120 (17.3 dB  12 dB)
High capacity: change sirMaxTti2 from 173 to 80 (17.3 dB  8 dB)
Ensure that sirMax is set to 100 (10 dB)
The 17.3 dB setting for sirMaxTti2 is too high even for single user peak rate
demos, where 14 dB is a more suitable value. For normal network operation
12 dB is a well balanced value (between capacity and peak rate). In high capacity
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cells with many EUL users sirMaxTti2 can be lowered to 8 dB to ensure that
noise rise is kept well in bounds.
For EUL 10 ms it is recommended to use sirMax 10 dB, both with and without
EUL. For high capacity cells when UL 384 kbps and UL 128 kbps are disabled it
may be possible to lower sirMax even further.
5.3.3
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility, EUL accessibility
•
CS & PS retainability, EUL retainability
•
UL RSSI
•
HSDPA & EUL cell throughput
Counter formulas can be found in [7] and [8].
5.4
Increase EUL Transmission Target Error
5.4.1
Improvement area
Retainability and Accessibility
5.4.2
Background
Uplink outer loop power control regulates the SIR target for EUL and is steered
by the Transmission Target Error, which sets the quality of the radio link in terms
of HARQ retransmissions [4].
Transmission target error is controlled by the parameters
transmissionTargetError for EUL 10ms users and
transmissionTargetErrorTtti2 for EUL 2ms users.
It has been seen in field trials that it is beneficial from an uplink interference and
EUL throughput perspective to increase TTE in the cell if there are more than 4 –
5 EUL users in the cell. The only negative impact is lower EUL peak rate [3]. The
lower uplink interference has a positive effect on retainability.
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5.4.3
Proposed change
Change transmissionTargetError from 10 to 100 (1%  10%)
Change transmissionTargetErrorTti2 from 20 to 50 (2%  5%)
For high capacity networks with many EUL 2ms users it is also possible to set
transmissionTargetErrorTti2 to 100 (10%).
5.4.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility, EUL accessibility
•
CS & PS retainability, EUL retainability
•
UL RSSI
•
HSDPA & EUL cell throughput
•
EUL HARQ retransmission rate
•
Latency for PS
Counter formulas can be found in [7] and [8].
5.5
Uplink initial SIR target
5.5.1
Improvement area
Retainability and Accessibility
5.5.2
Background
It has been seen in field trials that initial SIR target has a significant impact on
uplink interference, especially in highly loaded cells [3]. Lowering uplink
interference has a positive effect on retainability and accessibility.
The initial SIR target is set with the parameters:
•
ulInitSirTargetSrb for standalone SRB
•
ulInitSirTargetLow for RABs having SF ≥ 32
•
ulInitSirTargetHigh for RABs having SF = 16 or 8
•
ulInitSirTargetExtraHigh for RABs having SF ≤ 4
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5.5.3
Proposed changes
Change ulInitSirTargetSrb to 30 (3 dB)
Change ulInitSirTargetLow to 20 (2 dB)
Change ulInitSirTargetHigh to 70 (7 dB)
Change ulInitSirTargetExtraHigh to 70 (7 dB)
This setting is recommended for high capacity networks.
5.5.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
UL RSSI
Counter formulas can be found in [7] and [8].
5.6
Downlink initial SIR target
5.6.1
Improvement area
Retainability and Accessibility
5.6.2
Background
Downlink interference can be reduced by tuning the parameter dlInitSirTarget.
Field trials have shown that the dlInitSirTarget may be to large (depending on
network) and that excessive power is transmitted in the downlink at the start of
transmission.
The initial downlink DPDCH power depends on measured Ec/N0, Spreading
Factor, CPICH power, the parameter dlInitSirTarget and a backoff factor [4]. By
lowering dlInitSirTarget it is possible to lower downlink power and by that way
lower downlink interference.
5.6.3
Proposed change
Change dlInitSirTarget from 41 to 20 (4.1 dB  2 dB)
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5.6.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
•
CS & PS accessibility
•
CS & PS retainability
•
Power blocking and non-HS power consumption
•
HSDPA throughput
•
Mobility (SHO, IFHO) performance
•
DL BLER
Counter formulas can be found in [7] and [8].
5.7
BLER target interactive
5.7.1
Improvement area
Retainability and Accessibility
5.7.2
Background
Power control ensures that an agreed quality is kept on the connection in terms of
Block Error Rate (BLER). By adjusting BLER target it is possible to control
transmitted power on uplink and downlink.
It has been seen in field trials that it is possible to increase BLER target for
interactive RABs to reduce the transmitted power on uplink and downlink. This
has resulted in improved RSSI in uplink and lower power consumption in
downlink. The result has been seen in field as improved accessibility in downlink
due to less power blocking at admission. The parameter change also improves
capacity in uplink and downlink [3].
BLER is set with the following parameters:
•
blerQualityTargetUl for UL BLER
•
blerQualityTargetDl for DL BLER
The parameters are set per UeRc and Transport Channel (UeRcTrCh) and are
expressed as: 10*log(blerQualityTarget). For example setting the parameter
blerQualityTargetUl to -20 will result in a UL BLER target of 1% (-20 =
10*log(0.01)). Similarly setting blerQualityTargetUl to -13 will result in 5% UL
BLER
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RETAINABILITY & ACCESSIBILITY IMPROVEMENTS
5.7.3
Proposed change
For PS interactive RABs change:
blerQualityTargetUl and blerQualityTargetDl from 1% to 5%
The BLER targets should be adjusted on the uplink and downlink for single PS
DCH RABs (both SRB and DCH transport channels).
For HSDPA RABs field trials have shown that it is possible to change BLER
target for ADCH from 0.1% to 1%, and in some cases all the way to 5% with
positive effect on consumed downlink power (especially in cells with many
HSDPA users). No negative impact has been seen in KPIs, although for HSDPA
RABs it is recommended to do the change in steps (0.1%  1%  5%) while
closely monitoring HSDPA retainability.
For Multi-RABs the BLER target is adjusted on the PS DCH transport channel
only. BLER target should not be changed for SRB in this case since it may have a
negative effect on Speech retainability.
The parameter changes are summarized in Table 3.
Table 3
Summary of changes on blerQualityTargetUl and
blerQualityTargetDl.
RAB
TrCh
blerQualityTargetUl
blerQualityTargetDl
PS DCH/DCH
SRB
1%  5%
1%  5%
PS DCH
1%  5%
1%  5%
SRB
1%  5%
0.1%  1%  5%
PS DCH
1%  5%
–
SRB
–
0.1%  1%  5%
PS DCH
–
–
SRB
–
–
PS DCH
1%  5%
1%  5%
SRB
–
–
PS DCH
1%  5%
–
PS DCH/HS
PS EUL/HS
Multi-RABs Speech + PS DCH/DCH
Multi-RABs Speech + PS DCH/HS
In total there are more than 130 parameter changes involved, see [13] for all
details.
5.7.4
Observability
To evaluate the impact of the parameter changes the following KPIs should be
monitored:
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•
CS & PS accessibility
•
CS & PS retainability
•
RRC & RAB power blocking
•
UL RSSI
•
Latency for PS
Counter formulas can be found in [7] and [8].
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6
References
1. User Description, Capacity Management, 83/1553-HSD 101 02
2. User Description, Connection Handling, 4/1553-HSD 101 02
3. High Capacity RN parameter tuning, 3/100 56-HSD 101 02
4. User Description, Power Control, 80/1553-HSD 101 02
5. User Description, LA, RA and URA Planning, 2/100 56-HSD 101 02
6. Common Control Channel Guideline, 63/100 56-HSD 101 02/6
7. Guideline for HSPA Performance Indicators, 33/100 56-HSD 101 02/10
8. User Description, Radio Network KPI, 120/1553-HSD 101 02
9. User Description, Handover, 76/1553-HSD 101 02
10. User Description, Additional WCDMA Carrier Deployment, 148/100 56-HSD
101 02
11. User Description, Load Sharing, 3/1553-HSD 101 02
12. User Description, WCDMA RAN W12.1 Network Impact Report, 6/109 48HSD 101 02
13. Excel document: BLER target interactive.xls, EAB/FJW-12:1091
14. Feature Trial Instruction - Call Re-establishment, EAB/FJW-12:1068
15. Network Performance Optimization portal,
http://internal.ericsson.com/page/hub_globalservices/products/delivery/npo/in
dex.jsp?unit=BNET
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