Product Name
Confidentiality Level
LTE
CONFIDENTIAL
Product Version
Total 34 pages
eRAN
LTE KPI Improvement Solution User
Guide
Prepared By
Jian Bin
Date
Reviewed By
Date
Reviewed By
Date
Approved By
Date
Huawei Technologies Co., Ltd.
All rights reserved
2016-12-30
LTE KPI Improvement Solution User Guide
CONFIDENTIAL
About This Document
Change History
Date
Issue
Change Description
Author
2015-05-24
1.0
Completed the draft.
Jian Bin
2015-07-10
1.1
Jian Bin
2015-08-12
1.1
2015-11-06
1.3
2015-12-28
1.4
Corrected some incorrect
descriptions.
Corrected some incorrect
descriptions.
Updated solutions
according to eRAN11.1.
Updated the document
based on the review
comments.
2016-03-22
1.5
Updated solutions
according to eRAN12.0.
Jian Bin
2016-11-22
1.6
Updated solutions
according to eRAN12.1.
Deng Youliang
Jian Bin
Jian Bin
Jian Bin
Distribution List
Copy No.
Holder's Name & Role
1
System engineers (SEs)
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Contents
About This Document....................................................................................................................ii
1 Introduction....................................................................................................................................1
1.1 Purpose and Scope..........................................................................................................................................................1
1.1.1 Purpose........................................................................................................................................................................1
1.1.2 Scope...........................................................................................................................................................................1
1.1.3 Organization................................................................................................................................................................1
1.1.4 Relationship with Other Documents...........................................................................................................................2
1.1.5 Lifecycle......................................................................................................................................................................2
1.2 Open Issues.....................................................................................................................................................................2
1.3 Assumptions...................................................................................................................................................................2
2 Solution Overview........................................................................................................................3
2.1 Scenarios Analysis..........................................................................................................................................................3
2.2 Benefits...........................................................................................................................................................................3
2.3 General Solution.............................................................................................................................................................3
3 Application Guide.........................................................................................................................4
3.1 Solution to Access-related KPI Improvement................................................................................................................4
3.1.1 Description..................................................................................................................................................................4
3.1.2 Service-related Parameter Optimization....................................................................................................................11
3.1.3 Effect Evaluation Methods........................................................................................................................................12
3.1.4 Application Guide......................................................................................................................................................12
3.2 Solution to Service-Drop-related KPIs Improvement..................................................................................................13
3.2.1 Description................................................................................................................................................................13
3.2.2 Service-related Parameter Optimization....................................................................................................................15
3.2.3 Effect Evaluation Methods........................................................................................................................................17
3.2.4 Application Guide......................................................................................................................................................17
3.3 Solution to Handover-related KPIs Improvement........................................................................................................17
3.3.1 Description................................................................................................................................................................17
3.3.2 Service-related Parameter Optimization....................................................................................................................20
3.3.3 Effect Evaluation Methods........................................................................................................................................21
3.3.4 Application Guide......................................................................................................................................................21
4 Case Study....................................................................................................................................22
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4.1 Case 1: Improvement in the RACH Access Success Rate...........................................................................................22
4.1.1 Background................................................................................................................................................................22
4.1.2 Solution and Configuration.......................................................................................................................................22
4.1.3 Effect.........................................................................................................................................................................23
4.2 Case 2: Improvement in the RRC Connection Setup Success Rate.............................................................................23
4.2.1 Background................................................................................................................................................................23
4.2.2 Solution and Configuration.......................................................................................................................................23
4.2.3 Effect.........................................................................................................................................................................24
4.3 Case 3: Improvement in the E-RAB Setup Success Rate.............................................................................................24
4.3.1 Background................................................................................................................................................................24
4.3.2 Solution and Configuration.......................................................................................................................................24
4.3.3 Effect.........................................................................................................................................................................24
4.4 Case 4: Improvement in the Service Drop Rate...........................................................................................................25
4.4.1 Background................................................................................................................................................................25
4.4.2 Solution and Configuration.......................................................................................................................................26
4.4.3 Effect.........................................................................................................................................................................26
4.5 Case 5: Improvement in the Handover Success Rate...................................................................................................26
4.5.1 Background................................................................................................................................................................26
4.5.2 Solution and Configuration.......................................................................................................................................26
4.5.3 Effect Evaluation.......................................................................................................................................................28
5 Reference Documents..................................................................................................................29
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1
Introduction
1.1 Purpose and Scope
1.1.1 Purpose
This document serves as an application guide of the LTE KPI improvement solutions. It
describes feature portfolios and end-to-end (E2E) deliverable applications of the solutions and
provides guidelines for future solution-level application, maintenance and secondary
development of service solutions for existing LTE systems.
1.1.2 Scope
This document serves as a guide to Huawei solutions of the network KPI improvement for
different scenarios.
This document helps customers choose appropriate feature or function portfolio for their
network scenarios. The working principles, deployment, and maintenance of each feature are
not described in this document and are included in the corresponding feature parameter
description.
1.1.3 Organization
Chapter
Description
2
Describes the solution overview.
3

Introduces the application scenarios of the solution. LTE Uplink
Capacity Solution Design is the source of this document.

Provides values and objectives of the solution in the current version,
that is, the system effect after the solution is used.

Describes the general solution and provides conclusions based on
different scenarios without details.

Describes the solution application guide.

Provides detailed solutions for each scenario, involving parameter
configuration, effect evaluation, and troubleshooting.
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Describes application cases of the solution on commercial networks.
1.1.4 Relationship with Other Documents
LTE Uplink Capacity Solution Design is the source of this document.
1.1.5 Lifecycle
The draft of this document was completed at TR5.
This document was updated and finalized at TR6.
1.2 Open Issues
None
1.3 Assumptions
None
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2
Solution Overview
2.1 Scenarios Analysis
The solution helps increase the KPIs such as the access success rate and handover success
rate, and decrease the service drop rate.
2.2 Benefits
The solution is designed for scenarios of low access success rate and high service drop rate. It
brings better user experience by improving access-, service-drop-, and handover-related KPIs.
The solution describes how to evaluate, analyze, and improve network KPIs.
2.3 General Solution
The solution is as follows:

Improvement of access-related KPIs
Provide measures for improving access-related KPIs based on the causes of RACH
access failures, RRC connection setup failures, and E-RAB setup failures.

Improvement of service-drop-related KPIs
Provide measures for improving service-drop-related KPIs based on the causes of service
drops.

Improvement of handover-related KPIs
Provide measures for improving handover-related KPIs based on the causes of handover
failures in the handover preparation and execution phases.
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3
Application Guide
3.1 Solution to Access-related KPI Improvement
3.1.1 Description
Solution to Access-related KPIs Improvement includes:

Improvement of RACH access success rate

Improvement of RRC connection setup success rate

Improvement of E-RAB setup success rate
Table 1.1 lists the causes of RACH access failures and the improvement measures.
Table 1.1 RACH failure category, symptom and improvement measure
RACH Failure
Category
Symptom
Improvement Measure
Root sequence
conflict
The following two methods
can detect root sequence
conflict:
Check and optimize the root sequence conflict.

Use the PRACH root
sequence conflict
detection function to
trigger the root
sequence conflict
exception alarm. For
details, see Random
Access Control and
RACH Optimization
Feature Parameter
Description.

Use the OMStar and
engineering parameters
to check neighboring
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RACH Failure
Category
Symptom
CONFIDENTIAL
Improvement Measure
cell root sequence
conflict.
The PRACH channel
interference is obviously
higher than the PUSCH or
PUCCH interference.
PRACH
interference
Air interface
You can compare the
L.UL.Interference.PRACH
and
L.UL.Interference.PUSCH/
L.UL.Interference.PUCCH
counters.
Periodic and repeated
RACH access failures
occur.
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The failure can be gradually rectified as follows:

Check the PRACH interference source to resolve the
PRACH channel interference.

Select the PrachIrcSwitch option to improve PRACH
anti-interference capabilities. For details, see Receiver
Technology Feature Parameter Description.

Select the PrachFalseAlarmDetSwitch option. For
details, see Random Access Control and RACH
Optimization Feature Parameter Description.
The failure can be gradually rectified as follows:

Optimize RF settings to reduce poorly covered areas.

Adjust the T300 timer. It is recommended that the T300
timer be set to 1000 ms.

Extend the cell radius or activate the extended cell range
feature in scenarios such as lakeside and riverside that
experience extended cell range. For details, see Extended
Cell Range Feature Parameter Description.

Select the NonContRaOptSwitch option of the
CellAlgoSwitch.RachAlgoSwitch parameter to enable
optimization for UEs that access the cell during
handovers at places of longer distances to the eNodeB
than the cell radius.

Enable the high-speed mobility feature in high-speed
scenarios. For details, see High Speed Mobility Feature
Parameter Description.
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Table 1.2 lists the causes of RRC connection setup failures and the improvement measures.
Table 1.2 RRC connection setup failure category, cause for RRC connection setup failures,
symptom and improvement measure
RRC Connection
Setup Failure
Category
Cause for RRC
Connection Setup
Failures
Symptom
Improvement Measure
Resource
insufficiency
SRS resource
allocation failure
L.RRC.SetupFail.
ResFail.SRS > 0
The failure can be rectified using either of
the following methods:
PUCCH resource
allocation failure
Flow control or
overload
L.RRC.SetupFail.
ResFail.PUCCH >
0

If the number of UEs in a cell reaches the
maximum, you are advised to expand
the capacity of sites.

If the number of UEs in a cell does not
reach the maximum, it is recommended
that the SrsSubframeRecfSwitch
option of SrsAlgoSwitch be selected.
For details, see Physical Channel
Resource Management Feature
Parameter Description.
The PUCCH resource allocation failure
refers to the SRI allocation failure. The
failure can be rectified using either of the
following methods:

If the number of UEs in a cell reaches the
maximum, you are advised to expand
the capacity of sites.

If the number of UEs in a cell does not
reach the maximum, it is recommended
that the SriPeriodAdaptive option of
PUCCHcfg be selected. For details, see
Admission and Congestion Control
Feature Parameter Description.
A limited number of
UEs
L.RRC.SetupFail.
ResFail.UserSpec
>0
Expand the capacity of sites whose
resources are congested.
The RRC
Connection Request
message is discarded
due to flow control.
L.RRC.ConnReq.
Msg.disc.FlowCtrl
>0
Measures are as follows:
The RRC
Connection Reject
message is discarded
due to flow control.
L.RRC.SetupFail.
Rej.FlowCtrl > 0
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
Expand the capacity of sites whose
resources are congested.

If the expansion fails for the time being,
increase the value of the T302 timer to
delay the repeated access time of UEs.
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RRC Connection
Setup Failure
Category
Air interface fault
Abnormal UEs
CONFIDENTIAL
Cause for RRC
Connection Setup
Failures
Symptom
Improvement Measure
MME overload
L.RRC.SetupFail.
Rej.MMEOverloa
d>0
Check the cause of MME overload.
No RRC
CONNECTION
SETUP
COMPLETE
message from UEs
L.RRC.SetupFail.
NoReply > 0
The failure can be gradually rectified as
follows:
The TMSIs of UEs
with access
failures are
irregular.

Optimize RF settings to reduce poorly
covered areas.

Troubleshoot uplink interference.

Adjust the QRxLevMin parameter value.
The adjusted value must meet the
requirements for cell edge coverage on
live networks.

Set the SmartPreAllocationSwitch
parameter on. For details, see
Scheduling Feature Parameter
Description.

Select the SrbProbeSchSwitch option.
For details, see Scheduling Feature
Parameter Description.
A certain UE
repeatedly fails to
access networks.
L.RRC.ConnReq.
Msg >
L.RRC.ConnReq.
Att
The TMSIs of UEs
with access
failures are
densely
distributed.
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The failure can be gradually rectified as
follows:

Deselect the RrcSetupOptSwitch option
to avoid UE compatibility issues.

Increase the value of
FilterReptRrcConnReqTimer to filter
repeated RRC Connection Request
messages of abnormal UEs.

Adjust the RrcConnPunishThd
parameter value to reduce the impact of
abnormal UEs.

Set the FltrRptRrcConReqExtdSwitch
parameter on to filter repeated RRC
Connection Request messages of
abnormal UEs.
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Table 1.3 lists the causes of E-RAB setup failures and the improvement measures.
Table 1.3 E-RAB setup failure category, cause for E-RAB setup failures, symptom, and
improvement measure
E-RAB Setup
Failure Category
Cause for E-RAB
Setup Failures
Symptom
Improvement Measure
Transmission fault
Insufficient
downlink
transmission
resources
L.ERAB.FailEst.TNL.
DLRes > 0
Check for transmission alarms. For details,
see the alarm part in 3900 Series Product
Documentation.
Insufficient uplink
transport resources
L.ERAB.FailEst.TNL.
ULRes > 0
Insufficient SRS
resources
L.ERAB.FailEst.NoR
adioRes.SRS > 0
Resource
deficiency
Insufficient PUCCH
resources
L.ERAB.FailEst.NoR
adioRes.PUCCH >
0
Insufficient
downlink licensed
traffic volume
L.ERAB.FailEst.NoR
adioRes.DLThrpLi
c>0
Insufficient licensed
uplink traffic volume
L.ERAB.FailEst.NoR
adioRes.ULThrpLi
c>0
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The failure can be rectified using either of
the following methods:

If the number of UEs in a cell reaches the
maximum, you are advised to expand
the capacity of sites.

If the number of UEs in a cell does not
reach the maximum, it is recommended
that the SrsSubframeRecfSwitch
option of SrsAlgoSwitch be selected.
For details, see Physical Channel
Resource Management Feature
Parameter Description.
The PUCCH resource allocation failure
refers to the SRI allocation failure. The
failure can be rectified using either of the
following methods:

If the number of UEs in a cell reaches the
maximum, you are advised to expand
the capacity of sites.

If the number of UEs in a cell does not
reach the maximum, it is recommended
that the SriPeriodAdaptive option of
PUCCHcfg be selected. For details, see
Admission and Congestion Control
Feature Parameter Description.
Expand the capacity of sites whose
resources are congested, or increase
licensed traffic volume.
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E-RAB Setup
Failure Category
Air interface fault
CONFIDENTIAL
Cause for E-RAB
Setup Failures
Symptom
Improvement Measure
Low downlink
satisfaction rate
L.ERAB.FailEst.NoR
adioRes.DLSatis >
0
Change the downlink satisfaction rate
threshold or deselect the DlSwitch option.
For details, see Admission and Congestion
Control Feature Parameter Description.
Low uplink
satisfaction rate
L.ERAB.FailEst.NoR
adioRes.ULSatis >
0
Change the uplink satisfaction rate
threshold or deselect the UlSwitch option.
For details, see Admission and Congestion
Control Feature Parameter Description.
Insufficient UE
number specification
L.ERAB.FailEst.NoR
adioRes.UserSpec
>0
Expand the capacity of sites.
Insufficient
RRC_CONNECTE
D UE license
L.ERAB.FailEst.NoR
adioRes.RrcUserL
ic > 0
Expand the capacity of sites or add
RRC_CONNECTED UE license.
The retransmission
number of downlink
SRB RLC reaches
the maximum.
L.ERAB.FailEst.SRB
Reset > 0
The failure can be gradually rectified as
follows:
UE response timeout
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L.ERAB.FailEst.NoR
eply > 0

Optimize RF settings to reduce poorly
covered areas.

Troubleshoot uplink interference.

Adjust the QRxLevMin parameter value.
The adjusted value must meet the
requirements for cell edge coverage on
live networks.

Increase the number of downlink RLC
retransmissions (indicated by
eNodeBMaxRetxThreshold) to
enhance the downlink transmission
reliability.

Increase the value of
WaitRrcConnSetupCmpTimer to
increase tolerance duration. For details,
see Connection Management Feature
Parameter Description.

Set the SmartPreAllocationSwitch
parameter on. For details, see
Scheduling Feature Parameter
Description.

Select the SrbProbeSchSwitch option.
For details, see Scheduling Feature
Parameter Description.
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E-RAB Setup
Failure Category
Cause for E-RAB
Setup Failures
Symptom
Improvement Measure
Core network fault
The core network
fault
L.ERAB.FailEst.MM
E>0
The failure can be gradually rectified as
follows:

Work jointly with core network engineers
to check whether the value of the timer
on the core network side is too small.

Check based on the measures for air
interface faults.
Table 1.4 lists the feature names and reference documents involved in the solution.
Table 1.4 Feature ID, feature name, and reference document
Feature ID
Feature/Function Name
Introduced In…
Reference Document
LOFD-001094
Control Channel IRC
eRAN6.0
Receiver Technology Feature
Parameter Description
N/A
PrachFalseAlarmDetSwitc
h
eRAN7.0
Random Access Control and RACH
Optimization Feature Parameter
Description
LOFD-001007
High Speed Mobility
eRAN1.0
High Speed Mobility Feature
Parameter Description
LOFD-001008
Ultra High Speed Mobility
eRAN1.0
High Speed Mobility Feature
Parameter Description
LOFD-001009
Ultra-remote Cells
eRAN2.0
Extended Cell Range Feature
Parameter Description
N/A
SmartPreAllocationSwitch
eRAN6.0
Scheduling Feature Parameter
Description
N/A
SrbProbeSchSwitch
eRAN11.1
Scheduling Feature Parameter
Description
N/A
FltrRptRrcConReqExtdSwi
tch
eRAN12.0
Connection Management Feature
Parameter Description
Table 1.5 lists the features and functions involved in the solution.
Table 1.5 Feature ID, feature name, and feature description
Feature ID
Feature/Function Name
Feature/Function Description
LOFD-001094
Control Channel IRC
Improves the anti-interference capability of the PRACH.
N/A
PrachFalseAlarmDetSwitch
Identifies the detection and discard of false alarms to reduce
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the impact of false alarms on the RACH access success rate.
LOFD-001007
High Speed Mobility
Increases the UE access capability in high-speed frequency
offset scenarios.
LOFD-001008
Ultra High Speed Mobility
LOFD-001009
Ultra-remote Cells
Increases the UE access capability in ultra-remote cells.
N/A
SmartPreAllocationSwitch
Ensures that there are available scheduling resources in the
uplink to avoid KPI deterioration caused by missing
detection of SRs.
N/A
SrbProbeSchSwitch
Improves the signaling feedback success rate.
N/A
FltrRptRrcConReqExtdSwitch
Identifies the repeated accesses of abnormal UEs for a longer
time, removes the statistics about abnormal RRC connection
setup attempts, and reduces the impact of abnormal UEs on
the RRC connection setup success rate.
3.1.2 Service-related Parameter Optimization
The optimization of parameter adjustment is a progressive process. You are advised to
progressively adjust the parameter values based on the KPIs of local networks.
MO
Parameter
ID
Parameter
Name
Parameter
Description
Adjustment
CELLSEL/CELLRE
SEL
QRxLevMin
Minimum
Required RX
Level
Reduces the
number of UE
accesses in poorly
covered areas.
The value of the downlink
RSRP below -122 dBm
shows that an area is poorly
covered. You are advised to
set the parameter to -122
dBm. If further adjustment is
needed, you are advised to
increase its value by 2 dB at
a time.
UETIMERCONST
T300
Timer 300
Prolongs the
processing
duration of
abnormal UEs to
prevent access
failures due to the
processing
interruption by the
timer.
If the value of this parameter
is less than 1000 ms on the
live network, you are advised
to set the parameter to 1000
ms. If further adjustment is
needed, you are advised to
increase its value by 200 ms
at a time.
RRCCONNSTATET
IMER
T302
Timer 302
Delays the time of
UE re-access to
prevent eNodeB
against heavy
traffic.
You are advised to set it to
the maximum value of 16s.
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MO
Parameter
ID
Parameter
Name
Parameter
Description
Adjustment
SRBRLCPDCPCFG
/RLCPDCPPARAG
ROUP
eNodeBMax
RetxThreshol
d
MaxRetxThresho
ld for eNodeB
Results in a larger
number of
retransmissions to
enhance the
downlink
transmission
reliability.
You are advised to set it to
the maximum value of 32.
ENODEBCONNST
ATETIMER
WaitRrcConn
SetupCmpTi
mer
RRCConnSetup
Cmp Waiting
Timer
Prolongs the
waiting time to
achieve higher
access success
rate.
You are advised to set it to
the maximum value of 15s.
ENODEBCONNST
ATETIMER
SecCmpWaiti
ngTimer
SecurityModeCo
mplete Waiting
Timer
Prolongs the
waiting time to
achieve higher
access success
rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 35s.
ENODEBCONNST
ATETIMER
UpUeCapInfo
WaitingTimer
Unprotected
UeCapInfo
Waiting Timer
Prolongs the
waiting time to
achieve higher
access success
rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 35s.
ENODEBCONNST
ATETIMER
UuMessageW
aitingTimer
UU Message
Waiting Timer
Prolongs the
waiting time to
achieve higher
access success
rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 35s.
ENODEBCONNST
ATETIMER
S1MessageW
aitingTimer
S1 Message
Waiting Timer
Prolongs the
waiting time to
achieve higher
access success
rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 20s.
RRCCONNSTATET
IMER
FilterReptRrc
ConnReqTim
er
Filter Repeated
RRCConnReq
Timer
Increases the value
of this parameter
to filter more
repeated access of
abnormal UEs to
traffic
measurement.
You are advised to set it to
the maximum value of 15s.
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3.1.3 Effect Evaluation Methods
Definition of access-related KPIs:

RACH Access Success Rate = (L.RA.GrpA.ContResolution +
L.RA.GrpB.ContResolution + L.RA.Dedicate.Msg3Rcv)/(L.RA.GrpA.Att +
L.RA.GrpB.Att + L.RA.Dedicate.Att)

RRC Connection Setup Success Rate = L.RRC.ConnReq.Succ/L.RRC.ConnReq.Att

E-RAB Setup Success Rate = L.E-RAB.SuccEst/(L.E-RAB.AttEst–L.ERAB.FailEst.MME.X2AP)
This solution helps improve access-related KPIs.
3.1.4 Application Guide
The solution serves to improve RACH access success rate, RRC connection setup success rate
and E-RAB setup success rate. All of the three features can be activated at the same time. The
deployment and activation of each feature are not described in this document. For details, see
the corresponding feature parameter descriptions.
3.2 Solution to Service-Drop-related KPIs Improvement
3.2.1 Description
Table 1.6 lists the causes of service drops and the improvement measures.
Table 1.6 Cause for service drop, symptom and improvement measure
Cause for
Service Drop
Symptom
Improvement Measure
Transmission fault
L.E-RAB.AbnormRel.TNL > 0
Check for transmission alarms. For details, see the
alarm part in 3900 Series Product Documentation.
Handover fault
L.E-RAB.AbnormRel.HOFailure
>0
For details, see section 3.3 "Solution to Handoverrelated KPIs Improvement."
Uplink
interference
The value of
L.UL.Interference.Avg is
significantly greater than the
normal in idle mode.
Troubleshoot uplink interference.
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Cause for
Service Drop
Symptom
Improvement Measure
Air interface fault
L.E-RAB.AbnormRel.Radio > 0
The failure can be gradually rectified as follows:

Optimize RF settings to enhance indoor coverage.

Adjust the QRxLevMin parameter value. The
adjusted value must meet the requirements for
cell edge coverage on live networks.

Increase the number of downlink RLC
retransmissions (indicated by
eNodeBMaxRetxThreshold) to enhance the
downlink transmission reliability.

Increase the value of TimeAlignmentTimer to
reduce uplink timing errors and achieve better
uplink time alignment performance.

Increase the value of the TrafficRelDelay
parameter for a higher probability of UE
reestablishments.

Increase the value of
WaitRrcConnSetupCmpTimer to increase
tolerance duration. For details, see Connection
Management Feature Parameter Description.

Select the SrbProbeSchSwitch option. For details,
see Scheduling Feature Parameter Description.

Enable the ANR feature to solve problems caused
by missing neighboring cells. For details, see
ANR Feature Parameter Description.

Enable the PCI conflict detection feature to solve
PCI conflicts. For details, see PCI Conflict
Detection and Self-Optimization Feature
Parameter Description.
Network
congestion
L.E-RAB.AbnormRel.Cong > 0
Expand the capacity of sites whose resources are
congested.
A small sum of
normal releases
The sum of the L.ERAB.NormRel is significantly
small.
Decrease the value of the UeInactiveTimer
parameter to increase the number of normal UE
releases and avoid false high service drop rate
caused by small number of normal releases.
RRC connection
reestablishment
failure
L.RRC.ReEstFail.NoCntx > 0
The failure can be rectified as follows:
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Select the RrcReestOptSwitch option to increase
the reestablishment success rate and reduce service
drop rate.
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Table 1.7 lists of features and reference documents involved in the solution.
Table 1.7 Feature ID, feature name, and reference document
Feature ID
Feature/Function Name
Introduced In…
Reference Document
LOFD-002001
ANR Management
eRAN1.x
ANR Management Feature Parameter
Description
LOFD-002007
PCI Conflict Detection &
Self-Optimization
eRAN1.x
PCI Conflict Detection and SelfOptimization Feature Parameter
Description
N/A
SrbProbeSchSwitch
eRAN11.1
Scheduling Feature Parameter
Description
N/A
Reestablishment in
enhanced scenarios
eRAN11.x
For details, see the parameter
description.
Table 1.8 lists the features and functions involved in the solution.
Table 1.8 Feature ID, feature name, and feature description
Feature ID
Feature/Function
Name
Feature/Function Description
LOFD-002002
ANR Management
Enables the neighboring cell self-addition and selfoptimization functions to reduce the service drop rate caused
by missing or incorrect neighbor relationships.
LOFD-002007
PCI Conflict Detection &
Self-Optimization
Checks PCI conflicts and solves these problems to prevent
service drops caused by improper handover or PCI conflicts.
N/A
SrbProbeSchSwitch
Improves the signaling feedback success rate.
N/A
Reestablishment in
enhanced scenarios
Controls the eNodeB to support reestablishment in enhanced
scenarios, increases the reestablishment success rate, and
decreases the service drop rate.
3.2.2 Service-related Parameter Optimization
The optimization of parameter adjustment is a progressive process. You are advised to
progressively adjust the parameter values based on the KPIs of local networks.
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MO
Parameter ID
Parameter
Name
Parameter
Description
Adjustment
CELLSEL/CELLRE
SEL
QRxLevMin
Minimum
Required RX
Level
Reduces the
number of UE
accesses in poorly
covered areas.
The value of the downlink
RSRP below -122 dBm
shows that an area is poorly
covered. You are advised to
set the parameter to -122
dBm. If further adjustment
is needed, you are advised to
increase its value by 2 dB at
a time.
SRBRLCPDCPCFG
/RLCPDCPPARAG
ROUP
eNodeBMaxRetx
Threshold
MaxRetxThres
hold for
eNodeB
Results in a larger
number of
retransmissions to
enhance the
downlink
transmission
reliability.
You are advised to set it to
the maximum value of 32.
TATIMER
TimeAlignmentT
imer
Uplink time
alignment timer
Enhances the
uplink timing
reliability and
reduces the outofsynchronization
probabilities.
You are advised to set this
timer to INFINITY. At the
same time, select the
TimingAdvCmdOptSwitch
option, and set the
TACmdSendPeriod
parameter to SF928.
CELLSTANDARD
QCI
TrafficRelDelay
Traffic Release
Delay
A longer waiting
duration leads to
higher rate of
RRC connection
reestablishment
and lower service
drop rate.
You are advised to set this
parameter to 30s, or at least
not less than 15s.
ENODEBCONNST
ATETIMER
UuMessageWaiti
ngTimer
UU Message
Waiting Timer
A longer waiting
duration leads to
lower service
drop rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 35s.
ENODEBCONNST
ATETIMER
S1MessageWaiti
ngTimer
S1 Message
Waiting Timer
A longer waiting
duration leads to
lower service
drop rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 20s.
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MO
Parameter ID
Parameter
Name
Parameter
Description
Adjustment
ENODEBCONNST
ATETIMER
X2MessageWaiti
ngTimer
X2 Message
Waiting Timer
A longer waiting
duration leads to
lower service
drop rate.
If further adjustment is
needed, you are advised to
increase its value by 2s at a
time. It is recommended that
the value of the timer be less
than or equal to 20s.
RRCCONNSTATET
IMER
UeInactiveTimer
UE Inactivity
Timer
A smaller value
of this parameter
results in more
RRC connection
releases for UEs
to prevent worse
service drop rate
due to fewer
normal RRC
connection
releases.
You are advised to set this
parameter to 10s, not more
than 20s and less than 5s.
3.2.3 Effect Evaluation Methods
The KPI of the service drop rate is defined as follows: L.E-RAB.AbnormRel/(L.ERAB.AbnormRel + L.E-RAB.NormRel + L.E-RAB.NormRel.IRatHOOut)
This solution helps improve handover-related KPIs.
3.2.4 Application Guide
This solution improves service-drop-related KPIs, and the preceding features or functions can
be enabled at the same time. The deployment and activation of each feature are not described
in this document. For details, see the corresponding feature parameter descriptions.
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3.3 Solution to Handover-related KPIs Improvement
3.3.1 Description
Table 1.9 lists the causes of handover failures and the improvement measures.
Table 1.9 Handover failure category, handover failure cause, symptom, and improvement measure
Handover
Failure Category
Handover Failure
Cause
Symptom
Improvement Measure
Handover
preparation failure
(observing
handover target
cells)
PUCCH resource
allocation failure
leads to incoming
handover
preparation failure.
L.HHO.Prep.FailIn.A
dmitFail.PUCCH > 0
The PUCCH resource allocation failure
refers to the SRI allocation failure. Main
scenarios are as follows:

If the number of UEs in a cell reaches
the maximum, you are advised to
expand the capacity of sites.

If the number of UEs in a cell does not
reach the maximum, it is
recommended that the
SriPeriodAdaptive option of
PUCCHcfg be selected. For details,
see Admission and Congestion
Control Feature Parameter
Description.
The uplink and
downlink licensed
traffic leads to
incoming
preparation
handover failure.
L.HHO.Prep.FailIn.A
dmitFail.ULThrpLic >
0
The limited number
of UEs in RRC
connected mode
leads to incoming
handover
preparation failure.
L.HHO.Prep.FailIn.A
dmitFail.UserLic > 0
Expand the capacity of sites whose
resources are congested, or increase
licensed number of UEs in RRC
connection mode.
The limited number
of UEs in RRC
connected mode
leads to incoming
preparation
handover failure.
L.HHO.Prep.FailIn.A
dmitFail.UserSpec > 0
Expand the capacity of sites whose
resources are congested.
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Increase licensed traffic in the uplink and
downlink.
L.HHO.Prep.FailIn.A
dmitFail.DLThrpLic >
0
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Handover
Failure Category
Handover Failure
Cause
Symptom
Improvement Measure
Faults at the
transport network
layer lead to
incoming handover
preparation failures.
L.HHO.Prep.FailIn.T
NL > 0
The failure can be gradually rectified as
follows:
Insufficient uplink
transport resources
lead to incoming
handover
preparation failures.
L.HHO.Prep.FailIn.A
dmitFail.TNL.ULRes
>0
Insufficient
downlink transport
resources lead to
incoming handover
preparation failures.
Handover
execution failure
(observing
handover target
cells)
CONFIDENTIAL
Handover failure
caused by incorrect
configuration of
neighboring cells
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L.HHO.Prep.FailIn.A
dmitFail.TNL.DLRes
>0
The air interface
message shows that in
handover commands
the delivered PCI is
not the PCI in the
measurement report
(MR) sent by the UE.

Check whether there are missing SGW addresses in the target site.

Turn on the GTPU static detection
switch to check whether there is a
GTPU fault alarm. If so, troubleshoot
any GTPU faults.
Troubleshoot using any of the following
measures:

Expand the target site capacity.

Increase the transport resource group
bandwidth of the target site.

Increase the value of the
TRMULHOCACTH parameter.

Set the RSCGRPULCACSWITCH
parameter off in order not to apply
UL admission control to a resource
group. For details, see Transport
Resource Management Feature
Parameter Description.
Troubleshoot using any of the following
measures:

Expand the target site capacity.

Increase the transport resource group
bandwidth of the target site.

Increase the value of the
TRMULHOCACTH parameter.

Set the RSCGRPULCACSWITCH
parameter off in order not to apply
UL admission control to a resource
group. For details, see Transport
Resource Management Feature
Parameter Description.
Check and modify the configuration of
neighboring cells.
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Handover
Failure Category
CONFIDENTIAL
Handover Failure
Cause
Symptom
Improvement Measure
There are two
different PCIs, but
only one PCI is
configured in the
neighbor
relationship.
The cell information
in MR is inconsistent
with that in handover
commands.
Troubleshoot using either of the
following measures:
Overshoot coverage
Engineering
parameters indicate
that top neighboring
cells with handover
failures experience
overshoot coverage.
Optimize RF settings.
Poor coverage
Engineering
parameters indicate
that top neighboring
cells with handover
failures experience
overshoot coverage.
The failure can be gradually rectified as
follows:
Handover failures of
top UEs
Inter-frequency
handovers of
abnormal UEs fail.

Add missing neighbor relationships.

Enable the ANR function. For details,
see ANR Management Feature
Parameter Description.

Optimize RF settings.

Set the HoRarPwrEnhancedSwitch
parameter on. For details, see Power
Control Feature Parameter
Description.

Change the RarAndPagingCR
parameter value from 117 to 54.

Change the T304ForEutran
parameter value from 500 ms to 1000
ms.
Select the
INTER_FREQ_HO_SWITCH_OFF
option of the
UeCompat.BlkLstCtrlSwitch parameter
so that the eNodeB performs interfrequency redirection after receiving
inter-frequency measurement reports
from abnormal UEs.
Based on the handover failure cause, symptom, and improvement measure described in the
preceding table, Table 1.10 lists the feature ID, feature name, and reference document for each
solution.
Table 1.10 Feature ID, feature name, and reference document
Feature ID
Feature/Function Name
Introduced In…
Reference Document
LOFD-002002
ANR Management
eRAN1.0
ANR Management Feature
Parameter Description
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Feature ID
Feature/Function Name
Introduced In…
Reference Document
N/A
Handover RAR Power
Enhance
eRAN11.0
Power Control Feature
Parameter Description
Table 1.11 lists the features and the functions in the solution.
Table 1.11 Feature ID, feature name, and functions
Feature ID
Feature/Function
Name
Feature/Function Description
LOFD-002002
ANR Management
Enables the neighboring cell self-addition and self-optimization
functions to reduce the service drop rate caused by missing or
incorrect neighbor relationships.
N/A
Handover RAR Power
Enhance
Enables this function in downlink poor coverage or interference
scenarios to improve the preamble access success rate and
handover success rate dedicated to only one UE.
3.3.2 Service-related Parameter Optimization
The optimization of parameter adjustment is a progressive process. You are advised to
progressively adjust the parameter values based on the KPIs of local networks.
MO
Parameter ID
Parameter
Name
Parameter
Description
Adjustment
CELLDLSCHALGO
RarAndPagingCR
Code Rate for
Random Access
Response and
Paging Message
Allows higher
reliability of random
access response
message reception.
Set the parameter to
54. If further
adjustment is
needed, you are
advised to decrease
its value at the step
of 3.
RRCCONNSTATETI
MER
T304ForEutran
Timer304 for
EUTRAN
Increasing the value
of this timer allows
the UE to have more
access chances.
Set the timer to 1000
ms. If further
adjustment is
needed, you are
advised to set it to
2000 ms.
3.3.3 Effect Evaluation Methods
The handover-related KPIs are defined as follows:

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Preparation Success Rate of Outgoing Handover
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(L.HHO.IntraeNB.IntraFreq.ExecAttOut + L.HHO.IntraeNB.InterFreq.ExecAttOut +
L.HHO.IntereNB.IntraFreq.ExecAttOut + L.HHO.IntereNB.InterFreq.ExecAttOut)/
(L.HHO.IntraeNB.IntraFreq.PrepAttOut + L.HHO.IntraeNB.InterFreq.PrepAttOut +
L.HHO.IntereNB.IntraFreq.PrepAttOut + L.HHO.IntereNB.InterFreq.PrepAttOut)

Preparation Success Rate of Incoming Handover
(L.HHO.IntraeNB.ExecAttIn + L.HHO.IntereNB.ExecAttIn)/
(L.HHO.IntraeNB.PrepAttIn + L.HHO.IntereNB.PrepAttIn)

Execution Success Rate of Outgoing Handover
(L.HHO.IntraeNB.InterFreq.ExecSuccOut + L.HHO.IntraeNB.IntraFreq.ExecSuccOut +
L.HHO.IntereNB.IntraFreq.ExecSuccOut + L.HHO.IntereNB.InterFreq.ExecSuccOut)/
(L.HHO.IntraeNB.IntraFreq.ExecAttOut + L.HHO.IntraeNB.InterFreq.ExecAttOut +
L.HHO.IntereNB.IntraFreq.ExecAttOut + L.HHO.IntereNB.InterFreq.ExecAttOut)

Success Rate of Incoming Handover
(L.HHO.IntraeNB.ExecSuccIn + L.HHO.IntereNB.ExecAttIn)/
(L.HHO.IntraeNB.ExecAttIn + L.HHO.IntereNB.ExecAttIn)
This solution can be helpful in improving handover-related KPIs.
3.3.4 Application Guide
This solution improves handover-related KPIs, and the preceding features or functions can be
enabled at the same time. The deployment and activation of each feature are not described in
this document. For details, see the corresponding feature parameter descriptions.
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4
Case Study
4.1 Case 1: Improvement in the RACH Access Success Rate
4.1.1 Background
Operator A in country R had two top cells with low RACH access success rate. In severe
conditions, the RACH access success rate was lower than 10%, as shown in Figure 1.2.
Figure 1.2 RACH access success rate
4.1.2 Solution and Configuration
The statistics about the RACH success rate and the L.RA.GrpA.Att counter on the live
network indicate that the more times of the RACH access had, the poorer the success rate
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was. In addition, values of interference-related counters were normal. Therefore, the issue
might be caused by the access of non-false-alarm. Survey of the live network found that the
two cells were beside sea. UEs in them were possibly out of cell radius.
Figure 1.3 Cells on the network edge with low RACH access success rate
Enable Extended Cell Range. Set its parameters as follows:
MOD CELL: PreambleFmt = 1, CellRadius = 29000
4.1.3 Effect
The cell radius is extended from 15 km to 29 km. The RACH access success rate increases to
91%.
4.2 Case 2: Improvement in the RRC Connection Setup
Success Rate
4.2.1 Background
Cell 1 on a site of project XX suffered a continual low setup success rate of approximately
40% on average, failing to meet demands.
4.2.2 Solution and Configuration
Check results showed that the value of the L.UL.Interference.Avg counter was greater than
-105 dBm, which meant that the fault was caused by uplink interference.
By means of cell trace, the fault was that the RRC CONN CMP message from UEs could not
be received due to uplink intermodulation interference.
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Figure 1.4 Uplink intermodulation interference of a cell
4.2.3 Effect
The intermodulation interference was eliminated after the customer performed site
engineering rectification. The RRC Connection Setup Success Rate recovers to the normal
state.
4.3 Case 3: Improvement in the E-RAB Setup Success Rate
4.3.1 Background
After DRX (with both entry and exit thresholds being 1000) was enabled in a certain network
in country A, the E-RAB setup success rate of top problematic cells decreased by 0.08%.
It was detected that UEs in these cells occasionally did not send SR, and eNodeBs did not
send uplink scheduling indications to the UEs.
4.3.2 Solution and Configuration
Select the SmartPreAllocationSwitch option. The MML command is as follows: MOD
CELLALGOSWITCH: LocalCellId = x, UlSchSwitch = SmartPreAllocationSwitch-1;
4.3.3 Effect
After the SmartPreAllocationSwitch option was selected, the E-RAB setup success rate
became normal, as shown in Figure 1.5.
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Figure 1.5 E-RAB setup success rate on site B
4.4 Case 4: Improvement in the Service Drop Rate
4.4.1 Background
Network K in country L was found to suffer a high service drop rate. Since June 9, 2012, the
average service drop rate of the live network had deteriorated to 20% as field engineers
checked traffic statistics, as shown in Figure 1.6.
Figure 1.6 Service drop rate from May to June in network K
After reviewing the operation log, it was found that the UeInactiveTimer parameter value
was changed from 10s to 1800s, as shown in Figure 1.7.
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Figure 1.7 UeInactiveTimer value changed from 10s to 1800s
The setting of the UeInactiveTimer parameter value has a direct impact on UE status. If the
UE is constantly in connected mode, normal releases will significantly reduce so that service
drop rate will increase.
4.4.2 Solution and Configuration
Set the UeInactiveTimer parameter to 10s. The MML command is as follows: MOD
RRCCONNSTATETIMER: UeInactiveTimer = 10;
4.4.3 Effect
The service drop rate recovers to the normal state, as shown in Figure 1.8.
Figure 1.8 Service drops by hour
4.5 Case 5: Improvement in the Handover Success Rate
4.5.1 Background
The handover success rate in the network of operator C in country C was only 99.35%. After
analysis, top outgoing cells and top incoming cells were found. Overshoot coverage occurred
in the top cells, in some of which the PCIs in measurement cells and target cells were
inconsistent, causing handover failures.
4.5.2 Solution and Configuration
2.
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Locate the fault scope.
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After analyzing traffic measurement and CHR of cell pairs, the top problematic cells with
outgoing handover failures were found. The target cell for these failed outgoing handovers
was the same.
Source Cell
Number of Handover Failures in Target Cell of Guangchang_Cell2
Kuozhibu_Cell1
157
Guohang_Cell3
123
Bingguan_Cell1
72
Jiudian_Cell1
56
3.
Analyze counter correlations.
Analyze the counters of the target cell (from 10 September to 24 September). The intereNodeB incoming handover was the main problem, with a very low success rate.
Line Label
Times of
Incoming
Handover
Failure
Incoming
Handover Success
Rate
Inter-eNodeB
Incoming
Handover
Success Rate
Intra-eNodeB
Incoming
Handover
Success Rate
Guangchang_Cell2
5060
41.81%
25.09%
95.00%
Based on the measurement traffic of the RACH, the cells all sent RAR if receiving preambles
and the random access success rate was 85%.But the number of handover preambles received
by this cell was far less than the total number of attempts for incoming handovers. This
showed that a large number of handovers had not received preambles, causing outgoing
handover failures of source cells.
Line
Label
Sum: Number
of Dedicated
Preamble
Messages
Received Due
to Handovers
Sum: Number
of Responses
to the
Preamble
Messages
Received Due
to Handovers
Sum: Number of Times
That the eNodeB Receives
Message 3 from the UE for
the Response It sends to
the UE After Receiving
Dedicated Preamble
Messages from the Cell
Total
Number of
Attempts
for
Incoming
Handovers
Random
Access
Success
Rate After
Receiving
Handover
Preambles
Total
4076
4076
3492
8696
85.67%
UEs were likely to be handed over to an incorrect cell because a preamble was not received.
1.
Troubleshoot basic network planning and optimization.
2.
Analyze neighbor relationships of sites with failed outgoing handovers. The PCI of the
target cell Guangchang_Cell2 was unique. Therefore, PCI confusion was excluded. To
check whether there was PCI confusion in a measurement cell of the UE, a fake
neighboring cell with the same PCI was manually added to force the UE to report eCGI.
This aimed to check whether the neighbor relationship was correct.
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3.
CONFIDENTIAL
Based on the reported eCGI information, it was found that the eNodeB configured to
Guangchang_Cell2 was inconsistent with its cell ID. This proved that there were PCI
confusion and missing neighboring cells.
Figure 3.1 Target PCI of 223
Based on the eCGI information, the cell turned out to be the one 10 km away with the same
PCI of 223. The signal of the cell encountered overshoot coverage, which caused the incorrect
handover to Guangchang_Cell2 and the overall handover failures.
4.5.3 Effect Evaluation
After overshoot coverage is resolved, the counters of the handover success rate recover to the
normal state.
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5
CONFIDENTIAL
Reference Documents
4.
3GPP TS 36.331, "Radio Resource Control (RRC) protocol specification"
5.
3GPP TS 36.413, "S1 Application Protocol (S1AP)"
6.
3GPP TS 36.423, "X2 Application Protocol (X2AP)"
7.
Random Access Control and RACH Optimization Feature Parameter Description
8.
Admission and Congestion Control Feature Parameter Description
9.
Transport Resource Management Feature Parameter Description
10. Receiver Technology Feature Parameter Description
11. Extended Cell Range Feature Parameter Description
12. High Speed Mobility Feature Parameter Description
13. Scheduling Feature Parameter Description
14. ANR Management Feature Parameter Description
15. PCI Conflict Detection and Self-Optimization Feature Parameter Description
16. Connection Management Feature Parameter Description
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