toaz.info-zte-fdd-lte-radio-network-optimization-guideline-v14-1-pr_2dc3a4737c2e165b04159b0cb4f3e03c.pdf

ZTE Confidential Proprietary © 2010 ZTE Corporation. All rights reserved. 1
ZTE FDD LTE Radio
Optimization Guideline

Product Type Technical Description
Version Date Author Approved By Remarks
V1.3 2014-5-12 ZTE Not open to the Third Party
© 2010 ZTE Corporation. All rights reserved.
ZTE CONFIDENTIAL: This document contains proprietary information of ZTE and is not to be
disclosed or used without the prior written permission of ZTE.
Due to update and improvement of ZTE products and technologies, information in this document
is subjected to change without notice.

TABLE OF CONTENTS
1 Introduction ................................................................................................................ 8
2 Network optimization preparation ............................................................................ 8
2.1 Organization Structure................................................................................................. 9
2.2 Optimization Tools and Software................................................................................. 9
2.2.1 CNT............................................................................................................................10
2.2.2 CNA ...........................................................................................................................10
2.2.3 NETMAX....................................................................................................................11
2.2.4 CNP ...........................................................................................................................11
2.3 Cluster Definition .......................................................................................................11
3 Network Optimization Process ...............................................................................12
3.1 Optimization Milestone ..............................................................................................12
3.2 Pre-launch Optimization ............................................................................................13
3.2.1 Radio Frequency Verifying ........................................................................................13
3.2.2 Single Site Verification (SSV) ....................................................................................13
3.2.3 Cluster Optimization workflow ...................................................................................15
3.3 Soft Launch (Trial-running Period) Optimization .......................................................16
3.4 Launched Optimization ..............................................................................................17
4 Cluster Optimization ................................................................................................18
4.1 Single-Cell Coverage Analysis ..................................................................................18
4.1.1 Checking the Antenna Connection Sequence...........................................................19
4.1.2 Checking the Overshooting .......................................................................................20
4.1.3 Checking the Coverage of Antenna Side Lobe and Back Lobe ................................22
4.1.4 Checking the Zero-Coverage Cell .............................................................................23
4.2 Cluster Coverage Analysis ........................................................................................25
4.2.1 Overview....................................................................................................................25
4.2.2 Work Scope of Coverage Optimization .....................................................................25
4.2.3 Weak-Coverage Optimization....................................................................................26
4.2.4 SINR Optimization .....................................................................................................32
4.2.5 Overlapped Coverage Optimization ..........................................................................37
4.2.6 Pilot Frequency Pollution Analysis ............................................................................41
4.3 Handover Analysis.....................................................................................................45
4.3.1 Missed Matching of Neighboring Cells ......................................................................47
4.3.2 Wrong Matching of Neighboring Cells .......................................................................54
4.3.3 Ping-Pong Handover .................................................................................................54
4.3.4 Handover Latency......................................................................................................58
4.3.5 Handover Failure .......................................................................................................60
4.4 Downloading Rate Analysis.......................................................................................65
4.4.1 Overview....................................................................................................................65
4.4.2 Analysis Methods.......................................................................................................65
4.4.3 Analyzing the Cell with the Maximum Downloading Rate Less than 5M ..................67
4.4.4 Analyzing the Cell with the Average Downloading Rate Ranging from 5M to 10M...70
4.5 Access Analysis.........................................................................................................75
4.5.1 Call Failures...............................................................................................................75
4.5.2 RRC Connection Establishment Failures ..................................................................76
4.5.3 Authentication and Encryption Failures .....................................................................80
4.5.4 E-RAB Connection Establishment Failures ...............................................................82
4.6 Call Drop Analysis .....................................................................................................85

4.6.1 Caused by coverage problems..................................................................................85
4.6.2 Caused by handover problems..................................................................................86
4.6.3 Caused by interference problem ...............................................................................86
5 OSS KPI Optimization..............................................................................................87
5.1 Network Access Performance Optimization ..............................................................87
5.1.1 System Accessibility ..................................................................................................87
5.1.2 System Availability.....................................................................................................87
5.1.3 Commonly Used Methods .........................................................................................88
5.1.4 System Accessibility KPI ...........................................................................................90
5.1.5 System Availability KPI..............................................................................................98
5.2 Handover Performance Optimization ......................................................................101
5.2.1 Handover Flow.........................................................................................................101
5.2.2 Handover Performance KPI.....................................................................................106
5.2.3 Commonly Used Methods .......................................................................................106
5.2.4 Handover Optimization Process ..............................................................................106
5.2.5 No Handover Command Received upon the Sent Measurement Report ...............107
5.2.6 MSG1 Sending Exception at Destination Cell .........................................................109
5.2.7 RAR Reception Exception .......................................................................................110
5.3 E-RAB Drops Performance Optimization ................................................................112
5.3.1 Definition of E-RAB Drop Rate ................................................................................112
5.3.2 Formula of E-RAB Drop Rate ..................................................................................112
5.3.3 E-RAB Drop sampling point.....................................................................................112
5.3.4 E-RAB Drop Counters .............................................................................................113
5.3.5 Release Reason definition in3GPP TS 36.413........................................................113
5.3.6 OMM-level performance statistics analysis .............................................................115
5.3.7 OMM-level performance statistics analysis .............................................................116
5.3.8 Conclusion ...............................................................................................................116

FIGURES
Figure 2-1: LTE Radio Network Optimization Organization Structure................................................ 9
Figure 3-1: LTE Radio Network Optimization Milestone...................................................................12
Figure 3-2: Cluster Optimization Work Flow.....................................................................................15
Figure 4-1 CNA LTE COVER LINE................................................................................................18
Figure 4-2 CNA PCI RSRP ............................................................................................................19
Figure 4-3 Coverage Direction of Cell FE2 (PCI94).......................................................................20
Figure 4-4: Cell with Overshot Signals .............................................................................................21
Figure 4-5 PCI Coverage Analysis in CNA ....................................................................................21
Figure 4-6 Cell Coverage Before and After the Azimuth & RS Power Adjustment........................22
Figure 4-7 Overlapped Coverage Caused by Reflection ...............................................................23
Figure 4-8 PCI's RSRP Function....................................................................................................24
Figure 4-9 Weak Coverage Area Analysis -1.................................................................................26
Figure 4-10 Weak Coverage Area Analysis -2...............................................................................27
Figure 4-14 DT Test Results-1 .........................................................................................................29
Figure 4-15 Coverage Effect of Cell PCI48, PCI43 and PCI12 .....................................................30
Figure 4-16 DT Test Results-2.......................................................................................................30
Figure 4-17 Weak Coverage Analysis in Cell PCI30 -1 .................................................................31
Figure 4-18 Weak Coverage Analysis in Cell PCI30 - 2 ................................................................31
Figure 4-19 DT Test Results after Adjustment of Antenna Tilting and Azimuth ............................32
Figure 4-20 Low SINR Cell Analysis -1..........................................................................................33
Figure 4-24 Low SINR Cell Analysis - 5.........................................................................................35
Figure 4-25 Low SINR Caused by Handover Failure.....................................................................36
Figure 4-26 Handover Failure Analysis..........................................................................................36
Figure 4-27 Handover Success after Adjustment ..........................................................................37
Figure 4-28 Overlapped Coverage Analysis -1..............................................................................38
Figure 4-33 Overlapped Coverage Analysis ..................................................................................41
Figure 4-34 Pilot Frequency Pollution Analysis -1 .........................................................................42
Figure 4-38 Pilot Frequency Pollution............................................................................................44
Figure 4-39 Pilot Frequency Pollution Analysis .............................................................................45
Figure 4-40 Location Where the Handover Takes Place...............................................................46
Figure 4-41 Handover Results .......................................................................................................47
Figure 4-42 Signaling in Case of Missed Matching of Neighboring Cells ......................................48

Figure 4-43 Workflow of Analysis on Missed Matching of Neighboring Cells................................49
Figure 4-44 Signaling in Case of No Response for Measurement Report.....................................50
Figure 4-45 Analysis on Missed Matching of Neighboring Cells -1 ...............................................51
Figure 4-49 Handover Restores after Elimination of Missed Matching..........................................53
Figure 4-50 Ping-Pong Handover ..................................................................................................55
Figure 4-51 Workflow of Elimination of Ping-Pong Handover Problem .........................................56
Figure 4-52 Analysis on Ping-Pong Handover Problem ................................................................57
Figure 4-53 Signaling Process of Handover on Control Plane ......................................................59
Figure 4-54 Overtime Handover.....................................................................................................61
Figure 4-55 Workflow of Solving the Handover Failure Problem...................................................62
Figure 4-56 Handover Failure ........................................................................................................63
Figure 4-57 Analysis of Handover Failure -1 .................................................................................63
Figure 4-58 Analysis of Handover Failure -2 .................................................................................64
Figure 4-59 SINR Value after Adjustment of Antenna Downtilt .....................................................65
Figure 4-60 Workflow of Analyzing Traffic Problem.......................................................................66
Figure 4-61 Cells Whose Maximum Traffic is Less than 5M..........................................................68
Figure 4-62 DT Test Data of Area 1...............................................................................................68
Figure 4-63 DT Test Data of Area 2...............................................................................................69
Figure 4-64 Cells Whose Average Traffic Ranges from 5M to 10M ..............................................71
Figure 4-65 DT Test Data -1 ..........................................................................................................71
Figure 4-69 Cause Analysis Procedure for Call Failures...............................................................75
Figure 4-70 Procedure for Troubleshooting an RRC Connection Establishment Problem............77
Figure 4-71 Authentication Failure Message (Cause Value: MAC Failure)...................................81
Figure 4-72 Authentication Failure Message (Cause Value: Synch Failure) .................................82
Figure 5-1 OMM-Level Performance Statistics Analysis Procedure..............................................89
Figure 5-2 Cell-Level Performance Statistics Analysis Procedure ................................................90
Figure 5-3 RRC Connection Establishment Procedure .................................................................91
Figure 5-4 Initial E-RAB Connection Establishment Procedure.....................................................94
Figure 5-5 Initial Context Setup Procedure....................................................................................99
Figure 5-6 E-RAB Setup Procedure...............................................................................................99
Figure 5-7 Handover Process Diagram ..........................................................................................101
Figure 5-8 Signaling Process Diagram of Handover Inside the eNB .............................................103
Figure 5-9 X2 Handover Signaling Process Diagram.....................................................................104
Figure 5-10 S1 Handover Signaling Process Diagram...................................................................105
Figure 5-11 Process of Analyzing Handover Problem....................................................................107
Figure 5-12 Process Flow When No Handover Command Received upon the Sent Measurement
Report ........................................................................................................................109
Figure 5-13 Process of Analyzing Msg1 Problem ..........................................................................110
Figure 5-14 Process of Analyzing RAR Problem............................................................................110
Figure 5-15 LTE Call Drop Problem-Solving Workflow ..................................................................116

Tables
Table 2-1: Drive Test and Post Processing Tools .............................................................................. 9
Table 3-1: Single Site Verification:....................................................................................................14
Table 4-1 Cells with Zero Coverage...............................................................................................24
Table 4-2 Handover KPIs Table.....................................................................................................45
Table 4-3 RSRP When the Handover Takes Place .......................................................................46
Table 4-4 SINR Statistics When the Handover Takes Place .........................................................47
Table 4-5 Solutions for Handover Latency Problem ......................................................................60
Table 4-6 Cells Whose Maximum Traffic is Less than 5M.............................................................67
Table 4-7 Parameter Table for Cells Whose Maximum Traffic is Less than 5M ...........................67
Table 4-8 Cells Whose Average Traffic Ranges from 5M to 10M .................................................70
Table 5-1 System Accessibility Indicators and Recommended Values .........................................87
Table 5-2 System Availability Indicators and Recommended Values............................................87
Table 5-3 Commonly Used Performance Statistics Analysis Methods..........................................88
Table 5-4 Major Sampling Points in the RRC Connection Establishment Procedure ...................91
Table 5-5 RRC Connection Establishment Failure Counters ........................................................92
Table 5-4 Major Sampling Points in the Initial E-RAB Connection Establishment Procedure.......95
Table 5-7 Initial E-RAB Connection Establishment Failure Counters............................................96

1 INTRODUCTION
 The document presents the solution of FDD LTE radio network optimization for
Wireless Network.
 The construction of the wireless communication network is a gradual, dynamic
process. After a period of operation, with the increase of subscribers,
environment transformation and some other uncontrollable factors, there would
be decrease of connection success ratio, fall of call quality and faded signals etc.
The formerly planned network can no longer keep pace with the rapid
development. To make adjustments and expansion of the systemic resources
and related parameters, that is scope of network optimization.
 The objective of this document is to describe:
 Network optimization preparation
 Network Optimization process
 Cluster Optimization
 OSS KPI Optimization
2 NETWORK OPTIMIZATION PREPARATION
 Before the network optimization, the RNO (Radio Network Optimization)
manager should assure that manpower and equipments are available. At the
same time the optimization schedule should be made and the following
information is collected:
 Radio network planning report;
 Latest site configuration table and radio parameter configuration table;
 OMM statistic data;
 Subscriber complaints of the existing network;
 Requirements for network performance targets, including specific requirements for
the coverage, capacity and QoS of the network;
 The responsibility matrix definition
 The project acceptance criteria.

2.1 Organization Structure
 The following picture shows the organization structure.
Figure 2-1: LTE Radio Network Optimization Organization Structure

RF Optimization
PM
Cluster
Optimization
Person In
Charge
SSV
Person In
Charge
Analysis
Engineer
Analysis
Engineer
Field Test
Engineer
Field Test
Engineer
Analysis
Engineer
Analysis
Engineer
Drive Test
Engineer
Drive Test
Engineer
KPI Analysis
Engineer
SSV Team 1 SSV Team N
DT Team 1 DT Team N Cluster
Optimization
Team 2
KPI Analysis
Engineer
Cluster
Optimization
Team M
2.2 Optimization Tools and Software
 In this section, tools used to collect data, analyze data and improve the
performance of network during the various stages of the project are introduced.
The tools used in network optimization process are listed in following table:
Table 2-1: Drive Test and Post Processing Tools
No. Equipments Model
1 Data Collection Software CNT(Communication Network Test) or NEMO
2 Post Processing Software
CNA (Communication Network Analysis) or
NEMO
3 Test User Equipment
4 Test Laptop
5 GPS
6 Test Vehicle For Drive Test
7 Digital map Map used for drive test
8 Power inverter Power supply at test vehicle
9
PC Server (Hard disk
should be 500G at least)
To store test data & post processing data
&analysis report
10 USIM cards
12
Performance analysis
software
NETMAX (Performance analysis software)
13 Planning software
CNP(Communication Network Planning) or
Atoll/Aircom

2.2.1 CNT
 ZXPOS CNT is an advanced wireless network air interface test tool. It is used
for trouble shooting, evaluation, optimization, and maintenance of the mobile
network. This tool integrates the professional and final-user senses and feelings,
completely tests and analyzes the self-network and that of the competitors, and
provides precise measurement means for various network KPIs.
 ZXPOS CNT supports all standards of 2G (GSM/GPRS/EDGE, CDMA IS95/1X),
3G (TD-SCDMA, WCDMA, CDMA2000), and 4G (LTE) networks and various
frequency bands of 900/1800/2100/2600MHz, 850/1900MHz, and 450MHz.
 Support LTE test services including Ping, FTP, HTTP, and TCP/UDP data service
test
 Support LTE Qualcomm test terminal
 Support CW, spectrum and TopN scan by PCTEL scanner
 Support ms-level frame exporting function of key data
 Support KPI real-time statistics
 Support indoor and outdoor tests
 Simple configuration, easy operation, stable and reliable for test
 Support real-time statistics function to quickly obtain test results
 Support tests of new techniques and new service quickly with continuous research
innovation capability to meet test requirements on new techniques of operators
2.2.2 CNA
 ZXPOS CNA is an intelligent wireless network optimization analysis system. It
supports all 2G, 3G, and 4G networks such as
GSM/GPRS/EDGE/CDMA/EVDO/WCDMA/ HSDPA/HSUPA/TD-SCDMA/LTE.
 ZXPOS CNA provides network oriented data processing and analysis report on
network optimization. ZXPOS CNA also provides multi-service QoS analysis for
multi-network quality evaluation.
 The main function is as following:
 Support LTE data analysis and processing
 Support simultaneous loading and viewing of up to 108 test data

 Support KPI analysis of PING/FTP/HTTP/TCP/UDP services
 GIS analysis function
 Support diverse advanced analysis functions to locate reasons of multiple abnormal
problems
2.2.3 NETMAX
 ZXPOS NETMAX is an advanced tools and the first choice for analyzing and
locating the network faults based on large quantities of Measurement Report
(MR) and Call Detail Trace (CDT). The workload of drive test and analysis can
be largely reduced due to its call recurrence and intelligence analysis,
 Analyze and optimize the coverage status of the whole network;
 Analyze and optimize the worst cell.
 Trace the VIP subscribers and ensure their QoS.
 Locate the subscribers with complaint; trace and analyze the signaling during the
call.
 Analyze and optimize the performance of the terminal.
2.2.4 CNP
 CNP is main tool for LTE network planning and simulation, the main functions
include:
 Support GIS
 Support 3 types schedule method
 Support PCI planning
 Support adjacent neighbor list planning
 Support Monte Carlo simulation
 Support traffic simulation
2.3 Cluster Definition
 LTE Optimization will be done cluster by cluster, and the number of eNodeBs in
one cluster from 20 to 30. The main rules of cluster definition are:
 The geographical location

 The service distribution
 The same TAC region information
 The sites in a cluster should not too many and the overlap between clusters is
needed. The definition of cluster should be confirmed by customer and ZTE
together.
3 NETWORK OPTIMIZATION PROCESS
 In this section, three stages of optimization are introduced, and the high level
optimization plans are presented for each individual stage of network
implementation and performance acceptance. Items under consideration are
target of optimization, methods of optimization and output for optimization, etc.
3.1 Optimization Milestone
Figure 3-1: LTE Radio Network Optimization Milestone

Network Construction
Network Design
Soft Launch Optimization
Pre-Launch Optimization
Site Survey
Single Site Verification
Cluster Optimization
Installation & Commissioning & Test
Network Soft Launch
Start End
Launched Optimization
Network Commercial
Network Design Commissioning PAC FAC
 LTE radio network optimizations include three major stages: Pre-launch
Optimization, Soft Launch Optimization and Launched Optimization.
 The main objective of Pre-launch Optimization is to control RF network air
interference, assure network hardware functionality work normally, and ensure
the KPIs target of Preliminary Acceptance Test is achieved. Pre-launch
Optimization includes two steps:
1 Single Site Verification
2 Cluster Optimization

 The objective of Soft Launch Optimization is to assure that no Punch List items
exists in the System. The Punch List is the list that consists of all defects
identified during the respective Preliminary Acceptance Test, during the period
prior to Final Acceptance. When all items on the respective Punch List have
been resolved in the System, a Final Acceptance Certificate will be issued.
 The optimization after issuing FAC is named as Launched Optimization. The
network can be put into commercial services after FAC. The objective of
Launched Optimization is to assure the network performance stabilization when
subscribes are increasing. Launched Optimization is focused on customer
experiences, system load, capacity balance, resource utilization, etc.
3.2 Pre-launch Optimization
3.2.1 Radio Frequency Verifying
 The network quality, capacity and coverage are related to the interference level
of the system. It is necessary to measure radio frequency and assess the
interference level in the given LTE band.
 Radio frequency verification must get permission of the operator and local
Telecommunication Administration. Radio frequency verification contains two
phases. The first phase is before the network construction, during site survey to
verify if there is interference at the site location, which will be carried out in the
spectrum that operator has available for this carrier and measure the band
designated by the operator. The second phase is after the network is on-line,
and radio frequency verifying is used to locate interference source.
3.2.2 Single Site Verification (SSV)
 The goal of single site verification is to eliminate potential errors introduced
during the site construction and configuration phases, so that following RF
optimization can be based on a reasonable basis, or else if any problems are
identified during optimization, it will be time-consuming to find out what factors
are responsible for the unexpected results. Normally during single site
verification, functional requirements are the main concerns; service performance
of the single site is not strictly required.
 The check items involved in the SSV can be classified into several categories,
for example, the equipment related problems, the engineering related problems,
the configuration related problems, etc. Typical problems are presented in the
following table. These problems should be solved before the service related
SSV test can be performed, to be more specific, these tests include coverage
test, VoIP, FTP, Ping，etc.

Table 3-1: Single Site Verification:
Equipment related Engineering related Configuration related
Abnormal power alarm
PA alarm
Transmission broken
Board related alarms
Internal/external link alarms
Antenna VSWR alarm
Clock source/GPS alarm
Cell/eNodeB down alarm
SW version alarm
…
Feeder
Loose connection of
connectors
Unreasonable antenna
position
Signal obstacle by buildings
Wrong antenna tilt and
azimuth
…
Center frequency
PCI
TAC
Cell status
Transmission
bandwidth
PRACH Configuration
…
 Above mentioned problems are to be solved by corresponding technical staffs.
Most of equipment related problems are to be solved by base station engineers,
engineering related problems are to be solved by RF optimization engineers and
installation engineers together, and configuration related problems are to be
solved by RF optimization engineers and OMC engineers. After site verification,
it should be free of obvious problems that might cause the site incapable of
being put on air.
 The SSV process is mainly based on stationary check and drive test, and the
former means performing desktop check on items according to configuration
data, or walking around the site using test UEs. For the stationary check,
needed materials are as the following list:
 Technical Site Survey (TSS) report
 Planned Engineering Parameters
 Planned Radio Parameters
 Site Configuration Parameters.
 These materials might also be used in drive test verification of the site.
 Before Single Site Verification, the critical and major level alarms for sites should
be eliminated. Most part of configuration related items can be fulfilled by
stationary check, whether the transmission bandwidth and center frequency
configuration can match the design requirement, whether the cell is in state of
reserved or barred, etc. The verification of some other items can also be
stationary as compared to drive test method. For example, the UL/DL frequency
assignment, the Physical Cell Identifier, the TAC of cells can be identified by
using a test UE with engineering mode, but these items can also be verified by
drive test. The drive test can be used to identify problems related to coverage,
handover, service accessibility and data throughput, which in turn will drill down
to problems related to engineering and configuration faults, such as feeders,
insufficient transmission bandwidth configuration, etc.

 As a result of Single Site Verification, SSV report is the main output. Besides,
adjustment suggestions for the site should be proposed by SSV engineers for
implementation.
3.2.3 Cluster Optimization workflow
 Main objective of cluster optimization is coverage optimization, neighbor cell
optimization and solve service access failure, call drop, and handover failure,
throughput issues etc. It is analysis collected data from DT and stationary test
data to analyze and locate problems, optimize network and verify adjusted
schema, which is an iterative process to assure achieve cluster acceptance
standard.
 Cluster Optimization work flow as following.
Figure 3-2: Cluster Optimization Work Flow

TSS/SSV Report System Parameters
Engineer parameters Digital Map
Preparation
Initial Coverage Test
Problems Analysis
Optimization Suggestion
Executions
Verification
If problems
solved?
Submit Report
Yes
No
Engineer
Parameters
Adjusting Report
Cluster
Optimization
Report
Radio Parameters
Adjusting Report
If acceptable?
End
Yes
No
Output
 Before optimization of cluster, the work needed to be prepared is listed as
follows.

3 Cluster Optimization Test Schedule
 Generally the ratio of on-air eNodeB of one cluster is over 80%, the cluster
optimization can be executed. The prior cluster can be arranged to optimize first.
After the optimization suggestion is adopted, a new test schedule will be made
to do justify if it is effective.
4 Test Route Planning
 Before cluster optimization, it is necessary to definite test route. It is required to
keep the continuous coverage along test route when not all of sites are on air.
5 Network Parameters Checking
 Before cluster optimization, the system parameters should be imported into the
OMC, such as eNodeB ID, Cell ID, TAC, Neighbor List, etc.
6 Optimization Method Definition
 The methods of optimization include two aspects. One is engineering
parameters adjustment, such as antenna azimuth, down tilt, height, etc. Another
is radio parameters adjustment, such as channel power allocation, handover
parameters, etc.
7 Document Preparation
 The following documents are necessary to prepare before cluster optimization:
 Technical Site Survey report (TSS)
 Single Site Verification report (SSV)
 Site Engineering Parameters Table
 OMC Configuration Parameters
8 Optimization Equipments Preparation
 Optimization equipments include: data collection software, post-processing
software, test handset, Scanner, laptop, digital map, GPS, test vehicles, etc.
3.3 Soft Launch (Trial-running Period) Optimization
 When network construction and pre-launch optimization work are finished, the
network can be put into a soft-launch stage, which means friendly users with
special access right can begin to use services provided by network and
generate useful feedback for the enhancement of network performance. The
goal of soft-launch optimization is to further optimize the whole network in order

to provide a continuous service experience in the majority of desired coverage
area and assure that no Punch List items exists in the System. If any problems
are detected in the soft-launch optimization stage, they should be solved and
checked thoroughly in the whole network. These problems might cover diverse
areas such as the EPC, eNodeB, transmission, UE, etc. Improving the related
KPIs to be commercial launch ready is the main purpose.
 The main target in Soft Launch Optimization stage is focused on coverage,
neighbor relationship, RRM parameters, and border area of clusters. Neighbor
relationship optimization mainly includes missing neighbor, unidirectional
neighbor, inter-frequency neighbor, and inter-RAT neighbor. Handover related
parameters should be optimized as well. Other RRM parameters such as access
control, power configuration, load control, etc., should also be tuned selectively
to meet the traffic requirements.
 The soft-launch optimization is normally based on both drive test and friendly
user feedback. As a supplementary data source, the signaling tracing is needed
to help troubleshooting some inner system problems.
 Although in this stage, traffic statistics from trial users are not too much, the
KPIs report generated from soft-launched network should still be helpful to
analyze the problems. At the same time, some optimization aiding tools based
on OMC statistics can be put into use too, which may also be helpful at the early
age of the commercial network.
 The output from soft-launch stage optimization is the performance optimization
report for the whole network, and also the complete set of parameters that have
been tuned for the forthcoming commercial launch. Of course these parameters
are to be optimized further in a dynamic process, but they serve as a good
baseline for further improvement of system performance.
3.4 Launched Optimization
 The target in Launched Optimization stage is both the coverage and system
performance from OMC statistics. Normally, after large subscribers register, the
optimization goal is straight forward, that is, to keep stable and satisfactory end
to end system performance, and enhance the system KPIs. The daily KPIs from
OMC statistics should be monitored and optimized to designed level.
 As main inputs for this optimization stage, OMC statistics and customer
complaints are to be used with higher priority than drive test and walk test data,
because after the commercial launch, traffic in the network has become
sufficient for providing detailed statistics on each KPI. The end to end
performance monitoring result can also help in this stage of optimization, for
example, for problem drilling down, trouble shooting, KPIs comparison, and cell
traffic load.

 The optimization process in this stage is mainly driven by KPIs analysis result.
For selected KPIs, daily analysis is made to keep up-to-date view on the
dynamically changing network performance. If any problems are identified and
classified into specific domains, corresponding teams from different domains are
responsible for the trouble shooting work, and make possible adjustments and
verifications until the problematic KPIs fall into the acceptable level again.
 The output from this optimization stage would be daily and weekly KPI reports,
and also monthly performance test report through drive test. Typical or critical
trouble shooting reports made in this stage are documented and reported as
well.
4 CLUSTER OPTIMIZATION
4.1 Single-Cell Coverage Analysis
 After the thorough drive test of the network, you need to check the antenna
connection sequence, single-cell overshooting, antenna side/back lobe
coverage, and zero-coverage cell based on data obtained from this test so as to
work out the actual coverage of each cell.
 During the single-cell coverage analysis, you will use the LTE COVER LINE and
PCI RSRP functions provided by CNA. (or other DT analysis tool)

Figure 4-1 CNA LTE COVER LINE


Figure 4-2 CNA PCI RSRP

4.1.1 Checking the Antenna Connection Sequence
 Problem Description
 You will find the following problems when you are checking the antenna
connection sequence:
 Antenna connection to wrong cell cause that the terminal conducts handover
between two cells of the same schema, thus impacting SINR.
 Antenna connection to wrong cell leads to no configuration for neighboring cell
relationship, thus leading to call drops.
 During the test, you need to solve this kind of problem if any.
 Problem Analysis
 Analyze the test data and check whether the main coverage direction of current
cell is also covered by another cell. If yes, there may exist wrong antenna
connection.
 Also, check the accuracy of engineering parameters and PCI.
 If the LTE system shares the same antenna & feeder system with other system,
you should analyze the problem by considering both the LTE and other system
test data.
 Solution

 Modify engineering connection for the cell where wrong antenna connection
exists.
 Study Case
 The antenna in Beiting Square of Guangzhou University campus should have
covered the cell FE2 (PCI94). Actually, it covers the cell FE1 (PCI93). In this
case, the engineering parameters and PCI are proved to be accurate, so the
antenna connection in this area is wrong.
Figure 4-3 Coverage Direction of Cell FE2 (PCI94)

4.1.2 Checking the Overshooting
 Overshooting appears when signals of a cell are found in its non-neighboring
cells, and RSRP of this cell is larger than -100 dBm. Overshooting usually leads
to overlapped coverage, pilot frequency pollution and ping-pong handover.

Figure 4-4: Cell with Overshot Signals

 Find out the cell with overshot signals based on the test data and by using the
PCI coverage analysis function provided by CNA.
Figure 4-5 PCI Coverage Analysis in CNA

 Solution
 To solve the overshooting problem, adjust the antenna azimuth and RS power.
At the same time, pay attention to the coverage of this cell on other roads, and
how the terminal conducts handover between current cell and other cell. This is
because the adjustment of antenna azimuth and RS power in current area may
impact the coverage and handover of other area.
 If it is unable to solve the overshooting problem, increase the coverage effect of
the cell which is nearest to current cell, and make a proper neighboring cell
relationship configuration.

 Case
 Overshooting problem is found in the cell FE3 (PCI 125) in the teaching building
of Guangzhou Medical University. The engineer adjusts the antenna azimuth
and RS power in this cell, and finally solve this problem.
Figure 4-6 Cell Coverage Before and After the Azimuth & RS Power Adjustment


4.1.3 Checking the Coverage of Antenna Side Lobe and Back Lobe
 Strong coverage is found on the direction of antenna side lobe and back lobe. It
leads to pilot frequency pollution, poor SINR and abnormal handover.
 Find out the cell which has strong coverage at the direction of antenna side lobe
and back lobe by analyzing the test data and using the PCI coverage analysis
function provided by CNA. This problem is usually caused by reflection, wrong
feeder connection, wrong version file and wrong antenna.
 Solution
 Troubleshoot this problem based on actual situation.
 Case
 In the Arts Building of Guangzhou Foreign Language College, the coverage area
of cell FE1 (PCI 138) is found overlapped with the cell FE3 (PCI 140). This is
due to reflection of cell FE3 (PCI 140).

Figure 4-7 Overlapped Coverage Caused by Reflection



4.1.4 Checking the Zero-Coverage Cell
 Sometimes, no measurement value can be obtained for a cell in the test area.
On this occasion, you need to check all unused cells based on the test data and
try to find out whether this problem is caused by coverage or cell.
 Find out the zero-coverage cell by analyzing the test data and using the PCI
RSRP function provided by CNA.

Figure 4-8 PCI's RSRP Function

 Alternatively, you can find out the zero-coverage area by exporting PCI and
RSRP of all main serving cells and their neighboring cells into an excel, and
check this parameters in the excel. Compare the PCIs in this excel with the PCIs
of the whole test area. The cell without PCI can be considered as the cell with
zero coverage.
 Solution
 Check the working status, parameter configuration, location and coverage of
current cell.
 Case
 The cells with zero coverage are listed in the table below:
Table 4-1 Cells with Zero Coverage
NE ID PCI Reason Solution
6006_Guangzhou Traditional
Medical College, FE2
4 Broken link
2871_Western Inner Circle
Road, Guangzhou, FE4
0 Broken link
1008_Geigang, Guangzhou,
FE1
114
Wrong parameter
configuration

4.2 Cluster Coverage Analysis
4.2.1 Overview
 The co-frequency networking technology is widely adopted in LTE network.
However, this technology will cause severe co-frequency interference. Therefore,
the network optimization engineers should work hard to reduce co-frequency
interference and provide good network coverage.
 Engineers usually come across missed coverage, poor coverage, overshooting
and pilot frequency pollution. These problems appear when:
 Inaccurate RAN planning
 Inaccurate RAN planning may increase future network optimization workload.
Therefore, engineers should work hard to provide an accurate RAN planning.
 Location deviation between sites defined in network planning and actual sites
 Deviation between engineering parameters defined in network planning and
actual engineering parameters
 The actual antenna height, azimuth, inclination, and type are different what is
specified in the network planning, and thus the actual network coverage cannot
meet customer's requirement. These problems can be solved by future network
optimization, but great project cost is also involved.
 RAN environment
 RAN environment may change where the network construction is different from
original construction plan, or overshooting/pilot frequency pollution appears due
to complicated road type and signal reflection. In this case, engineers should
adjust the antenna azimuth and inclination angle so as to avoid signal reflection
and reduce the transmission distance of signals.
 New requirements on network coverage
 Coverage area, new sites and site relocation will bring new requirements on
network coverage.
4.2.2 Work Scope of Coverage Optimization
 Engineers usually come across missed coverage, poor coverage, overshooting,
pinhole coverage and pilot frequency pollution. The missed coverage problem
can be consider as poor coverage problem while overshooting and pilot
frequency pollution can be considered as overlapped coverage problem.

Therefore, the main task of network optimization is to eliminate poor coverage
area and overlapped coverage area.
4.2.3 Weak-Coverage Optimization
4.2.3.1 Definition of Weak-Coverage
 Weak coverage refers to the situation where signal is not strong enough to
guarantee a stable network and required network performance.
 The area whose RSRP is less than -110dBm is considered as a weak coverage
area.
4.2.3.2 How to Find out Weak-Coverage Area
 Perform the following steps to find out weak coverage area based on DT test
data:
 In the CNA, find Server Cell RSRP under the sub-node Measurement of MS1
from navigation tree on the left, right-click Server Cell RSRP and select View In
Map from the short-cut menu, or click and drag Server Cell RSRP into the map
window on the right.
Figure 4-9 Weak Coverage Area Analysis -1

 Find Dynamic Link under the MS1 node from the navigation tree on the left,
right-click it to select Add from the short-cut menu.


 In the pop-up dialog box, select LTE-SC Link and click Apply. Wait until the
success message is displayed.

 From the toolbar, click and select LTE-SC Link from the drop-down list.
The GPS dotted line is selected.


 Check the line connection of server cell and RSRP legends, and you can find
signal intensity of your desired area.

4.2.3.3 How to Eliminate Weak-Coverage
 Use the following methods to eliminate the weak coverage area:
 Adjust the antenna height, azimuth and tilting.
 Add new sites, RRU long-distance connection and cell long-distance connection.
 Adjust the RS power.
 Re-configure the neighboring cell relationship.

 As for the coverage in residential buildings and campus, you can use various
coverage solutions, for example small-sized plate-shape antenna and small-
sized omni-directional antenna.
 It is suggested that you adjust engineering parameters ahead of adjusting RS
power and other parameters.
4.2.3.4 Study Cases
 PCI148 Weak Coverage
 In the cell PCI48, the RSRP of an area is found lower than -110dBm.
Figure 4-14 DT Test Results-1

 As shown in the figure below, yellow arrow indicates the coverage effect of cell
PCI43, blue arrow indicates the coverage area effect of cell PCI48, and red
arrow indicates the cell PCI12. The coverage effect in PCI48 and PCI12 is not
so good because most signals are blocked by buildings, and poor coverage of
PCI43 is due to inner road coverage and green belt coverage.

Figure 4-15 Coverage Effect of Cell PCI48, PCI43 and PCI12

 Solution
 Based on the site survey results, adjustment of engineering parameters is
proved to be invalid for weak coverage elimination. In this study case, new cells
are added to improve the coverage effect.
 PCI30 Weak Coverage
 Weak coverage is found in the cell PCI30.
Figure 4-16 DT Test Results-2

 As shown in Figure 4-17, the section 1 is covered by the cell PCI30 and PCI18,
but the coverage effect in this section is quite weak.

Figure 4-17 Weak Coverage Analysis in Cell PCI30 -1

 As shown in Figure 4-18, the antenna azimuth for the cell PCI30 is proper. If you
find that there is no obstacle between cell PCI30 and section 1, you can adjust
the antenna azimuth about 30 degrees so as to increase the coverage effect for
section 1.
Figure 4-18 Weak Coverage Analysis in Cell PCI30 - 2

 Solution
 Check whether there is any obstacle at 120 degree of cell PCI30. If not, adjust
the antenna azimuth about 30 degrees clockwise.
 Lower the antenna tilting about 2 degrees for cell PCI18 so as to reduce its
interference on section 1. Afterwards, conduct drive test for the coverage area of
cell PCI18 so as to check whether this adjustment impacts the coveage area for
other sections.

Figure 4-19 DT Test Results after Adjustment of Antenna Tilting and Azimuth

4.2.4 SINR Optimization
4.2.4.1 SINR Definition
 SINR (signal to interference plus noise ratio) indicates the ratio between
strength of received transmission signals and strength of received interference
signals (including noises and interference).
 PDCCH SINR = RS power of best serving cell / interference from the coverage
cell
 SINR requirements vary with operators and network construction stages. China
Mobile requires that SINR of 95% cells should be larger than -3dB. In actual
projects, we will conduct network optimization to guarantee that SINR of 1%
cells in a project is less than -3dB, and SINR of 5% cells in a project is less than
0dB
 Root cause of Low SINR : weak coverage/Interference
4.2.4.2 How to Find a Cell of Low SINR
 Perform the following steps to find a cell of low SINR based on the DT test data:

Figure 4-20 Low SINR Cell Analysis -1




 From the toolbar, click and select LTE-SC Link from the drop-down list.
The GPS dotted line is selected.

 Check the line connection of server cell and RSRP legends, and you can find
out the signal intensity of your desired area.

Figure 4-24 Low SINR Cell Analysis - 5

4.2.4.3 How to Raise the SINR of a Cell
 Use the following methods to raise the SINR of a cell:
 Avoid handovers and overlapped coverage between cells of the same network
schema.
 Reduce the occurrence possibility of pilot frequency pollution area.
 Eliminate poor coverage area and overshooting area.
 Solve the RRC re-establishment problem caused by delayed handover, no
handover and handover failure.
4.2.4.4 Study Cases
 Low SINR in Cell PCI150 and Cell PCI144 Caused by Handover Failure
 The test UE fails to finish the handover from cell PCI150 to cell PCI144.

Figure 4-25 Low SINR Caused by Handover Failure

 eNodeB does not make judgement after the test UE sends out the measurement
report for cell PCI150. Two seconds later the test UE triggers RRC re-
establishment but is rejected. However, the neighboring cell relationship
configuraiton is proved to be correct.
 On this occasion, you can make a conclusion that no judgement on
measurement report and refusal on RRC re-establishment appear because of
low-speed measurement.
Figure 4-26 Handover Failure Analysis

 Solution
 Make an offset of 3dB when the test UE conducts handover from cell PCI150 to
cell PCI144.

Figure 4-27 Handover Success after Adjustment

4.2.5 Overlapped Coverage Optimization
4.2.5.1 Overlapped Coverage Definition
 At least two cells are found covering a continuous coverage area, and the
coverage effect from these cells meets network performance requirements. On
this occasion, this coverage area is regarded as an overlapped coverage area.
4.2.5.2 How to Find Overlapped Coverage

Figure 4-28 Overlapped Coverage Analysis -1




 From the toolbar, click and choose LTE-Cover Link > LTE All Cover
from the drop-down list. The CNA will conduct coverage analysis for all cells.
If you choose LTE-Cover Link > LTE Cell Cover from the drop-down list and
select a cell, the CNA will conduct coverage analysis for this selected cell.

 Check the coverage area of your desired cell based on RSRP analysis.


4.2.5.3 How to Solve Overlapped Coverage
 Use the following methods to eliminate overlapped coverage:
 Adjust the antenna azimuth, tilting and antenna height.
 Adjust RS power.
 Combine two cells when the angle between antennas for these two cells is too
small.
4.2.5.4 Study Cases
 Overlapped Coverage from Cell PCI160, PCI144 and PCI150
 The SINR of sections shown in figure is lower than -3dB.
 The coverage of cell PCI160 and that cell PCI150 is overlapped in section 1,
and ping-pong handover is also found in this section. The coverage of cell
PCI150 and that of cell PCI144 is also overlapped.

Figure 4-33 Overlapped Coverage Analysis

 Solution
 Adjust the tilting of cell PCI160 from 1 degree to 3 degrees.
4.2.6 Pilot Frequency Pollution Analysis
4.2.6.1 Definition of Pilot Frequency Pollution
 In LTE system, it can be considered that pilot frequency interference is posed on
a point when many strong pilot frequencies are found on a point but no main
pilot frequency exists.
 Before the definition of pilot frequency pollution is presented, you should be
familiar with three concepts: strong pilot frequency, main strong pilot frequency
and too many pilot frequencies.
 Strong Pilot Frequency
RSRP > -100dbm
 Main Strong Pilot Frequency
RSRP_number >= 4
 Too Many Pilot Frequency
RSRP(strongest)－RSRP(weakest) <= 6dB

 In LTE system, it is considered that pilot frequency pollution is posed on a point
when the following two conditions are met:
 RSRP of more than four cells is larger than -100dB.
 RSRP(strongest) － RSRP(weakest) <= 6dB
4.2.6.2 How to Find an Area with Pilot Frequency Pollution
Figure 4-34 Pilot Frequency Pollution Analysis -1

 Select IE Label Select from the Map toolbar.


 In the Label Select dialog box, select Server Cell PCI and click OK.

 PCIs of all main server cells are displayed.


 If more than one PCI is found in an area, it means that pilot frequency pollution
is posed on this area.
 You can also find the area with pilot frequency pollution by checking call drops
and handover failure through CNA/CNT.
4.2.6.3 How to Eliminate Pilot Frequency Pollution
 To eliminate pilot frequency pollution, you need to determine a cell and use it to
provide main strong pilot frequency. To enable a cell to provide main strong pilot
frequency:
 Adjust engineering parameters of antenna
 Adjust RS power.
4.2.6.4 Study Cases
 Pilot Frequency Pollution in Cell PCI113 and Cell PCI134
 SINR of the section covered by cell PCI113 and cell PCI134 is quite low.
Figure 4-38 Pilot Frequency Pollution

 As shown below, when the UE conducts handover from cell PCI113 to cell
PCI149, two measurement reports have not been judged. The section shown
below is covered by the third cell, and pilot frequency pollution is also found in
this section.

Figure 4-39 Pilot Frequency Pollution Analysis

 Solution
 Downtilt the antenna 3 degrees and pan azimuth 20 degrees counter-clockwise
in cell PCI 149.
4.3 Handover Analysis
 You usually perform the handover analysis from the following perspectives:
 Missed matching of neighboring cells
 Wrong matching of neighboring cells
 Ping-pong handover
 Handover latency
 Handover failure
 Before conducting the handover analysis, you need to collect statistics of
handover KPIs as shown below:
Table 4-2 Handover KPIs Table
Index
Handover
Success Rate
Handover
Start
Handover
Success
Handover
Failed
Date
1
2
3
4

5
 After all required statistics in this table is complete, you need to work out the
following information accordingly:
 Location where the handover takes place
Figure 4-40 Location Where the Handover Takes Place

 RSRP when the handover takes place
Table 4-3 RSRP When the Handover Takes Place
RSRP Statistics
RSRP
Range
> -80dBm > -90dBm > -100dBm > -110dBm <= -110dBm
Counts
Remarks



 Handover results

Figure 4-41 Handover Results

 Red curve and circle shown in this figure indicates that the handover failed.
 SINR when the handover takes place
Table 4-4 SINR Statistics When the Handover Takes Place
SN SINR Range July 5
th
July 7
th
July 16
th
1 <=-3dB 28 20 10
2 > -3dB 6 6 2
3 > 0dB 2 4 5
4 > 3dB 6 5 5
5 > 10dB 1 1 0
6 > =15dB 0 0 0
Total 36 22
4.3.1 Missed Matching of Neighboring Cells
4.3.1.1 Definition of Missed Matching of Neighboring Cells
 Missed matching of neighboring cell refers to the situation that the target
handover cell in the measurement report sent out by the UE cannot be found in
the neighboring cell list configured for the system. Missed matching of
neighboring cells usually lead to low downloading traffic, low SINR, RRC re-
establishment and call drops.
4.3.1.2 How to Find the Missed Matching of Neighboring Cells
 In LTE system, the UE does not conduct measurement based on the
neighboring cell list but conduct measurement for all cells all through workable

frequencies. Later on, the UE reports the cells which enjoy strongest signal
intensity which is beyond the handover threshold.
 When the missed matching of neighboring cells exists, you will find that:
 The UE tries to send out measurement report for several times.
 The UE does not receive any response from the system after it sends out the
measurement report.
 Low SINR (< -3dB)
 You need to analyze the handover failure and the measurement reports sent out
by the UE.
 If the UE sends out the measurement report but does not receive response from
the system, you can find the signaling tracing statistics as shown below:
Figure 4-42 Signaling in Case of Missed Matching of Neighboring Cells

 Comply with the workflow shown below to conduct the analysis on missed
matching of neighboring cells:

Figure 4-43 Workflow of Analysis on Missed Matching of Neighboring Cells

Obtain the neighboring cell list
from the signalling of RRC
Connection Reconfiguration
Find out the point where the UE sends out
measurement report but does no receive
response based on the DT test data
Find out the latest signalling of RRC
Connection Reconfiguration before the
measurement is reported
Check whether the PCIs
contained in the measurement
report can be found in the
neighboring cell list
Configure the
neighboring cell
relationship and
conduct the
verification test
N
Other reasons
Check the neighboring cell list
for the cell in the RRC
Connection Reconfiguration
signalling for this cell
Y
 As for this workflow, you should be clear of the following items:
 You need to find out the signaling which indicates that no response is made for
the measurement report based on the DT test data.
 You need to obtain the PCI of target handover cell based on the measurement
report.
 You need to obtain the neighboring cell list for the serving cell based on the test
data.
 If no PCI of the target handover cell can be found in the neighboring cell list, it
indicates that the missed matching of neighboring cell exists.

 If the PCI of the target handover cell can be found in the neighboring cell list, it
indicates the handover problem is caused by other factors but the missed
matching of neighboring cells.
4.3.1.3 How to Solve the Problem of Missed Matching of Neighboring Cells
 Add new neighboring cell
4.3.1.4 Study Cases
 In the signaling shown below, many measurement reports are sent out but no
response is received.
Figure 4-44 Signaling in Case of No Response for Measurement Report

 As shown in the following handover takes place according to last measurement
report, it is another cell but not the target cell where the handover takes place.
This handover takes place one minute after the first measurement report.
 The content of the first measurement report and that of the second
measurement report are the same:

Figure 4-45 Analysis on Missed Matching of Neighboring Cells -1

 The content of the third measurement report is shown below:

 The neighboring cell list contained in the RRC Connection Reconfiguration
signaling for the serving cell is shown below:


 In this neighboring cell list, you can find cell PCI19 but not the cell PCI20. It
indicates that cell PCI20 has not been configured as the neighboring cell for cell
PCI72, and thus handover between these two cells fails.


 Solution
 Set the cell PCI20 as the neighboring cell of cell PCI71.
 Verification Test Results
 In the figure below, you can find that the UE can conduct handover when
moving through these two cells and SINR restores to normal value.
Figure 4-49 Handover Restores after Elimination of Missed Matching


4.3.2 Wrong Matching of Neighboring Cells
4.3.2.1 Definition of Wrong Matching of Neighboring Cells
 Wrong matching of neighboring cells refers to the situation that two cells of the
same PCI are configured as neighboring cell for main serving cell, or PCI of
neighboring cell is the same as that of main serving cell.
4.3.2.2 How to Find Wrong Matching of Neighboring Cells
 Wrong matching of neighboring cells exists when:
 The handover fails frequently after the measurement report is sent out.
 The UE is not handed over to the cell of strongest signal intensity.
 SINR is quite low, usually lower than -3dB.
 At least two cells in the measurement list are of the same PCI.
4.3.2.3 How to Eliminate Wrong Matching of Neighboring Cells
 Modify the PIC of neighboring cell.
4.3.3 Ping-Pong Handover
4.3.3.1 Definition of Ping-Pong Handover
 Ping-pong handover refers to the situation that the UE conducts handover
frequently in the handover belt between more than two cells.
4.3.3.2 How to Find Ping-Pong Handover
 You can check the downloading rate and handover quantity through GIS. Ping-
pong handover exists when:
 The downloading rate is quite low.
 SINR is quite low.
 The UE conducts handover for more than three times in the handover belt.

Figure 4-50 Ping-Pong Handover

4.3.3.3 How to Eliminate Ping-Pong Handover
 Comply with the following workflow to solve the ping-pong handover problem:

Figure 4-51 Workflow of Elimination of Ping-Pong Handover Problem

Process the DT test data
through CAN and then export
a file containing location
information of handover
points
Display handover points in
MAPINFO
Display traffic in MAP
Eliminate ping-pong
handover problem
Ping-pong handover
exists?
Y
Solve this problem in the
same way of elimination of
pilot frequency pollution
N
4.3.3.4 Study Cases
 In the area shown below, traffic is quite low and the UE conducts handover
frequently.

Figure 4-52 Analysis on Ping-Pong Handover Problem


 More than 15 times of ping-pong handover take place when the UE moves
between cell PCI161 and cell PCI 150. Ping-pong handover leads to low SINR
and low traffic.

 Solution
 Lower the antenna tilting 3 degrees in both cell PCI161 and cell PCI150.
 After the adjustment of antenna downtilt, traffic and SINR in these two cells
restores, and ping-pong handover disappears.
4.3.4 Handover Latency
4.3.4.1 Definition of Handover Latency
 Handover latency here refers to the handover latency on control plane. The
latency starts at the time the UE receives the RRC Connection Reconfiguration
message, and ends at the time when the UE reports the MSG3 message.
4.3.4.2 How to Find Handover Latency
 The handover latency is considered to be quite large when it is larger than the
latency value set by the network operator.
 The signaling on control plane during the handover goes through two stages:
 Latency from the reception of RRC Connection Reconfiguration message to the
sending of MSG1 message
 Latency from the sending of MSG1 message to the reception of MSG2.
4.3.4.3 How to Solve the Handover Latency Problem
 Comply with the workflow shown below to solve the handover latency problem:

Figure 4-53 Signaling Process of Handover on Control Plane

Collect statistics of handover
latency on control plane CNA
Average handover latency is
larger than the latency set by
operator?
End
Is MSG1 re-sent
frequently?
There is something wrong with
PRACH
Is the latency from
MSG1 to MSG2 too
large?
There is something wrong with
RRC connection reconfiguration
Y
N
Y
N
N
Y
 You can try to solve the handover latency problem by using following methods.
However, methods listed here are applicable to frequent sending of MSG1
message but not the reception of downlink RAR.
 Obtain your desired data by using proper test devices and test terminals which
can help to obtain the signaling.

 If the MSG1 is not re-transmitted but the interval between MSG1 retransmission
and RRC connection reconfiguration message is quite large, check the value of
PRACH Config Index, which indicates the interval of PRACH transmission (for
more details, see protocol 36211.5.7). If the value of PRACH Config Index is
quite large, please set it to a lower value.
 If frequent MSG1 transmission is found, you need to collect statistics of packets
received on PRACH. Also, you need to the uplink interference information. If the
electrical level of interference is larger than -110dBm, please troubleshoot the
uplink interference problem or modify the value of expected PRACH reception
power. Also, you can adjust the detection threshold of absolution PRACH prefix.
 If the UE has received MSG1 and the system has sent out MSG2, there may be
something wrong with the uplink. In this case, you can adjust engineering
parameters, RS power, PCI, initial CCE convergence degree.
 For clear idea of troubleshooting methods for handover latency, see solutions
listed below:
Table 4-5 Solutions for Handover Latency Problem
SN
Uplink or
Downlink?
Solution Remarks
1
Uplink
Adjust the PRACH Config Index
2
Troubleshoot the uplink interference
problem
3
Raise the expected PRACH reception
power
4
Lower the detection threshold of the
absolute PRACH prefix
5
Downlink
Adjust the engineering parameters
6 Adjust the RS power
7 Adjust the PCI settings
8 Raise the initial convergence degree
4.3.5 Handover Failure
4.3.5.1 Definition of Handover Failure
 Handover failure starts from the time the RRC Connection Reconfiguration
message is sent out, and ends at the time the RRC reconnection is triggered.
 You can analyze this problem by using different measurement indexes, such as
RSRP and SINR.

4.3.5.2 How to Find Handover Failure
 As shown below, the UE fails to finish the handover usually due to overtime
handover.
Figure 4-54 Overtime Handover

4.3.5.3 How to Solve the Handover Failure Problem
 Comply with the workflow shown below to solve the handover failure problem:

Figure 4-55 Workflow of Solving the Handover Failure Problem

Check whether there is
any problem with RSRP,
SINR and MSG2
reception
Troubleshoot the
coverage problem
Check neighboring cells
Check whether there is
any problem with MGS1
transmission
Troubleshoot the
neighboring cell
problem
Troubleshoot the
MSG1 problem
Check whether the
threshold of synchronous
detection is too small
Modify the value of
related parameters
Check whether T304 works
overtime
Modify the value of
T304
End
Y
Y
Y
Y
Y
N
N
N
N
N
 If RSRP, SINR and RAR reception are abnormal, it indicates that the handover
failure is caused by poor downlink coverage and non-synchronization between
UE and target cell. On this occasion, you need to improve the network coverage
effect.
 During the neighboring cell check, what you have to do is to check whether
there exist cells of the same PCI.
 If the MSG1 transmission is abnormal, troubleshoot this problem by modifying
the value of handover latency.
 If the value of synchronization detection threshold is too small, non-
synchronization may appear, thus leading to RRC re-establishment.

 T304 overtime usually leads to handover overtime. In this case, reset the value
of T304 to a larger value.
4.3.5.4 Study Cases
 Handover failure is found in the area shown below:
Figure 4-56 Handover Failure

 Handover failure occurs in this area due to weak network coverage.
Figure 4-57 Analysis of Handover Failure -1


 As shown in Figure 4-58, the UE conducts handover between cell PCI304 and
PCI161. At the same time, the value of SINR is quite low, as shown in Figure
4-58.
Figure 4-58 Analysis of Handover Failure -2


 Solution
 Lower the antenna tilting 3 degrees in cell PCI60.

 After the adjustment of antenna tilting, the value of SINR restores and handover
failure problem disappear.
Figure 4-59 SINR Value after Adjustment of Antenna Downtilt

4.4 Downloading Rate Analysis
4.4.1 Overview
 Different from traditional networks, LTE network is a data service-based network,
and thus traffic serves as an important KPI of network performance.
 Main objectives of LTE network improvement include faster data rate, short
latency, lower cost and larger system capacity and coverage.
 During the LTE network optimization period, you usually need to solve the
following problems:
 Weak coverage, low SINR, inter-frequency interference and intra-frequency
interference
4.4.2 Analysis Methods
 Comply with the following workflow to analyze the traffic problem:

 Check whether any alarm is reported for the fault site.
 Check whether interference or weak coverage exists.
 Check engineering parameters and transmission.
 Write down problem description and check results and send this problem report
to R&D engineers.
Figure 4-60 Workflow of Analyzing Traffic Problem

Any alarm is reported for the
fault cell
Clear the alarm
Find out the area of low service rate
based on DT test data
Does the rate meet
requirements of radio
environment
Are the parameters of serving
cell meet requirements
Improve the coverage effect for the
area of low rate
Modify the value of abnormal
parameter
Is the transmission abnormal
Submit problem report to the
customer and ask help for solving
transmission problem
Y
Y
Y
Y
N
N
N
N
There may be something wrong with
the Version file. Report the problem
and problem location, track the
progress and verify the network
performance after adjustment

4.4.3 Analyzing the Cell with the Maximum Downloading Rate Less than
5M
 Export traffic data from the DT test data, and filter out all cells whose maximum
traffic is less than 5M.
Table 4-6 Cells Whose Maximum Traffic is Less than 5M
Index ServerCell PCI
Max PDCP Downlink PDU
Traffic (Mbit/s)
Date
1
2
Table 4-7 Parameter Table for Cells Whose Maximum Traffic is Less than 5M
Index PCI RSRP SINR
PDCP DL PDU Traffic
(Mbit/s)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

Figure 4-61 Cells Whose Maximum Traffic is Less than 5M

4.4.3.1 Area 1
Figure 4-62 DT Test Data of Area 1

 When the UE is conducting handover from cell PCI149 to cell PCI134, it sends
out measurement report but does not receive any response. It triggers RRC
connection re-establishment in target handover cell but is refused. Therefore, it
triggers the re-establishment of a new service.

 After the check of neighboring cell configuration, no wrong configuration is found.
However, cell PCI147 and cell PCI149 pose pilot frequency pollution over area 1,
thus leading to low SINR, handover failure and low bitrate.
 Solution
 Lower the power of cell PCI147 and cell PCI149 from 12 to 9, and increase the
power of cell PCI134 from 9 to 12.
 After the adjustment, when the UE moves through this area, it conducts
handover between cell PCI 86<—> cell PCI 134<—> cell PCI 133<—> cell PCI
113. Cell PCI147 and cell PCI149 pose no coverage on this area. Also, SINR is
raised to 10dB, and handover and rate restore to normal status.
4.4.3.2 Area 2
Figure 4-63 DT Test Data of Area 2

 As shown in figure below, when the UE moves through area 2, it conducts
handover between cell PCI32<—> cell PCI 64<—> cell PCI 4<—> cell PCI 64.
Ping-pong handover can be found when the UE moves between cell PCI41 and
cell PCI64, thus leading to call drops, service re-establishment and low rate.

 The cell PCI64 poses network coverage on a campus, and the coverage radius
here is quite small. When the UE conducts handover between cell PCI41 and
cell PCI64, signals from cell PCI64 fade away quickly, thus leading to low SINR,
call drops and no service traffic.
 Solution
 To solve the ping-pong handover problem, you need to eliminate cell PCI64's
coverage on this area. Therefore, lower the antenna inclination angle in this cell
3 degrees, or reduce the RS power in this cell.
 After the adjustment, ping-pong handover and call drops disappear, and traffic
also restores.
4.4.4 Analyzing the Cell with the Average Downloading Rate Ranging from
5M to 10M
Table 4-8 Cells Whose Average Traffic Ranges from 5M to 10M
SN PCI Average PDCP Traffic (Mbps) Date
1 64 0.07 2012/7/16
2 149 0.51 2012/7/16
3 61 3.65 2012/7/16
4 139 3.67 2012/7/16
5 134 4.56 2012/7/16
6 82 5.85 2012/7/16
7 114 5.91 2012/7/16
8 88 6.26 2012/7/16
9 2 8.47 2012/7/16
10 37 8.94 2012/7/16
11 94 9.11 2012/7/16
12 140 9.42 2012/7/16
13 121 9.42 2012/7/16

Figure 4-64 Cells Whose Average Traffic Ranges from 5M to 10M

4.4.4.1 Area 1
 See 4.4.3.1.
4.4.4.2 Area 2
Figure 4-65 DT Test Data -1


 As shown above, when the UE conducts handover between cell PCI11 and cell
PCI21, it sends out measurement report but eNodeB does not receive this report,
or UE does not receive the handover judgment sent by eNodeB, thus leading to
handover failure, service re-establishment and low rate.
 Area 2 is covered by cell PCI11, cell PCI21, cell PCI28 and cell PCI69, and
RSRP here is about -101dB. The cell PCI is about one kilometer away from this
area, namely its signal overshoot to this area. Also, cell PCI11 and cell PCI21
are not neighboring cells. Therefore, when the UE moves through cell PCI11, it
cannot receive handover judgment for handover to cell PCI21 from eNodeB
although it has sent the measurement report.
 Solution
 Lower the tilting in cell PCI11, or configure neighboring cell relationship for cell
PCI11 and cell PCI21.
4.4.4.3 Area 3

 When the UE is making phone calls or using data service in cell PCI25, it
detects strong RSRP from cell PCI68, so it triggers handover from PCI25 to

PCI68. However, the handover fails, service re-establishment is refused and no
traffic can be found in this area for a period of time.
 After the UE receives measurement judgment from eNodeB, it sends back the
Handover Reconfiguration Completion message. RS power in cell PCI68
disappear suddenly and the handover fails. The problem may be caused by cell
breakdown.
 Solution
 Troubleshoot problem in cell PCI68.
4.4.4.4 Area 4

 When the UE conducts handover from PCI27 to PCI39, handover fails. Call
drops, service re-establishment and low rate are also found in this area.
 The cell PCI29 covers the Information Building 3. However, the antenna of this
cell is installed in the center of building roof, thus leading to weak coverage over
this area.
 Solution

 Configure neighbour cell relationship for cell PCI27 and cell PCI37.
4.4.4.5 Area 5

 When the UE moves from cell PCI53 to PCI61, the UE sends out a lot of
handover requests to eNodeB, but does not receive any handover judgment.
 There are residential buildings between cell PCI53 and PCI61, and there is a
high-rise crossroad in area 5. On this occasion, signals from PCI53 fade away
quickly at the turning corner.
 Solution
 Lower the RS power of cell PCI53 from 12dBm to 9dBm, and raise the RS
power of cell PCI61 from 6dBm to 9dBm. Moreover, increase neighboring cell
offset by 3dB.
 After the adjustment, handover and rate in area 5 restore.

4.5 Access Analysis
4.5.1 Call Failures
 Figure 4-69 shows the cause analysis procedure for call failures.
Figure 4-69 Cause Analysis Procedure for Call Failures

Start
Identify a radio access problem
using a data analyzer
Drive test
data
Radio access failure
RRC connection
establishment failure
Authentication and
encryption failure
E-RAB setup failure
Troubleshoot an RRC
connection
establishment problem
Troubleshoot an
authentication and
encryption problem
Troubleshoot an E-RAB
setup problem
Troubleshoot an
abnormal problem
End
 The call failure cause analysis procedure can be explained as follows:
1. Using such drive test data analyzers as TEMS Discovery or ZXPOS CNA-FDD LTE,
determine the exact time when a radio access failure occurs, and then retrieve the
pilot information and signaling procedure before and after this failure occurs.
2. Align the time of the UE collected signaling with that of the STS signaling trace, and
then find the exact time of problem occurrence using the STS signaling trace tool.
3. Check whether any hardware alarm or notification is raised for the problematic cell
through the OMC, when a radio access failure occurs.

4. Using the STS signaling trace tool and UE signaling procedure, locate the radio
access failure problem by following this cause analysis procedure.
5. Analyze and solve the radio access problem by following the specific
troubleshooting procedure, including RRC connection establishment, authentication
and encryption, E-RAB connection establishment, and equipment fault.
4.5.2 RRC Connection Establishment Failures
4.5.2.1 Procedure for Troubleshooting an RRC Connection Establishment Problem
 An RRC connection establishment failure can be processed by using the UE
signaling procedure and STS signaling trace tool, as shown in Figure 4-70.

Figure 4-70 Procedure for Troubleshooting an RRC Connection Establishment
Problem
4.5.2.2 Cause Analysis
 An RRC connection establishment failure may be caused by one of the following
factors:
UE sent RRC
request
?
eNodeB received
RRC request
?
eNodeB sent setup
message
?
UE received setup
message
?
UE abnormal
problem
Congestion or other
problem
Adjust PDCCH
parameters
End
Yes
No
No
No
No
Yes
Yes
Yes
UE sent setup
complete message
?
eNodeB received
setup complete
message
?
Adjust PRACH
parameters
Cell reselection
Optimize cell
reselection
Radom Access
contention
Adjust UL open
loop power control
parameters
Yes
Yes
Yes
No
No
No
RRC setup problem
?
UE sent
Preamble
?
UE abnormal
problem
No
Yes
eNodeB received
Preamble
?
No
Yes
Adjust UL open
loop power control
parameters
UE received RA
reasons
?
Yes
Adjust PDCCH
parameters
No

 Call signaling interruption because the call is originated from a poorly covered cell
with weak signals
 Uplink RACH problem
 Paging failure during the TAU
 Cell reselection parameter misconfiguration: The call is not originated from the best
cell due to cell reselection time delay.
 RS power and power allocation parameter misconfiguration
 Traffic congestion
 Equipment fault
 It is highly likely that an RRC connection establishment failure may occur due to
the following factors:
 Weak signals in the downlink
 Uplink RACH problem
 Cell reselection parameter misconfiguration
 Equipment fault
4.5.2.3 Solutions to Highly Probable RRC Connection Establishment Problems
 To solve these highly probable problems, ZTE recommends the following
solutions:
 Perform the RF optimization to solve an undershooting or overshooting problem.
 Optimize the TA edges to reduce unnecessary location update. If possible, it is best
to include the TA edges in a sparsely populated area.
 To ensure that the UE can reselect a preferable cell for originating the call, optimize
the cell reselection parameters of the problematic cell.
 Modify such random access and power allocation parameters as PRACH, PCCH,
PDCCH, PDSCH, and Msg3 power offset, whenever necessary.
 Modify the RS power to cover the cell radius as expected.

4.5.2.4 Failing to Receive the RRC Connection Request Message
 Can you explain why the eNodeB fails to receive the RRC Connection Request
message that is sent from the UE?
 If the RSRP is relatively low in the downlink, you can infer that it may be caused by
a coverage problem.
 If the RSRP is not too low (-105 dBm or more) in the downlink, you can infer that it
may be caused by an RACH problem.
 This problem may usually be caused by these potential factors:
 Insufficient power ramping level
 Too low output power (UE)
 eNodeB fault (too high VWSR)
 Improper cell radius configuration
4.5.2.5 Failing to Receive the RRC Connection Setup Message
 After receiving the RRC Connection Request message from the UE, the
eNodeB sends the RRC Connection Setup message, but the UE fails to
receive the RRC Connection Setup message. This problem may usually be
caused by these potential factors:
 Poor coverage
 Inappropriate cell selection and reselection parameters
 To solve this problem, ZTE recommends the following solutions:
 If this problem is caused by poor coverage, ZTE recommends you enhance the
coverage if conditions permit. For example, you can add certain sites or optimize
the antenna and feeder system. If conditions do not permit, ZTE recommends you
improve the RS power and adjust the corresponding power allocation parameters.
 If this problem is caused by inappropriate cell selection and reselection parameters,
ZTE recommends you adjust the corresponding cell selection and reselection
parameters to speed up the cell selection and reselection procedure.

4.5.2.6 Delivering the RRC Connection Reject Message
 After receiving RRC Connection Request message, the eNodeB delivers the
RRC Connection Reject message to the UE. When finding the RRC
Connection Reject message, you need to check the specific cause value:
 Congestion: In this case, you need to check the network usage.
 Unspecified: In this case, you need to check the log information.
 When receiving the RRC Connection Setup message, the UE fails to deliver
the RRC Connection Setup Complete message. If the signals in the downlink
are normal, you can infer that this problem may be caused by a handset fault.
 When the UE delivers the RRC Connection Setup Complete message, the
eNodeB fails to receive the RRC Connection Setup Complete message. There
is a very small probability that this problem will occur because the transmit
power of the UE will be increased through the initial uplink power control.
Temporarily, no good solution is readily available to this problem.
4.5.3 Authentication and Encryption Failures
 When an authentication failure occurs, you need to analyze potential factors,
depending on the cause value (MAC Failure or Synch Failure) carried in the
Authentication Failure message that is sent from the UE to the MME.
4.5.3.1 MAC Failure
 During the authentication procedure, the UE checks the AUTN parameter
carried in the Authentication Request message that is sent from the MME.
When finding incorrect MAC information, the UE delivers the Authentication
Failure message that carries the cause value (MAC Failure) to the MME, as
shown in Figure 4-71.

Figure 4-71 Authentication Failure Message (Cause Value: MAC Failure)

UE MME
Stop T3418
AUTHENTICATION REQUEST
Start T3418 Stop T3460
AUTHENTICATION FAILURE (cause = "MAC failure")
Start T3460
IDENTITY REQUEST
Stop T3470
IDENTITY RESPONSE (IMSI)
Start T3470
Stop T3460
AUTHENTICATION RESPONSE
Start T3460
 Illegal subscriber
 Ki or OPc configuration inconsistency between the USIM and the HLR
4.5.3.2 Synch Failure
 During the authentication procedure, the UE checks the SQN parameter carried
in the Authentication Request message that is sent from the MME. When
finding incorrect SQN information, the UE delivers the Authentication Failure
message that carries the cause value (Synch Failure) to the MME, as shown in
Figure 4-72.

Figure 4-72 Authentication Failure Message (Cause Value: Synch Failure)

UE MME
Stop T3420
Start T3420 Stop T3460
AUTHENTICATION FAILURE (cause = "synch failure")
Start T3460
Perform
re-synch
with HSS
Stop T3460
AUTHENTICATION RESPONSE
Start T3460
 Illegal subscriber
 Equipment fault
4.5.4 E-RAB Connection Establishment Failures
 Based on the drive test data, the initial E-RAB connection establishment
success rate is measured from the time when the UE sends out the PDN
Connectivity Request message to the time when the UE returns the Activate
Default EPS Bearer Context Accept message.
 An E-RAB connection establishment failure may usually be caused by these
potential factors:
 Weak signals
 UE/MME rejects
 Parameter misconfiguration
 Corner effect
 Equipment faults

4.5.4.1 Weak Signals
 A weak signal or blind spot can become a very critical factor for the UE to get
access to the E-UTRAN, especially when the UE is put in mobility or the radio
environment is sharply changed. When the UE is put in mobility, especially the
RSRP is smaller than -110 dBm or the SINR is smaller than -3 dB (meaning that
the UE is stationed in a high path loss or low SNR coverage area), the Samsung
UE fails to demodulate signals and thereby experiences a radio access failure.
When the UE is motionlessly stationed in an isolated area (meaning that the
RSRP is smaller than -120 dBm), the UE can successfully get access to the LTE
network.
 Poor coverage
 A poor coverage problem may occur in the uplink or downlink:
 If a poor coverage problem occurs in the uplink, the eNodeB cannot receive or
demodulate the response message received from the UE. In this case, you
can check the RSSI to see if it is caused by radio interference in the uplink.
 If a poor coverage problem occurs in the downlink, the demodulation function
of the UE does not work very well. In this case, you need to optimize the RF.
 To achieve optimum coverage, ZTE recommends the following solutions:
 If a poor coverage problem occurs in the uplink, you need to check whether
radio interference is present in the uplink.
 If a poor coverage problem occurs in the downlink, you need to eliminate the
malfunctioning demodulation factors:
 Adding a new eNodeB
 Optimizing the RF
 Adjusting the antenna and feeder system
 Optimize the RS power
 The UE is not stationed in an optimum cell.
 In the case of a quick signal change, the location update of the stationed cell cannot
be implemented until the E-RAB connection is already established. As a result, the
E-RAB connection establishment can only be completed in a weak-signal cell, and
thereby causing a devastating failure.

 In this case, you need to increase the intra-frequency cell reselection threshold and
speed. This can force the UE to quickly station in an optimum cell.
4.5.4.2 UE/MME Rejects
 The UE rejects may usually be caused by these potential factors:
 The reject is resulted from the activated EPS bearer context.
 The reject is resulted from the security mode of the NAS layer.
 When the MME delivers the Attach Reject message, the cause value may
include:
 Network failure
 EPS services not allowed in this PLMN
 ESM failure
 No EPS bearer context activated
 For more information about the UE/MME rejects during the radio access
procedure, please refer to the corresponding message description guide.
 To solve this problem, ZTE recommends the following solutions:
 If a UE reject problem occurs because the UE is mal-functioning, you need to
upgrade the HW/SW version or replace the UE.
 If an MME reject problem occurs, you need to check the STS signaling trace data
on the eNodeB side to see if it is caused by a poor coverage or S1 link failure
problem. If not, you need to hand this problem to the core network technical
support team.
4.5.4.3 Parameter Misconfiguration
 When a radio access failure occurs, we need to first compare the parameters of
a well-functioning cell to those of a mal-functioning cell to see if they are
consistently configured. If not, check whether such a failure is caused by
parameter misconfiguration. In normal cases, it is recommended to enable the
intra-frequency measurement and cell reselection. To solve this problem, ZTE
recommends you configure scenario-specific parameters as required.

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