zte fdd lte radio network optimization guideline v1.4 (1)

8/18/2019 ZTE FDD LTE Radio Network Optimization Guideline V1.4 (1)

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ZTE Confidential Proprietary © 2010 ZTE Corporation. All rights reserved. 1

ZTE FDD LTE RadioOptimization Guideline


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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 bedisclosed or used without the prior written permission of ZTE.Due to update and improvement of ZTE products and technologies, information in this documentis subjected to change without notice.


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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


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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


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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 4-11 Weak Coverage Area Analysis -3 ............................................................................... 27 Figure 4-12 Weak Coverage Area Analysis -4 ............................................................................... 28 Figure 4-13 Weak Coverage Area Analysis -5 ............................................................................... 28 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 4-21 Low SINR Cell Analysis -2 .......................................................................................... 33 Figure 4-22 Low SINR Cell Analysis -3 .......................................................................................... 34 Figure 4-23 Low SINR Cell Analysis -4 .......................................................................................... 34 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 4-29 Low SINR Cell Analysis -2 .......................................................................................... 38 Figure 4-30 Overlapped Coverage Analysis -3 .............................................................................. 39

Figure 4-31 Overlapped Coverage Analysis -4 .............................................................................. 39

Figure 4-32 Overlapped Coverage Analysis -5 .............................................................................. 40 Figure 4-33 Overlapped Coverage Analysis .................................................................................. 41 Figure 4-34 Pilot Frequency Pollution Analysis -1 ......................................................................... 42 Figure 4-35 Pilot Frequency Pollution Analysis -2 ......................................................................... 43 Figure 4-36 Pilot Frequency Pollution Analysis -3 ......................................................................... 43 Figure 4-37 Pilot Frequency Pollution Analysis -4 ......................................................................... 43 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


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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 4-46 Analysis on Missed Matching of Neighboring Cells -2 ............................................... 51 Figure 4-47 Analysis on Missed Matching of Neighboring Cells -3 ............................................... 52 Figure 4-48 Analysis on Missed Matching of Neighboring Cells -4 ............................................... 53 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 4-66 DT Test Data -2 .......................................................................................................... 72 Figure 4-67 DT Test Data -3 .......................................................................................................... 73 Figure 4-68 DT Test Data -4 .......................................................................................................... 74 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


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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


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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, dynamicprocess. After a period of operation, with the increase of subscribers,environment transformation and some other uncontrollable factors, there wouldbe decrease of connection success ratio, fall of call quality and faded signals etc.The formerly planned network can no longer keep pace with the rapiddevelopment. To make adjustments and expansion of the systemic resourcesand 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 N ETWORK OPTIMIZATION PREPARATION Before the network optimization, the RNO (Radio Network Optimization)

manager should assure that manpower and equipments are available. At thesame time the optimization schedule should be made and the followinginformation 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 forthe coverage, capacity and QoS of the network;

The responsibility matrix definition

The project acceptance criteria.


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2.1 Organization Structure

The following picture shows the organization structure.

Figure 2-1: LTE Radio Network Optimization Organization Structure

RF OptimizationPM

ClusterOptimization

Person InCharge

SSVPerson InCharge

AnalysisEngineer

AnalysisEngineer

Field TestEngineer

Field TestEngineer

AnalysisEngineer

AnalysisEngineer

Drive TestEngineer

Drive TestEngineer

KPI AnalysisEngineer

SSV Team 1 SSV Team N DT Team 1 DT Team NCluster

OptimizationTeam 2

KPI AnalysisEngineer

ClusterOptimization

Team M

2.2 Optimization Tools and Software

In this section, tools used to collect data, analyze data and improve theperformance 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 ToolsNo. Equipments Model

1 Data Collection Software CNT(Communication Network Test) or NEMO

2 Post Processing Software CNA (Communication Network Analysis) orNEMO

3 Test User Equipment4 Test Laptop5 GPS6 Test Vehicle For Drive Test7 Digital map Map used for drive test8 Power inverter Power supply at test vehicle

9 PC Server (Hard diskshould be 500G at least)To store test data & post processing data&analysis report

10 USIM cards

12 Performance analysissoftware NETMAX (Performance analysis software)

13 Planning software CNP(Communication Network Planning) or Atoll/Aircom


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2.2.1 CNT

ZXPOS CNT is an advanced wireless network air interface test tool. It is usedfor trouble shooting, evaluation, optimization, and maintenance of the mobilenetwork. This tool integrates the professional and final-user senses and feelings,completely tests and analyzes the self-network and that of the competitors, andprovides 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 variousfrequency bands of 900/1800/2100/2600MHz, 850/1900MHz, and 450MHz.

Support LTE test services including Ping, FTP, HTTP, and TCP/UDP data servicetest

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 researchinnovation capability to meet test requirements on new techniques of operators

2.2.2 CNA

ZXPOS CNA is an intelligent wireless network optimization analysis system. Itsupports all 2G, 3G, and 4G networks such asGSM/GPRS/EDGE/CDMA/EVDO/WCDMA/ HSDPA/HSUPA/TD-SCDMA/LTE.

ZXPOS CNA provides network oriented data processing and analysis report onnetwork optimization. ZXPOS CNA also provides multi-service QoS analysis formulti-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


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Support KPI analysis of PING/FTP/HTTP/TCP/UDP services

GIS analysis function

Support diverse advanced analysis functions to locate reasons of multiple abnormalproblems

2.2.3 NETMAX

ZXPOS NETMAX is an advanced tools and the first choice for analyzing andlocating the network faults based on large quantities of Measurement Report(MR) and Call Detail Trace (CDT). The workload of drive test and analysis canbe 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 thecall.

Analyze and optimize the performance of the terminal.

2.2.4 CNP

CNP is main tool for LTE network planning and simulation, the main functionsinclude:

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 inone cluster from 20 to 30. The main rules of cluster definition are:

The geographical location


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The service distribution

The same TAC region information

The sites in a cluster should not too many and the overlap between clusters isneeded. The definition of cluster should be confirmed by customer and ZTEtogether.

3 N ETWORK O PTIMIZATION P ROCESS In this section, three stages of optimization are introduced, and the high level

optimization plans are presented for each individual stage of networkimplementation and performance acceptance. Items under consideration are

target of optimization, methods of optimization and output for optimization, etc.

3.1 Optimization MilestoneFigure 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-launchOptimization, Soft Launch Optimization and Launched Optimization.

The main objective of Pre-launch Optimization is to control RF network airinterference, assure network hardware functionality work normally, and ensurethe KPIs target of Preliminary Acceptance Test is achieved. Pre-launchOptimization includes two steps:

1 Single Site Verification

2 Cluster Optimization


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The objective of Soft Launch Optimization is to assure that no Punch List itemsexists in the System. The Punch List is the list that consists of all defectsidentified during the respective Preliminary Acceptance Test, during the periodprior to Final Acceptance. When all items on the respective Punch List havebeen resolved in the System, a Final Acceptance Certificate will be issued.

The optimization after issuing FAC is named as Launched Optimization. Thenetwork can be put into commercial services after FAC. The objective ofLaunched Optimization is to assure the network performance stabilization whensubscribes are increasing. Launched Optimization is focused on customerexperiences, 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 levelof the system. It is necessary to measure radio frequency and assess theinterference level in the given LTE band.

Radio frequency verification must get permission of the operator and localTelecommunication Administration. Radio frequency verification contains twophases. The first phase is before the network construction, during site survey toverify if there is interference at the site location, which will be carried out in thespectrum 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 introducedduring the site construction and configuration phases, so that following RFoptimization can be based on a reasonable basis, or else if any problems areidentified during optimization, it will be time-consuming to find out what factorsare responsible for the unexpected results. Normally during single siteverification, 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 thefollowing table. These problems should be solved before the service relatedSSV test can be performed, to be more specific, these tests include coveragetest, VoIP, FTP, Ping etc.


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Table 3-1: Single Site Verification:

Equipment related Engineering related Configuration related

Abnormal power alarmPA alarmTransmission brokenBoard related alarmsInternal/external link alarms

Antenna VSWR alarmClock source/GPS alarmCell/eNodeB down alarmSW version alarm…

FeederLoose connection ofconnectorsUnreasonable antennapositionSignal obstacle by buildingsWrong antenna tilt andazimuth…

Center frequencyPCITACCell statusTransmissionbandwidthPRACH 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 andinstallation engineers together, and configuration related problems are to besolved by RF optimization engineers and OMC engineers. After site verification,it should be free of obvious problems that might cause the site incapable ofbeing put on air.

The SSV process is mainly based on stationary check and drive test, and theformer means performing desktop check on items according to configurationdata, 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 bystationary check, whether the transmission bandwidth and center frequencyconfiguration can match the design requirement, whether the cell is in state ofreserved or barred, etc. The verification of some other items can also bestationary as compared to drive test method. For example, the UL/DL frequencyassignment, the Physical Cell Identifier, the TAC of cells can be identified byusing a test UE with engineering mode, but these items can also be verified bydrive test. The drive test can be used to identify problems related to coverage,handover, service accessibility and data throughput, which in turn will drill downto problems related to engineering and configuration faults, such as feeders,insufficient transmission bandwidth configuration, etc.


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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 forimplementation.

3.2.3 Cluster Optimization workflow

Main objective of cluster optimization is coverage optimization, neighbor celloptimization and solve service access failure, call drop, and handover failure,throughput issues etc. It is analysis collected data from DT and stationary testdata to analyze and locate problems, optimize network and verify adjustedschema, which is an iterative process to assure achieve cluster acceptancestandard.

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 problemssolved?

Submit Report

Yes

No

EngineerParameters

Adjusting Report

ClusterOptimization

Report

Radio ParametersAdjusting Report

If acceptable?

End

Yes

No

Output

Before optimization of cluster, the work needed to be prepared is listed asfollows.


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to provide a continuous service experience in the majority of desired coveragearea and assure that no Punch List items exists in the System. If any problemsare detected in the soft-launch optimization stage, they should be solved andchecked thoroughly in the whole network. These problems might cover diverseareas such as the EPC, eNodeB, transmission, UE, etc. Improving the relatedKPIs 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. Neighborrelationship optimization mainly includes missing neighbor, unidirectionalneighbor, inter-frequency neighbor, and inter-RAT neighbor. Handover relatedparameters should be optimized as well. Other RRM parameters such as accesscontrol, power configuration, load control, etc., should also be tuned selectivelyto meet the traffic requirements.

The soft-launch optimization is normally based on both drive test and friendlyuser feedback. As a supplementary data source, the signaling tracing is neededto help troubleshooting some inner system problems.

Although in this stage, traffic statistics from trial users are not too much, theKPIs report generated from soft-launched network should still be helpful toanalyze the problems. At the same time, some optimization aiding tools basedon OMC statistics can be put into use too, which may also be helpful at the earlyage of the commercial network.

The output from soft-launch stage optimization is the performance optimizationreport for the whole network, and also the complete set of parameters that havebeen tuned for the forthcoming commercial launch. Of course these parametersare to be optimized further in a dynamic process, but they serve as a goodbaseline for further improvement of system performance.

3.4 Launched Optimization

The target in Launched Optimization stage is both the coverage and systemperformance from OMC statistics. Normally, after large subscribers register, theoptimization goal is straight forward, that is, to keep stable and satisfactory end

to end system performance, and enhance the system KPIs. The daily KPIs fromOMC statistics should be monitored and optimized to designed level.

As main inputs for this optimization stage, OMC statistics and customercomplaints are to be used with higher priority than drive test and walk test data,because after the commercial launch, traffic in the network has becomesufficient for providing detailed statistics on each KPI. The end to endperformance monitoring result can also help in this stage of optimization, forexample, for problem drilling down, trouble shooting, KPIs comparison, and celltraffic load.


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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 thedynamically changing network performance. If any problems are identified andclassified into specific domains, corresponding teams from different domains areresponsible for the trouble shooting work, and make possible adjustments andverifications 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 criticaltrouble shooting reports made in this stage are documented and reported aswell.

4 C LUSTER O PTIMIZATION

4.1 Single-Cell Coverage Analysis

After the thorough drive test of the network, you need to check the antennaconnection sequence, single-cell overshooting, antenna side/back lobecoverage, and zero-coverage cell based on data obtained from this test so as towork out the actual coverage of each cell.

During the single-cell coverage analysis, you will use the LTE COVER LINE andPCI RSRP functions provided by CNA. (or other DT analysis tool)

Figure 4-1 CNA LTE COVER LINE


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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 antennaconnection sequence:

Antenna connection to wrong cell cause that the terminal conducts handoverbetween two cells of the same schema, thus impacting SINR.

Antenna connection to wrong cell leads to no configuration for neighboring cellrelationship, 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 currentcell is also covered by another cell. If yes, there may exist wrong antennaconnection.

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 systemtest data.

Solution


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Modify engineering connection for the cell where wrong antenna connectionexists.

Study Case

The antenna in Beiting Square of Guangzhou University campus should havecovered the cell FE2 (PCI94). Actually, it covers the cell FE1 (PCI93). In thiscase, the engineering parameters and PCI are proved to be accurate, so theantenna connection in this area is wrong.

Figure 4-3 Coverage Direction of Cell FE2 (PCI94)

4.1.2 Checking the Overshooting

Problem Description

Overshooting appears when signals of a cell are found in its non-neighboringcells, and RSRP of this cell is larger than -100 dBm. Overshooting usually leadsto overlapped coverage, pilot frequency pollution and ping-pong handover.


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Figure 4-4: Cell with Overshot Signals

Problem Analysis

Find out the cell with overshot signals based on the test data and by using thePCI 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, andhow the terminal conducts handover between current cell and other cell. This isbecause the adjustment of antenna azimuth and RS power in current area mayimpact the coverage and handover of other area.

If it is unable to solve the overshooting problem, increase the coverage effect ofthe cell which is nearest to current cell, and make a proper neighboring cellrelationship configuration.


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Case

Overshooting problem is found in the cell FE3 (PCI 125) in the teaching buildingof Guangzhou Medical University. The engineer adjusts the antenna azimuthand 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

Problem Description

Strong coverage is found on the direction of antenna side lobe and back lobe. Itleads to pilot frequency pollution, poor SINR and abnormal handover.

Problem Analysis

Find out the cell which has strong coverage at the direction of antenna side lobeand back lobe by analyzing the test data and using the PCI coverage analysisfunction 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 areaof cell FE1 (PCI 138) is found overlapped with the cell FE3 (PCI 140). This isdue to reflection of cell FE3 (PCI 140).


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Figure 4-7 Overlapped Coverage Caused by Reflection

4.1.4 Checking the Zero-Coverage Cell

Problem Description

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.

Problem Analysis

Find out the zero-coverage cell by analyzing the test data and using the PCIRSRP function provided by CNA.


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Figure 4-8 PCI's RSRP Function

Alternatively, you can find out the zero-coverage area by exporting PCI andRSRP of all main serving cells and their neighboring cells into an excel, andcheck this parameters in the excel. Compare the PCIs in this excel with the PCIsof the whole test area. The cell without PCI can be considered as the cell withzero coverage.

Solution

Check the working status, parameter configuration, location and coverage ofcurrent cell.

Case

The cells with zero coverage are listed in the table below:

Table 4-1 Cells with Zero CoverageNE ID PCI Reason Solution

6006_Guangzhou TraditionalMedical College, FE2 4 Broken link

2871_Western Inner CircleRoad, Guangzhou, FE4 0 Broken link

1008_Geigang, Guangzhou,FE1 114

Wrong parameterconfiguration


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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-frequencyinterference and provide good network coverage.

Engineers usually come across missed coverage, poor coverage, overshootingand 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 andactual engineering parameters

The actual antenna height, azimuth, inclination, and type are different what isspecified in the network planning, and thus the actual network coverage cannotmeet customer's requirement. These problems can be solved by future networkoptimization, but great project cost is also involved.

RAN environment

RAN environment may change where the network construction is different fromoriginal construction plan, or overshooting/pilot frequency pollution appears dueto complicated road type and signal reflection. In this case, engineers shouldadjust the antenna azimuth and inclination angle so as to avoid signal reflectionand reduce the transmission distance of signals.

New requirements on network coverage

Coverage area, new sites and site relocation will bring new requirements onnetwork 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 problemcan be consider as poor coverage problem while overshooting and pilotfrequency pollution can be considered as overlapped coverage problem.


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Therefore, the main task of network optimization is to eliminate poor coveragearea 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 toguarantee a stable network and required network performance.

The area whose RSRP is less than -110dBm is considered as a weak coveragearea.

4.2.3.2 How to Find out Weak-Coverage Area

Perform the following steps to find out weak coverage area based on DT testdata:

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 InMap from the short-cut menu, or click and drag Server Cell RSRP into the mapwindow 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.


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In the pop-up dialog box, select LTE-SC Link and click Apply . Wait until thesuccess message is displayed.


From the toolbar, click and select LTE-SC Link from the drop-down list.The GPS dotted line is selected.


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Check the line connection of server cell and RSRP legends, and you can findsignal 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.


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As for the coverage in residential buildings and campus, you can use variouscoverage 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 RSpower and other parameters.

4.2.3.4 Study Cases

PCI148 Weak Coverage

Problem Description

In the cell PCI48, the RSRP of an area is found lower than -110dBm.

Figure 4-14 DT Test Results-1

Problem Analysis

As shown in the figure below, yellow arrow indicates the coverage effect of cellPCI43, blue arrow indicates the coverage area effect of cell PCI48, and redarrow indicates the cell PCI12. The coverage effect in PCI48 and PCI12 is notso good because most signals are blocked by buildings, and poor coverage ofPCI43 is due to inner road coverage and green belt coverage.


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Figure 4-15 Coverage Effect of Cell PCI48, PCI43 and PCI12

Solution

Based on the site survey results, adjustment of engineering parameters isproved to be invalid for weak coverage elimination. In this study case, new cellsare added to improve the coverage effect.

PCI30 Weak Coverage

Problem Description

Weak coverage is found in the cell PCI30.

Figure 4-16 DT Test Results-2

Problem Analysis

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.


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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 youfind that there is no obstacle between cell PCI30 and section 1, you can adjustthe antenna azimuth about 30 degrees so as to increase the coverage effect forsection 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, adjustthe antenna azimuth about 30 degrees clockwise.

Lower the antenna tilting about 2 degrees for cell PCI18 so as to reduce itsinterference on section 1. Afterwards, conduct drive test for the coverage area ofcell PCI18 so as to check whether this adjustment impacts the coveage area forother sections.


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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 betweenstrength of received transmission signals and strength of received interferencesignals (including noises and interference).

PDCCH SINR = RS power of best serving cell / interference from the coveragecell

SINR requirements vary with operators and network construction stages. ChinaMobile requires that SINR of 95% cells should be larger than -3dB. In actualprojects, 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 than0dB

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:

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 InMap from the short-cut menu, or click and drag Server Cell RSRP into the mapwindow on the right.


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Figure 4-20 Low SINR Cell Analysis -1





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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 findout the signal intensity of your desired area.


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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 networkschema.

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, nohandover and handover failure.

4.2.4.4 Study Cases

Low SINR in Cell PCI150 and Cell PCI144 Caused by Handover Failure

Problem Description

The test UE fails to finish the handover from cell PCI150 to cell PCI144.


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Figure 4-25 Low SINR Caused by Handover Failure

Problem Analysis

eNodeB does not make judgement after the test UE sends out the measurementreport for cell PCI150. Two seconds later the test UE triggers RRC re-establishment but is rejected. However, the neighboring cell relationshipconfiguraiton is proved to be correct.

On this occasion, you can make a conclusion that no judgement onmeasurement report and refusal on RRC re-establishment appear because oflow-speed measurement.

Figure 4-26 Handover Failure Analysis

Solution

Make an offset of 3dB when the test UE conducts handover from cell PCI150 tocell PCI144.


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Figure 4-28 Overlapped Coverage Analysis -1





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Figure 4-32 Overlapped Coverage Analysis -5

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 toosmall.

4.2.5.4 Study Cases

Overlapped Coverage from Cell PCI160, PCI144 and PCI150

Problem Description

The SINR of sections shown in figure is lower than -3dB.

Problem Analysis

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 cellPCI150 and that of cell PCI144 is also overlapped.


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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 ona point when many strong pilot frequencies are found on a point but no mainpilot frequency exists.

Before the definition of pilot frequency pollution is presented, you should befamiliar with three concepts: strong pilot frequency, main strong pilot frequencyand too many pilot frequencies.

Strong Pilot Frequency

RSRP > -100dbm

Main Strong Pilot Frequency

RSRP_number >= 4

Too Many Pilot Frequency

RSRP(strongest) RSRP(weakest)


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Figure 4-35 Pilot Frequency Pollution Analysis -2

In the Label Select dialog box, select Server Cell PCI and click OK .


PCIs of all main server cells are displayed.



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If more than one PCI is found in an area, it means that pilot frequency pollutionis posed on this area.

You can also find the area with pilot frequency pollution by checking call dropsand 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 toprovide main strong pilot frequency. To enable a cell to provide main strong pilotfrequency:

Adjust engineering parameters of antenna

Adjust RS power.

4.2.6.4 Study Cases

Pilot Frequency Pollution in Cell PCI113 and Cell PCI134

Problem Description

SINR of the section covered by cell PCI113 and cell PCI134 is quite low.

Figure 4-38 Pilot Frequency Pollution

Problem Analysis

As shown below, when the UE conducts handover from cell PCI113 to cellPCI149, two measurement reports have not been judged. The section shownbelow is covered by the third cell, and pilot frequency pollution is also found inthis section.


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Figure 4-39 Pilot Frequency Pollution Analysis

Solution

Downtilt the antenna 3 degrees and pan azimuth 20 degrees counter-clockwisein 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 ofhandover KPIs as shown below:

Table 4-2 Handover KPIs Table

Index HandoverSuccess RateHandoverStart

HandoverSuccess

HandoverFailed Date

1

2

3

4


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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 StatisticsRSRPRange > -80dBm > -90dBm > -100dBm > -110dBm


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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 PlaceSN SINR Range July 5 th July 7 th July 16 th

1 -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 targethandover cell in the measurement report sent out by the UE cannot be found inthe neighboring cell list configured for the system. Missed matching ofneighboring 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 theneighboring cell list but conduct measurement for all cells all through workable


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frequencies. Later on, the UE reports the cells which enjoy strongest signalintensity 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 themeasurement report.

Low SINR (< -3dB)

You need to analyze the handover failure and the measurement reports sent outby the UE.

If the UE sends out the measurement report but does not receive response fromthe 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 missedmatching of neighboring cells:


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Figure 4-43 Workflow of Analysis on Missed Matching of Neighboring Cells

Obtain the neighboring cell listfrom the signalling of RRC

Connection Reconfiguration

Find out the point where the UE sends outmeasurement report but does no receive

response based on the DT test data

Find out the latest signalling of RRCConnection Reconfiguration before the

measurement is reported

Check whether the PCIscontained in the measurement

report can be found in theneighboring cell list

Configure theneighboring cellrelationship and

conduct theverification test

N

Other reasons

Check the neighboring cell listfor the cell in the RRC

Connection Reconfigurationsignalling 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 forthe measurement report based on the DT test data.

You need to obtain the PCI of target handover cell based on the measurementreport.

You need to obtain the neighboring cell list for the serving cell based on the testdata.

If no PCI of the target handover cell can be found in the neighboring cell list, itindicates that the missed matching of neighboring cell exists.


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If the PCI of the target handover cell can be found in the neighboring cell list, itindicates the handover problem is caused by other factors but the missedmatching 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

Problem Description

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

Problem Analysis

As shown in the following handover takes place according to last measurementreport, 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 secondmeasurement report are the same:


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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 Reconfigurationsignaling for the serving cell is shown below:


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In this neighboring cell list, you can find cell PCI19 but not the cell PCI20. Itindicates that cell PCI20 has not been configured as the neighboring cell for cell

PCI72, and thus handover between these two cells fails.


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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 whenmoving through these two cells and SINR restores to normal value.

Figure 4-49 Handover Restores after Elimination of Missed Matching


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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 thesame PCI are configured as neighboring cell for main serving cell, or PCI ofneighboring 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 handoverfrequently 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.


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Figure 4-51 Workflow of Elimination of Ping-Pong Handover Problem

Process the DT test datathrough CAN and then export

a file containing locationinformation of handoverpoints

Display handover points inMAPINFO

Display traffic in MAP

Eliminate ping-ponghandover problem

Ping-pong handoverexists?

Y

Solve this problem in thesame way of elimination of

pilot frequency pollution

N

4.3.3.4 Study Cases

Problem Description

In the area shown below, traffic is quite low and the UE conducts handover

frequently.


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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 cellsrestores, 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. Thelatency starts at the time the UE receives the RRC Connection Reconfigurationmessage, 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 thelatency 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 thesending 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:


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Figure 4-53 Signaling Process of Handover on Control Plane

Process the DT test data

Collect statistics of handoverlatency on control plane CNA

Average handover latency islarger than the latency set by

operator?

End

Is MSG1 re-sentfrequently?

There is something wrong withPRACH

Is the latency fromMSG1 to MSG2 too

large?

There is something wrong withRRC 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 MSG1message but not the reception of downlink RAR.

Obtain your desired data by using proper test devices and test terminals whichcan help to obtain the signaling.


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If the MSG1 is not re-transmitted but the interval between MSG1 retransmissionand RRC connection reconfiguration message is quite large, check the value ofPRACH Config Index, which indicates the interval of PRACH transmission (formore details, see protocol 36211.5.7). If the value of PRACH Config Index isquite large, please set it to a lower value.

If frequent MSG1 transmission is found, you need to collect statistics of packetsreceived on PRACH. Also, you need to the uplink interference information. If theelectrical level of interference is larger than -110dBm, please troubleshoot theuplink interference problem or modify the value of expected PRACH receptionpower. 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 besomething 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 solutionslisted below:

Table 4-5 Solutions for Handover Latency Problem

SN Uplink orDownlink? Solution Remarks

1

Uplink

Adjust the PRACH Config Index

2 Troubleshoot the uplink interferenceproblem

3Raise the expected PRACH receptionpower

4 Lower the detection threshold of theabsolute 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 Reconfigurationmessage is sent out, and ends at the time the RRC reconnection is triggered.

You can analyze this problem by using different measurement indexes, such asRSRP and SINR.


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4.3.5.2 How to Find Handover Failure

As shown below, the UE fails to finish the handover usually due to overtimehandover.

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:


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Figure 4-55 Workflow of Solving the Handover Failure Problem

Check whether there isany problem with RSRP,

SINR and MSG2reception

Troubleshoot thecoverage problem

Process the DT test data

Check neighboring cells

Check whether there isany problem with MGS1

transmission

Troubleshoot theneighboring cell

problem

Troubleshoot theMSG1 problem

Check whether thethreshold of synchronous

detection is too small

Modify the value ofrelated parameters

Check whether T304 worksovertime

Modify the value ofT304

End

Y

Y

Y

Y

Y

N

N

N

N

N

If RSRP, SINR and RAR reception are abnormal, it indicates that the handoverfailure is caused by poor downlink coverage and non-synchronization betweenUE 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 whetherthere exist cells of the same PCI.

If the MSG1 transmission is abnormal, troubleshoot this problem by modifyingthe value of handover latency.

If the value of synchronization detection threshold is too small, non-synchronization may appear, thus leading to RRC re-establishment.


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T304 overtime usually leads to handover overtime. In this case, reset the valueof T304 to a larger value.

4.3.5.4 Study Cases

Problem Description

Handover failure is found in the area shown below:

Figure 4-56 Handover Failure

Problem Analysis

Handover failure occurs in this area due to weak network coverage.

Figure 4-57 Analysis of Handover Failure -1


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As shown in Figure 4-58, the UE conducts handover between cell PCI304 andPCI161. At the same time, the value of SINR is quite low, as shown in Figure4-58.

Figure 4-58 Analysis of Handover Failure -2

Solution

Lower the antenna tilting 3 degrees in cell PCI60.



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After the adjustment of antenna tilting, the value of SINR restores and handoverfailure 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 thefollowing problems:

Weak coverage, low SINR, inter-frequency interference and intra-frequencyinterference

4.4.2 Analysis Methods

Comply with the following workflow to analyze the traffic problem:


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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 reportto R&D engineers.

Figure 4-60 Workflow of Analyzing Traffic Problem

Any alarm is reported for thefault cell Clear the alarm

Find out the area of l ow service ratebased on DT test data

Does the rate meetrequirements of radio

environment

Are the parameters of servingcell meet requirements

Improve the coverage effect for thearea of low rate

Modify the value of abnormalparameter

Is the transmission abnormal Submit problem report to thecustomer and ask help for solvingtransmission problem

Y

Y

Y

Y

N

N

N

N

There may be something wrong withthe Version file. Report the problem

and problem location, track theprogress and verify the networkperformance after adjustment


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4.4.3 Analyzing the Cell with the Maximum Downloading Rate Less than5M

Export traffic data from the DT test data, and filter out all cells whose maximumtraffic is less than 5M.

Table 4-6 Cells Whose Maximum Traffic is Less than 5M

Index ServerCell PCI Max PDCP Downlink PDUTraffic (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)

12

3

4

5

6

7

8

9

1011

12

13

14

15

16

17


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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

Problem Description

When the UE is conducting handover from cell PCI149 to cell PCI134, it sendsout measurement report but does not receive any response. It triggers RRCconnection re-establishment in target handover cell but is refused. Therefore, ittriggers the re-establishment of a new service.

Problem Analysis


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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 thepower of cell PCI134 from 9 to 12.


After the adjustment, when the UE moves through this area, it conductshandover between cell PCI 86< — > cell PCI 134< — > cell PCI 133< — > cell PCI113. 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

Problem Description

As shown in figure below, when the UE moves through area 2, it conductshandover 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 andcell PCI64, thus leading to call drops, service re-establishment and low rate.

Problem Analysis


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The cell PCI64 poses network coverage on a campus, and the coverage radiushere is quite small. When the UE conducts handover between cell PCI41 andcell 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'scoverage on this area. Therefore, lower the antenna inclination angle in this cell3 degrees, or reduce the RS power in this cell.


After the adjustment, ping-pong handover and call drops disappear, and trafficalso restores.

4.4.4 Analyzing the Cell with the Average Downloading Rate Ranging from5M to 10M

Table 4-8 Cells Whose Average Traffic Ranges from 5M to 10MSN 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 2012/7/165 134 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


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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


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Problem Description

As shown above, when the UE conducts handover between cell PCI11 and cellPCI21, 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 tohandover failure, service re-establishment and low rate.

Problem Analysis

Area 2 is covered by cell PCI11, cell PCI21, cell PCI28 and cell PCI69, andRSRP here is about -101dB. The cell PCI is about one kilometer away from thisarea, namely its signal overshoot to this area. Also, cell PCI11 and cell PCI21are not neighboring cells. Therefore, when the UE moves through cell PCI11, itcannot receive handover judgment for handover to cell PCI21 from eNodeBalthough it has sent the measurement report.

Solution

Lower the tilting in cell PCI11, or configure neigh

zte fdd lte radio network optimization guideline v1.4 (1)

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