Chapter No.: 1 Title Name: Zhang ffirs.inddComp. by: PVijaya Date: 06 Sep 2017 Time: 05:05:07 PM Stage: Proof WorkFlow:<WORKFLOW> Page Number: i

LTE Optimization Engineering Handbook

Chapter No.: 1 Title Name: Zhang ffirs.inddComp. by: PVijaya Date: 06 Sep 2017 Time: 05:05:07 PM Stage: Proof WorkFlow:<WORKFLOW> Page Number: ii

Chapter No.: 1 Title Name: Zhang ffirs.inddComp. by: PVijaya Date: 06 Sep 2017 Time: 05:05:07 PM Stage: Proof WorkFlow:<WORKFLOW> Page Number: iii

LTE Optimization Engineering Handbook

Xincheng Zhang

China Mobile Group Design Institute Co., Ltd.Beijing, China

Chapter No.: 1 Title Name: Zhang ffirs.inddComp. by: PVijaya Date: 06 Sep 2017 Time: 05:05:07 PM Stage: Proof WorkFlow:<WORKFLOW> Page Number: iv

This edition first published 2018© 2018 John Wiley & Sons Singapore Pte. Ltd

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Library of Congress Cataloging‐in‐Publication Data

Names: Zhang, Xincheng, 1970– author.Title: LTE optimization engineering handbook / Xincheng Zhang, China Mobile Group Design Institute Co., Beijing, China.Description: Hoboken, NJ, USA : Wiley, [2017] | Includes bibliographical references and index. | Identifiers: LCCN 2017019394 (print) | LCCN 2017022857 (ebook) | ISBN 9781119159001 (pdf) | ISBN 9781119158998 (epub) | ISBN 9781119158974 (cloth)Subjects: LCSH: Long-Term Evolution (Telecommunications)–Handbooks, manuals, etc. | Wireless communication systems–Handbooks, manuals, etc. | Computer network protocols–Handbooks, manuals, etc.Classification: LCC TK5103.48325 (ebook) | LCC TK5103.48325 .Z4325 2017 (print) | DDC 621.3845/6–dc23LC record available at https://lccn.loc.gov/2017019394

Cover Design: WileyCover Images: (Yin Yang) © alengo/Gettyimages; (Feng shui compass) © Liuhsihsiang/Gettyimages

Set in 10/12pt Warnock by SPi Global, Pondicherry, India

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About the Author xviPreface xvii

Part 1 LTE Basics and Optimization Overview 1

1 LTE Basement 31.1 LTE Principle 31.1.1 LTE Architecture 61.1.2 LTE Network Interfaces 71.2 LTE Services 111.2.1 Circuit‐Switched Fallback 121.2.2 Voice over LTE 131.2.3 IMS Centralized Services 161.2.4 Over the Top Solutions 161.2.5 SMS Alternatives over LTE 171.2.6 Converged Communication 191.3 LTE Key Technology Overview 191.3.1 Orthogonal Frequency Division Multiplexing 201.3.2 MIMO 211.3.3 Radio Resource Management 22

2 LTE Optimization Principle and Method 242.1 LTE Wireless Optimization Overview 242.1.1 Why LTE Wireless Optimization 242.1.2 Characters of LTE Optimization 242.1.3 LTE Joint Optimization with 2G/3G 252.1.4 Optimization Target 252.2 LTE Optimization Procedure 262.2.1 Optimization Procedure Overview 262.2.2 Collection of Mass Nerwork Measurement Data 282.2.3 Measurement Report Data Analysis 302.2.4 Signaling Data Analysis 312.2.5 UE Positioning 322.2.5.1 Timing Advance 332.2.5.2 Location Accuracy Evaluation 35

Contents

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2.2.5.3 Location Support 362.2.5.4 3D Geolocation 372.2.6 Key Performance Indicators Optimization 422.2.7 Technology Evolution of Optimization 432.3 LTE Optimization Key Point 442.3.1 RF Optimization 442.3.1.1 RSRP/RSSI/SINR/CINR 442.3.1.2 External Interference 482.3.2 CQI versus RSRP and SINR 512.3.2.1 CQI Adjustment 512.3.2.2 SINR Versus Load 542.3.2.3 SINR Versus MCS 562.3.3 Channel Power Configuration 582.3.3.1 RE Power 582.3.3.2 CRS Power Boosting 642.3.3.3 Power Allocation Optimization 662.3.4 Link Adaption 672.3.5 Adaptive Modulation and Coding 692.3.6 Scheduler 702.3.6.1 Downlink Scheduler 722.3.6.2 Uplink Scheduler 742.3.7 Radio Frame 752.3.8 System Information and Timers 762.3.8.1 System Information 762.3.8.2 Timers 812.3.9 Random Access 832.3.10 Radio Admission Control 852.3.11 Paging Control 862.3.11.1 Paging 862.3.11.2 Paging Capacity 922.3.11.3 Paging Message Size 952.3.11.4 Smart Paging 952.3.11.5 Priority Paging 962.3.12 MIMO and Beamforming 972.3.12.1 Basic Multi‐Antenna Techniques 1002.3.12.2 2D‐Beamforming 1012.3.12.3 2D MIMO and Parameters 1042.3.12.4 Massive‐MIMO 1052.3.13 Power Control 1072.3.13.1 PUSCH/PUCCH Power Control 1072.3.13.2 PRACH Power Control 1092.3.14 Antenna Adjustment 1112.3.14.1 Antenna Position 1122.3.14.2 Remote Electrical Tilt 1132.3.14.3 Antenna Azimuths and 

Tilts Optimization 1172.3.14.4 VSWR Troubleshooting 1182.3.15 Main Key Performance Indicators 120

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Part 2 Main Principles of LTE Optimization 123

3 Coverage Optimization 1253.1 Traffic Channel Coverage 1253.1.1 Parameters of Coverage 1263.1.2 Weak Coverage 1283.1.2.1 DL Coverage Hole 1283.1.2.2 UL Weak Coverage 1283.1.2.3 UL and DL Imbalance 1293.1.3 Overlapping Coverage 1293.1.4 Overshooting 1303.1.5 Tx1/Tx2 RSRP Imbalance 1323.1.6 Extended Coverage 1323.1.7 Cell Border Adjustment 1353.1.8 Vertical Coverage 1373.1.9 Parameters Impacting Coverage 1383.2 Control Channel Coverage 138

4 Capacity Optimization 1404.1 RS SINR 1404.2 PDCCH Capacity 1414.3 PUCCH Capacity 1444.3.1 Factors Affecting PUCCH Capacity 1454.3.2 PUCCH Dimensioning Example 1514.4 Number of Scheduled UEs 1524.5 Spectral Efficiency 1534.6 DL Data Rate Optimization 1544.6.1 Limitation Factor 1564.6.2 Model of DL Data Throughput 1574.6.3 UDP/TCP Protocol 1584.6.4 MIMO 1614.6.4.1 DL MIMO 1614.6.4.2 4Tx/4Rx Performance 1634.6.4.3 Transmission Mode Switch 1634.6.4.4 UL MU‐MIMO 1644.6.5 DL PRB Allocation and Utilization Mechanism 1654.6.6 DL BLER 1674.6.7 Impact of UE Velocity 1694.6.8 Single User Throughput Optimization 1704.6.8.1 Radio Analysis – Assignable Bits 1714.6.8.2 Radio Analysis – CFI and Scheduling 1714.6.8.3 Radio Analysis – HARQ 1714.6.9 Avarage Cell Throughput Optimization 1724.6.10 Cell Edge Throughput Optimization 1724.6.11 Some Issues of DL Throughput 1734.6.11.1 Antenna Diversity not Balanced 1734.6.11.2 DL Grant is not Enough 1734.6.11.3 Unstable Rate 175

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4.7 UL Data Rate Optimization 1754.7.1 Model of UL Data Throughput 1764.7.2 UL SINR and PUSCH Data Rate 1764.7.3 PRB Stretching and Throughput 1794.7.4 Single User Throughput Optimization 1804.7.4.1 Radio Analysis – Available PRBs 1814.7.4.2 Radio Analysis—Link Adaptation 1814.7.4.3 Radio Analysis – PDCCH 1824.7.5 Cell Avarage and Cell‐edge Throughput Optimization 1824.7.6 Some Issues of UL Throughput 1834.8 Parameters Impacting Throughput 185

5 Internal Interference Optimization 1885.1 Interference Concept 1885.2 DL Interference 1905.2.1 DL Interference Ratio 1915.2.2 Balance Between SINR and RSRP 1925.3 UL Interference 1925.3.1 UL Interference Detection 1945.3.2 Generation of UL Interference 1965.3.2.1 Cell Loading Versus Inter‐Cell Interference 1965.3.2.2 Unreasonable UL Network Structure 1975.3.2.3 Cross slot interference 1995.3.3 PUSCH Tx Power Analysis 2005.3.4 UL Effect of P0 and α 2025.3.5 PRACH Power Control 2045.3.6 SRS Power Control 2065.3.7 Interference Rejection Combinin 2095.4 Inter‐Cell Interference Coordination 2105.5 UL IoT Control 2105.5.1 UL Interference Issues and Possible Solutions 2105.5.2 UL IoT Control Mechanism 2105.5.3 PUSCH UL_SINR Target Calculation 2125.5.4 UL Interference Criteria 213

6 Drop Call Optimization 2166.1 Drop Call Mechanism 2166.1.1 Radio Link Failure Detection by UE 2176.1.2 RadioLink Failure Detection by eNB 2206.1.2.1 Link Monitors in eNB 2206.1.2.2 Time Alignment Mechanism 2216.1.2.3 Maximum RLC Retransmissions Exceeded 2246.1.3 RadioLink Failure Optimization and Recovery 2256.2 Reasons of Call Drop and Optimization 2276.2.1 Reasons of E‐RAB Drop 2276.2.2 S1 Release 2306.2.3 Retainability Optimization 2336.3 RRC Connection Reestablishment 2336.4 RRC Connection Supervision 239

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7 Latency Optimization 2447.1 User Plane Latency 2447.2 Control Plane Latency 2477.3 Random Access Latency Optimization 2477.4 Attach Latency Optimization 2487.5 Paging Latency Optimization 2507.6 Parameters Impacting Latency 250

8 Mobility Optimization 2548.1 Mobility Management 2558.1.1 RRC Connection Management 2568.1.2 Measurement and Handover Events 2568.1.3 Handover Procedure 2608.1.3.1 X2 Handover 2618.1.3.2 S1 Handover 2678.1.3.3 Key point of X2/S1 Handover 2678.2 Mobility Parameter 2698.2.1 Attach and Dettach 2728.2.2 UE Measurement Criterion in Idle Mode and Cell Selection 2738.2.3 Cell Priority 2768.3 Intra‐LTE Cell Reselection 2768.3.1 Cell Reselection Procedure 2788.3.2 Inter‐Frequency Cell Reselection 2798.3.3 Cell Reselection Parameters 2828.3.4 Inter‐Frequency Reselection Optimization 2838.4 Intra‐LTE Handover Optimization 2858.4.1 A3 and A5 Handover 2858.4.2 Data Forwarding 2908.4.3 Intra‐Frequency Handover Optimization 2918.4.4 Inter‐Frequency Handover Optimization 2928.4.5 Timers for Handover Failures 2968.5 Neighbor Cell Optimization 2978.5.1 Intra‐LTE Neighbor Cell Optimization 2978.5.1.1 Neighbor Relations Table 2978.5.1.2 ANR 2988.5.2 Suitable Neighbors for Load Balancing 2998.6 Measurement Gap 2998.6.1 Measurement Gap Pattern 2998.6.2 Measurement Gap Versus Period of CQI Report and DRX 3048.6.3 Impact of Throughput on Measurement Gap 3048.7 Indoor and Outdoor Mobility 3058.8 Inter‐RAT Mobility 3068.8.1 Inter‐RAT Mobility Architecture and Key Technology 3078.8.2 LTE to G/U Strategy 3098.8.3 Reselection Optimization 3148.8.3.1 LTE to UTRAN 3158.8.3.2 UTRAN to LTE 3198.8.4 Redirection Optimization 3208.8.4.1 LTE to UTRAN 320

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8.8.4.2 UTRAN to LTE 3228.8.5 PS Handover Optimization 3228.8.5.1 LTE to UTRAN 3228.8.5.2 UTRAN to LTE 3248.8.6 Reselection and Redirection Latency 3258.8.7 Optimization Case Study 3268.9 Handover Interruption Time Optimization 3268.9.1 Control Plane and User Plane Latency 3298.9.2 Inter‐RAT Mobility Latency 3328.10 Handover Failure and Improvement 3328.11 Mobility Robustness Optimization 3358.12 Carrier Aggregation Mobility Optimization 3418.13 FDD‐TDD Inter‐mode Mobility Optimization 3458.14 Load Balance 3468.14.1 Inter‐Frequency Load Balance 3468.14.2 Inter‐RAT Load Balance 3488.14.3 Load Based Idle Mode Mobility 3498.15 High‐Speed Mobile Optimization 3518.15.1 High‐Speed Mobile Feature 3538.15.2 Speed‐Dependent Cell Reselection 3548.15.3 PRACH Issues 3568.15.4 Solution for Air to Ground 358

9 Traffic Model of Smartphone and Optimization 3609.1 Traffic Model of Smartphone 3609.1.1 QoS Mechanism 3629.1.2 Rate Shaping and Traffic Management 3669.1.3 Traffic Model 3719.2 Smartphone‐Based Optimization 3729.3 High‐Traffic Scenario Optimization 3729.3.1 Resource Configuration 3749.3.2 Capacity Monitoring 3759.3.3 Special Features and Parameters for High Traffic 3779.3.4 UL Noise Rise 3799.3.5 Offload Solution and Parameter Settings 379

Part III Voice Optimization of LTE 383

10 Circuit Switched Fallback Optimization 38510.1 Voice Evolution 38510.2 CSFB Network Architecture and Configuration 38610.2.1 CSFB Architecture 38610.2.2 Combined Register 38710.2.3 CSFB Call Procedure 39210.2.3.1 Fallback Options 39210.2.3.2 RRC Release with Redirection 39310.2.3.3 CSFB Call Procedure 39510.2.4 Mismatch Between TA and LA 397

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10.3 CSFB Performance Optimization 40210.3.1 CSFB Optimization 40210.3.1.1 Main Issues of CSFB 40210.3.1.2 CSFB Optimization Method 40310.3.2 CSFB Main KPI 40710.3.3 Fallback RAT Frequency Configuration Optimization 40910.3.4 Call Setup Time Latency Optimization 41110.3.4.1 ESR to Redirection Optimization 41610.3.4.2 Twice Paging 41610.3.5 Data Interruption Time 41810.3.6 Return to LTE After Call Complete 41910.4 Short Message Over CSFB 42210.5 Case Study of CSFB Optimization 42310.5.1 Combined TA/LA Updating Issue 42310.5.2 MTRF Issue 42510.5.3 Track Area Update Reject After CSFB 42510.5.3.1 No EPS Bearer Context Issue 42810.5.3.2 Implicitly Detach Issue 42810.5.3.3 MS Identity Issue 42810.5.4 Pseudo Base Station 428

11 VoLTE Optimization 43411.1 VoLTE Architecture and Protocol Stack 43511.1.1 VoLTE Architecture 43511.1.2 VoLTE Protocol Stack 43511.1.3 VoLTE Technical Summary 43811.1.4 VoLTE Capability in UE 43911.2 VoIP/Video QoS and Features 44211.2.1 VoIP/Video QoS 44211.2.2 Voice Codec 44411.2.3 Video Codec 44611.2.4 Radio Bearer for VoLTE 44911.2.5 RLC UM 45411.2.6 Call Procedure 45711.2.6.1 LTE Attach and IMS Register 45811.2.6.2 E2E IMS Flow 45811.2.6.3 Video Phone Session Handling 46211.2.7 Multiple Bearers Setup and Release 46611.2.8 VoLTE Call On‐Hold/Call Waiting 46711.2.9 Differentiated Paging Priority 46811.2.10 Robust Header Compression 47011.2.10.1 RoHC Feature 47011.2.10.2 Gain by RoHC 47011.2.11 Inter‐eNB Uplink CoMP for VoLTE 47511.3 Semi‐Persistent Scheduling and Other Scheduling Methods 47711.3.1 SPS Scheduling 47711.3.2 SPS Link Adaptation 47811.3.3 Delay Based Scheduling 48111.3.4 Pre‐scheduling 482

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11.4 PRB and MCS Selection Mechanism 48411.4.1 Optimized Segmentation 48411.4.2 PRB and MCS Selection 48511.5 VoLTE Capacity 48611.5.1 Control Channel for VoLTE 48711.5.2 Performance of Mixed VoIP and Data 48811.6 VoLTE Coverage 49111.6.1 VoIP Payload and RoHC 49211.6.2 RLC Segmentation 49211.6.3 TTI Bundling 49811.6.4 TTI Bundling Optimization 50211.6.5 Coverage Gain with RLC Segmentation and TTI Bundling 50711.6.6 MCS/TBS/PRB Selection 50911.6.7 Link Budget 51011.7 VoLTE Delay 51311.7.1 Call Setup Delay 51611.7.1.1 Call Setup Time 51611.7.1.2 Reasons for Long Call Setup Time 51611.7.2 Conversation Start Delay 51911.7.3 RTP Delay 52111.7.4 Handover Delay and Optimization 52511.8 Intra‐LTE Handover and eSRVCC 52711.8.1 Intra‐Frequency Handover 52711.8.2 Inter‐Frequency Handover 52811.8.3 Single Radio Voice Call Continuity Procedure 52911.8.4 SRVCC Parameters Optimization 53911.8.4.1 Handover Parameters 53911.8.4.2 SRVCC–Related Timer 53911.8.5 aSRVCC and bSRVCC 54311.8.6 SRVCC Failure 54311.8.7 Reducing SRVCC Voice Gap and eSRVCC 54511.8.7.1 Voice Interruption Time during SRVCC 54511.8.7.2 eSRVCC 54911.8.8 Fast Return to LTE 55211.8.9 Roaming Behavior According to Network Capabilities 55511.9 Network Quality and Subjective Speech Quality 55511.9.1 Bearer Latency 55811.9.2 MoS 56111.9.2.1 Voice Quality 56111.9.2.2 Video Quality 57011.9.3 Jitter 57111.9.4 Packet Loss 57211.9.5 One Way Audio 57511.9.6 PDCP Discard Timer Operation 57611.10 Optimization 57711.10.1 Distribution of Main Indicators of Field Test 58011.10.2 Compression Ratio and GBR Throughput 58411.10.3 RB Utilization 58411.10.4 BLER Issue 587

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11.10.5 Quality Due to Handover 58911.10.6 eSRVCC Handover Issues 58911.10.7 Packet Loss 59211.10.7.1 Packet Loss due to Poor RF 59211.10.7.2 Packet Loss due to Massive users 59211.10.7.3 Packet Loss Due to Insufficient UL grant 59211.10.7.4 Packet Loss due to Handover 60111.10.7.5 Packet Loss Due to Network Issue 60111.10.8 Call Setup Issues 60111.10.8.1 Missed Pages 60211.10.8.2 IMS Issues 60411.10.8.3 Dedicated Bearer Setup Issues 60911.10.8.4 CSFB Call Issues 61211.10.8.5 aSRVCC Failure 61211.10.8.6 RF Issues 61211.10.8.7 Frequent TFT Updates 61711.10.8.8 Encryption Issue 61811.10.9 Call Drop 61911.10.9.1 Call Drop 61911.10.9.2 Radio Link Failure 62211.10.9.3 RTP‐RTCP Timeout 62411.10.9.4 RLC/PDCP SN Length Mismatch 62611.10.9.5 IMS Session Drop 62611.10.9.6 eNB/MME Initiated Drop 63211.10.10 Packet Aggregation Level 63211.10.11 VoIP Padding 63311.10.12 VoIP Ralated Parameters 63511.10.13 Video‐Related Optimization 63511.10.13.1 Video Bit Rate and Frame Rate 63711.10.13.2 Video MoS and Audio/Video Sync 63711.10.14 IMS Ralated Timer 63711.11 UE Battery Consumption Optimization for VoLTE 63811.11.1 Connected Mode DRX Parameter 64311.11.2 DRX Optimization 64411.11.2.1 State Estimation 64411.11.2.2 DRX Optimization and Parameters 64411.11.2.3 KPI Impacts with DRX 64811.11.3 Scheduling Request Periodicity and Disabling of Aperiodic CQI 65211.12 Comparation with VoLTE and OTT 65411.12.1 OTT VoIP User Experience 65411.12.2 OTT VoIP Codec 65711.12.3 Signaling Load of OTT VoIP 658

Part IV Advanced Optimization of LTE 663

12 PRACH Optimization 66512.1 Overview 66512.2 PRACH Configuration Index 66912.3 RACH Root Sequence 673

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12.4 PRACH Cyclic Shift 67412.4.1 PRACH Cyclic Shift Optimization 67412.4.2 Rrestricted Set 67912.5 Prach Frequency Offset 68212.6 Preamble Collision Probability 68312.7 Preamble Power 68412.8 Random Access Issues 68712.9 RACH Message Optimization 68912.10 Accessibility Optimization 69212.10.1 Reasons for Poor Accessibility 69212.10.2 Accessibility 69312.10.3 Accessibility Analysis Tree 69512.10.4 Call and Data Session Setup Optimization 69712.10.5 RACH Estimation for Different Traffic Profile 698

13 Physical Cell ID Optimization 70213.1 Overview 70213.2 PCI Optimization Methodology 70313.2.1 PCI Group Optimization 70513.2.2 PCI Code Reuse Distance 70513.2.3 Mod3/30 Discrepancy Analysis 70813.2.4 Collision and Confusion 70813.3 PCI Optimization 709

14 Tracking Areas Optimization 71114.1 TA Optimization 71214.1.1 TA Update Procedure 71314.1.2 TA Optimization and TAU Failure 71514.2 TA List Optimization 71614.3 TAU Reject Analysis and Optimization 719

15 Uplink Signal Optimization 72115.1 Uplink Reference Signal Optimization 72115.1.1 Coding Scheme of UL RS 72215.1.2 Correlation of UL Sequence Group 72315.1.2.1 UL Sequence Group Hopping 72515.1.2.2 UL Sequence Hopping 72615.1.2.3 UL Cyclic Shift Hopping 72615.1.3 UL Sequence Group Optimization 72715.2 Uplink Sounding Signal Optimization 72915.2.1 SRS Characters 73015.2.2 Wideband SRS Coverage 73615.2.3 Dynamic SRS Adjustment Scheme 73615.2.4 SRS Selection Dimension and Confliction 73715.2.5 SRS Conflict and Optimization 739

16 HetNet Optimization 74116.1 UE Geolocation and Identification of Traffic Hot Spots 74116.2 Wave Propagation Characteristics for HetNet 745

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16.3 New Features in HetNet 74616.4 Combined Cell Optimization 74716.5 Cell Range Expansion Offset 74816.6 HetNet Cell Reselection and Handover Optimization 751

17 QoE Evaluation and Optimization Strategy 75217.1 QoE Modeling 75317.2 Data Collecting and Processing 75617.3 QoE‐Based Traffic Evaluation 75717.3.1 Online Video QoE 75717.3.1.1 Video Quality Monitoring Methods 76117.3.1.2 RATE Adaptive Video Codecs 76317.3.1.3 Streaming KPI and QoE 76417.3.1.4 Video Optimization 76617.3.2 Voice QoE 76917.3.3 Data Service QoE 77017.3.3.1 Web browsing 77017.3.3.2 Online Gaming 77417.4 QoE Based Optimization 776

18 Signaling‐Based Optimization 78018.1 S1‐AP Signaling 78018.1.1 NAS signaling 78218.1.2 Inactivity Supervision 78318.1.3 UE signaling Management 78518.2 Signaling radio bearers 78618.3 Signaling Storm 78818.4 Signaling Troubleshooting Method 78818.4.1 Attach Failure 78818.4.2 Service Request Failure 79618.4.3 S1/X2‐Based Handover 79618.4.4 eSRVCC Failure 79818.4.5 CSFB Failure 800

Appendix 802Glossary of Acronyms 820References 823Index 825

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Xincheng Zhang graduated from the Beijing University of Posts and Telecommunications in 1992. He has worked in mobile communication for 25 years as a technical expert with a solid understanding of wireless communication technologies. Starting out in the early days of GSM roll-outs, he has many years of planning and optimization experience in 2G, 3G, 4G, and 5G networks, working in operator and vendor environments. He is working as a senior wireless network specialist in the fields of antenna arrays, analog/digital signal processing, radio resource management, and propagation modeling, and so on. He has participated in many large‐scale wireless communica-tion system designs and optimization for a variety of cel-lular systems using various radio access technologies, including GSM, CDMA, UMTS, and LTE.

About the Author

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Preface

Mobile communication has become ubiquitous and mobile Internet traffic is continuously growing due to the technology that provides broadband data rates (3G, LTE) and the growing number of mobile dongles and mobile devices like tablets or smartphones that enable the usage of a tremendous number of internet applications through the mobile access. Mobility, broad-band, and new device technology have changed the way people connect and communicate. Smartphones have changed the characteristics of the control and user plane, leading to a huge impact on RAN and e2e network capacity, end‐user experience, and perception of the network, which has changed with the advent of new devices and applications. Subscribers want the same internet experience that they have at home, anytime, anywhere, so the long‐term network is under strain and optimization is needed.

Many of the new services aim to enhance the experience of a phone conversation by allowing sharing of content other than speech. The quality of all these services needs to be monitored to ensure that users experience a high‐quality service. Low‐bit cost is an essential requirement in a scenario where high volumes of data are being transmitted over the mobile network. To achieve the proposed goals, a very flexible network that aggregates various radio access tech-nologies is created. This network should provide high bandwidth, from 50‐100 Mbps for high mobility users, to 1Gbps for low mobility users, technologies that permit fast handoffs, which is necessary in a QoS framework that enables fair and efficient medium sharing among users. The core of this network should be based on internet protocol version 6—IPv6, the probable convergence platform of future services. The other key factor to the success of the network is that the terminals must be able to provide wireless services anytime, everywhere, and must adapt seamlessly to multiple wireless networks, each with different protocols and technologies. Subscriber loyalty has shifted to devices and applications; quality of experience becomes the fundamental service provider’s differentiation.

In this background, the 3GPP long term evolution (LTE) is created and adopted all over the world. High‐speed, high‐capacity data standard for mobile devices is on its way to becoming a globally deployed standard for the fourth generation of mobile networks (4G) supported by all major players in the industry. LTE builds on EUTRAN, a new generation radio access network, and the evolved packet core (EPC), which provides flexible spectrum usage and bandwidths, high data rate, low latency, and optimized resource usage. As LTE has been used as a mobile broadband service, we need to understand the effects of the LTE terminals providing services and how to optimize the network. Actually, for operators, the challenge is not only to optimize 2G, 3G, and 4G but also how to balance the use of those systems, including WiFi. The entire service delivery chain needs to be optimized and the optimization aims to improve network efficiency and the mobile broadband service quality.

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It is known that LTE doesn’t have basic voice and SMS support. To mitigate this, 3GPP proposes a fallback to circuit‐switched (CS) network for voice and SMS. Although voice has loosened its weight in the overall user bill with the rise of more and more data services, voice is the dominant source of revenue for operators and is expected to remain so for the foreseeable future. On one hand, 3GPP defines the concept of CS fallback for the EPC, which forces the UE to fall back to the GERAN/UTRAN network where the CS procedures are carried out. On the other hand, voice over LTE will become a mainstream mobile voice technology. VoLTE ecosys-tem is building up fast due to its strong end‐to‐end VoLTE solution portfolio including the LTE radio, EPC, mobile softswitch, IMS, and its extensive delivery capabilities of complex end‐to‐end projects. It is the world’s most innovative voice solution for LTE‐based networks and big VoLTE growth is expected since wide‐scale commercial VoLTE started in Korea during 2012. The operators will want to have the best possible observability for this new voice service with fast call setup, low latency, and high speech quality. Actually, VoLTE will be among the most critical and complex technologies mobile operators will ever deploy as VoLTE testing is quite complex due to inherent intricacy of the technology covering the IMS/EPC core, radio net-work, and UE/IMS client. They expect to be able to monitor how their customers experience accessibility, retainability, as well as the quality of the voice service. Obviously, much of the observability is already in place, but there are reasons to believe that there are missing parts.

Under this background, to meet customers’ requirements for high‐quality networks, LTE trial networks must be optimized during and after project implementation. The basis and the main inputs that allowed the creation of this handbook were based on optimization experience, whereas the scope of this book is to provide network engineers with a set of processes and tasks to guide them through the troubleshooting and optimization. For a network optimization engi-neer, he/she needs to know how good the quality of mobile broadband applications is, and how the network capabilities impact the performance, and how to identify the most critical network KPIs that impact customer experiences.

This book is divided into four parts. The first is called “LTE Basics and Optimization Overview,” and proceeds with an introduction to general principles of data transfer of LTE. This chapter is dedicated to the reader who is not acquainted with this area. The second part, titled “Main Principles of LTE Optimization,” and the third part, “Voice Optimization of LTE,” makes up the core of the book, since it describes coverage, capacity, interference, mobility opti-mization, and includes two chapters that provide step‐by‐step optimization of CFSB and VoLTE. The fourth part “Advanced Optimization of LTE” takes a more applied perspective in PRACH, PCI, TA, QoE, Hetnet, and signaling optimization.

Thanks to the many people in China who shared their views acquired from years of experi-ence and valuable insights in wireless optimization, the Optimization Handbook covers the basics of optimization rules, solutions, and methods. It is evident that this book does not cover many other important areas of optimization of LTE networks. Nonetheless, I sincerely hope that readers will find the information presented to be interesting and useful to inspire you to go and do optimization with a renewed vigor in order to help you build a better LTE network.

January 1, 2017 Xincheng Zhang

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Part 1

LTE Basics and Optimization Overview

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LTE Optimization Engineering Handbook, First Edition. Xincheng Zhang. © 2018 John Wiley & Sons Singapore Pte. Ltd. Published 2018 by John Wiley & Sons Singapore Pte. Ltd.

3

Mobile networks are rapidly transforming—traffic growth, bit rate increases for the user, increased bit rates per radio site, new delivery schemes (e.g., mobile TV, quadruple play, IMS), and a multiplicity of RANs (2G, 3G, HSPA, WiMAX, LTE)—are the main drivers of the mobile network evolution. The growth in mobile traffic is mainly driven by devices (e.g., smartphone and tablet) and applications (e.g., mainly web browsing and video streaming). To cope with the increasing demand, mobile networks have based their evolution on increasingly IP‐centric solutions. This evolution relies primarily on the introduction of IP transport, and secondly, on a redesign of the core nodes to take advantage of the IP backbones.

The first commercial LTE network was opened by Teliasonera in Sweden in December 2009, and marks the new era of high‐speed mobile communications. The incredible growth of LTE network launches boomed between 2012 and 2016 worldwide. It is expected that more than 500 operators in nearly 150 countries will soon be running a commercial LTE network. Mobile data traffic has grown rapidly during the last few years, driven by the new smartphones, large displays, higher data rates, and higher number of mobile broadband subscribers. It is expected that the mobile broadband (MBB) subscriber numbers will double by 2020, reaching over 7 billion subscribers, that MBB data traffic will grow fourfold by 2020, reaching over 19 petabytes/month. The internet traffic, MBB subscriber, and relative mobile data growth is illustrated in Figure 1.1.

1.1 LTE Principle

To provide a fully mature, real‐time–enabled, and MBB network, structural changes are needed in the network. In 2005, the 3GPP LTE project was created to improve the Universal Mobile Telecommunications System (UMTS) mobile phone standard to cope with future require-ments, which resulted in the newly evolved Release 8 (Rel 8) of the UMTS standard. The goals include improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and better integration with other open standards. Long‐term evolution (LTE) is selected as the next generation broadband wireless technology for 3GPP and 3GPP2. The LTE standard supports both FDD (frequency division duplex), where the uplink and downlink channel are separated in frequency, and TDD (time division duplex), where uplink and downlink share the same frequency channel but are separated in time. After Rel 8, Rel 9 was a relatively small update on top of Rel 8, and Rel 10 provided a major step in terms of data rates and capacity with carrier aggregation, higher‐order Multi‐Input‐Multi‐Output (MIMO) up to eight antennas in downlink and four antennas in uplink. The support for heterogeneous network (HetNet) was included in Rel 10, also known as LTE‐Advanced (Figure 1.2).

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LTE Basement

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Figure 1.1 The internet traffic, MBB subscriber, and relative mobile data growth.

LTE Basement 5

Among the design targets for the first release of the LTE standard are a downlink bit rate of 100 Mbit/s and a bit rate of 50 Mbit/s for the uplink with a 20‐MHz spectrum allocation. Smaller spectrum allocation will of course lead to lower bit rates and the general bit rate can be expressed as 5 bits/s/Hz for the downlink and 2.5 bits/s/Hz for the uplink. Rel 10 (LTE‐Advanced), was completed in June 2011 and the first commercial carrier aggregation network started in June 2013 (Figure 1.3).

LTE provides global mobility with a wide range of services that includes voice, data, and video in a mobile environment with lower deployment cost. The main benefits of LTE include (Figure 1.4):

● Wide spectrum and bandwidth range, increased spectral efficiency and support for higher user data rates

GSM9.6 kbit/s

GPRS171.2 kbit/s

EDGE473.6 kbit/s

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HSPA+28.8 Mbit/s42 Mbit/s

LTE+300 Mbit/s

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Figure 1.2 3GPP standard evolution.

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Figure 1.3 Downlink data rate evolution.

LTE Optimization Engineering Handbook6

● Reduced packet latency and rich multimedia user experience, excellent performance for outstanding quality of experience

● Improved system capacity and coverage as well as variable bandwidth operation ● Cost effective with a flat IP architecture and lower deployment cost ● Smooth interaction with legacy networks

LTE air interface uses orthogonal frequency division multiple access (OFDMA) for downlink transmission to achieve high peak data rates in high spectrum bandwidth. LTE uses single carrier frequency division multiple access (SC‐FDMA) for uplink transmission, a technology that pro-vides advantages in power efficiency. LTE supports both FDD and TDD modes, with FDD, DL, and UL transmissions performed simultaneously in two different frequency bands, with TDD, DL, and UL transmissions performed at different time intervals within the same frequency band. LTE supports advanced adaptive MIMO, balance average/peak throughput, and coverage/cell‐edge bit rate. Compared to 3G, significant reduction in delay over air interface can be supported in LTE, and it is suitable for real‐time applications, for example, VoIP, PoC, gaming, and so on.

Spectrum is a finite resource and FDD and TDD system will support the future demand, which are shown in Figure 1.5. TDD spectrum can provide 100‐150MHz of additional bandwidth per operator, TD‐LTE spectrum with large bandwidth will be a key to operators future network strategy and one of the way to address capacity growth.

1.1.1 LTE Architecture

LTE is predominantly associated with the radio access network (RAN). The eNodeB (eNB) is the component within the LTE RAN network. LTE RAN provides the physical radio link between the user equipment (UE) and the evolved packet core network. The system archi-tecture evolution (SAE) specifications defines a new core network, which is termed as evolved packet core (EPC) including all internet protocol (IP) networking architectures (Figure 1.6).

Evolved NodeB (eNB): Provides the LTE air interface to the UEs, the eNB terminates the user plane (PDCP/RLC/MAC/L1) and control plane (RRC) protocols. Among other things, it performs radio resource management and intra‐LTE mobility for the evolved access system. At the S1 interface toward the EPC, the eNB terminates the control plane (S1AP) and the user plane (GTP‐U).

“Cell Edge” Tput~0.06bps/Hz

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Figure 1.4 Throughput of a user, 10 users evenly distributed in cell.

LTE Basement 7

Mobility Management Entity (MME): A control plane node responsible for idle mode UE tracking and paging procedures. The Non‐Access Stratum (NAS) signaling terminates at the MME. Its main function is to manage mobility, UE identities, and security parameters. The MME is involved in the EPS bearer activation, modification, deactivation process, and is also responsible for choosing the SGW for a UE at the initial attach and at time of intra‐LTE handover involving core network node relocation. PDN GW selection is also performed by the MME. It is responsible for authenticating the user by interacting with the home subscription server (HSS).

Serving Gateway (SGW): This node routes and forwards the IP packets, while also acting as the mobility anchor for the user plane flow during inter‐eNB handovers and other 3GPP technologies (2G/3G systems using S4). For idle state UEs, the SGW terminates the DL data path and triggers paging when DL data arrives for the UE.

Packet Data Network Gateway (PDN GW): Provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UEs. The PDN GW performs among other policy enforcement, packet filtering for each user and IP address allocation.

Policy and Charging Rules Function (PCRF): The PCRF supports policy control decisions and flow based charging control functionalities. Policy control is the process whereby the PCRF indicates to the PCEF (in PDN GW) how to control the EPS bearer. A policy in this context is the information that is going to be installed in the PCEF to allow the enforcement of the required services.

Home Subscription Server (HSS): The HSS is the master database that contains LTE user information and hosts the database of the LTE users.

1.1.2 LTE Network Interfaces

LTE network can be considered of two main components: RAN and EPC. RAN includes the LTE radio protocol stack (RRC, PDCP, RLC, MAC, PHY). These entities reside entirely within the UE and the eNB nodes. EPC includes core network interfaces, protocols, and entities. These entities and protocols reside within the SGW, PGW, and MME nodes, and partially within the eNB nodes.

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UE• IMEI (equipment)• IMSI (SIM card)• Temporary GUTI• User Plane IP

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• Mobility Management• Session Management• Security Management• Selects SGW based on TA• Selects PGW based on APN

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Figure 1.6 Nodes and functions in LTE.

LTE Basement 9

Uu: Uu is the air interface connecting the eNB with the UEs. The protocols used for the control plane are RRC on top of PDCP, RLC, MAC, and L1. The protocols used for the user plane are PDCP, RLC, MAC, and L1. LTE air interface supports high data rates. LTE uses OFDMA for downlink transmission to achieve high peak data rates in high spectrum bandwidth. LTE uses SC‐FDMA for uplink transmission, a technology that provides advantages in power efficiency.

S1: The interface S1 is used to connect the MME/S‐GW and the eNB. The S1 is used for both the control plane and the user plane. The control plane part is referred to as S1‐MME and the user plane S1‐U. The protocol used on S1‐MME is S1‐AP on the radio network layer. The transport network layer is based on IP transport, comprising SCTP on top of IP. The protocol used on S1‐U is based on IP transport with GTP‐U and UDP on top.

The X2 interface is a new type of interface between the eNBs introduced by the LTE to perform the following functions: handover, load management, CoMP, and so on. X2‐UP protocol tunnels end‐user packets between the eNBs. The tunneling function supports are identifica-tion of packets with the tunnels and packet loss management. X2‐UP uses GTP‐U over UDP/IP as the transport layer protocol similar to S1‐UP protocol. X2‐CP has SCTP as the transport layer protocol is similar to the S1‐CP protocol. The load management function allows exchange of overload and traffic load information between eNBs, which helps eNBs handle traffic load effectively. The handover function enables one eNB to hand over the UE to another eNB. A handover operation requires transfer of information necessary to maintain the services at the new eNB. It also requires establishment and release of tunnels between source and target eNB to allow data forwarding and informs the already prepared target eNB for handover cancellations.

NAS is a control plane protocol that terminates in both the UE and the MME. It is transparently carried over the Uu and S1 interface.

S6a: S6a interface enables transfer of subscription and authentication data between the MME and HSS for authenticating/authorizing user access to the EUTRAN. The S6a interface is involved in the following call flows, initial attach, tracking area update, ser-vice request, detach, HSS user profile management, and HSS‐initiated QoS modification, and so on.

S11: Reference point between MME and SGW. This is a control plane interface for negotiating bearer plane resources with the SGW.

The above‐mentioned LTE network interfaces are shown in Figure 1.7.IP connection between a UE and a PDN is called PDN connection or EPS session. Each

PDN connection is represented by an IP address of the UE and a PDN ID (APN). As shown in Figure 1.8, there are two different layers of IP networking. The first one is the end‐to‐end layer, which provides end‐to‐end connectivity to the users. This layers involves the UEs, the PGW, and the remote host, but does not involve the eNB. The second layer of IP networking is the EPC local area network, which involves all eNBs and the SGW/PGW node. The end‐to‐end IP communications is tunneled over the local EPC IP network using GTP/UDP/IP.

Moreover, in LTE, IDs are used to identify a different UE, mobile equipment, and network element to make the EPS data session and bearer establishment, which can refer to Annex “LTE identifiers” for reference; the summary of IDs is shown in Table 1.1.

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S6a InterfaceAAA interface betweenMME and HSS that enables user access to the EPS

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Figure 1.7 LTE network interfaces.