LTE Optimization Engineering Handbook PDF

LTE Optimization Engineering Handbook LTE Optimization Engineering Handbook Xincheng Zhang China Mobile Group Design Institute Co., Ltd. Beijing, China This edition first published 2018 © 2018 John Wiley & Sons Singapore Pte. Ltd All rights reserved. No part of this publication may be reproduc...

LTE Optimization Engineering Handbook LTE Optimization Engineering Handbook Xincheng Zhang China Mobile Group Design Institute Co., Ltd. Beijing, China This edition first published 2018 © 2018 John Wiley & Sons Singapore Pte. Ltd All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/ permissions. The right of Xincheng Zhang to be identified as the author of this work has been asserted in accordance with law. Registered Offices John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA John Wiley & Sons Singapore Pte. Ltd, 1 Fusionopolis Walk, #07-01 Solaris South Tower, Singapore 138628 Editorial Office 1 Fusionopolis Walk, #07-01 Solaris South Tower, Singapore 138628 For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Wiley also publishes its books in a variety of electronic formats and by print-on-demand. Some content that appears in standard print versions of this book may not be available in other formats. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. 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Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. 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, | 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–dc23 LC record available at https://lccn.loc.gov/2017019394 Cover Design: Wiley Cover Images: (Yin Yang) © alengo/Gettyimages; (Feng shui compass) © Liuhsihsiang/Gettyimages Set in 10/12pt Warnock by SPi Global, Pondicherry, India 10 9 8 7 6 5 4 3 2 1  v Contents About the Author xvi Preface xvii Part 1 LTE Basics and Optimization Overview 1 1 LTE Basement 3 1.1 LTE Principle 3 1.1.1 LTE Architecture 6 1.1.2 LTE Network Interfaces 7 1.2 LTE Services 11 1.2.1 Circuit‐Switched Fallback 12 1.2.2 Voice over LTE 13 1.2.3 IMS Centralized Services 16 1.2.4 Over the Top Solutions 16 1.2.5 SMS Alternatives over LTE 17 1.2.6 Converged Communication 19 1.3 LTE Key Technology Overview 19 1.3.1 Orthogonal Frequency Division Multiplexing 20 1.3.2 MIMO 21 1.3.3 Radio Resource Management 22 2 LTE Optimization Principle and Method 24 2.1 ­LTE Wireless Optimization Overview 24 2.1.1 Why LTE Wireless Optimization 24 2.1.2 Characters of LTE Optimization 24 2.1.3 LTE Joint Optimization with 2G/3G 25 2.1.4 Optimization Target 25 2.2 LTE Optimization Procedure 26 2.2.1 Optimization Procedure Overview 26 2.2.2 Collection of Mass Nerwork Measurement Data 28 2.2.3 Measurement Report Data Analysis 30 2.2.4 Signaling Data Analysis 31 2.2.5 UE Positioning 32 2.2.5.1 Timing Advance 33 2.2.5.2 Location Accuracy Evaluation 35 vi Contents 2.2.5.3 Location Support 36 2.2.5.4 3D Geolocation 37 2.2.6 Key Performance Indicators Optimization 42 2.2.7 Technology Evolution of Optimization 43 2.3 LTE Optimization Key Point 44 2.3.1 RF Optimization 44 2.3.1.1 RSRP/RSSI/SINR/CINR 44 2.3.1.2 External Interference 48 2.3.2 CQI versus RSRP and SINR 51 2.3.2.1 CQI Adjustment 51 2.3.2.2 SINR Versus Load 54 2.3.2.3 SINR Versus MCS 56 2.3.3 Channel Power Configuration 58 2.3.3.1 RE Power 58 2.3.3.2 CRS Power Boosting 64 2.3.3.3 Power Allocation Optimization 66 2.3.4 Link Adaption 67 2.3.5 Adaptive Modulation and Coding 69 2.3.6 Scheduler 70 2.3.6.1 Downlink Scheduler 72 2.3.6.2 Uplink Scheduler 74 2.3.7 Radio Frame 75 2.3.8 System Information and Timers 76 2.3.8.1 System Information 76 2.3.8.2 Timers 81 2.3.9 Random Access 83 2.3.10 Radio Admission Control 85 2.3.11 Paging Control 86 2.3.11.1 Paging 86 2.3.11.2 Paging Capacity 92 2.3.11.3 Paging Message Size 95 2.3.11.4 Smart Paging 95 2.3.11.5 Priority Paging 96 2.3.12 MIMO and Beamforming 97 2.3.12.1 Basic Multi‐Antenna Techniques 100 2.3.12.2 2D‐Beamforming 101 2.3.12.3 2D MIMO and Parameters 104 2.3.12.4 Massive‐MIMO 105 2.3.13 Power Control 107 2.3.13.1 PUSCH/PUCCH Power Control 107 2.3.13.2 PRACH Power Control 109 2.3.14 Antenna Adjustment 111 2.3.14.1 Antenna Position 112 2.3.14.2 Remote Electrical Tilt 113 2.3.14.3 Antenna Azimuths and Tilts Optimization 117 2.3.14.4 VSWR Troubleshooting 118 2.3.15 Main Key Performance Indicators 120  Contents vii Part 2 Main Principles of LTE Optimization 123 3 Coverage Optimization 125 3.1 Traffic Channel Coverage 125 3.1.1 Parameters of Coverage 126 3.1.2 Weak Coverage 128 3.1.2.1 DL Coverage Hole 128 3.1.2.2 UL Weak Coverage 128 3.1.2.3 UL and DL Imbalance 129 3.1.3 Overlapping Coverage 129 3.1.4 Overshooting 130 3.1.5 Tx1/Tx2 RSRP Imbalance 132 3.1.6 Extended Coverage 132 3.1.7 Cell Border Adjustment 135 3.1.8 Vertical Coverage 137 3.1.9 Parameters Impacting Coverage 138 3.2 ­Control Channel Coverage 138 4 Capacity Optimization 140 4.1 RS SINR 140 4.2 ­PDCCH Capacity 141 4.3 ­PUCCH Capacity 144 4.3.1 Factors Affecting PUCCH Capacity 145 4.3.2 PUCCH Dimensioning Example 151 4.4 ­Number of Scheduled UEs 152 4.5 Spectral Efficiency 153 4.6 ­DL Data Rate Optimization 154 4.6.1 Limitation Factor 156 4.6.2 Model of DL Data Throughput 157 4.6.3 UDP/TCP Protocol 158 4.6.4 MIMO 161 4.6.4.1 DL MIMO 161 4.6.4.2 4Tx/4Rx Performance 163 4.6.4.3 Transmission Mode Switch 163 4.6.4.4 UL MU‐MIMO 164 4.6.5 DL PRB Allocation and Utilization Mechanism 165 4.6.6 DL BLER 167 4.6.7 Impact of UE Velocity 169 4.6.8 Single User Throughput Optimization 170 4.6.8.1 Radio Analysis – Assignable Bits 171 4.6.8.2 Radio Analysis – CFI and Scheduling 171 4.6.8.3 Radio Analysis – HARQ 171 4.6.9 Avarage Cell Throughput Optimization 172 4.6.10 Cell Edge Throughput Optimization 172 4.6.11 Some Issues of DL Throughput 173 4.6.11.1 Antenna Diversity not Balanced 173 4.6.11.2 DL Grant is not Enough 173 4.6.11.3 Unstable Rate 175 viii Contents 4.7 ­UL Data Rate Optimization 175 4.7.1 Model of UL Data Throughput 176 4.7.2 UL SINR and PUSCH Data Rate 176 4.7.3 PRB Stretching and Throughput 179 4.7.4 Single User Throughput Optimization 180 4.7.4.1 Radio Analysis – Available PRBs 181 4.7.4.2 Radio Analysis—Link Adaptation 181 4.7.4.3 Radio Analysis – PDCCH 182 4.7.5 Cell Avarage and Cell‐edge Throughput Optimization 182 4.7.6 Some Issues of UL Throughput 183 4.8 Parameters Impacting Throughput 185 5 Internal Interference Optimization 188 5.1 Interference Concept 188 5.2 ­DL Interference 190 5.2.1 DL Interference Ratio 191 5.2.2 Balance Between SINR and RSRP 192 5.3 ­UL Interference 192 5.3.1 UL Interference Detection 194 5.3.2 Generation of UL Interference 196 5.3.2.1 Cell Loading Versus Inter‐Cell Interference 196 5.3.2.2 Unreasonable UL Network Structure 197 5.3.2.3 Cross slot interference 199 5.3.3 PUSCH Tx Power Analysis 200 5.3.4 UL Effect of P0 and α 202 5.3.5 PRACH Power Control 204 5.3.6 SRS Power Control 206 5.3.7 Interference Rejection Combinin 209 5.4 ­Inter‐Cell Interference Coordination 210 5.5 ­UL IoT Control 210 5.5.1 UL Interference Issues and Possible Solutions 210 5.5.2 UL IoT Control Mechanism 210 5.5.3 PUSCH UL_SINR Target Calculation 212 5.5.4 UL Interference Criteria 213 6 Drop Call Optimization 216 6.1 ­Drop Call Mechanism 216 6.1.1 Radio Link Failure Detection by UE 217 6.1.2 RadioLink Failure Detection by eNB 220 6.1.2.1 Link Monitors in eNB 220 6.1.2.2 Time Alignment Mechanism 221 6.1.2.3 Maximum RLC Retransmissions Exceeded 224 6.1.3 RadioLink Failure Optimization and Recovery 225 6.2 ­Reasons of Call Drop and Optimization 227 6.2.1 Reasons of E‐RAB Drop 227 6.2.2 S1 Release 230 6.2.3 Retainability Optimization 233 6.3 ­RRC Connection Reestablishment 233 6.4 ­RRC Connection Supervision 239  Contents ix 7 Latency Optimization 244 7.1 User Plane Latency 244 7.2 Control Plane Latency 247 7.3 Random Access Latency Optimization 247 7.4 Attach Latency Optimization 248 7.5 Paging Latency Optimization 250 7.6 Parameters Impacting Latency 250 8 Mobility Optimization 254 8.1 ­Mobility Management 255 8.1.1 RRC Connection Management 256 8.1.2 Measurement and Handover Events 256 8.1.3 Handover Procedure 260 8.1.3.1 X2 Handover 261 8.1.3.2 S1 Handover 267 8.1.3.3 Key point of X2/S1 Handover 267 8.2 ­Mobility Parameter 269 8.2.1 Attach and Dettach 272 8.2.2 UE Measurement Criterion in Idle Mode and Cell Selection 273 8.2.3 Cell Priority 276 8.3 ­Intra‐LTE Cell Reselection 276 8.3.1 Cell Reselection Procedure 278 8.3.2 Inter‐Frequency Cell Reselection 279 8.3.3 Cell Reselection Parameters 282 8.3.4 Inter‐Frequency Reselection Optimization 283 8.4 ­Intra‐LTE Handover Optimization 285 8.4.1 A3 and A5 Handover 285 8.4.2 Data Forwarding 290 8.4.3 Intra‐Frequency Handover Optimization 291 8.4.4 Inter‐Frequency Handover Optimization 292 8.4.5 Timers for Handover Failures 296 8.5 ­Neighbor Cell Optimization 297 8.5.1 Intra‐LTE Neighbor Cell Optimization 297 8.5.1.1 Neighbor Relations Table 297 8.5.1.2 ANR 298 8.5.2 Suitable Neighbors for Load Balancing 299 8.6 ­Measurement Gap 299 8.6.1 Measurement Gap Pattern 299 8.6.2 Measurement Gap Versus Period of CQI Report and DRX 304 8.6.3 Impact of Throughput on Measurement Gap 304 8.7 ­Indoor and Outdoor Mobility 305 8.8 ­Inter‐RAT Mobility 306 8.8.1 Inter‐RAT Mobility Architecture and Key Technology 307 8.8.2 LTE to G/U Strategy 309 8.8.3 Reselection Optimization 314 8.8.3.1 LTE to UTRAN 315 8.8.3.2 UTRAN to LTE 319 8.8.4 Redirection Optimization 320 8.8.4.1 LTE to UTRAN 320 x Contents 8.8.4.2 UTRAN to LTE 322 8.8.5 PS Handover Optimization 322 8.8.5.1 LTE to UTRAN 322 8.8.5.2 UTRAN to LTE 324 8.8.6 Reselection and Redirection Latency 325 8.8.7 Optimization Case Study 326 8.9 ­Handover Interruption Time Optimization 326 8.9.1 Control Plane and User Plane Latency 329 8.9.2 Inter‐RAT Mobility Latency 332 8.10 ­Handover Failure and Improvement 332 8.11 ­Mobility Robustness Optimization 335 8.12 ­Carrier Aggregation Mobility Optimization 341 8.13 ­FDD‐TDD Inter‐mode Mobility Optimization 345 8.14 ­Load Balance 346 8.14.1 Inter‐Frequency Load Balance 346 8.14.2 Inter‐RAT Load Balance 348 8.14.3 Load Based Idle Mode Mobility 349 8.15 ­High‐Speed Mobile Optimization 351 8.15.1 High‐Speed Mobile Feature 353 8.15.2 Speed‐Dependent Cell Reselection 354 8.15.3 PRACH Issues 356 8.15.4 Solution for Air to Ground 358 9 Traffic Model of Smartphone and Optimization 360 9.1 ­Traffic Model of Smartphone 360 9.1.1 QoS Mechanism 362 9.1.2 Rate Shaping and Traffic Management 366 9.1.3 Traffic Model 371 9.2 ­Smartphone‐Based Optimization 372 9.3 ­High‐Traffic Scenario Optimization 372 9.3.1 Resource Configuration 374 9.3.2 Capacity Monitoring 375 9.3.3 Special Features and Parameters for High Traffic 377 9.3.4 UL Noise Rise 379 9.3.5 Offload Solution and Parameter Settings 379 Part III Voice Optimization of LTE 383 10 Circuit Switched Fallback Optimization 385 10.1 ­Voice Evolution 385 10.2 ­CSFB Network Architecture and Configuration 386 10.2.1 CSFB Architecture 386 10.2.2 Combined Register 387 10.2.3 CSFB Call Procedure 392 10.2.3.1 Fallback Options 392 10.2.3.2 RRC Release with Redirection 393 10.2.3.3 CSFB Call Procedure 395 10.2.4 Mismatch Between TA and LA 397  Contents xi 10.3 ­CSFB Performance Optimization 402 10.3.1 CSFB Optimization 402 10.3.1.1 Main Issues of CSFB 402 10.3.1.2 CSFB Optimization Method 403 10.3.2 CSFB Main KPI 407 10.3.3 Fallback RAT Frequency Configuration Optimization 409 10.3.4 Call Setup Time Latency Optimization 411 10.3.4.1 ESR to Redirection Optimization 416 10.3.4.2 Twice Paging 416 10.3.5 Data Interruption Time 418 10.3.6 Return to LTE After Call Complete 419 10.4 ­Short Message Over CSFB 422 10.5 ­Case Study of CSFB Optimization 423 10.5.1 Combined TA/LA Updating Issue 423 10.5.2 MTRF Issue 425 10.5.3 Track Area Update Reject After CSFB 425 10.5.3.1 No EPS Bearer Context Issue 428 10.5.3.2 Implicitly Detach Issue 428 10.5.3.3 MS Identity Issue 428 10.5.4 Pseudo Base Station 428 11 VoLTE Optimization 434 11.1 ­VoLTE Architecture and Protocol Stack 435 11.1.1 VoLTE Architecture 435 11.1.2 VoLTE Protocol Stack 435 11.1.3 VoLTE Technical Summary 438 11.1.4 VoLTE Capability in UE 439 11.2 ­VoIP/Video QoS and Features 442 11.2.1 VoIP/Video QoS 442 11.2.2 Voice Codec 444 11.2.3 Video Codec 446 11.2.4 Radio Bearer for VoLTE 449 11.2.5 RLC UM 454 11.2.6 Call Procedure 457 11.2.6.1 LTE Attach and IMS Register 458 11.2.6.2 E2E IMS Flow 458 11.2.6.3 Video Phone Session Handling 462 11.2.7 Multiple Bearers Setup and Release 466 11.2.8 VoLTE Call On‐Hold/Call Waiting 467 11.2.9 Differentiated Paging Priority 468 11.2.10 Robust Header Compression 470 11.2.10.1 RoHC Feature 470 11.2.10.2 Gain by RoHC 470 11.2.11 Inter‐eNB Uplink CoMP for VoLTE 475 11.3 ­Semi‐Persistent Scheduling and Other Scheduling Methods 477 11.3.1 SPS Scheduling 477 11.3.2 SPS Link Adaptation 478 11.3.3 Delay Based Scheduling 481 11.3.4 Pre‐scheduling 482 xii Contents 11.4 ­PRB and MCS Selection Mechanism 484 11.4.1 Optimized Segmentation 484 11.4.2 PRB and MCS Selection 485 11.5 ­VoLTE Capacity 486 11.5.1 Control Channel for VoLTE 487 11.5.2 Performance of Mixed VoIP and Data 488 11.6 ­VoLTE Coverage 491 11.6.1 VoIP Payload and RoHC 492 11.6.2 RLC Segmentation 492 11.6.3 TTI Bundling 498 11.6.4 TTI Bundling Optimization 502 11.6.5 Coverage Gain with RLC Segmentation and TTI Bundling 507 11.6.6 MCS/TBS/PRB Selection 509 11.6.7 Link Budget 510 11.7 ­VoLTE Delay 513 11.7.1 Call Setup Delay 516 11.7.1.1 Call Setup Time 516 11.7.1.2 Reasons for Long Call Setup Time 516 11.7.2 Conversation Start Delay 519 11.7.3 RTP Delay 521 11.7.4 Handover Delay and Optimization 525 11.8 ­Intra‐LTE Handover and eSRVCC 527 11.8.1 Intra‐Frequency Handover 527 11.8.2 Inter‐Frequency Handover 528 11.8.3 Single Radio Voice Call Continuity Procedure 529 11.8.4 SRVCC Parameters Optimization 539 11.8.4.1 Handover Parameters 539 11.8.4.2 SRVCC–Related Timer 539 11.8.5 aSRVCC and bSRVCC 543 11.8.6 SRVCC Failure 543 11.8.7 Reducing SRVCC Voice Gap and eSRVCC 545 11.8.7.1 Voice Interruption Time during SRVCC 545 11.8.7.2 eSRVCC 549 11.8.8 Fast Return to LTE 552 11.8.9 Roaming Behavior According to Network Capabilities 555 11.9 ­Network Quality and Subjective Speech Quality 555 11.9.1 Bearer Latency 558 11.9.2 MoS 561 11.9.2.1 Voice Quality 561 11.9.2.2 Video Quality 570 11.9.3 Jitter 571 11.9.4 Packet Loss 572 11.9.5 One Way Audio 575 11.9.6 PDCP Discard Timer Operation 576 11.10 ­Optimization 577 11.10.1 Distribution of Main Indicators of Field Test 580 11.10.2 Compression Ratio and GBR Throughput 584 11.10.3 RB Utilization 584 11.10.4 BLER Issue 587  Contents xiii 11.10.5 Quality Due to Handover 589 11.10.6 eSRVCC Handover Issues 589 11.10.7 Packet Loss 592 11.10.7.1 Packet Loss due to Poor RF 592 11.10.7.2 Packet Loss due to Massive users 592 11.10.7.3 Packet Loss Due to Insufficient UL grant 592 11.10.7.4 Packet Loss due to Handover 601 11.10.7.5 Packet Loss Due to Network Issue 601 11.10.8 Call Setup Issues 601 11.10.8.1 Missed Pages 602 11.10.8.2 IMS Issues 604 11.10.8.3 Dedicated Bearer Setup Issues 609 11.10.8.4 CSFB Call Issues 612 11.10.8.5 aSRVCC Failure 612 11.10.8.6 RF Issues 612 11.10.8.7 Frequent TFT Updates 617 11.10.8.8 Encryption Issue 618 11.10.9 Call Drop 619 11.10.9.1 Call Drop 619 11.10.9.2 Radio Link Failure 622 11.10.9.3 RTP‐RTCP Timeout 624 11.10.9.4 RLC/PDCP SN Length Mismatch 626 11.10.9.5 IMS Session Drop 626 11.10.9.6 eNB/MME Initiated Drop 632 11.10.10 Packet Aggregation Level 632 11.10.11 VoIP Padding 633 11.10.12 VoIP Ralated Parameters 635 11.10.13 Video‐Related Optimization 635 11.10.13.1 Video Bit Rate and Frame Rate 637 11.10.13.2 Video MoS and Audio/Video Sync 637 11.10.14 IMS Ralated Timer 637 11.11 ­UE Battery Consumption Optimization for VoLTE 638 11.11.1 Connected Mode DRX Parameter 643 11.11.2 DRX Optimization 644 11.11.2.1 State Estimation 644 11.11.2.2 DRX Optimization and Parameters 644 11.11.2.3 KPI Impacts with DRX 648 11.11.3 Scheduling Request Periodicity and Disabling of Aperiodic CQI 652 11.12 ­Comparation with VoLTE and OTT 654 11.12.1 OTT VoIP User Experience 654 11.12.2 OTT VoIP Codec 657 11.12.3 Signaling Load of OTT VoIP 658 Part IV Advanced Optimization of LTE 663 12 PRACH Optimization 665 12.1 ­Overview 665 12.2 ­PRACH Configuration Index 669 12.3 ­RACH Root Sequence 673 xiv Contents 12.4 ­PRACH Cyclic Shift 674 12.4.1 PRACH Cyclic Shift Optimization 674 12.4.2 Rrestricted Set 679 12.5 ­Prach Frequency Offset 682 12.6 ­Preamble Collision Probability 683 12.7 ­Preamble Power 684 12.8 ­Random Access Issues 687 12.9 ­RACH Message Optimization 689 12.10 ­Accessibility Optimization 692 12.10.1 Reasons for Poor Accessibility 692 12.10.2 Accessibility 693 12.10.3 Accessibility Analysis Tree 695 12.10.4 Call and Data Session Setup Optimization 697 12.10.5 RACH Estimation for Different Traffic Profile 698 13 Physical Cell ID Optimization 702 13.1 ­Overview 702 13.2 ­PCI Optimization Methodology 703 13.2.1 PCI Group Optimization 705 13.2.2 PCI Code Reuse Distance 705 13.2.3 Mod3/30 Discrepancy Analysis 708 13.2.4 Collision and Confusion 708 13.3 ­PCI Optimization 709 14 Tracking Areas Optimization 711 14.1 ­TA Optimization 712 14.1.1 TA Update Procedure 713 14.1.2 TA Optimization and TAU Failure 715 14.2 ­TA List Optimization 716 14.3 ­TAU Reject Analysis and Optimization 719 15 Uplink Signal Optimization 721 15.1 ­Uplink Reference Signal Optimization 721 15.1.1 Coding Scheme of UL RS 722 15.1.2 Correlation of UL Sequence Group 723 15.1.2.1 UL Sequence Group Hopping 725 15.1.2.2 UL Sequence Hopping 726 15.1.2.3 UL Cyclic Shift Hopping 726 15.1.3 UL Sequence Group Optimization 727 15.2 ­Uplink Sounding Signal Optimization 729 15.2.1 SRS Characters 730 15.2.2 Wideband SRS Coverage 736 15.2.3 Dynamic SRS Adjustment Scheme 736 15.2.4 SRS Selection Dimension and Confliction 737 15.2.5 SRS Conflict and Optimization 739 16 HetNet Optimization 741 16.1 ­UE Geolocation and Identification of Traffic Hot Spots 741 16.2 ­Wave Propagation Characteristics for HetNet 745  Contents xv 16.3 ­New Features in HetNet 746 16.4 ­Combined Cell Optimization 747 16.5 ­Cell Range Expansion Offset 748 16.6 ­HetNet Cell Reselection and Handover Optimization 751 17 QoE Evaluation and Optimization Strategy 752 17.1 ­QoE Modeling 753 17.2 ­Data Collecting and Processing 756 17.3 ­QoE‐Based Traffic Evaluation 757 17.3.1 Online Video QoE 757 17.3.1.1 Video Quality Monitoring Methods 761 17.3.1.2 RATE Adaptive Video Codecs 763 17.3.1.3 Streaming KPI and QoE 764 17.3.1.4 Video Optimization 766 17.3.2 Voice QoE 769 17.3.3 Data Service QoE 770 17.3.3.1 Web browsing 770 17.3.3.2 Online Gaming 774 17.4 ­QoE Based Optimization 776 18 Signaling‐Based Optimization 780 18.1 ­S1‐AP Signaling 780 18.1.1 NAS signaling 782 18.1.2 Inactivity Supervision 783 18.1.3 UE signaling Management 785 18.2 ­Signaling radio bearers 786 18.3 ­Signaling Storm 788 18.4 ­Signaling Troubleshooting Method 788 18.4.1 Attach Failure 788 18.4.2 Service Request Failure 796 18.4.3 S1/X2‐Based Handover 796 18.4.4 eSRVCC Failure 798 18.4.5 CSFB Failure 800 Appendix 802 Glossary of Acronyms 820 References 823 Index 825 xvi About the Author 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.  xvii 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. xviii Preface It is known that LTE doesn’t have basic voice and SMS support. To mitigate this, 3GPP ­ roposes a fallback to circuit‐switched (CS) network for voice and SMS. Although voice has p 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  1 Part 1 LTE Basics and Optimization Overview  3 1 LTE Basement 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). LTE Optimization Engineering Handbook, First Edition. Xincheng Zhang. © 2018 John Wiley & Sons Singapore Pte. Ltd. Published 2018 by John Wiley & Sons Singapore Pte. Ltd.  140,000.0 Bandwidth demand Video Audio Streaming 120,000.0 Conferencing Video Streaming P2P 100,000.0 Video Streaming / TV VoIP Ecommerce 80,000.0 Web / Internet Web Surfing 60,000.0 Rich text Email 40,000.0 high VoIP (VoLTE) Text Email 20,000.0 low 0.0 low high Delay demand 2011 2012 2013 2014 2015 2016 2017 2018 2019 Internet traffic on LTE Mobile traffic type (Source: ABI Research) 8,000 Mobile Data Traffic 20 000 7,000 18 000 Europe LAT APAC total MEA NAM 6,000 16 000 MBB Subscriber in Million 14 000 5,000 12 000 4,000 10 000 8 000 3,000 6 000 2,000 4 000 1,000 2 000 0 0 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 MBB subscriber growth MBB data traffic Figure 1.1 The internet traffic, MBB subscriber, and relative mobile data growth.  LTE Basement 5 Phase 2+ Release 99 Release 6 Release 8 (Release 97) GPRS UMTS HSUPA LTE 171.2 kbit/s 2 Mbit/s 5.76 Mbit/s +300 Mbit/s Release 9/10 LTE Advanced HSPA+ GSM EDGE HSDPA 28.8 Mbit/s 9.6 kbit/s 473.6 kbit/s 14.4 Mbit/s 42 Mbit/s Phase 1 Release 99 Release 5 Release 7/8 Figure 1.2 3GPP standard evolution. 5G 10 Gbps Peak Average LTE-A 1 Gbps LTE 5G in 2020 (Ave. ~1Gbps 100 Mbps Peak ~5Gbps) HSDPA, HDR 10 Mbps Cat. 11 (Ave. ~240Mbps, Peak ~600Mbps) WCDMA, Cat. 9 (Ave. ~180Mbps, Peak ~450Mbps) 1 Mbps CDMA2000 Cat. 6 (Ave. ~120Mbps, Peak 300Mbps) Cat. 4 (Ave. ~24Mbps, Peak 150Mbps) 100 Kbps Cat. 3 (Ave. ~12Mbps, Peak 100Mbps) HSDPA (Ave. ~2Mbps, Peak 14Mbps) 2000 2005 2010 2015 2020 Figure 1.3 Downlink data rate evolution. 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 6 LTE Optimization Engineering Handbook 100% CDF “Average”Tput ~0.12bps/Hz 50% “Cell Edge”Tput ~0.06bps/Hz (95% coverage) 5% cell edge cell centre Tput Figure 1.4 Throughput of a user, 10 users evenly distributed in cell. 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).  LTE Basement 7 B42 250 (3,5GHz) TDD FDD 200 200 200 B43 150 (3,7GHz) B40 BW (MHz) (2,3GHz) B3 (1,8GHz) 100 100 B28 90 B7 (700MHz) 75 (2,6GHz) 70 60 60 50 B38 B2 50 B8 (2,6GHz) 35 (1,9GHz) B1 (900MHz) B5 25 B39 20 B10 (2,1GHz) (850MHz) (1,7/2,1GHz) (1,9GHz) 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 Frequency (MHz) Figure 1.5 Spectrum of LTE. 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.  HSS PCRF:Policy & Charging DNS Rules Function Subscription Profiles TA to SGW IP query Security information PGW: Packet Data Network UE APN to PGW query IMEI (equipment) MME (IP) address Gateway for UE MME IMSI (SIM card) S6a HSS:Home Subscriber Server Mobility Management Temporary GUTI Session Management EPC:Evolved packet Core User Plane IP Security Management PCRF SGW:Serving Gateway Selects SGW based on TA Selects PGW based on APN QoS rules UE:User Equipment Charging rules EUTRAN:Evolved UTRAN S1-MME S11 eNodeB:Enhanced Node B Gx Rx VLR:Visitor Location X2 Register PDN (i.e. IMS MSC:Mobile Switching S1u S5/S8 SGi or internet) Centre MME:Mobility Management eNB SGW PGW Entity Radio control and resource management Data forwarding Gateway between the internal Inter eNB communication via X2 Data buffering EPC network and external PDNs LTE Uu: LTE UTRAN UE User IP address allocation Interface User plane QoS enforcement 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.  Diameter SGi Interface IP S6a Interface Comunicates CPG SCTP HSS IMS/External with external L2 AAA interface between IP networks IP MME and HSS that Rx networks. L1 enables user access to L2 the EPS PCRF L1 GTP-C Diameter SGi S6a UDP Rx Interface TCP Transport policy IP control, charging and IP GTPv2-C S10 Interface Gx QoS control. L2 UDP L2 AAA interface between MME and HSS that L1 L1 IP enables user access to L2 the EPS S11 Interface PDN GW Gx Interface Control plane for creating, Provides transfer of L1 Diameter modifying and deleting policy and charging EPS bearers. S5/S8 Rules from PCRF to S10 TCP PDN Gw. S11 IP MME Serv GW S1-AP S1-MME Interface L2 SCTP S5/S8 Interface Reference point for Control and user L1 IP control plane protocol plane between E-UTRAN tunneling between L2 and MME S1-U GTP-C/GTP-U S1-MME Serving GW and L1 PDN GW UDP IP X2-AP GTP-U X2 Interface S1-U Interface GTP-U L2 Connects Reference point for SCTP UDP UDP L1 neigboring user plane protocol eNB IP eNBs between E-UTRAN IP X2 and MME L2 L2 L1 L1 Figure 1.7 LTE network interfaces.  LTE Basement 11 UE eNB MME SGW PGW RRC S1 Control plane S11 GTP-C S11 GTP-C Signaling Signaling end-to-end S1 S5 layer User plane DRB Bearer Bearer Uu eNB SGW S5/S8 PGW SGi P App D UE IP End to End service IP IP APN N address EPS Bearer (ID) PDCP PDCP GTPu GTPu GTPu E-RAB (ID) UDP UDP UDP RLC RLC IP IP IP MAC MAC L2 L2 L2 PHY PHY L1 L1 L1 S1-u Figure 1.8 LTE‐EPC control and data plane protocol stack. Table 1.1 Classification of LTE identification. Classification LTE identification UE ID IMSI, GUTI, S‐TMSI, IP address, C‐RNTI, UE S1AP ID, UE X2AP ID Mobile equipment ID IMEI Network element ID GUMMEI, MMEI, Global eNB ID, eNB ID, ECGI, ECI, P‐GW ID Location ID TAI, TAC Session/bearer ID PDN ID (APN), EPS bearer ID, E‐RAB ID, DRB ID, LBI, TEID 1.2 ­LTE Services LTE is an all packet‐switched technology. The telephony service on LTE is a packet‐switched mobile broadband service relying on specific support in LTE radio and EPC, which is needed to meet the expectations of telephony. On the other hand, the handling of voice traffic on LTE handsets is evolving as the mobile industry infrastructure evolves toward higher, eventually ubiquitous, and finally, LTE availability. Central to the enablement of LTE smartphones is to meet today’s very high expectation for the mobile user experience and to evolve the entire communications experience by augmenting voice with richer media services. Voice solutions of LTE include VoLTE/SRVCC, RCS, OTT, CSFB, SVLTE, and so on. LTE radio and EPC archi- tecture does not have a circuit‐switched (CS) domain available to handle voice calls as being done in 2G/3G. The voice traffic in the LTE network is handled through different procedures. The first one, which is mainly used, still remains on the circuit switch network (e.g., 2G or 3G) by maintaining either parallel connection and registration on these network or by switching to them whenever a voice call is initiated or terminated. The second one, which is when the voice call stands over LTE, the voice service is named VoLTE or VoIMS when the IP multi‐media system (IMS) service function is included. Video in LTE is one of the most importanr services. The demand for video content continues to grow among data services. Web video traffic growth has accelerated, as the number of internet‐ enabled devices has increased and more people depend on the mobile internet. Recently, a group of key operators, infrastructure, and device vendors announced a joint effort to facilitate the evolution of mobile communication toward RCS (rich communication suite). The core feature set of RCS includes the following services: enhanced phonebook, with service capabilities and presence enhanced contacts information; enhanced messaging, which 12 LTE Optimization Engineering Handbook enables a large variety of messaging options including chat and messaging history, and enriched call, which enables multimedia content sharing during a voice call. It is believed that RCS is a promising evolution in LTE, many operators have announced to support the RCS. 1.2.1 Circuit‐Switched Fallback The basic principle of circuit‐switched fallback (CSFB) is that once originating or receiving a CS voice call by the UE connected over LTE, it will move to either GSM or UMTS network (fallback) where the call proceeds. One major requirement for the realization of CSFB is the overlay of LTE with GSM, UMTS, or both. It is the quickest implementation both at terminal and at network sides and is mandatory for international roaming scenarios. With CSFB, UE will attach to the network through LTE, MME will ask MSC to update UE location in its database, when the UE is operating in LTE (data connection) mode and when a call comes in, the LTE network pages the device. The device responds with a special service request message to the network, and the network signals the device to move to 2/3G to accept the incoming call. Similarly for outgoing calls, the same special service request is used to move the device to 2/3G to place the outgoing call. CSFB for operator means very little investment since only few modifications are required in the network, additional interface (SGs) between MME and MSC is required shown in Figure 1.9. With basic CSFB implementation, the additional delay to set up the voice call is less than 1.3s to 3G or about 2.8s to 2G, which is acceptable from an end‐user perspective. This delay is sig- nificantly reduced with the activation of PS handovers when falling back to 3G and of RRC release with 3GPP Rel 9 redirections to 2G/3G. The CSFB option offers complete services and feature transparency by enabling mobile service providers to leverage their existing GSM/ UMTS network for the delivery of CS services, including prepaid and postpaid billing. SGs interface is used to carry signaling to move the access network carrying the voice traffic from 2/3G to the LTE and from LTE to 2/3G. This interface maintains a connection between the MSC/VLR and the MME and its main role is to handle signaling and voice by SGsAP application. Gn‐C interface is the interface connecting the MME to the SGSN in the pre‐Rel 8, it is replaced by the S3 for Rel 8 or later. This interface is required when a CSFB call is established to initial the signaling with SGSN. In case CSFB with PS handover the data established over the LTE will be carried over 2/3G network, the interface Gn‐C or S3 is used to establish the signaling sessions with the SGSN to forward pending data over the LTE toward the 2/3G packet core. To forward the data from the PGW, an additional interface named Gn‐U is required between the SGSN and the PGW in pre‐Rel 8 and the S4 interface between the SGSN and the SGW in Rel 8 or later. Uu UTRAN Iu-ps SGSN Gs Gb Iu-cs UE Um GERAN MSC/ A VLR Gn SGs S1-MME MME S11 LTE SGW S5/S8 PGW E-UTRAN S1-U Uu Figure 1.9 Standard architecture for CSFB.  LTE Basement 13 Data Voice LTE (eNode B) 2G/3G Base Station Figure 1.10 Dual radio handsets. CSFB is a single radio solution of handset, in order to make or receive calls, the UE must change its radio access technology from LTE to a 2G/3G technology, and uses network signaling to determine when to switch from the PS network to the CS network. The shortcoming is that someone on a voice call will not be able to use the LTE network for browsing or chatting, and so on. Except CSFB, dual‐radio handsets (SVLTE) shown in Figure 1.10 support simultaneous voice and data— voice provided through legacy 2G or 3G network and data services provided by LTE. Dual‐radio solutions use two always‐on radios (and supporting chipsets), one for packet‐switched LTE data and one for circuit‐switched telephony, and as a data fallback where LTE is not available. The dual radio has the benefit in which simultaneous CS voice and LTE data is available; the drawback is the complexity from the device point of view, since more radio components are required increasing the cost, size, and power consumption. Dual‐radio solutions also force the need for double subscriber registration leading to split legacy and LTE records in the subscriber data managers. As a matter of fact, lack of dual‐radio eco‐system for 3GPP markets and the top six main chipset vendors are addressing the 3GPP market with singe‐radio terminal and CSFB, while the top chipset vendors for 3GPP2 markets are supporting dual‐radio solution for the 3GPP2 market. The above considerations have lead to a clear split in the market for early LTE support of voice services with mobile networks based on 3GPP technologies adopting CSFB, while 3GPP2 markets have adopted a dual‐radio solution for early LTE deployments. CSFB addresses the requirements of the first phase of the evolution of mobile voice services, which commercially launched in several regions around the world in 2011. CSFB has become the predominant global solution for voice and SMS inter‐operability in early LTE handsets, primarily due to inherent cost, size, and battery life advantages of single‐radio solutions on the device side. CSFB is the solution to the reality of mixed networks today and throughout the transition to ubiquitous all‐LTE networks in the future phases of LTE voice evolution. 1.2.2 Voice over LTE After CSFB, LTE voice evolution introduces native VoIP on LTE (VoLTE) along with enhanced IP multimedia services such as video telephony, HD voice and rich communication suite (RCS) additions like instant messaging, video share, and enhanced/shared phonebooks. The voiceover LTE solution (VoLTE) is defined in the GSMA1 Permanent Reference Document (PRD) IR.92,2 based on the adopted one‐voice profile (v 1.1.0) from the One Voice Industry Initiative. Video‐related additions are described in GSMA IR.94. 1 At the 2010 GSMA mobile world congress, GSMA announced that they were supporting the one voice solution to provide voice over LTE. After that, industry aligned 3GPP based e2e solution for GSM equivalent voice services over LTE. 2 The VoLTE IR.92 is from October 2010 put in maintenance mode and only corrections of issues that may cause frequent and serious misoperation will be introduced. 14 LTE Optimization Engineering Handbook VoLTE specifies the minimum requirements to be fulfilled by network operators and terminal vendors in order to provide a high‐quality and interoperable voice over LTE service. The VoLTE solution is scalable and rapidly deployed, offering rich multimedia and voice services, seamless voice continuity across access networks, and the re‐use of existing network investments including business and operational support assets. In terms of the operators, the deployment of VoLTE means that it is opened to the mobile wideband speech path of evolution. Also, VoLTE can offer a competitive advantage by providing a superior voice service quality with HD voice and video, shortening setup times for the calls and guaranteeing bit rate, and offering simultaneous LTE data together with the voice call. Finally, a richer end‐user experience; to be able to provide end users the benefit of real‐time communications can be another VoLTE attraction. Better multimedia, video‐conferencing, or video chat while still maintaining a voice call, are all pos- sible revenue opportunities of VoLTE. Introducing VoLTE on a standard‐based IMS provides the service provider with a true converged network where services are available regardless of the access type network. Blending services with an IMS service architecture enables an opera- tor to cost‐effectively build integrated service bundles. VoLTE can evolve voice services into rich multimedia offerings, including HD voice, video calling, and other multimedia services (i.e., start a voice session, add and drop media such as video, and add callers, presence) available anywhere on any device, combining mobility with service continuity. VoLTE is an advancement from today’s voice and video telephony to full‐fledged multimedia communication to utilize the full potential of LTE and to improve customer experience. The IP‐based call is always anchored in IMS core network to carry and establish a voice call over an LTE network. Now, in both 3GPP and 3GPP2 markets, there is a clear consensus to adopt the IMS‐based VoLTE solution for the LTE deployments. Two transport modes are also used on the network and determines the quality of the voice call over an IP network. The VoIP’s best effort, mainly over the internet and based on some widely deployed applications, such as Skype, Google talk, and MSN, uses this mode with no guarantee of the quality. Other technology such as LTE propose to carry the VoIP with the guarantee of the quality of this call over the end‐to‐end network. For VoLTE, the installed solution aims at being partially compliant with GSMA PRD IR.92.3 One voice was an effort to use already‐defined standards to specify a mandatory set of functionality for devices, the LTE access network, the evolved packet core network, and the IP multimedia subsystem in order to define a voice and SMS over LTE solution using an IMS architecture. Some VoLTE handsets are already commercial including the features such as emergency call, location based services, and so on. In case VoLTE through IMS is the mode used, two connections are required with the LTE network—Rx interface between the P‐CSCF and the PCRF and the Gx interface between the PCRF and the PGW for dynamic PCC rules. The Gm interface is a virtual interface established between the SIP application on the end user and the P‐CSCF function of the IMS network where it is connected (Figure 1.11). Along with VoLTE introduction, 3GPP also standardized Single Radio Voice Call Continuity (SRVCC) in Rel 8 specifications to provide seamless continuity when an UE handovers from LTE coverage (E‐UTRAN) to UMTS/GSM coverage (UTRAN/GERAN). With SRVCC, which is depicted in Figure 1.12, the calls are anchored in IMS network while UE is capable of trans- mitting/receiving on only one of those access networks at a given time. SRVCC protocol evolution have different types according to the function. There are bSRVCC (before alerting 3 Complementary scenarios are also beign defined in the VoLTE profile extension (IR.93) to cope with the cases where LTE coverage needs to be complemented with existing WCDMA/GSM CS coverage.  LTE Basement 15 GERAN A Gb S4 SGSN Gn ISUP IMS S6d Sv IuPS IuCS Gm UTRAN Gi HSS S3/Gn MSC SGW Gm Rx Sv S5 S6a Gx EUTRAN S1-MME MME S11 PGW PCRF SGi S1-U Figure 1.11 Standard architecture for VoLTE. SR- VCC SR- CS Core VoLTE VCC Legacy SR- VCC RAN CS SRVCC IMS SR- SR- VCC VCC Evolved LTE Packet Core SR- RAN VCC SRVCC function CSFB CSFB Semi-Persistent Fast Return after Scheduling CSFB TTI Bundling Emergecy call on Common IMS VoLTE eSRVCC rSRVCC SRVCC Emergecy call aSRVCC vSRVCC RCS w/SRVCC Rel-8 Rel-9 Rel-10 Rel-11 Figure 1.12 SRVCC and evolution. SRVCC), aSRVCC (alerting phase SRVCC), vSRVCC (video SRVCC), and vSRVCC (reverse SRVCC, HO 3G/2G → LTE). Up to now, VoLTE launches are taking place in Korea, the United States (AT&T, T‐Mobile, Verizon), Russia (MTS), and Asia (NTT Docomo, SingTel, M1, Starhub, HKT). T‐Mobile U.S. launched VoLTE in Seattle on May 22, 2014. AT&T launched in three markets on May 23, 2014 with “crystal clear conversations.” SingTel launched on May 31, 2014 in Singapore using 4G Clear Voice. In 2015 and 2016, more and more countries launched VoLTE, like China, Canada, France, and Denmark. 16 LTE Optimization Engineering Handbook 1.2.3 IMS Centralized Services In a CS network telephony, services are provided by the MSC (based on the subscription data in the HLR). In IMS telephony, services are provided by the telephony application server. Multiple service engines introduce synchronization problems and differences in user experience. IMS centralized services avoids these problems by assuming that only one service engine will be used. IMS plays an essential role in IMS centralized services. The UE performs SIP (session initia- tion protocol) registration with the IMS network. IMS‐AKA (IMS‐authentication and key agreement) procedures are followed for authentication. Integrity protection, whereby integrity of SIP signaling messages is ensured, is mandatory. The use of ISIM (IP multimedia services identity module) or USIM (UMTS subscriber identity module) is required during the IMS authentication. SIP signaling messages are ASCII text messages and could thus be quite large. Hence, signaling compression is mandatory to reduce the bandwidth requirements, especially for over‐the‐air transmission. IMS centralized services (ICS) enable the use of the IMS telephony service engine for originating and terminating services regardless if a UE is connected via a LTE PS access network or connected via a GSM/WCDMA CS access network. For terminating calls, ICS determines the access network currently in use by a UE to deliver the call via the correct access network. ICS requires an IMS service centralization and continuity application server. 1.2.4 Over the Top Solutions At the same time, there are already a number of applications providing over the top (OTT) voice service on smartphones, which can be used over Wi‐Fi connection but also over cellular networks. OTT application is completely transparent to network and also out of operators’ control. OTT services are those provided without special consideration at the network level (i.e., no special treatment with respect to QoS). Examples of these types of services are YouTube, Vimeo, and DailyMotion, which are very popular today. Skype and GoogleTalk have nearly a billion registered users worldwide. Apple has sold countless iPhones and iPads, many of which are capable of FaceTime video calling. These services are provided directly by content providers (and usually over content delivery networks), generally without any arrangement with the network providers sitting between the content and its consumers. Nowadays, some OTT solutions, such as Skype and FaceTime, often come preinstalled on smartphones, and as these devices become much more widespread, the adoption of OTT solutions for video‐calling services will also increase. LTE supports high bandwidth, low latency, always online, all IP and other characteristics, it is convenient for the development of OTT. OTT application providers have delivered very popular voice, video, messaging, and location services that are shifting consumers’ attention and usage. In addition, while OTT players currently generate revenue using the operator’s network for service delivery, the operator itself doesn’t gain any associated increase in revenues. The Figure 1.13 shows MoS performance based on data from the South Korean market’s most OTT‐friendly operator. In the future, the proportion of OTT voice may be more and more high, especially in the area of long distance calls, as these solutions are familiar to subscribers and have driven user expec- tations. However, a fully satisfactory user experience cannot be provided by OTT solutions, as there are no QoS measures in place, no handover mechanism to the circuit‐switched network, no widespread interoperability of services between different OTT services and devices, and no guaranteed emergency support or security measures. Consequently, the adoption of OTT clients is directly dependent on mobile broadband coverage and the willingness of subscribers to use a service that lacks quality, security, and flexibility. For example, with VoLTE, using  LTE Basement 17 Range : – 105.000000 AND RSRP < = –95.000000 > – 95.000000 AND RSRP < = –80.000000 > – 80.000000 AND RSRP < = 0.000000 Figure 2.8 Optimization method by advanced geolocation algorithms. both indoors and outdoors, three dimensions in horizontal and vertical directions by using MRs from the user equipment, wherever they are, even within buildings. 2.2.5.1 Timing Advance Different UEs in the cell may have different position, and therefore, different propagation delay, thus this may affect uplink synchronization. eNB’s timing will be phase‐synced to GPS within 100ns to support timing advance (TA) to achieve the tight phase‐sync. TA characteristics can be assumed that uplink arrives 0.3us too late compared to downlink. This error needs to be minimized with a correction of the UL timing. Due to the minimum step length of 0.52us 34 LTE Optimization Engineering Handbook Table 2.2 Positioning methods. Method Handset impact Accuracy Availability Cell ID No impact From 200 m to 5 Km 200 m in urban to 5 Km in rural area CID/TA No impact From 100 m to >1Km Mainly use CGI/TA (GSM and LTE) or RTT (3G) and UERxTxDiff (LTE) E‐CGI (GSM) No impact 150‐400 m