LTE Optimization Engineering Handbook

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 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 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 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 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 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 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 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 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 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 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