Coordinated Multi-Point in Mobile Communications From Theory to Practice

Edited by

PATRICK MARSCH Nokia Siemens Networks, Wroctaw, Poland

GERHARD P. FETTWEIS Technische Universität Dresden, Germany

Pf CAMBRIDGE UNIVERSITY PRESS

Contents

List of Contributors Va9e x n i Acknowledgements xvii List of Abbreviations xviii Nomenclature and Notation xxiv

Part I Mo t i va t i on and Basics 1

1 Introduction 3

1.1 Motivation 3 1.2 Aim of this Book 5 1.3 Classes of CoMP Considered 5 1.4 Outline of this Book 6

2 An Operator's Point of View 7

2.1 The Mobile Internet - A Success Story so far 7 2.2 Requirements on Future Networks and Upcoming Challenges 8 2.3 The Role of CoMP 9 2.4 The Role of Field Trials 10

3 Information-Theoretic Basics 11

3.1 Observed Cellular Scenarios 11 3.2 Usage of OFDMA for Broadband Wireless Communications 11 3.3 Multi-Point Frequency-Flat Baseband Model Considered 13 3.4 Uplink Transmission 14

3.4.1 Basic Uplink Capacity Bounds 15 3.4.2 Full Cooperation in the Uplink 17 3.4.3 No Cooperation in the Uplink 17 3.4.4 Numerical Example 19

3.5 Downlink Transmission 19 3.5.1 Basic Downlink Capacity Bounds 20 3.5.2 Full Cooperation in the Downlink 22 3.5.3 No Cooperation in the Downlink 22 3.5.4 Numerical Example 23

vi Contents

3.6 Summary 24

4 Gains and Trade-Offs of Multi-Cell Joint Signal Processing 25

4.1 Modeling Imperfect Channel State Information (CSI) 25 4.1.1 Imperfect CSI in the Uplink 25 4.1.2 Imperfect CSI in the Downlink 27

4.2 Gain of Joint Signal Processing under Imperfect CSI 29 4.3 Trade-Offs in Uplink Multi-Cell Joint Signal Processing 32

4.3.1 Different Information Exchange and Cooperation Schemes 32 4.3.2 Numerical Results 35 4.3.3 Parallels between Theory and Practical Cooperation Schemes 37

4.4 Degrees of Freedom in Downlink Joint Signal Processing 37 4.5 Summary 38

Part II Pract ica l C o M P Schemes 39

5 CoMP Schemes Based on Interf.-Aware Transceivers or Interf. Coord. 41

5.1 DL Multi-User Beamforming with IRC 41 5.1.1 Introduction 41 5.1.2 Downlink System Model 43 5.1.3 Linear Receivers 44 5.1.4 Imperfect Channel Estimation 45 5.1.5 Resource Allocation and Fair User Selection 46 5.1.6 Single-Cell Performance 48 5.1.7 Multi-Cell Performance under Perfect CSI 50 5.1.8 Multi-Cell Performance under Imperfect CSI 52 5.1.9 Summary 54

5.2 Uplink Joint Scheduling and Cooperative Interference Prediction 54 5.2.1 Interference-Aware Joint Scheduling 56 5.2.2 Cooperative Interference Prediction 61 5.2.3 Practical Considerations 64 5.2.4 Applicability of Both Schemes to the Downlink 66 5.2.5 Summary 67

5.3 Downlink Coordinated Beamforming 68 5.3.1 Introduction 68 5.3.2 Single Receive Antenna at the Terminal 70 5.3.3 Multiple Receive Antennas at the Terminal 74 5.3.4 Summary 80

6 CoMP Schemes Based on Multi-Cell Joint Signal Processing 81

6.1 Uplink Centralized Joint Detection 81 6.1.1 Introduction 81 6.1.2 Joint Detection Algorithms 82

Contents vii

6.1.3 Local BS Processing with Limited Backhaul Constraint 87 6.1.4 Local or Partial Decoding with Limited Backhaul Constraint 90 6.1.5 Provisions for Uplink Joint Processing in WiMax and LTE 92 6.1.6 Summary 93

6.2 Uplink Decentralized Joint Detection 94 6.2.1 Practical Decentralized Interference Cancelation Scheme 95 6.2.2 Performance Assessment 104 6.2.3 Summary 108

6.3 DL Distributed CoMP Approaching Centralized Joint Transmission 108 6.3.1 System Model 110 6.3.2 Theoretical Limits for Static Clustering and DPC 111 6.3.3 Practical (Linear) Precoding 113 6.3.4 Scheme for Distributed, Centralized Joint Transmission 115 6.3.5 Summary 121

6.4 Downlink Decentralized Multi-User Transmission 121 6.4.1 Decentralized Beamforming with Limited CSIT 122 6.4.2 Multi-cell Beamforming with Limited Data Sharing 130 6.4.3 Summary 136

Part I I I Challenges Connected to C o M P 137

7 Clustering 139

7.1 Static Clustering Concepts 141 7.1.1 Non-Overlapping Clusters 142 7.1.2 Overlapping Clusters 145 7.1.3 Resulting Geometries 146

7.2 Self-Organizing Clustering Concepts 148 7.2.1 Self-Organizing Network Concepts in 3GPP LTE 148 7.2.2 Adaptive Clustering Algorithms 149 7.2.3 Simulation Results 152 7.2.4 Signaling and Control Procedures 157

7.3 Summary 159

8 Synchronization 161

8.1 Synchronization Concepts 161 8.1.1 Synchronization Terminology 161 8.1.2 Network Synchronization 163 8.1.3 Satellite-Based Synchronization 165 8.1.4 Endogenous Distributed Wireless Carrier Synchronization 166 8.1.5 Summary 169

8.2 Imperfect Sync in Time: Perf. Degradation and Compensation 170 8.2.1 MIMO OFDM Transmission with Asynchronous Interference 173 8.2.2 Interf.-Aware Multi-User Joint Detection and Transmission 176

viii Contents

8.2.3 System Level SINR Analysis 178 8.2.4 Summary 181

8.3 Imperfect Sync in Frequency: Perf. Degradation and Compensation 181 8.3.1 Downlink Analysis 182 8.3.2 Uplink Analysis 189 8.3.3 Summary 192

9 Channel Knowledge 193

9.1 Channel Estimation for CoMP 193 9.1.1 Channel Estimation - Single Link 194 9.1.2 Channel Estimation for CoMP 202 9.1.3 Multi-Cell Channel Estimation 204 9.1.4 Uplink Channel Estimation 206 9.1.5 Summary 208

9.2 Channel State Information Feedback to the Transmitter 208 9.2.1 Transmission Model 210 9.2.2 Sum-Rate Performance Measure 211 9.2.3 Channel Vector Quantization (CVQ) 211 9.2.4 Minimum Euclidean Distance Based CVQ 213 9.2.5 Maximum SINR Based CVQ 214 9.2.6 Pseudo-Maximum SINR based CVQ 215 9.2.7 Application to Zero-Forcing (ZF) Precoding 216 9.2.8 Resource Allocation 216 9.2.9 Simulation Results 216 9.2.10 Summary 218

10 Efficient and Robust Algorithm Implementation 219

10.1 Robust and Flexible Base Station Precoding Implementation 219 10.1.1 System Model 220 10.1.2 Transmit Filter Eigendecomposition 221 10.1.3 Transmit Filter Computations 222 10.1.4 The Order-Recursive Filter in Details 224 10.1.5 Example: SINR as Function of the Condition Number 226 10.1.6 Summary 227

10.2 Low-Complexity Terminal-Side Receiver Implementation 227 10.2.1 Introduction to Interference Rejection Combining (IRC) 228 10.2.2 IRC with Known Channel and Interference Covariance 231 10.2.3 Implementation Losses from Imperfect Channel Estimation 233 10.2.4 Losses from Spatial Interf.-and-Noise Covariance Estimation 237 10.2.5 Losses from Channel and Interference Estimation Errors 241 10.2.6 Summary 241

Contents ix

11 Scheduling, Signaling and Adaptive Usage of CoMP 243

11.1 Centralized Scheduling for CoMP 243 11.1.1 Introduction 243 11.1.2 System Model 244 11.1.3 Centralized Scheduling Problems 246 11.1.4 Analyses and Results 251 11.1.5 Summary 254

11.2 Decentralized Radio Link Control and Inter-BS Signaling 254 11.2.1 Resource Allocation 255 11.2.2 Link Adaptation 256 11.2.3 Radio Link Measurements 257 11.2.4 Uplink Power Control 258 11.2.5 Uplink Timing Advance 259 11.2.6 HARQ-related Timing Constraints for UL CoMP 259 11.2.7 Handover 262 11.2.8 Inter-BS Signaling 262 11.2.9 Summary 266

11.3 Ad-hoc CoMP 266 11.3.1 Introduction 267 11.3.2 Ad-Hoc CoMP With More Accurate CSI 269 11.3.3 Ad-Hoc CoMP with CSI Impairments 273 11.3.4 Ad-Hoc CoMP and HARQ 275 11.3.5 Summary 276

12 Backhaul 277

12.1 Fund. Limits of Interf. Mitigation with Limited Backhaul Coop. 277 12.1.1 Introduction 278 12.1.2 Uplink Scenario: Receiver Cooperation 281 12.1.3 Downlink Scenario: Transmitter Cooperation 286 12.1.4 UL-DL Reciprocity and Generalized Degrees of Freedom 287 12.1.5 Summary 291

12.2 Backhaul Requirements of Practical CoMP Schemes 291 12.2.1 Types of Backhaul Data and Scaling Laws 291 12.2.2 Specific Backhaul Requirements of Exemplary CoMP Schemes 294 12.2.3 Backhaul Latency Requirements 299 12.2.4 Backhaul Topology Considerations 300 12.2.5 Summary 300

12.3 CoMP Backhaul Infrastructure Concepts 301 12.3.1 Ethernet 301 12.3.2 Passive Optical Network 303 12.3.3 Digital Subscriber Line 305 12.3.4 Microwave 306 12.3.5 The X2 Interface 307 12.3.6 Backhaul Topology Concepts 307

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12.3.7 Summary 310

Part IV Performance Assessment 311

13 Field Trial Results 313

13.1 Real-time Impl. and Trials of Adv. Receivers and UL CoMP 313 13.1.1 Real-time Implementation and Lab Tests 314 13.1.2 Uplink Successive Interference Cancelation (SIC) Receiver 314 13.1.3 Uplink Macro Diversity Trials with Distributed RRHs 317 13.1.4 Summary 319

13.2 Assessing the Gain of Uplink CoMP in a Large-Scale Field Trial 319 13.2.1 Measurement Setup 320 13.2.2 Signal Processing Architecture and Evaluation Concept 321 13.2.3 Noise Estimation 322 13.2.4 Channel Equalization 322 13.2.5 Field Trial Results 325 13.2.6 Summary 330

13.3 Real-time Implementation and Field Trials for Downlink CoMP 331 13.3.1 Introduction 332 13.3.2 Enabling Features 334 13.3.3 Real-time Implementation 346 13.3.4 Field Trials 347 13.3.5 Summary 352

13.4 Predicting Pract. Achievable DL CoMP Gains over Larger Areas 353 13.4.1 Setup and Closed-Loop System Design 353 13.4.2 Measurement and Evaluation Methodology 356 13.4.3 Measurement Campaign 358 13.4.4 Summary 363

13.5 Lessons Learnt Through Field Trials 364

14 Performance Prediction of CoMP in Large Cellular Systems 367

14.1 Simulation and Link-2-System Mapping Methodology 367 14.1.1 General Simulation Assumptions and Modeling 368 14.1.2 Channel Models and Antenna Models 370 14.1.3 Transceiver Techniques 373 14.1.4 Link-to-System Interface 373 14.1.5 Key Performance Indicators 375 14.1.6 Summary 376

14.2 Obtaining Chn. Model Params. via Chn. Sounding or Ray-Tracing 376 14.2.1 Large-Scale-Parameters 377 14.2.2 Measurement-based Parameter Estimation 380 14.2.3 Ray-Tracing based Parameter Simulation 380 14.2.4 Comparison between Measurements and Ray-Tracing 382

Contents xi

14.2.5 Summary 387 14.3 Uplink Simulation Results 387

14.3.1 Compared Schemes 387 14.3.2 Simulation Assumptions and Parameters 389 14.3.3 Backhaul Traffic 391 14.3.4 Simulation Results 392 14.3.5 Summary 395

14.4 Downlink Simulation Results 396 14.4.1 Compared Schemes 396 14.4.2 Simulation Assumptions and Parameters 397 14.4.3 Detailed Analysis of Coordinated Scheduling/Beamforming 398 14.4.4 Backhaul Traffic 406 14.4.5 Simulation Results 406 14.4.6 Summary 408

Part V Outlook and Conclusions 409

15 Outlook 411 15.1 Using CoMP for Terminal Localization 411

15.1.1 Localization based on the Signal Propagation Delay 412 15.1.2 Further Localization Methods 416 15.1.3 Localization in B3G Standards 418 15.1.4 Summary 422

15.2 Relay-Assisted Mobile Communication using CoMP 423 15.2.1 Introduction 423 15.2.2 Reference Scenario 424 15.2.3 System and Protocol Description 425 15.2.4 Trade-Offs in Relay Networks 427 15.2.5 Numerical Evaluation of CoMP and Relaying 428 15.2.6 Cost/Benefit Trade-Off 428 15.2.7 Energy/Benefit Trade-Off 429 15.2.8 Computation/Transmission Power Trade-Off 430 15.2.9 Summary 432

15.3 Next Generation Cellular Network Planning and Optimization 432 15.3.1 Introduction 432 15.3.2 Classical Cellular Network Planning and Optimization 433 15.3.3 Physical Characterization of Capacity Gains through CoMP 435 15.3.4 Summary 443

15.4 Energy-Efficiency Aspects of CoMP 444 15.4.1 System Model 445 15.4.2 Effective Transmission Rates 447 15.4.3 Backhauling 448 15.4.4 Energy Consumption of Cellular Base Stations 449

xii Contents

15.4.5 System Evaluation 451 15.4.6 Summary 453

16 Summary and Conclusions 455

16.1 Summary of this Book 455 16.1.1 Most Promising CoMP Schemes and Potential Gains 455 16.1.2 Key Challenges Identified 457

16.2 Conclusions 458 16.2.1 About this Book 459 16.2.2 CoMP's Place in the LTE-Advanced Roadmap and Beyond 460

References 461 Index 479