Preface xv
List of Abbreviations xxi
Part I The Vision of 6G and Technical Evolution 1
1 Standards History of Cellular Systems Toward 6G 3
1.1 0G: Pre-Cellular Systems 4
1.2 1G: The Birth of Cellular Network 6
1.2.1 Nordic Mobile Telephone (NMT) 7
1.2.2 Advanced Mobile Phone System (AMPS) 8
1.3 2G: From Analog to Digital 9
1.3.1 Global System for Mobile communications (GSM) 10
1.3.2 Digital Advanced Mobile Phone System (D-AMPS) 11
1.3.3 Interim Standard 95 (IS-95) 11
1.3.4 Personal Digital Cellular (PDC) 12
1.3.5 General Packet Radio Service (GPRS) 12
1.3.6 Enhanced Data Rates for GSM Evolution (EDGE) 14
1.4 3G: From Voice to Data-Centric 15
1.4.1 Wideband Code-Division Multiple Access (WCDMA) 16
1.4.2 Code-Division Multiple Access 2000 (CDMA2000) 18
1.4.3 Time Division-Synchronous Code-Division Multiple Access
(TD-SCDMA) 21
1.4.4 Worldwide Interoperability for Microwave Access (WiMAX) 22
1.5 4G: Mobile Internet 23
1.5.1 Long-Term Evolution-Advanced (LTE-Advanced) 25
1.5.2 WirelessMAN-Advanced 28
1.6 5G: From Human to Machine 30
1.7 Beyond 5G 37
1.8 Conclusions 39
References 39
2 Pre-6G Technology and System Evolution 43
2.1 1G –AMPS 44
2.1.1 System Architecture 44
2.1.2 Key Technologies 46
2.1.2.1 Frequency Reuse 46
2.1.2.2 Cell Splitting 47
2.1.2.3 Sectorization 48
2.1.2.4 Handover 48
2.1.2.5 Frequency-Division Multiple Access 49
2.2 2G –GSM 49
2.2.1 System Architecture 50
2.2.1.1 Mobile Station Subsystem 50
2.2.1.2 Bases Station Subsystem 50
2.2.1.3 Network and Switching Subsystem 51
2.2.1.4 Operation and Support Subsystem 51
2.2.1.5 General Packet Radio Service 52
2.2.1.6 Gateway GPRS Support Node 53
2.2.2 Key Technologies 53
2.2.2.1 Time-Division Multiple Access 53
2.2.2.2 Frequency Hopping 54
2.2.2.3 Speech Compression 55
2.2.2.4 Channel Coding 55
2.2.2.5 Digital Modulation 56
2.2.2.6 Discontinuous Transmission (DXT) 56
2.3 3G –WCDMA 56
2.3.1 System Architecture 57
2.3.1.1 User Equipment 57
2.3.1.2 UMTS Terrestrial Radio Access Network 58
2.3.1.3 Core Network 59
2.3.2 Key Technologies 60
2.3.2.1 Code-Division Multiple Access 60
2.3.2.2 Rake Receiver 63
2.3.2.3 Turbo Codes 63
2.4 4G – LTE 64
2.4.1 System Architecture 65
2.4.1.1 Evolved Universal Terrestrial Radio Access Network 65
2.4.1.2 Evolved Packet Core 65
2.4.2 Key Technologies 68
2.4.2.1 Orthogonal Frequency-Division Multiplexing 70
2.4.2.2 Carrier Aggregation 71
2.4.2.3 Relaying 71
2.4.2.4 Heterogeneous Network 72
2.4.2.5 Coordinated Multi-Point Transmission and Reception 73
2.4.2.6 Device-to-Device Communications 73
2.4.2.7 License-Assisted Access 74
2.5 5G –New Radio 75
2.5.1 System Architecture 76
2.5.1.1 5G Core Network 77
2.5.1.2 Next Generation Radio Access Network 79
2.5.2 Key Technologies 81
2.5.2.1 Massive MIMO 81
2.5.2.2 MillimeterWave 82
2.5.2.3 Non-Orthogonal Multiple Access 83
2.5.2.4 SDN/NFV 84
2.5.2.5 Network Slicing 85
2.5.2.6 Polar Codes 86
2.6 Conclusions 87
References 87
3 The Vision of 6G: Drivers, Enablers, Uses, and Roadmap 89
3.1 Background 90
3.2 Explosive Mobile Traffic 92
3.3 Use Cases 94
3.4 Usage Scenarios 98
3.5 Performance Requirements 102
3.6 Research Initiatives and Roadmap 107
3.6.1 ITU 108
3.6.2 Third Generation Partnership Project 110
3.6.3 Industry 110
3.6.4 Europe 110
3.6.5 The United States 113
3.6.6 China 116
3.6.7 Japan 116
3.6.8 South Korea 117
3.7 Key Technologies 117
3.7.1 MillimeterWave 118
3.7.2 Terahertz Communications 118
3.7.3 Optical Wireless Communications 119
3.7.4 Massive MIMO 120
3.7.5 Intelligent Reflecting Surfaces 121
3.7.6 Next-Generation Multiple Access 122
3.7.7 Open Radio Access Network 123
3.7.8 Non-Terrestrial Networks 124
3.7.9 Artificial Intelligence 125
3.7.10 Communication-Computing-Sensing Convergence 127
3.8 Conclusions 128
References 128
Part II Full-Spectra Wireless Communications in 6G 131
4 Enhanced Millimeter-Wave Wireless Communications in
6G 133
4.1 Spectrum Shortage 134
4.2 mmWave Propagation Characteristics 136
4.2.1 Large-Scale Propagation Effects 137
4.2.1.1 Free-Space Propagation Loss 137
4.2.1.2 NLOS Propagation and Shadowing 139
4.2.1.3 Atmospheric Attenuation 141
4.2.2 Small-Scale Propagation Effects 143
4.2.3 Delay Spread and Coherence Bandwidth 145
4.2.4 Doppler Spread and Coherence Bandwidth 146
4.2.5 Angular Spread 149
4.3 Millimeter-Wave Channel Models 152
4.3.1 Large-Scale Fading 152
4.3.2 3GPP Channel Models 155
4.3.2.1 Urban Micro Scenario 155
4.3.2.2 Urban Macro Scenario 156
4.3.2.3 Indoor Scenario 157
4.3.3 Small-Scale Fading 159
4.4 mmWave Transmission Technologies 163
4.4.1 Beamforming 163
4.4.1.1 Digital Beamforming 164
4.4.1.2 Analog Beamforming 168
4.4.1.3 Hybrid Beamforming 169
4.4.1.4 3D Beamforming 173
4.4.2 Initial Access 175
4.4.2.1 Multi-Beam Synchronization and Broadcasting 176
4.4.2.2 Conventional Initial Access in LTE 178
4.4.2.3 Beam-Sweeping Initial Access in NR 181
4.4.3 Omnidirectional Beamforming 183
4.4.3.1 Random Beamforming 185
4.4.3.2 Enhanced Random Beamforming 187
4.4.3.3 Complementary Random Beamforming 190
4.5 Summary 192
References 193
5 Terahertz Technologies and Systems for 6G 195
5.1 Potential of Terahertz Band 196
5.1.1 Spectrum Limit 196
5.1.2 The Need of Exploiting Terahertz Band 198
5.1.3 Spectrum Regulation on Terahertz Band 203
5.2 Terahertz Applications 205
5.2.1 Terahertz Wireless Communications 205
5.2.1.1 Terabit Cellular Hotspot 205
5.2.1.2 Terabit Wireless Local-Area Network 206
5.2.1.3 Terabit Device-To-Device Link 206
5.2.1.4 Secure Wireless Communication 207
5.2.1.5 Terabit Wireless Backhaul 207
5.2.1.6 Terahertz Nano-Communications 208
5.2.2 Non-Communication Terahertz Applications 209
5.2.2.1 Terahertz Sensing 209
5.2.2.2 Terahertz Imaging 210
5.2.2.3 Terahertz Positioning 212
5.3 Challenges of Terahertz Communications 212
5.3.1 High Free-Space Path Loss 213
5.3.2 Atmospheric Attenuation 215
5.3.3 Weather Effects 222
5.3.4 Blockage 224
5.3.5 High Channel Fluctuation 226
5.4 Array-of-Subarrays Beamforming 228
5.5 Lens Antenna 231
5.5.1 Refraction of RadioWaves 232
5.5.2 Lens Antenna Array 233
5.6 Case Study – IEEE 802.15.3d 236
5.6.1 IEEE 802.15.3d Usage Scenarios 237
5.6.2 Physical Layer 240
5.6.2.1 Channelization 240
5.6.2.2 Modulation 242
5.6.2.3 Forward Error Correction 242
5.6.3 Medium Access Control 244
5.6.4 Frame Structure 246
5.6.4.1 Preamble 247
5.6.4.2 PHY Header 247
5.6.4.3 MAC Header 248
5.6.4.4 Construction Process of Frame Header 248
5.7 Summary 250
References 251
6 Optical and Visible Light Wireless Communications
in 6G 253
6.1 The Optical Spectrum 254
6.1.1 Infrared 254
6.1.2 Visible Light 256
6.1.3 Ultraviolet 257
6.2 Advantages and Challenges 258
6.3 OWC Applications 262
6.4 Evolution of Optical Wireless Communications 264
6.4.1 Wireless Infrared Communications 265
6.4.2 Visible Light Communications 266
6.4.3 Wireless Ultraviolet Communications 267
6.4.4 Free-Space Optical Communications 268
6.5 Optical Transceiver 268
6.6 Optical Sources and Detectors 271
6.6.1 Light-Emitting Diode 273
6.6.2 Laser Diode 276
6.6.3 Photodiode 280
6.7 Optical Link Configuration 283
6.8 Optical MIMO 286
6.8.1 Spatial Multiplexing 286
6.8.2 Spatial Modulation 289
6.9 Summary 292
References 292
Part III Smart Radio Networks and Air Interface
Technologies for 6G 295
7 Intelligent Reflecting Surface-Aided Communications for
6G 297
7.1 Basic Concept 298
7.2 IRS-Aided Single-Antenna Transmission 302
7.2.1 Signal Model 303
7.2.2 Passive Beamforming 306
7.2.3 Product-Distance Path Loss 309
7.3 IRS-Aided Multi-Antenna Transmission 310
7.3.1 Joint Active and Passive Beamforming 310
7.3.1.1 SDR Solution 312
7.3.1.2 Alternating Optimization 314
7.3.2 Joint Precoding and Reflecting 315
7.4 Dual-Beam Intelligent Reflecting Surface 318
7.4.1 Dual Beams Over Hybrid Beamforming 318
7.4.2 Dual-Beam IRS 321
7.4.3 Optimization Design 322
7.5 IRS-Aided Wideband Communications 325
7.5.1 Cascaded Frequency-Selective Channel 325
7.5.2 IRS-Aided OFDM System 327
7.5.3 Rate Maximization 330
7.6 Multi-User IRS Communications 331
7.6.1 Multiple Access Model 332
7.6.2 Orthogonal Multiple Access 333
7.6.2.1 Time-Division Multiple Access 334
7.6.2.2 Frequency-Division Multiple Access 336
7.6.3 Non-Orthogonal Multiple Access 337
7.7 Channel Aging and Prediction 339
7.7.1 Outdated Channel State Information 341
7.7.1.1 Doppler Shift 341
7.7.1.2 Phase Noise 343
7.7.2 Impact of Channel Aging on IRS 343
7.7.3 Classical Channel Prediction 345
7.7.3.1 Autoregressive Model 345
7.7.3.2 Parametric Model 347
7.7.4 Recurrent Neural Network 348
7.7.5 RNN-Based Channel Prediction 351
7.7.5.1 Flat-Fading Channel Prediction 352
7.7.5.2 Frequency-Selective Fading Channel Prediction 353
7.7.6 Long-Short Term Memory 355
7.7.7 Deep Learning-Based Channel Prediction 358
7.8 Summary 359
References 359
8 Multiple Dimensional and Antenna Techniques for 6G 363
8.1 Spatial Diversity 364
8.2 Receive Combining 366
8.2.1 Selection Combining 368
8.2.2 Maximal Ratio Combining 370
8.2.3 Equal-Gain Combining 373
8.3 Space-Time Coding 374
8.3.1 Repetition Coding 375
8.3.2 Space-Time Trellis Codes 377
8.3.3 Alamouti Coding 379
8.3.4 Space-Time Block Codes 381
8.4 Transmit Antenna Selection 383
8.5 Beamforming 386
8.5.1 Classical Beamforming 386
8.5.2 Single-Stream Precoding 390
8.6 Spatial Multiplexing 393
8.6.1 Single-User MIMO 394
8.6.2 MIMO Precoding 400
8.6.2.1 Full CSI at the Transmitter 400
8.6.2.2 Limited CSI at the Transmitter 403
8.6.3 MIMO Detection 406
8.6.3.1 Maximum-Likelihood Detection 406
8.6.3.2 Linear Detection 407
8.6.3.3 Successive Interference Cancelation 410
8.7 Summary 413
References 413
9 Cellular and Cell-Free Massive MIMO Techniques in 6G 417
9.1 Multi-User MIMO 418
9.1.1 Broadcast and Multiple-Access Channels 419
9.1.2 Multi-User Sum Capacity 422
9.1.3 Dirty Paper Coding 425
9.1.4 Zero-Forcing Precoding 428
9.1.5 Block Diagonalization 429
9.2 Massive MIMO 432
9.2.1 CSI Acquisition 433
9.2.2 Linear Detection in Uplink 435
9.2.2.1 Matched Filtering 436
9.2.2.2 ZF Detection 436
9.2.2.3 MMSE Detection 437
9.2.3 Linear Precoding in Downlink 437
9.2.3.1 Conjugate Beamforming 438
9.2.3.2 ZF Precoding 438
9.2.3.3 Regularized ZF Precoding 439
9.3 Multi-Cell Massive MIMO 439
9.3.1 Pilot Contamination 441
9.3.2 Uplink Data Transmission 444
9.3.3 Downlink Data Transmission 446
9.4 Cell-Free Massive MIMO 447
9.4.1 Cell-Free Network Layout 448
9.4.2 Uplink Training 449
9.4.3 Uplink Signal Detection 451
9.4.3.1 Matched Filtering 452
9.4.3.2 ZF Detection 452
9.4.3.3 MMSE Detection 452
9.4.4 Conjugate Beamforming 453
9.4.5 Zero-Forcing Precoding 455
9.4.6 Impact of Channel Aging 457
9.4.6.1 Channel Aging 457
9.4.6.2 Performance Degradation 460
9.5 Opportunistic Cell-Free Communications 464
9.5.1 Cell-free Massive Wideband Systems 464
9.5.2 Opportunistic AP Selection 466
9.5.3 Spectral Efficiency Analysis 468
9.6 Summary 472
References 472
10 Adaptive and Non-Orthogonal Multiple Access Systems in
6G 475
10.1 Frequency-Selective Fading Channel 476
10.2 Multi-Carrier Modulation 480
10.2.1 The Synthesis and Analysis Filters 480
10.2.2 Polyphase Implementation 483
10.2.3 Filter Bank Multi-Carrier 486
10.3 Orthogonal Frequency-Division Multiplexing 487
10.3.1 DFT Implementation 491
10.3.2 Cyclic Prefix 493
10.3.3 Frequency-Domain Signal Processing 496
10.3.4 Out-of-Band Emission 499
10.4 Orthogonal Frequency-Division Multiple Access 503
10.4.1 Orthogonal Frequency-Division Multiple Access 503
10.4.2 Single-Carrier Frequency-Division Multiple Access 505
10.4.3 Cyclic Delay Diversity 507
10.4.4 Multi-Cell OFDMA 510
10.5 Cell-Free Massive MIMO-OFDMA 512
10.5.1 The System Model 513
10.5.2 The Communication Process 516
10.5.2.1 Uplink Training 516
10.5.2.2 Uplink Payload Data Transmission 518
10.5.2.3 Downlink Payload Data Transmission 518
10.5.3 User-Specific Resource Allocation 519
10.6 Non-Orthogonal Multiple Access 520
10.6.1 Fundamentals of NOMA 521
10.6.1.1 Downlink Non-Orthogonal Multiplexing 522
10.6.1.2 Uplink Non-Orthogonal Multiple Access 525
10.6.2 Multi-User Superposition Coding 528
10.6.3 Uplink Grant-Free Transmission 531
10.6.4 Code-Domain NOMA 533
10.6.4.1 Low-Density Signature-CDMA/OFDM 533
10.6.4.2 Sparse Code Multiple Access 536
10.7 Summary 538
References 538
Index 541
