Wei Jiang, Ph.D., is a Senior Researcher with the German Research Center for Artificial Intelligence (DFKI). He has served as the leader of many EU or German research projects on 5G, 6G, AI, and Industry 4.0, and has extensive experiences in developing new technology and international standards related to wireless communications and networking by co-authoring 3 books, 90 articles and holding 30 patents.

Fa-Long Luo, Ph.D., is a Full Professor (Affiliate) of the ECE Department at the University of Washington, USA. He has over 39 years of research and leadership experience with holding 86 patents and having published 7 well-received books and 110 articles on wireless and signal processing.

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

[...]ope 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...