6G Key Technologies: A Comprehensive Guide

Cover
Title Page
Copyright
Contents
Preface
List of Abbreviations
Part I The Vision of 6G and Technical Evolution
Chapter 1 Standards History of Cellular Systems Toward 6G
1.1 0G: Pre‐Cellular Systems
1.2 1G: The Birth of Cellular Network
1.2.1 Nordic Mobile Telephone (NMT)
1.2.2 Advanced Mobile Phone System (AMPS)
1.3 2G: From Analog to Digital
1.3.1 Global System for Mobile Communications (GSM)
1.3.2 Digital Advanced Mobile Phone System (D‐AMPS)
1.3.3 Interim Standard 95 (IS‐95)
1.3.4 Personal Digital Cellular (PDC)
1.3.5 General Packet Radio Service (GPRS)
1.3.6 Enhanced Data Rates for GSM Evolution (EDGE)
1.4 3G: From Voice to Data‐Centric
1.4.1 Wideband Code‐Division Multiple Access (WCDMA)
1.4.2 Code‐Division Multiple Access 2000 (CDMA2000)
1.4.3 Time Division‐Synchronous Code‐Division Multiple Access (TD‐SCDMA)
1.4.4 Worldwide Interoperability for Microwave Access (WiMAX)
1.5 4G: Mobile Internet
1.5.1 Long‐Term Evolution‐Advanced (LTE‐Advanced)
1.5.2 WirelessMAN‐Advanced
1.6 5G: From Human to Machine
1.7 Beyond 5G
1.8 Conclusions
References
Chapter 2 Pre‐6G Technology and System Evolution
2.1 1G – AMPS
2.1.1 System Architecture
2.1.2 Key Technologies
2.1.2.1 Frequency Reuse
2.1.2.2 Cell Splitting
2.1.2.3 Sectorization
2.1.2.4 Handover
2.1.2.5 Frequency‐Division Multiple Access
2.2 2G – GSM
2.2.1 System Architecture
2.2.1.1 Mobile Station Subsystem
2.2.1.2 Bases Station Subsystem
2.2.1.3 Network and Switching Subsystem
2.2.1.4 Operation and Support Subsystem
2.2.1.5 General Packet Radio Service
2.2.1.6 Gateway GPRS Support Node
2.2.2 Key Technologies
2.2.2.1 Time‐Division Multiple Access
2.2.2.2 Frequency Hopping
2.2.2.3 Speech Compression
2.2.2.4 Channel Coding
2.2.2.5 Digital Modulation
2.2.2.6 Discontinuous Transmission (DXT)
2.3 3G – WCDMA
2.3.1 System Architecture
2.3.1.1 User Equipment
2.3.1.2 UMTS Terrestrial Radio Access Network
2.3.1.3 Core Network
2.3.2 Key Technologies
2.3.2.1 Code‐Division Multiple Access
2.3.2.2 Rake Receiver
2.3.2.3 Turbo Codes
2.4 4G – LTE
2.4.1 System Architecture
2.4.1.1 Evolved Universal Terrestrial Radio Access Network
2.4.1.2 Evolved Packet Core
2.4.2 Key Technologies
2.4.2.1 Orthogonal Frequency‐Division Multiplexing
2.4.2.2 Carrier Aggregation
2.4.2.3 Relaying
2.4.2.4 Heterogeneous Network
2.4.2.5 Coordinated Multi‐Point Transmission and Reception
2.4.2.6 Device‐to‐Device Communications
2.4.2.7 License‐Assisted Access
2.5 5G – New Radio
2.5.1 System Architecture
2.5.1.1 5G Core Network
2.5.1.2 Next Generation Radio Access Network
2.5.2 Key Technologies
2.5.2.1 Massive MIMO
2.5.2.2 Millimeter Wave
2.5.2.3 Non‐Orthogonal Multiple Access
2.5.2.4 SDN/NFV
2.5.2.5 Network Slicing
2.5.2.6 Polar Codes
2.6 Conclusions
References
Chapter 3 The Vision of 6G: Drivers, Enablers, Uses, and Roadmap
3.1 Background
3.2 Explosive Mobile Traffic
3.3 Use Cases
3.4 Usage Scenarios
3.5 Performance Requirements
3.6 Research Initiatives and Roadmap
3.6.1 ITU
3.6.2 Third Generation Partnership Project
3.6.3 Industry
3.6.4 Europe
3.6.5 The United States
3.6.6 China
3.6.7 Japan
3.6.8 South Korea
3.7 Key Technologies
3.7.1 Millimeter Wave
3.7.2 Terahertz Communications
3.7.3 Optical Wireless Communications
3.7.4 Massive MIMO
3.7.5 Intelligent Reflecting Surfaces
3.7.6 Next‐Generation Multiple Access
3.7.7 Open Radio Access Network
3.7.8 Non‐Terrestrial Networks
3.7.9 Artificial Intelligence
3.7.10 Communication‐Computing‐Sensing Convergence
3.8 Conclusions
References
Part II Full‐Spectra Wireless Communications in 6G
Chapter 4 Enhanced Millimeter‐Wave Wireless Communications in 6G
4.1 Spectrum Shortage
4.2 mmWave Propagation Characteristics
4.2.1 Large‐Scale Propagation Effects
4.2.1.1 Free‐Space Propagation Loss
4.2.1.2 NLOS Propagation and Shadowing
4.2.1.3 Atmospheric Attenuation
4.2.2 Small‐Scale Propagation Effects
4.2.3 Delay Spread and Coherence Bandwidth
4.2.4 Doppler Spread and Coherence Time
4.2.5 Angular Spread
4.3 Millimeter‐Wave Channel Models
4.3.1 Large‐Scale Fading
4.3.2 3GPP Channel Models
4.3.2.1 Urban Micro Scenario
4.3.2.2 Urban Macro Scenario
4.3.2.3 Indoor Scenario
4.3.3 Small‐Scale Fading
4.4 mmWave Transmission Technologies
4.4.1 Beamforming
4.4.1.1 Digital Beamforming
4.4.1.2 Analog Beamforming
4.4.1.3 Hybrid Beamforming
4.4.1.4 3D Beamforming
4.4.2 Initial Access
4.4.2.1 Multi‐Beam Synchronization and Broadcasting
4.4.2.2 Conventional Initial Access in LTE
4.4.2.3 Beam‐Sweeping Initial Access in NR
4.4.3 Omnidirectional Beamforming
4.4.3.1 Random Beamforming
4.4.3.2 Enhanced Random Beamforming
4.4.3.3 Complementary Random Beamforming
4.5 Summary
References
Chapter 5 Terahertz Technologies and Systems for 6G
5.1 Potential of Terahertz Band
5.1.1 Spectrum Limit
5.1.2 The Need of Exploiting Terahertz Band
5.1.3 Spectrum Regulation on Terahertz Band
5.2 Terahertz Applications
5.2.1 Terahertz Wireless Communications
5.2.1.1 Terabit Cellular Hotspot
5.2.1.2 Terabit Wireless Local‐Area Network
5.2.1.3 Terabit Device‐To‐Device Link
5.2.1.4 Secure Wireless Communication
5.2.1.5 Terabit Wireless Backhaul
5.2.1.6 Terahertz Nano‐Communications
5.2.2 Non‐Communication Terahertz Applications
5.2.2.1 Terahertz Sensing
5.2.2.2 Terahertz Imaging
5.2.2.3 Terahertz Positioning
5.3 Challenges of Terahertz Communications
5.3.1 High Free‐Space Path Loss
5.3.2 Atmospheric Attenuation
5.3.3 Weather Effects
5.3.4 Blockage
5.3.5 High Channel Fluctuation
5.4 Array‐of‐Subarrays Beamforming
5.5 Lens Antenna
5.5.1 Refraction of Radio Waves
5.5.2 Lens Antenna Array
5.6 Case Study – IEEE 802.15.3d
5.6.1 IEEE 802.15.3d Usage Scenarios
5.6.2 Physical Layer
5.6.2.1 Channelization
5.6.2.2 Modulation
5.6.2.3 Forward Error Correction
5.6.3 Medium Access Control
5.6.4 Frame Structure
5.6.4.1 Preamble
5.6.4.2 PHY Header
5.6.4.3 MAC Header
5.6.4.4 Construction Process of Frame Header
5.7 Summary
References
Chapter 6 Optical and Visible Light Wireless Communications in 6G
6.1 The Optical Spectrum
6.1.1 Infrared
6.1.2 Visible Light
6.1.3 Ultraviolet
6.2 Advantages and Challenges
6.3 OWC Applications
6.4 Evolution of Optical Wireless Communications
6.4.1 Wireless Infrared Communications
6.4.2 Visible Light Communications
6.4.3 Wireless Ultraviolet Communications
6.4.4 Free‐Space Optical Communications
6.5 Optical Transceiver
6.6 Optical Sources and Detectors
6.6.1 Light‐Emitting Diode
6.6.2 Laser Diode
6.6.3 Photodiode
6.7 Optical Link Configuration
6.8 Optical MIMO
6.8.1 Spatial Multiplexing
6.8.2 Spatial Modulation
6.9 Summary
References
Part III Smart Radio Networks and Air Interface Technologies for 6G
Chapter 7 Intelligent Reflecting Surface‐Aided Communications for 6G
7.1 Basic Concept
7.2 IRS‐Aided Single‐Antenna Transmission
7.2.1 Signal Model
7.2.2 Passive Beamforming
7.2.3 Product‐Distance Path Loss
7.3 IRS‐Aided Multi‐Antenna Transmission
7.3.1 Joint Active and Passive Beamforming
7.3.1.1 SDR Solution
7.3.1.2 Alternating Optimization
7.3.2 Joint Precoding and Reflecting
7.4 Dual‐Beam Intelligent Reflecting Surface
7.4.1 Dual Beams Over Hybrid Beamforming
7.4.2 Dual‐Beam IRS
7.4.3 Optimization Design
7.5 IRS‐Aided Wideband Communications
7.5.1 Cascaded Frequency‐Selective Channel
7.5.2 IRS‐Aided OFDM System
7.5.3 Rate Maximization
7.6 Multi‐User IRS Communications
7.6.1 Multiple Access Model
7.6.2 Orthogonal Multiple Access
7.6.2.1 Time‐Division Multiple Access
7.6.2.2 Frequency‐Division Multiple Access
7.6.3 Non‐Orthogonal Multiple Access
7.7 Channel Aging and Prediction
7.7.1 Outdated Channel State Information
7.7.1.1 Doppler Shift
7.7.1.2 Phase Noise
7.7.2 Impact of Channel Aging on IRS
7.7.3 Classical Channel Prediction
7.7.3.1 Autoregressive Model
7.7.3.2 Parametric Model
7.7.4 Recurrent Neural Network
7.7.5 RNN‐Based Channel Prediction
7.7.5.1 Flat‐Fading Channel Prediction
7.7.5.2 Frequency‐Selective Fading Channel Prediction
7.7.6 Long‐Short Term Memory
7.7.7 Deep Learning‐Based Channel Prediction
7.8 Summary
References
Chapter 8 Multiple Dimensional and Antenna Techniques for 6G
8.1 Spatial Diversity
8.2 Receive Combining
8.2.1 Selection Combining
8.2.2 Maximal Ratio Combining
8.2.3 Equal‐Gain Combining
8.3 Space‐Time Coding
8.3.1 Repetition Coding
8.3.2 Space‐Time Trellis Codes
8.3.3 Alamouti Coding
8.3.4 Space‐Time Block Codes
8.4 Transmit Antenna Selection
8.5 Beamforming
8.5.1 Classical Beamforming
8.5.2 Single‐Stream Precoding
8.6 Spatial Multiplexing
8.6.1 Single‐User MIMO
8.6.2 MIMO Precoding
8.6.2.1 Full CSI at the Transmitter
8.6.2.2 Limited CSI at the Transmitter
8.6.3 MIMO Detection
8.6.3.1 Maximum‐Likelihood Detection
8.6.3.2 Linear Detection
8.6.3.3 Successive Interference Cancelation
8.7 Summary
References
Chapter 9 Cellular and Cell‐Free Massive MIMO Techniques in 6G
9.1 Multi‐User MIMO
9.1.1 Broadcast and Multiple‐Access Channels
9.1.2 Multi‐User Sum Capacity
9.1.3 Dirty Paper Coding
9.1.4 Zero‐Forcing Precoding
9.1.5 Block Diagonalization
9.2 Massive MIMO
9.2.1 CSI Acquisition
9.2.2 Linear Detection in Uplink
9.2.2.1 Matched Filtering
9.2.2.2 ZF Detection
9.2.2.3 MMSE Detection
9.2.3 Linear Precoding in Downlink
9.2.3.1 Conjugate Beamforming
9.2.3.2 ZF Precoding
9.2.3.3 Regularized ZF Precoding
9.3 Multi‐Cell Massive MIMO
9.3.1 Pilot Contamination
9.3.2 Uplink Data Transmission
9.3.3 Downlink Data Transmission
9.4 Cell‐Free Massive MIMO
9.4.1 Cell‐Free Network Layout
9.4.2 Uplink Training
9.4.3 Uplink Signal Detection
9.4.3.1 Matched Filtering
9.4.3.2 ZF Detection
9.4.3.3 MMSE Detection
9.4.4 Conjugate Beamforming
9.4.5 Zero‐Forcing Precoding
9.4.6 Impact of Channel Aging
9.4.6.1 Channel Aging
9.4.6.2 Performance Degradation
9.5 Opportunistic Cell‐Free Communications
9.5.1 Cell‐free Massive Wideband Systems
9.5.2 Opportunistic AP Selection
9.5.3 Spectral Efficiency Analysis
9.6 Summary
References
Chapter 10 Adaptive and Non‐Orthogonal Multiple Access Systems in 6G
10.1 Frequency‐Selective Fading Channel
10.2 Multi‐Carrier Modulation
10.2.1 The Synthesis and Analysis Filters
10.2.2 Polyphase Implementation
10.2.3 Filter Bank Multi‐Carrier
10.3 Orthogonal Frequency‐Division Multiplexing
10.3.1 DFT Implementation
10.3.2 Cyclic Prefix
10.3.3 Frequency‐Domain Signal Processing
10.3.4 Out‐of‐Band Emission
10.4 Orthogonal Frequency‐Division Multiple Access
10.4.1 Orthogonal Frequency‐Division Multiple Access
10.4.2 Single‐Carrier Frequency‐Division Multiple Access
10.4.3 Cyclic Delay Diversity
10.4.4 Multi‐Cell OFDMA
10.5 Cell‐Free Massive MIMO‐OFDMA
10.5.1 The System Model
10.5.2 The Communication Process
10.5.2.1 Uplink Training
10.5.2.2 Uplink Payload Data Transmission
10.5.2.3 Downlink Payload Data Transmission
10.5.3 User‐Specific Resource Allocation
10.6 Non‐Orthogonal Multiple Access
10.6.1 Fundamentals of NOMA
10.6.1.1 Downlink Non‐Orthogonal Multiplexing
10.6.1.2 Uplink Non‐Orthogonal Multiple Access
10.6.2 Multi‐User Superposition Coding
10.6.3 Uplink Grant‐Free Transmission
10.6.4 Code‐Domain NOMA
10.6.4.1 Low‐Density Signature‐CDMA/OFDM
10.6.4.2 Sparse Code Multiple Access
10.7 Summary
References
Index
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