Wireless Communications Over Rapidly Time-Varying Channels

Transcription

1 Wireless Communications Over Rapidly Time-Varying Channels Edited by Franz Hlawatsch Gerald Matz ELSEVIER AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Academic Press is an imprint of Elsevier

2 Contents Preface About the Editors Contributing Authors Notations and Symbols Abbreviations xiii xv xvii xix xxv CHAPTER 1 Fundamentals of Time-Varying Communication Channels Introduction The Physics of Time-Varying Channels Wave Propagation Multipath Propagation and Time Dispersion Doppler Effect and Frequency Dispersion Path Loss and Fading Spatial Characteristics Deterministic Description Delay-Doppler Domain - Spreading Function Delay-Scale Domain - Delay-Scale Spreading Function Time-Frequency Domain - Time-Varying Transfer Function Time-Delay Domain - Time-Varying Impulse Response Extension to Multiantenna Systems Stochastic Description WSSUS Channels Extension to Multiantenna Systems Non-WSSUS Channels Underspread Channels Dispersion-Underspread Property Correlation-Underspread Property Approximate Eigenrelation Time-Frequency Sampling Approximate Karhunen-Loeve Expansion Parsimonious Channel Models Basis Expansion Models Parsimonious WSSUS Models Parsimonious Non-WSSUS Models Measurement Spread-Spectrum-Like Channel Sounding Multicarrier Channel Sounding 52 V

3 vi Contents Extension to Multiantenna Systems Measurement of Second-Order Statistics Conclusion 59 Acknowledgment 59 References 59 CHAPTER 2 Information Theory of Underspread WSSUS Channels The Role of a System Model A Realistic Model A Brief Literature Survey Capacity Bounds Answering Engineering-Relevant Questions A Discretized System Model The Channel Model Discretization of the Continuous-Time Input-Output Relation The Large-Bandwidth Regime: Diagonalized I/O Relation Power Constraints Definition of Noncoherent Capacity A Coherent-Capacity Upper Bound An Upper Bound on Capacity that Is Explicit in Сн(г, v) A Lower Bound on Capacity A Numerical Example Extension to the Multiantenna Setting Numerical Examples The Large-Bandwidth Regime: I/O Relation with Interference A Lower Bound on Capacity Numerical Examples The High-SNR Regime A Lower Bound on Capacity Numerical Examples Conclusions 110 References 112 CHAPTER 3 Algebraic Coding for Fast Fading Channels Introduction Fading Channel Model System Model Product Distance Based Code Design Signal Space Diversity and Product Distance Lattice Constellations 122

4 Contents vii 3.3 Lattices First Definitions Sublattices and Equivalent Lattices Algebraic Number Theory Algebraic Number Fields Integral Basis and Canonical Embeddings Algebraic Lattices Ideal Lattices Algebraic Rotations with High Product Distance Z" Ideal Lattices Rotated ^"-Lattice Codes A Simple Two-Dimensional Rotation Based on the Golden Number The Cyclotomic Construction Sphere Decoding The Sphere Decoder Algorithm The Sphere Decoder with Fading Performance of Rotated Constellations Conclusions 151 References 152 CHAPTER 4 Estimation of Time-Varying Channels-A Block Approach Introduction System and Channel Model System Model BEM Channel Model Channel Estimation Based on a Single Block Introduction Channel Estimation Data Model Channel Estimators Channel Identifiability Simulation Results Channel Estimation Based on Multiple Blocks Introduction Data Model and BEM for Multiple OFDM Symbols Channel Identifiability Based on Multiple Blocks Simulation Results Extension to MIMO Systems Introduction Single-Carrier System OFDM System Adaptive Channel Estimation 192

5 viii Contents 4.7 Conclusions 194 References 194 CHAPTER 5 Pilot Design and Optimization for Transmission over Time-Varying Channels Introduction Pilot Design: A Framework Modeling of Pilot-Assisted Transmission Transceiver Architectures Performance Criteria Optimal TDM Pilot Insertion Pattern in Single Carrier Systems Channel Model Periodic TDM Pilot Placement Receiver Structure Optimization Criteria Optimal TDM Pilot Placement Bibliographical Notes Alternative Pilot Insertion Strategy - Superimposed Training Kaiman Tracking with Superimposed Training Superimposed versus TDM Schemes: Performance Comparison Bibliographical Notes Resource Allocation: Amount of Training and Power Optimization Cutoff Rate Analysis Bibliographical Notes Pilot Design for MIMO Channels Pilot Design for Wideband Systems OFDMA Systems CDMA Systems Ultra Wideband Conclusion 227 Acknowledgment A The Kaiman Filter for TDM Training B Proof of Proposition C Proof of Lemma D Proof of Theorem References 233 CHAPTER 6 Equalization of Time-Varying Channels Introduction System Model Basic Assumptions The Structure of the Effective Channel Matrix Q 240

6 Contents ix 6.3 Coherent Equalization Coherent Equalization Criteria Coherent Equalization Tools Coherent Equalization for Time-Frequency Concentrated Modulation/Demodulation Coherent Equalization of Single-Carrier Modulation/Demodulation Noncoherent Equalization Noncoherent System Model Noncoherent Equalization Criteria Noncoherent Equalization Tools Noncoherent Equalization for Single-Carrier Modulation/Demodulation Noncoherent Equalization for Time-Frequency Concentrated Modulation/Demodulation Conclusion A Derivation of Posterior LLR Expression (6.36) B Derivation of the Noncoherent MLSD Expression (6.73) С Explanation of EM Recursion (6.91) D Info EM(B) Algorithms for Noncoherent Equalization 276 References 277 CHAPTER 7 OFDM Communications over Time-Varying Channels OFDMSystems System Model Effects of Rapidly Time-Varying Channels MIMO-OFDM ICI Mitigation Techniques Linear Equalization Nonlinear Equalization Transmitter Preprocessing Extension to MIMO-OFDM Time-Varying Channel Estimation Basis Expansion Model of LTV Channels Training-Based Channel Estimation Iterative Channel Estimation and Turbo Equalization Impact of Channel Estimation on BER Performance Channel Estimation in MIMO-OFDM Concluding Remarks System and Application Aspects Open Issues 328 References 329

7 x Contents CHAPTER 8 Multiuser MIMO Receiver Processing for Time-Varying Channels Introduction Multiuser MIMO Systems Tools for Complexity Reduction Iterative Approximation of the MAP Detector Reduced-Rank Model for the Time-Varying Channel The Krylov Subspace Method Sphere Decoding Iterative Multiuser MIMO Time-Varying Channel Estimation Signal Model Reduced-Rank LMMSE Channel Estimator Comparison of the Slepian and Fourier Bases Krylov Approximation of the Reduced-Rank LMMSE Channel Estimator Linear Joint Antenna Multiuser Detection Multiuser Detection in Chip Space Multiuser Detection in User Space Nonlinear Detection Exploiting the Reduced-Rank Channel Model Soft Sphere Decoding Computational Complexity Simulation Results Bit Error Rate Comparison Computational Complexity Comparison Conclusions 368 Acknowledgments A Computation of the Log-Likelihood Ratio (8.44) 369 References 371 CHAPTER 9 Time-Scale and Dispersive Processing for Wideband Time-Varying Channels Introduction Need for Wideband Channel Characterizations Examples of Wideband Dispersive Channel Characteristics Chapter Organization Narrowband Channel Characterization Narrowband Spreading Function Discrete Channel Characterization and Finite Approximations Wideband Delay-Scale Channel Characterization Narrowband and Wideband Conditions Wideband Spreading Function 384

8 Contents xi Discrete Delay-Scale Channel Characterization Finite Approximations Multipath-Scale Diversity Time-Scale Rake Receiver Wideband Dispersive Channel Characterization Dispersive Time-Frequency Structures Dispersive Spreading Function and Unitary Warping Relations Discrete Dispersive Channel with Physical Limitations Generalized Time-Frequency Rake Receiver Underwater Wireless Communication Channels Shallow Water Environment Model Time-Frequency Characteristics of Shallow Water Environments Mode Separation in Time-Frequency Dispersion Diversity Receiver Design Numerical Simulations for Shallow Water Communications Application Example Conclusions 410 References 411 Index 417