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  • Bl ind Multiuser Detection for Time-Frequency Spread Multicarrier C D M A

    by

    Wilson Tarn

    B . A . S c . University of British Columbia. Vancouver, Canada. 2005

    A THESIS S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF

    T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF

    M A S T E R OF A P P L I E D SCIENCE

    in

    T H E F A C U L T Y OF G R A D U A T E STUDIES

    (Electrical and Computer Engineering)

    T H E UNIVERSITY OF BRITISH C O L U M B I A

    October 2007

    Wilson Tarn, 2007

  • Abstract

    Multicarrier transmission technology has shown tremendous potential in realizing high

    data rates for next generation broadband wireless communication systems. Multicar-

    rier modulation schemes are robust to frequency selective fading which are inherent in

    broadband wireless channels. This thesis considers blind multiuser detection for the

    recently proposed time frequency spread multicarrier C D M A ( T F - M C - C D M A ) sys-

    tem in which the system uses both time and frequency domain spreading to achieve

    diversity in both time and frequency domains. The challenge for T F - M C - C D M A

    multiuser detection is to mitigate multiple access interference (MAI) in both the time

    and the frequency domain. The objective of this thesis is to develop and analyze

    the performance of blind multiuser detection algorithms for T F - M C - C D M A for three

    types of channel models: A W G N with M A I . slowly fading downlink Rayleigh multi-

    path channels, and the slowly fading downlink multipath channels with Doppler shift

    induced intercarrier interference (ICI).

    A new suboptimal decoupling technique for blind multiuser detection for T F - M C -

    C D M A in A W G N with M A I is proposed. It is found that the original T F - M C - C D M A

    blind multiuser detection problem can be suboptimally decoupled into two blind mul-

    tiuser D S - C D M A problems. These two problems can be solved separately using blind

    D S - C D M A multiuser techniques. Our effort focused on using blind linear multiuser

    detectors in which we investigated into four types of blind detection methods: blind

    direct matrix inversion (DMI) method, blind C M O E RLS method, blind subspace

    ii

  • multiuser detection method using SVD and PASTcl adaptive subspace tracking.

    The suboptimal decoupling technique for blind multiuser detection for T F - M C -

    C D M A is extended to slowly fading downlink Rayleigh multipath channels known as

    type I detectors. Computer simulation results show that type I detectors do not work

    well in slowly fading multipath channels even though such a scheme provides very-

    good performance in A W G N with M A I . In slowly fading channels, the orthogonality

    of the time domain signature sequences is preserved. We propose a type II detector

    which uses a cascade implementation with the time domain detection output acts as

    the input of the frequency domain detection. Computer simulations show that type

    II detectors provide much better performance than type I detectors.

    Blind multiuser detection for T F - M C - C D M A is further extended for slowly fading

    Rayleigh multipath channels with Doppler shift induced ICI. In mobile channels.

    Doppler shifts combined with multipath effects create random subcarrier frequency

    shifts which in turn cause subcarrier frequency mismatch. Such mismatch leads to the

    loss of orthogonality among subcarriers thus creating ICI. Our analysis shows that

    Doppler shifts induced ICI has the effect of destroying the common-channel property

    in downlink channels. The downlink T F - M C - C D M A signal becomes a quasi-uplink

    signal because of user dependent subchannel gains.

    The type II detector for slowly fading Rayleigh multipath channels is further

    extended to apply in such channels with Doppler shift induced ICI. It is shown through

    analysis and computer simulations that the proposed type II detectors implemented

    using C M O E RLS algorithm, blind subspace SVD algorithm, and the blind subspace

    PASTcl adaptive subspace tracking algorithm, without modifications, provide robust

    performance in multipath channels with Doppler shift induced ICI.

    in

  • Contents

    Abst rac t i i

    Contents v i i

    Lis t of Tables ix

    Lis t of Figures x i

    Lis t of Symbols x i i

    Lis t of Abbrevia t ions x i i i

    Acknowledgements x v i

    Dedica t ion x v i i

    1 In t roduct ion 1

    1.1 O v e r v i e w o f C u r r e n t W i r e l e s s C o m m u n i c a t i o n S y s t e m s 1

    1.1.1 L i m i t a t i o n s o f D S - C D J V I A i n B r o a d b a n d W i r e l e s s C h a n n e l s . . 2

    1.2 M u l t i c a r r i e r - b a s e c l T r a n s m i s s i o n 3

    1.2.1 M u l t i c a r r i e r C D M A 4

    1.2.2 T i m e - F r e q u e n c y S p r e a d M u l t i c a r r i e r C D M A 4

    1.3 C h a l l e n g e s a n d M o t i v a t i o n 5

    1.3.1 M u l t i u s e r D e t e c t i o n i n T F - M C - C D M A S y s t e m s 6

    i v

  • 1.3.2 Blind Signal Processing Techniques 6

    1.4 Review of Related Works 7

    1.5 Thesis Contributions 9

    1.6 Thesis Outline 12

    2 T i m e Frequency Spread Mul t i c a r r i e r Spread Spec t rum System

    M o d e l 13

    2.1 Introduction 13

    2.2 Transmitter Model 14

    2.2.1 Equivalent Complex Baseband Signal 16

    2.2.2 Allocation of Spreading Sequences 18

    2.3 Channel Models 21

    2.3.1 A W G N Channel 21

    2.3.2 Downlink Multipath Rayleigh Fading Channel 22

    2.3.3 Cyclic Prefix Insertion and Removal of Block ISI 26

    2.4 T F - M C - C D M A Demodulation 28

    2.4.1 Passbancl Model Demodulation 28

    2.4.2 Equivalent Complex Baseband Model Demodulation 30

    2.5 Summary 31

    3 B l i n d Mul t i u se r Detect ion for a T F - M C - C D M A Signal in A W G N 33

    3.1 Introduction . 33

    3.2 Linear Multiuser Detection for T F - M C - C D M A 34

    3.3 Adaptive Blind Multiuser Detection for T F - M C - C D M A 35

    3.3.1 Direct Matrix Inversion (DMI) Method 38

    3.3.2 C M O E Recursive Least Squares (RLS) Method 40

    3.3.3 Blind Subspace-Based Method 43

    v

  • 3.4 Performance Measure . . ' 47

    3.4.1 Receiver Complexity : 49

    3.5 Simulation Results 50

    3.6 Summary 53

    4 T F - M C - C D M A B l i n d Mul t iu se r Detect ion in Slowly Fading Rayle igh

    M u l t i p a t h Channel , 60

    4.1 Introduction 60

    4.2 Linear Multiuser Detection for T F - M C - C D M A in Frequency Selective

    Fading Channels 61

    4.3 Blind Multiuser Detection in Slowly Fading Channels 63

    4.3.1 Type I Receiver 64

    4.3.2 Type II Receiver 65

    4.3.3 C M O E RLS Blind Detection 68

    4.3.4 Blind Subspace Multiuser Detection 74

    4.4 Performance Evaluation Measure 79

    4.4.1 Receiver Complexity 79

    4.5 Simulation Results 83

    4.6 Summary 87

    5 T F - M C - C D M A B l i n d Mul t iu se r Detect ion in Downl ink M o b i l e

    Ray le igh Fading Channe l w i t h Doppler Induced I C I 92

    5.1 Introduction 92

    5.2 Modeling Intercarrier Interference 93

    5.3 Blind Multiuser Detection 96

    5.3.1 Type II Detection Formulation 97

    5.3.2 C M O E RLS Blind Detector 98

    v i

  • 5.3.3 Blind Subspace Multiuser Detection 99

    5.4 Simulation Results 103

    5.5 Summary 105

    6 Conclus ion and Future Research I l l

    6.1 Conclusion I l l

    6.2 Future Research 113

    6.2.1 MIMO T F - M C - C D M A Multiuser Detection 113

    6.2.2 Bayesian Monte-Carlo Blind Multiuser Detection for T F - M C -

    C D M A 114

    6.2.3 T F - M C - C D M A Blind Multiuser Detection in Fast Fading Chan-

    nels 115

    Bib l iography 116

    vii

  • List of Tables

    2.1 Summary of channel fading models in mobile wireless channels . . . . 26

    3.1 B l i n d T F - M C - C D M A D M I Receiver Algor i thm 40

    3.2 B l ind C M O E R L S Receiver Algor i thm 42

    3.3 B l i n d Subspace S V D Receiver Algor i thm 45

    3.4 B l i n d Subspace P A S T c l Receiver Algor i thm 48

    3.5 Summary of T F - M C - C D M A B l i n d Multiuser detection complexity for

    A W G N channel 50

    3.6 Simulation parameters 50

    4.1 Type I C M O E R L S B l i n d Receiver Algor i thm 72

    4.2 Type II C M O E R L S Bl ind Receiver Algor i thm 73

    4.3 Type I B l i n d Subspace (SVD) Receiver Algor i thm 77

    4.4 Type II B l i n d Subspace (SVD) Receiver Algor i thm 78

    4.5 Type I B l i n d Subspace P A S T c l Receiver Algor i thm 80

    4.6 Type II B l ind Subspace P A S T c l Receiver Algor i thm 81

    4.7 Summary of T F - M C - C D M A B l i n d Multiuser detection complexity for

    slowly fading Rayleigh multipath channels 83

    4.8 I T U - A Pedestrian Rayleigh Fading Channel Power delay profile . . . 84

    4.9 Simulation parameters 84

    5.1 Type II C M O E R L S Bl ind Receiver Algor i thm for multipath fading

    channels with Doppler induced ICI 99

    vi i i

  • 5.2 Type II Blind Subspace (SVD) Receiver Algorithm 101

    5.3 Type II Blind Subspace PASTd Receiver Algorithm 102

    5.4 Summary of simulation parameters 103

    ix

  • List of Figures

    2.1 T F - M C - C D M A transmitter model 14

    2.2 T F - M C - C D M A baseband transmitter implementation using I D F T / I F F T 17

    2.3 T F spreading sequence matrix 19