ADSL System Enhancement with Multiuser mbrooke/Thesis/liang.pdf  ADSL System Enhancement with Multiuser

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  • ADSL System Enhancement with Multiuser Detection

    A Thesis Presented to

    The Faculty of the Division of Graduate Studies


    Liang C. Chu

    In Partial Fulfillment of the Requirements for the Degree of

    Doctor of Philosophy in Electrical and Computer Engineering

    School of Electrical and Computer Engineering

    Georgia Institute of Technology

    Atlanta Georgia 30332

    July 2001

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    There are a number of people that should be recognized for their help and assistance

    during my thesis work. First of all I want to express my sincere gratitude to my thesis

    advisor professor Martin A. Brooke, who has given me the opportunity to complete my

    Ph.D. study at school of Electrical and Computer Engineering in Georgia Institute of

    Technology. I really appreciate the time for his advising and it is very rewarding and

    inspiring to discuss questions with professor Brooke. I also want to thank professor Nikil

    Jayant and professor John Copeland, who have taken an active part in advising and

    guiding me in my research and education.

    Furthermore, I gratefully acknowledge professor Donald L. Schilling, who always

    encourages my study during these years, since I was studying in my Masters degree with

    him at the City College of New York, CUNY. Also, I would like to thank professor

    Russell M. Mersereau and professor Zhong L. Wang for their supporting to serve in my

    thesis committee, and all my colleagues at school of Electrical and Computer

    Engineering, Georgia Tech.

    Finally, and most importantly, I sincerely thank my wife, Dr. Jing Li, who help and

    support me in my graduate study at Georgia Tech during these years, and deeply love and

    care about me always. Also, I greatly thank my parents, Mr. Hsun C. Chu, Ms. Sai Y.

    Feng, and my bother, Dr. Liang T. Chu, for their continuing care and encouragement all

    the times in my life. I would like to show my great appreciation to my families for their

    constant help, support and encouragement.

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    ADSL System Enhancement with Multiuser Detection


    Dr. Martin A. Brooke, Chairman

    Dr. John A. Copeland

    Dr. Nikil Jayant

    Date Approved

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    Table of the Contents

    Chapter One: Introduction 1

    Chapter Two: Background 5

    2. Problem on the DSL Spectral Compatibility with Crosstalk 5

    2.1. Current Crosstalk Model and Distribution 6

    2.1.1 NEXT and FEXT Modeling 8

    2.1.2 Crosstalk Noise Distribution 10

    2.2 Spectral Compatibility between Asymmetric and Symmetric DSL Systems 10

    2.2.1 Symmetric DSL Systems 11

    2.2.2 Studies on Crosstalk Noise between ADSL and SDSL 11

    2.2.3 Current Deployment Plan and Proposed Enhancement 15

    Chapter Three: DMT-ADSL Channel Modulation and Characteristics 16

    3. Multiuser Multitone Modulation System and ADSL 16

    3.1 Overview of Discrete Multitone 17

    3.2. Analysis of Discrete Multitone 22

    3.2.1 Channel Gap Analysis 22

    3.2.2 Margin of the DMT 23

    3.2.3 Performance Calculation 25

    3.2.4 Bit-loading and DMT-ADSL System 26

    Chapter Four: Channel Model and Multiuser Transmission 32

    4.1 Twisted Wire Pairs Characteristics 32

    4.1.1 Electrical Characteristics of Twisted-pair Wires 33

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    4.1.2 Telephone Channel 35

    4.2. Multiuser Transmission System 37

    4.2.1 Basic on Multiuser Detection 37

    4.2.2 Optimum Multiuser Detection 38 Linear Multiuser Detection in AWGA Channel 42

    Chapter Five: ADSL System Enhancement 45

    5.1. Multiuser Detection on DMT-ADSL System 45

    5.1.1 Theoretic Bounds on DMT-ADSL Channel 49

    5.1.2 Spectral Distribution on the Multiuser Channel Capacity 49

    5.1.3 Examples on Capacity Bound Analysis 58

    5.2. Joint Maximum-likelihood Sequence Estimation (JMLSE) 60

    5.2.1 DSL Co-channel Signal Model 60

    5.2.2 MLSE Receiver Design 62

    5.2.3 T/2-spaced MLSE Receiver 69

    5.2.4 Analyzing MLSE Receiver Structures 72

    5.2.5 Reduced Complexity Receiver Structures 76

    5.3.6 Joint MLSE for DMT-ADSL Receiver 78

    5.3 Preliminary Performance Studies 81

    Chapter Six: Low Complexity Enhancement on ADSL Receiver 85

    6.1 Tone-zeroing Method 85

    6.2. Low Complexity Joint MLSE 90

    6.2.1 Multi-stage JVA 90

    6.2.2 Multi-stage JVA with Feedback 95

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    6.2.3 Practical Enhanced ADSL Receiver 98

    6.2.4 Example and Comparison 101

    Chapter Seven: Performance Evaluations and Simulation Results on Enhanced ADSL

    Receivers 104

    7.1 Test Environment 105

    7.2 Test Channel Conditions 105

    7.3 Loop Characteristics 106

    7.4 Capacity Improvement 107

    7.5 Reach Improvement 107

    7.6 Disturber Scenarios 107

    7.7 Co-channel Transfer Functions 110

    7.8 Simulation Results 110

    Chapter Eight: Conclusions 115

    Chapter Nine: Recommendations 117

    Reference 119

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    Figure Page

    2.1.1 Near-end Crosstalk (NEXT) 7

    2.1.2 Far-end Crosstalk (FEXT) 7

    2.1.3 NEXT Power Sum Losses for 25 Pairs of PIC Cable Binder Group 9 PSD of 2B1Q SDSL at 1168, 1552 and 2320 kbps 13 Downstream ADSL Bit Rate with 1552 & 2320 kbps SDSL NEXT 14

    3.1.1 Basic Multitone Modulation Transmission 18

    3.1.2 Illustration of Frequency Bands for Multitone Transmission System 19 DMT Bit-Loading Concept 29 DMT-ADSL Frequency Spectrum 31 Transmission Line Segment 34 Basic Multiuser Transmission System 38

    5.1.1 ADSL Channel Model with k-l Crosstalk Signals 48 TPC Attenuation Function with Difference Length 50 Channel Attenuation and NEXT Coupling Characteristic 50 Channel Capacity Single vs. Multiuser Channels 56 Co-channel System Model 61 Basic Receiver Structure 77 Sophisticated Receiver Structure 77 Carrier Recovery in the Noise-free AWGN Channel 78

  • viii Joint ML Sequence Detection between Adjacent Pair 80

    5.3.1 BER for ADSL System with Single-user Detector and JMLSE 83

    5.3.2 ADSL System with SDSL Crosstalk on Single-user Detector and JMLSE 84

    6.1.1 Joint ML Crosstalk Signal Canceller with Tone Zeroing 87

    6.1.2 Margin on DMT-ADSL with Tone-zeroing Crosstalk Noise Cancellation 88 Two-stage JVA (without Feedback Section) 92 Single-user MLSE Computational Flow Structure 94 Two-stage JVA (with Feedback Section) 95 Desired Channel Performance with Three Methods 103

    7.3.1 Testing Loops 106

    7.6.1 Scatter Plot of Downstream ADSL Throughput with Mixed SDSL Crosstalk 108

    7.8.1 Rate-reach Curves for Test Loop #1 111

    7.8.2 Rate-reach Curves for Test Loop #2 112

    7.8.3 Rate-reach Curves for Test Loop #3 113

    9.1 Channel Attenuation and NEXT Characteristic 118

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    Table Page Worst-case Measurement for Telephone Channels 36

    7.6.1 Disturber Scenarios 109

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    In this thesis, a new approach on mitigating the cochannel interference (CCI), also

    called crosstalk, in the Asymmetric Digital Subscriber Line (ADSL) transmission system

    has been studied. This implementation ensures the spectral compatibility in the DMT-

    ADSL system together with other DSL services in a same binder cable.

    The major part of this thesis concerns a modified technique for high-speed

    communication over the ADSL telephone network. Discrete Multitone (DMT)-ADSL

    has been standardized in American National Standards Institute (ANSI) [1]. It offers bit

    rate up to 8 Mbps downstream and 1 Mbps upstream, depending on the deployment

    coverage ranges. A modified method based on multiuser detection is presented herein,

    which can mitigate the crosstalk interference in DMT-ADSL receiver.

    An important issue for ADSL is the problem with crosstalk, which is a major threat in

    ADSL receiver with other DSL services in a same binder. The performance on the

    mitigation of ADSL channel crosstalk impairment is the most important criteria for

    guaranteeing the Quality of Service (QoS) in an ADSL system. The essential issue of this

    thesis on optimizing the ADSL system transmission throughput is to modify its channel

    transceiver design. Treating an ADSL channel as a multiple-input and single-output

    (MISO) system with desired ADSL signal and cochannel interference signals is just like a

    multiuser communication channel model. Our modified ADSL multiuser detection can

    greatly outperform the currently deployed single-user receiver with either increasing

    transmission data rates, or extending deployment rages in impairment environments.

    Joint Maximum Likelihood Sequence Estimation (JMLSE) gives very good performance

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