Efficient Multi-Carrier Communication on the Digital Subscriber Loop
Total Page：16
File Type：pdf, Size：1020Kb
Efficient Multi-Carrier Communication on the Digital Subscriber Loop Donnacha Daly Department of Electrical and Electronic Engineering Faculty of Engineering and Architecture University College Dublin National University of Ireland A thesis presented to the National University of Ireland Faculty of Engineering and Architecture in fulfillment of the requirements for the degree of Doctor of Philosophy May 2003 Research Supervisors: Dr. C. Heneghan Prof. A. D. Fagan Head of Department: Prof. T. Brazil Abstract This thesis explores three distinct philosophies for improving the efficiency of multi-carrier com- munication on the digital subscriber loop. The first topic discussed is impulse response shortening for discrete multitone transceivers. The minimum mean-squared error impulse response shortener is reformulated to allow near-optimal rate performance. It is demonstrated that the best existing eigen-filter designed channel shortener is a particular case of the proposed reformulation. An adap- tive time-domain LMS algorithm is provided as an alternative to eigen-decomposition. The next part of the thesis examines bit- and power- loading algorithms for multitone systems. The problem of rate-optimal loading has already been solved. It is shown, however, that the rate-optimal solu- tion does not give best value for complexity, and that near optimal schemes can perform very well at a fraction of the computational cost. The final section of the thesis is a brief exposition of the use of wavelet packets to achieve multi-carrier communication. It is proposed that the non-uniform spectral decomposition afforded by wavelet packet modulation allows reduced inter-symbol inter- ference effects in a dispersive channel. Associated Publications D. Daly , C. Heneghan and A.D. Fagan, “Minimum mean-squared error impulse response short- ening for discrete multitone transceivers”, accepted for publication, IEEE Trans. Signal Process.. D. Daly , C. Heneghan and A.D. Fagan, “Power- and bit- loading algorithms for multitone com- munications”, accepted for IEEE Int. Symp. Image, Signal Process., Analysis, Rome, Italy, Sep. 2003. D. Daly , C. Heneghan and A.D. Fagan, “Optimal wavelet packet modulation”, in Proc. Irish Signals, Syst. Conf., Cork, pp. 47-52, June 2002. D. Daly , C. Heneghan, A.D. Fagan and M.Vetterli, “Optimal wavelet packet modulation under finite complexity constraint”, in Proc. IEEE Int. Conf. Acoust., Speech, Signal Process., Orlando FLA, Vol III, pp. 2789-2792, May 2002. D. Daly , C. Heneghan, and A.D. Fagan, “A minimum mean-squared error interpretation of resid- ual ISI channel shortening for discrete multitone transceivers” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Process., Salt Lake City, UT, May 2001. Acknowledgment I would primarily like to thank my family, that is my father Peter, my mother Marian and my brother Peter, who have been so supportive of me through the years. I would also like to express gratitude to those who have guided my thought both towards stimulating subjects and away from inevitible dead ends, over the course of my research. In particular, my supervisors Conor and Tony have, in their wisdom, steered me through a well focussed postgraduate career. I am grateful to Prof. Martin Vetterli of the Swiss Federal Institute of Technology, under whom it was a true inspiration to work. As I am notoriously pedantic (and vocal) when it comes to chewing over the intricacies of a particular problem, my gratitude is further extended to those who have had the patience to pick bones with me, whether it was at the whiteboard at two o’clock in the morning, or over a pint in Captain Cook’s in Lausanne. In no particular order, my eager co-conversants were Brian Clerkin, David Naughton, Ger Baldwin, Finbarr O’Regan, Mark Flannagan, Mark Herro, Damien Piguet, Julius Kusuma and Andrea Ridolfi. Finally, it remains to mention those in Mas- sana and Advanced Communication Networks with whom I had the pleasure of cooperating, much to the benefit of my signal processing knowhow. Again in no order, I would like to thank Brian Murray, Philip Curran, Ed Lalor, Ciaran McElroy, Alan Harnedy, Carl Murray, Albert Molina, Stephan Horvath and Antony Jamin. This work was sponsered by Science Foundation Ireland. For Dad I wandered out in the world for years You just stayed in your room I saw the crescent You saw the whole of the moon —Mike Scott, 1985 ii Contents 1 Introduction 1 1.1 Evolution of the Digital Subscriber Loop . 2 1.1.1 Voice Band Modems . 2 1.1.2 ISDN . 4 1.1.3 xDSL . 4 1.2 Multitone Communications — Literature Survey . 6 1.2.1 The Filterbank Transceiver . 6 1.2.2 Block Transforms — DMT . 8 1.2.3 Lapped Transforms — DWMT . 9 1.2.4 Over-Interpolated Filterbanks . 11 1.2.5 Near-Perfect Reconstruction . 12 1.2.6 Nonuniform Filterbanks . 12 1.2.7 Equalization . 15 1.2.8 Echo Cancellation . 16 1.2.9 Timing and Synchronization . 17 1.2.10 Peak-to-Average Power Ratio . 19 1.2.11 Bitstream Operations: Coding, Scrambling, and Interleaving . 20 1.3 Thesis Outline . 21 iii CONTENTS 2 DMT Communication on the Digital Subscriber Loop 22 2.1 DSL Channel Modeling . 22 2.1.1 The ADSL Test Loops . 23 2.1.2 The VDSL Test Loops . 25 2.1.3 Other DSL Elements . 25 2.1.4 Primary Line Constants: R; L; G; C . 26 2.1.5 Secondary Line Constants: Z0; γp . 28 2.1.6 ABCD Matrices . 31 2.1.7 Loop Transfer Function . 34 2.1.8 DAC, Anti-Aliasing Filters and Splitter . 34 2.1.9 Loop Impulse Response . 36 2.1.10 Noise, Crosstalk and Radio Frequency Interference . 36 2.2 Discrete Multitone Modulation . 42 2.2.1 DMT by Fast Fourier Transform . 42 2.2.2 Guard Band Insertion . 44 2.2.3 Cyclic Prefix vs. Guard Band . 46 2.2.4 Channel Estimation . 49 2.3 Chapter Summary . 49 3 Time Domain Equalization 50 3.1 Channel Shortening: State of The Art . 50 3.1.1 Minimum Mean Squared Error Impulse Response Shortening . 52 3.1.2 The Maximum Shortening Signal to Noise Ratio TEQ . 55 3.1.3 Maximum Bit Rate Impulse Response Shortening . 57 3.1.4 The Minimum Intersymbol Interference TEQ . 60 3.1.5 Summary of Existing Channel Shortening Algorithms . 61 iv CONTENTS 3.2 The DIR-optimized MMSE TEQ . 63 3.2.1 Special Case I: The min-ISI TEQ . 64 3.2.2 Special Case II: The MSSNR TEQ . 65 3.2.3 Special Case III: High SNR . 66 3.2.4 Adaptive LMS Implementation . 66 3.3 Simulation Results . 69 3.3.1 Simulation Setup . 69 3.3.2 Figures of Merit . 69 3.3.3 Performance Results . 70 3.3.4 Adaptive Implementation . 74 3.4 Chapter Summary . 78 4 Power- and Bit-Loading 79 4.1 Water-Pouring . 80 4.1.1 Power-Loading . 81 4.1.2 Bit-Loading . 83 4.2 Modulation Schemes . 85 4.2.1 Pulse Amplitude Modulation . 85 4.2.2 Quadrature Amplitude Modulation . 88 4.2.3 A Note on the Modulation Gap . 92 4.3 Loading Algorithms . 95 4.3.1 Optimal Loading . 95 4.3.2 Near-Optimal Loading . 100 4.3.3 Default Loading . 102 4.3.4 Constant Power Bit-Loading . 103 4.4 Simulation Results . 104 4.4.1 Willink’s Test Channel . 105 4.4.2 Loading for the DSL channels . 111 4.5 Chapter Summary . 116 v CONTENTS 5 Wavelet Packet Modulation 117 5.1 Introduction . 118 5.1.1 The Two-Channel Transmultiplexer . 118 5.1.2 Polyphase Analysis . 119 5.1.3 Perfect Reconstruction . 124 5.1.4 Worked Example . 126 5.1.5 Wavelet Packet Trees . 126 5.1.6 Equivalent Branch Filters . 129 5.1.7 Wavelet Packet Modulation: State of the Art . 132 5.2 Optimal Wavelet Packet Modulation . 134 5.2.1 Signal to Interference Ratio . 134 5.2.2 Tree Structuring . 135 5.2.3 Simulation Results . 137 5.2.4 Noise Effects . 141 5.3 Chapter Summary . 144 6 Conclusion 145 6.1 Summary of Novel Results . 145 6.1.1 Channel Shortening . 145 6.1.2 Bit-Loading . 146 6.1.3 Wavelet Packet Modulation . 146 6.2 Future Research . 147 6.2.1 Channel Shortening . 147 6.2.2 Bit-loading . 147 6.2.3 Wavelet Packet Modulation . 148 6.3 Concluding Remarks . 148 vi CONTENTS A DSL Test Loop Responses 149 B Solution to the Generalized Eigen-Problem 153 List of Figures 156 List of Tables 162 Bibliography 164 vii Chapter 1 Introduction Over the last 50 years there has been an ever-increasing demand for the means to reliably commu- nicate digital-data at high speeds. Table 1.1 lists some examples of.