Efficient Multi-Carrier Communication on the Digital Subscriber Loop

This thesis explores three distinct philosophies for improving the efficiency of multi-carrier communication 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 adaptive time-domain LMS algorithm is provided as an alternative to eigen-decomposition. The next part of the thesis examines bitand powerloading algorithms for multitone systems. The problem of rate-optimal loading has already been solved. It is shown, however, that the rate-optimal solution 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 interference effects in a dispersive channel. Associated Publications D. Daly , C. Heneghan and A.D. Fagan, “Minimum mean-squared error impulse response shortening for discrete multitone transceivers”, accepted for publication, IEEE Trans. Signal Process.. D. Daly , C. Heneghan and A.D. Fagan, “Powerand bitloading algorithms for multitone communications”, 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 residual ISI channel shortening for discrete multitone transceivers” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Process., Salt Lake City, UT, May 2001.