The application of wavelet based multi-carrier modulation in DSL systems

This thesis introduces a wavelet packet modulation (WPM) based multi-carrier modulation (MCM) system and its properties are studied and comparisons are made against the conventional discrete multi-tone (DMT) system, which is discrete Fourier transform (DFT) based. The proposed wavelet based system is shown to be more robust against narrow-band interference due to the superior spectral containment of its basis functions, resulting in better frequency selectivity. Various challenges related with the implementation of a WPM-MCM system are identified including higher sensitivity to timing errors and difficulties in realizing a frequency division duplex (FDD) system. Simulations are performed with a recursive least square (RLS) adaptive filter and a channel shortener as channel equalizers for the WPM and DMT based system respectively. It is shown that DMT with a channel shortener can reduce equalization complexity considerably and achieve reasonable data rate under severe channel attenuation conditions. On the other hand, the WPM based system with a longer RLS filter can achieve better performance in short range DSL channels. Finally, a filtered multi-tone (FMT) scheme is proposed to address the FDD implementation challenge of the WPM based system. It is shown that the FMT system has lower vulnerability to narrow-band radio frequency interference (RFI) when compared to conventional DMT based systems.