Performance Comparison of Time-Domain Equalization (TEQ) Techniques in a Discrete Wavelet Multitone (DWMT) System for Asymmetric Digital Subscriber Line (ADSL)

A Discrete Wavelet Multitone (DWMT) transceiver is proposed for the Asymmetrical Digital Subscriber Line (ADSL) channel, which promises greater subchannel spectral containment, as compared to the Fourier transform based conventional Discrete Multitone (DMT) system. Wavelet packet transform applied in DWMT system is robust against narrowband interference and impulse noise. It is also spectrally efficient, since it does not require cyclic prefixing. However, with a dispersive channel like ADSL, DWMT system requires an efficient equalization technique. A linear transversal filter based on zero-forcing (ZF) and minimum mean squared error (MMSE) algorithms are applied for equalizing the channel effect and performance of the proposed transceiver is compared to a DMT system with ZF-time domain equalizer. Moreover, the non-linear MMSEDecision Feedback Equalizer (MMSE-DFE) is applied to the system. It is shown that the wavelet-packet based DWMT system with MMSE equalizer gives improved results in comparison with ZF equalizer in DWMT and DMT systems. On the other hand, MMSE-DFE outperforms all the other equalization techniques, regarding bit error rate for ADSL in the presence of additive white Gaussian noise (AWGN) and channel crosstalk.