Equalizer design for discrete wavelet multitone transceiver.

Abstract

Discrete Wavelet Multi-tone (DWMT) is a multi-carrier technique that uses Wavelet Transform (WT) for modulation. A DWMT communication system is designed and an attempt is made to optimize the equalizer design and the structure of the DWMT receiver. Three plausible receiver designs consisting of a time domain equalizer (TEQ), several frequency domain equalizers (FEQ) and a combination of a simple TEQ and simple FEQs, are examined. The Linear equalizer (LE) is used as the TEQ, whereas the LE and the Decision Feedback Equalizer (DFE) are used as FEQs. These designs are simulated, tested on different twisted pair Very high-speed Digital Subscriber Loop (VDSL) channels and compared with each other in terms of their complexity and performance. The results indicate that the receiver designs consisting of only TEQ or only FEQs do not give a good signal reconstruction, in spite of using a large number of taps in the equalizers. On the other hand, the receiver structure consisting of a combination of a TEQ and FEQs was found to give a better performance, with lesser complexity in both the TEQ and the FEQs. A few taps in TEQ are found to be sufficient for eliminating most of the ISI in the signal. After demodulation, an FEQ with a few taps for each subchannel is sufficient to equalize the signal further and give a much lower Symbol Error Rate SER, as compared to both the previous structures. The DFE was found to give better performance than the LE. We conclude that the receiver design consisting of a simple TEQ and simple subchannel DFE-based FEQs, is most suitable for the DWMT transceiver among the three different designs tested for a DWMT system.