A spectrally flat time domain equalizer for rate improvement of multicarrier transceivers

Spectral flatness of the time domain equalizer (TEQ) is highly desirable in DMT transmission systems. Although several TEQ designs have been proposed throughout the literature, spectral flatness has not been included in the formulation of the optimality criterion (MMSE, shortened SNR, geometric SNR). Therefore the TEQ, although designed to shorten the channel (among other characteristics), may introduce some severe attenuation in frequency bands where the channel has a good SNR. This leads to poorer performance in terms of the achievable bit rate, despite the minimization of ISI (channel shortening). We include the spectral flatness of the TEQ as an additional optimality criterion. We show that the TEQ we obtain yields a rate improvement usually of the order of 5%, with the same computational complexity as the existing solutions (see Melsa, P. et al., IEEE Trans. on Commun., vol.44, no.12, p.1662-72, 1996; Nafie, M. and Gatherer, A., Proc. IEEE Int. Conf. on Commun., 1997).