Performance enhanced adaptive equalizers for multicarrier channels

Multicarrier modulation techniques are increasingly used in high bandwidth xDSL transceivers. Multicarrier quadrature amplitude modulation (QAM) systems offer an efficient method of maximizing the transmission bitrate over existing copper. The attenuation and crosstalk characteristics of the copper plant require careful equalization to realize the required bit error rate. Because this technique relies on the fast Fourier transform coupled with a cyclic redundant guard interval, the goal of equalization is not to exactly invert the channel characteristic, but to reduce the combined channel-equalizer effective impulse response length to less than or equal to some integer L, defined by the inclusion of the cyclic prefix in the transmitted sample sequence. This paper examines techniques to improve both the rate of error convergence of the adaptive equalizer and the residual inter-symbol interference of the system.