Equalization for discrete multitone transceivers to maximize bit rate

In a discrete multitone receiver, a time-domain equalizer (TEQ) reduces int ersymbol interference (ISI) by shortening the effective duration of the cha nnel impulse response. Current TEQ design methods such as minimum mean-squa red error (MMSE), maximum shortening SNR (MSSNR), and maximum geometric SNR (MGSNR) do not directly maximize bit rate. In this paper, we develop two T EQ design methods to maximize bit rate. First, we partition an equalized mu lticarrier channel into its equivalent signal, noise, and ISI paths to deve lop a new subchannel SNR definition. Then, we derive a nonlinear function o f TEQ taps that measures bit rate, which the proposed maximum bit rate (MBR ) method optimizes. We also propose a minimum-ISI method that generalizes t he MSSNR method by weighting the ISI in the frequency domain to obtain high er performance. The minimum-ISI method is amenable to real-time implementat ion on a fixed-point digital signal processor. Based on simulations using e ight different carrier-serving-area loop channels, 1) the proposed methods yield higher bit rates than MMSE, MGSNR, and MSSNR methods; 2) the proposed methods give three-tap TEQs with higher bit rates than 17-tap MMSE, MGSNR, and MSSNR TEQs; 3) the proposed MBR method achieves the channel capacity ( as computed by the matched filter bound using the proposed subchannel SNR m odel) with a five-tap TEQ; and 4) the proposed minimum-ISI method achieves the bit rate of the optimal MBR method.