Frequency domain equalization for high data rate multipath channels

High data rate transmission over multipath channels requires equalizers of long impulse response. In such cases, frequency domain implementation of the block least mean square (BLMS) algorithm offers low complexity growth relative to time domain techniques. The work presented herein is devoted to a study of the fast BLMS (FBLMS) algorithm implemented in the frequency domain using overlap-save sectioning and the fast Fourier transform (FFT). We examine the bit error rate (BER) performance for high data rate quadrature phase shift keying (QPSK) transmission over a multipath channel as well as the computational complexity of the FBLMS equalizer in comparison to the time domain implementation. Finally, we show how normalizing the step size of the FBLMS algorithm according to the power distribution of the input process results in a significant improvement in the equalizer convergence relative to the time domain methods.