A modified frequency-domain decision-feedback equalization for doubly-selective fading channels

A novel overlap-save frequency-domain decision-feedback equalizer (OLS-FD-DFE) is proposed to improve the problem that the conventional frequency-domain decision-feedback equalizer (FD-DFE) suffers from severe performance detriment in doubly-selective fading channels. The feedforward filter is designed with constraint on its time-domain values such that the effective taps have non-zero values only in a predefined range. Then, the overlap-save method is applied to divide the original block-wise convolution into several subblock-wise convolutions. When the length of subblock is less than the coherence time of the channel, the tolerance to the channel time-variation can be significantly improved, as long as the filter coefficients are updated according to the channel response. Simulation results show that if the mobile moves at the speed of 100 km/h, OLS-FD-DFE achieves 2×10^-5 bit error rate when the signal-to-noise ratio is 20 dB, while FD-DFE achieves only 8×10^-4 bit error rate in the same scenario.