Time-varying FIR decision feedback equalization of doubly-selective channels

We propose a minimum mean-square error (MMSE) time-varying (TV) finite impulse response (FIR) decision feedback equalizer (DFE) for doubly-selective (time- and frequency-selective) channels. We use the basis expansion model (BEM) to approximate the doubly-selective channel and to design the TV FIR DFE. This allows us to turn a large design problem into an equivalent small design problem, containing only the BEM coefficients of the doubly-selective channel and the BEM coefficients of the TV FIR feedforward and feedback equalization filters. Through computer simulations we show that the performance of the proposed TV FIR DFE approaches the performance of the block DF equalizer, while the equalization and the design complexity are generally much lower.