MMSE time-varying FIR equalization of doubly-selective channels

In this paper, we propose a time-varying (TV) finite impulse response (FIR) equalizer 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 equalizer. This structure allows us to turn a large design problem into an equivalent small design problem, containing only the BEM coefficients of both the doubly-selective channel and the TV FIR equalizer. Focus is on the minimum mean-square error (MMSE) solution, but the zero-forcing (ZF) solution is also discussed. Comparisons with the linear block equalizer (LBE) are made. Through computer simulations we show that the performance of the MMSE TV FIR equalizer approaches that of the MMSE LBE, while the design as well as the implementation complexity are much lower.