Frequency-Domain Iterative Message Passing Receiver for Faster-Than-Nyquist Signaling in Doubly Selective Channels

In this letter, we study the receiver design for a coded faster-than-Nyquist signaling system in time-variant intersymbol interference channels, also known as doubly selective channels. The conventional minimum mean squared error (MMSE) equalizer results in high complexity. We develop a low-complexity iterative message passing algorithm toward this end. By reformulating the problem into a linear state-space model, Gaussian message passing is performed on a vector-form factor graph. Furthermore, we consider the imperfect channel information scenario to improve the robustness of the proposed algorithm. Simulation results show that the proposed algorithm outperforms the variational inference method, and it performs close to the frequency-domain MMSE equalizer with much lower computational complexity.