Low-complexity soft demapper for OFDM fading channels with ICI

We present a low-complexity soft demapper that computes bit log-likelihood ratios (LLRs) while suppressing orthogonal frequency division multiplexing (OFDM) inter-carrier interference (ICI). The proposed demapper consists of two stages and can be realized in a fully-parallel architecture. We examine uncoded and low-density parity-check (LDPC) coded performance over frequency-selective Doppler fading channels. We compare the coded and uncoded performances of our demapper with those of an MMSE detector with successive detection (MMSE-SD) and also the match-filter (MF) bound. We show that the proposed demapper achieves optimal performance in the system operating-SNR region. Given the proposed near-optimal demapper, complex receiver designs that iterate between the detector and the decoder may not be worthwhile