A Hybrid ARQ Scheme for Faster than Nyquist Signaling with Iterative Frequency-Domain Detection

FTN (Faster Than Nyquist) signaling allows capacity gains but requires substantially complex equalization schemes, even for an ideal AWGN (Additive White Gaussian Noise) channel. Extending conventional FTN receivers for severely time- dispersive channels is not an option, since the receiver complexity becomes prohibitively high. In this paper we address the design of a receiver for FTN signaling over severely time-dispersive channels. To cope with the severe ISI (Inter-Symbol Interference) associated to the combined effects of FTN signaling and the time-dispersive channel we consider an iterative FDE scheme (Frequency-Domain Equalization) combined with a HARQ (Hybrid Automatic Repeat reQuest) especially designed taking into account the characteristics of FTN signals. We also present a simple, yet accurate model for the performance evaluation, considering multiple retransmissions per block. Our performance results show that we can have significant throughput gains, while maintaining essentially the receiver complexity of conventional, Nyquist-rate signaling schemes, even for severely time-dispersive channels.