A Frequency-Domain EP-based Receiver for Faster-Than-Nyquist Signaling

This paper proposes a new Frequency-Domain (FD) receiver based on Expectation Propagation (EP) for Faster-Than-Nyquist (FTN) signaling. Our system model is based on a circular convolution of the shaping filter leading to a Circular FTN (CFTN) waveform allowing a FD process at reception without cyclic prefix. We solve a Maximum A Posteriori criterion using EP combined with an original Gaussian family yielding a low-complexity FD Minimum Mean-Square Error (MMSE) equalizer combined with a Constellation Matcher in charge of realigning the symbol estimates with respect to the constellation. This new FD-EP receiver for FTN signaling is compared to RS-BCJR and M*-BCJR receivers as well as the MMSE equalizer. The proposed FD-EP receiver is shown to perform slightly better than MMSE at 1.5 bits/s/Hz, and represents a low complexity alternative compared to RS-BCJR or M*-BCJR. Furthermore, while existing receivers are not able to handle higher spectral efficiencies, our FD-EP allows FTN signaling to almost achieve its matched-filter bound at 3 bits/s/Hz with channel coding.