Discrete Time Faster-Than-Nyquist Signalling

Increasing the symbol rate up to 25% faster than the Nyquist criteria for a digital communications system with QPSK modulation with an AWGN channel does not significantly increase the bit error rate or required transmission bandwidth. This so-called Faster-than-Nyquist (FTN) signalling has not been used in commercially deployed communications systems since the previously proposed implementation schemes required large receiver complexity. This paper introduces a reformulation of FTN signalling in terms of a non-square matrix multiplied by a sample vector of modulated QPSK symbols. It is shown that with this formulation the receiver complexity to detect the transmitted data for an AWGN channel is well within the complexity bounds for standard digital communication systems. This formulation enables an analysis of FTN signalling directly comparing it to standard higher order modulation and data coding techniques.