Faster-Than-Nyquist Signaling for MIMO Communications

Faster-than-Nyquist (FTN) signaling is a non-orthogonal transmission technique, which has the potential to provide significant spectral efficiency improvement. This paper studies the capacity of FTN signaling for both frequency flat and for frequency selective (FS) multiple-input multiple-output (MIMO) channels. As FTN is another reason of frequency selectivity, we find that precoding in time (or equivalently spectrum shaping in frequency) and waterfilling in spatial domain is capacity achieving for frequency flat MIMO channels with FTN. Meanwhile, waterfilling in both spatial domain and spectrum domain, followed by spectrum shaping, is capacity achieving for FS MIMO channels with FTN.