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 point-to-point single-input single-output (SISO) and multiple-input multiple-output (MIMO) channels. Although the capacity of SISO FTN was studied previously, due to some incomplete prerequisites, the exact capacity expression was not found. In this paper we resolve these issues for SISO FTN and generalize the result to MIMO FTN. We show that joint waterfilling in time and space is capacity achieving for MIMO FTN.