  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 multiple-input multiple-output
(MIMO) channels. We show that precoding in time and waterfilling in space is
capacity achieving for frequency-flat MIMO FTN. For frequency-selective fading,
joint waterfilling in time, space and frequency is required.
