  Capacity computations are presented for Faster-Than-Nyquist (FTN) signaling
in the presence of interference from neighboring frequency bands. It is shown
that Shannon's sinc pulses maximize the spectral efficiency for a multi-access
channel, where spectral efficiency is defined as the sum rate in bits per
second per Hertz. Comparisons using root raised cosine pulses show that the
spectral efficiency decreases monotonically with the roll-off factor. At high
signal-to-noise ratio, these pulses have an additive gap to capacity that
increases monotonically with the roll-off factor.
