  Non-orthogonal communications play an important role in future communication
architectures. In such scenarios, the received signal is corrupted by an
interfering signal which is typically cyclostationary in continuous-time. If
the period of interference is synchronized with the sampling period, the
sampled interference is a discrete-time (DT) cyclostationary process. However,
in the common interference scenario, the period of the interference is not
necessarily synchronized with the sampling period. In such cases, the DT
interference is an almost cyclostationary process. In this work we characterize
the capacity of channels in which the noise arises from a sampled
cyclostationary Gaussian process. For the case of synchronous sampling,
capacity can be obtained in closed form. When sampling is not synchronized with
the symbol rate of the interference, the resulting channel is not information
stable, thus classic tools are not applicable. Using information spectrum
methods, we prove that capacity can be obtained as the limit of a sequence of
capacities of channels with cyclostationary noise. Our results characterize the
effects of changes in the sampling rate and sampling time offset on the
capacity of the resulting DT channel. In particular, we demonstrate that minor
variations in the sampling period can substantially affect capacity.
