  This paper is concerned with general interference channels characterized by a
sequence of transition (conditional) probabilities. We present a general
formula for the capacity region of the interference channel with two pairs of
users. The formula shows that the capacity region is the union of a family of
rectangles, where each rectangle is determined by a pair of spectral inf-mutual
information rates. Although the presented formula is usually difficult to
compute, it provides us useful insights into the interference channels. For
example, the formula suggests us that the simplest inner bounds (obtained by
treating the interference as noise) could be improved by taking into account
the structure of the interference processes. This is verified numerically by
computing the mutual information rates for Gaussian interference channels with
embedded convolutional codes.
