  The capacity of a network in which a multiple access channel (MAC) generates
interference to a single-user channel is studied. An achievable rate region
based on superposition coding and joint decoding is established for the
discrete case. If the interference is very strong, the capacity region is
obtained for both the discrete memoryless channel and the Gaussian channel. For
the strong interference case, the capacity region is established for the
discrete memoryless channel; for the Gaussian case, we attain a line segment on
the boundary of the capacity region. Moreover, the capacity region for the
Gaussian channel is identified for the case when one interference link being
strong, and the other being very strong. For a subclass of Gaussian channels
with mixed interference, a boundary point of the capacity region is determined.
Finally, for the Gaussian channel with weak interference, sum capacities are
obtained under various channel coefficient and power constraint conditions.
