K-user interference channels: General outer bound and sum-capacity for certain Gaussian channels

This paper derives an outer bound on the capacity region of a general memoryless interference channel with an arbitrary number of users. The derived bound is the first known outer bound region valid for any memoryless channel besides the cut-set bound, which is loose even in the two-user case. In Gaussian noise, classes of channels for which the proposed bound gives the sum-rate capacity are identified, including degraded channels and a class of Z-channels.