General relayless networks: representation of the capacity region

Using an information-spectrum approach, a limiting expression for the capacity region of a general network without relays combined of M transmitters observing K input messages, and L receivers, is found. This general setup accounts for the broadcast channel with common messages, the general interference channel, and the multiple access channel as special cases. It is demonstrated how the limiting expression can be used to yield a single-letter tight outer bound for the case of a two-user stationary memoryless degraded broadcast channel