Capacity theorems for the relay channel

The paper considers capacity theorems for the relay channel. A relay channel consists of an input, a relay output, a channel output, and a relay sender; the expression for the dependence of the received symbols on the inputs is given, and the channel is assumed to be memoryless. Capacity theorems are proved for the degraded relay channel, the reversely degraded relay channel, an arbitrary relay channel with feedback, and a general relay channel. Superposition block Markov encoding is used to show achievability of capacity of the channel, and converses are established. The capacities of the Gaussian relay channel and certain discrete relay channels are evaluated, and an achievable lower bound to the capacity of the general relay channel is established.