Coding Techniques for Primitive Relay Channels

We give a comprehensive discussion on coding techniques for the primitive relay channel, in which the channel input X is transmitted to the relay Y1 and the ultimate receiver Y over a channel p(y, y1|x) and the relay can facilitate the communication between the transmitter and the receiver by sending some information to the receiver over a separate noiseless link of capacity R0. In particular, we compare three known coding schemes, “decode-and-forward,” “compress-andforward,” and “hash-and-forward,” clarify their limitations, and explore further extensions. Possible unification of these coding schemes is also discussed, as well as a few open problems reflecting major difficulties in proving optimality.