Relaying functions for the multiple access relay channel

In this paper, we investigate the benefit of joint network-channel (JNC) distributed coding for the multiple-access half-duplex relay channel. In contrast with previous work, the orthogonality of the medium access is partially relaxed and the source-to-relay links are not error-free. More specifically, the sources are allowed to transmit simultaneously during the listening phase of the relay, while during the relay transmission phase, they are constrained to remain silent. The resulting collisions entail the need of more sophisticated joint multiuser detection and decoding procedures. Moreover, unsuccessful decoding at the relay may result from error propagation to the destination. This second issue is handled with different (digital or analog) relaying functions. We describe in detail the structure of the encoders, JNC coding, and the joint multiuser receiver structure. Furthermore, for the proposed protocol, we compare different relaying functions, and show through simulations, the benefit of the chosen cooperation introduced by the relay.