Joint Channel-Network Turbo Coding for the Non-Orthogonal Multiple Access Relay Channel

In this paper, we investigate the benefit of joint network-channel distributed coding for the multiple-access half-duplex relay channel. In contrast with previous work, the medium access is not orthogonal and the source-to-relay links are not error-free, which render the reality of wireless environments and notably complicate the problem. Indeed, due to the broadcast nature of wireless media, transmitted signals interfere at the relay and at the destination and form multiple-access channels. This entails the need of more sophisticated joint multiuser detection and decoding procedures. Moreover, improper (erroneous) distributed codes may result from unsuccessful decoding at the relay. This second issue is handled with selection relaying. We describe in detail the structure of the encoders, when and how JNC coding is performed, and the structure of the joint multiuser detectors and decoders. For a given spectral efficiency, we show through simulations that our approach provides substantial performance gains compared to conventional joint network-channel distributed coding for the orthogonal multiple-access half-duplex relay channel. Equivalently, for a targeted performance, our approach allows to transmit at higher rates.