Performance analysis of cooperative relaying systems with power-domain non-orthogonal multiple access

Non-orthogonal multiple access (NOMA) is one of the promising radio access techniques in 5G communication networks. In this paper, a cooperative NOMA relaying scheme with two-phase superposition coding is proposed to enhance the performance of NOMA relaying systems. In the proposed scheme, the source simultaneously transmits two symbols using superposition coding in the first time slot, while the relay decodes the symbols by employing the successive interference cancellation. In the second time slot, the relay forwards the two symbols with a new superposition coding to the destination, which jointly decodes them by employing maximum-ratio combining technology over the received signals from both the source and relay. In order to reveal the benefits of the proposed scheme, its achieved ergodic sum rate, outage probability, and throughput are analyzed with imperfect channel state information taken into account. Our examination shows that the proposed scheme can significantly outperform existing schemes in terms of achieving a higher ergodic sum rate, a lower outage probability, or higher throughput at the cost of a slightly increased complexity.