Performance of non-orthogonal multiple access: analysis using compute-and-forward cooperative relaying in 5G networks

With the increasing demand for high-speed mobile transmissions for 5G networks, the cooperative relay-aided non-orthogonal multiple access (CR-NOMA) has been highly considered. An efficient and reliable CR-NOMA not only depends on the network mechanism but on the network coding strategy at the relay. Even though conventional strategies have broadly been studied, they suffer from noise accumulation and interference. Lately, the compute-and-forward (CpF) strategy has been identified as a potential technique to mitigate interference and enhance outage probability. In this study, the authors present a mathematical formulation to examine the performance of CpF on downlink CR-NOMA. In the proposed formulation, a two-stage downlink cooperative relay network is considered to obtain analytical closed-form expressions of outage probability and bit error rate. The outage probabilities and bit error rates of existing relaying strategies are compared regarding the network model. The theoretical analysis shows that CpF requires half the number of relays desirable in amplify-and-forward and decode-and-forward strategies to achieve a proportionate outage probability in CR-NOMA. Finally, we present results to show that at a lower signal-to-noise ratio, the integration of CpF and NOMA enhances error performance irrespective of the number of users.