Sum Rate Maximization in Cooperative Non-Orthogonal Multiple Access Based 5G Wireless Networks

This paper addresses a coordinated direct and relay transmission (CDRT) network with a downlink non-orthogonal multiple access (NOMA) over Rayleigh fading channels. A Coordinated Direct and Relay Transmission network consists of a base station (BS), two downlink users (one near user and one far user or cell edge user), and a relay. The near user will receive its intended message directly from the BS, whereas the far user or cell edge user will access and be supported by a full-duplex (FD) decode and forward (DF) relay to receive its message. Since the paper considers a NOMA network, the near user will be allocated with a lower power and the far user will be allocated with a higher power to ensure user fairness. The first section of this study discusses the system model, signal models and associated signal-to-interference plus noise ratios (SINRs). The joint optimisation problem for maximising the minimum sum rate is defined in the second half. Mathematical analysis is used to generate the joint power allocation factor and the results of both optimal and non-optimal conditions are plotted using Monte-Carlo simulations. Through various analyses, this paper establishes that using optimal power allocation factors can significantly improve the system's performance.