Ergodic Capacity Analysis of Uplink Cooperative NOMA Network Based on Statistical Channel State Information

Non-orthogonal multiple access (NOMA) is a promising radio access technique for the fifth generation cellular networks as it offers a set of desirable benefits, such as greater spectrum efficiency compared to well-known orthogonal multiple access techniques. This paper primarily focuses on power-domain uplink NOMA which implements superposition coding at the transmitting nodes and successive interference cancellation at the receiving nodes. Specifically, in this paper we investigate the scenario of three users communicate with the base station simultaneously with the helping from a half-duplex and decode-and-forward relay under frequency selective multipath fading channels. In all existing publications on this topic, the power allocation at the transmitting nodes is decided based on the perfect channel state information (CSI) whereas in our work it’s decided based on statistical CSI. Under Rayleigh fading channels, we derive the exact and upper bound of the ergodic rates and show the boundary of the achievable ergodic rate regions for the transmitted symbols at the relay and base station. We also investigate the effect of relay location on the overall system performance and the importance of carefully choosing the power allocation factors. Simulation results show that the proper selection of the power allocation factors, and the relay location play jointly a decisive role regarding the performance of uplink NOMA. Moreover, NOMA always perform better than orthogonal multiple access.