Reactive relay selection strategy for NOMA systems

Non-Orthogonal Multiple Access is considered to be a promising candidate for 5G multiple access schemes due to its superior spectral efficiency,higher throughput,and lower transmission delay.To improve the outage performance of non-orthogonal cooperative systems,non-orthogonal multiple access system is studied in the downlink scenario.First,a distributed reactive relay selection scheme based on the decode-and-forward protocol is designed.Then,the closed-form results of the exact outage performance and the approximate results in a high signal-to-noise ratio of the two users are derived.Finally,the effects of the relay position,channel quality and relay number on the outage probability of the system are analyzed by simulation.At the same time,compared with the partial relay selection strategy,the performance advantage of the proposed reactive relay selection strategy is verified.