Relay Selection Methods for the Uplink NOMA System

To further improve the transmission reliability of the uplink non-orthogonal multiple access (NOMA) system, based on decode-and-forward (DF) protocol, we propose two relay selection (RS) schemes: React RS (RRS) and successive interference cancellation (SIC) RS (SRS). Firstly, fully considering the decoding situation at the relay, we analyze the closed-form results of the two RS schemes in terms of exact outage performance under the perfect and imperfect SIC technologies, which can be derived that both schemes have the same outage performance. Then, asymptotic results are given in the high signal-to-noise ratio (SNR) region and the best power allocation coefficient is analyzed. Finally, the correctness of the theoretical derivation is verified by simulation. The results show that the proposed schemes are superior and have the best interrupt performance when compared to other RS schemes.