A New Optimal Relay Selection Strategy for the Coincident Multi-User Access

Non-orthogonal multiple access (NOMA) has been recognized as one of the promising multiple access technologies to provide higher spectral efficiency and system capacity to address several challenges in the fifth generation (5G) wireless systems. Telemedicine in the process of being greatly advanced by the high-reliable communication in future 5G wireless systems. This paper proposed a novel optimal relay selection (RS) strategy for the cooperative NOMA to achieve the minimum outage probability, which means that the number of retransmissions in hybrid automatic repeat request (HARQ) is decreased and hence indirectly reduce the communication latency. Small latency ensures the validity of medical data, thereby improving the quality of service (QoS) in medical communications. In addition, compared to another optimal relay selection, namely two-stage strategy, the proposed enhanced max-min RS has a lower computational complexity and lower storage overhead. The proposed enhanced max-min RS strategy can reduce almost 43% storage overhead and 95% latency caused by selection strategy in the cooperative RS-NOMA system used for wireless medical communications.