Performance Analysis for Cooperative NOMA With Opportunistic Relay Selection

This paper focuses on an effective resource utilization scheme for the cooperative relay selection (RS) system with non-orthogonal multiple access (NOMA). In this work, an opportunistic suboptimal RS strategy is proposed that considers both of the users; as well as compared with the balanced and random RS schemes. For the proposed effective resource utilization scheme, the relay nodes are selected by incorporating a max-min selection manner to satisfy the quality of service (QoS) of the users; as well as the unselected relays continue receiving the signals transmitted from the base station (BS) for opportunities. In the meanwhile, the selected relay decodes the received superposed signals by employing the successive interference cancellation (SIC), and then reconstructs them into new NOMA signals, which will be forwarded to the users. Moreover, the closed-form expressions in terms of the sum rate (SR) and outage probability of the proposed transmission scheme are derived for independent Rayleigh fading channels. The provided simulation results show that the cooperative NOMA with the proposed effective RS scheme outperforms the existing works, and can also yield a significant performance gain over the orthogonal multiple access (OMA) scheme.