Performance of Adaptive OMA/Cooperative-NOMA Scheme With User Selection

For downlink signaling, we propose a simple scheme to select one of N near-users (NUs) and F far-users (FUs) and switch between orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA) signaling so as to improve the performance of the FUs significantly, while ensuring that the performance of NUs does not degrade below that achieved by OMA alone. We derive a closed-form expression for outage probability of the FU. Assuming that the selected near-user employs successive interference cancellation (SIC) and relays the FU symbols when NOMA is employed, we show that the FUs achieve a diversity of N + F when optimal combining is performed, while NUs achieve a diversity of N.