Outage Performance of Downlink Coordinated Direct and Relay Transmission with NOMA over Nakagami-m Fading Channels

In this paper, the outage performance of nonorthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) system is analyzed. Exact and asymptotic outage probabilities of both cell-center user (CCU) and celledge user (CEU) are derived. Our analysis is conducted based on the independent but not identically distributed (i.n.i.d) Nakagami-m fading model and the fixed-gain amplify-and-forward relaying protocol, and hence the result is applicable to general relay-aided communications, where only statistical channel state information is available. Monte Carlo simulation results are provided to verify the accuracy of the derived analytical expressions with comparison to conventional orthogonal multiple access (OMA) counterpart as well as the decode-and-forward NOMA-based CDRT, demonstrating the superiority of the proposed scheme.