Joint User and Relay Selection for Cooperative NOMA Networks

Abstract

This paper investigates the joint user and relay selection algorithm for cooperative non-orthogonal multiple access (NOMA) networks, where multiple users transmit messages to two destinations by utilizing multiple amplify-and-forward (AF) relays. To improve the outage performance of system, an optimal selection criterion is proposed at the user-relay pairs. We derive the closed-form analytical expressions on the outage probability, as well as the asymptotic expressions for large transmission power. Based on the derived analytical expressions, the effect of the number of relays and the target data rate on the outage performance are revealed. Results indicate that when the target data rate becomes small enough, the diversity order of the outage probability equals to the number of relays, while the target data rate grows without bound, the outage probability achieves one.