Performance Analysis of Relay Selection in Cooperative NOMA Networks

In this letter, we investigate the relay selection (RS) problem in cooperative non-orthogonal multiple access networks, where one base station communicates with two paired users with different priorities through multiple relays. A novel two-stage RS scheme is proposed to satisfy the quality-of-service requirements of both users by considering the employment of the instantaneous channel state information in the user ordering. We derive a closed-form expression of the outage probability and obtain the diversity order for the proposed scheme. The simulation results show that the proposed RS scheme achieves a lower outage probability than the existing RS schemes.