Outage probability of non-orthogonal multiple access schemes with partial relay selection

In this paper, the outage performance of nonorthogonal multiple access (NOMA) schemes in amplify-and-forward (AF) relay systems with partial relay selection is investigated. To this end, closed-form expressions for the outage probabilities at two users are derived, based on which an asymptotic analysis at high signal-to-noise ratio (SNR) is carried out to provide additional insights into the system performance. In particular, the diversity order at each user is explicitly obtained. Numerical results illustrate the impact of relay selection on the performance of the considered NOMA scheme. Also, computer simulation results are presented to validate the accuracy of the attained analytical results.