Performance analysis of the cooperative uplink-downlink NOMA and OMA scheme in cognitive radio network with max-min relay selection strategy

In this paper, we study the application of the non orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) scheme to cooperative cognitive radio network. We investigate a two phase cooperative NOMA where a secondary transmitter can transmit simultaneously with a primary transmitter via the uplink NOMA. We assign a larger power factor to the primary user (PU) to satisfy the quality of service (QoS) of the PU in overlay cognitive radio network. We purpose the cooperative NOMA scheme in which the one relay is selected between K relays, based on max-min relay selection strategy, to improve the performance of the PU and the secondary users (SUs). We investigate the outage probabilities of PU and the SUs with residual interference due to the imperfect successive interference cancelation (SIC). Then, the outage probabilities and diversity orders with perfect SIC for fixed power allocation and cognitive radio power allocation are derived in the closed form. We also calculate the outage probability and diversity order for the OMA scheme, as a benchmark. Finally, the simulation results are presented to confirm the accuracy of the theoretical results.