Performance Analysis of Cooperative NOMA Systems in Cognitive Radio Network

In the existing underlay cognitive radio literature, the outage performance of the secondary network is severely degraded due to the interference from the primary network and the interference threshold limit of the primary receiver to the secondary transmit power. In this paper, a cooperative Non-orthogonal multiple access (NOMA) based cognitive radio network is proposed, where multiple half-duplex (HD) relays are employed to extend the coverage area of the network. This proposed scheme allows the secondary transmitter (ST) to access the licensed spectrum but not while primary transmitter (PT) is transmitting. Hence, the secondary network can eliminate the PT interference at the relay node, which improves the outage performance of the secondary network. In addition, the closed-form expression for outage probability and ergodic rate for both primary and secondary network are derived. Through numerical results, it is shown that the performance of the secondary network is improved significantly. Furthermore, Monte Carlo simulation results are presented to validate the derived mathematical framework.