Reactive Relay Selection Scheme for Underlay CR-NOMA Networks

Non-orthogonal multiple access (NOMA) is recognized as a competing technology to address the challenges of 5th generation (5G) future wireless networks. In this context, Cognitive Radio (CR)-NOMA, a blend of CR and NOMA, holds the promise of throughput enhancement while protecting the privilege of primary users (PUs). This paper proposes a reactive relay scheme for cooperative CR-NOMA networks to select the best relay from potential Decode-and-Forward (DF) cognitive relay network which enables communication between a source and two destination users in the absence of direct path. The relay network operates in an underlay environment and aims to maximize the second hop SNR for the destination user with weak channel condition. For performance analysis, outage probability has been derived in closed form and the results have been verified through simulations.