Cooperative Dual Relay Overlay CR NOMA Network with Outdated CSI

In this paper, a dual relaying non-orthogonal multiple access (NOMA) scheme in an overlay cognitive radio network is proposed to improve the performance of a licensed primary receiver (PR) in the shadowing area as well as a NOMA secondary receiver (SR). Closed-form expressions for the outage probability of the PR and the SR are derived, which includes the unavoidable effect of the outdated channel state information (CSI) caused during the relay selection process. Analytical results showed the performance improvement of both of the PR and SR due to the spatial gain obtained from the proposed dual relays. It is also noticed that the less correlation between the actual and the outdated CSI incurred more performance degradation. Also, when the distance of relay-SR is shorter than relay-PR, it was noticed that the optimal power allocation to the PR was increased to maintain the minimum outage probability. The analytical outage probability expressions have been validated through simulations.