Performance Analysis of NOMA-Based AF Cooperative Overlay System With Imperfect CSI and SIC

This paper studies a new amplify-and-forward cooperative overlay cognitive radio (CR) non-orthogonal multiple access (AFCO-NOMA) system, where a primary network shares its license spectrum with a secondary network by using NOMA principles. An approximate closed-form expression for the outage probability of the proposed system is analyzed. Asymptotic expressions for the outage probability in high signal-to-noise ratio (SNR) regime of both secondary and primary destinations are derived assuming channel estimation error (CEE) and imperfect successive interference cancellation (SIC). Further, the optimal power allocation coefficients to maximize the system throughput for different target rates are determined to ensure priority to the primary user. The diversity order at the primary and secondary destinations are also derived. Moreover, the AFCO-NOMA system is compared with the OMA-based cooperative overlay system in terms of outage probability. The paper also studies the impact of various parameters such as power allocation coefficients, CEE, and detection threshold, on the outage performance of the proposed system. Monte Carlo simulations are used to confirm the correctness of the derived analytical results.