Hardware and Interference Limited Cooperative CR-NOMA Networks Under Imperfect SIC and CSI

The conflation of cognitive radio (CR) and non-orthogonal multiple access (NOMA) concepts is a promising approach to fulfill the massive connectivity goals of future networks given the spectrum scarcity. Accordingly, this paper investigates the performance of a cooperative CR-NOMA network in the presence of system impairments and interference. Our analysis is involved with the derivation of the end-to-end outage probability for primary and secondary networks by accounting for channel state information (CSI), hardware imperfections, and residual interference caused by successive interference cancellation errors as well as coexisting primary/secondary users. Moreover, a mathematically tractable upper bound on spectral efficiency (SE) with its high-SNR approximations are derived. Besides, we propose an optimal power allocation scheme for CR-NOMA users to guarantee their outage and SE fairness. The numerical results validated by Monte Carlo simulations show that the CR-NOMA network provides a superior outage performance over orthogonal multiple access. Furthermore, the higher level of system imperfections leads to the performance degradation of the CR-NOMA networks. As imperfections become more severe, the CR-NOMA is observed to deliver relatively inferior outage and SE performance as compared to the perfect system scenario.