Secure 5G downlink NOMA cognitive relay network: joint the impact of imperfect spectrum sensing and outdated CSI

This article studies the interweave cognitive network with non-orthogonal multiple access (NOMA) principle under the appearance of one eavesdropper. The best relay selection method is used by considering two users of main channels at the same time. The general accuracy and asymptotic theory expressions of the system performance for two NOMA cognitive secondary users, e.g., outage probability and interception probability are derived, and they are also verified through Monte Carlo simulation. On this basis, we also investigate the effects of important system parameters such as the relay number, outdated channel side information (CSI), imperfect spectrum sensing, NOMA power allocation and imperfect successive interference cancellation (SIC) factor. It can be concluded that the outage diversity order for the NOMA users in the main channels can achieve as the relay number K when the perfect CSI appears. But the outage diversity order decreases to only one when the outdated CSI appears. However the intercept probability of the wiretap channel only got the diversity order as zero regardless of relay. And the imperfect spectrum sensing, imperfect SIC and NOMA power allocation can not affect the diversity order although they affect the system performance.