Secrecy Outage Performance Analysis for Uplink CR-NOMA Systems With Hybrid SIC

In the uplink cognitive radio-inspired nonorthogonal multiple access (CR-NOMA) systems, the successive interference cancellation (SIC), and power control (PC) schemes were designed to enhance the outage performance but they lack the capability of protecting signals from being eavesdropped. This work investigates the secrecy performance of uplink CR-NOMA systems with the hybrid SIC and PC (HSIC-PC) scheme in the presence of a passive eavesdropper. Furthermore, through transmitting artificial noise (AN), a new scheme is proposed to improve the security of the cognitive user with HSIC-PC without deteriorating the primary user's quality of service. Specifically, the primary and secondary users transmit AN cooperatively to enhance the security of the secondary user. The secrecy performance of the proposed scheme is analyzed based on the relationship between the maximum interference power that the primary user can tolerate and the secondary user's channel gain. The analytical expressions for the secrecy outage probability (SOP) are derived, and the effect of parameters on the SOP is discussed. We also derive the analytical expressions of the asymptotic SOP in the high-power region to obtain further insights. Monte Carlo simulation results are performed to verify the analytical results. The results demonstrate that the proposed scheme performs better than the benchmarks.