Secrecy Performance of UAV-Assisted Underlay Cognitive STBC-NOMA Networks Under Non-Identical Nakagami-m Fading Channels

The spectrum efficiency of wireless communication networks can be enhanced by incorporating non-orthogonal multiple access (NOMA) and cognitive radio techniques, while unmanned aerial vehicles (UAVs) are a rapid and flexible entity for enhancing coverage performance. This paper considers UAV assisted underlay cognitive network (UCN) with space-time block coding aided NOMA (STBC-NOMA) approach. Herein, the UAV acts as a decode and forward relay to extend the coverage area of a secondary network. In particular, the UAV receives the signals from the secondary transmitter and then retransmits the decoded information to the users using the STBC-NOMA approach. We derive the secrecy outage probability (SOP) and ergodic secrecy rate (ESR) expressions for the secondary users in the presence of an eavesdropper in the network under nonidentical Nakagami-m fading channels. Further, we compare the performance of UAV-assisted UCN using the STBC-NOMA scheme against the NOMA and OMA schemes, which proves the superiority of the STBC-NOMA scheme over the NOMA and OMA schemes in terms of ESR and SOP. Moreover, we provide Monte Carlo simulations to verify the analytical findings.