Physical Layer Security for UAV-Based Full-Duplex Relay NOMA System

In this paper, we investigate the secrecy performance of an unmanned aerial vehicle (UAV)-based full-duplex (FD) relay non-orthogonal multiple access (NOMA) system over the Nakagami-m fading channel. A mobile UAV acts as an aerial relay station (ARS) to assist transmission from a source (S) to two users (D1, D2), in the presence of a ground internal eavesdropper (E). To ensure secure communication at users, we propose to insert an artificial noise (AN) component into the transmit signal at the full-duplex ARS (FD-ARS) with power allocated using the NOMA protocol. We analyze the secrecy outage performance of the system and the users and obtain the approximate secrecy outage probability (SOP) in various propagation environments, i.e., the dense urban, urban and suburban environments. It is demonstrated that using AN allows the users to achieve the secrecy over the signal-to-noise ratio. Also, the system achieves the best secrecy performance when the FD-ARS is closer to the further user while losing the secrecy when closer to the source. The FD-ARS system is shown to achieve better secrecy performance than the respective half-duplex (HD) ARS system.