Secrecy performance analysis of UAV-based full-duplex two-way relay NOMA system

In this paper, we investigate the secrecy performance of an unmanned aerial vehicle (UAV)-based full-duplex (FD) two-way relay non-orthogonal multiple access (TWR-NOMA) system with two terrestrial users and an eavesdropper. To ensure secure communications, a UAV acts as an aerial relay station, which not only forwards confidential information to legitimate users but also keeps emitting the jamming signal to degrade the performance of any potential eavesdropper. The ergodic secrecy rate (ESR) and secrecy outage probability (SOP) of users and the system are successfully investigated under the assumption of imperfect successive interference and self-interference cancellation. In addition, to provide a better understanding of the secrecy performance, mathematical expressions of asymptotic ESR, secrecy slope, asymptotic SOP, and secrecy diversity order are also studied. Simulation results demonstrate that the FD TWR-NOMA system attains better secrecy performance than that of the FD TWR-NOMA system with a terrestrial relay, the FD TWR-NOMA system without jamming signal, as well as the half-duplex TWR-NOMA system. The secrecy performance of the system is significantly enhanced when UAVs approach the remote user. Furthermore, there is a reasonable power allocation value for jamming and legitimate signals on the UAV to improve secrecy performance.