Secrecy performance optimization for UAV-based relay NOMA systems with friendly jamming

Friendly jamming and relay are effective schemes in physical layer security (PLS) for enhancing security in wireless communication. By deploying unmanned aerial vehicle (UAV)-assisted Non-Orthogonal Multiple Access (NOMA) transmission can extend coverage and enhancing spectrum efficiency. This paper studies the physical layer security of an UAV-based relay NOMA system, consisting of a source, multiple users, and an eavesdropper. To enhance secrecy performance, an additional UAV is employed to transmit jamming signals to the eavesdropper. Moreover, for a more practical approach, we also consider the imperfect collaboration between the jammer device and the legitimate user. The minimum average secrecy rate (MASR) of the users is maximized, assuming that the eavesdropper is capable of intercepting signals both from the source and from the relay UAV. An efficient iterative algorithm is proposed to solve the MASR maximum problem by optimizing UAV trajectories, transmit power, and power allocation coefficients. Simulation results demonstrate that the proposed system achieves 238% better MASR than the system without friendly jamming signals and 633% better than the non-optimal system. In addition, the ability to decode the received signal using successive interference cancellation also significantly affects the MASR of users in the system.