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

This paper investigates the secrecy performance of an unmanned aerial vehicle (UAV)-based cognitive relay non-orthogonal multiple access system and friendly jamming. Specifically, by utilizing the radio spectrum licensed to primary users, a UAV serves as an aerial relay to facilitate signal transmission from a secondary ground source to secondary ground users. To prevent the relayed signals from being intercepted by secondary ground eavesdroppers, a second UAV is deployed to transmit friendly jamming signals. The average minimum secrecy rate (AMSR) of the secondary users is maximized through the joint optimization of UAVs’ flight trajectories and the transmit powers of the system nodes, while explicitly accounting for uncertainties in the eavesdroppers’ locations, the adverse effects of friendly jamming on both secondary and primary users, and the imperfections in successive interference cancellation (SIC) at both the UAV and secondary users. A block coordinate descent (BCD) technique is employed to tackle the resulting non-convex AMSR maximization problem and obtain an efficient solution. Simulation results at the 70-$th$ time slot demonstrate that the proposed system achieves approximately 83.3% higher AMSR compared to a system without friendly jamming, around 1000% improvement over a non-optimized, non-jamming system, and also outperforms other benchmark schemes.