Secure UAV Relay Communication via Power Allocation and Trajectory Planning

Benefiting from high mobility and maneuverability, unmanned aerial vehicle (UAV) can be flexibly deployed in various wireless networks to improve coverage and connectivity. In this article, the system with a UAV, which relays confidential messages between a couple of unconnected ground nodes with the presence of an eavesdropper is considered. In order to maximize the overall end-to-end secure throughput in a given time period, the joint power allocation and trajectory planning are investigated. The formulated optimization problem is nonconvex, which is difficult to obtain the optimal solution with acceptable complexity. Therefore, we propose an iterative algorithm to achieve a suboptimal solution approximately. In the proposed approach, the joint optimization problem is firstly divided into two subproblems, i.e., the power allocation subproblem and the trajectory planning subproblem. The power is optimized by using the method of successive convex approximation with fixed trajectory, and the trajectory was optimized by successive convex approximation with fixed transmit power. Finally, the power and trajectory are optimized alternately. Since the two subproblems are approximated as convex problems, they can be solved efficiently with acceptable complexity. The simulation results show that remarkable gain in terms of secure throughput can be achieved by the proposed joint optimization algorithm.