Optimization of Aerial UAV Assisted Secure Wireless Communication System Based on Intelligent Reflecting Surface

Reconfigurable Intelligence Surface (RIS) can improve the surrounding bad propagation environment in a controllable way, which is considered as a potential technology in future wireless communication. At the same time, Unmanned Aerial Vehicle (UAV) has also been widely used in the field of wireless communication due to its mobility, flexibility, easy deployment and low cost. With the increasing complexity of the communication environment, the transmitted confidential information can be easily intercepted by potential eavesdroppers. To deal with this dilemma, an RIS-assisted UAV secure wireless communication system was studied, which consisted of a base station (Alice), a UAV, a RIS, a passive eavesdropper (Eve), and a User. The high mobility of the UAV and the adjustable ability of the RIS were used to prevent potential eavesdroppers. The proposed system maximizes the average secrecy rate by jointly optimizing the power allocation, RIS phase shift, and UAV trajectory from a physical layer security perspective. Due to the non-convexity of this problem, this scheme decomposes this problem into three sub-problems. Firstly, the lower bounds of the power allocation and the UAV trajectory were found by applying the first-order Taylor expansion respectively, and then the successive Convex Approximation (SCA) method was used to further solve the problem iteratively. Finally, the closed-form solution of the RIS phase shift was derived. The final data results show that the proposed scheme has low computational complexity, and the average secrecy rate of the system is significantly improved compared with the benchmark scheme.