In wireless communication system, buildings or active eavesdroppers by illegal devices can block the communication link between the transmitter and receiver. Utilizing the flexible mobility of UAV and the intelligent controllable characteristic of IRS in wireless environment, this paper proposed a safe transmission scheme of physical layer for IRS assisted UAV to maximize the averaged secrecy rate of the legitimate link. The scheme firstly utilized block coordinate descent method to decompose the average secrecy rate maximization problem of the system into three sub-problems: UAV-IRS flight trajectory optimization, IRS phase shift optimization and transmission power optimization. And then, this scheme transformed each subproblem into a convex optimization subproblem by utilizing relaxation variables, phase alignment and successive convex approximation methods, respectively. Furthermore, this paper used the alternating optimization method to obtain the maximum average secrecy rate of the system. Numerical simulation results show that the transmission power of the source node, the flight position and altitude of UAV-IRS and the number of IRS reflective elements are the main factors for improving the averaged secrecy rate of the legitimate link. The proposed scheme can effectively improve the average secrecy rate of the system with good convergence by comparing with the other two benchmark schemes.

[2023-03-16] Accepted Paper /doc/2022.12.0827/v1

[2023-09-05] Printed Article /doc/2022.12.0827/v2