IRS-Based Secure UAV-Assisted Transmission with Location and Phase Shifting Optimization

An intelligent reflection surface (IRS) can actively design the propagation channel via designing the phase shifting matrix to provide more secure transmission. Being mounted on the unmanned aerial vehicle (UAV), IRS is able to further leverage the mobility and flexible advantages of UAV. In this paper, we investigate the secure transmission of an IRS-assisted UAV network against an eavesdropper, where the IRS is mounted on the UAV. The secrecy rate is maximized by jointly optimizing the phase shifting matrix and the hovering location of IRS. Owing to the non-convexity of the optimized problem, we decompose it to two subproblems and alternatively solve them to derive the optimal UAV location and phase shifting matrix. First, we adopt the first-order Taylor expansion to change the non-convex UAV location optimization subproblem into a mathematical solvable convex version, and solve it through successive convex approximation (SCA) with a given phase shifting matrix. Then, with a given UAV hovering location, the phase shifting matrix is optimized via semidefinite relaxation (SDR) and SCA. Finally, simulation results are provided to evaluate the effectiveness of our proposed secure IRS-assisted wireless transmission scheme.