RIS-UAV Enabled Worst-Case Downlink Secrecy Rate Maximization for Mobile Vehicles

This paper considers worst-case downlink secure communication from base station (BS) to mobile legitimate vehicle at the presence of an eavesdropper, where reconfigurable intelligent surface mounted unmanned ariel vehicle (RIS-UAV) acts as an ariel passive relay to assist the communication. Our aim is to achieve the maximum worst-case downlink secrecy rate via optimizing power allocation, RIS passive beamforming and UAV trajectory. The formulated optimization problem is non-convex and non-smoothness, which is quite hard to solve directly. Therefore, we divide the original optimization problem into three subproblems, power allocation optimization, passive beamforming optimization and UAV trajectory optimization, which can be solved by applying successive convex approximation (SCA),
$\mathcal {S}$
-Procedure and semidefinite relaxtion (SDR). Finally, we propose an alternating iterative optimization algorithm to get suboptimal solutions by alternately optimizing the three subproblems. Numerical simulations show the effectiveness of the proposed scheme against the other benchmarks.