Robust Secure UAV Communications With the Aid of Reconfigurable Intelligent Surfaces

This paper investigates a novel unmanned aerial vehicles (UAVs) secure communication system with the assistance of reconfigurable intelligent surfaces (RISs), where UAV and ground user communicate each other, while an eavesdropper tends to wiretap their information. Due limited capacity UAVs, RIS is applied further improve quality communication. The time division multiple access (TDMA) protocol for communications between user, namely, downlink (DL) uplink (UL) communications. In particular, channel state information (CSI) eavesdropping channels assumed be imperfect. We aim maximize average worst-case secrecy rate by robust joint design UAV’s trajectory, RIS’s passive beamforming, transmit power legitimate transmitters. However, it challenging solve UL/DL optimization problem due its non-convexity. Therefore, we develop efficient algorithm based on alternating (AO) technique. Specifically, formulated divided into three sub-problems, successive convex approximation (SCA), $\mathcal {S}$ -Procedure, semidefinite relaxation (SDR) are tackle these non-convex sub-problems. Numerical results demonstrate that proposed can considerably compared benchmark algorithms, also confirm robustness algorithm.