Secure Transmission Design for STAR-RIS-Aided UAV networks with imperfect CSI

This paper investigates a secure communication network integrating a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS), with an unmanned aerial vehicle-assisted base station (UAV-BS). In particular, the trajectory and beamforming of the UAV-BS, as well as the coefficients matrices of the STAR-RIS, are jointly optimized to maximize the secrecy rate for the secure user. Furthermore, the coupling of variables in the original problem, along with the presence of bounded channel state information (CSI) errors, renders the problem particularly challenging to solve. Finally, a suboptimal solution to the original problem can be obtained using successive convex approximation (SCA) and alternating optimization (AO). The performance improvement is approximately $41 \%$ compared to the case with random phases and $15 \%$ over the case without trajectory optimization, as shown in the simulation results.