Weighted Sum Rate Maximization for RIS-Mounted UAV-Aided Cell-Free ISAC Systems

This paper considers the cell-free integrated sensing and communication (CF-ISAC) networks utilizing reconfigurable intelligent surface (RIS)-mounted uncrewed aerial vehicles (UAVs). We aim to maximize the sum of weighted sum rate within the whole ISAC period by jointly optimizing access points (APs)' transmit beamformings, RISs' phase shifts, user-RIS association, and UAVs' locations. To deal with a highly complex non-convex optimization problem, we propose an alternating optimization solution by decomposing the original problem into three subproblems. In particular, for optimizing APs' transmit beamformings, RISs' phase shifts, and user-RIS association, we convert the log-sum problem into a quadratically constrained quadratic programming problem using the Lagrangian dual principle and multi-ratio fractional programming. For optimizing UAVs' locations, the successive convex approximation technique is used to transform it into a convex problem. Simulation results highlight the considerable performance advantage of the proposed network compared to benchmark schemes employing fixed RISs, without RIS-mounted UAVs (URISs), and collocated network with URISs.