Joint Design of Trajectory and Near-Field Beamforming for STAR-RIS-Enabled ISAC

Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) can be assembled in the air-ground integrated sensing and communication (ISAC) to further enhance the performance. However, the near-field effect should be further considered with higher carrier frequency and increasing number of STAR-RIS elements. In this paper, we propose a STAR-RIS enabled air-ground near-field ISAC scheme, where the unmanned aerial vehicle (UAV) is deployed as a mobile base station and the semi-passive architecture is adopted to alleviate the severe path loss. We maximize the weighted sum rate to guarantee both the communication and sensing by modifying the beamforming vectors, the reflection/transmission matrices and the hovering location of UAV to match the near-field effect. To address this challenge, we first divide it into three subproblems, which are recast into convex ones by the semidefinite relaxation and successive convex approximation. Finally, we develop an alternate algorithm to iteratively solve them. Simulation results are shown to demonstrate the superiority and validity of the proposed scheme.