STAR-RIS Assisted Uplink ISAC With Monostatic Sensing

This letter designs an uplink integrated sensing and communication (ISAC) framework leveraging a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) for full-service coverage. The system supports a sensing target (ST) and a communication user (CU) in the transmission and reflection regions, respectively, through energy splitting (ES) in each time slot. To maximize the communication rate while ensuring the sensing requirement, we develop a low-complexity STAR-RIS beamforming solution with a common ES factor, adaptively selecting phase vectors for either channel power maximization or interference mitigation. This solution is further integrated into a nonlinear optimization (NLO) algorithm with nonidentical ES factors and a weighted bipartite matching algorithm for multiple ST-CU pairs. Simulation results confirm the superiority of the ES-based approach over time-switching and demonstrate the performance gains achieved by the proposed NLO and matching algorithms.