Integrated Sensing and Communication With Symbiotic Radio and RIS-Assisted Backscatter

To meet the demand for spectrum-efficient solutions in next-generation wireless communication, symbiotic radio (SR) and integrated sensing and communication (ISAC) systems are gaining traction. This letter introduces an innovative approach that integrates ISAC with SR. The proposed system leverages an SR, assisted by a reconfigurable intelligent surface (RIS), to enhance primary communication while enabling secondary data transmission through backscattering. Furthermore, a full-duplex base station (FD-BS) performs target sensing. The objective is to maximize the sum rate over the transmit/receive beamformers and RIS phase shifts while meeting minimum quality of service (QoS) requirements for both RIS data decoding and target sensing. To tackle this non-convex problem, we developed a block coordinate descent (BCD) algorithm using semi-definite relaxation (SDR), successive convex approximation (SCA), and sum rate lower bound derivation to transform it into a convex problem. Extensive simulations demonstrate that our design outperforms benchmarks by 50%.