Secrecy and Rate Optimization in Symbiotic Star-Ris-Aided D2d Communication

With the upcoming 6G networks, integrating advanced access techniques, resource-allocation schemes, and causal artificial intelligence capabilities plays an important role in addressing the growing demands for efficient utilization of communication resources. Symbiotic Communication allows resources to be efficiently allocated by establishing a symbiotic relationship between primary and secondary networks. Hence, in this paper, we consider a resource-service mutualism symbiotic relationship between a secure primary network and a simultaneously transmitting and reflecting (STAR) reconfigurable intelligent surface (RIS) aided device-to-device (D2D) secondary transmission. This relationship enables the secondary D2D network to share its STAR-RIS to help enhance the primary transmission secrecy rate. In exchange, the secondary D2D transmission gains access to the communication resources allocated to the primary transmission. We propose a multiobjective energy-splitting (ES) STAR-RIS optimization problem, simultaneously maximizing the primary transmission secrecy rate and the D2D sum rate. We propose a suboptimal block coordinate descent solution algorithm and evaluate the model through numerical analysis. The numerical results validate the effectiveness of the proposed model in improving the primary secrecy rate while granting a better sum rate for the secondary D2D transmission.