Weighted Sum-Rate Maximization for RIS-BD Assisted Multi-User Symbiotic Radio System Based on Parasitic Mode

Symbiotic radio (SR) garners significant attention for its potential to enhance spectrum efficiency and energy efficiency. This paper proposes a RIS-BD assisted multi-user symbiotic radio system based on parasitic mode, where primary users (PUs) and secondary users (SUs) achieve symmetric resource sharing through limited competition for transmission resources. To achieve the pareto optimum balancing system-wide transmission performance with user fairness, we address the optimization of the weighted sum-rate (WSR) under the condition of multiple constraints, including heterogeneous user transmission demands and the base station's maximum transmission power. To tackle this complex problem with coupled variables, we decompose it into three subproblems and design an alternating optimization-based algorithm to jointly optimize time slot access, user association, and active-passive beamforming. Simulation results demonstrate that, compared to conventional commensal mode, parasitic mode achieves more orderly resource sharing, supports high-quality transmission for differentiated users, and delivers significantly improved overall transmission performance.