Resource Allocation Design for RIS-Enhanced Backscatter Wireless-Powered Symbiotic Networks

The integration of simultaneous wireless information and power transfer (SWIPT) with backscatter and reconfigurable intelligent surface (RIS)-aided communication provides a promising paradigm to reduce the energy consumption. In this paper, we propose a RIS-enhanced hybrid backscatter and wireless-powered transmission scheme in the symbiotic radio network. Under this setting, we formulate the throughput maximization problem by jointly optimizing the transmit beamforming, passive beamforming, transmit power, backscatter coefficient, and slot allocation. Due to the coupled variables, the formulated optimization is non-convex. To solve it, an iterative algorithm is developed to decompose it into multiple subproblems. Specifically, we obtain the closed-form solutions for those variables in the single-user system. For the multi-user system, we solve the problem via the second-order cone programming (SOCP) and semi-definite programming (SDP) methods. Numerical simulations show that the proposed hybrid transmission scheme can effectively improve the network throughput.