Energy Efficient Optimization Scheme for Wireless Powered Active RIS in Downlink System

This letter proposes an active reconfigurable intelligent surface (RIS) optimization scheme for a downlink communication system. This scheme works in a time switching downlink framework, which is divided into two phases: a wireless power transfer (WPT) phase and a wireless information transmission (WIT) phase. The active RIS harvests energy from the base station in the WPT phase and reflects the amplified signal in the WIT phase. To improve the energy efficiency of this framework, we further formulate an optimization problem to jointly configure the phase shift of the RIS and allocate the time and power of these two phases. A two-step alternative optimization scheme is proposed to solve this problem near-optimally using convex optimization techniques. Experimental results show that the proposed scheme performs better than the comparison scheme.