Active STAR-RIS Assisted Wireless Information and Power Transfer Systems

In this paper, we propose an active simultaneously transmitting and reflecting reconfigurable intelligent surface (aSTAR-RIS) assisted wireless information and power transfer system. The aSTAR-RIS is employed to not only assist the downlink simultaneous wireless information and power transfer for the energy harvesting at the wireless powered devices (WPDs) and information receiving at the information receiving devices (IRDs), but also aid the uplink wireless information transmission from the WPDs to the hybrid access point. Our objective is to maximize the uplink sum-rate, considering the quality-of-service requirements of IRDs, by optimizing the power allocation, time scheduling, transmission and reflection beamforming at the aSTAR-RIS. To solve this non-convex problem, we propose an effective alternating optimization algorithm with semidefinite relaxation and fractional programming techniques. Numerical results demonstrate that the proposed aSTAR-RIS scheme can achieve up to 640.68% performance gains compared to the passive STAR-RIS scheme in our settings.