Performance Analysis for STAR-RIS Assisted SWIPT System over Rayleigh Fading Channel

In this paper, the performance of a multiple-insingle-output (MISO) simultaneous wireless information and power transfer (SWIPT) system assisted by simultaneous transmitting and reflecting reconfigurable intelligent surface (STARRIS) under fading channel is studied. Firstly, the joint BS active beamforming and STAR-RIS passive beamforming are discussed. Based on that and using the Gamma approximation method, the statistical characteristics of the equivalent cascaded channels for BS-IR and BS-ER assisted by STAR-RIS are analyzed and derived, including the first-order and second-order moments, as well as the distribution function (CDF) and probability density function (PDF). Furthermore, we define and derive the rate outage probability of IR and power outage probability of ER and their approximate expressions at high SNR. Finally, the theoretical analysis results are verified by numerical simulations, and it is confirmed that the number of STAR-RIS units has positive effects on improving the system outage performance.