Performance Analysis for Configured Active RIS-Aided Communication Systems

The reconfigurable intelligent surface (RIS) is a crucial wireless channel control technology in 6G systems. Unlike traditional passive RIS (PRIS), active RIS (ARIS) can overcome the "multiplicative fading" effect. However, the configuration of the reflecting elements can significantly impact the system performance. In this paper, we focus on the ARIS equipped with uniform planar array (UPA) reflecting elements. We provide the ergodic achievable rate (EAR) for both unconfigured and configured ARIS system with closed-form. The effects of reflecting element area on the signal-to-noise ratio (SNR) are investigated, and a model selection scheme is proposed to determine whether to use ARIS or PRIS. Moreover, we analyze the average received power (ARP) and amplification power in ARIS. Based on the results of the analysis, a joint reflecting element area and quantity optimization scheme is proposed to improve system performance. The simulation results verify the accuracy of the analysis and highlight the superiority of the ARIS-assisted communication system.