Double reconfigurable intelligent surface-assisted wireless communication system for energy efficiency improvement over weibull fading channels

In this paper, we propose a double reconfigurable intelligent surface (RIS)-assisted wireless communication system to improve energy efficiency when a direct link from source to destination is obstructed. First, we model a single RIS-assisted wireless communication system by deploying RIS midway between the source and destination link over the Weibull fading channel. Next, we consider the double-RIS system, in which RIS-1 (R-1) and RIS-2 (R-2) are near the source and destination respectively, with overall reflecting elements in the system equal to the single-RIS system. For both systems, we derive the closed-form expressions for the bounds (lower and upper) of ergodic capacity and exact closed-form expressions for outage probability. The accuracy of the presented theoretical framework is validated through Monte-Carlo simulations. From the comparison, we found that the double-RIS system surpasses the S-RIS system in terms of ergodic capacity and outage probability. Finally, we provide the ergodic capacity and energy efficiency analysis of both systems as a function of spectral efficiency by varying the position of RISs and notice that the double-RIS system with R-1 and R-2 near to source and destination is more energy efficient than the S-RIS system.