Energy Efficiency Optimization for Mutual-Coupling-Aware Wireless Communication System based on RIS-enhanced SWIPT

The widespread deployment of the Internet Things (IoT) is promoting interest in simultaneous wireless information and power transfer (SWIPT), performance which can be further improved by employing a reconfigurable intelligent surface (RIS). In this paper, we propose novel RIS-enhanced SWIPT system built on an electromagnetic-compliant framework. mutual-coupling effects whole are presented explicitly. Moreover, reconfigurability RIS no longer expressed reflection-coefficient matrix but impedances tunable circuit. For comparison, both no-coupling coupling-awareness cases discussed. particular, energy efficiency (EE) maximized cooperatively optimizing impedance parameters elements as well active beamforming vectors at base station (BS). case, considered problem split into several sub-problems solved alternatively due to its nonconvexity. Firstly, it transformed more solvable form applying Neuman series approximation, resolved iteratively. Then alternative optimization (AO) framework semi-definite relaxation (SDR), successive convex approximation (SCA), Dinkelbach’s algorithm applied solve each sub-problem decomposed from it. Owning similarity between two cases, one viewed reduced coupling case thus through similar approach. Numerical results reveal influence EE, especially with closely spaced elements. addition, physical beam designs demonstrate how assists various reflecting states different conditions.