RIS-Aided SWIPT Green Communications Under Imperfect CSI

This work investigates the performance of simultaneous wireless information and power transfer (SWIPT) in a reconfigurable intelligent surface (RIS)-aided green multiple input single output (MISO) communications under imperfect channel state information (CSI). With an aim to provide green and robust transmission, we formulate a multi-objective optimization problem (MOOP) to design transmit precoding vector (TPV) at the base station (BS) and phase shift matrix (PSM) at the RIS that maximizes the energy efficiency at the information receivers and harvested power at the energy receivers under the norm bounded CSI error model. Due to the conflicting objective functions and non-convex nature, the MOOP is simplified using the ϵ-constraint method. We then propose an alternating optimization-based iterative algorithm that utilizes semidefinite programming to determine the optimal TPV and PSM one by one until convergence is achieved. Via exhaustive simulations, we graphically demonstrate the effectiveness and robustness of the proposed algorithm. Furthermore, we assess the impact of several key parameters such as the number of RIS elements, available transmit power at BS and the minimum harvested power at each energy receiver on the performance of the considered system.