Energy Efficiency Optimization in RIS-Assisted Communication Systems With RIS Power Budget

Reconfigurable intelligent surface (RIS) technology has emerged as a promising energy efficient solution to enhance the transmission performance so as to enable sustainable future wireless networks of wireless communication systems. In this paper, we investigate the optimization of energy efficiency (EE) in a RIS-assisted multi-cell system under only statistical channel state information (CSI). We adopt a measurement-based RIS power consumption model with discrete phase shifts, obtained from a PIN diode-based RIS architecture, to accurately capture the practical power behavior of RIS hardware. Moreover, to account for scenarios with limited energy resources, we impose a maximum RIS power budget constraint. The RIS power constraint is incorporated into the objective function using the Lagrangian multiplier method. To solve the resulted problem, we propose an alternating optimization (AO) algorithm that integrates Dinkelbach's method for closed-form transmit beamforming updates with a complex circle manifold (CCM) approach for obtaining discrete RIS phase shifts. Simulation results show that the proposed method achieves EE close to the theoretical upper bound while maintaining limited RIS power consumption.