Energy-Efficient PMN-RIS Beamforming for Indoor mmWave Communication

Abstract

A promising method for enhancing millimeter-wave (mmWave) communications in indoor environments with limited blockage is reconfigurable intelligent surfaces (RISs). Although nearly-passive feature of RISs, the controller of RIS should be powered by grid to adjust the phase of RIS element, which limits the deployment of RISs. In this paper, a novel passive matching network (PMN)-RIS is proposed that all PMN-RIS elements are equipped with a PMN to store part of energy from incident waves to achieve RIS self-powering. Meanwhile, the amplify of reflection signals from the PMN-RIS element can be adjusted also to mitigate the co-interference among passive beams. To enhance the system performance, this paper explores an energy-efficient beamforming framework for PMN-RIS assisted communication system. The resource allocation are designed to maximize system energy efficiency, subject to maximal transmit power and minimal signal-to-interference-andnoise ratio (SINR) constraints. A Dinkelbach method and an alternating optimization approach are used to deal with the resulting non-convex design. To overcome the channel estimation error between PMN-RIS and UEs, a semi-definite program (SDP) method integrated with the S-Procedure is utilized. Simulation results demonstrate that PMN-RIS with optimized parameters can significantly enhance system energy efficiency.