Dynamic-Controlled RIS Assisted Multi-User MISO Downlink System: Joint Beamforming Design

Abstract

This paper investigates a multi-user multiple-input single-output (MISO) downlink communication system, which is assisted by a dynamic-controlled Reconfigurable Intelligent Surface (RIS). Firstly, we formulate a problem to optimize the active -and passive beamforming matrices with the goal of maximizing the sum rate (SR) of all users under the constraints of Quality of Service (QoS) requirements. A state selection matrix is creatively introduced to control the number of RIS elements used for reflection. And quantized phases are considered in order to be more practical, which is often neglected in existing works. Then, an algorithm based on block coordinate descent (BCD) is proposed to obtain the stationary solution. The algorithm can guarantee the optimal SR regardless of any proportion of closed RIS elements. Finally, we perform simulation verification and analysis the results of the proposed scheme and six baseline schemes. Simulation results show that the proposed scheme is much better than the existing schemes in terms of SR, and realizes good energy efficiency (EE) performance simultaneously. Moreover, the proposed scheme can achieve more significant EE gain by sacrificing less SR.