Achievable rate as affected by active elements distribution in reconfigurable intelligent surfaces for wireless communication

To increase constantly the achievable rate of reconfigurable intelligent surfaces (RISs)-assisted communication systems, the traditional approaches are to deploy a few active elements randomly on the passive RISs. However, the effect of the geometry distribution of the deployment of the active elements is ignored in performance analysis. In this article, three types of geometry distribution with active elements on RISs, denoted as random distribution, uniform distribution, and eight-queens distribution, are discussed to analyze the affect on achievable rate in RISs-assisted wireless communications. Specifically, the optimal achievable rate is obtained according to the predefined codebook, and the codebook is determined by the reflection beamforming codeword related to the active elements geometry distribution in RISs. Simulation results show that different geometry distribution of active elements in RISs causes different influences to achievable rates. The eight-queens distribution proposed in this article for active elements in RISs brings the highest achievable rate compared with random distribution and uniform distribution. In the passive RISs surface, the distribution of a few active elements is limited by the eight-queens, further enhancing the achievable rate of the wireless communication system. This method has a 7% improvement over the conventional method.