In this letter, we present in detail the system-level modeling of reconfigurable intelligent surface (RIS)-assisted cellular systems by considering a 3-dimensional channel model between base station, RIS, and user. We prove that the optimal placement of RIS to achieve wider coverage is exactly opposite to the base station, under the constraint of single RIS in each sector. We propose a novel beamforming design for RIS-assisted cellular systems and derive the achievable sum rate in the presence of ideal, discrete, and random phase shifters at RIS. Through extensive system-level evaluations, we then show that the proposed beamforming design achieves significant improvements as compared to the state-of-the-art algorithms.

翻译：本文详细阐述了可重构智能表面辅助蜂窝系统的系统级建模，考虑了基站、RIS与用户之间的三维信道模型。我们证明了在每扇区仅部署单个RIS的约束下，实现更广覆盖范围的RIS最优部署位置恰好在基站的对侧。针对RIS辅助蜂窝系统，我们提出了一种新颖的波束赋形设计方案，并推导了在RIS采用理想、离散及随机移相器条件下的可达和速率。通过广泛的系统级评估，我们证明该波束赋形方案相较于现有最优算法实现了显著的性能提升。