Recently, reconfigurable intelligent surfaces (RISs) have drawn intensive attention to enhance the coverage of millimeter wave (mmWave) communication systems. However, existing works mainly consider the RIS as a whole uniform plane, which may be unrealistic to be installed on the facade of buildings when the RIS is extreme large. To address this problem, in this paper, we propose a sparse array of sub-surface (SAoS) architecture for RIS, which contains several rectangle shaped sub-surfaces termed as RIS tiles that can be sparsely deployed. An approximated ergodic spectral efficiency of the SAoS aided system is derived and the performance impact of the SAoS design is evaluated. Based on the approximated ergodic spectral efficiency, we obtain an optimal reflection coefficient design for each RIS tile. Analytical results show that the received signal-to-noise ratios can grow quadratically and linearly to the number of RIS elements under strong and weak LoS scenarios, respectively. Furthermore, we consider the visible region (VR) phenomenon in the SAoS aided mmWave system and find that the optimal distance between RIS tiles is supposed to yield a total SAoS VR nearly covering the whole blind coverage area. The numerical results verify the tightness of the approximated ergodic spectral efficiency and demonstrate the great system performance.
翻译:最近,可重新测量的智能表面(RIS)引起了人们的高度注意,以扩大毫米波(mmWave)通信系统的覆盖面;然而,现有的工程主要将RIS视为整个统一平面,当RIS极大时,在建筑物表面安装可能不切实际;为了解决这个问题,我们在本文件中提议,为RIS建立几组稀多的次表层结构(SAoS)结构,该结构包含若干直角形状的子表层,称为RIS砖,可以分散地部署;SAOS辅助系统的近似垂直光谱效率得到推导,SAOS设计对性能的影响得到评估。根据大约的ERgodic光谱效率,我们为每个RIS图层获得了最佳的反省系数设计。分析结果表明,所收到的信号到噪音比率可以分别从四分立和线性地增长到在坚固和弱的LOS假设情景下可部署的RIS成像光谱(VR)光谱效率,我们把SAOS光谱系统显示的可见的区域现象视为整个SISAMS光谱级的深度测量结果。