The reconfigurable intelligent surface (RIS) is an emerging promising candidate technology for the sixth-generation wireless networks, where the element spacing is usually of sub-wavelength. Only limited knowledge, however, has been gained about the spatial-temporal correlation behavior among the elements in an RIS. In this paper, we investigate the joint spatial-temporal correlation models for an RIS in a wireless communication system. Joint small-scale spatial-temporal correlation functions are provided and analyzed for both ideal isotropic scattering and more practical non-isotropic scattering environments, where the latter is studied by employing an angular distribution derived from real-world millimeter-wave measurements. Analytical and simulation results demonstrate that the joint spatial-temporal correlation can be represented by a four-dimensional sinc function under isotropic scattering, while the correlation is generally stronger with more fluctuation for non-isotropic scattering with various motion directions.

中文翻译：

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可重构智能表面的小规模时空相关建模

可重构智能表面（RIS）是第六代无线网络的新兴候选技术，其元素间距通常为亚波长。然而，关于 RIS 中元素之间的时空相关行为的知识有限。在本文中，我们研究了无线通信系统中 RIS 的联合时空相关模型。为理想的各向同性散射和更实际的非各向同性散射环境提供并分析了联合小尺度时空相关函数，其中通过采用从现实世界毫米波测量得出的角分布来研究后者。