Reconfigurable intelligence surface (RIS) consists of a large number of low-cost passive reflecting elements has attracted significant attention from communication communities, which is mainly due to its ability to substantially improve the communication performance. In light of this, we develop a three-dimensional geometry-based multiple-input multiple-output propagation model in this article, which is mainly suitable for describing the high-speed railway communications assisted by RIS in macrocell environments, such as train-to-train scenarios. In such propagation model, the waves emitted from the mobile transmitter experience non line of sight propagation links before reaching the mobile receiver, as well as the RIS propagation links before reaching the receiver. We compute the expressions of the RIS-assisted high-speed railway channel propagation properties, for example, spatial-time cross-correlation functions, between different propagation links. Then, we study the temporal autocorrelation functions of the propagation links in the provided propagation model for distinct movement time instants. Analysis shows that the communication performance can be enhanced by rising the number and the size of RIS reflecting elements, and it is validated by numerical simulation results.

由大量低成本无源反射元件组成的可重构智能表面（RIS）引起了通信界的极大关注，这主要是由于其能够大幅提高通信性能。鉴于此，我们在本文中开发了一种基于三维几何的多输入多输出传播模型，该模型主要适用于描述宏小区环境下RIS辅助的高速铁路通信，例如车与车之间的通信。 -训练场景。在这种传播模型中，从移动发射机发出的电波在到达移动接收机之前经历非视距传播链路，并且在到达接收机之前经历RIS传播链路。我们计算了 RIS 辅助的高铁信道传播特性的表达式，例如不同传播链路之间的时空互相关函数。然后，我们研究了所提供的传播模型中不同运动时刻的传播链路的时间自相关函数。分析表明，通过增加RIS反射单元的数量和尺寸可以提高通信性能，并得到数值模拟结果的验证。