Reconfigurable intelligent surfaces (RISs) have attracted extensive attention from industry and academia. In RIS-assisted wireless communication systems, practical channel measurements and modeling serve as the foundation for system design, network optimization, and performance evaluation. In this paper, a RIS time-domain channel measurement system, based on a software defined radio platform, is developed for the first time to investigate the small-scale fading characteristics of RIS-assisted channels. We present RIS channel measurements in corridor and laboratory scenarios and compare the power delay profile of the channel without RIS, with RIS specular reflection, and with RIS intelligent reflection. The multipath component parameters and cluster parameters based on the Saleh-Valenzuela model are extracted. We find that the power delay profiles (PDPs) of the RIS-assisted channel fit the power-law decay model better than the common exponential decay model and approximate the law of square decay. Through intelligent reflection, the RIS can decrease the delay and concentrate the energy of the virtual line-of-sight (VLoS) path, thereby reducing the delay spread and mitigating multipath fading. Furthermore, the cluster characteristics of RIS-assisted channels are highly dependent on the measurement environment. In the laboratory scenario, a single cluster dominated by the VLoS path with smooth envelope is observed. On the other hand, in the corridor scenario, some additional clusters introduced by the RIS reflection are created.

翻译：可重构智能表面（RIS）已引起工业界和学术界的广泛关注。在RIS辅助的无线通信系统中，实际信道测量与建模是系统设计、网络优化和性能评估的基础。本文首次开发了基于软件定义无线电平台的RIS时域信道测量系统，以研究RIS辅助信道的小尺度衰落特性。我们在走廊和实验室场景中进行了RIS信道测量，并比较了无RIS、RIS镜面反射和RIS智能反射情况下的信道功率延迟分布。基于Saleh-Valenzuela模型提取了多径分量参数与簇参数。研究发现，RIS辅助信道的功率延迟分布（PDP）相比常见的指数衰减模型更符合幂律衰减模型，且近似遵循平方衰减规律。通过智能反射，RIS能够降低虚拟视距路径的时延并集中其能量，从而减少时延扩展并抑制多径衰落。此外，RIS辅助信道的簇特性高度依赖于测量环境。在实验室场景中，观测到由虚拟视距路径主导的单一簇，其包络平滑；而在走廊场景中，RIS反射会引入若干额外簇。