As a potentially revolutionary enabling technology for the sixth generation (6G) mobile communication system, 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 (SDR) 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 (PDP) 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 PDPs of the RIS-assisted channel fit the power-law 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 delay spread and mitigating multipath fading. Furthermore, the cluster characteristics of RIS-assisted channels are highly related to 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：作为第六代（6G）移动通信系统潜在的革命性使能技术，可重构智能超表面（RIS）已引起工业界和学术界的广泛关注。在RIS辅助无线通信系统中，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。本文首次基于软件定义无线电（SDR）平台开发了RIS时域信道测量系统，用于研究RIS辅助信道的小尺度衰落特性。我们展示了走廊和实验室场景下的RIS信道测量结果，并对比了无RIS、RIS镜面反射及RIS智能反射三种情况下的功率延迟分布（PDP）。基于Saleh-Valenzuela模型提取了多径分量参数和簇参数。研究发现：RIS辅助信道的PDP符合幂律衰减模型，并近似遵循平方衰减规律。通过智能反射，RIS可降低虚拟视距（VLOS）路径的时延并集中能量，从而减少时延扩展并缓解多径衰落。此外，RIS辅助信道的簇特性与测量环境高度相关。在实验室场景中，观察到由VLOS路径主导的单一平滑包络簇；而在走廊场景中，RIS反射引入了若干附加簇。