Wi-Fi channel state information (CSI), which is originally acquired for communication purposes, has recently been reused for sensing and radar-like functionalities. However, in practical Wi-Fi systems with independent clocks at the transmitter and receiver, the lack of a common delay and phase reference fundamentally precludes phase-coherent radar-like delay--Doppler analysis. By exploiting the line-of-sight (LoS) path component, i.e., the earliest-arriving direct path, as an over-the-air (OTA) reference for delay and phase, we propose an OTA LoS-path referencing scheme, termed LoSRef, that enables delay calibration and phase alignment under this practical constraint. Unlike conventional Wi-Fi bistatic radar systems that rely on wired reference signals or dedicated reference antennas, the proposed LoSRef-based framework enables phase-coherent bistatic radar-like operation that can be integrated into typically deployed Wi-Fi systems. Through human gait and respiration experiments in indoor environments, we demonstrate that phase-coherent channel impulse responses and corresponding delay--Doppler responses can be obtained using only commodity Wi-Fi devices. This enables physically interpretable human motion sensing, including gait-induced range variation and respiration-induced sub-wavelength displacement, as well as the extraction of target-induced dynamics up to 20 dB weaker than dominant static multipath components.

翻译：Wi-Fi信道状态信息（CSI）最初是为通信目的获取的，近年来被重新用于实现感知及类雷达功能。然而，在实际的Wi-Fi系统中，由于发射端与接收端时钟相互独立，缺乏共同的延迟与相位参考，从根本上阻碍了类似雷达的相位相干延迟-多普勒分析。通过利用视距路径分量（即最早到达的直接路径）作为延迟与相位的空中参考，我们提出了一种称为LoSRef的空中视距路径参考方案，可在上述实际约束下实现延迟校准与相位对齐。与依赖有线参考信号或专用参考天线的传统Wi-Fi双基地雷达系统不同，所提出的基于LoSRef的框架支持相位相干的类双基地雷达操作，并可集成于典型部署的Wi-Fi系统中。通过在室内环境中进行人体步态与呼吸实验，我们证明仅使用商用Wi-Fi设备即可获得相位相干的信道冲激响应及相应的延迟-多普勒响应。这使得可物理解释的人体运动感知成为可能，包括步态引起的距离变化和呼吸引起的亚波长位移，并能提取比主导静态多径分量弱达20 dB的目标动态特征。