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）最初为通信目的而获取，近期已被重新用于感知和类雷达功能。然而，在发射端与接收端具有独立时钟的实际Wi-Fi系统中，缺乏公共时延与相位参考从根本上阻碍了相位相干的类雷达时延-多普勒分析。通过利用视距（LoS）路径分量（即最早到达的直达路径）作为空中（OTA）时延与相位参考，我们提出一种称为LoSRef的OTA视距路径参考方案，该方案可在这一实际约束下实现时延校准与相位对齐。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，本文所提基于LoSRef的框架能够实现相位相干的类双基地雷达操作，并集成至典型部署的Wi-Fi系统中。通过室内环境下的人体步态与呼吸实验，我们证明仅使用商用Wi-Fi设备即可获取相位相干信道冲激响应及相应的时延-多普勒响应。这实现了具有物理可解释性的人体运动感知，包括步态引起的距离变化与呼吸引起的亚波长位移，以及提取比主导静态多径分量弱20dB的目标动态特征。