Wi-Fi sensing has attracted significant attention for human sensing and related applications. However, unsynchronized transmitters and receivers fundamentally preclude phase-coherent radar-like delay--Doppler analysis. By exploiting the line-of-sight (LoS) path, 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 in unsynchronized Wi-Fi systems. Unlike conventional Wi-Fi bistatic radar systems that rely on wired reference signals or dedicated reference antennas, the proposed LoSRef-based framework bridges the long-standing gap between conventional Wi-Fi sensing and Wi-Fi radar, enabling phase-coherent bistatic radar-like operation in a drop-in Wi-Fi sensing configuration. Through human gait and respiration experiments in indoor environments, we demonstrate that phase-coherent channel impulse responses and corresponding delay--Doppler responses are 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感知技术因其在人体感知及相关应用中的潜力而备受关注。然而，收发端之间的非同步性从根本上阻碍了类似雷达的相位相干时延-多普勒分析。通过利用视距路径（即最早到达的直达路径）作为时延和相位的空中参考，我们提出了一种OTA视距路径参考方案（称为LoSRef），该方案能够在非同步Wi-Fi系统中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，所提出的基于LoSRef的框架填补了传统Wi-Fi感知与Wi-Fi雷达之间的长期空白，使得在即插即用的Wi-Fi感知配置中实现相位相干的双基地雷达式操作成为可能。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时延-多普勒响应。这实现了物理可解释的人体运动感知，包括步态引起的距离变化和呼吸引起的亚波长级位移，并能提取出比主导静态多径分量弱达20 dB的目标动态特征。