Wi-Fi Radar via Over-the-Air Referencing: Bridging Wi-Fi Sensing and Bistatic Radar

2026-02-05

AI Summary

This work addresses the challenge of achieving phase-coherent radar sensing with asynchronous commercial Wi-Fi devices by proposing LoSRef, an over-the-air reference mechanism that leverages the line-of-sight (LoS) path as a self-calibration signal. This approach enables delay calibration and phase alignment without requiring wired connections or dedicated antennas. Building upon this method, the authors develop the first bistatic radar sensing framework deployable on off-the-shelf Wi-Fi hardware. By integrating channel impulse response extraction with delay-Doppler analysis, the system achieves physically interpretable sensing of sub-wavelength micromotions—such as human gait and respiration—and can even detect dynamic target signals up to 20 dB weaker than the dominant static multipath components.

Technology Category

• Humans and AI: Brain-Sensing and Analysis
• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Machine Learning: Hardware-aware ML

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Search and Retrieval-Augmented AI: Personalized, context-aware and across-device search
• Responsible Web: Machine-in-the-loop, human agency and autonomy

Abstract

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.

Problem

• Wi-Fi sensing
• phase coherence
• bistatic radar
• delay-Doppler analysis
• unsynchronized systems

Innovation

• Wi-Fi radar
• over-the-air referencing
• phase coherence
• bistatic sensing
• LoS path