Doppler Sensing Using WiFi Round-Trip Channel State Information

This paper presents a wireless Doppler sensing system using WiFi round-trip channel state information (RTCSI), which is implemented using the channel state information (CSI) from the Raspberry Pi CM4 onboard WiFi chip and a customized WiFi protocol. Utilizing the CSI phase in WiFi sensing is challenging as hardware asynchronization introduces significant phase errors. Similar to WiFi round-trip time (RTT) ranging, RTCSI was proposed to cancel the adverse effect of asynchronization through two-way communication. However, previous work mainly focuses on measuring RTCSI over frequency (different WiFi channels) to simulate a wide-band ranging. In this work, RTCSI is measured over time and a Doppler sensing prototype is built to detect a moving target in the wireless channel. Our findings show that this RTCSI-based Doppler sensing system is sensitive and effective in the real world. Moreover, it may be integrated with other techniques further to improve the performance in joint communications and sensing.