Pushing the Limit of Phase Offset for Contactless Sensing Using Commodity Wifi

In this paper, we propose BreathTrack2.0, a contactless breath tracking system based on commodity WiFi devices. Breath-Track2.0 could track the detailed breath status through the phase variation of channel state information(CSI). To achieve this, BreathTrack2.0 first combines the signal on multiple antennas and subcarriers with a joint Angle of Arrival(AoA) and Time of Flight(ToF) beamformer to strengthen the signal from human. Then, it utilizes the fact that the phase offsets introduced by the hardware imperfection are the same among different propagation paths to cancel the phase offsets. Finally, the phase variation of the extracted human signal is utilized to estimate the breath rate and indicate the detailed breath status. Real world experiments demonstrate that the proposed system could estimate the breath rate with the median accuracy of over 99% and could track the detailed status of human breath.