This paper presents a novel passive Doppler radar that can use ambient wireless signals to perform gesture sensing within a short distance from the radar. Since the proposed radar doesn’t require a cooperative source, there is no issue with radio interference.

In the experiment, a prototype radar was built and then tested to detect a moving hand with the captured WiFi signals that are sent out from a far IEEE 802.11b/g/n access point. Interestingly, this radar can identify several common gestures quite successfully.