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August 04, 2012

See-through-wall surveillance with WiFi

Researchers from the University College London were able to design a radar that can reportedly identify frequency changes, thus enabling them to detect moving objects and people. Karl Woodbridge and Kevin Chetty built a radar prototype that has a similar size of a suitcase. Inside the radar is a radio receiver that is composed of two antennas and a signal-processing unit. The researchers said that they were able to use the device to determine a person?s location, speed and direction. Interestingly, they also said that the device can see through a one-foot-thick brick wall and that it can remain undetected because it doesn’t emit radio waves. The researchers are hoping that the finished product will one day be used in the military. “The device could become sensitive enough to pick up on subtle motions the ribcage makes during breathing, which would allow the radar to detect people who are standing or sitting still,” said Woodbridge.

According to Woodbridge, some challenges remain which he and others involved in the research will attempt to resolve. The UCL team hopes to raise system sensitivity so that their system can pick up and detect not only people who are moving but also people who are standing or sitting still. The device, he said, may be made to be sensitive enough to pick up on subtle motions that the ribcage makes in breathing in and out.

Through-the-Wall Sensing of Personnel Using Passive Bistatic WiFi Radar at Standoff Distances



In this paper, we investigate the feasibility of uncooperatively and covertly detecting people moving behind walls using passive bistatic WiFi radar at standoff distances. A series of experiments was conducted which involved personnel targets moving inside a building within the coverage area of a WiFi access point. These targets were monitored from outside the building using a 2.4-GHz passive multistatic receiver, and the data were processed offline to yield range and Doppler information. The results presented show the first through-the-wall (TTW) detections of moving personnel using passive WiFi radar. The measured Doppler shifts agree with those predicted by bistatic theory. Further analysis of the data revealed that the system is limited by the signal-to-interference ratio (SIR), and not the signal-to-noise ratio. We have also shown that a new interference suppression technique based on the CLEAN algorithm can improve the SIR by approximately 19 dB. These encouraging initial findings demonstrate the potential for using passive WiFi radar as a low-cost TTW detection sensor with widespread applicability.



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