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from the shoot-out-the-lights,-unplug-the-wifi dept.
Researchers at University College London (UCL) have devised a system for detecting the Doppler shifts of ubiquitous Wi-Fi and mobile telephone signals to "see" people moving, even behind masonry walls 25 centimeters thick. The method, which could be useful in situations from hostage-takings to traffic control, won the Engineering Impact Award in the RF and Communications category at this National Instrument's NI Week 2015 meeting (which convened in Austin, Tex., 3-9 August).
Other researchers—notably Dina Katabi and Fadel Adib of MIT—have built through-wall radars in the household communication bands, but these are active radars that transmit as well as receive. The UCL technique uses only passive radiation—from Wi-Fi routers (using emissions in any of the IEEE 802.11 b, g, n, ac), ambient GSM and LTE mobile signals, and other sources—so there is nothing to betray the surveillance. The system calculates the positions of hidden target by comparing two signals: a reference channel, receiving the baseline signal from the Wi-Fi access point or other RF source, and a surveillance channel, which picks up Doppler-shifted waves reflecting from the moving subject.
Tan and company built their "high Doppler resolution passive Wi-Fi radar" on two multi-frequency, software-defined, FPGA-based transceivers (National Instruments' USRP, or Universal Software Radio Peripheral. The system compares the reference and surveillance signals, interprets the very small frequency shifts, and reveals the hidden subject's location and motion.
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(Score: 2) by inertnet on Wednesday August 12 2015, @09:32AM
This system will only detect and show movement. The question is how sensitive is it? Will it show heartbeats, or can you safely move at speeds less than 1 km/h without being detected. I'm guessing that it can be tricked by moving very slowly.
(Score: 0) by Anonymous Coward on Wednesday August 12 2015, @11:42AM
Your neighbor might be none the wiser but your girlfriend won't be happy either...
(Score: 0) by Anonymous Coward on Wednesday August 12 2015, @09:45PM
Produce a randomized signal that overpowers their reference.
If you do that it'll just come back as garbage.
Getting ahold of variable-spectrum transmission gear capable of blanketing all those possible frequencies is non-trivial. Producing discrete, powerful, and portable jamming units for when you are in need of them even less so.