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posted by janrinok on Wednesday August 12 2015, @05:56AM   Printer-friendly
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: 0) by Anonymous Coward on Wednesday August 12 2015, @03:57PM

    by Anonymous Coward on Wednesday August 12 2015, @03:57PM (#221734)

    Unless modern insulation features Faraday cage-esque wire mesh. It ain't blocking or stopping EM radiation.

  • (Score: 2) by Aiwendil on Wednesday August 12 2015, @05:34PM

    by Aiwendil (531) on Wednesday August 12 2015, @05:34PM (#221777) Journal

    The thing is just that, the newest houses here in sweden often have the problem that cellphones are effectivly blocked. It is at the point where that have to make small slits in foil of the windows in order to get a reception.

    And no, not wire mesh but actually surrounded by foil.