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Ambient Radar

Passive detection using ambient RF
 
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Primarily an indoor thing, although the principle probably would work outdoors also.

Thinking about an office, with it’s usual WiFi routers, the whole floor is bathed in GHz illumination from fixed sources, reflecting off a multitude of surfaces

A software-defined radio with a phased array antenna. An RNN trained on the “empty office” pattern, without necessarily identifying the RF sources, but will recognise disturbances (I.e. changes in the pattern).

Triggers security alarm if it detects an intruder. Probably could localise an intruder

Frankx, Oct 15 2019

Wi-Vi http://news.mit.edu...-moving-humans-0628
A bit late to the party, [Frankx]. Article from 2013. [neutrinos_shadow, Oct 15 2019]

Wikipedia: Passive radar https://en.wikipedi.../wiki/Passive_radar
Mentioned in my anno [notexactly, Oct 18 2019]

[link]






       It certainly works outside, for large objects like aircraft. The Chinese are the leaders in the field. But it requires very large antennae, and really only provides Yes/No detection - then you need to use other technologies to localize and identify.   

       It's also vulnerable to certain falsing effects, which means monitoring and evaluation can't be automated very well. It does demonstrate good effectiveness at indicating "stealth" vehicles, as it works by tracking a "moving absence" or "hole" rather than the response to a radar ping. It doesn't work for our Cube's cloaking device, tho.   

       We suspect your indoor ISM system would exhibit the same vulnerability. The detection threshold would have to be set so high that the value of the alert would be minimal. It would only work in very, very stable and controlled environments.
8th of 7, Oct 15 2019
  

       Using Wi-Fi signals for motion detection has been around for a while. See linky.
neutrinos_shadow, Oct 15 2019
  

       // It doesn't work for our Cube's cloaking device, tho.// That's chiefly because your Cube is a large Pampers cardboard box painted matt black, and is largely radar-transparent apart from the cut out and stuck on tinfoil letters saying "CBUE".   

       If millions of voices suddenly cried out in terror, you might be able to detect the disturbance in the force.
MaxwellBuchanan, Oct 15 2019
  

       // If millions of voices suddenly cried out in terror // it means they've just heard the horrifying words "And now an election broadcast by the labour party".   

       The cardboard box is just a playhouse we helped the Intercalary make to keep him amused and distracted on a wet Sunday afternoon.
8th of 7, Oct 15 2019
  

       That accounts for the spelling and the damp, then.
MaxwellBuchanan, Oct 15 2019
  

       Isn't this just passive radar [link] plus machine learning (which is probably already used)?   

       The guy who runs the RCModelReviews YouTube channel was working on a passive radar system for aerial drones, for collision avoidance purposes, to make ubiquitous drones compatible with safety. Last I checked on it (a couple of years ago), I think he was held back from further development by New Zealand's national RC aircraft club, which was trying to suppress the technology for some reason.   

       Wi-Vi [link] is actually active radar, with a dedicated transmitter, just happening to be Wi-Fi-compatible. It doesn't use ambient Wi-Fi signals. But it does do the comparison with a known background signal as described here.
notexactly, Oct 18 2019
  
      
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