MIT researchers use Wi-Fi to recognize people through walls

http://gizmodo.com/wifi-networks-can-now-identify-who-you-are-through-wall-1738998333

by thro1237 • 11 years ago

55 21 11 years ago

dang• 11 years ago

Url changed from http://www.theverge.com/2015/10/28/9625636/rf-capture-mit-wi..., which points to this.

what happens when two person stand behind one another. keeping their bodies close to each other. Is there is any way to detect how many person are actually standing there?

TeMPOraL2• 11 years ago

I also would like to know the theoretical answer. The practical will be, I guess, "wait for them to start moving around".

Natanael_L• 11 years ago

Physics is crazy: http://web.media.mit.edu/~raskar/cornar/

Jach4• 11 years ago

In theory I think it would be possible to detect this situation with SAR imaging techniques (and probably other techniques), you just need to have a large enough bandwidth in your transmission signal and be at a sufficient stand-off distance from the targets...

JusticeJuice• 11 years ago

Is there a reason why very little information showed up from the legs? Are jeans just great at absorbing but not reflecting wifi signals?

Jach4• 11 years ago

The problem is that legs make poor backwards reflectors due to their shape, so the reflected signals aren't detected since they're sent elsewhere. Though the material can make a huge difference too. (e.g. wool and nylon can significantly reduce the reflectivity, as can the presence of wrinkles.) The best reflective part of the body is the torso (especially the back) since it's relatively flat.

corvus_sapiens• 11 years ago

So recognition doesn't work if it was calibrated while you were wearing different clothing? That kills some of the use cases.

lordnacho• 11 years ago

Is there something special about the WiFi spectrum that makes this work? Does it work with any ambient radio frequency noise?

weland• 11 years ago

My guess is that you need to have the kind of wavelength that meaningfully interacts with human features and body composition (i.e. something that scatters and reflects off of you, instead of being absorbed). It's not specific to the WiFi spectrum though, there are plenty of frequency ranges that meet these requirements.

Jach4• 11 years ago

The benefit of wifi spectrum is that the parts are cheap and you generally won't get in trouble for transmitting signals without a license, which is what their system does. (It's not passive.) Unfortunately the wifi spectrum isn't that great for through-wall imaging in general -- you're going to lose a lot of transmission power if the wall is composed of just about anything besides drywall, glass, or wood, on top of the massive loss of power you get by default since the received signal's power is inversely proportional to the distance raised to the fourth power.

darkmighty2• 11 years ago

Is there a range of frequencies that does better? Don't frequencies that go through walls easily also go through bodies easily, or are there frequencies where the body is particularly reflective w.r.t. concrete walls?

tempodox• 11 years ago

All of a sudden, tin foil hats get a whole new meaning.

falcolas• 11 years ago

The problem with tinfoil hats is that it just makes your signature more unique. Tinfoil reflects radio waves better than skin and other clothing.

arama471• 11 years ago

Unless you change up the shape/location of the tinfoil regularly, in which case the system will likely think you're a different person every time.

aaronkrolik• 11 years ago

We had a wifi radar at school. Was scary good. Only downside was that it jammed wifi for half the engineering building

MIT researchers use Wi-Fi to recognize people through walls

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