Wi Vi system detects motion on the other side of a wall

Using Wi-Fi signals to see through walls

For emergency crews looking for someone trapped in a building or police in a standoff against an armed suspect, to cite two examples, the ability to see through walls could come in handy.

Researchers have attempted to develop that kind of technology, even with some success, but to date they’ve involved large radar arrays with enough power to send signals through walls and receive signals bounced back from what’s behind the wall. Not the kind of thing you can easily carry with you.

But a professor at the Massachusetts Institute of Technology is developing a way to use low-power Wi-Fi signals to detect motion on the other side of a wall or door, according MIT News.

Called Wi-Vi, the system works in a way similar to radar, but uses two transmitters to cancel out stationary objects and allow its single receiver to recognize movement.

“We wanted to create a device that is low-power, portable and simple enough for anyone to use, to give people the ability to see through walls and closed doors,” said Dina Katabi, a professor in MIT’s Department of Electrical Engineering and Computer Science, who is developing the system with graduate student Fadel Adib.

The result isn’t X-ray vision or anything that produces what looks like a human form. Instead, what you get what, as an MIT video shows,  looks a bit like a polygraph readout that can indicate someone moving toward or away from the wall, or even small movements like the wave of a hand.

Using two transmitting antennae gets around the fact that most of a Wi-Fi signal sent toward a wall will be reflected back by the wall, Katabi said. The second signal is the inverse of the first, so they cancel each other out with regard to a wall. The tiny portion of the signals that get through the wall likewise will cancel each other with regard to any static object, leaving the receiver to show movement, as the reflections between the two signals change.

Wi-Vi, which will be presented at the Sigcomm conference in Hong Kong in August, would have a number of public-sector applications, in disaster response, police work and military settings. And Katabi said it could be used by individuals who might think they’re being watched or followed.

It also has possibilities for gesture control applications without the line-of-sight requirement that current gesture systems have, Katabi said, allowing someone, for example, to turn off the light in one room from another room or interact with a game or simulation without being in the same room.

About the Author

Kevin McCaney is a former editor of Defense Systems and GCN.


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