Researchers See Through Walls With 'Wi-Vi'

Want Xray vision like the man of steel?
A technology that lets you see behind
walls could soon be built in to your cell
phone.
MIT professor Dina Katabi and graduate
student Fadel Adib have announced Wi­
Vi, a demonstration of a technology that
uses WiFi to allow a viewer to "see" a
person moving behind a wall. (WiVi
stands for "WiFi" and "vision.")
Previous work demonstrated that the
subtle reflections of wireless inter
signals bouncing off a human could be
used to track that person's movements,
but those previous experiments either
required that a wireless router was
already in the room of the person being
tracked, or "a whole truck just to carry
the radio," said Katabi.
The new device uses the same wireless
antenna as is found in a cell phone or
laptop and could in theory one day be
embedded in a phone. [See also " WiSee
Detects Your Gestures Using WiFi."]
The trick is canceling out all interfering
signals – Wi-Fi doesn't just bounce off
humans, but also walls, floors, and
furniture. And those signals are 10,000
to 100,000 times more powerful than
the reflections off a human body.
Katabi's wivi sends out two wireless
signals, one of which is the inverse of
the other. In what Katabi calls
"interference nulling," the two signals
cancel each other out unless they hit a
moving target – such as a human.
"To silence the noise, we change the
structure of the Wi-Fi signal so all the
undesired reflections cancel," she said.
The device is meant to be portable so,
for example, a person worried that
someone was hiding in the bushes could
do a quick scan for her personal safety.
WiVi could also serve as a high tech
baby monitor or help Superman – or
just cops – catch baddies.