June 28, 2013
MIT’s Wi-Vi Technology Uses Wi-Fi To See Through Walls
Michael Harper for redOrbit.com - Your Universe Online
Using technology that nearly all of us have in our homes, MIT researchers have developed a sort of x-ray vision device that can detect motion behind walls or other large objects. It's called Wi-Vi and it uses low power Wi-Fi antennas to bounce signals off any moving object, similar to the way radar and sonar works.
Wi-Vi was created by Dina Katabi, a professor in MIT's Department of Electrical Engineering and Computer Science, and her graduate student Fadel Adib.
When Wi-Fi signals are broadcast from the antennas, only a portion of the signals can make it through walls or other solid objects. Understanding this, Katabi and Adib developed a system which sends out additional signals and uses the reflections from static objects like the wall to draw a baseline. Wi-Vi is built with two Wi-Fi antennas, only one receiver and some clever coding to interpret the incoming signals. The two antennas send out a nearly identical signal with one inverse from the other. This reversing of the signals creates an identical signal when they hit a solid object, such as a wall, and are cancelled out. However if something is moving on the other side of the wall, the returning signals will be different from one another.
"So, if the person moves behind the wall, all reflections from static objects are cancelled out, and the only thing registered by the device is the moving human," explained Adib in a statement.
Though the thought of being able to track motions from another room may give some pause, the current setup isn't capable of displaying outlines of the human body. In fact, Wi-Vi only displays motion as a solid line on a graph, registering as a negative signal when the person moves away from the device and a positive signal when they move closer. Even if the person is only making small motions, such as writing on a white board, the Wi-Vi registers it on the display.
It's the idea and the implementation of Wi-Vi that makes it so different. Radar and sonar have been used for many years and Wi-Fi can be found in nearly any building. Yet it's the way this Wi-Fi signal is used and the code which inverses the signals and displays them as motion. It's an arrangement which the MIT team hopes will make Wi-Vi devices accessible and affordable to the general public as well as law enforcement and search and rescue teams. This technology could even fit in a smartphone without presenting a drain on battery life says Katabi, meaning volunteers could help locate people trapped in a collapsed building following an earthquake. When installed in a mobile device, Wi-Vi could even turn a smartphone into a personal safety device.
"If you are walking at night and you have the feeling that someone is following you, then you could use it to check if there is someone behind the fence or behind a corner," said Katabi.
Yet giving this tracking power to the general public could also create some new concerns about personal privacy.
Hanni Fakhoury, a staff attorney at the Electronic Frontier Foundation told ComputerWorld the law simply has not addressed any issues like the ones Wi-Vi could create.
"Your location is something that's worthy of privacy. We know that, even within your house, where you go can reveal a lot about yourself."
Katabi believes this technology could also be used to protect one's privacy, noting a caretaker could use Wi-Vi to monitor the motions of an elderly grandparent without installing cameras that may make them uncomfortable.
Katabi and Adib will present Wi-Vi at the Sigcomm conference in Hong Kong this August.