MIT WiTrack: Cheap, through-wall 3D motion tracking for gaming, fall detection, smart homes

A research group at MIT’s CSAIL has created a high-resolution, 3D motion tracking system that works through walls and other obstructions. From a static location connected to a computer, the system can track you as you walk around your house. Even when tracking you through walls or obstructions, it has enough resolution to detect gestures, such as lifting your arm. The system, called WiTrack, uses very simple hardware and software to perform the tracking — as a result, it is much cheaper, economically and computationally, than existing systems such as Kinect that use computer vision to track you. (Plus, Kinect doesn’t work through walls.)

WiTrack, despite sounding thoroughly Nintendoesque, is actually short for Wireless Track — and indeed, it uses radio waves to track your movement. Unlike MIT’s previous attempts at through-wall sensing, though, that used terrifyingly large antennae or conventional WiFi, WiTrack is a small system that uses its own custom-made low-power radio waves to track your movements. According to MIT, the radio waves are 100 times weaker than WiFi and 1000 times weaker than your mobile phone — so, probably on the order of 1 or 2 milliwatts.

WiTrack consists of four antennae — one that transmits radio waves, and three receivers. According to Fadel Adib, one of the researchers working on WiTrack, the transmitted radio waves are “structured in a particular way to measure the time from when the signal was transmitted until the reflections come back.” Because the three receivers are spaced apart, it’s possible to triangulate the delay of these reflected signals, to build up a 3D map. It sounds like software is then used to remove unwanted reflections — furniture, walls — leaving just the moving objects.

The accuracy of the system, according to its creators, is 10 to 20 centimeters (4-8 inches). In the video, you can see that this is more than enough to accurately track someone walking around a room. WiTrack apparently provides 3D tracking, but the video only provides a very simple (if rather awesome) example — lifting your hand to turn off the light in another room. It goes without saying, but a resolution of 10-20cm is nowhere near as accurate as the Xbox One Kinect, which is capable of resolving moves of just a few millimeters. WiTrack is also only capable of tracking one person — but the MIT researchers say they’re working on increasing that number.

Still, even if WiTrack in its current incarnation isn’t that useful for gaming or other fine interface control, there are still plenty of other uses. Having a computer track you around your house, without the need for some kind of wearable beacon, could lead towards some very cool use cases — lights and devices that turn on when you enter a room, and turn off when you leave. WiTrack could be invaluable for detecting when old people fall over — a scenario that currently requires elderly patients to wear sensors, or have cameras track them. There are military uses for seeing through walls, of course.

For a cheap and easy piece of technology that will only get better and more accurate with time, WiTrack is very impressive indeed.

Now read: Kinect for the Xbox One analyzed: Sensor revolution or marketing hype?