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MIT Develops Accurate System For Tracking People, Objects Via WiFi (softpedia.com)
An anonymous reader writes: MIT's Computer Science and Artificial Intelligence Laboratory has created a new system called Chronos that can accurately detect the position of electronic devices in a room -- as well as the users who are carrying them -- within tens of centimeters using Wi-Fi signals only. "Chronos works without the aid of any secondary sensors, only using a technology called time-of-flight calculation, which measures the time it takes data to travel from the WiFi access point to the user's device," according to an article on Softpedia, citing a paper (PDF) that the researchers presented at a USENIX symposium in March. "MIT researchers say that by multiplying the time-in-flight value they receive from each user with the speed of light, they were able to detect each user's distance to the central Wi-Fi access point."
Without bothering to RTFM, does this mean that if they have two (or more) WAPs and the device was connected to each that they could get an accurate location? As it is, it seems that by using in-flight times, they can only determine distance from the WAP which isn't so much a location but a locus of them.
All of the major WiFi equipment vendors (Cisco, Aruba, etc.) have offered this for some time -- though they don't claim anywhere near the MIT Lab's level of accuracy. For instance, Aruba calls their offering "ALE" or Aruba Location Engine. It sits as a separate virtual appliance and communicates to the central WiFi controller (AirWave in their parlance) or to the individual APs if they are operating in autonomous mode. It gets signal strength indications for each WiFi and bluetooth antenna in range of the APs (note: *not* just those devices that are Associated with the WiFi networks served by said APs) and feeds that into ALE. From there, you can map out the devices. Both Cisco and Aruba's products have very extensive APIs to access this info. Maybe they can enhance their offerings with MIT's new technology and get the location resolution improved a bit. For now, in the wild, it's often difficult to get a station (i.e. device) location down to better than a range of 3-10 meters.
I recall seeing the timing between stations on a wireless network being a common tactic to secure a network. If a station did not reply within a window defined by the time it would take for light to travel plus the time it would take for a secured device on the network to compute a reply then the packet was discarded. I'm sure that there are other methods to respond to such a packet beyond merely discarding it.
They seemed to make a big deal out of being able to do this with a single access point. Reading further I notice that they use other Wi-Fi devices on the network to compute a location which means that with only a single device on the network the ability to determine the location of that single device is diminished. To assure the location of a device they'd still need multiple access points and/or multiple client devices.
I assume that they take advantage of the MIMO capability of Wi-Fi devices that did not exist only a few years ago. This again is much like having multiple Wi-Fi access points, just treat each input and output antenna as a separate device and compute the location that way.
Perhaps I'm missing something important here but I'm not impressed.
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The only reason they get to call this an invention is because they're MIT... Phase detection/time of flight using multiple frequencies is nothing new; main limitation is the shitty clock most things have. Combined with the fact that you need fairly good signal chain components to do it properly. This system will still fuck up I'd guess when large metal objects come in play.