MIT Develops Accurate System For Tracking People, Objects Via WiFi

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."

No V-Chip here

[FrankHaynes]

Good thing I don't have a WiFi chip implanted into my skull. And I'm not glued to my goddamned phone, so MIT will need to step up its game if it wants to track ME.

Re:

[jenningsthecat]

Don't worry, the good folks at MIT have been able to track you for years. [theverge.com]

Damn! According to the link you provided they can "determine subtle differences in body shapes" and "determine a person's breathing patterns and heart rate". That means I have to forego the tin-foil hat in favour of a full-body Faraday suit! I guess it's time to get me some copper mesh and pay a visit to my tailor...

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[q4Fry]

I am pretty sure they could then design a detector that determined exactly where you were from even further away. And they'd definitely know it was you, too.

Triangulation?

[themightythor]

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.

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[Anonymous Coward]

With MIMO (or MISO, or anything multipath), you don't need the multiple WAPs because you've already got them (by bouncing off of walls, etc).

Actually, you could probably do it with just SISO too, but that would require extra processing (the MIMO system would basically already do the solving for you, you just need to interpret it).

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[AHuxley]

From the story "you need only one access point", "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 WiFi access point.".
Other older options needed more ie. "Previous WiFi tracking systems needed at least four"

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[R3d M3rcury]

Yes, for one WiFi base-station, distance doesn't tell you where you are--just how far you are. I could be five feet to the north, south, east, west, above, or below the WiFi base-station.

For that, you would probably need a few more and compare those values.

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[postbigbang]

Time domain reflectometry is a well-known science. What the article doesn't cite is that it needs a frame of reference to build a 3D model of a freespace. Otherwise, it takea an achingly long time to use small motions within a space to learn how the room reflects and how the geometry time-decays.

But it's from MIT, and uses WiFi, and sounds like it could have patent-worthy Breakthrough Technology! Must be great! We are saved again by MIT!. Sorry. Got carried away.

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[TapeCutter]

You need a minimum of three points to unambiguously triangulate a position. I really can't see why this is "news", three or more sensitive microphones placed in the area could also be used to locate individuals by their fart noises and the speed of sound, the question is why bother when there are more practical ways to do the same thing?

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[geekmux]

You need a minimum of three points to unambiguously triangulate a position. I really can't see why this is "news", three or more sensitive microphones placed in the area could also be used to locate individuals by their fart noises and the speed of sound, the question is why bother when there are more practical ways to do the same thing?

There's always a dozen ways to skin a cat, but feel free to elaborate as to the technology infrastructure in place today that would be more "practical" than WiFi. Sure, we've had 3D tracking technology in GPS for years, but not down to this level of accuracy, which is quite a bit more beneficial given the saturation of tracking devices in densely populated areas like malls or sporting events.

Unfortunately, in less than 10 years, the answer to every question regarding invasive tracking technology will simp

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[dolmen.fr]

Unfortunately, in less than 10 years, the answer to every question regarding invasive tracking technology will simply be "drone".

In a room?

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[Dins]

Sure. Doesn't have to be a big drone (in 10 years).

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[s.t.a.l.k.e.r._loner]

TFA specifically states that this method is revolutionary because it only requires ONE wifi access point. One proposed use is to provide password-less wifi access to customers in a cafe, but not to people outside the cafe as calculated by their actual physical locations.

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[parkinglot777]

You need a minimum of three points to unambiguously triangulate a position. I really can't see why this is "news", three or more sensitive microphones placed in the area could also be used to locate individuals by their fart noises and the speed of sound, the question is why bother when there are more practical ways to do the same thing?

If you read the paper (in PDF), you would see that they did use a form of Triangulation in order to figure location. It is stated in the 2nd step (using distance between 2 antennas).

Chronos follows a two-step procedure. In the first step, Chronos refines the distance measurements by utilizing geometric constraints, imposed by the relative locations of the antennas on the access point and the client. In the second step, Chronos formulates a quadratic optimization problem, based on the refined distances to get the accurate location of the client with respect to the access point.

Mathematically, we denote the separation between antenna i and antenna j on the access point ... Chronos uses a relaxed version of triangle inequality to eliminate erroneous distance measurements.

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[ceoyoyo]

It's simple trilateralization (well, bilateralization because they assume you're in the same plane as the AP).

With the separation of the antenna on most APs it's going to give pretty crappy localization.

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[LWATCDR]

4 if you need height.

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[Anonymous Coward]

They're using a single MIMO AP with multiple antennas and sub decimetre ( than the accuracy, and the antennas are not perfectly in a single line (eg offset middle antenna), than you can effectively coarsely triangulate the signal using a single AP.

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[dolmen.fr]

Why do you think there is free wifi in airport?
Is there any better place to spy high profile foreigners' devices than in airports?

active or passive?

[Joe_Dragon]

active or passive?

Commercially available for some time...

[planux]

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.

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[dinfinity]

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.

You contradicted yourself within the same sentence. When you say 'this' it means 'exactly this', not 'something like this'.

Not true localisation ???

[Anonymous Coward]

Don't think this actually does localisation, just ToF-type distance. So it can tell how far you are from the access point, but not direction (unless they are doing something funky with the multiple antenna). In the main this just seems to be using multiple wavelengths to sharpen up and remove ambiguity from measurements (eg you can tell the phase angle, but need multiple such measurements to know absolute phase difference and thus precise range.

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[Edis Krad]

I thought the same thing, so I roughly parsed the article. It requires at two antennae and needs to know the distance in between those. Basically is doing stereo vision using wifi instead of cameras.

Now I don't know if or how they managed to control each antenna separately, though they do mention they hacked a wifi driver. Also, in their implementation they cite using two devices, not one.

Sounds familiar

[blindseer]

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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[AmiMoJo]

Previously it was only possible to determine the direction of a device. Now they can determine the distance with an average error of ~20cm. They only need one device and one access point according to the paper.

This raises some significant privacy concerns. At the moment it looks like the device needs to be connected to the AP for it to work, fortunately, but I'm thinking that devices which broadcast lists of networks they know about could be vulnerable. Send some fake packets pretending to come from one of

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[Number10]

From the paper, it looks like this technique requires significant cooperation from the client. The client must put the wifi card in monitor mode and use a proprietary protocol to blast across the spectrum for 28ms (which pauses all traffic on the AP also). Also, the client needs to have 3 antennas spaced 12-30cm apart. Maybe some laptops and tablets have such a builtin antenna array but definitely not mobile phones or watches.

I doubt this will begin tracking people without their knowledge. It's still ve

Urgh

[solidraven]

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.

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[Anonymous Coward]

In fact, I'd call BS on the fact that they invented anything -- considering there's a company that sells this stuff already.

https://www.cognitivesystems.com/

Disclaimer: I know someone who works there.

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[solidraven]

Changes nothing to the principle. Again nothing spectacular to summarize it ... I'll put it this way: I've seen EE students come up with the same principle multiple times, and using multiple frequencies is a common technique to limit errors due to propagation path differences in the environment. Will still bugger out around big fat metal objects though.

Can detect electronic devices?

[Viol8]

So it can detect my casio watch can it?

Misleading article.

1 wifi access point BUT 4 antennas

[fygment]

From the paper cited, direction is calculated assuming 2 antennas on the access point and 2 antennas on the client ... and then doing an optimization to find the most likely location. When it is correct, you have good accuracy. So the most interesting part is the calculation of time of flight as that is tricky over small distances given how fast light travels.

If they wanted to make it directional without all the caveats, simply beamform the wifi from the access point, and have it scan in bearing, the way

A Nice Technical Advance

[mbone]

In order to do 10 cm ranging (or "time of flight," as in this paper), you need (with a reasonable SNR, say 10), to have a total bandwidth of order 300 MHz. The 802.15.4a UWB standard provides better than 10 cm ranging, but with a bandwidth of 500 MHz, considerably wider than the bandwidth of a 802.11 (WiFi) channels. especially for 802.11b and its successors at S band (2.4 GHz), which are no more than 40 MHz.

This new Chronos system reproduces some of the technical capabilities of 802.15.4 using, not wider c

Xirrus technology being copied is not news.

[David Levin]

The Xirrus Wi-Fi equipment has this capability built in. With the directional radio's the location has accuracy has always been this good. I don't see why MIT copying features already available to the public in existing technology is news. It is fine that some collegian wrote software to do the same thing as an existing product. But as someone else pointed out, all enterprise level Wi-Fi products have a version of this already.

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[mbone]

I am not aware of any company doing this sort of accuracy with 802.11 time of flight (ToF, or ranging), so this is news. Directional Radio (angle of arrival or AoA) is different technology, and will have different pros and cons versus ToF.

Been there. Done that.

[slydder]

We did this as a joke about 6 years ago at work using Fritz USB WiFi and Bluetooth Dongles. Nothing New here.