WiFi Triangulation

mikegroovy writes "WiFi software tracks you down: 'Positioning technology company Ekahau has released an updated version of its software, which allows devices to be physically tracked when they are connected to an 802.11 WLAN network.' Maybe connections that are made from the street(or outside of a predefined area) could be automatically disconnected... It may spell an end to warchalking."

Comments

Constantly diminishing signals are rare in RL

[addikt10]

Triangulation of EM is based on the assumption that the strength of a signal will diminish with the square of the distance from the source, or some other constant function with other signals.

When was the last time you were using wireless (especially through a wall) that had the same range from the access point in any direction?

I can't picture it working in a supermarket, with the metal shelving, compressors for the cold storage, etc. Sure, in a lab it'll work great, but with any kind of range or non-uniform building structures, not a chance.

No Triangulation , Just bump the power for War

[notestein]

After digging through their site, it seems that they locate you by the following:

Calibrate the positioning model - Move around the area while clicking the map to record sample points containing received signal strength intensity (RSSI) samples. No information about the access point locations is required

And it implies that triangulation is not involved:

Ekahau technology offers more comprehensive feature set than any competing technology on the market. The calibration-based approach is radically different from other commercial techniques, which mostly rely on signal propagation and triangulation for solving the location.

So perhaps if you bump the power of your signal from the outside they will think you are inside.

How does it work?

[Omega Hacker]

I can think of several ways it might work, but all of them present significant challengs. Relying on relative signal level would be ludicrous, because signal level changes dramatically with card orientation, reflections, and whatever's in the middle. Heck, I get significant variance in signal level on the fixed links between the antenna on my roof and neighbor's sites.

Using a GPS-like timing comparison might do the trick, but it's set up backwards. With GPS you have a bunch of atomic clocks in orbit, and one device correlates the relative signal phase between them. With APs, you have to have extremely accurate timing across all the APs, which is a very hard problem (I've researched it...). Once you have that, you can compare reception times of a packet from the device being tracked, and triangulate. Problem is 1 meter accuracy represents some scary clock accuracy numbers across several APs with just an Ethernet between them.

If anyone can think of any other way to pull this off (WITHOUT modifying the client, and ideally without any special hardware, i.e. implementable in the HostAP driver), post them here.

What about this

[iamdrscience]

Triangulation works great in two dimensions, but when you use a third you have to do quadrangulation (is that even a word? I'll bet it is) like say you work for a company in a five story office building, when you triangulate where a person is in relation to you distance wise and in which general direction, but you don't really know where he is, maybe he's 15 meters in front of you and maybe he's 5 meters in front of you, but three floors down. They could both register as the same with triangulation. I will start the quadrangulating WiFi revolution.

Re:What is warchalking about?

[NDeans]

Because they use chalk to make a )( symbol to designate an open AP.

As a sidenote, Schlotsky's restaraunts put up little plaques near the entrances to their stores with the open AP symbol. Such a nice thing to see, rather than the money hungry Starbucks shops charging by the minute for access.

Re:Uh oh

[Fnkmaster]

Funny thing happened the other day. My friend was over, opened up his laptop in the living room of my apartment, and started browsing. We had been making some DNS changes to a site we own, and he was checking them out, and told me they had propagated. I checked on box, and couldn't see them yet. This had us stymied for about 20 minutes until he checked his current IP address and hostname, which showed clearly that he was on Verizon DSL, whereas my apartment has ATT BB Cable - he was using the default Linksys SSID and his 802.11b card had picked up the neighbor's wireless access point accidentally. Whereupon we also discovered that we were easily able to use the default Linksys password to get onto the neighbor's router. Oh, and we found that our neighbor had three Windows boxes with open shares on them (nothing interesting in the shares though).

For a brief moment, I questioned why I am paying for a landline feed and not just piggybacking bandwidth off of my hapless neighbors.

Re:Assimetric aerial (and a new hobby)

[driehuis]

Yes, it will confuse it.

Their method will probably even fail if you switch WiFi cards. I've got a Compaq WL110 which has a range of about 10 feet. My Lucent card on the other hand sees the access point from 100 feet, without line-of-sight (I assume the radio waves bounce off the ceiling through the window; no other way to explain _that_ range).

My access point has antennas that can be moved into different polarisations, and in an off-colour configuration, access without line-of-sight becomes really spotty: it works in one place, and a few feet to the side it stops.

But it seems to me the point of the seller is not to track abusers, but rather to track known-good devices in a known area. That alone is a cool concept, if you see what contortions people go through now when designing warehouse positioning systems. I've seen the results of an automated fork lift running through the wall of a warehouse because the reflective pad that marked the end of the aisle was covered in grime.

Hmmmm, I can envision the next hobby: sit outside a warehouse with a 2.4GHz klystron, wait until you hear the fork lift come down the aisle, then switch on the jammer and watch the fireworks :-)