Triangulation

[murwil]

Anyone got any thoughts on trying to triangulate using a WiFi signal? I am looking for a resolution (measurable change in position) of about 10 - 20 ft. So that as you move the Wifi device around it's location can be identified?
Any thoughts on this would be appreciated.
murwil

[jatkins679]

I don't think that's going to work w/o some directional antenna to work with. It can be done with cellular calls and in fact that is one of the technologies that is to be used to be able to pinpoint a caller. But they use fairly directional antenna and multiple ones at that. Plus even then, the potential error is pretty good (within 100 meters radius), a lot more than what you want to do.

I think the best you'll probably be able to do is figure out what AP the client is using.

[murwil]

Yes, I think your right. - Though I thought Cell phones were using GPS for their locations.
Thanx for the feedback
murwil

[jatkins679]

Originally posted by murwil
Yes, I think your right. - Though I thought Cell phones were using GPS for their locations.
Thanx for the feedback
murwil

That's kinda interesting. Last time I checked, there were two options: the triangulation or GPS. GPS has it's advantages in that you don't need multiple antennas/cells to determine a caller's location, which would be advantageous in rural areas. But you need to incorporate a GPS antenna, which can be bulky, and you have the power draw on the phone battery.

Triangulation doesn't use the client's power and doesn't necessarily need a firmware upgrade. But you do need multiple antenna/cells to use it and it isn't very accurate.

Either way, right now it doesn't matter: all but two (I think) cell phone service providers missed the deadline last October to provide such locator services for 911 callers, the system known as Enhanced 911 (E911).

[TR-VA]

have you looked at the Ekahau solution ? They claim accuracy to around a few feet using a different technology than triangulation.
As far as cellphones are comcerned the industry is talking about TDOA and U-TDOA....
-TR

[dot11guru]

With Triangulation and 802.11b the best you can hope to get is about 30 feet or 10 meters. I think Newberry networks has the IP on the Triangulation over WLAN.

Without special hardware that can measure DTOA (Differential Time of Arrival) all you can hope for is RSSI (Relative Signal Strength Indicator). Unfortunately RSSI is not a very accurate measure of how far you are from an AP, just how well you hear the AP or how well the AP hears your client card. The .11 signal can experience multi-path (where it bounces off of objects: usually metal objects) before it gets to the receiver. This can change the RSSI significantly even if you are close to an AP, the RSSI may be very poor compared to an AP that might be further away, but has a better line of sight.