how triangulation of cell phones triangulate

I wanted to know how triangulating cell phones between towers works without GPS installed in a cellphone. So I set about on my quest (which frankly took ALL day)--and with the help of several people, especially John Metzler, I think I have finally put it all together into a workable understanding as so many people think this is just an *EASY* thing to do. IT IS NOT EASY.

If you live in the US and just bought your phone recently (and it is new); it will have some sort of location determination mechanism included for regulatory compliance reasons( like a GPS = Global Positioning Device). This is to help locate the phone in case of an emergency call, (as I had described in my posed questional situation.

Sprint, Nextel, Verizon Wireless, and Alltel all use what is called A-GPS or Assisted GPS, which is a means of using the cell network to accelerate acquisition of GPS satellites.

This involves using the cellular network to effectively "cue in " your location on the globe, so your cell phone doesn't have to do a blind search for all 28 GPS satellites. (Yes, there are 28 GPS satellites! Which is another tid-bit I learned while researching the triangulation of cell phones; how hard it is and is it even always possible.)

My reason for this research really had nothing to do with emergencies. I wanted to know if the *Mr. mean bad guy*; who was considering harm, could easily find his ex-wife/kids location in this manner.

Anyway, rather than having to do the blind search, the cellphone can look for the satellite that would most likely be visible in your area. (But...if you are indoors, a brick building or even under dense forest, this may not work at all.

There is also something called AFLT or Advanced Forward Link Trilateration, which is a fallback to cell network-based location determination when GPS satellites are not visible.

If you are on T-Mobile or AT&T Mobility, your handset may have GPS built in. Recent Blackberries typically do. But all GSM (the network used by T-Mobile and AT&T) phones will rely on what is called UTDOA or Uplink Time Difference of Arrival, which is a means of measuring an uplink from your cellphone to multiple cell sites. Got that? All perfectly clear to you now? :}

If the location of cell sites is known, then the variable you are going for is the handset's location. The time elapsed between arrival at each cell site is divided by the speed of light, giving you a location for your emergency call. (pretty sci-fi, aye!?)

There is also something known as simple Cell ID-based location, which will provide a coarse location estimate based on the nearest cell site. Accuracy will range from a few hundred meters to several kilometers, depending on cell density.

Most cellphones have an opt-in mechanism which allows you to turn off the location determination capability in your phone. (The Mr. Mean Bad Guy NEEDS to know that of course). But, by calling 911, you are in effect overriding that privacy setting and telling the cellular network operator to find you. Which obviously is a GOOD thing.

Also keep in mind that to deliver a wireless call, the cellular network operator needs to keep a record of what cell site you are near, so coarse location HAS to be kept in a register. This should be (is supposed to be by law) and is; in most cases, kept private.

This link below has TONS of further info on this topic if you are so inclined to learn a lot more on this subject - I am just amazed!!

http://www.gps-practice-and-fun.com/positioning-systems.html

You could be there reading, literally, for HOURS.

Best regards, Melanie

http://cell-phone-numbers.com