>
> Plus, they can get a fix on the phone in 300ms (good to about 25m),
> which is far faster than a GPS unit can do it. Basically, the phone is
> 'locked on' as soon as you turn it on and it finds a cell tower. And,
> apparently they've figured out a way to get a coarse fix on it even
> where there is only one tower, although when I pressured him, he just
> smiled and claimed it was a trade secret.
>
> Or so I've been told, but I trust the source since he's one of the
> smartest guys I ever met. :)
GSM (which is what all of these systems are based on) depends heavily on
knowing the flight time from the phone to the cell hardware (and back), in
order for TDMA to work correctly. 25m is special for a reason I don't
recall (possibly flight time for one clock, or something similar).
Triangulation is typically trivial with only two towers (your phone will
generally log into at least the strongest three or four cells) because
the towers use directional antennae, so the tower knows where the antenna
you're on is pointing and you can eliminate the shadow position (most of
the time). With one tower, you're down to describing an arc along which
the phone is probably located; still pretty good when it comes to finding
someone.
--
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\\ Tell him he should learn how to fish himself, \\ [EMAIL PROTECTED]
\\ and he'll hate you for a lifetime. \\ [EMAIL PROTECTED]
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