> > 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).
Right, with triangulation it's trivial.
> 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.
He seemed to imply that they could get it within 25m, even with one
phone. Like I said, I don't understand how, but I didn't question his
ability. Plus, he knows alot more about the stuff than I do.
Nate
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