From owner-freebsd-hackers  Sat May  6 11:50:14 2000
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Date: Sat, 6 May 2000 12:50:04 -0600 (MDT)
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From: Nate Williams <nate@yogotech.com>
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To: Mike Smith <msmith@FreeBSD.ORG>
Cc: nate@yogotech.com (Nate Williams), hackers@FreeBSD.ORG
Subject: Re: [OT] Finding people with GSM phones (was Re: GPS heads up ) 
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> > > 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.
> 
> Well, assuming they have 100% antenna overlap (not unlikely) you could 
> just do phase comparisons between the antennae getting the squirt.  If 
> these guys are as smart as you say (and I have no doubt at all about 
> that), 25m at near distance is probably not unrealistic.  

True.  Up close, you can triangulate.

> Ask him if they can still do it at 35km out (the outer limit for a normal 
> GSM cell).  That'd really spook me. 8)

He wasn't interested in talking about it when I started asking about
single cell towers, so I never pressed him on the issue.  Maybe he was
afraid that the 100m accuracy claim would be found out to be un-doable,
but the Feds claim 'it must be that accurate', and they aren't
interested in spending the $$ for GPS receivers in the handhelds.

Or, he's got it figured out, and is applying for a patent on it and
didn't want to reveal his secrets. :)


Nate


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