[2023] in cryptography@c2.net mail archive
Re: Mobile phones used as trackers
daemon@ATHENA.MIT.EDU (Phil Karn)
Tue Dec 30 21:18:04 1997
Date: Tue, 30 Dec 1997 18:06:43 -0800 (PST)
From: Phil Karn <karn@qualcomm.com>
To: foner@media.mit.edu
CC: davidw@datamgmt.com, cryptography@c2.net, perry@piermont.com,
karn@qualcomm.com
In-reply-to: <9712302054.AA04457@out-of-band.media.mit.edu> (message from
Lenny Foner on Tue, 30 Dec 1997 15:54:29 -0500)
>It is not completely unreasonable that the Swiss might be tracking
>phones to tens or hundreds of meters; there are US companies whose
>business it is to make such solutions available for celphone 911
>response and "law enforcement purposes" (as they put it). As to
>whether they really -are- doing so, that's for someone else to say.
As someone who has looked at how to do positioning for the FCC's
upcoming cellular 911 requirements, I can say that while several
workable approaches exist, it's just not all that easy to do
*reliably*. Even CDMA, which has a waveform not unlike GPS, has
problems with multipath reflections in urban environments.
So I suspect the article refers to being able to locate a user to a
cell, or to a sector of a multi-sectored cell. After all, that's
precisely the resolution the network needs to deliver your calls, and
to hand you off during calls.
Depending on the size of the cell or sector, you end up knowing the
user's location to anything from hundreds of meters in densely
populated areas to many km in rural or mountainous areas.
See the various books on the hunt for Kevin Mitnick for insights into
how cellular users can be located. They started with a cell/sector ID
(and a channel number) from the switch. This gave the approximate area
to begin using conventional RF direction finding techniques that many
hams will recognize from "fox hunting" contests.
Phil
