From: sommerfeld@orchard.medford.ma.us (Bill Sommerfeld)
Date: Wed, 22 Jun 94 06:34:54 PDT
To: karn@qualcomm.com
Subject: Re: Another Cellular Vict
In-Reply-To: <199406220101.SAA00348@servo.qualcomm.com>
Message-ID: <199406221242.IAA00419@orchard.medford.ma.us>
MIME-Version: 1.0
Content-Type: text/plain


   Which suggests a "stealth" phone that randomly dithers its round trip
   delay a la GPS selective availability...

Well, I'm not sure how well that would work...  The "dither" on the
RTT can't go negative (for obvious reasons :-) ).

Presumably the dither turns a "He's somewhere on this circle" into a
"He's somewhere inside this circle".

If you vary the dither over time, someone trying to track you would
wait for the RTT to hit a local minimum to get the most precise fix.

If the dither introduced by the phone has to be the same for all cell
sites, it gets even easier.


						- Bill