From: die@pig.jjm.com (Dave Emery)
Date: Sun, 19 Jun 94 15:36:42 PDT
To: cypherpunks@toad.com
Subject: Cell phone tracking
Message-ID: <9406192230.AA02687@pig.jjm.com>
MIME-Version: 1.0
Content-Type: text/plain



   Mike McNally writes: 
 > 
 > Jef Poskanzer writes:
 >  > It looks like at least some switches in Amerika are already equipped
 >  > to read out locations for individual phones.  
 > 
 > This is not actually that surprising.  All they need is to know which
 > phones are using a band on a cell site, and they narrow the search
 > down to a relatively small area.  I seriously doubt that they can do
 > triangulation (I mean, they *could*, but there's not much likelihood
 > that the cellular operators would incorporate something complicated
 
 
 	A company I am familiar with which does specialized classified
 interception systems for the NSA and other TLA's has built just such a
 system for the TLAs. 
 
 	It can locate a cellphone to within a few feet just as soon
 as it starts transmitting - it uses time of arrival techniques to 
 triangulate the cell phone's position.
 
 	How many of these are installed and where I do not know, but
 the technology has been developed and is in use. The system is multi-channel
 and can keep track of many cellphones at once - but as a practical
 matter it isn't hard to monitor the control channels and paging channels
 to locate the phone of interest and identify which of the 866 channels
 it is transmitting on so even simple doppler DF technology might work.
 
 	Considering that the LA area is the biggest cellular market in
 the country it wouldn't surprise me that some of the these systems
 are installed there.
 
 	And in the future Phil Karn's company Qualcomm's CDMA digital
 cellphones will provide few feet accuracy position as a byproduct of the
 spread spectrum receive correlator operation on every transmitting phone
 within range of more than one cell receiving site unless they actually
 aviod trying to make the measurement.  Most of the time more than one
 cell site tracks a given phone so they can vote on which one has the
 stronger signal - given that each of these sites has a precise estimate
 of the time of arrival of transissions from each phone it takes little
 more than netting of the time base (with GPS ?) between the cell sites to
 detemine cellphone positions since the positions of the cell site
 antennas are well known.  I suspect that if the hardware and software to
 do this (mostly software) is not part of the current base station that
 certain TLAs will pay to have it developed and implemented. 
 
					
					Dave Emery

					die@pig.jjm.com