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