At 10:32 AM +0100 2005-07-20, Michael.Dillon@btradianz.com wrote:
While I agree that GPS is the likely answer, I wasn't expecting the ability to work inside computer rooms and basements.
It doesn't need to work in basements, etc. It only needs to keep a record of the last location it was at when the signal faded away. The emergency service vehicles probably can't get any closer than that anyway.
I've been doing some reading on this subject. It seems that both GPS and tower triangulation methods suck. For GPS, the problems are signal acquisition and penetration in urban environments, especially with non-dedicated handheld devices. For tower triangulation, the problem appears to be areas with poor signal coverage where you might only be able to barely see one tower, and where TDoA, AoA, and EOTD aren't going to do you any good. In either case, simply keeping the last known signal lock may very well be one of the worst things you could do. It seems to me that we need to use both technologies in order to get any real hope of reasonably sustainable accuracy, either for E911 or any other location-aware technology. And I'm not convinced even that's enough. So, anyone want to place any bets on what's really going to happen? -- Brad Knowles, <brad@stop.mail-abuse.org> "Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety." -- Benjamin Franklin (1706-1790), reply of the Pennsylvania Assembly to the Governor, November 11, 1755 SAGE member since 1995. See <http://www.sage.org/> for more info.