On Fri, 6 Dec 2002, Vinay V wrote: > since mobiles use cellular technology, you can at any instant of time > have access at least three mobile base stations(since base stations > keep track of your movements, for ensuring proper call hand over). > This, can be used as the basis for triangulation To perform as postioning system beacons, GPS satellites not only 1) have known locations (time-plotted trajectories) and 2) broadcast timecode, but they 3) lock their time-code to atomic clocks -- and not just any old atomic clocks, but _onboard_ atomic clocks. Likewise, for cell towers to be able act as positioning system beacons, each would at least have to have its own onboard atomic clock. And atomic clocks are hard to get -- half of the world's atomic clocks are onboard those GPS satellites. The need for individual atomic clocks holds even if the reverse is tried -- triangulation of the vehicle from the clocks. However, what the cell towers could do without individual atomic clocks is broadcast GPS correction signals from their precisely known locations. This doesn't need to be done by cell towers specifically and it's already done by correction beacons scattered across the populated portions of the United States... http://www.northstarcmc.com/DGPS-MAP.HTM ...but the closer one is to a DGPS beacon, the more valid the correction code will be (according to a probability distribution function). Therefore, it might be helpful for vehicle triangulation if many cell towers broadcast DGPS signals. -Chris -- Subscription/unsubscription/info requests: send e-mail with subject of "subscribe", "unsubscribe", or "info" toWear-Hard Mailing List Archive (searchable): http://wearables.blu.org Please, *PLEASE* don't subscribe through a forward/expander/false domain
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