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RE: Cell towers as GPS beacons? (was: reply)

> -----Original Message-----
> From: Christopher Allen [mailto:]
> Sent: Friday, December 06, 2002 7:49 AM
> To: 
> Subject: Cell towers as GPS beacons? (was: reply)
> 
> 
> 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.
> 

But wouldn't this only improve the accuracy of your GPS determined
position? If all you do with cell towers is send more GPS data to a GPS
receiver you haven't taken advantage of the cellular signal from the
towers.

It seems to me that if the towers just included their GPS location in
messages you could use that information to define an area between the
towers that you are most likely to be located in. This is obviously a
large area and could be miles across, but for some purposes just knowing
you are in the middle of downtown Manhattan could be useful.

-Paul

R. Paul McCarty
Vitronics Inc
tel: (732) 389-0244 x30
fax: (732) 544-9431

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