gpsd and AGPS

Alexey Feldgendler alexey at
Fri Sep 28 09:57:00 CEST 2007

On Mon, 03 Sep 2007 21:24:45 +0200, Ken Yale <kyale at> wrote:

> Normally, ephemeris satellite data is downloaded at 50 bps from the  
> satellites, but only when the signal strength is above about -142 dBm.   
> Live ephemeris data is good for about 2 hours.  With a data connection  
> (I use a USB TCP/IP bridge to a PC, and then to the network), we can  
> download 7 days of ephemeris in 3 or 4 seconds, independent of GPS  
> signal conditions.

Wasn't the last sentence supposed to say "almanac"? As I understand, the  
ephemeris data is short-lived and doesn't make sense to cache ahead of  
time. The almanac, on the other hand, is valid for some days once acquired.

> - database of cellID --> initial position look up.  I understand network  
> operators cherish and protect this database.

Sure, the cell operators won't gladly share this data with anybody, but  
there's still something that could be done: the phone could learn the  
CellID <-> area association and use it later (if we are registered at some  
cell we've already been at, we can't be miles away from where we were last  
time at this cell).

Alexey Feldgendler <alexey at>
[ICQ: 115226275]

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