still GPS questions

Michael Born michael.born at
Tue Jun 17 18:37:31 CEST 2008

Hello OpenMoko community.

I read a lot of the GPS discussion on this mailing list, in the OpenMoko wiki 
and on wikipedia. Still there are things I don't get :-(
As I'm interested in the freerunner everything here refers to the GTA02.

There are two extensions to GPS - AGPS and DGPS. On page one of GTA02s GPS 
chips datasheet [1] is written that both are supported.

Concerning DGPS the datasheet seems to refer only to the "big" services (WAAS 
in America, EGNOS in Europe and MSAS in Japan). The services use 
geostationary satellites sending data for additional accuracy on the same 
frequency as the GPS signal. As far as I understand the GTA02 GPS chip 
automatically uses the WAAS/EGNOS/MSAS signals for better accuracy when they 
are available ([1], page 9, table 3-1, "Accuracy").
In principle the DGPS signal/data could be transfered to the freerunner by 
radio, gsm, wlan, lan,... so my first question is:
1. Are there other DGPS services in Germany available? Is it possible to 
receive this data and feed it into GTA02s GPS chip?

AGPS seems to be a mixture of different "assisting" things. 
First of all the possibility to feed ("almanac" and "ephemeris") infos about 
the GPS satellites to the chip so that it finds the satellites in 5 seconds 
instead of 35 seconds.
Freerunners ATR0635 chip offers AssistNOW(tm) which seems to be ublox service, 
offering "almanac" and "ephemeris" via internet.
2. Is this AssistNOW(TM) supported by the GTA02 software? Are there 
better/cheaper ways of getting up to date "almanac" and "ephemeris" into the 

Other AGPS features seem to rely on gsm communication with a server
- sending GPS data to that server which helps calculating the position
- getting additional data about the position from a server
- even get the precise position measured by gsm triangualtion
3. Which of these services are available in a common gsm network in 
Germany/Europe/worldwide? Can these services be used by GTA02?

Best regards


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