AGPS question

Helge Hafting helge.hafting at
Thu Mar 5 11:05:34 CET 2009

Leonti Bielski wrote:
> I have a second question:
> In agps package for u-blox you have to provide approximate location of
> your phone and radius (for example 150 kms).
> What does it change? If I provide some longitude and latitude and set
> some huge radius will it affect anything?
> Is it possible to eliminate it at all?
It is not really needed, it merely speeds up TTFF somewhat.

Uploading almanac and ephemeris really helps, as this necessary 
information then don't need to be downloaded slowly from the satellites.

An approximate location helps further. A wrong location may delay
the first fix instead, or make the device fail.

> My brother has N95 with Agps and he does not have to provide his
> location while using agps service.

An AGPS setup don't have to use a location. Or the approximate location 
can be supplied automatically as the tower location. You are necessarily 
within 20km of the tower - much closer if in a city. The tower can 
supply its location, or the phone can have a database of all tower 
locations.  The latter approach is the more realistic approach for 
openmoko users.  They rather helps building a cell database, than pay 
for AGPS service.

Helge Hafting

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