AGPS question

Daniel Willmann daniel at
Sun Mar 8 20:46:57 CET 2009

On Wed, 4 Mar 2009 20:33:15 +0100
Leonti Bielski <prishelec at> wrote:

> 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?

The GPS chip can only search for a limited number of SVs in parallel
(the new ublox5 chips comes with a one million correlators which more
or less allows it to search for all SVs in parallel) so in order to
know which SVs should be in view it needs:

1) Current time
2) approx. position of the GPS device
3) Almanac (coarse orbit information) of the SVs

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

Cellhunter tries to collect
GSM cell locations by making a game of it. After we have sufficient
coverage it will be possible to use that for initial position or even
for an approximate location in areas where GPS doesn't work.

Daniel Willmann
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