[maemo-users] Diablo released (AGPS)

From: Nils Faerber nils.faerber at kernelconcepts.de
Date: Wed Jun 25 11:47:22 EEST 2008
Andrew Daviel schrieb:
> On Tue, 24 Jun 2008, GROG! (Jeff Howie) wrote:
>> On Tue, Jun 24, 2008 at 1:26 PM, Joshua Layne <joshua at willowisp.net> wrote:
>> So assuming that AGPS _is_ included, would that be usable by an N800
>> with a bluetooth GPS?
> I have to agree with Josh.
> AFAIK, the AGPS interface to the GPS chip in the N810 is a serial link 
> using a proprietary TI protocol. AGPS is intended for use in cellphones 
> so it's unlikely to be implemented in a standalone device.

Well... AGPS (assisted GPS) is intended to shorten the time to first fix
(TTF) by uploading known data like ephimeris data up into the GPS
receiver. The "known data" can also be a precise known time, geographic
region etc. Bascially all data that can be used to help "guessing" your
initial position or help the corelation.
Some cellular networks broadcast position alike information as part of
the cellular infrastructure which can be used to helpthe GPS receiver.
But this is not the only method. There are also IP network based
services by some companies providing initial data, like ublox or Jentro.
Using the ephimeris data from ublox a ublox Antaris 5 receiver can have
a time to first after cold start of less than three seconds! SIRF-III
also supports AGPS (upload of ephimeris) in some configurations.

The "problem" with AGPS is that it does not help much in the offline
state. If you do not get up-to-date information from the network you are
back to the non AGPS time to first fix. Ephimeris data is valid IIRC 28h
so you have to update it every day.

> Hmm, just installed Diablo. No network traffic when starting wayfinder 
> map - I thought the AGPS patch was going to look for an ephemeris online.
> Hmm... as per 
> http://www.internettablettalk.com/forums/showpost.php?p=186839&postcount=641
> there's an app agps-ui beta from
> http://catalogue.tableteer.nokia.com/certified/pool/diablo/user/a/agps-ui/
> It uses supl-daemon to download something from 
> https://supl.nokia.com:7275
> Not sure at this point what effect this has - I'm indoors with too weak 
> a satellite signal to get a fix. Looks interesting ... certainly agps-ui 
> lets you choose your estimated position.

We already wondered what this GUI is good for ;)
Choosing your region? Oh well...

  nils faerber

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