GPS

[Al Johnson]

I'm not saying there isn't an antenna issue, but that we may be able to 
mitigate the effects on startup time.

On Monday 07 July 2008, Kai Römer wrote:
> Hi Al,
>
> Sounds really convincing, but how do you explain the constantly fast
> fix via external antenna then. I really think its an antenna issue.
>
> Also the difference of the GPGSV values support this idea.
>
> Tomorrow evening i will ask a specialist to check the antenna signal
> qualities. Maybe a cable is broken or there is a short circuit on the
> main board.
>
> I ll report about the results.
>
> CU Kai
>
> 2008/7/6 Al Johnson <openmoko at mazikeen.demon.co.uk>:
> > From what I've seen on the wiki the version of the Antares4 on the GTA02
> > doesn't have the memory needed to store almanac and ephemeris, last known
> > position or time. This means that every start is a true cold start,
> > unlike every other reasonably modern GPS we're comparing it to. It starts
> > up thinking the time is midnight on 30th November 1999 and seems to need
> > a fair bit of decent signal to convince it otherwise, contributing to the
> > long startup time.
> >
> > It looks like there is a way around this if you look at the documentation
> > for the assist. The AID-INI message needn't be supplied by a remote
> > server; we can generate it locally to provide the sort of data that's
> > stored internally most of the time. At the very least we have a fair idea
> > of the current time and date. We should also be able to store location,
> > almanac and ephemeris when we shut down the GPS, and provide it at the
> > next startup. We can also have a stab at current location, based perhaps
> > on cell ID or wifi data as discussed by some of the other threads, or on
> > user input.
> >
> > I'll try to patch together something to do this based on the example perl
> > client and server code, and see how much difference it makes.
> >
> > On Friday 04 July 2008, Kai Römer wrote:
> >> I can affirm this for 6 opemoko devices. i guess its an internal
> >> antenna issue. as soon as you connect a external antenna to it works
> >> like a charm. but fur me thats no solution.
> >>
> >> TTFF with external antenna (perfect condition): 40 to 60 seconds
> >> TTFF with internal antenna AGPS (perfect condition): more than 1:20
> >> minute but not always. its like gambling.
> >>
> >> I guess a miss design of the internal antenna.
> >>
> >> CU Kai
> >>
> >> 2008/6/23 Peter Kraker <peter.kraker at volja.net>:
> >> > This timings are insane unless you don't even have a valid almanac,
> >> > which is rare. This doesn't look right.
> >> >
> >> > Yorick Matthys pravi:
> >> >
> >> > Marcus Bauer said:
> >> >
> >> >
> >> > My experience with the Freerunner is ~12 minutes TTFF (time to first
> >> > fix) without use of agps and ~4-8 minutes TTFF with agps from
> >> > agps.u-blox.com using the software from openmoko.
> >> >
> >> > The Neo1973 (GTA01) had a TTFF without agps assistance of ~2 min.
> >> >
> >> >
> >> > 12 minutes without AGPS and 4-8min with AGPS??
> >> > I hope there was a thunderstorm inside the basement where you tested
> >> > this...
> >> >
> >> > :)
> >> >
> >> > Seriously, these just don't seem realistic.
> >> > Compare them for example with some other devices from 2003:
> >> > http://www.pocketgpsworld.com/ttffcomparisons.php.
> >> > Or from ublox: http://www.u-blox.com/technology/assistnow/ (table at
> >> > the bottom of the page)
> >> >
> >> > Surely there must be something wrong with your
> >> > software/settings/hardware/environment...
> >> > (or maybe they still have a lot of work to do on the GPS :))
> >> >
> >> > y