GPS

[Kai Römer]

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
>
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