A-GPS (was Re: Freerunner as a mobile gateway -> shipping container)

[Phil Vandry]

On 2011-05-24 08:42, Ed Kapitein wrote:
> You could overcome the TTFF problem by using the agps software from [1]
> It loads the needed data from the gps chip and uses that the next time
> you power on the gps unit.
> I usually get a fix in 2 minutes.

Hi Ed,

For some reason I thought the Antaris chip in the GTA02 didn't support
all of the AID message types but only AID-INI (which provides a basic
saved position and time but nothing else like almanac or ephemeris).
I think it has something to do with the facts that (a) the chip doesn't
send ACK messages in response to any AID-* messages, making it hard to
know if the messages you're sending are good, and (b) I've never managed
to get a Freerunner to send me a AID-DATA probe which is the message
that means "please send me any available aid data".

Why my Freerunners never send AID-DATA whereas the code you pointed
to clearly expects to receive it I have no idea. In any case, I decided
to try again. This time I just send it all the AID messages at
startup whether it asks for them or not. The results are good so far.

If the Freerunner has network connectivity within a few minutes of
startup, I subsequently get fresh AID data from the Internet and send
that too. The result is that the GPS gets two copies of the AID data,
one saved from the last shutdown and one fresh from the Internet. It
doesn't seem to mind.

Thanks for motivating me to try this A-GPS stuff again.

-Phil