R: Need info on AGPS

Harald Welte laforge at openmoko.org
Thu Jan 25 16:24:52 CET 2007

On Thu, Jan 25, 2007 at 02:38:20PM +0100, Michele Manzato wrote:
> Some additional questions on this subject:
> 1. Is there any "A-GPS standard" whatsoever?

no. It's a broad term for many variants of GPS

> 2. I have heard elsewhere (Wikipedia) that in A-GPS the computation effort
> is shared between the device and the A-GPS Server. According to a previous
> post, the device just downloads the ephemeris table so there isn't any
> actual "computation sharing", but rather a download of a pre-computed table
> download. Correct?

As far as I understand it: yes.  I will ask our GPS engineer to comment
on those questions.

> 3. A-GPS involves additional data traffic and thus (potential) additional
> costs. Does it use a normal GSM/GPRS IP-based data transfer? does it use
> some out-of-band GSM/GPRS control messages? or does it get data from
> broadcasts in the local cell (e.g. GSM cell-broadcast)?

AFAIK: GPRS.  so its up to you whether you want that extra traffic (and
cost, unless you're flat) or not.

> 4. if the answer to above is GPRS: is it possible to estimate in advance how
> much additional traffic (in Kbytes/day of full operation)?

I am sure it's a quite fixed amount of 

> 5. Are there any known estimations on the overall (A)GPS performance on the
> Neo (esp. fix time)

There are some numbers in the data sheet of our GPS chipset vendor, but
that data sheet is closed.  I will ask them to give us some
document/numbers that we can publicize.

> 6. Coming to the Neo1973. In order to save costs, can the "Assisted"
> function in A-GPS be disabled through software API?

yes, it can be disabled through preferences.

> 7. Is it possible to tell whether A-GPS is actually in use or not?

yes. either you have enabled it in preferences or nor ;)

> 8. Is it possible to tell/know which is the A-GPS server currently in use?


- Harald Welte <laforge at openmoko.org>          	        http://openmoko.org/
Software for the worlds' first truly open Free Software mobile phone

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