GPS

[Yorick Matthys]

Jisakiel wrote:

>Let's see if I understood correctly the concepts involved here, as I am still a little bit confused...
>
>- TTFF is when no almanac data is available. Unlike what's specified in http://wiki.openmoko.org/wiki/Neo_FreeRunner , is not 40 seconds but 12 minutes (no>small difference).
>- TTFF shouldn't happen almost never, given that mobile phone is always -but it's first boot *ever*- in normal state as defined here : http://en.wikipedia.org
>/wiki/Time_to_first_fix  . Unless we have moved in a 100km radius without gps enabled, mobile phone does not have the correct time, we are in a car / train,>and (dunnow if that's an AND or  OR) no previous almanac available, fixes should be a lot quicker. As in, how much?
>- AGPS should make ¿everything? ¿TTFF only? by downloading a small data package.
>
>My questions, then:
>
>- AGPS can be served by the gsm network without data transfer costs? I mean: does it *need* to download it from the internet (with its GPRS associated>connection and outrageous prices here in Spain), or is it transferred for free from the GSM operator? I understand this piece of information to be common to>every GPS phone, not just openmoko...?
>- In normal conditions a fix is quite quick (as in 2 or 3 seconds) and not too "expensive" in terms of battery or processing. Is that true?
>- If I get in a car fixes get slower unless I have gps constantly on (which should eat the battery fast).
>- Should I travel without network coverage (as in: by tube), when arrived at destiny fix will be slower. How much slower? Does AGPS help here?
>- Is it possible to get some triangulation info from the GSM towers the phone is connected to? Possible as in "here's how on the openmoko", not as in>"theoretically" ;), which I know that it is -my symbian phone does it, I remember some profile software which used that.
>
>
- TTFF is time to first fix, and it does not only apply to when there is no almanac data (http://en.wikipedia.org/wiki/Time_to_first_fix, you found the page but i think you didn't read it carefully)
- TTFF happens every time you power on the gps module
- AGPS decreases the TTFF time

Your questions:
- AGPS can NOT be served by the gsm network without data transfer costs. But you can also download it from your home network
you can use AGPS online or offline. Take a look at the bottom of http://www.u-blox.com/technology/assistnow/
online: valid max 4hours, offline valid max 14days
I am not sure if the offline can work in the freerunner (if it has EPROM it will work, otherwise maybe not, I can't find it in the wiki so I guess it has none)
- normal conditions: take a look page 2 of http://www.u-blox.com/products/Product_Summaries/ATR0630_35_Chip_Prod_Summary(GPS.G4-X-07008).pdf
- when you travel by tube i think you will get a fix very soon (If you had a fix before you entered the tube)
- somebody correct me if I'm wrong, but I don't think it has been implemented for the freerunner (yet)


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