locating via GSM, revisited

joerg at openmoko.org joerg at openmoko.org
Sun Apr 20 22:17:24 CEST 2008

Am Mo  21. April 2008 schrieb Andy Green:
> Somebody in the thread at some point said:
> |>>  To use this approach with GTA02 or GTA04/Diversity, it has to be
> | evaluated
> |>>  whether we can get he NCEL-list from our GSM-modems.
> |> Yes, we can, the info at
> |>
> |
> |> came from my GTA01 modem but it works also on the GTA02 modem.  In
> |>
> |
> |> we also get the Timing Advance value (called tav).  We need some stats
> |> :)
> |
> | Fine! Pleased to hear this :-)
> WAH now you're talking :-)  I was very interested when you talked about
> this before and hearing that this actually exists for GTAxx GSM is super
> great.
> |> I'm not sure about forcing a reselection of the station but my guess
> |> would be that there is a command for that also.
> |
> | If there's no such command already for it, we might probably be able
> to hack
> | it to the baseband firmware (OM may do this I guess).
> | Andy Green mentioned he thinks he might have seen such a command
> already. I
> | will have some long nights to study the specs for GTA02 GSM modem, so
> I can
> | tell for sure. Wouldn't mind to get a pointer instead.. ;-)
> (This is a misunderstand, I don't know anything about GSM commands.
> What I was saying here inbetween beers was that I know Sean Chiang is in
> control of the firmware enough to add his own commands, therefore I am
> pretty certain we can add it if it doesn't exist.)

Sorry, probably I remembered wrong, was a lot of highly important info I had 
to learn this day in London. Anyway we are half way there to doing this thing 
right now, even without new firmware :-)

> What I think we need to do with this stuff is feed it into one daemon,
> from GPS, WLAN AP and GSM masts alike.  These WLAN and GSM
> "fingerprints" have something deep in common, they are a list of
> transmitters with estimated distance (radius) and estimated error.  I
> think if we collect this datatype we can leverage it in very cool ways,
> with or without the advantage of GPS.

Yep! For GTA04 I like to see parts of this daemon running on the MPU, at least 
to the point where we can detect changes caused by movement so we know we 
have to wake the MCU. I guess this should be quite feasible for GSM and GPS, 
not sure about WLAN and how much intelligence we need on driver side to 
acquire a list of AP - like `iwlist wlan0 ap` or `iwlist wlan0 scan`.

Andy, what do you think about amount of RAM and ROM we need on the MSP430 to 
do things like this?

> Although pure signal strength or reflections can make variations in what
> we think about one transmitter, it is unlikely to affect the
> constellation of transmitters randomly spread around in the same way,
> this stuff could be more robust than one might expect.

That's exactly what I think. And the best part of the story is: from GSM we 
get a continuous position fix almost for free (unlike GPS or even WiFi), as 
long as GSM is registered anyway :-)))


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