locating via GSM, revisited

joerg at openmoko.org joerg at openmoko.org
Tue Apr 22 14:46:37 CEST 2008

Am Di  22. April 2008 schrieb Andy Green:
> Somebody in the thread at some point said:
> | Highly problematic it seems to me to do this forced cell reselect
> thing to get
> | TA for other than the current (most nearby) cell, the function named "BTS
> | test" on Nokia monitor [Display 17]. Probably that's about as illegal as
> | using police frequencies to mess around with, or creating your own
> | TV-station. In the end they might accuse you for tearing down the
> whole GSM
> | network by fraudulent or abusive usage.
> Well the impact of it is interesting if you don't have distance
> information from all but one transponder... you end up with a highly
> variable shape that is the intersection of all the circles (because you
> don't know the radius from the centre of each you should use), with one
> master annulus cutting through it from the station you are connected to
> and have a solid distance estimate for.
> Put together the result is an arc of shorter or longer length describing
> your location... if the arch length is small because the other stations'
> intersection is small, it's as good as a point location.  If there's
> only one other base station around anyway, the arc may be 2/3 of the
> circle and if your station is the only one, it is the whole annulus.
> But normally your location would appear as a little rainbow segment of
> one length or another.

Yep, exactly. I only hesitated to try and describe it this precise way ;-)
But usually it should be fairly small area and thus rather precise location.


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