Future of location services on OM

Didier Raboud didier at raboud.com
Sat Jan 10 15:47:45 CET 2009

Gergely Imreh wrote:

> Hi
> > (...)
> Oh, yeah, sounds easy...  The problem is that the cell does not
> broadcast any location information, so the best you can do is the go
> around town, record the signal strength, and try to guess where the
> signal is coming from. If there's plain sight it is relatively
> straightforward. We tried it in a city - echos, shielding from
> buildings... imagine the rest, the signal was all over the place. Not
> something that one can analyse without further knowledge or guesswork.
>  Can send you some logs if you want to check it out
> Having a "cell fingerprint" database - storing relative strengths of
> multiple cells together with the recorded GPS position - would provide
> better operation, but with a cost (in storage place, for example) that
> is just not worth the effort. With the current GSM methods one does
> not aim for supreme accuracy, just speed (you can locate which
> intersection in a city you are in a second, not within 10+ minutes it
> usually takes with my GPS).


by simplifying a little but, this could become easier : assume that you log
positions/cell relationships: for each cell ID, you compute the geometrical
barycenter of the positions. You then store this position and its accuracy
(the number of positions/cell relationships, maybe compute the geographical
spread of the points) that you used to compute the mean.

Assuming an dense, logging you would then have one position per cell, with
a "quality factor" (~ how many measures have produced this point), you
could then simply have a "nearest neighbour" approach to get to know where
you are.

It's true that you would not have the real antenna's positions, but you
would have positions where many people have "seen" the cell ID, which could
turn to be more accurate.

> Cheers,
>     Greg



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