locating via GSM, revisited

[Werner Almesberger]

joerg at openmoko.org wrote:
> From this data, we see it's quite possible to determine location to a 
> precision of around 100 x 100m or even better.
> Of course this depends on the density of BTS again.

Wait ... if I understand correctly, your experiments (great, by the
way ! Finally real facts ;-) indicate that you can measure some
differences if moving ~50m, correct ?

Now, how does this topology of relative signal strength translate to
anything we can use ? Can we translate it to a geographical location ?
If yes, how much error does the translation from signal path
charracteristics to 3D location cause ? Also, how easily can we get
the real location of the base stations ?

An alternative would be to use only a topology of signal strength,
and to derive hints from it. E.g., one may not be able to say that
location X is 117m at 32 deg from north, but one may be able to give
an estimate that it may be at 10 times the distance from the last data
point, if turning 45 deg counter-clockwise. (The latter part is
tricky, because one would have to project an angle between vectors in
an n-dimensional space to a losely correlated 2D space.)

On the way to this suggested destination, updated and hopefully more
accurate directions could be generated. Of course, there will be some
area where the directions are only noise.

Anyway, sounds like an interesting research project. "Terrestrial
navigation using GSM-based dynamic hypergeometries." :-)

- Werner