I these kind of system it is the field strength that is the most important
not the distance. A radio system needs signal strength and that is the
primary reason to measure it. There is a desire to get distance from it,
but this is more of a dream rather tham reality. In cellular systems, it
can be used and give pretty goos location in SOME cases.

I say, for the described situation, RF is NOT the way due to the timing
requirements.
Steve N.



"Sverre Holm" wrote in message
...
Signal strength as a coarse distance indication is only good at very
long ranges relative to wavelength. Even then it is uncertain.

New location systems based on WLAN (2.4 GHz) use field strength combined
with what seems to be some sort of adaptive algorithm that learns the
field
strength vs environment through repeated tests. See www.ekahau.com and
www.radionor.com. These companies promise location for 'free', as they can
locate laptops by using the existing hardware infrastructure of the
wireless
network. This is a very hot topic these days, and large business
opportunities are expected.

But accuracies are in the 1 m range, to get to 1 cm accuracy there does
not
seem to be any alternative to ultrasound systems, see demo on
www.sonitor.com.


--
Sverre Holm, LA3ZA
---------------------------------
www.qsl.net/la3za