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
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www.qsl.net/la3za