GPS
is based on the access and triangulation of information sourced from US military satellites and commercial satellites which have either been set up specifically for GPS, or (the now defunct) European Galileo project.

You'd be better off trying to sort out something that triangulates using radio signals, such as mobile masts, but there are already products out there which do this (let alone the countries whose governments actually control the mobile networks).

Let me know what you're thinking and I'll see who I can talk to. I know a few people in the field, especially those with a technical knowledge.
(Ethelred is watching cheese grow, Sun 5 Oct 2008, 1:27, Reply)