writes "A proposal has been, uh, proposed for a relatively low-cost method for producing regional satellite-based location system. Instead of putting up an expensive constellation of atomic-clock-carrying satellites in near-polar orbits, the proposal is to send timing signals from ground-based atomic clocks, to pre-existing geostationary satellites with poor latitude control. The "geostationary" satellites re-transmit the timing signals to earth, and triangulation then supplies location from the arrival times of the signals at the receiver.
The proposal paper on Arxiv also suggests that, since most existing communications satellites are designed for 2-way communications, this could provide a "cheap" back channel for (say) location-enabled emergency communications."Link to Original Source