[Alan Anderson]

GPS repeaters don't work the way you'd want them to. Any receiver getting signals from a repeater will just end up with the specific location of the repeater's sky-pointing antenna.

There have been occasional attempts to come up with a Field Positioning System using ultrasonic beacons. I tried to devise one myself a few years ago, based on the same idea as LORAN. The math got a lot more complicated than I expected.