There is this news about Currency Note Tracking with GPS using something called nano-GPS chips? Is this possible to track currency notes using GPS? Can Currency Notes be used as a reflector for GPS?
And GPS positioning works by calculating position using accurate timing signals from 4 or more satellites? (Cross-section of 4 spheres/wavefronts of signals from satellites?
As far as I know it works as one way communication from Satellite to GPS receiver..