My guess is he wants to track articles or people by tagging them with a beacon. Or do the reverse and make a machine that can navigate itself through buildings GPS can't penetrate.
In any case, by multilaterating, you time the interval it takes for a signal to go from a transmitter to a receiver. It's a Time Difference of Arrival (TDOA) method, and as long as you have 4 signals to time, you can calculate those 4 distances and locate the object on a 3D map. Four receivers and 1 transmitter, or vice versa.
...So as you'd imagine, multilateration shifts all the design complexity from angle measurement to time measurement. Since radio only takes around 3ns to travel 1 meter, the transmitter and receivers have to be calibrated and synchronized with nanosecond accuracy. As for devices that already use this: there are a few. One uses a wideband RF pulse for timing. Seoul National University has been using something called a Pseudolite system to get centimeter accuracy. WiFi is about to incorporate a function to locate WiFi equipment based on signal strength, but to much less accuracy.