GPS

The Global Positioning System (GPS) is a one-way ranging system. The GPS satellites emit signals — complex modulated radio waves — which propagate through space to receivers on or near the earth's surface. From the signals it intercepts, a receiver measures the ranges between its antenna and the satellites.

Sources:

Langley, R.B. (1996). GPS receivers and the observables. In: Kleusberg, A., Teunissen, P.J.G. (eds) GPS for Geodesy. Lecture Notes in Earth Sciences (vol 60). Springer, Berlin, Heidelberg.