A more advanced range determination technique, known as carrier phase measurement. This typically requires more advanced receiver technology and longer observation sessions. Currently, carrier phase measurement can only be used with relative positioning, as absolute positioning using this method is not yet well developed.
The technique aims to determine the number of cycles of the (sine-shaped) radio signal between sender and receiver. Each cycle corresponds to one wavelength of the signal, which in the L-band frequencies used is 19–24 cm. Since the number of cycles of the signal cannot be measured directly, it is determined (in a long observation session) from the change in carrier phase over time. Such a change occurs because the satellite is orbiting. From its orbit parameters and the change in phase over time, the number of cycles can be derived.