Carrier Phase Measurement

A GPS receiver may measure the fractional phase difference between the received carrier wave from the satellite and a locally generated copy (replica). The carrier wave measurement is a very precise measure of the distance between the satellite and the receiver, but the initial number of carrier wave cycles is unknown, and needs to be estimated before the carrier phase measurements can be effectively used.

The much better precision of the carrier phase measurement with respect to the pseudorange code measurement can be explained by much smaller period of the carrier compared to the code chip duration (for the L1 CAcode signal, 1540 periods of the carrier fit in one chip of the Pseudo Random Noise (PRN) spreading code).