Fig. 1. The principle of satellite navigation. The user-satellite range
measurements based on the times of transmission and receipt of the signals
are biased by a common amount due to offset between the satellite and
receiver clocks; they are called pseudoranges. Pseudorange measurements
from four satellites are needed to estimate the user position and the
corresponding receiver clock bias.
(c) Copyright 1999, The Institute of Electrical and Electronics Engineers, Inc.