The GNSS satellites continuously transmit navigation signals in two or more frequencies in L band. These signals contain ranging codes and navigation data to allow the users to compute the travelling time from satellite to receiver and the satellite coordinates at any epoch. The main signal components are described as follows: Carrier: Radio frequency sinusoidal signal at a given frequency. Ranging code: Sequences of 0s and 1s (zeroes and ones), which allow the receiver to determine the travel time of radio signal from satellite to receiver. They are called Pseudo-Random Noise (PRN) sequences or PRN codes. Navigation data: A binary-coded message providing information on the satellite ephemeris (Keplerian elements or satellite position and velocity), clock bias parameters, almanac (with a reduced accuracy ephemeris data set), satellite health status, and other complementary information.