The carriers and the codes are used mainly to determine the distance from the users
receiver to the GPS satellites.

The navigation message contains, along with other information, the coordinates (the
location) of the satellites as a function of time.

The transmitted signals are controlled by highly accurate atomic clocks onboard the
satellites.

satellites that transmit signals from space, on the basis of which time and position
of the user is measured.

Set of satellites is called as constellation.

GPS uses two satellite constellations i.e. NAVSTAR and GLONASS.

NAVSTAR (Navigation satellite timing and ranging)

NAVSTAR composed of 24 satellites, arrayed in 6 orbital planes, inclined 55
degrees to the equator and with a 12 hours period.

They orbit at altitudes of about 20,200km each.

* Each satellite contains four precise atomic clocks, only one of which is in used at a

time.

Control segment:

The control segment of the GPS system consists of a worldwide network of tracking
stations, with a master control station (MCS) located in the United States at
Colorado Springs, Colorado.

The primary task of the operational control segment is tracking the GPS satellites in
order to determine and predict satellite locations, system integrity, behavior of the
satellite atomic clocks, atmospheric data, the satellite almanac, and other
considerations.

This information is then packed and uploaded into the GPS satellites through the S-
band link.

Control segment consists of a group of 5 ground based monitor stations, three
antennas and a master control station.

The monitor stations measure signals from the SVs continuously and provides data
to the master control station.

The master control station calculates satellite ephemeris and clock correction
coefficients and forwards them to an antenna.

The antenna transmit the data to each satellite at least once a day. The SVs then send
subsets of the orbital ephemeris to GPS receivers over radio signals