The Global Positioning System (GPS) is a satellite-based navigation system consisting of 24 satellites in medium Earth orbit controlled by the US Air Force. A GPS receiver can determine its position by measuring the time delay of signals received from at least 3 satellites to calculate distance via trilateration. The system consists of space, control, and user segments, with the control segment monitoring satellite health and transmitting updates. GPS is mainly used for navigation, mapping, and has military applications.

1. Global Positioning System (GPS)

2. Overview
 Official name of GPS is NAVigational Satellite Timing
And Ranging Global Positioning System (NAVSTAR
GPS)
 Global Positioning Systems (GPS) is a form of Global
Navigation Satellite System (GNSS)
 Only completely functional one of its kind at this time
 First developed by the United States Department of
Defense
 Consists of two dozen GPS satellites in medium Earth
orbit (The region of space between 2000km and 35,786
km)

3. Overview (continued)
 Made up of two dozen satellites working in unison are
known as a satellite constellation
 This constellation is currently controlled by the United
States Air Force 50th Space Wing
 It costs about $750 million to manage and maintain the
system per year
 Mainly used for navigation, map-making and
surveying

4. Operation Overview
 A GPS receiver can tell its own position by using the
position data of itself, and compares that data with 3 or
more GPS satellites.
 To get the distance to each satellite, the GPS transmits a
signal to each satellite.
 The signal travels at a known speed.
 The system measures the time delay between the signal
transmission and signal reception of the GPS signal.
 The signals carry information about the satellite’s location.
 Determines the position of, and distance to, at least three
satellites, to reduce error.
 The receiver computes position using trilateration.

5. Trilateration

6. GPS Functionality
 GPS systems are made up of 3 segments
 Space Segment (SS)
 Control Segment (CS)
 User Segment (US)

8. Space Segment
 The space segment consist of 30 actively broadcasting
satellites in the GPS constellation.
 GPS satellites fly in circular orbits at an altitude of
20,200 km and with a period of 12 hours.
 Satellites are travelling at a speed of 7000 miles an
hour.
 They are powered by solar energy and built to last
about 10 years.

10. Space Segment (Continued)
 The satellites continuously orient themselves to point
their solar panels toward the sun and their antenna
toward the earth.
 Orbital planes are centered on the Earth
 Each planes has about 55° tilt relative to Earth's
equator in order to cover the polar regions.
 They also have rocket boosters to keep them flying in
the correct path.

11. Control Segment

12. Control Segment
 The control segment comprises of 5 stations.
 They measure the distances of the overhead
satellites every 1.5 seconds.
 Here the satellite orbit, clock performance and
health of the satellite are determined

13. Control Segment
 The CS consists of 3 entities:
 Master Control System
 Monitor Stations
 Ground Antennas

14. Master Control Station
 The master control station, located at Falcon Air Force
Base in Colorado Springs, Colorado, is responsible for
overall management of the remote monitoring and
transmission sites.

15. Monitor Stations
 Six monitor stations are located at Falcon Air Force
Base in Colorado, Cape Canaveral, Florida, Hawaii,
Ascension Island in the Atlantic Ocean, Diego Garcia
Atoll in the Indian Ocean, and Kwajalein Island in the
South Pacific Ocean.
 Each of the monitor stations checks the exact altitude,
position, speed, and overall health of the orbiting
satellites.

16. Monitor Stations (continued)
 The control segment uses measurements collected by
the monitor stations to predict the behavior of each
satellite's orbit and clock.
 The prediction data is up-linked, or transmitted, to the
satellites for transmission back to the users.

17. Ground Antennas
 Ground antennas monitor and track the satellites from
horizon to horizon.
 They also transmit correction information to
individual satellites.

18. GPS Transportable Ground Antenna
Cape Canaveral Air Force Station

19. GPS
Roof
Antenna

20. User Segment
 The user segment simply consist of us and our GPS
receiver.
 GPS receivers are generally composed of an antenna,
tuned to the frequencies transmitted by the satellites,
receiver-processors, and a highly-stable clock,
commonly a crystal oscillator).
 They can also include a display for showing location .
 As of recent, receivers usually have between twelve
and twenty channels.

21. GPS Used in Cars

22. GPS as Land Survey Equipment

23. GPS- U.S. Strategic Command

24. GPS Space Segment Video

25. Refrences
 US – Strategic Command
 US Public GPS “gps.gov”
 Geoview GPS Research
 Wikipedia : GPS Rooftop Antenna
 MIT GPS Lab

26. Thanks