1. 1
Global Positioning System (GPS)

2. What is GPS?
GPS, which stands for Global Positioning
System, is the only system today able to show
you your exact position on the Earth anytime,
in any weather, anywhere.
The three parts of GPS are:
•Space Segment
•User segment
•Ground Control segment

3. What is the GPS?
Orbiting navigational satellites
Transmit position and time data
Handheld receivers calculate
latitude
longitude
altitude
velocity
Developed by Department of
Defense

4. History of the GPS
1969—Defense Navigation Satellite System
(DNSS) formed
1973—NAVSTAR Global Positioning System
developed
1978—first 4 satellites launched
Delta rocket launch

5. History of the GPS
 1993—24th satellite
launched; initial
operational capability
 1995—full operational
capability
 May 2000—Military
accuracy available to all
users

6. Components of the System
The Space Segment
The Control Segment
The User Segment

7. 7
Components of the System
• Space segment
• Control segment
• User segment

9. Components of the System
Space segment
 24 satellite vehicles
 Six orbital planes
 Inclined 55o with respect to
equator
 Orbits separated by 60o
 20,200 km elevation above
Earth
 Orbital period of 11 hr 55
min
 Five to eight satellites visible
from any point on Earth
Block I Satellite Vehicle

10. The GPS Constellation

11. GPS Satellite Vehicle
 Four atomic clocks
 Three nickel-cadmium batteries
 Two solar panels
 Battery charging
 Power generation
 1136 watts
 S band antenna—satellite control
 12 element L band antenna—user
communication
Block IIF satellite vehicle (fourth
generation)

12. GPS Satellite Vehicle
 Weight
 2370 pounds
 Height
 16.25 feet
 Width
 38.025 feet including
wing span
 Design life—10 years
Block IIR satellite vehicle
assembly at Lockheed
Martin, Valley Forge, PA

13. Components of the System
User segment
 GPS antennas & receiver/processors
 Position
 Velocity
 Precise timing
 Used by
 Aircraft
 Ground vehicles
 Ships
 Individuals

14. Components of the System
Ground control segment
Master control station
Schreiver AFB, Colorado
Five monitor stations
Three ground antennas
Backup control system

15. GPS Communication and Control

16. GPS Ground Control Stations

17. Triangulation
Geometric Principle:
You can find one
location if you know its
distance from other,
already-known
locations.
How does Gps Works?

18. Triangulation

19. Triangulation

20. Signal From One Satellite
The receiver is
somewhere on
this sphere.

21. Signals From Two Satellites

22. Three Satellites (2D Positioning)

23. Three Dimensional (3D) Positioning

24. 3-D Trilateration
1 Satellite 2 Satellites
3 Satellites

25. Sources of Signal Interference
Earth’s Atmosphere
Solid Structures
Metal Electro-magnetic Fields

26. Obstruction

27. Atomic Clocks
GPS satellites use Atomic Clocks for
accuracy, but because of the expense,
most GPS receivers do not.

28. Line of Sight Transmissions
Line of sight is the ability
to draw a straight line
between two objects
without any other objects
getting in the way. GPS
transmission are line-of-
sight transmissions.
Obstructions such as trees, buildings, or natural formations
may prevent clear line of sight.

29. Light Refraction
Sometimes the GPS
signal from the
satellite doesn’t follow
a straight line.
Refraction is the
bending of light as it
travels through one
media to another.

30. Signal Refraction
Signals from satellites can be like light. When they
hit some interference (air patterns in the
atmosphere, uneven geography, etc.) they
sometimes bend a little.

31. Signal Interference
Sometimes the
signals bounce
off things
before they hit
the receivers.

32. Satellite Distribution
When the satellites are all in the same part of
the sky, readings will be less accurate.

33. PDOP
All of this combines
to make the signal
less accurate, and
gives it what we call
a high “PDOP.”
PDOP = Positional Dilution of Precision
11,000 miles
11,000 miles
11,000 miles
11,000 miles
•A PDOP of <4 is excellent
•A PDOP of 4-8 is good
•A PDOP of >8 is poor

34. In a Nutshell

35. Application of GPS Technology
• Location - determining a basic position
• Navigation - getting from one location to
another
• Tracking - monitoring the movement of people
and things
• Mapping - creating maps of the world
• Timing - bringing precise timing to the world