Introduction to global position system

1. Introduction to
Global Position System

2. Slide 2
What is GPS
 Space Segment
 Control Segment
 User Segment
The Global Positioning System (GPS) is a
Constellation of Earth-Orbiting Satellites
Maintained by the United States
Government for the Purpose of Defining
Geographic Positions On and Above the
Surface of the Earth. It consists of Three
Segments:

3. The GPS Constellation

4. Control
Segment
Space
Segment
User Segment
Three Segments of the GPS
Monitor Stations
Ground
Antennas
Master Station

5. 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)

6. Slide 6
Space Segment Description
Very high orbit
 20,200 km
– 1 revolution in
approximately 12 hrs
 For accuracy
 Survivability
 Coverage
24+ satellites
 6 planes with 55°
Inclination
 Each plane has 4 or 5
satellites
 Broadcasting position
and time information on
2 frequencies
 Constellation has
Spares

7. Slide 7
Control Segment
Master Control Station
Monitor Station
Ground Antenna
Colorado
Springs
Hawaii Ascension
Islands
Diego
Garcia
Kwajalein
Monitor and Control

8. Slide 8
Control Segment
(5) Monitor Stations
• Correct Orbit
and clock
errors
• Create new
navigation message
• Observe
ephemeris
and clock
Falcon AFB
Upload Station

9. Slide 9
User Segment
 Over $19 Billion invested by DoD
 Dual Use System Since 1985
(civil & military)
 Civilian community was quick to take
advantage of the system
 Hundreds of receivers on the market
 3 billion in sales, double in 2 years
 95% of current users
 DoD/DoT Executive Board sets GPS policy
PLGR

10.  Military.
 Search and rescue.
 Disaster relief.
 Surveying.
 Marine, aeronautical and terrestrial navigation.
 Remote controlled vehicle and robot guidance.
 Satellite positioning and tracking.
 Shipping.
 Geographic Information Systems (GIS).
 Recreation.
User Segment

11. ESSC 541-542 Lecture
4.14.0511
How the system works
Space Segment
24+ Satellites
The Current
Ephemeris is
Transmitted to
Users
Monitor
Stations
Diego Garcia
Ascension Island
Kwajalein
Hawaii
Colorado Springs
GPS Control
Colorado Springs
End
User

12. Slide 12
Distance Measuring
The whole system revolves around
time!!!
Distance = Rate x Time
• Rate = 186,000 miles per second
(Speed of Light)
• Time = time it takes signal to
travel from the SV to GPS receiver

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

14. Signals From Two Satellites

15. Three Satellites (2D Positioning)

16. Three Dimensional (3D) Positioning

17. Slide 17
Triangulation
Satellite 1 Satellite 2
Satellite 3 Satellite 4

18. Slide 18
Measuring Travel Time
SV Clocks
 2 Cesium & 2 Rubidium in
each SV
 $100,000-$500,000 each
Receiver Clocks
 Clocks similar to quartz watch
 Always an error between
satellite and receiver clocks (  t)
 Require 4 satellites to solve for
x, y, z, and  t

19. Slide 19
Common Problems - Errors
GPS
Antenna
Hard Surface
Satellite

20. Slide 20
GPS Multipath Errors
Effects of Multipath on the GPS Signal
•Avoid Reflective Surfaces
•Use A Ground Plane Antenna
•Use Multipath Rejection Receiver
GPS
Antenna
Hard Surface
Satellite