GPS is a satellite-based navigation system consisting of 24 satellites operated by the US Department of Defense. It provides positioning anywhere in the world without subscription fees. GPS determines location by measuring the time it takes signals from satellites to reach a receiver and using that to calculate the distance to the satellites, whose locations are known. Combining distance measurements to multiple satellites triangulates the receiver's position.

5. WHAT IS GPS?
• Satellite based
navigation system.
• Based on a
constellation of about
24 satellites
• Developed by the
United States
Department of
Defense (DOD)

6. WHAT IS GPS? • Can provide accurate
positioning 24 hours
a day, anywhere in
the world.
• No subscription fees
or setup charges to
use GPS.
• GPS satellites also
called NAVSTAR,
the official U.S.
DOD name for GPS

7. STRUCTURE
Space Segment Control Segment
User Segment

8. HOW GPS DETERMINES A LOCATION

9. HOW GPS DETERMINES A LOCATION
Things which need to be determined:
• Current Locations of GPS Satellites
• The Distance Between Receiver’s Position and the GPS
Satellites

10. CURRENT LOCATIONS OF GPS SATELLITES
• GPS satellites are orbiting the earth at an altitude
of 11,000 miles.
• The orbits, and the locations of the satellites, are
known in advance.
• GPS receivers store this orbit information for all of
the GPS satellites in an ALMANAC*.
* THE ALMANAC IS A FILE WHICH CONTAINS POSITIONAL INFORMATION FOR ALL OF THE
GPS SATELLITES

11. • All 24 satellites are
divided into 6 parts.
• There are 4 satellites
in each part.
• A definite orbit is
defined for each part.
• Each of these 3,000-
to 4,000-pound solar-
powered satellites.

12. DISTANCE BETWEEN RECEIVER’S
POSITION & THE GPS SATELLITES
• By measuring the amount of time taken by
radio signal (the GPS signal) to travel from
the satellite to the receiver.
• Radio waves travel at the speed of light, i.e.
about 186,000 miles per second.
• The distance from the satellite to the receiver
can be determined by the formula “distance =
speed x time”.

13. GPS ERROR BUDGET
Different errors can cause a deviation of +/- 50 -
100 meters from the actual GPS receiver position
which are :
ATMOSPHERIC CONDITIONS:
• Speed of GPS signal is affected by ionosphere
& troposphere.
• Which cause a deviation of 0 to 30 m. from the
actual position of receiver.

14. EPHEMERIS ERRORS:
• The predicted changes in the orbit of a
satellite.
• Which cause a deviation of 0 to 5 m.
from the actual position of receiver
CLOCK DRIFT:
• Due to different code generations in
satellite and receiver simultaneously.
• Which cause a deviation of 0 to 1.5 m.
from the actual position of receiver

15. MULTIPATH:
• Bouncing of GPS signal due to a
reflecting surface before reaching to
receiver antenna.
• Which cause a deviation of 0 to 1 m.
from the actual position of receiver

16. MEASURING GPS ACCURACY
The geometry of the constellation is evaluated by
Dilution Of Precision, or DOP .
DOP

17. INCREASING ACCURACY OF GPS
• Differential correction provides accuracy within 1-5 m.
• Coarse Acquisition receiver provides accuracy within
1-5m.
• Carrier Phase receivers provides accuracy within 10-30
cm.
• Dual-Frequency receivers are capable of providing sub-
centimeter GPS position accuracy.

18. APPLICATIONS
AVIATION AGRICULTURE
MARINE TIMING

19. SPACE RAILWAYS
ROADWAYS DISASTER RELIEF

20. Name Launch Date
NAVSTAR 64 (USA 206) August 17, 2009
GPS Operational Satellites
NAVSTAR 63 (USA 203) March 24, 2009
NAVSTAR 62 (USA 201) March 15, 2008
NAVSTAR 61 (USA 199) December 20, 2007
NAVSTAR 60 (USA 196) October 17, 2007
NAVSTAR 59 (USA 192) November 17, 2006
NAVSTAR 58 (USA 190) September 25, 2006
NAVSTAR 57 (USA 183) September 26, 2005
NAVSTAR 56 (USA 180) November 6, 2004
NAVSTAR 55 (USA 178) June 23, 2004
NAVSTAR 54 (USA 177) March 20, 2004
NAVSTAR 53 (USA 175) December 21, 2003
NAVSTAR 52 (USA 168) March 31, 2003

21. Name Launch Date
NAVSTAR 51 (USA 166) January 29, 2003
GPS Operational Satellites
NAVSTAR 50 (USA 156) January 30, 2001
NAVSTAR 49 (USA 154) November 10, 2000
NAVSTAR 48 (USA 151) July 16, 2000
NAVSTAR 47 (USA 150) May 11, 2000
NAVSTAR 46 (USA 145) October 7, 1999
NAVSTAR 44 (USA 134) November 6, 1997
NAVSTAR 43 (USA 132) July 23, 1997
NAVSTAR 39 (USA 128) September 12, 1996
NAVSTAR 38 (USA 126) July 16, 1996
NAVSTAR 37 (USA 117) March 28, 1996
NAVSTAR 36 (USA 100) March 10, 1994