GPS is a satellite-based navigation system consisting of 24 operational satellites owned by the US Department of Defense. It provides location and time information to GPS receivers anywhere in the world. The GPS satellites orbit Earth twice per day and transmit signal data that receivers use to calculate the user's position by determining the time delay of signals from multiple satellites. Factors like atmospheric conditions, clock drift and multipath can cause errors of 50-100 meters in positioning, which can be reduced to centimeters using techniques like differential correction.

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

5. 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

6. STRUCTURE
Space Segment Control Segment
User Segment

7. STRUCTURE
SPACE SEGMENT:
• GPS Satellite constellation composed of 24
operational satellites in space.
• These 24 satellites are placed in 6 circular
orbits of period equal to 12hrs and these orbits
are equally spaced with 60 degrees apart and
at an inclination angle of 55 degrees to equator

8. STRUCTURE
CONTROL SEGMENT:
• The control segment comprises of 5 ground stations
located on equator.(4-monitor and 1-master station)
• Monitor stations measure the distances of the
overhead satellites every 1.5 seconds and send the
corrected data to Master station.
• In Master station the satellite orbit, clock
performance and health of the satellite are determined
and determines whether repositioning is required.
• This information is sent back to the satellites using
ground antennas.

9. Control Segment
Space Segment
User Segment
Monitor Stations
Ground
Antennas
Master Station
STRUCTURE

10. STRUCTURE
USER SEGMENT:
• The User Segment consists of all earth-based
GPS receivers.
• The user segment is totally user community,
both civilian and military.

11. HOW GPS
DETERMINES
A LOCATION

12. 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

13. 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

14. • 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.

15. 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”.

16. 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.

17. 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

18. 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

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

20. 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.

21. GPS SIGNALS
• Coarse/Acquisition code.
• Precision code.
• Navigation message.
• Almanac.
• Data updates.

22. GPS FREQUINCIES
• L1 (1575.42 MHz)
• L2 (1227.60 MHz)
• L3 (1381.05 MHz)
• L4 (1379.913 MHz)
• L5 (1176.45 MHz)

23. FREQUENCY INFORMATION
• The C/A code is transmitted on the L1 frequency.
• The Precision-code is transmitted on both the L1 and L2
frequencies.
• L3 is used by the Defense Support Program to signal
detection of missile launches, nuclear detonations, and
other applications.
• L4 is used for additional correction to the part of the
atmosphere that is ionized by solar radiation.
• L5 is used as a civilian safety-of-life signal.

24. ADVANTAGES OF GPS
• GPS is extremely easy to navigate as it tells you to the
direction for each turns you take or you have to take to
reach to your destination.
• GPS works in all weather so you need not to worry of the
climate as in other navigating systems.
• The GPS costs you very low.
• The most attractive feature of this system is its100%
coverage on the planet.
• It also helps you to search the nearby restaurants, hotels
and gas stations and is very useful for a new place.
• Due to its low cost, it is very easy to integrate into other
technologies like cell phone.

25. DISADVANTAGES OF GPS
• GPS satellite signals are weak, so it doesn't work as well
indoors, underwater, under trees, etc.
• The highest accuracy requires line-of-sight from the
receiver to the satellite, this is why GPS doesn't work
very well in an urban environment.
• The US DoD (dept. of defence) can, at any time, deny
users use of the system (i.e. they degrade/shut down the
satellites).
• If you are using GPS on a battery operated device, there
may be a battery failure and you may need a external
power supply which is not always possible.

26. APPLICATIONS
AVIATION AGRICULTURE
MARINE TIMING

27. SPACE RAILWAYS
ROADWAYS DISASTER RELIEF

28. Name Launch Date
NAVSTAR 64 (USA 206) August 17, 2009
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
GPSOperationalSatellites

29. Name Launch Date
NAVSTAR 51 (USA 166) January 29, 2003
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
GPSOperationalSatellites