The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to users with GPS receivers. It was developed by the U.S. Department of Defense in the 1970s to overcome limitations of previous navigation systems. GPS uses 24 satellites that orbit the Earth and transmit signals that allow receivers to determine their precise location, speed and direction. The system works by calculating the time delay of signals from at least 3 satellites to determine the user's position through trilateration. GPS has both military and civilian applications including vehicle navigation, map-making, tracking valuable assets, and outdoor recreational activities.

1. Global positioning system
By
K.Gautham Reddy
2011A8ps364g
By
K.Gautham Reddy
2011A8PS364G

2. Introduction
• The Global Positioning System (GPS) is a space-based Global
navigation satellite system that provides location and time information.
• The project was started in 1973 to overcome the limitations of previous
navigation systems.
• GPS was created by the US department of defence and was originally
run with 24 satellites.
• Since 1994 the Global Positioning System has been available for civilian
use at no cost.
• Freely accessible by anyone with a GPS receiver.
• Main functions : Position and coordinates, Travel progress
reports, Accurate time measurement.

3. The need for positioning system
 Department of Defense were facing challenges to increase
security of the US.
During emergencies we require immediate tracking of
important people.
Logistic companies need tracing of their fleet for reliable
operations.
Personal valuables vehicles and goods when stolen or lost
were not easier to locate.

4. Components of the system
 A constellation of 24 satellites
 Six orbital planes
-Inclined 55 degrees with respect to
equator
 20,200 km elevation
above earth
 Orbital period of 11 hr 55 min
 Five to eight satellites visiblefrom any
point on Earth

5. Three segments of GPS
1) Space Segment-A constellation of 24 satellites
2) Control segment-A network of earth based facilities
3) User segment

6. OPERATION OF GPS
 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.

7. Determining GPS position
• The GPS receiver compares the time
a signal was transmitted by a satellite
with the time received.The time
difference tells the GPS receiver how
far away the satellite is.
•Suppose Satellite A to our position is
11,000 miles
• At this point we could be located
anywhere on the specified sphere
• Next, let us take another
measurement from a second satellite,
Satellite B
•Now our position is narrowed down
to the intersection of theses
two sphere
Satellite A
+
Satellite B
+

8. Satellite C
+
Determining GPS Position
Satellite A
Satellite B
+
+
•Taking another measurement from a 3rd
satellite narrows our position down even
further, to the two points
• These points are located where the 3rd
sphere cuts through the intersection of first
two spheres
•So by ranging from 3 satellites we can
narrow our position to just two points in
space
•We could make a 4th measurement from
another satellite to determine the true point
•However, GPS receivers use a 4th satellite
to precisely locate our position

9. Applications
 Military:
- Search and rescue missions
- Digital Assistant for soldiers
(personal navigation)
- Detect nuclear detonation with sensors on satellites
someone explode a nuclear weapon, the GPS system can find the
position by equiping it with sensors.
 Civilian:
- Used in map-making and land surveying
- Outdoor Activities (Hike/bike trails, GeoCaching)
- Various usages in many fields of industry
- Vehicle navigation (for cars, airplanes, and ships)
- Use GPS to determine position, speed, and direction

10. Limitations and drawbacks
 A stolen object can’t be traced out if Receiver is switched off or facing
power failure.
 Low batteries may reduce receiver sensitivity.
 Position of the receiver can’t be traced if kept under high EM
insulation.
 It requires a minimum of 4-5 satellites in order to give accurate
locations.
 Causes problem when the sky is obscured by canyon walls, mountains, or
tall buildings.
 Atmospheric conditions like geomagnetic storms makes it less accurate

11. Future of GPS
 Automobiles are tested on moving on their own without
the assistance of a driver.
 Tests have begun in using unmanned aircrafts.
 GPS has truly helped man to advance in more ways than
one.
 It is also going to bring a great revolution by its
development.

12. References
 http://en.wikipedia.org/wiki/Global_Positioning_System
 http://electronics.howstuffworks.com/gadgets/travel/gps.htm
 http://en.wikipedia.org/wiki/GPS_navigation_device
 http://www.ehow.com/about_5730112_objectives-global-
positioning-system.html
 http://www.ehow.com/about_6595713_purpose-gps-system-
started.html
 http://www.webmapsolutions.com/future-developments-gps-
technology