2. Contents
What is GPS ?
History of GPS
Concepts of GPS
Segments of GPS
How does it work ?
Communications
Applications
Conclusion
References
3. What is GPS ?
Acronym for “Global Positioning System”.
A space based radio navigation system.
Provides geolocation and time information to a GPS receiver.
Owned by US Government.
Operated by US Air Force.
Initially developed for military purposes.
4. History of GPS
Developed by US Department of Defense.
In 1969, the DNSS (Defense Navigation System Satellite) was formed.
In 1973, lead to the formation of NAVSTAR –GPS.
(Navigation System Using Timing and Ranging – GPS)
In 1978, the first experimental Block-I GPS satellite was launched.
By 1993, GPS achieved initial operational capability (IOC), indicating a full
constellation (24 satellites).
Full Operational Capability (FOC) was declared by 1995.
5. Concepts of GPS
Is based on time and the known position of specialized satellites.
The satellites carry very stable atomic clocks.
GPS satellites continuously transmit their current time and position.
A receiver monitors these satellites and solves equations to determine
positions.
At least four satellites must be in view of the receiver.
6. 3 Segments of GPS
Space
Segment
Control
Segment
User
Segment
7. Space Segment
Consists of a constellation of satellites.
Orbiting at an altitude of approximately 20,200 km.
About eight satellites are visible at any point.
Each satellite transmits low radio signals with a code.
Helps in calculating travel time.
Minimum four satellites are needed for a position.
8. Control Segment
Tracks the satellites.
Provides them with correct orbital & time information.
Composed of:
A master control station (MCS),
An alternate master control station,
4 dedicated ground antennas, and
6 dedicated monitor stations.
9. User Segment
Composed of all the users and their GPS receivers.
o Receiver is tuned to satellite frequency.
o Receives signal and provide position to the user.
The number of simultaneous users is limitless.
10. How GPS works ?
Receivers calculates the distance from each satellite.
receivers matches the satellite transmitted code to its own to get the delay.
Speed of light.
Signals leaves at time = x
Signal picked at time = x+3
Thus, distance is 3 times the speed
of light
11. Working Cont..
Once position of at least 4 satellite is known, receiver can determine a
positon.
First measurement narrows our
position to the surface of the sphere.
Second measurement narrows it down to
the intersection of 2 spheres.
13. Communications
Navigational signals transmitted by GPS satellites encode a variety of
information such as -
satellite positions
state of the internal clocks
health of the network
Transmitted on two separate carrier frequencies, one for public and another
for U.S. military.
14. Message Format
Each GPS satellite continuously broadcasts a navigation message on fixed
frequencies at a rate of 50 bits per second.
Each message is subdivided as follows :
16. Civilian Applications of GPS
Navigation - Satellite navigation in vehicles, aircraft and ships.
Clock Synchronization - Accuracy of GPS time signals is second only to the
atomic clocks.
Surveying – Survey locations to make maps and determine positions of
buildings.
Security - Include tracking of valuable cargoes and covert tracking of
suspects.
Scientific - Include environmental and atmospheric monitoring, animal
behavior studies.
17. Military Application of GPS
Navigation: Soldiers use GPS to find objectives, even in the dark or in
unfamiliar territory.
Target tracking: To track potential targets before flagging them as hostile.
Missile and projectile guidance: Allows accurate targeting of various military
weapons
Used for search and rescue operations.
18. Issues with GPS
Due to inaccurate time-keeping by the receiver's clock.
Atmospheric disturbances that distort the signals before they reach a
receiver.
Reflections from buildings and other large, solid objects.
Quality of electronic detector in the receivers.
Artificial errors from jamming devices.
