GLONASS: Used by Russian military till it was fully available for civilians in 2007.OTHER is still not launched.
Each satellite continually transmits messagesthat include:1.the time the message was transmitted2.precise orbital information
Instructed on: 24-Feb-2011 | Session: #06 GPS By: Mohanad Yehia Topic Code: TCW-05-2012 All Copy Rights Saved to the 7th Students’ Conference on Communication and Information Based in the Faculty of Computers and Information Cairo University – Egypt 2011/2012 www.scci-cu.com
AGENDA•What is GPS.•History of GPS.•How GPS works.•GPS applications.
What is GPS?• Global Positioning System.• Worldwide navigation system formed of 31 satellites and their ground stations.• Maintained by the United States government and is freely accessible by anyone with a GPS receiver.
Other systems• The Russian GLObal NAvigation Satellite System (GLONASS) .• European Union Galileo positioning system.• Chinese Compass navigation system.• Indian Regional Navigational Satellite System.
History of GPS• The GPS project was developed in 1973 to overcome the limitations of previous navigation systems.• GPS was created and realized by the U.S. Department of Defense and was originally run with 24 satellites.
History of GPS• In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 that strayed into prohibited airspace because of navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that GPS would be made available for civilian uses once it was completed.
History of GPS• Full Operational Capability was declared by Air Force Space Command in April 1995.• In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy declaring GPS to be a dual-use system.
History of GPS• In November 2004, QUALCOMM announced successful tests of assisted GPS for mobile phones.• The oldest GPS satellite still in operation was launched on November 26-1990 while the newest GPS satellite was launched on July 16- 2011.
How GPS works1. Trilateration.2. Measuring distance.3. The perfect timing.4. Position of satellites.
1-Trilateration Trilateration methods involve the determination of absolute or relative locations of points by measurement of distances, using the geometry of spheres or triangles.
2-Measuring distanceGPS receiver measures distance using the travel time of radio signals sent from satellites.example:Velocity (60 mph) x Time (2 hours) = Distance(120 miles).
3-The perfect timing• On the satellite side, timing is almost perfect because they have incredibly precise atomic clocks on board.• If their timing is off by just a thousandth of a second (at the speed of light) that translates into almost 200 miles of error
4-Position of satellites• The GPS receivers know the exact location of the satellites in range from the received radio signal.• The basic orbits are quite exact but just to make things perfect the GPS satellites are monitored by the Department of Defense.