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Global Positioning System

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  • Gps

    1. 1. GPS (Global Positioning System) Presented by Ashok Kumar Narendra Kumar Pankaj
    2. 2. <ul><li>The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. </li></ul><ul><li>US military owns it. </li></ul><ul><li>Provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth. </li></ul>Why do we need GPS?
    3. 3. Components of GPS Space Segment Control Segment User Segment <ul><li>24 GPS space vehicles(SVs). </li></ul><ul><li>20,200 km away from the Earth </li></ul><ul><li>55 o inclination </li></ul><ul><li>Satellites orbit the earth in 12 hrs. </li></ul><ul><li>Selecting one or more satellites </li></ul><ul><li>Acquiring GPS signals </li></ul><ul><li>Measuring and tracking </li></ul><ul><li>Comprises 5 stations. </li></ul><ul><li>Satellite orbit, clock performance </li></ul><ul><li>Measure the distances of the overhead satellites every 1.5 seconds and send the corrected data to Master control. </li></ul>
    4. 5. How GPS Works
    5. 6. How do you use these satellites to calculate your position? The Global Positioning System is a constellation of 24 satellites that is used to calculate your position.
    6. 7. Triangulation
    7. 11. <ul><li>It compares that signal with all the known codes (there are currently 37). </li></ul><ul><li>The receiver determines which satellite it is. </li></ul><ul><li>It decodes the timing information, multiplies by the speed of light to find the radius of the sphere. </li></ul><ul><li>Once it has done that for 3 satellites, it can determine the location. </li></ul>When GPS receives a signal
    8. 12. <ul><li>L1 freq. (1575.42 Mhz) carries the SPS code and the navigation message </li></ul><ul><li>L2 freq. (1227.60 Mhz) used to measure ionosphere delays by PPS receivers </li></ul>GPS Satellite Signal:
    9. 13. <ul><li>If the clocks are perfect sync the satellite range will intersect at a single point, otherwise not </li></ul><ul><li>The receiver looks for a common correction that will make all the satellite intersect at the same point </li></ul>Getting Perfect timing
    10. 14. <ul><li>95% due to hardware ,environment and atmosphere </li></ul><ul><li>Troposphere causes delays in code and carrier </li></ul><ul><li>Errors due to Multipath </li></ul><ul><li>Receiver noise </li></ul><ul><li>Gravitational potential distribution, Earth is not a perfect sphere </li></ul><ul><li>Other heavenly bodies attract the satellite </li></ul><ul><li>Not a perfect vacuum in the earth’s atmosphere </li></ul><ul><li>Solar radiation effects (largest unknown errors source) </li></ul>Error Sources
    11. 15. <ul><li>Poor GDOP </li></ul><ul><li>(Geometric Dilution of Precision) </li></ul><ul><ul><li>When angles from the receiver to the SVs used are similar </li></ul></ul><ul><li>Good GDOP </li></ul><ul><ul><li>When the angles are different </li></ul></ul>Errors due to geometry
    12. 16. <ul><li>Atmospheric errors can be removed by </li></ul><ul><ul><li>Dual freq measurement </li></ul></ul><ul><ul><li>(low freq get refracted more than high freq </li></ul></ul><ul><ul><li>thus by comparing delays of L1 and L2 errors can be eliminated) </li></ul></ul>Error correction
    13. 17. <ul><li>Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System </li></ul><ul><li>Uses a network ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. </li></ul>DGPS
    14. 18. <ul><li>To Study plate tectonics, volcanoes, and earthquakes </li></ul><ul><li>Surveyors use GPS for an increasing portion of their work </li></ul>Uses of GPS <ul><li>GPS is popular among hikers, hunters, snowmobilers, mountain bikers, and cross-country skier </li></ul>
    15. 19. We have GPS receivers operating all over the world. Southern California Hawaii Antarctica Australia Iceland Holland
    16. 20. <ul><li>They use codes! Binary codes. </li></ul><ul><li>Each satellite has a different code. </li></ul>How do GPS signals send all this information?
    17. 21. THANK YOU