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Gps
 

Gps

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Global Positioning System

Global Positioning System

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Gps Gps Presentation Transcript

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