GPS-Global positioning system


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GPS-Global positioning system

  1. 1. RADIO BASED NAVIGATION SYSTEM Radio-based navigation system developed by DOD initially operated in 1993 ,fully operated in 1995.
  2. 2. Trilateration intersection of spheres SV Ranging Timing why consistent, accurate clocks are required Determining Range of GPS Dilution of precision GPS involves THE FOLLOWING Space segment of GPS satellites. GPS Satellites Details. 2-Dimensional Example
  3. 3.  Total number of satellites are 30,24 are under work,6 are extra satellites.  Each satellite has 6 orbits.  3 satellites works for GPS, 4th satellite work for accuracy. 3 satellites for 2d fix.
  4. 4.  Satellite orbital distance 20,000km.  Orbital speed is 14,000km/hr  60 degrees apart and 55 degrees with respect to equatorial plane.  Use measurement of 4 satellites Distance=travel time*speed of light
  5. 5.  Distance from two satellites defines 2 points (in 2 dimensional space.)  The distance from a third satellite narrows the location to an “error triangle.”
  6. 6.  THREE SV RANGES KNOWN  Satellite-1) 20,000km radius  Satellite-2) 21,000km radius  Satellite-3) 22,000km radius Located at one of these 2 points However, one point can easily be Eliminated because it is either not on earth or moving at impossible Rate of speed.
  7. 7.  CESIUM ATOMIC CLOCKS are used in GPS satellites  Due to general theory= 45 microseconds special theory= 7 microseconds overall effect= 38 microseconds Hence GPS satellite are slowed by 38 microseconds If 1/100th of a second error occurs it introduce error of 1,860 miles.
  8. 8.  Receiver and satellite use same code  GPS sync with each satellite by shifting the timing of the start of an internally generated PRN code.  Compare incoming code with receiver generated code From satellite Measure time difference between the same part of code From receiver Series of ones and zeroes repeating every 1023 bits. So Complicated alternation of bits that pattern looks random thus called “pseudorandom code”.
  9. 9. Ionosphere (Charged Particles) Troposphere
  10. 10.  Technique used to correct some of these errors  Referred to as “differential GPS” or DGPS  In DGPS, two GPS receivers are used
  11. 11.  One receiver is located at an accurately surveyed point referred to as the “base station”  A correction is calculated by comparing the known location to the location determined by the GPS satellites  The correction is then applied to the other receiver’s (known as the “rover”) calculated position
  12. 12.  GPS system allows you to search the local area for nearby AMENITIES such as hotels, restaurants etc.  GPS is very useful during adventures.  GPS devices are perfect for water navigation. Since there are no landmarks in large bodies of water.
  13. 13.   PS  positioning-system     id=55