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GPS

GPS. Global Positioning System. TSM 352 - February 2014 Inés Resano Goizueta. I ntroduction. GPS: NAVSTAR GPS ( NAVigation System with Time and Ranging Global Positional System ) After S econd W orld War developed by USA army to determine exactly any position of their soldiers.

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GPS

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  1. GPS Global Positioning System TSM 352 - February 2014 Inés ResanoGoizueta

  2. Introduction • GPS: • NAVSTAR GPS (NAVigation System with Time and Ranging Global Positional System) • After Second World War • developed by USA army to determine exactly any position of their soldiers. • GLONASS (Soviet Union Russian Federation) • GALILEO (Europe)

  3. How it works Intersection of 3 spheres  2 points We need to know: Position of satellites Distance among them User: A or B? One does not make sense But, we do NOT need other satellite A B

  4. How it works (II) • 3 components (segments) to resolve • Spatial: 24 satellites in 6 orbits (20200 km, p 12h, atomic clock) • At least: 4 satellites over each point (>15▫) all time • Control: Fixed stations  define and track. • Master station: update and predict each path (next24h) • User: Deal data Exchange info Knows where each satellite is

  5. Calculus

  6. Calculus (II) • Triangulation methods • Topographic method to determinate the position of a land point. • Measures the distance of this point to some satellites. • Analytical  we have to use 4 satellites (exactly) • Practically  we need only 3. One solution is absurd. • Receptor in B • Know P1, P2 and P3  Satellite position. • Know r1, r2 and r3 distance satellite/receptor. • Fourth satellite  precision

  7. Calculus (III) • Measurement of distances • Time that takes the satellite´s signal to arrive at the receptor [0,06 s ] • Clocks (satellite and receptor) • Satellite´s clocks: Rubidium (), Cesium (), H() • Receptor´s clock: Quartz () Synchro nization? +1 satellite more

  8. errors Retarded signals because of ionosphere/atmosphere Clock problems Multi-way effect Diluted precision Selective availability (S/A) Anti Spoofing (A-S)

  9. errors (II) • Ionosphere and atmosphere issues • The speed of the signal through the ionosphere could be dismissing and vary depending on its density and the height.

  10. errors (III) • Clock problems • Satellite (atomic): small & master correction • Receptor: be aware & vary  FOURTH SATELLITE • Multi-way effect • Reflections: signals do not go straight to the receptor.

  11. errors (IV) • Diluted position: • Depending on the shape of the figure that they form. GOOD! BAD!

  12. errors (V) • Selective availability (SA) by USA: • Dithering: in order to avoid the access to good precision. • About 100 m of dispersion • May 2000 was deactivated. • Anti-spoofing (A-S) • It is not allow the access to P code. Signal is called Y code • Only USA Army and their allies can read the Y code.

  13. Thank you

  14. References • María González de AudicanaAmenábar, UPNA notes – topografía (2011) • Wikipedia: http://es.wikipedia.org/wiki/Sistema_de_posicionamiento_global • http://en.wikipedia.org/wiki/Global_Positioning_System

  15. Questions?

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