1. GLOBAL POSITIONING SYSTEM GPS TSM 352 - February 2014 Inés Resano Goizueta

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

4. How it works (II) Knows where each satellite is Deal dataExchange info

5. Calculus TRIANGULATION method Distance receptor / satellite Time Satellite signal Position Satellite

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) 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 Audicana Amenábar, UPNA notes – topografía (2011)  Wikipedia: http://es.wikipedia.org/wiki/Sistema_de_posicionamiento_gl obal http://es.wikipedia.org/wiki/Sistema_de_posicionamiento_gl obal  http://en.wikipedia.org/wiki/Global_Positioning_System http://en.wikipedia.org/wiki/Global_Positioning_System

15. Questions?