How the gps system works
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The GPS system uses 24 satellites and receivers to determine location. It requires a receiver, visibility of at least 3 satellites, and accurate time. The system has 3 segments: space (satellites), control (monitoring stations), and user (receivers). Satellites transmit timing signals, and receivers use differences to calculate distances and triangulate a precise position. Limitations include fewer visible satellites in obstructed areas.
How the gps system works
- 1. How The GPS System Works By: UMAIR SAEED
- 2. Basic Information • GPS is used to find your exact location on the world, to help you navigate. • It is a complex system developed by the military for their use.
- 3. What GPS Needs to Work • A receiver. • Three or four satellites “visible” for the GPS receiver to use to collect data. • The correct time.
- 4. Control Segment Space Segment User Segment Three Segments of the GPS Monitor Stations Ground Antennas Master Station
- 5. Four Basic Functions of GPS Position and coordinates. The distance and direction between any two waypoints, or a position and a waypoint. Travel progress reports. Accurate time measurement.
- 6. GPS System • 24 satellites + spares. • 6 orbital planes 55° inclination. • Each satellite orbits twice every 24 hours. • At least 4 satellites visible any time of day, anywhere in the world.
- 7. A 2 Dimensional Example • Time for the signal to reach GPS receiver is determined. • Distance is computed by multiplying by the speed of light. • Distance from two satellites defines 2 points (in 2 dimensional space).
- 8. A 2 Dimensional Example • The distance from a third satellite narrows the location to an “error triangle.”
- 9. Now for 3 Dimensions • Distance from a single satellite locates a position somewhere on a sphere.
- 10. Now for 3 Dimensions • Two measurements put the location somewhere on a circle at the intersection of the two spheres.
- 11. Now for 3 Dimensions • Three measurements put the location at one of two points at the intersection of the three spheres.
- 12. Now for 3 Dimensions • A fourth measurement selects one of the two points, and provides enough information to solve for the constant error.
- 19. Time Difference is Distance • Timing of the signals transmitted by the satellites is very accurate due to the dual atomic clocks on board each satellite. • The time difference between the two PRN codes represents the time it took the radio signal to travel from the satellite to the GPS receiver. • The distance or “range” to the satellite is given by the equation. range = time difference X speed of light
- 20. Satellite Position is Known • The position of each satellite is known with great accuracy. Current orbital position data is transmitted by each satellite. • Orbits are monitored by ground control stations. Corrected orbital information is uploaded several times a day. • Given the position of each satellite and the distance from the GPS receiver to each satellite, the position of the GPS receiver can be computed.
- 21. GPS Limitations – Fewer than 4 satellites visible • Your GPS needs to be able to receive a strong signal from at least 4 satellites to report an accurate position • Problems could be caused by… The sky is obscured by canyon walls, mountains, or tall buildings. Dense tree canopy. Especially if it’s wet. Antenna is shielded by metal from a car, aircraft or building. Low batteries may reduce receiver sensitivity.
- 22. Thanks….