Global Position Systems
How GPS works in five logical steps:
1. The basis of GPS is triangulation from satellites
2. GPS receiver measures distance from satellite using the travel time of radio signals
3. To measure travel time, GPS needs very accurate timing
4. Along with distance, you need to know exactly where the satellites are in space. Satellite location.High orbits and careful monitoring are the secret
5. You must correct for any delays the signal experiences as it travels through the atmosphere.
GPS Satellites
• 24 satellites
• 6 orbital planes
• 12 hour return interval for each satellite
Satellites are distributed among six offset orbital planes
Distance from satellite
• Radio waves = speed of light
– Receivers have nanosecond accuracy
(0.000000001 second)
• All satellites transmit same signal “string”
at same time
– Difference in time from satellite to time
received gives distance from satellite
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