Global Positioning System GPS

  
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The Global Positioning System (GPS) relies on more than two dozen GPS satellites orbiting the Earth. Each satellite transmits signals including a very precise clock plus satellite position information that allows a GPS receiver to determine its location, speed and direction. A GPS receiver calculates its position by measuring the distance between
Global Positioning System GPS - schematic

itself and three or more GPS satellites. Because the signal from the GPS satellite travels at a known speed, measuring the time delay between transmission and reception of each GPS radio signal allows the receiver to calculate the distance to each satellite. By determining the position of, and distance to, at least three satellites, the receiver can compute its position. GPS receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites to correct the receiver`s clock error. The GPS signal is circularly polarized with a typical center frequency of 1. 575 gigahertz. For best results, an active antenna amplifies the signal before delivering it via a coaxial cable to the GPS receiver. The GPS antenna should be mounted in a position that has a clear view of the sky so that the satellite signals can be received. GPS receivers typically do not work inside buildings, and may have trouble in vehicles or areas where the view of the sky is obstructed by tall buildings or dense foliage. Operating in urban areas can confuse the receiver due to signal reflections off buildings that result in multipath effects that lengthen the time it takes for a signal to reach the receiver, causing errors in the reported position. Some GPS receivers have a built-in Wide Area Augmentation System, or WAAS, that improves accuracy using a network of ground stations to provide additional information to the...



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