Overview of the GPS

explanatory Essay
1077 words
1077 words


In olden days, our ancestors used many different measures to find their way around the Earth. They used the positions of stars, landmarks were put up and detailed maps were drafted in order to prevent themselves from getting lost. In today’s day and age, it is much easier to know exactly where on Earth you are and find your way around without ever getting lost again - as long as you have a handy device known as a GPS.
I knew that GPS’s could be found in cars, boats, planes, computers and other new devices, but my interested in how exactly this system worked was aroused when I was listening to my dad teaching his friend, who had recently bought a GPS, how to use it.
After doing some research, I found that the GPS that my dad’s friend bought is not really a GPS, but a GPS receiver. The Global positioning System (GPS) is actually a “worldwide radio-navigation system” that consists of 24 satellites (27 in total - 24 operating and 3 as back-ups) that orbit the Earth. This satellite network was originally developed by the U.S military navigation system, which was later available to common people as well. The satellites, weighing 3,000 to 4,000 pounds each, are orbiting 11,000 nautical miles above the Earth’s surface, with five ground stations keeping them in check and in working condition. Each of the satellites makes two complete rotations every day, all of them positioned so that at least four satellites are “viewable” in the sky.
The GPS receiver uses four or more of these satellites to calculate its position by figuring out the distance of each of the satellite and using that information to deduce its own location. This mathematical principle is called trilateration, which is the process of finding the absolute or ...

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... of receiver clock when signal received
TS = reading of satellite clock when signal transmitted c = speed of light (in a vacuum) = 3.0 x 108

Fig 5: A diagram showing how the GP pseudorange observation is related to the satellite and receiver clocks

Works Cited

In this essay, the author

  • Explains the pseudorange model used to measure the distance from the satellite to the receiver. the receiver's clock time, t, determines when the measurement was sampled.
  • Explains that gps is a world-wide radio-navigation system that consists of 24 satellites that orbit the earth.
  • Explains how they adapted an example to understand the concept in a 2-d version.
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