GPS - GPS Systems, GPS Tracking. Overview

Our ancestors used to go to under sky at night and calculate their locations on the earth. They built landmarks, detailed maps and learned how to read the stars in the night sky.

But today, by the passage of time, in this modern era of technology, things are much changed and very much easier than before. For less than 100$, you can easily purchase a device which is capable of telling you about your exact location on the globe, any time, anywhere. This device is commonly known as GPS Receiver. When you are having a GPS Receiver, you have no chance to loss on the earth.

GPS, basically, stands for Global Positioning System. As its name describes, it’s a system which tells the exact position (location) of anything with GPS receiver enabled. When they say, “GPS”, they usually mean “GPS Receiver”. The Global Positioning System (GPS) is actually a complete system of 27 satellites (also called NAVSTAR, the official U.S. Department of Defence name) around the globe.

24 satellites are in operational mode and three are extra in case of a failure.

The United States military developed this satellite network as a military map-reading system, but soon they allowed its access to everybody on the globe without any license or permission. The first GPS satellite was launched in 1978. A full system of 24 satellites was achieved in 1994.

Each of satellite weighted 3,000 to 4,000 pound and these solar-powered satellites circles the globe about 12,000 miles above us, making two complete rotations, each day. A rough estimate of satellite’s speed is 7,000 miles an hour. The orbits are arranged in such a way that at any time, there are at least four satellites which are visible in the sky, anywhere on Earth.

Basically, job of a GPS receiver is to locate four or more of these satellites and calculate distance to each, and use this information to calculate its own location on the earth. This operation of calculation is based on a simple mathematical principle called “Trilateration”.

A GPS receiver’s working depends upon radio waves. But instead of using towers on the ground, it communicates with satellites that orbit the Earth.

GPS satellites rotate around the earth twice a day in a very precise orbit and transmit signal to earth. GPS receivers take this signal information and use triangulation to calculate the user's exact location. GPS receiver compares the time of a signal which was transmitted by a satellite with the time it was received by the receiver. The time difference tells the GPS receiver how far the satellite is.

GPS Receivers draw a sphere around each of three satellites located by them. These three spheres intersect in two points, one is in space, and one is on the ground. The point on the ground at which the three spheres intersect is your location.

Some GPS enabled phones use wireless-assisted GPS to determine its location on the earth. Wireless-assisted GPS can calculate user's location faster than a GPS-only receiver. Some wireless-assisted systems can work inside buildings like basements, under dense plants (jungle) and in city areas where traditional GPS receivers cannot receive signals and hence fails to calculate the location on earth.

A GPS receiver must receive the signals of at least three satellites to calculate a 2D position in terms of latitude and longitude and track movement. With four or more satellites in view, the receiver can determine the user's 3D position in terms of latitude, longitude and altitude. Once the user's position has been calculated, the GPS unit can calculate other information like speed, distance etc.