What is GPS?
The Global Positioning System (GPS) is a satellite-based navigation system. Originally intended for military applications, the system was made up of a network of 24 satellites placed into orbit by the U.S. Department of Defence. In the 1983, the U.S. government declared the system available for civilian use. Each GPS receiver needs at least the location four or more of these satellites in order to deduce its own latitude, longitude, and altitude. Therefore, the Global Positioning System is used for accurate global land navigation and tracking position.
System Segmentation
The GPS consists of three parts: the space segment, the control segment, and the user segment. The U.S. Air Force develops, maintains, and operates the space and control segments. GPS satellites broadcast signals from space, and in addition to the power to identify three-dimensional location of the receiver, this device is also able to calculate speed, bearing, track, trip distance, distance to destination, sunrise and sunset time. The user segment is composed of hundreds of thousands of U.S. and allied military staff for the operation and security of the GPS Precise Positioning Service, (a highly accurate military positioning, velocity and timing service which is only available to users authorized by the U.S. military.) Not to mention the tens of millions of civil, commercial, and scientific users of the Standard Positioning Service, (a positioning and timing service which is available to all GPS users with no direct charge. This level of service is much less precise, since these receivers are for the use of civilian use.)
The Space Segment
The space segment is composed of the orbiting GPS satellites, or Space Vehicles (SV), at angular differences to ensure each device receives better quality signals. The GPS design calls for six planes with four satellites each. Each set of satellites in orbit are 30, 105, 120, and 105 degrees apart, which sum up to 360 degrees. Orbiting approximately 20,200 kilometres above the Earth's atmosphere, each SV makes two complete, identical orbits each day. This means the GPS operates in any weather condition, anywhere in the world, 24 hours a day.
In general, GPS receivers contain an antenna, tuned to the frequencies transmitted by the satellites. The modern GPS has receive-processors, a highly stable clock, a display for providing location, and a speed display. The quality of the receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, as of 2010, receivers typically have between fifteen and twenty-two channels.