Global Positioning System (GPS)
Using GPS, you can find out precisely where you are on earth, and, when equipped with the appropriate mapping software, you can get driving instructions to bring you to your destination.
How GPS Works
The Global Positioning System consists of 27 earth-orbiting satellites (of which 24 are operational and 3 are backups) circling the earth twice each day. These satellites are arranged in six orbital paths
These satellites continuously emit coded positional and timing information using low-power radio waves at frequencies in the 1500 MHz range. GPS receivers on earth then pick up the signals and calculate the exact[1] positioning on earth. The orbits of the satellites are arranged in such a manner that at any one time, four satellites are visible. Thus, a GPS receiver is able to receive signals from these four satellites and, based on the various signals transmitted by them, derive positional information on earth.
Accuracy of GPS
GPS was originally developed in the 1980s by the U.S. Department of Defense for military use. Because it was designed primarily for the military, the U.S. Department of Defense introduced Selective Availability (SA) to degrade the signal accuracy and to encrypt sensitive information, so that civilian usage could be restricted. The satellites would deliberately broadcast wrong and randomly inaccurate signals, which would cause the precision of the GPS data to be within 100 meters. The accurate information could only be decoded by the military.
Because of the great commercial potential of GPS, in May 2000, President Clinton announced that the U.S. would no longer degrade the accuracy of GPS. With SA turned off, the accuracy of the GPS data could be within 5 meters.
In the second Gulf war against Iraq in 2003, the United States reportedly degraded the GPS system so that Iraq could not make use of GPS against U.S. forces. While this is good news for the military, it certainly affected all those who rely on GPS for their daily activities. So, if you arrived at the wrong destination using a GPS navigational system, now you know why!
Uses of GPS
The function of GPS is fairly straightforward — with a GPS receiver, you can obtain your positional information in the form of longitude, latitude, and altitude. What is important is the way you use this information. Some useful applications of GPS are described next.
Military use
As GPS was originally developed for military use, the U.S. Department of Defense is the main user of the technology. The use of GPS for guiding “smart” bombs has played an important role in recent wars, especially in the Persian Gulf.
Location Based Services (LBS)
GPS has been increasingly deployed in the commercial scene. Location Based Services make use of the knowledge of your precise location to provide location-sensitive services. For example, you can use location-based services to give you a list of restaurants near your current location.
Navigation services
GPS is popularly used for navigational purposes, such as driving and flying. A GPS-enabled PDA can help a driver to navigate unfamiliar cities. GPS is also widely used in the shipping industry as well as in airplane navigational systems. Courier companies such as UPS and FedEx make extensive use of GPS in their delivery infrastructures.
Tracking
Using GPS to track the whereabouts of people or objects is rapidly gaining acceptance. This is useful in the medical sector where patients suffering from diseases such as Alzheimer’s can wear a GPS watch, and when needed, press a panic button to reveal their exact location to their family members.
Mapping
GPS is also popularly used in mapping software, allowing you to combine a GPS receiver with mapping software to display your current location. This is useful for travelers or explorers who need navigational aids.
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