This Electronics Engineering Seminar Topic deals with the following:
1. INTRODUCTION
Have u ever been lost and wished there was an easy way to find out which way u needed to go? How about finding yourself out hiking and then not knowing how to get back to your camp or car? Ever been flying and wanted to know the nearest airport? Our ancestors had to go to pretty extreme measures to keep from getting lost. They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky. GPS is a satellite based radio navigation system which provides continuous, all weather, worldwide navigation capability for sea, land and air applications. So things are much, much easier today. For less than $100, you can get a pocketsized gadget that will tell you exactly where you are on Earth at any moment.
As long as you have a GPS receiver and a clear view of the sky, you’ll never be lost again. Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals. Precise positioning is possible using GPS receivers at reference locations providing corrections and relative positioning data for remote receivers. Surveying, geodetic control, and plate tectonic studies are examples. Time and frequency dissemination, based on the precise clocks on board the SVs and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
2. THE GPS EVOLUTION
GPS, which stands for Global Positioning System, is the only system today able to show you your exact position on the Earth anytime. The Global Positioning System is a constellation of satellites that orbit the earth twice a day, transmitting precise time and position (latitude, longitude and altitude) information. Cavemen probably used stones and twigs to mark a trail when they set out hunting for food. The earliest mariners followed the coast closely to keep from getting lost. When navigators first sailed into the open ocean, they discovered they could chart their course by the stars. The next major developments in the quest for the perfect method of navigation were the magnetic compass and the sextant.
The needle of a compass always points north, so it is always possible to know in what direction you are going. The sextant uses adjustable mirrors to measure the exact angle of the stars, moon, and sun above the horizon. GPS is one of the most fantastic utilities ever devised by man. GPS will figure in history alongside the development of the sea-going chronometer. This device enabled seafarers to plot their course to an accuracy that greatly encouraged maritime activity, and led to the migration explosion of the nineteenth century. GPS will affect mankind in the same way. There are myriad applications that will benefit us individually and collectively. The technology evolved from, Mr. Marconi’s transmission of radio waves. This was applied for society during the 1920′s by the establishment of radio stations, for which you only needed a receiver. The same applies for GPS- you only need a rather special radio receiver. Significant advances in radio were bolstered by large sums of money during and after the Second World War, and were even more advanced by the need for communications with early satellites and rockets, and general space exploration. The technology to receive radio signals in a small hand-held, from 20,000kms away, is indeed amazing. Throughout the 1960s the U.S. Navy and Air Force worked on a number of systems that would provide navigation capability for a variety of applications.
Disadvantages of other navigation systems:
- Landmark: Only work in local area. Subject to movement or destruction by environmental factors.
- Dead Reckoning: Very complicated. Accuracy depends on measurement tools which are usually relatively crude. Errors accumulate quickly.
- Celestial: Complicated. Only works at night in good weather. Limited precision.
- OMEGA: Based on relatively few radio direction beacons. Accuracy limited and subject to radio interference.
- LORAN: Limited coverage (mostly coastal). Accuracy variable, affected by geographic situation. Easy to jam or disturb.
- SatNav: Based on low-frequency doppler measurements so it is sensitive to small movements at receiver. Few satellites so updates are infrequent.
Many of these systems were incompatible with one another. In 1973 finally, the U.S. Department of Defense decided that the military had to have a super precise form of worldwide positioning. And fortunately they had the kind of money ($12 billion!) it took to build something really good. In short, development of the GPS satellite navigation system was begun in the 1970s by the US Department
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