GPS (Global positioning system) GPS (Global positioning system) is a satellite sourced navigation system developed by the Unites States Department of Defense and is administered by United States Air Force 50th Space Wing. With technological advances in leaps and bounds, a system was developed specifically for army utilization which is now widely used as GPS for precise tracking and mapping purposes, it was made available to civilians in 1980’s.

Worldwide positioning on your handheld does not put in the picture of how complex the GPS technology is. U.S. defense department spent $12 billion on developing this system which made Navigation and positioning a child’s play.

It uses a constellation linking 24 to 32 satellites orbiting earth that transmit well defined radio wave signals, which allow GPS receivers to establish their existing location, the timings, and their speed.

GPS satellites GP system makes use of the information provided by the GPS satellites orbiting around earth twice in every 24 hours at around 7000 miles per hour.All GPS satellites are equipped with solar panels and thus make use of solar energy to power the resources. They have backup batteries installed onboard to keep active whenever a solar eclipse or any such event takes place. These satellites are provided with small rocket boosters which can be deployed when they deviate from their original path.

Satellite signals Each of these satellites recurrently sends signals to the receivers on the earth which work out all the information. Based on these calculations the exact position can be known. These signals give out the location, speed and time with use of accurate orbital information and relative orbit distances of GPS satellites. The signal comprises of three basic parts - a pseudorandom code, ephemeris data and almanac data .Satellites transmit 2 low powered radio signals L1 and L2, civilian GPS makes use of L1 signal which has a frequency of 1575.42 MHz in UHF band. These signals are thus unable to pass through solid buildings, mountains etc. The pseudorandom code gives the information about the satellite which is identified by a unique code. Ephemeris data gives an account of the satellite position and other related orbital information. Almanac data is provided at regular intervals and it contains the valuable information about the current date and time which is very important to determine the position of the receiver.

Trilateration The GPS concept is based on “Trilateration” or in simple words “triangulation”. Trilateration is a method which uses the geometry of triangles to determine the relative positions. Computing the distances of different satellites we can determine the location of the receiver. Magellan and Garmin offer superior GPS receivers which are exceedingly accurate due to their parallel channel design. These receivers lock into satellites and maintain their link even in dense forest areas or regions which are highly populated and have large number of buildings. Certain atmospheric factors also affect the accuracy of these receivers. A GPS receiver locked in to 4 different satellites can accurately determine the three dimensions that is, the latitude, the longitude and the altitude. With a device locked into 2 satellites can conclude only 2d view that is, the longitude and the latitude. The GPS needs an highly accurate clock. The most perfect clock made upto date is the atomic clock. GPS makes use of this same clock in its satellites. But for the receiver end, installing clocks in the devices would have made it unaffordable so the developers came up with the idea of using a 4th dimension in determining the position. So a normal position can be easily established using signals from not three but four satellites.

MAGELLAN AND GARMIN Leading brands with GPS solutions, Garmin and Magellan have a variety of products on offer.

• For portable and on board navigators such a nuvi and zumo series from Garmin and Magellan maestro and triton series offer exceptional on-road and off road coverage for all types of vehicles. These navigational handhelds and fixed navigators are best for hiking, biking and camping purposes around the world whether you are in a vehicle or trekking by foot.
• Both Garmin and Magellan have equally competitive products for land, airborne and sea navigation, mining and agriculture machine products, vehicle navigation, and Aerospace solutions. They provide professional GPS solutions for avionics and safety, radars and autopilots, marine networking, sensors and boards for surveys and recreational application.
• Blackberry and PDA’s for Mobile and laptop integration with the GPS receivers is another range of products. Now you can have the GPS on the go with these revolutionary products on offer.
• Customized software solutions from Magellan and Garmin GPS‘ handheld for topographic, marine and street navigation. Fully detailed maps with extensive coverage points including lakes, mountains, streets, monuments, parks and comprehensive range of addresses make these a world class navigational equipments.

Newer and more accurate technology is flooding the market such as the upgradation to differential global positioning system (DGPS) offered by Garmin is cuurently deployed by the U.S. coastal guard which gives an accurate account of position with a range of three to five meters. Recent Garmin GPS receivers are equipped with WAAS (Wide Area Augmentation System) which corrects to the average of 3 meters by improving and transmitting GPS signals through beacon transmitters.

Limitations and error introduction in the GPS receivers

• Delays in the atmosphere while passing through Ionosphere and troposphere introduces delay time errors in the signals.
• Improper synchronization and correction of atomic clock time in satellite and receiver.
• Ephemeris errors- errors due to incorrect location co ordinates of the satellite.
• GPS does not work under water, under ground or inside the buildings.
• Needs clear Line of sight from the satellite to the receiver. Any obstructions due to buildings and dense flora introduce erroneous results.

GPS has a widespread use and thus has innumerous applications. They can be broadly categorized to military and civilian industry. Whether it is land, sea or air GPS has become seamlessly important. Surveyors, mariners and aviation industry have become highly dependent on these technological wonders. Others active customers include the automobile clients and recreational sports activity patrons. GPS has undoubtedly transformed the way of living and taken it to new heights.

Written by http://www.jhelectronics.com

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