About GPS

Developed by the United States Department of Defense, GPS is officially named Navstar GPS. Its name came from John Walsh, who was a key decision maker involving the budget for the technology program.

It is the only fully functional global navigation satellite system, utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals. The system enables a GPS receiver to determine its location, speed, direction, and time.

The satellite constellation is managed by the United States Air Force 50th Space Wing. In 1983, President Ronald Reagan issued a directive making the system available for free for civilian use as a common good. Since then, the technology has become a widely used aid in navigation worldwide, and a useful tool for mapmaking, land surveying, commerce, and scientific uses.

GPS - How it Works

A typical receiver calculates its position using the signals from four or more satellites. Four satellites are needed since the process needs a very accurate local time, more accurate than any normal clock can provide, so the receiver internally solves for time as well as position. The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth’s surface.

Each GPS satellite has an atomic clock, and continually transmits messages containing the current time at the start of the message. The signals travel at a known speed, the speed of light through outer space, and slightly slower through our atmosphere. The receiver uses the arrival time to compute the distance to each satellite, from which it determines the position of the receiver using geometry and trigonometry.

There are now around 33 actively broadcasting satellites in the GPS constellation. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements.

GPS - Receiver

GPS receivers are composed of an antenna, tuned to the frequencies transmitted by satellites, receiver-processors, and a highly stable clock. They may also include a display for providing location and speed to the user.

Conditions in the atmosphere affect the speed of the signals as they pass through the Earth’s atmosphere, especially the ionosphere. Correcting these errors is very important to improving position accuracy.

Changes in receiver altitude also change the amount of delay, due to the signal passing through less of the atmosphere at higher elevations.

GPS - Time

While most clocks are synchronized to Coordinated Universal Time, the atomic clocks on the satellites are set to Global Positioning Satellite time. The difference is that time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC.

GPS Recent News

GPS systems can alert drivers of what routes to avoid (New Kerala)
Wed, 19 Nov 2008
London, November 19 : The World Congress on Intelligent Transport Systems (ITS) in New York will see this week a presentation on how GPS systems can help track traffic snarls.

CSG Systems Integrates ComSonics GPS Capabilities to Workforce Management Solution (Business Wire via Yahoo! Finance)
Wed, 19 Nov 2008
ENGLEWOOD, Colo.----CSG Systems , a leading provider of customer interaction management and billing solutions, today announced it has formed a partnership with ComSonics, an industry-leading provider of GPS and cable management solutions.

Coyote Systems Chooses Jasper Wireless to Power World's First Real-Time GPS Speed Camera Alert System (Business Wire via Yahoo! Finance)
Wed, 19 Nov 2008
SUNNYVALE, Calif. & SURESNES, France----Jasper Wireless and Coyote Systems announced today their partnership to power mini-Coyote, the world’s first GPS-based alert system that informs drivers in real-time the location of fixed and mobile speed cameras.

Baldwinsville installs GPS devices on buses (WSYR 9 Syracuse)
Wed, 19 Nov 2008
Starting this week, the Baldwinsville School District will keep a closer eye on its school buses. The district installed global positioning systems on 24 of its buses.

Report: Conn. GPS system works, despite problems (Journal Inquirer)
Wed, 19 Nov 2008
Connecticut’s system for tracking criminal offenders with global positioning satellite technology can be very accurate, and is comparable with similar systems used nationwide despite some problems, a report released Monday concludes.

Airborne Systems Sets New Payload Record for Largest Autonomously Guided Ram-Air Parachute (PR Newswire via Yahoo! Finance)
Wed, 19 Nov 2008
Airborne Systems, a world leader in parachute design and manufacturing, announced today they successfully completed a test drop deploying 40,000 lbs. of payload under a single ram-air parachute, surpassing the previous payload record of 33,000 lbs. set in September.

Boeing to upgrade Air Force GPS satellite systems (Daily Breeze)
Tue, 18 Nov 2008
Boeing said it plans to perform a technological upgrade for the satellites being built in El Segundo. BUSINESS » Read stories and columns about the South Bay and beyond DAILY BREEZE BLOG » South Bay Biz Waves

Police ask victims to claim $500,000 in stolen goods (The Lantern)
Wed, 19 Nov 2008
Abigail Miner /The Lantern A myriad of stolen items, including digital cameras, GPS navigation systems, car stereos and televisions, will be on display at the Columbus Division of Police's Stolen Property Office Wednesday. The Columbus Division of Police Property Recovery Unit will hold a public viewing of stolen property today in an effort to return the property to theft victims. ...

ProLink Partners With Synergy LLC to Install Golf's Leading GPS System in the Middle East and India (PR Newswire via Yahoo! Finance)
Tue, 18 Nov 2008
ProLink Solutions -- a wholly-owned subsidiary of ProLink Holdings Corp. and the world's leading provider of Global Positioning Satellite golf course management systems and digital out-of-home on-course advertising -- today announces it has partnered with Synergy LLC to install the ProLink system at upscale golf courses and resorts throughout the Middle East and India.

Remote Intelligence Systems, Time Critical Decisions and Stellar Satellite Communications Ltd. Unveil New Dual Modem ... (Business Wire via Yahoo! Finance)
Tue, 18 Nov 2008
WINOOSKI, Vt.----Remote Intelligence Systems LLC. announces the introduction and market launch of the new ORBISAT 100 Dual Modem System.

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