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Gps Receivers Explained

By James Thomas

By now, you've likely heard about this hot new technology called GPS. Handheld GPS receivers are popular items that are being used by everyone from outdoors enthusiasts to average drivers. But, how many of us really understand the technology behind these modern-day marvels?

There is a whole lot of power and capability packed into a GPS receiver. They are linked to complex satellite systems in outer space, providing a reliable navigational system to users on earth. Many new cars have GPS receivers included as standard equipment. Hikers use them to find their destinations, and treasure hunters rely on them for Geocaching excursions.

Simply, a GPS is an electronic device that can determine ones precise location on earth. The entire system is anything but simple; and the GPS receiver is but a single and minute part of this immense network. GPS is the short form of Global Positioning System. This very large navigation system was developed and implemented by the United States Department of Defense (DOD). The system is composed of a network of 27 satellites, various ground stations located at points throughout the world and individual GPS receivers. Most of the 27 satellites in the GPS are active, and continuously send radio signals. GPS receivers use these signals to determine their geographical location.

Function The primary function of a GPS receiver is to pinpoint its actual location on earth using the signals it intercepts from GPS satellites. To do this, the GPS receiver must be able to locate and intercept signals from three or more GPS satellites. After intercepting the signals, GPS receivers use basic principles of mathematics called triangulation or trilateration to compute its actual position. Before any triangulation calculation can be implemented, however, the GPS receiver must verify two points:

1- The positions of at least 3 satellites 2- The distance between each satellite and the receiver.

GPS receivers decode the signals in order to determine the locations of at least three GPS satellites. The signals transmitted by GPS satellites are radio signals, and each contains three different bits of information: ephemeris data, almanac data and a pseudorandom code. The ephemeris data is the information that the GPS receiver needs to be able to determine the actual position of the satellite transmitting the signal.

The distance of a GPS receiver to a satellite is measured using the signals speed, or the time delay from the initial transmission of the signal, to its reception by the GPS. From this speed or time difference, the GPS receiver calculates the satellites distance.

With information about the location of at least three or four satellites, along with their individual distances, a GPS receiver utilizes the basic principle of triangulation to calculate its actual position in terms of altitude, latitude and longitude.

Accuracy GPS receivers are incredibly accurate, usually to within twenty meters of radius. It is possible, however, to increase this accuracy level using supplemental technologies. Some GPS receivers using multiple parallel channels can achieve an accuracy level to within fifteen meters. More complex systems such as DGPS (Differential GPS) and WAAS (Wide Area Augmentation System) can reduce this range to an impressive three meters.

Despite the use of these supplemental technologies, there are still many factors that can cause even the best GPS receivers to broadcast inaccurate locations. Among these factors are:

* Number of visible satellites * Radio signal delays caused by the passage through the ionosphere and troposphere * Signal multipath (bouncing of the signal as it hits an object) * Inaccuracy of GPS receiver clocks * Ephemeris errors (inaccuracy of the satellites reported locations) * Poor positioning of satellites (i.e.: satellites in a linear position, or in a tight grouping)

Some, but not all, of the GPS errors caused by these factors can be remedied by the software that is packaged with personal GPS receivers. If you are having difficulty with the accuracy of your GPS receiver, check your user guide or refer to the software to see if the problem can be fixed.

Technology has given us wonderful gifts and powers beyond imagination. A GPS receiver is one technological wonder that is so accessible, many people use them on a daily basis. If you travel locally or across country, or enjoy exploring the great outdoors, pick up a GPS receiver and youll always be able to find your way home.

About The Author

James Thomas contributes to several web magazines, on shopping and products and technology products themes.

Mapping Capabilities of the GPS Unit, If you plan to use your GPS receiver primarily in your vehicle, then built-in road maps are a prerequisite. As a bonus, most units allow you to download additional GPS maps. However, GPS units vary widely in the degree of detail provided in their on-screen maps. If you would like to view the surrounding terrain of a particular landmark area, then a GPS receiver with advanced mapping capabilities is better than the standard base model.
Get a great new discount Cobra GPS

Tip: It only works outdoors...The device works best under a clear sky. The satellite signal gets easily blocked by roofs, or even tall buildings nearby.
Get a great new Meridian GPS

Global Positioning Systems offer everything from hole overviews to Internet access "Shortgrass Technologies' Internet-based sports information system and financial ticker enables golfers to check college football scores on a Saturday afternoon or the price of stocks any weekday. Global positioning systems can track golf cars no matter where they are on the course, thus discovering bottlenecks and slower play. Golfers can order beverages and food en route to the turn, so golf clubs can offer more than a quick hot dog - a higher priced chicken sandwich, for instance...."

I always thought that GPS would go mainstream in automobiles first, and in a way I suppose it has, but maybe golfers will lead the real charge. I could have used a portable, library-centered GPS system myself to navigate the Chicago Public Library's Harold Washington Library when I was there last fall!

Lots of interesting articles from today's PC World. First up, Microsoft Takes on MapQuest: "MSN launches MapPoint online mapping service, offering maps, directions, and more."

Apparently this is going to be yet another component of MS' push for .Net services with hooks into other MSN services. MapPoint is XML-based, which makes it interesting in other ways, and there it launches with a phone-based direction service. The articles notes that this is another step towards location-based services. "For example, you might someday be able to click on a Windows Messenger buddy's name and retrieve a map showing the location of his or her home."

Good or bad? You make the call. I like parts of this, but I'm incredibly wary of .Net.

Qualcomm's Vision of the Wireless Future "When he finished, there were 20 brand-new, CDMA-based mobile handsets and devices arrayed on the table, the high-tech souvenirs of Belk's most recent trip to Hong Kong and Japan.... 'These are not PowerPoint slides,' Belk said. 'These are real devices that are already shipping in volume in Asia.' " at Business 2.0]

And there's the rub. When I do my presentations, that's all I have - pictures of prototypes or of devices not available in the U.S. Europe and Asia really are 18 months ahead of us in this area.

"Beale also discussed Qualcomm's gpsOne location technology.... It also opens the door for many new location-based services, such as traffic information and local weather forecasts. On Japan KDDI's network, there are already more than 20 location-based services available -- all of which are relatively inexpensive, costing less than $5 per month."

I'm looking forward to being able to travel and have information come to me automatically based on my location. For example, if I'm at a conference and I'm looking for a restaurant, I'd like my phone/PDA/whatever to know where I am and offer a list of nearby choices. Maybe it should tell me what movies or plays are on tonight and if there are still tickets available. You get the idea....

"Predictably, both Belk and Beale anticipate strong growth for the wireless industry as ever-more-compelling products and services become available and the industry settles on a single communication standard. How long will that take? Belk, whose career began in the personal computing business in 1983, likened the wireless industry today to the PC business of the 1980s. 'I wouldn't worry about the wireless industry yet, it's still relatively young,' he said. 'Just look how long it took the PC industry just to get to the point of standardized parallel cables.' "

Not to beat a dead horse, but the ebook industry is even younger than PCs, and PDAs have really only come into their own during the last few years. So don't count any of these technologies out just yet.

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