There currently are 24 operational satellites as part of the GPS satellite constellation, that orbit the earth with a orbital radius of ~16,000 miles (from the center of the earth). The satellite orbits are spaced out in 6 orbital planes (orbital plane is the plane surface formed by the path traced by the orbit of the satellite – it is nearly circular). The six orbital planes are separated by an angle of 60 degrees. Refer to the constellation figure below. Four to six satellites occupy each orbital plane. Article Source: http://www.articlesbase.com/gps-articles/gps-satellite-constellation-85046.html Steve Kinder is a GPS industry veteran with extensive experience in the GPS receiver design and manufacturing. His latest hobby is to spread the knowledge of GPS to everybody through tutorials and websites (www.gadgetknowledge.com/gps1.html). GPS Satellite Constellation
Author: Steve Kinder
In addition to the 24 operational satellites, there currently are 6 satellites in orbit that are maintained as spares, should any of the 24 operational satellites malfunction. The six spare satellites are kept operational for users to receive signals from them just like from the 24 satellites. However, the U.S. Government does not guarantee their availability at all times.
Remember that the GPS satellites are being launched since 1974. Satellites like everything else have limited lifespan. The GPS satellites have been designed to provide a lifespan of ~8 years. New satellites are being launched to space at regular intervals of time to make up for satellites that have lived out their lifespan.
When the satellites are launched into space, they are inserted to pre-calculated positions in their orbital planes. The pre-calculations ascertain that a GPS receiver located anywhere on earth and at all times, can receive signals from at least four satellites. This is required because earth blocks the GPS signals from passing through it. For a GPS receiver to be able to receive a signal from a satellite, the straight line-of-sight line should not have any obstructions in between. Since the satellites are flying around the earth, not all satellites are visible to a GPS receiver located somewhere on earth. Thus, though there are 30 operational satellites, not all of them can be visible at a location on earth, at any given time.
For a more comprehensive knowledge of GPS today, refer to websites such as www.gadgetknowledge.com/gps1.html
About the Author:
Not very often does a single system have such a large impact on the way we live. The Internet was revolutionary, so is GPS. Get to know GPS today and keep up with it before it permeates all over your lifestyle!
Wednesday, October 31, 2007
GPS Satellite Constellation
GPS Competitors
GLONASS: Article Source: http://www.articlesbase.com/gps-articles/gps-competitors-85371.html Steve Kinder is a GPS industry veteran with extensive experience in the GPS receiver design and manufacturing. His latest hobby is to spread the knowledge of GPS to everybody through tutorials and websites (www.gadgetknowledge.com/gps1.html). GPS Competitors
Author: Steve Kinder
The Russian Federation controls and operates a constellation of satellites and related ground stations called GLONASS, for purposes similar to GPS. GLONASS was developed and launched originally by the Soviet Union and has been in operation for several years now, similar to GPS. But since break up of the Soviet Union, the Russian Federation has not maintained GLONASS in a fully operational mode. The reasons are not technical in nature but are due to scarcity of money for maintenance of a fully operational constellation of GLONASS satellites. Similar to GPS, a certain minimum number of GLONASS satellites are required to achieve the fully operational status of providing view of at least four satellites everywhere on earth and at all times. Remember from discussions in the previous tutorial sections that the ‘sacred’ minimum number of satellites for fully operational status of GPS is twenty-four. So is there for GLONASS. Currently, however, the GLONASS satellite constellation consists of only twelve operational satellites. The Russian Federation has made announcements that it intends to upgrade GLONASS to fully operational status in the near future.
GALILEO:
The availability and accuracy of GPS is controlled by the US Government. Now if you consider the fact that GPS applications are permeating into many aspects of civilian lifestyle all over the world. Use of GPS in automobiles is ubiquitous today - pretty soon GPS use for applications such as life saving emergency co-ordination and other critical applications for the civilian community (during times of war and peace) can be expected to become ubiquitous. Thus, one might have a tendency to derive a conclusion that the US Government has a means of controlling the life style of civilians all over the world to a certain extent.
Such politics and other financial reasons (such as for obtaining financial benefits for European industry instead of US companies) led to the Europeans to design an entirely new global navigation system called GALILEO, over which they would have total control. Off course, if you ask the politicians, they might not want to tell you the story in a manner as explicit as presented here!
Currently, the GALILEO navigation system is in a design and development phase. The satellite constellation is not expected to be operational until year 2010. The system is expected to work similar to GPS and provide a similar usage for civilians all over the world.
For a more comprehensive knowledge of GPS today, refer to websites such as www.gadgetknowledge.com/gps1.html
About the Author:
Not very often does a single system have such a large impact on the way we live. The Internet was revolutionary, so is GPS. Get to know GPS today and keep up with it before it permeates all over your lifestyle!
GPS Applications for the Common Man
So, what the heck is GPS? What do you use it for or what can you use it for? Is it useful for you? Is it expensive? Questions, questions, questions, hmmmm. Article Source: http://www.articlesbase.com/gps-articles/gps-applications-for-the-common-man-85376.html Steve Kinder is a GPS industry veteran with extensive experience in the GPS receiver design and manufacturing. His latest hobby is to spread the knowledge of GPS to everybody through tutorials and websites. GPS Applications for the Common Man
Author: Steve Kinder
Well, think of GPS as an electronic gadget just like your radio. Once you knew how to use your radio, you never had to know how the radio works. The same can be said about GPS receivers – almost. Almost so because radios are cheap, but not GPS receivers. You can buy radios for ten bucks, whereas GPS receivers can cost you several thousand dollars. Expensive items always attract the ‘smart’ marketers. When you are buying GPS it can be useful to know some basics of how GPS works, just enough to get a good deal at the store.
For starters let us try to understand what can you use a GPS receiver for. Similar to your radio that can play audio from radio stations, there are several fundamental capabilities of a GPS receiver. Depending on the application, a set of GPS receiver capabilities are used. The GPS receiver is capable of calculating the following:
(1) GPS user’s location in terms of X, Y, Z co-ordinates
(2) Present time and date
(3) GPS user’s velocity, acceleration,..
That’s pretty much it. Examples:
Car navigation: A GPS receiver used for car navigation would employ capability (1) of a GPS receiver. A map database stored in digital format used in conjunction with capability 1 provides the requisite navigational capabilities.
Trucking management: If you are running a business where you deliver the goods using ground transportation such as trucks – lots of them. How you do you plan the route for all the trucks such that, you minimize fuel cost, minimize the time spent for offloading the goods that you are delivering and also reduce travel time. Well now, if you had a GPS receiver in each of the trucks, you would be able to record the delivery location and time for offloading. The next time, when you want to deliver a similar item, you know which truck to load it on based on past experience.
Depending on the application, GPS receivers in the market sell in a very broad price range. You can buy one for less than hundred dollars and one with all the bells and whistles for more than a grand. The right thing for you to do is to compare a comprehensive list of GPS receivers in the market and check against your application and budget. Websites like www.gadgetknowledge.com/gps1.html can get you started in the GPS arena. What you want to look for is a listing of GPS receivers in the market, a basic understanding of the various features/capabilities that you can expect out of your GPS receiver, a list of accessories that may be useful for your application and a tutorial introduction to what GPS is all about so that you make good use of your GPS receiver.
About the Author:
Not very often does a single system have such a large impact on the way we live. The Internet was revolutionary, so is GPS. Get to know GPS today and keep up with it before it permeates all over your lifestyle!
GPS History in Brief
The GPS satellite system for navigation was designed in the 1970s by the U.S. Department of Defense. It started out as a global navigation system for military land-based and air vehicles, with some limited use for the civilian population. But today, the tables have turned – there are more GPS receivers used by civilians than by the military! Article Source: http://www.articlesbase.com/gps-articles/gps-history-in-brief-85366.html Steve Kinder is a GPS industry veteran with extensive experience in the GPS receiver design and manufacturing. His latest hobby is to spread the knowledge of GPS to everybody through tutorials and websites (www.gadgetknowledge.com/gps1.html). GPS History in Brief
Author: Steve Kinder
Back in the 70’s, the military employed a variety of navigation systems such as LORAN (acronym for Long Range Radio Navigation), VOR (acronym for VHF Omni-directional Radio) and OMEGA, and a need was felt for a more accurate navigational aid which would be functional all day, all year and everywhere on Earth, irrespective of day or night or weather conditions. The military’s needs were to navigate its airplanes, tanks and personnel reliably. At that time, the U.S. Navy and the Air Force were in the pursuit of developing systems that would meet such requirements with programs such as Transit satellite system, Timation satellite system and Project 621B. The Department of Defense eventually formed a Joint Program Office (JPO), which consolidated the developments to date in to what we know today as the Global Positioning System (GPS).
The first GPS satellite was launched in 1974, and the GPS satellite constellation was declared fully operational in 1994. The satellites were/are designed and built by Rockwell International, Boeing and Lockheed-Martin.
Though GPS was designed by the DOD for the military, they did include some capabilities that could be useful for the civilian community. The GPS satellites transmit encrypted signals, which only the military has access to. The satellites also transmit non-encrypted signals, which can be detected in both military and civilian GPS receivers. The civilian signal is referred to as the C/A code signal (Coarse Acquisition).
A key parameter that describes GPS capability is positioning accuracy, which simply put, is the accuracy of the GPS receiver user's position computed in the GPS receiver. GPS system developers initially did not expect the civilian signal to provide position accuracy comparable with those obtained by the military signals. However, the designers soon realized that the civilian GPS receivers could employ several newly developed algorithms that could improve the position accuracy obtained in civilian GPS receivers dramatically. In order to limit the positional accuracy of civilian GPS receivers, they implemented degradations of the civilian GPS signal before being transmitted by the GPS satellites. The degradation capability is referred to as Selective Availability (SA). SA limited position accuracy in GPS receivers to ~50 meters. However, by late 1990s, President Clinton having realized the benefit of GPS to the civilian community, ordered SA degradation to be removed. With the removal of SA, the doors opened up for civilian users to use GPS for automotive tracking for driving assistance, fleet management, …….
For a more comprehensive knowledge of GPS today, refer to websites such as www.gadgetknowledge.com/gps1.html
About the Author:
Not very often does a single system have such a large impact on the way we live. The Internet was revolutionary, so is GPS. Get to know GPS today and keep up with it before it permeates all over your lifestyle!
GPS Accessories
Here's a typical list of accessories for your GPS receiver/systems that might be useful for you. Highly recommend that you review the reading material in the Features/Gimmicks section of www.gadgetknowledge.com/gps1.html, to obtain an understanding of the kind of accessories you may need for your GPS application. Go to the ‘Buy Them Here’ section for a list of places where you can buy the accessories. Article Source: http://www.articlesbase.com/gps-articles/gps-accessories-85378.html Steve Kinder is a GPS industry veteran with extensive experience in the GPS receiver design and manufacturing. His latest hobby is to spread the knowledge of GPS to everybody through tutorials and websites (www.gadgetknowledge.com/gps1.html). GPS Accessories
Author: Steve Kinder
Adapters & Battery Chargers
1. Battery chargers are available with adapters for International & Regional A/C outlets.
2. Buy cables to charge your GPS receiver batteries from your automobile's batteries, through the cigarette lighter socket in your automobile.
3. An additional battery can be of help, when you are headed out on one of those long trekking trips into the wilderness.
Antennas
1. External antennas can enhance your GPS receiver's signal reception.
2. Look for low profile antennas small in size.
3. External antennas are available with adhesive mounts or magnetic mounts or suction mounts (for example, for mounting on your car's windshield).
4. If you plan to mount the antenna outside your vehicle, make sure that it is waterproof.
Cables
1. Cables to connect your GPS to a computer's USB port. For example, you may want to plan your route on a computer and download it to your GPS.
2. Cables are available to power your GPS receiver from your automobile's cigarette lighter.
3. You may need long coaxial cables to connect your GPS receiver to the external antenna.
4. Cables can connect your iPod to your GPS unit.
5. Connect your GPS unit to your car stereo using a audio cable to hear turn-by-turn voice guidance loud and clear or simply to listen to MP3 music.
Carrying Cases
1. Carry cases to securely hold your GPS
Maps, Charts
1. When you buy a GPS receiver it is generally pre-loaded with regional maps or charts (maps for navigation on land and charts for navigation on water).
2. You may want to buy additional regional maps depending on where you want to go.
3. Typical maps available are for North America or Australia or UK or West Europe or USA or Italy/Greece or USA lakes,.......
Memory
1. You may need additional memory for your GPS to store bigger maps (maps are available for not just roads but for also points of interest such as restaurants, shopping complexes,...) and more advanced software versions.
2. Additional memory is available in forms, such as 128/256 MB Micro SD card, 32/64/128/256/512 MB Compact Flash Card, ...
For a more comprehensive knowledge of GPS today, refer to websites such as www.gadgetknowledge.com/gps1.html
About the Author:
Not very often does a single system have such a large impact on the way we live. The Internet was revolutionary, so is GPS. Get to know GPS today and keep up with it before it permeates all over your lifestyle!
What My Satellite GPS Can Do That your Road Atlas Can't
Television is not the only "cool" thing using satellites these days. For anyone who likes to travel or wander, the GPS satellite navigation systems that have been on the market for a few years are handy on-the-road companions. Some automotive manufacturers offer GPS in select car models however GPS can also be purchased after market and can be operated outside of the car as well. Satellite GPS navigates through signals received from the myriad of satellites orbiting earth and is extremely accurate using the maps that are loaded into its memory. Article Source: http://www.articlesbase.com/gps-articles/what-my-satellite-gps-can-do-that-your-road-atlas-cant-87379.html Christine Peppler shares information on home entertainment and home electronics products on her website at: http://www.homemedias.info.What My Satellite GPS Can Do That your Road Atlas Can't
Author: Christine Peppler
So what does a satellite GPS device offer that a road atlas doesn't? GPS satellite systems provide directions while traveling, generally through voice instructions which allow the person to keep their eyes on the road. No more pulling off to the side of the road to study a map, struggling to read illegible print, or trying to find just the right spot with only a dome light for illumination.
Satellite GPS devices are also "smart" as many can also provide updates on weather and traffic information and then assist in mapping an alternate route when barriers exist in the pre-planned route. This flexibility and problem solving make it an invaluable tool when traveling in an unfamiliar area.
Satellite GPS devices are also great to use when hiking, camping, cross country skiing, and participating in similar outdoor activities. Their small size and light weight make them a great tool outside of the car and are often recommended by outdoor enthusiasts and organizations for safety purposes.
Most satellite GPS devices sold in the US contain maps and points of interest such as airports, hospitals, and so forth to the tune of over one million locations. However, these devices aren't limited to the boundaries of the US obviously. For those who wish to use the device when traveling outside the country, many devices have flash cards which can be used to download the appropriate maps corresponding with their destination making satellite GPS a great travel companion.
For many potential users an important consideration is ease of use. Many satellite GPS devices, such as the portable Sony Nav-U, are ready to use right out of the box. It has maps and over 1.6 million points of interest loaded into its memory. It offers a full color 3.5" touch screen display and 2-way speaker system. Cost of an average satellite GPS device is in the range of $400 to $600 dollars but given years of good service and flexibility of use it would seem an excellent investment.
In the world of navigation or route finding, it seems that satellite GPS devices will eventually put basic road maps and compasses into the same realm as typewriters and carbon paper.
About the Author:
Which GPS Device is Right for You?
For those who drive significant distances or who frequently find themselves searching for things in unfamiliar surroundings, a GPS satellite receiver can certainly simplify life. Like most electronics devices however, the number of choices, brands, and features can make the selection of a device difficult and somewhat time consuming. Shoppers however can take some time to identify the features that would be most valuable for them, determine how much they are willing to spend, and then relax as the selection will be greatly simplified once these decisions are made. Article Source: http://www.articlesbase.com/gps-articles/which-gps-device-is-right-for-you-117164.html The author, Christine Peppler invites consumers to visit her website for simple, useful information and shopping for home electronics.Which GPS Device is Right for You?
Author: Christine Peppler
In a world of innumerable options, here are a few of the more critical characteristics to consider:
Will the device be used outside of the vehicle?
There are some ultra portable GPS devices designed for use in cars, vans, and trucks that offer the flexibility of use outside of the vehicle as well. To be useful, the device would need not only roadmaps but terrain information loaded. Certainly size and weight need to be considered if the device is to be carried; Bluetooth helps to make this option more feasible. Rechargeable batteries would also be important in these instances so that the GPS device could operate without being plugged in for several hours.
Is the screen sufficient?
Obviously the screen needs to be large enough to easily view, but small enough to not block the view of the driver. It is also wise to be sure that the screen is easy to view in any type of lighting condition; not only at night time but in bright sunlight as well. Most people also prefer a touch screen to navigate rather than one requiring the use of a stylus or some other type of access. For those who want to be sure they take their eyes off of the road as little as possible, a GPS device with voice commands is also critical.
How accurate is the information the GPS device provides?
There are a number of features to consider when trying to assure the accuracy of information. A device with WAAS (Wide Area Augmentation System) is able to pinpoint locations accurately to within a few feet; this may or may not be critical for a given user. Some devices will merely instruct drivers to "turn left" while others are capable of providing more detail by stating the name of the street when providing instructions. Some devices also provide real-time traffic information by using an FM frequency within the vehicle. The accuracy and detail of the maps included with the GPS device can vary as well so comparison shopping can be useful. The more "points of interest" on a map the more likely it will pinpoint the location a user is seeking. Keeping maps updated after purchase is usually up to the consumer. Some devices require the purchase of a CD to update the device while others accomplish this across the internet.
Is the device easy to use?
Again for many users, voice commands and a touch screen make a GPS device easier to use. Examining the menus to determine if they are user friendly is important. Many current models don't require any complex installation and are ready to go out of the box but some offer preloaded maps while others require buyers to install the maps themselves.
As with any purchase, consumers should identify their needs and their budget to determine which device would be the best choice. If pin point accuracy is needed a GPS device with WAAS might be crucial but if budget considerations rule, a device that allows the user to transfer maps from a PC to the device would be a more cost conscious choice than one with maps on the hard drive.
About the Author:
Tuesday, October 30, 2007
Gps Vehicle Tracking - Usage and Tips
If you are concerned about how fast your teen is driving, or if your spouse is being unfaithful, a gps vehicle tracking device can assist you in keeping tabs on them. Article Source: http://www.articlesbase.com/gps-articles/gps-vehicle-tracking-usage-and-tips-133647.html Tim Chirillo is an internet developer and part time private investigator.Gps Vehicle Tracking - Usage and Tips
Author: Tim Chirillo
A gps vehicle tracker is a usually a small device that you can attach to the bottom of the vehicle by a magnet, or you could secretly stash it inside the car somewhere.They come with a software program, where you can login from your favorite web browser and keep a real time track on exactly where the vehicle is.
Here are some of the really cool features.
Monitor the vehicles speed. If you are worried about your precious automobile being abused, you can set the gps vehicle tracking device to a certain speed you designate. If the car
exceeds this speed limit, you will be notified immediately. So if your child swears they aren't speeding, you will have the proof!
Keep track of your vehicle's whereabouts. From your computer you can track in real time exactly where your car is . Did your wife tell you she was going to the gym? Then why is her vehicle
miles away from the establishment? You will be able to tell. What about your teen? Did she go to the library or is she over that guy's house that you absolutely cannot stand?
Alerts when out of the designated area. As well as speeding alerts, you can set on your computer, remotely a certain area of where you believe the vehicle should be. For instance, you can input an address and a certain radius within that address. So, if your vehicle goes out of that radius, you will be alerted as well.
Since the gps vehicle tracking device is browser based to track activity, you can access your vehicle 24/7 from any computer, even while your at work. You will simply go to a web page, enter your login info,and bam, there are the stats are your car.
Some of the better devices even store up to 90 days of activity. So, you can see exactly how many times the driver went over your designated speed limit, or how many times they stopped at a certain address which you are suspicious of.
These devices are a cool gadget, and a tech lover's dream. You can now have all the information on your vehicle at your fingertips!
About the Author:
Visit his site for more info on Gps vehicle tracking
GPS Watches
GPS Watches Article Source: http://www.articlesbase.com/gps-articles/gps-watches-178003.html Looking for more information on GPS Watches check out www.gps-watches.net your guide to GPS Watches.GPS Watches
Author: Dhiraj Bandurkar
Technology has contributed a lot and is still contributing much to make our lives simple. It has eased communication to such an extent that we can be mobile and still stay in touch with each other. It is not only communication that is eased but a lot of other things which are more suitable to the changing needs of the fast paced individuals. One such change is in the way one used to find the directions. Gone are the days when maps and compass were used to find directions. Although such techniques were useful but not accurate as the new age GPS system, which is the most accurate way of finding directions using a digital map. GPS or the Global Positioning System works with the help of satellites orbiting the earth and allows you to use it in many applications other than finding directions.
Although GPS is used with many applications, it has found an all new dimension when used with the wrist watch. Yes! A GPS device included in your wristwatch is not a dream but reality. With the wide use of GPS technology many tech savvy companies have tried and developed a wrist watch which is equipped with GPS. Now there are many companies which offer you a wrist watch with GPS technology. The GPS wrist watches are meant for sportspersons and adventure buffs who want to spend more time in the open. This GPS watch is an expert navigator which can keep anyone on track in the mountains, forests, rivers or lakes without getting lost.
The GPS wrist watches are more or less like wrist computers and do have more than one set of functions. The only thing which you need to understand in the GPS wrist watches is the limited size of the screen and restricted number of keys mean which means that the device must have different modes for displaying sufficient information on each topic on the screen. The downside of such small screen is that you have to change modes al lot during complex operations. For example, if you want to access GPS and you happen to have the altitude mode on, you have to apply a fairly long sequence of keystrokes to go through the menu system. Some of the GPS watches do have as many as five different modes, which are time, altimeter/barometer, compass, GPS navigation and activity mode for measuring speed and distance.
The GPS watches are quite essential if you are planning an outdoor adventure. They are best to guide you to the location which you want to reach. They are also beneficial for trekking and mountaineering with the altimeter feature which keeps you updated on the height. Some of the latest GPS watches also have an Activity mode, which shows you the speed, distance traveled, time from start and other values. Your trail is recorded in the device memory and this information can later be used for the Track Back function, or viewing the route at home via a PC.
About the Author:
GPS Tracking Systems
GPS tracking systems serve for personal and global protection Article Source: http://www.articlesbase.com/gps-articles/gps-tracking-systems-185893.html Ofir SaharGPS Tracking Systems
Author: Ofir Sahar
GPS tracking Systems are designed for tracking vehicle fleets, equipment, and people. GPS tracking system is used for fleet management, protecting the vehicle and driver, and locating equipment and people.
The technology behind these GPS tracking systems is a full cellular (GSM CDMA) and location (GPS) system solution that includes both software and hardware set to provide the perfect vehicle tracking system for every place at any language.
Examples of the usage made by GPS tracking systems are:
Vehicle protection
Vehicle thefts cost insurance agencies and car owners billions of dollars in damages each yearGPS tracking systems are specifically designed to detect and minimize losses due to criminal activities. The system is designed to report events automatically and in real-time, for quick response.
Driver protection
The GPS systems control center focus is to support the client 24/7, by responding in a timely, responsible and professional manner for a routine or emergency situations: kidnapping situations, accident events, and more. All the operators are following the established procedures and act in the best interest and well being of each client while keeping the client's Right to Privacy.
Mobile Phone Activation
The system is synchronized between the hardware, the software and the client's mobile phone, to enable the client to send commands to his vehicle, receives his vehicle location and statuses and receives any required alert from the vehicle in friendly and easy to use application.
Real time vehicle alerts
The systems are able to send to your mobile phone any violations occurred by the vehicle (including high speed, driving out or entering an unauthorized zone, over heat, and more) or any other alert (accident, emergency, etc.).
About the Author:
Fleet Tracking System
GPS Satellite Navigation
Do you find that you have a lot of speedingtickets? Maybe you eve have trouble remembering where to reduce your speed? There are of course many ways to solve your problems. Even if you don’t have speeding problems you probably find you have navigation problems when you are in a new area of the city. Undetected is just one company that offers satellite navigation and speed camera detectors. If you are interested in GPS satellite navigation you should check out the products available and compare pricing. Article Source: http://www.articlesbase.com/gps-articles/gps-satellite-navigation-187044.html Written by Antonious Lamston. Find more information on GPS Satellite Navigation
Author: antoniouslamston
Undetected offers you a range of products including a dual satellite navigation system and speed camera. These units will help you navigate the city as well as reduce you speeding tickets, traffic violation fines, and traffic accidents. The Indic8tor is one of the latest GPS satellite navigation systems. This GPS will warn you when you enter a new speed zone, aid you in safe driving, and give you voice alerts.The voice will allow you to know when you are exceeding the limits as well as offer guidance. Another GPS navigation system is the Snooper S3 GPS.This GPS stores geographical coordinates and even tells you of "black spots" on the road. A black spot is usually considered an area where a lot of accidents happen. The Snooper S3 GPS will compare your position with a GPS antenna to give you the most up to date information on speeds and accident spots.
There are many other GPS satellite navigation systems available and tips on how to use them. You will want to understand the laws of your area as well as how these systems can help you reduce accidents or violations.Undetected will offer you information about the law as well as facts about the products they sell to help you find the best product for your vehicle.
About the Author:
gps sat nav
8 Advantages of a Gps System
Global positioning systems are widely in use today for navigation, map making, land surveying fishing, treks, and many scientific applications. GPS receivers can be incorporated into cars, boats, computers, mobile phones watches and more. Article Source: http://www.articlesbase.com/gps-articles/8-advantages-of-a-gps-system-215835.html Arthur Raise is a writer for GPS Reviews , the premier website to gps, best gps, gps systems, gps software, gps receiver, cheap gps, gps tracking system, discount gps, gps map, gps mapping and many more. 8 Advantages of a Gps System
Author: Arthur Raise
There are many advantages of having a gps system:
1. A gps system comes with a “panic” button. When this button is pressed an operator at the gps carrier can listen in on the conversation and either help you out or alert the authorities. This will keep you safe in case of accidents or hi jacks.
2. Your car will never loose your car at a football match or mall. The gps service will track the car for you and send its lights flashing.
3. If your vehicle is ever stolen the gps system will track the vehicle and the authorities will be able to get it back in no time.
4. A gps system in a car, boat, plane or haversack will ensure that you are never lost.
5. A gps system streamlines supply chains and truck movements. The system can track goods at any point of time and accurately predict when goods will reach their destination.
6. Gps systems are used to detect structural problems in buildings and roads and to predict disasters like earthquakes and so on. The scientific applications of a gps system are many.
7. A gps system can be used to locate a lost child, pet or family. The device is quite small and is like a watch or button on a collar.
8. A gps is a great exercise monitor and will help you keep track of your spped and so on.
A word of caution before signing up for a gps system find out what you are paying for and what the monthly fee will cover.
Gps systems have so many uses; they help determine weather patterns, can be used in conjunction with cameras, have varied use in military and have great use in surveying for volcanic eruptions, sink holes, movements in the earth’s plates and so on.
A word of caution before signing up for a gps system find out what you are paying for and what the monthly fee will cover. Log on to the internet and find out online what are gps services and what the costs are. Read all about gps systems and the pros and cons. Always compare rates and choose a package that suits you best. The World Wide Web is the most convenient market place to find affordable and useful gps packages.
About the Author:
About GPS
Global Positioning System Article Source: http://www.articlesbase.com/gps-articles/about-gps-223087.htmlAbout GPS
Author: anwar
The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). 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.
Developed by the United States Department of Defense, it is officially named NAVSTAR GPS (Contrary to popular belief, NAVSTAR is not an acronym, but simply a name given by Mr. John Walsh, a key decision maker when it came to the budget for the GPS program[1]). The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year,[2] including the replacement of aging satellites, and research and development. Despite these costs, GPS is free for civilian use as a public good.
GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, and scientific uses. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.
Simplified method of operation
A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS microwave signal gives the distance to each satellite, since the signal travels at a known speed - the speed of light. These signals also carry information about the satellites' location and general system health (known as almanac and ephemeris data). By determining the position of, and distance to, at least three satellites, the receiver can compute its position using trilateration.[3] Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites, using their atomic clocks to correct the receiver's own clock error.
[edit] Technical description
Unlaunched GPS satellite on display at the San Diego Aerospace museum
Unlaunched GPS satellite on display at the San Diego Aerospace museum
[edit] System segmentation
The current GPS consists of three major segments. These are the space segment (SS), a control segment (CS), and a user segment (US).[4]
[edit] Space segment
The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. The GPS design calls for 24 SVs to be distributed equally among six circular orbital planes.[5] The orbital planes are centered on the Earth, not rotating with respect to the distant stars.[6] The six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).[2]
Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day, so it passes over the same location on Earth once each day. The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.[7]
As of September 2007, there are 31 actively broadcasting satellites in the GPS constellation. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.[8]
[edit] Control segment
The flight paths of the satellites are tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA).[9] The tracking information is sent to the Air Force Space Command's master control station at Schriever Air Force Base in Colorado Springs, which is operated by the 2d Space Operations Squadron (2 SOPS) of the United States Air Force (USAF). 2 SOPS contacts each GPS satellite regularly with a navigational update (using the ground antennas at Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs). These updates synchronize the atomic clocks on board the satellites to within one microsecond and adjust the ephemeris of each satellite's internal orbital model. The updates are created by a Kalman filter which uses inputs from the ground monitoring stations, space weather information, and various other inputs.[10]
GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).
GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).
[edit] User segment
The user's GPS receiver is the user segment (US) of the GPS system. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, as of 2006, receivers typically have between twelve and twenty channels.
A typical OEM GPS receiver module, based on the SiRF Star III chipset, measuring 15×17 mm, and used in many products.
A typical OEM GPS receiver module, based on the SiRF Star III chipset, measuring 15×17 mm, and used in many products.
GPS receivers may include an input for differential corrections, using the RTCM SC-104 format. This is typically in the form of a RS-232 port at 4,800 bit/s speed. Data are actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data. As of 2006, even low-cost units commonly include Wide Area Augmentation System (WAAS) receivers.
Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol. NMEA 2000[11] is a newer and less widely adopted protocol. Both are proprietary and controlled by the US-based National Marine Electronics Association. References to the NMEA protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws. Other proprietary protocols exist as well, such as the SiRF and MTK protocols. Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth.
[edit] Navigation signals
Main article: GPS signals
GPS broadcast signal
GPS broadcast signal
Each GPS satellite continuously broadcasts a Navigation Message at 50 bit/s giving the time-of-day, GPS week number and satellite health information (all transmitted in the first part of the message), an ephemeris (transmitted in the second part of the message) and an almanac (later part of the message). The ephemeris data gives the satellite's own precise orbit and is output over 18 seconds, repeating every 30 seconds. The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for 6 hour time-outs. The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate. The almanac consists of coarse orbit and status information for each satellite in the constellation and takes 12 seconds for each satellite present, with information for a new satellite being transmitted every 30 seconds (15.5 minutes for 31 satellites). The purpose of the data is to assist in the acquisition of satellites at power-up by allowing the receiver to generate a list of visible satellites based on stored position and time, while an ephemeris from each satellite is needed to compute position fixes using that satellite. In older hardware, lack of an almanac in a new receiver would cause long delays before providing a valid position, because the search for each satellite was a slow process. Advances in hardware have made the acquisition process much faster, so not having an almanac is no longer an issue. An important thing to note about navigation data is that each satellite transmits only its own ephemeris, but transmits an almanac for all satellites.
Each satellite transmits its navigation message with at least two distinct spread spectrum codes: the Coarse / Acquisition (C/A) code, which is freely available to the public, and the Precise (P) code, which is usually encrypted and reserved for military applications. The C/A code is a 1,023 chip pseudo-random (PRN) code at 1.023 million chips/sec so that it repeats every millisecond. Each satellite has its own C/A code so that it can be uniquely identified and received separately from the other satellites transmitting on the same frequency. The P-code is a 10.23 megachip/sec PRN code that repeats only every week. When the "anti-spoofing" mode is on, as it is in normal operation, the P code is encrypted by the Y-code to produce the P(Y) code, which can only be decrypted by units with a valid decryption key. Both the C/A and P(Y) codes impart the precise time-of-day to the user. Frequencies used by GPS include
* L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future Block III satellites.
* L2 (1227.60 MHz): P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites.
* L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to signal detection of nuclear detonations and other high-energy infrared events. Used to enforce nuclear test ban treaties.
* L4 (1379.913 MHz): Being studied for additional ionospheric correction.
* L5 (1176.45 MHz): Proposed for use as a civilian safety-of-life (SoL) signal (see GPS modernization). This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances. The first Block IIF satellite that would provide this signal is set to be launched in 2008.
[edit] Calculating positions
[edit] Using the C/A code
To start off, the receiver picks which C/A codes to listen for by PRN number, based on the almanac information it has previously acquired. As it detects each satellite's signal, it identifies it by its distinct C/A code pattern, then measures the time delay for each satellite. To do this, the receiver produces an identical C/A sequence using the same seed number as the satellite. By lining up the two sequences, the receiver can measure the delay and calculate the distance to the satellite, called the pseudorange[12].
Overlapping pseudoranges, represented as curves, are modified to yield the probable position
Overlapping pseudoranges, represented as curves, are modified to yield the probable position
Next, the orbital position data, or ephemeris, from the Navigation Message is then downloaded to calculate the satellite's precise position. A more-sensitive receiver will potentially acquire the ephemeris data quicker than a less-sensitive receiver, especially in a noisy environment.[13] Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it. Receivers can substitute altitude for one satellite, which the GPS receiver translates to a pseudorange measured from the center of the earth.
Locations are calculated not in three-dimensional space, but in four-dimensional spacetime, meaning a measure of the precise time-of-day is very important. The measured pseudoranges from four satellites have already been determined with the receiver's internal clock, and thus have an unknown amount of clock error. (The clock error or actual time does not matter in the initial pseudorange calculation, because that is based on how much time has passed between reception of each of the signals.[clarify][citation needed]) The four-dimensional point that is equidistant from the pseudoranges is calculated as a guess as to the receiver's location, and the factor used to adjust those pseudoranges to intersect at that four-dimensional point gives a guess as to the receiver's clock offset. With each guess, a geometric dilution of precision (GDOP) vector is calculated, based on the relative sky positions of the satellites used. As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more guesses to the location and clock offset. The receiver then determines which combinations to use and how to calculate the estimated position by determining the weighted average of these positions and clock offsets. After the final location and time are calculated, the location is expressed in a specific coordinate system, e.g. latitude/longitude, using the WGS 84 geodetic datum or a local system specific to a country.
[edit] Using the P(Y) code
Calculating a position with the P(Y) signal is generally similar in concept, assuming one can decrypt it. The encryption is essentially a safety mechanism: if a signal can be successfully decrypted, it is reasonable to assume it is a real signal being sent by a GPS satellite.[citation needed] In comparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators. RAIM features do not protect against spoofing, since RAIM only checks the signals from a navigational perspective.
[edit] Accuracy and error sources
The position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal. The position accuracy is primarily dependent on the satellite position and signal delay.
To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version. By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about 1% of a bit time, or approximately 10 nanoseconds for the C/A code. Since GPS signals propagate nearly at the speed of light, this represents an error of about 3 meters. This is the minimum error possible using only the GPS C/A signal.
Position accuracy can be improved by using the higher-chiprate P(Y) signal. Assuming the same 1% bit time accuracy, the high frequency P(Y) signal results in an accuracy of about 30 centimeters.
Electronics errors are one of several accuracy-degrading effects outlined in the table below. When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft). These effects also reduce the more precise P(Y) code's accuracy.
Sources of User Equivalent Range Errors (UERE) Source Effect
Ionospheric effects ± 5 meter
Ephemeris errors ± 2.5 meter
Satellite clock errors ± 2 meter
Multipath distortion ± 1 meter
Tropospheric effects ± 0.5 meter
Numerical errors ± 1 meter
[edit] Atmospheric effects
Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth's atmosphere and ionosphere. Correcting these errors is a significant challenge to improving GPS position accuracy. These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the signal is affected for a longer time. Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors.
Because ionospheric delay affects the speed of microwave signals differently based on frequency—a characteristic known as dispersion—both frequency bands can be used to help reduce this error. Some military and expensive survey-grade civilian receivers compare the different delays in the L1 and L2 frequencies to measure atmospheric dispersion, and apply a more precise correction. This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code. To facilitate this on lower cost receivers, a new civilian code signal on L2, called L2C, was added to the Block IIR-M satellites, which was first launched in 2005. It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.
The effects of the ionosphere generally change slowly, and can be averaged over time. The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location. This correction is also valid for other receivers in the same general location. Several systems send this information over radio or other links to allow L1 only receivers to make ionospheric corrections. The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems such as WAAS, which transmits it on the GPS frequency using a special pseudo-random number (PRN), so only one antenna and receiver are required.
Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere. This effect is both more localized and changes more quickly than ionospheric effects and is not frequency dependent. These traits making precise measurement and compensation of humidity errors more difficult than ionospheric effects.
Changes in altitude also change the amount of delay due to the signal passing through less of the atmosphere at higher elevations. Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct.
[edit] Multipath effects
GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc. These delayed signals can cause inaccuracy. A variety of techniques, most notably narrow correlator spacing, have been developed to mitigate multipath errors. For long delay multipath, the receiver itself can recognize the wayward signal and discard it. To address shorter delay multipath from the signal reflecting off the ground, specialized antennas may be used to reduce the signal power as received by the antenna. Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay.
Multipath effects are much less severe in moving vehicles. When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions.
[edit] Ephemeris and clock errors
The navigation message from a satellite is sent out only every 30 seconds. In reality, the data contained in these messages tend to be "out of date" by an even larger amount. Consider the case when a GPS satellite is boosted back into a proper orbit; for some time following the maneuver, the receiver's calculation of the satellite's position will be incorrect until it receives another ephemeris update. The onboard clocks are extremely accurate, but they do suffer from some clock drift. This problem tends to be very small, but may add up to 2 meters (6 ft) of inaccuracy.
This class of error is more "stable" than ionospheric problems and tends to change over days or weeks rather than minutes. This makes correction fairly simple by sending out a more accurate almanac on a separate channel.
[edit] Selective availability
The GPS includes a feature called Selective Availability (SA) that introduces intentional, slowly changing random errors of up to a hundred meters (328 ft) into the publicly available navigation signals to confound, for example, guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.
SA typically added signal errors of up to about 10 meters (32 ft) horizontally and 30 meters (98 ft) vertically. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly, for instance the entire eastern U.S. area might read 30 m off, but 30 m off everywhere and in the same direction. To improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy.
During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in a decision to disable Selective Availability. This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy. But since SA was also denying the same accuracy to thousands of friendly troops, turning it off or setting it to an error of zero meters (effectively the same thing) presented a clear benefit.
In the 1990s, the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems. The military resisted for most of the 1990s, and it ultimately took an executive order to have SA removed from the GPS signal. The amount of error added was "set to zero"[14] at midnight on May 1, 2000 following an announcement by U.S. President Bill Clinton, allowing users access to the error-free L1 signal. Per the directive, the induced error of SA was changed to add no error to the public signals (C/A code). Selective Availability is still a system capability of GPS, and error could, in theory, be reintroduced at any time. In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA,[15] have stated that it is not intended to be reintroduced.
The US military has developed the ability to locally deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.[14]
One interesting side effect of the Selective Availability hardware is the capability to correct the frequency of the GPS caesium and rubidium atomic clocks to an accuracy of approximately 2 × 10-13 (one in five trillion). This represented a significant improvement over the raw accuracy of the clocks.[citation needed]
On 19 September 2007, the United States Department of Defense announced that they would not procure any more satellites capable of implementing SA. [16]
[edit] Relativity
According to the theory of relativity, due to their constant movement and height relative to the Earth-centered inertial reference frame, the clocks on the satellites are affected by their speed (special relativity) as well as their gravitational potential (general relativity). For the GPS satellites, general relativity predicts that the atomic clocks at GPS orbital altitudes will tick more rapidly, by about 45,900 nanoseconds (ns) per day, because they are in a weaker gravitational field than atomic clocks on Earth's surface. Special relativity predicts that atomic clocks moving at GPS orbital speeds will tick more slowly than stationary ground clocks by about 7,200 ns per day. When combined, the discrepancy is 38 microseconds per day; a difference of 4.465 parts in 1010.[17]. To account for this, the frequency standard onboard each satellite is given a rate offset prior to launch, making it run slightly slower than the desired frequency on Earth; specifically, at 10.22999999543 MHz instead of 10.23 MHz.[18]
GPS observation processing must also compensate for another relativistic effect, the Sagnac effect. The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined. The Lorentz transformation between the two systems modifies the signal run time, a correction having opposite algebraic signs for satellites in the Eastern and Western celestial hemispheres. Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.[19]
The atomic clocks on board the GPS satellites are precisely tuned, making the system a practical engineering application of the scientific theory of relativity in a real-world environment.
[edit] GPS interference and jamming
Since GPS signals at terrestrial receivers tend to be relatively weak, it is easy for other sources of electromagnetic radiation to desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible.
Solar flares are one such naturally occurring emission with the potential to degrade GPS reception, and their impact can affect reception over the half of the Earth facing the sun. GPS signals can also be interfered with by naturally occurring geomagnetic storms, predominantly found near the poles of the Earth's magnetic field.[20] Another source of problems is the metal embedded in some car windscreens to prevent icing, degrading reception just inside the car.
Man-made interference can also disrupt, or jam, GPS signals. In one well documented case, an entire harbor was unable to receive GPS signals due to unintentional jamming caused by a malfunctioning TV antenna preamplifier.[21] Intentional jamming is also possible. Generally, stronger signals can interfere with GPS receivers when they are within radio range, or line of sight. In 2002, a detailed description of how to build a short range GPS L1 C/A jammer was published in the online magazine Phrack.[22]
The U.S. government believes that such jammers were used occasionally during the 2001 war in Afghanistan and the U.S. military claimed to destroy a GPS jammer with a GPS-guided bomb during the Iraq War.[23] Such a jammer is relatively easy to detect and locate, making it an attractive target for anti-radiation missiles. The UK Ministry of Defence tested a jamming system in the UK's West Country on 7 and 8 June 2007. [24]
Some countries allow the use of GPS repeaters to allow for the reception of GPS signals indoors and in obscured locations, however, under EU and UK laws, the use of these is prohibited as the signals can cause interference to other GPS receivers that may receive data from both GPS satellites and the repeater.
Due to the potential for both natural and man-made noise, numerous techniques continue to be developed to deal with the interference. The first is to not rely on GPS as a sole source. According to John Ruley, "IFR pilots should have a fallback plan in case of a GPS malfunction".[25] Receiver Autonomous Integrity Monitoring (RAIM) is a feature now included in some receivers, which is designed to provide a warning to the user if jamming or another problem is detected. The U.S. military has also deployed their Selective Availability / Anti-Spoofing Module (SAASM) in the Defense Advanced GPS Receiver (DAGR). In demonstration videos, the DAGR is able to detect jamming and maintain its lock on the encrypted GPS signals during interference which causes civilian receivers to lose lock.[26]
[edit] Techniques to improve accuracy
[edit] Augmentation
Main article: GNSS Augmentation
Augmentation methods of improving accuracy rely on external information being integrated into the calculation process. There are many such systems in place and they are generally named or described based on how the GPS sensor receives the information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provide additional navigational or vehicle information to be integrated in the calculation process.
Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.
[edit] Precise monitoring
The accuracy of a calculation can also be improved through precise monitoring and measuring of the existing GPS signals in additional or alternate ways.
After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere. The spacecraft broadcast ionospheric model parameters, but errors remain. This is one reason the GPS spacecraft transmit on at least two frequencies, L1 and L2. Ionospheric delay is a well-defined function of frequency and the total electron content (TEC) along the path, so measuring the arrival time difference between the frequencies determines TEC and thus the precise ionospheric delay at each frequency.
Receivers with decryption keys can decode the P(Y)-code transmitted on both L1 and L2. However, these keys are reserved for the military and "authorized" agencies and are not available to the public. Without keys, it is still possible to use a codeless technique to compare the P(Y) codes on L1 and L2 to gain much of the same error information. However, this technique is slow, so it is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies (see GPS modernization, below). Then all users will be able to perform dual-frequency measurements and directly compute ionospheric delay errors.
A second form of precise monitoring is called Carrier-Phase Enhancement (CPGPS). The error, which this corrects, arises because the pulse transition of the PRN is not instantaneous, and thus the correlation (satellite-receiver sequence matching) operation is imperfect. The CPGPS approach utilizes the L1 carrier wave, which has a period 1000 times smaller than that of the C/A bit period, to act as an additional clock signal and resolve the uncertainty. The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS working to within 1% of perfect transition reduces this error to 3 centimeters (1 inch) of ambiguity. By eliminating this source of error, CPGPS coupled with DGPS normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy.
Relative Kinematic Positioning (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to an accuracy of less than 10 centimeters (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK).
[edit] GPS time and date
While most clocks are synchronized to Coordinated Universal Time (UTC), the Atomic clocks on the satellites are set to GPS time. The difference is that GPS 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 time was set to match Coordinated Universal Time (UTC) in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset (19 seconds) with International Atomic Time (TAI). Periodic corrections are performed on the on-board clocks to correct relativistic effects and keep them synchronized with ground clocks.
The GPS navigation message includes the difference between GPS time and UTC, which as of 2006 is 14 seconds. Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. New GPS units may not show the correct UTC time until after receiving the UTC offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight bits) which, at the current rate of change of the Earth's rotation, is sufficient to last until the year 2330.
As opposed to the year, month, and day format of the Julian calendar, the GPS date is expressed as a week number and a day-of-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6, 1980 and the week number became zero again for the first time at 23:59:47 UTC on August 21, 1999 (00:00:19 TAI on August 22, 1999). To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137.
[edit] GPS modernization
Main article: GPS modernization
Having reached the program's requirements for Full Operational Capability (FOC) on July 17, 1995,[27] the GPS completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to modernize the GPS system. Announcements from the Vice President and the White House in 1998 initiated these changes, and in 2000 the U.S. Congress authorized the effort, referring to it as GPS III.
The project aims to improve the accuracy and availability for all users and involves new ground stations, new satellites, and four additional navigation signals. New civilian signals are called L2C, L5 and L1C; the new military code is called M-Code. Initial Operational Capability (IOC) of the L2C code is expected in 2008.[28] A goal of 2013 has been established for the entire program, with incentives offered to the contractors if they can complete it by 2011.
[edit] Applications
The Global Positioning System, while originally a military project, is considered a dual-use technology, meaning it has significant applications for both the military and the civilian industry.
[edit] Military
Please help improve this article by expanding this section.
See talk page for details. Please remove this message once the section has been expanded.
The military use GPS for the following purposes:
[edit] Navigation
GPS allows soldiers to find objectives in the dark or in unfamiliar territory, and to coordinate the movement of troops and supplies.
[edit] Target tracking
Various military weapons systems use GPS to track potential ground and air targets before they are flagged as hostile. These weapons systems pass GPS co-ordinates of targets to precision-guided munitions to allow them to engage the targets accurately.
Military aircraft, particularly those used in air-to-ground roles use GPS to find targets (for example, gun camera video from AH-1 Cobras in Iraq show GPS co-ordinates that can be looked up in Google Earth).
[edit] Missile and projectile guidance
GPS allows accurate targeting of various military weapons including ICBMs, cruise missiles and precision-guided munitions.
Artillery projectiles with embedded GPS receivers able to withstand forces of 12,000G have been developed for use in 155 mm howitzers.[29]
[edit] Search and Rescue
Downed pilots can be located faster if they have a GPS receiver.
[edit] Reconnaissance and Map Creation
The military use GPS extensively to aid mapping and reconnaissance.
[edit] Other
The GPS satellites also carry nuclear detonation detectors, which form a major portion of the United States Nuclear Detonation Detection System.[30]
[edit] Civilian
See also: GPS applications
This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.
This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.
Many civilian applications benefit from GPS signals, using one or more of three basic components of the GPS; absolute location, relative movement, time transfer.
The ability to determine the receiver's absolute location allows GPS receivers to perform as a surveying tool or as an aid to navigation. The capacity to determine relative movement enables a receiver to calculate local velocity and orientation, useful in vessels or observations of the Earth. Being able to synchronize clocks to exacting standards enables time transfer, which is critical in large communication and observation systems. An example is CDMA digital cellular. Each base station has a GPS timing receiver to synchronize its spreading codes with other base stations to facilitate inter-cell hand off and support hybrid GPS/CDMA positioning of mobiles for emergency calls and other applications.
Finally, GPS enables researchers to explore the Earth environment including the atmosphere, ionosphere and gravity field. GPS survey equipment has revolutionized tectonics by directly measuring the motion of faults in earthquakes.
To help prevent civilian GPS guidance from being used in an enemy's military or improvised weaponry, the US Government controls the export of civilian receivers. A US-based manufacturer cannot generally export a GPS receiver unless the receiver contains limits restricting it from functioning when it is simultaneously (1) at an altitude above 18 kilometers (60,000 ft) and (2) traveling at over 515 m/s (1,000 knots).[31]
[edit] History
Please help improve this article by expanding this section.
See talk page for details. Please remove this message once the section has been expanded.
The design of GPS is based partly on the similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. Additional inspiration for the GPS system came when the Soviet Union launched the first Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. They discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.
The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. Using a constellation of five satellites, it could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology the GPS system relies upon. In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first world-wide radio navigation system.
The first experimental Block-I GPS satellite was launched in February 1978.[28] The GPS satellites were initially manufactured by Rockwell International and are now manufactured by Lockheed Martin.
[edit] Timeline
* In 1972, the US Air Force Central Inertial Guidance Test Facility (Holloman AFB) conducted developmental fight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.
* In 1978 the first experimental Block-I GPS satellite was launched.
* In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 in restricted Soviet airspace, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS system would be made available for civilian uses once it was completed.
* By 1985, ten more experimental Block-I satellites had been launched to validate the concept.
* On February 14, 1989, the first modern Block-II satellite was launched.
* In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing.
* By December 1993 the GPS system achieved initial operational capability[32]
* By January 17, 1994 a complete constellation of 24 satellites was in orbit.
* Full Operational Capability was declared by NAVSTAR in April 1995.
* In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive[33] declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset.
* In 1998, U.S. Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety.
* On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded signal globally.
* In 2004, the United States Government signed a historic agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system.
* In 2004, U.S. President George W. Bush updated the national policy, replacing the executive board with the National Space-Based Positioning, Navigation, and Timing Executive Committee.
* November 2004, QUALCOMM announced successful tests of Assisted-GPS system for mobile phones.[3]
* In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.
* The most recent launch was on 17 November 2006. The oldest GPS satellite still in operation was launched in August 1991.
* On September 14, 2007, the aging mainframe-based Ground Segment Control System was transitioned to the new Architecture Evolution Plan. [4]
[edit] Satellite numbers
Name Launch Period No of satellites launched, inc. launch failures Currently in service
Block I 1978-1985 11 0
Block II 1985-1990 9 0
Block IIA 1990-1997 19 15+11
Block IIR 1997-2004 12 12
Block IIR-M 2005- 3 3
Total 54 (plus one not launched) 30+1
1One test satellite
[edit] Awards
Two GPS developers have received the National Academy of Engineering Charles Stark Draper prize year 2003:
* Ivan Getting, emeritus president of The Aerospace Corporation and engineer at the Massachusetts Institute of Technology, established the basis for GPS, improving on the World War II land-based radio system called LORAN (Long-range Radio Aid to Navigation).
* Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
One GPS developer, Roger L. Easton, received the National Medal of Technology on February 13, 2006 at the White House.[34]
On February 10, 1993, the National Aeronautic Association selected the Global Positioning System Team as winners of the 1992 Robert J. Collier Trophy, the most prestigious aviation award in the United States. This team consists of researchers from the Naval Research Laboratory, the U.S. Air Force, the Aerospace Corporation, Rockwell International Corporation, and IBM Federal Systems Company. The citation accompanying the presentation of the trophy honors the GPS Team "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago."
[edit] Other systems
Main article: Global Navigation Satellite System
Other satellite navigation systems in use or various states of development include:
* Beidou — China's regional system that China has proposed to expand into a global system named COMPASS.
* Galileo — a proposed global system being developed by the European Union, joined by China, Israel, India, Morocco, Saudi Arabia and South Korea, Ukraine planned to be operational by 2011–12.
* GLONASS — Russia's global system which is being restored to full availability in partnership with India.
* Indian Regional Navigational Satellite System (IRNSS) — India's proposed regional system.
* QZSS - Japanese proposed regional system, adding better coverage to the Japanese islands.
[edit] See also
Satellite navigation systems Portal
Nautical Portal
* RAIM
* SIGI
* radio navigation
* High Sensitivity GPS
* Degree Confluence Project Use GPS to visit integral degrees of latitude and longitude.
* Exif, GPS data transfer.
* Geotagging
* Geocaching
* NaviTraveler.com, - a GPS point sharing community.
* GPS Drawing Digital mapping and drawing with GPS tracks.
* GPS tracking
* GPS/INS
* Assisted GPS
* GPX (XML schema for interchange of waypoints)
* ID Sniper rifle
* OpenStreetMap, free content maps and street pictures (GFDL)
* Telematics: Many telematics devices use GPS to determine the location of mobile equipment.
* The American Practical Navigator—Chapter 11 "Satellite Navigation"
* Point of Interest
* Automotive navigation system
* NextGen
[edit] Notes
1. ^ Parkinson, B.W. (1996), Global Positioning System: Theory and Applications, chap. 1: Introduction and Heritage of NAVSTAR, the Global Positioning System. pp. 3-28, American Institute of Aeronautics and Astronautics, Washington, D.C.
2. ^ a b GPS Overview from the NAVSTAR Joint Program Office. Accessed December 15, 2006.
3. ^ HowStuffWorks. How GPS Receivers Work. Accessed May 14, 2006.
4. ^ globalsecurity.org [1].
5. ^ Dana, Peter H. GPS Orbital Planes. August 8, 1996.
6. ^ What the Global Positioning System Tells Us about Relativity. Accessed January 2, 2007.
7. ^ USCG Navcen: GPS Frequently Asked Questions. Accessed January 3, 2007.
8. ^ Massatt, Paul and Brady, Wayne. "Optimizing performance through constellation management", Crosslink, Summer 2002, pages 17-21.
9. ^ US Coast Guard General GPS News 9-9-05
10. ^ USNO. NAVSTAR Global Positioning System. Accessed May 14, 2006.
11. ^ NMEA NMEA 2000
12. ^ http://gge.unb.ca/Resources/HowDoesGPSWork.html
13. ^ AN02 Network Assistance (HTML). Retrieved on 2007-09-10.
14. ^ a b Office of Science and Technology Policy. Presidential statement to stop degrading GPS. May 1, 2000.
15. ^ FAA, Selective Availability. Retrieved Jan. 6, 2007.
16. ^ http://www.defenselink.mil/releases/release.aspx?releaseid=11335
17. ^ Rizos, Chris. University of New South Wales. GPS Satellite Signals. 1999.
18. ^ The Global Positioning System by Robert A. Nelson Via Satellite, November 1999
19. ^ Ashby, Neil Relativity and GPS. Physics Today, May 2002.
20. ^ Space Environment Center. SEC Navigation Systems GPS Page. August 26, 1996.
21. ^ The hunt for an unintentional GPS jammer. GPS World. January 1, 2003.
22. ^ Low Cost and Portable GPS Jammer. Phrack issue 0x3c (60), article 13]. Published December 28, 2002.
23. ^ American Forces Press Service. CENTCOM charts progress. March 25, 2003.
24. ^ [2]
25. ^ Ruley, John. AVweb. GPS jamming. February 12, 2003.
26. ^ Commercial GPS Receivers: Facts for the Warfighter. Hosted at the Joint Chiefs website, linked by the USAF's GPS Wing DAGR program website. Accessed on 10 April, 2007
27. ^ US Coast Guard news release. Global Positioning System Fully Operational
28. ^ a b Hydrographic Society Journal. Developments in Global Navigation Satellite Systems. Issue #104, April 2002. Accessed April 5, 2007.
29. ^ XM982 Excalibur Precision Guided Extended Range Artillery Projectile. GlobalSecurity.org (2007-05-29). Retrieved on 2007-09-26.
30. ^ Sandia National Laboratory's Nonproliferation programs and arms control technology.
31. ^ Arms Control Association. Missile Technology Control Regime. Accessed May 17, 2006.
32. ^ United States Department of Defense. Announcement of Initial Operational Capability. December 8, 1993.
33. ^ National Archives and Records Administration. U.S. GLOBAL POSITIONING SYSTEM POLICY. March 29, 1996.
34. ^ United States Naval Research Laboratory. National Medal of Technology for GPS. November 21, 2005
[edit] External links
Wikimedia Commons has media related to:
Global Positioning System
Government links
* GPS.gov—General public education website created by the U.S. Government
* National Space-Based PNT Executive Committee—Established in 2004 to oversee management of GPS and GPS augmentations at a national level.
* USCG Navigation Center—Status of the GPS constellation, government policy, and links to other references. Also includes satellite almanac data.
* The GPS Joint Program Office (GPS JPO)—Responsible for designing and acquiring the system on behalf of the US Government.
* U.S. Naval Observatory's GPS constellation status
* U.S. Army Corps of Engineers manual: NAVSTAR HTML and PDF (22.6 MB, 328 pages)
* PNT Selective Availability Announcements
* GPS SPS Signal Specification, 2nd Edition—The official Standard Positioning Signal specification.
* Federal Aviation Administration's GPS FAQ
Introductory / tutorial links
* How does GPS work? TomTom explains GPS, navigation, and digital maps
* GPS Academy Garmin interactive video web site explaing what exactly GPS is and what it can do for you
* HowStuffWorks' Simplified explanation of GPS and video about how GPS works.
* Trimble's Online GPS Tutorial Tutorial designed to introduce you to the principles behind GPS
* GPS and GLONASS Simulation(Java applet) Simulation and graphical depiction of space vehicle motion including computation of dilution of precision (DOP)
Technical, historical, and ancillary topics links
* Dana, Peter H. "Global Positioning System Overview"
* Satellite Navigation: GPS & Galileo (PDF)—16-page paper about the history and working of GPS, touching on the upcoming Galileo
* History of GPS, including information about each satellite's configuration and launch.
* Chadha, Kanwar. "The Global Positioning System: Challenges in Bringing GPS to Mainstream Consumers" Technical Article (1998)
* GPS Weapon Guidance Techniques
* RAND history of the GPS system (PDF)
* GPS Anti-Jam Protection Techniques
* Crosslink Summer 2002 issue by The Aerospace Corporation on satellite navigation.
* Improved weather predictions from COSMIC GPS satellite signal occultation data.
* David L. Wilson's GPS Accuracy Web Page A thorough analysis of the accuracy of GPS.
* Innovation: Spacecraft Navigator, Autonomous GPS Positioning at High Earth Orbits Example of GPS receiver designed for high altitude spaceflight.
* The Navigator GPS Receiver GSFC's Navigator spaceflight receiver.
* Neil Ashby's Relativity in the Global Positioning System
[show]
v • d • e
Satellite navigation systems
Historical Flag of the United States Transit
Operational Flag of the Soviet Union / Flag of Russia GLONASS · Flag of the United States GPS
Developmental Flag of the People's Republic of China Beidou/COMPASS · Flag of Europe Galileo · Flag of India IRNSS · Flag of Japan QZSS
Related topics EGNOS · GAGAN · GPS·C · LAAS · MSAS · WAAS
[show]
v • d • e
Time signal stations
Longwave DCF77 · HBG · JJY · MSF · TDF · WWVB
Shortwave BPM · CHU · RWM · WWV · WWVH · YVTO
GNSS time transfer Beidou · Galileo · GLONASS · GPS · IRNSS
Defunct time stations OMA · VNG
[show]
v • d • e
Global structure in Systems, Systems sciences and Systems scientists
Categories Category:Conceptual systems · Category:Physical systems · Category:Social systems · Category:Systems · Category:Systems science · Category:Systems scientists · Category:Systems theory
Systems Biological system · Complex system · Complex adaptive system · Conceptual system · Cultural system · Dynamical system · Economic system · Ecosystem · Formal system · Global Positioning System · Human organ systems · Information systems · Legal system · Metric system · Nervous system · Non-linear system · Operating system · Physical system · Political system · Sensory system · Social system · Solar System · System · Systems of measurement
Fields of theory Chaos theory · Complex systems · Control theory · Cybernetics · Holism in science · Sociotechnical systems theory · Systems biology · System dynamics · Systems ecology · Systems engineering · Systems theory · Systems science
Systems scientists Russell L. Ackoff · William Ross Ashby · Gregory Bateson · Ludwig von Bertalanffy · Kenneth E. Boulding · Peter Checkland · C. West Churchman · Heinz von Foerster · Charles François · Jay Wright Forrester · Ralph W. Gerard · Debora Hammond · George Klir · Niklas Luhmann · Humberto Maturana · Donella Meadows · Mihajlo D. Mesarovic · Howard T. Odum · Talcott Parsons · Ilya Prigogine · Anatol Rapoport · Francisco Varela · John N. Warfield · Norbert Wiener
Retrieved from "http://en.wikipedia.org/wiki/Global_Positioning_System"
About the Author:
