Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Satellite Navigation shopping experience:

1. Compare - without doubt the biggest advantage that the Satellite Navigation offers shoppers today is the ability to compare thousands of Satellite Navigation at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Satellite Navigation? Wrong! If the Satellite Navigation is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Satellite Navigation then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Satellite Navigation? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Satellite Navigation and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Satellite Navigation wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Satellite Navigation then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Satellite Navigation site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Satellite Navigation, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Satellite Navigation, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.



Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. A GNSS allows small electronics receivers to determine their location (longitude, latitude, and altitude) to within a few metres using time signals transmitted along a line of sight by radio from satellites. Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments.

As of 2007, the United States NAVSTAR Global Positioning System (GPS) is the only fully operational GNSS. The Russian GLONASS is a GNSS in the process of being restored to full operation. The European Union Galileo positioning system is a next generation GNSS in the initial deployment phase, scheduled to be operational in 2010. China has indicated it may expand its regional Beidou navigation system into a global system. India IRNSS, a next generation GNSS is in developmental phase and is scheduled to be operational around 2012.

GNSS classification GNSS that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:http://www.ifatca.org/docs/gnss.pdf IFATCA - A Beginner’s Guide toGNSS in Europe







History and theory Early predecessors were the ground based Decca Navigator System, LORAN and Omega Navigation System systems, which used terrestrial longwave radio transmitters instead of satellites. These systems broadcast a radio pulse from a known "master" location, followed by repeated pulses from a number of "slave" stations. The delay between the reception and sending of the signal at the slaves was carefully controlled, allowing the receivers to compare the delay between reception and the delay between sending. From this the distance to each of the slaves could be determined, providing a fix (position).

The first satellite navigation system was Transit (satellite), a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect: the satellites traveled on well-known paths and broadcast their signals on a well known frequency. The received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position.

Part of an orbiting satellite's broadcast included its precise orbital data. In order to ensure accuracy, the US Naval Observatory continuously observed precisely the orbits of these satellites. As a satellite's orbit deviated, the USNO would send the updated information to the satellite. Subsequent broadcasts from an updated satellite would contain the most recent accurate information about its orbit.

Modern systems are more direct. The satellite broadcasts a signal that contains the position of the satellite and the precise time the signal was transmitted. The position of the satellite is transmitted in a data message that is superimposed on a code that serves as a timing reference. The satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation. The receiver compares the time of broadcast encoded in the transmission with the time of reception measured by an internal clock, thereby measuring the time-of-flight to the satellite. Several such measurements can be made at the same time to different satellites, allowing a continual fix to be generated in real time.

Each distance measurement, regardless of the system being used, places the receiver on a spherical shell at the measured distance from the broadcaster. By taking several such measurements and then looking for a point where they meet, a fix is generated. However, in the case of fast-moving receivers, the position of the signal moves as signals are received from several satellites. In addition, the radio signals slow slightly as they pass through the ionosphere, and this slowing varies with the receiver's angle to the satellite, because that changes the distance through the ionosphere. The basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centered on four satellites. Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.

Civil and military uses The original motivation for satellite navigation was for military applications. Satellite navigation allows for hitherto impossible precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from mis-directed weapons. (See smart bomb). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war. and a GPS receiver

In these ways, satellite navigation can be regarded as a force multiplier. In particular, the ability to reduce unintended casualties has particular advantages for wars being fought by democracies, where public relations is an important aspect of warfare. For these reasons, a satellite navigation system is an essential asset for any aspiring military power.

GNSS systems have a wide variety of uses:



Note that the ability to supply satellite navigation signals is also the ability to deny their availability. The operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires. Thus, as satellite navigation becomes an essential service, countries without their own satellite navigation systems effectively become client states of those which supply these services.

The same applies to the use of smart bombs: the operator of a satellite navigation system can effectively degrade the performance of smart bombs being used by other states using its satellite navigation system to that of gravity bombs, or even offset them from their targets in such a way as to render them useless.

Current global navigation systems GPS The United States' Global Positioning System (GPS), which as of 2007 is the only fully functional, fully available global navigation satellite system. It consists of up to 32 medium Earth orbit satellites in six different orbital planes, with the exact number of satellites varying as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is currently the world's most utilized satellite navigation system.

GLONASS The formerly Soviet, and now Russian, global navigation system is called GLONASS. It was a fully functional navigation constellation but since the collapse of the Soviet Union has fallen into disrepair, leading to moving gaps in coverage and only partial availability. It is expected to return to full global availability by 2010 with the help of India, who is participating in the restoration project. India signs GLONASS agreement India, Russia Agree On Joint Development Of Future Glonas Navigation System

Proposed global navigation systems Compass China has indicated they intend to expand their regional navigation system, called Beidou or Big Dipper, into a global navigation system; a program that has been called Compass in China's official news agency Xinhua News Agency. The Compass system is proposed to utilize 30 medium Earth orbit satellites and five geostationary satellites. Having announced they are willing to cooperate with other countries in Compass's creation, it is unclear how this proposed program impacts China's commitment to the international Galileo position system.

DORIS Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a France precision system. DORIS information page

Galileo The European Union and European Space Agency agreed on March 2002 to introduce their own alternative to GPS, called the Galileo positioning system. At a cost of about Pound sterling £2.4 billion,BBC - Galileo the required satellites will be launched between 2006 and 2008 and the system will be working, under civilian control, from 2010. The first experimental satellite was launched on 28 December 2005. Galileo is expected to be compatible with the GPS modernization system that will be operational by after 2012. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy.

IRNSS The Indian Regional Navigational Satellite System (IRNSS) is a proposed autonomous regional satellite navigation system to be constructed and controlled by the Indian government. It is intended to provide an absolute position accuracy of better than 20 meters throughout India and within a region extending approximately 1,500 to 2,000 km around it. A goal of complete Indian control has been stated, with the space segment, ground segment and user receivers all being built in India. The government approved the project in May 2006, with the intention it be implemented within six to seven years.

QZSS The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and enhancement for Global Positioning System covering Japan. The first satellite is scheduled to be launched in 2008. Japan Seeking 13 Percent Budget Hike for Space Activities

GNSS Augmentation GNSS Augmentation involves using external information, often integrated into the calculation process, to improve the accuracy, availability, or reliability of the satellite navigation signal. There are many such systems in place and they are generally named or described based on how the GNSS 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, the European Geostationary Navigation Overlay Service, the Multi-functional Satellite Augmentation System, Differential GPS, and Inertial Navigation Systems.

Topics to be covered

See also

External links

Information on specific GNSS systems

Organizations related to GNSS:

Supportative or illustrative sites

References



Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. A GNSS allows small electronics receivers to determine their location (longitude, latitude, and altitude) to within a few metres using time signals transmitted along a line of sight by radio from satellites. Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments.

As of 2007, the United States NAVSTAR Global Positioning System (GPS) is the only fully operational GNSS. The Russian GLONASS is a GNSS in the process of being restored to full operation. The European Union Galileo positioning system is a next generation GNSS in the initial deployment phase, scheduled to be operational in 2010. China has indicated it may expand its regional Beidou navigation system into a global system. India IRNSS, a next generation GNSS is in developmental phase and is scheduled to be operational around 2012.

GNSS classification GNSS that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:http://www.ifatca.org/docs/gnss.pdf IFATCA - A Beginner’s Guide toGNSS in Europe







History and theory Early predecessors were the ground based Decca Navigator System, LORAN and Omega Navigation System systems, which used terrestrial longwave radio transmitters instead of satellites. These systems broadcast a radio pulse from a known "master" location, followed by repeated pulses from a number of "slave" stations. The delay between the reception and sending of the signal at the slaves was carefully controlled, allowing the receivers to compare the delay between reception and the delay between sending. From this the distance to each of the slaves could be determined, providing a fix (position).

The first satellite navigation system was Transit (satellite), a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect: the satellites traveled on well-known paths and broadcast their signals on a well known frequency. The received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position.

Part of an orbiting satellite's broadcast included its precise orbital data. In order to ensure accuracy, the US Naval Observatory continuously observed precisely the orbits of these satellites. As a satellite's orbit deviated, the USNO would send the updated information to the satellite. Subsequent broadcasts from an updated satellite would contain the most recent accurate information about its orbit.

Modern systems are more direct. The satellite broadcasts a signal that contains the position of the satellite and the precise time the signal was transmitted. The position of the satellite is transmitted in a data message that is superimposed on a code that serves as a timing reference. The satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation. The receiver compares the time of broadcast encoded in the transmission with the time of reception measured by an internal clock, thereby measuring the time-of-flight to the satellite. Several such measurements can be made at the same time to different satellites, allowing a continual fix to be generated in real time.

Each distance measurement, regardless of the system being used, places the receiver on a spherical shell at the measured distance from the broadcaster. By taking several such measurements and then looking for a point where they meet, a fix is generated. However, in the case of fast-moving receivers, the position of the signal moves as signals are received from several satellites. In addition, the radio signals slow slightly as they pass through the ionosphere, and this slowing varies with the receiver's angle to the satellite, because that changes the distance through the ionosphere. The basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centered on four satellites. Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.

Civil and military uses The original motivation for satellite navigation was for military applications. Satellite navigation allows for hitherto impossible precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from mis-directed weapons. (See smart bomb). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war. and a GPS receiver

In these ways, satellite navigation can be regarded as a force multiplier. In particular, the ability to reduce unintended casualties has particular advantages for wars being fought by democracies, where public relations is an important aspect of warfare. For these reasons, a satellite navigation system is an essential asset for any aspiring military power.

GNSS systems have a wide variety of uses:



Note that the ability to supply satellite navigation signals is also the ability to deny their availability. The operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires. Thus, as satellite navigation becomes an essential service, countries without their own satellite navigation systems effectively become client states of those which supply these services.

The same applies to the use of smart bombs: the operator of a satellite navigation system can effectively degrade the performance of smart bombs being used by other states using its satellite navigation system to that of gravity bombs, or even offset them from their targets in such a way as to render them useless.

Current global navigation systems GPS The United States' Global Positioning System (GPS), which as of 2007 is the only fully functional, fully available global navigation satellite system. It consists of up to 32 medium Earth orbit satellites in six different orbital planes, with the exact number of satellites varying as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is currently the world's most utilized satellite navigation system.

GLONASS The formerly Soviet, and now Russian, global navigation system is called GLONASS. It was a fully functional navigation constellation but since the collapse of the Soviet Union has fallen into disrepair, leading to moving gaps in coverage and only partial availability. It is expected to return to full global availability by 2010 with the help of India, who is participating in the restoration project. India signs GLONASS agreement India, Russia Agree On Joint Development Of Future Glonas Navigation System

Proposed global navigation systems Compass China has indicated they intend to expand their regional navigation system, called Beidou or Big Dipper, into a global navigation system; a program that has been called Compass in China's official news agency Xinhua News Agency. The Compass system is proposed to utilize 30 medium Earth orbit satellites and five geostationary satellites. Having announced they are willing to cooperate with other countries in Compass's creation, it is unclear how this proposed program impacts China's commitment to the international Galileo position system.

DORIS Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a France precision system. DORIS information page

Galileo The European Union and European Space Agency agreed on March 2002 to introduce their own alternative to GPS, called the Galileo positioning system. At a cost of about Pound sterling £2.4 billion,BBC - Galileo the required satellites will be launched between 2006 and 2008 and the system will be working, under civilian control, from 2010. The first experimental satellite was launched on 28 December 2005. Galileo is expected to be compatible with the GPS modernization system that will be operational by after 2012. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy.

IRNSS The Indian Regional Navigational Satellite System (IRNSS) is a proposed autonomous regional satellite navigation system to be constructed and controlled by the Indian government. It is intended to provide an absolute position accuracy of better than 20 meters throughout India and within a region extending approximately 1,500 to 2,000 km around it. A goal of complete Indian control has been stated, with the space segment, ground segment and user receivers all being built in India. The government approved the project in May 2006, with the intention it be implemented within six to seven years.

QZSS The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and enhancement for Global Positioning System covering Japan. The first satellite is scheduled to be launched in 2008. Japan Seeking 13 Percent Budget Hike for Space Activities

GNSS Augmentation GNSS Augmentation involves using external information, often integrated into the calculation process, to improve the accuracy, availability, or reliability of the satellite navigation signal. There are many such systems in place and they are generally named or described based on how the GNSS 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, the European Geostationary Navigation Overlay Service, the Multi-functional Satellite Augmentation System, Differential GPS, and Inertial Navigation Systems.

Topics to be covered

See also

External links

Information on specific GNSS systems

Organizations related to GNSS:

Supportative or illustrative sites

References



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