Global Navigation Satellite System
Encyclopedia
A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic
receivers to determine their location (longitude
, latitude
, and altitude
) to within a few metres using time signal
s transmitted along a line-of-sight
by radio from satellite
s. Receivers calculate the precise time as well as position, which can be used as a reference for scientific experiments. A satellite navigation system with global coverage may be termed a global navigation satellite system or GNSS.
As of October 2011, the United States
NAVSTAR Global Positioning System
(GPS) and the Russia
n GLONASS
are fully globally operational GNSSs. The People's Republic of China
is in the process of expanding its regional Beidou navigation system
into the global Compass navigation system
by 2020. The European Union's
Galileo positioning system
is a GNSS in initial deployment phase, scheduled to be fully operational by 2020 at the earliest. Several countries including France, Japan and India are in the process of developing regional navigation systems.
Global coverage for each system is generally achieved by a satellite constellation
of 20–30 Medium Earth Orbit
(MEO) satellites spread between several orbital planes. The actual systems vary, but use orbit inclinations of >50° and orbital period
s of roughly twelve hours (height 20,000 km / 12,500 miles).
Early predecessors were the ground based DECCA
, LORAN
and Omega
radio navigation
systems, which used terrestrial longwave
radio transmitters instead of satellites. These positioning system
s 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
.
The first satellite navigation system was Transit
, 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 (USNO) continuously observed the precise 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 orbital data (from which the position of the satellite can be calculated) and the precise time the signal was transmitted. The orbital data 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 using an adapted version of trilateration
: see GNSS positioning calculation
for details.
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 filter
ing to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.
). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war
.
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 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.
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.
(GPS) consists of up to 32 medium Earth orbit
satellites in six different orbital plane
s, 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.
n, Global'naya Navigatsionnaya Sputnikovaya Sistema (Global Navigation Satellite System), or GLONASS
, was a fully functional navigation constellation in 1995. After the collapse of the Soviet Union, it fell into disrepair, leading to gaps in coverage and only partial availability. It was recovered and restored in 2011.
has indicated they intend to expand their regional navigation system, called Beidou
or Big Dipper, into a global navigation system by 2020 a program that has been called Compass in China's official news agency Xinhua
. The Compass system is proposed to utilize 30 medium Earth orbit
satellites and five geostationary satellites. A 12-satellite regional version (covering Asia and Pacific area) is expected to be completed by 2012.
and European Space Agency
agreed in March 2002 to introduce their own alternative to GPS, called the Galileo positioning system
. At an estimated cost of EUR 3.0 billion, the system of 30 MEO
satellites was originally scheduled to be operational in 2010. The estimated year to become operational is 2014. The first experimental satellite was launched on 28 December 2005 . Galileo is expected to be compatible with the modernized GPS
system. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy. Galileo is now not expected to be in full service until 2020 at the earliest and at a substantially higher cost.
.
precision navigation system.
which would be under the total control of Indian government. The government approved the project in May 2006, with the intention of the system to be completed and implemented by 2014. It will consist of a constellation of 7 navigational satellites. All the 7 satellites will be placed in the Geostationary orbit (GEO)
to have a larger signal footprint and lower number of satellites to map the region. It is intended to provide an all-weather absolute position accuracy of better than 7.6 meters throughout India
and within a region extending approximately 1,500 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.
system and enhancement for GPS
covering Japan
. The first demonstration satellite was launched in September 2010.
, the European Geostationary Navigation Overlay Service
, the Multi-functional Satellite Augmentation System
, Differential GPS
, and Inertial Navigation System
s.
networks are able to track transceiver units with accuracy of a few kilometers using doppler shift calculations from the satellite. The coordinates are sent back to the transceiver unit where they can be read using AT commands or a graphical user interface
. This can also be used by the gateway to enforce restrictions on geographically bound calling plans.
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
receivers to determine their location (longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
, latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
, and altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
) to within a few metres using time signal
Time signal
A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:...
s transmitted along a line-of-sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
by radio from satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
s. Receivers calculate the precise time as well as position, which can be used as a reference for scientific experiments. A satellite navigation system with global coverage may be termed a global navigation satellite system or GNSS.
As of October 2011, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
NAVSTAR Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) and the Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n GLONASS
GLONASS
GLONASS , acronym for Globalnaya navigatsionnaya sputnikovaya sistema or Global Navigation Satellite System, is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces...
are fully globally operational GNSSs. The People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
is in the process of expanding its regional Beidou navigation system
Beidou navigation system
The BeiDou Navigation System or BeiDou Navigation Satellite System is a project by China to develop an independent satellite navigation system...
into the global Compass navigation system
Compass navigation system
The COMPASS system is a project by China to develop an independent global satellite navigation system.COMPASS is not an extension to the previously deployed Beidou-1, but a new GNSS similar in principle to GPS, GLONASS, and Galileo.-General:The new system will be a constellation of 35 satellites,...
by 2020. The European Union's
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
Galileo positioning system
Galileo positioning system
Galileo is a global navigation satellite system currently being built by the European Union and European Space Agency . The €20 billion project is named after the famous Italian astronomer Galileo Galilei...
is a GNSS in initial deployment phase, scheduled to be fully operational by 2020 at the earliest. Several countries including France, Japan and India are in the process of developing regional navigation systems.
Global coverage for each system is generally achieved by a satellite constellation
Satellite constellation
A group of artificial satellites working in concert is known as a satellite constellation. Such a constellation can be considered to be a number of satellites with coordinated ground coverage, operating together under shared control, synchronised so that they overlap well in coverage and...
of 20–30 Medium Earth Orbit
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....
(MEO) satellites spread between several orbital planes. The actual systems vary, but use orbit inclinations of >50° and orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
s of roughly twelve hours (height 20,000 km / 12,500 miles).
Classification
Satellite navigation systems that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:- GNSS-1 is the first generation system and is the combination of existing satellite navigation systems (GPS and GLONASS), with Satellite Based Augmentation Systems (SBAS) or Ground Based Augmentation Systems (GBAS). In the United States, the satellite based component is the Wide Area Augmentation SystemWide Area Augmentation SystemThe Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...
(WAAS), in Europe it is the European Geostationary Navigation Overlay ServiceEuropean Geostationary Navigation Overlay ServiceThe European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo systems by reporting on the reliability and accuracy of the signals...
(EGNOS), and in Japan it is the Multi-Functional Satellite Augmentation SystemMulti-Functional Transport SatelliteMultifunctional Transport Satellites are a series of weather and aviation control satellites. They are geostationary satellites owned and operated by the Japanese Ministry of Land, Infrastructure and Transport and the Japan Meteorological Agency , and provide coverage for the hemisphere centred on...
(MSAS). Ground based augmentation is provided by systems like the Local Area Augmentation SystemLocal Area Augmentation SystemThe Local Area Augmentation System is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers located around the airport send data to a central location at the airport. This data is used to formulate a correction message, which...
(LAAS).
- GNSS-2 is the second generation of systems that independently provides a full civilian satellite navigation system, exemplified by the European Galileo positioning system. These systems will provide the accuracy and integrity monitoring necessary for civil navigation. This system consists of L1 and L2 frequencies for civil use and L5 for system integrity. Development is also in progress to provide GPS with civil use L2 and L5 frequencies, making it a GNSS-2 system.¹
- Core Satellite navigation systems, currently GPS, Galileo and GLONASS.
- Global Satellite Based Augmentation Systems (SBAS) such as Omnistar and StarFireStarFire (navigation system)StarFire is a wide-area differential GPS developed by John Deere's NavCom and precision farming groups. StarFire broadcasts additional "correction information" over satellite L-band frequencies around the world, allowing a StarFire-equipped receiver to produce position measurements accurate to well...
. - Regional SBAS including WAAS(US), EGNOS (EU), MSAS (Japan) and GAGAN (India).
- Regional Satellite Navigation Systems such as China's BeidouBeidou navigation systemThe BeiDou Navigation System or BeiDou Navigation Satellite System is a project by China to develop an independent satellite navigation system...
, India's yet-to-be-operational IRNSS, and Japan's proposed QZSSQZSSThe Quasi-Zenith Satellite System , is a proposed three-satellite regional time transfer system and Satellite Based Augmentation System for the Global Positioning System, that would be receivable within Japan. The first satellite 'Michibiki' was launched on 11 September 2010...
. - Continental scale Ground Based Augmentation Systems (GBAS) for example the Australian GRAS and the US Department of Transportation National Differential GPSDifferential GPSDifferential Global Positioning System is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations....
(DGPS) service. - Regional scale GBAS such as CORS networks.
- Local GBAS typified by a single GPS reference station operating Real Time KinematicReal Time KinematicReal Time Kinematic satellite navigation is a technique used in land survey and in hydrographic survey based on the use of carrier phase measurements of the GPS, GLONASS and/or Galileo signals where a single reference station provides the real-time corrections, providing up to centimetre-level...
(RTK) corrections.
History and theory
Decca Navigator System
The Decca Navigator System was a low frequency hyperbolic navigation system that was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings...
, LORAN
LORAN
LORAN is a terrestrial radio navigation system using low frequency radio transmitters in multiple deployment to determine the location and speed of the receiver....
and Omega
OMEGA Navigation System
OMEGA was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations.-History:OMEGA was originally developed by the United States Navy for military aviation users...
radio navigation
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...
systems, which used terrestrial longwave
Longwave
In radio, longwave refers to parts of radio spectrum with relatively long wavelengths. The term is a historic one dating from the early 20th century, when the radio spectrum was considered to consist of long, medium and short wavelengths...
radio transmitters instead of satellites. These positioning system
Positioning system
A positioning system is a mechanism for determining the location of an object in space. Technologies for this task exist ranging from worldwide coverage with meter accuracy to workspace coverage with sub-millimetre accuracy.- Interplanetary systems :...
s 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
Fix (position)
In position fixing navigation, a position fix or simply a fix is a position derived from measuring external reference points.The term is generally used with manual or visual techniques such as the use of intersecting visual or radio position lines rather than the use of more automated and accurate...
.
The first satellite navigation system was Transit
Transit (satellite)
The TRANSIT system, also known as NAVSAT , was the first satellite navigation system to be used operationally. The system was primarily used by the U.S...
, a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
: the satellites traveled on well-known paths and broadcast their signals on a well known frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the 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 (USNO) continuously observed the precise 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 orbital data (from which the position of the satellite can be calculated) and the precise time the signal was transmitted. The orbital data is transmitted in a data message that is superimposed on a code that serves as a timing reference. The satellite uses an atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...
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 using an adapted version of trilateration
Trilateration
In geometry, trilateration is the process of determinating absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. In addition to its interest as a geometric problem, trilateration does have practical applications in surveying and...
: see GNSS positioning calculation
GNSS positioning calculation
The global navigation satellite system positioning for receiver's position is derived through the calculation steps, or algorithm, given below....
for details.
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 filter
Kalman filter
In statistics, the Kalman filter is a mathematical method named after Rudolf E. Kálmán. Its purpose is to use measurements observed over time, containing noise and other inaccuracies, and produce values that tend to be closer to the true values of the measurements and their associated calculated...
ing 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 bombSmart bomb
Smart bomb has several meanings:* In weapons, a smart bomb is a precision-guided munition* Smart Bomb Interactive, a video game development studio based in Salt Lake City, Utah...
). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war
Fog of war
The fog of war is a term used to describe the uncertainty in situation awareness experienced by participants in military operations. The term seeks to capture the uncertainty regarding own capability, adversary capability, and adversary intent during an engagement, operation, or campaign...
.
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.
GPS
The United States' Global Positioning SystemGlobal Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) consists of up to 32 medium Earth orbit
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....
satellites in six different orbital plane
Orbital plane
Orbital plane may refer to:*Orbital plane *In anatomy, it refers to a specific area of the maxilla...
s, 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 RussiaRussia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n, Global'naya Navigatsionnaya Sputnikovaya Sistema (Global Navigation Satellite System), or GLONASS
GLONASS
GLONASS , acronym for Globalnaya navigatsionnaya sputnikovaya sistema or Global Navigation Satellite System, is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces...
, was a fully functional navigation constellation in 1995. After the collapse of the Soviet Union, it fell into disrepair, leading to gaps in coverage and only partial availability. It was recovered and restored in 2011.
Compass
ChinaChina
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
has indicated they intend to expand their regional navigation system, called Beidou
Beidou navigation system
The BeiDou Navigation System or BeiDou Navigation Satellite System is a project by China to develop an independent satellite navigation system...
or Big Dipper, into a global navigation system by 2020 a program that has been called Compass in China's official news agency Xinhua
Xinhua News Agency
The Xinhua News Agency is the official press agency of the government of the People's Republic of China and the biggest center for collecting information and press conferences in the PRC. It is the largest news agency in the PRC, ahead of the China News Service...
. The Compass system is proposed to utilize 30 medium Earth orbit
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....
satellites and five geostationary satellites. A 12-satellite regional version (covering Asia and Pacific area) is expected to be completed by 2012.
Galileo
The European UnionEuropean Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
and European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
agreed in March 2002 to introduce their own alternative to GPS, called the Galileo positioning system
Galileo positioning system
Galileo is a global navigation satellite system currently being built by the European Union and European Space Agency . The €20 billion project is named after the famous Italian astronomer Galileo Galilei...
. At an estimated cost of EUR 3.0 billion, the system of 30 MEO
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....
satellites was originally scheduled to be operational in 2010. The estimated year to become operational is 2014. The first experimental satellite was launched on 28 December 2005 . Galileo is expected to be compatible with the modernized GPS
GPS modernization
The United States' Global Positioning System , having reached Fully Operational Capability on July 17, 1995, has 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...
system. The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy. Galileo is now not expected to be in full service until 2020 at the earliest and at a substantially higher cost.
Comparison of systems
| System | GPS | GLONASS | Galileo | COMPASS |
|---|---|---|---|---|
| Political entity | United States | Russia | European Union | China |
| Coding Channel access method In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same multi-point transmission medium to transmit over it and to share its capacity... |
CDMA | FDMA/CDMA | CDMA | CDMA |
| Orbital height | 20180 km (12,539.3 mi) | 19130 km (11,886.9 mi) | 23220 km (14,428.3 mi) | 21150 km (13,142 mi) |
| Period | 11.97 hours (11 h 58 m) | 11.26 hours (11 h 16 m) | 14.08 hours (14 h 5 m) | 12.63 hours (12 h 38 m) |
| Evolution per sidereal day |
2 | 17/8 | 17/10 | (36/19) |
| Number of satellites |
At least 24 | 30, including 23 operational 4 in preparation 2 on maintenance 1 reserve (30 when CDMA signal launches) |
2 test bed satellites in orbit, 22 operational satellites budgeted |
5 geostationary orbit (GEO) satellites, 30 medium Earth orbit (MEO) satellites |
| Frequency | 1.57542 GHz (L1 signal) 1.2276 GHz (L2 signal) |
Around 1.602 GHz (SP) Around 1.246 GHz (SP) |
1.164–1.215 GHz (E5a and E5b) 1.215–1.300 GHz (E6) 1.559–1.592 GHz (E2-L1-E11) |
1.561098 GHz (B1) 1.589742 GHz (B1-2) 1.20714 GHz (B2) 1.26852 GHz (B3) |
| Status | Operational | Operational, CDMA in preparation |
In preparation | 10 satellites operational, 25 additional satellites planned |
Beidou 1
Chinese regional network to be expanded into the global COMPASS Navigation SystemCompass navigation system
The COMPASS system is a project by China to develop an independent global satellite navigation system.COMPASS is not an extension to the previously deployed Beidou-1, but a new GNSS similar in principle to GPS, GLONASS, and Galileo.-General:The new system will be a constellation of 35 satellites,...
.
DORIS
Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a FrenchFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
precision navigation system.
IRNSS
The Indian Regional Navigational Satellite System (IRNSS) is an autonomous regional satellite navigation system being developed by Indian Space Research OrganisationIndian Space Research Organisation
The Indian Space Research Organisation is an independent Indian governmental agency established in 1969 for the research and development of vehicles and activities for the exploration of space within and outside of Earth’s atmosphere. Headquartered in Bangalore...
which would be under the total control of Indian government. The government approved the project in May 2006, with the intention of the system to be completed and implemented by 2014. It will consist of a constellation of 7 navigational satellites. All the 7 satellites will be placed in the Geostationary orbit (GEO)
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
to have a larger signal footprint and lower number of satellites to map the region. It is intended to provide an all-weather absolute position accuracy of better than 7.6 meters throughout India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and within a region extending approximately 1,500 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.
QZSS
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transferTime transfer
Time transfer is a scheme where multiple sites share a precise reference time. Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomenon with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to...
system and enhancement for GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
covering Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. The first demonstration satellite was launched in September 2010.
Augmentation
Examples of augmentation systems include the Wide Area Augmentation SystemWide Area Augmentation System
The Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...
, the European Geostationary Navigation Overlay Service
European Geostationary Navigation Overlay Service
The European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo systems by reporting on the reliability and accuracy of the signals...
, the Multi-functional Satellite Augmentation System
Multi-functional Satellite Augmentation System
Multi-functional Satellite Augmentation System is a Japanese SBAS , i.e. a satellite navigation system which supports differential GPS designed to supplement the GPS system by reporting on the reliability and accuracy of those signals...
, Differential GPS
Differential GPS
Differential Global Positioning System is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations....
, and Inertial Navigation System
Inertial navigation system
An inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...
s.
Low Earth orbit satellite phone networks
The two current operational low Earth orbit satellite phoneSatellite phone
A satellite telephone, satellite phone, or satphone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites...
networks are able to track transceiver units with accuracy of a few kilometers using doppler shift calculations from the satellite. The coordinates are sent back to the transceiver unit where they can be read using AT commands or a graphical user interface
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
. This can also be used by the gateway to enforce restrictions on geographically bound calling plans.
See also
- Acronyms and abbreviations in avionicsAcronyms and abbreviations in avionics-A:*ACARS: Aircraft Communications Addressing and Reporting System.*ACAS: Airborne Collision Avoidance System.*ACP: Audio Control Panel.*ACS: Audio Control System.*ADAHRS: Air Data and Attitude Heading Reference System.*ADC: Air Data Computer....
- Differential GPSDifferential GPSDifferential Global Positioning System is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations....
- Global Positioning SystemGlobal Positioning SystemThe Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
- Galileo (satellite navigation)
- GLONASSGLONASSGLONASS , acronym for Globalnaya navigatsionnaya sputnikovaya sistema or Global Navigation Satellite System, is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces...
- GPS-aided geo-augmented navigation
- Wide Area Augmentation SystemWide Area Augmentation SystemThe Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...
- European Geostationary Navigation Overlay ServiceEuropean Geostationary Navigation Overlay ServiceThe European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo systems by reporting on the reliability and accuracy of the signals...
- GNSS reflectometryGNSS reflectometryGNSS reflectometry involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. It is also known as GPS reflectometry....
- Space Integrated GPS/INS (SIGI)
- Receiver Autonomous Integrity Monitoring
- Software GNSS ReceiverSoftware GNSS ReceiverA Software GNSS Receiver is a GNSS receiver that has been designed and implemented following the philosophy of Software-defined radio.A GNSS receiver is an electronic device that receives and digitally processes the signals from a GNSS satellite constellation in order to provide position, velocity...
- GeoinformaticsGeoinformaticsGeoinformatics is the science and the technology which develops and uses information science infrastructure to address the problems of geography, geosciences and related branches of engineering.-Overview:...
- List of emerging technologies
Information on specific GNSS systems
- ESA information on EGNOS
- Information on the Beidou system
- German Federal Waterways Administration Traffic Technologies Centre Information on GPS / DGPS
Organizations related to GNSS
- United Nations International Committee on Global Navigation Satellite Systems (ICG)
- Korean GNSS Technology Council (GTC)
- Institute of Navigation (ION) GNSS Meetings
- The International GNSS Service (IGS), formerly the International GPS Service
- International Global Navigation Satellite Systems Society Inc (IGNSS)
- International Earth Rotation and Reference Systems Service (IERS) International GNSS Service (IGS)
- National Geodetic Survey Orbits for the Global Positioning System satellites in the Global Navigation Satellite System
- UNAVCO GNSS Modernization
- Asia-Pacific Economic Cooperation (APEC) GNSS Implementation Team
- Fédération Aéronautique Internationale (FAI) GNSS Flight Recorder Approval Committee (GFAC)
Sat Nav Manufacturers
Supportive or illustrative sites
- Sat Nav information for consumers
- GPS and GLONASS Simulation (Java appletJava appletA Java applet is an applet delivered to users in the form of Java bytecode. Java applets can run in a Web browser using a Java Virtual Machine , or in Sun's AppletViewer, a stand-alone tool for testing applets...
) Simulation and graphical depiction of the motion of space vehicles, including DOPDilution of precision (GPS)Dilution of precision , or geometric dilution of precision , is a term used in GPS and geomatics engineering to specify the additional multiplicative effect of GPS satellite geometry on GPS precision.-Introduction:...
computation. - GPS, GNSS, Geodesy and Navigation Concepts in deep
- Product comparison between State of the Art receivers of the leading manufacturers