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===QZSS===
===QZSS===
{{Main article|Quasi-Zenith Satellite System}}
{{Main article|Quasi-Zenith Satellite System}}
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional [[time transfer]] system and enhancement for [[Global Positioning System|GPS]] covering [[Japan]]. The first demonstration satellite was launched in September 2010.<ref>{{cite web |url=http://qzss.jaxa.jp/is-qzss/qzss_e.html |title=JAXA Quasi-Zenith Satellite System |accessdate=2009-02-22 |publisher=JAXA}}</ref>
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional [[time transfer]] system and enhancement for [[Global Positioning System|GPS]] covering [[Japan]]. The first demonstration satellite was launched in September 2010.<ref>{{cite web |url=http://qzss.jaxa.jp/is-qzss/qzss_e.html |title=JAXA Quasi-Zenith Satellite System |accessdate=2009-02-22 |publisher=JAXA |deadurl=yes |archiveurl=https://web.archive.org/web/20090314085502/http://qzss.jaxa.jp/is-qzss/qzss_e.html |archivedate=2009-03-14 |df= }}</ref>


==Comparison of systems==
==Comparison of systems==

Revision as of 08:17, 11 November 2017

For satellite navigation in automobile navigation systems, see Automotive navigation system.

A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows small electronic receivers to determine their location (longitude, latitude, and altitude/elevation) to high precision (within a few metres) using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking). The signals also allow the electronic receiver to calculate the current local time to high precision, which allows time synchronisation. Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.

A satellite navigation system with global coverage may be termed a global navigation satellite system (GNSS). As of December 2016, only the

BeiDou-2 GNSS by 2020.[2] India, France and Japan
are in the process of developing regional navigation and augmentation systems as well.

Global coverage for each system is generally achieved by a

orbital planes. The actual systems vary, but use orbital inclinations of >50° and orbital periods
of roughly twelve hours (at an altitude of about 20,000 kilometres or 12,000 miles).

Classification

Satellite navigation systems that provide enhanced accuracy and integrity monitoring usable for civil navigation are classified as follows:[3]

  • GNSS-1[
    Local Area Augmentation System (LAAS).[citation needed
    ]
  • GNSS-2[citation needed] 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; including aircraft. This system consists of L1 and L2 frequencies (in the L band of the radio spectrum) 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[citation needed]
  • Core Satellite navigation systems, currently GPS (United States), GLONASS (Russian Federation), Galileo (European Union) and Compass (China).
  • Global Satellite Based Augmentation Systems (SBAS) such as Omnistar and StarFire.
  • Regional SBAS including WAAS (US), EGNOS (EU), MSAS (Japan) and
    GAGAN
    (India).
  • Regional Satellite Navigation Systems such as China's
    QZSS
    .
  • Continental scale Ground Based Augmentation Systems (GBAS) for example the Australian GRAS and the joint US Coast Guard, Canadian Coast Guard, US Army Corps of Engineers and US Department of Transportation National Differential GPS (DGPS) service.
  • Regional scale GBAS such as CORS networks.
  • Local GBAS typified by a single GPS reference station operating
    Real Time Kinematic
    (RTK) corrections.

History and theory

Ground based

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 travelled on well-known paths and broadcast their signals on a well-known radio 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 its most recent ephemeris
.

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

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 centred 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

Main article: GNSS applications
GPS
receiver

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

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.

Global navigation satellite systems

geostationary orbit (and its graveyard orbit), with the Van Allen radiation belts and the Earth to scale.[a]
The Moon's orbit is around 9 times as large as geostationary orbit.[b] (In the SVG file,
hover over an orbit or its label to highlight it; click to load its article.)
launched GNSS satellites 1978 to 2014

GPS

Main article: Global Positioning System

The United States' Global Positioning System (GPS) consists of up to 32

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

Main article: GLONASS

The formerly Soviet, and now Russian, Global'naya Navigatsionnaya Sputnikovaya Sistema (Russian: ГЛОбальная НАвигационная Спутниковая Система, GLObal NAvigation Satellite System), or GLONASS, is a space-based satellite navigation system that provides a civilian radionavigation-satellite service and is also used by the Russian Aerospace Defence Forces. The full orbital constellation of 24 GLONASS satellites enables full global coverage.

Galileo

Main article: Galileo (satellite navigation)

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 expected to be in full service in 2020 and at a substantially higher cost.[1]
The main modulation used in Galileo Open Service signal is the Composite Binary Offset Carrier (CBOC) modulation.

BeiDou-2

Main article:
BeiDou Navigation Satellite System

China has indicated they plan to complete the entire second generation Beidou Navigation Satellite System (BDS or BeiDou-2, formerly known as COMPASS), by expanding current regional (Asia-Pacific) service into global coverage by 2020.[2] The BeiDou-2 system is proposed to consist of 30 MEO satellites and five geostationary satellites. A 16-satellite regional version (covering Asia and Pacific area) was completed by December 2012.

Regional navigation satellite systems

BeiDou-1

Main article:
Beidou Navigation Satellite System

Chinese regional (Asia-Pacific, 16 satellites) network to be expanded into the whole BeiDou-2 global system which consists of all 35 satellites by 2020.

NAVIC

Main article:
NAVIC

The NAVIC or NAVigation with Indian Constellation is an autonomous regional satellite navigation system developed by

space segment, ground segment and user receivers all being built in India.[10] All seven satellites, IRNSS-1A, IRNSS-1B, IRNSS-1C, IRNSS-1D, IRNSS-1E, IRNSS-1F, and IRNSS-1G, of the proposed constellation were precisely launched on 1 July 2013, 4 April 2014, 16 October 2014, 28 March 2015, 20 January 2016, 10 March 2016 and 28 April 2016 respectively from Satish Dhawan Space Centre.[11][12] The system is expected to be fully operational by August 2016.[13]

QZSS

Main article: Quasi-Zenith Satellite System

The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional

time transfer system and enhancement for GPS covering Japan. The first demonstration satellite was launched in September 2010.[14]

Comparison of systems

System
BeiDou
 Galileo GLONASS
GPS
NAVIC
QZSS
Owner China
EU
 Russia United States India Japan
Coverage Regional
(Global by 2020) 		Global Global Global Regional Regional
Coding
CDMA
CDMA
FDMA
CDMA
CDMA
CDMA
Orbital altitude 21,150 km (13,140 mi) 23,222 km (14,429 mi) 19,130 km (11,890 mi) 20,180 km (12,540 mi) 36,000 km (22,000 mi) 32,000 km (20,000 mi)
Period 12.63 h (12 h 38 min) 14.08 h (14 h 5 min) 11.26 h (11 h 16 min) 11.97 h (11 h 58 min) 1436.0m (IRNSS-1A)
1436.1m (IRNSS-1B)
1436.1m (IRNSS-1C)
1436.1m (IRNSS-1D)
1436.1m (IRNSS-1E)
1436.0m (IRNSS-1F)
1436.1m (IRNSS-1G) 		 
Revolutions per
sidereal day
 17/9 17/10 17/8 2    
Number of
satellites 		5 geostationary orbit (GEO) satellites,
30 medium Earth orbit (MEO) satellites 		18 satellites in orbit,
15 fully operation capable,
11 currently healthy,
30 operational satellites budgeted 		28 (at least 24 by design) including:[15]
24 operational
2 under check by the satellite prime contractor
2 in flight tests phase 		31 (at least 24 by design)[16] 3 geostationary orbit (GEO) satellites,
5 geosynchronous (GSO) medium Earth orbit (MEO) satellites 		In 2011 the Government of Japan has decided to accelerate the QZSS deployment in order to reach a 4-satellite constellation by the late 2010s, while aiming at a final 7-satellite constellation in the future
Frequency 1.561098 GHz (B1)
1.589742 GHz (B1-2)
1.20714 GHz (B2)
1.26852 GHz (B3) 		1.164–1.215 GHz (E5a and E5b)
1.260–1.300 GHz (E6)
1.559–1.592 GHz (E2-L1-E11) 		Around 1.602 GHz (SP)
Around 1.246 GHz (SP) 		1.57542 GHz (L1 signal)
1.2276 GHz (L2 signal) 		1176.45 MHz(L5 Band)
2492.028 MHz (S Band) 		 
Status 22 satellites operational,
40 additional satellites 2016-2020 		18 satellites operational
12 additional satellites 2017-2020 		Operational Operational 6 satellites fully operational,
IRNSS-1A partially operational 		 
Precision 10m (Public)
0.1m (Encrypted) 		1m (Public)
0.01m (Encrypted) 		4.5m – 7.4m 15m (Without DGPS or WAAS) 10m (Public)
0.1m (Encrypted) 		1m (Public)
0.1m (Encrypted)
System
BeiDou
 Galileo GLONASS
GPS
NAVIC
QZSS

Augmentation

GPS Aided GEO Augmented Navigation (GAGAN) and inertial navigation systems
.

DORIS

Main article:
DORIS (geodesy)

Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a French precision navigation system. Unlike other GNSS systems, it is based on static emitting stations around the world, the receivers being on satellites, in order to precisely determine their orbital position. The system may be used also for mobile receivers on land with more limited usage and coverage. Used with traditional GNSS systems, it pushes the accuracy of positions to centimetric precision (and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of Earth rotation and deformations), in order to build a much more precise geodesic reference system.[17]

Low Earth orbit satellite phone networks

The two current operational low Earth orbit

AT commands or a graphical user interface.[18][19]
This can also be used by the gateway to enforce restrictions on geographically bound calling plans.

Positioning calculation

Main article:
GNSS positioning calculation

See also

Notes

  1. ^ Orbital periods and speeds are calculated using the relations 4π2R3 = T2GM and V2R = GM, where R is the radius of orbit in metres; T is the orbital period in seconds; V is the orbital speed in m/s; G is the gravitational constant, approximately 6.673×10−11 Nm2/kg2; M is the mass of Earth, approximately 5.98×1024 kg (1.318×1025 lb).
  2. ^ Approximately 8.6 times (in radius and length) when the Moon is nearest (that is, 363,104 km/42,164 km), to 9.6 times when the Moon is farthest (that is, 405,696 km/42,164 km).

References

  1. ^ a b "Galileo goes live!". europa.eu. 2016-12-14.
  2. ^ a b "Beidou satellite navigation system to cover whole world in 2020". Eng.chinamil.com.cn. Retrieved 2011-12-30.
  3. ^ "A Beginner's Guide to GNSS in Europe" (PDF). IFATCA. Retrieved 20 May 2015.
  4. ^ "Galileo goes live!". europa.eu. 14 December 2016.
  5. ^ "Boost to Galileo sat-nav system". BBC News. 25 August 2006. Retrieved 2008-06-10.
  6. ^ "Commission awards major contracts to make Galileo operational early 2014". 2010-01-07. Retrieved 2010-04-19.
  7. ^ "GIOVE-A launch News". 2005-12-28. Retrieved 2015-01-16.
  8. ^ "India to develop its own version of GPS". Rediff.com. Retrieved 2011-12-30.
  9. ^ S. Anandan (2010-04-10). "Launch of first satellite for Indian Regional Navigation Satellite system next year". Beta.thehindu.com. Retrieved 2011-12-30.
  10. ^ "India to build a constellation of 7 navigation satellites by 2012". Livemint.com. 2007-09-05. Retrieved 2011-12-30.
  11. ^ The first satellite IRNSS-1A of the proposed constellation, developed at a cost of 16 billion (US$280 million),[3] was[4] launched on 1 July 2013 from Satish Dhawan Space Centre
  12. ^ "ISRO: All 7 IRNSS Satellites in Orbit by March". gpsworld.com. 2015-10-08. Retrieved 2015-11-12.
  13. ^ Laiqh A. Khan (May 24, 2016). "'NAVIC could be operationalised during July-August this year'". The Hindu. Retrieved September 2, 2017.
  14. ^ "JAXA Quasi-Zenith Satellite System". JAXA. Archived from the original on 2009-03-14. Retrieved 2009-02-22. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  15. ^ "GLONASS status". Retrieved 2015-07-24.
  16. ^ "GPS Space Segment". Retrieved 2015-07-24.
  17. ^ "DORIS information page". Jason.oceanobs.com. Retrieved 2011-12-30.
  18. ^ "Globalstar GSP-1700 manual" (PDF). Retrieved 2011-12-30.
  19. ^ [1] Archived November 9, 2005, at the Wayback Machine

Further reading

  • Office for Outer Space Affairs of the United Nations (2010), Report on Current and Planned Global and Regional Navigation Satellite Systems and Satellite-based Augmentation Systems. [2]

External links

Information on specific GNSS systems

Organizations related to GNSS

Supportive or illustrative sites

Retrieved from "https://en.wikipedia.org/w/index.php?title=Satellite_navigation&oldid=809769688"