A satellite navigation or sat nav system is a system That uses satellites to Provide autonomous geo-spatial positioning. It Allows small electronic receivers to determine Their rental ( longitude , latitude , and altitude / elevation ) to high precision (Within A Few meters) 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 a satellite receiver. The results of this study are summarized as follows: Which allows time synchronization. Satnav systems operate independently of any telephonic or internet reception, but 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 United States NAVSTAR Global Positioning System (GPS), the Russian GLONASSand the European Union’s Galileo are global operational GNSSs. The European Union’s Galileo GNSS is scheduled to be fully operational by 2020.  China is in the process of the Expanding Regional icts BeiDou Navigation Satellite System into the overall BeiDou-2 GNSS by 2020.  France ,
Global coverage for each satellite system constellation of 18-30 medium Earth orbit (MEO) satellites spread between several orbital planes . The actual systems vary, aim wears orbital inclinations of> 50 ° and orbital periods of Roughly twelve hours (at an altitude of about 20.000 km or 12,000 miles).
Satellite navigation systems that provide enhanced accuracy and integrity for civil navigation 
- GNSS-1 [ citation needed ] is the first generation of satellite navigation systems (GPS and GLONASS), with Satellite Based Augmentation Systems (SBAS) or Ground Based Augmentation Systems (GBAS). In the United States, the satellite is based on the Wide Area Augmentation System (WAAS), in Europe it is the European Geostationary Navigation Overlay Service (EGNOS), and in Japan it is the Multi-Functional Satellite Augmentation System(MSAS). Ground based augmentation is provided by the Local Area Augmentation System (LAAS). [ Citation needed ]
- GNSS-2 [ citation needed ] is the second generation of systems that provide a full civilian satellite navigation system, exemplified by the European Galileo positioning system. These systems will provide accuracy and integrity monitoring 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 Beidou , India’s NAVIC , and Japan’s proposed QZSS .
- Continental Scale Ground Based Augmentation Systems (GBAS) for example the Australian GRAS and the 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 radio navigation has long been practiced. The DECCA , LORAN , GEE and Omega systems used terrestrial longwave radio transmitters which broadcast a radio pulse from a known “master” location, followed by a pulse repeated from a number of “slave” stations. The delay between the reception of the master signal and the slave signals allows the receiver to deduce the distance to each of the slaves, 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 radio frequency . The received frequency will differ slightly from the broadcast frequency because of the motion 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 broadcasting its orbital data. In order to ensure accuracy, the US Naval Observatory (USNO) continuously observed the precise orbits of these satellites. As a satellite orbit deviated, the USNO would send the 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 ephemeris is transmitted in a data message which 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 broadcasting in the transmission of three satellites to each satellite. Several such measurements can be made at the same time to different satellites,
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 some 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 slowly as they pass through the ionosphere, and this slowing varies with the receiver’s angle to the satellite, because that changes through the ionosphere. The basic computation of the.
Civil and military uses
The original motivation for satellite navigation was for military applications. Satellite navigation allows the 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 can be used to determine the fog of war .
The ability to provide satellite navigation signals is also available to deny their availability. The operator of a satellite navigation system has the ability to degrade or eliminate satellite navigation services over any territory.
Global navigation satellite systems
The United States’ Global Positioning System (GPS) 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 most utilized satellite navigation system.
The formerly Soviet , and now Russian , Glo bal’naya Na vigatsionnaya S putnikovaya S Istema ( Russian : ГЛОбальная НАвигационная Спутниковая Система , GLObal NAvigation Satellite System), GLONASS gold, is a space-based satellite navigation system That Provides a civilian navigation satellite Service and is also used by the Russian Aerospace Defense Forces. The full orbital constellation of 24 GLONASS satellites allows full global coverage.
The European Union and European Space Agency agreed in March 2002 to introduce their own alternative to GPS, called the Galileo positioning system . Galileo is operational est devenu 15 December 2016 (Global Early Operational Capability (EOC))  At an estimated cost of EUR 3.0 trillion,  the system of 30 MEO satellites Was Originally scheduled to be operational in 2010. The original year to Become operational Was 2014.  The first experimental satellite Was lancé is 28 December 2005.  Galileo is expected to be consistent with the Modernized GPS system. The receiver 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 higher cost.  The main modulation used in Galileo Open Service is the Composite Binary Offset Carrier (CBOC) modulation.
China HAS Indicated They Plan to Complete Entire the second generation Beidou Navigation Satellite System (BDS gold BeiDou-2, formerly known as COMPASS), by Expanding current regional (Asia-Pacific) Global Service into coverage by 2020.  The BeiDou- 2 Proposed system is 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
Chinese regional (Asia-Pacific, 16 satellites) network to be expanded into the whole BeiDou-2 global system which consists of all satellites by 2020.
The NAVIC or NAVIGATION with Indian Constellation is an autonomous regional satellite navigation system developed by Indian Space Research Organization (ISRO) which would be under the total control of Indian government . The government approved the project in May 2006, with the intention of the system completed and implemented on April 28, 2016. It will consist of a constellation of 7 navigational satellites.  3 of the satellites will be placed in the Geostationary orbit (GEO) and the remaining 4 in the Geosynchronous orbit (GSO) to have a larger signal of satellite to map the region. It is intended to provide an all-weather absolute position of better than 7.6 meters throughout India and within 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.  All seven satellites IRNSS-1A , IRNSS-1B , IRNSS-1C , IRNSS-1D , IRNSS-1E , IRNSS-1F , and IRNSS-1G , of the Proposed constellation Were PRECISELY lancé 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 Center .   The system is expected to be fully operational by August 2016. 
The Quasi-Zenith Satellite System (QZSS), is a proposed satellite-based satellite- time-transfer system for GPS covering Japan . The first demonstration satellite was launched in September 2010. 
Comparison of systems
(Global by 2020)
|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)
|Revolutions per sidereal day||17/9||17/10||17/8||2|
|5 geostationary orbit (GEO) satellites,
30 medium Earth orbit (MEO) satellites
|18 satellites in orbit,
15 fully operational capable,
11 currently healthy,
30 operational satellites budgeted
|28 (at least 24 by design) including: 
|31 (at least 24 by design) ||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 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)
|1.614-1.215 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
|4.5m – 7.4m||15m (Without DGPS or WAAS)||10m (Public)
GNSS augmentation is a method of Improving a navigation system’s attributes, Such As accuracy, reliability, and availability, through the integration of external information into the calculation process, for example, the Wide Area Augmentation System , the European Geostationary Navigation Overlay Service , the Multi -functional Satellite Augmentation System , Differential GPS , and inertial navigation systems .
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 use and coverage. GNSS systems, with precise geodesic reference systems, are used to determine the accuracy of the geodesic reference system. 
Low Earth orbit satellite phone networks
The two current operational low orbit satellite phone networks are able to track transceiver units with accuracy of a few miles 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.
- Spaceflight portal
- Acronyms and abbreviations in avionics
- GNSS reflectometry
- GPS-aided geo-augmented navigation
- GPS spoofing
- List of emerging technologies
- Receiver Autonomous Integrity Monitoring
- Software GNSS Receiver
- Space Integrated GPS / INS (SIGI)
- Jump up^ Orbital periods and speeds are Calculated using the 4π² relationshipsR³ = T²GMandV²R = GM, WhereR= radius of orbit in meters,T= orbital period in seconds,V= orbital speed in m / s ,G= gravitational constant ≈ 6.673×10– 11 Nm² / kg²,M= mass of Earth ≈ 5.98×10 24 kg.
- Jump up^ Approximately 8.6 times when the moon is nearest (363,104 km ÷ 42,164 km) to 9.6 times when the moon is farthest (405,696 km ÷ 42,164 km).
- ^ Jump up to:a b “Galileo goes live!” . europa.eu. 2016-12-14.
- ^ Jump up to:a b “Beidou satellite navigation system to cover whole world in 2020 ‘ . Eng.chinamil.com.cn . Retrieved 2011-12-30 .
- Jump up^ “A Beginner’s Guide to GNSS in Europe” (PDF) . IFATCA . Retrieved 20 May 2015 .
- Jump up^ “Galileo goes live!” . europa.eu. 14 December 2016.
- Jump up^ “Boost to Galileo sat-nav system” . BBC News. 25 August 2006 . Retrieved 2008-06-10 .
- Jump up^ “Commission awards major contracts to make Galileo operational early 2014” . 2010-01-07 . Retrieved 2010-04-19 .
- Jump up^ “GIOVE-A launch News” . 2005-12-28 . Retrieved 2015-01-16 .
- Jump up^ “India to develop its own version of GPS” . Rediff.com . Retrieved 2011-12-30 .
- Jump up^ S. Anandan (2010-04-10). “Launch of first satellite for Indian Regional Satellite System next year” . Beta.thehindu.com . Retrieved 2011-12-30.
- Jump up^ “India to build a constellation of 7 satellite navigation by 2012” . Livemint.com. 2007-09-05 . Retrieved 2011-12-30 .
- Jump up^ The first satellite IRNSS-1A of the proposed constellation, developed at a cost of 16 billion (US $ 280 million),  was launched on 1 July 2013 from Satish Dhawan Space Center
- Jump up^ “ISRO: All 7 IRNSS Satellites in Orbit by March” . gpsworld.com. 2015-10-08 . Retrieved 2015-11-12 .
- Jump up^ http://www.thehindu.com/news/national/karnataka/navic-could-be-operationalized-during-julyaugust-this-year/article8639174.ece . Missing or empty( help ) |title=
- Jump up^ “JAXA Quasi-Zenith Satellite System” . JAXA . Retrieved 2009-02-22 .
- Jump up^ “GLONASS status” . Retrieved 2015-07-24 .
- Jump up^ “GPS Space Segment” . Retrieved 2015-07-24 .
- Jump up^ “DORIS information page” . Jason.oceanobs.com . Retrieved 2011-12-30 .
- Jump up^ “Globalstar GSP-1700 manual” (PDF) . Retrieved 2011-12-30 .
- Jump up^  ArchivedNovember 9, 2005, at theWayback Machine.