The Beidou Navigation Satellite System ( BDS , simplified Chinese : 北斗卫星导航系统 ; traditional Chinese : 北斗衛星導航系統 ; pinyin : Běidǒu Weixing dǎoháng xìtǒng ) is a Chinese navigation satellite system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, and a full-scale global navigation system that is currently under construction.
The first BeiDou system, officiellement called Expired the BeiDou Satellite Navigation Experimental System ( simplified Chinese : 北斗卫星导航试验系统 ; traditional Chinese : 北斗衛星導航試驗系統 ; pinyin : Běidǒu Weixing dǎoháng Shiyan xìtǒng ) and Also Known As BeiDou-1, Consists of Three satellites and offers limited coverage and applications. It has been offering navigation services, mainly for customers in China and neighboring regions, since 2000.
The second generation of the system, called Expired officiellement the BeiDou Navigation Satellite System (BDS) and COMPASS Also Known As gold BeiDou-2, will be a global navigation satellite system consistant en 35 satellites and is under construction as of January 2015 . It is operational in China in December 2011, with 10 satellites in use,  and began offering services to customers in the Asia-Pacific region in December 2012.  It is planned to begin serving global customers at its completion in 2020 .
In-mid 2015, China started the build-up of the third generation BeiDou system (BDS-3) in the global constellation. The first BDS-3 satellite was launched on 30 September 2015.  As of March 2016, BDS-3 in-orbit validation satellites have been launched. 
Selon China Daily fifteen Years After the satellite system Was lancé, it is now Generating a turnover of $ 31.5 trillion per annum for major companies Such As China Aerospace Science and Industry Corp., AutoNavi Holdings Ltd, and China North Industries Group Corp. 
Beidou has been described as a satellite navigation system for overloading GPS in global usage, and is expected to be more accurate than the GPS once it is fully completed.   
The official English name of the system is BeiDou Navigation Satellite System .  It is named after the Big Dipper constellation , which is known in Chinese as Běidǒu . The name literally means “Northern Dipper”, the name given by ancient Chinese astronomers to the seven bright stars of the Ursa Major constellation .  Historically, this set of stars was used to navigate the North Star Polaris . As such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system.
Conception and initial development
Chen Fangyun and his colleagues in the 1980s.  According To the China National Space Administration , the development of the system Would Be the carried out in three steps: 
- 2000-2003: experimental BeiDou navigation system consisting of 3 satellites
- By 2012: regional BeiDou navigation system covering China and neighboring regions
- By 2020: global BeiDou navigation system
The first satellite, BeiDou-1A , was launched on 30 October 2000, followed by BeiDou-1B on 20 December 2000. The third satellite, BeiDou-1C (a satellite backup), was put into orbit on 25 May 2003. [  The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system.
On 2 November 2006, China announced that from 2008 BeiDou would offer an open service with an accuracy of 10 meters, timing of 0.2 microseconds, and speed of 0.2 meters / second.  [ citation needed ]
In February 2007, the fourth and last satellite of the BeiDou-1 system, BeiDou-1D (sometimes called BeiDou-2A , serving as a backup satellite), was launched.  It was reported that the satellite had suffered from a malfunction system but was then fully restored.  
In April 2007, the first satellite of BeiDou-2, known as the Compass-M1 (to validate frequencies for the BeiDou-2 constellation) was successfully put into its working orbit. The second BeiDou-2 satellite constellation Compass-G2 Was lancé is 15 April 2009.  On 15 January 2010, the official website of the BeiDou Navigation Satellite System Went online,  and the system’s third satellite ( Compass-G1 ) was the carried into orbit by ict has Long March 3C rocket is 17 January 2010.  On 2 June 2010, the fourth satellite successfully into orbit was lancé.  The fifth orbiter was launched into space from Xichang Satellite Launch Center by an LM-3I carrier rocket on 1 August 2010.  Three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C .  Another satellite, the Beidou-2 / Compass IGSO-5 (fifth inclined geosynchonous orbit) satellite, was launched from the Xichang Satellite Launch Center by a March-3A on 1 December 2011 (UTC).  The Beidou-2 / Compass IGSO-5 (fifth inclined geosynchonous orbit) satellite, was launched from the Xichang Satellite Launch Center by a March-3A on 1 December 2011 (UTC).  The Beidou-2 / Compass IGSO-5 (fifth inclined geosynchonous orbit) satellite, was launched from the Xichang Satellite Launch Center by a March-3A on 1 December 2011 (UTC). 
Chinese involvement in Galileo system
In September 2003, China intended to join the European Galileo positioning system project and was to invest € 230 million ( USD 296 million, GBP 160 million) in Galileo over the next few years.  At the time, it was believed that China’s “BeiDou” navigation system would then only be used by its armed forces.  In October 2004, China officially joined the Galileo Joint Undertaking (GJU) and the National Remote Sensing Center of China (NRSCC) . Based on the Sino-European Cooperation Agreement on Galileo program, China Galileo Industries (CGI) , the prime contractor of the China’s involvement in Galileo programs, Was founded in December 2004.  By April 2006, eleven cooperation projects dans le Galileo framework HAD beens signed entre China and EU.  However, the Hong Kong-based South China Morning Post reported in January 2008 that China was unsatisfied with its role in the Galileo project and was to compete with Galileo in the Asian market.   However, the Hong Kong-based South China Morning Post reported in January 2008 that China was unsatisfied with its role in the Galileo project and was to compete with Galileo in the Asian market.   However, the Hong Kong-based South China Morning Post reported in January 2008 that China was unsatisfied with its role in the Galileo project and was to compete with Galileo in the Asian market. 
- In November 2014, Beidou became part of the World-Wide Radionavigation System (WWRNS) at the 94th meeting of the International Maritime Organization (IMO) Maritime Safety Committee,  which approved the Navigation Safety Circular of the Beidou Navigation Satellite System (BDS).  
- At Beijing time 21:52, March 30, 2015, the first new-generation BeiDou Satellite navigation (and the 17th overall) was successfully set to orbit by a Long March 3C rocket.  
Experimental system (BeiDou-1)
BeiDou-1 is an experimental regional navigation system, which consists of three satellite satellites and one backup satellite. The satellites themselves were based on the Chinese DFH-3geostationary communications satellite and had a launch weight of 1,000 kilograms (2,200 pounds) each. 
Unlike the American GPS , Russian GLONASS , and European Galileo systems, which use medium Earth orbit satellites, BeiDou-1 uses satellites in geostationary orbit . The Earth’s satellite system is a large satellite constellation.  The area that can be served from 70 ° E to 140 ° E and from latitude 5 ° N to 55 ° N. A frequency of the system is 2491.75 MHz. 
The first satellite, BeiDou-1A, was launched on October 31, 2000. The second satellite, BeiDou-1B, was successfully launched on December 21, 2000. The last satellite satellite of the constellation, BeiDou-1C, was launched on May 25 , 2003. 
In 2007, the official Xinhua News Agency reported that the resolution of the BeiDou system was as high as 0.5 meters.  With the existing terminals it appears that the calibrated accuracy is 20m (100m, uncalibrated). 
In 2008, a BeiDou-1 ground terminal cost around CN ¥ 20,000 RMB ( US $ 2,929), almost 10 times the price of a conventional GPS terminal.  The price of the terminals was explained due to the cost of imported microchips. At the China High-Tech Fair ELEXCON of November 2009 in Shenzhen , a BeiDou terminal priced at CN ¥ 3,000RMB was presented. 
- Over 1,000 BeiDou-1 terminals were used after the 2008 Sichuan earthquake , providing information from the disaster area. 
- As of October 2009, all Chinese border guards in Yunnan are equipped with BeiDou-1 devices. 
According to Sun Jiadong , the chief designer of the navigation system, “Many organizations have been using our system for a while. 
The new-generation BeiDou satellites support short message service. 
Global system (BeiDou Navigation Satellite System or BeiDou-2)
BeiDou-2 (formerly known as COMPASS)  is not an extension to the older BeiDou-1, but rather supersedes it outright. The new system will be a constellation of 35 satellites, qui include 5 geostationary orbit satellites for backward compatibility with BeiDou-1, and 30 non-geostationary satellites (27 in medium Earth orbit and 3 in inclined geosynchronous orbit ),  That will Offer complete coverage of the globe.
The ranging signals are based on the CDMA principle and complex-have typical structure of Galileo gold Modernized GPS . Similar to the other global navigation satellite systems (GNSSs), there will be two levels of positioning service: open (public) and restricted (military). The public service will be available globally to general users. When all the GNSSs Currently planned are Deployed, users of multi-constellation receivers will benefit from a total of over 100 satellites, qui will Significantly Improve all aspects of positioning, Especially availability of the signals in so-called urban canyons .  The general designer of the COMPASS navigation system is Sun Jiadong ,
There are two levels of service provided to the Chinese government and military.   The free civilian service has a 10-meter location-tracking accuracy, synchronized clocks with an accuracy of 10 nanoseconds, and measurements speeds to within 0.2 m / s. The restricted military service has a location accuracy of 10 centimeters,  can be used for communication, and will provide information about the system status to the user. To date, the military service has been granted only to the People’s Liberation Armyand to the Military of Pakistan .   
Frequencies for COMPASS are allocated in four bands: E1, E2, E5B, and E6 and overlap with Galileo. The fact that it is possible to use the E1 and E2 bands, which are allocated for Galileo’s publicly regulated service.  However, under International Telecommunication Union (ITU) policies, the first nation to start broadcasting in a specific frequency will have priority to that frequency, and any subsequent users will be required to obtain permission. That their broadcasts do not interfere with the original nation’s broadcasts. It now appears that Chinese COMPASS satellites will start transmitting in the E1, E2, E5B, and E6 bands before Europe’s Galileo satellites and thus have primary rights to these frequency ranges. 
COMPASS satellite receiver, satellite receiver, satellite receiver, satellite receiver, satellite receiver, satellite receiver.
Compass-M1 is an experimental satellite lancé for testing and validation signal and for the filing frequency is 14 April 2007. The role of Compass-M1 for Compass is similar to the role of the GIOVE satellites for the Galileo system. The orbit of Compass-M1 is nearly circular, has an altitude of 21,150 km and an inclination of 55.5 degrees.
Compass-M1 transmitted in 3 bands: E2, E5B, and E6. In each frequency band two coherent sub-signals have been detected with a phase shift of 90 degrees (in quadrature ). These signals are referred to as “I” and “Q”. The “I” components have shorter codes and are likely to be intended for the open service. The “Q” components have much longer codes, are more interference resistive, and are not intended for the restricted service.
The investigation of the transmitted signals after the launch of compass -M1 on 14 April 2007. Soon after in June 2007, CNES engineers reported the spectrum and structure of the signals.  A month later, researchers from Stanford University reported the complete decoding of the “I” signals components.   The knowledge of the codes of a group of engineers at Septentrio to build the COMPASS receiver  and report tracking and multipath characteristics of the “I” signals on E2 and E5B. 
|Modulation code||BPSK (2)||BPSK (2)||BPSK (2)||BPSK (10)||BPSK (10)||BPSK (10)||BPSK (1)|
|Carrier frequency, MHz||1561.098||1561.098||1207.14||1207.14||1268.52||1268.52||1575.42|
|Chip rate, Mchips / s||2046||2046||2046||10,230||10,230||10,230||1023|
|Code period, chips||2046||??||2046||??||10230||??||1023|
|Code period, ms||1.0||> 400||1.0||> 160||1.0||> 160||1.0|
|Symbols / s||50||??||50||??||50||??||50|
|Navigation frames, s||6||??||6||??||??||??||6|
|Navigation sub-frames, s||30||??||30||??||??||??||30|
|Navigation period, min||12.0||??||12.0||??||??||??||12.5|
Characteristics of the “I” signals on E2 and E5B are the same to the civilian codes of GPS (L1-CA and L2C), but Compass signals have somewhat greater power. The notation of Compass signals used in this page follows the naming of the frequency bands and agrees with the notation used in the American literature on the subject, but the notation used by the Chinese seems to be different and is quoted in the first row of the table.
In December 2011, the system went into operation on a trial basis.  It has been provided providing navigation, positioning and timing data to China and the neighboring area for free from 27 December. During this trial run, Compass will offer positioning accuracy within 25 meters, but the satellites are launched. Upon the system’s official launch, it provides information to the nearest 10 m, measure speeds within 0.2 m per second, and provide signals for clock synchronization accurate to 0.02 microseconds. 
The BeiDou-2 system initiating services for the Asia-Pacific region in December 2012.  At this time, the system could provide positioning data between longitude 55 ° E to 180 ° E and from latitude 55 ° S to 55 ° N . 
In December 2011, Xinhua stated that “[t] he basic structure of the Beidou system has now been established, and engineers are now conducting comprehensive system test and evaluation. And the neighboring areas before the end of this year, according to the authorities. ”  The system becomes operational in the China region that same month.  The global navigation system shoulds be finished by 2020.  As of December 2012, 16 satellites for BeiDou-2-have-been lancé, 14 of ’em are in service.
|Satellite launches||Currently in orbit
|(Last update: January 16, 2017)
For a more complete list, see list of BeiDou satellites
The regional Beidou-1 system was decommissioned at the end of 2012.
The first satellite of the second-generation system, Compass-M1 was launched in 2007. It was followed by further nine satellites during 2009-2011, achieving functional regional coverage. A total of 16 satellites were launched during this phase.
In 2015, the system began its transition towards global coverage with the first launch of a new generation of satellites,  and the 17th one within the new system. On July 25, 2015, the 18th and 19th satellites were successfully launched from the Xichang Satellite Launch Center , marking the first time for China to launch two satellites at once on a March 3b / Expedition-1 carrier rocket . The Expedition-1 is an independent upper stage capable of delivering one or more spacecraft into different orbits. On November 29, the 20th satellite was launched, carrying a hydrogen maser for the first time within the system. 
In 2016, the 21st, 22nd and 23rd satellites were launched from Xichang Satellite Launch Center ,  the last two of which entered into service on August 5 and November 30, respectively.  
- Global Positioning System
- Chinese coordinate systems
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