Китайская спутниковая навигационная система "Бэйдоу"

Chinese satellite navigation system

The BeiDou Navigation Satellite System (BDS; ) is a satellite based radio navigation system owned and operated by the China National Space Administration. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a BDS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more BDS satellites. It does not require the user to transmit any data, and operates independently of any telephonic or Internet reception, though these technologies can enhance the usefulness of the BDS positioning information. The current service, BeiDou 3 (third generation BeiDou), provides full global coverage for timing and navigation, along with Russia's GLONASS, the European Galileo, and the US's GPS. It consists of satellites in three different orbits, including 24 satellites in medium circle orbits (covering the world), 3 satellites in inclined geosynchronous orbits (covering the Asia–Pacific region), and 3 satellites in geostationary orbits (covering China). The BeiDou 3 system was fully operational in July 2020. In 2016, BeiDou 3 reached millimeter level accuracy with post processing. Predecessors included BeiDou 1 (first generation BeiDou), consisting of three satellites in a regional satellite navigation system. Since 2000, the system has mainly provided navigation services within China. In December 2012, as the design life of BeiDou 1 expired, it stopped operating. The BeiDou 2 (second generation BeiDou) system was also a regional satellite navigation system containing 16 satellites, including 6 geostationary satellites, 6 inclined geosynchronous orbit satellites, and 4 medium earth orbit satellites. In November 2012, BeiDou 2 began to provide users with regional positioning services in the Asia–Pacific region. Within the region, BeiDou is more accurate than GPS. In 2015, fifteen years after the satellite system was launched, it was generating a turnover of $31.5 billion per annum for major companies such as China Aerospace Science and Industry Corporation, AutoNavi, and Norinco. The industry has grown an average of over 20% in value annually to reach $64 billion in 2020.

The official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper asterism, which is known in Chinese as The name literally means "Northern Dipper", the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star. As such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system.

In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million (US$296 million, £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. Based on the Sino European Cooperation Agreement on Galileo program, China Galileo Industries (CGI), the prime contractor of China's involvement in Galileo programs, was founded in December 2004. By April 2006, eleven cooperation projects within the Galileo framework had been signed between China and the EU.

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, 30 March 2015, the first new generation BeiDou Navigation satellite (and the 17th overall) was successfully set to orbit by a Long March 3C rocket. On 20 April 2019, a BeiDou satellite was successfully launched. Launch occurred at 22:41 Beijing time, and the Long March 3B delivered the BeiDou navigation payload into an elliptical transfer orbit ranging between 220 kilometres and 35,787 kilometres, with an inclination of 28.5° to the equator, according to U. S. military tracking data. On 23 June 2020, the final BeiDou satellite was successfully launched, the launch of the 55th satellite in the BeiDou family. The third iteration of the BeiDou Navigation Satellite System provides global coverage for timing and navigation, offering an alternative to Russia's GLONASS and the European Galileo positioning system, as well as the US's GPS.

In 2018, the Pakistan Armed Forces received access to BeiDou for military purposes. In 2019, the Saudi Ministry of Defense signed an agreement for military use of BeiDou. In 2021, the first China Africa BeiDou System Cooperation Forum was held in Beijing.

BeiDou 1 was an experimental regional navigation system, which consisted of four satellites (three working satellites and one backup satellite). The satellites themselves were based on the Chinese DFH 3 geostationary communications satellite and had a launch weight of 1,000 kg each. Unlike the American GPS, Russian GLONASS, and European Galileo systems, which use medium Earth orbit satellites, BeiDou 1 used satellites in geostationary orbit. This means that the system does not require a large constellation of satellites, but it also limits the coverage to areas on Earth where the satellites are visible.

The first satellite, BeiDou 1A, was launched on 31 October 2000. The second satellite, BeiDou 1B, was successfully launched on 21 December 2000. The last operational satellite of the constellation, BeiDou 1C, was launched on 25 May 2003. With the existing user terminals it appears that the calibrated accuracy is 20 m (100 m, uncalibrated).

In 2008, a BeiDou 1 ground terminal cost around , almost 10 times the price of a contemporary GPS terminal. The price of the terminals was explained as being due to the cost of imported microchips. At the China High Tech Fair ELEXCON of November 2009 in Shenzhen, a BeiDou terminal priced at was presented.

Over 1000 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 were equipped with BeiDou 1 devices. Sun Jiadong, the chief designer of the navigation system, said in 2010 that "Many organizations have been using our system for a while, and they like it very much".

BeiDou 1 was decommissioned at the end of 2012, after the BeiDou 2 system became operational.

BeiDou 2 (formerly known as COMPASS) is not an extension to the older BeiDou 1, but rather supersedes it outright. The new system is a constellation of 35 satellites, which 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 offer complete coverage of the globe. The ranging signals are based on the CDMA principle and have complex structure typical of Galileo or modernized GPS. Similar to the other global navigation satellite systems (GNSSs), there are two levels of positioning service: open (public) and restricted (military). The public service is available globally to general users. When all the currently planned GNSSs are deployed, users of multi constellation receivers will benefit from a total over 100 satellites, which 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, who is also the general designer of its predecessor, the original BeiDou navigation system. All BeiDou satellites are equipped with laser retroreflector arrays for satellite laser ranging and the verification of the orbit quality.

There are two levels of service provided – a free service to civilians and licensed service to the Chinese government and military. The free civilian service has a 10 metre location tracking accuracy, synchronizes clocks with an accuracy of 10 nanoseconds, and measures speeds to within 0.2 m/s. The restricted military service has a location accuracy of 10 cm, can be used for communication, and will supply information about the system status to the user. In 2019, the International GNSS Service started providing precise orbits of BeiDou satellites in experimental products.

Frequencies for COMPASS are allocated in four bands: E1, E2, E5B, and E6; they overlap with Galileo. The fact of overlapping could be convenient from the point of view of the receiver design, but on the other hand raises the issues of system interference, especially within 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 prior to using that frequency, and otherwise ensure that their broadcasts do not interfere with the original nation's broadcasts. As of 2009, it appeared that Chinese COMPASS satellites would 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 M1 is an experimental satellite launched for signal testing and validation and for the frequency filing on 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°. The investigation of the transmitted signals started immediately after the launch of Compass M1 on 14 April 2007. Soon after in June 2007, engineers at CNES 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 allowed 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.

In December 2011, the system went into operation on a trial basis. It started providing navigation, positioning and timing data to China and the neighbouring area for free from 27 December 2011. During this trial run, Compass offered positioning accuracy to within 25 metre and the precision improved as more satellites were launched. Upon the system's official launch, it pledged to offer general users positioning information accurate to the nearest 10 m, measure speeds within 0.2 metre per second, and provide signals for clock synchronisation accurate to 0.02 microseconds. The BeiDou 2 system began offering services for the Asia Pacific region in December 2012. The new generation BeiDou satellites support short message service. The system became operational in the China region that same month. As of December 2012, 16 satellites for BeiDou 2 had been launched, with 14 in service. As of December 2017, 150 million Chinese smartphones (20% of the market) were equipped to utilize BeiDou.

In 2018, Taiwan's National Communications Commission announced that it would be illegal to use BeiDou products in Taiwan without its approval.