GNSS

Global Navigation Satellite System (GNSS) is a space-based radio navigation and positioning system that can provide users with all-weather three-dimensional coordinates, speed and time information anywhere on the earth's surface or in near-Earth space.

A Global Navigation Satellite System (GNSS) includes one or more constellations of satellites and their augmentation systems needed to support a particular job.

The four major global satellite navigation system suppliers announced by the International Committee on Global Navigation Satellite Systems include Beidou Satellite Navigation System (BDS) of China, Global Positioning System (GPS) of the United States, GLONASS of Russia and GALILEO of the European Union.Among them, GPS is the first global navigation and positioning system in the world, and GLONASS has become the second largest satellite navigation system in the world after its rapid recovery. Both of them are in the process of modernization and renewal. GALILEO is the first fully civilian satellite navigation system, which is in the experimental stage; BDS is a global satellite navigation system independently built and operated by China.It provides all-weather, all-day, high-precision positioning, navigation and timing services for global users.

Development and evolution

On October 4, 1957, the Soviet Union successfully launched the world's first man-made earth satellite. When two young scholars at the Applied Physics Laboratory of Hopkins University in the United States received the satellite signal, they discovered the Doppler shift effect formed between the satellite and the receiver, and asserted that it could be used for navigation and positioning.At their suggestion, the United States built the first satellite navigation system in the world in 1964, namely the "Meridian", which consists of six satellites to form a constellation for positioning and navigation of naval vessels at sea. In 1967, the Meridian system was decrypted and made available for civilian use.

Thus it can be seen that the global positioning system (GPS) was constructed in the late 1970s, and the global navigation satellite system (GNSS) composed of multiple constellations will be constructed in 2020.They belong to the second generation of navigation satellite systems, including GPS of the United States, Glonas Satellite Navigation System of Russia (global navigationsatellite system). GLONASS, China's BeiDou navigation satellite system (BDS)And Europe's Galileo navigationsatellite system (Galileo), as well as Japan's Quasi-Zenith zenith satellite system (QZSS).And the Indian Regional Navigation Satellite System (Indian regionalnavigational satellite system, IRNSS). IRNSS is also called navigation with Indian constellation (NavIC).The above five countries, except China, all hold corresponding satellite-based augmentation systems as GNSS service providers. They are the wide area augmentation system (WAas) of the United States, Differential Correction Monitoring System (differential correctionsand monitoring, SDCM) in RussiaEuropean geostationary navigation overlay service, EGNOS), India's GPS aided geo augmented navigation (GAGAN)And Japan's multi-functional satellite augmentation system (MSAS).

The BeiDou navigation satellite [regional] system (BDS-2) built by China is a regional system because its development path of satellite navigation system is different from that of other countries. Its BeiDou navigation satellite system with global coverage (BDS-3) also includes satellite-based augmentation system functions.

To sum up, the so-called second-generation navigation satellite system refers to GNSS, which refers to the global satellite navigation system in general, and is a concept of systems including global systems, regional systems and satellite-based augmentation systems. So will there be a third generation navigation satellite system. There should be, because all countries that have built global satellite navigation systems are considering or promoting the next innovative action plan of satellite navigation systems, as well as considering integrated navigation constellations with communications.

On April 19, 2023, the National Space Administration announced that China is demonstrating the construction of a constellation of communication and navigation satellites around the moon, and the first launch may take place around 2024. Simply put, this will be the lunar version of Beidou Navigation System, which can provide relay communication, navigation and other services for future lunar operations, and provide information support for more complex lunar exploration missions.

short message communication services.

Application status

In recent years, China has continuously strengthened the manufacturing and launching of Beidou navigation satellites and the construction of ground systems, and the infrastructure of the Beidou navigation system has been gradually improved. It is expected that by the end of 2020, the construction of the Beidou-3 system will be fully completed, and the accuracy of space signals will be better than 0.5 meters.Beidou system has been widely used in transportation, agriculture, forestry and fishery, hydrological monitoring, weather forecasting, disaster relief and mitigation and other fields, and has been widely used in land rights confirmation in Indonesia, construction in Kuwait, land testing in Uganda, precision agriculture in Myanmar, offshore piling in Maldives, warehousing and logistics in Thailand, airport timing in Pakistan, and power inspection in Russia.

The 28nm process RF baseband integrated SoC chip supporting the new signal of Beidou 3 has been widely used in the Internet of Things and consumer electronics, the latest 22nm process dual-frequency positioning chip has met the market application conditions, and the full-frequency integrated high-precision chip is being developed. The world's first high-precision baseband chip "Tianqin II," which fully supports the Beidou 3 civil navigation signal system, was officially released in Beijing, and the performance of the Beidou chip will go up to a higher level.Its performance index is equivalent to that of similar products in the world.By the end of 2019, the cumulative sales of domestic Beidou navigation chip modules have exceeded 80 million pieces, and the sales of high-precision boards and antennas have occupied 30% and 90% of the domestic market share, and have been exported to more than 100 countries and regions.

The China Satellite Navigation and Positioning Reference Service System has been put into use, which can provide free and open real-time sub-meter navigation and positioning services to the public. The Beidou system has made breakthroughs in high-precision algorithm and high-precision board manufacturing, and the use of RTK (Real-time kinematic, real-time kinematic difference) technology can improve the accuracy to centimeter level, and the future development space of high-precision positioning technology is broad.The National Beidou Precision Service Network has provided Beidou precision services for various industry applications in more than 400 cities across the country, effectively promoting the optimization and improvement of smart city infrastructure.

Beidou Navigation Satellite System is widely used in ship transportation, highway transportation, railway transportation, maritime operations, fishery operations, forest fire prevention, environmental management and monitoring, covering the army, public security, customs and other units with special command and dispatch requirements, producing significant economic and social effects. With the continuous improvement and perfection of the functions and performance of Beidou Satellite Navigation System, the application scale and scope of Beidou will gradually expand and have a promising future.

In terms of offshore operations, the Beidou Fishing Vessel Terminal and Operation Platform of China Shipbuilding Industry System Engineering Research Institute, and the Beidou Dredging Vessel Monitoring Terminal and Operation Platform have been developed. In 2016, the Institute developed a number of Beidou series systems according to market demand, such as Beidou distress rescue terminal, Beidou-based "smart ship" navigation system and electronic customs clearance system.At the beginning of the 13th Five-Year Plan, the demonstration project of inland river ship supervision based on Beidou was jointly launched by the Ministry of Transport and the Equipment Development Department of the Central Military Commission, and achieved good results. The environment for statutory inspection and testing of Beidou emergency radio position indicating beacon has been successfully established.In terms of highway and railway transportation, the Beidou Navigation Satellite System can be used to monitor the safety of facilities and the transportation process of vehicles. According to statistics, Beidou terminals have been installed in about 4.8 million dangerous goods vehicles, buses and liner buses nationwide, and the efficiency of monitoring and managing each vehicle and the level of maintaining safety in the process of road transportation have been effectively improved.In terms of forest fire prevention, disaster relief and mitigation, Beidou Navigation Satellite System, with its precise positioning technology, accurately and timely reporting and sharing of disaster information, real-time command and dispatch, short message communication function and emergency communication function, has significantly improved the decision-making and deployment capabilities and response capabilities of disaster relief and mitigation.In the aspect of environmental monitoring, the system application formed by a series of meteorological observation terminal equipment based on Beidou not only improves the observation accuracy of the domestic high-altitude meteorological sounding system, but also improves its automation level and emergency observation ability.

The application of Beidou satellite navigation system has infinite possibilities. In October 2019, during the National Day parade, the Beidou parade training and assessment assistant system developed by the Army Military Transportation Academy can ensure that the overall speed of 580 vehicles in 32 teams is controlled at 10 km/H, and its positioning accuracy reaches centimeter level, which has surpassed the world's advanced level.With the continuous improvement of Beidou system and the continuous enhancement of its system construction, it is expected to complete the global network in June 2020, and realize global short message communication, satellite-based enhancement, international search and rescue, precision positioning and other services.

In 2020, the completion and opening ceremony of Beidou 3 Global Satellite Navigation System was held in Beijing on the morning of July 31. The Beidou-3 global satellite navigation system has been fully completed and put into service, marking the decisive victory of the "three-step" development strategy of the project, and China has become the third country in the world to have an independent global satellite navigation system.

Related news

The last networking satellite of China's Beidou-3 Global Navigation Satellite System was originally scheduled to be launched at 10:00 on June 16, 2020. However, the official announcement on the 16th said that during the pre-launch test of the Long March 3B carrier rocket, technical problems were found, the launch mission was delayed and the launch time was to be determined.

In an interview with the media, Li Gou, a front-line technical expert of the Beidou 3 project, said, "First of all, it is a pity that we did not wait for the exciting moment as scheduled. On the evening of the 15th, when we carried out the pre-launch functional inspection according to the process, we found a technical problem.". Pre-launch functional examination is a comprehensive physical examination of the rocket before it takes off.Rocket is a complex system, and the biggest characteristic of space launch is its high risk, so it is a common phenomenon to postpone launch all over the world. Because of the high risk of space launch, the biggest goal of engineers and technicians is to ensure that every launch is foolproof and that every launch is successful. In order to achieve this goal, the developer also has one of the most basic principles, that is, no doubts, no hidden dangers.Therefore, in view of this technical problem, the developer decided to postpone the launch after careful study. The whole system is in good condition, and the developer has the ability to find out the cause as soon as possible, solve the problem and reorganize the launch.

There are four major global satellite navigation systems (globalnavigation satellite system, GNSS), including China's Beidou Satellite Navigation System (BeiDou navigation satellite system). BDS), global positioning system (GPS) of the United StatesThe European Union's Galileo satellite navigation system (Galileo navigation satellite system) and the Russian GLONASS satellite navigation system (global orbitingnavigation satellite system). GLONASS）。Among them, BDS and GPS have served the whole world and have the same performance; in terms of functions, BDS has more regional short message and global short message functions than GPS. Although GLONASS has been in service all over the world, its performance is slightly inferior to that of BDS and GPS, and its orbit inclination is large, which leads to its poor performance in low latitudes. The quality of Galileo observations is good, but the stability of the on-board clock is slightly poor, resulting in poor reliability of the system.

On July 31, 2020, the Beidou-3 system was officially launched, and the network of Beidou-3 was completed half a year ahead of schedule. The official launch of the system marked the successful completion of the "three-step" development strategy of Beidou, and China became the third country in the world to have an independent global satellite navigation system.

GPS system

Origin and development

The United States Department of Defense (DOD) decided to establish the Joint Office of GPS Program in 1973. The global navigation and position system based on time and distance measurement (navigation system with time and ranging, NAVSTAR/GPS) is jointly develope by that military.The construction of the whole system is divided into three stages: the first stage (1973-1979), the feasibility verification stage of the system principle scheme (including equipment development); the second stage (1979-1983), the stage of system test research (testing the system equipment) and system equipment development; Phase 3 (1983-1988), engineering development and completion phase.From the launch of the first GPS satellite in 1978 to the completion of the satellite constellation configuration of 21 working satellites and 3 spare satellites on March 10, 1994, the U.S. Department of Defense officially declared that GPS had full operational capability in April 1995.GPS has been built for 20 years, and its system is composed of space segment, operation control segment and user segment. The whole constellation is rated to have 24 satellites, which are distributed in six medium orbit planes. Its excellent performance is praised as a revolution in the field of navigation. GPS provides a standard positioning system (SPS).And precise positioning service (PPS), the positioning accuracy level of SPS is 100 meters (95% probability) when the influence of selective availability (SA) is included, and it is 20 ~ 30 meters without SA. The timing accuracy is 340 ns, and the positioning accuracy of PPS is within 10 meters.

Modernization of GPS

The first landmark action of the GPS modernization plan put forward in 1996 is to cancel the SA technology of GPS satellites from May 1, 2000, which artificially deteriorates the positioning accuracy, resulting in an order of magnitude improvement in positioning accuracy.Over the past 20 years, the United States has continued to promote its modernization program, investing more than $20 billion, with the main goal of improving the level of satellite and ground segment operation and control in the space segment, separating military and civilian signals, and increasing the number of civilian signals from one to four while strengthening military performance, in addition to retaining the C/a code civilian signals on the L1 frequency point. Civil L1C and L2C codes are added to the original L1 and L2 frequency points, and a civil signal of L5 frequency point is added.The redundancy of civil signals is greatly increased, thereby improving the positioning accuracy of the system, the availability and integrity of the signals, the continuity of service, and the capability of resisting wireless interference; and the real-time kinematic (RTK) with high accuracy is also facilitated.Measurements and applications on long and short baselines are also useful for aircraft precision approach and landing, mapping, precision agriculture, mechanical control and civil indoor enhancement applications, and Earth science research.

The modernization of GPS is a systematic work, which includes the modernization of space satellite segment, ground operational control segment, new operational control system (OCX) and user equipment segment. The core of GPS modernization is to increase the number of L5 frequency points and civil signals and change the system to achieve interoperability with other GNSS signals. The last GPS IIIF is expected to be launched in 2034, marking the end of the GPS modernization process.

GLONASS system

Origin, development and modernization

In 1976, the Soviet government issued a decree on the establishment of GLONASS, and established corresponding scientific research institutions to carry out engineering design. On October 12, 1982, the first GLONASS satellite was successfully launched. In January 1996, the global network of 24 satellites was declared to be fully operational.After the collapse of the Soviet Union, GLONASS entered a difficult stage of maintenance. At the beginning of 2000, only seven satellites of the system worked normally and were on the verge of collapse. In August 2001, the Russian government adopted the GLONASS Recovery and Modernization Plan for the period 2002-2011. The first modern satellite GLONASS-M was successfully launched in December 2001.Until 2012, the system returned to full service with 24 satellites.

By 2020, GLONASS has three generations of satellites: the first generation of satellites is the traditional GLONASS basic model; the second generation of satellites is the GLONASS-M modern satellite; the third generation is the newly developed GLONASS-K satellite, and the K satellite series is divided into K1 and K2 models.

The GLONASS constellation consists of 24 satellites in three orbital planes. Its conventional signals use frequency division multiple access (frequencydivision multiple access, FDMA) instead of code division multiple access (code division multiple access, CDMA) as used by other GNSS.Like conventional GPS signals, GLONASS signals include two pseudo random noise code (PRN) ranging codes: ST) code and high precision (Visokaya Tochnost, VT) code are modulated onto L1 and L2 carriers.GLONASS ST codes have also been transmitted on the L2 frequency of the GLONASS-M satellite. The transmitted signal is a right-handed circularly polarized wave like a GPS signal. GLONASS-K1 transmits CDMA signals on the new L3 frequency (1202.025MHz), and GLONASS-K2 will also provide CDMA signals on L1 and L2 frequencies, enabling compatibility and interoperability with other GNSS.The signal-in-space space user range errors (SISRE) of GLONASS-K1 satellite is about 1 meter, while that of GLONASS-K2 satellite is 0.3 meter.

Galileo system

European global navigation satellite systems (E-GNSS) is Galileo.Galileo's first and second experimental satellites, GIOV-A and GIOV-B, were launched in 2005 and 2008 to verify key technologies, followed by four working satellites to verify technologies related to Galileo's space and ground segments. Design and on-orbit verification (IOV)After the completion of the phase, the deployment of other satellites will be further carried out, and it is planned to reach the full operational capability (FOC) of 24 satellites in 2018-2020.

Galileo also consists of a space segment, an operation and control segment, and a user segment. The constellation has 24 satellites in three medium Earth orbit planes. The main frequency bands of Galileo signal operation are E1, E5 and E63. Each of them transmits an independent signal with the center frequencies of 1575.42, 1191.795 and 1278.75 MHz, respectively. E5 is divided into two sub-signals, E5a and E5b.To achieve compatibility and interoperability with GPS, the center frequencies of Galileo's E1 and E5a2 signals coincide with GPS's L1 and L5. Galileo's E5b coincides with GLONASS's G3 signal center frequency for the same purpose of compatibility and interoperability.

Although the information provided by Galileo is still position, speed and time, the types of services provided by Galileo are far more than those provided by GPS. GPS only has two kinds of civil standard positioning service (SPS) and military precision positioning service (PPS), while Galileo provides five kinds of services, namely:

(1) open service (OS), which is similar to SPS of GPS and is provided free of charge;

② Life safety services (safetyof life service, SoLS);

③ commercial service (CS);

④ public regulated service (PRS);

⑤ search and rescue support service (SAR).

The first four are the core services of Galileo, and the last one is to support the search and rescue satellite (SARsat) service. Due to the difficulty of the actual operation of life safety services, it has not been mentioned in recent years. Even so, the Galileo service is more varied and unique, providing integrity broadcast, service assurance, and civilian control and local area enhancement.

Galileo's public service provides free positioning, navigation and timing services for the public navigation market. Life safety services may be compatible with ICAO (International Civil Aviation Organization) Standards and Recommendations (standards and recommendedpractices, SARPS).It is comparable to the "vertical guidance method" and provides integrity information. Commercial service is a value-added service for public service, which has the authentication function of encrypted navigation data and provides guaranteed service commitment for professional applications of ranging and timing. Public licensed services are dedicated to European/national security applications, licensed or critical applications, and activities of strategic importance, where satellite signals are more reliable and robust and are controlled by Member States.The public service positioning accuracy provided by Galileo is usually 15 ~ 20 meters (single frequency) and 5 ~ 10 meters (dual frequency). It can reach 1 meter when the public concession service has local enhancement, and it can reach 0.1 to 1.0 meter when the commercial service has local enhancement.

Other systems

In addition to the four global systems mentioned above, it also includes regional systems and augmentation systems, among which the regional systems include QZSS of Japan and IRNSS of India, and the augmentation systems include WASS of the United States, MSAS of Japan, EGNOS of the European Union, GAGAN of India and NIG-COMSAT-1 of Nigeria.