GLONASS system
The former Soviet Union (now Russia) established a global satellite navigation system similar to that of the United States in the world, called GLONASS. GLONASS stands for Global Navigation Satellite System. It is a satellite navigation system built by the former Soviet Union in the early 1980s. It also consists of three parts: satellite constellation, ground monitoring station and user equipment. It is managed and controlled by the powerful Russian space department. At present, Europe has accurately established 33 global systems, called Galileo, which are under construction from 2005 to 2008. People think that these three systems should be compatible with each other. In other words, users can achieve positioning if they want to capture the signals of any combination of the three systems.
Although GLONASS industry has been built, due to the current economic situation in Russia, it is still unable to spare financial resources to maintain its full operation. Therefore, there are only 1 1 active satellites in GLONASS constellation (6 and 7 of them didn't work normally until March 2003), so its impact is very small.
Note: A refers to GLONASS 88, the first M star of GLONASS, which has not been working normally since its launch.
Americans analyze that GLONASS has problems in technology, management, policies and resources. The source of GLONASS' funds is still unclear. The Russian government stated that the financial responsibility of GLONASS should be paid by the Russian Space Agency and handed over to the National Defense Control System Bureau. The Russian government has also been looking for investment institutions to rebuild the GLONASS system.
(1). Constellation and signal
The satellite constellation of GLONASS system consists of 24 satellites, which are evenly distributed on three approximate circular orbital planes. There are 8 satellites on each orbital plane, with an orbital height of19100km, an operating period of 1 1 hour15min and an orbital inclination of 64.
Different from American GPS system, GLONASS system uses frequency division multiple access (FDMA) to distinguish different satellites according to carrier frequency (GPS is code division multiple access (CDMA), and satellites are distinguished according to modulation codes). The frequencies of the two carriers broadcast by each GLONASS satellite are l 1 = 1, 602+0.5625k (MHz) and L2= 1, 246+0.4375k(MHz), where k = 1 ~ 24 is each. The carrier frequency of all GPS satellites is the same, which is L 1= 1575.42MHz and L2= 1227.6MHz.
Two kinds of pseudo-random noise codes are also modulated on the carrier of GLONASS satellite: S code and P code. Russia has adopted an open policy of both military and civilian use and no encryption for GLONASS system.
GLONASS satellite was put into orbit by Proton carrier rocket. The satellite adopts a three-axis stabilization system with a total mass of 1400kg and a designed orbit life of 5 years. All GLONASS satellites use an accurate cesium atomic clock as a frequency reference. The first GLONASS satellite was launched on June 52002. Up to now, * * * has launched more than 80 GLONASS satellites, the last time was 200 1 12 1, when three satellites were launched. Russia plans to change the broadcasting frequency of the system to GPS frequency and obtain technical support from Merrockwell.
GLONASS system is mainly used for navigation and positioning. Of course, just like GPS system, it can also be widely used in various levels and types of measurement applications, GIS applications and time-frequency applications.
(2).GLONASS positioning accuracy
The single point positioning accuracy of GLONASS system is 16m in horizontal direction and 25m in vertical direction. In order to further improve the positioning ability of Glonass system and open up a broad civil market, the Russian government plans to update it to Glonass-M system in four years. The contents include: perfecting some ground monitoring and control station facilities; Extend the on-orbit life of satellites to 8 years; The high positioning accuracy of the system is achieved: the position accuracy is improved to 10 ~ 15m, the timing accuracy is improved to 20 ~ 30 ns, and the speed accuracy is 0.01m/s. ..
(3) Comparison between 3. GLONASS and Global Positioning System
(4) What are the advantages of 4)GPS+GLONASS dual-system navigation and positioning?
1) Double the number of visible satellites: After the networking of GLONASS satellite constellation is completed, the total number of satellites available for navigation and positioning will double. When the number of satellites visible above the horizon is a pure GPS system, it is generally 7-11; GPS+GLONASS system can reach 14-20. In mountainous areas or cities, sometimes due to obstacles, pure GPS may not work, but GPS+GLONASS can.
2) Improve the production efficiency: In the measurement application, the observation time required for GPS measurement depends on the time required for carrier phase ambiguity resolution. The longer the observation time or the more satellites can be observed, the more data can be used to solve the carrier phase ambiguity, and the better the reliability of the solution. In order to improve production efficiency, rapid positioning, real-time dynamic measurement (RTK) or post-processing dynamic measurement are often used. However, in order to meet certain accuracy requirements, the carrier phase ambiguity must be solved correctly. The more satellites can be observed, the shorter the observation time required to solve the carrier phase ambiguity, so GPS+GLONASS can improve the production efficiency.
3) Improve the reliability of observation results: The reliability of observation results measured and positioned by satellite system mainly depends on the number of satellites used in positioning calculation. Therefore, GPS+GLONASS will greatly improve the reliability of observation results.
4) Improve the accuracy of observation results: The geometric distribution (DOP value) of observation satellites relative to stations directly affects the accuracy of observation results. The more satellites can be observed, the geometric distribution of observation satellites relative to stations can be greatly improved, thus improving the accuracy of observation results.
Global satellite navigation system in Europe (Galileo)
2. 1. Galileo plan
Galileo system is an independent global multi-mode satellite positioning and navigation system in Europe, which provides high-precision and high-reliability positioning services and realizes completely non-military control and management. Galileo system was initiated by ESA and the European Union, and received a lot of financial support. It can not only make Europe get rid of its dependence on the United States and Russia in traffic management and telemetry facilities construction, but also bring huge economic benefits to European equipment manufacturing and application services and create many new employment opportunities.
Galileo system can be compatible with American GPS and Russian GLONASS. In the future, any user can collect the data of each system or the combination of data of each system to meet the requirements of positioning and navigation. Galileo system can distribute real-time meter-level positioning accuracy information, which is not available in existing satellite navigation systems. At the same time, Galileo system can guarantee to provide services under many special circumstances, and users can be notified within a few seconds if something goes wrong. The application of Galileo system is especially suitable for occasions with special requirements for safety, such as running trains, navigation vehicles and aircraft landing.
2.2. System composition
Galileo system consists of four parts: space part, ground part, user part and environment part.
Spatial segmentation
It consists of 30 MEO satellites distributed in three orbits, with 10 satellites on each orbital plane, 9 in normal operation and 1 satellite in standby operation; The inclination of the track surface is 56 degrees.
Ground part
Comprises a global ground control part, a global ground task part, a global regional network, a navigation management center, ground support facilities and ground management institutions.
user group
User segmentation is mainly user receivers and their equivalent products. Galileo system will consider to form a composite satellite navigation system with GPS and GLONASS navigation signals, so the user receiver will be a versatile and compatible receiver.
Environment section
The environmental part usually includes ionosphere, troposphere, multipath effect and radio interference.
2.3. The Galileo Plan is being implemented.
On March 26th, 2002, the transportation ministers of EU 15 countries unanimously decided to officially launch the Galileo satellite navigation and positioning system. This indicates that Europe will have its own satellite navigation and positioning system in 2008, and will end the situation that the US Global Positioning System (GPS) dominates the world.
The total investment of Galileo's planned construction is about 3.25 billion euros, of which the start-up definition phase will cost 1. 1 billion euros, and the European Space Agency and the European Union will bear 50% respectively. Another 210.50 billion euros is the cost of system development and full deployment, including launching 30 satellites. The European Commission hopes that private enterprises can bear at least two-thirds of the costs. Some experts in the European Union said: "Galileo system not only has more satellites than GPS, but also can measure ground objects with an accuracy of 1 cm, with a much smaller error range, and its performance is safer, more accurate and more reliable than GPS. By establishing this system, the EU will greatly promote the development of the European space industry. "
The Galileo plan of the European Union has been brewing for a long time. As early as the 1990s, the European Union has been studying and demonstrating the feasibility of this plan, and more than 65,438+000 enterprises from EU member countries have participated in this work. In June 2000, at the World Radiocommunication Conference, the European Union finally obtained the L-band frequency resources needed to implement Galileo, which created the necessary conditions for Galileo's smooth implementation. In 2006 10, the European Space Agency decided to allocate 550 million euros for the technical development of Galileo. On March 26th, 2002, the European Union once again expressed its determination to start the Galileo project at the Barcelona Summit. At this meeting, the transport ministers also decided to take out 450 million euros from the EU's disposable finance.
Galileo project is a global satellite navigation and positioning system project in Europe, aiming at building GPS independent of the United States. The European Space Agency and its member country France are the most active advocates of this plan. After the completion of this plan, Europe will not only have its own satellite positioning system to provide guaranteed navigation and positioning services for roads, railways, air and sea vehicles, but also gain industrial and commercial benefits and win conditions for establishing a European security and defense system. Palazzi O, a senior EU official in charge of transportation and energy, pointed out: "We think it is very important to have one more system in space, because it is also good news for Americans. We want them to know that once the GPS system is attacked, they can rely on the Galileo system of the European Union. "
2.4. What are the differences and advantages between Galileo and GPS?
It is reported that the Galileo satellite positioning system will be composed of 30 orbiting satellites with an orbital height of 24,000 kilometers and an inclination of 56 degrees, which are distributed on three orbital planes, and each orbital plane carries 9 working stars and 1 in-orbit backup stars. Galileo will provide users with accurate positioning services with an error of no more than 1 m.
Compared with GPS, Galileo has great differences and advantages. For example, Galileo system has a large number of satellites, high orbital position and few orbital surfaces; Galileo is more used for civil use, and it can provide three kinds of signals for ground users: free signals, encrypted signals that need to be paid for, and encrypted signals that need to meet higher requirements. Its accuracy is improved in turn, the highest accuracy is 10 times higher than that of GPS, and even the signal accuracy for free use reaches 6 meters. If GPS can only find the street, Galileo can find the garage door. Therefore, Galileo users can choose according to their own needs, and the positioning accuracy is better than GPS. In fact, the biggest difference between Galileo and GPS is that its service is guaranteed, giving users a sense of practicality.
European satellite augmentation system EGNOS
According to the plan of ESA, the implementation phase of EGNOS began with 1998, and its prototype satellite experimental bed (ESTB) was put into use in February 2000. EGNOS uses additional information to enhance GPS and GLONASS to ensure the accuracy and perfection of multimodal transport application. It is a kind of GNSS implemented in Europe, and it is the basis for the future development of satellite navigation system services. The space part of EGNOS consists of navigation transponders installed on synchronous satellites Inmarsat III AOR-E and IOR and ESA Artimis satellite.
China's navigation and positioning satellites
In 2000, China successfully launched two navigation and positioning satellites, named "Beidou Navigation Test Satellite". According to the satellite launch bulletin, China will establish the first generation navigation and positioning system to meet the needs of all-weather regional independent satellite navigation system. Its satellite navigation and clock information can be used in many fields, such as road and railway transportation, as well as marine applications.
Inmarsat (International Maritime Satellite Organization)
For a long time, Inmarsat has been hoping to realize the plan involving 36 satellites, including GPS enhancement, to serve global logistics tracking and management, as well as global voice and data communication. Due to the huge investment, the plan will take 20 years to implement. This international management model, called GNSS, hopes to build a network that combines Inmarsat capabilities with GPS, GLONASS and Galileo.
Japan Global Navigation Satellite System
Japan has developed a new global navigation system (MTSAT) and a satellite augmentation system (MSAS). They hope that when the system is extended to Asia and other regions, it can improve flight safety and save a lot of transportation costs. Using the same concept of GPS augmentation in the United States, MSAS and WAAS can provide seamless and accurate navigation between the United States and Japan.
The services of Qualcomm, Rockwell International and American Mobile Satellite AMSC Company use location information to provide services for land fleet and sea fleet respectively. Qualcomm's system is called OmniTracs and OmniExpress. The former provides two-way communication, automatic vehicle positioning, comprehensive dispatching and background integration capabilities, while the latter provides voice and two-way data communication capabilities and GPS vehicle positioning services.
GPS enhanced service of private equity fund
In addition to the GPS system, which is usually controlled by the government, some private enterprises are also considering establishing private GPS enhanced constellations, including companies such as Synchronetics, Hughe and Boeing. Synchronetics proposes to establish a regional positioning system, in which 12 synchronous satellites working in six locations transmit GPS L 1 and L2 signal frequencies, and establish three international user coverage areas: North America, South America and Central America, Europe, Africa and the Middle East, and Asia-Pacific region.
Hughes Space and Communication Company has designed the 14+ 1 medium orbit or synchronous satellite system to provide global coverage of GPS L 1 and L2, as well as navigation, communication and GPS enhancement services. Boeing Company sent a letter to FCC in 1998, planning to manufacture, launch and operate a constellation consisting of 16 medium-orbit satellites. At the same time, it provides ground-based services, aviation industry communication and GPS enhancement, and provides communication, navigation and air traffic investigation services by using GPS L 1 and 2GHz frequency bands.
Other navigation modes
There are a series of navigation methods available, including Roland -C, TACAN (Tactical Air Navigation) and microwave landing system. These ground systems cannot provide DGPS accuracy, and in the long run, they can only be backup applications. They can enhance the satellite navigation system, but they are irreplaceable.
conclusion
To sum up, we can draw the following conclusions:
(1). Satellite navigation system is one of the national infrastructures that the information society must have, especially in China, a developing country with vast territory, rich resources, large population and rapid economic growth.
(2) No single satellite navigation system can guarantee people to use it at any time and place. Therefore, while actively creating conditions to establish their own systems, we should also seriously carry out international cooperation to win the initiative of multi-system interaction and * * *, which is also one of the driving forces for our participation in Galileo cooperation;
(3) In the process of designing modern satellite navigation system, we should adhere to the guiding principle of keeping pace with the times and have a sense of technological advancement. Therefore, like Galileo's plan, we should take the environment segment as the four components of the satellite navigation system, and compare it with the space segment, the ground control segment and the user segment, so as to make the new generation system more accurate, more functional and better, and cooperate with Galileo to engage in more distinctive and advantageous work;
(4) The purpose of establishing satellite navigation system is application, so the application service should be put in the first place at all times, which is the essence of market orientation that is usually emphasized. In fact, from the literature analysis of Galileo's definition stage, its ground control part is divided into three aspects: global, regional and local. In fact, the latter two aspects are for application services, and infrastructure is for better application services. In fact, it may be more scientific and practical to combine these two aspects with the user segment (equipment), which is called application segment, and then classify them into four components of satellite navigation system (space segment, environment segment, ground control segment and application segment). After all, application is service. Since the beginning of GPS, two services have been mentioned: standard positioning service (SPS) and precise positioning service (PPS), and Galileo provided more services, up to five. In fact, Galileo's full name is "European satellite navigation service", which shows how good his intentions are. I have to say it again here: "The application of service in satellite navigation system is just one of them."