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Detailed introduction of Beidou navigation
The abbreviation of Beidou-1 satellite positioning system is BD, and the radio frequency bands registered in ITU are L-band (transmitting) and S-band (receiving). The English of Beidou second-generation satellite positioning system is Compass, and the radio frequency band registered in ITU is L-band.
The basic functions of Beidou-1 system include: positioning, communication (short message) and time service.
The function of Beidou II system is the same as GPS, that is, positioning and timing.
[Edit this paragraph] System working principle
"Beidou-1" satellite positioning measures the distance between the user and the first satellite, and the sum of the distances between the user and the two satellites, thus knowing that the user is at the intersection of a sphere centered on the first satellite and an ellipsoid focused on the two satellites. In addition, the central control system can find the user's elevation value from the digital topographic map stored in the computer, and can know that the user is on an ellipsoid parallel to the earth reference ellipsoid. Therefore, the central control system can finally calculate the three-dimensional coordinates of the user's point, which is encrypted and sent to the user through the outbound signal.
"Beidou-1" covers the heart area between 5-55 north latitude and 70-140 east longitude, the largest part and the smallest part, and the widest part is around 35 north latitude. Its positioning accuracy is horizontal 100 m (1σ), and it is 20 m after setting the calibration station (similar to differential state). Working frequency: 249 1.75MHz system can accommodate 540,000 users per hour.
[Edit this paragraph] Compared with GPS system,
1. Coverage: Beidou navigation system is a regional navigation system covering China. The coverage is about 70- 140 east longitude and 5-55 north latitude. GPS is an all-weather navigation system covering the whole world. It can be guaranteed that 6-9 satellites can be observed anywhere on the earth at any time (in fact, at most 1 1 satellite can be observed).
2. Satellite number and orbital characteristics: Beidou navigation system sets two geosynchronous satellites on the equatorial plane of the earth, and the equatorial angular distance of each satellite is about 60. GPS will set 24 satellites on six orbital planes, with an equatorial inclination of 55 and an equatorial angular distance of 60. The satellite is in quasi-synchronous orbit, circling the earth once 1 1 hour and 58 minutes.
3. Positioning principle: Beidou navigation system is active two-way ranging two-dimensional navigation. The ground center control system solves the calculation of three-dimensional positioning data for users. GPS is passive pseudo-code one-way ranging three-dimensional navigation. The self-positioning solution independently solved by the user equipment is done there rather than by the user equipment. In order to make up for the fragility of this system, GPS is developing the technology of interstellar transverse data link, so that GPS satellites can operate independently when the main control station is destroyed. Beidou-1 system ruled out this possibility in principle. Once the central control system is damaged, the system cannot continue to work.
4. Real-time performance: The positioning application of Beidou-1 user should be transmitted back to the central control system, which will calculate the user's three-dimensional position data and then transmit it back to the user, during which it will go back and forth through the geostationary satellite once, plus satellite forwarding, the processing delay of the central control system will be longer, so the positioning error will be increased for high-speed moving objects. In addition, Beidou-1 satellite navigation system also has its own characteristics, and its short message communication function is not available in GPS.
To sum up, Beidou navigation system has the advantages of few satellites, low investment and simple and cheap user equipment, which can realize navigation and positioning, communication and other purposes in a certain area, and can meet the demand of navigation and positioning for land, sea and air traffic in China at present. The disadvantage is that it can't cover the polar regions, the positioning accuracy near the equator is poor, and it can only be actively positioned in two dimensions, and it needs to provide user elevation data, which can't meet the requirements of highly dynamic and confidential military users, and the number of users is limited to some extent. But the most important thing is that Beidou-1 navigation system is the initial starting system of satellite guidance independently established in China. In addition, the system does not rule out the wide application of GPS in the domestic civil market. On the contrary, China's GPS wide-area differential system will be established on this basis. The positioning accuracy of GPS civil code receiver interfered by SA can be revised from 100 meters to several meters, which can better promote the use of GPS in the people. Of course, we also need to realize that with the continuous development of our army's high-tech weapons, the information guarantee requirements for navigation and positioning are getting higher and higher.
[Edit this paragraph] Double-star positioning is different from "multi-star" positioning.
"A generation of Beidou only uses two satellites for positioning, which is less expensive and faster than GPS," said Model Yao. This is determined by China's national conditions, and it also puts forward special requirements for the technical route of Beidou generation. "So our positioning system has its own characteristics."
Both GPS in the United States and GLONASS in Russia use 24 satellites to form a network (GPS also has 3 spare satellites, while GLONASS lost several satellites due to financial problems). These satellites continuously send back accurate time and position to the ground station. GPS receiver uses the signals sent by GPS satellites to determine the positions of satellites in space, and calculates the distance between them according to the transmission time of radio waves. After calculating the relative positions of at least 3 ~ 4 satellites, the GPS receiver can use trigonometry to calculate its own position. Each GPS satellite has four high-precision atomic clocks and a real-time updated database, which records the current positions and trajectories of other satellites. When a GPS receiver determines the position of a satellite, it can download the position information of all other satellites, which helps it to obtain the information of other satellites more quickly.
"1983, academician Chen Fangyun, winner of the' two bombs and one satellite' meritorious medal, and his collaborators put forward the idea of positioning and navigation by using two synchronous fixed-point satellites. After analysis and preliminary field test, it has been proved to be effective, "said Huang Bingying, a researcher at China Institute of Metrology. This system is called "Double Star Positioning System".
The basic technical route adopted by the first generation of "Beidou" originally came from Mr. Chen Fangyun's idea of "double star positioning" and was formally established 1994. Beidou satellite navigation system can be located by three parts: space satellite, ground control center station and user terminal. The first generation Beidou is different from GPS system, and the calculation of all users' positions is not carried out on satellites, but at the ground central station. Therefore, the ground central station can keep the position and time information of all Beidou users, and be responsible for the monitoring and management of the whole system.
Active and passive are the key differences.
"Beidou uses active positioning, while GPS and GLONASS use passive positioning," said Model Yao. "This is their qualitative difference."
The so-called active positioning means that users need to contact and transmit through the ground central station, so communication does not need to go through other communication satellites, and the multi-purpose satellite conforms to the national conditions of China. GPS and GLONASS have no communication function, mainly because passive positioning without ground station transfer service can not provide communication service.
Regionality is based on the technical level.
Beidou navigation system is a regional navigation system covering China. Ran Chengqi, deputy director of China Satellite Navigation Engineering Center, said that the development of Beidou positioning and navigation system is of great significance. It has some advantages that GPS system does not have. For example, on the basis of static map, the real-time situation of road congestion can be reflected on the navigator.
Beidou is a regional satellite navigation system, which can only be used all day in China and its surrounding areas. Both GPS and GLONASS are global navigation and positioning systems. As long as the satellite signals are not covered or interfered, they can receive the three-dimensional coordinates of any point in the world. "Regionality is determined by the technical characteristics, level and national demand of China's dual-star positioning," said Model Yao.
The space part of GPS and GLONASS is a satellite network with a height of about 20,000 kilometers. The satellites of GPS are evenly distributed in six orbital planes, and the satellites of GLONASS are evenly distributed in three orbital planes, constantly rotating around the earth. In this way, more than four satellites can be observed at any time in the world, and high-precision three-dimensional positioning data can be obtained through them.
Beidou-1 is a geostationary satellite with a high orbit of 36,000 kilometers from the ground. The reason why we have to be at such a high altitude is because we only have two positioning satellites and cannot cover the whole earth. If we orbit the earth in low orbit, we will not be able to monitor our area at some time every day.
The second generation Beidou can be called "China's GPS"
"China will not develop the second generation Beidou in one step, nor will it stop at the first generation and develop the second generation," said Model Yao. "We will continue to supplement the number of satellites, increase functions and improve the overall level on the basis of the first generation." The scientist who will continue to undertake the design of the second generation Beidou said: "The second generation Beidou can be called China's GPS, but it will still have one more communication than GPS, which provides a preparation for China to develop the key technology of the second generation Beidou. For example, Fan Benyao said that the Beidou-1 backup satellite is newly equipped with a laser reflector for satellite positioning, which can be accurately positioned within a few centimeters with reference to other stars. The success of satellite positioning shows that this technology is effective and reliable. In this way, when we constantly launch new satellites to build the second generation Beidou system, many satellites will find their own positions and form a standard network. In addition, the life span of the three stars of Beidou-1 is 8 years, and experts are constantly studying it. It is estimated that the life of the next satellite will reach 10 years. At present, the service life of GPS satellites is about 12 years, while that of GLONASS satellites is 3 to 5 years.
"The most brilliant application of atomic clock in the 20th century is that it constitutes the core of global positioning system," said Huang Bingying, and navigation stars and ground stations cannot do without it. At present, there are three kinds of atomic clocks: rubidium clock, cesium clock and hydrogen clock. The atomic clock with compact structure, high reliability and long service life is the need of the development of global positioning system. Structurally, the minimum volume of rubidium clock has reached 6 cubic centimeters; In terms of frequency stability, hydrogen clock is the best; Cesium atomic clock is the best in terms of long-term frequency stability and accuracy. At present, the cesium atomic clock named "Laser Cooling-Frequency Standard of Cesium Atomic Fountain" is used in the National Time Service Center of China Institute of Metrology, and ——UTC(NIM), the time service standard of China, is provided by it and is constantly calibrated with international standards. When Beidou is completed, all fields of the national economy will benefit more from it.
On May 25th, 2003, China sent the third Beidou-1 navigation and positioning satellite into space in xichang satellite launch center, which indicated that China had the first generation of perfect satellite navigation and positioning system. Beidou satellite navigation and positioning system is the first generation of all-weather and all-weather regional navigation system that provides satellite navigation information. It consists of two working stars and a spare star. The first two Beidou-1 satellites were launched on June 3rd and February 2nd, 2000, respectively.
Beidou satellite navigation system can provide comprehensive services such as positioning, communication and timing for many industries and units with special dispatching and command needs, such as ship transportation, road traffic, railway transportation, field operation, hydrological forecasting, forest fire prevention, fishery production, survey and design, and environmental monitoring.
In 2000, two satellites of Beidou navigation and positioning system were successfully launched, which indicated that China had its own first-generation satellite navigation and positioning system, which was of great economic and social significance for meeting the needs of China's national economy and national defense construction and promoting the development of China's satellite navigation and positioning cause. Beidou navigation and positioning system consists of Beidou navigation and positioning satellite, ground control center and Beidou user terminal.
The service area of Beidou navigation and positioning system is China and neighboring countries. The system can be widely used in many industries, such as ship transportation, road transportation, railway transportation, offshore operation, fishery production, hydrological forecasting, forest fire prevention, environmental monitoring, and other units with special command and dispatch needs, such as the army, public security and customs.
[Edit this paragraph] Three functions of Beidou system
Fast positioning: Beidou system can provide all-weather, high-precision and fast real-time positioning service for users in service area, with positioning accuracy of 20-100m;
Short message communication: Beidou system user terminal has two-way message communication function, and users can send 40-60 Chinese short message messages at a time;
Because the data containing vehicle position and state information is required to be real-time. At the same time, the information communication between the vehicle and the dispatching center is actually a way of data communication, and the amount of information will generally not exceed the length of GSM short messages. Therefore, the short message service of GSM can basically meet the needs of system communication. Secondly, the cost of sending data by SMS is much lower than other ways (such as voice channel).
Compared with other traditional methods such as radio, the GSM short message network system has the following advantages:
1, high speed, good real-time performance, and no dropped calls;
2. Two-way communication is possible, and terminal information can be returned in time;
3. The equipment is small in size and easy to operate;
4, because the control center does not need to set up a high-power transmitting station, the installation cost will be greatly reduced;
5, covering a wide geographical environment.
Accurate time service: Beidou system has accurate time service function, which can provide users with time synchronization accuracy of 20ns- 100ns.
[Edit this paragraph] Beidou satellite positioning system civil service provider
At present, there are five, the best of which are Shenzhou Tian Hong (Beijing Shenzhou Tian Hong Technology Co., Ltd.) and Big Dipper (Beijing Big Dipper Satellite Navigation Technology Co., Ltd.).
The website of Shenzhou Tian Hong Company is: www.chinatopcom.com.
The website of the Big Dipper is www.navchina.com.
[Edit this paragraph] Industry standard for civil terminal equipment of Beidou-1 satellite positioning system
Technical requirements and use requirements of terminal equipment of Beidou No.1 civil vehicle (ship) (standard number is JT/T590-2004)
Technical requirements and use requirements of Beidou-1 civil data acquisition terminal equipment (standard number is JT/T59 1-2004)
Technical requirements and use requirements of terminal equipment on Beidou-1 civil vehicle (ship) (standard number is JT/T592-2004)
[Edit this paragraph] Five advantages of Beidou application
At the same time, it has positioning and communication functions without the support of other communication systems;
Covering China and neighboring countries and regions, with 24-hour all-weather service and no communication area;
Especially suitable for large-scale monitoring and management of group users and data transmission applications of users in unsupported areas;
Unique central node positioning processing and command user machine design can solve "where am I" and "where are you" at the same time;
Autonomous system, high-intensity encryption design, safe, reliable and stable, suitable for key departments.
[Edit this paragraph] Beidou-1 GPS played an important role in the Wenchuan earthquake.
Beidou-1 played an important role in the case of communication interruption.
The Beidou-1 system independently developed by China plays an important role in the case of communication interruption, and the Beidou system carried by the disaster relief forces is sending back various disaster and rescue information one after another.
The navigation and positioning system of Beidou-1 satellite monitored that a unit carrying Beidou-1 terminal set off at noon 12, and quickly advanced from Marcand, Heishui and Lixian to Wenchuan along the 3 17 national road at a speed of about 6 kilometers per hour. It has advanced nearly 40 kilometers in 6 hours and has entered Wenchuan County, about 40 kilometers away from the county seat.
Due to the communication obstruction, the satellite navigation and positioning command center in Beijing initially judged that the unit belonged to the Sichuan Armed Police Corps. The complaint center is learning more about the situation.
[Edit this paragraph] Beidou satellite system will be applied to Beijing Olympic Games for the first time.
From the 2007 Shanghai International Navigation Industry and Technology Development Forum, which opened on February 5, 65438, it was learned that the Beidou satellite navigation system independently developed by China has entered the initial application stage and has regional navigation capabilities. In 2008, the system will be applied to Beijing Olympic Games for the first time. During the Beijing Olympic Games, together with the existing GPS satellite positioning system, it will play a "double insurance" role in the positioning and monitoring of traffic and venue safety.
"At present, the Beidou satellite navigation system has five navigation satellites, some of which will be launched before 2008." Ran Chengqi, deputy director of China Satellite Navigation Engineering Center, said at the press conference that in 2003, China has built the Beidou navigation test system, which has the functions of positioning, timing and transmitting messages to China and its surrounding areas, and has been applied to civil fields such as transportation, fishery, exploration and forest fire prevention. The Beidou satellite navigation system built in the later period has more perfect functions.
It is reported that the 08 system will serve the traffic scheduling or venue monitoring of the Beijing Olympic Games. At that time, it will superimpose its monitoring function with the traffic congestion provided by Beijing traffic department, so that drivers can not only know which route has the shortest distance, but also find a route with the shortest time in combination with the real-time situation of the road. It is estimated that Beidou satellite navigation system will be used in Shanghai 20 10 years ago.
Beidou navigation system is a regional navigation system covering China. Ran Chengqi, deputy director of China Satellite Navigation Engineering Center, said that the development of Beidou positioning and navigation system is of great significance. It has some advantages that GPS system does not have. For example, on the basis of static map, the real-time situation of road congestion can be reflected on the navigator.
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