Comparison of BeiDou generation and GPS Technology

Now the second generation of BeiDou has gradually matured. The second generation of BeiDou, like GPS, is a passive Positioning System, which is different from that of the second generation of BeiDou. What are the technical features of the Beidou generation:

1. Coverage: the Beidou Navigation System is a regional navigation system covering China. Covering the east longitude about 70 ° A 140 °, north latitude 5 ° A 55 °. GPS is a global all-weather navigation system. It ensures that 6-9 satellites can be observed at any location and at any time on the Earth (in fact, up to 11 billion satellites can be observed ).

2. Number of satellites and orbital characteristics: the Beidou Navigation System sets the equator angle distance of the two satellites on the Earth's equator plane to about 60 °. GPS is to set up 24 satellites on 6 orbital planes, 55 ° orbital equator inclination, and 60 ° orbital equator angle. Satellite quasi-synchronous orbit, around the Earth 11 hours a week 58 minutes.

3. Positioning principle: the Beidou Navigation System is a two-dimensional active two-way ranging navigation system. The calculation of the ground center control system allows users to locate 3D data. GPS is a three-dimensional navigation of passive pseudo-code one-way ranging. The User device independently computes the 3D positioning data. The working principle of "Beidou No. 1" has brought two problems: first, the user positioning has lost the concealment of the radio, which is quite unfavorable in the military. On the other hand, because the equipment must contain a transmitter, therefore, it is at a disadvantage in terms of volume, weight, price, and power consumption.

4. Positioning Accuracy: the three-dimensional positioning accuracy of BeiDou Navigation System is about several dozen meters, and the timing precision is about ns. GPS 3D positioning accuracy P code has been increased from 16 m to 6 m, C/A code has been increased from 25-m to 12 m, and the timing accuracy is about 20 NS a few days ago.

5. User Capacity: Because the Beidou Navigation System is an active two-way ranging inquiry-response system, the user's equipment and the Earth's synchronous satellite must not only receive inquiry signals from the ground center control system, user devices are also required to send response signals to the synchronous satellite. In this way, the user capacity of the system depends on the channel blocking rate, inquiry signal rate, and user response frequency permitted by the user. Therefore, the user equipment capacity of the Beidou Navigation System is limited. GPS is a one-way ranging system. As long as the user device receives the navigation message sent by the navigation satellite, the location can be located. Therefore, the User device capacity of GPS is unlimited.

6. survivability: Like all navigation and positioning satellite systems, "Beidou 1" is based on the work of the central control system and satellite, however, "Beidou No. 1" is significantly more dependent on the central control system, because the Positioning Solution Is there rather than completed by the user equipment. To make up for this system vulnerability, GPS is developing the interstellar horizontal data link technology so that GPS satellites can run independently after the master site is destroyed. In principle, the "Beidou No. 1" system removes this possibility. Once the central control system is damaged, the system cannot continue to work.

7. Real-time performance: the Positioning Application of "Beidou No. 1" users should be sent back to the central control system. The central control system calculates the user's 3D location data and then sends it back to the user, in the meantime, it will take a round trip through the earth's static satellite, coupled with satellite forwarding, the processing of the central control system, the time delay will be longer, so for high-speed motion bodies, it will increase the positioning error. In addition, the "Beidou No. 1" satellite navigation system has its own characteristics. Its Short Message Communication function is not available in GPS.

To sum up, the Beidou Navigation System has multiple purposes, including a small number of satellites, a small investment, simple and inexpensive user equipment, and can realize navigation, positioning, and communication in a certain area, it can meet the current needs of China's land, sea and air transportation navigation and positioning. The disadvantage is that it cannot cover the polar regions, and the positioning accuracy near the equator is poor. It can only be two-dimensional active positioning, and user elevation data must be provided, which cannot meet the requirements of highly dynamic and confidential military users, the number of users is limited. But most importantly, the "Beidou No. 1" navigation system is an independent satellite navigation system established by China. Its successful development marks that China has broken the monopoly of the United States and Russia in this field, solved the problem of China's autonomous satellite navigation system. It is a successful, practical, and initial startup system with little investment. In addition, the system does not exclude the widespread use of GPS in the domestic civil market. On the contrary, China's wide-area differential GPS system will be built on this basis. The positioning accuracy of GPS Civil Code receivers affected by SA can be improved from a hundred 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 military's high-tech weapons, there is a growing demand for information support for navigation and positioning. The Beidou Navigation System is only a self-developed and simple navigation system that meets the needs of the Sihua construction in the near future. Therefore, we must learn from the successful experiences of GPS and GLONASS in foreign countries on the basis of the development of "Beidou No. 1, developing China's second generation satellite navigation system, we have reason to believe that in the near future, we will be able to possess advanced, applicability, dual-military and civilian use, anti-interference, anti-destruction, and other features, the "Beidou No. 2", which is suitable for China's national conditions, will be shown in front of everyone, and our satellite navigation system will be more perfect.