Satellite Positioning System GPS Beidou GNSS difference

2018/1/15 18:55:49

Compass satellite navigation system (BDS)


"Beidou" more and more into the public horizons, on November 5, 2017, Long March III B carrier rocket, "One Sword Double Star" successfully fired the first 24, the 25th Beidou Navigation Satellites . "Beidou" is a global navigation satellite system independently developed, independently developed and operated independently by China.


Taking this mission as a starting point, by the end of 2018, 18 Beidou satellites will be launched and their service areas will cover the countries along the "Belt and Road" and their neighboring countries. By 2020, the network of 35 Beidou-3 satellites will be completed , To provide related services worldwide.


Global Positioning System (GPS)


Global Positioning System (GPS) is a US military dual-purpose navigation and positioning satellite system. GPS transmits dual-frequency navigation signals at frequency L1 = 1575.42MHz and modulates P (Y) and C / A codes in an orthogonal manner. When L2 = 1227.60 P (Y) code is modulated at the frequency of MHz, additional delay due to ionospheric correction by dual-frequency transmission.


Among them, the C / A code rate of 1.023Mbps, corresponding to 43dB processing gain, P (Y) code rate of 10.23Mbps, processing gain of 53dB, GPS signal to the ground maximum signal does not exceed -153dBW.


The information it sends to the user receiver includes satellite status, satellite ephemeris, satellite clock bias correction parameters, and time.


Global Navigation Satellite System (GNSS)


This is a general term, in addition to GPS, GLONASS, GALILEO and BDS four navigation satellite systems, including Japan's MSAS, India's GAGAN and Nigeria's NIG-GOMSAT-1 and so on.


Therefore, GNSS is a star-level radionavigation system that uses artificial satellite as a navigation station and provides all-weather and high-precision position, velocity and time information for all kinds of military and civilian carriers in the world on land, sea, air and sky. It is also called space-based positioning, Navigation and timing system.


Why does satellite positioning need at least four?


According to the principle of three-ball intersection point, the user terminal receives the satellite information through passive and calculates the distance to the satellite according to the time difference. According to the three-dimensional distance formula, the location information of the user terminal is obtained by using the three equations. In principle, three satellites Can achieve the purpose of positioning.


However, the satellite clock and the clock used by the user terminal are not synchronized, and the distance can not be accurately calculated by using the time difference. Therefore, the fourth satellite is needed to calculate the clock error, and further converted into latitude, longitude and altitude according to the calculated three-dimensional position. Specific technology can refer to professional books.


"Bei Dou system" unique technology


"Big Dipper," the biggest feature is the navigation and communications are closely linked, which is not available in other navigation systems. For example, in the desert, prairie and other places, cell phones can not be used, "Beidou" can play an important role.


Beidou the third is the use of tri-band signals, you can better eliminate the ionospheric effects, improve positioning reliability, enhance data pre-processing capabilities, greatly improving the ambiguity of the fixed efficiency.


Beidou "positioning accuracy will be raised to 2.5 meters to 5 meters level, with the Beidou foundation enhancement system to provide initial services, can provide the rice level, sub-meter, decimeter level, or even centimeter level service (and so on no doubt ..).


BeiDou terminal can be reported through the location of the message, the management center through the user's location report, at any time to grasp the location of each terminal. As a result, the cost of such a chip can be reduced after the many ideas, such as sharing bicycles, "BeiDou Cai", the elderly children's positioning watches, "Beidou + logistics", "Beidou + payment", the new "Beidou +" life The first mode of production, do not let the imagination limit its application ...


The Beidou-3 satellite network, laying an "inter-satellite link" in space, can be connected to all the satellites in the constellation without relying on global stations, and the satellite can continue to provide services even if it is disconnected from the ground.