When we think of GPS, we naturally think of navigation and positioning, and GPS is almost a basic function in smartphones nowadays. We understand it from the beginning of the car navigation device, cell phone positioning, but its military rolegps gnss module as early as the Gulf War began to shine, its main military role are cruise missiles and precision-guided bombs, to provide favorable conditions for the flight of fighter jets and bomb drops, etc..
Since positioning and navigation are so important, our country should also develop its own satellite navigation system! Of course, it also has a more culturally rich name: Beidou satellite navigation system.
In ancient times, people did not have satellites, nor did they have haze, but they had wisdom. Through observation and thinking, people found that they could use the Big Dipper and the North Star to guide the direction and even the time.
BeiDou Navigation Satellite System, BDS
"BeiDou is increasingly in the public eye, and on November 5, 2017, the 24th and 25th BeiDou-3 satellites were successfully launched by a Long March 3B carrier rocket with "one arrow and two stars". "Beidou is a global navigation satellite system independently developed, developed and operated by China.
Taking this mission as the starting point, by the end of 2018, 18 Beidou satellites will be launched, covering the service area of countries along the "Belt and Road" and neighboring countries; by 2020, the network of 35 Beidou-3 satellites will be completed, providing relevant services to the world.
GPS is a dual-use navigation and positioning satellite system of the United States. GPS transmits navigation signals in dual frequencies, with the frequency point L1=1575.42MHz, modulating P(Y) code and C/A code in an orthogonal way, and modulating P(Y) code at the frequency point L2=1227.60MHz, and correcting the additional delay generated by the ionosphere through dual-frequency transmission.
Among them, the code rate of C/A code is 1.023Mbps, which corresponds to a processing gain of 43dB, and the P(Y) code rate is 10.23Mbps with a processing gain of 53dB, and the maximum signal of GPS signal reaching the ground does not exceed -153dBW.
The information it sends to the user receiver includes satellite status, satellite ephemeris, satellite clock deviation correction parameters and time, etc.
This is a collective term that includes the four major navigation satellite systems, GPS, GLONASS, GALILEO and BDS, as well as Japan's MSAS, India's GAGAN and Nigeria's NIG-GOMSAT-1.
So GNSS is a star radio navigation system using artificial satellites as navigation stations, providing all-weather, high-precision position, velocity and time information for all kinds of military and civilian carriers on land, sea, air and sky around the world, also known as space-based positioning, navigation and timing systems.
According to the principle of three-sphere intersection and fixed point, the user terminal receives satellite information through passive and calculates the distance to the satellite by itself according to the time difference, and relies on three equations to get the location information of the user terminal according to the distance formula in three dimensions, and in principle, three satellites can be used to achieve the purpose of positioning.
However, the satellite clock and the clock used by the user terminal are not synchronized, so the distance cannot be accurately calculated by the time difference, so a fourth satellite is needed to carry out the solution of the clock difference, and then further convert to latitude, longitude and altitude according to the calculated three-dimensional position. The specific implementation technology can be found in professional books.
The most important feature of "Beidou" is the close combination of navigation and communication, which is not available in other navigation systems. For example, Beidou can play an important role in places such as deserts and grasslands, where cell phones cannot be used.
Beidou-3 uses a triple-frequency signal, which can better eliminate the influence of the ionosphere, improve positioning reliability, enhance data pre-processing capabilities, and greatly improve the efficiency of fuzziness fixing.
The positioning accuracy of Beidou will be improved to 2.5 meters to 5 meters, and with the initial service provided by the Beidou ground-based augmentation system, it will be possible to provide services at the meter, sub-meter, decimeter, and even centimeter levels (wait a little longer...). .
Beidou terminals can report their location through short messages, while the management center keeps track of the location of each terminal through the user's location report. In this way, when the chip cost comes down, there will be many ideas, such as bicycle sharing, "Beidou dishes", location watches for the elderly and children, "Beidou + logistics", "Beidou + payment "Don't let your imagination limit its application...
The Beidou-3 satellite network, which lays an "inter-star link" in space, can be connected to all the satellites in the constellation without relying on global stations, and the satellites can continue to provide services even if contact with the ground is broken.