Speaking of GPS, everyone is very familiar with it. As a rising star, China's domestic positioning service, Beidou, referred to as BDS, has now reached the forefront of the world. GPS/BDS, Europe's Galileo positioning system, and Russia's GLONASS are currently the four most widely used positioning services, providing support for a large number of civilian/military equipment. This article will briefly explore what the core of these positioning services is.
First of all, we need to understand where the core positioning data comes from? Of course, it is the satellite, that is, the positioning satellite. If the device wants to obtain its own position, it needs to receive data from at least 4 positioning satellites in the same time period to calculate its own position. Why? The core lies in - distance calculation. Positioning satellites running in extraterrestrial orbits are constantly broadcasting their position, coordinates and other core information to the world at all times. The core function of the GPS chip is to receive this information. It is used to receive and parse all this data.
Second, we need to understand why satellite broadcast data is the core. There is a key piece of information in the positioning satellite broadcast data - time. The satellite uses an extremely high-precision clock to ensure the synchronization of the positioning satellite system. As a ground device, the GPS device will have a key piece of information - time difference after knowing its own time. You can subtract the time in the received information (the time when the satellite sends this broadcast information) from its own time. The time difference obtained is the time consumed by this information during the transmission process. The transmission medium is electromagnetic waves, so naturally use the speed of light as the ideal parameter. The speed of light multiplied by this time difference can get the distance between the current device and the positioning satellite.
Third: You need to understand how the distance data described in the previous article is converted into your own coordinates. As mentioned in the previous article, you need to receive data from at least four satellites to calculate your own coordinates. In three-dimensional space, a satellite is a point. Its position is known, and the current device's position from the satellite is known. Then the point that meets the distance from the satellite is a circle. Then the second satellite data, the third, and the fourth satellite data are the second, third, and fourth circles. The intersection of these four circles is the point that satisfies the distance to the four satellites at the same time. It is equal to the calculated distance. That is, calculating such a point in three-dimensional space requires three sets of satellite positions and distance data, so at least four are required. But it is better to receive more sets of data. Why? Because of the error, even if the satellite uses the most accurate clock, there will be a small error. At the same time, its own position information will also have errors. Then there is the data, that is, the speed of electromagnetic waves passing through the earth's ionosphere during transmission will have a large deviation from the speed of light. At the same time, the GPS's own time deviation, receiving speed deviation, calculation time deviation, etc. will be magnified many times in the calculation. It is true that a slight difference leads to a huge error. Therefore, at least one or more sets of data need to be introduced. These data are used to correct the deviation in the calculation.
Then there are the emotions about the rise of Beidou in recent years. On July 7, 1993, the famous Galaxy incident occurred. A Chinese ship was cut off from GPS service by the United States, causing it to lose its way in the Indian Ocean and had to stop sailing. Under pressure from the United States, it was able to return after accepting the humiliating request of the United States to inspect the ship. China then sought cooperation with Europe's Galileo positioning system, but Europe only had a brief period of intimacy with China. With the resignation of pro-China leaders and pressure from the United States, the cooperation sought with the Galileo system ended in being fooled. But China did not give up. Satellites were launched one by one, and technology was improved again and again. From the most backward to the forefront step by step, China's Beidou system has finally made a name for itself. At present, the positioning accuracy can reach 0.5m when the signal is good. It is the system with the highest positioning accuracy in the world.
