This article comes from WeChat public account: caoz’s nightmare (ID: caozsay) , author: caozsay

Some things I thought were common sense, but later I discovered that they were not common sense. And when I wanted to share it with everyone, after being dialed by a master, I unexpectedly found that what I know is also biased. With that in mind, write an article.

The origin is the working principle of GPS. I always thought it was common sense. But today I will extend this topic.

I. How is the mobile phone positioned?

There are three methods for mobile phone positioning.

Method 1: Based on the WIFI hotspot you are currently in contact with, if this WIFI hotspot is a publicly searchable hotspot, there is a corresponding address information. Then your position can be locked within a certain radius of that position.

With WIFI positioning , your position can only be confirmed within a certain radius, and it cannot accurately identify your position and speed.

Method 2: Based on mobile base station positioning , your mobile phone signal is interacted through the mobile base station. The geographical location of mobile base stations is clear. When your mobile phone can get signals from multiple base stations, and different base stations have different strength attenuation, then you can get roughly based on the positions of these base stations and your signal attenuation. Your current position range, and approximate movement speed, if you are inside a vehicle with a certain speed.

Method 3: The most accurate is through Satellite positioning You see, although WIFI, base stations, and satellites are specific from near to far; the accuracy of positioning is indeed getting more and more accurate.

Then satellite positioning actually includes different options. In the past, GPS unified the world. Everyone mentioned that satellite positioning is GPS, but in fact there are many different satellite positioning systems. GPS is still the largest in the world. In addition, there are Galileo in Europe, Beidou system in China, etc.

In fact, many domestic smartphones and satellite navigation chips already support the Beidou system. The signs that users see may still be GPS. But the positioning services may actually come from different systems.

Then the phone will automatically select the appropriate system for positioning and navigation based on the signal strength. Generally, users do not need to choose which satellite system to use. So you do n’t need to ask me how to switch to the Beidou system, the phone will be used when it thinks it is appropriate.

Second, the principle of satellite positioning

This is what I think is common sense, but many people have misunderstandings.

First, the satellite doesn’t know where you are and it doesn’t care. Secondly, your mobile phone will not transmit signals to satellites, and positioning and navigation satellites are not responsible for interacting with mobile phone terminals.

Technically, is it difficult for mobile phones to transmit signals to satellites, and it seems not difficult, isn’t it possible to have satellite communication phones, but there are two problems. First, the required power will be relatively large, Occasionally, communication is not necessary. The mobile phone locates in real time. If interactive information is needed, the battery cannot support it. Second, Satellite does not have such a powerful response system. Countless mobile phones worldwide Zhong requests the location. The frequency of this request does not scare people. Put a group of servers on the satellite? Is it possible?

Of course, you said that Musk wasn’t going to engage in global satellite networking, it’s awesome, but at least the current technology cost is too high, which is unrealistic.

Then there is a third, that is, Positioning doesn’t need to be so troublesome.

In fact, the job of navigating satellites is extremely simple, that is, broadcasting, broadcasting your own position and your own time. Each so-called GPS chip (habitually so