[series of troubles caused by inaccurate positioning] Part 2: what's wrong with the weak satellite signal

For each use of mobile navigation App For users of , What I'm most afraid to hear is “ The satellite navigation signal is weak ” This tip , Because that means the location is inaccurate , Users may not be able to get accurate guidance . So what's the matter with the weak signal ？ There is no shelter , Why can't you get the signal . Today, let's briefly talk about the causes of weak signal , And ways to avoid it .

At present, the time when Gaode map broadcasting signal is weak , During navigation , The mobile phone did not report the satellite positioning results . We analyze the problem of weak signal , Here's why ：

so , In most cases （80%）, Indeed, the satellite signal is weak , Not enough for satellite positioning , In a few cases, the number of satellites is enough , The signal is strong enough , But still unable to locate , The reason may be that the satellite message received by the equipment is abnormal , As a result, the satellite position cannot be calculated smoothly , Or the message information given by different satellites is contradictory , It is difficult to determine the user's real location .

that , What causes the device to fail to find the star , Or we can find stars, but the signal is weak ？ There are two possibilities ：

1. There are electromagnetic interference sources around the mobile phone , Cause satellite signals to be masked under other signals , Unable to lock satellite . Satellite signals from 2 From a satellite 10000 kilometers away , When it reaches the ground, the signal strength has been seriously attenuated , And 4G/5G Signal comparison , Its strength is only 4G/5G One trillion times the signal , Therefore, the satellite signal receiving antenna in your impression is generally like this ：

Ordinary users do not have this condition , At least it has to be a star chain

But in fact, for mobility , Positioning satellite antennas are made very small , such as

This size still can't be made into a mobile phone , The antenna in the mobile phone looks like this

The antenna becomes so small , The signal reception effect must be much worse , Therefore, the positioning signal has done a lot of processing in the design , So that it can be recognized and decoded even if it is very weak . The main method , Is to reduce the data transmission rate （ According to Shannon's Theorem ）, Send a bit longer , Final GPS The data transmission rate of is only 50Bit/ second , To send a complete location message, you need 6 second . As a contrast ,5G The data rate can reach Gb/s. For all that , There is still a certain probability that the terminal equipment cannot successfully read the satellite message , Especially in the strong electromagnetic environment .

Strong electromagnetic environment is not near the high-power signal source in our imagination , Because the location signal is very weak , Any signal source may interfere with the positioning signal , Especially in the frequency band of positioning signal , Mainly 1.1G-1.6GHz This interval , There are many interference sources in this section , The harmonics of some other frequency band signals will also interfere with the positioning signal , For example, all kinds of electronic equipment in the car .

Now some mobile phone manufacturers are making some detection tools to identify the interference source on the car , Before this function is improved , Ordinary users can try to change the placement of mobile phones in the car , For example, stay away from the center console , Put it close to the windshield , See if the signal can be restored . Be careful , Because a satellite message needs 6 Seconds to read , So after changing the position, you need to wait a few seconds to see the effect . If conditions permit , You can walk out of the car , Completely eliminate the interference in the car . If it can be outside the car, it can't be inside the car , It means it's not the problem of the mobile phone .

A digression ,Spacex After launching the satellite chain , Many people imagine , In the future, whether you can directly use your mobile phone to make satellite calls , In principle, it's not very realistic , Although the orbit of satellite chain is much lower than that of positioning satellite （ Hundreds of kilometers vs 2 Thousands of kilometers ）, But signal attenuation is inevitable , Even if you can receive satellite signals , Its data rate is also very low , More difficult is to let the satellite receive the signal of the mobile phone （ The positioning signal is completely unidirectional , Mobile phones don't need to send messages in reverse ）. The method given by iridium before is to equip it with a huge antenna . This may be a way to solve the problem of weak signal in the future （ Add a jack to the phone , You can connect an external antenna ）

2. If in a completely empty place , I still can't locate it outside the car , And there are no other electronic devices around , The big probability is the problem of mobile phones . In this case , Only through “ Restart the solution ” To solve the . Many users will try to navigate again after a problem , Or restart the map App, In fact, this method probably doesn't work , Because at this time, the mobile phone system cannot locate , Not a map App Unable to locate , restart App There is no effect .

According to our observation , Mobile phones of various mobile phone manufacturers , There are such problems in varying degrees , This is mainly affected by GNSS Chip and antenna influence , generally speaking , The chip quality of high-end models will be better , The tracking and calculation ability of satellite signals is also stronger , The probability of problems with old models is relatively higher .

Last , If the user cannot find the interference source , I don't want to restart my phone , There's no way to navigate ？ Of course not. , Goldmap has done a lot of work to optimize the navigation experience under weak signals . from 2019 Year begins , Gaud map is online Intelligent positioning function , It is the ability to provide continuous positioning for weak signal scenes . Intelligent positioning mainly adopts the following capabilities to provide continuous positioning capability ：

• Sensor extrapolation ： Use the accelerometer on your mobile phone 、 gyroscope 、 The geomagnetic meter is used to judge the speed change and direction change of the mobile phone , Then match with the map to judge the current road , So even after entering the tunnel , The logo can also move continuously . This inertial navigation mode is used in 30 High positioning accuracy can be maintained within seconds , No matter how long it takes, it is necessary to combine other positioning methods to maintain accuracy .
• Network point estimation ： Network location is another important location capability on mobile phones , When there is no satellite signal indoors, the positioning is realized through network positioning , The principle is to use the scanned peripheral base stations and Wifi To complete the positioning , Its accuracy is in 30 rice -200 Rice doesn't wait . Usually in the urban area Wifi It's denser , The positioning effect is quite good , You can only rely on base stations in the suburbs or on highways , There will be some jams or delays in the logo update .
• Satellite weak signal solution ： For mobile devices, there are scanning satellites , But the scene that cannot give the positioning results , Golde did some algorithm optimization , In this case, the satellite positioning results can still be provided .