For every mobile navigation App user, the most dreaded reminder is “weak satellite navigation signal”, because it means that the location is not correct and users may not be able to get accurate guidance. So what about the weak signal? I can’t get a signal when there’s no cover. Today we briefly talk about the cause of weak signal, as well as the method to avoid.
At present amap broadcast weak time, during the navigation process, the mobile phone did not report the satellite positioning results. We have made an analysis on the problem of weak signal, the reasons are as follows:
Visible, in most cases (80%), is indeed a satellite signal is weak, not for satellite positioning, a few cases satellite number is enough, the signal is strong enough, but I still can’t locate, reason could be that the device receives satellite abnormal packets, calculated cause cannot successful satellite location, or different satellite are inconsistent message information, It is difficult to determine the real location of the user.
So, what’s the reason why the device can’t find stars, or it can find stars but the signal is weak? There are two possibilities:
**1. There are electromagnetic interference sources around the mobile phone, so that the satellite signal is covered by other signals and the satellite cannot be locked. ** The satellite signal is sent from the satellite 20,000 kilometers away, and the signal strength has been seriously attenuated when it arrives at the ground. Compared with 4G/5G signal, its strength is only 1/1 trillion of 4G/5G signal, so the impression of satellite signal receiving antenna is generally like this:
Regular users don’t have that, at least not with Starlink
But in fact, for mobility, GPS satellite antennae are made very small, like
That’s still not the size to fit a cell phone, the antenna in a cell phone looks like this
With antennas getting so small, reception is bound to be much worse, so positioning signals are designed to be recognized and decoded even if they are faint. The main method is to slow down the data transmission rate (according to Shannon’s theorem) and take longer to send a bit, resulting in a GPS data transmission rate of only 50 bits per second, and a complete location message takes six seconds to send. For comparison, 5G will have a data rate of gigabytes per second. However, there is a certain probability that the terminal device will fail to read the satellite message, especially in a strong electromagnetic environment.
Strong electromagnetic environment near the power source is not our imagination, because of the positioning signal is very weak, any signal may cause interference to positioning signal, especially the positioning signal spectrum, main is 1.1 G – 1.6 GHz this interval, the interval of the interference sources, some other harmonic spectrum signal will interfere with the positioning signal, Like all the electronics in the car.
At present, some mobile phone manufacturers are making some detection tools to identify interference sources in the car. Before this function is perfected, ordinary users can try to change the position of mobile phones in the car, such as away from the central console, near the windshield, to see whether the signal can be restored. Note that since a satellite message takes 6 seconds to complete, it takes several seconds to see the effect after changing position. Conditional words, you can go out of the car, completely eliminate the interference in the car. If it works outside the car but not inside, it’s not the phone.
Said a digression, capsules after satellite launched star chain, a lot of people think, whether can use mobile phones directly play after satellite phone, tell from the principle of not too realistic, actually, although the satellite orbit star chain positioning satellite orbit that are lower than many (hundreds of kilometers vs 20000 km), but the signal attenuation is inevitable, even to receive satellite signals, Data rates are also very low, making it harder for satellites to pick up the phone’s signal (the GPS signal is completely one-way, so the phone doesn’t need to send a message backwards). Iridium’s previous solution was a giant antenna. This could be a future solution to the problem of weak signal (add a jack to the phone for external antenna)
**2. If you are in a completely open area and still can’t locate outside the car, and there are no other electronic devices nearby, it is most likely that the mobile phone problem. ** In this case, the only solution is to restart the system. Many users will try to re-navigate or restart the map App after problems occur. In fact, this method is probably useless, because at this time, the mobile phone system cannot locate, rather than the map App cannot locate, and restarting the App has no effect.
According to our observation, mobile phones from various mobile phone manufacturers have different degrees of such problems, which are mainly affected by GNSS chips and antennas. Generally speaking, high-end models use better chip quality, satellite signal tracking and calculation ability is also stronger, while the probability of problems with older models is relatively higher.
Finally, if the user can’t find the interference source and doesn’t want to restart the phone, there is no way to navigate? Of course not. Amap has done a lot of work to optimize the navigation experience for weak signals. Since 2019, Amap has launched the smart location function, which is the ability to continuously locate a scene with weak signal. Intelligent positioning provides continuous positioning by using the following capabilities:
- Sensor calculation: The accelerometer, gyroscope and geomagnetometer on the phone are used to determine the speed and direction changes of the phone, and then map matching to determine the current road, so that the logo can continue to move even after entering the tunnel. This inertial navigation method can maintain high positioning accuracy for up to 30 seconds, and for longer periods of time, it is necessary to combine with other positioning methods to maintain accuracy.
- Network point calculation: Network positioning is another important positioning capability of mobile phones. When there is no satellite signal indoors, the positioning is achieved through network positioning. Its principle is to complete the positioning by using the scanned surrounding base stations and Wifi, with the accuracy ranging from 30 meters to 200 meters. Generally, Wifi in urban areas is more intensive, and the positioning effect is better. In suburbs or expressways, we can only rely on base stations, and there will be some delays or delays in the update of car signs.
- Weak signal solution of satellite: For the scenario where mobile devices have detected the satellite but cannot provide the positioning result, Autonavi has made some algorithm optimization, so that the satellite positioning result can still be provided in this case.