Mobile positioning principle-gps/glonass/Beidou + WIFI + Base Station

Satellite positioning System-gps/glonass/Beidou:

About GPS, GLONASS, Beidou, Galileo system of popular Science please Google itself.

GPS is the most widely used global positioning network and is standard for almost all smartphones. In a few years, Russia's GLONASS positioning function also gradually joined the smart phone chip, and GPs to form a dual positioning system, positioning speed greatly improved. China's self-developed Beidou navigation system, also began to appear in some high-end models. As for the Galileo system in Europe, there is no phone support.

The advantage of satellite positioning system is that the accuracy is high, the error is usually within 15 meters. The GPS chip will receive the synchronization signal of many satellites in the sky, then calculate the specific latitude and longitude according to the phase difference of the signal. It is one of the core technologies of GPs to keep multiple satellite signals in sync and control the error below nanosecond level.

It is the famous GPS application Gpstestplus of Android platform, can see this machine supports GPS and GLONASS dual positioning System (dot is GPS satellite, triangle is GLONASS satellite), and positioning satellite projection on the celestial sphere.

WiFi Location:

The router will broadcast the SSID by default (unless the user manually configures the feature to turn off), and the broadcast frame contains the MAC address of the router. At this time, the acquisition device for MAC information acquisition and signal strength information collection, and upload to the server, after the calculation of the server, save as "mac-latitude and longitude" mapping. Google's street-view collection, for example, was once classified as illegal in Germany because of privacy concerns. At home, through the backdoor function collection of the user's smartphone application, it is the main way for the data company to obtain "mac-latitude and longitude" mapping information. In general, the user around will have multiple WiFi signal source, at this time the phone will silently resolve all WiFi MAC address, if some WiFi information in the database already exists, you can according to the signal strength, deduced the latitude and longitude of unknown WiFi. If there is no known wifi, and the phone happens to be on the GPS, you can also complete the data collection. The user unknowingly collects all the data for the map company. As you can imagine, this amount of data is very large.

Base Station positioning:

The number of base stations is far less than WiFi, and the base station has public location data, so the acquisition is relatively simple.

Precision for multiple positioning pathways:

Satellite Positioning System > WIFI > Base Station (Cellular network). Therefore, the priority is also the highest satellite positioning system.

For Android devices, for example, if the user does not turn off the GPS function, the GPS is preferred, and the clock calibration, latitude and longitude data are read from the GPS module. If also open WiFi and base station, it will use WiFi and base station auxiliary location, reduce the calculation steps of GPS chip, improve the positioning speed, this is A-gps.

If the GPS is turned off, and the WiFi module remains on, the hand can read the MAC address and signal strength of all surrounding WiFi signals and upload it to a company (usually a map provider) server, and the server will return latitude and longitude when queried and calculated. WiFi coverage is generally only within 50 meters, so the positioning accuracy is very close to the satellite positioning system.

If the WiFi module is also turned off, then only the base station (cellular network) is available. At this time the cell phone will receive the cell ID of the base station, upload to the server query, the server also returns latitude and longitude. But at this time the accuracy is poor, the error is generally above 100, after all, the base station coverage is also very large, only by the signal strength is difficult to calculate the precise position.

Note that the Wi-Fi and the base station method, all need to network, or how do you contact the server? However, when the WiFi module is turned on, WiFi scanning and information acquisition can be done without having to connect to an AP, and the base station is the same, without having to turn on the cellular network. Because a query request is made to the server, it can take both cellular data traffic and WiFi traffic.

In the Apple system, the user cannot control the opening and closing of the GPS module, so the location path will be determined according to the situation. WiFi or base stations are automatically used indoors.

Mobile positioning principle-gps/glonass/Beidou + WIFI + Base Station