Mobile Phone Positioning principles

Mobile Positioning Technology widely used on mobile phones currently has three types: network-based cell identification and positioning, integrated GPS Positioning and A-GPS positioning.

(1) network-based

That is, the cell identification and positioning technology. The GSM mobile communication network is composed of many cell-like communities, each of which has its own number. Because mobile phone communication complies with the specifications of cellular technology, as long as mobile phones are not in offline mode, it is easy to know which cell phone is located. the positioning accuracy depends on the size of the cell radius of the mobile terminal, ranging from several hundred meters to dozens of kilometers. Compared with other technologies, this technology has the lowest precision and charges a certain monthly usage fee.

(2) Integrate GPS

The Global Positioning System provided by go-Vern-ment. 24 GPS satellites are distributed on 6 track planes, 10 thousand kilometers from the ground, and run around the Earth for 12 hours, so that more than four satellites can be observed at any time on the ground. Integrated GPS Positioning requires the built-in GPS module of the mobile phone. However, this module only has the receive function and does not have the launch function. 24 GPS satellites are constantly transmitting information containing time, satellite points, and other important parameters to the earth. After receiving the information from our mobile phone, the mobile phone calculates the distance from the mobile phone to each Satellite Based on the sequence and time difference of the signals sent by multiple satellites at the same time, and then uses the distance formula in three-dimensional coordinates, the three satellites form three equations to calculate the location of the mobile phone (x, y, z ). Considering the error between the satellite clock and the mobile phone clock, there are actually four unknowns, X, Y, Z, and the clock difference. Therefore, we need to introduce 4th satellites to form four equations for solution, to obtain the longitude and latitude of the mobile phone. In fact, mobile phones can usually lock more than four satellites. At this time, mobile phones can be divided into several groups based on the satellite constellation distribution, each group of four, then, the algorithm selects a group with the smallest error for positioning.

(3) Auxiliary GPS

That is, assist GPS, A-GPS, is a network-assisted global positioning system, this method is actually "cell identification and positioning + integrated GPS Positioning + remote data computing + GPRS Information Transmission ". To assist GPS positioning, mobile operators need to provide the GPS location of their mobile communication tower, and add a location server to the mobile network, GPS reference stations also need to be built on the ground (for real-time satellite observation and providing global real-time star data to positioning servers ).

The GPS positioning process is as follows:

1,The mobile phone transmits the GPS location of the nearest mobile communication tower to the location server over the network;
2,The location server transmits the current GPS calendar information over the mobile communication tower (similar to the mobile phone location) to the Mobile Phone Based on the GPS Position of the mobile communication tower, the information will be immediately stored as a calendar database on drive C of the mobile phone;
3,The mobile phone reads the calendar database and receives specified satellite signals (eliminating the need for heavy signal reception, data computing, and filtering optimal satellite groups );
4,After the mobile phone receives a specified satellite signal, it calculates the distance between the mobile phone and the satellite, calculates the specific location of the mobile phone, and then displays it on the screen;
5,The mobile phone automatically selects a Satellite Based on Time changes (time changes cause satellite offset) and the location changes (the elevation angle changes due to location Movement), and refresh the C-disk calendar database in real time;
6,Repeat steps 3rd, 4th, and 5th on the mobile phone.
7,Description of other important links: ① if the mobile phone has been successfully positioned, the phone drive C will always have a calendar database, and the shutdown or removal of the battery will not be lost. ②. After each secondary GPs start, the system first reads the star database of disk C and then receives the satellite signals specified by the star database. There are three scenarios:. if a satellite signal exists and the specified satellite is still in the air, the system locates immediately without a network prompt, this is the reason why the positioning software can be directly located when the time interval and location movement are not large; B. if there is no satellite signal, the system will always search for the satellite, and no network connection prompt will appear on the screen; C. if a satellite signal exists, but the specified satellite is no longer in the sky, the calendar database becomes invalid. The mobile phone starts to redo all the steps from step 1, and a connection prompt is displayed on the screen.