How does Beidou system work? It has been pointed out that if the distance between a point with unknown coordinates and the other three points A, B and C can be measured, and the coordinates of the three points A, B and C can be known, the accurate coordinates of the point can be calculated according to the established mathematical model. Beidou system also uses this method, but it only uses two distance values provided by two synchronous satellites located above the equator. The third distance value uses the distance between an unknown point and the center of the earth, which can be obtained by adding the user's own altitude to the radius of the earth. In this way, because the geocentric coordinates are known, the specific coordinates of the user machine can be solved by three distance values and three-point coordinates.

One is Beidou-1 satellite navigation and positioning system.

Beidou-1 satellite positioning system is independently developed by China, which provides users with all-weather and regional satellite positioning system by using geosynchronous satellites. It can quickly determine the geographical location of the target or user, and provide navigation information for users and competent departments.

Second, the satellite function.

The Beidou-1 satellite positioning system is independently developed by China, which uses geosynchronous satellites to provide users with all-weather and regional satellite positioning systems. Its main functions are:

1, positioning

Quickly determine the geographical location of the target or user, and provide navigation information for users and competent departments.

Step 2 communicate

Bidirectional short digital message communication can be realized between users and between users and the central control system.

3. Timing

The central control system regularly broadcasts timing information ("timing" refers to the most accurate time reported by radio signals at a certain time every day), and at the same time provides users with a time delay correction value ("time delay" refers to the time from the speaker to the receiver to hear the content).

Beidou-1 satellite navigation and positioning system is not affected by communication signals and spatial distance. After satellite positioning, a chief commander can connect several "Beidou-1" terminals similar to mobile phones, and each terminal can write short messages of more than 40 words and send them to designated mobile phones, which is very beneficial to the transmission of rescue information in earthquake areas.

Third, the working principle

The Beidou-1 satellite positioning system consists of two stationary satellites (800e and 1400e), an on-orbit backup satellite (1 10.50e), a central control system, a calibration system and various user computers. The working process of the system is as follows: first, the central control system sends inquiry signals to satellites 1 and 2 at the same time, and broadcasts them to users in the service area through satellite transponders.

Users respond to the query signal of one of the satellites, and send response signals to both satellites at the same time, which are forwarded back to the central control system through the satellites. The central control system receives and demodulates the signals sent by users, and then carries out corresponding data processing according to the service content applied by users.

For positioning applications, the central control system measures two time delays: the delay of sending an inquiry signal from the central control system and forwarding it to the user through the satellite, and the delay of sending a positioning response signal by the user and forwarding it back to the central control system through the same satellite; And the delay of sending the inquiry signal from the central control to the user through the same satellite, and the delay of the user sending the response signal and forwarding it back to the central control system through another satellite.

Since the positions of the central control system and the two satellites are known, the sum of the distances between the user and the first satellite and between the user and the two satellites can be calculated from the above two delays, thus knowing that the user is at the intersection of a sphere centered on the first satellite and an ellipsoid focused on the two satellites.

In addition, the central control system can find the user's elevation value from the digital topographic map stored in the computer, and can know that the user is on an ellipsoid parallel to the earth reference ellipsoid. Therefore, the central control system can finally calculate the three-dimensional coordinates of the user's point, which is encrypted and sent to the user through the outbound signal.

"Beidou-1" covers the heart area between 5-55 north latitude and 70-140 east longitude, the largest part and the smallest part, and the widest part is around 35 north latitude. Its positioning accuracy is horizontal 100 m (1σ), and it is 20 m after setting the calibration station (similar to differential state). Working frequency: 249 1.75mhz system can accommodate 540,000 users per hour.