Timing principle of gps timing equipment and Beidou timing equipment
Both GPS satellite and Beidou satellite are equipped with atomic clocks (cesium atomic clock or rubidium atomic clock). With an accurate clock and constant calibration of the ground station, the time of the satellite system will be very accurate. The satellite will broadcast a time in its own message, and the signal edge of this time broadcast strictly corresponds to this time value. By measuring this edge, an accurate changing edge can be recovered locally, which is synchronized with the transmission time. The navigation message provides the "week number" of the current time, counting from the starting time of Beidou or GPS system. In addition, the current day of the week can be known by calculating the information of the pseudo-random code modulated on the carrier, and the time service function can be realized by using this information.
Common time service methods of gps time service equipment and Beidou time service equipment
At present, the mainstream time synchronization signals and interfaces are 1PPS/ 1PPM, IRIG-B code, RS-232 serial port and NTP network timing. The timing accuracy of 1PPS/ 1PPM pulse and IRIG-B code can reach nanosecond level at the highest, while the timing accuracy of RS-232 and NTP can generally reach millisecond level. 1PPS/ 1PPM, IRIG-B code and RS-232 all need special interfaces and cables, while NTP mode can adopt network mode.
A) 1PPS/ 1PPM time service mode This format time signal outputs a pulse signal every second or minute. Obviously, the pulse output does not contain specific time information.
B) IRIG*** has several coding standards: A, B, D, E, G and H, among which IRIG-B code and DC code are the most widely used in time synchronization applications.
(BC level shift), AC code
(1kHz sine carrier amplitude modulation) and other formats. The IRIG-B signal is output one frame per second, and each frame is one second long. A frame * * * has 100 symbols, and binary 0, 1 and position flag bits are represented by symbols with different pulse widths.
c)
Time output of RS-232 serial port timing mode sends a series of date and time information of ASCII code through EIA standard serial interface. Rich information such as parity, clock status and diagnosis results can be inserted into the time message. This method can visually see the current time information on the computer with software, and correct the computer time at any time, which is very convenient to use.
D) Network Timing Method Network timing is to use NTP protocol to deliver unified standard time on the Internet. The specific implementation scheme is to specify several time servers on the network to provide time services for users, and these time servers should be able to compare with each other to improve accuracy. All PCs, servers and other devices in the local area network are synchronized with the time server through the network. NTP protocol automatically judges the network delay and makes time compensation for the obtained data. So as to keep that time of LAN equipment uniform and accurate.
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