Method for correcting clock of automatic ship identifying terminal equipment

Abstract

The invention relates to a method for correcting a clock of automatic ship identifying terminal equipment. The method comprises the following steps that: a clock correcting module acquires a UTC (universal time coordinated) time through a GPS (global position system) module and calculates errors of a local time through the UTC time; the error of a local clock is calculated after the errors are accumulated for a period; three levels of clock adjusting parameters are calculated through the errors; a clock compensating module compensates the local time according to the three levels of clock adjusting parameters so as to control the error of the local clock within a relatively small range, then the purpose of clock correction is achieved. By utilizing the method, AIS (automatic identification system) ship automatic identification terminal equipment can correct the error caused by the inaccuracy of the local clock, ensure that the synchronous error between the local time and the UTC time is not larger than 0.1 time slot (2.6ms) within half an hour under the condition that the UTC time reference is lost, and ensure that the AIS time synchronization in broadcast messages is still met. Therefore, the problem that the message transmission of other equipment is influenced when the AIS ship automatic identifying terminal equipment transmits a message due to the fact that the equipment time is not synchronous with the UTC time is solved.

Description

technical field [0001] The invention relates to a ship automatic identification terminal system, in particular to a method for calibrating its own clock of a ship automatic identification terminal device. Background technique [0002] The ship automatic identification system (AIS) obtains the current position information through the global positioning system (GPS), and transmits its own ship position, ship speed, course and other dynamic information as well as ship name, call sign, draft and dangerous goods and other static data through the VHF (VHF) channel to broadcast to nearby ships and shore stations. By receiving the broadcast ship information, the surrounding ships can grasp the ship information in the nearby sea area in time, and take necessary avoidance actions to improve the safety of ship navigation. [0003] The AIS work is based on TDMA (Time Division Multiple Access) technology. The AIS system uses two frequencies in the VHF band to work, and divides one minut...

AI Technical Summary

Problems solved by technology

However, the local clock of the terminal device is not accurate enough, and the clock accuracy of each device varies and is easily affected by the external environment.

Changes in external temperature, etc. may cause changes in the clock frequency, which in turn affects the accuracy of the local clock

Due to the inaccuracy of the device clock, the time in the device will soon deviate from the real UTC time, causing the device time to be out of sync with UTC time. At this time, the message sent by the AIS terminal device may affect the message sent by other devices

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