Research And Implementation Of Timing Synchronization Technology Of Ship-born AIS Station

The ship Automatic Identification System (AIS) is a kind of aids to navigation system that gradually became mature in recent years, which is playing an important system in today’s maritime traffic. AIS equipments are mainly composed of base station equipments and ship station equipments, and are the aids to navigation in them concentrating network, communication, computer and electronic displaying technology. It plays a very important role in terms of maritime traffic commanding, ship collision avoidance, information sharing, ship sailing condition and weather monitoring.AIS works in the VHF bands using Time-Division Multiple Access methods, mainly including SOTDMA, ITDMA, RATDMA,CSTDMA and so on. Before the ship station enters the network, in order to make the ship station and the network have the same time benchmark, the system time of the ship station needs to be processed that synchronized with the network. Therefore, the key technologies that the paper mainly studies and realizes include:the technology of synchronous status switch management and maintenance of time synchronization; direct synchronization and indirect synchronization process technology; the technology of storage and management of synchronous data. By the technologies, time of the system and the network is synchronous so that it provides the system stable, reliable and accurate time synchronization accuracy.The system mainly realizing the following functions is based on ARM7processor. The hardware system designs several functions including:PPS pulse signal provided by GPS module access; UART module realizing transport of time synchronized messages; ARM timers controlling system clock of the station to complete the synchronization state transitions. The software system uses C language programming in the Keil complier environment to implement controlling system time synchronization and functions that system needed. In the process of direct synchronization, it needs to receive NMEA0183format message to extract the UTC time information as well as the PPS pulse signal that GPS module provides. In indirect synchronization process, it needs to continuously receive and parse the ITU-R M.1371AIS message in order to obtain the time synchronization information that is necessary for indirect synchronization. Synchronous information should be stored and the storage area of the information should be managed to maintain the timeliness of information.The contents of this thesis are a part of research of National Support Program "key technology and system development of AIS/GNSS ship borne navigational equipment (2012BAH36B02) undertaken by the Institute of Navigation".