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AIS
AIS (Automatic Identification System) is a system for measuring position and distributing position data in broadcast mode so that every vessel within radio range can have position information about nearby vessels. Base stations on land can also be a part of the same system giving position and information of all AIS-vessels within radio range. Seatex has manufactured proprietary AIS systems for many years and is now broadening the AIS product range by developing UAIS (Universal Automatic Identification System) according to international (IEC, IMO) specifications. As the relevant specifications are not yet ready from the standardising bodies, there is still some development to be done, especially on the radio protocol part and on functionality and interface issues. The current generation of AIS transponders are based on a TDMA radio protocol that allocates time slots for each transponder, making it possible for each transponder to transmit in one time slot and listen in the rest of the timeslots. TDMA with fixed allocation of timeslots as described here makes the communication process robust and secure. The Seatex transponder is designed as shown: The Seatex UAIS transponder system consists of two units: The AIS transponder itself and the operator (laptop PC) unit. The transponder unit is typically mounted in a rack or in the technical area of the vessel. The transponder unit gets it input from a GPS antenna, an IALA antenna and a VHF antenna respectively. The VHF antenna is also used for transmitting. The operator unit consists of a laptop PC with display, keyboard and a pointing device (roller ball) and is placed in a position convenient for the operator. High and free mounting of the antennas is of major importance to get exact and reliable performance from the system. Each transponder is connected to a PC running a map application where important data relating to the vessels are displayed. Specifically, the vessel icon, position, identity and speed of the subject vessel as well as those of surrounding vessels are shown. The speed of the vessel is computed by the GPS receiver. All information from one transponder is transmitted in one timeslot and displayed on all display units. The application can also handle text messaging from one transponder to another. The operator may write his message on the PC and transfer it to another transponder at will. The system supports canned messages. The operator may pick a standard message from a list and transmit it to another vessel. Information on the screen is layered; i.e. the operator may choose which information windows he would like to see. Less important information may be switched off in order not to clutter the operator's view. The Seatex transponder may easily be interfaced to other systems or applications on board the vessel. The transponder itself has RS-232 output ports for this purpose.
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