SUMMARYThe Automatic Identification System (AIS) is a VHF communication system that provides identification/ location information to vessels and shore stations by exchanging data such as position, identification, course, speed, etc. Recently, the interest in detecting and tracking ships at distances from coastlines larger than what can be accomplished by normal terrestrial VHF communications has grown, driven by requirements of long-range applications such as better handling of hazardous cargo, improved security and countering illegal operations. This paper presents an extension of AIS to a long-range positioning reporting through a constellation of LEO satellites. It outlines technical challenges like the high rate of message collisions from ships in the field of view of a satellite. Technical solutions are proposed at system and subsystem level to address these challenges. A computer-based system simulator is used to assess the system performance and carry out a high-level system sizing. Results show that a relatively small constellation of LEO satellites can guarantee good ship position detection probability as well as a reporting time interval of a few hours. System performance aspects to be addressed in future work are the possible impact of terrestrial mobile communications interference as well as variations of the estimated traffic data.

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