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Ph.D. thesis

Reception of AIS signals by satellite

Advisor

Jean-Yves Tourneret

Co-advisors

Matial Coulon
David Bonacci

Partners

This thesis is conducted in partnership with the DGA and the CNES.

Abstract

The Automatic Identification System (AIS) is a system allowing ships to exchange some information via VHF radio. This information include the identifier, status, position, direction and speed of the transmitter ship. The AIS messages can be received both by boats to avoid collision for example and by shore stations to monitor traffic.
The objective of this thesis is to allow the reception of AIS messages by a low Earth orbit satellite without modifying the existing ship equipments. Through the AIS, it would be possible to know the position of all ships in the world. Several services are possible, such as global maritime control or the continuous position knowledge of the boats for shipowners. This system presents several technical problems, the first concerns the strength of the received signals. Indeed, the emitters used on ships have not been dimensioned to send messages to satellites which leads to a low signal to noise ratio. Furthermore, the medium access method used by the AIS, the self-organised time-division multiple-access (SOTDMA), avoids the collisions between messages from the viewpoint of a ship in his cell but is not effective from the viewpoint of satellites because their listening scope is much larger and covers more than one cell.
In this thesis, we propose to use new types of error correction strategies on the messages received by taking advantage of the presence of a CRC in the messages. Indeed, the CRC can be considered as a source of redundancy that therefore can be used to correct errors. The methods for sources separation are also studied.