Conference Paper

CRC-Assisted Error Correction in a Trellis Coded System with Bit Stuffing

Authors: Prévost Raoul, Coulon Martial, Bonacci David, Le Maitre Julia, Millerioux Jean-Pierre and Tourneret Jean-Yves

In Proc. Workshop on Statistical Signal Processing (SSP), Nice, France, June 28-30, 2011, pp. 381-385.

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This paper introduces a new error correction strategy using cyclic redundancy checks (CRC) for a trellis coded system in the presence of bit stuffing. The proposed receiver is designed to simultaneously demodulate, decode and correct the received message in the presence of bit stuffing. It is based on a Viterbi algorithm exploiting the conditional transitions of an appropriate extended trellis. The receiver is evaluated with automatic identification system (AIS) messages constructed with a 16 bit CRC and a Gaussian Minimum Shift Keying (GMSK) modulation. The stuffed bits are inserted after any sequence of five consecutive bits 1 as requested by the AIS recommendation. Simulation results illustrate the algorithm performance in terms of packet error rate. A gain of more than 2,5 dB is obtained when compared to the conventional GMSK receiver.

Digital communications / Localization and navigation and Space communication systems

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PhD Thesis

Décodage et localisation AIS par satellite

Author: Prévost Raoul

Defended in October 2012

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The automatic identification system (AIS) is a system allowing ships and coast stations to exchange some information by VHF radio. This information includes the identifier, status, location, direction and speed of the emitter. The aim of this thesis is to allow the reception of AIS messages by low Earth orbit satellites without modifying the existing ship equipments. With this system, it becomes possible to know the position of all ships over the Earth. As a consequence, several new services become available, such as global traffic monitoring or determining boat location (for ship-owners). Satellite reception of AIS signals is subjected to a higher noise level when compared to ground level reception. This noise makes classical demodulation and decoding methods unusable. A first contribution of this thesis is to develop new demodulators using error correction methods. These demodulators take advantage of the presence of a cyclic redundancy check (CRC) block in the messages as well as known information about the structure of messages and data. Generalizations of the proposed receiver have also been studied in order to take into account the phase noise of the received signals and the possible collision of messages sent simultaneously by several vessels. The last part of this thesis is devoted to the study of localization methods for ships that do not transmit their location in AIS messages. This localization takes advantage of information contained in the received messages such as the propagation delay and the carrier frequency shift due to the Doppler effect, and a ship movement model.

Digital communications / Localization and navigation and Space communication systems

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PhD Defense Slides

Décodage et localisation AIS par satellite

Author: Prévost Raoul

Defended in October 2012

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The automatic identification system (AIS) is a system allowing ships and coast stations to exchange some information by VHF radio. This information includes the identifier, status, location, direction and speed of the emitter. The aim of this thesis is to allow the reception of AIS messages by low Earth orbit satellites without modifying the existing ship equipments. With this system, it becomes possible to know the position of all ships over the Earth. As a consequence, several new services become available, such as global traffic monitoring or determining boat location (for ship-owners). Satellite reception of AIS signals is subjected to a higher noise level when compared to ground level reception. This noise makes classical demodulation and decoding methods unusable. A first contribution of this thesis is to develop new demodulators using error correction methods. These demodulators take advantage of the presence of a cyclic redundancy check (CRC) block in the messages as well as known information about the structure of messages and data. Generalizations of the proposed receiver have also been studied in order to take into account the phase noise of the received signals and the possible collision of messages sent simultaneously by several vessels. The last part of this thesis is devoted to the study of localization methods for ships that do not transmit their location in AIS messages. This localization takes advantage of information contained in the received messages such as the propagation delay and the carrier frequency shift due to the Doppler effect, and a ship movement model.

Digital communications / Localization and navigation and Space communication systems

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Patent

Procédé de décodage et décodeur

Authors: Prévost Raoul, Coulon Martial, Bonacci David, Le Maitre Julia, Millerioux Jean-Pierre and Tourneret Jean-Yves

n° FR2970130, July 2012.

Digital communications / Space communication systems

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Procédé de correction de messages contenant des bits de bourrage

Authors: Prévost Raoul, Coulon Martial, Bonacci David, Le Maitre Julia, Millerioux Jean-Pierre and Tourneret Jean-Yves

n° FR2970131, July 2012.

Digital communications / Space communication systems

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Talk

Réception de signaux AIS par satellite

Author: Prévost Raoul

Seminars of IRIT SC group, September 2011

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Le système d’identification automatique (AIS) est un système permettant aux navires de s’échanger certaines informations, dont leur position, par radio. L’objectif du travail réalisé est de permettre la réception des messages AIS par un satellite en orbite basse sans modifier le matériel existant équipant les navires. Il sera ainsi possible de connaître la position de tous les navires à travers le monde. Plusieurs services sont possibles, comme le contrôle maritime ou, pour les armateurs, la connaissance permanente de la position de leurs bateaux. Ce séminaire présentera le correcteur d’erreurs élaboré afin de s’affranchir du niveau élevé de bruit et les méthodes permettant de prendre en compte les propriétés des signaux AIS.

Digital communications / Localization and navigation and Space communication systems

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