Journal Paper

CRC-Based Detection Algorithms for AIS Signals Received by Satellite

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

Int. J. Satell. Commun. Network., vol. 31, no. 4, pp. 157-176, July/August, 2013.

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This paper addresses the problem of demodulating signals transmitted in the automatic identification system. The main characteristics of such signals consist of two points: (i) they are modulated using a trellis-coded modulation, more precisely a Gaussian minimum shift keying modulation; and (ii) they are submitted to a bit stuffing procedure, which makes more difficult the detection of the transmitted information bits. This paper presents several demodulation algorithms developed in different contexts: mono-user and multi-user transmissions, and known/unknown phase shift. The proposed receiver uses the cyclic redundancy check (CRC) present in the automatic identification system signals for error correction and not for error detection only. By using this CRC, a particular Viterbi algorithm, on the basis of a so-called extended trellis, is developed. This trellis is defined by extended states composed of a trellis code state and a CRC state. Moreover, specific conditional transitions are defined to take into account the possible presence of stuffing bits. The algorithms proposed in the multi-user scenario present a small increase of computation complexity with respect to the mono-user algorithms. Some performance results are presented for several scenarios in the context of the automatic identification system and compared with those of existing techniques developed in similar scenarios.

Digital communications / Space communication systems

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Conference Paper

Utilisation partielle du CRC pour la correction d'erreurs des signaux AIS reçus par satellite

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

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), September 8-11, 2015.

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This paper deals with the demodulation of automatic identification system (AIS) signals received by a satellite. More precisely, an error correction algorithm is presented, whose computational complexity is reduced with respect to that of a previously considered approach. This latter approach makes use of the cyclic redundancy check (CRC) of a message as redundancy, in order to correct transmission errors. In this paper, the CRC is also considered as a correction tool, but only a part of it is used for that purpose; the remaining part is only used as an error detection means. This novel approach allows the decoding performance to be adapted to the noise power, and provides a reduction of the computational complexity. Simulation results obtained with and without complexity optimization are presented and compared in the context of the AIS system.

Digital communications / Localization and navigation and Space communication systems

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Partial CRC-Assisted Error Correction of AIS Signals Received by Satellite

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

In Proc. Int. Conf. Acoust., Speech and Signal Processing (ICASSP), Florence, Italy, May 4-9, 2014.

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This paper deals with the demodulation of automatic identification system (AIS) signals received by a satellite. More precisely, an error correction algorithm is presented, whose computational complexity is reduced with respect to that of a previously considered approach. This latter approach makes use of the cyclic redundancy check (CRC) of a message as redundancy, in order to correct transmission errors. In this paper, the CRC is also considered as a correction tool, but only a part of it is used for that purpose; the remaining part is only used as an error detection means. This novel approach allows the decoding performance to be adapted to the noise power, and provides a reduction of the computational complexity. Simulation results obtained with and without complexity optimization are presented and compared in the context of the AIS system.

Digital communications / Localization and navigation and Space communication systems

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Ship Localization Using AIS Signals Received by Satellites

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

In Proc. European Signal and Image Processing Conference (EUSIPCO), Marrakech, Morocco, September 9-13, 2013.

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This paper addresses the problem of ship localization by using the messages received by satellites and transmitted by the automatic identification system (AIS). In particular, one considers the localization of ships that do not transmit their actual position in AIS signals. The proposed localization method is based on the least squares algorithm and uses the differences of times of arrival and the carrier frequencies of the messages received by satellite. A modification of this algorithm is proposed to take into account the displacement model of the ships as additional measurements. This modification shows a significant localization improvement.

Signal and image processing / Localization and navigation and Space communication systems

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Poursuite de phase durant la démodulation et le décodage des signaux AIS reçus par satellite

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

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), September 3-6, 2013.

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This paper presents a demodulation algorithm for automatic identification system (AIS) signals received by a satellite. The main contribution of this work is to consider the phase recovery problem for an unknown modulation index, coupled with a time-varying phase shift. The proposed method is based on a demodulator introduced in a previous paper based on a Viterbi-type algorithm applied to an extended trellis. The states of this extended trellis are composed of a trellis-code state and of a cyclic redundancy check state. The bit stuffing mechanism is taken into account by defining specific conditional transitions in the extended trellis. This algorithm estimates and tracks the phase shift by modifying the Euclidean distance used in the trellis. Simulation results obtained with and without phase tracking are presented and compared in the context of the AIS system.

Digital communications / Localization and navigation and Space communication systems

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Joint Phase-Recovery and Demodulation-Decoding of AIS Signals Received by Satellite

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

In Proc. Int. Conf. Acoust., Speech and Signal Processing (ICASSP), Vancouver, Canada, May 26-31, 2013.

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This paper presents a demodulation algorithm for automatic identification system (AIS) signals received by a satellite. The main contribution of this work is to consider the phase recovery problem for an unknown modulation index, coupled with a time-varying phase shift. The proposed method is based on a demodulator introduced in a previous paper based on a Viterbi-type algorithm applied to an extended trellis. The states of this extended trellis are composed of a trellis-code state and of a cyclic redundancy check state. The bit stuffing mechanism is taken into account by defining special conditional transitions in the extended trellis. This algorithm estimates and tracks the phase shift by modifying the Euclidean distance used in the trellis. Simulation results obtained with and without phase tracking are presented and compared in the context of the AIS system.

Digital communications / Localization and navigation and Space communication systems

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Extended Constrained Viterbi Algorithm for AIS Signals Received by Satellite

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

In Proc. European Conference on Satellite Telecommunications (ESTEL), Rome, Italy, October 2-5, 2012.

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This paper addresses the problem of error correction of AIS messages by using the a priori knowledge of some information in the messages. Indeed, the AIS recommendation sets a unique value or a range of values for certain fields in the messages. Moreover, the physics can limit the range of fields, such as the speed of the vessel or its position (given the position of the receiver). The repetition of the messages gives also some information. Indeed, the evolution of the ship position is limited between messages and the ship ID is known. The constrained demodulation algorithm presented in this article is an evolution of the constrained Viterbi algorithm (C-VA). It is based on a modified Viterbi algorithm that allows the constraints to be considered in order to correct transmission errors by using some new registers in the state variables. The constraints can be either a single value or a range of values for the message fields. Simulation results illustrate the algorithm performance in terms of bit error rate and packet error rate. The performance of the proposed algorithm is 2 dB better than that obtained with the receiver without constraints.

Digital communications / Localization and navigation and Space communication systems

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Interference Mitigation and Error Correction Method for AIS Signals Received by Satellite

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

In Proc. European Signal and Image Processing Conference (EUSIPCO), Bucharest, Romania, August 27-31, 2012.

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This paper addresses the problem of error correction in a multi-user trellis coded system in the presence of bit stuffing. In particular, one considers the situation in which automatic identification system (AIS) signals are received by a satellite. The proposed receiver uses a cyclic redundancy check (CRC) for error correction. A Viterbi algorithm based on a so-called extended trellis is developed. This trellis is defined by extended states composed of a trellis-code state and a CRC state. Moreover, special conditional transitions are defined in order to take into account the possible presence of bit stuffing. The proposed algorithm was first developed in a single-user context. It is generalized in this paper to a multi-user scenario by designing an interference mitigation method. This method allows one to derive a demodulation algorithm whose complexity is almost identical to that obtained in the single-user context. Some performance results are presented in the context of AIS and compared with results provided by existing techniques.

Digital communications / Localization and navigation and Space communication systems

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Advanced Concepts for Satellite Reception of AIS Messages

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

In Proc. Toulouse Space Show (TSS), Toulouse, France, June 25-27, 2012.

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This paper addresses the problem of demodulating messages received by a low-orbit satellite (altitude between 700 and 800 km) and transmitted by vessels using the Automatic Identification System (AIS). AIS is a Self-Organized Time Division Multiple Access (SO-TDMA) system, in which vessels periodically transmit information (mainly including MMSI – identification code of the ship– and its GPS position). The main application of the actual AIS system is collision avoidance between ships but a satellite reception would lead to a global supervision of maritime traffic, which could be of great interest for a lot of applications (military but also civil applications as fleet surveillance and monitoring).

Digital communications / Localization and navigation and Space communication systems

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Une technique de correction d’erreur basée sur le CRC pour des systèmes codés en treillis contenant des bits de bourrage

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

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), Bordeaux, France, September 5-8, 2011.

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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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