Joint phase-recovery and demodulation-decoding of AIS signals received by satellite

International audienceThis 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

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

National audienceThis 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.Cet article présente un algorithme de démodulation des signaux du système d’identification automatique (AIS) reçus par satellite. La principale contribution de ce travail est de considérer le problème d’estimation de la phase pour un indice de modulation inconnu couplé avec un décalage de phase variant dans le temps. La méthode proposée consiste à étendre la méthode de démodulation présentée dans un précédent article utilisant un algorithme de Viterbi appliqué sur un treillis étendu. Les états de ce treillis étendu sont composés d’un état du codeur en treillis et d’un état du contrôle de redondance cyclique (CRC). Les bits de bourrage sont pris en compte en définissant des transitions spécifiques dans le treillis étendu. Cet algorithme estime et poursuit le décalage de phase en modifiant la distance euclidienne utilisée dans le treillis. Les résultats de simulations obtenus avec et sans poursuite de la phase sont présentés et comparés dans le contexte du système AI

Ship localization using AIS signals received by satellite

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

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory. Athena is a versatile observatory designed to address the Hot and Energetic Universe science theme, as selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), X-IFU aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over a hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR (i.e. in the course of its preliminary definition phase, so-called B1), browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters, such as the instrument efficiency, spectral resolution, energy scale knowledge, count rate capability, non X-ray background and target of opportunity efficiency. Finally, we briefly discuss the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, touch on communication and outreach activities, the consortium organisation and the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. The X-IFU will be provided by an international consortium led by France, The Netherlands and Italy, with ESA member state contributions from Belgium, Czech Republic, Finland, Germany, Poland, Spain, Switzerland, with additional contributions from the United States and Japan.The French contribution to X-IFU is funded by CNES, CNRS and CEA. This work has been also supported by ASI (Italian Space Agency) through the Contract 2019-27-HH.0, and by the ESA (European Space Agency) Core Technology Program (CTP) Contract No. 4000114932/15/NL/BW and the AREMBES - ESA CTP No.4000116655/16/NL/BW. This publication is part of grant RTI2018-096686-B-C21 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. This publication is part of grant RTI2018-096686-B-C21 and PID2020-115325GB-C31 funded by MCIN/AEI/10.13039/501100011033

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. (abridged).Comment: 48 pages, 29 figures, Accepted for publication in Experimental Astronomy with minor editin

Techniques de détection multi-utilisateurs pour les communications multifaisceaux par satellite

Nous nous intéressons dans cette thèse à la définition et l'évaluation de techniques de détection multi-utilisateurs pour le traitement des interférences co-canal sur la voie retour des systèmes de communication multifaisceaux par satellite. L'utilisation de ces techniques peut en effet permettre de tolérer des C/I plus faibles que ceux des systèmes classiques, et ainsi autoriser des motifs de réutilisation de fréquence plus efficaces d'un point de vue capacité. L'accès et les formes d'ondes envisagés sont inspirés de la norme DVB-RCS. Nous proposons des algorithmes d'élimination itérative d'interférence adaptés au contexte envisagé. Ces algorithmes incluent notamment la ré-estimation de certains paramètres du canal (réponses en amplitude et en phase des signaux sur les différents faisceaux, fréquences des signaux). Ils sont dans un premier temps évalués en terme d'erreur d'estimation et de taux d'erreurs binaire sur des configurations d'interférences fictives. Nous montrons qu'ils permettent d'obtenir des dégradations (par rapport au cas d'un utilisateur seul) très réduites sur des configurations caractérisées par des C/I très faibles. Nous nous intéressons dans un second temps à l'évaluation de ces algorithmes sur une couverture multifaisceaux. Des simulations effectuées sur une couverture construite à partir d'un modèle d'antenne multi-sources à réflecteur permettent une comparaison des différents algorithmes envisagés dans un contexte réaliste

Techniques de détection multi-utilisateurs pour les communications multifaisceaux par satellite

Nous nous interessons dans cette thèse à la définition et à l'évaluation de techniques de détection multi-utilisateurs pour le traitement des interférences co-canal sur la voie retour des systèmes de communication multifaisceaux par satellite. L'utilisation de ces techniques peut en effet permettre de tolérer des C/I plus faibles que ceux des systèmes classiques, et ainsi autoriser des motifs de réutilisation de fréquence plus efficaces d'un point de vue capacité. L accès et les formes d ondes envisagés sont inspirés de la norme DVB-RCS. Nous proposons des algorithmes d élimination itérative d interférence adaptés au contexte envisagé. Ces algorithmes incluent notamment la ré-estimation de certains paramètres du canal (réponses en amplitude et en phase des signaux sur les différents faisceaux, fréquences des signaux). Ils sont dans un premier temps évalués en terme d erreur d estimation et de taux d erreurs binaire sur des configurations d interférences fictives. Nous montrons qu ils permettent d obtenir des dégradations (par rapport au cas d un utilisateur seul) très réduites sur des configurations caractérisées par des C/I très faibles. Nous nous intéressons dans un second temps à l évaluation de ces algorithmes sur une couverture multifaisceaux. Des simulations effectuées sur une couverture construite à partir d un modèle d antenne multi-sources à réflecteur permettent une comparaison des différents algorithmes envisagés dans un contexte réaliste.This thesis is devoted to the definition and the evaluation of multiuser detection techniques to mitigate co-channel interference on the reverse link of multibeam satellite systems. These techniques can cope with lower C/I than classical systems: they can consequently allow more capacity efficient frequency reuse strategies. The considered access and waveforms are inspired by the DVB-RCS standard. We propose iterative interference cancellation algorithms adapted to the satellite context. They include estimation of beamforming coefficients and frequency offsets of received signals. These algorithms are first evaluated in terms of bit error rate and of channel estimation error on fictitious interference configurations. We show that they lead to very limited degradations (with respect to the single user case) on interference configurations characterized by very low C/I. We then consider evaluations on a multibeam coverage Simulation results on a multibeam coverage designed on a Focal Array Fed Reflector antenna allow comparing the algorithms in a realistic context.PARIS-Télécom ParisTech (751132302) / SudocSudocFranceF

Similitudes et différences entre la théorie du contrôle des systèmes chaotiques à temps discret et à temps continu

International audienceFor linear systems, the basic notions of control theory, such as commandability, observability, detectability and stabilizability, are the same for discrete-time and continuous-time systems. The situation is quite different for nonlinear systems such as chaotic systems, particularly due to the loss of continuity for discrete-time systems. The first consequence of this discontinuity is the existence of one-dimensional discrete autonomous chaotic systems. The differences between the dynamics of nonlinear systems made of maps and ordinary differential equations lead to very different properties. The most obvious is the loss of linearity in the input for maps; more precisely, even if the behavior of the state at iteration k+1 depends linearly on the input, this does not guarantee that at iteration k+2 the dependence remains linear. Basically, the composition and differentiation of nonlinear functions generate totally different topological and structural behaviours. This contribution is devoted to the comparison between the structural properties for commandability, observability and flatness for these two types of dynamical system

Similitudes et différences entre la théorie du contrôle des systèmes chaotiques à temps discret et à temps continu

International audienceFor linear systems, the basic notions of control theory, such as commandability, observability, detectability and stabilizability, are the same for discrete-time and continuous-time systems. The situation is quite different for nonlinear systems such as chaotic systems, particularly due to the loss of continuity for discrete-time systems. The first consequence of this discontinuity is the existence of one-dimensional discrete autonomous chaotic systems. The differences between the dynamics of nonlinear systems made of maps and ordinary differential equations lead to very different properties. The most obvious is the loss of linearity in the input for maps; more precisely, even if the behavior of the state at iteration k+1 depends linearly on the input, this does not guarantee that at iteration k+2 the dependence remains linear. Basically, the composition and differentiation of nonlinear functions generate totally different topological and structural behaviours. This contribution is devoted to the comparison between the structural properties for commandability, observability and flatness for these two types of dynamical system

Partial CRC-assisted error correction of AIS signals received by satellite

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