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Journal Paper

New CO² Concentration Predictions and Spectral Estimation Applied to the Vostok Ice Core

Authors: Bonacci David and Lacaze Bernard

IEEE Transactions on Geoscience and Remote Sensing, vol. 56, issue 1, pp. 145-151, January, 2018.

The Vostok ice core provides measurements of the CO 2 concentration during the last 414 × 10 3 years (yr). Estimations of power spectra show peaks, with the strongest one corresponding to a time period of around 100 × 10 3 yr. In this paper, a new reconstruction method from irregular sampling is used, allowing more accurate estimation of spectral peaks. This method intrinsically decomposes the analyzed signal as a sum of sines, providing amplitudes but also phase measurements of periodic tendencies (due to the nature of the studied phenomena). This decomposition can be conducted with noisy and inaccurate measurements of the sampling instants and the concentrations. The widely used Vostok data were chosen as an example, but the method could also be applied to data from other places (e.g., dome C, Antarctica) or to study other phenomena as nitrogen dioxide NO 2 , methane CH 4 , oxygen isotope 18 O (closely linked to temperature), deuterium 2 H, or dust concentrations.

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Conference Paper

A Frequency-Domain Band-MMSE Equalizer for Continuous Phase Modulation over Frequency-Selective Time-Varying Channels

Authors: Chayot Romain, Thomas Nathalie, Poulliat Charly and Boucheret Marie-Laure

In Proc. European Signal Processing Conference (EUSIPCO), Rome, Italy, September 3-7, 2018.

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In this paper, we consider single carrier continuous phase modulations (CPM) over frequency selective time-varying channels. In this context, we propose a new low-complexity frequency-domain equalizer based on the minimum mean square error (MMSE) criterion exploiting efficiently the band structure of the associated channel matrix in the frequency domain. Simulations show that this band-MMSE equalizer exhibits a good performance complexity trade-off compared to existing solutions.

Digital communications / Aeronautical communication systems and Space communication systems

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Smooth Bias Estimation for Multipath Mitigation Using Sparse Estimation

Authors: Lesouple Julien, Barbiero Franck, Faurie Frédéric, Sahmoudi Mohamed and Tourneret Jean-Yves

In Proc. 21st International Conference on Information Fusion (FUSION), Cambridge, England, July 10-13, 2018.

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Multipath remains the main source of error when using global navigation satellite systems (GNSS) in constrained environment, leading to biased measurements and thus to inaccurate estimated positions. This paper formulates the GNSS navigation problem as the resolution of an overdetermined system, which depends nonlinearly on the receiver position and linearly on the clock bias and drift, and possible biases affecting GNSS measurements. The extended Kalman filter is used to linearize the navigation problem whereas sparse estimation is considered to estimate multipath biases. We assume that only a part of the satellites are affected by multipath, i.e., that the unknown bias vector is sparse in the sense that several of its components are equal to zero. The natural way of enforcing sparsity is to introduce an `1 regularization associated with the bias vector. This leads to a least absolute shrinkage and selection operator (LASSO) problem that is solved using a reweighted-l1 algorithm. The weighting matrix of this algorithm is designed carefully as functions of the satellite carrier to noise density ratio and the satellite elevations. The smooth variations of multipath biases versus time are enforced using a regularization based on total variation. An experiment conducted on real data allows the performance of the proposed method to be appreciated.

Signal and image processing / Localization and navigation

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Multipath Mitigation in Global Navigation Satellite Systems using a Bayesian Hierarchical Model with Bernoulli Laplacian Priors

Authors: Lesouple Julien, Tourneret Jean-Yves, Sahmoudi Mohamed, Barbiero Franck and Faurie Frédéric

In Proc. IEEE Worshop on Statistical Signal Processing (SSP), Freiburg Im Breisgau, Germany, June 10-13, 2018.

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A new sparse estimation method was recently introduced in a previous work to correct biases due to multipath (MP) in GNSS measurements. The proposed strategy was based on the resolution of a LASSO problem constructed from the navigation equations using the reweighted-l1 method. This strategy requires to adjust the regularization parameters balancing the data fidelity term and the involved regularizations. This paper introduces a new Bayesian estimation method allowing the MP biases and the unknown model parameters and hyperparameters to be estimated directly from the GNSS measurements. The proposed method is based on BernoulliLaplacian priors, promoting sparsity of MP biases.

Signal and image processing / Localization and navigation

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Patent

PROCÉDÉ ET SYSTÈME DE TRANSMISSION DE PAQUETS DE DONNÉES À TRAVERS UN CANAL DE TRANSMISSION (RA) À ACCÈS ALÉATOIRE

Authors: Zamoum Selma, Gineste Mathieu, Lacan Jérôme, Boucheret Marie-Laure and Dupé Jean-Baptiste

n° 071277 FR RQDLV 14-05-18 YTA-LRE, May 2018.

Digital communications / Space communication systems

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Journal Paper

Two-Color Scheme for a Multi-Beam Satellite Return Link : Impact of Interference Coordination

Authors: Couble Yoann, Rosenberg Catherine, Chaput Emmanuel, Dupé Jean-Baptiste, Baudoin Cédric and Beylot André-Luc

IEEE Journal on Selected Areas in Communications, vol. 36, pp. 993-1003, May 2018.

The return link of broadband satellite systems has recently received more attention due to the spread of multi-beam antennas which enable spatial frequency reuse, and thus increase drastically the number of users that can potentially be served by one satellite. While interference isolation has so far been the way to go, with regular four-color frequency reuse scheme, there is a growing interest in densifying the frequency usage as is being done in cellular networks. In this paper, we address the return link radio resource allocation challenges, from spectral resource allocation to user scheduling, including modulation and coding scheme (MODCOD) selection. Our contributions highlight the potential gains of a two-color scheme and shed light on several levers to reap its benefits through interference management. We first consider the possibility to use a two-color scheme, while keeping the MODCOD selection and the scheduling local to each beam and we show that even though it yields a potential performance gain (+16%) with respect to the state of the art (SoA) (based on four colors), it is not viable due to a very high-block loss rate. Therefore, we propose a simple-yet fast and efficient-coordinated MODCOD selection process that alleviates the need of estimating interference and reduces drastically decoding failures. This coordination step offers significant gains (+58%) over the SoA, while leaving the per beam scheduler unchanged. Finally, we formulate a joint user scheduling and MODCOD selection problem across all beams and propose an offline heuristic to solve it efficiently. We obtain a 83% gain with respect to the SoA, but with higher computational complexity. Still, it confirms the great potential of coordinated scheduling.

Networking / Space communication systems

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PhD Thesis

Fiabilisation des Transmissions Optiques Satellite-Sol / Reliability of Satellite-to-Ground Optical Communication

Author: Canuet Lucien

Defended on April 16, 2018.

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Optical wavelengths are an alternative to radio-frequency links for future satellite-to-ground transmissions. They are envisioned in the framework of payload/telemetry data transfer (optical downlinks from LEO satellites) or communication (bi-directional optical links with GEO satellites). However, as it propagates through the atmosphere, the optical wave can be deeply affected by atmospheric turbulence which induces randomspatial and temporal variations of its amplitude and phase. Variations in amplitude translate into fluctuations of the collected power (scintillation). The phase distortions affect the spatial distribution of the power at the focal plane of the telescope causing deleterious losses when the incident flux needs to be coupled to an optoelectronic detector or to a single-mode optical fiber. Such losses result in dynamical attenuations of the received signal-called fading- and hence potentially to the loss of information. The most recent feasibility studies highlight the use of two types of fading mitigation techniques : adaptive optics systems and digital techniques (coding and interleaving). To limit the complexity and cost of such systems, the optimization of these mitigation techniques should be conducted jointly. The main objective of this thesis is therefore the investigation of the complementarity of physical (adaptive optics) and digital data reliability mechanisms (interleaving, correcting and erasure codes in a cross-layer approach).

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Patent

PROCÉDÉ D'ALLOCATION DE FRÉQUENCES DANS UN SYSTÈME DE RADIOCOMMUNICATION SATELLITAIRE MULTIFAISCEAUX, ET SYSTÈME ASSOCIÉ

Authors: Baudoin Cédric, Couble Yoann, Deleu Thibault, Dupé Jean-Baptiste and Chaput Emmanuel

n° 071015 FR RQDLV 26-02-18 BRU-AMA, February 2018.

Networking / Space communication systems

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Talk

Patch-Based Regularization in Multiband Imaging Inverse Problems

Author: Bioucas Dias José Manuel

Seminar of TeSA, Toulouse, February 16, 2018.

Qualité des Observations pour les systèmes Sensor Webs

Author: Auger Antoine

Seminar of TeSA, Toulouse, February 16, 2018.

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Les systèmes dits Sensor Webs sont des middlewares informatiques assurant la communication entre les capteurs et les applications. En tant que véritables médiateurs, la popularité de ces systèmes n’a cessé de grandir depuis l’apparition des tout premiers capteurs. Plus récemment, l’émergence de nouveaux paradigmes tels que l’Internet des Objets (IoT) a complètement révolutionné les systèmes basés sur les capteurs en général. Parmi eux, les Sensor Webs ne dérogent pas à cette règle et doivent maintenant répondre à de nouveaux défis, notamment en termes d’intégration, de Qualité des Observations (QoO) et d’adaptation système. Dans le cadre de ma thèse, j'ai proposé une nouvelle génération de Sensor Webs capables d’adapter la QoO distribuée de manière autonomique et spécifique à chaque application (QASWS). Premièrement, j'introduirai un framework générique destiné aux chercheurs et développeurs souhaitant concevoir leur propre solution QASWS. Dans un deuxième temps, je montrerai comment j'ai utilisé ce framework afin de développer une plateforme d’intégration pour l’évaluation de la QoO à la demande (iQAS). Après avoir évalué ses performances, je présenterai trois cas d’utilisation pour la plateforme iQAS. Finalement, je conclurai ma présentation en imaginant l’apport de certains paradigmes transverses vis-à-vis de la QoO dans un futur proche.

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Activity Report

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Toulouse Space Show

TeSA was present at the Toulouse Space Show 2018. 3 great days!

TeSA in Freiburg, Germany

Julien Lesouple, TeSA PhD, presented a paper at SSP 2018.

TeSA in Boston

Lorenzo Ortega, TeSA PhD, invited by Pau Closas (left) at Northeastern University.