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Article de conférence

Les Signaux à Bande Large au Service de la Réflectométrie par GNSS à Site Bas

Auteurs : Lubeigt Corentin, Vilà-Valls Jordi, Lestarquit Laurent et Chaumette Eric

In Proc. Groupe de Recherche et d'Etudes de Traitement du Signal et des Images (GRETSI), Nancy, France, September 5-9, 2022.

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Pendant plus de trente ans, les signaux Global Navigation Satellite System (GNSS) ont été utilisés comme signaux d’opportunité comme en GNSS Reflectometry (GNSS-R). L’étude de la réflexion de ces signaux sur le sol peut en effet conduire à l’estimation de paramètres sur la surface de réflexion ou sur la hauteur du récepteur. Lorsque cette hauteur est faible, le récepteur est à site bas et la proximité du sol entraîne de fortes interférences entre les signaux direct et réfléchi ce qui rend difficile une estimation non biaisée des différentes observables. Cette difficulté peut néanmoins être levée grâce à des signaux GNSS occupant des bandes de plus en plus larges. For more than three decades, Global Navigation Satellite System (GNSS) signals have been seen as signals of opportunity as in GNSS Reflectometry (GNSS-R). The study of the reflections from the ground of such signals can indeed lead to many features regarding the reflecting surface and the receiver’s height. When this height is small, the receiver is said ground-based and the vicinity to the ground induces important interferences between the direct and the reflected path which make it difficult to process to obtain an unbiased altimetry product. However, this difficulty can be leveraged thanks to recent wideband GNSS signals.

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Traitement du signal et des images et Réseaux / Localisation et navigation

Réseaux récurrents d’attention pour la régression de séries temporelles

Auteurs : Perrier Victor, Lochin Emmanuel, Tourneret Jean-Yves et Gélard Patrick

In Proc. Groupe de Recherche et d'Etudes de Traitement du Signal et des Images (GRETSI), Nancy, France, September 5-9, 2022.

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Cet article étudie une nouvelle architecture récurrente basée sur l’attention, plus légère et moins coûteuse en temps de calcul qu’un réseau d’attention global. Nous détaillons en quoi ce type d’architecture permet d’atteindre de meilleures performances que des réseaux récurrents plus classiques, dans le cas de la régression de séries temporelles. Nous montrons son intérêt pour la prédiction de l’état d’un réseau de communication, et plus particulièrement pour la détection de la congestion.

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Réseaux / Systèmes spatiaux de communication

Article de journal

Accounting for Acceleration – Signal Parameters Estimation Performance Limits in High Dynamics Applications

Auteurs : Mc Phee Hamish Scott, Ortega Espluga Lorenzo, Vilà-Valls Jordi et Chaumette Eric

IEEE Transactions on Aerospace and Electronic Systems, Early Access, July, 2022.

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The derivation of estimation lower bounds is paramount to designing and assessing the performance of new estimators. A lot of effort has been devoted to the range-velocity estimation problem, a fundamental stage on several applications, but very few works deal with acceleration, being a key aspect in high dynamics applications. Considering a generic band-limited signal formulation, we derive a new general compact form Cramér-Rao bound (CRB) expression for joint time-delay, Doppler stretch, and acceleration estimation. This generalizes and expands upon known delay/Doppler estimation CRB results for both wideband and narrowband signals. This new formulation, especially easy to use, is created based on baseband signal samples, making it valid for a variety of remote sensors. The new CRB expressions are illustrated and validated with representative GPS L1 C/A and Linear Frequency Modulated (LFM) chirp band-limited signals. The mean square error (MSE) of a misspecified estimator (conventional delay/Doppler) is compared with the derived bound. The comparison indicates that for some acceleration ranges the misspecified estimator outperforms a well specified estimator that accounts for acceleration.

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Traitement du signal et des images / Localisation et navigation et Systèmes spatiaux de communication

Non-Binary PRN-Chirp Modulation: A GNSS Fast Acquisition Signal Waveform

Auteurs : Ortega Espluga Lorenzo, Vilà-Valls Jordi et Chaumette Eric

IEEE Communications Letters, Early Acces, p. 1, June 22, 2022.

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In this article, we propose a new non-binary modulation which allows both Global Navigation Satellite Systems (GNSS) synchronization and the demodulation of non-binary symbols, without the need of a pilot signal, with the aim to provide a fast first position, velocity and time fix. The waveform is constructed as the product of i) a pseudo-random noise sequence with good auto-correlation and cross-correlation properties, and ii) a chirp spread spectrum family, which allows to demodulate non-binary symbols even if the signal phase is unknown. In order to demodulate the data, a bank of non-coherent matched filters is proposed. Because of the particular modulation structure, the receiver is capable to demodulate the navigation message faster while allowing the basic GNSS signal processing functionalities. Illustrative results are provided to support the discussion.

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Traitement du signal et des images / Localisation et navigation et Systèmes spatiaux de communication

Article de conférence

Attention Networks for Time Series Regression and Application to Congestion Control

Auteurs : Perrier Victor, Lochin Emmanuel, Tourneret Jean-Yves et Gélard Patrick

In Proc. 4th International Workshop on Network Intelligence (IFIP Networking), Catania, Italy, June 13-16, 2022.

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This paper studies a new attention-based recurrent architecture, lighter and less computationally expensive than a global attention network. This type of architecture achieves better performance than commonly used recurrent networks for time series regression. An application to congestion control is considered, where the history of round trip times (RTT) evolution history is used to monitor congestion control. The performance of the proposed new congestion control strategy is evaluated with both synthetic and real traces, showing that it can be efficiently used to estimate the congestion state of a network.

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Réseaux / Systèmes spatiaux de communication

How Attention Deep Learning Can Improve Copa Congestion Control Performance

Auteurs : Perrier Victor, Lochin Emmanuel, Tourneret Jean-Yves, Kuhn Nicolas et Gélard Patrick

In Proc. International Wireless Communications and Mobile Computing Conference (IWCMC), Dubrovnik, Croatia, May 30-June 3, 2022.

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Most modern congestion control algorithms, that aim to optimize delay and throughput, exploit more metrics than the sole packet loss congestion information. These additional metrics are mostly based on the round trip time evolution and allow congestion controls to reach better performance, in particular on wireless and cellular links as demonstrated by Copa, BBR, or REMY. Basically, these metrics allow congestion control to estimate the queuing level of the path and its evolution, to assess the presence of congestion. Actually, a good estimation of this level obviously prevents congestion losses, but also allows assessing a ratio of error link losses among the whole observed losses. The consistency and accuracy of these metrics are key to good congestion control performance, and this explains, for instance, the good performance of Copa currently in production at Facebook. However, these metrics remain challenging and the quest of an accurate and practical estimation seems complex. This paper investigates how a novel deep learning algorithm, known as Attention, can help in assessing queuing evolution and status on an end-to-end path. Among others, we focus on the evolution of the total time spent by packets in the buffers, which is the key metric of Copa. The results unequivocally demonstrate a better accuracy of this metric used by Copa.

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Réseaux / Systèmes spatiaux de communication

Séminaire

Tensor Sparse Representation Learning for Single-Snapshot Compressive Spectral Video Reconstruction

Auteur : Leon Lopez Kareth

Seminar of TéSA, Toulouse, May 12, 2022.

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As a multidimensional extension of matrices, tensors (≥3D) are a natural tool for representing and processing multidimensional data arrays. Capturing and recovering this multidimensional data is a long-term challenge in image processing and related fields. In particular, four-dimensional (4D) spectral videos contain highly redundant information across the spatial (2D), spectral (1D) and temporal (1D) axes which can be exploited through a data-learned sparse basis or dictionary. However, in compressive spectral video acquisition (where the data is compressed), tackling dictionary learning is time-consuming since it increases the computational complexity and presents drawbacks for real-time processing, where offline learning is required. In this talk, I will briefly introduce tensor representation and decomposition, and its application on spectral videos in a compressive sensing scenario. Then, I will present an approach to exploit tensor sparse representation for jointly learning the transform basis and the recovering from compressed measurements of a spectral video. I will show some results of the performance of the developed framework compared with matrix-based recovery approaches, including dictionary learning.

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Traitement du signal et des images / Observation de la Terre

An overview of Dark Matter theories and Zoom on the WIMP scenario

Auteur : Mimouni Kin

Seminar of TéSA, Toulouse, May 12, 2022.

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Dark Matter is a very active field of research in modern particle physics both on the theory and the experimental side. In this seminar, I will give a pedagogical introduction to particle Dark Matter physics and sketch the main challenges of this area of research. I will first present the astrophysical and cosmological evidence for Dark Matter and its general properties that can be inferred from observation. I will then move to the field of particle physics and discuss the general requirements of a viable Dark Matter model as well as the on-going experimental efforts to detect a potential Darl Matter particle. I will finish by showing a specific Dark Matter model, the supersymmetric WIMP, on which I have worked during my thesis.

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Autre

Présentation de soutenance de thèse

Performances des Protocoles de Transport dans les Constellations de Satellites

Auteur : Boubaker Amal

Defended on May, 2022

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Satellite constellations have taken a new impetus in recent years with even more ambitious future rojects. The momentum has lasted long enough to raise the interest of the research community in addressing the adequacy of protocols mainly designed and used for terrestrial networks, to these satellite communications. There are thus versions of TCP specially designed for satellite networks [1]-[5]. Nevertheless, these previous works could turn out to be obsolete, in particular due to the recent versions of TCP based, for instance, on hybrid-type congestion control algorithms. The question we tackled in this thesis is : are the recent versions of TCP, such as CUBIC and BBR, able to meet the needs in such an environment ? We evaluated the differences between past and currently deployed TCP stacks. We gave an overview of the evolution of the use of protocols from a transport layer point of view of CUBIC and BBR. We identified the sources of delay variation in satellite constellations in order to study their impact and frequency. Modern variants of TCP accommodate this, especially for long flows. We then looked at the fairness between the flows with or without different variants. We highlighted some levels of unfairness in the heterogeneous contexts that are fairly consistent with those found in the terrestrial context. All of these studies were conducted through discrete event simulations but also emulations in order to obtain more realistic results.

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Réseaux / Systèmes spatiaux de communication

Thèse de Doctorat

Performances des Protocoles de Transport dans les Constellations de Satellites

Auteur : Boubaker Amal

Defended on May 4, 2022.

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Satellite constellations have taken a new impetus in recent years with even more ambitious future rojects. The momentum has lasted long enough to raise the interest of the research community in addressing the adequacy of protocols mainly designed and used for terrestrial networks, to these satellite communications. There are thus versions of TCP specially designed for satellite networks [1]-[5]. Nevertheless, these previous works could turn out to be obsolete, in particular due to the recent versions of TCP based, for instance, on hybrid-type congestion control algorithms. The question we tackled in this thesis is : are the recent versions of TCP, such as CUBIC and BBR, able to meet the needs in such an environment ? We evaluated the differences between past and currently deployed TCP stacks. We gave an overview of the evolution of the use of protocols from a transport layer point of view of CUBIC and BBR. We identified the sources of delay variation in satellite constellations in order to study their impact and frequency. Modern variants of TCP accommodate this, especially for long flows. We then looked at the fairness between the flows with or without different variants. We highlighted some levels of unfairness in the heterogeneous contexts that are fairly consistent with those found in the terrestrial context. All of these studies were conducted through discrete event simulations but also emulations in order to obtain more realistic results.

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Réseaux / Systèmes spatiaux de communication

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