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Conference Paper

Controlled Delay Scheduler for VoIP over LEO constellations on LMS channels

Authors: Tauran Bastien, Lochin Emmanuel, Lacan Jérôme, Arnal Fabrice, Gineste Mathieu and Kuhn Nicolas

In Proc. 9th Advanced Satellite Multimedia Systems Conference (ASMS), Berlin, Germany, September 10-12, 2018.

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Satellite transmissions can suffer from high channel impairments, especially on the link between a satellite and a mobile end-user. To cope with these errors, physical and link layer reliability schemes have been introduced at the price of an end-to-end delay increase resulting in high jitter. Unfortunately, both the delay and the jitter negatively impacts on multimedia traffic. As a matter of fact, not taking into account the channel state greatly decreases the Quality of Experience (QoE) of VoIP users. In this paper, we propose to solve this issue by scheduling data transmission as a function of the channel condition. We first investigate existing scheduling mechanisms and analyze their performance for VoIP traffic with the objective to lower both latency and jitter, which are the most important metrics to achieve a consistent VoIP service. We select the best candidate among several schedulers and propose a novel algorithm specifically designed to carry VoIP over LEO constellations. Our simulations show that in some scenarios, we double the QoE of VoIP users.

Networking / Space communication systems

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Shared Position Technique for Interfered Random Transmissions in Satellite Communication

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

In Proc. 9th Advanced Satellite Multimedia Systems Conference (ASMS), Berlin, Germany, September 10-12, 2018.

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In this paper we propose a new random access (RA) channel technique for the return link of satellite communications. It concerns slotted transmissions. This proposed method called Shared POsition Technique for Interfered random Transmissions (SPOTiT), is based on a shared knowledge between the receiver and each of the terminals. The shared information is about the time slot locations on which the terminal transmits its replicas as well as the preamble to use. The presented random version of SPOTiT aims to reduce the complexity of replicas localization process of the legacy technique Multireplica Decoding using Correlation based Localisation (MARSALA). It presents a less complex system without degrading performance and with no extra signaling information. Thus, SPOTiT is applied at the same level as MARSALA, i.e. when Contention Resolution Diversity Slotted Aloha (CRDSA) fails in retrieving more packets. This technique combined with CRDSA significantly reduces the number of data localization correlations, while maintaining the same performance as in CRDSA/MARSALA in terms of packet loss ratio and throughput.

Digital communications / Space communication systems

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PhD Defense Slides

Optimisation de la gestion des ressources sur la voie retour

Author: Couble Yoann

Defended on September 3rd, 2018.

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Networking / Space communication systems

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Conference Paper

Aircraft Vibration Detection and Diagnosis for Predictive Maintenance using a GLR Test

Authors: Urbano Simone, Chaumette Eric, Goupil Philippe and Tourneret Jean-Yves

In Proc. IFAC Symposium on Fault Detection, Supervision and Safety for Technical Processes (SAFEPROCESS), Warshaw, Poland, August 29-31, 2018.

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This paper studies a statistical approach to detect and diagnose a particular type of vibration impacting the control surfaces of civil aircraft. The considered phenomenon is called Limit Cycle Oscillation (LCO). It consists of an unwanted sustained oscillation of a control surface due to the combined effect of aeroelastic phenomena and an increased level of mechanical free play in the elements that connect the control surface to the aerodynamic surface. The stateof-the-art for LCO prevention is mainly based on regular free play checks performed on ground during maintenance operations. The detection is mainly achieved by the crew, and especially the pilot who can fill in a so-called “vibration reporting sheet” to describe the phenomena felt during the flight. Thus, the pilot sensitivity to vibration is still the only reference for LCO detection. In the Flight Control System (FCS) of modern aircraft there exist already several certified algorithms for the detection of vibrations of different nature, which use dedicated local sensors to monitor the control surface behaviour. The same kind of sensors have been chosen in a local approach, which eases the isolation of the vibration sources. This paper studies a new statistical approach based on the Generalized Likelihood Ratio Test (GLRT) in order to improve the state-of-the-art for LCO detection and diagnosis. The test and its theoretical performance are derived and validated. A straightforward method compliant with real-time implementation constraint for LCO prediction is proposed. A Monte Carlo test campaign is performed in order to assess the robustness and the detection/diagnosis performance of the proposed algorithm under different operating conditions.

Signal and image processing / Aeronautical communication systems and Space communication systems

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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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Journal Paper

A New Decision-Theory-Based Framework for Echo Canceler Control

Authors: Imbiriba Tales, Bermudez José, Tourneret Jean-Yves and Bershad Neil

IEEE Transactions on Signal Processing, vol. 66 , issue 16 , pp. 4304-4314, August 2018.

A control logic has a central role in many echo cancellation systems for optimizing the performance of adaptive filters, while estimating the echo path. For reliable control, accurate double-talk and channel change detectors are usually incorporated to the echo canceler. This work expands the usual detection strategy to define a classification problem characterizing four possible states of the echo canceler operation. The new formulation allows the use of decision theory to continuously control the transitions among the different modes of operation. The classification rule reduces to a low-cost statistics, for which it is possible to determine the probability of error under all hypotheses, allowing the classification performance to be accessed analytically. Monte Carlo simulations using synthetic and real data illustrate the reliability of the proposed method.

Signal and image processing / Localization and navigation

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Multifractal Analysis of Multivariate Images using Gamma Markov Random Field Priors

Authors: Wendt Herwig, Combrexelles Sébastien, Altmann Yoann, Tourneret Jean-Yves, Mclaughlin Stephen and Abry Patrice

SIAM Journal on Imaging Sciences, vol. 11, issue 2, pp. 1294-1316, 2018.

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Texture characterization of natural images using the mathematical framework of multifractal (MF) analysis, enables the study of the fluctuations in the regularity of image intensity. Although successfully applied in various contexts, the use of MF analysis has so far been limited to the independent analysis of a single image, while the data available in applications are increasingly multivariate. This paper addresses this limitation and proposes a joint Bayesian model and associated estimation procedure for MF parameters of multivariate images. It builds on a recently introduced generic statistical model that enabled the Bayesian estimation of MF parameters for a single image and relies on the following original key contributions : First, we develop a novel Fourier domain statistical model for a single image that permits the use of a likelihood that is separable in the MF parameters via data augmentation. Second, a joint Bayesian model for multivariate images is formulated in which prior models based on gamma Markov random fields encode the assumption of the smooth evolution of MF parameters between the image components. The design of the likelihood and of conjugate prior models is such that exploitation of the conjugacy between the likelihood and prior models enables an efficient estimation procedure that can handle a large number of data components. Numerical simulations conducted using sequences of multifractal images demonstrate that the proposed procedure significantly outperforms previous univariate benchmark formulations at a competitive computational cost.

Signal and image processing / Earth observation

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Conference Paper

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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Journal Paper

QoE enhancements on Satellite Networks through the Use of Caches

Authors: Thibaud Adrien, Fasson Julien, Arnal Fabrice, Pradas David, Dubois Emmanuel and Chaput Emmanuel

International Journal of Satellite Communications and Networking, pp. 1-13, June, 2018.

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A high throughput does not necessarily translate to a good Quality of Experience, especially in a satellite context. The round trip time, for instance, also has a tremendous impact on the reactivity of applications and thus on the Quality of Experience. Content delivery networks are massively used for over‐the‐top services in terrestrial network: They reduce the load of network and the delay as they draw the content closer to the end user. In a satellite system, the content delivery network presents a good opportunity for enhancing the end users' Quality of Experience and can change the conventional use of performance‐enhancing proxies. This paper investigates the satellite as access link for home networks or a backhaul link for small cells for a 5G perspective. We analysed the impact of caching on both gateway side and satellite terminal side for 2 on‐trend services: web browsing and adaptive video streaming (dynamic adaptive streaming over HTTP). The main contribution is an evaluation of transparent caching through a satellite platform. The caching policy is out of the scope of this paper. One large part of the testbed is based on an open‐source platform, OpenSAND that emulates the satellite system. To confirm the results, some real experiments have been conducted on a commercial satellite link. As expected, the transparent caching at the satellite terminal side can increase the Quality of Experience to its upper border as long as the content is available in the cache. For the satellite gateway cache, the performances exceed the expectations. Although the application experiences the satellite delay in this case, the traversal time of different Internet service provider networks also delays the delivery of content. Then it may have a greater impact on reactivity than the satellite itself. Through careful analysis of the different results, we noticed some issues. Transparent caching is unable to cache encrypted or dynamic content. Moreover, a misuse of caching can provoke bad behaviour of dynamic adaptive streaming over HTTP mechanisms and severely decrease the Quality of Experience. We designed a solution that in addition to solving the issue, alleviates the storage space of satellite terminal caches.

Networking / Space communication systems

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Activity Report

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PhD positions available at TeSA

PhD subjects available on the CNES site.
On line application before the 1st of April.

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Romain Chayot and Charles-Ugo Piat-Durozoi become Doctors

Congratulations!

Welcome to our new PhD students!

On this picture: Thomas, Vinicius and François (from left to right).