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Conference Paper

Optimal Configuration for Satellite PEPs using a Reliable Service on Top of a Routers-Assisted Approach

Authors: Lopez Pacheco Dino and Lochin Emmanuel

In Proc. International Workshop on Satellite and Space Communications (IWSSC), Siena, Italy, September 09-11, 2009.

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Routers-assisted congestion control protocols, also known as Explicit Rate Notification (ERN) protocols, implement complex algorithms inside a router in order to provide both high link utilization and high fairness. Thus, routers assisted approaches overcome most of the end-to-end protocols problems in large bandwidth-delay product networks. Today, routers-assisted protocols cannot be deployed in heterogeneous networks (e.g., Internet) due to their non-compliance with current network protocols. Nevertheless, these approaches can be deployed in satellite networks in the context of splitting PEPs. In this work, as routers-assisted protocols can use TCP algorithms to enable reliability, we aim at understanding and providing a detailed view of the impact of such algorithms on the performance obtained by routers-assisted protocols over satellite links. In particular, we both study XCP and P-XCP proposals over long delay, lossy and asymmetric links and propose a ns-2 implementation of the P-XCP protocol to the satellite community. To the best of our knowledge, this study is the first one which tackles the impact of TCP internal mechanisms on top of XCP protocol. Our main conclusion is that TCP New Reno Slow But Steady variant on top of P-XCP is to date, the most optimal configuration for satellite proxies.

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Networking / Space communication systems

Modèles de Markov cachés appliqués au masquage de perte de paquets en voix sur IP

Authors: Koenig Lionel, André-Obrecht Régine, Mailhes Corinne and Fabre Serge

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), September 8-11, 2009.

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Packet loss due to misrouted or delayed packets in voice over IP leads to huge voice quality degradation. This paper presents a packet loss concealement algorithm which is inde pendant from the vocoder. This method relies on hidden Marko v model (HMM). A new voicing parameter is introduced to get ove r voiced/unvoiced sound separation and use a unique HMM. Since best parameter for prediction are not necessarily the best ones for synthesis, we introduce two separate vectors: the first one dedicated to the analysis of the signal and the second one featured for the synthesis of missing part. Performances of the proposed system are evaluated on parts of well-known speech corpora, leading to promising results.

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Signal and image processing / Space communication systems

Unmixing Hyperspectral Images Using a Normal Compositional Model and MCMC Methods

Authors: Eches Olivier, Dobigeon Nicolas, Mailhes Corinne and Tourneret Jean-Yves

In Proc. IEEE Workshop on Stat. Signal Processing (SSP), Cardiff, Wales, UK, August 31 - September 3, 2009.

This paper studies a new unmixing algorithm for hyperspectral images. Each pixel of the image is modeled as a linear combination of endmembers which are supposed to be random in order to model uncertainties regarding their knowledge. More precisely, endmembers are modeled as Gaussian vectors with known means (resulting from an endmember extraction algorithm such as the famous N-FINDR or VCA algorithm). This paper proposes to estimate the mixture coefficients (referred to as abundances) using a Bayesian algorithm. Suitable priors are assigned to the abundances in order to satisfy positivity and additivity constraints whereas a conjugate prior is chosen for the variance. The computational complexity of the resulting Bayesian estimators is alleviated by constructing an hybrid Gibbs algorithm to generate abundance and variance samples distributed according to the posterior distribution of the unknown parameters. The associated hyperparameter is also generated. The performance of the proposed methodology is evaluated thanks to simulation results conducted on synthetic and real images.

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Signal and image processing / Earth observation

A New Feature Vector for HMM-Based Packet Loss Concealment

Authors: Koenig Lionel, André-Obrecht Régine, Mailhes Corinne and Fabre Serge

In Proc. European Signal and Image Processing Conference (EUSIPCO), Glasgow, Scotland, August 24-28, 2009.

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Packet loss due to misrouted or delayed packets in voice over IP leads to huge voice quality degradation. Packet loss con- cealment algorithms try to enhance the quality of the speech. This paper presents a new packet loss concealment algorithm which relies on one hidden Markov model. For this purpose, we introduce a continuous observation vector well-suited for silence, voiced and unvoiced sounds. We show that having a global HMM is relevant for this application. The proposed system is evaluated using standard PESQ score in a real- world application.

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Signal and image processing / Other

A Method of Computation for Worst-Case Delay Analysis on Spacewire Networks

Authors: Ferrandiz Thomas, Frances Fabrice and Fraboul Christian

In Proc. IEEE International Symposium on Industrial Embedded Systems (SIES 2009), Lausanne, Switzerland, July 8-10, 2009.

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SpaceWire is a standard for on-board satellite networks chosen by the ESA as the basis for future data-handling architectures. However, network designers need tools to ensure that the network is able to deliver critical messages on time. Current research only seek to determine probabilistic results for end-to-end delays on wormhole networks like SpaceWire. This does not provide sufficient guarantee for critical traffic. Thus, in this paper, we propose a method to compute an upper-bound on the worst-case end-to-end delay of a packet in a SpaceWire network.

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Networking / Other

A Continuous Voicing Parameter in the Frequency Domain

Authors: Koenig Lionel, André-Obrecht Régine, Mailhes Corinne and Fabre Serge

In Proc. Int. Conf. on Speech and Computer (SPECOM), Saint Petersbourg, Russia, June 23-25, 2009.

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In automatic speech analysis, voicing articulatory is often defined as a binary decision: voiced or unvoiced. Lin- guists agree that this articulatory should be continuous. In this paper, we present a new approach to compute a con- tinuous voicing indicator of a speech frame. This voic- ing percentage is then evaluated in both a segmentation process and a speech recognition task. Promising results show that this continuous voicing percentage may be used as a reliable voicing indicator.

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Signal and image processing / Other

A Non-Stationary Index Resulting from Time and Frequency Domains

Authors: Martin Nadine and Mailhes Corinne

In Proc. Condition Monitoring (CM 2009), Dublin, Ireland, June 23-25, 2009.

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Detecting the presence of non-stationarity events in a signal is a challenge that is still not taken up. The aim of this paper is to make a contribution to this key issue. We already proposed a non-stationarity detection defined in time-frequency domain in order to control the invariance of the time-frequency statistics. In this paper, in order to be not limited by the time and frequency resolution of a time-frequency approach, we propose another test in frequency domain. In frequency domain, the problem can be cast by taking advantage of the normalized-variance properties of a spectral estimator when analyzing non-stationary signals. This second test will confirm, invalidate or detect new frequency localizations of non-stationarities. Finally, the main contribution of the paper is to propose a stationary index defined so as to merge the information given by these two tests and to allow an alarm to be raised for a high level of non-stationarities. Applications on real-world signals show the pertinence of this new index.

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Signal and image processing / Other

PhD Thesis

Safe Navigation for Vehicles

Author: Spangeberg Mariana

Defended in June 2009

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Satellite navigation has acquired an increased importance during these last years, on the one hand due to the imminent appearance of the European GALILEO system that will complement the American GPS, and on the other hand due to the great success it has encountered in the commercial civil market. An important part of this success is based on the technological development at the receiver level that has rendered satellite navigation possible even in difficult environments. Today’s objective is to prepare the utilisation of this kind of signals for land vehicle applications demanding high precision positioning. One of the main challenges within this research domain, which cannot be addressed by classical coupling techniques, is related to the system capability to provide reliable position estimations. The enhancement in dead-reckoning technologies (i.e. size reduction of MEMS-based sensors or gyroscopes) cannot all by itself reach the necessary confidence levels if exploited with classical localization and integration algorithms. Indeed, these techniques provide a position estimation whose reliability or confidence level it is very difficult to quantify. The feasibility of these applications relies not only on an extensive research to enhance the navigation algorithm performances in harsh scenarios, but also and in parallel, on the possibility to maintain, thanks to the presence of additional sensors, a high confidence level on the position estimation even in the absence of satellite navigation signals.

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Signal and image processing / Localization and navigation

Application des techniques multiporteuses OFDM pour futurs systèmes de télécommunications par satellite

Author: Ho Anh Tai

Defended in March 2009

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This thesis studies the applicability of OFDM techniques for future satellite telecommunications systems. In particular, he treats the synchronization problem at the receiver for satellite broadcasting systems in Ka band. The system uses QAM modulation with M phase stages and works in continuous mode, at small signal to noise ratio (typically at Eb/N0 = 0dB). The main objective of this thesis is to propose a receiver synchronization structure using as least resources as possible in order to optimize spectral efficiency. Two studies are carried out. The first study consists of proposing and validating a synchronization structure in the aim of optimizing spectral efficiency. The second study evaluates the performance of this structure then, compares it with existing standards such as DVB-S and DVB-S2 in terms of spectral efficiency. For first study, synchronization errors have been identified and their impact on system performance evaluated. These results prove that excepting clock frequency error, other synchronization errors have to be estimed and corrected. The transmission in continuous mode for fixed satellite broadcasting system allows the use of NDA (Non-Data-Aided) loop structure in order to avoid the use of pilots, then improve spectral efficiency. However, these algorithms need a coarse synchronization stage in order to limit interference terms. So, the synchronization includes a coarse stage in order to limit interference terms and a finer stage in order to improve system performance. For coarse synchronization stage, simulation results prove that algorithms using guard interval give better performance than whom using pilots. The second study evaluates performance of the proposed structure. In coarse synchronization stage, this evaluation allows to specify guard interval length then, calculate and compare system performance in terms of spectral efficiency with its in DVB-S and DVB-S2 standards. Then, performance evaluation of fine synchronization stage allows to calculate degradations of the proposed structure in the absence and in presence of phase noise models, one of important parameters in a telecommunications system. This stage allows not only to define operating points of the proposed structure in presence of phase noise models in existing standards but also to define phase noise mask of Wiener model supported by this structure. Finally, a study on the hanging time of the proposed structure allows to evaluate the time neccesary to this structure, based on blind algorithms, to be converged. Another study also evaluates the complexity of this structure. This study shows that the synchronization structure proposed in this thesis uses little resources both in terms of spectral efficiency and number of calculations.

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Digital communications / Space communication systems

Conference Paper

Modelling New Indoor Propagation Models for WLAN Based on Empirical Results

Authors: Sadiki Tayeb and Paimblanc Philippe

In 11th IEEE International Conference on Computer Modelling and Simulation (UKSIM'09), pp. 585-588, Cambridge, United Kingdom, March 25-27 2009.

This paper presents the modelling of new WLAN models for different indoor environments. This work was carried out in the frame of the FIL project which is funded by the French research agency ANR, in collaboration with Thales Alenia Space France. Based on the standard Opnet models for WLAN nodes, the propagation loss estimation for these types of environment has been improved. We derive an empirical model for spatial registration patterns of mobile users as they move within a TeSA Labs wireless local area network (WLAN) environment and register signal power from different access points. Such a model can be very useful in a variety of simulation studies of the performance of mobile wireless systems, to address issues such as resource management and mobility management protocols. We base the model on extensive experimental data from a TeSA Labs 2.4 GHz WiFi LAN installation. We divide the empirical data available to us into training and test data sets, develop the model based on the training set, and evaluate it against the test set. The new scenarios used to simulate these new propagation models are shown. Finally, results, conclusions and further work are given.

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Signal and image processing and Digital communications / Localization and navigation

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