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Conference Paper

Ionospheric Code Delay Estimation in a Single Frequency Case for Civil Aviation

Authors: Ouzeau Christophe, Bastide Frédéric, Macabiau Christophe and Roturier Benoît

In Proc. 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS) Fort Worth, TX USA, September 26-29, 2006

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Ionosphere is a dispersive medium that can strongly affect GPS and GALILEO signals. Ionospheric delay affecting the GPS and GALILEO pseudorange measurements is the larger source of ranging error, if left uncorrected. In addition, this perturbation is difficult to model and thus difficult to predict. A multi-frequency receiver can identify and correct errors induced by the ionosphere, as in the nominal case, two frequencies are sufficient to determine precisely the ionospheric delay. However, if affected by radio frequency interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate techniques aimed at sustaining multi-frequency performance when a multiconstellation receiver installed in an aircraft is suddenly affected by radiofrequency interference, during critical phases of flight. The case of a loss of all but one frequency is studied in [Shau-Shiun Jan, 2003]. In this case, the usual code-carrier divergence technique is analyzed, consisting in computing the difference between the signal code and the carrier phase measurements. This difference is twice the ionospheric delay plus ambiguity plus errors, from which the ionospheric delay can be extracted. If a cycle slip occurs, the integer ambiguity appearing as a constant offset in the code-carrier difference causes this technique not to be valid. In the case of a single frequency receiver, a Kalman filter can be used to determine if a cycle slip occurs, introducing ambiguities of all satellites in view in the state vector as mentioned in [Lestarquit, 1995]. This Kalman filter can be initialized in the dual frequency mode, and left running when only one frequency is left. The aim of this paper is first to propose a method for single frequency ionospheric delay estimation after the loss of multiple frequency tracking, and also to analyse the performance of this method with regards to the civil aviation requirements. The proposed technique includes the detection of cycle slips.

Signal and image processing / Aeronautical communication systems and Localization and navigation

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PhD Thesis

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

Author: Millerioux Jean-Pierre

Defended in September 2006

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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.

Digital communications / Space communication systems

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Conference Paper

A Spectral Identity Card

Authors: Mailhes Corinne, Martin Nadine, Sahli Kheira and Lejeune Gérard

In Proc. European Signal and Image Processing Conference (EUSIPCO), Firenze, Italy, September 4-8, 2006.

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This paper studies a new spectral analysis strategy for detecting, characterizing and classifying spectral structures of an unknown stationary process. The spectral structures we consider are defined as sinusoidal waves, narrow band signals or noise peaks. A sum of an unknown number of these structures is embedded in an unknown colored noise. The proposed methodology provides a way to calculate a spectral identity card, which features each of these spectral structures, similarly to a real I.D. The processing is based on a local Bayesian hypothesis testing, which is defined in frequency and which takes account of the noise spectrum estimator. Thanks to a matching with the corresponding spectral window, each I.D. card permits the classification of the associated spectral structure into one of the following four classes: Pure Frequency, Narrow Band, Alarm and Noise. Each I.D. card is actually the result of the fusion of intermediate cards, obtained from complementary spectral analysis methods.

Signal and image processing / Other

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Condition Monitoring Using Automatic Spectral Analysis

Authors: Mailhes Corinne, Martin Nadine, Sahli Kheira and Lejeune Gérard

In Proc. European Workshop on structural health monitoring, Granada, Spain, July 5-7, 2006.

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Within the frame of machinery maintenance, spectral analysis is a helpful tool. Therefore, an automatic spectral analysis tool, capable to identify each component of a measured signal would be of interest. This paper studies a new spectral analysis strategy for detecting, characterizing and classifying all spectral components of an unknown process. Indeed, any vibration signal can be considered as a mixture of components, a component being either a sinusoidal wave, or a narrow band one. We assume that a sum of an unknown number of these components is embedded in an unknown colored noise. The complete methodology we propose provides a way to feature each component in the spectral domain. The first idea is not to choose one specific spectral analysis method but, rather, to concatenate the results of complementary algorithms. For each one, the noise spectrum is estimated by a nonlinear filter and spectral component detection is managed with a local Bayesian hypothesis testing. This test is defined in frequency and takes account of the noise spectrum estimator. Thanks to a matching with the corresponding spectral window, each component detected is classified into one of the following four classes: Pure Frequency, Narrow Band, Alarm and Noise. The second main idea is then to propose a fusion of the classification results, leading to a complete description of each spectral component present in the signal. This spectral classification is particularly interesting within the context of condition monitoring. Examples are given on real vibratory signals and show the performance of the proposed automatic method, which is particularly well adapted to signals having a high number of components.

Signal and image processing / Other

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Décorrélation des images hyperspectrales avec une décomposition 3D en ondelettes

Authors: Christophe Emmanuel, Mailhes Corinne and Duhamel Pierre

In Proc. Workshop on transform based ICA for audio, video and hyperspectral images data reduction and coding, Paris, France, July 6-7,2006.

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La quantité de données produite par les capteurs hyperspectraux nécessite un algorithme de compression efficace qui restè a définir. Les propriétés statistiquesparticulì eres devraient permettre d'obtenir des algorithmes de compression efficaces Etant données ses propriétés et sa faible complexité, la transformée en ondelettes est un candidat prometteur pour la décorrélation des images hyperspectrales. Ce papier propose une méthode pour trouver la décomposition en ondelettes optimale pour les images hyperspectrales et in-troduit la possibilité d'une décomposition non isotropique. La décomposition donnant le meilleur compromis débit-distortion est choisie. Cette décomposition donne de bien meilleures per-formances en terme de débit-distortion que la décomposition isotropique classique. L'inconvénient de cette décomposition optimale réside dans sa complexité importante. Une seconde décomposition, fixe cette fois, est définie et montre des perfor-mances quasi optimales tout en gardant une complexité faible.

Signal and image processing / Earth observation

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Best Anisotropic 3D-Wavelet Decomposition in a Rate-Distorsion Sense

Authors: Christophe Emmanuel, Mailhes Corinne and Duhamel Pierre

In Proc. IEEE Int. Conf. Acoust., Speech and Signal Processing (ICASSP), Toulouse, France, May 14-19, 2006.

Hyperspectral sensors have been of a growing interest over the past few decades for Earth observation as well as deep space exploration. However, the amount of data provided by such sensors requires an efficient compression system which is yet to be defined. It is hoped that the particular statistical properties of such images can be used to obtain very efficient compression algorithms. This paper proposes a method to find the most suitable wavelet decomposition for hyperspectral images and introduces the possibility of non isotropic decomposition. The decomposition is made by choosing the decomposition that provides an optimal rate-distortion trade-off. The obtained decomposition exhibits better performances in terms of rate-distortion curves compared to isotropic decomposition for high bitrates as well as for low bitrates.

Signal and image processing / Space communication systems

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A Wifi Network for Surveillance of Airport Mobiles

Authors: Bonacci David, and Castanié Francis

In Proc. Int. Workshop on Intelligent Transportation (WIT), Hamburg, Germany, March 14-15, 2006.

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Due to the continuous increase of airport traffic, there is the need to improve the safety of vehicle ground movements in the different airport areas and to improve also the efficiency of airport operations: several tens to hundreds of ground vehicles are sharing areas with the normal air traffic. The CLESTA project contributes to the solution of this problem by developing a new low-cost and modular platform with three components, namely, on-board system, communication network and ground system. The paper presents the platform architecture focussing into its innovative characteristics to provide, in an airport environment, the surveillance, control and guidance services for the airport main actors. This project led by M3 Systems, in partnership with TeSA and ENAC laboratories, and Intuilab company, aims at designing and deploying a positioning system for airport ground vehicles with service messages transmitted via a Wireless Network (Wifi, WiMax, ...) deployed outside in the airport area. In this context, technical objectives of the project consist in developing the software required for transmitting and processing of the service messages.

Digital communications and Networking / Localization and navigation

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Impact of SISMA Computation Algorithm on User Integrity Performance

Authors: Paimblanc Philippe, Macabiau Christophe, Lobert Bruno and Van Den Bossche Mathias

In Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, pp. 709-716, January 18-20 2006.

The European satellite navigation system GALILEO will provide radionavigation signals for a variety of applications. Safety Of Life users will get a safe navigation service through ranging signals carrying integrity information. The Galileo Integrity Baseline algorithm includes the transmission of three parameters allowing users to monitor their integrity level. These parameters are the Signal-In-Space Accuracy (SISA: prediction of the minimum standard deviation of a Gaussian distribution overbounding the Signal-In-Space error in the fault-free case), the Signal-In-Space Monitoring Accuracy (SISMA: minimum standard deviation of a Gaussian distribution overbounding the difference between Signal- In-Space error and its estimation by ground control stations) and the Integrity Flag, which accounts for satellite status (it can be set to 'OK', 'DON'T USE' or 'NOT MONITORED'). These parameters are part of the input of the user integrity algorithm, which computes user integrity risk at the alert limit and compares it to the Integrity Risk requirement corresponding to user's phase of flight. The work presented in this paper studies the influence of the algorithm used for computation of SISMA on user integrity and system availability. The algorithms used to compute SISMA are the reference Least-Squares and several robust methods, designed to reject wrong measurements and decrease ground system False Alarm rate (fault-free satellites flagged 'DON'T USE').

Signal and image processing / Localization and navigation

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Journal Paper

Quality Criteria Benchmark for Hyperspectral Imagery

Authors: Christophe Emmanuel, Leger Dominique and Mailhes Corinne

IEEE Transactions on Geoscience and Remote Sensing, vol. 43, n° 9, pp. 2103 - 2114, September, 2005.

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Hyperspectral data appear to be of a growing interest over the past few years. However, applications for hyperspectral data are still in their infancy as handling the significant size of the data presents a challenge for the user community. Efficient compression techniques are required, and lossy compression, specifically, will have a role to play, provided its impact on remote sensing applications remains insignificant. To assess the data quality, suitable distortion measures relevant to end-user applications are required. Quality criteria are also of a major interest for the conception and development of new sensors to define their requirements and specifications. This paper proposes a method to evaluate quality criteria in the context of hyperspectral images. The purpose is to provide quality criteria relevant to the impact of degradations on several classification applications. Different quality criteria are considered. Some are traditionnally used in image and video coding and are adapted here to hyperspectral images. Others are specific to hyperspectral data.We also propose the adaptation of two advanced criteria in the presence of different simulated degradations on AVIRIS hyperspectral images. Finally, five criteria are selected to give an accurate representation of the nature and the level of the degradation affecting hyperspectral data.

Signal and image processing / Earth observation

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Conference Paper

Implementation Of Robust Estimation Algorithms in the GALILEO Baseline Integrity Check

Authors: Paimblanc Philippe, Macabiau Christophe, Lobert Bruno, Van Den Bossche Mathias and Lannelongue Stéphane

Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, pp. 1327-1338, September 13-16 2005.

The European satellite navigation system GALILEO will provide radio-navigation signals for a variety of applications. Safety Of Life users will get a safe navigation service through ranging signals carrying integrity information. The Galileo Integrity Baseline algorithm includes the transmission of three parameters allowing users to monitor their integrity level. These parameters are the Signal-In- Space Accuracy (SISA: prediction of the minimum standard deviation of a Gaussian distribution overbounding the Signal-In-Space error in the fault-free case), the Signal-In-Space Monitoring Accuracy (SISMA: minimum standard deviation of a Gaussian distribution overbounding the difference between Signal-In-Space error and its estimation by ground control stations) and the Integrity Flag, which accounts for satellite status (it can be set to “OK”, “DON’T USE” or “NOT MONITORED”). The work presented in this paper studies the possibility of computing SISMA using a statistically robust algorithm, so as to reject wrong measurements and decrease ground system False Alarm rate (fault-free satellites flagged “DON’T USE”).

Signal and image processing / Localization and navigation

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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).