Scientific Production

SEARCH

Search

Conference Paper

Compliance of Single Frequency Ionospheric Delay Estimation and Cycle Slip Detection with Civil Aviation Requirements

Authors: Ouzeau Christophe, Macabiau Christophe, Roturier Benoît and Escher Anne-Christine

In Procc. National Technical Meeting of The Institute of Navigation, San Diego, USA, January 22-24, 2007

DOWNLOAD DOCUMENT

Ionosphere is a dispersive medium that can strongly affect GPS and GALILEO signals. Ionospheric delay affecting the GPS and GALILEO single frequency pseudorange measurements is the largest source of ranging error. In addition, this perturbation is difficult to model and thus difficult to predict. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS and GALILEO navigation signals at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO signals will bring their contribution as some of them will be transmitted at the same frequencies as the GPS signals. 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 the performance of techniques trying to sustain multi-frequency performance when a multi-constellation receiver installed in an aircraft loses dual frequency capability, during critical phases of flight. After a loss of several frequencies leading to a single frequency degraded mode, a receiver can use code and carrier phase pseudoranges made on only one carrier frequency to estimate the ionospheric delay. To achieve this estimation, the receiver can use the difference between code and carrier phase measurements. Indeed, this quantity can be modelled as twice the ionospheric delay plus noise, multipath, and the carrier phase ambiguity. The ionospheric delay can then be extracted from this, provided the ambiguity is properly removed. This can be achieved after convergence of a Kalman Filter for example, but then cycle slips need to be monitored. The probability of a cycle slip to occur is low but not negligible for civil aviation purposes. Several causes of cycle slips may be identified. For instance multipath, dynamics, signal blockage and ionospheric scintillation may be sources of this type of rupture in carrier phase measurements. Cycle slips may have random magnitudes. Those ones have to be detected and corrected with a performance compliant with civil aviation requirements for integrity, continuity, accuracy and availability. This problem of cycle slip detection is a priority before analyzing the accuracy of the single frequency iono corrected pseudorange. We propose to follow the methodology exposed below to assess the performance of potential algorithms of detection (and estimation) of cycle slips. First, the cycle slip detection and correction ability will be defined by the smallest cycle slip detectable with a required probability of missed detection. This smallest detectable cycle slip implies a bias on position error depending on geometry. Therefore, availability of protection against cycle slips compatible with APV 1 and APV 2 for instance, depends on geometry and must be computed at every second. The main goal of this paper is to know exactly the impact of the capability of cycle slip detection algorithms on the availability of reliable single frequency iono corrected pseudoranges.

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

READ MORE

PhD Thesis

Compression des Images Hyperspectrales et son Impact sur la Qualité des Données

Author: Christophe Emmanuel

Defended in October 2006

DOWNLOAD DOCUMENT

Hyperspectral images present some specific characteristics that should be used by an efficient compressionsystem. This thesis focuses on the definition and the optimization of a full wavelet compression system for hyperspectral images. In compression, wavelets have shown a good adaptability to a wide range of data, while being of reasonable complexity. Zerotree based compression algorithms are among the best for image compression. Therefore, in this work, efficient compression methods based on zerotree coding (EZW, SPIHT) are adapted on a near-optimal wavelet decomposition for hyperspectral images. Performances are compared with the adaptation of JPEG 2000 for hyperspectral images. End users of hyperspectral images are often interested only in some specific features of the image (resolution, location) which depend on the application. A further adaptation of the proposed hyperspectral image compression algorithm is presented to allow random access to some part of the image, whether spatial or spectral. Resolution scalability is also available, enabling the decoding of different resolution images from the compressed bitstream of the hyperspectral data while reading a minimum amount of bits from the coded data. Final spatial and spectral resolutions are chosen independantly. Finally, any lossless compression method cannot be characterized without the definition of a distortion measure. Therefore, a group of five quality criteria presenting a good complementarity is defined. The purpose is to make sure the compression algorithm does not impact significantly the data quality. A new method using these five criteria shows a good ability to discriminate between different degradations. Application of this method to the newly defined algorithm shows that the degradation remains low for compression rate around 1.0 bit per pixel per band.

Signal and image processing / Earth observation

READ MORE

PhD Defense Slides

Compression des Images Hyperspectrales et son Impact sur la Qualité des Données

Author: Christophe Emmanuel

Defended in October 2006

DOWNLOAD DOCUMENT

Hyperspectral images present some specific characteristics that should be used by an efficient compressionsystem. This thesis focuses on the definition and the optimization of a full wavelet compression system for hyperspectral images. In compression, wavelets have shown a good adaptability to a wide range of data, while being of reasonable complexity. Zerotree based compression algorithms are among the best for image compression. Therefore, in this work, efficient compression methods based on zerotree coding (EZW, SPIHT) are adapted on a near-optimal wavelet decomposition for hyperspectral images. Performances are compared with the adaptation of JPEG 2000 for hyperspectral images. End users of hyperspectral images are often interested only in some specific features of the image (resolution, location) which depend on the application. A further adaptation of the proposed hyperspectral image compression algorithm is presented to allow random access to some part of the image, whether spatial or spectral. Resolution scalability is also available, enabling the decoding of different resolution images from the compressed bitstream of the hyperspectral data while reading a minimum amount of bits from the coded data. Final spatial and spectral resolutions are chosen independantly. Finally, any lossless compression method cannot be characterized without the definition of a distortion measure. Therefore, a group of five quality criteria presenting a good complementarity is defined. The purpose is to make sure the compression algorithm does not impact significantly the data quality. A new method using these five criteria shows a good ability to discriminate between different degradations. Application of this method to the newly defined algorithm shows that the degradation remains low for compression rate around 1.0 bit per pixel per band.

Signal and image processing / Earth observation

READ MORE

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

DOWNLOAD DOCUMENT

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

READ MORE

PhD Thesis

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

Author: Millerioux Jean-Pierre

Defended in September 2006

DOWNLOAD DOCUMENT

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

READ MORE

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.

DOWNLOAD DOCUMENT

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

READ MORE

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.

DOWNLOAD DOCUMENT

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

READ MORE

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.

DOWNLOAD DOCUMENT

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

READ MORE

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

READ MORE

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.

DOWNLOAD DOCUMENT

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

READ MORE

Activity Report

READ MORE

Pau Closas, Northeastern Univ Boston, in TeSA

TeSA welcomes him with a research fellowship for July!

INP INNOV' 2019

Plenty of laurels for TeSA: congratulations to all!

Julien Lesouple, Sylvain Cluzel and Simone Urbano become Doctors

Congratulations!