Potentialités des séquences d’étalement chaotiques pour l’amélioration duTEEB d’un systèmeDS-CDMA asynchrone

The use of chaotic sequences as spectral spreading sequences in a Direct Sequence-Code Division Multiple Access is proposed in this paper. The simulation of the system is performed with the system simulator Omnisys. The chaotic spreading sequences are generated from a non-linear recursive equation. The Bit Error Rate of this system is compared with theBER of the same system using binary Gold sequences. The results show that chaotic sequences can improve performances in terms of allowable number of users.     

Étude théorique et expérimentale d’une modulation simplifiée par déplacement de fréquence d’indice 1/2 à phase continue

The minimum shift keying modulation (MSK)to which a lot of recent publications have been done,presents some advantage about linear and non-linear distortions towards common 2 or 4 Phase Shift Keying (PSK)modulations. The simplified MSK modulation described in this paper is obtained by linear filtering of a coherent 2 phase shift keying modulation. Then the demodulator can be implemented with a matched filter followed by a coherent demodulator using only one carrier recovery circuit. In the first part of this paper, the modulator and the demodulator are described. After, some theorical results in the presence of noise and other impairments are given. In CCETT laboratories at Rennes, a modem has been realized at a data rate of 2,048 Mbit/s and performs at 0,8 dB of the theoretical results.     

Utilisation de la corrélation pondérée dans un processus de détection d’intrusions

Generally, an intruder must perform several actions, organized in an intrusion scenario, to achieve his or her malicious objectives. Actions are modeled by their pre and post conditions, which are a set of logical predicates or negations of predicates. Pre conditions of an action correspond to conditions the system’s state must satisfy to perform the action. Post conditions correspond to the effects of executing the action on the system’s state. When an intruder begins his intrusion, we can deduce, from the alerts generated byidss (Intrusion Detection Systems), several possible scenarios, by correlating attacks, that lead to multiple intrusion objectives. However, with no further analysis, we are not able to decide which are the most plausible ones among the possible scenarios. We propose in this paper to define an order over the possible scenarios by weighting the correlation relations between successive attacks composing the scenarios. These weights reflect to what level executing some actions are necessary to execute some action B. We will see that to be satisfactory, the comparison operator between two scenarios must satisfy some properties.     

Étude du comportement d’une boucle de Costas en modulation MAQ 16 en présence d’évanouissements sélectifs

This paper gives the variance of the phase recovered by a conventional quadriphase Costas loop in 16 Qam modulation in the presence of a selective fading, represented as a three rays simplified model. The power spectral density of the phase error is computed using a spectral estimation technique. The phase error variance is evaluated for different values of the fade depth, the location of the maximum attenuation in the frequency band and the delay of the reflected ray. Finally the relation between the performance degradation and phase noise is given, assuming a gaussian p.d.f. of the phase error.     

À propos de la conception de systèmes d’aide aux déplacements des déficients visuels

This paper aims to contribute to studies related to visual handicap in order to reduce/eliminate it with new technologies. It addresses shortly the main principle of 3D world human perception, the main rules for environmental pertinent data acquisition and their processing. The proposed state of art on blind people travel assisting aids (taa) allow to understand the requirements for new aids design. A few examples of research project show how solution from new information technologies (such as artificial vision, virtual reality, high densityvlsi, tactile systems, GPS, wireless networks, etc) can be integrated in new systems. These examples allow also to determine which concepts should be targeted when designing any new travel assistance for blind people autonomous and safe displacement, and to characterise new devices.     

Reconnaissance des défauts et traitement d’images pour les composés III–V

This paper resumes the most recent results in the field of defect detection and analysis in III–V compounds by image analysis. The correlation of the defects with the specifications of the integrated circuits is especially emphasized. The production of integrated circuits or optoelectronic integrated circuits from III–V compounds is intended to bring large improvements in speed, power and radiation or thermal hardness. Such a development requires a precise control of the material quality and we will consider the relation between microscopic imperfections and device specifications through imaging techniques. This paper contents five chapters respectively devoted to: crystal growing and dislocation imaging; possible role of the deep centerEl2 in GaAs; correlation of defects withFet specifications; infrared transmission and scattering imaging; numerical processing and instruments. Computer assisted processing of image now gives a large aptitude for image transformation synthesis and recording; it allows also to conceive numerical processing and instruments. Computer assisted processing of images gives a large aptitude for image transformation, synthesis and recording; it allows to conceive a diagnostic of the quality of the wafer with respect to the structure that is be elaborated on.     

Retour d’expérience sur différentes applications de réseau actif

Active network technologies, started by D. Tennenhouse’s work atmit in 1995 have led a lot of promises on the evolution of data networks. Active networks aim at integrating new application-level functionalities into active nodes within the network, in a flexible and extensible way. The research works on active networks have raised at the same time as the definition of new open network architectures (e.g., Tina model) and the deployment of intelligent networks merging telecom networks with distributed systems fields. This concept of “programmable networks” led to many technology-oriented projects, but has not identified relevant applications highlighting the benefits of the technology. During the three last years, our laboratory has tackled this gap and prototyped some use cases of open programmable networks. The paper gives an overview of each of these use cases and focuses on the integration with existing network elements both at transfer and management planes. Then it presents some assessments and perspectives. We show that programmable networks are optimizing globally resources to be deployed although they impose an overhead at node level, thanks to efficient integration choices. We present two scenarios of deployment of current programmable network platforms within the same network configuration than a realwan network.     

Le dépôt et la cristallisation d’une couche mince organique au moyen d’un faisceau laser

An original technique to prepare thin organic films is presented. These materials are of interest for integrated optics. Films are formed after scanning of compacted powder of pom (3-methyl 4-nitropyridine 1-oxyd) with continuous wave Ar ion laser. The action of the laser is to evaporate organic molecules from the compact and cristallize them on a supporting substrate. The developments and limits of this technique are discussed.