Analyse de signaux à composantes quasi sinusoïdales

Estimation of spectral lines of a finite duration observation can be viewed as an application for linear prediction models. The authors discuss the feasibility in describing a quasisinusoidal signal with noise, either as a sum of spectral lines in additive noise or as anarma noise with few poles near the unit circle. To both of these models, correspond two problems of estimation which aims are two different characterizations of the observation. In these two cases, is given the form of the maximum likelihood estimator, and the consequences of the use of one estimator instead of the other are examined.     

Analyseur scalaire de réseau millimétrique couvrant de 16 à 250 GHz

The growing needs to cover the millimeter range have hitherto been restrained by the heaviness and cost of the necessary devices. The problem of available sources is a difficult one : some (Gunn diodes) are small and workable, but very narrowly tunable ; others (bwo tubes) are quite widely tunable, but cumbersome and relying on high-voltage power supplies. The very high frequency range (over 100 GHz) requires klystrons (whose lifetime is short) or carcinotrons (which are powerful, but correspond to a huge investment in terms of money and space). We present here a recently marketed system based on an original idea. Very convenient, workable and lightweight, it is, up to now, the only device in the world which permits to work in the most extended millimeter range, from 16 to 250 GHz continuously, without a great number of sources or any removable drawers. The dynamic range measured is superior to 70 dB from 16 to 94 GHz, and better than 50 dB up to 170 GHz.     

Décodage à sortie souple des réseaux de points

We present a universalmse algorithm for lattice decoding in dimensions up to 1024 for both Gaussian and Rayleigh fading channels. This algorithm can be applied to decode high diversity multidimensional rotations. The decoding is performed by a decision feedback equalizer and provides soft output which allows a concatenation of the lattice codes with other type of error-correcting codes. The problem of selecting a good rotation is also considered, and we show that a high dimensional random rotation exhibits very good performance on a Rayleigh fading channel.     

ACTIF: une aide à la conception de systèmes de transports interopérables en france

This article introducesActif the French its framework architecture :

– for readers already in the its domain, it will give a global and prospective view on this project and light on the “stakeholders” role with respect to ITS deployment ;

– for the newcomers, it shall introduce the issues of interoperability and information exchange between systems, and help understand how theActif approach may be similar to the systems engineering approach they are familiar with in their domain.

     

Architecture d’un réseau actif à base de services Web

This paper presents a novel active architecture for building and deploying network services:aswa, Web Services based Active network Architecture. At the architectural level,aswa defines an active node whose functionalities are divided into the Node Operating System, the Execution Environment, and the Active Applications. At the implementation level,aswa is a Web Services based platform where new components could be added and deployed, in order to dynamically modify network nodes behavior. Applications can be developed with any language and communicate across heterogeneous environments, and across Internet and Intranet structures. At the deployment levelaswa uses an active node approach, and offers a controlled deployment mode. In terms of security, Authentication of deployed code and protection of the nodes is achieved by the use ofhttps and the header extensions of thesoap envelope. Finally to validate this architecture,aswa defines a Firewall as an Active Application to secure the code deployment.     

Compression de données brutes et d’images de radar à synthèse d’ouverture

This paper draws a state of the art of synthetic aperture radar (sar) data compression. Both raw data and synthesized image compression have been investigated. Compression of radar raw signal and sar image are considered separately since those two cases are specific. Also, Radar raw/image compression remains different from optical image compression and has to be considered with specific strategies that are adapted to the context.     

Analyse de la stabilité spectrale d’un laser DFB à trois sauts de phase (3PS-DFB)

The aim of this article is to analyze the spectral stability of the three phase shift distributed feedback (3ps-dfb) laser by using Time domain model (tdm). We have developed a software that simulates static and dynamic properties of distributed feedback (dfb) multi-sections laser at large signal. The best single-mode stability operation up to 18mW of the 3ps-dfb is achieved for three phase shifts at (π, π, π) whatever the phase position. These results showed that the 3ps-dfb laser was a much more suitable structure to realize stable single-mode high-power operation for a coherent optical communication system.     

Nouvelle expression temporelle de ľimpédance interne des conducteurs à section rectangulaire

In this paper, a new time domain internal impedance formula for characterizing the skin effect in interconnects of rectangular cross section is proposed. The comparison with the simulation results of a method involving frequency domain exact formula validates the present model and illustrates its accuracy. We have also shown the lack of precision of the formulations based on conductor losses varying as √ f In order to predict the responses of lossy planar transmission lines, the used methods are the time domain — frequency domain transformation (tdfd) and the finite difference time domain algorithm (fdtd). Theses techniques of analysis are applied to the mtl equations under quasi — tem approximation.     

Contribution à la modélisation de lignes hyperfréquences supraconductrices à haute température critique par la méthode FDTD

The purpose of this study is to determine the electrical behaviour of high-Tc superconductor microstrip lines. TheFdtd method is used to put into discrete terms Maxwell’s equations. The two-fluid model has been chosen to describe the behaviour of the superconductor. The variation of electrical parameters such as surface resistance as a function of frequency up to 60 GHz is presented.     

Les terminaux de télécommunication face à l’environnement radioélectrique

This paper presents the work being carried out in the Emc field for the new telecommunication terminals so that the french telecommunications network should not be disturbed and a good service quality could be maintained even in presence of high level radio frequency ambients.     

Modèles de télétrafic pour le réseau à intégration de services du satellite TELECOM 1

The author discusses models of multiservice circuit switched communications systems where, in particular, the amount of transmission capacity (e.g. bit rate) depends on the call type. Two modes of call set up are considered: «on demand» with blocked calls cleared and «reservation» where capacity is previously reserved for planned calls. The latter mode is described generally and, for particular cases, we suggest interpretations leading to birth process and multiservice queue models. The models have been studied for evaluating the performance of the telecom 1business communication network but derived exact and approximate results should be useful in other applications.     

Réalisation d’un opérateur de traitement numérique rapide par une machine à flux de données

The authors describe a fast, parallel and static data flow architecture that is used for Fast Riccati Operator (Fro)design. This operator has a cellular, regular structure easy to integrate, and is intended to resolve with high speed execution the matrix Riccati equation for filtering purpose. To evaluate its performances, two solving algorithms, Lindquist and quasilinéarisation, are represented and simulated by data flow Petri nets, defined for this purpose. Simulation results are compared to real needs in search and tracking situations.     

Étude du comportement du transistor à effet de champ au GaAs sous injection optique quasi ponctuelle

This paper describes the observed phenomena while a mesfet is illuminated with a circular spot of about 1.5 μmdiameter. The various depletion regions of the device are highlighted by this technique. The experimental results can partly be explained by the photovoltaic effect associated with these depletion regions and the photoconductive effect in the channel. The high values obtained for the photoconduction responsivity are ascribed to the photoconduction mecanism itself and to the widening of the channel at the substrate interface and at the surface.     

Détermination des directions de normale d’onde de signaux variant dans le temps. Application aux émissions naturelles TBF détectées à bord de satellites

A method for studying the polarization of an electromagnetic plane wave, the characteristics of which vary rapidly in time, is described. This method is based upon the concept of the (instantaneous) complex representation of a polarized signal. It is possible in particular to yield the wave normal direction as a function of both time and frequency. The accuracy of the method is studied, as a function of both the signal-to-noise ratio and of the eccentricity of the polarization ellipse. This method is applied to the determination of wave normal directions of natural Vlf signals propagating in the whistler mode within the magneto sphere. Important variations in the propagation characteristics of the signals are evidenced.     

Mesures de propagation en polarisation circulaire sur un trajet Satellite-Terre à l’aide du satellite SIRIO 1

In this paper are described the characteristics of cnet experimental Earth station at Gometz La Ville, and the propagation measurements which were made there on signals transmitted by the Italian experimental communication satellite sirio 1,then are shown some examples of rough data and statistics obtained.     

Sur un modèle précis de la permittivité effective statique de la ligne microruban suspendue uniforme applicable à la technique des LECF

An accurate modelling of static effective permittivity ?_eff of a uniform suspended microstrip line is presented. This modelling is built on the variational method of moments (Vm). But this method requires high times computing for line of arbitrary shape, the width w of the uniforme line is reduced by the thickness h₁ of the air gap. The stratified microstrip patch antennas with an air gap, of arbitrary shape present this type of situation in the analysis with the method of the Finished Coupled Elementary Lines (F.c.e.l). A formal model proposed in this work, is free of integration and derivation, and is connecting the physical parameters (such as the relative permittivities ?_ri of the mediums i = 1,2…) with those of the geometrical structure (u = w/h₁ and m — h₂/h₁ where h₂ is the thickness of dielectric). The new model is valid for the full 1 ≤ ?_r ≤20, 0.5 ≤m≤ 1.5, 10^?2 ≤ult; +∞ ranges. The model is successfully compared with mesured data. This work give an accurate evaluation of ?_eff then the frequency dependence of the effective permittivity can be easily determined.     

Détermination du facteur de multiplication M pour un fonctionnement optimal des photodétecteurs à avalanche

The purpose of this paper is relative to the determination of the multiplication factor Mfor an optimum behaviour of the avalanche photodetector. Two types of avalanche photodetector s are compared: a silicon structure n ⁺ πpπp ⁺ Read diode and a GaAlAs heterostructure. Calculating the Noise Equivalent Power (nep)of the whole system, the law S_i(f) =2q I_phoM_x is used, where the parameter x is determined experimentally in both avalanche photodetectors. The exponent x (between 2 and 4) dominates in the nep expression and the ideal nep for the avalanche photodetector system is obtained when x equals 2.     

Méthodes d’analyse et de synthèse de quelques “ microantennes” à large bande en mode quasi transversal électromagnétique

The transmission line model has been utilized to determine the input impedance, the bandwidth, the radiation patterns and the mutual impedance of several microstrip antennas such as the arbitrary shape patch antennas and the wideband flat dipole which is an hybrid radiating source. We suppose that the dominant mode of propagation is the quasiTem one having negligible variation of fields in the transverse direction. Nevertheless a general scattering problem of an arbitrary shaped tridimensional antenna solved by moments method and the finite difference approach applied to integral equations has explained the very large bandwidth microstrip antenna behaviour. The wideband flat dipole has been used in flat arrays, with more than several hundred of such elements, and in microstrip phased arrays with beam steering in a large angular sector.     

Dynamique des lasers à fibre dopée à I’erbium

The dynamics of the erbium doped fiber laser is analysed both experimentally and theoretically. This laser operates spontaneously in self-pulsing, in sinusoidal or in CW regime. Experiments have allowed to determine the control parameters : the cavity losses, the pumping rate and the ion pairs concentration. An antiphase dynamics is observed when the laser operates simultaneously at 1.55 µn and 1.536 µm. The self-pulsing behavior is attributed to a fast energy transfer which occurs between two neighboring ions (pair induced quenching). A simple model considering the active medium as a mixture of isolated ions and ions pairs is developped and leads to a good qualitative agreement with the experimental results.