Récepteurs en râteau pour les systèmes à étalement de spectre par séquences directes

This paper investigates the structure of a continuous and a discrete time Rake receivers. The former receiver is the most used and consists on combining the output of correlators locked on the most significant paths. Since the conventional synchronisation module of this receiver is not able to distinguish closer paths, we propose a maximum likelihood acquisition algorithm and an enhanced tracking loop. The latter receiver was recently suggested and works without the knowledge of path delays and their number. It is based on a global estimation of the impulse response of the multipath channel convolutionned with the shaping filter. Performance comparison of the two receivers is established for the fdd mode of the umts interface.     

Synthèse sur la réduction conjointe de bruit et d’écho pour lés systèmes mains-libres

In the context of modern telecommunications, hands-free systems allow to talk in a more natural way, without handling a telephone. This leads to new problems which were negligible in classical telephony: the superposition of energetic noise and echo on the speech signal. To solve these problems and to provide a sufficient speech quality, a joint reduction of these perturbations is needed. This paper presents a synthesis of solutions retained to achieve this reduction in the context of mono-channel and two-channel observations.     

Discrimination des modes pour l’étude des discontinuités dans les circuits planaires

The study of the dispersion phenomena of a planar transmission line in boxed structure is very intricate. In this paper we will try to determine the origin of the different modes by varying the geometrical parameters of the structure at a given frequency. We will also study the complex modes and their effects on thee characterisation of the planar discontinuities.     

Synthèse optimale d’un réseau de télécommunication avec contraintes de sécurité

A commonly used method for achieving a prescribed security level in a telecommunication network is to manage extra capacities all over the network. This paper describes a number of computational methods, both exact and approximate, for determining a minimum cost network of extra capacities needed to achieve security under any given trunk dimensioning, routing and grouping policy. From a mathematical point of view, it is shown that the problem reduces to the determination of a minimum cost network subject to a number of non simultaneous multicommodity flow requirements. Since real life instances of such problems commonly result in very large linear programs of many thousands of variables and constraints, the techniques of linear programming would be unacceptably time and space-consuming. Instead, it is shown how the use of Lagrangean relaxation in conjunction with sub-gradient optimization schemes can lead to efficient and easy-to-implement solution methods. The various procedures described in this paper form the heart of a general software product for long and medium term planning applications (Supersec program) which has already been used to investigate the economical implications of security requirements in telecommunication networks.     

Modélisation des discontinuités d’un objectif radar par des points brillants

In order to study the scattering of a monochromatic electromagnetic wave by a complex radar target, specialists usually modelize the target by a discrete scatterers model. The majority of the scatterers are represented by specular points of reflexion on the surface of the target, but the radar cross section (rcs) is also a function of surface discontinuities. In this article, we develop a method which allows us to replace the discontinuities by groups of point contributors of which the positions and thercs are given. Eventhough thercs are generally functions which decrease as the frequency increases, which can at times be neglected, it can be shown there exists quite frequentlyrcs which are independent of the wavelength. General formulae are given. It is emphasized that the physical optic integral may be used to calculatercs eventhough the conditions of application are not correct. For this reason a number of coefficients including the polarisations are used. The formulae of these coefficients are given. As a result an evaluation of thercs may be simplified, and the same method may be used to study the specular regions and the surface discontinuities.     

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.     

L’évaluation du succès de l’EDI dans lesPME: un modèle intégrateur

EDI is by far the Information Technology (IT) that has aroused, these last ten years, many interesting works in the field of theSME organizational development. The absence of federative conceptual framework is probably behind the great diversity of results, especially in the area of the prediction of its adoption and the evaluation of its success. These observations are behind a five years field research carried by an objective ofEDI success evaluation by end users. This article contributes to validate an “abductive” approach. To be made, it summarizes and classifies theoretical foundations of an analysis of thisIT impacts, and formulate an evaluation model using a system approach. Each of the three levels of the studied system (processing factor keys of success, quality of theEDI acceptance process, and success or internal performance) fact thus the object of premises allowing to confront observations of the four field enterprises to the conceptual framework and concepts identified in the review of the literature. Results of this approach using an appropriate qualitative methodology on cases of enterprises users ofEDI have allowed to validate the structure of the model and to refine the constructs of the different variables, that, so as to commit ulterior empirical works destined for validate the aimed explanatory of the model.     

Amélioration des performances des systèmes à haut débit par une méthode de réduction de la diaphonie dans les câbles multiconducteurs de télécommunications

dsl (Digital Subscriber Line) technology provides low cost access to the consumers and sources of information for any one subscribing to classical analogical telephony. Indeed xdsl services enable high-speed digital transmission on conventional telephone lines. For sixteen years that the internet has risen, a great number of offers proposing increasing bit rate have been developed. Considering this increasing demand of high bit rate access, telecommunication operators perpetually work on finding solutions to optimize the copper lines channel. In that way, we present here a new method of crosstalk reduction in a multiconductor telecommunication cable. Interests and limitations of this method are presented and some simulations on a frequency band extending to 30 MHz will picture those theoretical results.     

Evaluation des performances du réseau en anneau AMBRE pour distribution d’abonnés

ambre is an integrated services digital loop-like network for public local communication. Each communication is a sequence of fixed-length packets separated by fixed-length silences. Performance evaluation is carried through in terms of access-time and transport delays with emphasis on inter packet delay fluctuations.