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.     

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.     

Correction de deux paquets d’erreurs par un code de Reed-Solomon

Algebraic decoding procedures can be greatly simplified in case the number of errors being corrected is small. The authors present here a decoder which is capable of correcting errors occuring on four bits packets. The considered code is a (15, 11) Reed-Solomon code over GF (16). A Meggitttype decoder has been selected. The hardware implementation consists of 49 ttl (ls) packages and operates for the present at a rate of 5 Mbit/s. The utilisation of this decoding scheme is considered for other Reed-Solomon codes.     

Structure des bifurcations d’un endomorphisme du cercle en lui-même dans un plan de parametres

One studies the bifurcations structure of the endo-morphism of the circle into itself T defined by : \(Tx_n = x_n + \Omega - \frac{K}{{2\pi }}\sin (2\pi x_n )\) (mod. 1) in a part of the parameter plane (K, Ω). One makes appear a mixing between two bifurcations structure : the boxes in files one which appears in dijfeomorphisms of the circle and the box within a box one which appears in one-dimensional endomorphism defined by a polynomial of second or third degree.     

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.     

Internet et performance de l’entreprise: Étude de l’organisation industrielle de 104PME en Loire-Atlantique

What is the influence between Internet and the enterprise performance? This study presents the relationship between the Internet applications (web, business intelligence, e-commerce, internal communication, cross-companies cooperation) and growth and profit of Small and Medium Enterprises (SMEs). If a direct “impact” is tested, an indirect relationship is nevertheless submitted to a test through intermediary variables i.e. industrial organization according to Pavitt (1984) and the structure. The study of 104SMEs in Loire-Atlantique (France) did not find any direct “impact” of Internet applications on enterprise performance. On the other hand, an indirect influence was found, especially through the specific use of Internet bySMEs belonging to “mass production”, “specialized supplier” and “high tech” industries.     

Codage pour modulation d’amplitude en quadrature à grand nombre d’états avec partition à plusieurs niveaux

We present a new multilevel coding technique for the quadrature amplitude modulation with a high number of states (64-QAM and 256-QAM). The constellation is partitioned into four subsets, two bits coded with the samebch code selecting the label of each subset. We show that our system, with a double error correctingbch code, gives better results, considering redundancy, decoding simplicity and performance, than the systems known bx now (using the Reed-Solomon code (64,62), the Lee-Nakamura and Hamming codes). Preliminary differential encoding of the two coded bits and utilisation of a transparentbch code can solve the phase ambiguity problem in a simple way.