Conception des systèmes de protection des réseaux d’énergie à basse tension contre les impulsions électromagnétiques à haute altitude et la foudre

An exoatmospheric nuclear burst creates, by interactions photonsmatters, an electromagnetic field (electromagnetic pulse- Emp ). Its coupling with links,particularly overhead power ac supply lines of ground stations, induced a parasitic electrical pulse fast and intense, susceptible to perturb, damage or destroy down stream electrical or electronic equipments. Otherwise, the lightning can also generates, on the same links, electrical pulses with some différents characteristics. After a quick recall of the problem and specifications, the design methodology of protective devices against this pulse created by nemp and lightning, for ac power lines, is given. This method implement computed aided design (cad)and specific experimental ways. The protection efficiency is evaluated and validated, exemples of achievements described.     

Recherche locale à voisinage variable pour le routage optique dans des réseaux utilisant des routeurs latins

This paper proposes an approach based on Variable Neighbourhood Search (vns) to solve the Routing and Wavelength Assignment (rwa) problem in optical networks including latin routers. It can be summed up as establishing routing (finding intermediate routers on optical paths between each origin/destination pair) and wavelength assignment of these optical paths in such networks. The problem will be tackled according to two scenarii: to optimize the number of established connections (scenario 1) or to answer as well as possible an accurate traffic array (scenario 2). In traditional optical networks (without latin routers), one often separates routing and wavelength assignment because of the general problem complexity (each of the two sub-problems isnp-hard). However, latin routers introduce constraints connecting routing and assignment, this requires a simultaneous treatment of the two problems. A local search heuristic,vnsfor, based on the definition of different neighbourhoods (with simple and double moves) is proposed in this paper to provide us with solutions close to the optimum. Experimental results show howvnsfor leads to better solutions, according to both scenarii, in comparison with the reference algorithmlonca.     

Décodage Syndromique à Complexité Réduite Pour Codes Convolutifs

The decoding of convolutional codes in the maximum likelihood sense is carried out in a traditional way with the Viterbi algorithm (Va). We proposed a soft and hard input decoder where theVa, associated with an relevant metric, is applied to identify the error vector rather than the information message. In this paper, we show that, with this type of decoding, the exhaustive computation of a majority ofAcs (Add Compare Select) is unnecessary. Moreover, we show that optimal performance is achieved in the case of a hard input decoder, and that performance closed to the optimum is achieved in the case of a soft input decoder, while offering of a reduction of the complexity which is all the more important than the Ec/No ratio is high (e. g. for ratio Ec/No greater than 3 dB, more than 80 % of theAcs can be avoided). We also propose an algorithm allowing rejecting a frame without having to carry out any iteration of theVa.     

Contrôle de puissance dans les réseaux ad-hoc

In an ad-hoc network, mobile stations communicate with each other using multi-hop wireless links. There is no stationary infrastructure such as base stations. Each node in the network also acts as a router, forwarding data packets for other nodes. In this architecture, mobile stations have a multi-hop path, via other mobile stations acting as intermediaries or relays, to indirectly forward packets from source to destination. Adjusting the transmitted power is extremely important in ad-hoc networks due to at least the following reasons. The transmitted power of the radio terminals determines the network topology. The network topology in turn has considerable impact on the throughput (fraction of packets, sent by a source, and successfully received at the receiver) performance of the network. The need for power efficiency must be balanced against the lifetime of each individual node and the overall life of the network. Power control problem can be classified in one of three categories. The first class comprises of strategies to find an optimal transmitted power to control the connectivity properties of the network. The second class of approaches could be called power aware routing. Most schemes use some shortest path algorithm with a power based metric, rather than a hop count based metric. The third class of approaches aim at modifying the mac layer. We use distributed power control algorithms initially proposed for cellular networks. We establish a classification of power control algorithms for wireless ad-hoc networks. We evaluate these algorithms in anIeee 802.11b multi-hop wireless ad-hoc LAN environment. Results show the advantage of power control in maximizing signal-to-interference ratio and minimizing transmitted power.     

Étude et réalisation de modulateurs et de démodulateurs directs quadriphases pour la régénération à bord des satellites relais

This paper presents the study of a four phase remodulation demodulator which is part of a microwave signal regenerator for communications payload or data relay satellites. At first, 3.87 GHz biphase (bpsk) balanced modulator has been produced, using planar technology with slotlines and microstrip lines engraved on an Epsilam-type substrate, and two beam-lead Schottky diodes. Under modulation, carrier and even harmonic rejection of better than 50 dB is obtained, with insertion losses lower than 2 dB. A fourphase (qpsk) modulator is also produced using two bpsk modulators. Each phase state is achieved at ± 1.3° with 5.2 dB of insertion losses and a residual amplitude modulation of ± 0.14 dB. Carrier and even harmonic rejection of 45 dB is obtained.     

Sur une expression des puissances d’une matrice et son application aux réseaux itérés

Annals of Telecommunications - Après une brève introduction, dans unepremière partie, l’auteur donne (I), de lapuissance d’une matrice d’ordre 2, une expression...     

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.     

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.