Présentation d’une technique 3D d’accélération de la recherche de rayons application aux télécommunications microcellulaires

Development of telecommunications using mobile phones requires the installation of many base stations (BTS) in order to cover the large number of cells which make up the network. Existing systems (GSM, DSC) use carrier frequencies within the microwave range. Ideally, operators should have simulation software to determine the position of BTS. This software would be used initially to determine the geometric configuration of the cells. The next step would be to optimise the radiation pattern of each BTS antenna. In this article we present a method for determining radioelectric coverage based on image theory adapted to the problem, which is more accurate and less time-consuming than conventional methods.     

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.     

Étude statistique de la dépolarisation « anormale »

The importance of the anomalous depolarization has been checked on the slant path Ats-6 Gometz-la-Ville. Statistical analysis of the data shows that ice depolarization occurs as frequently as rain depolarization and is very important. Statistics of the ice crystal canting angles have been computed together with differential phase shift. From the results obtained, the effect of ice crosspolarization on a dualpolarized microwave link with M-ary Psk is investigated and emphasizes the necessity of implementing crosspolarization cancellation devices.     

Étude du couplage d’une onde électromagnétique externe et d’une ligne de transmission aérienne non uniforme

In this paper, a flexible and efficient method for analyzing the electromagnetic field to nonuniform multiwire aerial lines coupling is proposed. This analysis in based upon the finite- difference time- domain (fdtd) algorithm. The transient responses of nonuniform lines excited by different waves obtained by this method are compared with those of Spice and literature. The good agreement between all the simulation results validates the proposed approach.     

Conception et réalisation d’un simulateur de canal hertzien

The paper presents the design and implementation of a line-of-sight (Los)microwave channel simulator. The basic principle is to reproduce channel transfer functions given by their amplitude and group delay characteristics by driving a linear transversal filter with precomputed data. The transfer functions can be either collected from measurements in the field or derived from any analytical modelling of the Los microwave channel. It is shown that a thirteen tap filter with a 70 MHz period leads to accurate realtime simulations of selective fading in a 50 MHz bandwidth. The control interface, microprocessorbased, allows an efficient and smooth use of the simulator. Finally,hardware problems and technological solutions related to the implementation are presented.     

Étude temporelle du couplage d’une onde

This paper deals with a temporal approach of interaction between an external electromagnetic wave and an arbitrary multiconductor transmission lines (Mtl). The loads of the circuits can be linear like resistance elements or non linear as is the case of field effect transistor (Mesfet). The numerical technique used is the finite differences time domain (Fdtd) witch givesMtl temporal responses with good stability. Good agreement between the results obtained by the proposed method and those by literature and Spice model verifies the validity of theFdtd algorithm.     

Minimisation de la consommation d’Énergie dans les réseaux ad hoc

An ad hoc network is a collection of wireless devices forming a temporary network independently of any administration or fixed infrastructure. The main benefits of this new generation of mobile networks are flexibility and their low cost. Wireless devices have maximum utility when they can be used “anywhere at anytime “. However, one of the greatest limitations to that goal is the finite power supplies. Since batteries provide limited power, a general constraint of wireless communication is the short continuous operation time of mobile terminals. This constraint is more important for the ad hoc networks, since every terminal has to perform the functions of a router. Therefore, energy consumption should be a crucial issue while designing new communication protocols and particularly ad hoc routing protocols. We propose, in this paper, some extensions to the most important on-demand routing algorithm,Aodv (Ad hoc On demand Distance Vector). The discovery mechanism in these extensions uses energy as a routing metric. These algorithms improve the network survivability by maintaining the network connectivity, which is the strong requirement for a high-quality communication. They carry out this objective with low message overhead for computing routes and without affecting the other network protocol layers.     

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.     

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...     

Étude de la précision de l’estimation de la densité spectrale de puissance croisée,obtenue par transformation de fourier de la fonction de corrélation

The authors compare two different estimators of the crosscorrelation function and show that they give equivalent estimators in the frequency domain. They calculate the first and second order moments of the estimator of the cross-spectral-density (DSPC)due to the statistical errors and the quantification of inputs. From these general formulas, they perform numerical calculations for a particular case and they compare them to practical measurements. They show the interesting fact, that the variance of the statistical errors on the dspc is inferior by estimating its phase than by estimating its module. Furthermore, the quantification of the inputs may influence the variance of the phase of the DSPC estimated.