Modèle de boucles à verrouillage de phase numériques fonctionnant à faible rapport signal sur bruit

Literature is overwhelmed with many schemes of digital phase-locked loops (dpll).So a model as general as possible appeared to be badly needed. This paper reports a tentative model which allows for analysis and characterisation of a large number of dplls operating at low signal-to-noise power ratio. This model can be used for designing new circuits and evaluating their performance. The model is tested considering a first order dpll and a dpll implemented with a sequential filter. Both acquisition and tracking performances are examined.     

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.     

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.     

Réflectomètre à haute résolution

Measurement capabilities of a single mode optical time domain reflectometer (Otdr) are given. Fault location accuracy is 1 m (when the group index of refraction is known) and spatial resolution is 3 m.     

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.     

Modération du comportement dynamique ďun éclateur à gaz

pots installation protection against overvoltages generated by the lightning is a necessity for every operator. France Télécom employ so various protective devices among which gas surge arresters. Naturally the study of these devices can not be done without experiments in real size. However a modelling of gas surge arresters would allow a better specification of their characteristics. The aim of this study is to have a good representation of the voltage in the borders of the gas surge arrester, and a good restoration of the current answer. We propose a modelisation of the surge arrester, as well as its implanting under Simulink (Matlab). New obtained model gives good results as in voltage as by current. He is totally confirmed compared with experimental measurements obtain during a campaign of trigerred lightning at S^t Privat ? Allier by France Télécom.     

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.     

Oscillateurs à TEC accordables par varactor dans la bande 18–40 GHz

This paper describes the design, analysis and experimental results of 18–26 GHz fundamental and 26–40 GHz doubler voltage controlled oscillator. They use field effect transistors and hyperabrupt GaAs varactor diodes. The interest of such circuits are a good integration, a high speed frequency tuning capability and a high frequency of oscillation allowing to achieve ultra wide bandVco by frequency transposition at lower frequencies.     

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.     

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.     

Pyromètre à fibre optique pour la mesure des basses températures

Optical fibres made of fluoride glass allow surface temperature measurement of various objects uneasy to reach, mobile or located in adverse environments. Such an infrared fibre, with transmittance extending beyond 5 μm, allows transmission ofIr radiation to anIr sensor which transforms it into a usable signal. The set-up realised can take measurements down to 50 °C, and 30 °C in a next future. The sensor signal is pre-amplified and then processed by a lock-in amplifier. AnIr reference internal source is used to deliver a known constant level to the sensor and allows absolute temperature measurements. The present measurement accuracy obtained with a blackbody at 200 °C is ± 0.5 °C. We are about to use such a device for monitoring irradiated fuel rods temperature in the Superphenix 1 breeder power plant.     

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.     

Correction d’erreurs sur une liaison par satellite à 34 Mbit/s

The authors are presenting here a method to correct 2 errors on the 56 bits header of a data packet conveyed on a satellite link at a 34 Mbit/s rate. The error correction function is performed by a bch (63, 51) code,truncated to (56, 44) by obliteration of 7 unused bits. By the means of pre-calculated tables made of high integrated rom memories, and using an octet based computation, the correction function can be performed in less than one microsecond at the 34 Mbit/s transmission rate.     

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.     

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.     

Codage audio haute qualité (20 Hz-15 kHz) en sous bandes à débit réduit (64 kbit/s) et à faible retard (5 ms)

In this paper, we present a new method for high quality audio coding at low delay and low bit rate for telecommunications applications such as audioconfe-rence or videoconference. The developped coder is adapted to code generic audio signals at a bit rate of 64 kbit/s with a delay close to 5 ms in the 20-15000 Hz bandwidth. The method is based on speech coding as well as audio coding concepts. The coder combines subband decomposition of the input signal and LD-CELP techniques. We introduce in this structure of coding a psychoacoustic model which allows to allocate an optimal bit rate on each subband according to perceptual properties of the human hearing. In order to satisfy the bit rate requirement of the psychoacoustic model and to reduce the complexity of such a coding algorithm, we suggested a new method of vector quantization based on lattice quantization. This method allows to quantify the residual signal in the LD-CELP coder and avoid the complexity of the full search. Objective and subjective tests have been made on a test set of audio signals which is a critical sub-set used by ISO. Formal tests showed that the quality of the proposed coder is comparable to the best implementation of the MPEG-1, Layer II, but our solution has the advantage of reaching a very low delay (5 ms).     

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.     

Quelques résultats théoriques et expérimentaux sur la modulation par déplacement de fréquence à deux états et à phase continue d’indice 0,5 (MSK)

Minimumshift keying modulation seems to be very attractive for digital transmission systems in particular because an only small degradation can be expected on non linear channels. In the first part of this paper, some general features of the signal are recalled. After a theoretical method for the calculation of the bit error rate in presence of inter symbol interference is described; the results are compared with experimental values, obtained with a modulator demodulator build incnet laboratories in Lannion.