Vol. 59 n°3-4, March-April 2004
Open Topics
1D Dielectric electromagnetic band gap (EBG) resonator antenna design
Ludovic LEGER*, Cédric SERIER*, Régis CHANTALAT*, Marc THEVENOT*, Thierry MONEDIÈRE*, Bernard JECKO*
* IRCOM (CREAPE) - CNRS UMR 6615 - 123 Av Albert Thomas 87060 Limoges - France
Abstract: This article presents a new methodology allowing to design a planar electromagnetic band-pap antenna (choice of the EBG material, sizing, feeding). This kind of antenna has already been presented. EBG antennas are very thin (compared with parabolic reflectors) high gain antennas. This article makes easier the realization of EBG antennas whatever the operating frequency, the gain, or still the bandwidth. A study about the sensitivity of the material properties on the performances is also presented. Finaly two exemples using this design method are described.
Key words: Dielectric antenna, Periodic structure, Unidimensional medium, Flat plate, Parallel plate, Forbidden band, Artificial dielectric, Dielectric resonator, Quality factor, Directivity, Bandwidth, Antenna synthesis.
Variable neighbourhood search for optical routing in networks using latin routers
Laurent MÉRIC*, Gilles PESANT*,**, Samuel PIERRE*
* Département de génie informatique ; École Polytechnique de Montréal ; C.P. 6079, succ. Centre-ville, Montréal, Québec, Canada H3C 3A7
** Centre de Recherche sur les Transports, Université de Montréal ; CP 6128, Succ. Centre-ville, Montréal, Québec, Canada H3C 3J7.
Abstract: 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 is NP-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 how VNSFOR leads to better solutions, according to both scenarii, in comparison with the reference algorithm LONCA.
Key words: Optical telecommunication, Wavelength division multiplexing, Wavelength division switching, Network routing, Optical path, Latin square, Heuristic method.
Electronic Retina based Vision Systems An Adequation Algorithm-Architecture-Application Approach
Yang NI*
* GET/Institut National des Télécommunications ; 9, rue Charle Fourier, 91011 Evry, France
Abstract: Electronic retina is a combination between in situ signal processing and image sensing on a same silicon chip. This smart image sensing, realizable in common CMOS technology, is a valuable technique in real-time vision systems. In order optimize the global performance of a vision machine where different levels of processing are needed, this technique can not be considered simply as an intelligent image sensor design problem. Because the local onsensor information processing in an electronic retina should be placed in a more general context including algorithms, architectures and applications. This paper tries to give an overview on the electronic retina based vision systems and especially on the roles that an electronic retina can play in real-time vision systems.
Key words: Computer vision, Retina, Signal processing, Image sensor, Integrated optoelectronic circuit, Optical receiver, Stereoscopy, System architecture.
Improving parallel EKF-based nonlinear channel equalization using unscented transformation
Rim AMARA*, Sylvie MARCOS**
* Unité signaux et systèmes, Belvédère, 1000 Tunis, Tunisie
** Laboratoire des signaux et systèmes, CNRS-Supélec, plateau de Moulon, 91192, Gif-Sur-Yvette, France
Abstract: The paper presents a new review of parallel Kalman filtering for nonlinear channel equalization. A Network of Extended Kalman Filters (NEKF) has already been suggested for this purpose. This equalizer gives recursively a minimum mean squared error (MMSE) estimation of a sequence of transmitted symbols according to a state formulation of a digital communication scheme. It is essentially based on two mechanisms: the approximation of the non Gaussian a posteriori probability density function (pdf) of the symbol sequence by a Weighted Gaussian Sum (WGS) ; and the local linearization of the nonlinear channel function for each branch of the network. Since the linearization, bearing on scattered symbol states, is one of the major limitations of the NEKF, a new Kalman filtering approach, the Unscented Kalman Filter (UKF) suggested by Julier and Uhlman is considered in this paper for an interesting adaptation to the equalization context. The UKF algorithm is based on the equations of a Kalman filter, as the optimal linear minimum variance estimator, and on determining conditional expectations based on a kind of deterministic Monte-Carlo simulations. The new equalizer referred to as the Network of UKF (NUKF), thus combines density approximation by a WGS and the Unscented Transformation (UT) principle to circumvent the linearization brought within each EKF and is shown to perform better than the NEKF based equalizer for severe nonlinear channels. Also, an adaptive version of the NUKF is developed using the k-means clustering algorithm for noise-free channel output identification, since the NUKFbased algorithm does not require the knowledge of the channel nonlinearity model.
Key words: Equalization, Non linear channel, Bayes method, Non linear filtering, Cluster analysis, Kalman filtering.
High-level synthesis for behavioral design of the MAP algorithm for turbo decoder
David GNAEDIG*,**,***, Emmanuel BOUTILLON*, Éric MARTIN*, Amor NAFKHA*, Michel JÉZÉQUEL**, Jacky TOUSCH***, Nathalie BRENGARTH***
* LESTER. Université de Bretagne Sud - BP 92116 - 56321 Lorient Cedex, France.
** GET/ENST Bretagne, Technopôle Brest-Iroise - CS 83818 - 29238 Brest Cedex 3, France.
*** TurboConcept, Technopôle Brest-Iroise - 115 avenue Claude Chappe - 29280 Plouzané, France.
Abstract: The productivity in circuit design have significantly increased during past 20 years, thanks to spanning over several levels of abstraction: from polygons (masks description), to transistors, to logic gates and then to RTL description. For each abstraction level, the productivity increases by one order of magnitude with respect to the previous level. High-level synthesis makes it possible to rise to a new level of abstraction and to improve the design of telecommunication systems. The capabilities of the high-level synthesis tools are presented and evaluated through an example of a non trivial algorithm: the Forward-Backward (MAP) algorithm used in turbo decoders. First, the MAP algorithm is divided into hierarchical levels. In order to control the allowed complexity for the high-level tool Monet, the high-level synthesis is carried out on intermediate levels. The results of the several synthesis experiments are presented and analyzed. This study enables us to determine the limits and imperfections of the currently available high-level synthesis tools.
Key words: Error correcting code, Decoding, Turbo code, A posteriori probabilité, Convolutional code, System synthesis, System architecture, Computer aided design.
Analysis and modelling of the static effective permittivity of suspended microstrip line
Tarik Bouzian BERBAR*, Mehdi SI MOUSSA*, Ahmed ZERGUERRAS*
* Laboratoire Télécommunications, Département Électronique, École Nationale Polytechnique, 10 av. Hassen Badi, BP 182 EL-Harrach, Alger Algérie.
Abstract: New numerical quasi-static model for the computer aided design (CAD) and analysis of suspended microstrip lines is reported. This model is applicable up to er = 20 and over the range 0.001 £u £1000, where u = w/h1 is the structure's variable (w is the width of the strip and h1 is the air gap's thickness). The practical cases are limited to a thickness h1 of the same order of h2 which is the dielectric's thickness. This yields to choose 0.5 £m £1.5. The parameter m is dependent on the structure's variable u. This model is conceived to corroborate the results of the variational approach in any point of its ranges of validity, with a raised error with 1.2%. Although the variational approach allows accurate values of the effective permittivity, but the computing time is relatively high which quickly becomes prohibitory if the Finished Coupled Elementary Lines method is used. The present model is an improvement over the previous variational method as it not only takes lower computing time but it also valid up to high values of er and over the range 0.001 £u £1000. This work is important by the fact that it seeks to visualise the formal model of the effective permittivity, generally masked in a direct variational treatment.
Key words: Transmission, Microwave line, Suspended microstrip line, Permittivity, Static conditions, Modeling, Variational calculus, Numerical calculation.
Maximum a posteriori decorrelating discrete-time rake receiver
Mohamed SIALA*
* SUP'COM, Cité Technologique des Communications - Route de Raoued km 3,5 - 2083 El Ghazala Ariana - Tunisie
Abstract: Recently, a discrete-time version of the rake receiver has been proposed, as an alternative to the conventional continuous-time rake receiver, to overcome the need for complex path searching and tracking procedures. This discrete-time version is able to tackle diffuse multipath channels, avoiding by the way any required knowledge on the delays associated to the most significant channel paths. Unfortunately, it has been found to be very sensitive to channel estimation quality and leads to a significant degradation in performance in practice. To reduce this degradation, we propose and investigate in this paper an optimum structure of this discrete-time rake receiver, according to the maximum a posteriori criterion. Derived from an uncorrelated version of the discrete-time channel, provided by the Karhunen-Loève orthogonal expansion theorem, this structure requires for its operation more or less precise estimates of the discrete-time channel statistics. Consequently, for a precise characterization and evaluation of the enhancement in performance provided by this new structure, we propose to use both perfect and estimated statistics of the discrete-time channel. The estimated statistics, derived in conformity with the maximum likelihood criterion, are carried on a symbol-by-symbol basis. The performance of this new structure is evaluated through theoretical and simulation results and compared to that of the conventional discrete-time rake receiver with perfect and estimated discrete-time channel state information. In this evaluation, a diffuse multipath Rayleigh fading propagation channel with classical Doppler power spectrum and exponentially decaying multipath intensity profile is used.
Key words: Optimum receiver, A posteriori probability, Discretization, Rayleigh Fading, Multipath propagation, Discrete time filter, Multichannel circuit, Direct sequence spread spectrum, Maximum likelihood, Statiscical estimation, Decorrelation.
Joint phase and timing synchronization for cdma signals optimized in a multi-user context
Eric SIMON*, Kosai RAOOF*, Laurent ROS*
* LIS Grenoble, BP46, 38402 Saint Martin d'Hères, France
Abstract: This paper is concerned with the problem of joint phase and delay synchronization for DS-CDMA signals in a multi-user context. We propose a novel version of a standard algorithm optimized for the multi-user case. A brief study of the standard algorithm shows that the task of timing recovery is the most degraded. So the improvement will concern this timing recovery. The optimized version consists in inserting a prefilter in the delay loop, and in calculating its coefficients in order to minimize the timing variance. The resolution of such a problem with the Lagrange-multiplier method yields an analytical expression of the prefilter coefficients. The optimized algorithm performances are then evaluated by simulations. The main result of this study shows that a very short prefilter can increase the timing recovery performances and the phase recovery performances too, due to the interaction between those two tasks.
Key words: Code division multiple access, Synchronisation, Timing recovery, Phase locked loop, Tracking, Minimal variance, Numerical simulation, Optimization.
Bandwidth Sharing under the Assured Forwarding Per-Hop Behavior
Octavio MEDINA*, Julio OROZCO*,**, David ROS*
* GET/ENST Bretagne, Rue de la Châtaigneraie, CS 17607, 35576 Cesson Sévigné cedex, France
** IRISA/INRIA Rennes, Campus Universitaire de Beaulieu, 35042 Rennes Cedex, France
Abstract: The DiffServ's Assured Forwarding (AF) Per-Hop Behavior (PHB) Group defines a differentiated forwarding of packets in four independent classes, each class having three levels of drop precedence. Specific end-to-end services based on this PHB are still being defined. A particular type of service that could assure a given rate to a traffic aggregate has been outlined elsewhere. In such a service, a fair distribution of bandwidth is one of the main concerns. This paper presents experimental work carried out to evaluate how AF distributes bandwidth among flows under different load conditions and traffic patterns. We focused on the effect that marking mechanisms have on bandwidth sharing among flows within a single AF class. The traffic types we used include UDP flows, individual and aggregated TCP flows, mix of TCP and UDP, TCP sessions with heterogeneous round-trip times, as well as color-blind and color-aware re-marking at the aggregation point for TCP flows. Tests were performed on real and simulated networks. We have found certain conditions under which AF distributes bandwidth fairly among nonadaptive UDP flows and TCP aggregates. Finally, we evaluate a basic rule for setting the parameters of the two-rate Three-Color Marker conditioning algorithm (trTCM) in order to achieve a better bandwidth distribution for TCP flows.
Key words: Packet transmission, Network routing, Priority, Resource sharing, Bandwidth, Fairness.
Measure of the temperature-depth profile by an S band radiometric receiver for biomedical applications
Seddik BRI (1, 2), Lahbib ZENKOUAR(2), Adil SAADI(3), Larbi BELLARBI (2), Mohamed HABIBI(3), Ahmed MAMOUNI(4)
(1) Laboratoire de Génie Électrique de Meknès (LGEM), Université My. Ismaïl, ESTM, Département Génie Électrique, BP 3103, km 5, Route d'Agouray, Meknès - Maroc
(2) Laboratoire d'Électronique et Communications (LEC), EMI, Av. Ibn Sina, BP 765, Agdal, Rabat-Maroc
(3) Laboratoire d'Automatique et de Micro-ondes (LAMO), Université IBN Tofail, Faculté des Sciences, Département de physique, Kénitra-Maroc.
(4) IEMN, UMR CNR 8520, Université de Lille1, France.
Abstract: The authors present a method for measuring the temperature-depth profile in a lossy material by applying Kalman algorithm to radiometric signals. The method employs a correlation microwave radiometer. It uses both short-range weighting functions and the delay times of the correlator. An experimental verification of this new thermal inversion approach is presented. The thermal noise is received in the microwave domain, by a S band radiometer by using an automatic experimental bench. A feature of this method is that it can be used in biomedical applications.
Key words: Temperature measurement, Microwave radiometer, Biomedical application, Dissipative medium, Correlation, Kalman filtering.
Ionic current in MOS structures
Hamid BENTARZI*, Rachid BOUDERBALA**, Ahmed ZERGUERRAS***
* Laboratoire de Simulation et de Caractérisation de Semi-Conducteur (SCCSLAB), Département Électronique et Electrotechnique, Faculté d'Ingénierie, Université de Boumerdes, Algérie ; sccslab@yahoo.fr
** IAP, Boumerdes, 35000, Algérie.
*** Département Electronique, Ecole Nationale Polytechnique, Alger 16000, Algérie.
Abstract: A New approach of determining dynamic ionic current-voltage characteristic that is due to ion transport phenomenon in the oxide is presented. In this approach, the formulation of I-V characteristics of MOS device can be achieved through the use of the theoretical model of mobile ion distribution in oxides. The used theoretical model of ion distribution is based on the concept that the equilibrium concentration of the ions is obtained when the combined mobilizing forces, namely, thermal diffusion, internal, and external electric fields, become just sufficient to provide necessary activation energy to the ions to surmount the effective potential well. The obtained I-V curve is compared with the experimental curves under varying bias conditions by a slow linear ramp voltage at high temperature (TVS technique). An agreement between the experimental and computed curves provides a support to this method which in turn it gives formulation that is easier to apply for deriving the theoretical I-V characteristic.
Key words: MOS structure, Ionic conduction, Current voltage characteristic, Semiconductor device, Silicium dioxyde, Charge carrier concentration.
