Pierre Degauque

Modeling in-Vehicle Wideband Wireless Channels Using Reverberation Chamber Theory

In this paper, the wideband channel is studied inside a vehicle. Propagation inside a recent car (model bought in 2006) is investigated and the power delay profile is measured for three different scenarios. Two kinds of transmission bandwidths are studied, 200 MHz around 5 Ghz and an ultra-wideband bandwidth of 3 Ghz around 4.5 GHz. The ultra-wideband measurements allow to clearly identify the propagation mechanism in this kind of environment. For each scenario, an exponential model for the power delay profile is shown to be in good agreement. A theoretical model based on reverberation chamber theory is proposed. It allows to predict the rms delay spread inside the car. A comparison with measurements inside a reverberation chamber is presented.

Reverberation Chamber Environment for Testing Communication Systems: Applications to OFDM and SC-FDE

The impulse response in a reverberation chamber is investigated from an experimental and theoretical point of view. A full description is thus proposed based on measurements and confirmed by means of theoretical insights. In particular, the K factor of each tap is emphasized. BER simulations for OFDM and single carrier frequency domain equalization (SC-FDE) systems are applied on this channel model and compared to the 802.11n channel model showing some differences mainly for the OFDM transmission.

Adaptable measurement testbed for wireless systems applied to mimo channel modeling

A new experimental way of testing MIMO systems is proposed by means of two reverberation chambers coupled through a waveguide. The modularity of this experimental setup is emphasized and some theoretical and experimental results are presented. The effect of the waveguide on the propagation channel is pointed out. I. INTRODUCTION MIMO systems have gained a lot of attention since they promise an increase of the capacity with a very high spectral efficiency. The knowledge of the propagation mechanisms is crucial in order to define reliable, precise and adaptive channel models. Theoretical researches have been carried out in order to obtain such a channel model (1). However, a model must be supported by measurements campaigns. Those measurements are highly environment dependent and it is difficult to reproduce or to control the environment. In this paper, a new measurement system is proposed which allows to control and to reproduce different specific environments. This measurement testbed is composed of two reverberation chambers coupled through a waveguide. First, the theoretical modeling of the chambers is presented. To model accurately the channel we have to deepen the understanding of the propagation in the waveguide. The basics of waveguide modal analysis are presented. Then, the power weight of each mode is computed. From this result, we are able to understand intu- itively the propagation mechanism in waveguide like systems and the notion of independent paths with different amount of power. To fulfill the understanding of the waveguide, the radiation of each mode in the receiving chamber is deduced. Some numerical results are provided. A channel model is then presented in order to take into account all the parameters of our system. Measurement results are finally provided, pointing out the ability to obtain different propagation conditions. A discussion about the benefits and the drawbacks of this system concludes the paper. II. THE COUPLED REVERBERATION CHAMBERS The proposed testbed is composed of two mode stirred reverberation chambers (MSRC) of about 16m 3 each. MSRC have first been developed for susceptibility testing of electronic devices. Since they allow to produce a dense and isotropic multipath environment, they are now also used for testing antenna characteristics (such as correlation between antennas, mutual coupling or embedded element pattern) and wireless communications systems (2), (3). By means of the movement of the mechanical stirrer, the boundary conditions are changed and a new distribution of the propagating plane waves in the chamber is obtained. The originality in this paper is the use of two chambers to model separate environments for the emitter and the receiver. Those chambers are coupled through a waveguide (cf. Fig. 1) whose transverse dimensions can be changed in order to modify the channel characteristics between the emitter and the receiver. The waveguide allows to obtain independent propagation paths, and to control the degrees of freedom of the channel.

Characterization of a confined environment based on acoustic and reverberation chamber theory. Comparison with the case of a car

The study of propagation inside confined environments leads to very specific results. Specular reflections are not dominant and the result is more comparable with diffuse scattering. Evaluating this channel can be done using acoustic theory. However, this theory is described by a parameter, eta whose physical meaning lacks of description. Reverberation chamber theory can therefore be applied to estimate for example the delay spread inside a confined environment. This theory also suffers of some drawbacks. The most important is that it is only valide for sufficiently high Q factor. A car is a classical confined environment. Therefore, measurements inside a car are presented showing some common characteristics with a reverberation chamber.

Remarks on the computation of the propagation of high frequency waves in a tunnel

RésuméL’étude de la propagation des ondes électromagnétiques à haute fréquence en milieu confiné est souvent abordée par la théorie des rayons. Dans le cas particulier d’un tunnel ou d’un couloir de très grande longueur, des hypothèses simplificatrices sont souvent introduites dans le calcul du champ. L’objet de cet article est de quantifier l’erreur commise et donc de préciser les zones de validité de ces approximations.AbstractThe theoretical study of the propagation of high frequency waves in confined areas is usually based on a ray theory. In the special case of a tunnel or of a very long corridor, simplifying hypotheses are usually introduced for the field calculation. The objective of this paper is to quantify the error and thus to predict the validity of such approximations.

Etude des perturbations induites par une décharge orageuse sur un câble de télécommunication

ResumeCet article présente tout d’abord des résultats expérimentaux montrant les formes et amplitudes des signaux parasites apparaissant sur un câble de télécommunication situé au voisinage d’une décharge orageuse. Les campagnes de mesures se sont déroulées à Saint-Privat-d’Allier (France). Nous nous intéresse-rons successivement au courant induit sur la gaine extérieure de câbles aériens de différentes longueurs et aux tensions de mode commun apparaissant aux bornes des impédances de charge. Nous donnerons également quelques résultats obtenus sur une ligne enterrée. Le courant defoudre étant mesuré à la base de l’éclair, on effectuera une comparaison entre les résultats expérimentaux et les prévisions théoriques, faites à partir du calcul du champ électrique rayonné par l’éclair et du couplage de celui-ci à une structure filaire en utilisant la théorie des lignes de transmission.AbstractExperimental results presented in this paper show the waveform and magnitude of the interference signals that occur on a telecommunication cable located nearby a lightning discharge. The measurements were performed at Saint-Privat-d’Allier (France). We then study the current induced in the outer shield of aerial cables of several lengths and in the common mode voltages which appear on the load impedances. We also give a few results obtained from a buried cable. We will compare experimental results and theoretical predictions that are based on the computation of the electric field radiated by the lightning current and on the coupling of the electric field with the wire structure. This last point is approached through the transmission line theory.

Couplage entre le champ électromagnétique rayonné par un coup de foudre et une ligne de télécommunication aérienne ou enterrée

AnalyseCet article présente le calcul du courant induit par un coup de foudre sur un câble de télécommunications en présence du sol à l’aide de la théorie des lignes de transmission. Le champ électromagnétique associé à l’arc en retour d’une décharge orageuse est obtenu en modélisant le canal foudre par une antenne verticale située au-dessus d’un sol parfaitement conducteur. Le couplage avec la ligne est ensuite abordé en considérant le sol réel. A partir de ce modèle le courant induit sur une ligne aérienne est déterminé pour différentes positions du point d’impact du coup de foudre et une comparaison avec des résultats expérimentaux obtenus durant la dernière campagne « foudre » de Saint-Privat-d’Allier est également effectuée. Pour obtenir la réponse d’un câble enterré à une onde électromagnétique, les auteurs déterminent en premier lieu l’exposant linéique de propagation et des autres paramètres linéiques du câble. Ils étudient ensuite l’influence de l’origine des potentiels sur ces paramètres et montrent en particulier que le choix de cette origine à l’infini permet de rendre compte de l’énergie se propageant dans le sol parallèlement au câble.AbstractThis paper describes the determination of the current induced by a lightning discharge on a telecommunications cable using a transmission line theory. The electromagnetic field due to the return stroke is calculated by modeling the channel by a vertical antenna situated above a perfectly conducting ground. The electromagnetic coupling to a telecommunications line is then determined by introducing the finite conductivity of the ground into the transmission line model. Examples are given for various positions of the lightning discharge with respect to telecommunications cable. A comparison with results obtained during the last experiment at Saint-Privat-d’Allier is also presented. To get the response of a buried cable the authors first determine the propagation constant and the primary parameters of the line. The reference for the voltage is also analysed. The authors show that the choice of the origin at the infinity allows to take into account the energy propagating in the ground parallel to the cable.

Méthode d’optimalisation d’une liaison électromagnétique entre terminaux souterrains

SommaireLes auteurs étudient un système de télécommunications entre stations enterrées, constitué par un émetteur et un récepteur dont les antennes sont disposées dans des galeries souterraines. L’efficacité de ce moyen de liaison électromagnétique dépend de nombreux paramètres. Dans une première partie, nous rappelons la méthode de calcul bien connue du rayonnement d’une antenne horizontale placée à une profondeur h dans un milieu conducteur et nous mettons en évidence les domaines de validité des approximations faites et les paramètres significatifs dont dépend la liaison. Dans une seconde partie, nous exposons une méthode d’optimalisation et nous traitons plusieurs exemples.