Showing papers in "Annales Des Télécommunications in 1981"

A model-oriented approach to measure rain-induced cross-polarization

Abstract: In this paper a new model oriented approach to measuring rain-induced cross-polarization is outlined: it aims at characterising the physical properties of the depolarising medium rather than at directly measuring the channel depolarization, which is the variable of direct interest for system design. This approach, which allows subsequent determination of depolarization has the advantages of allowing a better understanding of the propagation mechanism, thus yielding information applicable to any system configuration and establishing common procedure to compare cross-polarization data obtained in different circumstances. Different experimental configurations are reviewed together with their ability to identify and assess various possible models for the depolarizing medium.

Synthèse optimale d’un réseau de télécommunication avec contraintes de sécurité

Abstract: Un des moyens possibles pour assurer un certain taux de securite dans un reseau de Telecommunications est l’usage de capacites de reserve. Cet article decrit un ensemble de methodes exactes et approchees permettant de determiner un reseau de reserve de cout minimal, pour une politique donnee de dimensionnement, de routage et de groupage des faisceaux de circuits. D’un point de vue mathematique, le probleme apparait comme celui de la determination d’un reseau permettant d’ecouler au moindre cout P multiflots non simultanes. Les dimensions des problemes reels de ce type peuvent atteindre des dizaines de milliers de variables et de contraintes et rendent illusoire l’emploi des techniques classiques de la programmation lineaire. L’article montre que l’utilisation systematique de la relaxation lagrangienne et des methodes de sousgradient peut conduire a des methodes de resolution efficaces et de mise en œuvre relativement aisee. L’ensemble des methodes decrites dans cet article a ete integre dans une chaine de programmes de planification a moyen et long terme (programmeSupersec)et a permis une etude systematique des problemes technico-economiques lies a la securite dans les reseaux.

Propagation characteristics of millimetre and centimetre waves of ETS-II classified by rainfall types

Abstract: A propagation experiment at the frequencies of 1.7, 11.5 and 34.5 GHz using Engineering Test Satellite Type IIEts-II was conducted at the Kashima earth station of the Radio Research Laboratories (Rrl).Several meteorological parameters were also measured simultaneously at the station using rain gauge networks, a C-band rain radar, a 35 GHz radiometer and meteorological instruments.

Analysis and prediction of cross-polarization on earth-space links

Abstract: A two-tier Gaussian model for raindrops, which assumes Gaussian distributions both for instantaneous canting angle and time-varying mean canting angle, together with gross features of ice particles, provide a theoretical framework to organize the experimental data and to yield functional dependence of cross-polarization on frequency, polarization and elevation angle. Agreement has been obtained between measured depolarization data and theoretical results which are essentially independent of details of ice clouds. In particular, a linear relation has been found between cross-polarization amplitude and frequency throughout the centimeter wavelengths for a given earth-space path.

Differential propagation constants on slant paths through snow and ice crystals as measured by 16.5 GHz polarization-diversity radar

Abstract: Radar determinations of differential propagation constants at a wavelength of 1.82 cm on slant paths through heavy snow and ice crystals are reported. Also reported are measurements of differential propagation effects in the melting layer. The slant path results indicate an increase of differential phase shift with height, to a value at 2000 m which may exceed 1.3 deg/ km, being typically several times that at the surface. This effect is attributed to a change in the hydrometeors, as they precipitate, from ice crystals to snow aggregates. Differential propagation effects in the melting layer are small.

OTS propagation measurements during thunderstorms

Abstract: Otspropagation measurements are described which comprise a complete determination of the incoming polarizations for both linearly and circularly polarized beacons. Auxiliary equipment includes radars, E-field sensors and a microphone array. General trends in the propagation data are discussed and two basic models are proposed for the observed correlations between electrostatic field and cross-polarization. A detailed analysis, with radar data, is now given for one thunderstorm. A method for the prediction of the linear cross-polarization from the circular is shown to work well for this ice-dominated event. Fast lightning-induced, cross-polar jumps are described, and by relating them to acoustic thunder location data, the physical models for particle alignment are discussed.

Use of dual-polarization radar data for evaluation of attenuation on a satellite-to-earth path

Abstract: Using conventional (single-polarization) radar data to assess attenuation due to rain on satellite-to-Earth paths requires the assumptions that the drops have a particular statistical distribution of sizes, and that the drops are of water. In the very localised regions of intense rain which influence such paths most severely, these assumptions can lead to large errors. This paper presents comparisons between direct measurements of attenuation and those computed using data from a dual-polarization radar technique. This technique can considerably reduce the errors of radar-derived estimates of attenuation. It also gives a clear distinction between ice and water.

Site diversity measurements of low-angle fading and comparison with a theoretical model

Abstract: Since 1974, several experiments have been conducted at Eureka, Canada (80° N, 86° W), to investigate the properties of lowangle fading. For a variety of site diversity configurations, it was found that neither a horizontal spacing of 500 m nor a vertical spacing of 20 m provided good diversity performance. For a vertical spacing of 180 m, however, fading at the two sites was essentially uncorrelated. Lowangle fading was more prevalent and severe in the summer and absent when the atmosphere was wellmixed or during radiative temperature inversions. A model of the refractive index structure of the atmosphere has been developed which predicts these characteristics and shows that deep fades need not result from interference fading.

Calcul des affaiblissements dus à la pluie sur un trajet Terre-satellite

Abstract: Une etude anterieure montre qu’un modele de precipitation base sur le concept de cellules de pluie permet de prevoir de facon satisfaisante l’affaiblissement lineique pour des faisceaux hertziens a des frequences superieures a quelques gigahertz. L’objet de cet article est d’etendre ce modele aux trajets obliques. On commence par identifier divers types de precipitations. On etudie ensuite les effets de l’altitude sur l’affaiblissement lineique en tenant compte des changements de la densite de l’air et de la temperature. Finalement, la geometrie du modele est adaptee aux trajets obliques. Le calcul revele un bon accord entre les observations et le modele.

Échantillonnage des images de télévision: analyse dans le domaine spatio-temporel et dans le domaine de Fourier

Abstract: Cet article presente le probleme de l’echantillonnage spatio-temporel des images de television. Apres avoir donne les notations utilisees dans le domaine spatiotemporel, le domaine video et les domaines de Fourier, les auteurs introduisent la notion de structure d’echantillonnage puis le theoreme d’echantillonnage spatio-temporel. Les transformees de Fourier des quatre structures choisies sont ensuite calculees. L’analyse objective des degradations d’echantillonnage est alors effectuee dans le domaine spatio-temporel et dans le domaine de Fourier pour diverses configurations d’image (mires sinusoidales et contours spatio-temporels). Le probleme de l’optimalisation de lechantillonnage est aborde ainsi que le probleme du filtrage spatio-temporel et celui de lechantillonnage de la couleur.

Multipath depolarization theory combining antenna with atmospheric and ground reflection effects

Abstract: A formulation combining three sources of cross polarization in multipath propagation is given. The first relates to finite antenna isolation which becomes worse for off-axis multipath reception. Antenna amplitude and phase patterns are most important. The second, associated with atmospheric refractive index variations, requires asymmetric gradients for both linear and circular polarization. This by itself is the least signifiant source of depolarization but these rays cause variable interference between themselves and with other rays. The third is due to rays reflected once or twice from the ground. For linear polarization, inclined ground reflectors are required, but for circular polarization, polarization-dependent reflection coefficients are sufficient to give cross-polarization.

Measurements of cross-polarization discrimination at 11 and 17 GHz

Abstract: Measurements of microwave fading and depolarization were carried out near Ottawa, Canada at 11 GHz and 17 GHz on two adjacent 16 km paths. The clearair fading data at 11 GHz agree approximately with ccir predicted values, but the 17 GHz data are more than an order of magnitude less severe than the predictions. The conditional distributions of clearair crosspolarized signal level are approximately lognormal and are dominated by multipath effects at small percentages of time. Rain depolarization is observed to be much less severe than clearair depolarization. These measurements imply that dualpolarization frequency reuse systems are likely to be limited by clearair depolarization in the 11 GHz band in this geographical region.

Summary of studies on scattering of centimetre and millimetre waves due to rain and hail

Abstract: This review is synthetically produced from the author’s own and coauthored papers and outlines the results of investigations on the scattering of centimetre and millimetre waves due to rain. The paper first summarizes the fundamental single scattering properties of spherical and nonspherical raindrops. Then several practical problems, such as crosspolarization, bistatic scattering, etc, are briefly dealt with. Some of the effects of multiple and incoherent scattering on received signals are also discussed.

New radar studies of slant-path attenuation due to rain

Abstract: Approximately 40 h of data from the summer of 1976 were employed in a comparison of radar and radiometer estimates of slant-path attenuation due to rain. McGill Radar Weather Observatory is situated 20 km west of Montreal; the radiometers, separated by 18 km at two sites located about 90 km northwest of the radar, had fixed antennas pointed approximately southeast at an elevation of 18.5 deg. Values of radar reflectivity along the two radiometer paths were used to calculate the slant-path attenuation at 13 GHz as a function of time with a 1 min resolution for direct comparison with the radiometer measurements. It was found that the cumulative distribution of attenuation inferred by radar from each site could be made to agree satisfactorily with the radiometer distribution assuming that rain was present everywhere along the path with a Marshall-Palmer distribution and applying a 1 dB correction to the independently-determined radar calibration. This agreement, close to within a fraction of a decibel, gives confidence to the use of radar records in compiling attenuation statistics. An example is presented of a new application of such records, namely the assessment of rain-induced interference over adjacent earth-space paths.

Circular cross-polarization measurements on earth-space paths at 11,7 GHz

Abstract: Rain and icecrystal depolarization measurements were made on earthspace paths at four locations across Canada using the circularlypolarized 11.7 GHz beacon transmission from thectssatellite. Results show that when rain is the dominant depolarization mechanism, crosspolarization discrimination (xpd)is statistically related to copolar attenuation (cpa)according toxpd =U−20 logcpawith U showing improvement with increasing elevation angle. Icecrystal depolarization events, with accompanying differential phase shifts as large as 20°, were also observed. An analysis separating these events from the data demonstrates that at 11.7 GHz icecrystal depolarization degradesxpdstatistics by less than 1 dB at the small percentages of time.

Application d’une nouvelle méthode de résolution des équations de Maxwell à l’étude de la propagation des ondes électromagnétiques dans les guides périodiques

Abstract: Les auteurs proposent une nouvelle methode pour l’etude de la propagation d’une onde electromagnetique dans un guide de revolution parfaitement conducteur, a generatrice periodique. La resolution des equations de Maxwell ecrites sous forme covariante est faite dans un systeme de coordonnees non orthogonales adapte aux conditions aux limites. Les solutions sont ecrites sous la forme d’un produit de series de Fourier et de Fourier-Bessel, ce qui conduit a la recherche des vecteurs propres et des valeurs propres d’une matrice caracteristique du guide. Les resultats numeriques et experimentaux sont confrontes pour quelques types de guide periodique.

Simultaneous propagation measurements in the 12 GHz band on SIRIO and OTS satellite links

Abstract: Results are compared from attenuation measurements, carried out on two different satellite links in 1979 at the Deutsche Bundespost experimental ground station Leeheim (near Darmstadt). Considerable differences were observed between the two links. Rain intensity measurements performed at various locations in the vicinity of the receive site also show significant deviations, which in turn may be due to orographic features.

Cross-polarization measurements at Martlesham Heath (UK)using OTS

Abstract: Slant-path propagation measurements using transmissions to and from theOtssatellite are being carried out at Martlesham Heath (Uk)at an elevation angle of 29.9°. The measurements allow the determination of the attenuation and cross-polarization for circularly-polarized signals at 14.5 and 11.8 GHz and attenuation and cross-polarization for a linearly-polarized signal at 11.6 GHz. This paper reports the results of cross-polar measurements made during the summer of 1978 together with examples of particularly severe cross-polar effects from 1979. The measurements are compared with both aCcircurve relating cross-polar discrimination to fade depth for rain and theoretical curves supplied by Essex University. The results clearly demonstrate the superior cross-polar performance of linear polarization compared to circular polarization.

First attempts at modelling earth-to-space radio propagation using SIRIO measurements in the 11 and 18 GHz bands

Abstract: A bi-dimensional statistical model for earth-to-space radio links, characterized by effective rain rates and rain path lengths is proposed. These parameters refer to an equivalent homogeneous slab of rain having depth and rain rate such as to produce similar values of measured attenuations. Input data for the present study were attenuation data at 11.6 GHz (absolute and differential over a 520 MHz band) and 17 GHz, collected by theSiriosatellite: these data were found to be jointly log-normally distributed as were the effective rain rate and path length. A straightforward application of the model is the extrapolation of attenuation statistics to higher frequencies: the effectiveness of the method, when applied to 11.6 GHz data is tested against the data at 17 GHz; both the statistics and the time profiles are excellently reproduced. This suggests the use of a differential radiometer working at a relatively low frequency in order to acquire reliable higher frequency statistics and effective model parameters.

Theory for measuring the effective polarization parameters of rain from orthogonal linearly-polarized transmissions

Abstract: The theory is presented for one method of determining the effective polarization parameters of rain from propagation measurements over a line-of-sight link The method requires the transmission of orthogonal linearlypolarized signals and a set of three amplitude and two relative phase measurements Approximate equations are given for determining both instantaneous and «statistical parametric» values of the effective parameters in a twoparameter Gaussian model of the raindrop canting angle distribution The instantaneous values could be useful for comparison with in-situ measurements, while the statistical parametric values are required for prediction of rain depolarization statistics

OTS and radiometric slant-path measurements at Martlesham Heath (UK)

Abstract: Slant-path propagation measurements using transmissions to and from theOtssatellite are being carried out at an elevation angle of 29.9°. The measurements allow the determination of the attenuation at 14.5 and 11.8 GHz for circular polarization and 11.575 GHz for linear polarization. The satellite beacons are also being used for the calibration of 12.1 and 14.8 GHz radiometers. 20 and 30 GHz radiometers are also operated on the site. Rain fades in excess or 15 dB and 10 dB at 14.5 GHz and 11.8 GHz respectively have so far been observed but the effect of wet snow on the earth station aerial surface is much more severe than this. Measurements of rain attenuation ratio between 14.5 GHz and 11.8 GHz indicate a value of 1.5 ± 0.1 and spectrum analysis of scintillations on the received satellite beacons indicate spectral components of up to about 5 Hz.

A computer simulation of XPD degradation due to multipath propagation

Abstract: A computer program has been constructed to study degradation inXpd(cross-polarization discrimination) due to multipath propagation. The geometric optics limit is used. The program will accept any analytic index of refraction including those with discontinuities in n or ∇n. Antenna effects are included and all reflected, refracted, direct and ground reflected rays can be considered. Using a realistic index of refraction and realistic discontinuity, we have found that, after the antenna pattern, the major influence onXpdis interference between the ground-reflected wave and the direct wave. There is also significant interference due to the waves reflected from the refractive index discontinuity which may arrive without ground reflection or may be reflected once or twice from the ground.

Le filtrage adaptatif en télécommunications

Abstract: L’article presente une synthese detaillee sur un algorithme d’apprentissage iteratif destine a optimiser le filtrage numerique en presence d’observations aleatoires de statistique inconnue, afin d’extraire un signal utile correle avec l’observation. C’est l’algorithme du gradient stochastique, qui minimise l’ecart quadratique moyen entre la sortie d’un filtre adaptatif et le signal utile. Dans les telecommunications, cet algorithme trouve des applications telles que l’egalisation des liaisons de transmission a haut debit et l’annulation d’echo. L’article rappelle son fondement, resume les conditions de son utilisation en transmission de donnees, met en evidence la difficulte d’une demonstration de convergence, enonce le premier theoreme approprie a des applications pratiques aux transmissions de donnees, detaille le calcul de l’ecart quadratique moyen residuel, dans le cas ou le pas d’incrementation est fixe.

Propagation oblique dans les bandes de fréquences des 11 et 14 GHz

Abstract: Apres avoir indique les caracteristiques de la station experimentale de telecommunication par satellite duCnet,on presente les resultats de mesures de propagation effectuees, d’une part, de novembre 1977 a novembre 1978, a l’aide des signaux emis par le satellite experimental de telecommunication italienSirio Iet d’autre part de janvier a novembre 1979 avec le satellite europeenOts,8353 heures d’enregistrement de donnees utiles ont ete memorisees avecSirio Iet 7 879 avecOts.

Rain attenuation on earth-satellite links: a prediction method based on point rainfall intensity statistics

Abstract: A method is proposed for predicting rain attenuation statistics for earth-satellite links from a knowledge of the ground point rainfall intensity cumulative distribution representative of the area where the earth station is located. The sensitivity of predictions to various parameters of the method is considered. Comparison between predicted and experimental results obtained in five European locations is encouraging and indicates that point rainfall intensity data may be utilized for predicting rain attenuation statistics on slant paths.

Probability distribution of rain-induced cross-polarization

Abstract: The cross-polarization discrimination of a radiorelay link using two orthogonal polarizations has been calculated from the statistical distribution of the rain intensity, and the size, deformation and canting angle of raindrops. At frequencies of 18.8 GHz and 28.8 GHz and for a path length of 20 km the results are plotted as a function of the path-averaged rain rate. Furthermore, the distributions of the cross-polarization discrimination in the worst case for a path perpendicular to the main wind direction are obtained from the statistical distribution of the path-averaged rain rate for linear and circular polarizations.

Ice depolarization at 11.7 and 19 GHz on slant paths in Virginia, USA

Abstract: Measurements of attenuation and cross-polarization on slant paths from theCtsandComstarD2 satellites to Blacksburg, VA, have been in progress for three years The data for 1977 and 1978 have been analyzed to determine the extent of severe ice depolarization on these paths, and a number of events have been identified The behaviour of the observed cross-polarization at 117 and 19 GHz in two events has been compared with current theory for ice depolarization

Améliorations du modèle pour le calcul des atténuations dues à la pluie sur un un trajet Terre-espace et étude de sensibilité aux paramètres

Abstract: Dans une publication recente, un modele de cellule de pluie destine a la prevision des attenuations sur des trajets terrestres a ete etendu au cas des trajets obliques La presente etude aborde les problemes poses par le developpement du modele et son application a des configurations nouvelles De plus, une analyse specifique conduit a preciser le fonctionnement du modele dans les conditions courantes d’utilisation, et permet de connaitre la sensibilite des resultats aux principaux parametres qui le specifient

Propagation measurements due to rain and ice using the OTS satellite over the period January 1979–May 1980

Abstract: In this paper, we summarize propagation measurements along a slant path to the Orbital Test Satellite, OTS Measurements were made using the circularly polarized beacon at 11786 GHz We present possible explanations for some of the measured propagation activity using a theoretical model incorporating rain, ice and a segmented rain and ice path We also discuss measurements made with two electric field probes Lastly the effect of a rain event on a glass-fibre radorne is illustrated and compared to the same event received via a co-located radome-less antenna

Evaluation en trafic d’une procédure de ligne: le système de signalisation CCITT n∘ 7

Abstract: Apres une breve description du fonctionnement de la procedure de ligne du systeme de signalisationccittn∘ 7, cette note en etudie les performances (temps d’attente a remission, charge maximale) en fonction du trafic, du temps de boucle, et en presence d’erreurs. Cela permet, sur le plan des performances en trafic (temps d’attente moyen et maximal)une comparaison de deux variantes. Dans le cas de l’une d’elles (methode avec retransmission cyclique preventive) le probleme de determination de la taille de la memoire tampon est aborde.