Adaptive beamforming for large arrays in satellite communications systems with dispersed coverage

Conventional multibeam satellite communications systems ensure coverage of wide areas through multiple fixed beams where all users inside a beam share the same bandwidth. We consider a new and more flexible system where each user is assigned his own beam, and the users can be very geographically dispersed. This is achieved through the use of a large direct radiating array (DRA) coupled with adaptive beamforming so as to reject interferences and to provide a maximal gain to the user of interest. New fast-converging adaptive beamforming algorithms are presented, which allow to obtain good signal to interference and noise ratio (SINR) with a number of snapshots much lower than the number of antennas in the array. These beamformers are evaluated on reference scenarios

On convergence of the auxiliary-vector beamformer with rank-deficient covariance matrices

The auxiliary-vector beamformer is an algorithm that generates iteratively a sequence of beamformers which, under the assumption of a positive definite covariance matrix R, converges to the minimum variance distortionless response beamformer, without resorting to any matrix inversion. In the case where R is rank-deficient, e.g., when R is substituted for the sample covariance matrix and the number of snapshots is less than the number of array elements, the behavior of the AV beamformer is not known theoretically. In this letter, we derive a new convergence result and show that the AV beamformer weights converge when R is rank-deficient, and that the limit belongs to the class of reduced-rank beamformers

Robust approaches to remote calibration of a transmitting array

We consider the problem of estimating the gains and phases of the RF channels of a M-element transmitting array, based on a calibration procedure where M orthogonal signals are sent through M orthogonal beams and received on a single antenna. The received data vector obeys a linear model of the type y ¼ AFg þ n where A is an unknown complex scalar accounting for propagation loss and g is the vector of unknown complex gains. In order to improve the performance of the least-squares (LS) estimator at low signal to noise ratio (SNR), we propose to exploit knowledge of the nominal value of g, viz g. Towards this end, two approaches are presented. First, a Bayesian approach is advocated where A and g are considered as random variables, with a non-informative prior distribution for A and a Gaussian prior distribution for g. The posterior distributions of the unknown random variables are derived and a Gibbs sampling strategy is presented that enables one to generate samples distributed according to these posterior distributions, leading to the minimum mean-square error (MMSE) estimator. A second approach consists in solving a constrained least-squares problem in which h ¼ Ag is constrained to be close to a scaled version of g. This second approach yields a closed-form solution, which amounts to a linear combination of g and the LS estimator. Numerical simulations show that the two new estimators significantly outperform the conventional LS estimator, especially at low SNR

The Limerick bubbly flow rig: design, performance, hold-up and mixing pattern

peer-reviewedAs Euler-Euler CFD simulations of bubbly flows suffer from uncertainties due to the many underpinning models, there is an obvious need of accurate experimental data for validation. With this in mind, a new bubbly flow test rig was built to be operated with and without liquid co-flow, with bubble size as uniform as possible in the range 4–7 mm, and with a very even horizontal bubble distribution. We designed the gas sparging system such that we can also produce an essentially bi-modal bubble size distribution. The column consists of two square sections to allow for studying the mixing of two originally separated bubbly flows with either the same or a different bubble size. The bubbles are produced from 2 × 196 needles, bubble sizes are determined with high-speed imaging and with a simple acoustical method, overall volume fractions in the column by means of air chamber pressure measurements. Overall volume fractions are presented as a function of gas and liquid flow rates, with slip velocity mostly increasing with increasing void fraction. First results are obtained on (a) producing bi-model bubble size distributions and the pertinent volume fractions in the column, and (b) flow patterns in the case of unequal aeration

La complémentarité stratégique entre grande entreprise et PME en matière d'innovation

Le rôle respectif joué d’une part par les grandes entreprises et, d’autre part, par les PME en matière d’innovation technologique fait l’objet de nombreuses controverses dans la littérature en sciences de gestion. Prolixe sur ce sujet, cette littérature s’est moins intéressée, jusqu’à une date récente, aux interrelations existantes entre firmes de toutes tailles dans le processus d’innovation. Les observations récentes concernant ces interrelations en particulier dans les nouvelles technologies permettent d’avancer qu’il existe en matière d’innovation technologique une complémentarité stratégique entre grandes firmes et PME. Dans une première partie, cet article met en évidence cette complémentarité stratégique entre grandes et petites entreprises dans les industries fondées sur la science (IFS). La troisième partie de cet article est consacrée aux implications de ces analyses en matière de « création » et de « diffusion » de l’innovation dans les IFSIn management literature the respective importance of big firms on the one hand and small and medium firms on the other is a highly controversial subject. While management literature has long proved verbose in this area, little attention has been paid, until recently, to the existing relations between firms of all sizes during the innovation process.Recent studies concerning such relations, particularly in respect of new technologies, lead us to the following conclusion: in the technological process there does indeed exist a strategic complementarity between big and small firms. The first part of this article concentrates on this complementarity. The second part analyses the characteristics and the dynamics of the strategic commplementarity between big and small firms in science-based industries. The third part of the article is devoted to the implications of this analysis concerning technological strategies and the production and distribution of innovations in science-based industries.El papel respectivo desarrollado por las grandes empresas y por otra parte por las PyME en materia de inovacion technologica es objecto de numerosas controversias en la literatura de ciencias de gestión.Esta literatura se interesa menos desde hace poco tiempo po las inter- relaciones que existen entre las empresas de cualquier dimension en el proceso de inovacion. Las recientes observaciones relativas a estas inter- relaciones, en particular en las nuevas tecnologias, permiten decir que en la inovacion existe una complementaridad estratégica entre las grandes y pequeñas empresas.En una primera parte, este articulo pone de relieve esta complementaridad. Una segunda parte define las características entre las grandes y pequeñas empresas en las industrias fundadas sobre la ciencia. La tercera parte de este articulo se interesa a las implicaciones de estos analisis que se aplican a la « creation » y la « difusión » de la inovacion en las industrias fundadas sobre la ciencia

Science-technologie et stratégies industrielles dans les pays en voie de développement : rôle des FMN et autres acteurs

Larue de Tournemine Régis. Science-technologie et stratégies industrielles dans les pays en voie de développement : rôle des FMN et autres acteurs. In: Tiers-Monde, tome 29, n°113, 1988. Multinationales et développement, sous la direction de Wladimir Andreff et Jean Masini. pp. 121-136

Progrès technique et dépenses dans les techniques avancées : le cas des dépenses spatiales européennes

[fre] Le taux de rendement des dépenses de recherche est très variable d'un projet à l'autre. Pour des projets de recherche complexe (Espace, physique des hautes énergies), l'évaluation de ce taux de rendement paraît être une gageure.. L'article présente la problématique et les résultats d'une étude sur les « Effets économiques » des dépenses effectuées pour les programmes spatiaux européens, dans le cadre de l'Agence Spatiale Européenne (ESA).. Cette étude repose sur l'analyse des informations fournies par une centaine de firmes européennes impliquées dans les programmes spatiaux européens. Les résultats obtenus permettent de préciser l'importance relative des catégories d'effets économiques induits par les dépenses spatiales : effets induits en matière d'innovations technologiques, effets induits sur le volume des ventes, effets induits sur l'organisation et les méthodes (de production, de gestion), effets induits sur le facteur travail (amélioration du savoir-faire, du niveau des connaissances technologiques, etc).. L'ensemble de ces résultats permet d'illustrer la manière dont les grands programmes publics de recherche contribuent à une modification de la production et de la productivité de tout un ensemble de firmes. [eng] The rate of return on research expenses is very variable from one project to another. For complex research projects (Space, High Energy Physics), the variation of this rate of return appears to be no more than a guess.. The article presents the problem and the results of a study on the "Economie Effects" of expenses made for European Space Programs, under the hospices of the European Space Agency (ESA).. This study is based upon the analysis of information furnished, by approximatively one hundred european firms engaged in the European Space Programs. The results obtained allow us to indicate precisely the relative importance of the categories of economic effects produced by Space expenses, effects produced in the area of technological innovations, effects produced upon the volume of sales, effects produced upon organization and methods (of production, of management), effects produced upon the labour factor (improvment of skills, of the level of technological knowledge...).. These results together allow us to illustrate the way, in which the large public research programs contribute to a modification of the production and of the productivity of an entire group of firms.

Sratégie et comportement des entreprises dans une technologie nouvelle : le cas de l'industrie du laser d'usinage

[eng] This article proposes an overview of the industrial configurations as well as firms'strategy among the companies producing and/or selling industrial lasers. The international competition in this field is caracterized by the U.S. leadership and by original efforts of R&D in Japan. Three « actors » play a major role in this market : suppliers, users and institutional organizations that are located between supply and demand. For the EEC firms it should be profitable to cooperate and to stimulate synergies in the following directions : Development of technical information — promotion of joint R&D — promotion of basic technology and industrial promotion an some segments of the market. [fre] Cet article propose une synthèse des situations industrielles et des stratégies des entreprises qui produisent et/ou commercialisent des lasers d'usinage. La concurrence internationale en ce domaine est caractérisée par la position leader des États-Unis et par des efforts originaux de R&D au Japon. Trois catégories « d'acteurs » ont un rôle déterminant sur ce marché, les offreurs, les demandeurs et les organismes intermédiaires entre l'offre et la demande. Pour les entreprises de la CEE, iI serait souhaitable d'unir leurs efforts dans une perspective de synergie selon divers axes : le développement de l'information — la promotion des recherches coopératives possibles — la promotion des technologies de base et la promotion industrielle sur certains créneaux.

Sratégie et comportement des entreprises dans une technologie nouvelle : le cas de l'industrie du laser d'usinage

[eng] This article proposes an overview of the industrial configurations as well as firms'strategy among the companies producing and/or selling industrial lasers. The international competition in this field is caracterized by the U.S. leadership and by original efforts of R&D in Japan. Three « actors » play a major role in this market : suppliers, users and institutional organizations that are located between supply and demand. For the EEC firms it should be profitable to cooperate and to stimulate synergies in the following directions : Development of technical information — promotion of joint R&D — promotion of basic technology and industrial promotion an some segments of the market. [fre] Cet article propose une synthèse des situations industrielles et des stratégies des entreprises qui produisent et/ou commercialisent des lasers d'usinage. La concurrence internationale en ce domaine est caractérisée par la position leader des États-Unis et par des efforts originaux de R&D au Japon. Trois catégories « d'acteurs » ont un rôle déterminant sur ce marché, les offreurs, les demandeurs et les organismes intermédiaires entre l'offre et la demande. Pour les entreprises de la CEE, iI serait souhaitable d'unir leurs efforts dans une perspective de synergie selon divers axes : le développement de l'information — la promotion des recherches coopératives possibles — la promotion des technologies de base et la promotion industrielle sur certains créneaux.