1,720,954 research outputs found
Contribution à l'estimation d'un canal radio mobile MIMO-OFDM utilisant les SVR
No full textThe performance of wireless communication systems is largely governed by the wireless channel environment. Usually, transmission that are carried out on mobile radio channel are selective in time and frequency. To overcome the channel selectivity and allow high transmission data rate, new approaches for synchronization, equalization and channelestimation are needed.The use of Support Vector Machines (SVMs) has shown several advantages in re-gression, prediction and estimation over some of the classical approaches due to its improved generalization capabilities. Moreover, the introduction of complex algebra in the SVM formulation can provide us with a more natural and flexible framework whendealing with complex symbols and constellations.The current thesis work focuses on the study and development of efficient channel estimation algorithms based on complex Support Vector Machines Regression (SVR) that are specifically adapted to pilot-aided OFDM (Orthogonal Frequency Division Mul-tiplexing) structure and applied to Long Term Evolution (LTE) downlink system. The mathematical model of the LTE mobile radio channel is described and simulated for various scenarios based on 3GPP specifications. According to this model, a nonlinear complex SVR is proposed for SISO-OFDM system. The principle of the proposed kernel-based learning algorithm is to exploit the information provided by the reference signals to estimate the channel frequency response. The proposed approach is based on two separate phases: learning phase and estimation phase. In learning phase, we estimate first the subchannels pilot symbols and in estimation phase, frequency responses of data subchannels are determined by means of SVM interpolation mechanism. In addition, a nonlinear complex Multiple Support Vector Machines Regression (M-SVR) algorithm adapted to MIMO (Multiple Input Multiple Output) architecture is proposed to esti-mate the multipath fading channel in MIMO-OFDM system with both STBC (Space Time Bloc Coding) and V-BLAST (Vertical Bell Laboratories layered Space Time) schemes.The feasibility of our approaches is confirmed by computer simulation results achieved for LTE downlink model. This experiments allow to analyze the performance of the SVR technique and the suitability of the ε-Huber cost function in the mobile radio multipath fading channel presenting non-Gaussian impulsive noise interfering with OFDM refer-ence symbols under high mobility conditions.La performance des systèmes de communication sans fils dépend largement des car-actéristiques du canal radio mobile. Généralement, la plupart des transmissions sontréalisés sur des canaux sans fils sélectifs en temps et en fréquence. Afin de surmonter lasélectivité du canal et permettre un débit de transmission de données élevé, de nouvellesapproches pour la synchronisation, l’égalisation et l’estimation de canaux sont néces-saires. L’utilisation des machines à vecteur support (SVM) a montré plusieurs avantagesdans les domaines de régression, estimation et prédiction par rapport à certaines ap-proches classiques grâce à ses capacités de généralisation. En outre, l’introduction del’algèbre complexe dans la formulation des SVMs a fourni un cadre plus souple et naturellorsqu’on traite des constellations et symboles complexes.Les travaux de recherche introduits dans cette thèse portent sur l’étude et le développe-ment des algorithmes d’estimation de canal efficaces et robustes basés sur les machinesà vecteur support pour la régression (SVR) particulièrement adaptés à la structureOFDM (Orthogonal Frequency Division Multiplexing) avec des symboles pilotes. Cesalgorithmes seront ensuite appliqués à un système LTE (Long Term Evolution). Lemodèle mathématique du canal radio mobile LTE est décrit et simulé pour différentsscénarios basés sur les spécifications 3GPP. Selon ce modèle, l’estimateur SVR nonlinéaire complexe est proposé pour le système SISO-OFDM. Le principe de cet al-gorithme d’apprentissage basé sur les fonctions noyaux est d’exploiter les informa-tions fournies par les symboles pilotes pour estimer la réponse fréquentielle du canal.L’approche proposée repose sur deux phases distinctes: la phase d’apprentissage et laphase d’estimation. Dans la phase d’apprentissage, nous estimons d’abord les sous-canaux des symboles pilotes, puis dans la phase d’estimation, les réponses fréquentiellesdes sous-canaux de données seront déterminées par le mécanisme d’interpolation SVM.En outre, un algorithme non linéaire complexe basé sur les machines à vecteur supportpour la régression multiple (M-SVR ) adapté à l’architecture MIMO (Multiple InputMultiple Output) est proposé pour estimer le canal dans les systèmes MIMO-OFDMexploitant les techniques STBC (Space Time Bloc Coding) et V-BLAST (Vertical BellLaboratories layered Space Time). La faisabilité de nos approches est assistée pardes résultats de simulation obtenus pour le modèle LTE. Ces expériences permettentd’analyser les performances de la technique SVR et la pertinence de la fonction coûtε-Huber dans un canal radio mobile à trajets multiples présentant un bruit impulsionnelnon-Gaussian interférant avec les symboles pilots sous des conditions de haute mobilité
Support Vector Machines Regression for MIMO-OFDM Channel Estimation
Get PDFIn this paper, we propose a robust highly selective nonlinear channel estimator for Multiple -Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system using complex Support Vector Machines Regression (SVR) and applied to Long Term Evolution (LTE) downlink under high mobility conditions .The new method uses the information provided by the pilot signals to estimate the total frequency response of the channel in two phases: learning phase and estimation phase. The estimation algorithm makes use of the reference signals to estimate the total frequency response of the highly selective multipath channel in the presence of non-Gaussian impulse noise interfering with pilot signals. Thus, the algorithm maps trained data into a high dimensional feature space and uses the Structural Risk Minimization (SRM) principle to carry out the regression estimation for the frequency response function of the highly selective channel. The simulations show the effectiveness of the proposed method which has good performance and high precision to track the variations of the fading channels compared to the conventional LS method and it is robust under high mobility conditions.DOI: http://dx.doi.org/10.11591/ij-ai.v1i4.183
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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