1,720,958 research outputs found
General approach for the comparison of spectrum efficiency of digital mobile radio systems
No full textEvaluation of spectrum efficiency in mobile radio systems is often performed by different authors starting from different working assumptions; that yields results that are not easily comparable outside the `scenario' where they have been achieved. This paper attempts to settle this controversial matter providing some criteria for overcoming these difficulties. The results of this investigation allow to assess that relative capacity comparisons are fairly independent of some quality parameters, such as specified outage probability, or propagation parameters, such as the standard deviation of lognormal shadowing, so that these parameters need not complicate the comparison of competing approaches. As a consequence, a very simple scenario, providing an adequate basis for deriving constant efficiency curves, turns out to be of great relevance for comparisons. Associated with it, a graphic tool, allowing to perform quick relative comparisons among systems, is presented
Evaluation of spectral efficiency of high capacity mobile radio systems for different scenarios
No full textThe authors discuss the problems related to a proper definition and evaluation of spectral efficiency in order to find out which aspects are relevant for comparison among different solutions, and which aspects determine only the final absolute value. In particular, it is shown that different coverage strategies and propagation conditions not only affect the absolute value of spectral efficiency but also the comparison among different systems. The concept of a 'scenario' for evaluation and comparison is introduced, and examples of computation of spectral efficiency are given in a deterministic and in a statistical scenario (in the presence of log-normal fading). A reference optimum system is introduced in order to be able to express system spectral efficiency in a relative way
A measurement-based methodology for the determination of validity domains of prediction models in urban environment
No full textThe choice of a given propagation model has a major impact on the accuracy and effectiveness of cellular planning, especially in urban environment, where a higher degree of detail is required. Rigorous models, such as those based on ray optics, are generally heavily time-consuming; furthermore, they are accurate only if high-resolution databases (of buildings, land usage, etc.) are available, and the cost of these databases is increasingly affecting the operators' budget. Therefore, one should use them only in their "validity domain," i.e., the area where they are both reliable and necessary: using complex tools where it's not needed implies an overhead in terms of computation time and, above all, database cost. For this reason, increasing interest and effort are being devoted by operators, manufacturers, and system planners in general to determine the validity domains of propagation models in urban environment. In this paper, we introduce a new methodology, based on objective indicators related to field strength statistics, to determine these domains. © 2000 IEEE
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
A new statistical approach for urban environment propagation modeling
No full textField prediction is an essential component of the planning process of cellular radio systems. This task is particularly time- and money-consuming in urban environment, where cell size is of the order of a few hundred meters, and the influence of the city structure (building size and dimension, street width, orientation, etc.) cannot be neglected in the field prediction. For this reason, traditional statistical models such as the well-known Okumura-Hata, cannot be used in this environment, and the prediction is accomplished by means of accurate but time-consuming methods, such as ray-tracing, which require detailed and very expensive databases of the building and street layout of the city under investigation. In this correspondence, we propose a new methodology, which is based on the decomposition of propagation in its basic mechanisms, corresponding to different propagation planes, which can be treated independently from each other. This allows us to build a model which is as simple, fast, and easy to use as the traditional statistical models, with the advantage that it requires only a few statistical parameters thus realizing the need of high-resolution databases
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
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