1,721,041 research outputs found
Capacity analysis under generalized composite fading conditions
No full textNovel composite fading models were recently proposed based on inverse gamma distributed shadowing conditions. These models were extensively shown to provide remarkable modeling of the simultaneous occurrence of multipath fading and shadowing phenomena in emerging wireless scenarios such as cellular, off-body and vehicle-to-vehicle communications. Furthermore, the algebraic representation of these models is rather tractable, which renders them convenient to handle both analytically and numerically. The present contribution presents the major theoretical and practical characteristics of the η - μ / inverse gamma composite fading model, followed by a thorough ergodic capacity analysis. To this end, novel analytic expressions are derived, which are subsequently used in the evaluation of the corresponding system performance. In this context, the offered results are compared with respective results from cases assuming conventional fading conditions, which leads to the development of numerous insights on the effect of the multipath fading and shadowing severity on the achieved capacity levels. It is expected that these results will be useful in the design of timely and highly demanding wireless technologies, such as wearable, cellular and inter-vehicular communications as well in wireless power transfer based applications in the context of the Internet of Things.</p
Achievable fixed rate capacity in emerging wireless systems (invited paper)
No full textThe F composite fading model was recently proposed as an accurate and tractable statistical model for the characterization of the simultaneous occurrence of multipath fading and shadowing conditions encountered in realistic wireless communication scenarios. In the present contribution we capitalize on the distinct properties of this composite model to derive the achievable capacity over F composite fading channels assuming fixed rate quality of service requirements. To this end, novel exact and tractable analytic expressions are derived for both the exact and the truncated channel inversion strategies. This also enables the derivation of additional simplified approximate and asymptotic expressions for these cases, which provide meaningful insights on the effect of fading conditions on the overall system performance. This is particularly useful in the context of numerous emerging wireless applications of interest that exhibit stringent fixed rate requirements such as vehicular communications, body area networks and telemedicine, among others.</p
Achievable ergodic capacity under f composite fading conditions
No full textThe F composite fading model was recently proposed as an accurate and tractable statistical model for the characterization of the composite fading conditions encountered in realistic wireless communication scenarios. In the present contribution we capitalize on the distinct properties of this composite model to evaluate the achievable ergodic capacity over F composite fading channels. To this end, we derive an exact closed-form expression for the ergodic capacity, which is subsequently used as a benchmark for the derivation of a tight approximation and a particularly accurate asymptotic representation for large average signal-to-noise ratio values. The derived analytic expressions are provided in closed-form and benefit from their analytical and numerical tractability. This enables the development of meaningful insights on the effect of fading conditions of different severity levels on the overall system performance. Also, it allows the accurate quantification of the signal to noise ratio required in target quality of service requirements under different composite fading conditions.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Generalization of Space-Time Block Coded-Spatial Modulation for High Data Rate VLC Systems (Invited Paper)
No full text<p>Visible light communication (VLC) is a promising solution to the current congestion in radio frequency (RF) spectrum. It achieves that by exploiting the huge unregulated visible light portion of the electromagnetic spectrum in order to enable high-speed short range wireless communications, as well as, providing an sufficient lighting. This new solution is envisioned to provide a considerably wider bandwidth that can accommodate ubiquitous broadband connectivity to indoor users and further offload data traffic from overloaded cellular networks. However, VLC suffers from several limitations, such as the limited modulation bandwidth of light-emitting diodes (LEDs) that degrades the overall system spectral efficiency. In this respect, several interesting solutions have been proposed in the recent literature to overcome this limitation, such as the implementation of efficient optical modulation and multipleinput-multiple-output (MIMO) schemes. In this paper, we investigate the performance of multiple active spatial modulation (MASM) integrated with orthogonal space time block codes (STBC) for indoor VLC systems. Additionally, in ordered to reduce the receiver complexity, a simplified version of the joint maximum likelihood (ML) detector is proposed which has a linear complexity with respect to the number of transmit LEDs and the constellation size. Extensive computer simulations demonstrate that STBC-MASM improves the overall system performance compared to MASM with a considerably simplified detection. </p>Peer reviewe
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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