1,720,967 research outputs found
Iterative multiuser resource allocation for inhome Power Line Communications
No full textIn a multiuser scenario, the bit-loading, which has proven decisive in resource optimization for Power Line Communications (PLCs), has to be coupled with channel assignment to fully exploit its potential. Unfortunately, finding the most performing combination of channel and power allocation leads to integer (or mixed) programming problems, which are known to be NP-hard. To overcome the complexity of the resulting optimization problem, in this paper we propose an iterative solution that is able to guarantee both fairness and Quality of Service (QoS) to the users when the overall power consumption of the system is bounded and each subchannel emission is limited. This solution embeds a Connection Admission Control (CAC) that allows to leave out badly-connected users that otherwise would negatively affect the comprehensive system performance. Numerical results compare the presented resource allocation with the common greedy-based single user approach. © 2011 IEEE
Power-Constrained Physical-Layer Goodput Maximization for Broadband Power Line Communication Links
No full textPower Line Communication (PLC) systems are currently envisioned as a possible solution for distributing multimedia contents and allowing Internet access with a capillary (already built) network without demanding further infrastructure. The real challenge for PLCs consists in providing connectivity where Public Switch Telephone Network (PSTN)-based Internet Access and/or Wi-Fi/WiMAX seem to be unable to solve the problem of Digital Divide. In this paper we introduce a new metric, i.e. the goodput, to balance transmission rate and bit error rate (BER) in resource allocation issues for Power Line Communication systems. In detail, we state the well-known integer bit-loading problem as a goodput maximization with constraints on the power consumption and the maximum decoding time. The use of Trellis Coded Modulation (TCM) allows to pursue the goodput maximization weighing error probability and transmission rate which would have otherwise been in trade-off. Numerical results are presented to stress how our solution improves system performances, both in ideal conditions and with additional impairments such as crosstalk and impulsive noise, with respect to the conventional Maximum Rate (MR) and Minimum BER (MB) approaches and to validate the suitability of TCMs in comparison with higher complexity codes
An image processing approach to distributed access for multiantenna cognitive radios
No full textIn dynamic and opportunistic access for cognitive radios, the leading trend is to split the available spectrum into separated channels and make the scavenging users access the ones considered free. However, it is likely that even the "occupied" ones do not use up all the resource but leave enough room for other connections. In this paper we present a method that handles the spectrum sensing with the tools of image processing. In detail, by means of the Wigner-Ville transform we are able to analyze the time and frequency features of the received interference, and to represent them as a greyscale image in which brightness reveals the spectrum occupancy. Then, through a proper mask definition and matching algorithm we shape a signal that fills up the "spectrum holes" and exploits the spatial dimension offered by the multiple antennas in order to set up a connection satisfying a specified quality requirement (i.e., the transmission rate). © 2010 IEEE
Cognitive constrained Pulse Shaping for UWB Systems
No full textThe interference induced by UWB communication on systems operating in the frequency range between 0 and 10.6GHz is the main reason why the essential role in these systems' design is played by the pulse shape selection. That's why an accurate shaping choice can lead to avoid severe performance reduction and to guard systems coexistence. To this end, FCC (and ETSI in the near future) gave strict indications about the spectral limits to be respected, so as to define, as the purpose of UWB systems realization, the compliance with this spectral mask. The, widely used, choice of Gaussian-like pulses is, however, largely suboptimal from a power emission point of view since they are unable to maximize the signal-to-noise ratio (SNR). Goal of this contribution is to achieve a good compromise, in a cognitive way, between spectral emission, rate and synchronization errors robustness, via a modified version of the Parks-McClellan method, considering channel impairments due to its frequency-selective nature, to the inter-pulse interference and in-band interference. ©2010 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
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
A cross-layer approach to the optimal flow, power and rate control for maximum-throughput delivery of VBR traffic over wireless connections
No full textThe delivering of variable bit rate (VBR) encoded media contents to nomadic end-users through the 'last-hop' wireless connection, rises up several challenges related to the fading-impaired and time-varying nature of the wireless medium itself. In detail, a still open question concerns the closed-form design of cross-layer control policies to maximise the average throughput while taking into account constraints comprising layers of the protocol stack from the physical (PHY) up to the application (APP) one. To overcome the computational cost entailed by dynamic programming solutions, the approach we follow aims at the maximisation (on a per-slot basis) of the throughput averaged over the fading statistic and conditioned on the queuestate. To show the performance of the proposed controller, (tight) upper and lower bounds have been derived for the average throughput and numerical tests have been presented to give insight into the connection bandwidth vs. queuedelay tradeoff. Copyright © 2011 Inderscience Enterprises Ltd
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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