1,721,019 research outputs found
Error Detection Strategies for CRC-Concatenated Polar Codes under Successive Cancellation List Decoding
Full text linkIn this work we introduce a framework to study the trade-off between the undetected error rate (UER) and overall frame error rate (FER) of CRC-concatenated polar codes in the short blocklength regime. Three approaches to improve the tradeoff under successive cancellation list (SCL) decoding are outlined. Two techniques are based on the optimum threshold test introduced by Forney in 1968, whereas a third technique partitions the CRC code parity bits in two sets, where one set is used to prune the SCL decoder list, and the other set is used for error detection. The performance of the three schemes is analyzed via Monte Carlo simulations, and compared with a finite-length achievability bound based on Forney’s random coding bound
Coherent vs IM/DD Transmissions for FSO Communications in the Presence of Atmospheric Turbulence
Full text linkWe investigate the performance of free-space optical communication systems in the presence of atmospheric turbulence with the purpose of assessing the advantages that a coherent communication system can bring with respect to a conventional intensity modulation/direct detection system. The perspective is an information theoretic one, hence we evaluate the mutual information and the corresponding outage probability of both channels, with traditional symbol constellations, as a pragmatic approximation to the capacity, or to the outage capacity, of those channels. In addition, we analyze non-uniform symbol constellations, in order to evaluate the possible shaping gain that can be achieved under different channel conditions
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
CLOSE-TO-CAPACITY DECODING ON THE PACKET ERASURE CHANNEL (PEC)
No full textResearch on packet-layer coding is driven by two main factors: keeping encoding/decoding complexity low, while finding suitable code designs to approach channel capacity. A class of codes that fulfills these requirements perfectly is the one of low-density parity-check (LDPC) codes. Recent works showed that nearly optimal performance can be achieved with high decoding speed, down to low error rates and even for small and moderate block sizes. This is thanks to maximum-likelihood (ML) aided decoding techniques in combination with a judicious code design. A review of the ML decoding approach will be first presented, followed by further insights on the code design. Performance and decoding speed assessments will be both provided in terms of simulation and field test results
Analysis and simulation of cryptographic techniques based on sparse graph with application to satellite and airborne communication systems
No full textIn view of the future diffusion of quantum computers, many of the cryptographic systems currently in use must be rethought. This drastic but concrete preview has led us to reflect on a possible solution based on error correction code theory. In fact, many lines of thought are in agreement with the possibility of using error correctly codes not only for channel encoding, but also for encryption. In 1978 McEliece was the first to propose this idea, at those time not very much considered because with worse performance in the area of cryptography compared to other techniques, but today re-evaluated. The Low Density Parity Check codes (LDPC) are state-of-art in error correction
since they can be decoded efficiently close to the Shannon capacity. Thanks to new advances in the algorithmic aspects of code theory and progress on linear-time encodable/decodable codes it is possible to achieve capacity even against adversarial noise. This thesis work mainly focuses on the decoding
(or in terms of cryptography in the decryption) of LDPC codes through the implementation of Hard Decision Iterative Decoding with the aim of studying the performances for different codes belonging to the same LDPC family in terms of error correction capability
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