1,720,970 research outputs found
The odd couple: Protocols and channel coding
No full textLEC codes represent a new and very promising proposal for Forward Error Correction (FEC) applied to packet
erasures. This proposal has been formulated on the basis of excellent performance that can be obtained by iteratively
decoded, long codes based on sparse graphs. Basically, they are able to overcome the complexity limitations of other
types of codes, while preserving very good erasure correction capability. This solution consists in introducing a packet oriented
coding scheme at the upper layers, in order to permit the automatic correction, on the receiver side, of
missing information
Recovering from packet losses in CCSDS links
No full textData unit losses in deep space communications
are currently faced using retransmission techniques which are
however inefficient due to the large round trip delays. For this
reason, the Consultative Committee for Space Data Systems
(CCSDS) has recently considered packet erasure correcting codes
for inclusion in its recommendations for space data system
standards. Erasure correcting codes are expected to replace
(or drastically reduce) retransmission requests. Erasure codes
operate on packets instead of bits and are usually implemented
above at the upper layers of the communication stack. In this
paper, the implementation of erasure codes within the CCSDS
communication stack is considered. Moreover, a comparison in
terms of decoding complexity when using a maximum likelihood
(ML) erasure decoder in the Control Center is performed
between possible solutions, namely Raptor codes and low-density
parity-check (LDPC) codes
Design and Analysis of Concatenated Schemes for Applications Requiring Very Low Error Rates
No full textGoing 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
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BANDWIDTH EFFICIENT CONCATENATED CODES FOR EARTH OBSERVATION TELEMETRY
No full textInternational Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, NevadaTelemetry for Earth-Observation missions is characterized by very high data rates and stringent requirements. Channel codes both power and bandwidth efficient must be used to improve downlink performance and to achieve the very low values of error rates needed at the received side. In this paper, we review and analyzed three codes of possible interest for these applications: turbo codes, serial turbo codes and product codes. These schemes are evaluated and compared both by simulation and analytical techniques. A particular attention is devoted to complexity, a key issue for practical implementation at high data rates.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection
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
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