1,720,983 research outputs found
Study and design of decoder architectures of Low-Density Parity-Check and Turbo Codes for high-rate flexible communication systems
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Capacity of Interference Exploitation Schemes in Multibeam Satellite Systems
No full textWe propose a framework, based on the combined use of single- and multiuser detection, to jointly optimize the achievable rates of two signals sharing the same frequency in the forward link of a multibeam satellite system. We propose then the application of the described framework to two different scenarios of interest. First, we consider a uniform coverage scenario, aimed at maximizing the average throughput per beam in a realistic coverage condition. We compare different solutions, based on alternative frequency reuse schemes and different receiver strategies. We demonstrate that the use of multiuser detection can achieve significant gains over a reference strategy based on single-user detection. Next, we analyze a “hotspot” case, where resources are pulled from empty beams to serve a beam with a high service demand. Also in this case, we compare several strategies and frequency reuse schemes. We show that the best performance is achieved by a scheme adopting 3 colors and single-user detectio
Guest editorial IJSCN special issue on ASMS/SPSC 2014
Full text linkThis special issue of the Wiley International Journal of Satellite Communications and Networking hosts a selection of papers from the seventh Advanced Satellite Multimedia Systems (ASMS) Conference and the 13th Signal Processing for Space Communications (SPSC) Workshop held in Livorno, Italy on 8 to 10 September 2014. The joint event was organized through a collaborative effort of the University of Bologna, the Institute of Communications and Navigation of DLR (German Aerospace Center), the European Space Agency (ESA), under the auspices of the Association ‘Toscana Spazio’ and the SatNEx III Network of Experts and in cooperation with the University of Pisa.
The ASMS conference and SPSC workshop have become recognized events for industry and research institutions to exchange up-to-date information about recent advances and emerging technologies in the field of mobile satellite communication systems. The ESA's SPSC workshop dates back to 1988 when pioneering work in digital signal processing for satellite communications was first presented by worldwide authorities in the field. In addition, following the successful path opened by the 2006 edition of ASMS and continued with the 2008, 2010 and 2012 editions, the scope of the conference has been further widened, as the small though important change in its name by replacing the word ‘mobile’ with ‘multimedia’ testifies. This is remarkable not only because the major part of the SATCOM market belongs to broadcasting and broadband access operators but also fundamentally because the convergence of broadcast, mobile and fixed satellite communications is essential to offer seamless connectivity anywhere at any time, which is recognized as the key element for the successful deployment of future satellite systems.
This issue collects the extended versions of six of the best papers presented at the last ASMS/SPSC joint event. The papers have been selected with the aim of providing an insight into the developments and findings in this exciting field.
In the first paper, the authors investigate different techniques to improve the spectral efficiency of systems based on the DVB-S2 standard, whenever the transmitted signal bandwidth cannot be increased because it has already been optimized to the maximum value allowed by transponder filters.
The second paper deals with the design of packet-level forward error correction (FEC) coding technique and pre-distortion adaptive optics technology for a digital transmission scheme to be employed in optical feeder links in a geostationary satellite communication system. Performances are evaluated in both up and downlink.
The third paper proposes a new approach for blind feedforward and feedback recovery of the symbol timing, which needs just one or two samples per symbol. The method is characterized by a second filter operated in parallel to the receiver matched filter and allows avoiding the typical jitter floor irrespective of the selected modulation scheme.
The fourth paper deals with the issue of boosting the capacity of xDSL networks in the presence of geographical gaps by exploiting the downlink of multibeam satellites for the delivering of packed-based traffic. To cope with time-varying channel and interference, the paper proposes a novel link resource adaptation scheme.
The fifth paper addresses the problem of modulation and coding scheme selection in the return link of a mobile satellite system and proposes to use an affine combination of both open loop and closed loop signal quality indicators to perform this selection. The combination weights are dynamically adapted according to the ACK/NAK exchange between both ends, without making any assumptions on the channel distribution
Last but not least, the sixth paper analyses the performance of two Contact Graph Routing (CGR) enhancements, namely CGR-ETO and Overbooking Management. These two enhancements have been recently included in the official CGR version as part of the Interplanetary Overlay Network DTN implementation maintained by NASA.
In closing, the guest editors would like to thank all individuals and organizations that made this issue possible, including the European Commission, the Association ‘Toscana Spazio’, Wiley Interscience, the ASMS/SPSC 2014 Technical and Scientific Committees, all anonymous reviewers and all authors. In particular, we are grateful to Prof. Barry Evans, the Editor-in-Chief of the International Journal on Satellite Communications and Networking, for kindly inviting us once more to conduct this editorial process, as already done for past events.
Given the great success of the join event, we are finally pleased to announce that the next ASMS/SPSC Conference is in fact supposed to take place in Palma de Mallorca (Spain) from 5 to 7 September 2016. More information is available at http://www.asmsconference.org/
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 highly efficient receiver for satellite-based Automatic Identification System signal detection
Full text linkAn innovative receiver architecture for the satellitebased Automatic Identification System (AIS) has been recently proposed. In this paper, we describe a few modifications that can be introduced on the algorithms for synchronization and detection, that provide an impressive performance improvement with respect to the previous system. The receiver architecture has been designed for an on-board implementation, and for this reason all algorithms have been realized keeping the complexity as low as possible. A prototype for the proposed receiver has been implemented by the University of Parma and CGS S.p.A. Compagnia Generale per 10 Spazio under the ESA project FENICE
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