1,721,018 research outputs found
Optical Wireless Communications - An Emerging Technology
No full textWireless transmission via optical carriers opens doors of opportunity in areas as yet largely unexplored. Offering significant technical and operational advantages, optical wireless communication (OWC) can be, in some applications, a powerful alternative to and, in others, complementary to existing radio frequency (RF) wireless systems. Variations of OWC can be employed in a diverse range of communication applications ranging from very short-range (on the order of millimetres) optical interconnects within integrated circuits through outdoor inter-building links (on the order of kilometres) to satellite links (larger than 10,000 kilometres). In many respects, OWC research is still in its infancy and calls for extensive research to begin to harness the enormous potential of the optical spectrum. This COST Action will serve as a high-profile consolidated European scientific platform for interdisciplinary OWC research activities, spanning from characterization of diverse propagation media to modeling, design and development of devices, components, algorithms/protocols and systems. It will make significant contributions to the fundamental scientific understanding, technical knowledge, engineering design and applications while promoting community awareness of this emerging field. Development of novel and efficient communication technologies resulting from integrated research activities made possible through this Action will be a significant enabler for future-generation heterogeneous communication networks supporting a wide range of wireless services/applications
Non-coherent communication in wireless point-to-point and relay channels: a geometric approach
No full textWe address the problem of non-coherent transmission in block Rayleigh fading channels. We focus on the point-to-point MIMO channel and the wireless relay channel without direct link.
The problem of non-coherent space-time coding can be given a geometric interpretation as a packing problem in the Grassmann manifold. We use the differentiable structure of the Grassmann manifold for code constructions for the non-coherent channel. We present several novel constructions which exploit the geometry of the Grassmann manifold. We propose code constructions from spherical codes and lattice packings and develop a method for recursive construction of high-dimensional codes.
We also address the problem of non-coherent transmission in wireless relay networks. We focus on one-way and two-way relaying protocols with half-duplex constraints on the terminals. For the one-way relaying network we present novel distributed space-time codes based on Grassmann codes for the point-to-point MIMO channel. For the two-way relaying channel we first introduce the concept of non-coherent communication, showing that non-coherent communication is possible, although no channel knowledge is present at neither the terminals nor at the relays. Further, we present bounds on the achievable two-way rate in the non-coherent setup. We show that the upper and the lower bound meet in the high SNR regime and differ from the capacity within a constant. As a byproduct we derive the degrees of freedom of the two-way network and show that amplify-and-forward is optimal strategy in the non-coherent setup. Motivated from the results, we present two communication schemes. The first one is a differential scheme which extends over the known differential schemes for one-way relaying and adapts to the specifics of the two-way channel. The second scheme is a genuine non-coherent scheme, designed for the block channel model
Optical Wireless Communications - An Emerging Technology
No full textWireless transmission via optical carriers opens doors of opportunity in areas as yet largely unexplored. Offering significant technical and operational advantages, optical wireless communication (OWC) can be, in some applications, a powerful alternative to and, in others, complementary to existing radio frequency (RF) wireless systems. Variations of OWC can be employed in a diverse range of communication applications ranging from very short-range (on the order of millimetres) optical interconnects within integrated circuits through outdoor inter-building links (on the order of kilometres) to satellite links (larger than 10,000 kilometres). In many respects, OWC research is still in its infancy and calls for extensive research to begin to harness the enormous potential of the optical spectrum. This COST Action will serve as a high-profile consolidated European scientific platform for interdisciplinary OWC research activities, spanning from characterization of diverse propagation media to modeling, design and development of devices, components, algorithms/protocols and systems. It will make significant contributions to the fundamental scientific understanding, technical knowledge, engineering design and applications while promoting community awareness of this emerging field. Development of novel and efficient communication technologies resulting from integrated research activities made possible through this Action will be a significant enabler for future-generation heterogeneous communication networks supporting a wide range of wireless services/applications
Cooperative Radio Communications for Green Smart Environments
No full textSmart Environments (SEs), like the human body, energy efficient buildings, vehicular or urban environments, are populated by many devices connected by wireless networks. The radio channel is central to SEs, as it impacts the design of transmission techniques and communication protocols. Radio communications in SEs need to be green and based on cooperative paradigms to mitigate the effect of interference and improve efficiency. This Action addresses research issues in the field of cooperative radio communications to make our society cleaner, safer, and more energy efficient. The main goal of the Action is to increase knowledge of cooperative communications applied to Green SEs (GSEs), by exploring and developing new methods, models, techniques, strategies and tools, in a context enriched by deep industry-academia links. Training of young researchers is also one of its main objectives, to be pursued e.g. via annual training schools. Europe will benefit from the activities of this Action, as GSEs will be one of the key components of the broader field (and exploding market) of the Internet of Things, a domain of interest to many large and small companies in Europe. COST is the ideal framework, as it allows very efficient cooperation among industries and academia
Cooperative Radio Communications for Green Smart Environments
No full textSmart Environments (SEs), like the human body, energy efficient buildings, vehicular or urban environments, are populated by many devices connected by wireless networks. The radio channel is central to SEs, as it impacts the design of transmission techniques and communication protocols. Radio communications in SEs need to be green and based on cooperative paradigms to mitigate the effect of interference and improve efficiency. This Action addresses research issues in the field of cooperative radio communications to make our society cleaner, safer, and more energy efficient. The main goal of the Action is to increase knowledge of cooperative communications applied to Green SEs (GSEs), by exploring and developing new methods, models, techniques, strategies and tools, in a context enriched by deep industry-academia links. Training of young researchers is also one of its main objectives, to be pursued e.g. via annual training schools. Europe will benefit from the activities of this Action, as GSEs will be one of the key components of the broader field (and exploding market) of the Internet of Things, a domain of interest to many large and small companies in Europe. COST is the ideal framework, as it allows very efficient cooperation among industries and academia
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
Degrees of Freedom Analysis of the Non-coherent Block Fading MAC Channel
No full textWe study a two-user multiple-input multiple-output (MIMO) fading multiple-access channel (MAC), where two terminals wish to communicate with a third one. The channels between the terminals are MIMO block fading channels with channel coefficients which are constant in a block of length T, and then change in an independent realization. The system model follows the model introduced by Hochwald and Marzetta. We consider a non-coherent channel model, where all terminals
are aware of the statistics of the fading but not of its realization. Instead of using pilots for channel estimation, we assume communication where the information is communicated by the use of subspaces, following the geometric approach introduced by Zheng and Tse. We focus on the high signal-to-noise ratio (SNR) regime. In particular, we study the pre-log region, defined as the limiting ratio of the achievable-rate region to log SNR as the SNR tends to infinity
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