1,721,273 research outputs found
Cognitive Radio Vehicular Ad Hoc Networks: Design, Implementation, and Future Challenges
No full textThis chapter addresses the research issues related to the design and implementation of Cognitive Radio Vehicular Ad Hoc Networks (CRVs). CRVs are composed of vehicles equipped with reconfigurable Software Defined Radio (SDR) devices and intelligent Cognitive Radio (CR) functionalities, allowing to reconfigure all the aspects of the radio control, including the operating spectrum frequencies. As a result of the increased capacity provided by the opportunistic spectrum access, CRVs can meet the increasing bandwidth demands of existing applications for VANETs, and contribute to support a new generation of applications based on inter vehicular communication. At the same time, some important issues and system characteristics must be considered in the design and implementation of CRVs, which thus cannot be considered a direct application of common CR principles to the vehicular environment. For instance, the mobility of each vehicle is shown to have a significant negative impact on the spectrum sensing operations, in general. However, this fact could be turned into a performance gain if the mobility is predictable or restricted, like in CRVs, as discussed in this chapter. Cooperation can be seen as a natural way to increase the spectrum awareness of each vehicle in a urban environment. At the same time, it poses new questions on how it must be implemented and coordinated with the local sensing activity. In this chapter, we review the distinctive characteristics of CRVs. We provide a survey of existing solutions for spectrum management proposed in the literature and at the same time we discuss the open research problems which at present constitute an obstacle to the effective deployment of these systems
A Cross Layered MAC and Clustering Scheme for Efficient Broadcast in VANETs
No full textIn this paper, we illustrate the design of a crosslayered
MAC and clustering solution for supporting
the fast propagation of broadcast messages in a
Vehicular Ad Hoc Network (VANET). A distributed
dynamic clustering algorithm is proposed to create a
dynamic virtual backbone in the vehicular network.
The vehicle-members of the backbone are responsible
for implementing an efficient messages propagation.
The backbone creation and maintenance are
proactively performed aiming to balance the stability
of backbone connections as well as the cost/efficiency
trade-off and the hops-reduction when forwarding
broadcast messages. A fast multi-hop MAC forwarding
mechanism is defined to exploit the role of backbone
vehicles, under a cross-layered approach. Simulation
results show the effectiveness of the mutual support of
proactive clustering and MAC protocols for efficient
dissemination of broadcast messages in VANETs
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
Traffic integration in personal, local and geograhical wireless networks
Get PDFCurrently, users identify wireless networks with the first and second generation of cellular-telephony networks. Although voice and short messaging have driven the success of these networks so far, data and more sophisticated applications are emerging as the future driving forces for the extensive deployment of new wireless technologies. In this chapter we will consider future wireless technologies that will provide support to different types of traffic including legacy voice applications, Internet data traffic, and sophisticated multimedia applications. In the near future, wireless technologies will span from broadband wide-area technologies (such as satellite-based network and cellular networks) to local and personal area networks. Hereafter, for each class of networks, we will present the emerging wireless technologies for supporting service integration. Our overview will start by analyzing the Bluetooth technology that is the de-facto standard for Wireless Personal Area Networks (WPANs), i.e. networks that connect devices placed inside a circle with radius of 10 meters. Two main standards exist for Wireless Local Area Networks (WLANs): IEEE 802. and HiperLAN. In this chapter we focus on the IEEE 802.11 technology, as it is the technology currently available on the market. In this chapter, after a brief description of the IEEE 802.11 architecture, we will focus on the mechanisms that have been specifically designed to support delay sensitive traffics
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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