1,720,997 research outputs found
Design and self-management of wireless networked systems with model-driven optimization
No full textWireless networked systems are becoming increasingly popular, with a growing number of deployments and diverse applications. This leads to increasing complexity of these systems, as due to the shared nature of the wireless medium the amount of network resources available is constantly decreasing. These networks have to operate in challenging and dynamic conditions, and accommodate diverse and often contradictory objectives stated by multiple stakeholders. Often wireless networks are integral parts of larger systems, like the Internet, and need to utilize existing imperfect software and hardware components, which results in additional heterogeneity and implementation challenges. All this makes design, planning, and run-time management of wireless networked systems a demanding task. In this thesis we address some of these challenges through a model-driven optimization methodology, which is formalized using category theory. We state a meta-optimization problem based on requirements of network players, operational context, applicable models that consider for both parameter- and component-based solutions. In order to simplify the problem we propose applying the mapping functions of abstraction, transformation, and decomposition, while considering the aspects of information loss or disruption in the problem formulation. We show on selected case studies how the proposed methodology can be employed at both static (design, planning) and dynamic (run-time management) stages of a network's life-cycle. In particular, we demonstrate that this methodology is effective for a detailed design and implementation of a self-optimizing system for wireless home networks, and optimization of protocol stacks for wireless sensor systems with an ontology-driven framework. Since modeling is a crucial aspect of network optimization, we also propose and investigate several types of models in this work. Directed labeled graphs and their network motifs are used for identification of the networking context in the CSMA/CA based networks. We show how spatial network structure affects characteristics of these graphs, such as node degree distributions and occurrence patterns of small network motifs. We also propose a novel graph edge labeling based on clustered correlation coefficients that capture network dynamics imposed by tunable network parameters. We argue that this robust metric can lead to faster network optimization in a variety of operational conditions. We also consider modeling of the temporal context. In particular, based on power spectrum measurements we obtain online hidden semi-Markov models of network activity patterns and apply them as part of a dynamic spectrum access scheme. Additionally, we exploit metaheuristic mechanisms for cross-layer optimization and network planning that aim at robustness, performance maximization and optimizability of the system. We investigate how the size and the structure of the state space, the availability of valid models and utility functions influence the convergence of these methods. Our results show that for network problems it is often better to invest in careful problem formulation and long execution of simple metaheuristics rather than going for their custom modifications besides the simplest ones. The proposed approaches have being extensively prototyped or proven through simulation based experimentation. In particular we have focused on small-scale wireless networked systems that utilize IEEE 802.11 radio interfaces and wireless sensor networks. We have also experimented with the WARP software defined radio platforms
Design and self-management of wireless networked systems with model-driven optimization
No full textWireless networked systems are becoming increasingly popular, with a growing number of deployments and diverse applications. This leads to increasing complexity of these systems, as due to the shared nature of the wireless medium the amount of network resources available is constantly decreasing. These networks have to operate in challenging and dynamic conditions, and accommodate diverse and often contradictory objectives stated by multiple stakeholders. Often wireless networks are integral parts of larger systems, like the Internet, and need to utilize existing imperfect software and hardware components, which results in additional heterogeneity and implementation challenges. All this makes design, planning, and run-time management of wireless networked systems a demanding task. In this thesis we address some of these challenges through a model-driven optimization methodology, which is formalized using category theory. We state a meta-optimization problem based on requirements of network players, operational context, applicable models that consider for both parameter- and component-based solutions. In order to simplify the problem we propose applying the mapping functions of abstraction, transformation, and decomposition, while considering the aspects of information loss or disruption in the problem formulation. We show on selected case studies how the proposed methodology can be employed at both static (design, planning) and dynamic (run-time management) stages of a network's life-cycle. In particular, we demonstrate that this methodology is effective for a detailed design and implementation of a self-optimizing system for wireless home networks, and optimization of protocol stacks for wireless sensor systems with an ontology-driven framework. Since modeling is a crucial aspect of network optimization, we also propose and investigate several types of models in this work. Directed labeled graphs and their network motifs are used for identification of the networking context in the CSMA/CA based networks. We show how spatial network structure affects characteristics of these graphs, such as node degree distributions and occurrence patterns of small network motifs. We also propose a novel graph edge labeling based on clustered correlation coefficients that capture network dynamics imposed by tunable network parameters. We argue that this robust metric can lead to faster network optimization in a variety of operational conditions. We also consider modeling of the temporal context. In particular, based on power spectrum measurements we obtain online hidden semi-Markov models of network activity patterns and apply them as part of a dynamic spectrum access scheme. Additionally, we exploit metaheuristic mechanisms for cross-layer optimization and network planning that aim at robustness, performance maximization and optimizability of the system. We investigate how the size and the structure of the state space, the availability of valid models and utility functions influence the convergence of these methods. Our results show that for network problems it is often better to invest in careful problem formulation and long execution of simple metaheuristics rather than going for their custom modifications besides the simplest ones. The proposed approaches have being extensively prototyped or proven through simulation based experimentation. In particular we have focused on small-scale wireless networked systems that utilize IEEE 802.11 radio interfaces and wireless sensor networks. We have also experimented with the WARP software defined radio platforms
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
Network and protocol architectures for future satellite systems
No full textSince their conception, satellite communications have been regarded as a promising tool for all environments where the terrestrial infrastructure is limited in capacity or to take advantage of the multicasting/broadcasting capabilities inherent in satellite technology. Recent advances have seen satellite technology mature to a more prominent role in the telecommunications domain. In particular, the design of novel satellite payload concepts for Geostationary (GEO) satellite platforms, as well as renewed interest in Low Earth Orbit (LEO) satellite constellations have made the integration of satellite and terrestrial networks almost compulsory to ensure new services meet the requirements for high user-rate and quality of experience that could not be achieved using either of the two technologies independently. From this viewpoint, convergence of satellite and terrestrial technologies also requires considering the most recent trends in networking, with special attention being paid to the potential new architectures that have been recently proposed in the framework of Future Internet. This monograph explores the main components of the scenarios above, putting particular emphasis on the networking aspects. To this end, novel protocols such as Multi Path TCP (MPTCP) and networking trends such as Information Centric Networking (ICN) are explored by demonstrating their applicability in some scenarios that deploy both satellite and terrestrial segments. Particular attention is given to smart gateway diversity schemes which advocate the use of sophisticated multi-path transmission schemes to exploit the multi-homing features offered by present day devices. The second part of the monograph is dedicated to content-based networking, which is becoming increasingly popular driven by the pervasiveness of the Internet in everyday life. In this regard, applications to satellite communications are illustrated and the technical challenges to be further addressed are highlighted
Exploiting Caching, Proxy Re-encryption, Incentives, and Wi–Fi Direct for Authorized Content Distribution
No full textAbstractUbiquitous access to the Internet is becoming critical. Direct cellular network connectivity of mobile devices is not always possible or desirable, for various reasons. We design and discuss a scheme that can be used to distribute authorized content to devices through Wi-Fi Direct and discuss how to provide incentives to the devices connected to the Internet to securely relay traffic, taking into consideration their available energy and bandwidth
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
Mobility-based Proactive Multicast for Seamless Mobility Support in Cellular Network Environments
Full text linkInformation-Centric Networking (ICN) is receiver driven, asynchronous and location-independent, hence it natively supports client-mobility. However, post-handover delay is a problem for delay-sensitive mobile applications, as they need to (re-)submit their subscriptions and wait for them to get resolved and (probably re-) transmitted before receiving the demanded data. To avoid this problem and optimize performance, this paper proposes a Mobility based Proactive Multicast (MPM) scheme. Unlike reactive or blind multicast solutions proposed in the past, MPM takes autonomous decisions locally at various network access points (cells) prior to the movement of mobile clients, using a semi-Markov mobility prediction model that predicts next-cell transitions, along with anticipating the duration between the transitions for an arbitrary user in a cellular network. Since cellular backhaul links are typically a bottleneck, MPM trades-off effectively part of the capacity of the (congested) backhaul link for a decreased delay experienced by users after handovers thanks to a congestion pricing scheme used for backhaul capacity allocation. Our preliminary performance evaluation results show that MPM captures well the temporal locality of mobile requests due to the semi-Markov mobility predictio
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
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