Página 14 dos resultados de 2591 itens digitais encontrados em 0.031 segundos

Energy Harvesting Two-Hop Communication Networks

Orhan, Oner; Erkip, Elza
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/07/2015 Português
Relevância na Pesquisa
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Energy harvesting multi-hop networks allow for perpetual operation of low cost, limited range wireless devices. Compared with their battery operated counterparts, the coupling of energy and data causality constraints with half duplex relay operation makes it challenging to operate such networks. In this paper, a throughput maximization problem for energy harvesting two-hop networks with decode-and-forward half-duplex relays is investigated. For a system with two parallel relays, various combinations of the following four transmission modes are considered: Broadcast from the source, multi-access from the relays, and successive relaying phases I and II. Optimal transmission policies for one and two parallel relays are studied under the assumption of non-causal knowledge of energy arrivals and finite size relay data buffers. The problem is formulated using a convex optimization framework, which allows for efficient numerical solutions and helps identify important properties of optimal policies. Numerical results are presented to provide throughput comparisons and to investigate the impact of multiple relays, size of relay data buffers, transmission modes, and energy harvesting on the throughput.; Comment: 29 pages, 6 figures

The scaling of human interactions with city size

Schläpfer, Markus; Bettencourt, Luis M. A.; Grauwin, Sebastian; Raschke, Mathias; Claxton, Rob; Smoreda, Zbigniew; West, Geoffrey B.; Ratti, Carlo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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The size of cities is known to play a fundamental role in social and economic life. Yet, its relation to the structure of the underlying network of human interactions has not been investigated empirically in detail. In this paper, we map society-wide communication networks to the urban areas of two European countries. We show that both the total number of contacts and the total communication activity grow superlinearly with city population size, according to well-defined scaling relations and resulting from a multiplicative increase that affects most citizens. Perhaps surprisingly, however, the probability that an individual's contacts are also connected with each other remains largely unaffected. These empirical results predict a systematic and scale-invariant acceleration of interaction-based spreading phenomena as cities get bigger, which is numerically confirmed by applying epidemiological models to the studied networks. Our findings should provide a microscopic basis towards understanding the superlinear increase of different socioeconomic quantities with city size, that applies to almost all urban systems and includes, for instance, the creation of new inventions or the prevalence of certain contagious diseases.

Towards Green and Infinite Capacity in Wireless Communication Networks: Beyond The Shannon Theorem

Elmusrati, Mohammed
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/07/2015 Português
Relevância na Pesquisa
35.74%
New and novel way for resources allocation in wireless communication has been proposed in this paper. Under this new method, it has been shown that the required power budget becomes independent of the number of served terminals in the downlink. However, the required power depends only of the coverage area, i.e. the channel losses at the cell boarder. Therefore, huge number (theoretically any number) of terminals could be supported concurrently at finite and small downlink power budget. This could be very useful to support the downlink signalling channels in HSPA+, LTE, and 5G. It can be very useful also to support huge D2D communication downlinks. Moreover, and based on the same concept, a new system configuration for a single link point-to-point communication has been presented. With this new configuration, the achieved data rate becomes independent of the required transmit power. This means that any data rate can be achieved at the target BER and with small and finite transmit power. This seems violating with some major results of the Shannon theorem. This issue will be discussed in details in this article.; Comment: Version of this paper has been submitted to IEEE Transaction on Wireless Communication

A Packet Scheduling Strategy in Sensor Networks with SGMH Protocol

Cherian, Mary; Nair, T. R. Gopalakrishnan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/07/2011 Português
Relevância na Pesquisa
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Data communication in sensor networks can have timing constraints like end to end deadlines. If the deadlines are not met either a catastrophe can happen in hard real time systems or performance deterioration can occur in soft real time systems. In real time sensor networks, the recovery of data through retransmission should be minimized due to the stringent requirements on the worst case time delays. This paper presents the application of Stop and Go Multihop protocol (SGMH) at node level in wireless sensor networks for scheduling and hence to meet the hard real time routing requirements. SGMH is a distributed multihop packet delivery algorithm. The fractions of the total available bandwidth on each channel is assigned to several traffic classes by which the time it takes to traverse each of the hops from the source to the destination is bounded. It is based on the notion of time frames (Tfr). In sensor networks packets can have different delay guarantees. Multiple frame sizes can be assigned for different traffic classes.; Comment: 4 pages, 5 figures, IEEE , International Conference ICCCNT 2010, India, IEEE Explore- 2010, ISBN 978-1-4211-6591, pp 1-4, 30th September 2010

Energy-Efficient Shortest Path Algorithms for Convergecast in Sensor Networks

Augustine, John; Han, Qi; Loden, Philip; Lodha, Sachin; Roy, Sasanka
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/02/2009 Português
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We introduce a variant of the capacitated vehicle routing problem that is encountered in sensor networks for scientific data collection. Consider an undirected graph $G=(V \cup \{\mathbf{sink}\},E)$. Each vertex $v \in V$ holds a constant-sized reading normalized to 1 byte that needs to be communicated to the $\mathbf{sink}$. The communication protocol is defined such that readings travel in packets. The packets have a capacity of $k$ bytes. We define a {\em packet hop} to be the communication of a packet from a vertex to its neighbor. Each packet hop drains one unit of energy and therefore, we need to communicate the readings to the $\mathbf{sink}$ with the fewest number of hops. We show this problem to be NP-hard and counter it with a simple distributed $(2-\frac{3}{2k})$-approximation algorithm called {\tt SPT} that uses the shortest path tree rooted at the $\mathbf{sink}$. We also show that {\tt SPT} is absolutely optimal when $G$ is a tree and asymptotically optimal when $G$ is a grid. Furthermore, {\tt SPT} has two nice properties. Firstly, the readings always travel along a shortest path toward the $\mathbf{sink}$, which makes it an appealing solution to the convergecast problem as it fits the natural intuition. Secondly, each node employs a very elementary packing strategy. Given all the readings that enter into the node...

Triadic closure dynamics drives scaling-laws in social multiplex networks

Klimek, Peter; Thurner, Stefan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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Social networks exhibit scaling-laws for several structural characteristics, such as the degree distribution, the scaling of the attachment kernel, and the clustering coefficients as a function of node degree. A detailed understanding if and how these scaling laws are inter-related is missing so far, let alone whether they can be understood through a common, dynamical principle. We propose a simple model for stationary network formation and show that the three mentioned scaling relations follow as natural consequences of triadic closure. The validity of the model is tested on multiplex data from a well studied massive multiplayer online game. We find that the three scaling exponents observed in the multiplex data for the friendship, communication and trading networks can simultaneously be explained by the model. These results suggest that triadic closure could be identified as one of the fundamental dynamical principles in social multiplex network formation.; Comment: 5 pages, 3 figures

Structural limitations of learning in a crowd: communication vulnerability and information diffusion in MOOCs

Gillani, Nabeel; Yasseri, Taha; Eynon, Rebecca; Hjorth, Isis
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/11/2014 Português
Relevância na Pesquisa
35.74%
Massive Open Online Courses (MOOCs) bring together a global crowd of thousands of learners for several weeks or months. In theory, the openness and scale of MOOCs can promote iterative dialogue that facilitates group cognition and knowledge construction. Using data from two successive instances of a popular business strategy MOOC, we filter observed communication patterns to arrive at the "significant" interaction networks between learners and use complex network analysis to explore the vulnerability and information diffusion potential of the discussion forums. We find that different discussion topics and pedagogical practices promote varying levels of 1) "significant" peer-to-peer engagement, 2) participant inclusiveness in dialogue, and ultimately, 3) modularity, which impacts information diffusion to prevent a truly "global" exchange of knowledge and learning. These results indicate the structural limitations of large-scale crowd-based learning and highlight the different ways that learners in MOOCs leverage, and learn within, social contexts. We conclude by exploring how these insights may inspire new developments in online education.; Comment: Pre-print version. Published version available at http://dx.doi.org/10.1038/srep06447

Modeling the Dynamics of Social Networks

Kryssanov, Victor V.; Rinaldo, Frank J.; Kuleshov, Evgeny L.; Ogawa, Hitoshi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/05/2006 Português
Relevância na Pesquisa
35.74%
Modeling human dynamics responsible for the formation and evolution of the so-called social networks - structures comprised of individuals or organizations and indicating connectivities existing in a community - is a topic recently attracting a significant research interest. It has been claimed that these dynamics are scale-free in many practically important cases, such as impersonal and personal communication, auctioning in a market, accessing sites on the WWW, etc., and that human response times thus conform to the power law. While a certain amount of progress has recently been achieved in predicting the general response rate of a human population, existing formal theories of human behavior can hardly be found satisfactory to accommodate and comprehensively explain the scaling observed in social networks. In the presented study, a novel system-theoretic modeling approach is proposed and successfully applied to determine important characteristics of a communication network and to analyze consumer behavior on the WWW.; Comment: 8 pages, 3 figures. Preprint (as of May 24, 2006)

Bounding Transport Complexity for Content Dissemination in Online Social Networks

Wang, Cheng; Zhang, Zhen-Zhen; Zhou, Jieren
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.74%
In this paper, we address the issue on measuring the transport difficulty for content dissemination in online social networks (OSNs). We define a new metric, called \emph{transport load}, to measure the load imposed by the OSN on the carrier communication network. It involves two key factors: data arrival process at users and transport distance of messages. Furthermore, we define the fundamental limit of transport load as the \emph{transport complexity}, i.e., the \emph{minimum required} transport load for an OSN over a given carrier communication network. To model the content dissemination in OSNs, we formulate the geographical distribution feature of dissemination sessions in OSNs by introducing a four-layered system model. It consists of physical layer, social layer, content layer, and session layer. We dig the mutual relevances among these four layers as the preconditions for bounding the transport complexity. Specifically, taking into account the scale-free property of users' degree centrality in OSNs, we introduce the Zipf's distribution to describe the friendship degree of users. Furthermore, in order to model the interest-driven session patterns in real-world OSNs, we define a new session pattern, called Social-InterestCast. Combining with the users' behaviour in real-life OSNs and the experimental results of our evaluation...

Regional properties of global communication as reflected in aggregated Twitter data

Kallus, Zsofia; Barankai, Norbert; Kondor, Daniel; Dobos, Laszlo; Hanyecz, Tamas; Szule, Janos; Steger, Jozsef; Sebok, Tamas; Vattay, Gabor; Csabai, Istvan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/11/2013 Português
Relevância na Pesquisa
35.74%
Twitter is a popular public conversation platform with world-wide audience and diverse forms of connections between users. In this paper we introduce the concept of aggregated regional Twitter networks in order to characterize communication between geopolitical regions. We present the study of a follower and a mention graph created from an extensive data set collected during the second half of the year of $2012$. With a k-shell decomposition the global core-periphery structure is revealed and by means of a modified Regional-SIR model we also consider basic information spreading properties.; Comment: 13 pages, 12 figures

Community detection and role identification in directed networks: understanding the Twitter network of the care.data debate

Amor, B.; Vuik, S.; Callahan, R.; Darzi, A.; Yaliraki, S. N.; Barahona, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/08/2015 Português
Relevância na Pesquisa
35.74%
With the rise of social media as an important channel for the debate and discussion of public affairs, online social networks such as Twitter have become important platforms for public information and engagement by policy makers. To communicate effectively through Twitter, policy makers need to understand how influence and interest propagate within its network of users. In this chapter we use graph-theoretic methods to analyse the Twitter debate surrounding NHS England's controversial care.data scheme. Directionality is a crucial feature of the Twitter social graph - information flows from the followed to the followers - but is often ignored in social network analyses; our methods are based on the behaviour of dynamic processes on the network and can be applied naturally to directed networks. We uncover robust communities of users and show that these communities reflect how information flows through the Twitter network. We are also able to classify users by their differing roles in directing the flow of information through the network. Our methods and results will be useful to policy makers who would like to use Twitter effectively as a communication medium.; Comment: 27 pages, 6 figures, to appear in 'Dynamic Networks and Cyber-Security'

Relay Augmentation for Lifetime Extension of Wireless Sensor Networks

Brazil, Marcus; Ras, Charl; Thomas, Doreen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/01/2013 Português
Relevância na Pesquisa
35.74%
We propose a novel relay augmentation strategy for extending the lifetime of a certain class of wireless sensor networks. In this class sensors are located at fixed and pre-determined positions and all communication takes place via multi-hop paths in a fixed routing tree rooted at the base station. It is assumed that no accumulation of data takes place along the communication paths and that there is no restriction on where additional relays may be located. Under these assumptions the optimal extension of network lifetime is modelled as the Euclidean $k$-bottleneck Steiner tree problem. Only two approximation algorithms for this NP-hard problem exist in the literature: a minimum spanning tree heuristic (MSTH) with performance ratio 2, and a probabilistic 3-regular hypergraph heuristic (3RHH) with performance ratio $\sqrt{3}+\epsilon$. We present a new iterative heuristic that incorporates MSTH and show via simulation that our algorithm performs better than MSTH in extending lifetime, and outperforms 3RHH in terms of efficiency.

Gracefully Degrading Consensus and $k$-Set Agreement in Directed Dynamic Networks

Biely, Martin; Robinson, Peter; Schmid, Ulrich; Schwarz, Manfred; Winkler, Kyrill
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/01/2015 Português
Relevância na Pesquisa
35.74%
We study distributed agreement in synchronous directed dynamic networks, where an omniscient message adversary controls the availability of communication links. We prove that consensus is impossible under a message adversary that guarantees weak connectivity only, and introduce vertex-stable root components (VSRCs) as a means for circumventing this impossibility: A VSRC(k, d) message adversary guarantees that, eventually, there is an interval of $d$ consecutive rounds where every communication graph contains at most $k$ strongly (dynamic) connected components consisting of the same processes, which have at most outgoing links to the remaining processes. We present a consensus algorithm that works correctly under a VSRC(1, 4H + 2) message adversary, where $H$ is the dynamic causal network diameter. On the other hand, we show that consensus is impossible against a VSRC(1, H - 1) or a VSRC(2, $\infty$) message adversary, revealing that there is not much hope to deal with stronger message adversaries. However, we show that gracefully degrading consensus, which degrades to general $k$-set agreement in case of unfavourable network conditions, is feasible against stronger message adversaries: We provide a $k$-uniform $k$-set agreement algorithm...

Small But Slow World: How Network Topology and Burstiness Slow Down Spreading

Karsai, M.; Kivelä, M.; Pan, R. K.; Kaski, K.; Kertész, J.; Barabási, A. -L.; Saramäki, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.74%
Communication networks show the small-world property of short paths, but the spreading dynamics in them turns out slow. We follow the time evolution of information propagation through communication networks by using the SI model with empirical data on contact sequences. We introduce null models where the sequences are randomly shuffled in different ways, enabling us to distinguish between the contributions of different impeding effects. The slowing down of spreading is found to be caused mostly by weight-topology correlations and the bursty activity patterns of individuals.

Universal and Distinct Properties of Communication Dynamics: How to Generate Realistic Inter-event Times

de Melo, Pedro O. S. Vaz; Faloutsos, Christos; Assunção, Renato; Alves, Rodrigo; Loureiro, Antonio A. F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/03/2014 Português
Relevância na Pesquisa
35.74%
With the advancement of information systems, means of communications are becoming cheaper, faster and more available. Today, millions of people carrying smart-phones or tablets are able to communicate at practically any time and anywhere they want. Among others, they can access their e-mails, comment on weblogs, watch and post comments on videos, make phone calls or text messages almost ubiquitously. Given this scenario, in this paper we tackle a fundamental aspect of this new era of communication: how the time intervals between communication events behave for different technologies and means of communications? Are there universal patterns for the inter-event time distribution (IED)? In which ways inter-event times behave differently among particular technologies? To answer these questions, we analyze eight different datasets from real and modern communication data and we found four well defined patterns that are seen in all the eight datasets. Moreover, we propose the use of the Self-Feeding Process (SFP) to generate inter-event times between communications. The SFP is extremely parsimonious point process that requires at most two parameters and is able to generate inter-event times with all the universal properties we observed in the data. We show the potential application of SFP by proposing a framework to generate a synthetic dataset containing realistic communication events of any one of the analyzed means of communications (e.g. phone calls...

Visualizing BACnet data to facilitate humans in building-security decision-making

Tonejc, Jernej; Kaur, Jaspreet; Karsten, Adrian; Wendzel, Steffen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
35.74%
Building automation systems (BAS) are interlinked networks of hardware and software, which monitor and control events in the buildings. One of the data communication protocols used in BAS is Building Automation and Control networking protocol (BACnet) which is an internationally adopted ISO standard for the communication between BAS devices. Although BAS focus on providing safety for inhabitants, decreasing the energy consumption of buildings and reducing their operational cost, their security suffers due to the inherent complexity of the modern day systems. The issues such as monitoring of BAS effectively present a significant challenge, i.e., BAS operators generally possess only partial situation awareness. Especially in large and inter-connected buildings, the operators face the challenge of spotting meaningful incidents within large amounts of simultaneously occurring events, causing the anomalies in the BAS network to go unobserved. In this paper, we present the techniques to analyze and visualize the data for several events from BAS devices in a way that determines the potential importance of such unusual events and helps with the building-security decision making. We implemented these techniques as a mobile (Android) based application for displaying application data and as tools to analyze the communication flows using directed graphs.; Comment: 12 pages...

Adaptive CMOS Circuits for 4G Wireless Networks

Rosa, José M. de la; Ismail, Mohammed
Fonte: Conselho Superior de Investigações Científicas Publicador: Conselho Superior de Investigações Científicas
Tipo: Presentación Formato: 7199702 bytes; application/pdf
Português
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35.74%
The extraordinary growth of wireless communication technologies has prompted the emergence of a large number of new applications and standards. These new standards -like WMAN or UWB- are complementing the existing ones -such as GSM, UMTS or WLAN- and it is forecasted that the fourth generation (4G) of wireless terminals will make the convergence of services provided by cellular phones, satellite, long-range and short-range connectivity possible, giving rise to the so-called always-best-connected systems. The implementation of these systems in future handheld wireless devices will require low power low cost multi-standard multi-band chipsets, capable to operate over the different co-existing communication protocols, signal conditions, battery status, etc. The efficient implementation of these chipsets demands for reconfigurable building blocks that can adapt to the large number specifications with minimum power dissipation and at the lowest cost.; Nanometer CMOS processes are expected to be the base technologies to develop this new generation of RF transceivers, assuring mass production at low cost through increased integration levels and extensive use of digital signal processing. Fuelled by the technology evolution, the trend is to move the digitizing component as close as possible to the antenna...

A Practical implementation of high-speed communication using digital subscriber line technology

Engle, Todd
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
35.74%
This thesis creates a plan for the practical implementation of high-speed communication for residences and businesses. By implementing low-cost, high-speed communication on a global scale, tremendous benefits can occur in areas such as Internet communication, interactive multimedia, telecommuting, and distance learning. Despite several successful trials of various high-speed communication technologies, many barriers remain before deployment can occur to the general public. This thesis proposes a plan to bridge the gap between theoretical test studies and global implementation. This thesis evaluates three communication systems as potential solutions for high-speed communication and selects one system as the solution. The three candidate systems are Digital Subscriber Line technologies (collectively referred to as xDSL), Integrated Services Digital Network (ISDN), and cable modem. The chosen technology solution, xDSL, allows twisted-pair copper wire (i.e. telephone lines) to be used for high-speed communication. The choice of xDSL as the technology solution is based on many factors, all of which correspond to practicality. The intent of this thesis is not the promotion of xDSL; rather, the primary objective is to create a plan to quickly and globally implement a low-cost...

Wireless body area network platform utilizing energy-efficient routing of physiological data

Prieto, Alvaro
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
35.74%
Wireless Body Area Networks (WBANs) consist of several wireless sensors located around a human body. These sensors may measure several biological signals, movement, and temperature. Due to major improvements in power consumption and constantly shrinking devices, WBANs are becoming ubiquitous. As a side effect present because of the small form factor of these devices, the battery size is limited. While the sensors themselves may be extremely power efficient, all of the measured data must be transmitted over a much less efficient wireless link. One benefit of WBANs is that they rarely include more than a dozen wireless devices over a small area. This constraint allows for the use of routing techniques not suitable for larger wireless sensor networks(WSNs). Presented in this work is a novel global routing algorithm link-cost function to maximize network lifetime in WBANs. Also included are a basic software framework for developing WBANs, a sample Wireless Electrocardiogram (ECG) application, and a simple link cost algorithm development platform.

The reinforcement of “cordial man” in the connections between senators and citizens in online social networks; O reforço do “homem cordial” nas conexões entre senadores e cidadãos nas redes sociais online

Tavares, Daniel Nardin; Quiroga, Tiago
Fonte: Universidade de São Paulo. Instituto de Estudos Brasileiros Publicador: Universidade de São Paulo. Instituto de Estudos Brasileiros
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 04/05/2015 Português
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The aim of this paper is promote the analysis of the so-called social networks, in a Brazilian cultural point of view. With the development of the new Information and Communication Technologies, the possibility of a quick, direct contact among representatives and people at the Brazilian Congress was open. Through a data collection within the Senate’s office of communication of the Senators from the 54th Legislature, it was found that the cultural component is the main subject of the online messages between the people and the representatives, which are remarkable the aspects of the Sérgio Buarque de Holanda’s “cordial man”, whose traces mean to be renewed or even gets deeper.; O presente artigo busca contribuir com as análises das chamadas redes sociais online a partir do viés cultural, especificamente o brasileiro. Com as novas tecnologias de comunicação, abriu-se a possibilidade de ser estabelecido o contato direto e rápido entre representantes e representados no Congresso Nacional, desde que sejam usuários de uma mesma plataforma de comunicação. Com base em levantamento junto às assessorias de comunicação dos senadores da 54ª legislatura, verificamos que a substância cultural é um forte componente das trocas de mensagens presentes no aparato técnico propiciado pelo ambiente online...