Página 18 dos resultados de 3715 itens digitais encontrados em 0.055 segundos

Parallel Processing For Gravity Inversion

Frasheri, Neki
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/publishedVersion; info:eu-repo/semantics/bookPart; info:eu-repo/semantics/conferenceObject
Publicado em /10/2015 Português
Relevância na Pesquisa
47.335547%
In this paper results of recent updates of a simple algorithm for the inversion of gravity anomalies for 3D geosections in parallel computer systems are presented. A relaxation iterative principle was used updating step by step the geosection distribution of mass density. Selection of updates was done on basis of least squares error match of the update effect with the observed anomaly. Locally weighted least squares combined with the linear trend were used to obtain good inversion results for two-body geosections.; Proceedings of: Second International Workshop on Sustainable Ultrascale Computing Systems (NESUS 2015). Krakow (Poland), September 10-11, 2015.

A Mobile Device Prototype Application for the Detection and Prediction of Node Faults in Wireless Sensor Networks

Marcus, Anthony; Cardei, Ionut; Furht, Borko; Salem, Osman; Mehaoua, Ahmed
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/01/2014 Português
Relevância na Pesquisa
47.334844%
Various implementations of wireless sensor networks (i.e. personal area-, wireless body area- networks) are prone to node and network failures by such characteristics as limited node energy resources and hardware damage incurred from their surrounding environment (i.e. flooding, forest fires, a patient falling). This may jeopardize their reliability to act as early warning systems, monitoring systems for patients and athletes, and industrial and environmental observation networks. Following the current trend and widespread use of hand held, mobile communication devices, we outline an application architecture designed to detect and predict faulty nodes in wireless sensor networks. Furthermore, we implement our design as a proof of concept prototype for Android-based smartphones, which may be extended to develop other applications used for monitoring networked wireless personal area and body sensors used in other capacities. We have conducted several preliminary experiments to demonstrate the use of our design, which is capable of monitoring networks of wireless sensor devices and predicting node faults based on several localized metrics. As attributes of such networks may change over time, any models generated when the application is initialized must be updated periodically such that the applied machine learning algorithm maintains high levels of both accuracy and precision. The application is designed to discover node faults and...

Societal Implicit Memory and his Speed on Tracking Extrema over Dynamic Environments using Self-Regulatory Swarms

Ramos, Vitorino; Fernandes, Carlos; Rosa, Agostinho C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/11/2005 Português
Relevância na Pesquisa
47.33946%
In order to overcome difficult dynamic optimization and environment extrema tracking problems, We propose a Self-Regulated Swarm (SRS) algorithm which hybridizes the advantageous characteristics of Swarm Intelligence as the emergence of a societal environmental memory or cognitive map via collective pheromone laying in the landscape (properly balancing the exploration/exploitation nature of our dynamic search strategy), with a simple Evolutionary mechanism that trough a direct reproduction procedure linked to local environmental features is able to self-regulate the above exploratory swarm population, speeding it up globally. In order to test his adaptive response and robustness, we have recurred to different dynamic multimodal complex functions as well as to Dynamic Optimization Control problems, measuring reaction speeds and performance. Final comparisons were made with standard Genetic Algorithms (GAs), Bacterial Foraging strategies (BFOA), as well as with recent Co-Evolutionary approaches. SRS's were able to demonstrate quick adaptive responses, while outperforming the results obtained by the other approaches. Additionally, some successful behaviors were found. One of the most interesting illustrate that the present SRS collective swarm of bio-inspired ant-like agents is able to track about 65% of moving peaks traveling up to ten times faster than the velocity of a single individual composing that precise swarm tracking system.; Comment: 20 pages...

Network Coding for Distributed Storage Systems

Dimakis, Alexandros G.; Godfrey, P. Brighten; Wu, Yunnan; Wainwright, Martin J.; Ramchandran, Kannan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/03/2008 Português
Relevância na Pesquisa
47.333276%
Distributed storage systems provide reliable access to data through redundancy spread over individually unreliable nodes. Application scenarios include data centers, peer-to-peer storage systems, and storage in wireless networks. Storing data using an erasure code, in fragments spread across nodes, requires less redundancy than simple replication for the same level of reliability. However, since fragments must be periodically replaced as nodes fail, a key question is how to generate encoded fragments in a distributed way while transferring as little data as possible across the network. For an erasure coded system, a common practice to repair from a node failure is for a new node to download subsets of data stored at a number of surviving nodes, reconstruct a lost coded block using the downloaded data, and store it at the new node. We show that this procedure is sub-optimal. We introduce the notion of regenerating codes, which allow a new node to download \emph{functions} of the stored data from the surviving nodes. We show that regenerating codes can significantly reduce the repair bandwidth. Further, we show that there is a fundamental tradeoff between storage and repair bandwidth which we theoretically characterize using flow arguments on an appropriately constructed graph. By invoking constructive results in network coding...

Load & Backhaul Aware Decoupled Downlink/Uplink Access in 5G Systems

Elshaer, Hisham; Boccardi, Federico; Dohler, Mischa; Irmer, Ralf
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/10/2014 Português
Relevância na Pesquisa
47.34392%
Until the 4th Generation (4G) cellular 3GPP systems, a user equipment's (UE) cell association has been based on the downlink received power from the strongest base station. Recent work has shown that - with an increasing degree of heterogeneity in emerging 5G systems - such an approach is dramatically suboptimal, advocating for an independent association of the downlink and uplink where the downlink is served by the macro cell and the uplink by the nearest small cell. In this paper, we advance prior art by explicitly considering the cell-load as well as the available backhaul capacity during the association process. We introduce a novel association algorithm and prove its superiority w.r.t. prior art by means of simulations that are based on Vodafone's small cell trial network and employing a high resolution pathloss prediction and realistic user distributions. We also study the effect that different power control settings have on the performance of our algorithm.; Comment: 6 pages, 6 figures. Submitted to the IEEE International Conference on Communications (ICC 2015)

Design of a Transport Triggered Architecture Processor for Flexible Iterative Turbo Decoder

Shahabuddin, Shahriar; Janhunen, Janne; Juntti, Markku
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/01/2015 Português
Relevância na Pesquisa
47.349673%
In order to meet the requirement of high data rates for the next generation wireless systems, the efficient implementation of receiver algorithms is essential. On the other hand, the rapid development of technology motivates the investigation of programmable implementations. This paper summarizes the design of a programmable turbo decoder as an applicationspecific instruction-set processor (ASIP) using Transport Triggered Architecture (TTA). The processor architecture is designed in such manner that it can be programmed to support other receiver algorithms, for example, decoding based on the Viterbi algorithm. Different suboptimal maximum a posteriori (MAP) algorithms are used and compared to one another for the softinput soft-output (SISO) component decoders in a single TTA processor. The max-log-MAP algorithm outperforms the other suboptimal algorithms in terms of latency. The design enables the designer to change the suboptimal algorithms according to the bit error rate (BER) performance requirement. Unlike many other programmable turbo decoder implementations, quadratic polynomial permutation (QPP) interleaver is used in this work for contention-free memory access and to make the processor 3GPP LTE compliant. Several optimization techniques to enable real time processing on programmable platforms are introduced. Using our method...

Analyzing Peer Selection Policies for BitTorrent Multimedia On-Demand Streaming Systems in Internet

Rodrigues, Carlo Kleber Da Silva
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/02/2014 Português
Relevância na Pesquisa
47.33946%
The adaptation of the BitTorrent protocol to multimedia on-demand streaming systems essentially lies on the modification of its two core algorithms, namely the piece and the peer selection policies, respectively. Much more attention has though been given to the piece selection policy. Within this context, this article proposes three novel peer selection policies for the design of BitTorrent-like protocols targeted at that type of systems: Select Balanced Neighbour Policy (SBNP), Select Regular Neighbour Policy (SRNP), and Select Optimistic Neighbour Policy (SONP). These proposals are validated through a competitive analysis based on simulations which encompass a variety of multimedia scenarios, defined in function of important characterization parameters such as content type, content size, and client interactivity profile. Service time, number of clients served and efficiency retrieving coefficient are the performance metrics assessed in the analysis. The final results mainly show that the novel proposals constitute scalable solutions that may be considered for real project designs. Lastly, future work is included in the conclusion of this paper.; Comment: 19 PAGES

The Necessity for Hardware QoS Support for Server Consolidation and Cloud Computing

Merino, Javier; Puente, Valentin; Gregorio, José Ángel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/06/2012 Português
Relevância na Pesquisa
47.33946%
Chip multiprocessors (CMPs) are ubiquitous in most of today's computing fields. Although they provide noticeable benefits in terms of performance, cost and power efficiency, they also introduce some new issues. In this paper we analyze how the interference from Virtual Private Servers running in other cores is a significant component of performance unpredictability and can threaten the attainment of cloud computing. Even if virtualization is used, the sharing of the on-chip section of the memory hierarchy by different cores makes performance isolation strongly dependent on what is running elsewhere in the system. We will show in three actual computing systems, based on Sun UltraSparc T1, Sun UltraSparc T2 and Intel Xeon processors, how state-of-the-art virtualization techniques are unable to guarantee performance isolation in a representative workload such as SPECweb2005. In an especially conceived near worst-case scenario, it is possible to reduce the performance achieved by a Solaris Zones consolidated server for this suite of benchmarks in a Sun Fire T1000 and a Sun Enterprise T5120 by up to 80%. The performance drop observed by a Xen consolidated server running in a HP Proliant DL160 G5 is almost 45%. For all systems under study...

An Easy Cellular Gateway for Providing Shared Services and Data

Lemlouma, Tayeb; Luciana, Julien; Oza, Bastien; Sierra, Leandro; Salaün, Mikaël
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/10/2012 Português
Relevância na Pesquisa
47.331084%
In this paper, we present a new framework that links the two worlds of wired and cellular users sharing systems. The approach is to propose an easy gateway that enables the use of cellular networks based services by wireline users and applications. The idea is to use a mobile terminal or wireless equipment for sharing cellular services, available thanks to its cellular network, to other users that use the wireline Internet. The software application acts as a gateway between the cellular and the wired network; it is responsible for supporting the services provided by the wireless network and make them accessible and usable, in a standard and easy way, by anyone on the wireline network. The gateway software can be integrated easily on any complex architecture since it can interact with any cellular modem. The paper describes an implementation prototype where some examples of services, such as the ability of using messaging services and calls streaming, are experimented. The proposed platform combines different standards to guarantee the use of our gateway in heterogeneous environments.; Comment: 6 pages; The Fifth International Conference on Systems and Networks Communications, ICSNC 2010

Temporal Locality in Today's Content Caching: Why it Matters and How to Model it

Ahmed, Mohamed; Traverso, Stefano; Garetto, Michele; Giaccone, Paolo; Leonardi, Emilio; Niccolini, Saverio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.333276%
The dimensioning of caching systems represents a difficult task in the design of infrastructures for content distribution in the current Internet. This paper addresses the problem of defining a realistic arrival process for the content requests generated by users, due its critical importance for both analytical and simulative evaluations of the performance of caching systems. First, with the aid of YouTube traces collected inside operational residential networks, we identify the characteristics of real traffic that need to be considered or can be safely neglected in order to accurately predict the performance of a cache. Second, we propose a new parsimonious traffic model, named the Shot Noise Model (SNM), that enables users to natively capture the dynamics of content popularity, whilst still being sufficiently simple to be employed effectively for both analytical and scalable simulative studies of caching systems. Finally, our results show that the SNM presents a much better solution to account for the temporal locality observed in real traffic compared to existing approaches.; Comment: 7 pages, 7 figures, Accepted for publication in ACM Computer Communication Review

A Quantitative Measure Of Fairness And Discrimination For Resource Allocation In Shared Computer Systems

Jain, R.; Chiu, D.; Hawe, W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/09/1998 Português
Relevância na Pesquisa
47.3448%
Fairness is an important performance criterion in all resource allocation schemes, including those in distributed computer systems. However, it is often specified only qualitatively. The quantitative measures proposed in the literature are either too specific to a particular application, or suffer from some undesirable characteristics. In this paper, we have introduced a quantitative measure called Indiex of FRairness. The index is applicable to any resource sharing or allocation problem. It is independent of the amount of the resource. The fairness index always lies between 0 and 1. This boundedness aids intuitive understanding of the fairness index. For example, a distribution algorithm with a fairness of 0.10 means that it is unfair to 90% of the users. Also, the discrimination index can be defined as 1 - fairness index.; Comment: DEC Research Report TR-301, September 1984

The "Hot Potato" Case: Challenges in Multiplayer Pervasive Games Based on Ad hoc Mobile Sensor Networks and the Experimental Evaluation of a Prototype Game

Chatzigiannakis, Ioannis; Mylonas, Georgios; Akribopoulos, Orestis; Logaras, Marios; Kokkinos, Panagiotis; Spirakis, Paul
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/02/2010 Português
Relevância na Pesquisa
47.34922%
In this work, we discuss multiplayer pervasive games that rely on the use of ad hoc mobile sensor networks. The unique feature in such games is that players interact with each other and their surrounding environment by using movement and presence as a means of performing game-related actions, utilizing sensor devices. We discuss the fundamental issues and challenges related to these type of games and the scenarios associated with them. We also present and evaluate an example of such a game, called the "Hot Potato", developed using the Sun SPOT hardware platform. We provide a set of experimental results, so as to both evaluate our implementation and also to identify issues that arise in pervasive games which utilize sensor network nodes, which show that there is great potential in this type of games.

Optimal Energy-Efficient Regular Delivery of Packets in Cyber-Physical Systems

Guo, Xueying; Singh, Rahul; Kumar, P. R.; Niu, Zhisheng
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/02/2015 Português
Relevância na Pesquisa
47.3473%
In cyber-physical systems such as in-vehicle wireless sensor networks, a large number of sensor nodes continually generate measurements that should be received by other nodes such as actuators in a regular fashion. Meanwhile, energy-efficiency is also important in wireless sensor networks. Motivated by these, we develop scheduling policies which are energy efficient and simultaneously maintain "regular" deliveries of packets. A tradeoff parameter is introduced to balance these two conflicting objectives. We employ a Markov Decision Process (MDP) model where the state of each client is the time-since-last-delivery of its packet, and reduce it into an equivalent finite-state MDP problem. Although this equivalent problem can be solved by standard dynamic programming techniques, it suffers from a high-computational complexity. Thus we further pose the problem as a restless multi-armed bandit problem and employ the low-complexity Whittle Index policy. It is shown that this problem is indexable and the Whittle indexes are derived. Also, we prove the Whittle Index policy is asymptotically optimal and validate its optimality via extensive simulations.; Comment: 6 pages conference

Directional Initial Access for Millimeter Wave Cellular Systems

Barati, C. Nicolas; Hosseini, S. Amir; Mezzavilla, Marco; Rangan, Sundeep; Korakis, Thanasis; Panwar, Shivendra S.; Zorzi, Michele
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/11/2015 Português
Relevância na Pesquisa
47.33946%
The millimeter wave (mmWave) bands have recently attracted considerable interest for next-generation cellular systems due to the massive available bandwidths at these frequencies. However, a key challenge in designing mmWave cellular systems is initial access -- the procedure by which a mobile establishes an initial link-layer connection to a base station cell. MmWave communication relies on highly directional transmissions and the initial access procedure must thus provide a mechanism by which initial transmission directions can be searched in a potentially large angular space. Design options are compared considering different scanning and signaling procedures to evaluate access delay and system overhead. The channel structure and multiple access issues are also considered. The analysis demonstrates significant benefits of low-resolution fully digital architectures in comparison to single stream analog beamforming.

Comments on "Consensus and Cooperation in Networked Multi-Agent Systems"

Chebotarev, Pavel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/09/2010 Português
Relevância na Pesquisa
47.3473%
This note corrects a pretty serious mistake and some inaccuracies in "Consensus and cooperation in networked multi-agent systems" by R. Olfati-Saber, J.A. Fax, and R.M. Murray, published in Vol. 95 of the Proceedings of the IEEE (2007, No. 1, P. 215-233). It also mentions several stronger results applicable to the class of problems under consideration and addresses the issue of priority whose interpretation in the above-mentioned paper is not exact.; Comment: 3 pages, 11 references

Systematic Design of Trust Management Systems for Wireless Sensor Networks: A Review

P, Raghu Vamsi.; Kant, Krishna
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.33946%
Conventional cryptography methods alone are not adequate for secure routing in Wireless Sensor Networks (WSNs). These networks are more vulnerable to security attacks due to their diverse applications, lack of supervision and limitations in view of resource, processing and storage. To mitigate these problems, trust is widely used as a tool to provide better security by aiding routing protocols. In recent years, numerous researchers have proposed wide variety of solutions based on trust. However, all these solutions carry their own design. In this paper, we attempt to present steps for a systematic design of trust management systems for WSNs. In addition, we address the techniques followed by scholars in implementing trust frameworks. Furthermore, we provide discussion on state-of-the-art research in designing trust systems with summary and comparisons.; Comment: The paper has been withdrawn due to typesetting mistakes

Heterogeneous Cellular Networks Using Wireless Backhaul: Fast Admission Control and Large System Analysis

Zhao, Jian; Quek, Tony Q. S.; Lei, Zhongding
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.34994%
We consider a heterogeneous cellular network with densely underlaid small cell access points (SAPs). Wireless backhaul provides the data connection from the core network to SAPs. To serve as many SAPs and their corresponding users as possible with guaranteed data rates, admission control of SAPs needs to be performed in wireless backhaul. Such a problem involves joint design of transmit beamformers, power control, and selection of SAPs. In order to tackle such a difficult problem, we apply $\ell_1$-relaxation and propose an iterative algorithm for the $\ell_1$-relaxed problem. The selection of SAPs is made based on the outputs of the iterative algorithm. This algorithm is fast and enjoys low complexity for small-to-medium sized systems. However, its solution depends on the actual channel state information, and resuming the algorithm for each new channel realization may be unrealistic for large systems. Therefore, we make use of random matrix theory and also propose an iterative algorithm for large systems. Such a large system iterative algorithm produces asymptotically optimum solution for the $\ell_1$-relaxed problem, which only requires large-scale channel coefficients irrespective of the actual channel realization. Near optimum results are achieved by our proposed algorithms in simulations.; Comment: Submitted to IEEE Journal on Selected Areas in Communications...

Band-Sweeping M-ary PSK (BS-M-PSK) Modulation and Transceiver Design

Alaa, Ahmed M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/01/2014 Português
Relevância na Pesquisa
47.34994%
Channel Estimation is a major problem encountered by receiver designers for wireless communications systems. The fading channels encountered by the system are usually time variant for a mobile receiver. Besides, the frequency response of the channel is frequency selective for urban environments where the delay spread is quite large compared to the symbol duration. Estimating the channel is essential for equalizing the received data and removing the Inter-Symbol Interference (ISI) resulting from the dispersive channel. Hence, conventional transceivers insert pilot symbols of known values and detect the changes in it in order to deduce the channel response. Because these pilots carry no information, the throughput of the system is reduced. A Novel modulation scheme is presented in this work. The technique depends on using a carrier signal that has no fixed frequency, the carrier tone sweeps the band dedicated for transmission and detects the transfer function gain within the band. A carrier signal that is Frequency Modulated (FM) by a periodic ramp signal becomes Amplitude Modulated (AM) by the channel transfer function, and thus, the receiver obtains an estimate for the channel response without using pilots that decrease the systems throughput or data rate. The carrier signal itself acts as a dynamic frequency domain pilot. The technique only works for constant energy systems...

A Survey of Millimeter Wave (mmWave) Communications for 5G: Opportunities and Challenges

Niu, Yong; Li, Yong; Jin, Depeng; Su, Li; Vasilakos, Athanasios V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/02/2015 Português
Relevância na Pesquisa
47.332544%
With the explosive growth of mobile data demand, the fifth generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mmWave) bands to greatly increase communication capacity. There are fundamental differences between mmWave communications and existing other communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage. These characteristics of mmWave communications pose several challenges to fully exploit the potential of mmWave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control. To address these challenges, we carry out a survey of existing solutions and standards, and propose design guidelines in architectures and protocols for mmWave communications. We also discuss the potential applications of mmWave communications in the 5G network, including the small cell access, the cellular access, and the wireless backhaul. Finally, we discuss relevant open research issues including the new physical layer technology, software-defined network architecture, measurements of network state information, efficient control mechanisms, and heterogeneous networking, which should be further investigated to facilitate the deployment of mmWave communication systems in the future 5G networks.; Comment: 17 pages...

Cooperative localization using angle of arrival measurements: sequential algorithms and non-line-of-sight suppression

Ananthasubramaniam, Bharath; Madhow, Upamanyu
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/06/2012 Português
Relevância na Pesquisa
47.333276%
We investigate localization of a source based on angle of arrival (AoA) measurements made at a geographically dispersed network of cooperating receivers. The goal is to efficiently compute accurate estimates despite outliers in the AoA measurements due to multipath reflections in non-line-of-sight (NLOS) environments. Maximal likelihood (ML) location estimation in such a setting requires exhaustive testing of estimates from all possible subsets of "good" measurements, which has exponential complexity in the number of measurements. We provide a randomized algorithm that approaches ML performance with linear complexity in the number of measurements. The building block for this algorithm is a low-complexity sequential algorithm for updating the source location estimates under line-of-sight (LOS) environments. Our Bayesian framework can exploit the ability to resolve multiple paths in wideband systems to provide significant performance gains over narrowband systems in NLOS environments, and easily extends to accommodate additional information such as range measurements and prior information about location.; Comment: 31 pages, 11 figures, related to MELT'08 Workshop proceeding