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IFIP Wireless Days, WD

作者： Antonios Alexiou Christos Bouras Vasileios Kokkinos Evangelos Rekkas Research Academic Computer Technology Institute Patras Greece and Computer Engineering and Informatics Department University of Patras Greece

The spread of multimedia data has drastically differentiated the current landscape of Universal Mobile Telecommunication System (UMTS) networks, posing the need for further enhancements in its Radio Resource Management (RRM) strategies. Introduced in 3rd Generation Partnership Project (3 GPP) Release 6, the Multimedia Broadcast/Multicast Services (MBMS) framework aims at the efficient usage of network and radio resources for the transmission of multimedia services. The main requirement during the provision of MBMS multicast services is to minimize the transmission power of UMTS base stations. To this direction, several mechanisms have been proposed that either allow a simultaneous deployment of Point-to-Point (PTP) and Point-to-Multipoint (PTM) transmissions, or a single transport channel deployment (PTP or PTM) in a cell at any given time. Main objective of this paper is to study these mechanisms, compare them in terms of power consumption, underline the advantages that they may offer; and finally to propose enhancements that will ensure the lowest possible power consumption during MBMS transmissions.

关键词： 3G mobile communication Power control Energy consumption computer networks Telecommunication computing Digital multimedia broadcasting Base stations Data engineering informatics Multimedia systems

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Comparison of Routing and Wavelength Assignment Algorithms in WDM Networks

Comparison of Routing and Wavelength Assignment Algorithms i...

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IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference

作者： K. Christodoulopoulos K. Manousakis E. Varvarigos Computer Engineering and Informatics Department Greece Research Academic Computer Technology Institute University of Patras Patras Greece

We design and implement various algorithms for solving the static RWA problem with the objective of minimizing the maximum number of requested wavelengths based on LP relaxation formulations. We present a link formulation, a path formulation and a heuristic that breaks the problem in the two constituent subproblems and solves them individually and sequentially. The flow cost functions that are used in these formulations result in providing integer optimal solutions despite the absence of integrality constraints for a large subset of RWA input instances, while also minimizing the total number of used wavelengths. We present a random perturbation technique that is shown to increase the number of instances for which we find integer solutions, and we also present appropriate iterative fixing and rounding methods to be used when the algorithms do not yield integer solutions. We comment on the number of variables and constraints these formulations require and perform extensive simulations to compare their performance to that of a typical min-max congestion formulation.

关键词： Wavelength routing Wavelength assignment WDM networks Telecommunication traffic Wavelength division multiplexing Optical fiber networks Optical fiber communication computer networks Algorithm design and analysis Cost function

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Versatile approximation of the lung field boundaries in chest radiographs in the presence of bacterial pulmonary infections

Versatile approximation of the lung field boundaries in ches...

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IEEE Symposium on Bioinformatics and Bioengineering (BIBE)

作者： Dimitris K. Iakovidis Department of Informatics and Computer Technology Technological Educational Institute of Lamia Lamia Greece

The most common radiographic manifestation of bacterial pulmonary infections are foci of consolidation which are visible as bright shadows interfering with the interior lung intensity. In critically-ill patients this interference can be severe leading to vague or invisible lung field boundaries which are difficultly distinguished even by experienced physicians. This problem is amplified if the radiographs are of low quality as obtained with a portable x-ray device, routinely used in intensive care units. This paper proposes a pioneering methodology that copes with lung field detection in both stationary and portable chest radiographs by combining statistical grey-level intensity information and directional edge maps. The boundaries of the lung fields are approximated by consecutive intuitively manipulated parametric curves. Conventional and state of the art lung field detection approaches address only stationary radiography, and only a few of them cope with pulmonary infections. The proposed methodology features unsupervised operation, it is not iterative, it is not limited by the patientspsila positioning, and it is tolerant to the presence of consolidations and boundary discontinuities of the lung fields. Its performance is validated on various stationary radiographs and on a set of portable radiographs obtained from patients with bacterial pulmonary infections.

关键词： Lungs Microorganisms Diagnostic radiography Image edge detection Interference Active shape model Educational technology Iterative methods Image processing Merging

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Vehicular wireless burst switching network: Enhancing rural connectivity

Vehicular wireless burst switching network: Enhancing rural ...

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2008 IEEE Globecom Workshops, GLOBECOM 2008

作者： Farahmand, Farid Patel, Ankitkumar N. Jue, Jason P. Soares, Vasco G. Rodrigues, Joel J. Department of Computer Electronics and Graphics Technology Central Connecticut State University New Britain CT 06050 United States Department of Computer Science University of Texas at Dallas Richardson TX 75083 United States Institute of Telecommunications Networks and Multimedia Group Portugal Department of Informatics University of Beira Interior Covilhã Portugal

ISBN: (纸本)9781424430628

This paper introduces a network architecture called Vehicular Wireless Burst Switching (VWBS). The main objective of this architecture is to provide low-cost connectivity solution for isolated and dispersed regions with no networks infrastructure. The proposed architecture is based on the concept of Delay Tolerant Networks (DTN) and can be applied to various scenarios, including rapid deployment of emergency communication systems when all communication links have failed. In this paper, we present an overview of VWBS networks and show how their performance, in terms of average packet delays, can be improved using store-and-forward devices called relay nodes. Furthermore, we introduce several heuristic algorithms, which can be used to place minimum number of relay nodes. Through computer simulations, we compare the performance of the algorithms and their tradeoffs. We conclude our work by examining possible open research issues in VWBS. © 2008 IEEE.

关键词： Network architecture

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Design space exploration for a coarse grain accelerator

Design space exploration for a coarse grain accelerator

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2008 Asia and South Pacific Design Automation Conference, ASP-DAC

作者： Mehdipour, Farhad Noori, Hamid Zamani, Morteza Saheb Inoue, Koji Murakami, Kazuaki Research Institute for Information Technology Computing and Communication Center Kyushu University Fukuoka Japan Department of Informatics Graduate School of Information Science and Electrical Engineering Kyushu University Fukuoka Japan Department of IT and Computer Engineering Amirkabir University of Technology Tehran Iran

ISBN: (纸本)9781424419227

In the design process of a reconfigurable accelerator employing in an embedded system, multitude parameters may result in remarkable complexity and a large design space. Design space exploration as an alternative to the quantitative approach can be employed to find a right balance between the different design parameters. In this paper, a hybrid approach is introduced to analytically explore the design space for a coarse grain accelerator and determine a wise design point exploiting data extracted from applications, quantitatively. It also provides flexibility for taking into account new design constraints as well as new characteristics of applications. Furthermore, this approach is a methodological approach which reduces the design time and results in a point which satisfies the design goals. ©2008 IEEE.

关键词： Design

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Routing and scheduling in grids

Routing and scheduling in grids

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International Conference on Transparent Optical Networks

作者： Konstantinos Christodoulopoulos Emmanouel Varvarigos Computer Engineering and Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

We propose QoS-aware scheduling algorithms for grid networks that are capable of optimally or near-optimally assigning computation and communication tasks to grid resources. The routing and scheduling algorithms to be presented take as input the resource utilization profiles and the task characteristics and QoS requirements, and co-allocate resources while accounting for the dependencies between communication and computation tasks.

关键词： Availability Processor scheduling Clustering algorithms Routing Heuristic algorithms Quality of service Delay

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Smooth Multicast Congestion Control for Adaptive Multimedia Transmission

Smooth Multicast Congestion Control for Adaptive Multimedia ...

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Conference on Next Generation Internet Networks, NGI

作者： Christos Bouras Apostolos Gkamas Georgios Kioumourtzis Computer Engineering and Informatics Department University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

In this paper we introduce an equation-based smooth multicast congestion control for adaptive multimedia transmission over best-effort wired networks. Target of the proposed schema is (a) smooth transmission rate, in order to minimize the audio-video (AV) encoding and decoding distortion and (b) TCP friendly transmission. The "smoothness" lays in the way the TCP-friendly transmission rate is filtered. We integrate the congestion control functions in the RTP protocol and use the RTCP sender and receiver reports to provide the necessary feedback information for the sender's adaptive transmission rate. The performance evaluation of the smooth adaptation and TCP-friendliness is conducted through a number of simulations with the network simulator software (ns2). Our intention is to use this congestion control in the context of a proposed framework for multimedia transmission over wired and wireless networks.

关键词： Programmable control Adaptive control Bandwidth Feedback Multicast protocols Delay Decoding Equations Data communication Wireless application protocol

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A trusted architectural model for interconnecting testbeds of wireless sensor networks

A trusted architectural model for interconnecting testbeds o...

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International Symposium on Electronics in Marine (ELMAR)

作者： Ioannis Chatzigiannakis Vasiliki Liagkou Paul G. Spirakis Department of Computer Engineering and Informatics University of Patras Patras Greece Research Academic Computer Technology Institute Patras Greece

ISBN: (纸本)9781424433643

Designing wireless sensor networks is inherently complex; many aspects such as energy efficiency, limited resources, decentralized collaboration, fault tolerance have to be tackled. To be effective and to produce applicable results, fundamental research has to be tested, at least as a proof-of-concept, in large scale environments, so as to assess the feasibility of the new concepts, verb their large scale effects (not only at technological level, but also as for their foreseeable implications on users, society and economy) and derive further requirements, orientations and inputs for the research. In this paper we focus on the problems of interconnecting existing testbed environments via the Internet and providing a virtual unifying laboratory that will support academia, research centers and industry in their research on networks and services. In such a facility important issues of trust, security, confidentiality and integrity of data may arise especially for commercial (or not) organizations. In this paper we investigate such issues and present the design of a secure and robust architectural model for interconnecting testbeds of wireless sensor networks.

关键词： Testing Wireless sensor networks Large-scale systems Energy efficiency Collaboration Fault tolerance IP networks Web and internet services Data security Robustness

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Preface to the special issue of evolutionary computation and its applications

IEEJ Transactions on Electronics, Information and Systems

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IEEJ Transactions on Electronics, Information and Systems 2008年第3期128卷 333-333页

作者： Kawakami, Hiroshi Tsujimura, Yasuhiro Graduate School of Informatics Kyoto University Japan Department of Computer and Information Engineering Nippon Institute of Technology Japan

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Efficient models for timetable information in public transportation systems

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ACM Journal of Experimental Algorithmics 2008年第PP1–39期12卷 1–39页

作者： Pyrga, Evangelia Schulz, Frank Wagner, Dorothea Zaroliagis, Christos Max-Planck-Institut für Informatik University of Karlsruhe CTI University of Patras Max-Planck-Institut für Informatik 66123 Saarbrücken Stuhlsatzenhausweg 85 Germany Department of Computer Science University of Karlsruhe 76128 Karlsruhe Germany R.A. Computer Technology Institute Patras University Campus 26500 Patras N. Kazantzaki Str Greece Department of Computer Engineering and Informatics University of Patras 26500 Patras Greece

We consider two approaches that model timetable information in public transportation systems as shortest-path problems in weighted graphs. In the time-expanded approach, every event at a station, e.g., the departure of a train, is modeled as a node in the graph, while in the time-dependent approach the graph contains only one node per station. Both approaches have been recently considered for (a simplified version of) the earliest arrival problem, but little is known about their relative performance. Thus far, there are only theoretical arguments in favor of the time-dependent approach. In this paper, we provide the first extensive experimental comparison of the two approaches. Using several real-world data sets, we evaluate the performance of the basic models and of several new extensions towards realistic modeling. Furthermore, new insights on solving bicriteria optimization problems in both models are presented. The time-expanded approach turns out to be more robust for modeling more complex scenarios, whereas the time-dependent approach shows a clearly better performance. © 2008 ACM.

关键词： Itinerary query Public transportation system Shortest path Timetable information

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