390 research outputs found

    The Distributed MIMO Scenario: Can Ideal ADCs Be Replaced by Low-resolution ADCs?

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    This letter considers the architecture of distributed antenna system, which is made up of a massive number of single-antenna remote radio heads (RRHs), some with full-resolution but others with low-resolution analog-to-digital converter (ADC) receivers. This architecture is greatly motivated by its high energy efficiency and low-cost implementation. We derive the worst-case uplink spectral efficiency (SE) of the system assuming a frequency-flat channel and maximum-ratio combining (MRC), and reveal that the SE increases as the number of quantization bits for the low-resolution ADCs increases, and the SE converges as the number of RRHs with low-resolution ADCs grows. Our results furthermore demonstrate that a great improvement can be obtained by adding a majority of RRHs with low-resolution ADC receivers, if sufficient quantization precision and an acceptable proportion of high-to-low resolution RRHs are used.Comment: 4 pages, to be published in IEEE Wireless Communications Letter

    Interoperability of Information Systems and Heterogenous Databases Using XML

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    Interoperabilily of information systerrrs is the most critical issue facing businesse! that need to access information from multiple idormution systems on tlifferent environments ancl diverse platforms. Interoperability has been a basic requirement for the modern information systems in a competitive and volatile business environment, particularly with the advent of distributed network system and the growing relevance of inter-network communications. Our objective in tltis paper is to develop a comprehensiveframework tofacilitate interoperability smong distributed and heterogeneous information systems and to develop prototype software to validate tlte application of XML in interoperability of infurmation systems and databases

    Distributed Hierarchical IDS For MANET Over AODV+.

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    In this paper, we introduce background knowledge of wireless ad hoc networking mobile ad hoc network (MANET) as well as intrusion detection system (IDS) and mobile agents. This research study surveys, studies and compares the existing intrusion detection based on mobile agent for mobile ad hoc networks. Based on our best knowledge from previous researches we design distributed hierarchical /D^S inclusive of network-based and host-based intrusion detection system with due consideration to their characteristics on ad hoc on4emand distance vector routing protocol (AODV+)

    Distributed Object Medical Imaging Model

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    Abstract- Digital medical informatics and images are commonly used in hospitals today,. Because of the interrelatedness of the radiology department and other departments, especially the intensive care unit and emergency department, the transmission and sharing of medical images has become a critical issue. Our research group has developed a Java-based Distributed Object Medical Imaging Model(DOMIM) to facilitate the rapid development and deployment of medical imaging applications in a distributed environment that can be shared and used by related departments and mobile physiciansDOMIM is a unique suite of multimedia telemedicine applications developed for the use by medical related organizations. The applications support realtime patients’ data, image files, audio and video diagnosis annotation exchanges. The DOMIM enables joint collaboration between radiologists and physicians while they are at distant geographical locations. The DOMIM environment consists of heterogeneous, autonomous, and legacy resources. The Common Object Request Broker Architecture (CORBA), Java Database Connectivity (JDBC), and Java language provide the capability to combine the DOMIM resources into an integrated, interoperable, and scalable system. The underneath technology, including IDL ORB, Event Service, IIOP JDBC/ODBC, legacy system wrapping and Java implementation are explored. This paper explores a distributed collaborative CORBA/JDBC based framework that will enhance medical information management requirements and development. It encompasses a new paradigm for the delivery of health services that requires process reengineering, cultural changes, as well as organizational changes

    A Note About the Semantics of Delegation

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    In many applications, mobile agents are used by a client to delegate a task. This task is usually performed by the agent on behalf of the client, by visiting various service provider's sites distributed over a network. This use of mobile agents raises many interesting security issues concerned with the trust relationships established through delegation mechanisms between client and agent, agent and service provider and client and service provider. In this paper we will explain why the traditional semantics of delegation used by existing access control mechanisms, either centralised or distributed, are generally not satisfactory to prevent and detect deception and why these problems are even more critical when these semantics are used in mobile agent paradigms.Non peer reviewe

    Real-time and distributed applications for dictionary-based data compression

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    The greedy approach to dictionary-based static text compression can be executed by a finite state machine. When it is applied in parallel to different blocks of data independently, there is no lack of robustness even on standard large scale distributed systems with input files of arbitrary size. Beyond standard large scale, a negative effect on the compression effectiveness is caused by the very small size of the data blocks. A robust approach for extreme distributed systems is presented in this paper, where this problem is fixed by overlapping adjacent blocks and preprocessing the neighborhoods of the boundaries. Moreover, we introduce the notion of pseudo-prefix dictionary, which allows optimal compression by means of a real-time semi-greedy procedure and a slight improvement on the compression ratio obtained by the distributed implementations

    An experience in building a parallel and distributed problem-solving environment

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    We describe our experimentation with the design and implementation of specific environments, consisting of heterogeneous computational, visualization, and control components. We illustrate the approach with the design of a problem-solving environment supporting the execution of genetic algorithms. We describe a prototype steering parallel execution, visualization, and steering. A life cycle for the development of applications based an genetic algorithms is proposed.publishersversionpublishe

    A Rapid Heuristic for Scheduling Non-Preemptive Dependent Periodic Tasks onto Multiprocessor

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    International audienceWe address distributed real-time applications represented by systems of non-preemptive dependent periodic tasks. This system is described by an acyclic directed graph. Because the distribution and the scheduling of these tasks onto a multiprocessor is an NP-hard problem we propose a greedy heuristic to solve it. Our heuristic sequences three algorithms: assignment, unrolling, and scheduling. The tasks of the same, or multiple, periods are assigned to the same processor according to a mixed sort. Then, the initial graph of tasks is unrolled, i.e. each task is repeated according to the ratio between its period and the least common multiple of all periods of tasks. Finally, the tasks of the unrolled graph are distributed and scheduled onto the processors where they have been assigned. Then, we give the complexity of this heuristic, and we illustrate it with an example. A performance analysis comparing our heuristic with an optimal Branch and Cut algorithm concludes that our heuristic is effective in terms of scheduling success ratio and speed

    Object-oriented Tools for Distributed Computing

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    Distributed computing systems are proliferating, owing to the availability of powerful, affordable microcomputers and inexpensive communication networks. A critical problem in developing such systems is getting application programs to interact with one another across a computer network. Remote interprogram connectivity is particularly challenging across heterogeneous environments, where applications run on different kinds of computers and operating systems. NetWorks! (trademark) is an innovative software product that provides an object-oriented messaging solution to these problems. This paper describes the design and functionality of NetWorks! and illustrates how it is being used to build complex distributed applications for NASA and in the commercial sector
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