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详细分析了传统的TCP拥塞控制算法在无线多跳网络环境下面临的问题,指出无线多跳环境下的MAC层信道竞争以及TCP拥塞窗口的过激增长机制是影响TCP性能的主要原因,提出一种新的TCP跨层拥塞控制机制TCP-CR.该机制中节点通过MAC层维护的链表信息,将冲突概率定时向源节点的传输层进行反馈,源节点根据获取的反馈信息做出拥塞窗口调整.仿真结果证明,该机制中源节点能有效根据当前MAC层网络状况做出及时动态调整,从而提高TCP的吞吐量. 相似文献
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基于网络协议层框架充分分析了TCP应用到Ad Hoc网络导致性能下降的原因,包括:物理层中易损耗的无线信道, MAC层中的过度竞争和不公平接入,网络层中节点移动引起的频繁路由失效,传输层中TCP采用的不合适机制,包括基于窗口的传输、基于数据包丢失的拥塞指示,拥塞窗口的慢启动和AIMD、对ACK自定时的依赖;提出了全新的适合Ad Hoc网络特性的跨层优化拥塞控制协议CCOC(cross-layer optimal congestion control).CCOC运用了跨层设计框架来改进MAC层的接入信道公平性、检测虚假链路失效、减少路由失效次数、加快路由切换后的重启动、运用SACK实现可靠传输和实施非线性优化论指导设计的自适应优化策略;描述了CCOC的协议体系结构;实施了详细的NS仿真实验,仿真结果表明,在几乎所有的仿真场景和移动环境下,CCOC比TCP和ATCP在许多重要性能指标,如吞吐量和公平性方面都有了明显的改进. 相似文献
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移动Ad Hoc网络的跨层优化拥塞控制 总被引:2,自引:0,他引:2
基于网络协议层框架充分分析了TCP应用到Ad Hoc网络导致性能下降的原因,包括:物理层中易损耗的无线信道, MAC层中的过度竞争和不公平接入,网络层中节点移动引起的频繁路由失效,传输层中TCP采用的不合适机制,包括基于窗口的传输、基于数据包丢失的拥塞指示,拥塞窗口的慢启动和AIMD、对ACK自定时的依赖;提出了全新的适合Ad Hoc网络特性的跨层优化拥塞控制协议CCOC(cross-layer optimal congestion control).CCOC运用了跨层设计框架来改进MAC层的接入信道公平性、检测虚假链路失效、减少路由失效次数、加快路由切换后的重启动、运用SACK实现可靠传输和实施非线性优化论指导设计的自适应优化策略;描述了CCOC的协议体系结构;实施了详细的NS仿真实验,仿真结果表明,在几乎所有的仿真场景和移动环境下,CCOC比TCP和ATCP在许多重要性能指标,如吞吐量和公平性方面都有了明显的改进. 相似文献
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在无线传感器网络(WSNs)中,基于跨层竞争的同步媒体接入控制(MAC)在一周期内可安排多个数据包的多跳传输,传统的协议在同一个数据窗口传输请求数据包和确认数据包,降低了数据窗口的多跳流量的建立,也降低了在多跳场景中的数据包传输率和传输时延性能.本文提出了基于新的基于跨层竞争的同步MAC(CLC-MAC)协议,CLC-MAC协议引用新的周期结构,且其包含两个独立窗口,并由该窗口分别传输数据请求包和确认包,即请求包在数据窗口传输,而确认包在休眠窗口传输.实验数据表明:与先锋路由帧MAC(PRMAC)协议相比,CLC-MAC协议的端到端传输时延和数据包传输率的性能均得到了提高. 相似文献
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在无线传感器网络中,媒体访问控制(MAC)层协议影响着整个网络的性能。根据无线传感器网络对节点能耗和时延的要求,本文提出了一种基于跨层设计的节能MAC协议。利用物理层、MAC层和路由层之间的信息交互,在保证可靠通信的基础上,实现在一个监听/睡眠周期内数据多跳传输,缩短数据传输时延,并且有效控制网络数据传输的冗余度,降低冗余节点能量消耗。性能分析和仿真结果表明,节能MAC协议能够有效地降低网络时延并且减少节点能耗。 相似文献
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时延受限且能量高效的无线传感网络跨层路由 总被引:4,自引:0,他引:4
如何通过网络的多跳中继把传感器节点收集的信息快速、高效地传输至基站,是无线传感器网络的基本问题.研究发现,MAC(media access control)层的睡眠调度和无线信道的不规则性均会对路由协议的效率产生较大影响.虽然传统分层设计的网络协议有着模块化的优点,但各层之间的相互独立却导致网络的整体性能不能达到最优.此外,已有协议通常采用牺牲时延以提高能量效率的方法,会给时延敏感系统带来不能容忍的端到端时延.提出一种时延受限且能量高效的跨层路由协议(delay-constrained and energy-efficient cross-layer routing,简称DECR),该协议在做出路由决定时考虑MAC层以及链路层的相关信息,其目标是在将端到端时延控制到低于预定上界的前提下最优化节点的能量效率.理论分析和实验结果表明,所提出的跨层路由协议具有较好的性能. 相似文献
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S. Shaw 《Journal of Computer Assisted Learning》1993,9(2):93-99
Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained. 相似文献
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European Community policy and the market 总被引:1,自引:0,他引:1
C. Lloyd 《Journal of Computer Assisted Learning》1993,9(2):86-91
Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven. 相似文献
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融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。 相似文献
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Wayne O’Brien Author Vitae 《Journal of Systems and Software》2008,81(11):1997-2013
Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them. 相似文献
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This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives. 相似文献
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Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what
is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic
sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and
its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of
an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify
robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can
or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest.
This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January
31–February 2, 2008 相似文献
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David Poole 《Computational Intelligence》1989,5(2):97-110
Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given. 相似文献
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Watts S. Humphrey 《Annals of Software Engineering》2002,14(1-4):39-72
This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)SM and Team Software Process (TSP){SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical. 相似文献
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基于复小波噪声方差显著修正的SAR图像去噪 总被引:4,自引:1,他引:3
提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。 相似文献
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R. NOSS 《Journal of Computer Assisted Learning》1987,3(1):2-12
Abstract This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development. 相似文献