During the past few years, wireless local area networks (WLANs) have become extremely popular. The IEEE 802.11 protocol is the dominating standard for WLANs employing the distributed coordination function (DCF) as its...
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During the past few years, wireless local area networks (WLANs) have become extremely popular. The IEEE 802.11 protocol is the dominating standard for WLANs employing the distributed coordination function (DCF) as its essential medium access control (MAC) mechanism. This paper presents a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay and the packet drop probability for both the basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. The mathematical model is used to study the effectiveness of the RTS/CTS scheme at high data rates and the performance improvements of transmitting a burst of packets after winning the contention for medium access. Packet bursting considerably increases both throughput and packet delay performance but lowers the short-term fairness on medium access.
In this paper, the practical application of some well recognised fuzzy methods and neural networks techniques to modelling marine diesel engine cylinder dynamics using real-time data and expert knowledge has been cons...
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In this paper, the practical application of some well recognised fuzzy methods and neural networks techniques to modelling marine diesel engine cylinder dynamics using real-time data and expert knowledge has been considered. The simulation was done in Matlab environment with real-time data originated from 2-stroke marine diesel propulsion engine on test bed during final testing, combined with knowledge elicited from engine experts and experienced test bed operators. Takagi-Sugeno fuzzy model has been designed based on cylinder pressure data after their clustering using fuzzy subtractive method. Model parameter tuning was investigated using ANFIS with combined learning algorithms: least-squares and back-propagation gradient descent method. The model obtained can be of practical importance in engine working regime adjustment, predicting cylinder data in faulty sensor case or adaptive threshold tuning within faults detection and identification.
The paper summarises the outcomes from a study into developing a coherent roadmapping strategy for eTraining and eLearning technologies in Europe. The presented roadmap defines the priority areas for future research, ...
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The paper summarises the outcomes from a study into developing a coherent roadmapping strategy for eTraining and eLearning technologies in Europe. The presented roadmap defines the priority areas for future research, with a view to respond to needs of the emerging European Professional eTraining. It is based on the results from a gap analysis performed on the state of the art in R&D versus the desired futures reflecting the future market needs.
It is generally believed that the queueing behavior of an arrival process is most sensitive to its first and second order statistics. In this paper, we show that this is not generally true. We consider the queueing be...
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It is generally believed that the queueing behavior of an arrival process is most sensitive to its first and second order statistics. In this paper, we show that this is not generally true. We consider the queueing behavior of two classes of sources. The first class is the superposition of multiple discrete autoregressive sources of order 1 (referred to as DAR(1) sources), and the second class is a single DAR(1) source having the same first and second order statistics as the superposed source. In particular, we show that in the homogeneous case, the mean queue lengths of the two models are identical, but the queue length variances of the two models are significantly different depending on the correlation of individual sources.
This panel paper presents the views of six researchers and practitioners of simulation modeling. Collectively we attempt to address a range of key future challenges to modeling methodology. It is hoped that the views ...
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ISBN:
(纸本)9780780387867
This panel paper presents the views of six researchers and practitioners of simulation modeling. Collectively we attempt to address a range of key future challenges to modeling methodology. It is hoped that the views of this paper, and the presentations made by the panelists at the 2004 Winter Simulation Conference will raise awareness and stimulate further discussion on the future of modeling methodology in areas such as modeling problems in business applications, human factors and geographically dispersed networks; rapid model development and maintenance; legacy modeling approaches; markup languages; virtual interactive process design and simulation; standards; and Grid computing.
This panel paper presents the views of six researchers and practitioners of simulation modeling, Collectively we attempt to address a range of key future challenges to modeling methodology. It is hoped that the views ...
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This panel paper presents the views of six researchers and practitioners of simulation modeling, Collectively we attempt to address a range of key future challenges to modeling methodology. It is hoped that the views of this paper, and the presentations made by the panelists at the 2004 Winter Simulation Conference will raise awareness and stimulate further discussion on the future of modeling methodology in areas such as modeling problems in business applications, human factors and geographically dispersed networks;rapid model development and maintenance;legacy modeling approaches;markup languages;virtual interactive process design and simulation;standards;and Grid computing.
In this article,(1) we discuss some issues that arise when ontologies are used to support corporate application domains such as electronic commerce (e-commerce) and some technical problems in deploying ontologies for ...
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In this article,(1) we discuss some issues that arise when ontologies are used to support corporate application domains such as electronic commerce (e-commerce) and some technical problems in deploying ontologies for real-world use. In particular, we focus on issues of ontology integration and the related problem of semantic mapping, that is, the mapping of ontologies and taxonomies to reference ontologies to preserve semantics. Along the way, we discuss what typically constitutes an ontology architecture. We situate the discussion in the domain of business-to-business (B2B) e-commerce. By its very nature, B2B e-commerce must try to interlink buyers and sellers from multiple companies with disparate product-description terminologies and meanings, thus serving as a paradigmatic case for the use of ontologies to support corporate applications.
To view virtual universities as an extension of real universities and of distant learning Institutes, new concepts in the area of distributed systems and virtual universities are needed. Mobile agents satisfy many req...
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Focus of attention plays an important part in our perception of the world around us. Visual search is a combined effort of the top-down (cognitive cue) and bottom-up (low-level feature conspicuity) processes. Often du...
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Focus of attention plays an important part in our perception of the world around us. Visual search is a combined effort of the top-down (cognitive cue) and bottom-up (low-level feature conspicuity) processes. Often during visual search our attention involuntarily gets directed to some irrelevant conspicuous objects, such as a bright object, regardless of the cued object. Objects that share similar characteristics with the cued object also influence our attention. In this paper we analyze the mechanism of visual search based on color cues in natural images as well as computer generated images. We demonstrate the characteristics of the visual scene search by tracing the focus of attention path using data from RIT's human eye tracking system. The results are compared with the computer simulation results of our model in which we capture the interaction between the two systems and explain the behavioral dependencies. The top-down system is implemented using a neural network mimicking the working memory area of the brain and the bottom-up system is implemented using saliency maps.
We present two error estimation approaches for bounding or correcting the error in functional estimates such as lift or drag. Adjoint methods quantify the error in a particular output functional that results from resi...
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