基于OPNET的WiMAX的研究与仿真分析

微波存取全球互通(WiMAX)是一种定位于无线城域网的宽带接入技术,该技术以IEEE 802.16标准为基础,为用户提供范围更广、速率更高的宽带无线接入,因而针对该协议进行网络建模与仿真具有重要的研究价值。在对802.16协议深入研究的基础上,在OPNET仿真环境中设计了仿真模型,基于RTPS算法、NRTPS算法、ERTPS算法进行了仿真分析。     

WiMAX安全研究

研究了最新的WiMAX IEEE802.16d/e的安全机制问题.WiMAX在融合了PMP与MESH接入方式同时,仍然存在诸多安全漏洞.对当前安全方面的主要研究工作思路进行了总结,并提出协议改进向.     

WiMAX网络不同模式下的位置管理策略分析

在固定无线城域网基础上支持其移动性的IEEE802.16e[1]是一种有效的移动宽带无线接入解决方案,将HMIPv6[2]与IEEE802.16e有机结合,可以使切换的时延和丢包率都明显减小。IEEE802.16同时支持Mesh模式,可以获得更大的网络覆盖范围以及降低设备成本。本文从理论上分析了在无线Mesh网络中采用传统位置管理策略的网络开销,并与典型的采用HMIPv6的WiMAX网络进行了对比。分析结果表明,WiMAX Mesh网络需要结合拓扑特性考虑更加有效的位置管理策略,以更好地支持移动性及多种业务的应用。     

WiMAX拓展实时轮询调度机制分析

为了提高无线资源的利用率,使WiMAX系统更好地支持语音业务,基于IEEE 802.16e协议的QoS调度体系,提出了针对带有静默压缩语音业务的拓展实时轮询调度机制的具体实现方案.而且通过对方案中关键参数的分析,给出了一种QoS保证方法.方法根据用户时延对数据带宽分配进行补偿,并按照用户负载情况动态地调整轮询请求带宽的分配周期.使用OPNET软件进行了系统级性能评估,结果表明所提出的方法可有效地降低用户上行接入时延和上行丢包率,从而提高了通信质量.     

IEEE 802.16e空闲模式的优化与性能分析

在应用IEEE 802.16e协议的无线城域网中,为了节约移动终端的电池能量,可以采用空闲模式节能机制;文中分析了IEEE 802.16e协议中的空闲模式的节能机制,并且为了更进一步节约电池能量,引入关闭期,建立了带启动期和关闭期的多重休假Geom/G/1排队系统;使用嵌入Markov链方法,推导出排队模型的性能指标,得到IEEE 802.16e中空闲模式节能方案中相应的数据帧平均响应时间、平均数据帧数、系统切换率及能量节省率;并且利用数值例子刻画了性能指标和系统配置参数之间的关系.     

基于移动IPv6及MBWA的纯IP移动网络实现技术

介绍了移动IPv6协议对IP移动性的支持,以及IP移动宽带无线接入(MBWA)技术IEEE802.16e及IEEE802. 20标准,探讨了基于IPv6及MBWA结合的纯IP(Pure IP)移动通信网络实现技术。     

IEEE802.16e标准安全机制的改进

指出了IEEE802.16e安全机制中所存在的严重漏洞。针对无线移动设备存在存储容量有限、处理速度慢、带宽低等问题,利用无线公钥设施中的证书标识符URL和椭圆曲线加密算法对IEEE802.16e中的密钥管理协议（PKM）进行了改进。仿真结果表明改进后的安全机制更适合于无线网络环境。     

移动WiMAX的切换机制

实现链路的无缝切换是支持移动网络的关键技术。为了使切换过程中的包丢失和包延迟最小,对IEEE802.16e标准中规定的移动宽带无线接入系统的切换过程进行研究。针对WiMAX网络体系结构中的系统内切换、系统间切换以及实现端到端QoS保证的切换3种主要切换方式,介绍相应的切换机制,描述主要切换流程,并给出改进机制和最新研究成果。     

IEEE802．16d系统的帧同步和频率同步研究

基于IEEE 802.16协议的WiMAX技术是目前BWA系统的热点之一,对于NLOS非视距传输环境,IEEE802.16d协议采用了OFDM技术作为调制方式.文章针对OFDM对定时和频偏敏感的问题进行了研究,给出了适用于IEEE 802.16d帧结构的帧同步和频偏估计算法,仿真结果表明该算法具有良好的性能.     

IEEE 802.16e上行测距研究

IEEE802.16e/ WiMAX无线网络中,由于每个用户端与基站的距离各不相同,需要采用有效的测距机制对用户信号进行上行同步和功率控制。首先分析了IEEE802.16e的测距原理,包括测距码的产生、发送与检测算法等;然后,给出了上行基站测距处理的各个功能单元,如测距码、功率检测和时延估计的设计流程;最后,在IEEE802.16e基站系统中完成了上行测距处理的实现,测试结果表明给出的测距方案可行。     

Only connect: teaching, technology and telesis

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.     

European Community policy and the market

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.     

一种自适应子融合集成多分类器方法

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。     

Avoiding semantic and temporal gaps in developing software intensive systems

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.     

Designing economic np control charts: A programmed simulation approach

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.     

The development of robot art

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     

Explanation and prediction: an architecture for default and abductive reasoning

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.     

Three Process Perspectives: Organizations, Teams, and People

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.     

基于复小波噪声方差显著修正的SAR图像去噪

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。     

How do children do mathematics with LOGO?

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.