能量效率和碰撞概率联合优化的协作频谱感知算法

协作频谱感知能提高认知无线电网络的感知性能。随着认知网络频谱感知性能的提高,一方面感知网络将会消耗更多的能量;另一方面次用户拥有更多的机会接入授权频谱,次用户的吞吐量不断增加,同时在通信过程中主用户与次用户发生碰撞的概率也不断增大。本文提出了一种联合优化能量效率和碰撞概率的协作频谱感知算法,通过最优感知检测点判断节点所处信道状态,融合中心舍弃信道状态不好的节点使其不参与数据融合,既消除了信道状态不好的节点对全局判决的不良影响,又提高了能量利用率。仿真结果表明,该算法提高了网络的频谱检测性能,并延长了感知网络的生命周期。     

基于可信度的加权协作频谱检测算法

协作频谱检测技术可以有效解决认知无线网络本地检测存在的信道衰落、隐藏终端等问题。论文研究了加权协作频谱检测技术,提出一种基于可信度的协作频谱检测算法。每个感知节点基于最大最小值特征值检测完成本地频谱检测,并与融合中心的全局检测结果进行比较估计各自感知节点的频谱检测可信度;融合中心利用切尾平均法计算参与频谱协作检测的可信度门限,并选择可信度大于门限的感知节点参与协作频谱检测。该算法有效降低了认知网络协作检测的复杂性,提高了频谱检测性能,在噪声波动环境下具有良好的鲁棒性。仿真结果表明,算法频谱检测性能要优于其它加权算法1~3 dB,节省系统开销43.75%左右。     

基于可信度的认知无线电协同频谱检测

认知无线电中随着参与协同检测的认知用户数目的增大,频谱检测性能逐渐增强。但是过多的认知用户参与协同检测,会使整个认知无线电网络的灵敏度降低,同时也会造成巨大的系统开销。针对上述问题,提出了一种新的基于可信度的协同频谱检测方法。在满足目标错误概率的条件下,该算法只选择可信度较高的一些认知用户参与协同频谱检测。仿真结果表明当认知用户中存在恶意节点或者故障节点时,该算法同传统算法相比较,频谱检测性能更好,具有更强的健壮性。     

基于Agent的协作频谱感知算法

为了提高认知无线电频谱感知技术的性能, 提出一种新的基于Agent的协作频谱感知算法。该算法在本地检测中使用多门限能量检测,同时将认知节点估计的信噪比的值发送到Agent控制中心,在控制中心根据每一个认知节点发送的信噪比的值和该节点与发射机的距离进行权衡,选取可靠性和有效性较高的认知节点参与判决融合。仿真结果表明,该算法能够很好地提高认知无线电网络的协作频谱感知能力,同时在一定程度上减少了原有协作感知算法中参与感知节点的数目。     

基于噪声估计的加权协同频谱感知技术

频谱感知是认知无线电研究的关键技术之一,能量检测法是典型的频谱感知方法。针对传统的能量检测法和协同频谱感知存在的局限性,提出一种基于估计噪声的加权协同频谱感知方法,不同认知用户分别通过估计被测频段相邻保护（过渡）频带的噪声特性,近似作为授权用户频带内的噪声特性,以此估计噪声作为信任度进行加权协同数据融合。仿真结果表明,该方法能有效提高频谱检测性能。     

认知无线电网络中基于信任度的频谱感知技术

提出了一种在认知无线网络控制信道带宽受限条件下基于信任度的双门限协同频谱感知算法。首先每个认知用户基于双检测门限独立进行频谱感知,但只有部分可靠的认知用户通过控制信道向认知无线网络基站发送本地感知结果。当所有的用户都不可靠时,选取信任度最高的认知用户发送本地感知结果进行判决。理论分析和仿真表明,同常规能量检测算法相比较,该算法能够在控制信道带宽受限条件下,以较少的网络开销获得更好的频谱感知性能。     

衰落信道下提高协作频谱感知能力的方法

由于协作频谱感知能够更准确地确定主用户的存在与否,因此,它被认为是认知无线电技术中的一个重要研究分支.在协作频谱感知中,各认知用户需要通过报告信道发送其本地判决结果(0或1)到融合中心(FC).然而,在实际中,报告信道通常受衰落的影响,这将降低频谱感知的检测性能.针对这个问题,首先,文中提出一种基于认知用户选择的协作频谱感知算法.该算法通过减小由衰落信道引入的误码概率来提高协作频谱感知的检测性能.其基本思想为:只有具有较好瞬时信道增益报告信道的认知用户才将其本地二进制判决结果发送到FC,否则,该认知用户不发送其本地检测结果到FC.其次,提出一种基于空时编码的协作频谱感知方法.通过在CR网络中,利用空间分集增益来降低由衰落型报告信道引入的误码概率,从而提高检测性能.最后,对提出的这两种协作频谱感知方法的检测性能进行理论分析研究,并对其进行数值仿真.仿真结果表明:相比于传统的协作频谱感知,本文提出的这两种协作频谱感知算法都能提高对主用户的检测性能.     

基于奇异值分解的宽带频谱感知改进算法

对认知无线电中宽带频谱感知的信号检测问题进行研究,在信道位置和带宽随机分布的条件下,提出一种基于Hankel矩阵奇异值分解的改进算法完成宽带频谱的频率点奇异性检测并获得各子频段的起始频率和带宽,有效实现盲宽带频谱感知,同时利用提出的三种性能评价参数对该算法与多尺度小波变换算法进行了性能对比。通过实际接收微波信号及仿真OFDM信号感知实验验证,该算法有效抑制了噪声不确定性,滤除了伪奇异点,提高了宽带频谱感知性能。     

认知无线电网络双天线多信道MAC协议

在认知无线电网络中,媒体接入控制(MAC)协议的主要功能包括信道感知、选择和接入控制,其中感知时间和传输时间的长度对网络的性能有着重要的影响。在动态无线网络环境下,如何合理分配感知时间和传输时间是个挑战性问题。提出了一种双天线多信道分布式认知无线电MAC（TM-MAC）协议,不需要在传输之前对信道进行感知。节点可以在其它节点传输数据的同时对频谱资源进行检测,然后利用空闲的频谱资源通信。建立了数学模型分析在饱和网络状况下MAC协议的吞吐量。仿真分析表明TM-MAC协议能够有效提高网络的吞吐量。     

基于节点识别的协作频谱检测算法

在认知无线网络协作频谱感知过程中,感知节点所处的恶劣信道环境会导致本地频谱检测结果发生偏差,有时一些故障节点或恶意节点发送的误导信息来干扰认证网络融合中心的全局判决.根据认知网络感知节点的历史感知信息,将感知节点分为可信节点、不可信节点和故障或恶意节点,提出了一种基于节点识别的协作频谱检测算法.在该算法中,融合中心舍弃故障或恶意节点,使其不得参与数据融合,同时也不考虑不可信节点当前发送的本地检测结果.这样,一方面消除了故障或恶意节点对全局频谱判决的影响,另一方面降低了融合中心计算复杂度.仿真结果表明,该算法能有效克服故障或恶意节点的干扰,提高认证网络协作频谱检测性能.     

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.