超宽带信号功率谱的仿真分析

超宽带(UWB)信号及其功率谱分布是研究超宽带通信系统与其它通信系统频谱共存与兼容问题时,需要考虑的重要因素.根据超宽带信号功率谱的特点,从控制超宽带信号功率谱分布的角度,就高斯单周期脉冲及其各阶导函数、不同的信息调制方式和跳时码参数对超宽带信号功率谱的影响,进行了计算机仿真和分析,并总结出控制超宽带信号功率谱分布的方法,从而为解决超宽带通信系统与其他通信系统频谱共存问题,提供了有益的思想和方法.     

多址干扰抑制混沌超宽带脉冲设计

针对超宽带多址干扰问题,采用高斯7阶导脉冲作为UWB原始脉冲,使用厄米特矩阵特征向量分解算法设计UWB正交脉冲序列,采用Logistic混沌序列作为跳时码进行混沌跳时-脉位调制,生成混沌超宽带脉冲,从而达到抑制多址干扰的目的。最后,分析CTH-PPM UWB系统的抗多址干扰性能。仿真结果表明CTH-PPM UWB系统抗多址干扰性能明显优于TH-PPM UWB系统,具有更强的抗多址干扰能力。     

UWB信号功率谱仿真模型

超宽带（UWB）信号及其功率谱分布是研究超宽带通信系统与其它通信系统频谱共存与兼容问题时，需要考虑的重要因素。该文利用UWB信号的数学模型，在MATLAB环境下建立了产生UWB信号的发生器，并将其与Simulink仿真相结合，实现了对UWB信号功率谱密度的实时观测与控制。这为分析研究UWB信号功率谱分布提供了有效便捷的平台。文中还应用该仿真模型对具有不同参数的UWB信号功率谱进行了仿真，验证仿真模型的可行性。     

一种新的认知超宽带自适应脉冲设计

为了解决超宽带系统与窄带系统共存的难点问题,根据认知无线电原理,以正弦高斯脉冲作为原始脉冲,采用实数编码的遗传算法和设计凯塞滤波器相结合的新方法,得到一种优化的自适应脉冲,并对陷波前后脉冲进行了链路预算.仿真结果表明:提出的自适应脉冲具有良好的窄带干扰抑制能力,时间复杂度低,能快速生成认知无线电系统所需脉冲,上述方法灵活,并且能够自适应地在多个频段陷波,且陷波后传输性能良好,其功率谱利用率高而且符合美国FCC频谱规范.     

基于PSO算法的UWB发射脉冲优化研究

超宽带(UWB)通信系统通常采用高斯脉冲和Hermite脉冲作为发射脉冲,从其产生原理分析,发射脉冲不能同时满足时域和频域的共同约束条件。以高斯发射脉冲为例设计先加入去毛刺电路、高通滤波器等改进电路以实现时域优化,再在频域上用粒子群(PSO)算法对改进的发射脉冲电路的电参数进行优化,并做了注入干扰的仿真实验。实验表明:经PSO算法优化后的改进的UWB发射脉冲性能大大改善,满足UWB通信系统的各项指标要求。     

TH-UWB系统抗干扰性能研究

从频域角度探讨TH-UWB系统对窄带干扰的抑制能力,采用信号功率谱分析方法,研究UWB系统的调制技术和脉冲成形技术,提出线性组合高斯单周脉冲设计陷波频谱.理论分析及计算机仿真结果表明,合理选择超宽带信号调制方式和脉冲,可在一定程度上提高超宽带系统抗干扰能力.应用提出的线性组合高期单周脉冲作为UWB发射信号,可以有效减小UWB信号对外界的干扰.     

UWB和802.11a WLAN的兼容性分析

研究了超宽带(UWB)通信系统与基于IEEE802.11a标准的WLAN设备之间的兼容问题。介绍了UWB和WLAN的理论基础,给出了干扰信号对系统SIR(信号与干扰的比率)影响的仿真结果。结果显示,在视距(LOS)环境中,UWB干扰对802.11a系统的性能影响不大;在非视距(NLOS)环境中,UWB信号对802.11aWLAN系统的性能有很大影响,而802.11aWLAN干扰也会严重影响UWB接收机的性能。对研究UWB系统与其它通信系统的共存有一定的参考价值。     

基于认知系统的编码调制体系研究

利用NMSK(N重最小频移键控)的旁瓣快速衰减特性,提出了一种新型OFDM-NMSK编码调制体系用于降低OFDM认知无线电系统的带外干扰。该方法仅通过关闭干扰频段上的相应NMSK子载波,能够快速生成符合要求的频谱凹槽深度,从而实现与其地窄带系统的共存。理论与仿真表明,与传统的相邻频带编码(AFC)方法相比,OFDM-NMSK编码效果更佳。     

一种新的超宽带脉冲信号优化设计方法

从数值逼近理论出发按照Chebyshev最佳一致逼近准则将超宽带信号设计成符合FCC频谱模板的信号,与同类方法相比更容易控制设计精度,具有更高的频谱利用率,改善了UWB通信系统的性能,方法适用于不同的频谱模板.在理论分析的基础上对方法进行了阐述和模拟仿真,仿真结果验证了该超宽带脉冲信号设计方法的有效性.     

毫米波通信的低复杂度时变信道估计算法

当毫米波通信系统工作于时变信道场景中时,为解决通信用户快速位移导致的方位角计算误差和信道估计算法精度下降等问题,通常要消耗大量计算资源。因此,基于用户在快时变信道场景下的信号传输特征,首先在确定毫米波传输信号方位时采用对角加载方法,根据高斯白噪声先验信息得到对角加载方法的参数;然后采用对角带矩阵分解方法对所得到的信道干扰矩阵模型进行处理,从而降低信道估计与均衡算法的复杂度。仿真结果表明,所提算法能够使工作在时变信道条件下的通信系统以低于常规算法的运算复杂度处理系统中的干扰,且不降低传输性能。     

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.