一种数据辅助的OFDM符号定时同步算法

针对正交频分复用系统的同步偏差敏感性,提出了一种新的符号定时同步算法。该算法通过新设计的训练序列结构,得到新的符号定时偏移估计函数表达式。仿真结果表明,该算法有效地克服了Schmidl、Minn和Park算法中的符号定时缺陷,并且在低信噪比下能实现更准确的同步;另外,该算法在同等条件下符号定时偏移估计的均方误差更低。     

OFDM定时和频率同步改进算法

在OFDM系统算法中,针对Minn算法存在符号定时和频率同步精度不高,定时模糊等问题,提出了一种OFDM改进同步算法.改进算法依照Minn算法原有的序列pattern,用ZC序列作为新的训练序列,并多次进行相关得以提高精度,最后给出了新的定时尺度函数和频偏估计函数.由于ZC序列具有相关峰尖锐和零旁瓣的特点,使得系统的同步定时估计和频率估计更加精准.理论分析和仿真结果表明,改进算法的定时尺度非常尖锐,频偏估计的均方误差较低.     

改进CAZAC序列的OFDM时频同步算法

针对先前一些算法存在定时模糊以及存在较大干扰峰干扰的问题,提出了一种基于加权CAZAC序列的OFDM系统同步方案。利用训练序列共轭对称特性进行符号定时和频偏估计。利用训练序列延迟相关和对称相关的特点进行定时和粗频偏估计,能够有效抑制干扰从而得到更好的估计性能。利用循环前缀的冗余信息进行小数倍频偏精细估计。此外分析了整数倍频偏对时域CAZAC序列的影响。采用时域循环移位进行整数倍频偏估计。通过与其他算法的仿真对比可以得出,多径衰落信道下所提算法能够取得较高的定时准确率和频偏估计精度。     

基于CAZAC序列的MIMO-OFDM定时同步算法

针对MIMO-OFDM系统定时同步中的精确度问题,提出一种基于CAZAC序列的定时同步方法。通过CAZAC序列优化帧的定时目标、准确度以及结构,使得帧和符号同步同时实现,简化定时算法。帧同步和符号同步的联合实现,降低了定时算法的计算量并能够准确定义信道的第一径,能够在时域实现整数频偏的估计,在提高同步精度的同时降低了系统的复杂度,通过仿真验证了算法在Rayleigh衰落信道中性能的明显改善。     

一种OFDM系统定时偏移估计新算法

提出一种利用时域训练序列的定时估计算法。在分析Schimdl算法和Minn算法的缺点的同时,提出了算法,并在两种信道中进行了仿真,仿真结果表明算法在性能上有所提高。     

MIMO OFDM系统联合时频同步算法

为了解决多输入多输入多输出(Multiple imput multiple output,MIMO)正交频分复用(Orthogonal frequency division multiplexing,OFDM)系统的时间和频率偏移估计问题,提出了一种基于恒幅零自相关(Constant amplitude zero auto correlation,CAZAC)序列的联合时频同步算法。同步前导包括两个相同长度的训练符号。在接收端,分别计算两个本地训练序列与接收信号的互相关,利用CAZAC序列的特性可以检测出所有收发天线对之间的时间偏移和整数频率偏移;然后对接收信号进行整数频偏补偿,利用两个训练符号之间的关系可以估计出小数频率偏移。分析和仿真结果表明,该算法与传统的同步算法相比,不但具有更高的同步概率,而且能够估计出所有收发天线对之间的频率偏移。     

一种OFDM系统中的符号定时同步方法

正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)足一种高效的数据传输技术,具有良好的抗频率选择性衰落能力,并且提高了频谱利用率.但是OFDM对同步误差十分敏感,特别是符号同步误差.这样会导致解凋性能迅速恶化,从而使整个OFDM系统性能下降.传统的MLE算法虽对符号定时估计很有效,但在ISI干扰情况下性能不高,Schmidl提出的利用训练序列的同步算法虽对符号定时估计很有效,但在ISI干扰以及低信噪比情况下性能不高.通过对Schmidl算法的改善,提出了一个新的改善算法.通过Matlab的模拟仿真表明,在信噪比较低时,新的算法定时估计性能优于Schmidl的算法.     

基于训练序列的OFDM频率同步改进算法

针对现有正交频分复用(OFDM)通信系统中频率同步算法存在的同步精度不高、估计范围较小等问题,设计了一种训练序列结构,并给出了相应的估计函数,提出了基于训练序列的频率同步改进算法。频率同步改进算法是在准确的符号定时之后,根据时域训练序列结构的共轭对称性,利用新的度量函数求出小数倍频偏;根据接收端频域训练序列的循环移位估计整数倍频偏。理论分析和仿真结果表明,改进算法频偏估计的均方误差较低,扩大了小数倍频偏估计范围,提高了整数倍频偏的正确检测概率。     

OFDM系统改进的训练序列结构及时频同步算法

提出了一种改进的基于Zadoff-Chu(ZC)序列的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统时频同步算法。该算法构造了一个具有共轭重复关系结构的训练序列,首先利用时域训练序列前后的共轭特性完成定时同步,同时得到整数倍频偏估计,使定时结果不受频率同步性能影响,然后在获取精确的定时同步之后利用训练序列的重复性完成小数频偏估计。理论分析和仿真结果表明,在高斯信道和多径信道下,改进算法的定时估计和频偏估计均方误差较低,同时扩大了整数和小数频偏估计范围,降低了系统计算复杂度。     

基于IEEE 802.11a突发OFDM系统的帧同步与符号定时同步算法研究

本文对基于IEEE802.11a突发OFDM系统的帧同步与符号定时同步算法进行了研究,并对符号定时误差的影响进行了分析。针对目前许多符号定时同步算法存在着算法复杂、门限值随信号能量变化等缺点,提出了一种利用短训练符号特性的符号定时同步算法。分析和仿真结果表明,该算法能够有效地提高系统的误码性能,并且具有门限自适应、算法运算量低的特点,适合于突发OFDM系统的快速符号定时同步。     

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。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

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.     

基于QTE的蒙古文显示机制研究与实现

蒙古语言是中国蒙古族使用的通用语言,由于蒙古文区别于其他文字的书写方式和其自身变形机制等特点,在很多通用的文字处理引擎中都不被支持。在嵌入式产品开发与应用领域中Linux加QTE已经成为流行方式。该文给出了一种在QTE环境上实现基于标准Unicode的蒙古文点阵显示和变形算法, 并自定义了支持蒙古文的QTE组件,扩展了QTE功能,为在Linux加QTE方式的嵌入式体系结构中处理蒙古文提供了一种解决方法。     

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.     

基于AD9626的模拟信号采集存储卡设计

自然界的绝大部分信号都是以模拟的形式存在,因此模拟信号的采集转换存储在数字时代十分关键。文章讨论了在雷达信号处理领域基于AD9626的AD采集存储卡的设计原理、硬件结构和程序设计与芯片配置等问题,为今后相关领域的研究提供了可参考的方案。     

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     

A human-computer interface for non-computer specialists

The COM teleconferencing system was designed to be easy to use for both beginners and people with much computer experience. A number of design choices in organizing the human-computer interface were considered very carefully. These design problems are not unique for teleconferencing applications, but will appear in many other developments of human-computer interfaces for non-computer specialists. This report discusses naming conventions, menu format, user commands, help facility and the treatment of ‘type ahead’ from the users.