基于高效纠错码的无线光通信系统性能分析

介绍了弱湍流信道条件下光强闪烁的对数正态分布模型,结合大气信道特点,推导了自由空间光通信未编码系统和RS编码系统在开关键控(OOK)、脉冲位置调制(PPM)、差分脉冲位置调制(DPPM)和数字脉冲间隔调制(DPIM)方式下的平均误码率公式,并用数值仿真的方法分析了它们的平均误码率性能。仿真结果表明,采用RS编码可以有效地增加信噪比增益,改善大气湍流对通信链路性能的恶化,能够提高系统的抗干扰能力,在无线光通信系统中将有一定的应用前景。     

无线光通信中LDPC码在DPIM调制下的优化设计

介绍了DPIM调制阶数和LDPC码码率的关系,分析了选取调制阶数及码率使通信系统达到最佳效果的途径。同时介绍了DPIM调制方式的误码率的计算方法,为1T一旋转LDPC码在无线光通信DPIM下的仿真研究奠定了理论基础,在DPIM调制方式下对1T一旋转LDPC码进行了仿真性能分析。     

基于DHPIM调制可见光通信系统的研究

针对智能交通可见光通信系统采用OOK、PPM和DPIM等调制方式系统的接收机信噪比不理想的问题,研究双头脉冲间隔调制(DHPIM),分析DHPIM对系统接收机信噪比的影响。首先介绍DHPIM调制工作原理,比较各种调制方式系统占用的带宽,接着分析比较了几种典型天气条件下DHPIM调制系统接收机信噪比,最后在同一种天气下,分析比较了系统采用DHPIM等多种调制方式接收机的信噪比。仿真结果表明,在同一天气下DHPIM调制系统接收机信噪比高于OOK、PPM和DPIM等调制系统接收机信噪比。因此与OOK、PPM、DPIM相比,DHPIM可显著提高系统接收机信噪比,更适合于智能交通可见光通信系统。     

光通信中一种有效的差分脉冲位置宽度调制

考虑脉冲位置调制(PPM)在解调时需要严格的时钟同步和符号同步,而且功率越高,时隙越窄的问题,结合差分脉冲位置调制(DPPM)和脉冲宽度调制(PWM)提出了一种有效的调制方式--差分脉冲位置宽度调制(DPPM+PWM).研究了采用DPPM+PWM的红外通信系统在加性高斯白噪声干扰下的性能,对DPPM+PWM的符号结构、发射功率、带宽需求、传输容量以及误包率等特性进行了分析,并通过仿真与开关键控(OOK),PPM,PPM等调制方式进行了比较.结果表明DP-PM+PWM频带利用率高,传输容量大,不需要符号同步,且增加了脉冲信号的长度,大大简化系统实现,是一种很有实际应用价值的调制方式.     

无线光通信中DPIM调制下LDPC码需求分析

介绍APD检测输出的概率分布,并且介绍DPIM调制原理,讨论在无线光通信中DPIM调制方式下,LDPC码应用的两个瓶颈问题.通过将DPIM调制改进为定长DPIM调制解决第一个问题.在APD检测输出概率分布的理论基础上,通过对LDPC码译码算法的改进,解决第二个问题.     

可见光通信调制方式及其性能的思考

为了能够使白光LED的室内照明以及通信的双重功能实现,需要根据可见光通信的相关特点,在对双头脉冲间隔调制(DH-PIM)、数字脉冲间隔调制(DPIM)、脉冲位置调制(PPM)、开光键控调制(OOK)的结构情况进行分析的基础上,将一种新型的反向双头脉冲间隔调制(RDH-PIM)的方式提出来.在对各种调制方式的编码结构、平均发射功率以及带宽的要求进行分析和比较后,进行仿真的结果表明,OOK具有的带宽需求最小,RDH-PIM能够获得的平均发射功率最大,同时在带宽利用流程方面RDH-PIM要比PPM和DPIM具有更大的优势.作为一类折中的调制方式,RDH-PIM在进行无线光通信的过程中是具备着一定的应用价值的.     

基于System View的串行MSK调制与解调的仿真研究

MSK作为一种性能优良的调制方式,被广泛应用于卫星通信和无线移动通信中的数据传输.串行MSK调制多用于数据速率较高的场合,在工程实现上有着较为广泛的应用.简要分析了基于带通滤波器和基于低通滤波器的两种MSK串行调制与解调方式,利用通信系统仿真软件SystemView,对两种调制与解调方式进行了仿真,给出了详细的仿真电路,并通过仿真分析了不同干扰条件下的抗干扰性能.     

基于正交空时块编码的MIMO自由空间光通信

合适的编码方案可以减小通信系统的误码率,在自由空间光通信中显得尤为重要.空时编码技术是一种空间域和时间域相结合的分组编码方式,它能有效抵抗衰落,改善系统的误码性能.文中首先将Alamouti空时码的正交性和Q-PPM调制技术相结合,提出了一种适合于强度调制/直接检测式光通信的编码方法.其次分析了该系统在无衰落无背景辐射、有衰落无背景辐射、无衰落有背景辐射和有衰落有背景辐射时的误码性能.最后,通过Monte-Carlo仿真实验进一步证明了该理论的正确性.结果表明:采用该编码方法不仅能实现1速率传输,而且能有效抵抗衰落,克服大气湍流所产生的闪烁效应.当误字率为2×10^-3时,相对于1×1系统而言,2×1系统的发送功率被节约了约3.5 dBJ,2×2系统的发送功率被节约了约9 dBJ.     

DH-PIM调制最优检测门限研究与仿真

通过建立基于两点假设的无线光通信系统模型,推导了系统误码率公式,在分析DH-PIM(双头脉冲间隔调制)调制结构的基础上,给出了该调制方式的误时隙率表达式,进而推导了基于最小误时隙率的最优检测门限数学表达式.最后,通过计算杌软件MATLAB进行仿真验证,结果表明,最优门限下DH-PIM调制方式的差错性能相对于其它门限有了明显的提高.     

数字集群系统中电路级失真的建模与仿真

在设计低功率数字集群通信终端时,系统中的电路级失真效应是一个不容忽视的问题.文中以基于调制方式的TETRA数字集群系统为例,首先简略介绍了调制和基带差分解调的原理,然后通过理论分析对电路级失真效应进行建模,重点分析了增益和相位不平衡以及直流偏移效应对系统误码性能的影响.通过对整个通信系统进行计算机仿真,定量地研究了电路级失真效应对系统误码性能的影响.仿真结果证明,电路级失真效应对数字集群系统误码性能的影响不容忽视.在实际系统的设计中,必须考虑采取合适的数字补偿措施对其进行补偿.     

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.     

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     

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.     

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.