直扩多用户超宽带系统在室内衰落信道下的BER表达式

基于室内多径衰落信道统计模型,分析并仿真了直扩二相相移键控多用户超宽带无线通信系统的比特误码率性能.通过理论分析,推导出了系统比特误码率性能的解析表达式,该表达式表示为脉冲宽度、脉冲重复周期、用户数以及脉冲波形等信道参数和系统参数的函数,从而可以方便、统一地分析这些参数对系统性能的影响.仿真结果与基于理论分析的数值计算结果相当吻合,表明直扩二相相移键控超宽带系统的多址干扰为正态分布.     

预估稀疏度的压缩感知超宽带信道估计算法研究与仿真实验

设计了信道估计算法实验的一个拓展内容——预估稀疏度的压缩感知超宽带信道估计算法研究与仿真实验,提出一种预估稀疏度的压缩感知超宽带信道估计算法。该算法引入稀疏度预估计,在自适应匹配之前快速估计出信号的稀疏度,避免自适应匹配时步长选择不合理对信道估计结果产生影响。在稀疏度预估计和匹配追踪两个阶段挑选原子时使用广义Dice系数准则来进行每一阶段的最优原子选择工作,并在匹配最优原子阶段引入正则化对已选原子进行二次筛选。     

IR-UWB通信同步跟踪系统仿真实验设计

结合我校通信电子电路、通信原理、现代通信系统等课程,设计了信息工程专业通信系统综合实验的一个拓展内容———超宽带通信同步跟踪系统仿真实验。本仿真实验在Simulink平台下,基于超前-滞后锁相环搭建了超宽带通信同步跟踪系统。该系统在单用户状态下,选用PPM调制方式、AWGN信道传输,实现了在加性高斯白噪声信道下点对点的通信,成功反映了PPM调制方式的特点,完成了脉冲超宽带(IR-UWB)信号的同步跟踪。在Simulink建模过程中,利用既有模块与Sfunction编程设计相结合完成了系统仿真,并使同步误差函数值可视化,充分说明该系统的优越性。     

基于空时分组码的多天线超宽带OFDM系统性能研究

在对多带(MB)OFDM UWB通信系统进行研究分析的基础上,提出一种基于空时分组码(STBC)的多输入多输出(MIMO)MB-OFDM超宽带通信系统,并详细介绍了系统模型和空时分组码的编译码原理,对系统性能进行了仿真。仿真结果表明,在改进的S-V多径信道环境下,和传统空时分组码相结合的MB-OFDM系统不仅具有更高的信道容量和分集增益,而且误码性能有所提高。     

超宽带平均传输参考接收机性能分析与研究

研究了一种一般的平均传输参考接收机的结构,并推导了该结构下的误码性能。该结构充分利用了超宽带信道准静态的特点,将一个接收比特的参考脉冲累加求平均作为模板信号,从而降低加性噪声的影响。在IEEE802．15．3a标准下0-4m非直射路径的信道下,采用Scholt＇z单循环脉冲和二进制相移键控调制,分别在不同脉冲重复数和不同积分时间情况下,对平均传输参考接收机进行性能仿真与对比。另外,还将该接收机与一般的传输参考接收机和一种改善的传输参考接收机在接收性能方面进行了理论和仿真对比。     

广义Rice／Lognormal信道模型研究

文章针对卫星移动通信信道的特点,提出了一个适用于陆地卫星移动通信的信道模型——广义Ricc／Lognormal信道模型。并对所提出信道模型的统计特性进行了数学推导。通过计算机仿真表明,该SOS模型能够较好地仿真卫星移动通信信道。     

Rummler信道模型的Systemview仿真研究

无线信道是移动通信的传输媒介,信道性能优劣直接影响通信质量,要提高无线通信质量就必须改善信道性能.阐述了移动信道的特点,介绍了几种典型移动信道的模型,重点分析了Rummler信道模型,在此基础上构建出Rummler信道的仿真电路.采用电路与通信系统专用仿真软件Systemview对其进行仿真,给出了仿真波形图,并对仿真结果进行了分析.仿真结果表明Rummler信道模型可以适应不同环境的电波传播衰落,具有更强的灵活性.     

基于MATLAB的智能控制系统的信道建模

本文首先对数字基带信号、数字频带信号、数字基带传输系统、数字频带传输系统、有线信道、无线信道等通信名词给出了概念性的介绍;详细阐述了有线信道、无线信道的类型及信道中的传输损耗;并针对此次主要借助的仿真软件——MATLAB进行了简单的概述;以曼彻斯特码作为数字基带传输的码型,建立传输线的等效电路模型,借助MATLAB软件仿真信号在有线信道中的传输过程,建立了多径信道、菜斯信道、高斯白噪声信道三种无线信道模型,借助MATLAB软件仿真信号在无线信道中的传输过程。     

一种最优无线电信道分配方案

在信道复用距离为常数,相邻的基站信道相差的条件下,研究了蜂窝状通信系统的最优信道分配问题。给出了此信道分配问题的数学模型,并论证了该模型求出的是最优解,并深入阐述了通信系统的信道分配问题。     

超宽带技术及应用

超宽带技术是一种全新的无线通信技术。该文在介绍超宽带概念的基础上,对其一些关键技术进行了介绍和分析,指出了超宽带的当前应用,并对今后的研究动态进行了探讨。     

谈新《学生体质健康标准》下的高校体育改革

新《学生体质健康标准》的实施,将对高校体育教学工作产生深远的影响。分析研究《标准》实施对高校体育改革的导向意义,提出高校体育改革的一些思路。     

The Effects of Incomplete Rating Designs in Combination With Rater Effects

Researchers have explored a variety of topics related to identifying and distinguishing among specific types of rater effects, as well as the implications of different types of incomplete data collection designs for rater‐mediated assessments. In this study, we used simulated data to examine the sensitivity of latent trait model indicators of three rater effects (leniency, central tendency, and severity) in combination with different types of incomplete rating designs (systematic links, anchor performances, and spiral). We used the rating scale model and the partial credit model to calculate rater location estimates, standard errors of rater estimates, model–data fit statistics, and the standard deviation of rating scale category thresholds as indicators of rater effects and we explored the sensitivity of these indicators to rater effects under different conditions. Our results suggest that it is possible to detect rater effects when each of the three types of rating designs is used. However, there are differences in the sensitivity of each indicator related to type of rater effect, type of rating design, and the overall proportion of effect raters. We discuss implications for research and practice related to rater‐mediated assessments.     

From expectancy-value theory to situated expectancy-value theory: A developmental,social cognitive,and sociocultural perspective on motivation

Eccles and colleagues’ expectancy-value theory of achievement choice has guided much research over the last 40+ years. In this article, we discuss five “macro” level issues concerning the theory. Our broad purposes in taking this approach are to clarify some issues regarding the current status of the theory, make suggestions for next steps for research based in the theory, and justify our decision to call the theory Situated Expectancy-Value Theory (SEVT). First, we note how visual representations of the model make it appear static, linear, and monolithic, something that was not intended from its inception. Second, we discuss definitions of the major psychological constructs in the model, focusing on our and others’ elaboration of the task value component, particularly the “cost” component. In this section we also discuss research on the development of expectancies and values. Third, we discuss the often-neglected middle part of the model focused on how individuals understand and interpret their own performance as well as the many messages they receive from different socializers regarding their activity participation and performance. In the fourth section we discuss the situative and culturally-focused aspects of the model, stressing the impact of the situation and cultural background on children’s developing expectancy and value hierarchies. The fifth issue (one that we mention in several of the previous sections) concerns the importance of understanding the development of individuals’ hierarchies of expectancies of success and subjective task values and how they relate to performance, choice, and engagement.     

Now相关概率不确定时态数据模型

时间是自然界无所不在的客观属性,随着数据库技术的发展,时态信息在数据库系统中的作用日益重要。本文描述了有效时间与不确定性等概念,分析了概率不确定时态数据模型,引入时态变量,提出一种新的时态信息模型,并简单讨论了在此数据模型上的时态关系演算。     

高校教师职业道德规范内容之我见

高校教师是高等学校办学育才的根本,而高校教师队伍中存在着的种种问题需要高校教师职业道德规范加以约束。探讨高校教师职业道德规范的内容对于尽快建立起完善的高校教师职业道德建设制度具有重要意义     

Origin(?) of the universe

In this part of the series we discuss the standard cosmological model valid close to the big bang epoch. The origin of light nuclei is believed to have taken place within the first three minutes or so when the universe was very hot and dominated by radiation. Subsequently, it cooled down and today we should see radiation decoupled from matter but spread almost homogeneously all over the universe with a black body spectrum. This expectation has been realized by the discovery of the microwave background in 1965. Jayant V Narlikar Director, Inter-University Centre for Astronomy and Astrophysics, works on action at a distance in physics, new theories of gravitation and new models of the universe. He has made strong efforts to promete taaching and research in astronomy in the universities and also writes extensively in English and Marathi for a wider audience on science and other topics.     

Standardized Parameters in Misspecified Structural Equation Models: Empirical Performance in Point Estimates,Standard Errors,and Confidence Intervals

In practice, models always have misfit, and it is not well known in what situations methods that provide point estimates, standard errors (SEs), or confidence intervals (CIs) of standardized structural equation modeling (SEM) parameters are trustworthy. In this article we carried out simulations to evaluate the empirical performance of currently available methods. We studied maximum likelihood point estimates, as well as SE estimators based on the delta method, nonparametric bootstrap (NP-B), and semiparametric bootstrap (SP-B). For CIs we studied Wald CI based on delta, and percentile and BC_a intervals based on NP-B and SP-B. We conducted simulation studies using both confirmatory factor analysis and SEM models. Depending on (a) whether point estimate, SE, or CI is of interest; (b) amount of model misfit; (c) sample size; and (d) model complexity, different methods can be the one that renders best performance. Based on the simulation results, we discuss how to choose proper methods in practice.     

The story of large electron positron collider

We discuss the experiments carried out with LEP (large electron positron collider) that verified the standard model of the fundamental particles of nature. Some experiments planned for the future to detect Higgs particle are also discussed.     

加强高等院校教学质量管理体系的建设

本分析了高等院校合校及扩招后所面临教学质量问题,阐述了高校建立教学质量管理体系的必要性。对高等院校采用ISO 9000系列标准建立以过程为基础的教学质量管理体系模式进行讨论,具体运用PDCA过程方法对专业建设教学质量的持续改进提出建议。     

剩余类模上线性方程组解的判定与结构

在剩余类模上及剩余类环上探讨了矩阵的等价标准形，讨论了线性方程组解的判定与结构问题。