共查询到20条相似文献，搜索用时 328 毫秒
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在超宽带（UWB）通信系统里，当用户数增加和脉冲重复频率下降时，多址干扰会严重影响系统容量和性能．文章提出了UWB-MA系统多用户检测算法．仿真结果表明，多用户检测接收机性能优于传统单用户检测接收机． 相似文献
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为了简化时隙ALOHA-CDMA系统的时间同步设备,提出了一种可用于卫星VSAT网络内向信道的应答式时隙ALOHA-CDMA信道模型.将端站分为M个子系统,利用主站发出周期性询问信号,建立了信道模型;通过扩频多址干扰(MAI)和分组检测概率的推导,计算出该信道的稳态吞吐量;并将扩散过程理论用于该信道的稳定性分析,得到扩散系数a(r)、漂移系数b(r)和信道平稳分布P(r).仿真结果表明,该系统可以显著提高信道吞吐性能和信道利用率,且存在1～2个稳定平衡点.应答式时隙ALOHA-CDMA信道可以降低卫星VSAT系统及分组无线网络系统的组网成本. 相似文献
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This paper presents an improved error function of dithered signed-error constant modulus algorithm （IDSE-CMA） for blind multiuser interference suppression in DS/CDMA systems. It uses a different error function to replace the former one in sign operation of the DSE-CMA and compares their performance in multiple access interference （MAI） suppression ability. Simulations indicate that the new algorithm has better performance than the similar CMA in terms of convergence speed and steady-state performance： 相似文献
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针对现阶段广泛应用信号子空间跟踪算法PAST算法在低信噪比和强多址干扰情况下,估计出信号子空间有较大的误差而提出一种新的信号子空间概念。通过理论分析和仿真,验证了新的算法能够克服PAST算法的缺点。并在此基础上构成的一种新的MMSE检测器,该检测器具有良好的误码率和抗“远-近”能力,结构简单,计算复杂度低,而且对信号子空间维数大小估计错误时并不敏感。 相似文献
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在分析多载波码分多址(MC-CDMA)的原理基础上, 提出了一种基于复小波包的MC-CDMA系统. 同时, 研究了该系统分别采用等增益合并和最大比合并时在Nakagami-m衰落信道下的性能; 并推导了相应的误码率表达式. 该系统能克服通常MC-CDMA系统由于插入循环前缀(CP)所带来的频谱效率的下降. 理论分析和仿真结果表明:该系统要优于通常MC-CDMA系统和基于实小波包的MC-CDMA系统, 有着优越的抗多径衰落和多址干扰能力,而且该系统也优于采用CP的通常MC-CDMA系统. 相似文献
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重复代码是程序中最常见的代码“坏味道”.在改进的Kontogiannis度量方法及基于过程蓝图的参数化匹配检测方法基础上,提出以过程蓝图为基础,设计出一个重复代码自动探测工具,并给出实现系统结构.同时论述了工具种各模块的设计与实现方法,着重讨论了重复代码检测器及存储结构的设计。 相似文献
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In this paper, an asynchronous cooperative cellular system applied with space-time block coding(STBC)is investigated. A signal detector is proposed based on parallel interference cancellation(PIC), to cancel the inter-symbol interference(ISI)caused by the imperfect synchronization. Simulation results show that the proposed PIC detector can effectively suppress the ISI, but there is still a comparatively high error floor, due to the co-channel interference(CCI)of the cellular system. 相似文献
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姚洁 《宁德师专学报(自然科学版)》2009,21(2):168-174
在CDMA（Code Divisin Muhiple Access,码分多址）通信系统中,由于多个用户的随机接人,所使用的扩频码集一般并非严格正交,码片之间的非零互相关系数将引起各用户间的干扰,这种干扰称为多址干扰．为了能够有效的抑制CDMA移动通信系统中的多址干扰,抗“远近效应”,就引进了多用户检测（MUD）．多用户检测技术在传统检测的基础上,能有效地消除MAI的影响,从而改善系统性能,增大系统容量．对系统中的多用户检测技术和与之密切相关的MMSE检测技术进行了研究． 相似文献
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Many scholars agree on the general theoretical structure of metacognition, which is what informed the development of the Metacognitive Awareness Inventory (MAI). Although self-report instruments such as the MAI suffer many threats to validity, they continue to be used in research and practice because of their convenience. With the MAI, studies have varied in the way they calculate scores and in their adherence to the intended theory. In this study, we address these shortcomings and propose modifications in calculating MAI scores. Using confirmatory factor analysis (CFA) and multidimensional random coefficients multinomial logit (MRCML) item-response modeling, we examined how well the intended functioning of the MAI matched the data from 622 undergraduate students. The results support scoring the MAI as two dimensions, knowledge and regulation of cognition, but indicate that the 52-item instrument has poor fit. Using iterative CFA and MRCML models, we tested subsets of items that represent the theory and had good fit. We followed up with tests of between-group and time invariance. The results support the use of a 19-item subset for between-group comparisons, with provisional evidence for its use in longitudinal studies. 相似文献
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门涛 《乐山师范学院学报》2013,28(5):43-45
验证码能够有效抵御网络中机器程序的自动登录行为,防止机器程序群发垃圾邮件和自动投票等非法行为。但是随着图像识别技术和人工智能的发展,传统的验证码面临着被机器程序自动破解的危险。文章在分析不同验证码的优缺点后,提出一种基于人眼视觉暂留现象的动态验证码,利用有效字符和干扰字符混合组成多帧动态图像,普通用户可以轻易识别,而机器程序难以区分,理论分析和模拟实验证明该验证码简单有效。 相似文献
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为了提高无线自组网通信网络吞吐量和数据包发送成功率,提出一种基于准同步 CDMA 的自组网MAC 协议,并对其收发电路进行设计。在采用零相关区序列的准同步 CDMA 系统中,到达接收端的各用户信号存在一定的相对时延,如果用户信号相对时延控制在零相关窗口范围之内,可以达到近似于同步的效果,同时零相关序列的相关性能大大提高了系统抗多址干扰和多径干扰能力。仿真结果表明,该协议的系统吞吐量是未采用零相关序列系统的 5 倍,在数据包发送数为 50 时仍有 30%的发送成功率。 相似文献
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大众化教育高等学校学生英语词汇语义建构能力和词汇产出能力普遍偏低。针对这种现象,简述了汉语背景下英语词汇习得基本特征,指明母语干扰在习得过程中占有主导地位。排除干扰应坚持重深编码法、防分解储存过分泛用、注重语境作用等原则。就此,提出三大策略——强化干扰意识、开发和利用英语语境、勤查权威辞典文献。 相似文献
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美国对外干涉是其维护世界霸权的重要手段。二战后初期,美国对危地马拉阿本斯政府改革进行的以＂成功行动＂为代号的干涉,就是一个被美国奉为经典的对外干涉行动。通过回顾美国对危地马拉改革干涉的原因、过程、手段和结果,分析美国对外干涉的实质,以期有助于我们理解当今美国在世界上采取干涉活动的本质理念。 相似文献
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Li‐fang Zhang 《教育心理学》2010,30(4):481-494
The principal objective of this study was to explore the predictive power of thinking styles for metacognition when self‐rated abilities were taken into account. As a preliminary step, the study examined the psychometric properties of the Metacognitive Awareness Inventory (MAI). Four hundred and twenty‐four university students from mainland China responded to the MAI, the Thinking Styles Inventory‐Revised II, and the Self‐Rated Ability Scale. The study ascertained the reliability and validity of the MAI. More importantly, results suggested that three creativity‐generating styles (hierarchical, liberal and legislative) and the executive style predicted metacognition beyond self‐rated abilities. Practical significance of the main research finding was discussed for university faculty members, students and university senior managers. 相似文献
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《Contemporary educational psychology》2002,27(1):51-79
Two studies were conducted to investigate measures of children's metacognition. Experiment 1 presented two versions of a self-report inventory, the Jr. MAI, appropriate for assessing metacognition in children in grades 3–9. Factor analyses are interpreted that illustrate how the items measure components of metacognition. Experiment 2 further addressed properties of the two versions and compared the instrument to other inventories, teacher ratings of children's metacognition, and student achievement scores. Findings indicated high correlations between the Jr. MAI and an existing metacognitive problem-solving inventory (Fortunato, Hecht, Tittle, & Alvarez, 1991). Moderate correlations between the Jr. MAI and other self-report instruments of metacognition while reading (Jacobs & Paris, 1987; Schmitt, 1990) and low correlations between the Jr. MAI and teacher ratings of metacognition and overall achievement scores were also found. Gender and grade level differences in metacognition are presented and discussed. The instruments are appended. 相似文献
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The research questions addressed in this study were: what types of epistemological beliefs do elementary students have; what
types of metacognition do elementary students have; and what are the relationships among students’ perceived characteristics
of constructivist learning environment, metacognition, and epistemological beliefs. A total of 626 students enrolled in sixth,
seventh, and eight grades of nine elementary public schools located in Ankara, Turkey constituted the participants of this
study. Constructivist learning environment survey (CLES), Junior metacognitive awareness inventory (Jr. MAI), and Schommer
epistemological belief questionnaire (EB) were administered to students. Factor Analysis of Jr. MAI revealed both knowledge
of cognition and regulation of cognition items were loaded into one factor. Confirmatory factor analysis of EB revealed a
four factor structure namely innate ability, quick learning, omniscient authority, and certain knowledge. Regression analyses
revealed that metacognition and omniscient authority were significant predictors of personal relevance dimension of CLES.
Metacognition was found as the only predictor of the student negotiation. Innate ability and metacognition significantly contributed
to uncertainty. This study revealed that the elementary students with different mastery levels hold different epistemological
beliefs and multi-faceted nature of elementary school students’ metacognition was seemed to be supported with this study.
It was found that metacognition contributed to model more than epistemological beliefs for all three dimensions of CLES. 相似文献