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1.
研究一种铁路远程通信信号的采集模型并进行仿真分析,通过提取高铁远程单工控制通信信号最佳冲击脉冲,并进行信号处理,实现高速铁路CTCS-3级列车运行控制系统车-地间通信传输。提出一种基于单频包络瞬时值统计的高铁远程单工控制通信信号最佳冲击脉冲提取算法,高铁CTCS-3列车运行控制系统车-地间通信传输模型,对多径信道特征干扰下,对列车控制中心接收到脉冲响应信号进行线性滤波,计算接收端的指向性增益,实现高铁远程单工控制通信信号产生的最佳冲击脉冲响应提取。仿真结果表明,该算法有效模拟地面列控中心接收到的CTCS-3系统的信道混响,提取最佳冲击响应脉冲,有效滤除噪声干扰,提高了CTCS-3高速列车运行控制系统的车-地间通信传输质量。 相似文献
2.
在网络切换和数据通信中,会产生一种伪随机时频跳变网络谐振信号,需要对这种谐振信号进行信号抑制,提高网络的安全性和稳定性,对网络谐振信号的信息容量估计是实现谐振信号抑制的基础。提出一种基于人工免疫的伪随机时频跳变网络谐振信号的信息容量估计算法,首先进行伪随机时频跳变网络系统的总体设计,计算网络跳变信号在人工免疫进化过程中免疫节点的位置和尺度参数,引入自适应转发控制策略,构建数据信息链优先链路选择准则,预测信号的下一个跳变点,得到多路复用波束域约束指向形成信号容量的输出结果,通过对信号容量的准确估计,可以避免网络出现启动滞后、服务器负载、消息消耗以及颤抖等现象。实验结果表明,该算法对伪随机时频跳变网络谐振信号的信息容量估计精度高,抑制性能和检测性能较好,确保了网络系统的稳定。 相似文献
3.
通过对铁路调度信号的自动控制和通信系统设计,实现对列车运行系统通信性能的改善。传统的铁路调度信号通信控制方法采用单频包络瞬时值统计的通信信号最佳冲击脉冲响应匹配方法进行通信控制算法设计,当列车运行区间为随机分布式,通信性能不好。提出一种基于线性反馈匹配滤波的铁路调度信号通信控制算法。进行铁路调度通信信号和铁路无线通信信道模型构建,信号分离的同时采用线性反馈匹配滤波技术实现支路信号同相相加,设计线性反馈滤波器,进行通信干扰抑制,实现基于线性反馈匹配滤波的铁路调度信号通信控制算法改进。研究表明,该算法能克服常规控制模型在铁路机车到达阶段不具有鲁棒性的弱点,非稳定阶段前比传统方法更平滑,在铁路调度信号通信中,具有较小的误码率,展示了较好的通信性能和控制性能。 相似文献
4.
在主动探测自导系统设计中,混响数据分段Itakura距离的准确估计是实现自导系统测距,提高目标信号检测性能的基础,且Itakura距离可以评价对混响数据的局部平稳性。当前的混响数据Itakura距离估计算法采用基于局部高斯色噪声混响估计模型,当相邻数据段与需检测信号脉宽一致时,距离估计精度不好。提出一种基于Rayleigh分布分段副本相关检测的混响数据Itakura距离算法,构建混响数据包络模型实现对混响包络概率分布特征的准确描述,采用基于频率选择性衰落的自适应噪声抵消算法对混响数据包络模型进行简化,对混响数据进行Rayleigh分布下的概率密度特征分割,设计分段副本相关检测器,计算该组数据中相邻数据段之间Itakura距离,实现目标Itakura测距。实验结果表明,改进算法对Itakura距离估计精度较高,局部平稳性影响较小。在精确探测制导等领域具有很好应用价值。 相似文献
5.
对网络攻击信号检测中,需要对网络威胁态势预测的抗体虚警概率阈值估计,提高攻击信号检测性能。传统方法采用伪随机时频跳变的信息容量估计方法实现阈值估计和攻击信号检测,当攻击信号为非线性谐振信号时,检测性能不好。提出一种改进的网络威胁态势预测的抗体虚警概率阈值估计算法。构建多路复用器输入输出网络威胁态势预测算法,通过病毒信息特征预处理为免疫性分析提供信息特征数据基础。得到网络跳变向量和观测向量的标准正态阈值,将网络接收端和发送端数据的信息熵作为信道传递向量函数,在人工免疫进化过程中实现对免疫节点的抗体的虚警概率阈值估计,提高网络攻击信号的检测性能,降低网络威胁态势抗体虚警概率。仿真实验得出,该算法得到的估计结果精确,有效提高了攻击信号的检测性能,确保网络安全。 相似文献
6.
混合网络下的差异化异常跳频,是一种新的高速短波通信体系,实际的混合网络中存在较高的预测阶数和虚检频率,采用传统跳变频率检测方法,无法精确检测出跳变频率,存在较大的频率失调量。提出一种基于MUSIC方法和Duffing混沌振子的混合网络下差异化异常跳变频率检测方法,分析了混合网络下的差异化异常跳变信号特征,采用MUSIC方法对差异化异常跳变频率进行初步估算,通过Duffing混沌振子对差异化异常跳变频率进行进一步检测,实现混合网络下的差异化异常跳变频率的高精度检测。仿真结果证明了该方法的有效性,具有较高的检测精度和较低的检测误差。 相似文献
7.
网络入侵搅动下的网络失稳控制方法研究 总被引：1，自引：0，他引：1
当前的网络入侵防御都以先发式预防为主,没有充分考虑入侵后对网络的有效控制。当前的网络控制中,很难消除网络被入侵后的不可靠性,造成入侵后网络失稳状态明显。传统的网络失稳控制的控制阀值无法起到最优控制作用。提出一种跟踪微分时延误差补偿的失稳网络入侵波动后的稳定与镇定方法,设计了一种信号跟踪微分器,追踪网络控制信号的波动,运用二阶自抗扰控制器,抑制入侵后带来的网络信号波动。结合抑制情况,对产生的时延误差进行补偿,保证网络在时间信号上的稳定。运用物理波动信号控制模拟入侵后的网络控制,进行仿真实验,该方法可以保证在网络产生入侵波动后,使得网络时延和信号失稳被控制在较为稳定的状态,优化效果明显。 相似文献
8.
在分组交换网络通信系统中,由于带宽频移键控产生谐振干扰,导致信号传输不稳定,甚至产生误码和丢包。提出一种基于连续小波变换与带宽时延-尺度耦合特性构建的复杂网络带宽频间谐振抗干扰算法。对抗干扰模型进行时间-尺度分析,把干扰信号模型分解成一组带宽双曲调频信号,并分析信号时间平移与尺度伸缩等同效应,有效抑制谐振干扰。仿真验证了算法的有效性,时间-尺度建模分析结果准确,有效抑制了网络带宽频间谐振干扰,大幅降低了复杂分组交换网络通信的误码率,对提高网络安全性能具有积极意义。 相似文献
9.
在微波通信中,采用微波通信分集接收技术能很好实现信道均衡和多径干扰抑制,增加发射功率或带宽。传统方法采用自适应均衡技术进行微波通信分集跟踪,两点间直线距离内无障碍时,信号分集效果较好,但不能适用于多途分集接收,信道交叉时对信号源的跟踪效果不好。提出一种基于波特间隔线性反馈的微波通信分集接收技术,建立微波通信信道模型和微波通信协议设计,同一信号的不同独立衰落复制品加以合并处理,在信号分离的同时采用波特间隔线性反馈技术实现支路信号同相相加,正好抵消衰落的相位偏移,达到瞬态集中的目的。从而大幅度改进无线链路性能,实现强有力的接收。仿真实验表明,采用该算法能有效提高波束形成的垂直指向性,能在强混响复杂深海通信环境中实现对微弱多径衰落微波信号的分集接收,误码率从16.21%降低为0.98%。 相似文献
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11.
Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors. 相似文献
12.
A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007. 相似文献
13.
Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction. 相似文献
14.
《中国科学院院刊(英文版)》2008,22(1):2-3
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing. 相似文献
15.
《中国科学院院刊(英文版)》2008,22(1)
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants." 相似文献
16.
Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies. 相似文献
17.
Puay Tang 《The Information Society》1998,14(1):19-31
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means. 相似文献
18.
Milton Mueller 《The Information Society》2001,17(3):151-163
Long-standing conflict between domain name registrants and trademark holders prompted the Internet Corporation for Assigned Names and Numbers (ICANN) to create a global, mandatory arbitration procedure known as the Uniform Dispute Resolution Policy (UDRP). The UDRP has been used in 2166 cases involving 3938 domain names as of 1 November 2000. The policy gives the initiator of a complaint, generally a trademark holder, the right to choose which ICANN-accredited dispute resolution service provider (RSP) will handle the case. During the preparation of the UDRP,some feared that complainant selection would lead to "forum shopping" that might bias the results. This article performs a statistical assessment of the forum-shopping thesis and finds support for it. There are statistically significant differences in the various RSPs' propensity to take away names from defendants; there are also major differences in the number of cases brought to each RSP. RSPs who take away names have the larger share of cases. The study examines other variables that might explain differences in market share, such as price, the plaintiff's nationality, or the time taken to decide a case. It finds that nationality and time also are correlated with market share. The study concludes that shopping for a favorable outcome is an important factor in the UDRP. 相似文献
19.
Prof. Raymond C.K. Chen a neuropsychologist with the CAS Institute of Psychology has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology.…… 《中国科学院院刊(英文版)》2008,22(1):15-15
Prof. Raymond C.K. Chen, a neuropsychologist with the CAS Institute of Psychology, has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology. 相似文献
20.
Leah A. Lievrouw 《The Information Society》1998,14(2):83-96
The main premise of this article is that in information societies generally, and in virtual social contexts particularly, a distinctive style of interaction to facilitate the communication of difference, heterotopic communication , has emerged. It rests on two cultural foundations: an ideological belief in the positive, socially integrating power of communication, and a prevailing ethic of instrumental rationality, subjective individualism, and strategically practiced self-interest. The former is demonstrated by the use of simulation and spectacle as sources of information; exhibitionism/voyeurism as a communicative style; and the awareness of surveillance. The latter is seen in the competitive use of knowledge as a commodity; a surface globalism masking deep parochialism; lateral as well as vertical information inequity; and the use of public versus private as strategies for engagement rather than as spaces. Those who engage in heterotopic communication resort to their 'own devices' both in the sense of personal agendas, strategies, interests, and interpretations, and in the form of the telecommunication tools that help realize them. These personal and technological devices allow individuals with the right educational and technical resources to avoid exposure to disagreement, difference, or other information that does not serve their direct purposes or reflect their particular views of the world; yet they also help convey the appearance of openness, availability, and cooperation. This style of interaction is used strategically in combination with information and communication technologies to gain social or economic advantages, but it may encourage social separatism and parochialism, inhibit the negotiation of disputes, and emphasize competing interests. 相似文献