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.     

基于载波频偏盲补偿的MIMO OFDM系统同步算法

给出了基于载波频偏盲补偿的MIMO OFDM系统同步算法:首先,将接收到的序列进行载波频偏盲补偿;然后,进行粗时间同步和载波频偏估计;最后,应用估计出的载波频偏进行载波频偏补偿,利用经过载波频偏补偿后的序列进行符号定时同步。该算法最大限度地抑制了载波频偏对符号定时同步的影响。仿真试验证明,该算法有着良好的性能。     

CMMB系统同步算法FPGA实现及验证

为了提高CMMB系统广播信号接收同步精度,提出了一种使用CMMB信标进行载波和定时精确同步的算法。首先通过基于循环前缀的算法进行小数倍频偏估计和定时粗同步,再利用同步信号中伪随机序列的相关特性进行整数倍频偏估计和精确定时同步。仿真表明,在高斯白噪声下,CMMB系统同步算法的小数倍频偏性能与基于循环前缀的算法相当,但可以进行整数倍估计且定时精度高,在多径信道下,CMMB系统同步算法的估计精度优于基于循环前缀算法。实验结果验证了仿真的正确性。     

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OFDM时频同步算法

针对Schmidl和Minn算法存在符号定时和频率同步精度不高,频率同步运算量大的缺点,提出一种新的基于CAZAC序列的OFDM同步算法.算法利用2个相同的CAZAC序列作为一个训练符号,并对第二个序列用CAZAC序列进行加权,在接收端利用训练符号所包含数据的重复性和CAZAC序列的相关性,进行符号定时同步;然后利用CAZAC序列具有的时域移位特性进行整数倍频偏估计.算法在时域完成,因运算量较小.仿真结果表明,新算法克服了Schmidl和Minn算法的缺点,在AWGN和多径信道下,均能精确同步并进行较大范围的频偏估计.特别是在信噪比较低时采用该算法能实现更准确的同步.     

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。     

窄带物联网中下行同步技术研究

基于窄带物联网系统研究下行同步技术,实现低信噪比和高频偏环境下的同步技术方案,具有较高的实际研究意义。为此,重点研究基于窄带物联网的智能电网下行同步技术的实现方案。并针对低信噪比和高频偏引起的窄带物联网下行同步性能下降问题,提出使用差分相关和PMF+FFT算法的改进方案,实现PSS定时监测过程和频偏检测过程。通过搭建对应的下行同步信道链路级仿真平台,与原有的分段相关算法进行比较分析。结果表明,该方案能显著地改善定时检测精度,并有效消除频偏的影响,同时分析了各模块性能提升状况。     

LTE小区搜索中定时与频偏估计算法研究

在长期演进（LTE）的小区搜索中,定时同步与频偏估计是一个非常重要的同步过程。基于分段相关算法,提出了一种改进算法。利用分段相关算法具有抗频偏的优点结合差分运算,并采用对接收端信号进行累积处理方法,提高了定时同步精度。将本地PSS信号累积相加的结果与接收信号进行相关运算,有效降低了算法的运算量。同时利用本地PSS信号与接收PSS信号的相关性,提出一种有效的频偏估计算法。理论分析与仿真实验表明,与传统算法相比,提出的定时与频偏估计算法有效提高了估计精度,减小了运算量。     

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。     

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.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.     

The Distributed Time-Triggered Simulation Scheme: Core Principles and Supporting Execution Engine

Distributed real-time simulation is a young technology field but its practice is under increasing demands. In recent years the author and his collaborators have been establishing a new approach called the distributed time-triggered simulation (DTS) scheme which is conceptually simple and easy to use but widely applicable. The concept was initiated in the course of developing a new-generation object-oriented real-time programming scheme called the time-triggered message-triggered object (TMO) programming scheme. Some fundamental issues inherent in distributed real-time simulation that were learned during recent experimental studies are discussed along with some approaches for resolving the issues. An execution engine developed to support both the TMOs engaged in control computation and the TMOs engaged in DTS is also discussed along with its possible extensions that will enable significantly larger-scale DTSs.     

Software-Konfigurationsmanagement in großen Softwareprojekten

Zusammenfassung Mit zunehmender Größe der Softwaresysteme verschärfen sich die für die Software-Herstellung typischen Probleme: Beherrschen großer Objektmengen, Erhalten der Systemkonsistenz, Kontrolle der ständigen Änderungseinflüsse und Gewährleisten einer langen Lebensdauer. Die Disziplin Konfigurationsmanagement bildet den methodischen Ansatz, diese Probleme besser zu beherrschen. Software-Konfigurationsmanagement faßt die Herstellung von Softwaresystemen als eine Abfolge von kontrollierten Änderungen an gesicherten Zwischen- und Endergebnissen auf. Dargestellt werden die Objekte und Funktionen des Software-Konfigurationsmanagements sowie die hierfür in großen Software-Projekten benötigten Methoden, Instanzen und Hilfsmittel.     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and     

Editorial:Brain-machine interface(BMI) and cyborg intelligence

正Brain-machine interfaces(BMIs)aim at building a direct communication pathway between the brain and an external device,and represent an area of research where significant progress has been made during the past decade.Based on BMIs,mind information can be read out by neural signals to control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate     

SCIENCE CHINA Information Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate