X信道中一种改进的空时编码传输方案

为提高空时编码传输效率,提出一种在X信道中为每个用户配置2根天线的改进空时编码传输方案。每个用户采用全速率全分集空时分组码,将每个码字的部分元素旋转适当的角度,并且对每个码字进行两层预编码。通过一层预编码使得每个接收端的非期望接收码字对齐,在每个码字中引入零向量以及接收端的线性运算,消除每个接收端的非期望接收码字。通过另一层预编码使得每个接收端的期望接收码字正交传输,从而消除多用户干扰。仿真结果显示,与相同场景中已有空时编码传输方案相比,该方案能有效提高传输效率,且可靠性较优。     

基于空时编码和干扰对齐的干扰消除方法

对于每个用户配置4根天线的X信道,提出了一种基于空时编码和干扰对齐的干扰消除方法。设计了4×4的速率为2的空时码字,并且在码字中引入零向量。首先通过干扰对齐将每个接收端接收到的非期望接收码字对齐,然后对接收信号进行线性操作以消除非期望接收的码字,最后对接收信号进行非线性运算使得期望接收的码字互不干扰。所提方案的自由度为16/3,分集增益为8。仿真结果显示,所提方案的可靠性优于相同场景中的已有方案。     

MIMO-MAC中一种新的空时码传输方案

已有的研究表明,预编码可以消除4用户的多输入多输出多址接入信道（MIMO-MAC）中的多用户干扰,然而,该方法需要大量的反馈信息。针对该问题,提出了该场景中一种无反馈的干扰消除方法。每个用户采用完美空时分组编码,通过合理地设计每个编码的发送方式,使得接收端对接收信号进行线性处理后消除了多用户干扰。与已有方案相比,所提方案在不改变传输效率、每个符号平均发送功率以及分集增益的同时,极大地降低了反馈量。仿真结果验证了所提方案的有效性。     

协同MIMO移动Ad Hoc网络中的一种新型Alamouti编码

针对协同MIMO(Multi-Input Multi-Output)移动ad hoc网络无线带宽相对有限、无线信道噪声干扰强烈而导致的信号传输质量不佳等问题,提出一种基于反相对称调制法的Alamouti空时编码方案。通过在编码过程中加入噪声相消运算环节而大大减小接收端接收到的噪声干扰强度;重点分析此种方案的编译码过程,并通过理论分析和系统仿真表明,相较于传统的Alamouti空时编码,此方案可使传输系统获得更优越的抗噪声性能和更小的传输误码率,大大提高了系统传输可靠性。     

MIMO-MAC中一种改进的干扰消除方法

针对两用户的多输入多输出多址接入信道(MIMO-MAC)中存在共道干扰的问题,提出一种基于有限反馈的干扰消除方法,每个用户根据反馈信息对将要发送的信号进行对角化处理。通过合理设计预处理矩阵,对接收信号进行线性处理以消除共道干扰,从而提高系统的可靠性,使得接收端可以逐个符号地最大似然译码,降低译码复杂度。仿真结果表明,若接收端配置2根天线且系统采用4QAM调制,则当误比特率为10-3时,与已有基于有限反馈的干扰消除方案相比,该方案能获得2 dB的增益。     

多用户CDMA系统中Turbo-BLAST迭代检测算法

将V-BLAST结构和CDMA技术相结合,构造了多用户CDMA系统模型,提出了一种联合多用户检测和Turbo迭代思想的多用户检测算法.该方案首先利用解相关算法对接收信号进行空时多用户检测.以去除用户间干扰.然后再对期望用户的接收信号进行软干扰抵消迭代检测,以去除天线间干扰.解相关后数据检测仅和单个用户的天线数目有关,算法复杂度较低.仿真结果表明,构造的空时多用户模型可使各用户检测相对独立,有利于已有单用户Turbo-BLAST方案的应用.     

窃听环境下轮流中继网络的安全传输方案

针对含有多个窃听者、多个中继的无线通信网络的传输安全问题,提出了一种新的轮流中继安全传输方案。以降低系统平均安全中断概率为目标,所提方案在源节点发送保密信息的过程中,在每个传输时隙均选择一个最优中继对前一时隙接收到的信号进行转发以干扰窃听者,并在目的节点处进行干扰消除。为评估系统性能,推导得到了系统平均安全中断概率的闭式表达式。仿真结果验证了理论分析结果的正确性,并表明与传统中继协作方案相比,所提方案可显著降低系统的平均安全中断概率。     

基于码本的多用户有限反馈预编码方法

为改善多用户系统中由有限反馈导致的性能缺失,提出了一种基于码本的预处理有限反馈预编码方法。该方法在接收端根据部分子载波信道信息采用最大信干比准则从预置码本中选取码字反馈给发送端,在发送端根据子载波簇的相关性重构各子载波预编码矩阵,对发送信号进行线性变换以达到容量最优,在接收端利用干扰用户信息对接收阵列信号进行预处理消除部分干扰信息,从而补偿由于有限反馈导致的性能缺失。实验结果表明,所提出的方法在保证反馈链路开销与系统误码性能的情况下,有效地改善了系统吞吐量。     

一种支持云计算的遥感影像数据组织模型研究

当主用户和次用户在地理上存在一定距离时,由于次用户到达主用户系统的信号不同步,会产生异步干扰,此干扰不但影响主用户系统,使得其干扰增大,也会影响次用户系统,使得次用户系统传输速率损失,特别是误比特性能上升。为了消除异步干扰对主次用户系统的影响,提出了一种基于最小均方误差的预编码方法,此方法在预编码阶段就预先消除了异步干扰,并且是在保证主用户的服务质量基础上进行的。通过分析和仿真结果表明,所提方案在对主用户系统干扰受限的条件下,有效提升了次用户系统和次用户系统的容量,同时提高了次用户系统传输的可靠性。     

认知无线电中发射端多波束形成算法及接收端低旁瓣波束形成算法

在认知用户基站发射端,针对多用户产生多波束使每个波束的主瓣方向对准目标信号 而零陷对准干扰方向,实现多用户同频通信从而提高频谱的利用率。而接收端需要波束形成 算法具有抗干扰的能力,因此,本文提出了适用于授权用户基站接收端的低旁瓣波束形成算 法,在主用户面对干扰时,其接收信号质量不会大幅下降。仿真实验验证了本文的算法。     

Call for Papers The 6^th International Conference on Grid and Cooperative Computing

Recent years have seen rapid advances in various grid-related technologies, middleware, and applications. The GCC conference has become one of the largest scientific events worldwide in grid and cooperative computing. The 6th international conference on grid and cooperative computing (GCC2007) Sponsored by China Computer Federation (CCF),Institute of Computing Technology, Chinese Academy of Sciences (ICT) and Xinjiang University ,and in Cooperation with IEEE Computer Soceity ,is to be held from August 16 to 18, 2007 in Urumchi, Xinjiang, China.     

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.     

法律信息库系统

本文分析了法律数据库的结构和特点，介绍了采用面向对象设计方法和超文本数据库技术开发和实现法律信息库系统将作为重要网络资源之一为不同用户进行法律咨询服务。     

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.     

International Journal of Automation and Computing Table of Contents

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Information for authors

正SCIENCE CHINA Information Sciences(Sci China Inf Sci),cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China,and published by Science China Press,is committed to publishing highquality,original results of both basic and applied research in all areas of information sciences,including computer science and technology;systems science,control science and engineering(published in Issues with odd numbers);information and communication engineering;electronic science and technology(published in Issues with even numbers).Sci China Inf Sci is published monthly in both print and electronic forms.It is indexed by Academic OneFile,Astrophysics Data System(ADS),CSA,Cabells,Current Contents/Engineering,Computing and Technology,DBLP,Digital Mathematics Registry,Earthquake Engineering Abstracts,Engineering Index,Engineered Materials Abstracts,Gale,Google,INSPEC,Journal Citation Reports/Science Edition,Mathematical Reviews,OCLC,ProQuest,SCOPUS,Science Citation Index Expanded,Summon by Serial Solutions,VINITI,Zentralblatt MATH.     

Erratum to: Fast global kernel fuzzy c-means clustering algorithm for consonant/vowel segmentation of speech signal

正Erratum to:J Zhejiang Univ-Sci C(ComputElectron)2014 15(7):551-563doi:10.1631/jzus.C1300320The original version of this article unfortunately contained mistakes.Algorithm 6 should be as follows:Algorithm 6 FGKFCM-F clustering Input:(1)X={x_1,x_2,…,x_N},,x_iR~d,i=1,2,…,N,the dataset;(2)C,1C≤N,the number of clusters;(3)ε0,the stopping criterion;     

Journal of Zhejiang University-SCIENCE C (Computers & Electronics) Total contents

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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.