认知无线电网络双天线多信道MAC协议

在认知无线电网络中,媒体接入控制(MAC)协议的主要功能包括信道感知、选择和接入控制,其中感知时间和传输时间的长度对网络的性能有着重要的影响。在动态无线网络环境下,如何合理分配感知时间和传输时间是个挑战性问题。提出了一种双天线多信道分布式认知无线电MAC（TM-MAC）协议,不需要在传输之前对信道进行感知。节点可以在其它节点传输数据的同时对频谱资源进行检测,然后利用空闲的频谱资源通信。建立了数学模型分析在饱和网络状况下MAC协议的吞吐量。仿真分析表明TM-MAC协议能够有效提高网络的吞吐量。     

基于QoS的分布式认知无线电网络多信道MAC协议

在分布式认知无线电网络中,动态资源利用不足和中心控制单元的缺失使其MAC层协议的设计面临很多挑战。针对认知无线电网络的特点,提出了一种新的MAC协议,该协议通过在信道预约阶段优先考虑对时延要求较高的应用,来保证网络对这类应用的QoS;同时还解决了认知无线电网络中频谱的利用率低和隐藏终端两个热点问题。为分析研究该协议的性能,首先提出了一种新的分析模型。然后将这种新的MAC协议与两种典型的MAC协议进行了仿真对比,结果表明该协议提高了网络的吞吐量。最后通过数值分析和仿真证实了本协议设计简单高效,具有较高的频谱利用率,不但满足了时延敏感性应用的QoS需求,而且还能有效地解决多信道隐藏终端的问题。     

认知无线电网络路由协议综述

认知无线电网络中的节点具有动态频谱接入的特点,进而产生可用频谱的不规则性,这与传统无线多跳网络有很大不同,从而导致了认知无线电网络路由面临新的挑战.在介绍认知无线电网络路由的特点之后,对路由协议进行了初步分类.然后着重分析了目前认知无线电网络较为重要的路由协议的主要机制,详细比较了路由协议的主要类别和特点,最后总结了好的认知无线电网络路由协议的特点,并对未来发展趋势进行了初步展望.     

认知无线电网络分布式多信道MAC协议*

在认知无线电网络中,MAC协议用于信道感知、选择和接入控制。以单网卡多信道MAC（MMAC）协议为基础,依据IEEE 802.22标准定义的静默期管理的两阶段感知策略,提出一种认知无线电网络分布式多信道MAC（CR-MMAC）协议。将两阶段感知机制和分布式协商融入MMAC协议,利用空闲频谱进行数据传输,并在MMAC协议ATIM窗的数据信道协商阶段引入预约机制,以避免选择同一信道的认知节点对在后续数据传输阶段再利用CSMA/CA造成的竞争碰撞。仿真对比分析表明,CR-MMAC协议能提高网络吞吐量、降低通信时     

认知无线网络信道接入协议

由于认知无线网络(cognitive radio network,简称CRN)固有"二次利用"的特性,使其日益得到重视.而作为CRN核心构成的MAC(medium access control)协议,业已成为当前各研究机构的一个热点.主要对频谱感测技术、信道接入技术等MAC层核心设计问题进行了探讨,并针对认知无线网络MAC的特性及需求进行了分析,然后对设计MAC频谱感知技术、信道接入技术、频谱共享技术等相关研究进展进行了归类总结.最后指出了当前面临的主要研究难点及挑战,并提出了一些方向性建议.     

MAC Protocols for Cognitive Radio Networks

由于认知无线网络(cognitive radio network,简称CRN)固有“二次利用”的特性,使其日益得到重视.而作为CRN核心构成的MAC(medium access control)协议,业已成为当前各研究机构的一个热点.主要对频谱感测技术、信道接入技术等MAC层核心设计问题进行了探讨,并针对认知无线网络MAC的特性及需求进行了分析,然后对设计MAC频谱感知技术、信道接入技术、频谱共享技术等相关研究进展进行了归类总结.最后指出了当前面临的主要研究难点及挑战,并提出了一些方向性建议.     

认知无线电网络MAC层协议研究

认知网络按照一定的准则划分为若干个簇,簇内共享一条信道用于交换控制信息,这种以分簇的方式实现按区域共享信道是认知无线电MAC层频谱共享问题的解决方法之一.为了使分簇结构更加有效的工作,本文提出了一种针对分簇结构的MAC层协议.在该协议中,信道接入时间被划分成一系列的超级帧,超级帧的各个时段均对应簇节点的具体操作,以此支撑簇结构稳健地应对主用户行为.仿真结果表明,本文提出的MAC协议在中高网络负载情况下能获得较高的网络吞吐量以及较低的传输时延.     

认知车载网中基于TDMA/CSMA的混合多信道MAC协议研究

在传统车载自组网(Vehicular Ad Hoc Network, VANET)中采用认知无线电(Cognitive Radio, CR)技术可以解决无线电频谱资源短缺的问题,该技术形成了新兴的认知车载网络(CR-VANET),其关键技术之一是设计高效可靠的介质访问控制(Medium Access Control, MAC)协议。MAC协议在很大程度上影响着车载移动环境的吞吐量,丢包率和传输时延等性能,基于认知车载网中MAC协议的要求,提出了一种TDMA与CSMA相结合的多信道MAC协议(CRTC-MAC)。在固定时隙分配时采用基于无竞争的TDMA访问策略,在动态时隙分配时采用基于竞争的CSMA接入方案,并在此基础之上对传统的TDMA和CSMA访问方式进行了改进。性能分析和仿真结果表明,所提出的MAC协议能有效降低节点间数据包传输时所产生的碰撞,改善网络性能。     

基于跨层议价博弈的认知无线电网络资源优化分配策略

如何合理分配有限的频谱资源是认知无线电网络的核心问题之一.通过对物理层功率控制和MAC层带宽分配需求的研究,建立以最大化系统吞吐量为目标的跨层优化模型.并在该模型的基础上设计一种基于跨层议价博弈的带宽与功率分配算法(Bandwidth and Power Allocation Algorithm-Cross Layer Bargaining Game,BPAA-CLBG).仿真结果表明该算法可以有效地提高认知无线电网络的频谱利用率,且在系统吞吐量方面较现有算法有明显的改善.     

大规模认知无线电网络的时延分析

时延作为无线网络的最基本的性能之一,对网络信息分发、路由协议设计、节点部署等都具有重要意义。与传统的无线网络不同,认知无线电网络的频谱资源具有动态变化性,该特性会对网络时延产生极大的影响。因此,如何对动态频谱环境下的大规模认知无线电网络进行时延分析,是一项很具挑战性的课题。为此,首先对动态频谱环境进行建模,将认知用户的频谱接入过程建模为一个连续时间的马尔可夫链,并建立认知用户的生存函数来量化授权用户活动以及信道数量对频谱环境的影响;其次,将上述模型与首次通过渗流理论结合起来,研究了大规模认知无线电网络时延的伸缩规律,并获取了更为精确的时延与距离比的上限值。理论分析及仿真结果表明,动态频谱环境与密度一样会对时延产生极大影响。研究结论对认知无线电网络的设计具有重要的指导意义。     

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.     

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.     

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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