802.16d协议OFDM接入同步误差影响研究

本文首先对802.16协议以及物理层正交频分复用(OFDM)接入方式的协议规范进行了简单介绍。然后在阐述了OFDM的原理和实现技术之后重点针对同步误差的对802.16d物理层OFDM接入方式的影响进行了研究与仿真,并得出结论。     

IEEE802.16d固定宽带无线接入技术及应用

宽带无线接入技术发展很快,方式很多,IEEE802.16d是另一种宽带无线接入方式,主要应用于城域范围,可应用于话音、图像、视频及数据等的传输,也是家庭等“最后一英里”接入方式手段之一并具有诸多优点。本文对IEEE802.16d进行了较为详细地介绍和分析,包括主要特点、协议模型、空中接口规范物理层、MAC层以及主要应用。     

IEEE802.16d固定宽带无线接入技术及应用

宽带无线接入技术发展很快,方式很多,IEEE802.16d是另一种宽带无线接入方式,主要应用于城域范围,可应用于话音、图像、视频及数据等的传输,也是家庭等“最后一英里”接入方式手段之一并具有诸多优点。本文对IEEE802.16d进行了较为详细地介绍和分析,包括主要特点、协议模型、空中接口规范物理层、MAC层以及主要应用。     

IEEE802．16d系统的帧同步和频率同步研究

基于IEEE 802.16协议的WiMAX技术是目前BWA系统的热点之一,对于NLOS非视距传输环境,IEEE802.16d协议采用了OFDM技术作为调制方式.文章针对OFDM对定时和频偏敏感的问题进行了研究,给出了适用于IEEE 802.16d帧结构的帧同步和频偏估计算法,仿真结果表明该算法具有良好的性能.     

IEEE 802.16d WMAN物理层仿真及性能分析

作为一种固定宽带无线接入系统，IEEE 802.16d可以提供高达70Mbps的峰值传输速率以支持不同QoS类型的综合数据业务的部署。其物理层协议为支持这一高带宽特性集合了多种调制和信道编码技术，包括随机化、RS-CC编码、交织、多种数字调制技术、OFDM技术，还有可选择采用的空时编码技术。这些技术综合起来的系统性能如何，至今还没有详细准确的结果，而这些结果却是支持自适应链路技术的重要基础参数。文章按照16d协议对物理层进行了仿真和性能分析，提出并验证了用于性能分析的理论近似公式。     

WiMAX安全研究

研究了最新的WiMAX IEEE802.16d/e的安全机制问题.WiMAX在融合了PMP与MESH接入方式同时,仍然存在诸多安全漏洞.对当前安全方面的主要研究工作思路进行了总结,并提出协议改进向.     

无线宽带固定接入系统的安全性分析

无线宽带固定接入系统提供了一种高速、灵活的接入方式，文章介绍了802.16标准的认证机制，利用BAN逻辑进行了安全性分析。针对协议分析的结果，提出了基于基站证书的协议的改进。     

WiMAX认证方案研究

WiMAX安全要实现两大目标:一是为整个无线网络提供机密性保护;二是提供网络接入控制功能。IEEE802.16的安全子层采用了认证客户端/服务器密钥管理协议,在该协议中基站(即服务器)能够对分发给客户端SS的密钥进行控制。本文首先分析了WiMAX网络物理层和MAC层面临的安全威胁,然后给出了WiMAX网络安全体系架构。最后,对散列消息认证码(HMAC)、X.509证书和可扩展认证协议(EAP)进行了详细的介绍。     

IEEE 802.16及WiMAX技术和应用介绍

本文简要介绍宽带无线接入技术(BWA)的技术概要和发展新动态,重点介绍了IEEE802.16标准的物理层技术,并简单讨论了WiMAX与其它无线技术的相容性问题     

一个提高WiMax服务质量的带宽分配调度算法研究

随着接入网络作为连接用户终端与核心网络的纽带的倍受关注,用户越来越关注数据传输的QoS(服务质量)问题。在IEEE802.16协议的MAC层定义了比较完善的QoS机制。但QoS机制中的核心问题,带宽调度算法,协议没有作出明确的阐述和定义。该文在已有典型算法基础上,吸收、采纳了已有算法中适合于IEEE802.16协议的带宽调度的方法,并结合IEEE802.16协议关于QoS的定义,提出了一个针对IEEE802.16协议的PMP(点对多点)模式下集中式的带宽分配调度算法。并在NS2模拟环境下对算法进行了测试。     

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