窄带信道中基于接收信号相位的密钥容量研究

无线信道具有互易性、时变性和空变性等特点,合法双方可以利用无线信道的特性生成共享密钥。基于此,提出一种密钥容量的求解方法。对窄带信道中基于相关随机源模型的窃听信道进行合理建模,利用信息论及随机信号分析理论,对基于接收信号相位信息的密钥容量进行推导,得到密钥容量的表达式。仿真结果表明,密钥容量随信噪比与合法双方信道相关系数的增大而增大,且基于接收信号相位的密钥容量小于基于接收信号的密钥容量,因此,合法双方为得到更长的密钥,可以进行接收信号包络、相位信息的联合提取。     

不同环境下无线信道密钥生成性能研究

在无线通信物理层安全的研究中,通信双方的信道具有很好的短时互易性,可以从无线信道中提取出相似的信道特征并生成一致的密钥.该技术可以利用无线信道天然的随机性为无线通信系统实时的分配对称密钥.本文利用通用软件无线电平台(USRP)设计并实现了实时的无线信道密钥生成系统.基于设计的无线密钥生成系统,本文在室内房间、室内走廊、空旷室外三种不同场景中的终端固定、终端移动以及人员走动三种不同信道环境下长时间测量了无线信道并生成了密钥.通过分析合法通信双方和窃听者信道状态信息(CSI)的互易性、CSI信息泄露率、CSI随机性、密钥随机性四个指标,详细分析了不同场景及环境下无线信道密钥生成技术的安全性与可靠性.通过实验表明,空旷室外信道随机性最高,室内走廊随机性其次,室内房间随机性最低.此外,周围环境变化愈快,信道随机性愈高.通过选择合适的密钥生成参数,都可以在不同的场景及环境下生成满足随机性要求的密钥.     

非完美信道估计条件下多比特量化无线密钥生成性能分析

针对无线密钥生成过程中的信道估计误差导致信道测量参数互易性差,严重影响通信双方生成密钥一致性的问题,提出了非完美信道估计条件下多比特量化无线密钥生成方案。首先,建立信道估计误差模型,研究非完美信道估计对无线密钥生成的影响,然后设计添加保护带的多比特密钥量化器,通过优化量化参数改善无线密钥性能。推导得到了密钥不一致率（KDR）和有效密钥速率（EKGR）的闭式表达结果,并揭示了导频信号功率、量化阶数和保护带与以上两个密钥性能指标的关系。仿真结果表明：增大发送导频功率可以有效降低密钥不一致率,提高量化阶数可以提升密钥生成速率但KDR也随之升高,增大量化阶数同时选择合适的保护带大小可以有效降低KDR。     

基于侧边协作系统的物理层密钥生成方案

传统侧边协作系统下用于生成密钥的信道特征值是协作信道与直接信道的乘积,这种方案的密钥生成速率较低。为提高密钥生成速率,提出利用两个独立信道的信道特征之和来生成密钥。在前两个时隙,合法通信双方通过信道探测,获得其直接信道的信道状态信息。在后两个时隙,合法双方分别获得各自与协作信道之间的信道状态信息。最后利用直接信道与协作信道的和作为随机密钥源。基于侧边协作系统,分两种情况介绍该方案：单个侧边协作节点,单个双向协作节点。仿真结果表明,该方案可以获得更高的密钥生成速率,并且随着SNR的增加,该方案泄露的信息量趋向于一个常数。     

基于相位响应独立性的衰落信道加密方法

现有的密钥加密方法无法保证密钥分发的安全性。针对上述问题,提出了一种基于信道相位响应独立性的衰落信道加密方法。通过将发送方和窃听方之间的信道化为两个信道的级联计算得出密钥各态历经的安全容量,在此基础上,对离散PSK信源加密的参数进行了讨论,最终实现信息的加密。仿真结果表明,当合法接收方的接收信号相位估计误差为0．001时,误码率会迅速上升为0．5。     

基于纠缠的BB84协议仿真研究

将传统的量子密钥分发协议与纠缠光子对的纠缠特性相结合,提出了一种改进的BB84协议--基于纠缠的BB84协议.为了考察该协议的可行性,利用量子计算语言分别针对协议的正确性和安全性进行了仿真验证,并进一步考察衰落信道对协议工作的影响.仿真结果显示:理想情况下,协议安全工作时密钥生成效率为14/30,接近理论值50%;在存在第三方窃听时,其密钥生成效率仅为5/30,远远小于50%,由此通信双方可以判断出第三方窃听存在.由于信道衰落的影响,实际密钥生成效率远远低于理论值.得出结论:基于纠缠的BB84协议也是绝对安全可靠、切实可行的量子密钥分发协议;为提高密钥生成效率,应尽量减小信道衰落.最后,对协议的应用进行了展望.     

无线传感器网络中一种新的无条件安全密钥协商模型

针对现有无条件安全密钥协商模型中存在的问题,提出了一种获取初始随机相关信息的新模型。实验结果表明,与现有模型相比,新模型和原信源模型和原信道模型在功能上等价,但新模型在保证合法通信双方之间的误比特率不变的情况下,增加了窃听方的误比特率,弱化了窃听方的优势,提高了密钥协商的总信息率。     

物理层安全星座模糊设计方法的性能研究

物理层安全加密技术是一种有效保证信息安全传输的物理层安全方法。此技术通过相位旋转、调制星座多样性、符号模糊、幅度调节和符号顺序变化等手段设计信号星座,保护调制方式与调制符号信息。现有的物理层安全加密技术存在密钥共享不保密和星座模糊度不足等缺点。多符号模糊(Mutiple Inter-symbol Obfuscation,MIO)方案采用人工噪声符号密钥与已调符号矢量叠加的加密方法来解决星座模糊度不足的问题。受MIO的启发,文中将信道系数与已调符号矢量叠加,提出了一种基于星座模糊设计(Constellation Obfuscatio Design,COD)的物理层安全加密方案。在TDD模式和信道互易的条件下,将合法信道的信道系数作为密钥,来解决密钥预分享不保密的问题。文中详细介绍了发端加密与合法接收端解密的完整传输过程,并针对高阶累积量的调制识别和智能攻击型窃听者进行接收处理分析;推导出瑞利衰落信道下的合法接收端误码率理论公式;对合法接收端、高阶累积量的调制识别窃听端和智能攻击型窃听端的误码率进行仿真,并对比了MIO方案合法接收端、窃听端的性能。仿真结果显示:合法接收端误码率为1×10-4时,COD方案的信噪比比MIO方案的低6 dB;对COD方案加密后,当信噪比为0时,调制识别成功率为11.8%,调制识别成功率最高可达25%且在信噪比大于40 dB后保持稳定;前3个数据包中,COD方案智能攻击型窃听端的误码率始终为0.284,知晓起始密钥的MIO方案窃听端的误码率则较低;信噪比在0~54 dB范围内时,合法接收端的误码率性能始终优于调制识别窃听端和智能攻击型窃听端。因此,所提COD方案能够保障安全通信,抵御调制识别和智能攻击型窃听者的攻击,并且COD方案的有效性和可靠性均优于MIO方案。     

物理层安全专栏序言(中英文)

物理层安全技术特别是无线物理层安全技术,利用通信系统物理层的信息为通信提供安全保护,在网络安全、电子对抗中有着广泛的应用.它利设备指纹对设备身份进行识别,进而实施接入控制;利用信道特征为通信双方建立对称密钥,进而保护传输数据的安全;或者通过加大合法信道与窃听信道的差异,使得敌手的窃听变得更加困难.     

一种基于反馈的喷泉码安全传输方法*

针对维纳窃听模型下喷泉码安全传输方法对合法信道质量优势要求高的问题,引入反馈设计了一种喷泉码安全传输方案。在二进制删除信道模型下,合法接收端以一定间隔向发送端反馈输入符号解码情况,发端编码器据此对编解码过程进行更新,尽可能削弱窃听者端前后译码过程的联系,实现合法信道的质量优势不断累积。实验仿真证明,在同等信道条件下本文方法可以有效降低窃听者端输入符号的译出率,且当合法信道与窃听信道质量接近时本文的方案性能提升更为明显。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.