Access control in wireless sensor networks

Nodes in a sensor network may be lost due to power exhaustion or malicious attacks. To extend the lifetime of the sensor network, new node deployment is necessary. In military scenarios, adversaries may directly deploy malicious nodes or manipulate existing nodes to introduce malicious “new” nodes through many kinds of attacks. To prevent malicious nodes from joining the sensor network, access control is required in the design of sensor network protocols. In this paper, we propose an access control protocol based on Elliptic Curve Cryptography (ECC) for sensor networks. Our access control protocol accomplishes node authentication and key establishment for new nodes. Different from conventional authentication methods based on the node identity, our access control protocol includes both the node identity and the node bootstrapping time into the authentication procedure. Hence our access control protocol cannot only identify the identity of each node but also differentiate between old nodes and new nodes. In addition, each new node can establish shared keys with its neighbors during the node authentication procedure. Compared with conventional sensor network security solutions, our access control protocol can defend against most well-recognized attacks in sensor networks, and achieve better computation and communication performance due to the more efficient algorithms based on ECC than those based on RSA.     

用C#.NET设计与实现三种数据库接口的统一模式

目前,在许多工程开发的过程中,都要和数据库相关联。例如:Oracle 9i,SQL Server 2000和Access 2003等。虽然每种数据库与Visual Studio.NET 2003中的C#连接方式多种多样,但也有很多相似之处,可以将相似的地方用统一方法写成实用的接口。这样可以很好地对C#Windows Forms程序和ASP.NET程序进行架构的组织,配合微软最近推出的ASP.NET 2.0版本的架构。可以将数据实体层(即数据库层)、业务逻辑层、界面表示层等进行分类。针对这3种数据库与C#.NET接口的相似性来写一种具有统一模式的接口。     

电子商务下商品价格变动分析

本文基于西方经济学的局部均衡分析范式探讨由于电子商务降低产品边际成本，最终会对市场结构和社会物价水平造成的影响。得出了电子商务的普及有提高社会总产出和福利水平的作用的结论。     

后3G时代LTE异军突起

介绍了下一代无线网络LTE(Long Term Evolution,长期演进)的背景和发展状况.分析了LTE的技术特征,阐述了LTE网络结构与核心技术,并通过与WiFi(WirelessFidelity)及WiMAX(World wide Inter operability for Microwave Access)的各项性能作比较,着重分析了LTE的技术优势.最后,指出了LTE在个人通信市场所面临的应用前景与挑战.     

三网融合下PON网络维护管理方法探讨

目前三网融合在我国已经进入了实施启动阶段。本文介绍了在三网融合进程中电信运营商PON网络的状况,分析了电信运营商PON网络维护管理工作的现状和问题,提出了基于网络资源管理系统的PON网络维护管理模式。     

A NEW ANALYZING APPROACH TO MODELING SLOTTED MULTIPLE ACCESS SYSTEMS

In this paper, the analyzing approaches proposed by Zhao Dongfeng, et al.(1997) have been extensively studied. The average cyclic times of the slotted multiple access systems are analyzed by using the average cycle method. Analytic formulae for mean values of a successful period and a colliding period and an idle period are derived. The upper bounds of the system throughput with capture effect and collision resolution are provided. Finally, the simulation results of the slotted multiple access channels are given.     

全球移动卫星系统投资风险分析

在人们普遍给予全球移动通信系统高技术高效益评价的同时，其高投入高成本所带来的高负险也是不容忽视的。根据市场竞争的观点它同样面临着行为内和行业外多种力量的竞争。特别是近年来地面无线通信的迅速发展对该产业的怅惘敢巨大冲击。     

中国移动电话用户市场调查

中国移动电话市场发展迅速，目前用户总数已位居世界第三。近期的市场调查表明，移动电话市场中呈现出品牌意识强，中低档手机市场大，购机者关心因素多，个人购机比例高等现象。另外，中文手机仍然占主体，黑色手机备受用户青睐。     

On hedging in finite security markets

A market is considered where trading can take place only at discrete time points, the trading frequency cannot grow without bound, and the number of states of nature is finite. The main objectives of the paper are to show that the market can be completed also with highly correlated risky assets, and to describe an efficient algorithm to compute a self-financing hedging strategy. The algorithm consists off-line of a backwards recursion and on-line of the solution, in each period, of a system of linear equations; it is a consequence of a proof where, using a well-known mathematical property, it is shown that uniqueness of the martingale measure implies completeness also in our setting. The significance of ‘multistate’ models versus the familiar binomial model is discussed and it is shown how the evolution of prices of the (correlated) risky assets can be chosen so that a given probability measure is already the unique equivalent martingale measure.     

Amalgamation of partitions from multiple segmentation bases: A comparison of non-model-based and model-based methods

The segmentation of customers on multiple bases is a pervasive problem in marketing research. For example, segmentation service providers partition customers using a variety of demographic and psychographic characteristics, as well as an array of consumption attributes such as brand loyalty, switching behavior, and product/service satisfaction. Unfortunately, the partitions obtained from multiple bases are often not in good agreement with one another, making effective segmentation a difficult managerial task. Therefore, the construction of segments using multiple independent bases often results in a need to establish a partition that represents an amalgamation or consensus of the individual partitions. In this paper, we compare three methods for finding a consensus partition. The first two methods are deterministic, do not use a statistical model in the development of the consensus partition, and are representative of methods used in commercial settings, whereas the third method is based on finite mixture modeling. In a large-scale simulation experiment the finite mixture model yielded better average recovery of holdout (validation) partitions than its non-model-based competitors. This result calls for important changes in the current practice of segmentation service providers that group customers for a variety of managerial goals related to the design and marketing of products and services.