Variability study for 3G and beyond mobile communications

Convolutional codes have been widely used in DS-CDMA systems for good performance and relatively low decoding complexity. In this article we, starting from the theoretical point, study the performance of convolutional codes in an environment where E/sub b//N/sub 0/ changes sinusoidally. We study four cases of this scenario. For each case we obtain some conclusions and give their analysis. In this article a very important characteristic, named additivity, is acquired.     

利用总积分散射仪研究不同清洗技术下的基片表面粗糙度

为了探讨不同清洗工艺对基片表面微观粗糙度的影响,利用总积分散射(TIS)仪分别对不同条件下超声清洗的K9玻璃基片,End-hall离子源清洗的K9玻璃基片和Kaufmann离子源清洗的熔石英基片的表面均方根(RMS)粗糙度进行了系统表征.结果表明,K9玻璃基片经不同条件下的超声波清洗后,由于清洗过程中表面受到损伤,其RMS粗糙度均有所增加;而对于End-hall离子源和Kaufmann离子源清洗的基片,其表面RMS粗糙度的变化受清洗过程中离子束流、清洗时间和离子束能量等实验参量的影响较为明显,选择合适的实验参量可以降低基片表面粗糙度.     

Small AC Driving Voltage for MZI-Based GaAs–GaAlAs Electrooptic Modulators/Switches With Coplanar Electrodes

We report a method to achieve a small ac driving voltage for high-speed multimode interference Mach-Zehnder interferometer GaAs-GaAlAs electrooptic modulators and switches with coplanar electrodes for polarization-insensitive operation. By biasing the devices in the reverse break-down region, the ac driving voltage can be as small as 3 V. Such a small ac driving voltage is important for high-speed optical modulators and switches. The physics behind this small ac driving voltage is also discussed.     

基于本体的语义检索技术在题库中的应用

传统的题库并未考虑到题目的语义及题目之间的关系.针对这个问题,介绍了语义网络和本体的概念,探讨了应用本体来构造题库中题目的有关知识,从而形成用知识型题库的方法和基于本体的语义搜索技术来分析题目所涵盖知识点的方法.     

面向卫星-地面协同通信系统的物理层安全传输设计

为增强多窃听者场景下的卫星-地面协同通信系统数据传输安全性,首先建立以卫星链路物理层安全传输速率最大化为优化准则、地面链路传输质量和信号发送功率为约束条件的卫星-地面协同传输优化问题.由于该优化问题的非凸性,随后通过引入辅助变量,将原问题分解为主、次两个子问题进行迭代求解,其中主问题为一维搜索问题,次问题则需进一步借助半正定松弛和矩阵变换方法转换为等价凸优化问题.最终,提出一种基于物理层安全的卫星-地面协同传输设计方案.计算机仿真结果表明,信号发射功率和卫星天线数的增加可提升系统安全速率,而窃听者数量的增加则会使得系统安全性降低.     

EPON关键技术及其展望

无源光网络接入技术由于其支持高带宽和长距离等特性,将成为解决最后一公里问题的最佳方案.文章对以太无源光网络(EPON)的ONU自动发现、ONU测距、动态带宽分配等关键技术进行了分析和研究,最后对其技术发展方向10G EPON以及WDM-PON进行了展望.     

Predistribution and local collaboration-based group rekeying for wireless sensor networks

When a sensor network is deployed in a hostile environment, an adversary may launch such attacks as eavesdropping the communications and compromising sensor nodes. Using the compromised nodes, he may inject false sensing reports or modify the reports sent by other nodes. To defend against these attacks, researchers have proposed symmetric group key-based schemes. In these schemes, however, if a large number of nodes are compromised, many (sub)group keys will be revealed. This greatly endangers the filtering schemes, making them very ineffective or even useless. To address this problem, we propose a family of predistribution and local collaboration-based group rekeying (PCGR) schemes, which update the compromised group keys to prevent the compromised nodes from understanding the communications between noncompromised nodes or injecting false data. These schemes are designed based on a simple while controversial idea – preload future group keys into sensor nodes before their deployment. To protect the preloaded keys from being disclosed by compromised nodes, we propose a novel technique that requires neighboring nodes to collaborate to derive the future group keys. To the best of our knowledge, our schemes are the first set of distributed group rekeying schemes for sensor networks without involving online key servers. Extensive analysis and simulations are conducted to evaluate the proposed schemes, and the results show that the proposed schemes can achieve a good level of security, outperform several previous group rekeying schemes, and significantly improve the effectiveness of false data filtering.     

盐城市区有线电视网络规划建设方案

从盐城有线电视网络的现状出发,结合新技术、新业务的发展要求,提出了网络改造的紧迫性和必要性。在改造模式上,骨干网采用正反两个方向的信号环组建自愈型光纤环网,接入网采用业内领先的EPON、IAN和EOC技术建设高带宽、高可靠性的双向有线电视网络,真正把盐城有线电视网打造成为宽带综合业务数字网。     

Protel99SE制板Multisim8仿真电路

分析Multisim8和Protel99SE电子设计自动化（EDA）软件各自优势。提出一种将这两种软件相结合的电子电路设计方法。通过典型实例给出从Muhisim8电路仿真设计到Protel99SE印制电路板设计的基本流程．并验证该设计方法的有效性和实用性。