浅谈挠性线路板外角精度的控制

文章以挠性线路板的外角精度控制为主题,根据影响外角精度的因素,再结合在生产制作过程中逐渐积累的一些经验,综合讲述了如何提高具有外角要求产品的精度。     

通信电源系统的蓄电池维护方案之探讨

通信电源设备中蓄电池的测试和维护是一项重要而繁重的工作，选用最佳的方案及优质的测试维护设备能让您的工作事半功倍，万无一失。     

Interference power statistics in ad-hoc and sensor networks

There exist accurate calculation methods for estimation of interference power sum statistics in fixed-topology wireless networks based on the log-normal shadowing radio model. Here we publish essential additions to these estimation methods to expand their use to sensor networks and ad-hoc networks with changing topology. In our calculations we take into account radio propagation conditions, density of nodes, size of the network, traffic load per node and MAC protocol characteristics. The accuracy of our calculation method is verified by simulations. We highlight the influence of MAC protocols on interference and show that an increase in network size or in node density does not necessarily lead into higher interference values. Our results can be deployed to estimate the network capacity. Ramin Hekmat received M.Sc. degree in electrical engineering from Delft University of Technology (TU Delft) in the Netherlands in 1990. He worked since then for several telecommunication companies in the Netherlands and the United States in Research and Development as well as managerial positions. In September 2005 he obtained Ph.D. degree for his work related to Ad-hoc Networks form TU Delft. Currently he is working as assistant professor in the faculty of Electrical Engineering, Mathematics and Computer Science of TU Delft. His prime research interest includes multi-user communication systems, wireless communications and peer-to-peer networks. Email: r.hekmat@ewi.tudelft.nl Mailing address: Delft University of Technology Electrical Engineering, Mathematics and Computer Science P.O. Box 5031 2600 GA Delft The Netherlands. Piet Van Mieghem has obtained the Master and Ph. D. in Electrical Engineering from the K.U.Leuven (Belgium) in 1987 and 1991, respectively. He has joined the Interuniversity Micro Electronic Center (IMEC) from 1987-1991. He was a visiting scientist at MIT, department of electrical engineering from 1992-1993. From 1993 to 1998, he was working in Alcatel Corporate Research Center in Antwerp where he has gained experience in performance analysis of ATM systems and network architectural concepts of both ATM networks (PNNI) and the Internet. Currently, he is full professor at Delft University of Technology with a chair in telecommunication networks. The main theme of the research is evolution of the Internet architecture towards a broadband and QoS-aware network. Email: p.vanmieghem@ewi.tudelft.nl Mailing address: Delft University of Technology Electrical Engineering, Mathematics and Computer Science P.O. Box 5031 2600 GA Delft The Netherlands.     

Analysis of bandwidth allocation algorithms for wireless personal area networks

A major issue in the design and operation of ad hoc networks is sharing the common spectrum among links in the same geographic area. Bandwidth allocation, to optimize the performance of networks in which each station can converse with at most a single neighbor at a time, has been recently studied in the context of Bluetooth Personal Area Networks. There, centralized and distributed, capacity assignment heuristics were developed, with applicability to a variety of ad hoc networks. Yet, no guarantees on the performance of these heuristics have been provided. In this paper, we extend these heuristics such that they can operate with general convex objective functions. Then, we present our analytic results regarding these heuristics. Specifically, we show that they are β-approximation (β<2) algorithms. Moreover, we show that even though the distributed and centralized algorithms allocate capacity in a different manner, both algorithms converge to the same results. Finally, we present numerical results that demonstrate the performance of the algorithms. Randeep Bhatia received the Ph.D. degree in Computer Science from University of Maryland, the M.S. degree in Mathematics and Computer Science from University of Illinois at Chicago and the B.Tech. degree in Computer Science and Engineering from Indian Institute of Technology, Delhi. He is currently with the High Speed Networks Research Department at Bell Labs, Lucent technologies, working on network design, traffic engineering and scheduling algorithms. His current research interests are in the area of QoS for multimedia services in wireless data networks. Adrian Segall received the B.Sc. and M.Sc. degrees in electrical engineering from the Technion, Israel Institute of Technology in 1965 and 1971, respectively, and the Ph.D. degree in electrical engineering with a minor in statistics from Stanford University in 1973. After serving active duty in the Israel Defense Forces, he joined in 1968 the Scientific Department of Israel’s Ministry of Defense. From 1973 to 1974 he was a Research Engineer at System Control Inc., Palo Alto, CA and a Lecturer at Stanford University. From 1974 to 1976 he was an Assistant Professor of Electrical Engineering and Computer Science at the Massachusetts Institute of Technology. From 1987 to 1998 he was on the faculty of the Department of Computer Science at the Technion. He is presently Benjamin Professor of Computer-Communication Networks in the Department of Electrical Engineering, Technion, Israel Institute of Technology. From 1982 to 1984 he was on leave with the IBM T.J.Watson Research Center, Yorktown Heights, NY. He held visiting positions with IBM, AT&T and Lucent Bell Labs. His current research interests are in the area of optical networks, wireless, sensor and ad-hoc networks. Dr. Segall is an IEEE Fellow and has served in the past as Editor for Computer Communication Theory of the IEEE Transactions on Communications, Editor for the IEEE Information Theory Society Newsletter and Senior Editor for the IEEE Journal on Selected Areas in Communications. He was selected as an IEEE delegate to the 1975 IEEE-USSR Information Theory Workshop, and is the recipient of the 1981 Miriam and Ray Klein Award for Outstanding Research and of the 1990 Taub Award in Computer Science. Gil Zussman received the B.Sc. degree in Industrial Engineering and Management and the B.A. degree in Economics (both summa cum laude) from the Technion—Israel Institute of Technology in 1995. He received the M.Sc. degree (summa cum laude) in Operations Research from Tel-Aviv University in 1999 and the Ph.D. degree in Electrical Engineering from the Technion—Israel Institute of Technology in 2004. Between 1995 and 1998, he served as an engineer in the Israel Defense Forces. He is currently a Postdoctoral Associate in the Laboratory for Information and Decision Systems in MIT. His current research interests are in the area of ad hoc and sensor networks. In particular, he is interested in energy efficient protocols, medium access control protocols, and personal area networks. Gil received the Knesset (Israeli Parliament) Award for distinguished students, the Best Student Paper Award at the IFIP-TC6 Networking 2002 Conference, and the IEEE Communications Magazine Best Paper Award at the OPNETWORK 2002 Conference. In 2004 he received the Marie Curie Outgoing International Fellowship and the Fulbright Fellowship.     

Accurate estimation of capacities and cross-traffic of all links in a path using ICMP timestamps

The estimation of the link capacity and its available bandwidth in an end-to-end path is crucial for network management, admission control and flow control for adaptive applications. This paper introduces an estimation mechanism able to accurately estimate the available bandwidth of all links in an end-to-end path, through its capacity and cross-traffic estimation. The estimation procedures resort to the dispersions of packet pairs and trains using the concepts of ICMP Timestamp and Traceroute that, efficiently used together, enable the measurement of the dispersions in all links in the path. These mechanisms were evaluated through simulation experiments, where we analyzed the influence of the several network parameters on each estimation mechanism. The results show that these estimation methods are able to accurately estimate both the capacity and the cross-traffic of all links in a path with moderate length and with low overhead.     

移动通信网位置区和路由区的规划思路分析

首先介绍了移动通信网中位置区和路由区的概念,对影响规划位置区的容量和边界划分等诸多因素进行了分析,并结合工程经验和数据分析,总结出位置区及路由区的规划和边界划分原则。     

Modular Precoding Based on Zero Forcing in Large Scale Antenna Systems with Imperfect Channel State Information

In Large scale antenna systems (LSAS), the user number is usually much less than the number of base station antennas. By leveraging this characteristic, Modular precoding based on zero forcing (MZF) is pro-posed to achieve higher spectrum efficiency than Maximum ratio combining (MRC), while preserve the advantage of distributive processing. The achievable rates of the MZF, MRC and Zero forcing (ZF) are derived under the general-ized model of imperfect Channel state information (CSI). The imperfect CSI model includes the channel estimation delay, the noise in the pilot channel, and the pilot contam-ination. The analytical achievable rates match the simula-tions even with a small number of base station antennas. When the antenna number approaches to infinity, the an-alytical achievable rates of MZF converge to the analytical achievable rates of ZF.     

面向无线网络容量和覆盖优化的分组调度算法

为了实现无线网络资源的高效利用,该文基于增强边缘用户调度公平性的目标提出一种通过参数来调节覆盖和容量目标的比例公平(-CCPF)分组调度算法,其可用于网络覆盖和容量优化(CCO)。该文首先证明该算法的收敛性,之后基于业务量分布、功率调整及该分组调度算法提出CCO机制,并在长期演进(LTE)网络下的一个试验的规则场景和一个基于实际网络数据的非规则场景中进行了仿真,验证了该机制能够在覆盖-容量优化机制下,实现更合理的资源利用率(RO),并同比例公平(-PF)算法相比在理论场景和实际场景下平均用户吞吐量分别提升了19%和33%。     

UMTS性能增强技术研究

指出开发UMTS性能增强技术的关键驱动因素,介绍了扩容天线、多用户检测和软件无线电技术的基本原理与功能,并提出了一种面向分组的体系结构。