基于PCI总线的信令采集卡的硬件设计

引言 为了满足未来无线多媒体通信需求,早在1985年国际电联就提出了第三代移动通信的概念,许多国家和地区的著名电信设备制造商先后提出了十多种无线接口建议,经过充分协商和融和,最后形成了三大主流标准,即欧洲与日本提出的WCDMA、美国提出的CDMA2000和中国提出的TD-SCDMA.     

高铁3G覆盖难点技术研究

文章针对高铁的位置更新问题提出LAC和RAC规划方法,对存在的移动切换和重选问题提出过渡区等方法并对切换算法提出建议,对高铁长隧道以及特大桥难点覆盖问题提出解决办法,对于山区和海域铁路的信号覆盖规划有一定的参考价值。     

编辑部的故事

把第二把火烧旺 老孙上次在编辑部的故事里请大家向《网管员世界》杂志提出建议和意见,有不少热心的读者就立即给老孙提出了不少意见和建议,很多读者提出的意见和建议非常中肯,非常具有建设意义,老孙在这里谢谢大家了。如果有些读者因为最近这段时间工作太忙或者有其他事情耽误了,没有来得及将您的意见和建议提出来,不要紧,您可以随时给我发电子邮件,提出您的意见和建议,     

分布式仿真系统实时性实现技术研究

针对分布式仿真系统的结构和特点,阐述了计算实时性、通讯实时性和调度实时性3个方面影响系统仿真实时性的主要原因。对于计算实时性问题,提出基于扩展实时操作系统的多线程技术。对于通讯实时性问题,提出采用UDP协议和共享内存技术;对于调度实时性问题,提出采用硬件和软件同步结合的方法来实现时钟同步。通过实践表明,提出的方法是可行和有效的。     

改进的Rabin密码体制安全性分析

Shamir和Schorr对Rabin数字签名方案提出一种有效的攻击方法,称为Shamir攻击.为了避免Shamir攻击,本文提出一种有效的比特位扰乱法(Bit Perturbation).基于Rabin公钥密码体制,Harn和Kiesler提出一种改进的公钥密码体制、数字签名方案和认证加密方案.本文指出Harn和Kiesler提出的密码体制是不安全的,并设计一种安全的数字签名方案.     

网络编码在网络安全中的应用

网络编码的思想在1999年由杨伟豪和张珍首次提出,由Ahlswede等人进一步发展和扩充,安全的网络编码也随即提出。蔡亍和杨伟豪首先针对单信源有向无圈网络给出了安全网络编码的定义和模型,其他研究者也各自提出了不同的安全模型,如J P Vilela提出了轻量级安全的网络编码,K Bhattad提出了弱安全的网络编码等,另外还有抗拜占庭攻击的网络编码。网络编码理论亦在网络纠错中得到了应用,杨伟豪和蔡宁推广了经典纠错码,引入了网络纠错码,杨胜豪在杨伟豪和蔡亍研究的基础上,研究了线性网络编码的重量性质。     

云安全管理体系和建设研究

云安全是云计算和云服务发展面临的重要挑战,云安全所涉及的技术和管理方面的问题也是多方面的.本文对云安全管理体系和建设提出建议,首先分析云计算的安全需求,提出云安全管理体系建议,并对云计算不同发展阶段的重点项目提出安全保障建议.     

从信息安全中挖掘服务和业务价值

从两部委对信息安全监控提出的新需求入手,分析并提出了信息安全发展的两个趋势——个性化和全面有效覆盖。面对新需求通过两个建设方案实例分析,提出如何从信息安全中挖掘服务和业务价值。最后总结了创造信息安全服务价值面临的挑战,并提出信息安全服务架构的思路。     

基于UWB的Ad hoc网络资源分配的研究

基于超宽带的Ad hoc网络的应用,提出了为多媒体业务提供QoS支持的自适应的资源分配方案。方案考虑了超宽带和Ad hoc网络的特性,同时也考虑了QoS的要求。提出的资源分配方案采取了业务区分和资源预留的方法,为链路分配网络资源（速率、功率）。根据吞吐量,丢包率和时延,对提出的方案做了详尽的性能评估,仿真结果证明了提出的方案的优越性。     

对一个基于身份的多重签密方案的分析和改进

Waters提出了一个标准模型下的基于身份的加密和签名方案,Paterson和Schuldt在此基础上提出了一个基于身份的签名方案.Zhang和Xu在上述两个方案的基础上,提出了一个基于身份的多重签密方案.本文指出Zhang-Xu的方案会受到私钥随机化攻击,并在标准模型下提出了一个改进的基于身份的多重签密方案,其中将解...     

A design methodology for low-leakage and high-performance buffer based on deviant behavior of gate leakage

Based on the observation that both subthreshold and gate leakage depend on transistors width, this paper introduces a feasible method to fast estimate leakage current in buffers. In simulating of leakage current with swept transistor width, we found that gate leakage is not always a linear function of the device geometry. Subsequently, this paper presented the theoretical analysis and ex- perimental evidence of this exceptional gate leakage behavior and developed a design methodology to devise a low-leakage and high-performance buffer with no penalty in area using this deviation.     

快速MCP型光电倍增管中暗电流的分析与研究

简单介绍了快速ＭＣＰ型光电倍增管的结构，着重分析了该管型暗电流的来源，最后提出了减小暗电流可采取的一些必要措施。     

微波晶体管电流增益和基极电流非理想因子的温度特性

本文研究了微波晶体管电流增益H_FE和基极电流非理想因子n随温度变化的机理,给出了电流增曾H_FE的温度模型,指出:(1)中电流时电流增益H_PE具有正温度系数,而在小电流时随温度上升迅速增大,在大电流时增大减缓,并会出现负增值,(2)基极电流非理想因子n具有负温度系数.实验结果和理论分析一致.     

电流测量线圈及其在TEA脉冲激光器中的应用

本文提供了电流测量线圈的误差公式。用电流测量线圈测量了TEA脉冲CO2激光器的放电电流。     

一种脉冲振荡电路的分析与设计

采用开关元件控制的恒流充放电是产生稳定非正弦振荡波的主要方法。文章利用施密特(Schmitt)触发器为核心的状态延迟及转换元件，并采用恒流充放电技术，配合精确的时序控制，实现了一种高稳定的低功耗矩形波振荡电路。     

大电流监测信号提取的光收发及信号处理

近年来,大电流的监测成了人们十分关心的问题,这是由于大电流有强磁、高压、电流大等一系列的直接监测所不能克服的问题。这就需要把高压大电流的强电信号,经过提取后变成能在实验室中直接观测的弱电信号。为此,如何从高压大电流的信号中提取出随实时信号变化而实时变化的小信号就变成了一个关键问题。详细介绍了监测信号提取的光收发电路原理和后续信号处理电路,分析了各部分的作用,给出了必要的分析结果。     

Gridded Electron Guns and Modulation of Intense Beams

Gridded guns are useful for producing modulated electron beams. This modulation is generally limited to simple gating of the beam but may be used to apply structure to the beam pulse shape. In intense beams, this structure spawns space-charge waves whose dynamics depend in part on the relative strengths of the velocity and density variations which comprise the initial current modulation. In this paper, the strengths of beam current and velocity modulation produced in a gridded electron gun are calculated, and it is shown that under normal conditions, the initial modulation is dominated by density variation rather than velocity variation     

Design of Components and Circuits Underneath Integrated Inductors

In this paper, we present a study of the eddy current effect of devices placed underneath and inside an on-chip inductor. We verified the performance of such area-saving structures through electromagnetic (EM) simulations and measurement of test structures. We used layout techniques to minimize eddy current loss and magnetic coupling between the devices and the inductor, and constructed a complete voltage-controlled oscillator (VCO) inside an inductor. Measurement results show that this compact VCO has an equal performance in phase noise and output power as compared to a traditional VCO while reducing the area by about 50%. The techniques presented in this paper are general and can be implemented in most layouts without extra post-processing steps.     

Reconstruction of conductivity and current density images using only one component of magnetic field measurements

Magnetic resonance current density imaging (MRCDI) is to provide current density images of a subject using a magnetic resonance imaging (MRI) scanner with a current injection apparatus. The injection current generates a magnetic field that we can measure from MR phase images. We obtain internal current density images from the measured magnetic flux densities via Ampere's law. However, we must rotate the subject to acquire all of the three components of the induced magnetic flux density. This subject rotation is impractical in clinical MRI scanners when the subject is a human body. In this paper, we propose a way to eliminate the requirement of subject rotation by careful mathematical analysis of the MRCDI problem. In our new MRCDI technique, we need to measure only one component of the induced magnetic flux density and reconstruct both cross-sectional conductivity and current density images without any subject rotation.     

Wide-Dynamic-Range and High-Sensitivity Current-to-Voltage Converters

A wide dynamic range and a high sensitivity are often incompatible with each other in analog circuits, such as signal converters or amplifiers. In this paper, we present a method of developing current-to-voltage converters featuring both. It comprises two current-to-voltage conversions. One is to convert the DC component, i.e., the average level of the current input, into a voltage with a nonlinear compression. The other is to apply a “linear” conversion to the signal component of the input current. This conversion is considered to be “linear” as the gain is made to be almost constant if the varying signal is rippling at a given current level, and to increase if the level is changed to be lower. Hence, the gain is adaptive to the input current, i.e., getting stronger if the current signal is weaker, and vice versa. This adaptability is implemented by (a) an adaptive bias by means of the voltage converted from the DC component of the input current, and (b) the current-dependent finite drain-source resistances of MOS transistors. A low-pass current filter is used, in the proposed conversion operation, to separate the DC component of the input current from the signal one. We propose, in this paper, a basic structure of the filter and techniques to improve the filtering quality over a wide current range, also an approach to an effective reduction of the effect of the device mismatch as well. A design example of the proposed conversion is presented in this paper. The simulation results have shown its dynamic range of 5-decades and its sensitivity high enough to detect sub-nA current variations.