Minimum Duration Outage for CDMA Cellular Systems: A Level Crossing Analysis

Traditionally, outage for CDMA cellular systems has been defined as the signal level (or, more precisely, the signal-to-interference ratio (SIR)) falling below a required threshold. In real cellular environments, it is not the instantaneous drop of the signal strength below the threshold that determines outage. It is, in fact, the duration of time below a threshold that determines outage for cellular systems. Moreover, the static analysis of outage precludes the time correlation in the signals which is important in real systems owing to mobility, fading and power control. In this paper, we analyze minimum duration outages for such systems, where outage is defined as an excursion of the SIR below a level for a certain minimum duration. We formulate the outage condition as a level crossing problem and extend asymptotic results from the theory of level crossings to derive analytical results for the probability of outage. This method enables us to include the time correlation of signals in the analysis as well. The validity of the asymptotic results is verified using some exact results as well as simulations. These minimum duration outages have implications in redefining user capacity and handoff performance.     

粗糙集傅立叶神经网络及在故障诊断中应用

提出了粗糙集和傅立叶神经网络相结合的方法,进行粗糙集布尔逻辑离散化,并在此基础上求取初始隶属函数,以提高隶属函数准确性;再使用傅立叶神经网络进行诊断网络训练。以连续搅拌反应釜故障诊断为实例,研究结果表明,此方法可以减少网络训练时间并提高诊断精度,有效进行故障诊断。     

万安水电站汛期运行研究

万安水电站位于赣江中游，肩负有上下游防洪任务，下游防洪控制点为吉安、石上两站．电站正常运行后，正常蓄水位和防洪高水位均为100．00m，防洪限制水位和死水位均为90．00m．受移民条件限制，初期运行上述特征水位均降低，主汛期4～6月库水位控制在85．00m，发电水头比正常运行降低5m，机组出力受阻达40％以上，致使电站效益不能充分发挥，而4～6月恰为用电高峰期，电网缺电十分严重．为解决主汛期发电和防洪的矛盾，提出了汛期采用预泄办法提高运行水位的方法，即在水文气象预报的有效预见期（18～24h）内，按8800m3／s控制下泄，使库水位从8800m或90．00m泄至85．00m，可满足万安水电站防洪的两个约束条件，即回水对赣州市的影响既不超过0．3m，也不会加重下游的防洪负担．经过1993年6月的实际运行，证明此方法是可行和有效的，提高万安水电站的运行水位，既增加了经济效益，又提高了运行水头，改善了机组工况．     

三峡水轮发电机组高水头区的运行问题

本文从三峡电站水库调度方式出发，分析了机组运行特点以及由这些特点而引起的机组运行稳定性问题、气蚀及泥沙磨损等问题。指出增大最高水头运行时的导叶相对开度是解决上述问题的根本途径，并对与此相关的一些问题进行了讨论。     

Majority and minority carrier traps in monocrystalline CulnSe2

Electron and hole traps in Bridgman-grown monocrystalline CuInSe₂ were investigated by carrying out deep level transient spectroscopy measurements on homojunctions, Al-CuInSe₂ (p-type), and Au-CuInSe₂ (n-type) Schottky junctions. Three hole trap levels and two electron trap levels were observed on these devices. Effects of oxygen and etching on the electron trap level at 182 ±15 meV from the conduction band edge were specifically studied. It was found that the election trap densities in the homojunctions prepared using the CuInSe₂ samples treated in NH₂NH₂ solution, which absorbes oxygen atoms in the samples, were larger than the electron trap densities in the homojunctions prepared using untreated samples. Moreover, the electron trap densities in the homojunctions after prolonged heat treatment in O₂ were less than that without prolonged heat treatment. The results thus suggested that oxygen atoms in CuInSe₂ can reduce the electron trap density of p-type CuInSe₂. The effects of chemical etching on these electron traps were also studied. The excess indium atoms in the CuInSe₂ were considered to affect the electron traps.     

New privilege-based visual cryptography with arbitrary privilege levels

Recently, Hou et al. introduced a novel (2, n) privilege-based visual cryptography scheme (PVCS) with various privilege levels of shadow images. In this scheme, a shadow with a higher privilege contributes more recovered information, while a lower privileged shadow has the less recovery capability. Moreover, the visual quality of stacked result depends on the total sum of privilege levels for all involved shadows in reconstruction. Unfortunately, the PVC scheme has the inconsistency of the contrast of recovered image and the sum of privilege levels. Accordingly, an enhanced Hou et al.’s (2, n)-PVC scheme (EPVCS) is proposed to solve this inconsistency problem. However, the EPVCS is not a general solution to implement all PVCSs with arbitrary privilege levels, and it also has the unequal whiteness of shadows. In this paper, we first extend Hou et al.’s (2, n)-EPVCS with a correct privilege levels achieving the consistency of the contrast and the sum of privilege levels. Then we construct a (2, n)-PVCS to allow arbitrary privilege levels and provide the equal whiteness for each shadow.     

Design and Dimensioning of a WDM Mesh Network to Groom Dynamically Varying Traffic

In this paper, we address the traffic grooming problem in WDM mesh networks when the offered traffic is characterized by a set of traffic matrices—a variant of dynamically changing traffic. We justify the need to address this problem in mesh networks and also argue for the validity of our approach to solve this problem. Our primary objective is to design the network in terms of the number of wavelengths and transceivers required to support any offered traffic matrix. We provide a simple and generic framework to minimize the number of transceivers needed in the network. Simulation results have been presented in contrast with a possible approach, to enable comparison with our solution strategy. An ILP formulation of our approach is also presented.     

基于粗糙集的交通信号控制决策研究

粗糙集理论能够在分析大量经验数据基础上找到用于判断决策的规则,同时允许决策对象中存在一些不太完整的属性,并通过推理得出基本上确定的规则。将粗糙集理论与交通控制结合起来,对交通控制过程中的属性进行了分析,并将粗糙集理论的知识获取和决策分析算法应用到交通信号控制中,提出了一种系统的交通信号控制知识获取和决策的方法,是在解决城市交通状况决策问题上的一次有益的尝试。     

基于LabVIEW的闪变仪软件设计

LabVIEW是虚拟仪器中的一种图形化编程语言,不但能够完成一半的数学运算与逻辑运算和输入输出功能,还带有专门用于数据采集和仪器控制的库函数和开发工具,以及专业的数学分析程序包,基本上可以满足复杂的工程计算和分析要求.由电网电压波动引起的照明灯光闪烁现象,即闪变,给人们的日常工作和生活带来了许多不便.为了统一国际上闪变测试方法与评价标准,国际电工委员会(IEC)制定了闪变仪的测试功能和设计规范.采用低级通用的运算模式,分析了IEC闪变仪灯-眼-脑环节各部分的输入输出信号.根据IEC制定的闪变仪的设计规则,利用LabVIEW建立了数字式闪变仪灯-眼-脑环节的模型,使之能对电压数字信号进行分析处理,得到电压瞬时闪变视感度.仿真结果验证了用灯-眼-脑传递函数形式来逼近视感度系数,能够得到正确的结果.     

基于市县一体平台的县（区）数字电视整转的实践

在基于市县一体的技术业务平台实施县（区）级有线电视数字化整转和运维中,充分结合武进自身管理和个性需求特点,在分前端建设、网络改造、大功率中波台的干扰问题、节目授权、机卡配对、整转断模、机顶盒维修等方面有许多创新举措,使全区30万用户的整转和运维工作取得了快速高效、平稳有序、安全运行的良好成效。