在Ad Hoc网络中TCP-SACK性能研究及改进

在Ad Hoc网中,经常发生链路失效和路由变化。TCP把数据包的丢失归结为链路拥塞,所以TCP在Ad Hoc网中表现很差。在本文中通过应用一种新的方法,基于传输包乱序检测与响应方法,研究TCP在Ad Hoc网中的性能。通过实验结果表明,此算法解决了,提高了网络的吞吐量。     

Ad Hoc网络中TCP协议的性能及其改进策略

Ad Hoc 网络的动态自组织特性使得传统的传输层协议不再适用。文中首先阐述 TCP 协议在 Ad Hoc 网络中存在的问题,然后介绍 TCP 协议在无线网络中的改进,接着详细分析 Ad Hoc 网络中 TCP 协议的性能并讨论其改进策略和方法,最后对全文进行小结,并指出今后的工作方向。     

Ad Hoc网络中SNMP代理的研究和实现

研究了在基于TCP／IP体制的Ad Hoc网络中,利用简单网络管理协议SNMP和网管代理解决严重和复杂的网络管理问题。在分析SNMP协议工作原理的基础上,探讨了SNMP代理的工作流程、组成模块和实现方式,并搭建Ad Hoc网络实验环境进行了测试验证。实验结果表明,通过SNMP协议和代理,能够有效管理和控制Ad Hoc网络中的关键参数,降低了系统的复杂程度和技术风险。     

Ad Hoc网络中TCP协议性能分析及其改进策略

TCP协议是传输层最为重要的协议之一,也是因特网实现的关键.但是由于TCP是为有线网络设计的,它固有的机制无法适用无线网络,改进TCP使其适应蓬勃发展的无线网络成为一个迫切需要解决的问题.首先阐述了TCP协议在Ad Hoc网络中存在的问题,然后介绍了TCP协议在无线网络中的改进.接下来,详细分析了Ad Hoc网络中TC...     

吉比特网络CUBIC拥塞控制算法仿真研究

分析了TCP RENO的不足,比较了BIC算法和CUBIC算法,采用响应函数理论比较了三种TCP算法.在吉比特网络环境下对CUBIC算法进行了仿真.仿真研究表明,CUBIC算法能在高速网络环境中有效的提升网络速度,在拥塞丢包严重,网络流量很低时快速恢复网络速度;同时因为拥塞窗口波动太大,高速TCP流的吞吐量变化太大,带宽的利用率很不稳定.     

传输层网络编码性能分析

底层网络随机丢包导致的传输控制协议(TCP)传输性能恶化的问题由来已久.为了保障TCP的吞吐量在无线网络环境下依然能够保持在较好的性能,通过分析传输层网络编码(TCP/NC)协议的基本原理,分别利用NS-2搭建了软件仿真平台和Wi-Fi开发板搭建了硬件仿真平台.在2种平台上分别测试了传输层网络编码的性能并且分析了TCP的拥塞窗口和吞吐量性能.实验结果表明:传输层网络编码能够有效克服底层的随机丢包带来的影响,提升TCP吞吐量.     

Ad Hoc网络负载均衡路由协议研究

网络负载是影响Ad Hoc网络性能的重要因素,网络负荷比较重时,局部的拥塞将导致网络性能的下降,分析研究现有负载均衡路由协议,并利用链路层信息,结合原Ad Hoc路由协议AODV提出了一种跨层负载均衡的路由协议方案,在选路过程中引入负载均衡机制,均衡网络流量,以提高网络时延、分组到达率等性能.最后用NS2软件仿真证明了改进路由算法的优越性.     

TFRC协议在Ad Hoc网络中的改进及仿真

由于TFRC协议不适合Ad hoc网络环境,这将限制TFRC协议在Ad hoc络中的应用。针对TFRC协议在Ad hoc网络中存在的问题,本文在TFRC算法的基础上提出了一种基于丢包区分机制的TFRC拥塞控制策略,它不仅考虑到了差错误码,切换、连接中断引起的丢包对传输的影响,而且还考虑到了实际的链路本身的差错控制导致的乱序包对算法性能的影响,解决TTFRC算法在Ad hoc网络中因不能正确区分拥塞丢包和误码丢包而造成性能下降的问题,改善TTFRC在Ad hoc网络中的性能。仿真结果表明改进协议的性能优于TFRC。     

基于带宽测量技术的TCP拥塞窗口在线学习方法

为了改进传输层协议提高吞吐量,本文提出了一种基于ACK时间间隔的在线学习方法（TCP-Learning）,该方法采用可用带宽测量技术,快速学习网络链路中可用剩余带宽并能够迅速调整TCP拥塞窗口。仿真结果表明,在链路处于良好状态下,TCP-Learning吞吐量略优于Reno和Vegas等传统拥塞控制算法,但在链路较差情况下,TCP-Learning吞吐量明显优于Reno和Vegas等传统拥塞控制算法。     

卫星网中基于时间戳的TCP拥塞控制算法研究

TCP(传输控制协议)拥塞控制机制直接使用在卫星网中存在很多不足。针对卫星网通信时延长、网络环境变化复杂的特点，利用TCP协议中的时间戳扩展选项，设计实现了一种改进的TCP重传和拥塞控制算法，能够根据RTr(Round Trip Time，往返时间)的变化对网络情况进行预测，从而及时重传数据包并调整窗口大小，仿真实验证明改进算法能够很好地提高TCP性能。     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.