伪基站的工作原理和运行特点

伪基站的设备是一种高科技仪器,一般由主机和笔记本电脑组成.通过短信群发器、短信发信机等相关设备能够搜取以其为中心、—定半径范围内的手机卡信息,通过伪装成运营商的基站,任意冒用他人手机号码强行向用户手机发送诈骗、广告推销等短信息。     

玻璃布包装中锥度收卷的内张力分布及其参数确定

介绍了玻璃布包装过程中收卷张力控制系统的工作原理,并针对在该包装收卷过程中易产生折皱的问题,分析了包装收卷过程中的张力变化规律及其影响因素.从弹性理论出发,给出了锥度张力收卷后卷装的内张力分布公式,通过这些研究,可对不同锥度系数下的包装收卷情况进行估计.最后,给出了不同卷装条件下避免折皱的锥度系数的确定方法.     

常用表面收卷机的结构及特点

在薄膜的生产线中把生产出来的薄膜卷绕在纸芯上成为一卷的辅助设备称为收卷机或卷取机。收卷机的形式有多种，按照卷取的原理一般分为表面收卷、中心收卷、表面跟中心结合式收卷、间隙式收卷等形式。按照收卷的工位分又有单工位、双工位或多工位收卷等形式。这里介绍表面收卷机常见的几种结构形式。     

全自动IC芯片键合机的结构设计及原理

键合是IC元件生产的重要封装过程或工序,需要在芯片键合机上完成.讨论了全自动IC芯片键合机的关键机械结构和原理,包括分片进料结构、送料结构、收料结构、芯片拾放装置的结构、顶针机构、晶圆供送装置等.     

彩色照相冲扩设备技术原理及操作维护（8）

彩色照相冲扩设备技术原理及操作维护（８）上海八一电影机械厂张仁清防光门及防光机构：画幅框从这个包有防止无线进入黑色绒布长条口插入或拉出，而相纸不会因漏光而跑光。收纸导轮：用作相纸在收纸箱入口处导向。收纸摆轮：当收纸完毕给收纸卷一个拉力，使收纸电机电源...     

基于分数阶滑模控制的高精度印刷机纠偏系统研究

目的 解决卷对卷印刷收卷不齐的问题，提高收卷精度。方法 对印刷机收卷纠偏原理进行分析，建立收卷纠偏系统数学模型，提出基于分数阶滑模控制的纠偏算法，分析其稳定性。在不同收卷线速度、不同跑偏干扰输入信号的条件下进行仿真。搭建收卷纠偏实验平台，对2种控制方法进行收卷纠偏控制实验。结果 仿真结果表明，分数阶滑模控制器比传统PID控制器具有较好的动态性能和稳态性能。实验结果表明，分数阶滑模控制算法比传统PID控制具有更高的纠偏精度。结论 分数阶滑模控制算法可以有效提高印刷机收卷纠偏精度，满足高精度印刷要求。     

大功率谐波滤波器的器件选择

介绍了短波发信机用的大功率谐波滤波器器件的选择方法。从大功率谐波滤波器的理论基础，到具体的工程计算都进行了详尽的分析和推导。文中充分考虑了工程实践中会遇到的可靠性等多方面的问题，具有较强的实用指导作用。     

商用制冰机的性能研究

主要介绍商用风冷制冰机的工作原理,并通过试验研究影响商用制冰机性能指标的主要因素,验证环境温度和水温变化对制冰机的制冰时间和收冰时间影响较大,制冰时间长短决定制冰机的产冰量、耗电量、耗水量等,其中环境温度对制冰时间影响最大,对制冰机的影响最为显著.     

平版印刷机收纸牙排运行平稳性探讨

通过对单张纸平版印刷机收纸牙排的运动特性分析,得出了收纸牙排获得良好运动工作状态的条件,同时经过分析讨论给出了设计收纸牙排时应考虑的因素.要获得收纸牙排良好的运行工作特性,应从其结构、材料、收纸牙排的运动导轨及相关辅助措施方面进行综合考虑,以得到满足收纸咬牙排在运送印张时的工作平稳性要求.     

某薄壁壳体收带工艺改进

分析了弹体收带工艺产生的变形问题,理论计算弹带收带所需挤压力,确定收带弹体变形产生的原因,通过改进收带工艺和夹爪结构、优化调整收带芯子与弹体内膛配合间隙,减少了薄壁弹体收带变形,降低了收带废品率,保证了薄壁弹体收带质量,节约了生产成本.     

Water-vapor detection using asynchronous THz sampling

The use of a fiber-coupled terahertz (THz) transmitter/receiver pair for spectroscopic detection of water vapor is investigated. Transmission signals of an alumina cylinder demonstrate that the measurement approach can be applied in a windowless ceramic combustor. First, a conventional commercial transmitter/receiver pair is used to make measurements for frequencies to 1.25 THz. Water-vapor absorption is clearly evident within the alumina transparency window and is readily modeled using existing databases. A variety of data-acquisition schemes is possible using THz instrumentation. To assess signal-collection techniques, a prototype THz transmitter/receiver pair is then used with the asynchronous optical-sampling (ASOPS) technique to obtain asynchronous THz-sampling signals to 1 THz without the need for an optomechanical delay line. Two mode-locked Ti:sapphire lasers operating at slightly different repetition rates are used for pumping the transmitter and receiver independently to permit a complete time-domain THz signal to be recorded. The resulting repetitive phase walkout is demonstrated by collecting power spectra of room air that exhibit water-vapor absorption.     

Ultrasonic Phased Array Device for Acoustic Imaging in Air

An ultrasonic phased array device is developed to provide mobility aid for visually impaired people. To perform acoustic imaging, two different linear transducer arrays are constructed using commercially available transducers. The transmitter and receiver arrays are formed with six and four transducer elements, respectively. Individual transducer elements are discrete components with a radius of 1.9 wavelengths and a half-power beamwidth of 43$^{circ}$ at 40.8 kHz center frequency. The transmitter array is formed by aligning the transducers with minimum spacing between the elements. Even this placement leads to the occurrence of unwanted grating lobes in the array response and decreases the field-of-view to 30$^{circ}$ . To eliminate these grating lobes, the elements of the receiver array are placed with a different spacing. Forming the receiver and transmitter arrays with nonidentical element spacing makes the grating lobes to appear at different places. Since the response of the overall system is the product of the directivity patterns of receiver and transmitter arrays, the grating lobes diminish for the overall system and the field-of-view increases.      

一种新型IP OVER WDM城域网的节点结构

提出了一种基于波分复用（WDM）,分组交换,副载波复用和波长变换技术的新型全光城域网节点结构,网络拓扑采用环形,网络节点采用可调输出固定输入的选波原则以利于数据的多重接入,副载波复用和基于级联半导体光放大器的波长变换,实现了射频副载波路由信息与基带IP数据包的同步复用和IP数据包的透明传输。     

Performance of Magnetic Pulsed-Eddy-Current System Using High Dynamic and High Linearity Improved Giant MagnetoResistance Magnetometer

Eddy-current nondestructive testing is commonly carried out using single-frequency time-harmonic excitations. Pulsed excitation offers a simple and effective alternative to classical eddy-current techniques and is classically implemented with coil(s) (transmitter and/or receiver). We present a pulsed-eddy-current-system alternative using a high-performance giant magnetoresistance magnetometer is presented. An analytical solution of the magnetic flux density created by the transient eddy current is given. Comparison with experimental results shows that the approximations are accurate (1% or better). System performances are presented and discussed versus sensor characteristics and compared to classical ones (transmitter/receiver coil systems)     

Performance of a laser microsatellite network with an optical preamplifier

Laser satellite communication (LSC) uses free space as a propagation medium for various applications, such as intersatellite communication or satellite networking. An LSC system includes a laser transmitter and an optical receiver. For communication to occur, the line of sight of the transmitter and the receiver must be aligned. However, mechanical vibration and electronic noise in the control system reduce alignment between the transmitter laser beam and the receiver field of view (FOV), which results in pointing errors. The outcome of pointing errors is fading of the received signal, which leads to impaired link performance. An LSC system is considered in which the optical preamplifier is incorporated into the receiver, and a bit error probability (BEP) model is derived that takes into account the statistics of the pointing error as well as the optical amplifier and communication system parameters. The model and the numerical calculation results indicate that random pointing errors of sigma(chi)2G > 0.05 penalize communication performance dramatically for all combinations of optical amplifier gains and noise figures that were calculated.     

Pointing efficiency in Gaussian beam coherent ladar

Random pointing errors in coherent ladar tend to cause a reduction in measured signal power due to misalignment among the transmitter, receiver, and (hard) target. A simple model for the size of this impact, in terms of the size of the pointing error, would be useful in the design and evaluation of coherent ladar systems. To be most applicable to monostatic systems, the model should also include correlation between transmitter and receiver pointing errors. We derive an analytic expression for the reduction in average signal power, which we call pointing efficiency, based on Gaussian beam coherent ladar with Gaussian pointing errors that includes arbitrary correlation between transmitter and receiver pointing errors.     

New absolute vector error correction technique for a transmitter/receiver module

The authors demonstrate how a transmitter (Tx), a reciprocal transmitter/receiver (Tx/Rx) signal path and two unidirectional receiver (Rx) paths can be used together with short, open, and load standards for the absolute vector error correction (AVEC) of a Tx/Rx module. Once calibrated, this Tx/Rx module can then provide accurate vector measurements of the signals that are flowing into and/or out of the test port. This novel AVEC technique is one of the key concepts in the design of a wideband absolute vector signal measurement system, which overcomes the limitations of traditional measurement instruments by combining the features of vector signal analysers, spectrum analysers, and vector network analysers. The AVEC method is validated using numerical simulation data for a simplified baseband test circuit. The AVEC technique is then extended to the calibration of wideband, high-frequency Tx/Rx modules that involve frequency up/down conversion mixers in a follow-on paper     

Message encoding and decoding using an asynchronous chaotic laser diode transmitter-receiver array

We have numerically investigated a chaotic laser diode transmitter-receiver array scheme (CLDTRAS), which is a secure digital communication scheme using a difference between two types of transmitter-receiver array consisting of two self-pulsating laser diodes (LDs), i.e., a receiver LD and a transmitter LD. By analyzing the bit error rate, particularly its dependence on the parameter mismatches of the hardware and channel noise and on the correlation coefficient between a transmitter LD and receiver LD, we examined the problems of sensitivity to parameter mismatches and channel noise and a dependence on chaos synchronization between a transmitter LD and a receiver LD. The former makes communication difficult, and the latter makes it possible for an eavesdropper to estimate the receiver LD using chaos synchronization and to forge the hardware. Then we studied the effects of the bit error rate for various values of the threshold, which determines a binary message, and for various numbers of transmitters-receivers making up a LD transmitter-receiver array. It has been shown that a highly noise-tolerant and hardware-dependent communication scheme can be achieved with the LD transmitter-receiver array, whose transmitter and receiver LDs are asynchronous with respect to each other, by choosing the proper threshold and increasing the number of LD transmitters-receivers. Since it is possible to communicate without chaos synchronization, it becomes difficult to forge hardware and to eavesdrop with the forged hardware even if the key is stolen.     

Interpolation-based precoding with limited feedback for MIMO-OFDM systems

The channel state information (CSI) at the transmitter can significantly improve the performance of multiple-antenna systems. However, providing full knowledge of CSI at the transmitter may not be affordable in many practical cases. Thus, exploiting the partial channel knowledge to improve system performance seems to be attractive. An interpolation based limited feedback precoding scheme (ILFP) for MIMO-OFDM systems is proposed. In this scheme, both the transmitter and the receiver store the codebook of precoding matrices constructed offline using two-variable joint vector quantisation. Considering the correlation between OFDM subcarriers, they are divided into subcarrier clusters. At the receiver, precoding is carried out on the clusters, and then the precoding information is conveyed to the transmitter by limited bits of feedback. At the transmitter, the precoding matrices for each subcarrier are obtained by interpolation according to the feedback. Simulation results show that the proposed scheme outperforms the existing schemes.     

WCDMA空中接口RLC层的AM传输方式关键技术的研究

以WCDMA标准为依据，简要介绍了该标准空中接口方案的无线链路控制子层（RLC层）,并对RLC层确认数据传输方式中发送／接收缓冲区的设置以及状态报告的形成进行了深入探讨。