A Switched Diversity Receiving System for Mobile Radio

A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio. The input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit. The system has been measured on simulated Rayleigh fading channels and has been found to give a significant improvement to both voice and data signals.     

Visual Communication Systems for the Deaf

The paper is in two parts. The first (Section II) describes six years' operating experience with an in-house switched videotelephone system installed in the headquarters of the Royal National Institute for the Deaf, London. The system, which has recently been extended to 10 terminals, has confirmed the usefulness and practicality of switched television for both deaf-to-hearing and deaf-to-deaf communication. Proper attention is required, however, to terminal design and maintenance procedures. In the second part (Sections III and IV) consideration is given to extending the system to permit communication over the public switched telephone network. This demands considerable data compression of the images. Experiments are reported using six deaf subjects in which the tolerance of signing, lip-reading, and fingerspelling to temporal, spatial, and contrast coding distortions was investigated. The results suggest that just-comfortable communication can be achieved at around 100 kbits/s and just-possible communication at around 5 kbits/s, with further reductions appearing feasible.     

Chopper stabilization of MOS operational amplifiers using feed-forward techniques

A monolithic chopper amplifier system has been developed that reduces the effective offset voltage of an NMOS operational amplifier to a few microvolts without compromising bandwidth. Internally, two amplifiers are used, connected in a switched feed-forward configuration. The system is realized in a standard silicon gate enhancement/depletion process.     

基于FPGA的内网安全防护系统关键技术研究

鉴于目前交换网络中安全防范的不足,提出了基于FPGA硬件的内网安全防护系统。该系统针对交换网络中流行的攻击手段及潜在的安全威胁,实时监听网络流量,发现并终止攻击,同时修复网络,以保障安全。测试结果表明：该系统对局域网内的主要攻击具有检测和防御功能,可以应用在通常的交换网络中实现安全防护。     

开关磁阻电机故障诊断系统研究

本文以TMS320F2812为控制器,以四相8/6型开关磁阻电机(SRM)为控制对象,设计了一种性能优良的具有故障诊断功能的开关磁阻电机调速系统。本文介绍了开关磁阻电机调速系统的工作原理,包括功率变换器,电流检测,位置检测,速度检测等硬件电路,并重点分析了系统的故障运行情况。最后给出了实验波形,说明开关磁阻电机具有良好的容错性能。     

连续泵浦Nd:YAG声光调Q铌酸钡钠腔内倍频激光器

在连续泵浦的Nd:YAG激光器中采用声光Q开关、Ba_2NaNb_5O_(15)晶体进行腔内倍频,获得峰值功率为2.56千瓦、重复频率为1千赫、脉宽为75毫微秒、波长为0.53微米的激光输出。并进行了应用实验,取得了满意的效果。     

输出可调谐振开关电容变换器潜电路分析

对输出可调谐振开关电容变换器中存在的潜电路进行了研究,对潜电路状态及其激励条件进行了分析,讨论了减小潜电路影响的措施。仿真对比分析证明,输出可调谐振开关电容变换器的输出功率存在限制;同时,采取适当的限制措施,对提高系统响应和抑制电源干扰和负载变化有较好的作用。     

浅谈IMS和PSTN/CS网络的互通

IP多媒体子系统自从3GPP UMTS Release5后已经被加入到通用移动通信系统(UMTS)的核心网络中.现在,UMTS网络主要包含以下3个域:电路交换(CS)、分组交换(PS)和IP多媒体子系统(IMS).IMS需要同原有相对陈旧的网络电路交换(CS)网络及公用电话交换网(PSTN).本文主要针对IMS同PSTN/CS网络的互通进行了概述.     

switched beam CDMA系统中小区容量和覆盖半径的计算

本文推导了switched beam系统中干扰因子的计算式，以及中断概率、基站接收机灵敏度、移动台最大可允许的发射功率、信干比的期望值、路径损耗与小区覆盖半径、小区容量的关系式，并以直线天线阵为例，计算了小区容量和小区的覆盖半径。     

开关电流网络的信号流图分析法

开关电流作为一种新的电流模式技术已经成为电流模式信号处理的前沿课题。本文引入偶镜和奇镜的概念,提出了开关电流网络的信号流图分析法,并把它用于对开关电流滤波器的分析研究。计算机仿真结果验证了本文方法的正确性和可行性。     

一种5阶1位∑-△调制器的设计

提出了一种稳定的5阶∑-△调制器的设计与调试方法.电路采用5阶级联结构,主要用CMOS开关电容技术实现,文章重点放在调制器结构的设计及几种防止系统发散和改进性能的途径上.模拟实验表明,经过改进的系统有较好的性能.     

Unified BER and optimum threshold analysis of binary modulations in simple and cascaded Rayleigh fading channels with switched combining

Following a unified analytical framework, the bit error rate (BER) of several coherent and non‐coherent binary modulation schemes is derived for a switched diversity system. The two variants of switched combining that have been investigated are switch and stay combining and switch and examine combining. For channel modelling, at first a simple slow flat fading channel is assumed, where the amplitude attenuation obeys the Rayleigh distribution. Later the BER calculations are repeated for cascaded Rayleigh fading channel case. Rayleigh fading is the most popular model for electromagnetic signal propagation in wireless media when both or either of the transmitter/receiver is fixed. On the other hand, when both the transmitter and the receiver are mobile, a cascaded (or double) Rayleigh fading model is better suited. The applicability of these two models, namely simple and cascaded Rayleigh model, has been indicated by several theoretical studies and their suitability is established by various field measurements. In our paper, simple closed‐form BER expressions as a function of switching threshold have been found and optimum switching thresholds have been computed for both these models as well as for both types of diversity combining described earlier. The results presented in this paper can be very useful for communication system designers to analyze link quality of switched diversity assisted systems in various wireless environments. Copyright © 2010 John Wiley & Sons, Ltd.     

Transformer-Based Dual-Mode Voltage-Controlled Oscillators

In this brief, we propose to use a transformer-based resonator to build a dual-mode oscillator, e.g., a system capable of oscillating at two different frequencies without recurring to switched inductors, switched capacitors, or varactors. The behavior of the resonator configured as a one-port and a two-port network is studied analytically, and the dependence of the quality factor on the design parameters is thoroughly explored. These results, combined with the use of traditional frequency tuning techniques, are applied to the design of a wide-band voltage-controlled oscillator (VCO) that covers the frequency range 3.6-7.8 GHz. The performance of the designed VCO, implemented in a digital 0.13-mum CMOS technology, has been studied by transistor-level and 2.5D electromagnetic simulation (Agilent Momentum). A typical phase noise performance at 1-MHz offset of -104 dBc/Hz has been predicted, while the power consumption ranges from 1 to 8 mW, depending on the VCO configuration     

一种新型的开关电容Hopfield神经网络

人工神经网络的单片集成是一个受到广泛关注的问题。采用开关电容技术对此进行了研究。讨论了连续时间Ｈｏｐｆｉｅｌｄ神经元的两种开关电容实现方案。提出了利用开关电容网络来实现连续的Ｈｏｐｆｉｅｌｄ神经网络的新方法。该方法便于单片集成，且得到的网络结构具有对寄生参数不灵敏的优点     

GSM在排水泵站远程监控系统中的应用

对于实时性要求不高的远程被控对象，目前可以应用基于PSTN(公共交换电话网)和基于GSM(移动通信网)的低成本远程监控系统来设计，对这二种方法进行了比较。详细介绍了基于GSM的低成本远程监控系统组成以及实现方法，已经成功应用在排水泵站远程监控中。     

一种开关电源的时序控制电路设计

具有时序控制的开关电源正在毫米波系统中得到广泛应用。分析了时序控制的基本原理,对影响电源时序控制的各种因素进行了探讨,对现有的时序控制方案进行了分析,提出了开关电源时序控制的基本方法。基于以上方法,较全面地评估了时序控制电路的上电时序控制、掉电时序控制以及短路或过流保护控制。最后采用该方案设计了一个实验电路,仿真和实验电路测试结果表明,分析设计满足要求。     

基于DSP的开关磁阻电机调速系统研究与设计

为对开关磁阻电机调速进行实时控制,设计了一款基于DSP的TMS320F2812数字信号处理器为控制核心,设计开发了开关磁阻电机调速系统。以模块化的思想设计了MCU控制系统、位置检测系统、不对称功率电路等模块。给出了软件设计的思想和方法,完成了嵌入式软件系统的开发。该调速系统结构简单、成本低廉、起动转矩大及调速范围宽等优点,具有很好的发展前景。     

A Novel All-Optical Routing Architecture for Optical Packet Switched Networks

Increasing bandwidth demand, mostly driven by the Internet Protocol (IP), has made researchers consider to deploy all-optical devices into packet switched networks. Despite huge bandwidth of the optical communication links (optical fiber) the usable capacity is limited due to bottlenecks (congestions) at the switching nodes. In this paper, a novel all-optical routing architecture is proposed for optical packet switched networks. In the design, practical optical devices (gratings, threshold elements, optical delays, and couplers) have been improved and exploited in order to integrate into an all-optical routing device. The system has been implemented and simulated by using an photonics simulation package (VPI-Virtual Photonics). The packets conveying a three-bit routing information tag at the bit rate of 10 Gbps have been successfully routed between two links. Some of the components are standard tools of the simulation package and some needed to be designed using the transfer function or theory developed in the literature. Noise and losses associated to the nonideal nature of the components are considered in the simulation as well.     

基于XML—RPC的海量存储管理系统的设计与实现

海量存储系统是由管理节点、数据节点通过高速交换网络互联形成的分布式存储系统。它支持CIFS、NFS、WebDAV等多种访问协议,具有高性能、高可用、高扩展等特性,是设计和实现管理系统时面临的挑战。为了实现基于Web的管理系统,针对该系统的分布式结构和丰富特性,本文提出了基于AJAX和XML—RPC技术的海量存储管理系统架构,并描述了其管理系统的主要组成部分和工作过程。     

A 20-50 GHz RF MEMS single-stub impedance tuner

A novel radio-frequency (RF) microelectromechanical system (MEMS) single-stub impedance tuner has been developed. The design is based on combining the loaded line technique with the single-stub topology to obtain wide impedance coverage with high |/spl Gamma//sub MAX/|. The tuner consist of ten switched MEMS capacitors producing 1024(2/sup 10/) different impedances. The design has been optimized for noise parameter and load-pull measurements of active devices and shows excellent measured impedance coverage over the 20-50 GHz frequency range.