共查询到20条相似文献,搜索用时 31 毫秒
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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. 相似文献
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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. 相似文献
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《Solid-State Circuits, IEEE Journal of》1981,16(6):745-748
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. 相似文献
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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. 相似文献
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Aniruddha Chandra Chayanika Bose Manas Kr. Bose 《International Journal of Communication Systems》2011,24(2):153-167
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. 相似文献
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Transformer-Based Dual-Mode Voltage-Controlled Oscillators 总被引:1,自引:0,他引:1
Bevilacqua A. Pavan F. P. Sandner C. Gerosa A. Neviani A. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2007,54(4):293-297
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 相似文献
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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 相似文献
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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。 相似文献
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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。 相似文献
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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. 相似文献
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《Microwave and Wireless Components Letters, IEEE》2005,15(4):205-207
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. 相似文献