KKT-based iterative algorithm for beamforming in cognitive radio system

In this paper,we consider the downlink channel of multi-user multi-input single-output(MU-MISO)system in cognitive radio network,where the cognitive base station(CBS)resort to beamforming scheme to relief co-channel interference.The design criterion is to minimize the transmit power at CBS,subject to the signal-to-interference-plus-noise-ratio(SINR)constraints of cognitive users(CUs)and the interference constraints at primary users(PUs).Standard conic optimization packages can handle the problem,however,the...     

Four-way radial waveguide power divider with high power-handling capacity

In this paper,a novel four-way radial waveguide power divider with low insertion loss and high power-handling capacity is proposed.This power divider consists of an input coaxial waveguide,a central probe,a radial waveguide,four equispaced identical coupling probes,four equispaced identical adjusting posts and four output coaxial waveguides.The novel coupling probes and the adjusting posts are used to realize favorable uniform power division.A power divider with the center frequency of 4.1 GHz is designed,fabricated and measured.Good agreement between simulation and experiment is noted.The measured 15 dB return-loss bandwidth of the power divider is about 600 MHz.The measured 0.5 dB insertion loss bandwidth is wider than 700 MHz.The differences and isolations between the output ports are also discussed.The power-handling capacity of the power divider is analyzed through simulation,and the result proves its usability in high power applications.     

一种最小电压应力的软开关无桥PFC技术研究

针对传统桥式整流升压功率因数校正(PFC)电路效率较低的缺点,提出了一种最小电压应力的软开关无桥PFC电路拓扑.在理论分析和仿真验证的基础上,研制了一台300 W的实验样机.结果表明,改进的无桥PFC电路拓扑具有通态损耗低、电流采样简单,能实现开关管零电压关断和零电流开通,同时实现整流二极管零电压导通和接近零电流软关断...     

Editor's Message

On behalf of the editorial staff of China Communications,we would like to extend our sincere thanks to you for your knid concern for our journal.Now we are here to make a specification that the previous English periodical of China Communications has been revised into a Chinese-English edition,for the sake of keeping pace with the development of the communications industry as well as providing readers home and abroad with more information.     

用小波变换的模极大值提取调制信号频率

利用小波变换系数的模值与信号奇异性指数之间的关系,从调频信号中提取出调制信号的频率.其方法是:对调频信号进行小波变换,取适当尺度上的小波系数进行平方,得到小波变换模极大值的分布曲线,对该曲线进行小波强制滤波,得到反映调制信号频率的光滑曲线,计算该曲线的频率,即可得调制信号的频率.经过计算机仿真,证明该方法是可行的.     

与基于电感器的开关稳压器相比，高压充电泵可简化电源转换

充电泵（或称开关电容器电压转换器）填补了线性稳压器和基于电感器的开关稳压器之间的性能空白,为不喜欢电感器的工程师提供了另一种设计选择。与LDO相比,充电泵需要一个额外的电容器（“浮动”电容器）才能工作,但一般来说成本仅略有增加,同时充电泵具有更高的输出噪声电平,     

工业通信网络中高速光电耦合器的应用

工业通信网络带来独特的应用挑战并需要优化方案以便高效运行,在现今的工厂中,许多不同的可编程设备必须精确控制以便可以和谐运行,工业设备、控制器、传感器、致动器和其他组件间的通信通道必须实时运作,并且可以抵抗电气噪声干扰并提供安全电气隔离,另外,随着工业控制系统的日益复杂,工业通信网络也必须提供更高的吞吐量或生产力输出。     

基于自抗扰控制器的变风量空调解耦控制

变风量空调是一个多输入多输出的系统,由于具有多个回路,各个回路之间相互影响,具有强耦合、非线性和大时滞等特点.常规PID控制存在稳定性与精确性的矛盾.文中根据自抗扰控制原理,分析了变风量空调系统的耦合关系,通过扩张状态观测器实现对系统总扰动的估计和补偿,实现解耦控制.文中将其用于变风量空调末端的主回路温度控制系统.仿真实验结果表明,与PID控制相比,自抗扰控制器的超调量、时滞等得到了明显改善.     

基于LabWindows/CVI的发动机标定系统开发

文中针对通用小型发动机的特点,基于LabWindows/CVI虚拟仪器技术,以Keyword Protocol 2000 （KWP2000）为ECU （Engine Control Unit）与上位机的通信协议,开发了通用小型发动机的标定系统.该系统的主要功能有实时显示采集的数据、在线参数的调整、数据保存等.     

使用隔离门驱动器抑制混合动力驱动的电压瞬变(dV/dt)噪声

正介绍在设计实用并且可靠的动力驱动电路时工程师经常面临的一个挑战是高共模噪声,共模噪声(Common mode noise),或称为电压瞬变(dV/dt)噪声,通常由系统中高电压电源间的高频率开关动作产生,本篇文章将讨论混合动力驱动应用中电压瞬变噪声的可能来源并提出建议解决方案。