改进型统计幅度成形在OFDM中的设计

统计幅度成形(PAS)可使加性高斯白噪声(AWGN)信道以低于香农信道容量的任意速率进行传输。文章讨论了改进型的统计幅度成形,将统计幅度成形与正交频分复用(OFDM)相结合用于频率选择性衰落信道中。相比直接在每个OFDM子信道中使用统计幅度成形,改进型统计幅度成形只使用一个概率分布匹配器(CCDM)来产生成形比特。改进型统计幅度成形缩小了成形间隔,并实现了传输速率的匹配。从仿真结果可以看出,在误码率低于10-3的情况下,相同的误码率改进型成形分布的传输速率比均匀分布的传输速率高0.07 bit/s/Hz,只低于香农限0.24 bit/s/Hz,即证明改进型统计幅度成形比均匀分布能以更高的传输速率可靠的传输数据。     

幅度失配对SIC检测器误码性能影响的定量分析

基于幅度失配率,使用高斯近似方法给出有幅度失配的串行干扰消除检测器(SIC)的近似误码率递推公式。利用该公式,讨论了SIC中由于幅度失配而引起的误码率特性。通过引入正数来刻画有幅度失配SIC误码性能与其上限(无幅度失配误码性能)的损失度,使用Lagrange中值定理和近似分析方法,推导出幅度失配率与信噪比以及之间的定量分析公式。仿真表明,该定量分析公式揭示了幅度失配对系统性能的影响程度。     

频率合成器、功率合成器、均衡器、衰减器

Y2002-63119-637 0217558高阶 Bode 型可变幅度波数字均衡器设计的新方法=A novel approach to the design of higher-order Bode-typevariable-amplitude wave-digital equalizers[会,英]/Nowrouzian,B.&Fuller,A.T.G.//The IEEE In-ternational Symposium on Circuits and Systems Vol.2 of5.—637～640(HE)     

一种超宽带、高线性度正交调制器

基于SiGe工艺设计了一款超宽带、高线性度的正交调制器电路,主要包含本振移相模块、混频器模块和输出模块。其中本振正交信号产生电路采用RC多相滤波器结构,在超宽带下生成正交信号,并采用限幅放大器对信号的幅度和相位进行校准;混频器采用Gilbert双平衡混频器电路结构,并使用电阻负反馈结构和电感峰化技术,可满足超宽带、高线性度、高镜像抑制的设计要求;输出模块采用有源巴伦实现差分转单端功能。芯片供电电压为5 V,工作频率范围为50 MHz～6 GHz,输出1 dB压缩点最高可达到14.7 dBm@2 GHz,边带抑制为-60 dBc,载波泄露为-44.8 dBm,噪底可低至-166 dBm/Hz。可广泛应用于各类接收机和通信系统中。     

面向植被边坡的地基SAR高相干点选择

基于高相干点进行相位分析,才能有效保证地基SAR（Synthetic Aperture Radar,合成孔径雷达）形变测量的准确性。在差分干涉测量领域中,广泛使用幅度离差法,可以有效地选择出岩石、建筑物等PS（Permanent Scatterer,永久散射体）点作为高相干点,但对于植被边坡,采用该方法选择出高相干点数量较少,不利于差分干涉处理。在星载SAR领域,普遍采用StaMPS方法解决植被边坡的高相干点选择问题。本文探索了StaMPS方法在地基SAR领域的适用性,提出采用非PS点来计算相干系数门限,并引入DS（Distributed Scatterer,分布式散射体）选择技术,进一步提高了高相干点的数量。对一处植被边坡的实验结果表明,相比于幅度离差法和StaMPS方法,改进方法在提高高相干点数量的同时,有效保证了其相位质量。      

创新、简单而又高效节能的PFC解决方案

开关电源因具有良好的输入电压调整率和负载调整率、高转换效率以及体积小巧等优势,如今几乎为所有电子系统采用。不过,由于开关电源属于非线性元件,因此可产生与输入电压异相的高幅度窄脉冲。电流脉冲的高谐波含量与电源的无功输入同时存在,容易降低AC电源的供电效能,从而造成EMI问题和能源损耗。     

复杂噪声环境下的语音端点检测系统

提出了一套完整的复杂噪声环境下非实时语音信号端点检测系统。首先进行基于样本幅度的预分类处理，然后使用门限过零率算法处理整体幅度很小的样本；整体幅度较大的样本使用引入了自适应噪声估计策略和段落包络幅度特征的改进算法。实际测试表明，在复杂噪声环境下此系统正确率达90．7％，可满足实际系统需求。     

接插元件、继电器、开关、熔断器

Y98-61391-179 9905678用于输电线路保护的相位和幅度比较器的设计=De-sign of phase and amplitude comparators for transmissionline protection[会,英]/Sachdev,M.S.& Sidbu,T.S.//1997 IEEE Conference on Communications,Powerand Computing-Wescanex.—179～184(MaG)本文介绍了采用相位和幅度比较技术的多相继电器的设计。所提出的设计适合于采用微处理器的实现。利用模拟数据评估了比较器的性能,给出了一些结果。参6     

L波段射频幅相检测电路的设计

介绍了幅度和相位检测的工作原理，给出了一种单片式L波段幅度及相位检测电路的设计方案，与传统的设计方法相比，单片式L波段幅度及相位检测电路具有体积小等特点。最后给出了测试结果，结果表明射频幅度相位检测电路的设计性能优越、可靠性高。     

数字电位器在雷达多通道接收机中的应用

近代雷达多通道接收机采用机械电位器进行通道间幅度校准,机械电位器不能在舰载机的湿热及高震动条件下稳定可靠的工作,为避免这一缺点,拟采用数字电位器替代机械电位器。在分析了现有机械电位器应用电路的基础上,提取出数字电位器性能指标要求,然后使用数字电位器模型进行了分析、仿真。最后选用X9312进行了常温试验和高低温试验,实验结果表明数字电位器可以替代机械电位器进行多通道接收机幅度较准,从而使改进后的多通道接收机适用于舰载机的工作环境。     

GEMNET: a generalized, shuffle-exchange-based, regular, scalable,modular, multihop, WDM lightwave network

GEMNET is a generalization of shuffle-exchange networks and it can represent a family of network structures (including ShuffleNet and de Bruijn graph) for an arbitrary number of nodes. GEMNET employs a regular interconnection graph with highly desirable properties such as small nodal degree, simple routing, small diameter, and growth capability (viz. scalability). GEMNET can serve as a logical (virtual), packet-switched, multihop topology which can be employed for constructing the next generation of lightwave networks using wavelength-division multiplexing (WDM). Various properties of GEMNET are studied     

Thermodynamics of copper matte converting: Part III. Steady-state volatilization of Au,Ag, Pb,Zn, Ni,Se, Te,Bi, Sb,and As from slag,matte, and metallic copper

A comprehensive compilation of various thermodynamic data required for a complete analysis of copper matte converting reactions is presented. The data comprise estimated free energies of formation for such gases as SeO, SeS, TeO, TeS, BiO, BiS, SbO, SbS, AsO, and AsS, as well as activity coefficients in dilute copper alloys and vapor pressures of various elements and compounds. The volatilization of minor elements in steady-state reactors comprising gas and several condensed phases is mathematically formulated, and a parameter which governs the volatilization in such reactors is defined and named volatilization constant. The vapor pressures of various volatile species are calculated thermodynamically for the Noranda Process reactor by assuming equilibrium conditions. The volatilization constants of various minor elements are expressed explicitly as functions of oxygen and sulfur activities. Formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT     

Bits, symbols, bauds, and bandwidth

The use of clear, concise, and unambiguous language in telecommunications engineering is vital to communicate a desired meaning and understanding. Terminology should be based on rigorous engineering principles and traceable to well known and dependable sources. This article deals with four everyday terms commonly encountered in the popular semi-technical press as well as in serious engineering periodicals. The misuse of these and other terms can lead to low-balled cost proposals, court litigation, and patent infringement cases. Imagine how an engineering student can be confused when she/he typically encounters bandwidth measured in bits per second     

Novel planar, square-shaped, dielectric-waveguide, single-, and dual-mode filters

This paper presents a novel concept of a square-shaped dielectric-waveguide resonator, which can easily realize a dielectric-waveguide cross-coupled filter or a dielectric-waveguide dual-mode filter, using the conventional printed circuit board (PCB) process. This planar dielectric-waveguide resonator has a higher Q value than a microstrip resonator. The physical mechanisms of both single- and dual-mode filters are elucidated. Some new coupling structures are developed for undergoing the PCB process. Filter design procedures are detailed. Design curves for the coupling coefficients of internal- and external-coupling structures are determined by full-wave finite-element-method electromagnetic calculations. Measurement results are highly consistent with theory for all trial filters. This study offers an effective means of producing low-cost high-performance planar circuit filters.     

PBX技术.市态.营销.选购

本文介绍了ＰＢＸ交换机的技术及市场需求态势。并提出ＰＢＸ产品的营销要素及其用户在选购时应遵循的原则。     

Dilemmas,uncertainty, risks,and board performance

This paper traces the origins of the words risk, uncertainty, governance and development and argues that a deeper understanding of each allows more effective decision taking in the boardroom. It argues that the role of the board of directors is to balance and rebalance continuously their irresolvable dilemma — ‘how do we drive our enterprise forward while keeping it under prudent control?’ It argues that it is the board’s role to focus on uncertainty, rather than risk, and this requires a different set of intellectual skills from board members to be able to cope with monitoring a range of diverse scenarios. This is crucial for a board to develop stronger ways of both leading their organisation and of ensuring the connectedness of the learning within and between the board and the operational unit’s risk taking. It advocates that to achieve this a board must develop new ways of learning — especially of thinking strategically and becoming more sensitised to the dynamics of their changing external environments. This will take them well beyond the comforts of their specialist managerial disciplines and into the true world of directing. The paper demonstrates the importance of continuous learning in reducing organisational uncertainty and risk. It uses the ‘Learning Board’ process and model as the central processor of both strategic and operational learning to create an annual rhythm for the board’s year.