A Wide-Band High-Linearity Down-Conversion Mixer for Cable Receptions

分析了一种宽带高线性度的用于有线接收机的下变频混频器.该设计采用0.35μm SiGe BiCMOS工艺.射频输入信号频率范围设计为1～1.8GHz,测得的1dB压缩点达到 14.23dBm,最大转换增益为8.31dB,最小噪声系数为19.4dB,在5V供电情况下,直流功耗为54mW.     

Performance analysis of prioritized parallel transmission MAC protocol in all‐IP wireless WAN

Prioritized parallel transmission MAC (PPTM) protocol is proposed for all‐IP wireless wide area network (WAN). In this paper, we analyse its performance and compare it with modified channel load sensing protocol (MCLSP). We model PPTM as a non‐preemptive priority queueing system and obtain a close form of transmission time delay for each priority class, throughput of the scheme, and number of packets in the queue in the Poisson arrival case. We find that PPTM achieves less transmission time delay than MCLSP does for high priority data. Hence, the overall performance of the system using PPTM is significantly improved. We verify the conclusions with simulation via a simplified all‐IP wireless WAN. Copyright © 2006 John Wiley & Sons, Ltd.     

宽输入共模电压范围电流检测放大器的研究与设计

针对高端电流检测放大器输入级对宽输入共模电压范围的要求,对宽输入共模电压范围放大器的输入结构开展了研究,提出了一种宽共模输入范围的输入级结构,特点是具有低输入偏置电流,并能兼顾高低共模电平工作的需要.给出了整个电流检测放大器的电路设计.该放大器在1.5μm BCD工艺下设计实现.芯片的测试结果表明,当采用5V单电源供电时,电路的输入共模范围可达0~30V,最大总误差不超过1.67%.     

网络视频监控系统建设

本文通过对网络视频监控产品以及对工程建设得失的分析,以期为运营商今后的工程建设提供参考和借鉴.     

后3G时代LTE异军突起

介绍了下一代无线网络LTE(Long Term Evolution,长期演进)的背景和发展状况.分析了LTE的技术特征,阐述了LTE网络结构与核心技术,并通过与WiFi(WirelessFidelity)及WiMAX(World wide Inter operability for Microwave Access)的各项性能作比较,着重分析了LTE的技术优势.最后,指出了LTE在个人通信市场所面临的应用前景与挑战.     

On an initial‐boundary value problem for a wide‐angle parabolic equation in a waveguide with a variable bottom

We consider the third‐order Claerbout‐type wide‐angle parabolic equation (PE) of underwater acoustics in a cylindrically symmetric medium consisting of water over a soft bottom B of range‐dependent topography. There is strong indication that the initial‐boundary value problem for this equation with just a homogeneous Dirichlet boundary condition posed on B may not be well‐posed, for example when B is downsloping. We impose, in addition to the above, another homogeneous, second‐order boundary condition, derived by assuming that the standard (narrow‐angle) PE holds on B, and establish a priori H² estimates for the solution of the resulting initial‐boundary value problem for any bottom topography. After a change of the depth variable that makes B horizontal, we discretize the transformed problem by a second‐order accurate finite difference scheme and show, in the case of upsloping and downsloping wedge‐type domains, that the new model gives stable and accurate results. We also present an alternative set of boundary conditions that make the problem exactly energy conserving; one of these conditions may be viewed as a generalization of the Abrahamsson–Kreiss boundary condition in the wide‐angle case. Copyright © 2008 John Wiley & Sons, Ltd.     

Layer structure estimation of three‐dimensional crystal and two‐dimensional molecular film for fluorinated comb copolymers

Comb copolymers containing both hydrogenated and fluorinated side‐chains were prepared by copolymerization using acrylic or methacrylic monomers in several ratios. The crystal structures of these copolymers and layer structures of their organized molecular films were investigated by wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and out‐of plane X‐ray diffraction. Further, to selectively estimate the regularity of shorter fluorocarbon side‐chains, organized molecular films of copolymers were investigated by polarized near‐edge X‐ray adsorption fine structure (NEXAFS) spectroscopy. From the results of these measurements, it was inferred that these copolymers formed highly ordered layer structures, and a long spacing was predominantly determined by the arrangement of hydrogenated side‐chains, except in copolymers having extremely high fluorocarbon contents. In the case of the organized molecular films, the fluorinated side‐chains of methacrylate copolymers cannot form a highly ordered arrangement, whereas those of acrylate copolymers were oriented on monolayers. However, in both cases, the hydrogenated side‐chains predominantly formed layer structures in the organized films, and the fluorinated side‐chains did not contribute to the formation of the layer structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 534–546, 2008     

宽开通信侦察中多信号盲分离应用研究

宽开通信侦察系统可以大大提高搜索速度,提高信号的截获概率,但如何快速有效地分离出同时截获的多信号是一个急待解决的难题,盲分离技术为多信号分离提供了一种新的思路,实验结果表明盲分离技术在宽开通信侦察中的有效性,并显示出它在通信侦察中的广阔前景。     

Quality of offering on the world wide web

The definition of quality in a ‘life’ environment, such as that of the World Wide Web has proven to have many, often conflicting interpretations. Factors such as the point of view, the expertise and type of usage of the critic can influence dramatically such a definition and its results. Thus, the key point is to distance oneself from single perspectives and obtain a complete picture of the system as a single entity working towards a specific goal. This paper is an attempt at creating a general model of quality procedures. It will concentrate mainly in customer service, system viability and quality of offering evaluation. Some of the material mentioned is based on adapted classical models that can be used equally to apply and observe standards of offerings in the wider WEB community. Copyright © 2002 John Wiley & Sons, Ltd.