基于快速折叠算法和时频分析的LPI跳频信号截获

该文提出了一种新的低截获概率(LPI)跳频信号的截获方法,该方法基于快速折叠算法和时频分析.在低信噪比环境下,该方法能有效检测跳频信号;通过恰当地选择折叠周期范围和分辨率,能实现对跳频参数如跳频周期、跳变时刻和跳频频率的估计.仿真结果和性能分析表明,该方法能有效截获信噪比为0dB的跳频信号,与自适应门限检测方法相比具有更好的性能.     

一种基于时频分析的跳频信号参数盲估计方法

本文提出了一种采用平滑伪WVD(SPWVD)时频分析来估计未知跳频信号参数的方法，该方法可以在不需要知道信号任何先验参数的情况下，估计出跳频信号的跳周期(hop duration)，跳变时刻(hop timing)和跳频频率(跳频图案)等参数。文中对跳频信号的WVD、PWVD和SPWVD结果作了比较，指出了SPWVD的优点，给出了基于SPWVD估计跳频信号参数的具体算法步骤，并进行了性能分析。     

基于中频存储和并行DSP的短波跳频侦察

介绍了采用中频信号存储和DSP并行处理技术的试验平台和基于该试验平台的短波跳频信号侦察方法,不但能够实现常规定频信号的搜索截获和分析测量,同时可对跳频、突发等短持续信号截获和识别。能快速截获50跳/s的跳频信号并获取其完备的频率集,测频精度优于50Hz。     

基于STFT与WVD的雷达信号分析检测方法

对未知LFM雷达信号进行参数估计是截获分析、分选识别及干扰实施敌方低截获概率雷达信号的前提。本文分析了雷达信号参数检测方法 WVD,并对该方法在对雷达信号检测时产生的交叉项引入了STFT线性变换进行处理。仿真实验表明,该方法在充分发挥了WVD对信号的分析处理能力的同时能有效地抑制交叉项影响。     

基于FRFT与WVD的旋转LFM信号参数估计

为了克服传统的全域搜索法在旋转LFM信号参数估计过程的繁琐问题,提出基于分数阶傅里叶变换(FRFT)与魏格纳分布(WVD)的旋转LFM信号参数估计方法.通过分析旋转LFM信号的性质和特性,给出了该信号的FRFT形式.基于WVD良好的时频分辨率,得到了清晰的调频信号时频分布,并且给出旋转LFM信号参数估计的具体步骤.仿真实验结果表明,该方法有效可行.     

基于RSPWVD的Link16信号跳周期估计算法

针对Link16信号快跳频、抗截获的特点,文章提出了一种基于重分配平滑伪魏格纳维尔分布(RSPWVD)的Link16信号跳周期估计算法。该算法首先应用RSPWVD时频分析获得Link16信号的时频分布,进而通过重心法获得相邻两跳的中心时刻,最后通过加权平均各个中心时刻的差值求得Link16信号的跳周期。分析和仿真结果表明,该算法可以有效地对Link16信号的跳周期进行估计,不仅克服了传统算法不能有效解决时延脉冲带来的影响的缺点,而且也提高了估计的准确性。     

利用ASTFT谱有效抑制WVD交叉项的方法

该文分析TWigner-Ville Distribution(WVD)中自项与交叉项相互关系,提出了一种利用自适应短时傅里叶变换(ASTFT谱)有效抑制WVD交叉项的新方法.该方法首先对信号进行ASTFT得到信号的ASTFT谱图,以确定出信号分量在时频平面内的位置,然后将ASTFT谱作为窗函数对信号的WVD进行加窗处理,从而有效消除掉WVD中的交叉项,并保留WVD的高分辨率和能量聚集性等优良特性.最后通过实例验证了该方法的有效性.     

基于时频分析的跳频信号的参数盲估计方法

采用平滑伪Wigner—Ville分布（SPWVD）来估计跳频信号载波频率,提取频率脊线,对频率脊线进行一次小波变换来估计未知跳频信号的参数,该方法可以在不需要知道跳频信号任何先验参数的情况下,估计出信号的码元速率,载波频率改变时刻。对频率编码信号的WVD,PWVD和SPWVD结果作了比较,指出了SPWVD的优点,给出了基于时频分析跳频信号参数估计的具体算法步骤．计算机仿真表明该方法是行之有效的。     

椭圆球面波信号Wigner-Ville分布显式渐近求解方法

针对现有的椭圆球面波函数(PSWFs)信号时频分析无显式表达式、数值仿真误差不可控、时频分布结果对称性缺失等问题,该文引入Legendre多项式以及Wigner-Ville分布(WVD),提出一种PSWFs信号WVD显式渐近求解方法。该方法根据误差要求,生成所需阶数的Legendre多项式WVD自项、交叉项,进而与对应的WVD-Legendre系数相乘后线性叠加,获取PSWFs信号WVD显式渐近表达式。理论及数值仿真结果表明,所提方法能够产生满足误差要求的PSWFs信号WVD显式渐近表达式,且能够有效保持信号原有的时域、频域对称性。此外,在相同采样点数情况下,相对于基于数值解的PSWFs信号WVD,所提方法获得的PSWFs信号WVD频域分辨率更高。     

新截获模型下的对称三角LFMCW信号的检测与参数估计

针对现有参数估计方法需要以信号的调频周期起点为截获时间起点的假设,结合“连续波”信号的特点和电子侦察的实际,建立新的对称三角线性调频连续波(STLFMCW)信号截获模型,提出了一种STLFMCW信号检测与参数估计方法.该方法在分析多周期STLFMCW信号模糊函数的基础上,利用Radon-Ambiguity变换(RAT)估计信号的调频斜率并确定分数阶傅里叶变换(FRFT)的最优阶数,根据截获模型下信号新的时间频率关系,再通过相应阶数上FRFT估计调制周期、调制带宽和载频.与现有方法相比,该方法克服了对信号截获时间起点限制,只需截获信号包含至少两个完整的正调频部分或负调频部分就可估计出信号的各个参数.蒙特卡罗仿真实验表明,本文的参数估计方法在低信噪比下具有很好的鲁棒性.     

高效实现FPGA数字下变频的多类滤波器分组级联技术

对各种实现数字下变频的方法进行比较,在对数字下变频已有的许多高效的算法做了总结和归纳后,为了解决系统实现时乘法器需求过高的局限,通过合理的滤波器分解和级联、选择适当的滤波器系数和流水线技术,给出了系统的FPGA实现方案,并在Virtex-5上给出了Verilog具体实现和仿真,结果证明:FPGA设计的DDC各项指标满足系统设计要求。     

Smart instruments

Various aspects of the nature of intelligence as applied to measurement science such as mathematical capability, signal routing, signal conditioning, and processing are discussed. The state-of-the-art in providing intelligence in instruments is reviewed. The decreasing cost and increasing capability of CPU, memory, and peripheral-control functions involving the application of microcomputer electronics is described. Design considerations such as precision, economy, and simplicity are outlined as well as some limitations on intelligence. Trends in smartinstrument design are discussed and some predictions future developments are made.     

移动证券业务中的安全机制研究

本文首先介绍了移动证券业务中对于敏感交易信息的加密和解密过程,提出了具体的安全性要求。然后,给出了一种可以用于移动证券业务的安全机制,该安全机制采用了两密钥的三重DES算法进行加解密;密钥分为传输密钥和交易密钥两种,每种密钥经过三级分散处理;同时引入了动态密钥下载、密钥版本更新等新功能,很好地满足了移动证券业务对于安全性的要求。接着,给出了该安全机制的一个具体实现过程,最后是安全性分析和结论。     

近距爆破源振动采集系统

本文根据工程爆破测试的需要,提出了一种近爆点的振动信号采集节点的设计方案。该节点中使用一种新型的MEMS拾振器,采用Altera公司FPGA作为主控制器芯片,其中集成控制逻辑单元与NiosII软核嵌入式处理器,二者结合成为单芯片控制器方案。控制器运用多路FIFO进行数据缓冲,顺序传输数据至外部存储器,实现了多路数据的同步采集。拾振器与数据记录仪结合成为一体化的信号采集节点。该节点采样频带宽,体积小。适合近爆区域恶劣环境地震波信号的采集,节点可以灵活布置组成不同测试方案。     

Compact Quantum-Dot Microbeads with Sub-Nanometer Emission Linewidth

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Here, microbeads capable of generating single-peak laser emission with a sub-nanometer linewidth are demonstrated. The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single-mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 µm in the air. Sub-nm lasing emission is maintained even inside high-index surroundings, such as organic solvents and biological tissues. Feasibility of intracellular tagging and multi-color imaging in vivo is demonstrated.     

Evaluation of technology options for LSI processing elements

A general overview of the semiconductor technologies available for the manufacture of microprocessor and bit slices is given. Both MOS as well as bipolar processes are covered. Advantages and disadvantages of PMOS, NMOS, CMOS, TTL, ECL, and I²L are discussed. Several of the more special-purpose technologies are briefly mentioned. A comparison is done on the basis of performance, cost, and application, and suggestions are made as to which technology will service best which application. A general prediction is made as to which processes will survive as main stream technologies and what developments can be expected in the near future with respect to improvements. Applications are separated into cost-sensitive low-chip-count areas and high-performance bit-slice-oriented approaches.     

Launching Efficiency of the HE/sub 11/, Surface-Wave Mode on a Dielectric Tube

A theoretical investigation into the launching of dipolar surface waves on a dielectric tube is presented. The source under consideration is a transversely oriented point electric dipole situated on the axis of the tube. It is found that the source excites only the dominant HE/sub 11/ mode when the outer radius of the tube is sufficiently small. Phase and group characteristics as well as some field distributions are given for the source-free case; however, these are independent of the choice of the source, and are dependent only on the particular mode being excited. Surface-wave as well as radiated powers are obtained in terms of the current in the source dipole, and the launching efficiency of the surface waves is determined as a function of the tube radius, wall thickness, and permittivity of the material. Finally, comparisons are made between the dielectric tube and the solid rod which was investigated previously as possible surface-wave transmission lines, and also the launching efficiencies for these two cases.     

Error propagation analysis for underwater cooperative multi-hop communications

The potential gains of cooperative communication and multi-hopping in underwater acoustic communication channels is examined. In particular, performance of such systems is compared to a comparable single hop system (direct transmission) with a common transmission distance. The effects of error propagation with decode and forward at each relay are explicitly treated and it is shown that strong gains can be achieved by multi-hopping (an effective SNR gain) as well as cooperation, which contributes to a diversity gain. We observe that cooperative diversity gains are retained even when considering error propagation. The analysis is done via a Markov chain analysis for both regular linear and grid networks. Our initial analysis is for single path channels; the effects of inter-symbol interference as well as multi-user interference are examined. It is found that due to the strong decay of signal power as a function of transmission distance, multi-user interference is not as significant as inter-symbol interference. In both cases, cooperative and multi-hopping gains are observed.     

Flux transfer devices

Flux transfer device theory is reviewed. In such devices, generalized magnetic flux, defined as the time integral of voltage, is used to describe the device characteristics. The Josephson junction and inductor are the main circuit elements in flux transfer devices, because they maintain a constant value for the time integral of voltage. Flux transfer devices are based on either an RF SQUID (superconducting quantum interference device) or a fluxon device. Four devices, including the parametric quantron and the quantum flux parametron, are reviewed as applications of the RF SQUID. The fluxon feedback oscillator and a soliton device are also reviewed as applications of fluxon devices. The quantum flux parametron is then described. The parametron principle and the fundamental properties of the quantum flux parametron such as gain, switching speed, and power dissipation are discussed. Logic circuits and a memory cell are also reviewed. A novel analog-to-digital converter is proposed as an application of the quantum flux parametron     

空气压缩机站监控系统的实现

以某空气压缩机站监控系统为例,介绍了空气压缩机的工艺流程及监控系统硬件配置、软件设计和功能。该系统上位机采用iFix进行软件开发,界面友好,操作方便。通过智能控制模块对现场设备进行数据采集并监控设备运行和故障状态,实现了手动、远程控制及故障保护等功能。