基于小波Radon变换检测线性调频信号

对信号小波分析的结果进行Radon变换,简称小波Radon变换。通常情况下,线性调频信号小波变换的结果在时间尺度图上呈现曲线的形式,而在时频图上呈现直线的形式。通过Radon变换检测时频平面上的直线,可以精确地得到调频信号的参数。仿真结果表明,小波Radon变换是一种较好的线性调频信号检测方法。     

基于GA-ML-PMHT的多基站无源协同定位方法

针对无源协同定位系统中低可观测目标的航迹初始及维持问题,提出一种基于遗传算法的极大似然概率多假设的多基站无源协同定位方法。首先,建立多基站无源协同定位系统数学模型。其次,提出基于极大似然概率多假设的无源协同定位航迹初始算法,并首次利用遗传算法解决极大似然概率多假设中的优化求解问题,以提高目标检测跟踪性能。最后,通过滑窗法实现航迹维持。仿真结果表明,所提方法能够有效解决多基站无源协同定位系统中低可观测目标的航迹初始及维持问题。     

解二维卷积型积分方程的正则化方法

基于傅立叶变换和Tikhonov的正则化方法,讨论了解二维卷积型积分方程的正则化方法。     

The “signature” of a coherent system and its application to comparisons among systems

Various methods and criteria for comparing coherent systems are discussed. Theoretical results are derived for comparing systems of a given order when components are assumed to have independent and identically distributed lifetimes. All comparisons rely on the representation of a system's lifetime distribution as a function of the system's “signature,” that is, as a function of the vector p= (p₁, … , p_n), where p_i is the probability that the system fails upon the occurrence of the ith component failure. Sufficient conditions are provided for the lifetime of one system to be larger than that of another system in three different senses: stochastic ordering, hazard rate ordering, and likelihood ratio ordering. Further, a new preservation theorem for hazard rate ordering is established. In the final section, the notion of system signature is used to examine a recently published conjecture regarding componentwise and systemwise redundancy. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 507–523, 1999     

二进制偏移载波调制信号畸变误差评估指标研究

随着全球卫星导航系统的发展，二进制偏移载波（BOC）调制信号被广泛采用。全面评估BOC信号的畸变误差对于导航系统的信号完好性评估与监测具有重要意义。前文对于BOC信号的畸变研究较少，没有解析评估BOC信号畸变误差的指标与方法。本文针对三种常见的信号畸变，给出了完善的畸变误差评估指标，能够全面评估畸变误差。同时采用提出的评估指标对北斗全球系统B1频段上的基线信号BOC(14,2)及MBOC(6,1,1/11)信号进行评估。文中提出的畸变误差评估指标能够用于评估现代卫星导航信号的畸变误差，对现代导航信号体制设计及完好性监测均具有指导意义。     

一种差分空时分组码及其性能分析

文中介绍了一种差分空时分组码的编译方法及其性能分析,与之对比,先导入单天线时差分调制的概念及其方法,理论分析表明,采用无需信道估值的差分空时分组码与相干检测空时分组码相比其性能差3 dB,但与单天线相比仍有接近于10 dB的分集增益。     

基于Butterworth分布的跳频信号参数估计

能够有效地估计接收到的跳频信号参数是干扰跳频通信的关键。针对接收到的未知任何先验参数的跳频信号,提出了一种基于Butterworth分布的跳频信号参数估计算法。由于Butterworth分布具有较好的时频聚集性和抑制交叉项性能,该算法能够在低信噪比条件下有效提取并估计出跳频信号的跳频周期、跳变时刻和跳频频率。仿真结果证明了该算法对跳频信号参数估计的有效性。     

Tail hazard rate ordering properties of order statistics and coherent systems

We study tail hazard rate ordering properties of coherent systems using the representation of the distribution of a coherent system as a mixture of the distributions of the series systems obtained from its path sets. Also some ordering properties are obtained for order statistics which, in this context, represent the lifetimes of k‐out‐of‐n systems. We pay special attention to systems with components satisfying the proportional hazard rate model or with exponential, Weibull and Pareto type II distributions. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007     

Progressive Type‐II censoring and coherent systems

A new connection between the distribution of component failure times of a coherent system and (adaptive) progressively Type‐II censored order statistics is established. Utilizing this property, we develop inferential procedures when the data is given by all component failures until system failure in two scenarios: In the case of complete information, we assume that the failed component is also observed whereas in the case of incomplete information, we have only information about the failure times but not about the components which have failed. In the first setting, we show that inferential methods for adaptive progressively Type‐II censored data can directly be applied to the problem. For incomplete information, we face the problem that the corresponding censoring plan is not observed and that the available inferential procedures depend on the knowledge of the used censoring plan. To get estimates for distributional parameters, we propose maximum likelihood estimators which can be obtained by solving the likelihood equations directly or via an Expectation‐Maximization‐algorithm type procedure. For an exponential distribution, we discuss also a linear estimator to estimate the mean. Moreover, we establish exact distributions for some estimators in the exponential case which can be used, for example, to construct exact confidence intervals. The results are illustrated by a five component bridge system. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 512–530, 2015     

合成双射流冲击平板流场结构与模态分解分析

为揭示合成双射流冲击平板流场结构特征,通过大涡模拟方法对合成双射流冲击平板流动进行了仿真,采用有限时间Lyapunov指数方法对流场的拉格朗日涡结构进行了识别,并与欧拉框架下的速度矢量和涡量结果进行了对比分析。结果表明,在合成双射流两股射流交替作用下,射流核心区涡系结构较为复杂且涡量丰富,远离核心区存在一对稳定的涡结构,且拉格朗日涡结构与涡量对应较好,为合成双射流冲击冷却的布局设计提供了指导。另外,流场本征正交分解表明,第一阶模态关于激励器出口中心轴线大致对称,其能量占总体能量的35%,前6阶模态的能量占80%;根据前6阶模态所反映的流场特性,合成双射流冲击平板流场具有高度的对称性。