分数阶傅里叶滤波在欺骗干扰中的应用研究

分数阶傅里叶变换较之于传统傅里叶变换能更有效地将线性调频信号与噪声分离.但分数阶傅里叶域频谱能量的聚集性受信号占空比及调频带宽两方面影响,当占空比较小并且调频带宽很宽时,往往难以得到尖锐的谱峰.本文提出短时滑窗方式的分数阶傅里叶滤波方法,分析了时频域截断对其频谱的影响,在此基础上提供一种低信噪比情况下线性调频信号的检测准则,进而详细论述分数阶傅里叶域滤波的流程.仿真结果表明,运用这种准流水方式的滤波方法处理盲信号,信噪比可提高10dB以上,而有用信号的能量损失却极小.在雷达的欺骗干扰领域应用此方法可提高干扰性能.     

分数阶傅里叶域滤波器组的一般化设计方法

 分数阶傅里叶变换相对于传统的傅里叶变换具有灵活的时频分析特性,在最优分数阶傅里叶域进行滤波可以实现对某些非平稳信号的最优检测和参数估计以及对某些干扰和噪声的滤除.分数阶傅里叶域滤波器组理论的提出弥补了分数阶傅里叶域滤波不具备多尺度分析以及运算量过大的缺点,但现有的分数阶傅里叶域准确重建滤波器组设计方法不具备形式一般化的特点,很难满足很多实际工程的需要.本文从分数阶傅里叶域多抽样率信号处理基本理论和分数阶卷积定理出发,推导出了分数阶傅里叶域准确重建滤波器组的一般化设计方法,为分数阶傅里叶域滤波器组理论在实际工程中的推广应用奠定了理论基础.最后,仿真实验验证了本文所提分数阶傅里叶域滤波器组一般化设计方法的有效性.     

宽带恒定束宽盲波束形成算法

针对传统盲源分离算法对宽带阵列信号适用性较差的问题,提出一种基于时频分析的宽带恒定束宽盲波束形成算法。该算法首先将接收信号变换到时频域上并提取出单源点。然后,对单源点聚类并求解信号在不同频点上的导向矢量。最后,通过提出一种信号来向未知的空间响应变化约束方法,实现宽带恒定束宽盲波束形成。该算法避免了将宽带盲波束形成转换为卷积混合的盲源分离,因而不存在时域盲源分离算法中系统参数随滤波器阶数急剧增加的问题,也不存在频域算法中排序和幅度模糊的问题。仿真结果表明,算法能够较好地实现宽带信号的盲分离,且输出信干噪比高于时域、频域以及时频域盲源分离算法,实测数据的处理结果验证了该算法的实用性。      

基于变换域和时域联合处理的雷达同频干扰抑制方法

针对舰艇编队情况下线性调频脉冲体制雷达间同频干扰的问题,该文提出一种分数阶傅里叶域滤波处理与时域反异步处理相结合的干扰抑制方法。通过分数阶傅里叶域自适应滤波对与目标回波信号调频率不同的干扰信号做抑制处理,同时根据分数阶傅里叶变换的可逆性,逆变换到时域后采用相邻周期反异步方法进一步消除与目标回波信号调频率相同或相近的同频干扰。仿真试验表明,该方法相对传统方法能够有效抑制与目标回波信号调频率不同的同频干扰,同时对于在时域与目标回波信号完全重合或部分重合的干扰信号也有较好的抑制效果,干扰抑制处理增益达到29 dB以上。该方法为提高同型雷达编队组网能力提供了设计参考。     

基于FRFT域自适应滤波的脉冲压缩技术

雷达回波中往往存在严重的干扰,采用线性调频信号(linear frequency modulation,LFM)的脉冲压缩雷达系统中,直接对回波信号进行脉冲压缩往往得不到好的效果。文中利用线性调频信号在分数阶傅里叶变换(fractional fourier transform,FRFT)中的强能量聚集性的特点,在分数阶傅里叶域对混合回波进行自适应滤波,再将滤波后的信号变换回时域进行脉冲压缩处理。自适应滤波算法采用一种改进的变步长NLMS算法,相对于传统固定步长NLMS算法有较好的滤波结果。仿真结果表明,经过分数阶傅里叶域自适应滤波后的信号在脉冲压缩后的目标检测结果有了很大的改善,明显提高了脉冲压缩雷达的检测性能。     

DSSS系统LFM干扰抑制技术研究

针对传统的傅里叶变换只能对平稳干扰信号具有较好的抑制能力而对非平稳的LFM干扰信号不能有效抑制,该文引入了分数阶傅里叶变换（FRFT）,在分数阶傅里叶域给出了一种LFM信号最佳旋转角度确定的算法,并利用该算法对LFM在分数阶傅里叶域进行干扰抑制。仿真结果表明,该算法能够准确确定LFM信号在分数阶傅里叶域的最佳旋转角度,...     

基于均匀圆阵的宽带相干LFM信号定位方法

本文提出一种基于均匀圆阵的宽带相干LFM信号定位方法。首先，算法根据LFM信号在分数阶傅里叶域的能量聚焦性，对接收信号做分数阶傅里叶变换，实现宽带信号的窄带化处理；其次，利用圆阵的虚拟轴向平移形成的相位差构造空间平滑矩阵，完成相干信号的解相干处理；最后，对空间平滑矩阵进行奇异值分解得到相邻阵元接收数据的相位差，结合相位差反演参数估计算法得到二维角度参数估计的闭式解。仿真实验验证了算法对宽带相干LFM信号定位的有效性。     

无源雷达直达波参数估计方法研究

无源探测作为一种经济安全的被动探测手段近年来获得学术界的广泛关注,在非合作外辐射无源雷达系统中,准确快速地估计直达波的参数是无源探测的前提。本文以基于非合作chirp雷达的无源雷达系统为平台,围绕直达波参数估计问题展开研究。对于工程上常见的时频混叠,且时间不同步的多分量chirp信号,提出一种基于分数阶傅里叶域滤波的chirp信号参数估计方法。该方法根据时频域滤波的原理,首先通过分数阶傅里叶变换估计chirp分量的调频斜率;然后通过逆分数阶傅里叶变换将多分量chirp信号分离为若干个单分量chirp信号,并在时域估计每个chirp分量的脉冲宽度;最后构造dechirp滤波器,对分离后的chirp分量进行解线性调频,估计每个chirp分量的中心频率。仿真实验证明,本方法相较于时频图像的方法,具有更高的估计精度和计算效率,而且本方法可以实时处理,易于工程化实现。     

一种基于分数阶傅里叶变换的OFDM系统 及其均衡算法

在快速时变信道环境下,由于子载波间干扰(ICI)的影响,传统OFDM系统性能有较大下降.本文提出了一种基于分数阶傅里叶变换的OFDM系统,它用分数阶傅里叶变换代替傅里叶变换进行子载波调制与解调;同时,文中给出了最优分数阶傅里叶变换阶次的选取方法,并根据最小均方误差(MMSE)准则设计了分数阶傅里叶域乘性滤波器在接收端进行均衡.分析和数值仿真结果表明,最优分数阶傅里叶域的乘性滤波算法较频域方法有更好的均衡效果.     

一种新的变换域自适应LMS滤波算法

为了改善时变系统中的LMS算法收敛速度,一般可以在变换域进行自适应处理。通过研究和分析分数阶傅里叶变换与时-频平面的关系,提出在分数阶傅里叶变换域进行自适应时-频滤波。所提出的方法首先搜索最佳变换域,然后在分数阶傅里叶变换域进行LMS自适应滤波。仿真结果表明,与目前一些基于变换域的方法对比,新方法通过对时-频平面的旋转,可以显著加速算法收敛性。     

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.     

Uncertainty, Value, Communication, and Problematic Integration

This essay discusses problematic integration (PI) theory, a general perspective on the nature of the dynamic relationship between communication and tensions among expectations and desires and considers the relevance and potential value of PI theory to questions foundational to the field of communication research. The paper begins with a discussion of the main propositions of PI theory, then considers the relationship between the theory and emerging analyses of uncertainty, attending in particular to the meanings of uncertainty and the tensions among uncertainties, wants, and wishes.