天波超视距雷达空域干扰抑制

天波超视距雷达杂波会妨碍自适应波束形成抑制副瓣干扰."空阔区"脉冲压缩后作副瓣相消可以改善干扰的影响,而降维的旁瓣相消降低了算法的计算量.分析了所提方法的性能,仿真试验验证了所提方法运算量相对较少,干扰抑制效果好的特点.     

基于小波影响锥的天波雷达瞬态干扰抑制方法

针对瞬态干扰严重影响天波超视距雷达（OTHR）目标检测性能的问题,提出了一种基于小波影响锥的瞬态干扰抑制方法。该方法利用一维离散平稳小波变换确定信号的奇异点（瞬态干扰）,然后将每一奇异点对应的影响锥内的小波细节系数置零,最后通过一维逆离散平稳小波变换重构数据。该方法避免了杂波抑制和插值重构,运算量小,实用性强。对天波雷达实测数据的处理实验表明：提出的方法是有效的。     

天波超视距雷达中流星余迹干扰模型

已获得的实测数据表明,天波超视距雷达在3MHz-30MHz的工作频段内存在明显的流星余迹干扰.流星余迹干扰会对天波超视距雷达探测目标的距离和多普勒信息造成负面影响,严重时会影响到天波超视距雷达的正常工作.根据流星余迹的散射特性,结合天波超视距雷达的工作方式,建立了流星余迹干扰模型,为在天波超视距雷达中研究抑制流星余迹干扰技术提供了帮助.仿真结果与实测数据基本一致,验证了模型的有效性.     

天波雷达欠密度流星余迹干扰抑制算法

针对欠密度流星余迹干扰影响天波超视距雷达目标检测的问题,提出了基于总体最小二乘旋转不变估计信号参数(Total Least Squares-Estimating Signal Parameter via Rotational Invariance Techniques TLS-ESPRIT)的欠密度流星余迹干扰抑制算法.首先应用复数据经验模式分解估算流星余迹干扰的位置,并将该位置的回波数据组成Hankel矩阵,然后采用TLS-ESPRIT方法求解Hankel矩阵,解得流星余迹干扰的时域回波,最后从回波数据中去除流星余迹干扰的时域回波,得到流星余迹干扰抑制后的回波数据.与现有流星余迹抑制算法相比,该方法减少了流星余迹干扰的残余和提高了目标的信杂比(SCNR).     

Broadband interference excision for software-radio spread-spectrumcommunications using time-frequency distribution synthesis

A new method is introduced for interference excision in spread-spectrum communications that is conducive to software-radio applications. Spare processing capacity in the receiver permits the use of time-frequency techniques to synthesize a nonstationary interference from the time-frequency domain using least squares methods. The synthesized signal is then subtracted from the incoming data in the time domain, leading to jammer removal and increased signal-to-interference-and-noise ratio at the input of the correlator. The paper focuses on jammers with constant modulus that are uniquely described by their instantaneous frequency characteristics. With this a priori knowledge, the jammer signal amplitude is restored by projecting each sample of the synthesized signal to a circle representing its constant modulus. With the phase matching provided by the least squares synthesis method and amplitude matching underlying the projection operation, a significant improvement in receiver performance/bit-error rates is achieved over the case where no projection is performed. Software-radio aspects including computational complexity and processing modes are also discussed     

天波超视距雷达抑制流星余迹干扰方法的研究

工作在高频波段的超视距雷达（OTHR）会受到流星余迹的干扰，这种干扰的存在，严重影响了OTHR的正常工作，流星余迹干扰在高局部短时间幅度是很强的，与海杂波产生差拍，表现为奇异性特征，利用子波变换对信号的奇异性具有很好的检测效果，提出了用二进制子波变换的方法有效检测和消除流星余迹瞬态干扰，这种方法与正交子滤波器比较，有较高的灵敏度和精度，并且在消除流星余迹干扰后，使信噪比得到提高。实测数据的仿真结果表明这种算法的有效性和实用性。     

Joint time-frequency ISAR using adaptive processing

A new joint time-frequency inverse synthetic aperture radar (ISAR) algorithm that combines ISAR processing with the joint time-frequency signal representation is presented as a means of extracting the nonpoint-scattering features from the standard ISAR image. The adaptive Gaussian representation, applied to the range aids of the ISAR image, is used as the time-frequency processing engine. This technique uses Gaussian basis functions to adaptively parameterize the data and, as a consequence, the point-scattering mechanisms and resonance phenomena can be readily separated based on the width of the Gaussian bases. The adaptive joint time-frequency ISAR algorithm is tested using data generated by the moment-method simulation of simple structures and the chamber measurement data from a scaled model airplane. The results show that nonpointscattering mechanisms can be completely removed from the original ISAR image, leading to a cleaned image containing only physically meaningful scattering centers. The nonpoint-scattering mechanisms, when displayed in the frequency-aspect plane, can be used to identify target resonances and cutoff phenomena     

A time-frequency analysis method for radar scattering

A time-frequency analysis method to study electromagnetic scattering is presented and demonstrated using canonical objects. The time-frequency analysis method utilizes the Bargmann transform to formulate the signal representation in phase space. The use of the Bargmann transform leads to an attractive parametric signal representation in terms of complex polynomials, and elliptical filters can be constructed to crop or extract selected areas of the phase plane. The signal representation and filtering operations are demonstrated using scattering responses from spheres and thin wires, and the prominent scattering features are identified and extracted     

Joint time-frequency analysis for investigation of layered masonry structures using penetrating radar

Joint time-frequency analysis of penetrating radar response has been tested using simulated and experimental data as a processing tool for detecting stratified features inside a masonry structure. The radar response has been simulated exploiting the formalism of the propagators inside a finite number of dielectric layers. Experimental testing has been carried out by varying the thickness of the hollow space between two walls.     

Optimum interference excision in spread spectrum communicationsusing open-loop adaptive filters

A generalized approach for interference suppression in PN spread spectrum communications using open-loop adaptive excision filtering is introduced. The excision filter coefficients under this technique depend on the jammer power and its instantaneous frequency (IF) information, and both values can be gained in the time-frequency domain. The dependency of the excision filter characteristics on the interference power, which was absent in past contributions in this area, is of significant importance as it allows optimum tradeoff between interference removal and the amount of self-noise generated from the induced correlation across the PN chip sequence, due to filtering. This tradeoff is bounded by the two extreme cases of no self-noise, which implies preprocessing disabled, and full interference excision, which the case previously considered. In this paper, we derive the FIR excision filters that maximize the receiver signal-to-noise ratio for narrowband interference and discuss the generalization to nonstationary jamming environment     

Narrow-band interference excision in spread-spectrum systems usingself-orthogonalizing transform-domain adaptive filters

Among many transform-domain interference excision techniques, transform-domain adaptive filtering has many advantages. It is based on a true optimization of some particular performance parameters such as the bit-error rate (BER). Moreover, it is insensitive to jammer frequency. However, transform-domain adaptive filtering also has the drawback of being incapable of tracking a rapidly changing interference because most adaptive algorithms require time to converge to the optimal solution. In this paper, a self-orthogonalizing transform-domain least mean square (SO-TRLMS) algorithm is used to speed up the convergence. Compared to a traditional transform-domain least mean square (TRLMS) algorithm, the SO-TRLMS algorithm can significantly improve the convergence rate of the LMS algorithm, thus making the transform-domain adaptive filtering technique more suitable for real-time processing. In order to show how the system performance is affected by various factors such as interference power and the transform used, this paper presents an analytical result for the BER performance that is applicable for arbitrary orthogonal linear transforms. Simulation results are also presented to demonstrate the validity of the analysis     

基于时频分析的雷达信号到达角估计

现有的空间时频分布(STFD)的信号表示只适用于窄带、连续信号的分析，而雷达侦察系统要求对脉冲、线性调频等信号同时进行到达角(DOA)、频率和信号时域参数的估计。本文给出了现有空间时频分布对雷达信号DOA估计的条件，并提出了基于修正STFD矩阵的DOA估计算法。通过对各阵元输出作时频分析，估计信号的频率参数，然后据此构造方向向量和修正STFD矩阵，即可构造MUSIC空间谱。该算法不受基于现有STFD算法的条件限制。     

Joint time-frequency analysis for radar signal and image processing

The Fourier transform has been widely used in radar signal and image processing. When the radar signals exhibit time- or frequency-varying behavior, an analysis that can represent the intensity or energy distribution of signals in the joint time-frequency (JTF) domain is most desirable. In this article, we showed that JTF analysis is a useful tool for improving radar signal and image processing for time- and frequency-varying cases. We applied JTF analysis to radar backscattering and feature extraction; we also examined its application to radar imaging of moving targets. Most methods of JTF analysis are non-parametric. However, parametric or model-based methods of time-frequency analysis, such as adaptive Gaussian and chirplets, are more suitable for radar signals and images     

一种基于时间-频率特征分析的自适应信道化技术

针对按频率均匀划分子信道的数字信道化技术缺乏灵活性、资源利用率低等问题,提出了一种基于信号时间-频率特征分析的自适应信道化技术.对中频数据进行时-频分析,根据信号时-频特征参数差异对子信道进行跟踪、聚类,自适应动态调整参与反变换的子信道,实现宽带复杂调制信号的完整截获、跟踪、分离.仿真分析结果验证了算法的有效性,且其计...     

波束倾斜修正在天波超视距雷达中的应用

为了修正天波超视距雷达由于波束倾斜引入的方位估值偏差,基于一维相扫雷达波束扫描的原理,分析和阐述了雷达波束倾斜产生的原因,并详细推导了天波超视距雷达波束倾斜修正量的解算过程.通过对典型的场景分析,结果表明:波束倾斜修正的效果取决于对到达波仰角的估计精度.     

Direction of arrival estimation using adaptive directional time-frequency distributions

Time-frequency distributions (TFDs) allow direction of arrival (DOA) estimation algorithms to be used in scenarios when the total number of sources are more than the number of sensors. The performance of such time–frequency (t–f) based DOA estimation algorithms depends on the resolution of the underlying TFD as a higher resolution TFD leads to better separation of sources in the t–f domain. This paper presents a novel DOA estimation algorithm that uses the adaptive directional t–f distribution (ADTFD) for the analysis of close signal components. The ADTFD optimizes the direction of kernel at each point in the t–f domain to obtain a clear t–f representation, which is then exploited for DOA estimation. Moreover, the proposed methodology can also be applied for DOA estimation of sparse signals. Experimental results indicate that the proposed DOA algorithm based on the ADTFD outperforms other fixed and adaptive kernel based DOA algorithms.     

频率选择性高斯干扰信道中的时频联合干扰对齐方案

为了弥补传统干扰对齐方案只在一维域上对齐的不足,提出了一种时频联合干扰对齐方案。通过把频率选择性高斯干扰信道分割成多个并行的高斯干扰信道后引入时频联合干扰对齐矩阵,对这些并行信道在时域和频域同时进行干扰对齐。基于最优化方法,提出了一种计算时频联合干扰对齐矩阵的算法。数值仿真表明该方案和传统干扰对齐方案获得相同性能的条件下,能大幅度地缩短译码延时或减少频带资源的使用,所提方案是传统一维域算法在二维域的扩展,能够提供更加灵活的时频资源分配手段。     

Transient analysis of data-normalized adaptive filters

This paper develops an approach to the transient analysis of adaptive filters with data normalization. Among other results, the derivation characterizes the transient behavior of such filters in terms of a linear time-invariant state-space model. The stability, of the model then translates into the mean-square stability of the adaptive filters. Likewise, the steady-state operation of the model provides information about the mean-square deviation and mean-square error performance of the filters. In addition to deriving earlier results in a unified manner, the approach leads to stability and performance results without restricting the regression data to being Gaussian or white. The framework is based on energy-conservation arguments and does not require an explicit recursion for the covariance matrix of the weight-error vector.     

自适应对消在去除探地雷达信号直达波的应用

基于自适应对消和探地雷达信号中的直达波的性质,提出了一种自适应直达波滤除方法,通过对模拟实验数据和实测数据的处理,验证了这一方法的有效性.另外,还给出了其它方法对同样数据的处理结果,通过与这些方法相比较,自适应直达波滤除法是一种运算量少、信号失真小、并可实时处理的方法.