杂波环境中改善雷达性能的自适应多卜勒处理

脉冲多卜勒雷达信号处理机能够完成探测目标及估算其径向速度的功能。在严重的气象干扰、箔条干扰及其他干扰的杂波环境下,除了采用某些自适应抑制杂波影响的方法以外,探测损耗是不能允许的。本文的目的是:怎样通过采用脉冲多卜勒信号处理机中的自适应多卜勒滤波来改善雷达性能,也讨论和分析利用伯格最大熵法(MEM)的自造应多卜勒处理的实用方法。分析的结果是基于模拟杂波数据。     

采用自适应杂波白化滤波器和多卜勒滤波器组的雷达杂波抑制算法的性能

本文描述了一种采用自适应杂波白化滤波器(WF)和多卜勒滤波器组(DFB)的雷达杂波抑制算法。如与由动目标显示(MTI)和多卜勒滤波器组(DFB)级联所组成的常规的非自适应杂波抑制算法相比较,其性能得到了改善。     

三脉冲动目标检测器

由于现有的数字技术,现在动目标检测器(MTD)为了抑制杂波就有可能使用由杂波地图自适应控制的脉冲多卜勒滤波器。本文叙述由三个多卜勒滤波器形成的一个三脉冲 MTD,并且在三个脉冲一批内完成相参多卜勒处理:CFAR 检测和视频积累与自适应杂波地图相结合去控制三个多卜勒通道从而提供了10脉冲处理器绝大部分优点。一个实验性的三脉冲 MTD 已经做出,并且在 L 波段警戒雷达上作了试验。本文给出了处理器的执行过程和表示性能的试验结果。     

机载相控阵雷达的自适应杂波抑制

机载雷达的杂波抑制问题比地面雷达更为严重,因为由于平台运动而使地回波变成为多卜勒有色的。从而使杂波功率既依赖于方位角又依赖于多卜勒频率。这种两维谱只能用两维滤波抑制,它要求在时间和空间上都要对回波埸取样。这已由采用相干脉冲串的相控阵雷达所证实。平台运动造成杂波背景随时间变化。平台速度的任何变化都造成杂波多卜勒特性的变化,因此,两维滤波必须是自适应的。本文提供最佳自适应杂波抑制的一些新成果,作为对照,也提供了次最佳方法(波束形成器加自适应时间滤波器)。可以看出,任何次最佳方法都很难达到最佳空间——时间杂波滤波器的优异性能。     

机载相控阵雷达的自适应杂波抑制

由于平台运动使地面回波具有多卜勒有色谱,所以机载雷达的杂波抑制问题比地面雷达更严重,因此杂波功率取决于方位和多卜勒频率。这种二维谱只能由在空间和时间回波埸上采样的二维滤波器抑制。这已为应用相干脉冲串的相控阵雷达所证实。平台运动使杂波背景随时间而变化,而平台速度的任何变化都会引起杂波回波多卜勒特性的变化。因此,二维滤波器必须是自适应的。本文介绍最佳自适应杂波抑制方面的某些新结果。为了比较起见,还介绍了一种次最佳方法(波束形成器加自适应时间滤波器)。结果是用任何次最佳方法来替代都很难获得最佳空间-时间杂波滤波器的有利特性。     

抑制气象杂波用的自适应动目标显示器

本文介绍自适应杂波锁定环的数字式实现方法。杂波锁定环的目的是估计杂波的平均多卜勒频率。用这种估计将杂波频谱移到零多卜勒频率。环路后面的固定式动目标显示(MTI)对消器抑制掉移动后的杂波。实验模拟表明,这种杂波锁定环是可行的。实验结果说明,这种对消器比一般固定式对消器效果好得多,但比不上10脉冲动目标检测(MTD)处理机。然而,这种MTD比本文所介绍的自适应信号处理机复杂得多。     

采用最大熵法的自适应脈冲多卜勒雷达信号处理

脉冲多卜勒雷达信号处理的功能是检测所存在的目标和估计它们的径向速度。如果目标被埋没在严重的非平稳杂波和噪声环境中,那么除非采用某些自适应信号处理方法,否则检测损失也许会达到不可容忍的地步。当前关于距离门脉冲多卜勒雷达系统自适应多卜勒滤波用的几种待选算法的研究,证明了Burg提出的最大熵法(MEM)的优越性。本文慨述采用最大熵法的自适应信号处理器的基本要求,并示出推导自适应多卜勒滤波器响应函数的典型最大熵法,这些响应函数是从严重杂波环境下仿真的和实际的雷达回波两者中得到的。应用最大熵法,可在一个波束停留期内完成对严重杂波环境的自适应,从而使信号对杂波加噪声的性能接近最佳。     

抑制气象杂波的自适应动目标显示器

本文介绍自适应杂波锁定环的数字实现法.这种锁定环的用途是估算杂波的平均多卜勒频率.通过估算将杂波频谱移向零多卜勒频率.固定式动显(MTL)对消器跟踪此环路抑制移动的杂波。模似试验说明了这种环的可行性.结果表明,所推荐的对消器的工作大大优于固定式对消器,而没有10—脉冲动目标检测(MTD)处理机性能好.但是动目标检测器要比本文介绍的较简单的自适应处理机复杂得多。     

自适应MTI及多卜勒滤波器组的杂波处理

很多情况下雷达目标掩没在杂波背景内,需要进行杂波处理。如果预先知道杂波参数但目标速度未知,则可以设计出一组多卜勒滤波器并使每个滤波器在某种意义上是最佳的。然而,一般情况下,杂波参数是随距离和方位变化的,它是未知的或者仅仅部分已知。在这种情况下有必要采取自适应处理。本文介绍的自适应 MTI 采用 Gram-Schmidt 自适应开环处理器。可以看出,在有杂波的环境中和脉冲数固定不变时,多卜勒滤波前采用自适应 MTI 可以使性能得到改善。还可以看出。在多卜勒滤波前采用自适应 MTI 比采用固定二项式加权 MTI能得到更好的性能。     

最佳处理器、脉冲多卜勒处理器和MTI处理器抗杂波性能比较

本文介绍了几种相干处理器的抗杂波性能。对每一种处理器在对目标径向速度的随机分布作了假定,并且包含脉冲重复频率参差的情况下,确定了信号干扰比改善因子与目标多卜勒速度的函数关系和检测概率与信号干扰比的函数关系。所考虑的相干处理器包括用两种方法实现的6脉冲有限脉冲响应(FIR)多卜勒滤波器链,6脉冲自适应动目标显示器(MTI)和3脉冲自适应MTI。为了参考也研究了最佳相干处理器。在柱状图概述中用一个叫做“杂波因子”的品质因数描述了所有处理器的相对性能。用杂波因子可以对不同类型相干处理器的性能直接定量地进行比较。     

空间平滑自适应阵列的优化

在多路径环境中，空间平滑是消除相干干扰对自适应阵列处理系统影响的有效方法。我们注意到空间平滑自适应阵列的权系数往往是在子阵列上得到的。这意味着存在一些剩余自由度可以用来改善自适应阵列的性能。本文提出了一种新方法，利用阵列自由度使得自适应阵列的响应具有期望的特性。我们指出如何优化空间平滑自适应阵列使得白噪声功率或者阵列的副瓣昼降低。数值结果说明了新方法的有效性。     

四元数域宽带鲁棒自适应波束形成

该文提出一种基于四元数的宽带鲁棒自适应波束形成方法。在利用四元数构造阵元输出的基础上,通过期望信号复包络对齐技术,建立四元数域宽带对合增广宽线性信号模型,以联合利用四元数阵列输出矢量的3种对合信息和2阶统计特性以及信号非圆信息,采用信号加干扰子空间投影方式,有效提取期望信号,抑制多个不相关干扰和噪声,进而实现四元数域宽带鲁棒自适应波束形成。同其它宽带波束形成方法相比,该方法对非圆信号的接收性能提升,可以实现阵列虚拟孔径扩展,有效克服指向误差带来的性能下降问题。计算机仿真结果验证了该方法的性能。      

Reactance domain MUSIC algorithm for electronically steerable parasitic array radiator

Conventional adaptive array antenna processing must observe signals on all of the array antenna elements. However, because the low-cost electronically steerable parasitic array radiator (ESPAR) antenna has only a single-port output, none of the signals on the antenna's parasitic elements can be observed. A direct application of most of the algorithms for the conventional adaptive array antenna is impractical. In this paper, A technique of estimation of direction-of-arrivals (DoAs) is proposed for the ESPAR antenna. This technique is based on the modified MUltiple SIgnal Classification (MUSIC) algorithm. The correlation matrix used in the MUSIC algorithm is estimated from the signal received through the single-port output of the ESPAR antenna as it switches over a set of antenna patterns. Simulation results show that DoAs can be estimated by the reactance domain MUSIC algorithm for ESPAR antennas. Furthermore, the statistical performance on estimation error variance of the reactance domain MUSIC estimator is analyzed and compared with the Crame/spl acute/r-Rao lower bound. Analytic and empirical results show that high-resolution DoAs estimation can be achieved by using the reactance domain MUSIC algorithm for ESPAR antennas.     

Robust Adaptive Beamformers Based on Worst-Case Optimization and Constraints on Magnitude Response

In this paper, novel robust adaptive beamformers are proposed with constraints on array magnitude response. With the transformation from the array output power and the magnitude response to linear functions of the autocorrelation sequence of the array weight, the optimization of an adaptive beamformer, which is often described as a quadratic optimization problem in conventional beamforming methods, is then reformulated as a linear programming (LP) problem. Unlike conventional robust beamformers, the proposed method is able to flexibly control the robust response region with specified beamwidth and response ripple. In practice, an array has many imperfections besides steering direction error. In order to make the adaptive beamformer robust against all kinds of imperfections, worst-case optimization is exploited to reconstruct the robust beamformer. By minimizing array output power with the existence of the worst-case array imperfections, the robust beamforming can be expressed as a second-order cone programming (SOCP) problem. The resultant beamformer possesses superior robustness against arbitrary array imperfections. With the proposed methods, a large robust response region and a high signal-to-interference-plus-noise ratio (SINR) enhancement can be achieved readily. Simple implementation, flexible performance control, as well as significant SINR enhancement, support the practicability of the proposed methods.     

A lossless compression scheme for Bayer color filter array images.

In most digital cameras, Bayer color filter array (CFA) images are captured and demosaicing is generally carried out before compression. Recently, it was found that compression-first schemes outperform the conventional demosaicing-first schemes in terms of output image quality. An efficient prediction-based lossless compression scheme for Bayer CFA images is proposed in this paper. It exploits a context matching technique to rank the neighboring pixels when predicting a pixel, an adaptive color difference estimation scheme to remove the color spectral redundancy when handling red and blue samples, and an adaptive codeword generation technique to adjust the divisor of Rice code for encoding the prediction residues. Simulation results show that the proposed compression scheme can achieve a better compression performance than conventional lossless CFA image coding schemes.     

基于脉动阵的高速自适应波束调零处理器

在实时自适应波束形成中，用三角咏动阵列构成自适应阵列调零处理器在空域抑制干扰得到广泛的重视。本文提出了一种无输出单元的双速率脉动阵的硬件实现结构。文中针对日益突出的通信瓶颈问题，结合此类脉动阵，提出了一种更快速的脉动阵实现方法，最后给出了仿真结果，验证了该结构的可行性和有效性。     

PSO Assisted DD-ESB Beamforming with Robust Capabilities

This paper deals with adaptive array beamforming based on the decision-directed eigenspace-based (DD-ESB) technique with robust capabilities. It has been shown that DD-ESB adaptive beamformer demonstrates the advantages of better output signal-to-interference plus noise ratio performance and less sensitivity to pointing error over conventional ESB beamformers without any specific training bits. In conjugation with particle swam optimization assisted scheme to obtain more correct desired user’s transmitted bits from the output of the ESB, the more correct steering vector of the desired user can be reconstructed for DD-ESB adaptive beamforming in the presence of larger pointing error and relatively low interference-to-noise ratio. Computer simulations are provided to illustrate the effectiveness of the proposed approach.     

A Constraint-Elimination Technique for Linearly Constrained Array Processing

A new technique is presented for the problem of linearly constrained multi-channel-array processing. The purpose of the array processing is to reject undesired noise, in the minimum-mean-squared-error sense, while responding to any signal coming from a particular direction with a preset, constrained frequency response. In the constraint-elimination technique proposed in this paper, the original constrained-array-processing problem is transformed to the simple unconstrained-Wiener-filtering problem. Transformation of the problem is achieved by introducing a ?compensating? channel to the multichannel processor. Input to the compensating channel is the channel-averaged input. The constraint is then eliminated by expressing the filter weights of the compensating channel in terms of those of the original processor. An adaptive algorithm is derived by applying the stochastic approximation to the simplified Wiener-filtering problem. Simulation experiments verify that the constrained-array-processing problem is properly transformed to the unconstrained one by the proposed technique. Additional experiments show that the adaptive algorithm generally reduces output power while maintaining the constrained frequency response to the desired signal.     

Adaptive array beamforming based on an efficient technique

This paper presents a new processing technique for adaptive array beamforming. We first properly decompose the optimal weight vector associated with the original array beamformer into several adaptive weight subvectors. An adaptive algorithm based on the conventional RLS algorithm is derived to update the weight subvectors. The required computational complexity is also evaluated for the proposed technique. The convergence rate of the proposed technique is mainly affected by the size of the largest weight subvector. Faster convergence speed and less array sensitivity to the pointing errors can be achieved by using the proposed technique. Several simulation results are included for illustration and comparison     

Bit-serial VLSI implementation of delayed LMS adaptive FIR filters

The delayed least-mean-square (DLMS) algorithm is useful for adaptive finite impulse response (FIR) filtering applications where high throughput rates are required. In the paper, a bit-serial bit-level systolic array based on new schemes for multiplication and inner-product computation is presented to implement DLMS adaptive N-tap FIR filters. The architecture is highly regular, modular, and thus well-suited to VLSI implementation. It has an efficiency of 100% and a throughput rate of one filter output per 2B cycles, where B is the word length of input data. In addition, the proposed array uses a small delay of [(4B+N/2+4)/2B] in the filter coefficient adaptation, where [x] is the smallest integer greater than or equal to x. This ensures that the DLMS algorithm can have good performance under proper selection of the step size. Based on a conservative design technique of static complementary metal oxide semiconductor (CMOS) logic, it is shown that the proposed system can be realized in a single chip for most practical applications