基于波束形成与SSA的多麦克风噪声消除

提出一种基于波束形成技术与信号子空间滤波器的多麦克风噪声消除方法。利用波束形成器的空域滤波特性,使波束主瓣对准期望信号方向,零陷对准噪声方向,消除观察信号中弱相关与不相关噪声。利用信号子空间滤波器进一步消除波束形成器输出信号中的残余噪声。实验采用NOISEX92语音库,结果表明该方法具有较低的算法复杂度,有效降低了背景噪声。     

一种宽带恒定束宽自适应波束形成算法

在宽带恒定束宽波束形成中,强干扰信号是导致波束性能下降的一个重要原因.为了抑制强干扰信号特别是快速运动中的强干扰信号,提出了一种宽带恒定束宽自适应波束形成算法.首先采用一种具有零陷控制特性的自适应波束形成技术形成参考波束图,然后利用二阶锥规划的方法计算出其它子带上与参考波束图既有相同主瓣响应又有相同零陷响应的自适应权向量,同时通过对白噪声增益的限制来保证算法的稳健性.不仅具有恒定束宽波束的特性,而且具有自适应波束零陷控制的特性,从而保证对强干扰信号有较强的抑制能力.仿真结果验证了该算法的有效性.     

一种自适应稳健波束形成器的仿真研究

针对阵列信号处理问题,关于特征空间的波束形成器是一类重要的稳健波束形成方法,只需已知信号源的个数,就可以达到很好的稳健效果。但这种方法需要不断求解特征空间,当采用批处理方法时存在稳健权值与快拍匹配不够好的缺点,并且若阵元数较大,求解特征子空间需要较大的运算量。为加快收敛速度和提高信噪比,提出主分量分析（PCA）多层感知神经网络可以自适应学习信号的主子空间,引入到特征空间稳健波束形成器的自适应实现中去。采用基于加权信息子空间（WINC）网络具有较快的收敛速度,能够并行计算信号的主子空间,从而很好的实现了自适应稳健波束形成,并进行仿真分析。结果表明,验证的算法具有较好的稳健性能。     

改进的辅助变换相干干扰抑制波束形成技术

提出一种相干干扰下自适应波束形成方法。该方法同时约束非相干干扰与相干干扰,更好地实现对此两类干扰方向的自适应零陷滤波。采用变换预处理,避免抑制期望信号;恢复噪声特性并采用对角加载技术,增强算法稳健性;采用拉格朗日乘子法得到最优波束形成算法。理论分析与仿真结果表明,保持阵列孔径不变时,该算法提高了输出信干噪比和稳健性。     

基于协方差矩阵重构的稳健自适应波束形成算法综述

Capon波束形成器作为理论上最优的波束形成器具有良好的干扰抑制能力。然而Capon波束形成器对于模型失配误差非常敏感,尤其是针对协方差矩阵和期望信号导向矢量误差,波束形成器的性能会严重下降,这大大降低了波束形成器的稳健性。目前,一系列基于协方差矩阵重构的稳健自适应波束形成算法被提出,这些算法核心思想都是利用Capon功率谱一定的角度范围内积分来重构出协方差矩阵。本文首先介绍了波束形成的信号模型,然后在Capon波束形成器的基础上,介绍了4种基于协方差矩阵重构的稳健自适应波束形成技术,最后对未来波束形成技术的研究热点进行了展望。     

自适应阵列智能天线抗干扰性能研究

分析了自适应阵列智能天线的基本原理,给出了基于复数LMS算法的自适应阵列智能天线波束形成方法,同时对该智能天线抗干扰性能进行了Matlab仿真,理论分析和仿真结果表明:自适应阵列智能天线阵能够实时地调整天线方向,使天线的主波束对准期望信号方向,零陷对准干扰方向从而抑制干扰信号,在干扰和低信噪比环境下,接收端使用智能天线可以大大降低误码率,该智能天线具有较强的抗干扰性能。     

盲源分离与波束形成融合抑制方向性强干扰研究

针对强干扰严重影响线列阵声纳弱目标检测的问题,融合盲源分离（Blind source separation,BSS）与波束形成提出了一种抑制方向性强干扰的方法.首先在干扰方位形成波束得到干扰信号估计,然后对阵列接收信号的每个子带采用盲源分离方法得到分离信号和解混矩阵估计,并通过对分离信号和干扰信号进行子带谱相关抑制干扰,再将抑制干扰后的分离信号重构回阵元域信号,最后采用波束形成方法完成目标方位估计.利用模拟器数据和海试数据对方法进行了验证,结果表明,该方法能有效地抑制方向性强干扰,明显提高了弱目标信号的空间谱能量,增强了声纳检测弱目标的能力.     

用于高动态GPS接收机的微分约束最小功率抗干扰方法

本文提出了一种基于微分约束最小功率法的高动态全球定位系统(GPS)接收机的自适应抗干扰方法.该方法对最小功率法在干扰的来向上加微分约束,能够加宽天线波束在干扰来向上形成零陷的宽度,用以应对高动态环境中干扰波达方向随时间的快速变化.和常规的基于微分约束的加宽零陷方法相比,本文方法不需要知道或估计信号和干扰来向信息.本文不仅在空域探讨了该方法,还将该方法推广到空时二维自适应处理来抑制宽带色散多径干扰.仿真结果证明了该方法的有效性.     

基于静态波束综合的波束域预处理算法

针对自适应波束形成的波束域方法在波束覆盖区域外存在强相关干扰源时多目标方位估计失效的问题,提出采用静态波束综合的波束域预处理算法。该算法利用多波束系统输出确定干扰大致方位,再以常规波束的权矢量为期望权矢量,通过求解最优化问题得到最优权矢量,在波束覆盖区域外的相关干扰源附近方位形成较宽零陷。仿真结果表明,该算法在相关和非相关干扰源情况下,均能较好的抑制干扰,进一步提高了波束域预处理方法的抗干扰能力。     

一种基于协方差矩阵重构和EMP的宽带波束形成算法

在宽带波束形成中,若干扰信号从主瓣方向进入,会引起主瓣畸变、旁瓣电平抬高,从而使波束性能严重恶化。为了解决波束形成中的这些问题,研究了一种基于协方差矩阵重构和特征投影预处理（EMP）的宽带波束形成算法。该算法首先通过EMP算法求取阻塞矩阵,对接收信号进行干扰相消预处理阻塞掉主瓣干扰;然后通过相干信号子空间（CSM）方法、协方差矩阵重构求取合理的协方差矩阵;最后进行波束形成。在主瓣干扰、旁瓣干扰同时存在的情况下,该算法能够自适应地阻塞主瓣干扰、抑制旁瓣干扰,解决了存在主瓣干扰情况下宽带波束形成的波形畸变问题。计算机仿真验证了该算法有效性。     

一种精确控制旁瓣的自适应波束形成算法

提出了一种精确控制旁瓣和抑制干扰的自适应波束形成算法。它是通常的最小方差无畸变（MVDR）波束形成算法的改进形式，使阵列输出信号功率最小的同时，保持目标信号方向的无失真响应，并且严格保证旁瓣低于某一给定值，抑制干扰。在仿真过程中，充分应用了二阶锥规划（second—order cone programming）算法，并与MVDR波束形成算法进行比较，验证了方法的正确性，同时研究了该算法的稳健性。     

一种基于酉变换的修正ESB波束形成算法仿真

为了减小基于特征空间（ESB）自适应波束形成算法的运算量并提高小快拍数条件下的自适应波束形成性能,该文提出了一种基于酉变换的修正ESB自适应波束形成算法。该算法利用酉变换将复协方差矩阵转换为实矩阵,然后对其求逆和特征分解进行自适应波束形成,因此其运算量比ESB自适应波束形成算法小得多。由于计算变换后的矩阵的过程具有前后向平均的效果,相当于快拍数加倍,从而可提高小快拍数时波束形成的性能,增大输出信干噪比。算法在智能天线中的仿真结果表明,该算法具有比ESB算法更优的性能。     

Correlated channel model-based secure communications in dual-hop wireless communication networks

This article is focused on secure relay beamformer design with a correlated channel model in the relay-eavesdropper network. In this network, a single-antenna source-destination pair transmits secure information with the help of an amplify-and-forward (AF) relay equipped with multiple antennas, and the legitimate and eavesdropping channels are correlated. The relay cannot obtain the instantaneous channel state information (CSI) of the eavesdropper, and has only the knowledge of correlation information between the legitimate and eavesdropping channels. Depending on this information, we derive the conditional distribution of the eavesdropping channel. Two beamformers at the relay are studied for the approximate ergodic secrecy rate: (1) the generalized match-and-forward (GMF) beamformer to maximize the legitimate channel rate, and (2) the general-rank beamformer (GRBF). In addition, one lower-bound-maximizing (LBM) beamformer at the relay is discussed for maximizing the lower bound of the ergodic secrecy rate. We find that the GMF beamformer is the optimal rank-one beamformer, that the GRBF is the iteratively optimal beamformer, and that the performance of the LBM beamformer for the ergodic secrecy rate gets close to that of the GRBF for the approximate secrecy rate. It can also be observed that when the relay has lower power or the channel gain of the second hop is low, the performance of the GMF beamformer surpasses that of the GRBF. Numerical results are presented to illustrate the beamformers’ performance.     

稳键的自适应空间波束形成语音增强算法研究

为了进一步改善波束形成的降噪性能,研究了一种稳键后置滤波自适应空间波束形成算法.用麦克风代替传统波束形成器的延时抽头线,使所有的麦克风都有一阶的滤波器,利用经典的线性约束最小方差准则使空间波束形成产生语音参考信号,同阻塞矩阵输出的噪声参考信号一起经自适应多路相消器,从而有效的消除干扰噪声;最后结合后置滤波技术进一步改善语音质量.实验结果表明,相对于传统后置滤波自适应波束形成算法,在消噪性能上有明显的改善且具有更高的输出信噪比.     

雷达电子战系统的宽带数字波束形成实时实现

雷达电子战信号系统中宽带数字波束形成算法在工程中难以实时实现。要满足算法实时性要求主要面临两个瓶颈:其一是长点FFT运算量较大,难以实时实现;其二是多波束电子扫描时运算模块间实时数据传输量过大,难以保证实时传输。提出了一种应用在基于RapidIO总线信号处理平台的宽带数字波束形成的实时实现方案。该方案采用了FFT的二维分解算法,利用分模块流水线方法实现了长点FFT实时运算。采用分频段宽带数字波束形成算法,有效减少了多波束电子扫描时运算模块间实时数据传输量。该方案应用在基于RapidIO总线的数字信号处理平台的实时性能分析和算法仿真结果验证了该方案的可行性。该方案在雷达电子战系统应用中具有一定的理论研究意义和工程应用前景。     

New Insights Into the MVDR Beamformer in Room Acoustics

The minimum variance distortionless response (MVDR) beamformer, also known as Capon's beamformer, is widely studied in the area of speech enhancement. The MVDR beamformer can be used for both speech dereverberation and noise reduction. This paper provides new insights into the MVDR beamformer. Specifically, the local and global behavior of the MVDR beamformer is analyzed and novel forms of the MVDR filter are derived and discussed. In earlier works it was observed that there is a tradeoff between the amount of speech dereverberation and noise reduction when the MVDR beamformer is used. Here, the tradeoff between speech dereverberation and noise reduction is analyzed thoroughly. The local and global behavior, as well as the tradeoff, is analyzed for different noise fields such as, for example, a mixture of coherent and non-coherent noise fields, entirely non-coherent noise fields and diffuse noise fields. It is shown that maximum noise reduction is achieved when the MVDR beamformer is used for noise reduction only. The amount of noise reduction that is sacrificed when complete dereverberation is required depends on the direct-to-reverberation ratio of the acoustic impulse response between the source and the reference microphone. The performance evaluation supports the theoretical analysis and demonstrates the tradeoff between speech dereverberation and noise reduction. When desiring both speech dereverberation and noise reduction, the results also demonstrate that the amount of noise reduction that is sacrificed decreases when the number of microphones increases.      

Noise Statistics Update Adaptive Beamformer With PSD Estimation for Speech Extraction in Noisy Environment

This paper addresses the problem of extracting a desired speech source from a multispeaker environment in the presence of background noise. A new adaptive beamforming structure is proposed for this speech enhancement problem. This structure incorporates power spectral density (PSD) estimation of the speech sources together with a noise statistics update. An inactive-source detector based on minimum statistics is developed to detect the speech presence and to track the noise statistics. Performance of the proposed beamformer is investigated and compared to the minimum variance distortionless response (MVDR) beamformer with or without a postfilter in a real hands-free communication environment. Evaluations show that the proposed beamformer offers good interference and noise suppression levels while maintaining low distortion of the desired source.      

Subspace position measurement in the presence of occlusion

An eigenspace-based method for measuring camera and/or object position in the presence of occlusions is described. Following the formation of a global eigenspace during a training phase, input images are divided into subsections for which a local set of projections is stored. Local occlusions in each subsection are detected by eigenspace reconstruction error. Only unoccluded subsections are then recombined dynamically to implement the nearest-neighbor search of the manifold and to avoid ambiguity in the subspace. Experimental results are described to demonstrate this technique for the measurement of the position of two metallic parts in the presence of significant occlusion.     

DFT宽带波束形成器简化权系数法性能分析

由于处理芯片内存空间是有限的,在实际声呐和雷达信号处理机中应用DFT宽带波束形成器时,通常采用简化权系数分配法降低加权向量的存储量,使其能够完全存储于处理芯片的内存中,为处理机的实时性提供了可靠保证。简化权系数分配法会降低波束形成器的阵增益,并使得输出信号产生相位差,从而影响系统检测和估计性能。本文给出了该近似方法的性能分析,并通过仿真实验验证了其对阵增益和相位的影响,最后结合仿真结果说明如何进行相位补偿以及如何选取简化权系数法的频段宽度以保证系统的稳健性。