基于稀疏约束和SRV约束的宽带自适应波束形成

针对传统的宽带MVDR自适应波束形成中,抑制干扰的同时会抬高旁瓣电平,且过多的线性约束会导致波束输出的SINR性能下降的问题,提出了一种基于SRV约束和稀疏约束的低旁瓣、高增益宽带自适应波束形成方法.该方法在窄带MVDR自适应波束形成基础上,通过增加波束图稀疏约束来降低波束的旁瓣电平,同时利用空间响应偏差(SRV)约束将窄带算法推广到宽带MVDR 自适应波束形成中,极大地降低了算法的复杂度,改善了波束输出的SINR 性能.与传统方法相比,该方法在降低宽带波束的旁瓣电平的同时,还具有良好的干扰抑制效果.数值仿真实验验证了该方法的有效性.     

一种改进的基于LC-GSC的主瓣干扰抑制方法

针对线性约束广义旁瓣相消器(LC-GSC)存在主瓣干扰时天线自适应方向图会出现主瓣波束畸变及副瓣电平升高的问题,给出了一种通过阻塞矩阵对数据进行预处理的主瓣干扰抑制方法,对线性约束广义旁瓣相消器进行了改进,先利用阻塞矩阵预处理实现主瓣干扰抑制,再通过线性约束广义旁瓣相消器进行波束形成,有效地解决了波束主瓣变形及旁瓣电平升高的问题。仿真分析验证了改进方法的有效性。     

旁瓣电平软约束下干扰功率搜索的波束形成

实际中,期望信号或干扰的先验方向信息往往不能精确已知(即存在阵列流形误差),当信噪比超过一定门限时,线性约束自适应波束形成器对阵列流形误差有高敏感性从而导致输出信干噪比下降。为解决上述问题,该文提出一种旁瓣电平软约束条件下搜索人工干扰功率值的波束形成方法。在粗估干扰来波方向的基础上,约束旁瓣最大峰值起伏在一定范围内,采用子空间投影和加宽干扰零陷区的技术提高波束形成器的鲁棒性,通过粗、精两种模式的搜索获得干扰零陷区的注入功率值估计,具有良好的干扰抑制效果和对阵列流形误差不敏感的特性。计算机仿真验证了方法的有效性和鲁棒性。     

一种小样本下的方向图副瓣控制算法

为解决常规方向图控制算法中的方向图副瓣较高、样本量较小时方向图起伏较大的问题,提出了一种小样本下的方向图副瓣控制算法。该算法在最小方差无失真响应（MVDR）波束形成器中,将输出方向图的低副瓣控制和降低样本处理数量的方法相结合,通过对MVDR波束形成器的最优权矢量附加Dolph-Chebyshev锥化权和把阵列权矢量约束于噪声子空间,得到的方向图在小样本情况下干扰置零的同时,解决了副瓣电平过高和方向图不稳定的问题,减小了快变干扰的影响。计算机仿真实验证实了所提算法的有效性。     

一种稳健的自适应波束形成器

当信号噪声比超过一定的门限时,线性约束自适应波束形成器对天线的幅相误差有很高的敏感度,即使在误差很小的情况下,期望信号也会如同干扰一样被抑制掉。该文通过对广义旁瓣相消器的阻塞矩阵加以改进,提出了一种对阵列天线误差有良好稳健性的自适应波束形成器。该方法基于广义旁瓣相消器结构,可方便地进行部分自适应,降低运算量。     

阵列雷达数字波束形成技术仿真与研究

本文首先介绍了数字波束形成的基本原理,随后对普通波束形成及基于LCMV准则和MVDR准则的单多波束自适应形成技术分别进行了原理介绍和仿真分析。仿真结果表明,基于自适应技术的数字波束形成能有效提取有用信号,并在干扰方向上形成零陷,有效的抑制噪声和干扰,大大提高了阵列雷达的天线性能。     

数字信号处理中MUSIC方法的新教学思路

多重信号分类MUSIC算法是基于信号与噪声子空间正交性的一种超分辨谱估计方法.自适应波束形成技术则是通过在干扰信号波达方向上置零来实现输出信干噪比最大化.通过在所有感兴趣波达方向上扫描,波束形成器也可以用来实现波达方向估计.MUSIC算法和波束形成技术的原理看似不同.然而,有文献表明,MUSIC算法可被表示为一个波束形成器.基于这一事实,在本文中,我们首先介绍了MUSIC算法和最小无失真响应波束形成技术MVDR的原理.然后,给出MUSIC算法和MVDR波束形成器的等价表示形式.最后,将MUSIC算法与MVDR波束形成器进行比较.通过上述内容的讲解,可以使学生获得关于MUSIC算法新的认识.     

时域宽带自适应波束形成器设计

针对现有含反馈支路的时域宽带自适应波束形成器运算量大、干扰抑制能力受限的问题,基于广义旁瓣相消结构,引入一条固定系数的全极点反馈支路,设计一种新的时域宽带自适应波束形成器,减少了前向支路所需抽头延迟线个数即自适应权个数,从而降低了运算量,加快了收敛速度。全极点反馈支路以逼近包含干扰频带的带通滤波器为目标进行离线最优化设计,在保证稳定性的同时,增强了波束形成器的干扰抑制能力。仿真结果表明：与现存含反馈支路的时域宽带自适应波束形成器相比,采用相同的自适应算法,设计的波束形成器收敛更快、干扰抑制能力更强;实现相同的 SINR 改善时,新的波束形成器所需运算量远小于现存波束形成器。     

强干扰下的波束形成

提出强干扰条件下等距线阵的波束形成方法。该方法将空间角度映射到数字频率,对阵列方向图的设计就等效于对FIR滤波器的零点设计。在强干扰方向形成零陷可采用零点修改法与零点增加法2种设计方法,由于该2种方法均会使波束主瓣方向略有改变,且对旁瓣的抑制能力有所下降,所以要设计方向图指向正确且对旁瓣电平有要求的方向图时需要进行迭代设计。仿真结果表明,该2种设计方法适用于强干扰条件下弱信号的接收。     

正交预处理波束指向抗干扰算法研究

MVDR 算法可形成波束指向并对干扰进行很好的抑制,但存在计算复杂度高、不易硬件实现的问题,提出了一种正交预处理波束形成算法,分步实现波束指向和抗干扰功能,且计算复杂度低,便于工程应用。通过理论推导及算法仿真,验证了该方法的有效性。     

Sidelobe Suppression for Robust Beamformer Via the Mixed Norm Constraint

Applying a sparse constraint on the beam pattern has been suggested to suppress the sidelobe of the minimum variance distortionless response (MVDR) beamformer recently. To further improve the performance, we add a mixed norm constraint on the beam pattern. It matches the beam pattern better and encourages dense distribution in mainlobe and sparse distribution in sidelobe. The obtained beamformer has a lower sidelobe level and deeper nulls for interference avoidance than the standard sparse constraint based beamformer. Simulation demonstrates that the SINR gain is considerable for its lower sidelobe level and deeper nulling for interference, while the robustness against the mismatch between the steering angle and the direction of arrival (DOA) of the desired signal, caused by imperfect estimation of DOA, is maintained too.     

LCMV波束形成削弱多波束测深声呐的隧道效应

分析了海底多波束测深声呐中存在的隧道效应的产生机理,指出旁瓣干扰是导致隧道效应的重要因素。在最小方差无失真响应(Minimum Variance Distortionless Response)波束形成的原理基础上,提出使用线性约束最小方差(Linear Constrained MinimumVariance)波束形成技术来抑制隧道效应,该方法可以通过引入主瓣约束保证在抑制隧道效应的同时,主瓣不会因为干扰而发生畸变。通过计算机仿真实验,证明了LCMV波束形成算法抑制隧道效应的有效性。     

Sidelobe suppression for adaptive beamforming with sparse constraint on beam pattern

To suppress the sidelobe level of adaptive beamforming, sparse constraint on beam pattern is added to the conventional minimum variance distortionless response (MVDR) beamformer. The sparse constraint is an Lp-norm which can be explained as a diversity measure to evaluate the sparsity of the beam pattern. The proposed beamformer can not only reduce the sidelobe level, but also increase robustness against the mismatch problem caused by imprecise knowledge of the desired source.     

基于改进不确定集的稳健波束形成算法

基于不确定集约束的稳健MVDR波束形成算法在一定程度上依赖于期望信号导向矢量误差的先验知识,且当导向矢量失配较严重时干扰抑制性能也有所下降。为此,提出了一种基于投影变换的改进算法。该方法将约束方向矢量向信号干扰子空间投影,并作为新的约束方向矢量,从而等效于减小了期望信号导向矢量误差。这样,误差不确定参数只需设置为一较小的实数即可在任意导向矢量失配时获得最优的输出性能。计算机仿真结果证明了所提波束形成器具有较强的稳健性能。     

A New Post-filter Algorithm Combined with Two-step Adaptive Beamformer

The optimal microphone array, in the sense of minimum mean square errors (MMSE), includes two processing blocks: the minimum variance distortionless response (MVDR) beamformer and the single-channel Wiener filter, which acts as post-filter. In this paper, we propose a new post-filter algorithm based on assumptions that both the noise power attenuation factor (NPAF) and signal power attenuation factor (SPAF) are time invariant in the reverberant room. The algorithm recursively estimates both factors from available measurements and uses them in estimation of the post-filter parameters. Additionally, to overcome the problem of the poor performance of the MVDR beamformer in reverberant conditions, we propose the usage of the two-step (TS) MVDR algorithm. This algorithm improves the robustness of the beamformer and its ability to suppress the interferences using an estimate of the desired speaker transfer function. Although TS MVDR beamformer and proposed post-filter can work separately, or combined with other algorithms, the best performance is obtained when they work together. The performance of the proposed combination of new post-filter algorithm and TS MVDR beamformer is tested in a simulated reverberant room and compared with similar algorithms, which gave rather good results.     

A multiple time scale modularized adaptive beamformer

This paper analyzes the cascaded equivalent form of the minimum variance distortionless response (MVDR) beamformer. A unique feature of the modularized MVDR (M²VDR) beamformer is the ability to distribute adaptive degrees of freedom (DOF) among beamformer stages. This property of the M²VDR beamformer allows DOF to be adapted over different time scales. As a consequence of the multiple stage decomposition adaptive beamformer weights appear in a form which suggest an apparent increase in the number of DOF. To properly analyze this ease an alternative interpretation of adaptive DOF is introduced to establish the equivalence between the MVDR beamformer and its cascaded realization. In the second part of this paper the distribution for the output power estimate of a P stage M²VDR beamformer is derived. Analysis reveals the necessity of placing constraints on the adaptation time assigned to each beamformer stage. Simulation experiments are presented that demonstrate the applicability of the M ²VDR beamformer in resolving closely spaced sources under impulsive interference conditions     

一种改进的基于干扰源定向的零点预处理算法

基于在零陷对准干扰信号的情况下，零陷过深导致主瓣展宽、副瓣较高，使得主波束形状不佳等问题，提出了一种改进算法，该算法可以在准确抑制干扰信号的同时保持良好的主波束形状及副瓣电平；同时提出了原算法对干扰来向误差较为敏感的改进办法。计算机仿真结果证明了新算法的有效性。     

Modified null broadening adaptive beamforming: constrained optimisation approach

A constrained optimisation approach for null broadening adaptive beamforming is proposed. This approach improves the robustness of the traditional MVDR beamformer by broadening nulls for interference direction and the mainlobe for the desired direction. This optimisation is efficiently solved by semidefinite programming. The proposed approach, when applied to high altitude platform communications using a vertical linear antenna array, provides significantly better coverage performance than a previously reported null broadening technique