自适应波束形成算法的现状与发展动态

近十年自适应波束形成算法在通信、雷达、声纳、生物医学工程等科技领域中得到了极为广泛的应用.在实际应用中,如果信号源、天线阵列出现误差,传统的自适应波束形成算法性能将会下降.但是对于稳健的自适应波束形成算法,环境及天线阵列的误差和不确定性是必须要考虑的关键问题.这里对稳健的自适应波束形成算法的研究现状与发展动态进行了较为详细的评述.     

基于子空间跟踪的递推稳健自适应波束形成*

为了解决实时系统应用中,通用秩信号模型的稳健自适应波束形成算法受计算复杂度高的限制这一问题,基于子空间跟踪理论,运用梯度下降法提出了一种递推稳健自适应波束形成算法,有效降低了计算量,提高了系统性能,改善了阵列输出的信干噪比。仿真结果表明,该算法具有快速收敛性与优越的稳健性。     

波束形成算法研究与改进

近年来,智能天线在抗干扰方面应用广泛,多种不同的自适应波束成形算法被相继提出。首先讨论了LMS、GSC、MMSE三种波束形成算法的性能,对于均匀线性阵列天线,在相同条件的情况下,通过计算机仿真比较了三种算法的特点。最后提出了对MMSE算法的改进,通过对单个天线逐个权值的调整,使阵列输出信号与参考信号差异最小,减少计算复杂度,自适应地产生最优权值,实现了很好的抗干扰效果。     

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。     

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。     

基于改进最速下降LCMV算法的稳健波束形成

基于线性约束最小方差准则(LCMV)的自适应波束形成技术,在理想条件下能够在期望信号方向保证增益最大,同时在干扰方向形成零陷.但在实际阵列系统中,指向误差、阵元位置误差以及阵元相位误差均使得传统的LCMV准则算法出现性能下降.针对最优权矢量解算问题,提出了基于牛顿法及可变加载约束的改进SD-LCMV算法,并将两者与线性约束LMS算法及递归稳健LCMV算法进行仿真对比,结果验证了改进算法对误差的稳健性.     

基于水平极化定向天线阵的数字波束形成算法

研究窄带多径环境下基于短波水平极化定向天线阵列的数字波束形成算法,短波定向天线阵列流型复杂无法确定建模,常采用盲波束形成算法。针对现有盲波束形成算法所需先验信息多、弱信号效果差、使用范围有限且复杂度较高等问题,设计了一种短波多极化异构阵列协同处理方案,提出了基于自适应加载投影反馈的多径增强波束形成算法。该异构阵列包含短波垂直极化全向天线阵和短波水平极化定向天线阵,充分利用两种极化阵列优点,算法综合利用空间平滑、协方差矩阵求逆和空间投影等方法,通过自适应加载处理提高波形估计的稳健性。算法计算简便,所需先验信息少,非理想条件适应性强。推导了算法的实现过程和误差分析,计算机仿真验证了算法的有效性。     

采用二阶锥规划和压缩感知的方向图综合算法

针对常规自适应方向图综合在求解最优权值向量时需经过复杂的广义矩阵求逆运算,计算过程繁琐,占用存储空间大的缺陷,提出一种采用二阶锥规划与压缩感知理论的改进自适应方向图综合算法。改进的算法将传统算法中的误差性能函数通过数学变换转换成标准二阶锥规划形式快速求解。同时应用压缩感知理论将大规模阵列权值稀疏化处理,从而得到最优天线阵列权值向量并减少训练时间。仿真结果表明,采用二阶锥规划与压缩感知的改进算法在大规模阵列天线方向图综合时求解速度快,运算精度高,且在应用压缩感知后形成的方向图有较低旁瓣,干扰方向零陷深,接近满阵时的波束性能。     

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。     

基于单权值顺序优化准则的自适应波束优化算法

为了降低自适应天线阵列波束成形算法的复杂度,加快算法的收敛速度,基于单权值顺序优化SWO准则,给出了自适应阵列成形算法权值的快速收敛和更新方法。通过对该算法的理论分析与仿真,结果表明,相对于其它自适应波束优化算法,新方法能获得更高的收敛速度。而且在无须预设参数的前提下,基于单权值顺序优化准则的算法在能够达到与基于最小均方误差准则（MMSE准则）的优化算法相似性能的同时,使运算复杂度下降,收敛速度提高,因而更具有可实现性。     

基于蚁群优化算法的非均匀子阵划分技术

对于大型阵列天线应用于空域抗干扰系统中,为了降低硬件成本和减少计算复杂度,一般通过子阵划分技术将整个阵列划分为若干子阵,子阵内部采用模拟波束形成,子阵间采用数字自适应波束形成;由于均匀划分方法的波束形成方向图中存在栅零点,提出一种基于蚁群算法的非均匀子阵划分技术,将阵列最大输出信干噪比作为适应度函数,应用了概率计算与轮盘赌相结合的路径规划方法;结合信息素初始浓度和启发式信息范围,设计了新的适应度函数值与信息素更新的转换关系;最后对所提算法进行仿真,结果表明在不同规模、不同输入干噪比、不同期望信号扫描角度下,所提算法在输出信干噪比上优于均匀划分方法,且没有栅零点产生,与全阵元的自适应波束形成方向图、输出信干噪比相近,验证了该方法的有效性。     

Mobile satellite reception with a virtual satellite dish based on a reconfigurable multi-processor architecture

Traditionally, mechanically steered dishes or analog phased array beamforming systems have been used for radio frequency receivers, where strong directivity and high performance were much more important than low-cost requirements. Real-time controlled digital phased array beamforming could not be realized due to the high computational requirements and the implementation costs. Today, digital hardware has become powerful enough to perform the massive number of operations required for real-time digital beamforming. With the continuously decreasing price per transistor, high performance signal processing has become available by using multi-processor architectures. More and more applications are using beamforming to improve the spatial utilization of communication channels, resulting in many dedicated digital architectures for specific applications. By using a reconfigurable architecture, a single hardware platform can be used for different applications with different processing needs.In this article, we show how a reconfigurable multi-processor system-on-chip based architecture can be used for phased array processing, including an advanced tracking mechanism to continuously receive signals with a mobile satellite receiver. An adaptive beamformer for DVB-S satellite reception is presented that uses an Extended Constant Modulus Algorithm to track satellites. The receiver consists of 8 antennas and is mapped on three reconfigurable Montium TP processors. With a scenario based on a phased array antenna mounted on the roof of a car, we show that the adaptive steering algorithm is robust in dynamic scenarios and correctly demodulates the received signal.     

Adaptive minimum bit error rate beamforming assisted receiver for QPSK wireless communication

This paper considers interference limited communication systems where the desired user and interfering users are symbol-synchronized. A novel adaptive beamforming technique is proposed for quadrature phase shift keying (QPSK) receiver based directly on minimizing the bit error rate. It is demonstrated that the proposed minimum bit error rate (MBER) approach utilizes the system resource (antenna array elements) more intelligently, than the standard minimum mean square error (MMSE) approach. Consequently, an MBER beamforming assisted receiver is capable of providing significant performance gains in terms of a reduced bit error rate over an MMSE beamforming one. A block-data based adaptive implementation of the theoretical MBER beamforming solution is developed based on the classical Parzen window estimate of probability density function. Furthermore, a sample-by-sample adaptive implementation is also considered, and a stochastic gradient algorithm, called the least bit error rate, is derived for the beamforming assisted QPSK receiver.     

最速下降与共轭梯度在数字波束形成中的研究

在自适应波束形成技术中,共轭梯度法是求解最优化问题的一种常用方法,最速下降法在不需要矩阵求逆的情况下,通过递推方式寻求加权矢量的最佳值。文中将最速下降法与共轭梯度法有机结合,构造出一种混合的优化算法。该方法在每次更新迭代过程中,采用负梯度下降搜索方向,最优自适应步长,既提高了共轭梯度算法的收敛速度,又解决了最速下降法在随相关矩阵特征值分散程度增加而下降缓慢的问题,具有收敛速度快,运算量低的特点。计算机仿真给出了五阵元均匀线阵的数字波束形成系统实例,分别从波束形成、误差收敛及最佳权值等方面与传统LMS 算法进行了比较分析,结果表明了该方法的可行性与有效性。     

Adaptive processing for beamforming with coherent interference using uniform circular arrays

The paper deals with the problem of adaptive array beamforming using a uniform circular array (UCA) in the presence of coherent interference. The well-known scheme of spatial smoothing (SS) widely used to tackle the coherent problem in the cases of 1-D uniform linear array (ULA) and uniform rectangular array (URA) cannot work for the UCA case. This is mainly due to the fact that the direction vector of each signal received by a UCA does not possess a Vandermonde structure. In this paper, we present a method based on subarray beamforming in conjunction with an averaging scheme to effectively mitigate the effect due to coherent interference in the UCA case. Theoretical analysis regarding the validity of the proposed method is also presented. Several simulation examples are provided for showing the effectiveness of the proposed method.     

Robust beamforming methods for multipath signal reception

Novel robust beamforming algorithms are proposed to avoid signal cancellation in a multipath environment. The robustness is achieved by forcing the array responses to the signal of interest and its multipath signals in the pre-estimated clusters to be no less than unity while minimising the output power. Since the array responses to all the multipath signals are constrained, they will not cancel the signal of interest completely as in the conventional adaptive beamforming methods. The effectiveness of the proposed algorithms is verified by computer simulations.     

Wideband beamforming for multipath signals based on frequency invariant transformation

It is well known that the performance of conventional adaptive beamformers degrades severely due to the presence of coherent or correlated interferences(multipath propagation) and various techniques have been developed to improve the performance of the beamformer.However,most of the work in the past has been focused on the narrowband case.In this paper,the wideband beamforming problem in the presence of multipath signals is addressed,with a novel approach proposed by employing a pre-processing stage based on the frequency invariant beamforming(FIB) technique.In this approach,the received wideband array signals are first processed by an FIB network,and then a traditional narrowband adaptive beamformer or an appropriate instantaneous blind source separation(BSS) algorithm can be applied to the network outputs.It is shown that with the proposed structure,cancellation of the desired signal is reduced,leading to a significantly improved output signal to interference plus noise ratio(SINR).     

宽线性波束形成技术综述

在圆信号的假设条件下,传统的线性波束形成技术仅仅利用了天线阵列观测矢量的协方差矩阵。然而,现代通信领域中的很多人工调制信号具有非圆特性,观测矢量不仅存在协方差矩阵,还存在伪协方差矩阵。宽线性波束形成技术是针对非圆信号环境提出的一类新技术,该类技术通过构造一个包含天线阵列观测矢量及其共轭的扩展观测矢量,建立有利于特定方向信号接收的目标函数及约束,推导出相应的扩展权重矢量。同传统线性波束形成技术相比,宽线性波束形成技术对非圆信号的接收性能有了明显提升,近年来,该类技术成为国内外研究热点之一。本文介绍了圆信号和非圆信号定义,给出了阵列模型并介绍了最小方差无畸变响应波束形成,对各种宽线性波束形成算法进行了综述,并对宽线性波束形成技术的下一步研究方向进行了展望。     

Bidirectional microphone array with adaptation controlled by voice activity detector based on multiple beamformers

Multimedia Tools and Applications - Ambient noise suppression in a reverberant room is usually performed by the microphone array. The adaptive beamforming, whose typical representative is minimum...