Generalized eigenvector problem for Hermitian Toeplitz matrices and its application to beamforming

The generalized eigenvector problem (GEP) for Hermitian Toeplitz matrices is studied and some properties related to its eigenvectors and the associated eigenfilters are derived. Zero locations of the eigenfilters are also investigated and all of the results are applied to the maximum SINR (signal-to-interference-plus-noise ratio) beamforming problem based on ULAs (uniform linear arrays), since maximizing output SINR can be formulated as a generalized eigenvector problem where the matrix pair consisting of the desired signal correlation matrix and interference plus noise correlation matrix. Theoretical analysis based on a three-element ULA is provided, supported by simulations.     

Adaptive null steering beamformer implementation for flexible broad null control

An implementation of adaptive null steering beamformer for flexible broad null control, based on constrained recursive updating of array response zeros and spatial FIR filters, is presented. The design allows the beamformer to form broad nulls and control their widths readily. The new method is of great advantage for sensor array in which the number of array elements is very large compared with the number of interferences the array is designed to suppress. The new beamformer is useful and effective in the environment where both stationary and moving interference signals exist since it can steer both sharp and controlled broad nulls in the appropriate directions. When compared with the conventional LMS covariance matrix taper (CMT) based broad null synthesis method, the proposed beamformer has a faster convergence rate; and compared with the QR-RLS CMT based broad null synthesis method, the proposed method has a lower complexity.     

A novel acoustic emission beamforming method with two uniform linear arrays on plate-like structures

A novel acoustic emission (AE) source localization approach based on beamforming with two uniform linear arrays is proposed, which can localize acoustic sources without accurate velocity, and is particularly suited for plate-like structures. Two uniform line arrays are distributed in the x-axis direction and y-axis direction. The accurate x and y coordinates of AE source are determined by the two arrays respectively. To verify the location accuracy and effectiveness of the proposed approach, the simulation of AE wave propagation in a steel plate based on the finite element method and the pencil-lead-broken experiment are conducted, and the AE signals obtained from the simulations and experiments are analyzed using the proposed method. Moreover, to study the ability of the proposed method more comprehensive, a plate of carbon fiber reinforced plastics is taken for the pencil-lead-broken test, and the AE source localization is also realized. The results indicate that the two uniform linear arrays can localize different sources accurately in two directions even though the localizing velocity is deviated from the real velocity, which demonstrates the effectiveness of the proposed method in AE source localization for plate-like structures.     

传声器阵列声压级在线校准*

在户外环境中对某一目标噪声源进行声压级测量时,由于单个传声器不能在多声源干扰情况下有效监测目标信号,为了有效抑制非目标信号的干扰,通常利用传声器阵列进行波束形成从而对目标信号进行增强。MEMS传声器阵列由于体积小,价格低等优点而得到广泛使用,为了解决在户外进行噪声监测时,MEMS然而MEMS传声器阵列器件的工艺误差和灵敏度退化问题会导致波束形成滤波器的性能下降存在由器件工艺误差和老化所导致的声压级测量不准确问题,从而影响声压级的测量结果。为了解决这一问题,本文介绍了一种通过比较补偿参考传声器与传声器阵列之间的测量声压级之偏差进行从而实时在线校准的方法。该方法利用TDOA多声源定位方法在时频点上对实时采集的信号对所采集的信号在时频点上挑选有效目标信号进行有效挑选,并利用参考传声器的标准频响特性去修正阵列的声压级测量误差值。为了验证方法的可行性,本文通过实验比较了不同环境噪声干扰下的测量声压级差与无干扰条件下的测量声压级差的一致性,结果证明该校准方法在具有较好高的精确性和鲁棒性,并且可推广于任意一种阵型的传声器阵列声源定位装置噪声监测装置。     

Physical layer security using beamforming techniques for 5G and beyond networks: A systematic review

It has been predicted that by the year 2030, 5G and beyond 5G (B5G) networks are expected to provide hundreds of trillions of gigabytes of data for various emerging applications such as augmented, mixed, and virtual reality (AR/MR/VR), wireless computer-brain interfaces (WCBI), connected robotics and autonomous systems. Most of these applications share data with each other using an open channel, i.e., the Internet. The open and broadcast nature of wireless channel makes the communication susceptible to various types of attacks (e.g., eavesdropping, jamming). Thus, there is a strong requirement to enhance the secrecy of wireless channel to maintain the privacy and confidentiality of transmitted data. Physical layer security (PLS) has evolved as a novel concept and robust alternative to cryptography-based techniques, which have a number of drawbacks and practical issues for 5G and beyond networks. Beamforming is an energy-efficient PLS technique, that involves steering of the transmitted signal in a particular direction, while considering that an intruding user attempts to decode the transmitted data. Motivated from these points, this article summarizes various beamforming based PLS techniques for secure data transmission in 5G and B5G networks. We investigate the eight most promising techniques for beamforming in PLS: Non-Orthogonal Multiple Access (NOMA), Full-Duplex Networks, Massive Multiple-Input Multiple-Output (MIMO), Cognitive Radio (CR) Network, Relay Network, Simultaneous Wireless Information and Power Transfer (SWIPT), UAV Communication Networks and Space Information Networks, and Heterogeneous Networks. Moreover, various physical layer threats and countermeasures associated with 5G and B5G networks are subsequently covered. Lastly, we provide insights to the readers about constraints and challenges for the usage of beamforming-based PLS techniques in various upcoming future applications.     

时间相干信道下波束赋形系统的有限反馈方法

该文提出一种新的基于树形码书的有限反馈方法,由于相邻帧的时间相干性,信道向量的量化码字可建模为一阶有限状态马尔可夫链,当前帧信道向量被量化到前一帧最大转移概率码字的子码字上,该子码字的索引以1 bit反馈给发射端。链路仿真结果表明本文所提方法相比普通反馈方法可明显改善误码率性能,某些条件下还可降低反馈速率。     

多径环境中多用户波束形成与DOA估计

该文讨论了多径环境中多用户的波束形成与DOA估计问题,采用了解相关检测器来估计用户空间特征,提出了循环空间平滑算法(CSS)基于空间平滑的保持阵列权值维数不变的多用户波束形成算法,其理论依据是采样信号协方差矩阵的逆矩阵循环传递等效于对其求均值;利用了估计出的用户空间特征构造协方差矩阵进行空间平滑的高分辨DOA估计.仿真结果说明了循环空间平滑算法应用于多用户波束形成具有更优的抗干扰性能。     

有限反馈MISO-OFDM系统中基于误码率的波束成形

该文提出了一种在有限反馈条件下多入单出正交频分复用(MISO-OFDM)系统中基于误码率的波束成形方案。将OFDM符号的所有子载波分成若干簇,从码本中选择能够最小化该簇每个子载波的平均误码率的码字,作为该簇的波束成形向量。此方案既能降低反馈量,又能取得较低误码率。同时,为避免所提方案中探求最优解时的穷尽搜索,还基于簇内不同子载波信道频响之间的相关性提出了一种简化的次优算法。仿真结果表明,在典型参数设置下,所提方案能够以较低计算复杂度取得比其他已有方案更好的误码率性能。     

空间重采样法恒定束宽波束形成器设计

本文视均匀线列阵为连续线阵的均匀离散采样，将宽带方位估计中的空间重采样思想用到恒定束宽波束形成器设计中，并从滤波器设计的观点出发，将阵元权系数等效为空间滤波器的脉冲响应，提出用恢复公式计算不同频率所对应的阵元权系数，从而利用频域波束形成的方法完成恒定束宽波束形成器设计。     

一种改进的极化敏感阵列解相干算法

在相干信号源情形下,常用的极化敏感阵列信号处理方法(如参数估计、波束形成等)会出现性能下降甚至失效的现象。该文在极化平滑算法的基础上提出一种改进的解相干算法,通过对各子相关矩阵选择适当的加权系数,使平滑之后的相关矩阵具有Toeplitz的形式,进而消除信号之间的相干性。该文推导了最优加权系数的表达式及最大解相干信号个数,并利用加权平滑之后的相关矩阵完成了参数估计和波束形成。计算机仿真结果表明改进的方法具有比常规极化平滑算法更优越的性能,且适用于非均匀噪声和相干噪声的情况。