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。     

相关阵在抑制局部相关噪声中的应用

本文提出用阵元间互相关作为基元加权求和形成波束(相关阵)，并给出用来抑制线阵局部强相关干扰的一种权向量实现方法。海上试验数据处理结果表明，利用本文提出的权向量实现相关阵比CBF阵有较高的信噪比增益和较好的抗噪声干扰能力。     

一种前视阵列SAR系统的天线设计和分析方法

阵元数太多导致前视阵列SAR系统天线成本高和设计复杂,如何以较少的阵元数获取较高的成像质量是前视阵列SAR系统面临的重难点问题.根据系统成像质量要求,结合波束扫描、栅瓣抑制等技术,本文提出一种稀疏收发天线阵的设计方法.理论分析和仿真实验结果表明,该方法在保证一定成像质量的前提下,有效降低了阵元数量,提高了系统信噪比,具有一定的应用价值.     

Polarization reconfigurable microstrip phased array

In this paper, the design and the experimental validation of a polarization reconfigurable microstrip phased array is presented. The reconfigurability between the right-handed (RHCP) and left-handed (LHCP) circular polarization is achieved using electronic switches (PIN diodes) combined with truncated corners microstrip radiators. In the design, special attention was given to the matter of reducing back lobe radiation effects using the concept of asymmetric positioning of the radiators with respect to the ground plane. Afterward, the main lobe axial ratio behavior for several beam steering and side lobe level conditions are investigated. Finally, the polarization reconfigurability is achieved and the design is validated through the good agreement between theoretical and experimental results.     

Energy efficiency maximization for IRS-assisted NOMA networks

In this paper, we consider a non-orthogonal multiple access (NOMA) system assisted by intelligent reflecting surface (IRS). As an emerging technology that has received widespread attention, IRS can reconfigure the wireless channel environment by adjusting the relationship between the incident angle and the exit angle, thereby improving system performance. Our goal is to use the flexible assistance of IRS to achieve the maximum energy efficiency of the NOMA system. Our design objects are the beam vector design of the base station and the phase matrix design of the IRS. The original problem is highly non-convex. We consider using the block coordinate descent method to design the phase matrix and beam vector separately. Simulation results show that our proposed scheme has better performance than traditional OMA and systems without IRS assistance.     

Frequency Downconverting Fiber Grating-Based Beamformers for High-Capacity Phased Arrays

A technique is presented to remove the beat noise limitation in multibeam beam formers using a simple all-optical microwave frequency downconversion technique prior to performing the true-time delay equalization in the optical domain. The frequency conversion concept enables a significant increase in beam-number capac ity to be achieved due to the elimination of beat noise limits, and also effectively removes the power penalty due to chromatic dispersion limitations of the chirped grating units in the beamformer. The Bragg grating requirements for the frequency converting beamforming network are analyzed and show that tanh-profile apodized gratings can meet the isolation, reflectivity, and narrow bandwidth requirements. For an X-band phased array, more than a twofold increase in beam capacity is shown through the use of the frequency conversion technique with the grating-based beamformer, and the resulting beamformer has the minimum number of optical interconnects with true-time delay operation.     

Transverse oscillations for tissue motion estimation

This paper gives an overview of the methods developed for tissue motion estimation using transverse oscillation images (TO). TO images are specific radiofrequency ultrasound images featuring oscillations in both spatial directions. The initial studies on TO were published in the late 1990s. This paper reviews the main ideas and applications behind this motion estimation approach. First the origin and motivation of TO is briefly reviewed. Then the beamforming methods that lead to TO images are given, detailing the receive-only approach and the transmit-and-receive approach using synthetic aperture data. The different medical applications where TO has been used are discussed (blood flow, elastography and echocardiography), showing how it can improve motion estimation. Finally, the future perspectives of TO are outlined.