基于传输公平性的多无人机通感一体化空间部署与波束成形设计

针对农村偏远地区通信不畅的临时突发性问题,该文提出一种自适应的多无人机(UAV)辅助通感一体化(ISAC)机制,在地面用户和感测目标呈簇状随机分布的情况下,通过合理调度多无人机实现覆盖式通信保障,为无人机使能的通感一体系统提供了一种新的解决思路和方案。该文主要研究了无人机空间部署及其对地面设备的波束成形等问题,在空地关联约束条件下,系统可通过优化无人机的通信和感知波束成形变量组,最大限度地提高用户传输可达速率的下限,同时保证基本的通感需求。为了有效解决所考虑的非凸优化问题,该文借助基于高斯核的均值漂移算法(MS),用以处理关联策略中的混合整型线性问题,此外,结合2次变换与连续凸逼近(SCA)的相关技巧,采用块坐标下降(BCD)的方式优化波束成形,以获取次优解。数值结果验证了自适应机制的有效性。     

基于二次型约束的鲁棒自适应波束形成算法

针对期望信号方向向量存在偏差会导致自适应波束形成算法的性能急剧下降这一问题,该文提出了一种基于二次型约束的鲁棒自适应波束形成算法。通过对期望信号波达方向附近范围内的方向向量的误差模值进行约束,来提高算法的鲁棒性,并在此约束条件下对权重向量进行优化求解,且优化解中的参数能够准确求出。该算法可有效地控制波束主瓣区域内信号的畸变,并能够抑制方向向量偏差所带来的影响,提高了系统的鲁棒性,同时使干扰和噪声的功率输出最小,保证了对干扰信号的抑制能力,改善了阵列输出的信干噪比,使其更接近最优值。仿真结果验证了所提算法的有效性与优越性。     

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.     

相干环境下LCMV自适应阵列抗干扰问题研究

相干干扰环境下,自适应阵列性能会急剧下降,常用的处理方法是空间平滑。然而,采用常规均匀空间平滑的自适应阵列对相干干扰的抑制能力较差,而且会损失阵列孔径。该文提出一种改进的相干干扰抑制方案：首先,提出了一种自适应的加权空间平滑(Weighted Spatial Smoothing, WSS)算法,它将各子阵的相关矩阵进行加权平均,可以最大程度地解相干;然后,在WSS基础上,利用线性约束最小方差(LCMV)准则得到子阵波束形成器最佳权矢量;最后,提出了一种利用子阵间的相位关系对全阵做波束形成的方法。该方案大大提高了阵列对抗相干干扰的能力,同时避免了一般空间平滑后阵列的孔径损失。理论分析和仿真结果说明了方法的有效性和稳健性。     

多维正交天线的鲁棒波束成形算法分析

将服务质量(QoS)概念引入码分多址(CDMA)系统鲁棒波束成形(BF)的分析,通过对基站端天线阵元空间排列的调整,使接收信号同时在三维空间进行处理,使用凸优化算法对各维信号进行多目标约束优化,最终形成所需的合成发射波束模式。文中最后给出了仿真结果,并与WUSIC及MMSE算法进行了性能比较。     

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.     

Broadband optimal contrast resolution beamforming

This paper proposes a novel receive beamformer architecture for broadband imaging systems that uses unique finite impulse response (FIR) filters on each channel. The conventional delay-and-sum (DAS) beamformer applies receive apodization by weighting the signal on each receive channel prior to beam summation. Our proposed FIR beamformer passes the focused receive radio frequency (RF) signals through multi-tap FIR filters on each receive channel prior to summation. The receive FIR filters are constructed to maximize the contrast resolution of the system’s spatial response. The broadband FIR beamformer produces spatial point spread functions (PSFs) with narrower mainlobe widths and lower sidelobe levels than spatial PSFs produced by the conventional DAS beamformer.We present simulation results showing that FIR filters of modest tap lengths (3-7) can yield marked improvement in image contrast and point resolution. Specifically we show that 7-tap FIR filters can reduce sidelobe and grating lobe energy by 30 dB and improve contrast resolution by as much as 20 dB compared to conventional apodization profiles. This improvement in contrast resolution comes at the expense of a decrease in beamformer sensitivity. We investigate the effects of phase aberration and show in simulation results that the multi-tap FIR beamformer outperforms the unaberrated DAS beamformer by 8-12 dB even in the presence of moderate aberration characterized by a root-mean-square strength of 28 ns and a full-width at half-maximum correlation length of 3.6 mm. We show experimental results wherein multi-tap FIR filters decrease sidelobe energy in the resulting 2D spatial response while achieving a narrow mainlobe. We also show results where the FIR beamformer improves the contrast to noise ratio (CNR) in simulated B-mode cyst images by more than 4 dB. Our algorithm has the potential to significantly improve ultrasound beamforming in any application where the system response is reasonably well characterized. Furthermore, this algorithm can be used to increase contrast and resolution in one-way beamforming systems such as acousto-optic and opto-acoustic imaging.     

一种改进的奇异值分解语音增强方法

该文将多麦克语音增强方法用于单麦克语音增强,给出了一种改进的奇异值分解语音增强方法。该方法首先对输入矩阵进行雅克比奇异值分解,用得到的奇异值矢量构造语音增强滤波器;然后用输入矩阵与滤波器权矢量相乘来构造各路信号;最后采用麦克风阵列波束形成的方法,得到增强后的语音信号。仿真结果表明,该方法能有效地去除加性噪声,并且改善了语音质量。     

分布式卫星SAR的波束形成和多视处理成像

针对分布式卫星SAR的正侧视工作模式,该文建立了雷达信号的回波模型,提出了分布式卫星SAR中单个星载SAR的成像算法和利用波束形成和多视处理合成分布式卫星SAR图像的算法。理论分析和仿真结果表明:该算法能在不改变图像分辨力的情况下提高图像的信噪比和抑制相干斑,改善图像质量。     

Ergodic capacity analysis for SIMO cognitive fading channel in spectrum sharing environment

We consider the Signal-to-Interference plus Noise Ratio (SINR) balancing problem involving joint beamfoming and power allocation in the Cognitive Radio (CR) network, wherein the Single-Input Multi-Output Multiple Access Channels (SIMO-MAC) are assumed. Subject to two sets of constraints: the interference temperature constraints of Primary Users (PUs) and the peak power constraints of Cognitive Users (CUs), a low-complexity joint beamforming and power allocation algorithm called Semi-Decoupled Multi-Constraint Power Allocation with Constraints Preselection (SDMCPA-CP) for SINR balancing is proposed. Compared with the existing algorithm, the proposed SDMCPA-CP can reduce the number of matrix inversions and matrix eigen decompositions significantly, especially when large numbers of PUs and CUs are active, while still providing the optimal balanced SINR level for all the CUs.