球体表面圆环阵模态域稳健高增益波束形成方法研究

通过对考虑障板影响下噪声互谱矩阵的精确求解,给出了一种计算刚性球体表面圆环阵阵增益的模型,并在此基础上提出了一种模态域二阶锥规划稳健高增益波束形成方法。该方法根据相位模态波束形成理论,将阵元域稳健加权向量转换为模态域的稳健模态系数,从而设计出不同模态阶数下的稳健高增益波束。由于采用了白噪声增益约束以及低频段较低的模态阶数,该方法提高了超增益波束形成器的稳健性。仿真结果表明该方法能够提供更多的稳健波束形成的方案,在多个关联的波束性能指标之间获得比常规方法和阵元域稳健性方法更合理的折衷。      

一种稳健的柔性阵波束形成方法

由于航向、航速的改变以及水流、风浪等因素的影响,柔性线列阵在实际应用过程中阵型畸变是不可避免的。一方面,这种畸变使得许多假设阵型无畸变的波束形成方法的性能受到严重的影响;另一方面,目前很多的阵型估计方法仍不是很成熟,很难准确估计阵元的实际位置。本文提出将柔性阵列分为一段阵元位置已知的子阵和若干段阵元未知的子阵,利用不同子阵接收信号的互相关即可获得所需要的波束形成加权系数,从而在不需要知道阵元确切位置信息的情况下实现目标方法的估计。     

利用水平阵模态域波束形成判别声源深度*

针对近水面声源和水下声源的深度判别问题,根据近水面声源难以激发低阶模态的物理现象,研究利用声源波数谱结构和波数位置的不同来分辨近水面声源和水下声源。通过采用MVDR的谱估计方法进行模态域波束形成,补偿水平阵各阵元之间各号简正波的相位差,获得主瓣窄、旁瓣低的声源信号波数谱。波数谱的波数位置与频率呈近似线性关系,水中声速剖面、海底参数、海深都会影响波数谱的具体结构和位置。此外,声源信号的到达角估计误差同样也会影响波数谱主瓣的位置估计。数值仿真结果表明,在浅海负跃层声速剖面条件下,可利用水平阵模态域波束形成判别声源深度,区分近水面声源和水下声源。     

高增益对角减载波束形成方法研究

实际的海洋噪声包括不相关噪声成分和相关噪声成分,针对不相关噪声仅仅影响接收数据协方差矩阵对角元素的这一现象,提出一种基于对角减载技术的高增益最小方差无畸变响应法(minimum variance distortionless response,MVDR).在稳健性足够的前提下,首先,按照一定准则选取约束量,利用加权向量范数约束法保证方法的稳健性。然后,利用牛顿迭代法计算得到对角减载系数。最后,将减去对角减载系数的协方差矩阵应用到MVDR波束形成方法中。仿真和海试数据处理结果表明,对角减载MVDR波束形成方法在保证稳健性的同时,提高了阵增益和多目标分辨能力。通过调整减载系数,能够在稳健性与阵增益之间进行折中。     

圆柱阵子阵分级处理的稳健超指向性波束形成方法

提出了圆柱阵子阵分级处理的稳健超指向性波束形成方法。首先建立了圆柱阵分两级子阵进行波束形成的信号模型,接着利用空间均匀噪声场中噪声互谱矩阵的循环特性得到基于特征波束分解与综合模型的圆柱阵超指向性的最优解,然后仿真研究了其误差敏感度函数、阵增益和波束图等性能指标,并与圆柱阵的传统全局处理方法进行了对比。提出的分两级子阵处理的超指向性方法与传统全局处理方法相比不仅降低了数据存储量和波束形成计算量,而且进一步提升了稳健性,并且在低频段的阵增益远远高于常规波束形成的值,对水下声呐阵列的设计具有一定的参考价值。     

一种基于模态域波束形成的水平阵被动目标深度估计

水面水下目标分辨与识别一直是被动声呐探测领域的难题.利用一种水平阵模态域波束形成算法获得己知方位目标声源的各阶模态强度,将其与不同深度的各阶参考模态强度进行匹配,最终实现了对声源的深度估计.仿真结果表明,该算法可以在信噪比为-10 dB的情况下,用300Hz带宽的信号样本,实现对声源深度的有效估计.系统分析了不同参数和不同波导条件对该方法目标深度估计性能的影响.其中,阵元数越多,模态样本数越多,计算频段越宽,方位估计精度越高,有效阵长越长,深度估计的性能越好.阵元间距和波导深度的变化不会影响该方法的深度估计性能,并且该方法的深度估计性能在声速剖面、海底参数等波导条件存在扰动时具有鲁棒性.     

一种稳健的恒定束宽波束形成方法

考虑到信号的方向信息存在误差时,宽带聚焦变换波束形成方法的稳健性会急剧下降,为了克服这种缺点,将稳健的二阶锥规划波束形成用于聚焦变换方法中,提出一种稳健宽带恒定束宽波束形成方法并将其应用于声呐探测。二阶锥规划波束形成是通过对阵列流形进行约束求解得到准确的权值,从而减少聚焦数据误差,避免估计畸变,得到恒定束宽,提高了聚焦变换恒定束宽波束形成器的性能。借助计算机对圆环形传感器阵列在宽频段内进行恒定束宽波束优化设计,并进行了实验研究,结果表明该方法对信号信息误差有很好的宽容性,能实现我们期望得到的恒定束宽波束图,能应用于实际的声呐探测中。并且比传统的二阶锥恒定束宽方法有更高的稳健性。     

陆架斜坡海域声场特性对常规波束形成阵增益的影响

常规波束形成是水下阵列信号处理中最基本的处理环节.陆架斜坡海域特殊地形所带来的水下声场变会影响阵增益.以往的研究中,只关注声场相关性对阵增益的影响.本文基于水声信号传播理论,研究常规束形成阵增益与陆架斜坡海域水下声场之间的关系,证明声场相关性和传播损失是影响阵增益的内在因素并推导了各向同性噪声场中常规波束形成阵增益与两者之间的关系式.结果表明:1)常规波束形成阵增益声场相关性和声传播损失共同决定,其最大值不超过10lg M;2)当两个不同接收位置的传播损失相似时,阵各阵元间的声场相关性越高,阵增益越大;3)当两个不同接收位置的传播损失相差较大时,阵增益与声相关性不再是正相关关系.利用RAM声场软件,在陆架斜坡海域上坡波导环境中,对水平阵常规波束形成增益与声场相关性和传播损失的关系进行仿真验证.     

典型概率密度背景下四阶累积量波束形成的阵增益

在理论上零均值高斯分布噪声的四阶累积量恒等于零,而实际噪声和混响的概率密度是影响四阶累积量波束形成技术性能的关键问题。本文针对海洋环境噪声与海底混响的瞬时幅度分布,分别推导了四阶累积量波束形成阵增益函数;建立了阵增益与阵元数、海洋环境噪声和海底混响统计特性的四阶矩和二阶矩及输入信噪比的关系;确定了与常规波束形成阵增益之间存在临界信噪比,高于临界信干比时四阶累积量波束形成可以获得比常规波束形成更高的阵增益与分辨率。实验数据处理结果验证了四阶累积量波束形成阵增益和分辨率理论结果的一致性。     

波束空间能量约束的稳健自适应波束形成

为改善波束形成器在一定失配条件下的工作性能,提出了一种稳健自适应波束形成方法。该方法通过设计信号在波束空间能量分布的约束条件,利用阵列数据协方差矩阵,结合迭代二阶锥规化方法,实现信号驾驶向量的估计,最后利用该估计得到最小方差无失真响应波束形成器。该方法在较恶劣的失配条件下也可以自适应地准确估计信号驾驶向量并保证其成分无失真地通过,使系统的稳健性得到改善。数据仿真结果表明,该方法在理想条件下与成熟的对角加载法性能相当,在失配条件下则优于后者。     

On direct optimization in mode space for robust supergain beamforming of circular array mounted on a cylinder

A direct robust supergain method in mode space for the circular array mounted on an infinite rigid cylinder was proposed,and then it was also applied to the circular array mounted on a finite rigid cylinder which is more practical.According to the concept of phase modes,the beam pattern is expanded into a series of eigen-beams multiplying by modal coefficients. The modal noise cross spectral matrix is calculated from sound scattering theory.In the original modal robust supergain method,the coefficient vector in mode space is transformed indirectly from the weighting vector in sensor space.The method presented here gives the most suitable modal coefficient vector directly under the related constraint conditions based on the second-order cone programming.The results of simulation show that the direct modal robust supergain method can not only improve robustness using the white noise gain constraint, but also change the mode orders to provide compromise between array gain and robustness in low frequencies.Beam performance measures such as sidelobe level can be optimized as well as array gain,so this method can give more effective schemes for designing practical robust supergain beamformers.     

Robust supergain beamforming for circular array via second-order cone programming

The phenomenon of supergain for a circular array and its robust beamforming are presented. The coplanar superdirective array gain of the circular array, although it is not so extreme as an endfire line array, outperforms a lot over that of a conventional delay-and-sum beamformer in isotropic noise fields when the inter-element spacings are much smaller than one-half wavelength. However, optimum beamforming algorithms can be extremely sensitive to slight errors in array characteristics. The performance are known to degrade significantly if some of underlying assumptions on the sensor array is violated. Therefore, white noise gain constraint is used to improve the robustness of the supergain beamformer against random errors. We show that the design of the weight vector of robust supergain beamformer can be reformulated as a form of second-order cone programming and resolved efficiently via the well-established interior point method. Results of computer simulation for a 24-element circular array confirm satisfactory performance of the approach proposed in this paper.     

刚性圆柱体上圆阵波束形成性能分析

以环绕在刚性圆柱体上的均匀圆阵为阵列模型,分析了刚性圆柱体对圆阵响应的影响,在声场分解所得到的相位模式空间,推导了相位模式波束形成阵列和延迟求和波束形成阵列的白噪声增益和指向性指数的定量表达式,分析了它们在不同频率段的变化规律。在存在和不存在刚性圆柱体两种情况下,对两种阵列性能进行了对比分析。研究了圆阵与圆柱体之间存在间隙时对阵列接收信号及阵列性能的影响。仿真结果表明,在两种情况下相位模式波束形成处理都具有频率不变的指向性,但在低频段牺牲了阵列的鲁棒性;延迟求和波束形成处理在整个频率段具有较好的鲁棒性,但随频率的降低其波束指向性下降,直至变成各向同性阵列。存在刚性圆柱体时,两种阵列鲁棒性均有了一定的提高,前者的指向性不变,而后者的指向性得到了提高。圆阵与圆柱体之间的间隙会降低阵列在高频段的鲁棒性。     

Beamforming with a circular array of microphones mounted on a rigid sphere (L)

Beamforming with uniform circular microphone arrays can be used for localizing sound sources over 360°. Typically, the array microphones are suspended in free space or they are mounted on a solid cylinder. However, the cylinder is often considered to be infinitely long because the scattering problem has no exact solution for a finite cylinder. Alternatively one can use a solid sphere. This investigation compares the performance of a circular array mounded on a rigid sphere with that of such an array in free space and mounted on an infinite cylinder, using computer simulations. The examined techniques are delay-and-sum and circular harmonics beamforming, and the results are validated experimentally.     

双基地多输入多输出虚拟阵列的稳健低旁瓣波束优化技术

双基地多输入多输出(MIMO)系统需要对目标的波达角和波离角进行二维估计,针对高分辨算法中阵列协方差矩阵处理运算量大以及估计性能对阵列流形失配敏感的缺陷,提出了一种基于二阶锥规划的抗阵列流形失配的双基地MIMO虚拟阵列波束优化算法.该方法利用MIMO的波形分集技术与双基地的目标定位解算,通过波达角和波离角在双基地定位椭圆上的对应关系,将双基地MIMO的二维合成方向矢量转化为一维的虚拟阵列流形,并证明了双基地MIMO虚拟阵列的波束图等效为发射波束图在接收阵角度域上的响应和接收波束图的合成.在优化波束图旁瓣的同时,该算法兼顾了固定方向上的相干干扰抑制,并提高了双基地MIMO虚拟阵列波束优化抗阵列流形失配的能力.通过波束图和方位谱优化的仿真分析和水池试验,验证了算法的有效性.     

声矢量圆阵相位模态域目标方位估计

为了实现矢量传感器在圆阵阵型下的应用,文中提出了一种适合于声矢量圆阵的目标方位估计算法。该算法首先将声矢量圆阵阵元域信号分解为一系列相互正交的相位模态,在相位模态域构造声压和质点振速的互协方差矩阵,然后进行MUSIC方位估计.理论分析和仿真结果表明,文中算法比相同阵型的声压阵MUSIC方位估计算法具有更好的噪声抑制能力、方位估计性能以及多目标分辨能力,试验结果也表明本文算法具有更好的噪声抑制能力以及更好的目标方位估计性能。该算法实现了声压和质点振速的相干处理,充分利用了声矢量传感器的平均声强抗噪原理,具有较强的抗各向同性噪声能力,并可以将子空间类DOA(Direction of Arrival)估计算法和相位模态域阵列信号处理技术有机结合起来,实现了声矢量传感器在圆阵阵型条件下的高分辨DOA估计。     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Adaptive beamforming for array signal processing in aeroacoustic measurements

Phased microphone arrays have become an important tool in the localization of noise sources for aeroacoustic applications. In most practical aerospace cases the conventional beamforming algorithm of the delay-and-sum type has been adopted. Conventional beamforming cannot take advantage of knowledge of the noise field, and thus has poorer resolution in the presence of noise and interference. Adaptive beamforming has been used for more than three decades to address these issues and has already achieved various degrees of success in areas of communication and sonar. In this work an adaptive beamforming algorithm designed specifically for aeroacoustic applications is discussed and applied to practical experimental data. It shows that the adaptive beamforming method could save significant amounts of post-processing time for a deconvolution method. For example, the adaptive beamforming method is able to reduce the DAMAS computation time by at least 60% for the practical case considered in this work. Therefore, adaptive beamforming can be considered as a promising signal processing method for aeroacoustic measurements.     

Optimization of direct modulation rate for circular microlasers by adjusting mode Q factor

Semiconductor microcircular lasers have been investigated as potential light sources for photonic integrated circuits and optical interconnections for more than two decades. However, the direct modulation bandwidths of the circular microlasers remain a challenge, especially when being compared with other microlasers, such as photonic crystal lasers. In this paper, microcircular lasers connected to an output waveguide are investigated for high‐speed direct modulation with optimized mode Q factors. Small signal modulation with a resonance frequency of f_R = 12.5 GHz is realized for a AlGaInAs/InP circular microlaser with a radius of 10 µm at 290 K. Furthermore, clear eye diagrams are observed at 12.5 Gbit/s for a 15‐µm radius circular microlaser with f_R = 6.9 GHz.