一种适用于大测绘带合成孔径声呐的运动补偿方法

当合成孔径声呐测绘带较大时,运动误差的空变效应严重,经典的相位中心重叠算法难以适用。为此,提出了一种适用于大测绘带合成孔径声呐的运动补偿方法。首先使用混合调制的拉格朗日时延估计算法对前后两帧回波的时延进行估计,之后使用线性回归方法拟合出运动误差,最后利用运动误差的估计值对回波进行逐点精确补偿。仿真数据的结果表明,该算法能够获得比相位中心重叠算法更好的运动估计结果,运动补偿后成像分辨率接近理论分辨率。使用该算法分别对高、低频合成孔径声呐的湖试数据进行了处理,水下地貌和小目标的成像质量均有明显提高。     

基于动态阈值匹配追踪的主动声呐直达波抑制方法

双基地声呐中的直达波干扰可以通过重构抵消的方式进行抑制。这种方法需要对直达波信道进行估计,传统的正交匹配追踪算法的收敛速度慢,分步正交匹配追踪等算法在提高收敛速度时牺牲了信道估计精度,导致回波检测能力下降。本文提出一种动态阈值匹配追踪算法估计直达波的信道响应,在提高收敛速度的同时兼顾了信道估计精度。在仿真环境中,达到同样的直达波抑制效果,所提算法与传统正交匹配追踪算法相比,收敛速度显著提升,检测输出的回波强度比分步正交匹配追踪算法高4dB;海试数据处理结果中,所提方法迭代收敛速度较正交匹配追踪算法提升4倍;输出的回波强度比分步正交匹配追踪算法高2dB。     

混沌系统的时间延迟同步误差分析

对Pecora和Carroll的混沌自同步方案的延迟同步误差进行了研究.在计算机上对Lorenz混沌系统伪装的延迟同步误差进行了模拟:给定系统参数,对应不同延迟时间,得出了均方误差与采样步长的关系曲线;给定系统参数和延迟时间,对应不同采样步长,得到了混沌时间序列的误差曲线;给定采样步长,对应不同的系统参数,获得了混沌时间序列的尺度效应和均方误差与采样步长的关系曲线.提出了减小延迟同步误差的一些方法,得到一些对混沌同步和混沌控制应用有意义的结果. 关键词： 混沌同步 时间同步 误差分析     

一种基于误差补偿的多元混沌时间序列混合预测模型

针对多元混沌时间序列的预测问题, 考虑到单纯改进储备池算法无法明显地提高预测精度, 提出一种基于误差补偿的时间序列混合预测模型. 实际观测的数据既包含线性特征又包含非线性特征. 首先利用自回归移动平均模型预测线性特征, 使得残差数据仅含非线性特征; 然后, 建立正则化回声状态网络模型预测; 最后, 将非线性部分的预测值与线性部分的预测值相加, 以实现高精度的多元混沌时间序列预测. 基于Lorenz和太阳黑子-黄河径流量时间序列的仿真实验验证了本文所提模型的有效性. 关键词： 回声状态网络 混沌 多元时间序列预测 误差补偿     

一种基于自相关的激光脉冲编码信号解码方法

激光脉冲编码是半主动激光制导武器采用的一种抗干扰措施,为满足半主动激光制导武器光电对抗的需要,以激光信号的脉冲到达时间(TOA)为参数,依据激光脉冲编码信号的时间相关性,提出了一种通过首先对由脉冲到达时间组成的脉冲到达时间序列作自相关处理,计算出信号的重复周期,然后再在一个信号周期内,通过确定脉冲重复间隔的时间值、个数和位序来鉴别信号码型,从而实现信号解码的方法。阐述了该解码方法的原理及实现。原理实验和数字仿真实验证明,对于当前半主动激光制导武器采用的大多数激光脉冲编码信号,采用该解码方法,一般在4个信号周期时间内就能实现解码。     

一种基于弱监督学习的声图小目标快速检测方法

小目标检测是声呐图像理解中最引人瞩目,同时又极具挑战性的任务之一。该文基于离散余弦变换和K-近邻聚类,提出了一种快速检测方法。离散余弦变换用于生成图像的指纹,是原始图像在二维频域的一种稀疏表达;改进的K-近邻模型对于带有标签数据的需求量相对较低,提升了算法的处理效率和对弱监督场景的适应性。经试验验证,该方法可在准确率和召回率之间达到一个恰当的平衡点,同时在实时成像的合成孔径声呐图像小目标检测中,获得了较为可靠的结果。     

基于合成频率步进线性调频信号的合成孔径激光雷达成像

为解决合成孔径激光雷达(SAL)所需高重复频率大带宽相干光源问题,提出了合成频率步进线性调频信号（SFSCS）的方案,并进行了基于SFSCS信号SAL (SFSCS-SAL)的成像理论和实验演示研究。采用多台独立的窄带宽高重复频率线性调频激光器构成SFSCS信号,给出了SFSCS-SAL的成像数据方程和图像形成方法。理论分析表明:在一定条件下,SFSCS-SAL的成像处理与常规SAL相同;但是,与单个子脉冲激光器SAL相比,SFSCS-SAL的距离向成像分辨率提高至少N倍（N为构成SFSCS的独立激光器数目）。实验演示中,利用一台1550 nm波段的线性调波长激光器,通过光学斩波的方法模拟生成了子脉冲数为3的SFSCS信号。以此SFSCS信号作为探测光源,建立了SFSCS-SAL实验装置,对强散射目标和弱散射扩展目标,均实现了高分辨率成像。实验结果与理论分析一致。     

基于合成频率步进线性调频信号的合成孔径激光雷达成像

为解决合成孔径激光雷达(SAL)所需高重复频率大带宽相干光源问题,提出了合成频率步进线性调频信号(SFSCS)的方案,并进行了基于SFSCS信号SAL(SFSCS-SAL)的成像理论和实验演示研究。采用多台独立的窄带宽高重复频率线性调频激光器构成SFSCS信号,给出了SFSCS-SAL的成像数据方程和图像形成方法。理论分析表明:在一定条件下,SFSCS-SAL的成像处理与常规SAL相同;但是,与单个子脉冲激光器SAL相比,SFSCS-SAL的距离向成像分辨率提高至少N倍(N为构成SFSCS的独立激光器数目)。实验演示中,利用一台1550nm波段的线性调波长激光器,通过光学斩波的方法模拟生成了子脉冲数为3的SFSCS信号。以此SFSCS信号作为探测光源,建立了SFSCS-SAL实验装置,对强散射目标和弱散射扩展目标,均实现了高分辨率成像。实验结果与理论分析一致。     

一种基于示波器触发功能频率测量新方法

示波器两通道输入两路信号,通道1输入未知信号,通道2输入已知信号,扫描方式选择在锁定模式,触发选择置于通道2,垂直方向显示选择通道1,调节已知信号频率,最大能使未知信号稳定下来的频率即为未知信号的频率。简化了频率测量操作,在实际应用中具有极大的参考价值。     

一种基于远场图像的稀疏光学合成孔径系统共相探测新方法的仿真研究

稀疏光学合成孔径系统中,共相探测环节检测子孔径间的相位平移误差,为系统高分辨力的实现提供重要支持. 文章从基本的物理原理出发,分析了系统远场与相位平移误差的关系,并以此为基础,从数学上阐明了 相位平移误差对系统远场图像的影响机制.进一步,针对典型的两孔径系统,提出了一种新的基于远场相似度 的共相探测方法,并对其可行性、原理性偏差和动态范围进行了仿真分析.结果表明,该方法在原理上可实现 对两孔径系统相位平移误差的良好标定,且避免了一些既有方法可能存在的2π模糊性及无法判断符号的问题,具有一定的动态范围,为共相探测新技术的进一步研究提供了有效参考.     

Image sharing scheme based on discrete fractional random transform

We present a novel image sharing algorithm based on the discrete fractional random transform (DFRNT). The secret image is shared into several shadow images in the DFRNT domain together with some noise images as the encryption keys to increase the security. The decryption only requires a part of shadow images and therefore is independent of those noise images. The (t,n) threshold sharing scheme can be implemented completely by the proposed algorithm. The numerical simulations have demonstrated the effectiveness of this image sharing scheme.     

Image encryption based on double random amplitude coding in random Hartley transform domain

We propose an image encryption scheme based on double random amplitude coding technique by using random Hartley transform, which is defined according to the random Fourier transform. The significant feature of this algorithm is that the encrypted image is real and convenient for storage as well as transfer of the encrypted information. Moreover, the algorithm has enhanced security and the correct information of original image can be well protected under bare decryption, blind decryption and brute force attacks. Numerical simulation results are also presented in support of the proposed scheme.     

Physical random access signal design for 5G mobile satellite communication systems

In view of the distinctive characteristics of satellite communication, the physical random access signals used in the terrestrial mobile communication system have to be modified or redesigned for the satellite communication system. In this paper, we boost the random access signal energy by repeating the short Zadoff–Chu (ZC) sequence based preamble signal used in the terrestrial system. Different long ZC sequences are used to scramble this cascaded sequence to distinguish different random access signals for multiple random access user equipments. For correlation performance optimization, properties of the roots for both the short and long ZC sequences are mathematically analyzed and derived. Finally, we illustrate how to construct a root set for these different long ZC sequences based on the obtained propositions in a practical way. This analytical framework provides a useful insight into ZC sequence-based random access signal design and performance analysis in mobile satellite communication systems.     

Double-image encryption based on discrete fractional random transform and chaotic maps

A novel double-image encryption algorithm is proposed, based on discrete fractional random transform and chaotic maps. The random matrices used in the discrete fractional random transform are generated by using a chaotic map. One of the two original images is scrambled by using another chaotic map, and then encoded into the phase of a complex matrix with the other original image as its amplitude. Then this complex matrix is encrypted by the discrete fractional random transform. By applying the correct keys which consist of initial values, control parameters, and truncated positions of the chaotic maps, and fractional orders, the two original images can be recovered without cross-talk. Numerical simulation has been performed to test the validity and the security of the proposed encryption algorithm. Encrypting two images together by this algorithm creates only one encrypted image, whereas other single-image encryption methods create two encrypted images. Furthermore, this algorithm requires neither the use of phase keys nor the use of matrix keys. In this sense, this algorithm can raise the efficiency when encrypting, storing or transmitting.     

Novel image encryption algorithm based on multiple-parameter discrete fractional random transform

A new method of digital image encryption is presented by utilizing a new multiple-parameter discrete fractional random transform. Image encryption and decryption are performed based on the index additivity and multiple parameters of the multiple-parameter fractional random transform. The plaintext and ciphertext are respectively in the spatial domain and in the fractional domain determined by the encryption keys. The proposed algorithm can resist statistic analyses effectively. The computer simulation results show that the proposed encryption algorithm is sensitive to the multiple keys, and that it has considerable robustness, noise immunity and security.     

Blind image watermarking based on discrete fractional random transform and subsampling

This paper proposes a blind watermarking scheme based on discrete fractional random transform. The watermark information can be a binary sequence, a gray level image or a set of decimal fractions sampled from a given source signal. The host image is subsampled into four subimages, and the high correlations among their discrete fractional random transform coefficients are exploited for watermark embedding. Based on this self-reference strategy, the watermark can be extracted without the aid of the host image. As a fragile watermarking technique, our scheme can be used in tamper detection. Besides, it can be used in self-embedding for a large payload is provided. Meanwhile, security of the watermark is preserved due to the randomness of the discrete fractional random transform. Experimental results demonstrate the effectiveness of our scheme.     

基于旋转不变技术信号参数估计的激光扫频干涉测量方法

激光扫频干涉测量技术具有无测距盲区、非接触、单次测量多目标的能力.通过傅里叶变换可提取目标拍频频率,进而解算距离.然而受激光器调频带宽限制,通过傅里叶变换得到的目标分辨率受限于固有分辨率.为解决该问题,本文提出采用基于旋转不变技术的信号参数估计(ESPRIT)算法对测量信号进行频谱分析.实验通过插值拟合法校正测量信号拍...     

Filtering noisy chaotic signal via sparse representation based on random frame dictionary

The denoising problem of impure chaotic signals is addressed in this paper. A method based on sparse representation is proposed, in which the random frame dictionary is generated by a chaotic random search algorithm. The numerical simulation shows the proposed algorithm outperforms those recently reported alternative denoising methods.     

时频分析在超宽带散射信号处理中的应用

简要介绍了伪Wigner分布和小波变换信号处理中的分析方法,描述了在超宽带散射信号分析中的应用情况,对一些简单形状的金属散射体的双站背向散射信号作了实际测量,并且用伪Wigner分布和小波分析方法对这些信号进行了时频分析,由此验证了超宽带信号在目标探测和识别方面的优越性。     

被动线谱检测的子带分解和分方位区间融合算法

目标辐射噪声中低频线谱丰富,而且谱级比高、强度稳定,相比调制谱检测具有优越性。基于子带分解处理的现有融合方法适用在信噪比相对较高情况下,而当干扰是相干的或强宽带信号时,对线谱目标有效检测仍没很好解决。本文从子带空间谱统计特性出发,利用线谱谱级高出连续谱10-25dB;线谱频带所在方位区间的输出方位波动小,而其他分区间的输出方位波动大特点,提出了一种在信噪比低,多目标并存情况下更有效的弱线谱提取融合方法。理论仿真和海试实验数据处理结果验证该方法具有创新性、较常规方位稳定算法适用范围更广、检测效果更好,适合工程应用。