线性调频连续波信号参数估计算法

提出了一种线性调频连续波信号参数估计算法。利用短时傅里叶变换得到信号的时频变化曲线,根据时频曲线的周期特性对它进行频谱分析,找出信号参数与相关谱线的位置、幅度之间的关系,从而估计出信号的主要参数。仿真结果表明,文中提出的算法能够精确估计出线性调频连续波信号的参数,在信噪比大于-8 dB的情况下性能稳定,具有很好的估计精度。     

采用STFT幅度值的长信号相位恢复算法

针对以往基于短时傅里叶变换(STFT)幅度值的相位恢复（STFTMPR）算法仅能处理一组较短的信号,并且信号的STFT幅度测量值的长度只能是质数的情况,提出了一种基于STFT幅度值的长信号相位恢复（LS-STFTMPR）算法。把一组长信号变化成几组较短的数组信号,通过改进的最小二乘（LS）法获取梯度下降（GD）法的迭代初始值,然后最小化各数组信号的非凸损失函数,并最终收敛到全局最小值。实验结果表明,在恢复一组较长信号的时候,所提算法的性能明显优于STFTMPR算法,并且具有较强的抗噪声能力。     

短时分数阶傅里叶变换对调频信号的时频分辨能力

调频信号的检测和参数估计一直是信号处理领域的研究热点之一。为深入挖掘短时分数阶傅里叶变换对调频信号的时频分析优势,从短时分数阶傅里叶变换的定义出发,推导了其时频分辨能力与信号参数的关系,并与短时傅里叶变换进行了对比分析。结论表明,短时傅里叶变换时频分辨能力与信号频率变化率有关,而短时分数阶傅里叶变换几乎不受调频率变化率影响。最后,通过对比仿真实验证明,对于频率变化率较小的信号,两者时频分辨效果差别不明显,对于频率变化率较大的信号,短时分数阶傅里叶变换的时频分辨效果更好。     

基于分数阶Fourier变换的模糊函数及其在二次调频信号参数估计应用中的研究

作为处理非平稳信号的一种重要工具,模糊函数(ambiguity function,AF)已经被广泛应用于雷达信号处理、声纳技术等领域,并对线性调频信号信号的参数估计具有极好的处理能力。但对应用于众多领域的二次调频信号,模糊函数就显得无能为力了。作为Fourier变换的更广义形式,分数阶Fourier变换(Fractional Fourier transform)近年来受到了广泛关注。为解决二次调频信号的估计问题,本文研究了基于分数阶Fourier变换的模糊函数,给出了这种变换的一些新的重要性质,如共轭对称性、Moyal公式、时移性等,推导出了它与经典模糊函数、基于分数阶Fourier变换的Wigner分布、短时Fourier变换、小波变换等其他时频变换的关系。作为应用,最后本文用这种分数阶模糊函数来估计二次调频信号,应用实例的仿真结果表明了分数阶模糊函数在估计二次调频信号参数方面的可行性和有效性。      

基于稀疏表示的声频目标识别方法研究

提出分别利用短时傅里叶变换和小波变换进行特征提取和稀疏表示分类(SRC)的车辆识别方法.其中,短时傅里叶变换(STFT)和离散小波变换(DWT)分别从每个传感节点收集到的声音信息中提取车辆的特征向量,SRC通过特征训练集建立一个过完备字典来求解稀疏最优化问题,从而实现分类识别.实验结果表明,短时傅里叶变换提取特征并进行分类的效果高于用小波变换进行特征提取并分类的方法,也高于利用MFCC提取车辆声音特征并进行分类的方法.     

Octonion short-time linear canonical transform

We investigate the octonion short-time linear canonical transform (OCSTLCT) in this paper. First, we propose the new definition of the OCSTLCT, and then several important properties of newly defined OCSTLCT, such as bounded, shift, modulation, time-frequency shift, inversion formula, and orthogonality relation, are derived based on the spectral representation of the octonion linear canonical transform (OCLCT). Second, by the Heisenberg uncertainty principle for the OCLCT and the orthogonality relation property for the OCSTLCT, the Heisenberg uncertainty principle for the OCSTLCT is established. Finally, we give an example of the OCSTLCT.     

一种多天线接收的全响应CPM信号解调方法

由于需要使用匹配滤波器组和复杂的符号与载波同步算法,CPM优化接收机结构复杂。而其非相干解调接收机结构简单,但在低信噪比时,性能较差。针对CPM的这些局限,结合接收天线分集技术,提出了一种适用于全响应CPM信号的非相干解调方法。在该方法中对每路信号进行短时傅立叶变换后进行插值处理来获得谱线包络最大处的频率;然后将各个支路上的输出进行合并,从而直接估计出对应的基带波形;再在基带信号的基础上进行同步处理,恢复出传输的信息。仿真结果表明:该方法可以有效地将对全响应CPM信号进行解调,只要选择合适的接收天线数,可以使非相干解调的性能接近相干解调的性能。     

Molecular bases of stress relaxation and viscosity of polymers, 1a) New empirical relations

Experiments with several polymers led to new relations which describe stress relaxation at small shears and show the influence of the molecular structure on relaxation. Bubble-free melts of anionically polymerized polystyrenes with the molecular masses (relative molecular mass is referred to as molecular mass throughout this paper)M=6 10² to 1.8 10⁶ g mol^–1 and their blends are studied at several temperatures and at timest>3 ms. As the stress (10² to 10⁶ Pa) deforms the rheometer, a new mathematical method was developed to correct the relaxations. The energy-elastic stress is separated from the entropy-elastic stress. The relaxations of the latter do not confirm the Rouse theory as is proportional to exp (–¦t ^1/2¦) forM<4000. For M>4000 the relaxations deviate from the theoretical functions as well. The initial modulus G(0) then depends onM, and is not proportional to ¦t ^–1/2¦. A new and simple function describes the relaxation of melts with entangled molecules at long times. The influences of concentration and chemical structure on relaxation are formulated for weak intermolecular forces. Published data for the constantD of self-diffusion are used in calculating values ofD for a constant free volume making use of the initial velocity of relaxation and its dependence on temperature. ThenDM ^–1 holds forM<1.3 10⁴ andDM ^–2 for largerM. Correct values of viscosity are calculated from the empirical functions of stress relaxation.Part 2 cf.In memoriam Professor Dr. Drs. h.c. Otto Bayer     

Short-Time Dynamics of the Random n-Vector Model

Short-time critical behavior of the random n-vector model is studied by the theoretic renormalization-group approach.Asymptotic scaling laws are studied in a frame of the expansion in ε = 4 - d for n ≠ 1 and √ε for n = 1respectively.In d ＜ 4,the initial slip exponents θ′ for the order parameter and θ for the response function are calculated up to the second order in ε ＝ 4 - d for n ≠ 1 and √ε for n ＝ 1 at the random fixed point respectively.Our results show that the random impurities exert a strong influence on the short-time dynamics for d ＜ 4 and n ＜ n_c.     

Monte Carlo Simulation of the Non-universal Short-Time Behavior for a Kinetic 2-D Ising Model

The short-time dynamic process for the two-dimensional Ising model with the nearest-neighbor coupling and the next-nearest-neighbor antiferromagnetic coupling in the critical domain is simulated by the Monte Carlo method. From the power law behavior of the initial order increase, the critical points and the initial dynamic exponent θ are determined.