Generalized instantaneous parameters and window matching in thetime-frequency plane

The concept of instantaneous parameters, which has previously been associated exclusively with 1-D measures like the instantaneous frequency and the group delay, are extended to the 2-D time-frequency plane. Such generalized instantaneous parameters are associated with the short-time Fourier transform. They may also be interpreted as local moments of certain time-frequency distributions. It is shown that these measures enable local signal behavior to be characterized in the time-frequency plane for nonstationary deterministic signals. The usefulness of the generalized instantaneous parameters is demonstrated in their application to optimal selection of windows for spectrograms. This is achieved through window matching in the time-frequency plane. An algorithm is provided that illustrates the performance of this window matching. Results based on simulated and real data are presented     

平面波展开结合矩量法分析频率选择表面

为了快速分析频率选择表面（FSS）,利用天线阵列理论,引入FSS单元之间互导纳的概念,得到互导纳方程。当FSS阵列无限大时,可以应用Floquet定理简化该方程,同时对方程中某些收敛较慢的项进行平面渡展开,利用矩量法求解。采用该思路我们计算了几种多层FSS及多频FSS,并和实测结果进行对比,得到了较满意的结果。不仅如此,该方法相对其他的单一数值方法具有速度快、收敛好的特点。     

Delay-correlation-aware SSTA based on conditional moments

Corner-based Timing Analysis (CTA) becomes more and more pessimistic as feature size shrinks. This trend has motivated the development of Statistical Static Timing Analysis (SSTA). In this paper, we propose a new path-based SSTA framework that allows the estimation of path delay distributions and delay correlations by propagating iteratively mean and variance of cell delay. These moments, conditioned on input slope and output load values, are pre-characterized by an improved method: log-logistic distribution based input signals and inverters as output load. In applications, the delay gains of this SSTA framework with respect to CTA are shown to be significant. It is also highlighted that the discrepancy of critical paths orderings obtained by SSTA and CTA depends on two factors: cell-to-cell delay correlation and standard deviation of cell delay.     

Instantaneous spectra and instantaneous frequency

A simple relation exists between the instantaneous frequency and the instantaneous spectrum of an analytic signal which does not depend on an assumption that the instantaneous frequency varies slowly.     

瞬时测频技术在无线电监测中的应用

0引言频率测量是无线电日常监测工作中的一项重要任务,它是检查无线电台(站)用频情况的一种有效手段。目前常用的测频方法主要针对平稳随机信号,抗     

Instantaneous frequency and energy distribution of a signal

A theory is derived on a signal representation in an instantaneous frequency vs. time plane. It is observed that the usual frequency vs. time representation does not give a specific pattern for the signal. It is shown that by switching the frequency axis to an instantaneous frequency axis, and by distributing the energy of the signal on an instantaneous frequency vs. time plane it is possible to build up a coherent theory. As an example, patterns of speech signals (sustained vowels) are represented.     

低信噪比情况下调频信号的瞬时频率估计

提出一种基于互Wigner-Ville分布(XWVD)的瞬时频率迭代估计方法.理论分析了该方法的收敛性,通过仿真比较了各种瞬时频率估计方法在噪声下的估计方差,证明此方法在低信噪比情况下对估计线性调频信号的瞬时频率有较好的效果.并采用加窗的方法改进了此算法,仿真结果证明,改进的方法对非线性调频信号的瞬时频率进行了有效估计.     

INSTANTANEOUS DOPPLER FREQUENCY FOR SQUINT SAR IMAGING

Instantaneous Doppler frequency for squint SAR imaging has been found with Chirp Scaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth signal in the squint SAR data processing, and the different slant range targets have different Doppler frequencies. From the mathematical model of SAR echo signal, this paper carefully analyzes the instantaneous azimuth frequency, the instantaneous Doppler frequency component of the azimuth frequency and the impact of range chirp on azimuth frequency, which explains that Doppler frequency should be properly selected for correct SAR imaging in the squint SAR. The results of point target simulation experiments show that the way is reasonable for the squint SAR and can effectively complete range compression and azimuth focusing, and improve images‘ quality.     

基于光采样的瞬时测频技术研究

传统高频微波信号瞬时测频(Instantaneous Frequency Measurement,IFM)技术受模拟数字转换器(Analog To Digital Converter,ADC)影响很大.提出了一种新的光采样方法,放弃传统的ADC,利用光强度调制器将高频微波信号调制到低重复频率采样光脉冲上,进而达到光采样的目的.利用快速傅里叶变换(Fast Fourier Transform,FFT)结合线性调频z变换(Chirp-z Transform,CZT)的方法,提高频谱分辨率,对欠采样条件下产生的频率余数进行准确估计,进而通过中国余数定理对信号频率进行重构.实验模拟表明,该方法可以对39 GHz带宽内信号频率进行准确测量.     

应用WVD估计AM-FM信号的瞬时频率

该文研究了应用WVD谱峰检测估计AM-FM信号的瞬时频率的方法及其性能。理论分析表明;对线性调频的AM-FM信号,只要其幅度的WVD在频率为零处取得最大值在任意时刻都成立,则基于WVD谱峰检测得到的瞬时频率估计是无偏的,并给出了估计的方差。仿真实验使用高斯包络的线性调频信号表明,利用WVD可以有效地估计AM-FM信号的瞬时频率。     

A note on conditional moments of random signals in Gaussian noise (Corresp.)

This correspondence generalizes some recent results on relations between minimum-variance estimates of random signals in Gaussian noise and likelihood ratios.     

Instantaneous microwave frequency measurement based on hybrid microwave photonic filter

A novel photonic technique for instantaneous microwave frequency measurement based on hybrid microwave photonic filter （HMPF） is proposed and experimentally demonstrated. The HMPF is composed of an all-pass filter and a band-pass filter with negative coefficients. By properly controlling the power relationship between the all-pass filter and the band-pass filter, the HMPF can realize a monotonic frequency response, and then a unique relationship be- tween the output power and the input frequency is established. A high measurement resolution can be achieved for a given frequency range.     

瞬时频率雷达信号脉内调制识别技术

雷达信号的脉内调制识别是雷达侦察信号处理的重要组成部分。随着信号环境愈趋复杂,雷达信号调制识别难度越来越大。首先根据调频和调相两类信号3 d B带宽明显差异的特征,实现类间粗分类识别。继而基于改进瞬时自相关算法提取的信号瞬时频率,将FSK信号和PSK信号进行类内细分类识别。在不同的信噪比条件下,经过多次仿真实验验证,与传统算法相比,此新信号识别算法具有更高的效率和准确度。     

Instantaneous frequency estimation using the Wigner distributionwith varying and data-driven window length

The estimation of the instantaneous frequency (IF) of a harmonic complex-valued signal with an additive noise using the Wigner distribution is considered. If the IF is a nonlinear function of time, the bias of the estimate depends on the window length. The optimal choice of the window length, based on the asymptotic formulae for the variance and bias, can be used in order to resolve the bias-variance tradeoff. However, the practical value of this solution is not significant because the optimal window length depends on the unknown smoothness of the IF. The goal of this paper is to develop an adaptive IF estimator with a time-varying and data-driven window length, which is able to provide quality close to what could be achieved if the smoothness of the IF were known in advance. The algorithm uses the asymptotic formula for the variance of the estimator only. Its value may be easily obtained in the case of white noise and relatively high sampling rate. Simulation shows good accuracy for the proposed adaptive algorithm     

频谱面的精确定位研究

本文通过理论分析和实验研究,应用傅里叶分析、CCD和微机对信号进行采集与处理,成功地解决了频谱面的精确定位问题,相对精度≈0.25％。     

Instantaneous frequency estimation of nonlinear frequency-modulatedsignals in the presence of multiplicative and additive noise

This paper addresses the problem of estimating the instantaneous frequency (IF) of monocomponent nonlinear, not necessarily polynomial, frequency modulated (FM) signals affected by stationary multiplicative and additive noise. Both noise processes are assumed to be complex circular Gaussian and independent. The peak of the polynomial Wigner-Ville distribution (PWVD) is proposed here as an IF estimator. We derive analytical expressions for the bias and asymptotic variance of the estimator and propose an algorithm to select the optimal window length to resolve the bias-variance tradeoff in the IF estimation. Simulation results are presented to confirm the theoretical results     

某些有机晶体的倍频效应与分子偶极矩之间的关系

初步论证了有机共轭分子的偶极矩与其倍频效应的联系,并采用EHMO法对4-硝基吡啶-1-氧的3位和2位甲基衍生物及4-硝基苯胺的2位和8位卤素衍生物的分子偶极矩进行了理论计算,合成并测定了它们的倍频性能和偶极矩.实验结果与理论预测规律相吻合.     

Instantaneous frequency estimation of quadratic and cubic FMsignals using the cross polynomial Wigner-Ville distribution

The cross polynomial Wigner-Ville distribution (X-PWVD) is applied to instantaneous frequency (IF) estimation of polynomial FM signals. The X-PWVD is used in a simple iterative algorithm, similar to the one proposed by Boashash and O'Shea (see ibid., vol.41, no.3, p.1439, 1993) for the cross Wigner-Ville distribution (X-WVD). The advantage of the X-PWVD over the polynomial Wigner-Ville distribution is that the former is linear with respect to the observed signal and as a result it attains the Cramer-Rao bound at lower signal-to-noise ratios (SNRs)     

Filter functions for computing multipole moments from the magnetic field normal to a plane

A technique for calculating the magnetostatic multipole moments (and therefore complete biomagnetic information) from measurements of the normal component of the magnetic field on a plane is described. The technique involves multiplying the measured values by a set of unique filtering functions and integrating. A new formulation and method for calculating the filtering functions is introduced. The method uses expansions in basis sets and matrix inversion. Proofs are given of the nonsingularity of the matrices. Computer simulations of the application of the technique to a circular current loop and a current dipole in a spherical conductor are described.     

基于短时傅立叶变换的跳频序列瞬时频率估计

采用了G函数的方法来模拟跳频序列，然后利用短时傅立叶变换对它进行分析与瞬时频率的估计。该方法能够有效地描绘出跳频信号的频率随时间跳变的规律（跳频图案），具有很高的时间一频率分辨率。计算机仿真验证了应用短时傅立叶变换分析跳频序列的有效性和实用性。