噪声背景下一种正弦信号频率估计的新插值算法

本文研究噪声中正弦信号频率的估计问题.结合DFT变换和插值方法,提出了一种基于DFT变换系数的频率估计算法,其计算简单.结果表明,该方法有效地改善了频率估计精度,且便于工程实现.     

基于改进DFT相位差的正弦波频率估计

针对基于离散傅里叶变换( DFT)相位差的正弦波频率估计方法对频偏敏感的问题,提出了一种改进DFT相位差频率估计方法。首先推导了DFT相位差法频率估计的均方误差,然后提出了基于Rife插值的改进DFT相位差频率估计方法,较好地解决了正弦波频率估计对频偏敏感的问题。仿真实验结果表明,改进方法在各种频偏下均能取得较高的估计精度,估计性能接近克拉美罗限( CRLB)。     

六点拟合的正弦信号的插值多项式测频

本文提出一种新的快速测量正弦信号频率的方法,它主要利用三次多项式插值函数来拟合6个经过DFT变换的数据点,然后通过求插值函数的极值点来进行频率估计。仿真结果证明方法的有效性和简便性。     

六点拟合的正弦信号的插值多项式测频

本文提出一种新的快速测量正弦信号频率的方法,它主要利用三次多项式插值函数来拟合经过DFT变换的数据点,然后通过求插值函数的极值点来进行频率估计。仿真结果证明方法的有效性和简便性,并对其CPLD快速实现进行探讨。     

一种改进的CPFSK信号频率估计方法

针对突发信号解调中多普勒频偏大的问题,提出了一种改进的连续相位移频键控信号(CPFSK)频率估计方法.首先接收信号平方运算使信号的调制指数加倍,再通过一次离散傅里叶变换(DFT),用搜索信号平方谱谱峰的方法实现突发信号频率估计.仿真实验表明,在低信噪比条件下,该算法的频率估计精度比经典的相位差频率估计算法提高了20%;该算法与广泛用于高动态突发信号的频率插值估计算法相比,同道干扰信道下信干比改善可达4 dB,DFT长度缩短约1/3.     

一种频率无关的正弦信号相量计算方法

为寻求一种频率无关的实时相量计算方法,通过分析传统算法,提出一种可变数据窗正弦相量插值计算方法。该算法通过等间隔采样获得信号一个周期左右的样本数据,采样数据计算出信号的基波频率并确定信号的一个基频周期所需的最大采样点数N,计算信号N点DFT和N+1点DFT,再利用两次DFT计算结果进行线性插值得到信号真实频点上各次谐波的实部和虚部,计算出信号各次谐波的幅值和瞬时相位。仿真分析和实际测量表明,该算法的计算精度和实时性较高,能够满足频率随机变化的应用要求。     

基于DFT插值的宽带波束形成器设计

本文提出一种基于DFT插值的宽带波束形成器设计方法。首先推导了具有频率不变波束图的连续线阵的灵敏度函数与离散线列阵加权系数之间的关系；接着给出了基于DFT插值的宽带波束形成器设计的两个步骤：（1）使用窄带波束形成器的设计方法计算在参考频率下基阵的加权系数；（2）根据参考频率下基阵的权系数与其它子带权系数之间的关系，利用DFT插值的方法求出其它子带的加权系数。最后，给出了一个设计实例说明本文方法的有效性。     

循环移位离散Chirp-Fourier变换

离散Fourier变换(DFT)具有循环移位的特性。同样,源于DFT的离散Chirp-Fourier变换(DCFT)也具有循环移位的特性。该文提出了循环移位DCFT的概念,并根据这一概念给出了一种新的chirp信号的检测方法。该方法充分利用了chirp信号和噪声的特点,即chirp信号的调频率和初始频率不随时间变化而噪声的调频率和初始频率随时间随机变化,因此该方法具有更好的检测性能。与DCFT方法相比,实验结果表明,在低信噪比下该文提出的chirp信号的检测方法达到了良好的效果。     

基于广义柯西分布的最大后验准则频谱估计方法

经典的频谱估计方法和现代的频谱估计方法在低信噪比及小数据量的情况下,谱估计的分辨率和方差性能不能满足实际应用需要。因此,提出一种高分辨率、高精度DFT变换的新方法,此方法特别适用于线性频谱的估计。该方法基于最大后验概率准则,建立广义柯西-高斯分布模型,克服了短数据情况下的DFT变换分辨率低的缺点,具有收敛快、频率分辨率高、频率精度高的优点。计算机仿真结果证实了新方法的有效性。     

一种高精度单频信号频率估计算法

根据离散傅里叶变换(DFT)理论和其系数的特点,提出了一种信号离散傅里叶变换系数来构造频率修正项的单频信号频率估计算法。算法利用峰值及前后1个位置的DFT变换系数得到频率修正项的初始值,再迭代计算修正后峰值前后位置的DFT系数来得到频率修正项的精细值。理论分析和仿真结果表明,算法在低信噪比下具有好的频率估计精度并能减少迭代次数。     

一种频域卷积反演的新方法

本文提出了一种卷积反演的新方法。这种方法也是通过离散傅里叶变换(DFT)在频域实现的,但是避免了通常所用的离散傅里叶变换方法当位于分母位置的信号频谱有零点存在时计算失效的问题。本文讨论了新方法与普通离散傅里叶变换方法之间的关系,并且给出了计算示例。     

Sinusoidal transforms in OFDM systems

A method for using sinusoidal transforms as an alternative to the discrete Fourier transform (DFT) for orthogonal frequency division multiplexing (OFDM) wireless transmission methods is presented. These transforms satisfy the cyclic convolution properties of the DFT when used with a symmetric extension. Analysis of interference in OFDM systems reveals that under certain channel conditions or modulation constellations, throughput is enhanced when using sinusoidal transforms rather than the DFT.     

一种MPSK信号载频高精度实时估计算法

常用的对多阶相移键控(MPSK)载频进行高精度估计的算法运算量大,不适合实时处理。针对此问题,提出了一种新的MPSK信号载频高精度实时估计算法,对非线性变换后信号进行正交下变频和2级DFT处理,可对载频频率高精度的实时估计。通过计算机仿真试验验证了该算法的估计精度与直接DFT频率估计方法近似。     

基于混合贝叶斯网络的混合系统安全性分析方法

安全关键系统的安全性分析模型本质上是离散和连续失效分布共存的混合模型.传统的故障树和马尔科夫链分析方法仅能处理离散分布或指数分布的系统,难以对混合系统进行安全性分析.针对该问题,以DFT系统安全模型为基础,提出一种基于混合贝叶斯网络的混合系统安全性分析新方法.首先,利用狄拉克函数和单位阶跃函数分别表示动态故障树节点间的确定性关系和时序关系,将动态故障树转换为贝叶斯网络.然后,通过分段多项式来拟合网络节点的不同失效分布,提出一种k段n次多项式混合贝叶斯网络来表示动态故障树.最后,给出该混合贝叶斯网络的推理算法.实验分析表明本方法能有效地进行混合系统安全性分析.     

A nonlinear time-frequency analysis method

An alternative method of time-frequency signal analysis is introduced and is compared with the conventional discrete Fourier transfer (DFT)-based methods. The structure of the proposed algorithm and its mathematical properties are presented. The proposed algorithm has a nonlinear structure that provides a frequency-adaptivity feature. It can be implemented both in analog and in digital form and is particularly suitable for real-time applications where computational efficiency is important. A comparison is made with the DFT in terms of algorithm efficiency, sensitivity, and complexity. It is shown that compared with the DFT, the algorithm is more efficient for real-time applications and is less sensitive to noise and variations in the frequency and sampling rate while maintaining simplicity of the structure and computational efficiency. Slower convergence rate of the algorithm, compared with the DFT, constitutes its main shortcoming.     

Inverse Z-transform by Mobius inversion and the error bounds ofaliasing in sampling

A general algorithm based on two special Mobius inversion formulae is developed to compute the inverse Z-transform. This approach to Fourier analysis uses what is called the arithmetic Fourier transform (AFT). With the new AFT algorithm. One can compute the inverse Z-transform of an infinite two-sided sequence. It is compared with the conventional DFT approach. Both methods have aliasing errors due to sampling. The error bounds of the aliasing effects in the DFT and the new proposed method are established and compared. In general, the AFT algorithm is not so vulnerable to the aliasing errors in the high-frequency components as the DFT approach     

An Integer Approximation Method for Discrete Sinusoidal Transforms

Approximate methods have been considered as a means to the evaluation of discrete transforms. In this work, we propose and analyze a class of integer transforms for the discrete Fourier, Hartley, and cosine transforms (DFT, DHT, and DCT), based on simple dyadic rational approximation methods. The introduced method is general, applicable to several blocklengths, whereas existing approaches are usually dedicated to specific transform sizes. The suggested approximate transforms enjoy low multiplicative complexity and the orthogonality property is achievable via matrix polar decomposition. We show that the obtained transforms are competitive with archived methods in literature. New 8-point square wave approximate transforms for the DFT, DHT, and DCT are also introduced as particular cases of the introduced methodology.     

The quick Fourier transform: an FFT based on symmetries

This paper looks at an approach that uses symmetric properties of the basis function to remove redundancies in the calculation of the discrete Fourier transform (DFT). We develop an algorithm called the quick Fourier transform (QFT) that reduces the number of floating-point operations necessary to compute the DFT by a factor of two or four over direct methods or Goertzel's method for prime lengths. By further application of the idea to the calculation of a DFT of length-2^M , we construct a new O(NlogN) algorithm, with computational complexities comparable to the Cooley-Tukey algorithm. We show that the power-of-two QFT can be implemented in terms of discrete sine and cosine transforms. The algorithm can be easily modified to compute the DFT with only a subset of either input or output points and reduces by nearly half the number of operations when the data are real     

Power converter line synchronization using a discrete Fourier transform (DFT) based on a variable sample rate

Line synchronization of grid connected power converters is a well recognized problem when the grid is weak, or derives from a remote area power supply with poor frequency regulation. Such systems can suffer significant line voltage distortion due to notches caused by power device switching and/or low frequency harmonic content, which can easily corrupt the output of a conventional zero crossing detector. This paper presents a method of filtering the incoming grid voltage using a recursive discrete Fourier transform (DFT). The filter provides a high degree of noise immunity but does produce a phase shift between the incoming grid voltage and the filtered output voltage when the DFT time window does not match the grid period. Two methods of compensating this phase shift are presented, based on tracking the drift in the phase predicted by the recursive DFT. The first method makes a deadbeat adjustment to the time window (thereby changing the sampling rate) while the second approach calculates the phase error based on the linear phase response of the DFT. These compensation algorithms can correct for discrepancies of at least 25% between the DFT time window and the system period, and can track grid frequencies with slew rates as high as 40 Hz/s with negligible phase shift (<2/spl deg/) between the grid voltage input and the filtered output waveforms.     

频域宽带波束形成器优化设计

将常规频域宽带波束形成运用到电子战侦察系统存在一个问题：分块DFT处理会造成时域输出波形在块衔接处产生周期性失真,影响系统对信号时域参数的检测。为解决上述问题,在分析失真产生原因的基础上提出采用交叠DFT处理对传统方案予以改进,该方法首先对预处理数据进行交叠分段,再完成DFT运算及后续窄带处理。最后的仿真通过对比改进前后方案时域输出波形的保真度,验证改进后方法能有效缓解时域输出波形失真对系统的影响,并为工程实现提供了依据。