使用合成滤波器组的SAS方位向非均匀采样信号重构

针对多子阵合成孔径声纳(Synthetic Aperture Sonar,SAS)在方位向上非均匀采样对后续成像处理带来的方位向失真的影响,给出了基于滤波器组的方位向非均匀采样信号重构算法.该算法利用SAS方位向周期性非均匀采样信号与经过分析滤波器组的信号之间的相似性,将周期非均匀采样信号通过合成滤波器组进行重构得到均...     

轨道不平顺非均匀采样信号的变频抽样重构技术

目前的谱分析方法都是基于用均匀采样（等间隔采样）数据描述轨道不平顺特征,而机车实际运行速度的变化必然导致采样的非均匀性,使分析结果严重失真。本文提出变频抽样重构技术可消除非均匀采样信号中车速变化的影响。     

基于多通道重构的SAR方位的性能分析和算法研究

SAR DPCMAB(方位向多相位中心多波速模式)能够提高方位向采样率,同时却带来非均匀采样的问题,通过频谱重构算法能够有效的恢复原信号频谱。但是在SAR传感器运行过程中存在通道特性不一致,采样时刻偏差,噪声等干扰因素,导致重构后的信号出现频谱噪声,重构精度收到影响。研究一种基于方位向相位中心偏移天线技术的机载SAR实现方法。通过在方位向上安置相位中心偏移的多个波束来降低系统对脉冲重复频率的要求,从而在保证方位向分辨率不变的条件下能够扩展机载SAR的测绘带宽。针对由PRF的变化造成的方位信号非均匀采样,采用多通道重构算法来恢复均匀采样信号。并以两通道机载SAR为例,通过仿真实例验证该算法的有效性。     

一种用于飞机识别的三维建模方法

提出了基于垂距逐步递推的自由曲面自适应数据采样的新算法,给出了应用该算法对复杂曲面物体外形重构和建模方法。自由曲面自适应数据采样时,首先运用逆向工程测量方法,获得曲面的截面数据点列,用非均匀三次B样条曲线拟合出截面轮廓曲线;然后利用基于垂距的数据采样算法,对拟合曲线上的数据点进行重新采样,达到优化数据点的分布及减少描述曲线数据量的目的。最后运用蒙面法完成物体外形轮廓曲面重构和建模。仿真结果表明算法简便、有效。     

非均匀采样下Savitzky-Golay算法的研究

简单介绍了均匀采样下Savitzky-Golay滤波与非均匀采样,提出一种基于数据的非均匀采样的Savitzy-Golay算法,并对该算法进行matlab建模验证比较,简要说明了其可行性。     

非均匀采样信号的能量/功率测量

本文分析了采样信号的非均匀性对于能量／功率测量的影响，推导了非均匀采样信号在时域与频域上的能量对应关系，得出了利用非均匀采样序列计算信号的能量／功率收敛于真值的条件。仿真结果验证了理论的正确性。     

星载分离相位中心方位多波束SAR方位向非均匀采样

星载分离相位中心方位多波束合成孔径雷达可同时实现高分辨率、宽测绘带成像.本文进行进一步分析指出,该技术会产生方位向非均匀采样,并最终可导致虚假目标产生.提出了几种消除方位向非均匀采样影响的算法.通过对各种算法进行比较指出,滤波器组法是最为高效的一种算法.     

压缩传感-稀疏信号的采样与重构

介绍了一种新的信号处理方法-压缩传感,充分利用信号在变换域的稀疏结构知识进行信号的采样与重构。它包括三个要素:稀疏表示矩阵、非相干测量矩阵和重构算法。对时域和频域稀疏信号的采样与重构进行了仿真,并分析了信号长度、测量值、信号稀疏级和信噪比对重构误差的影响关系。     

气体泄漏声源的时域压缩波达方向估计研究

针对现有压缩感知算法中对模拟信号压缩采样的不足以及传统测量矩阵存储量和计算量大等问题,提出一种基于模拟信号时域压缩的波达方向(DOA, Direction Of Arrival)估计算法,并应用于气体泄漏声源方位估计研究。首先建立气体泄漏声源DOA估计模型,然后设计一种直接非均匀随机欠采样方案,并构造相对应的形式简单的等效测量矩阵,实现对模拟声源信号的直接压缩采样,避免了传统测量矩阵数据量大及计算复杂度高等问题,最后采用子空间追踪算法进行重构,实现了较快的计算速度和较高的重构精度。理论分析和实验表明,该算法能成功实现气体泄漏声源的DOA估计,且在显著降低信号采样率和计算复杂度的同时,实现了较高的估计精度和分辨率,估计性能更佳。     

非均匀采样正弦波形的最小二乘拟合算法

针对非均匀采样序列提出了一种四参数正弦波形曲线拟合方法.它借助于频率已知的三参数正弦曲线拟合算法实现,既可以在非均匀采样条件下获得正弦波采样序列的4个参数拟合值,也可用于均匀采样条件下正弦波形采样序列的曲线参数拟合.其特点是将幅度、频率、相位和直流分量4个参数的四维非线性最优化问题转化成频率参数的一维线性搜索和最优化问题.其优点是无需先验初值估计,具有良好的收敛性、鲁棒性,以及明确的收敛区间.仿真及实验均证明了该方法的有效性和可行性.该方法可用于解决非均匀采样和均匀采样下正弦波测量序列的参数拟合问题.     

Digital spectra of nonuniformly sampled signals: fundamentals andhigh-speed waveform digitizers

A digital spectral representation of a nonuniformly sampled signal is derived, and a spectrum analysis of a nonuniformly sampled sinusoid is presented. It is found that the spectrum of a nonuniformly sampled sinusoid comprises uniformly spaced line spectra; in addition, the signal-to-noise ratio is obtained in closed form. The theories are then applied to analyze the harmonic distortion introduced in high-speed waveform digitizers due to time-base errors. Specifically, waveform digitizers are analyzed which utilize interleaving/multiplexing and random equivalent time-sampling techniques and the monolithic A/D converter technology to extend their capabilities. Theoretical results are confirmed by experimental results with a real waveform digitizer     

Digital spectra of nonuniformly sampled signals. II. Digitallook-up tunable sinusoidal oscillators

For Part I see ibid., vol.37, no.2, June 1988. The author presents theories and applications of a digital spectrum analysis technique for a class of nonuniformly sampled signals. The structure of the harmonic components present in a digitally synthesized sine wave is analyzed using a table look-up method. The digital table look-up method offers several desirable features, such as high-frequency stability and precision control of both the frequency and the phase of the generated sine wave. However, undesirable spurious harmonic components are generated when one tries to tune to different frequencies by manipulating the memory-addressing mechanism rather than loading a new waveform sample into the waveform memory, which is generally time-consuming and sometimes infeasible. The frequencies, amplitudes, and phrases of all the spurious harmonic components are derived in closed form     

另一类幅度非均匀取样信号的数字频谱及补偿算法研究

研究了高速并行数字化系统中由ADC增益的不一致性造成的幅度非均匀取样信号的特点,推导出了这类幅度非均匀采样信号的数字频谱表达式,详细分析了输入正弦信号时的数字频谱,得到了系统的信噪比表达式。提出了一种利用IFFT运算对输出信号的频谱进行重构的补偿方法,计算机仿真验证了该方法的有效性。     

Digital Processing of Unevenly Sampled Signals by Means of Fitted Splines

Digital processing is considered for unevenly sampled signals. Fitted splines are used. A digital processing algorithm is proposed. An example is given illustrating the algorithm.     

A new digital correlation flaw detection system

A new portable digital random signal flaw detection system is described which uses a digital delay line to replace the acoustic delay line of the original random signal system. Using this new system, a comparison was made between the two types of transmit signals which have been used in previous systems—m-sequences and random signals. This comparison has not been possible with these previous correlation flaw detection systems. Results indicated that for high-speed short code operation, the m-sequences produced slightly lower range sidelobes than typical samples of a clipped random signal. For normal long code operation, results indicated that system performance is essentially equivalent in resolution and signal-to-noise ratio using either m-sequences or clipped and sampled random signals. Further results also showed that for normal long code operation, the system produces outputs equivalent in resolution to pulse-echo systems, but with the added benefit of signal-to-noise ratio enhancement.     

轨道不平顺非均匀采样信号分析

目前的轨道谱分析是基于用等间隔采样数据描述轨道不平顺特征,而机车实际运行速度的变化必然导致采样的非均匀性,传统的谱分析方法必然产生原理误差。为提高非均匀采样信号分析的准确性,研究了平稳随机过程非均匀采样序列,导出了非均匀采样信号的功率谱表达式,应用该表达式分析了采样间隔服从正态分布的非均匀采样情况,证明了非均匀采样信号功率谱表达式包含了均匀采样这种特例,涵盖了经典理论,验证了新公式的正确性,并提出了进行轨道谱分析时用于求取功率谱表达式中所含有的采样间隔的概率密度函数等统计特征量的方法。     

Detection of Number of Wideband Signals Based on Support Vector Machine

In array signal processing, number of signals is often a premise of estimating other parameters. For the sake of determining signal number in the condition of strong additive noise or a little sample data, an algorithm for detecting number of wideband signals is provided. First, technique of focusing is used for transforming signals into a same focusing subspace. Then the support vector machine (SVM) can be deduced by the information of eigenvalues and corresponding eigenvectors. At last, the signal number can be determined with the obtained decision function. Several simulations have been carried on verifying the proposed algorithm.     

Perfect reconstruction of digital spectrum from nonuniformlysampled signals

In this paper, we consider the problem of reconstructing the digital spectrum from a set of nonuniformly spaced time samples of a signal. Specifically, we deal with the situation where the timing offsets of each sampling instance are known and have a periodic structure. Examples include the random equivalent time sampling system of a digital scope, and an ultra high speed waveform digitizing system with interleaved A/D converters. An algorithm which allows one to reconstruct the digital spectrum perfectly is derived, and a numerical example is presented. The algorithm is noniterative and precise, and should prove to be useful in many applications     

A new algorithm for improving the accuracy of periodic signalanalysis

Digital periodic signal analysis often requires synchronized sampling with the signal being analyzed. In certain practical situations, however, this condition is difficult to satisfy. As a result, a number of undesirable effect such as the spectral leakage associated with the discrete Fourier transform (DFT), and the truncation errors in digital wattmeters arise and degrade system performance. This paper presents a new approach which attempts to remedy the underlying problem. The basic idea of the proposed method is to modify the actual sampled sequence such that it becomes an ideal sample sequence which is synchronized with the signal subjected to sampling. A simple algorithm for modifying the sampled sequence on-line is derived based on interpolation. The proposed approach requires quite modest additional computational burden which makes it suitable for real-time signal professing. To illustrate the practical applicability of the proposed algorithm, the paper considers two distinct but common cases. First, it shows how the proposed method can be used in the case of DFT analysis of harmonic signals, and secondly, it considers the digital wattmeter application area in electrical power-system measurement. Results show that the proposed algorithm is capable of reducing both the leakage effect in DFT analysis and truncation errors in digital wattmeters     

Digital-to-analog (D/A) converters with nonuniformly sampledsignals

In this paper, we investigate the problem of the D/A converter with nonuniformly sampled input data. The input digital data were obtained by sampling the intended analog waveform at nonuniform time intervals, and we look into the question: “Given that the timing offset of each data sample is known, would it be beneficial, in terms of the output signal-to-noise ratio, to use this offset to adjust the playback timing of the D/A converter?” We examine two different timing strategies. The first approach simply plays out the signal at a uniform rate, while the second one uses the known timing offset to adjust the D/A converter playback timing accordingly. The closed-form expressions of the spectrum of the D/A converter output signals are derived. From these expressions, we find that the spectrum structure, for the case where the timing offsets are compensated, is the infinite sum of the weighted shift to the baseband spectrum. For the uniform playout approach, the spectrum structure is much more complicated where each shifted spectrum is modified by a different weighting function of the frequency. Although the spectrum structure may be conceptually simpler for the case where the timing offsets are compensated, it is by no means clear that either method is better than the other in terms of the output waveform quality. We then apply the results to analyze the direct digital synthesis output sine waves. The signal-to-noise ratio, SNR, for both cases is derived in simple closed form. It is found that for the case where the timing offsets are compensated, the SNR can be greatly enhanced by appropriate selection of operation parameters