A nonparametric spectrum estimation method for dispersion and attenuation analysis of borehole acoustic measurements

Dispersion and attenuation analysis can be used to determine formation anisotropy induced by fractures,or stresses.In this paper,we propose a nonparametric spectrum estimation method to get phase dispersion characteristics and attenuation coefficient.By designing an appropriate vector filter,phase velocity,attenuation coefficient and amplitude can be inverted from the waveform recorded by the receiver array.Performance analysis of this algorithm is compared with Extended Prony Method(EPM)and Forward and Backward Matrix Pencil(FBMP)method.Based on the analysis results,the proposed method is capable of achieving high resolution and precision as the parametric spectrum estimation methods.At the meantime,it also keeps high stability as the other nonparametric spectrum estimation methods.At last,applications to synthetic waveforms modeled using finite difference method and real data show its efficiency.The real data processing results show that the P-wave attenuation log is more sensitive to oil formation compared to S-wave;and the S-wave attenuation log is more sensitive to shale formation compared to P-wave.

SAR STEREO IMAGING ALGORITHM BASED ON CAPON SPECTRUM ESTIMATION

This letter presents a novel approach for the Synthetic Aperture Radar (SAR) stereo imaging based on the Capon spectrum estimation technique. In order to deal with nonuniform sampling space and lead to super resolution in the elevation direction, Capon approach is used to focus the SAR data on a certain height. Results obtained on simulated data demonstrate the feasibility of the Capon based algorithm. Compared with the classical Fast Fourier Transform (FFT), the Capon based algo-rithm shows better resolution quality.

SPATIAL SPECTRUM ESTIMATION OF COHERENT SOURCES IMPINGING ON NONUNIFORM ARRAYS

The problem of bearing estimation of coherent signal impingiog on an array ofarbitrary geometry is studied.Both approaches are developed,the first one synthesizes theobserved array data into the outputs of a linear uniform array and then processes them viaconventional techniques such as spatial smoothing etc.The second approach is based on theinvariant subspace rotation operation which is equivalent to the translational displacement ofthe artay,linearly independent signal vectors are obtained thereby to span perfectly the signalsubspace.As compared with the conventional processing techniques,the approach based oninvariant subspace rotation does not lead to an effective decrease in aperture size and thereforea decrease in resolution capability.The computer simulations are conducted to demonstrate theeffectiveness of the presented approaches.

S-transformation based integrated approach for spectrum estimation, storage, and sensing in cognitive radio

Cognitive Radio (CR) uses the principle of dynamic spectrum allocation to improve the utilization of spectrum bands. The estimation of missing data is essential for maintaining an uninterrupted quality of service in the CR. However, the existing methods are not suitable for interpolating missing data in high frequency signals. The storage of spectrum occupancy information is crucial for learning the spectrum usage and prediction. The existing techniques for wideband spectrum sensing suffer from poor edge detection capabilities. This paper proposes an STransformation (ST) based approach to solve these problems. For missing samples, the proposed method improves the accuracy of estimation. The ST can also be used to store the spectrum occupancy information. The simulation results show that the proposed scheme outperforms others by improving the accuracy of edge detection. Further, the simple implementation of the ST in the frequency domain is an advantage for the real time application.

2-D SPATIAL-SPECTRUM ESTIMATION FORWIDE-BAND SOURCES BASED ON INTERPOLATED CIRCULAR ARRAYS

In array signal processing, 2-D spatial-spectrum estimation is required to determine DOA of multiple signals. The circular array of sensors is found to possess several nice properties for DOA estimation of wide-band sources. C. U. Padmini, et al.(1994) had suggested that the frequency-direction ambiguity in azimuth estimation of wide-baud signals received by a uniform linear array (ULA) can be avoided by using a circular array, even without the use of any delay elements. In 2-D spatial-spectrum estimation for wide-band signals, the authors find that it is impossible to avoid the ambiguity in source frequency-elevation angle pairs using a circular array. In this paper, interpolated circular arrays are used to perform 2-D spatial-spectrum estimation for wide-band sources. In the estimation, a large aperture circular array (Υ】λmin/2) is found to possess superior resolution capability and robustness.

Classical and modern power spectrum estimation for tune measurement in CSNS RCS

Precise measurement of betatron tune is required for good operating condition of CSNS RCS. The fractional part of betatron tune is important and it can be measured by analyzing the signals of beam position from the appointed BPM. Usually these signals are contaminated during the acquisition process, therefore several power spectrum methods are used to improve the frequency resolution. In this article classical and modern power spectrum methods are used. In order to compare their performance, the results of simulation data and IQT data from J-PARC RCS are discussed, It is shown that modern power spectrum estimation has better performance than the classical ones, though the calculation is more complex.

The characteristics of frequency-time azimuth spectrum estimation by a vector hydrophone in shallow water

The mechanism of interaction between the energy flows of the far-field ship noise and the near-field platform is studied, and the characteristics of frequency-time azimuth spec- trum is discussed. Based on normal modes theory in acoustic vector fields, the model of the near-field platform is established, and the simulated result is similar to the investigation in shallow water. The frequency-time aziinuth spectrum of the energy flow is investigated by the vector hydrophone changes with frequency. The energy flow of the far-field ship noise interacts with the near-field platform, so four kinds of stripes are shown in the frequency4ime azimuth spectrum, which is the same with the investigation of sea trial. The estimation of direction of arrival appears inaccuracy, and varies with frequency. The main factor that affects the charac- teristics of frequency-time azimuth spectrum of resultant energy flow is the difference of sound pressure level. The estimation of the direction of arrival benefits from this when a number of sources exist in shallow water.

Maximum likelihood spectrum estimation method and its application in seismo－magnet－icrelation

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Refractivity estimations from an angle-of-arrival spectrum

This paper addresses the probability of atmospheric refractivity estimation by using field measurements at an array of radio receivers in terms of angle-of-arrival spectrum. Angle-of-arrival spectrum information is simulated by the ray optics model and refractivity is expressed in the presence of an ideal tri-linear profile. The estimation of the refractivity is organized as an optimization problem and a genetic Mgorithm is used to search for the optimal solution from various trial refractivity profiles. Theoretical analysis demonstrates the feasibility of this method to retrieve the refractivity parameters. Simulation results indicate that this approach has a fair anti-noise ability and its accuracy performance is mainly dependent on the antenna aperture size and its positions.

Estimation of dynamic stress spectrum distribution in structural fatigue test

The determination of structural dynamic stress spectrum distribution is of great signifi- cance in the structural fatigue strength evaluation as well as reliability design. In previous empirical data processing methods, the data grouping and distribution fitting were excessively coarse and contained distinctive defects. This paper proposed an effective approach to statistically group actual measured dynamic stress data and validly extrapolate the combined distribution to fit the dynamic stress spectrum distribution. This approach has been verified its effectiveness through chi-square test, stress spectrum extrapolation and damage calculation in dynamic stress study.

Direction of Arrival Estimation under Spread Spectrum Reference Signal Assisted Radio

In the present work, a direction of arrival estimator, under spread spectrum reference of signal-assisted radio operating in a Rayleigh fading channel, is proposed. The analysis, which is applied to general receiver antenna array configurations, demonstrates the high performance of the estimator which is due to the double dispreading (code word and reference signal). The probability distribution function of the estimator is extracted and the system’s robustness in regard to large number of interferers is demonstrated.

Spectrum Requirements Estimation for the Future IMT Systems: Current Work and Way Forward

In order to satisfy the spectrum requirements of the future international mobile telecommunication (IMT) systems, to realize scientific allocation and usage of spectrum resources and to avoid spectrum waste brought by allocation in advanced, there is a need to make a reasonable estimation for the spectrum demands of future IMT systems. The estimation results can also provide guidelines for the subsequent spectrum planning and assignment work. This paper gives a description of study progress of related spectrum estimation for future IMT systems. From the analysis of current work and practical situation, the key factors in the estimation methodology are summarized to provide a reference for the following work.

Application of X-band Polarimetric Phased-array Radars in Quantitative Precipitation Estimation

The performance of different quantitative precipitation estimation(QPE) relationships is examined using the polarimetric variables from the X-band polarimetric phased-array radars in Guangzhou,China.Three QPE approaches,namely,R(ZH),R(ZH,ZDR) and R(KDP),are developed for horizontal reflectivity,differential reflectivity and specific phase shift rate,respectively.The estimation parameters are determined by fitting the relationships to the observed radar variables using the T-matrix method.The QPE relationships were examined using the data of four heavy precipitation events in southern China.The examination shows that the R(ZH) approach performs better for the precipitation rate less than 5 mm h-1, and R(KDP) is better for the rate higher than 5 mm h-1, while R(ZH,ZDR) has the worst performance.An adaptive approach is developed by taking the advantages of both R(ZH) and R(KDP) approaches to improve the QPE accuracy.

IRS-Enabled Spectrum Sharing:Interference Modeling,Channel Estimation and Robust Passive Beamforming

Intelligent reflecting surface(IRS),with its unique capability of smartly reconfiguring wireless channels,provides a new solution to improving spectrum efficiency,reducing energy consumption and saving deployment/hardware cost for future wireless networks.In this paper,IRS-enabled spectrum sharing is investigated,from the perspectives of interference modeling,efficient channel estimation and robust passive beamforming design.Specifically,we first characterize the interference in a spectrum sharing system consisting of a single primary user(PU)pair and a single secondary user(SU)pair,and extend it to the large-scale network by leveraging the Poisson point process(PPP).Then,we propose an efficient channel estimation framework based on decoupling the cascaded IRS channels.Moreover,the tradeoff between spectrum efficiency and energy efficiency is derived from the view of channel estimation accuracy.Finally,we discuss the robust passive beamforming design in presence of imperfect channel estimation and nonideal/discrete phase shifts.It is hoped that this paper provides useful guidance for unlocking the full potential of IRS for achieving efficient spectrum sharing for future wireless networks.

2-D spatial-spectrum estimation for wide-band signals without a priori knowledge of the number of sources

In array signal processing,the existing methods for DOA estimation of wide-band signals are only related to the azimuth estimation when the number or sensors is known.It is shown that a circular array possesses several nice properties.2-D spatial-spectrum estimation for wide-band sources is performed by using a circular array of sensors with sample delay lines.Further,the Choi' s approach is extended,which was suggested to estimate DOA of narrow-band signals when the number of sensor was unknown,to wide-band signal processing.The extended approach is shown to be quite adequate for wide-band signal subspace spatial-spectrum estimation (BASS-LE),and a large aperture (r>λvin/2) circular array is found to possess superior resolution capability and robustness.

NEW AUTOREGRESSIVE MOVING AVERAGE SPECTRUM ESTIMATION AND CEPSTRUM ALGORITHM

Based on the deduction of the C parameter estimation, a new method to estimate C Parameters from the AR parameters of the ARMA model and auto-related function is proposed , The method reduces the computation complexity of the conventional interative algorithm in MA parameter estimation, thus make the algorithm of ARMA model spectral estimation simpler. On account of this method, a new algo- rithm of cepstrum analysis is put forward . Computer simulation indicates that the proposed cepstrum al- gorithm has the merits of few sidelobes and high resolution . And the algorithm is very useful to the ding- nosis of machinery failure .

基于重构健康指标的锂电池容量估计

针对锂电池搁置引起的退化特征局部再生分量和噪声波动分量所呈现出的非线性和非平稳性,利用奇异谱分析方法对健康指标中蕴含的主要衰退特征和噪声信号进行识别和分离得到了重构健康指标。使用马里兰大学高级生命周期工程中心(CALCE)锂电池数据集中CS2-35,CS2-36和CS2-37电池数据对所提重构健康指标结合多项式回归进行容量估计的效果进行验证。结果表明,使用重构健康指标对锂离子电池容量估计的平均RMSE为0.030 2,平均MAE为0.022 3,且适应度系数超过0.98。对下一步进行锂离子电池剩余使用寿命在线预测具有重要意义。

带残余频偏的软扩频信号伪码序列盲估计

针对带残余频偏的软扩频信号伪码序列盲估计难的问题,提出一种奇异值分解(singular value decomposition,SVD)结合全数字锁相环(digital phase locked loop,DPLL)的方法。所提方法首先对待处理信号通过不重叠分段生成数据矩阵,每段信号长度为一倍伪码周期;然后利用其自相关矩阵的右上角元素估计失步点进行同步,并且在重新计算自相关矩阵后根据较大特征值个数估计进制数;最后通过多次快速SVD算法结合DPLL最终实现伪码序列的盲估计。仿真结果显示,所提方法在低信噪比条件下可以有效估计出带残余频偏的软扩频信号的伪码序列,并且性能优于其他对比方法。

基于核密度估计的起重机应力谱编制方法研究

准确获得起重机金属结构的应力谱是疲劳寿命评估的前提,基于短期实测应力数据样本外推至全寿命周期内应力谱的方法是当前常用的一种方法,针对起重机疲劳寿命评估中常用的基于威布尔分布统计模型外推方法存在的一些不足,文中提出了基于核密度估计的起重机应力谱的外推流程和方法,并以岸边集装箱起重机为研究对象,利用文中给出的流程、方法外推应力循环幅值数据。外推数据统计分析结果显示:基于核密度估计方法生成的数据较好地反映了测试数据的统计特征,与基于威布尔统计模型的外推方法相比,具有不需要进行先验假设、拟合精度高的特点。

基于频域介电谱曲线分解的氧化锌避雷器老化状态评估

氧化锌避雷器是电力系统的重要组成设备,其老化状态直接关系到对过电压的防护效果,开展氧化锌避雷器的老化状态评估具有重要意义。该文针对氧化锌避雷器内部不均匀老化分布,提出一种基于频域介电谱曲线分解的氧化锌避雷器老化状态评估方法。首先,通过构建氧化锌避雷器介电响应等效电路,研究了氧化锌避雷器频域介电谱分解方法,根据整支避雷器频域介电谱分解可以得到避雷器内部各区域氧化锌阀片的频域介电曲线;其次,利用Havriliak-Negami方程对氧化锌阀片频域介电谱特征参数进行了提取,基于极限学习机建立了氧化锌阀片老化状态评估模型,提出氧化锌避雷器老化评估方法流程;最后,通过多重雷击模拟实验,制备了不同老化状态的氧化锌阀片与避雷器实物样本,对所提老化评估方法进行了分析与验证。结果表明,整支避雷器频域介电谱分解与测试结果的平均误差小于3%,所提方法能够有效地对避雷器频域介电谱进行分解并获取各区域的频域介电谱;针对整支避雷器,该文所提方法对各区域老化状态的评估准确率为93.3%,能够有效地对避雷器进行老化评估。