Cross-correlation Time Delay Estimation Research Articles

Precise disturbance localization of long distance fiber interferometer vibration senor based on an improved time–frequency variation feature extraction scheme

Locating intrusions with high accuracy is crucial for prompting long distance distributed optical fiber vibration sensing systems to practical applications in engineering filed. To achieve the high measurement accuracy and real-time performance simultaneously, in this paper, an intensity-modulated ultra-long distance distributed optical fiber vibration sensing system using an asymmetric dual Mach-Zehnder interferometer is experimentally established. More importantly, a positioning approach based on an ameliorated time–frequency feature extraction scheme is proposed with both theoretically analysis and experimental demonstration. In particular, an endpoint detection algorithm based on differential operation is firstly utilized to rapidly and accurately locate the endpoints of the received vibration signals. Thus the large-band width signals can be successfully acquired by setting an approximate window. Then, the ameliorated time–frequency feature extraction scheme based on a maximal overlap discrete wavelet packet transform is applied to eliminate the asymmetry of the large-band width signals, as it could lead to an erroneous positioning result when directly using a cross-correlation time delay estimation algorithm. Finally, the vibration positions along the sensing fiber link of the established sensing system can be successfully demodulated with the help of the extracted time–frequency features. To validate the effectiveness of the proposed scheme, vibration positioning tests were conducted in a real perimeter security scenario. And the results show that a mean positioning error of 11.12 m and a mean processing time of 0.276 s have been realized in a sensing length of 101 km. Thus, it is believed that through continuous technological advancements and refine algorithm optimization, the long distance distributed optical fiber vibration sensor founded on the proposed positioning strategy is poised to play an important role in the practical engineering applications.

Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas

The properties of the edge ion-scale turbulence are studied using the beam emission spectroscopy (BES) diagnostic on MAST. Evidence of the formation of large-scale high-amplitude coherent structures, filamentary density blobs and holes, 2–4 cm inside the plasma separatrix is presented. Measurements of radial velocity and skewness of the density fluctuations indicate that density holes propagate radially inwards, with the skewness profile peaking at 7–10 cm inside the separatrix. Poloidal velocities of the density fluctuations measured using cross-correlation time delay estimation (CCTDE) are found to exhibit an intermittent behaviour. Zonal-flow analysis reveals the presence of poloidally symmetric coherent oscillations – low-frequency (LF) zonal flows and geodesic acoustic modes (GAM). Shearing rates of the observed zonal flows are found to be comparable to the turbulence decorrelation rate. The observed bursts in density-fluctuation power are followed by quiescent periods with a transient increase in the power of sheared flows. Three-wave interactions between broadband turbulence and a GAM are illustrated using the autobispectral technique. It is shown that the zonal flows and the density-fluctuation field are nonlinearly coupled and LF zonal flows mediate the energy transfer from high- to low-frequency density fluctuations.

Wavelet transform-based cross-correlation in the time-delay estimation applications

The article discusses the application of wavelet analysis for the time-frequency time-delay estimation. The proposed algorithm is wavelet transform-based cross-correlation time delay estimation that applies discrete time wavelet transform to filter the input signal prior to computation of cross-correlation function. The distinguishing feature of the algorithm that it uses the variation of continuous wavelet transform to process the discrete signals instead of dyadic wavelet transform that is normally applied to the case. Another feature that the implication of convolution theorem is used to compute coefficients of the wavelet transform. This makes possible to omit redundant discrete Fourier transforms and significantly reduce the computational complexity. The principal applicability of the proposed method is shown in the course of a computational experiments with artificial and real-world signal. So the method demonstrated expected selectivity for the signals localized in the different frequency bands. The application of the method to practical case of pipeline leak detection was also successful. However, the study concluded that this method provides no specific advantages in comparison with the conventional one. In the future, alternative applications in biological signal processing will be considered.

Application of the denoising technique based on improved FastICA algorithm in cross-correlation time delay estimation

Cross-correlation is a common time delay estimation method. However, in the actual measurement environment, the near-end and far-end sensors are often disturbed by the correlated noise, which seriously affects the accuracy of time delay estimation and even leads algorithm is proposed, and the steepest descent is introduced to reduce the sensitivity of FastICA algorithm to initial values. The useful acoustic data and disturbing acoustic data were measured respectively in a simulated granary. From these data, the signals contaminated by noise were generated by a mixing matrix and used for testing the performance of the proposed method. The testing results show that the proposed method can effectively suppress the influence of correlated noise on cross-correlation time delay estimation, and improve the accuracy of estimation.

An Adaptive Time Delay Estimation Method for Broadcast Audio Based on Power Cepstrum

Abstract This paper proposes an adaptive time delay estimation method for broadcast audio based on power cepstrum. First, it adds two real-time broadcast audio signals with the same content but with a time delay to obtain a mixed signal, then segment the mixed signal, and obtain a power cepstrum for each mixed signal. Afterwards, the time delay of the two audio signals is determined by using the feature that the power cepstrum of the mixed signal can peak at the time delay. The experimental results show that this method can obtain more accurate time delay results. And it has higher robustness and faster than traditional methods such as generalized cross-correlation time delay estimation algorithm.

Negative Pressure Wave Leakage Location Algorithm Based on Difference Cross-Correlation Delay Estimation

Accurate estimate the time difference of the leakage negative pressure wave signals reached both sides of the sensor at the two sides of the leakage point is the key to accurate location of the leakage point. Based on the theoretical analysis of cross-correlation time delay estimation algorithm and characteristics of negative pressure wave signal, a cross-correlation delay estimation method for pipeline leakage negative pressure wave signal is proposed. Through wavelet transform, signal conversion and cross correlation function analysis of discrete negative pressure wave signal sequence obtained by high-speed sampling, the time difference of the negative pressure wave signal monitored by the sensors on both sides of the leakage point can be accurately obtained. In the laboratory’s 102.8 meters pipeline, leakage was simulated through the valve, the time delay estimation and leak location experiment of the sensor at the two ends of the pipeline were analyzed, and compared with the wavelet analysis method. The experimental results show under the condition that the leakage is 10%, 5% and 2% of the total pipeline volume, the cross-correlation analysis algorithm has a positioning error interval of 0.97%-1.46%, which is better than the current positioning error 0.48%-2.43% of the wavelet analysis algorithm. At the same time, it avoids the influence of different wavelet types and analysis scales in the wavelet analysis algorithm on positioning accuracy, and is more suitable for pipeline leakage monitoring system to real-time online monitoring needs, has a wide application value.

Direction of Arrival Estimation Using Two Hydrophones: Frequency Diversity Technique for Passive Sonar.

The traditional passive azimuth estimation algorithm using two hydrophones, such as cross-correlation time-delay estimation and cross-spectral phase estimation, requires a high signal-to-noise ratio (SNR) to ensure the clarity of the estimated target trajectory. This paper proposes an algorithm to apply the frequency diversity technique to passive azimuth estimation. The algorithm also uses two hydrophones but can obtain clear trajectories at a lower SNR. Firstly, the initial phase of the signal at different frequencies is removed by calculating the cross-spectral density matrix. Then, phase information between frequencies is used for beamforming. In this way, the frequency dimension information is used to improve the signal processing gain. This paper theoretically analyzes the resolution and processing gain of the algorithm. The simulation results show that the proposed algorithm can estimate the target azimuth robustly under the conditions of a single target (SNR = −16 dB) and multiple targets (SNR = −10 dB), while the cross-correlation algorithm cannot. Finally, the algorithm is tested by the swell96 data and the South Sea experimental data. When dealing with rich frequency signals, the performance of the algorithm using two hydrophones is even better than that of the conventional broadband beamforming of the 64-element array. This further validates the effectiveness and advantages of the algorithm.

White Light Scanning Interferometry Based on Generalized Cross-Correlation Time Delay Estimation

Based on generalized cross-correlation time delay estimation (GCTDE), a new white light scanning interferometry (WLSI) method is proposed, in which the profile information usually achieved with the zero optical path difference (ZOPD) position is replaced with the relative displacement of interference signal between different pixels. Because all spectral information of interference signal (envelope and phase) and filter is utilized, the proposed GCTDE-based WLSI method reveals the advantages of higher accuracy and better noise suppression capability. Especially, in the case where the shape of interference signal envelope is irregular, the proposed method can achieve profile measurement with high accuracy while the conventional ZOPD position locating method cannot work. Moreover, by introducing laser interferometry system to calibrate the vertical displacement of a piezoelectric ceramic transducer scanning system, the measuring accuracy of the proposed GCTDE-based WLSI is further improved. Both the simulation and the experimental results demonstrate the significant accuracy advantage of the proposed GCTDE-based WLSI.

Time delay estimation based on variational mode decomposition

In order to improve the time delay estimation of colored noise signals, this article proposes generalized cross-correlation time delay estimation based on variational mode decomposition. First of all, we put forward the signal energy detection criterion to extract the effective signal from the signal, which can reduce the amount of calculation and improve the real-time performance. Second, the effective signal is decomposed into a number of intrinsic mode functions using variational mode decomposition. The correlation coefficients of each intrinsic mode function and the original signal are calculated. The article reconstructed signal with intrinsic mode functions which extract useful intrinsic mode functions by defaulting the correlation coefficient threshold. Finally, this article uses generalized cross-correlation to estimate time delay of the reconstructed signal. Theoretical analysis and simulation results show that the accurate time delay estimation can be obtained under the condition of color noise by the proposed method. The measurement accuracy of the proposed method is 15 times that of the generalized cross-correlation, and the running time of the proposed method is 4.0601 times faster than that of the generalized cross-correlation algorithm. The proposed method can reduce the computation and the running time of the system and also improve the measurement accuracy.

Power station boiler furnace water-cooling wall tube leak locating method based on acoustic theory

In a coal-fired power plant, measures such as early forecasting of boiler tube explosions, timely leak discovery, and the identification of the leak location prior to explosion are important to proper shutdown procedures, reduction of repair time, and minimization of financial losses. This study used a three-dimensional space location algorithm based on the time delay of arrival (TDOA) to determine the location of water-cooling wall tube leaks in real time. The location precisions of the Chan algorithm and the Chan–Taylor collaborative algorithm were compared. The location simulation showed that the time delay estimation and the number of sensors greatly impacted the location precision. The Chan–Taylor approach performed better than Chan alone. Data from the field experiments showed that the maximum likelihood (ML) windows-based generalized cross-correlation time delay estimation resulted in a more accurate TDOA. Then, the Chan–Taylor collaborative algorithm with an 8-element acoustic array could be used as a real-time location monitor for water-cooling wall leaks.

Time Delay Signal Processing Research in Sound Source Localization Technology

Time delay estimation is a key technology of array signal processing, which is designed to estimate the time delay of the sound source signal reaches different sensor. Because of differences in the weighting function method, existing methods of generalized cross-correlation time delay estimation have their own anti-noise and anti-reverberation characteristics. In this paper, the existing various delay estimation algorithm comprehensive is compared, which reveals their advantages and disadvantages, and further improved direction of time delay estimation algorithm is given.

Research on Water Pipeline Leak Location

With the accelerated process of urbanization, water pipeline leak problem becomes more and more serious. If this problem dose not solved in a timely manner, water resource waste, even serious geological disasters will be caused. In order to locate the water pipeline leak position, we studied the characters and mechanism of the leakage acoustic signals in this paper, and analyzed the spectrum characters of acoustic signal with different leakage quantity and noise on pipeline diameter sudden change point. Based on this, we designed and implemented a set of software, using wavelet denoising method and cross-correlation time delay estimation method for leak location. Finally, we conducted an experiment based on the cast iron pipeline with a diameter of 1.5 inch using the proposed software, and compared the results obtained by different processing approaches. As a conclusion, the experiment results and the theoretical expectations are basically the same.

Acoustic Source Localization Based on Generalized Cross-correlation Time-delay Estimation

In the existing acoustic emission (AE) localization methods, the estimation localization method based on the time difference of arrival (TDOA) has less computation and higher accuracy of positioning and is easy to implement the real-time systems and thus it becomes a commonly used method in the acoustic source localization methods. In this method, the most important thing is time delay estimation (TDE) that directly affects the accuracy of positioning. In this paper, we analyze the performance of several weighting functions in the generalized cross-correlation time-delay estimation algorithm and give the simulation results. By comparison, PHAT weighting is characterized by small fluctuations, sharp peak and strong anti-jamming ability and it is the best choice for acoustic source localization in the generalized cross-correlation time-delay estimation algorithm.