Time-delay Estimation Technique Research Articles

A New Adaptive Sliding-Mode Control Scheme for Application to Robot Manipulators

This paper presents a new adaptive sliding-mode control (ASMC) scheme that uses the time-delay estimation (TDE) technique, then applies the scheme to robot manipulators. The proposed ASMC uses a new adaptive law to achieve good tracking performance with small chattering effect. The new adaptive law considers an arbitrarily small vicinity of the sliding manifold, in which the derivatives of the adaptive gains are inversely proportional to the sliding variables. Such an adaptive law provides remarkably fast adaptation and chattering reduction near the sliding manifold. To yield the desirable closed-loop poles and simplify a complicated system model by adapting feedback compensation, the proposed ASMC scheme works together with a pole-placement control (PPC) and a TDE technique. It is shown that the tracking errors of the proposed ASMC scheme are guaranteed to be uniformly ultimately bounded (UUB) with arbitrarily small bound. The practical effectiveness and the fast adaptation of the proposed ASMC are illustrated in simulations and experiments with robot manipulators, and compared with those of an existing ASMC.

A novel method for estimating external force: Simulation study with a 4-DOF robot manipulator

This paper proposes an algorithm to estimate external force exerted on the end-effector of a robot manipulator using information from joint torque sensors (JTS). The algorithm is the combination of Time Delay Estimation (TDE) and input estimation technique where the external force is considered as an unknown input to the robot manipulator. Based on TDE’s idea, the estimator which does not require an accurate dynamics model of the robot manipulator is developed. The simultaneous input and state estimation (SISE) is used to reject not only nonlinear uncertainties of the robot dynamics but also the noise of measurements. The performance of the proposed estimation algorithm is evaluated through simulation and experiment of a four degree-of-freedom manipulator and it demonstrates the stability and feasibility in estimating the external force. The estimation results show that this approach allows inexpensive sensors as joint torque sensors to be used instead of expensive ones as force/torque sensors in robot applications.

Analysis on the azimuthal velocity fluctuation of drift-wave turbulence and zonal flow via dynamic programming based time-delay estimation technique in a linear magnetized plasma device

The effective measurement of plasma turbulence flow field is of great help for better understanding the turbulence in magnetically confined plasmas, and experimentally verifying the theoretically predicted phenomenon such as zonal flows. In this article, the dynamic programming based time-delay estimation technique is employed for the first time to estimate azimuthal velocity fluctuation of drift-wave turbulence in a linear magnetized plasma generated via a hot cathode plasma source. Analysis results clearly reproduce the zonal flow structure which is spontaneously generated by nonlinear energy transfer from the drift-wave turbulence. Moreover, via the comparison among the zonal flow (ZF) characteristics estimated respectively by the turbulent fluctuations of plasma located in different frequency regions, we further evaluate the dependences of accuracy and response for estimating ZF property using this newly developed time-delay estimation algorithm on the level of relative incoherent noise in the carrier waves. This work provides an example and reference value for deeper exploration on plasma turbulence and in particular the relevant flow field with the help of the dynamic programming based time-delay estimation technique.

The Performance of the Modified GCC Technique for Differential Time Delay Estimation in the Cooperative Sensor Network

In this paper, a modified GCC technique (or FPT) for time delay estimation (TDE) is described. A flipped parameter (FP) can be defined for any sensor and is estimated during the observation period. Unlike classical TDE methods that evaluate the cross-correlation function, FPT requires flipped correlation evaluation based on each single sensor signal. The proposed technique gives accurate results for both coherent and non-coherent signals with symmetrical spectrum around the central frequency. The use of FPT method is especially significant for distributed sensor networks. The main features of the FPT are tested in a noisy simulation environment and the results are compared with classical methods. DOI: http://dx.doi.org/10.5755/j01.eee.19.8.2445

Velocimetry of edge turbulence during the dithering L–H transition with dynamic programming based time-delay estimation technique in the EAST superconducting tokamak

A dual gas puff imaging (GPI) system has been successfully assembled on the Experimental Advanced Superconducting Tokamak (EAST) and applied for the study of the dithering L–H transition in the 2012 spring campaign. A new method i.e., the dynamic programming based time-delay estimation technique, has been applied to the 64 × 64 pixels GPI video images to yield time-dependent two-dimensional velocity fields at the plasma edge on EAST. Local poloidal flow velocities up to ∼−3 km s−1 (in the electron diamagnetic direction) and radial flow velocities up to ∼−2 km s−1 (inward) are found inside the separatrix during a dithering burst. The radial and poloidal cross-correlation length, flow velocity and auto-correlation time inside the separatrix increase preceding the dithering burst and decrease following the dithering burst. These observations provide strong evidence for the shear flows playing an important role during the dithering L–H transition.

A Novel Scheme for Time Delay Estimation in the Fractional Fourier Transform Domain

A time delay estimator based on the fractional bispectrum is proposed; and it is suitable for the chirp signal. The proposed time delay estimation technique can outperform the conventional time delay estimation methods associated with the bispectrum in the Fourier domain under the correlated Gaussian noises at lower SNR. Simulation results demonstrate the validity of this estimation method.

On physical interpretation of two dimensional time-correlations regarding time delay velocities and eddy shaping

Time delay estimation (TDE) techniques are frequently used to estimate the flow velocity from fluctuating measurements. Tilted structures carried by the flow lead to misinterpretation of the time delays in terms of velocity direction and amplitude. It affects TDE measurements from probes, and is also intrinsically important for beam emission spectroscopy and gas puff imaging measurements. Local eddy shapes estimated from 2D fluctuating field are necessary to gain a more accurate flow estimate from TDE, as illustrated by Langmuir probe array measurements. A least square regression approach is proposed to estimate both flow field and shaping parameters. The technique is applied to a test case built from numerical simulation of interchange fluctuations. The local eddy shape does not only provide corrections for the velocity field but also quantitative information about the statistical interaction mechanisms between local eddies and E×B flow shear. The technique is then tested on gaz puff imaging data collected at the edge of EAST tokamak plasmas. It is shown that poloidal asymmetries of the fluctuation fields—velocity and eddy shape—are consistent at least qualitatively with a ballooning type of turbulence immersed in a radially sheared equilibrium flow.

Envelope and Wavelet Transform for Sound Localisation at Low Sampling Rates in Wireless Sensor Networks

High sampling frequencies in acoustic wireless sensor network (AWSN) are required to achieve precise sound localisation. But they are also mean analysis time and memory intensive (i.e., huge data to be processed and more memory space to be occupied which form a burden on the nodes limited resources). Decreasing sampling rates below Nyquist criterion in acoustic source localisation (ASL) applications requires development of the existing time delay estimation techniques in order to overcome the challenge of low time resolution. This work proposes using envelope and wavelet transform to enhance the resolution of the received signals through the combination of different time-frequency contents. Enhanced signals are processed using cross-correlation in conjunction with a parabolic fit interpolation to calculate the time delay accurately. Experimental results show that using this technique, estimation accuracy was improved by almost a factor of 5 in the case of using 4.8 kHz sampling rate. Such a conclusion is useful for developing precise ASL without the need of any excessive sensor resources, particularly for structural health monitoring applications.

Influence of layer roughness for road survey by ground penetrating radar at nadir: theoretical study

In civil engineering, conventional methods used to estimate the thickness of pavements assume flat interfaces. In contrast, this study uses a rigorous electromagnetic method called propagation-inside-layer-expansion (PILE) to simulate the radar backscattered signal at nadir from a rough pavement made up of two rough interfaces separating homogeneous media. The statistical distribution of the first two echoes is studied by comparison with the default flat case, together with their frequency behaviour. Within the scope of road pavement survey by ground penetrating radar, the scattering model is finally used to assess the performance of the estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm, one of the well-known high-resolution time-delay estimation techniques.

Comparison of Time-Delay Estimation Techniques in Acoustic Environment

The calculation of time delay between a signal and its echo received at a microphone has been proven to be a useful parameter. Speech enhancement, speaker localization, speech and speaker recognition are few applications of TDE methods. We are implementing various methods for the estimation of time delay. These methods are implemented in MATLAB. The reason for choosing the MATLAB as the analysis and simulation tool is that it has more flexible choices to support the simulation and is easy to do modification or data recording. These methods are crosscorrelation (CC), phase transform (PHAT). Various time-delay estimation techniques based on the cross-correlation functions are compared through simulations and measurements. Their simulation results are compared in terms of computation complexity, hardware implementation, precision, and accuracy.

Dynamic programming based time-delay estimation technique for analysis of time-varying time-delay

A new time-delay estimation (TDE) technique based on dynamic programming is developed to measure the time-varying time-delay between two signals. The dynamic programming based TDE technique provides a frequency response five to ten times better than previously known TDE techniques, namely, those based on time-lag cross-correlation or wavelet analysis. Effects of frequency spectrum, signal-to-noise ratio, and amplitude of time-delay on response of the TDE technique (represented as transfer function) are studied using simulated data signals. The transfer function for the technique decreases with increase in noise in signal; however it is independent of signal spectrum shape. The dynamic programming based TDE technique is applied to the beam emission spectroscopy diagnostic data to measure poloidal velocity fluctuations, which led to the observation of theoretically predicted zonal flows in high-temperature tokamak plasmas.

用时延估计法提高光纤光栅中心波长检测精度

用时延估计法提高光纤光栅中心波长检测精度

Flipped parameter technique applied on source localization in energy constraint sensor arrays

In this paper novel flipped parameter technique (FPT) for time delay estimation (TDE) in source localization problem is described. We propose passive source localization technique based on the development of an energy efficient algorithm that can reduce intersensor and interarray communication. We propose a flipped parameter (FP) which can be defined for any sensor in distributed sensor subarrays during the observation period. Unlike classical TDE methods that evaluate cross-correlation function, FPT requires evaluation based upon single sensor signal. The computed cross correlation between a signal and its analytic 'flipped' pair (flipped correlation) is a smooth function which peak (time delay) can be accurately detected. Flipped parameters are sufficient to determine all differential delays of the signals related to the same source. The flipped parameter technique can be used successfully in two-step methods of passive source localization with significantly less energy in comparison to the classic cross correlation. The use of FPT method is especially significant for the energy constrain distributed sensor subarrays. Using synthetic seismic signals, we illustrate the error of the source localization for classical and proposed method in the presence of noise. We demonstrate the performance improvement in noise environment of the proposed technique in comparison to the classic methods that use real signals. The proposed technique gives accurate results for both coherent and non-coherent signals.

Discrete time-delay control of an autonomous underwater vehicle: Theory and experimental results

A discrete time-delay control (DTDC) law for a general six degrees of freedom unsymmetric autonomous underwater vehicle (AUV) is presented. Hydrodynamic parameters like added mass coefficients and drag coefficients, which are generally uncertain, are not required by the controller. This control law cancels the uncertainties in the AUV dynamics by direct estimation of the uncertainties using time-delay estimation technique. The discrete-time version of the time-delay control does not require the derivative of the system state to be measured or estimated, which is required by the continuous-time version of the controller. This particularly provides an advantage over continuous-time controller in terms of computational effort or availability of sensors for measuring state derivatives, i.e., linear and angular accelerations. Implementation issues for practical realization of the controller are discussed. Experiments on a test-bed AUV were conducted in depth, pitch, and yaw degrees of freedom. Results show that the proposed control law performs well in the presence of uncertainties.

Real‐time image quality assessment with mixed Lagrange time delay estimation autoregressive (MLTDEAR) model

A proposal to assess the quality of scanning electron microscope images using mixed Lagrange time delay estimation technique is presented. With optimal scanning electron microscope scan rate information, online images can be quantified and improved. The online quality assessment technique is embedded onto a scanning electron microscope frame grabber card for real-time image processing. Different images are captured using scanning electron microscope and a database is built to optimally choose filter parameters. An optimum choice of filter parameters is obtained. With the optimum choice of scan rate, noise can be removed from real-time scanning electron microscope images without causing any sample contamination or increasing scanning time.

Examination of the velocity time-delay-estimation technique

The one-dimensional time-delay-estimation (TDE) velocity technique infers the velocity of plasma fluctuations using cross-correlations between two spatially separated signals, and here this technique is evaluated using experimental results and numerical simulations. Probe arrays and a fast-framing imaging camera are used to measure the azimuthal fluctuation propagation speed in a cylindrical magnetized plasma device. The time-averaged TDE velocity field obtained in this way is found to be approximately 30% larger than Mach probe measurements of the plasma fluid velocity, suggesting that the TDE method infers the plasma E×B velocity and presumably a diamagnetic flow. The TDE technique is also applied to turbulent simulation data with known velocity fields. The results show that for the TDE parameters chosen here, the TDE technique can be used to infer the large-scale, slowly varying velocity, but that small scale or turbulent velocity fields cannot be reliably inferred.

Time delay estimation using fractional Fourier transform

The need for time delay estimation (TDE) between two signals arises quite often in many areas such as radar, sonar, etc. Several TDE techniques have been proposed in the literature using various signal transforms such as the conventional Fourier transform and the Hilbert transform. In this paper, use of the fractional Fourier transform (FRFT) for TDE is proposed. Some of the proposed estimators use the magnitude of the FRFT of the signals, whereas others depend on the phase angle of it. The problem of TDE in the statistical framework is also generalized using the FRFT and the maximum likelihood (ML) estimator for the time delay is obtained. To validate the proposed approach, simulation results for some of the proposed estimators are presented.

Fast simulated annealing algorithm for BAEP time delay estimation using a reduced order dynamic model

The extraction of Brainstem Auditory Evoked Potentials (BAEPs), from the EEG background, is of high clinical interest. The present paper can be considered as a continuation of our previous work related to the BAEP estimation in endocochlear pathologies. In our previous published work, we proposed a technique for time delay estimation on the basis of the BAEPs in response to successive stimulations. Put in a different manner, our objective was the estimation of the dynamics of the cochlea that is responsible for the delayed responses. The estimation technique was based on optimization of a non-linear criterion by means of Simulated Annealing Time Delay Estimation (SATDE) algorithm. However, it is well known that such heuristic algorithms are time consuming and largely depend on the number of parameters to be estimated. The present paper demonstrates that modeling the non-stationarity of responses considerably decreases the convergence time to the global minimum. The newly proposed method in this paper, called Fast Simulated Annealing Time Delay Estimation (FSATDE) algorithm, has been validated on both simulated and real signals.

Performance of GCC- and AMDF-Based Time-Delay Estimation in Practical Reverberant Environments

Recently, there has been an increased interest in the use of the time-delay estimation (TDE) technique to locate and track acoustic sources in a reverberant environment. Typically, the delay estimate is obtained through identifying the extremum of the generalized cross-correlation (GCC) function or the average magnitude difference function (AMDF). These estimators are well studied and their statistical performance is well understood for single-path propagation situations. However, fewer efforts have been reported to show their performance behavior in real reverberation conditions. This paper reexamines the GCC-and AMDF-based TDE techniques in real room reverberant and noisy environments. Our contribution is threefold. First, we propose a weighted cross-correlation (WCC) estimator in which the GCC function is weighted by the reciprocal of AMDF. This new method can sharpen the peak of the GCC function, which corresponds to the true time delay and thus leads to a better estimation performance as compared to the conventional GCC estimator. Second, we propose a modified version of the AMDF (MAMDF) estimator in which the delay is determined by jointly considering the AMDF and the average magnitude sum function (AMSF). Third, we compare the performance of the GCC, AMDF, WCC, and MAMDF estimators in real reverberant and noisy environments. It is shown that the AMDF estimator can yield better performance in favorable noise conditions and is slightly more resilient to reverberation than the GCC method. The GCC approach, however, is found to outperform the AMDF method in strong noisy environments. Weighting the correlation function by the reciprocal of AMDF can improve the performance of the GCC estimator in reverberation conditions, yet its improvement in noisy environments is limited. The MAMDF algorithm can enhance the AMDF estimator in both reverberant and noisy environments.

Performance of GCC-and AMDF-based time-delay estimation in practical reverberant environments

Recently, there has been an increased interest in the use of the time-delay estimation (TDE) technique to locate and track acoustic sources in a reverberant environment. Typically, the delay estima...