High resolution techniques for Loran-C skywave delay estimation

Two high-resolution estimation techniques are applied to the problem of estimating the delays of the skywave components of signals input to Loran-C receivers. Their performance is evaluated and compared with that of a Fourier-based spectral-division technique. Simulation results show that the high-resolution algorithms improve the accuracy of the estimates significantly and estimate the skywave delay successfully in situations in which the Fourier-based method fails     

Loran-C skywave delay detection using ARMA algorithm

The autoregressive moving average technique (ARMA) is applied to the problem of estimating the delay of Loran-C skywaves. The performance of this technique is evaluated and compared with Fourier-based methods. The simulation results show that the ARMA algorithm yields a significantly greater estimation accuracy and that it can also operate successfully with very noisy signals     

Time delay estimation using the cross bispectrum

The cross bispectrum phase can be effectively used to estimate the time required for a nonGaussian signal to propagate between a pair of spatially separated sensors in the presence of highly correlated Gaussian noise. The authors present a consistent estimator of the phase of the cross bispectrum, derive the exact distribution of the phase of a complex Gaussian sample bispectrum, and show that in most cases the exact distribution can be approximated by a Gaussian distribution. Using this Gaussian approximation, the authors derive the variance of the time delay estimate computed from the sample cross bispectrum of a signal in additive correlated noise. These results allow the performance of time delay estimators based on the cross bispectrum phase to be quantified as a function of the sample size, the skewness of the signal, the signal-to-noise ratio (SNR), and the noise correlation     

Time delay estimation using higher order statistics

The problem of time delay estimation in spatially correlated Gaussian noises is addressed. New normal equations based upon higher order statistics of the sensor measurements are established, from which a new adaptive algorithm for time delay estimation is proposed. Simulation examples are presented to illustrate the effectiveness of this algorithm     

Adaptive subsample delay estimation using windowed correlation

An on-line delay estimation algorithm based upon the windowed average magnitude difference function (AMDF) that is suitable for determining the subsample delay between two noisy signals is introduced. The new estimator uses the AMDF to directly update the delay estimate, which is in turn used to adapt the coefficients of a fractional delay filter (FDF). The new estimator consists predominately of addition and subtraction operations and outperforms conventional FDF based estimators in low signal-to-noise ratio situations.     

Multipath delay estimation using a superresolution PN-correlationmethod

This paper addresses the problem of high-resolution estimation of a multipath channel delay profile. We propose several improvements to the so-called superresolution pseudo-noise sequence correlation method (SPM) and analyze its performance on time-varying channels. SPM is based on the multiple signal classification (MUSIC) algorithm, which requires decorrelation of the multipath echoes. The proposed improvements enable SPM-based delay estimation in the presence of narrowband interference, and they reduce the necessary transmission window while preserving multipath echo decorrelation. These improvements are analyzed and are applied to underwater acoustic experimental data     

Multipath time delay estimation using regression stepwise procedure

Consider a multipath signal whose individual signals are deterministic known pulses. Our problem is to estimate the amplitudes and delay times of individual signals. Our main idea is to consider the multipath signal as a multiple regression model where each time sample is considered to be a possible arrival time of a pulse that may not be real. We use the regression stepwise procedure to select true pulses and eliminate the false pulses. By using this procedure, the number of pulses in a multipath signal does not need to be known. The results of a Monte Carlo simulation study with sinusoidal and trapezoidal pulses are presented to demonstrate the accurate estimation of arrival times and amplitudes by the regression stepwise procedure     

RMS delay spread estimation technique using non-coherent channelmeasurements

A method is presented for deriving the RMS delay spread from non-coherent wideband channel measurements (measured amplitude transfer functions). A frequency-domain model of the frequency-selective, Rician fading channel is used, allowing a theoretical evaluation of the transfer function's level crossing statistics     

Joint angle and delay estimation using shift-invariance techniques

In a multipath communication scenario, it is often relevant to estimate the directions and relative delays of each multipath ray. We derive a closed-form subspace-based method for the simultaneous estimation of these parameters from an estimated channel impulse response, using knowledge of the transmitted pulse shape function. The algorithm uses a two-dimensional (2-D) ESPRIT-like shift-invariance technique to separate and estimate the phase shifts due to delay and direction of incidence with automatic pairing of the two parameter sets. Improved resolution is obtained by enlarging the data matrix with shifted and conjugated copies of itself     

Real-time DSP-based time delay estimation using two sensors

There are few available approaches for time delay estimation (TDE) which offer with a potential to be implemented as real-time-embedded systems. Most of these lose accuracy in reverberant and highly noisy environments. In this paper, we initially proposed a 2-dimensional (2D) signal based on the cross-correlation. Then, we proposed two approaches for TDE, based on this 2D signal. There are two main advantages for using the proposed approaches. The first merit is that using a large amount of information about the correlation between the received signals allows a more robust TDE against noise and reverberation, when compared to the other possible techniques. The second one is that the number of samples to calculate the TDE algorithms is decreasing significantly, which is reducing the computational complexity. This paper also proposes a feasible hardware structure to implement the proposed approaches on digital signal processor embedded systems in real time.     

Bounded delay timing analysis and power estimation using SAT

This paper presents a satisfiability based approach that can be used for accurate estimation of both the critical delay and dynamic transition power consumption of circuits using an event propagation model. The accuracy of the model depends on the accuracy of the gate delays. The speed and efficiency of modern Boolean SAT solvers permits us to model complicated delay models like the Bounded Delay Model, which is better able to capture realistic variations in gate delays due to process variations and changes in operating conditions. We show that timing analysis with bounded delays yields a more accurate critical delay for a circuit than with fixed gate delays. In spite of the high complexity due to unpredictable gate delays, our SAT based approach gives good performance on benchmark circuits, even with a Bounded Delay Model derived from a real industrial library.     

Time delay and spatial signature estimation using knownasynchronous signals

This paper considers the problem of estimating the parameters of known signals received asynchronously by an array of antennas. The parameters of primary interest are the time delays of the signals and their spatial signatures at the array. Estimates of the signal directions of arrival are also considered but are of secondary importance in this work. Maximum likelihood algorithms and more computationally efficient approximations are developed for both the case where all received signals are identical (the channel estimation/overlapping echo problem) and where they are all distinct. Conditions are also derived under which the standard matched filter approach yields consistent and statistically efficient parameter estimates. The issue of solution uniqueness is addressed, and in particular, an upper bound on the number of signals whose parameters may be uniquely identified is derived for a number of different cases. Typically, the bound is far greater than the number of sensors and is limited only by the number of data samples collected. Some representative simulation examples are also included to illustrate the algorithms' performance relative to the Cramer-Rao bound     

Adaptive subsample delay estimation using a modified quadrature phase detector

An online delay estimation algorithm based upon an analogue quadrature phase detector that is suitable for determining the subsample delay between two noisy sinusoidal signals is introduced. The new technique is based on the recently proposed discrete-time quadrature-delay estimator (QDE). The algorithm uses the in-phase and quadrature-phase components of the received signals to produce a bias-free estimate of the delay between the input signals. The technique directly minimizes the delay error estimate, which is in turn used to adapt the coefficients of a simple fractional-delay filter (FDF). The algorithm is insensitive to variations in the amplitudes of the input signals, and does not require an accurate prior estimate of the frequency of the input sinusoids. The algorithm directly updates the delay error estimate, which is in turn used directly as the coefficient input to an adaptive FDF. The technique is simple to implement and has a reduced complexity compared to other adaptive techniques. Simulations show that in the presence of system noise, the new estimator outperforms conventional FDF-based estimators.     

Joint estimation of time delay and frequency delay in impulsivenoise using fractional lower order statistics

New methods for time delay estimation and joint estimation of time delay and frequency delay in the presence of impulsive noise are introduced. First, degradation of the conventional approaches based on second-order statistics is shown both theoretically and experimentally. Then, a new class of robust algorithms are developed using the theory of alpha-stable distributions, including the fractional lower order covariance (FLOC) method, which is formulated for the time delay estimation problem and the fractional lower order ambiguity function (FLOAF), which is defined for the joint estimation of time delay and frequency delay. It is shown that these new methods are robust for both Gaussian and non-Gaussian impulsive noise environments. The improved performance is clearly demonstrated through detailed analysis and comprehensive simulations with computer-generated data as well as actual radar and sonar clutter data     

基于时延分集的MIMO多径信道盲估计算法

发送时延分集在空时编码中是一种有效可行的方法。本文提出了一种基于发送时延分集的多径信道估计方法,指出如果发送时延大于信道时延,多输入多输出（MIMO）信道可以转化为特殊的单输入多输出信道,通过对信道输出进行子空间分解可以估计出信道参数。仿真结果显示了本文算法的有效性。     

Coherence and time delay estimation

This paper presents a tutorial review of work in coherence and time delay estimation. A review of coherence research and development is presented. A derivation of the ML estimator for time delay is presented together with an interpretation of that estimator as a special member of a class of generalized cross correlators. The performance of the estimator is given for both high and low signal-to-noise ratio cases. The proposed correlator is implemented and stimulated with synthetic data. The results are compared with performance predictions and found to be in good agreement.     

Joint estimation of PN code delay and multipath using the extendedKalman filter

The problem of delay estimation in the presence of multipath is considered. It is shown that the extended Kalman filter (EKF) can be used to obtain joint estimates of time-of-arrival and multipath coefficients for deterministic signals when the channel can be modeled as a tapped-delay line. Simulation results are presented for the EKF joint estimator used for synchronization in a direct-sequence spread-spectrum system operating over a frequency-selective fading channel. A simplified model of the EKF joint estimator is considered for analysis purposes. The evolution in time of the tracking error probability density function and the nonlinear tracking error variance are examined through numerical solution of the Chapman-Kolmogorov equation. The nonlinear tracking error variance is compared to both the linear error variance estimate directly provided by the EKF and the Cramer-Rao lower bound     

Phase spectrum method for time delay estimation using twin-plane electrical capacitance tomography

Flow velocity distribution can be measured by means of a twin-plane tomography system and cross-correlation techniques. However, the use of these techniques based on finding the argument that maximises an estimated cross-correlation function (CCF) of corresponding pixels from two planes, in practice is limited by their low accuracy in reconstructed concentration. Presented is a method permitting the time delay to be measured with higher accuracy. The method is based on utilising the phase of the cross-spectral density of the CCF to estimate a time delay. The method is found to be more promising than the classical correlation method.     

Medium wave skywave beams

The author discusses the advantages and drawbacks of skywaves and why they are avoided by domestic medium-wave broadcaster. He reports some results of a computer investigation of problems encountered with medium-wave antennas coupled to a skywave propagation medium. Experimental results are given showing skywave patterns for broadcasts from Alaska, one using a horizontal and the other a vertical antenna. It is concluded for these two examples that remarkable medium-wave coverage could be obtained using available frequencies     

An investigation of time delay estimation in room acoustic environment using magnitude ratio

This paper investigates the relation between the nonstationary sound source and the frequency domain magnitude ratio of two microphones based on short-term frequency analysis. The fluctuation level of nonstationary sound sources is modeled by the exponent of polynomials from the concept of moving pole model. According to this model, the sufficient condition for utilizing the fluctuation level and magnitude ratio to estimate the time delay between two microphones is suggested. Simulation results are presented to show the performance of the suggested method.