Non-synchronous Sampling Research Articles

A Novel Non-Synchronous Sampling Method for Harmonic/Interharmonic Measurement sn Power Systems

Abstract A novel non-synchronous sampling method for harmonic/interharmonic measurement in power system is proposed. The method consists of two main steps. In the first step, the leakage effect of DFT is reduced through transfom’s on the consecutive points of DFT. In the second step, the amplitude, frequency and phase angle of the harmonics are calculated through the corresponding interpolation methods. Compared to the commonly used windowed DFT method, the proposed method does not need the construction and storage of window functions. Therefore, it simplifies the implementation and improves the precision of harmonic measurement. The performance of the novel method is compared with DFT interpolation methods and windowed DFT interpolation method through simulation experiments.

数字全息图的非同步采样对再现像的影响

数字全息图的非同步采样对再现像的影响

Limit theorems in the Fourier transform method for the estimation of multivariate volatility

In this paper, we prove some limit theorems for the Fourier estimator of multivariate volatility proposed by Malliavin and Mancino (2002, 2009) [14,15]. In a general framework of discrete time observations we establish the convergence of the estimator and some associated central limit theorems with explicit asymptotic variance. In particular, our results show that this estimator is consistent for synchronous data, but possibly biased for non-synchronous observations. Moreover, from our general central limit theorem, we deduce that the estimator can be efficient in the case of a synchronous regular sampling. In the non-synchronous sampling case, the expression of the asymptotic variance is in general less tractable. We study this case more precisely through the example of an alternate sampling.

Calibration of Rogowski Coils at Power Frequencies Using Digital Sampling

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new high-accuracy system for power-frequency calibration of Rogowski coils is described in this paper. The calibration system is based on nonsynchronous digital sampling. An automated prototype of the calibration system operates at currents of up to 2000 A. A semiautomated system is capable of operating at currents of up to 60 000 A. The best uncertainty <formula formulatype="inline"><tex Notation="TeX">$(k = 2)$</tex></formula> of the calibration system is estimated to be better than 50 <formula formulatype="inline"><tex Notation="TeX">$\mu\hbox{A/A}$</tex> </formula> for magnitude and 50 <formula formulatype="inline"><tex Notation="TeX">$\mu\hbox{rad}$</tex></formula> for phase. </para>

Non-synchronous Optical Sampling and Data-Pattern Recovery Using a Repetition-Rate-Tunable Carbon-Nanotube Pulsed Laser

We demonstrate a non-synchronous all-optical sampling system using a carbon-nanotube mode-locked laser with a tunable repetition-rate. This allows a stable and unambiguous waveform reconstruction without the inherent limitation encountered in conventional non-synchronous optical sampling such as the time-direction ambiguity and the frequency-hole or sparse-sampling phenomena. Real-time eye-diagram reconstruction of 160 Gbit/s return-to-zero (RZ) signals with sub-picosecond resolution and data-pattern recovery with sequence length up to 217 - 4 has be realized.

Asymptotic normality of a covariance estimator for nonsynchronously observed diffusion processes

We consider the problem of estimating the covariance of two diffusion- type processes when they are observed only at discrete times in a nonsynchronous manner. In our previous work in 2003, we proposed a new estimator which is free of any 'synchronization' processing of the original data and showed that it is consistent for the true covariance of the processes as the observation interval shrinks to zero; Hayashi and Yoshida (Bernoulli, 11, 359-379, 2005). This paper is its sequel. Specifi- cally, it establishes asymptotic normality of the estimator in a general nonsynchronous sampling scheme.

A software sampling frequency adaptive algorithm for reducing spectral leakage

Spectral leakage caused by synchronous error in a nonsynchronous sampling system is an important cause that reduces the accuracy of spectral analysis and harmonic measurement. This paper presents a software sampling frequency adaptive algorithm that can obtain the actual signal frequency more accurately, and then adjusts sampling interval base on the frequency calculated by software algorithm and modifies sampling frequency adaptively. It can reduce synchronous error and impact of spectral leakage; thereby improving the accuracy of spectral analysis and harmonic measurement for power system signal where frequency changes slowly. This algorithm has high precision just like the simulations show, and it can be a practical method in power system harmonic analysis since it can be implemented easily.

Doppler and frequency-offset synchronization in wideband OFDM

When the orthogonal frequency-division multiplexing (OFDM) signal is appreciably wideband, as in underwater communications, a single Doppler-shift parameter is inadequate to model the Doppler effect, and a rate parameter is required as well. Such a model also accommodates nonsynchronized sampling of the received signal. We establish conditions for the identifiability of the Doppler parameters, and show how they affect the placement of null subcarriers (NSC). We derive the maximum-likelihood (ML) estimator and the corresponding conditional Crame/spl acute/r-Rao lower bound. We show that the vector formulation is amenable to estimation of signal parameters via rotational invariance techniques (ESPRIT) analysis, leading to a suboptimal but closed-form estimator. If the rate parameter is left uncompensated, we establish that the effective SNR is drastically reduced, which further leads to an increased bit error rate (BER). The ML estimator is demonstrated by numerical simulations that show that the performance of the estimator approaches the Crame/spl acute/r-Rao lower bound in the moderate-to-high SNR regions.

Frame Synchronization Exploiting Cauchy Distribution in DMT-Based xDSL Modems

This letter considers frame synchronization in non-synchronized sampling discrete multi-tone (DMT) based asymmetric digital subscriber line (ADSL)/very high speed DSL (VDSL) systems in the presence of timing error. We propose a frame synchronization method which is based on the observation that the normalized correlation between two sequences separated by the FFT length is Cauchy random variable. The proposed approach uses less number of correlators, reducing computational complexity as well as demodulation delay than a previous approach [1]. Therefore, ADSL/VDSL modems can be more power efficient and computationally less complex via the proposed frame synchronization method. Simulation results demonstrate the effectiveness of the proposed approach, comparing with the previous approach.

Multi-rate receivers with IF sampling and digital timing correction

This contribution deals with the design of a fully digital multi-rate receiver, operating on non-synchronized bandpass samples. Issues related to aliasing, sample rate conversion and timing correction are considered. We compare various receiver alternatives in terms of the BER degradation caused by aliasing and non-ideal timing correction. In particular, we focus on a low-complexity receiver performing sample rate conversion prior to matched filtering by means of an interpolator. We show that the BER degradation can be reduced to about 0.1 dB by careful selection of the system parameters, but at the expense of a large oversampling factor. A similar BER degradation can be achieved at a considerably smaller oversampling factor by including a simple digital anti-aliasing filter in front of the interpolator. We will develop a new type of anti-aliasing filter based on CIC filters. The distortion introduced by this CIC-type filter can be compensated for, by replacing the matched filter by an optimized receiver filter.

Polynomial-based maximum-likelihood technique for synchronization in digital receivers

Maximum-likelihood estimation theory provides a general framework for developing near-optimum (with respect to the Cramer-Rao bound) synchronization schemes for digital communication systems. A new technique for jointly estimating the symbol timing and carrier phase in digital receivers for linear digital modulations with nonsynchronized sampling is established for both data-aided and nondata-aided systems using a block-based feedforward architecture. This technique is a practical, fully digitally implemented synchronization concept based on a low-order polynomial approximation of the likelihood functions using the Farrow-based interpolator. It is shown that low oversampling, like two samples per symbol, can be used in timing recovery without compromising the system performance. This results in efficient overall receiver implementation. It is also demonstrated that the quality of the interpolator design has a big effect on the performance of the synchronization scheme. Frequency-domain optimized polynomial interpolator designs provide significantly better performance than the well-known Lagrange interpolators.

Periodic timing error components in feedback synchronizers operating on nonsynchronized signal samples

This letter shows that the synchronization error resulting from a timing recovery loop, operating on nonsynchronized samples of a noisy sinusoid, contains periodic components. This periodic timing jitter is caused solely by nonideal interpolation between the nonsynchronized signal samples and is absent when using synchronized sampling. The results of our linearized tracking analysis are confirmed by computer simulations.

Design of optimal interpolation filter for symbol timing recovery

We propose an optimal interpolation filter for symbol timing recovery in a digital receiver where the input analog-to-digital (A-D) conversion sampling clock is not synchronized to the transmitter symbol clock. The optimal filter is designed by minimizing the mean-square error (MSE) at the output of the receiver, assuming that the correct timing difference between the nonsynchronized input samples and the correct strobe synchronized to the symbol is given. The MSE minimization procedure results in a system of linear equations which can easily be solved to yield the optimal filter coefficients. We also analyze the symbol tracking performance of a symbol synchronizer that employs the proposed optimal interpolation filter. Although the proposed optimal filter is designed assuming the availability of the correct timing difference, we show that it minimizes the timing estimation error variance even when the computed timing difference values deviate from the ideal, we also show that the timing estimation is virtually unbiased if the length of the interpolation filter is greater than or equal to 4. Simulation results are included to show the performance improvement realizable by employing the optimal interpolation filter.

Digitally redesigned PAM controller and ideal state reconstructor for input time-delay/nondelay systems with nonsynchronous sampling

This paper develops a new digitally redesigned pulse-amplitude modulated (PAM) controller for a continuous-time input time-delay/nondelay system with nonsynchronous sampling. The concept of the law of the mean from the input integral calculus is utilized for the development of the equivalent digital predictor controllers from the available analog predictor controllers. As a result, the digitally controlled states closely match the original continuous-time states. To implement the developed discrete-time state-feedback PAM controller, this paper also develops an ideal discrete-time state using nonsynchronously sampled input-output data of the continuous-time input delay/nondelay system without establishing a dynamic observer.

On Modeling of Integrated Communication and Control Systems

In a two-part paper [1,2], Ray and Halevi reported modeling of Integrated Communication and Control Systems (ICCS). Varying and distributed delays are introduced in the control system due to asynchronous time-division multiplexing in the communication network. This correspondence illustrates the relationship of Ray and Halevi’s approach to that of Kalman and Bertram [3] under nonsynchronous sampling.

Some basic results on nonsynchronous and multirate sampling

It is shown that the infinite summation form of the starred transform for nonsynchronous and multirate sampled-data systems does not contain the usual additive term which is dependent on the value of the function at t =0. This justifies the direct utilization of the conventional block diagram representations in the generation of frequency response data.

A general z-transform formula for sampled-data systems

In this paper a generalized formulation for the convolution z transform is presented. The advent of this formulation could cover most of the sampled-data cases discussed in the literature. This includes nonsynchronized, cyclic rate, multirate, and nonsynchronized multirate sampling. Furthermore, the use of this formula lies in its applications to certain forms of nonlinear discrete analysis, as well as to time-varying cases. Each of the applications is singled out, and the proper references are cited.