• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 추계종합학술대회 B
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• pp.628-631
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• 2008

원격탐지를 목적으로 하는 레이다 시스템에서는 일반적으로 도플러 필터뱅크를 적용하여 목표물 반사 신호들의 스펙트럼을 분석함으로서 반사 신호의 크기 및 속도정보 등을 얻게 된다. 이러한 스펙트럼 추정방법은 오래 전부터 널리 이용되고 있는 FFT(Fast Fourier Transform) 기법을 이용한 것으로 대부분의 레이다 시스템에서 채택하고 있는 방식이다. 그러나 레이다 시스템에서의 목표물 반사 신호 획득시간이 현저히 짧은 경우, 즉 고속으로 이동하는 항공기용 시스템이나 매우 빠른 목표물들의 즉각적인 탐지가 목적인 시스템에서는 기존 FFT 스펙트럼 추정방식으로는 높은 도플러 주파수 해상도를 얻을 수 없기 때문에 정확도가 현저히 떨어질 수 있다. 따라서 본 논문에서는 이러한 문제점을 극복하기 위하여 해상도 문제가 발생하지 않는 파라메터 추정방식인 AR 스펙트럼 추정 방법에 대하여 고찰하였다.

• Communications for Statistical Applications and Methods
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• 제14권3호
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• pp.561-576
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• 2007

Five plotting positions are applied to the computation of probability weighted moments (PWM) on the parameters of the generalized logistic distribution. Over a range of parameter values with some finite sample sizes, the effects of five plotting positions are investigated via Monte Carlo simulation studies. Our simulation results indicate that the Landwehr plotting position frequently tends to document smaller biases than others in the location and scale parameter estimations. On the other hand, the Weibull plotting position often tends to cause larger biases than others. The plotting position (i - 0.35)/n seems to report smaller root mean square errors (RMSE) than other plotting positions in the negative shape parameter estimation under small samples. In comparison to the maximum likelihood (ML) method under the small sample, the PWM do not seem to be better than the ML estimators in the location and scale parameter estimations documenting larger RMSE. However, the PWM outperform the ML estimators in the shape parameter estimation when its magnitude is near zero. Sensitivity of right tail quantile estimation regarding five plotting positions is also examined, but superiority or inferiority of any plotting position is not observed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2170-2190
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• 2012

There are nowadays strong demands for intelligent surveillance systems, which can infer or understand more complex behavior. The application of crowd density estimation methods could lead to a better understanding of crowd behavior, improved design of the built environment, and increased pedestrian safety. In this paper, we propose a new crowd density estimation method, which aims at estimating not only a moving crowd, but also a stationary crowd, using images captured from surveillance cameras situated in various public locations. The crowd density of the moving people is measured, based on the moving area during a specified time period. The moving area is defined as the area where the magnitude of the accumulated optical flow exceeds a predefined threshold. In contrast, the stationary crowd density is estimated from the coarseness of textures, under the assumption that each person can be regarded as a textural unit. A multilayer neural network is designed, to classify crowd density levels into 5 classes. Finally, the proposed method is experimented with PETS 2009 and the platform of Gangnam subway station image sequences.

• 대한전기학회논문지:전력기술부문A
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• 제55권7호
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• pp.265-272
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• 2006

This paper describes a method of parameter estimation of time series data using discrete Fourier transform(DFT). DFT have been mainly used to precisely and rapidly obtain the frequency of a signal. In a dynamic system, a real part of a mode used to learn damping characteristics is a more important factor than the frequency of the mode. The parameter estimation method of this paper can directly estimate modes and parameters, indicating the characteristics of a dynamic system, on the basis of the Fourier transform of the time series data. Real part of a mode estimates by subtracting a frequency of the Fourier spectrum corresponding to 0.707 of a magnitude of the peak spectrum from a peak frequency, or subtracting a frequency of the power spectrum corresponding to 0.5 of the peak power spectrum from a peak frequency, or comparing the Fourier(power) spectrum ratio. Also, the residue and phase of time signal calculate by simple equation with the real part of the mode and the power spectrum that have been calculated. Accordingly, the proposed algorithm is advantageous in that it can estimate parameters of the system through a single DFT without repeatedly calculating a DFT, thus shortening the time required to estimate the parameters.

• 대한교통학회지
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• 제19권6호
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• pp.131-142
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• 2001

Previous OD matrix estimation methods from link traffic counts have focused on the formulation of mathematical model and its solution algorithm. Thereby those methods have assumed that true or real OD is similar to the target OD and paid little attention to the properties of the change of OD structure. Although it is general situation that each OD pair increases or decreases due to significant land use and to large time variation between target OD with real OD, those methods have set unrealistic assumptions that target OD increases or decreases uniformly and that the OD structure does not change. Therefore those methods have showed poor performance of OD estimation in general situation. To cope with the problem. this paper suggests a new concept of OD matrix structure and shows the shortcomings of previous method′s dependancy on target OD matrix. We divide "OD trips" into "OD scale" and "OD structure". Where OD scale is a quantitative magnitude of OD trips and "OD structure" is ordinal OD scale. This paper use the same solution algorithm developed by Baek et al. (2000) for analysing the OD structure. Results of numerical examples show that the performance of the method is better than that of previous methods, while the previous methods have better performance in estimation only when OD trips increase or decrease. In addition to, if OD structure does not change, the results show that the error of estimation is low relatively regardless of the large difference of trips between target OD and real OD. This paper also shows that the model performance on OD structure and on OD trips is low as the number of origins that OD structure is changed increase. From the results we suggest that the change of OD structure can be more important information than the difference between target OD and real OD in OD estimation steps.

• 조명전기설비학회논문지
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• 제26권2호
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• pp.34-43
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• 2012

This paper describes system modeling and controller design method in the measured signal by discrete Fourier transform. Transfer function of the second order system is estimated by the dominant parameter which is computed in the magnitude and the phase of Fourier spectrum of the measured signal. In addition, the controller was designed by the estimated transfer function, and the results were compared. The proposed estimation method of transfer function contains only a very simple mathematical process. Therefore, it is effective to design the controller in the measured signal when the output of the system contains the characteristics of complex exponential functions case. The proposed method was applied on Op-Amp system to verify the efficiency and the reliability. The results show that the proposed algorithms are highly applicable to the system modeling and controller design in the measured data.

• 한국음향학회지
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• 제18권7호
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• pp.112-117
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• 1999

잡음에 강한 음성인식시스템을 위하여 주파수 차감법을 사용할 경우 음성 신호마저 차감하여 신호를 더욱 부식시키는 경우가 존재한다. 본 연구에서는 이러한 경우를 위해서 프레임 마다 추정 잡음과 차감 신호의 SNR(Signal to Noise Ratio) 함수로부터 반연속 HMM(Hidden Markov Model)의 가우시안 함수를 변형 및 결정하는 방법을 제안한다. 이 방법의 타당성을 위해 프레임마다 추정 잡음의 오류 정도가 추정 잡음의 크기와 관계함을 신호 파형 형태로써 보였으며, 이러한 이유에서 SNR을 기준으로 가우시안 함수를 변형 및 결정하게 된다. 실험에서 80㎞/h 이상의 속도로 달리는 차량 내에서 배경 잡음과 음성이 혼합되었을 때의 음성 인식율을 평가하였다. 그 결과 주파수 차감한 경우와 차감하지 않은 경우에 비해 본 논문에서 제안한 SNR에 의한 가우시안 결정 방법이 더욱 향상된 인식율을 보였다.

• 전기학회논문지
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• 제64권12호
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• pp.1756-1760
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• 2015

This paper focuses on a priori signal to noise ratio (SNR) estimation method for the speech enhancement. There are many researches for speech enhancement with several ambient noise cancellation methods. The method based on spectral subtraction (SS) which is widely used in noise reduction has a trade-off between the performance and the distortion of the signals. So the need of adaptive method like an estimated a priori SNR being able to making a high performance and low distortion is increasing. The decision directed (DD) approach is used to determine a priori SNR in noisy speech signals. A priori SNR is estimated by using only the magnitude components and consequently follows a posteriori SNR with one frame delay. We propose a modified a priori SNR estimator and the weighted rational transfer function for speech enhancement with wind noises. The experimental result shows the performance of our proposed estimator is better Perceptual Evaluation of Speech Quality scores (PESQ, ITU-T P.862) compare to the conventional DD approach-based systems and different noise reduction methods.

• Journal of Power Electronics
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• 제18권1호
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• pp.234-250
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• 2018

This paper presents a new load sharing control for use between paralleled three-phase inverters in an islanded microgrid based on the online line impedance estimation by the use of a Kalman filter. In this study, the mismatch of power sharing when the line impedance changes due to temperature, frequency, significant differences in line parameters and the requirements of the Plug-and-Play mode for inverters connected to a microgrid has been solved. In addition, this paper also presents a new droop control method working with the line impedance that is different from the traditional droop algorithm when the line impedance is assumed to be pure resistance or pure inductance. In this paper, the line impedance estimation for parallel inverters uses the minimum square method combined with a Kalman filter. In addition, the secondary control loops are designed to restore the voltage amplitude and frequency of a microgrid by using a combined nominal value SOGI-PLL with a generalized integral block and phase lock loop to monitor the exact voltage magnitude and frequency phase at the PCC. A control model has been simulated in Matlab/Simulink with three voltage source inverters connected in parallel for different ratios of power sharing. The simulation results demonstrate the accuracy of the proposed control method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 B
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• pp.620-622
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• 1998

This paper presents a method for estimating parameters of high frequency transient signals when noise is added. The parameters to be estimated are the magnitude, frequency, and decay rate of the signals. An approach based on only the extended Kalman filter (EKF) is highly dependent on choosing a correct value of variance of noise. The proposed method adopts an adaptive Kalman filter (AKF). Having very little information of the noise, This method avoids deterioration of the filter performance caused by choosing an inaccurate variance of the noise. The dependence of the EKF method upon the noise variance and the efficiency of the AKF method are shown.