• 전기학회논문지
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• 제62권5호
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• pp.667-672
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• 2013

In this paper, we propose a multi-impedance changes localization method of on-voltage underground power cable using the wavelet transform based time-frequency domain reflectometry (WTFDR). To localize the impedance change in on-voltage power cable, the TFDR is the most suitable among reflectometries because the inductive coupler is used to inject the reference signal to the live cable. At this time, the actual on-voltage power cable has multi-impedance changes such as the automatic section switches and the auto load transfer switches. However, when the multi-impedance changes are generated in the close range, the conventional TFDR has the cross term interference problem because of the nonlinear characteristics of the Wigner-Ville distribution. To solve the problem, the wavelet transform (WT) is used because it has the linearity. That is, using WTFDR, the cross term interference is not generated in multi-impedance changes due to the linearity of the WT. To confirm the effectiveness and accuracy of the proposed method, the actual experiments are carried out for the on-voltage underground power cable.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.451-454
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• 2005

현재, 신호를 해석하기 위한 많은 방법들이 제시되고 있으며, 대표적인 방법으로는 퓨리에 변환과 웨이브렛 변환이 있다. 이러한 방법들에서, 퓨리에 변환은 모든 주파수 범위에 대해 cosine과 sine 파형의 조합으로써 신호를 표현하지만, 신호 내에서 특정 주파수 성분이 발생한 시간정보를 제공하지 않으며, 분석 신호의 전체적인 특징만을 나타낸다. 따라서 이러한 한계를 극복하기 위해, 다중해상도 해석이 가능한 웨이브렛 변환이 음성과 영상처리, 컴퓨터 비전 등의 광범위한 분야에서 응용되고 있다. 그리고 웨이브렛 변환은 스케일 변수에 따라 변화하는 윈도우를 사용하여 시간-주파수 국부성을 나타낸다. 본 논문에서는 cosine과 sine 형태의 웨이브렛을 사용하여, 퓨리에 변환의 새로운 접근법을 제시하였으며, 주파수-시간 평면의 유한한 지점에서 신호의 특징을 분석하였다.

• 제어로봇시스템학회논문지
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• 제12궈1호
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• pp.41-46
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• 2006

Ubiquitous location based services, offer helpful services anytime and anywhere by using real-time location information of objects based on ubiquitous network. Particularly, autonomous mobile robots can be a solution for various applications related to ubiquitous location based services, e.g. in hospitals, for cleaning, at airports or railway stations. However, a meaningful and still unsolved problem for most applications is to develop a robust and cheap positioning system. A typical example of position measurements is dead reckoning that is well known for providing a good short-term accuracy, being inexpensive and allowing very high sampling rates. However, the measurement always has some accumulated errors because the fundamental idea of dead reckoning is the integration of incremental motion information over time. The other hand, a localization system using RFID offers absolute position of robots regardless of elapsed time. We construct an absolute positioning system based on RFID and investigate how localization technique can be enhanced by RFID through experiment to measure the location of a mobile robot. Tags are placed on the floor at 5cm intervals in the shape of square in an arbitrary space and the accuracy of position measurement is investigated . To reduce the error and the variation of error, a weighting function based on Gaussian function is used. Different weighting values are applied to position data of tags since weighting values follow Gaussian function.

• 한국정보통신학회논문지
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• 제6권4호
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• pp.513-518
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• 2002

본 논문에서는 웨이브렛을 이용한 임펄스 노이즈 제거 방범을 제시하며, 노이즈 제거에서 웨이브렛의 시간과 주파수 국부성은 신호의 상세 정보를 포함하고 있으므로, 기존의 방법들에 비해 우수한 결과를 제공한다. 임계치에 의한 노이즈 제거와 웨이브렛에 의한 신호의 slope를 이용하여, 노이즈 제거 효과를 최대로 함과 동시에 원신호의 edge를 인식하도록 하였다. 객관적인 판단을 위해, 테스트 신호고서 HeaviSine과 DTMF를 사용하였으며, 서로 다른 크기를 갖는 임펄스 노이즈를 동일한 시간에 원신호에 중첩하여 시뮬레이션 하였다.

• Journal of information and communication convergence engineering
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• 제5권1호
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• pp.1-6
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• 2007

In the process of the acquisition, storage, transmission of signals, noises are generated by various causes and the degradation phenomenon by noises tends to generate serious errors for the signal with information. So, in order to analyze and remove these noises, studies on numerous mathematical methods such as the Fourier transform have been implemented. And recently there have been many ongoing wavelet-based denoising algorithms representing excellent characteristics in time-frequency localization and multiresolution analysis, but the method to remove additive white Gaussian noise (AWGN) and the impulse noise simultaneously was not given. So, to reconstruct the corrupted signal by noises, in this paper a novel wavelet-based denoising algorithm was proposed and using signal-to-noise ratio (SNR) this method was compared to conventional methods.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1093-1101
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• 2015

Partial Discharge (PD) is a physical phenomenon, which causes defects and damages to the insulation. This phenomenon is regarded as the most important source of fault and defect in power transformers. Therefore, methods of high speed and precision are considered of special importance for the maintenance of transformers in localization of the origin of partial discharge. In this paper, the transformer winding is first modeled in a transient state by using RLC ladder network and multiconductor transmission line (MTL) models. The parameters of the two models were calculated by Ansoft Maxwell software, and the simulations were performed by Matlab software. Then, the PD pulses were applied to the models with different widths of pulses. With regard to the fact that the signals received after the application of PD had a variable frequency nature over time, and based on the wavelet transform and signal energy, a new method was presented for the localization of PD. Ultimately; the mentioned method was implemented on a 20 kV winding distribution transformer. Then, the performances of the models used in this paper, including RLC and MTL models, were compared in different frequency bands for the correct distinction of partial discharge location.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.264-267
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• 2000

This paper describes a real-time 3D sound localization algorithm to be implemented with the use of a Bow power embedded DSP. This algorithm first divides the audible frequency band into three, on the basis of the analysis of the sound reflection and diffraction effects through different media from a certain sound source to human ears, and then in each subband a specific procedure is devised fur the 3D sound localization so as to operate real-time on a low power embedded DSP This algorithm aims at providing a listener with the 3D sound effects through a headphone at low cost and low power consumption.

• ETRI Journal
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• 제38권4호
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• pp.634-644
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• 2016

Channel-based radio-frequency fingerprinting such as a channel impulse response (CIR), channel transfer function (CTF), and frequency coherence function (FCF) have been recently proposed to improve the accuracy at the physical layer; however, their empirical performance, advantages, and limitations have not been well reported. This paper provides a comprehensive empirical performance evaluation of RF location fingerprinting, focusing on a comparison of received-signal strength, CIR-, CTF-, and FCF-based fingerprinting using the weighted k-nearest neighbor pattern recognition technique. Frequency domain channel measurements in the IEEE 802.11 band taken on a university campus were used to evaluate the accuracy of the fingerprinting types and their robustness to human-induced motion perturbations of the channel. The localization performance was analyzed, and the results are described using the spatial and temporal radio propagation characteristics. In particular, we introduce the coherence region to explain the spatial properties and investigate the impact of the Doppler spread in time-varying channels on the time coherence of RF fingerprint structures.

• 제어로봇시스템학회논문지
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• 제15권6호
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• pp.641-648
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• 2009

Currently several kinds of sensor localization methods have been developed for terrestrial wireless sensor networks. This study, in order to extend the field to underwater environments, a localization technique is studied for UWSNs (Underwater Wireless Sensor Networks). In underwater environments, RF (Radio Frequency) signal is not suitable for underwater usage because of extremely limited propagation. Because of that reason UWSNs should be constituted with acoustic modems. But, to realize underwater application, we can borrow many design principles from ongoing research for terrestrial environments. So, in this paper we introduce the modified localization algorithm using ToA method which is based on the terrestrial research. First of all, we study the localization techniques for terrestrial environments where we investigate possible methods to underwater environment. And then the appropriate algorithm is presented in the underwater usage. Finally the proposed underwater based localization algorithm is evaluated by using computer.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.200-204
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• 2005

The use of beamforming method and de-Dopplerization technique was applied in studying the rotating sound sources. Acoustic analysis of a moving sound source required that the measured sound signals be do-Dopplerized and restored as of the original emission signals. Two main issues of the signal reconstruction in time domain are addressed herein: First, to remove Doppler effect from the measured data and to restore the original emission data of the moving source. The difference of the time domain beamforming from the frequency domain beamforming was mentioned. Also, the time domain beamforming method is deployed in the test and the comparisons were made to the frequency domain results. The time domain signal reconstruction was numerically simulated prior to the application. To validate the de-Dopplerization Performance, the rotating Point sources were examined and localized by the use of a phased array of microphone. The application of prop-rotor was conducted in a hovering condition. The results of reconstructing time signals of rotating sources and its locations were shown in the power distribution maps. In the prop-rotor measurements, the acoustic source locations were successfully verified in varying positions for different frequencies of interest.