• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.1
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• pp.31-38
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• 1991

A direct digital control technique of a current source using the phase-controlled rectifier is presented. A digital firing technique without sensing the line voltage is proposed. This scheme generates firing pulses directly from error signal between command and output voltage. Thus the phase detection transformers filters and zero-crossing detector are unnecessary. The synchronism is modeled and analized. Also a software synchronization algorithm is presented without a look up table and controls the system in real time with fast dynamic characteristics. Using the single-chip microprocessor 8097BH, the direct digital control is implemented with minimal hardware structure. Using the time-weighted performance index, the optimal discrete IPM control technique is also proposed to control the current of the PCR.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.488-493
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• 2008

This paper represents a dual-mode type transmission technique for a high reliable narrow-band power line communication(PLC) modem, and its design and implementation of a system-on-chip(SoC). The proposed transmission technique is based on a Chirp modulation for the purpose of overcoming time variations of power line channel environments in the narrow-bandwidth of the frequency range of 95-145.5 kHz. The designed modem is fabricated utilizing a mixed 0.18 ${\mu}m$ CMOS technology. Especially, according to the power line channel environments the data transmission rate can be selectively changed into 2.5 kbps and 480 bps. The total hardware complexity of the implemented chip is about 50,000 gates, the power consumption is about 26mW, and the operating frequency is up to 5.12 MHz.

• MALSORI
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• no.46
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• pp.37-50
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• 2003

In this paper, we evaluate and compare the performance of speech/music discrimination based on various feature parameters and classifiers. As for feature parameters, we consider High Zero Crossing Rate Ratio (HZCRR), Low Short Time Energy Ratio (LSTER), Spectral Flux (SF), Line Spectral Pair (LSP) distance, entropy and dynamism. We also examine three classifiers: k Nearest Neighbor (k-NN), Gaussian Mixure Model (GMM), and Hidden Markov Model (HMM). According to our experiments, LSP distance and phoneme-recognizer-based feature set (entropy and dunamism) show good performance, while performance differences due to different classifiers are not significant. When all the six feature parameters are employed, average speech/music discrimination accuracy up to 96.6% is achieved.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.284-288
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• 2005

This paper proposes the direct detection method of phase angle for the power source, which is based on the PLL method. The proposed method using a bidirectional photo-coupler is used to directly detect the zero crossing of phase voltage and calculate the angular frequency in the controller based on a M/T algorithm. Through the method, the additional installation space in the traditional method using a potential transformer can be minimized and it can be easy to design. The paper presents straightforward schematic circuits, design and experimental results.

• The Journal of the Acoustical Society of Korea
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• v.6 no.3
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• pp.31-42
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• 1987

An ultrasonic pulse-echo diagnostic system for tissue characterization with the estimation of attenuation coefficients is developed and its performance has been examined by system implementation. The system divided into the ultrasonic generator, A/D converter, data communication, computer for signal processing. The methods for estimating the spatial distribution of acoustic attenuation coefficients using the moment analysis are proposed. The experimental results indicate the potential of the methods for tissue characterization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.2
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• pp.172-179
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• 1991

In this paper we have proposed an efficient coding algorithm using directional filtering. First an image is transformed by using DCT which has better energy compaction and then the transformed image is divided into a low frequency component and several high frequency components. The transformed coefficients of each parts are transmitted respectively by using huffman code and these are transformed inversely at receiver. For the directional components total edge images are reconstructed at zero crossing points. We are able to reduce the amount of data by getting of complex component and making directional angles 90. As a results, this proposed method is better than that of Kunt in respect of processing time and memories. We have 38dB of image quality with objective measurement of PSNR and 0.26bpp of compression ratio which is acceptable.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.351-354
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• 2004

최근 MPEG-7 등에서 컨텐츠 내용 기반 검색에 대한 연구가 이루어지고 있다. 내용 기반 검색은 기존의 키워드기반 검색이 아닌 컨텐츠 내의 특징 벡터를 추출하여 이와 일치하는 것을 찾는 작업으로써 차세대 디지털 방송 등에 적응될 예정이다. 본 논문은 긴 오디오 stream에서 찾고자 하는 오디오의 위치를 빨리 찾을 수 있는 고속 검객 방법을 제시한다. 기존의 방법에서는 zero-crossing rate만을 이용하여 검색을 했었으나 본 논문에서는 오디오 신호의 특성을 표현할 수 있는 여러 가지 특징 벡터들을 이용한 고속 검색 방법을 고찰 한다. 본 논문의 가장 중요만 부분은 active search 알고리즘과 히스토그램, 그리고 적절하게 조합된 다중 특징 벡터들을 이용한 오디오 검색의 정확도와 속도를 향상시키는데 있다.

• Proceedings of the KIEE Conference
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• 2003.11b
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• pp.87-90
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• 2003

There are generally two temperature control methods using ac voltage regulators - the phase control method and the on-off control method. The phase control method uses thyristor's angles of extinction for the output power regulation and the on-off control method uses the control of on and off times for the output power regulation. Both of methods have the problems that are the unbalance of the three phase and surge current caused system's destruction. The main object of this study proposes a solution of problems of surge currents and unbalance of three phase when thyristor voltage regulator is switching. To solve the problem, It is proposes that the solution of surge currents is using a tap transformer and an additional switch with adjustable resistance and applies zero crossing of switching voltage of two input line to power load. This method is discuss and verified by computer simulations and experiments.

• The Transactions of the Korea Information Processing Society
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• v.7 no.7
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• pp.2238-2245
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• 2000

In this papr, eatue parameters, extracted using Wavelet transform for Korean isolated worked speech, are sued for speech detection and recognition feature. As a result of the speech detection, it is shown that it produces more exact detection result than eh method of using energy and zero-crossing rate on speech boundary. Also, as a result of the method with which the feature parameter of MFCC, which is applied to he recognition, it is shown that the result is equal to the result of the feature parameter of MFCC using FFT in speech recognition. So, it has been verified the usefulness of feature parameters using Wavelet transform for speech analysis and recognition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.967-974
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• 2017

Reaction wheel shows nonlinear torque response on low-speed region due to friction. Thus precise satellite attitude control on this region is hard to achieve. Previous research tries to solve this problem, by compensating friction or applying dither command. However, due to difficulties of drag torque modeling or frequent zero wheel speed crossing, these methods are not suitable to apply on the real satellite attitude control. To solve this problem, we propose the attitude controller gain adjustment method based on the attitude error.