• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.9
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• pp.2218-2230
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• 2012

In this paper, we propose an efficient channel delay estimation method for orthogonal frequency-division multiplexing (OFDM) systems, especially over doubly-selective fading channels which are selective in both the symbol time domain and subcarrier frequency domain. For the doubly-selective fading channels in single frequency network (SFN), long and strong echoes exist and thus the conventional discrete Fourier Transform (DFT) based channel delay estimation system often fails to produce the exact channel delay profile. Based on the analysis of the discrete-time frequency response of the channel impulse response (CIR) coefficients in the DFT-based channel delay estimation system, we develop a method to effectively extract the true CIR from the aliased signals by employing a simple narrow-band low-pass filter (NB-LPF). The performance of the proposed system is verified using the COST207 TU6 SFN channel model.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.211-214
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• 2000

In this paper, a discrete-time S-dimensional chaos circuit (S = 1,2,3,4,...) with array structure is proposed. By employing array structure which consists of 1-dimensional chaos circuits, the proposed circuit can achieve long working-life. This feature is favorable to exploit as a building block of chaos application systems to get into home electric appliances. Further more, the proposed circuit synthesized using switched-current (SI) techniques is suitable for integration. Concerning the proposed circuit, SPICE simulations are performed. SPICE simulations showed that the proposed circuit can generate the chaotic signals in spite of the fault of the building blocks of the proposed circuit. The proposed circuit is integrable by a standard BiCMOS technology.

• Journal of Industrial Technology
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• v.16
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• pp.191-195
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• 1996

This paper deals with the tapped time delay circuit with SCF(Switched Capacitor Filters). This filter is composed of lossless discrete integrator and the SCF has 2-phase clocks. Experimental results have shown that telephone signals (0~4kHz) could be delayed in the range of sampling frequency 80kHz. But above the range, operational amplifiers and analog switchs have been difficult in the normal operating condition.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.5
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• pp.1610-1629
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• 2021

Failures frequently occurred in manufacturing machines due to complex and changeable manufacturing environments, increasing the downtime and maintenance costs. This manuscript develops a novel deep learning-based method named Multi-Domain Convolutional Neural Network (MDCNN) to deal with this challenging task with vibration signals. The proposed MDCNN consists of time-domain, frequency-domain, and statistical-domain feature channels. The Time-domain channel is to model the hidden patterns of signals in the time domain. The frequency-domain channel uses Discrete Wavelet Transformation (DWT) to obtain the rich feature representations of signals in the frequency domain. The statistic-domain channel contains six statistical variables, which is to reflect the signals' macro statistical-domain features, respectively. Firstly, in the proposed MDCNN, time-domain and frequency-domain channels are processed by CNN individually with various filters. Secondly, the CNN extracted features from time, and frequency domains are merged as time-frequency features. Lastly, time-frequency domain features are fused with six statistical variables as the comprehensive features for identifying the fault. Thereby, the proposed method could make full use of those three domain-features for fault diagnosis while keeping high distinguishability due to CNN's utilization. The authors designed massive experiments with 10-folder cross-validation technology to validate the proposed method's effectiveness on the CWRU bearing data set. The experimental results are calculated by ten-time averaged accuracy. They have confirmed that the proposed MDCNN could intelligently, accurately, and timely detect the fault under the complex manufacturing environments, whose accuracy is nearly 100%.

• Journal of the Korean Institute of Navigation
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• v.18 no.4
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• pp.137-146
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• 1994

In this paper, a new algorithm to measure the ultrasonic travel time is proposed, which is fundamental to estimate distance depth and volume in several media. Pulse wave has been used to measure travel time of transmitted signal. However, due to the characteristic of transducer and propagation, the received signal is so distorted that it is difficult to measure travel time, which is propagation, the received signal is so distorted that it is difficult to measure travel time, which is to be time difference between transmitted and received signals. In this proposed method, transmitted and received signal are transformed respectively into norm phase newly designed by this paper and displayed on phase-time curve. And travel time is simply determined by the arithmetic numerical mean of time difference at the identical norm phase on the phase-time curves of transmitted and received signals. This method has several features; firstly, travel time is calculated analytically with high accuracy by least square error method, secondly, it is useful to compare the difference of signal magnitude for time information, thirdly, noise and discrete errors are relatively small, finally, the measurement accuracy is not influenced by D.C. bias. In particular, this method is useful and applicable to measuring very short distance and sound speed with high accuracy.

• Journal of Broadcast Engineering
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• v.28 no.1
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• pp.100-108
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• 2023

In hybrid block-based video coding, transform coding converts spatial domain residual signals into frequency domain data and concentrates energy in a low frequency band to achieve a high compression efficiency in entropy coding. The state-of-the-art video coding standard, VVC(Versatile Video Coding), uses DCT-2(Discrete Cosine Transform type 2), DST-7(Discrete Sine Transform type 7), and DCT-8(Discrete Cosine Transform type 8) for primary transform. In this paper, considering that DCT-2, DST-7, and DCT-8 are all linear transformations, we propose an inverse transform that reduces the number of multiplications in the inverse transform by using the linearity of the linear transform. The proposed inverse transform method reduced encoding time and decoding time by an average 26%, 15% in AI and 4%, 10% in RA without the increase of bitrate compared to VTM-8.2.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.33-39
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• 2003

Wavelet transform analysis results show a spectrum energy distribution of CWT along scale factors distinguish the partial, full and over penetration in a electron beam welding by analyzing the curve of spectrum energy at small scale, middle and large scale range, respectively. Two types of signals collected by Ion collector and x-ray sensors and analyzed. The acquired signals from sensors are very complicated since these signals are very closely related the dynamics of keyhole which interact the very high density energy with materials during welding. The results show the wavelet transform is more effective to diagnosis than Fourier Transform, further for the general welding defects which are not a periodic based, but a transient, non-stationary and time-varying phenomena.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.76-81
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• 2011

Power system frequency is the main index of power quality indicating an abnormal state and disturbances of systems. The nominal frequency is deviated by sudden change in generation and load or faults. Power system is used as frequency relay to detection for off-nominal frequency operation and connecting a generator to an electrical system, and V/F relay to detection for an over-excitation condition. Under these circumstances, power system should maintain the nominal frequency. And frequency and frequency deviation should accurately measure and quickly estimate by frequency measurement device. The well-known classical method, frequency estimation technique based on the DFT, could be produce the gain error in accuracy. To meet the requirements for high accuracy, recently Wavelet transforms and analysis are receiving new attention. The Wavelet analysis is possible to calculate the time-frequency analysis which is easy to obtain frequency information of signals. However, it is difficult to apply in real-time implementation because of heavy computation burdens. Nowadays, the computational methods using the Wavelet function and transformation techniques have been searched on these fields. In this paper, we apply the Recursive Discrete Wavelet Transform (RDWT) for the frequency estimation. In order to evaluate performance of the proposed technique, the user-defined arbitrary waveforms are used.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.288-290
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• 2006

This paper presents the real-time water tank wireless control in a ship using duplex RF modules and PLC(Programmable logic Controller). The purpose of this paper is developing HMI(Human Machine Interface) for automation equipments. The system can low a cost because long wires are no more used. Analog signals of the water gauge and flow meter are changed to discrete signals by the micro-processor. The PLC checks the volume of water and runs On or Off of the valve and pump. Duplex RF modules send and receive data between the water tank and control room. Everywhere the Internet is used, operators are able to check the status of the system by the web-server.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.71-77
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• 2002

The spectrum of impulse response signal which is obtained from an impulse hammer testing is used for frequency response function, nevertheless it has serious faults when the record length for the signal processing is not very long. The faults cannot be avoided with the conventional signal analyzer that is processing all the signals as if they are always periodic. The signals generated by the impact hammer are undoubtedly non-periodic because of the damping, and are acquired for limited recording time due to the memory as well as the computation performance of the signal analyzer. This paper will make clear the relation between the faults and the length of recording time, and propose the way for solving the faults.