• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.7
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• pp.891-897
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• 2013

The power system frequency plays an important role in monitoring and controlling the power system. The frequency can be measured through discrete Fourier transform (DFT) coefficients of its positive fundamental frequency. The accuracy of the frequency estimate is severely affected by noise in the power system signal and the leakage effect of the negative fundamental frequency in DFT. This paper proposes a DFT-based frequency estimation algorithm to cope with the noise as well as the leakage effect. In this algorithm, two suitable digital filters are introduced to reduce efficiently frequency estimate error due to the noise. These filters are designed to use a digital bandpass filter and a second-degree integrator. The effectiveness of the proposed algorithm in reduction of frequency estimate error is verified through simulations on noise, harmonics and frequency deviation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.789-796
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• 2008

This paper describes a single-phase active power filter based on a newly developed digital controller. The developed controller utilizes FFT(Fast Fourier Transform) algorithm to extract the reference signal from the load current, considering the phase-angle delay of each order of harmonics. Optimized technique was applied for whole control algorithm to implement the real-time operation of developed controller. The performance of developed controller for a single-phase active power filter was verified through computer simulations with PSCAD/EMTDC. The feasibility of hardware implementation was confirmed by building and testing a prototype. The developed digital controller for a single-phase active power filter can compensate the harmonic current generated by the power supply for digital equipment.

• Journal of Korea Society of Digital Industry and Information Management
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• v.5 no.4
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• pp.127-137
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• 2009

This paper is proposed that in-output Digital module is acquired a vibration signal of a rotating machinery by Data Acquisition System. The module is designed to get ride of nose through low pass filter on the vibration signal from sensors and set the gain value for being able to sampling AC to DC, and also the sampled data by sampler and the conversed data by DIP/FPGA is supplied to the analyzer for analysis at a software tool. The DIP(Digital Signal Processor) of the Digital input/output Board makes Average voltage, Peak to Peak voltage, RMS(Root Mean Square) and Gap voltage, also FFT(Fast Fourier Transform) for rotating vibration diagnosis.

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.263-269
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• 2012

In this paper, we propose a new dual optical encryption method for binary data and secret key based on 2-step phase-shifting digital holography for a cryptographic system. Schematically, the proposed optical setup contains two Mach-Zehnder type interferometers. The inner interferometer is used for encrypting the secret key with the common key, while the outer interferometer is used for encrypting the binary data with the same secret key. 2-step phase-shifting digital holograms, which result in the encrypted data, are acquired by moving the PZT mirror with phase step of 0 or ${\pi}/2$ in the reference beam path of the Mach-Zehnder type interferometer. The digital hologram with the encrypted information is a Fourier transform hologram and is recorded on CCD with 256 gray level quantized intensities. Computer experiments show the results to be encryption and decryption carried out with the proposed method. The decryption of binary secret key image and data image is performed successfully.

• Journal of the Optical Society of Korea
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• v.19 no.4
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• pp.334-339
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• 2015

Terabit-per-second (Tb/s) transmission capacity for the next generation of long-haul communication networks can be achieved using multicarrier optical super-channel technology. In an elastic orthogonal frequency division multiplexing (OFDM) super-channel transmission system, demultiplexing a portion of an entire spectrum in the form of a subband with minimum power is critically required. A major obstacle to achieving this goal is the analog-to-digital converter (ADC), which is power-hungry and extremely expensive. Without a proper ADC that can work with low power, it is unrealistic to design a 100G coherent receiver suitable for a commercially deployable optical network. Discrete Fourier transform (DFT) is often seen as a primary technique for understanding partial demultiplexing, which can be attained either optically or electronically. If fairly comparable performance can be achieved with an all-optical DFT circuit, then a solution independent of data rate and modulation format can be obtained. In this paper, we investigate two distinct OFDM super-channel receiver models, based on electronic and all-optical DFT-technologies, for partial carrier demultiplexing in a multi-Tb/s transmission system. The performance comparison of the receivers is discussed in terms of bit-error-rate (BER) performance.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.8
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• pp.1360-1365
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• 2010

In this paper, we propose a distance relaying algorithm using a Discrete Fourier Transform (DFT)-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Most distance relays are based on estimating phasors of the voltage and current signals. A DFT is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. For this reason, distance relays have a tendency to over-reach or under-reach in the presence of DC offset components in a fault current. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. The error due to DC offsets in a DFT is calculated and eliminated using the outputs of an even-sample-set DFT and an odd-sample-set DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated for a-phase to ground faults on a 345 kV, 50 km, simple overhead transmission line. The Electromagnetic Transient Program (EMTP) is used to generate fault signals. The evaluation results indicate that adopting the proposed algorithm in distance relays can effectively suppress the adverse influence of DC offsets.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.203_204
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• 2009

In this paper, we propose a Fourier transform-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Discrete Fourier Transform (DFT) is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. In this paper, the error due to DC offsets in a DFT is calculated and eliminated using the outputs of quaternity DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated by using computer-simulated signals and EMTP-generated signals. A performance evaluation showed that the proposed algorithm was not affected by system and fault conditions. Thus, the proposed algorithm can effectively suppress the adverse influence of DC offsets in a relaying signal.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.570-595
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• 2017

Robust and perceptually-adaptive image watermarking algorithms have mainly targeted gray-scale images either at the modeling or embedding levels despite the widespread availability of color images. Only few of the existing algorithms are specifically designed for color images where color correlation and perception are constructively exploited. In this paper, a new perceptual and high-capacity color image watermarking solution is proposed based on the extension of Tsui et al. algorithm. The $CIEL^*a^*b^*$ space and the spatio-chromatic Fourier transform (SCFT) are combined along with a perceptual model to hide watermarks in color images where the embedding process reconciles between the conflicting requirements of digital watermarking. The perceptual model, based on an emerging color image model, exploits the non-uniform just-noticeable color difference (NUJNCD) thresholds of the $CIEL^*a^*b^*$ space. Also, spread-spectrum techniques and semi-random low-density parity check codes (SR-LDPC) are used to boost the watermark robustness and capacity. Unlike, existing color-based models, the data hiding capacity of our scheme relies on a game-theoretic model where upper bounds for watermark embedding are derived. Finally, the proposed watermarking solution outperforms existing color-based watermarking schemes in terms of robustness to standard image/color attacks, hiding capacity and imperceptibility.

• Bulletin of the Korean Chemical Society
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• v.10 no.2
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• pp.123-128
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• 1989

Calorimetric study in conjunction with Fourier-transform infrared (FTIR) spectroscopic study was carried out on the blends of poly(ethylene oxide) (PEO) with isotactic, atactic and syndiotactic poly(methyl methacrylate) (i-, a-, and s-PMMA). From the differential scanning calorimetric (DSC) measurements, the three types of blends show a depression of the melting temperatures. This indicates that PEO is compatible with i-, a-, and s-PMMA. But the largest melting point depressions of PEO are always found in the blends with s-PMMA. For PEO/a-PMMA and PEO/s-PMMA, the degree of crystallinity as a function of composition deviates substantially from that of the ideal blend in which no interaction between the components exists. The FTIR spectra of all three types of blends are recorded. In order to observe the microstructural changes of PEO in blends, we analyzed the spectra using digital weighted subtraction and addition techniques. It was concluded that the microstructures of PEO are strongly perturbed by the PMMA's. Among these blends PEO microstructure in PEO/s-PMMA blends is most greatly influenced. It indicates that the blending is most preferred with s-PMMA than a- and i-PMMA. It can be explained on the basis of the molecular structure of PMMA's.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.439-441
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• 2019

Deep learning has become a powerful and robust algorithm in Artificial Intelligence. One of the most impressive forms of Deep learning tools is that of the Convolutional Neural Networks (CNN). CNN is a state-of-the-art solution for object recognition. For instance when we utilize CNN with MNIST handwritten digital dataset, mostly the result is well. Because, in MNIST dataset, all digits are centralized. Unfortunately, the real world is different from our imagination. If digits are shifted from the center, it becomes a big issue for CNN to recognize and provide result like before. To solve that issue, we have created frequency images from spatial images by a Fast Fourier Transform (FFT).