• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.4
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• pp.286-292
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• 2004

This paper presents a polyphase filtered orthogonal frequency division multiplexing (PF-OFDM) technique. The proposed structure uses a modified discrete Fourier transform (MDFT) transmultiplexer to achieve greater spectral efficiency than an OFDM system, while preserving backward compatibility with it. The prototype PF-OFDM filter has excellent time and frequency localization properties, which matte it possible to eliminate a guard interval (or cyclic prefix) and easily suppress interchannel interference (ICI). This modulation technique uses a single DFT structure, in contrast to a MDFT transmultiplexer, which requires two DFT polyphase filter banks. The PF-OFDM modulation is .justified over multipath Rayleigh fading channels.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.118-120
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• 2001

This paper presents a distance relaying algorithm based on the Discrete Fourier Transform(DFT) for elimination of DC-Offset. When the DFT is applied to current signal. the real and imaginary parts of fundamental component consist of fundamental component itself and DC-Offset. The DC-Offset is calculated by four consecutive values of the imaginary components, so that the fundamental component can be accurately estimated. Performance evaluation is presented for A-phase ground faults on 154kV 80km overhead transmission line. The proposed algorithm is inspected by software simulation and hardware simulation.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.171-173
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• 1995

Slot field harmonics exist in air gap due to inevitable slot constructure of induction motors. They give rise to noise by the electromagnetic vibration and mechanical pulsation. We calculate the slot field harmonics for varying the ratio of slot width vs teeth pitch using the carter's coefficent. We computate the flux density in air gap by FEM(Finite Element Method) and analyze it in frequency domain using DFT(Discrete Fourier Transform). We develop the new algorithm mixing FEM with DFT.

• Journal of Korea Multimedia Society
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• v.8 no.11
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• pp.1510-1519
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• 2005

We proposed a digital watermarking method that it is possible to identify the copyright because the watermark is detected in the first print-scan and to protect a forgery because the watermark is not detected in the second print-scan. The proposed algorithm uses LPM and DFT transform for the robustness to the distortion of pixel value and geometrical distortion. This methods could improve watermark detection performance and image quality by selecting maximum sampling radius in LPM transform. After analyzing the characteristics of print-scan process, we inserted the watermark in the experimentally selected frequency bands that survives robustly to the first print-scan and is not detected in the second print-scan, using the characteristic of relatively large distortion in high frequency bands of DFT As the experimental result, the original proof is possible because average similarity degree 5.13 is more than the critical value 4.0 in the first print-scan. And the detection of forgery image is also possible because average similarity degree 2.76 is less than the critical value 4.0 in the second print-scan.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.179-187
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• 2010

This paper proposes a new anti-islanding method for single-phase grid-connected photovoltaic (PV) systems using Goertzel algorithm. The proposed scheme is based on inducing increases or decreases of frequencies of load voltage and current that is in the form of existences or periodical variations of the reactive power components. The frequency detection is needed to apply this power variation method to the grid-connected power converter. The proposed method is able to get a fast detection for anti-islanding without the effect of harmonics and noises. The simulation and experiment results validate the effectiveness of the proposed method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.2
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• pp.495-513
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• 2020

The correlation identification of the subsurface is a novel electrical prospecting method which could suppress stochastic noise. This method is increasingly being utilized by geophysicists. It achieves the frequency response of the underground media through division of the cross spectrum of the input & output signal and the auto spectrum of the input signal. This is subject to the spectral leakage when the cross spectrum and the auto spectrum are computed from cross correlation and autocorrelation function by Discrete Fourier Transformation (DFT, "To obtain an accurate frequency response of the earth system, we propose an improved correlation identification method which uses all phase Fast Fourier Transform (APFFT) to acquire the cross spectrum and the auto spectrum. Simulation and engineering application results show that compared to existing correlation identification algorithm the new approach demonstrates more precise frequency response, especially the phase response of the system under identification.

• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.71-77
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• 2009

OFDM(Orthogonal Frequency Division Multiplexing) signals sutler serious nonlinear distortion in the nonlinear HPA(High Power Amplifier) because of high PAPR(Peak Average Power Ratio). Nonlinear distortion can be improved by a pre-distorter, but this pre-distorter is insufficient when the PAPR is very high in an OPFDM system. In this paper, a DFT(Discrete Fourier Transform) transform technique is introduced for PAPR reduction. It is especially important to consider the memory effect of HPA for more precise predistortion. Therefore, in this paper, we consider two models, the TWTA(Traveling-Wave Tube Amplifier) model of Saleh without a memory effect and the HPA memory polynomial model that has a memory effect. We design a pre-distorter and an adaptive pre-distorter that uses the NLMS(Normalized Least Mean Square) algorithm for the compensation of this nonlinear distortion. Without the consideration of a memory effect, the system performance would be degraded, even if the pre-distorter is used for the compensation of the nonlinear distortion. From the simulation results, we can confirm that the proposed system shows an improvement in performance.

• Journal of Broadcast Engineering
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• v.24 no.5
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• pp.879-891
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• 2019

This paper provides performance evaluations of various channel estimation schemes for Advanced Television Systems Committee (ATSC) 3.0 multiple-input multiple-output (MIMO) system under a fixed reception environment. ATSC 3.0 MIMO system can obtain high spectral efficiency and improved reception performance compared to conventional terrestrial broadcasting systems. The ATSC 3.0 MIMO defines Walsh-Hadamard and null pilot encoding algorithms and the amplitude and phase of MIMO pilots are different from those of single-input single-output pilots. At the receiver, linear and discrete Fourier transform (DFT)-based interpolations can be used for the channel estimation. This paper provides the various combinations of the interpolation schemes for channel estimation in time and frequency dimensions, and then analyzes the performance of the various combinations through the computer simulation. The results of computer simulation show that the combination of the linear interpolation in the time dimension and then DFT-based interpolation in the frequency dimension can obtain the best performance among the considered combinations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.4
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• pp.789-796
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• 2013

It is known that the detection of hopping signals without any information about hopping duration and hopping frequency is rather difficult. This paper considers the blind detection of hopping signal's information such as hopping duration and hopping frequency from the sampled wideband signals. In order to find hopping information from the wideband signals, multiple narrow-band filters are required in general, which leads to huge implementation complexity. Instead, this paper employs the polyphase DFT(discrete Fourier transform) filterbank to reduce the implementation complexity. This paper propose hopping signal detection algorithm from the polyphase DFT filterbank output. Specifically, based on the binary image processing, the proposed algorithm is developed to decrease the memory size and H/W complexity. The performance of the proposed algorithm is evaluated through the computer simulation and FPGA (field programmable gate array) implementation.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2020.11a
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• pp.87-90
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• 2020

GPU의 발전과 함께 성장한 딥러닝(Deep Learning)은 영상 분류 문제에서 최고의 성능을 보이고 있다. 그러나 합성곱 신경망 기반의 모델을 깊게 쌓음에 따라 신경망의 표현력이 좋아짐과 동시에 때로는 학습이 잘되지 않고 성능이 저하되는 등의 부작용도 등장했다. 성능 향상을 방해하는 주요 요인 중 하나는, 차원감소 목적에 따라 필연적으로 정보 손실을 겪어야 하는 풀링 계층에 있다. 따라서 특성맵(Feature map)의 차원감소를 통해 얻게 되는 비용적 이득과 모델의 분류 성능 사이의 취사선택(Trade-off)이 존재한다. 그리고 이로부터 자유로워지기 위한 다양한 연구와 기법이 존재하는데 Spectral Pooling도 이 중 하나이다. 본 논문에서는 이산 푸리에 변환(Discrete Fourier Transform, DFT)을 이용한 Spectral Pooling에 대한 소개와, 해당 풀링의 성질을 통상적으로 사용되고 있는 Max Pooling과의 성능 비교를 통해 분석한다. 또한 영상 내 고주파수 부분에서 특히 더 강건하지 못하다는 맥스 풀링의 고질적인 문제점을, Spectral Pooling과의 하이브리드(Hybrid) 구조를 통해 어떻게 극복해나갈 것인지 그 가능성을 중심으로 실험을 수행했다.