• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.12
• /
• pp.1715-1720
• /
• 2016

In the upcoming 5-generation mobile communication system, various techniques for improving the power efficiency and spectral efficiency have been proposed. 5G mobile communication system also have been studied a lot of multi-carrier-based modulation techniques like the 4G mobile communication system. In this paper, we analyzed the conventional system structure of the Zero-tail DFT-s-OFDM and UW (Unique Word) -DFT-s-OFDM system based on DFT-s-OFDM system in these techniques. UW and zero are added and used each system, and CP is removed. the result of quality of systems for simulation, OOB(Out of Band) power of Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM use the less time resource as long as CP length, also both systems are reduced about 11dB than DFT-s-OFDM system. In these result, Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM system are more effective than DFT-s-OFDM system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.12
• /
• pp.1091-1099
• /
• 2015

UFMC(Universal-Filtered Multi-carrier) and FBMC(Filter Bank Multi-carrier) system are receiving attention as candidate waveforms for 5G mobile communication system. But, these systems have high PAPR(Peak to Average Power Ratio) problem because these systems use a number of subcarrier. In this paper, we propose DFT(Discrete Fourier Transform) spreading based DFT-s(spreading)-UFMC system and DFT-s-FBMC system in order to overcome the PAPR drawback. In order to evaluate PAPR performance of the proposed systems, we design and simulate OFDM(Orthogonal Frequency Division Multiplexing), UFMC, FBMC, DFT-s-OFDM, DFT-s-UFMC, DFT-s-FBMC system. As simulation results, each PAPR performance of DFT-s-OFDM system, DFT-s-UFMC system, and DFT-s-FBMC system rise by 2.7 dB, 2.8 dB, and 1.1 dB respectively by DFT spreading technique.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.4
• /
• pp.415-423
• /
• 2016

High PAPR (Peak-to-Average Power Ratio) characteristic causes some problems like system performance degradation and OOB (Out-of-Band) power increasement under the HPA (High Power Amplifier) nonlinearity condition. UFMC (Universal Filtered Multi-Carrier) and FBMC (Filter Bank Multi-Carrier) are regarded as 5G(Generation) candidate waveforms. In this paper, we evaluate and analyze performance of these systems with DFT-s (Discrete Fourier Transform Spreading) technique under the nonlinear HPA environment. In this paper, we describe OFDM (Orthogonal Frequency Division Multiplexing), UFMC, FBMC, DFT-s-OFDM, DFT-s-UFMC, and DFT-s-FBMC system, and evaluate BER (Bit Error Rate) performance of these systems. As simulation results, BER performance degradation by HPA nonlinearity of DFT-s-OFDM and DFT-s-UFMC is greatly overcome by DFT spreading technique. However, BER performance degradation by HPA nonlinearity of DFT-s-FBMC system is little overcome.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.7
• /
• pp.610-615
• /
• 2014

Filterbanks have been widely used in the field of multi-channel signal processing for their simple efficient implementation architectures. Especially, the polyphase DFT(Discrete Fourier Transform) filterbank is the most preferred filterbank for the uniform spaced multi-channel processing due to its simplicity. In frequency hopped communication systems, however, the use of the polyphase DFT filterbank is limited due to its undesirable transient response from hop-to-hop transitions. In this paper, the transient response of polyphase DFT filterbanks in the hop-to-hop transition was analyzed, and the efficient methods to overcome such a problem was proposed. Simulation results showed that the proposed schemes could resolve this issue efficiently.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.35 no.6
• /
• pp.556-561
• /
• 2022

Computational material science as an application of Density Functional Theory (DFT) to the discipline of material science has emerged and applied to the research and development of energy materials and electronic materials such as semiconductor. However, there are a few difficulties, such as generating input files for various types of materials in both the same calculating condition and appropriate parameters, which is essential in comparing results of DFT calculation in the right way. In this tutorial status report, we will introduce how to create crystal structures and to prepare input files automatically for the Vienna Ab initio Simulation Package (VASP) and Gaussian, the most popular DFT calculation programs. We anticipate this tutorial makes DFT calculation easier for the ones who are not experts on DFT programs.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.1A
• /
• pp.51-57
• /
• 2002

In this paper, a simple interpolation technique in a frequency domain is proposed for the discrete Fourier transform(DFT) algorithm. Frequency and phase resolution capabilities of the DFT algorithm can be significantly improved by the proposed interpolation technique without increase of a DFT size(the number of points for the DFT). The new technique uses a diving point in amplitude and phase spectrums. As an application, the technique can be used for joint estimation of fine frequency and phase offsets in burst mode digital transmission. Simulation results show that the joint estimator using the technique is robust to estimation errors.

• Proceedings of the IEEK Conference
• /
• 2003.07e
• /
• pp.2192-2195
• /
• 2003

This parer proposes a power-line phase measurement algorithm which is based on the recursive implementation of sliding-DFT. Usage of the single DFT coefficient in the conventional sliding-DFT based power-line phase measurement brings a significant error propagation when implemented in hardware with finite word-length arithmetic operations. The proposed algorithm utilizes all the N-point DFT coefficients in the recursion. Performance degradation caused by the finite word- length implementation of the algorithm is analyzed and verified with computer simulations. The robustness of the proposed phase measurement algorithm against the erroneous implementation is also confirmed by the performance analysis and simulation.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.50 no.12
• /
• pp.584-589
• /
• 2001

This paper presents an implementation method of multi-channel synchronized phasor measurement device, which is based on the ASIC implementation of the sliding-DFT. A time-shared multiplier structure is proposed to minimize the number of gates required for the implementation. The design is verified by the timing simulation of its operation. The effect of coefficient approximation in the recursive implementation of the sliding-DFT is analytically derived and verified with the computer simulations.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.57 no.2
• /
• pp.102-108
• /
• 2008

AC generator plays an important role of power system. The large AC generator fault may lead to large impacts or perturbations in power system. And then the protection of a generator has very important role in maintaining stability in a power system. In present, the DFT(discrete Fourier transform) based RDR(ratio differential relay) had been widely applied to a internal fault of a generator stator winding. But DFT has a serious drawback. In the course of transforming a target signal to frequency domain, time information is lost. DWT uses a time-scale region. This paper proposes an advanced fault detection algorithm using DWT(discrete Wavelet transform) to enhance the drawback of conventional DFT based relaying. To evaluate the performance of the proposed relaying, we used the test data which were sampled with 720 [Hz] per cycle and obtained from ATP(alternative transient program) simulation. And we made a comparative study of conventional DFT based RDR and the proposed relaying.

• Proceedings of the KIEE Conference
• /
• 2007.11c
• /
• pp.55-58
• /
• 2007

본 논문은 교류발전기의 보호방식에 대하여 검토하였고 종래의 교류발전기의 주보호방식인, 비율차동계전방식에 대하여 서술하였다. 87G에서의 고장전후의 전류를 수집하기 위해서 ATP를 이용하여 간소한 발전기 사고 시뮬레이션 방식을 제안하였다. 또 그 사고모의 데이터를 이용하여 고정자권선 보호를 위한 DFT 기반 디지털 비율차동계전기법에 대하여 타당성을 검증하였다.