• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.3
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• pp.10-19
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• 2009

In this paper, an efficient optical watermark method using multiple phase wrapping and real-valued decoding key is proposed. In the embedding process, two zero-padded original images placed in two quadrants on input plane are multiplied with two statistically independent random phase patterns and are Fourier transformed, respectively. Two encoded images are obtained by taking the real-valued data from these Fourier transformed images. And then two phase-encoded patterns, used as a hidden image and a decoding key, are generated by the use of multiple phase wrapping from each of the encoded images. A transmitted image is made from the linear superposition of the weighted hidden images and a cover image. In reconstruction process, the mirror reconstructed images can be obtained at all quadrants by the inverse-Fourier transform of the product of the transmitted image and the decoding key. Computer simulation and optical experiment are demonstrated in order to confirm the proposed method.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.4
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• pp.53-60
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• 2007

In a known plaintext scenario, fast correlation attack is very powerful attack on stream ciphers. Most of fast correlation attacks consider the cryptographic problem as the suitable decoding problem. In this paper, we introduce advanced multi-pass fast correlation attack which is based on the fast correlation attack, which uses parity check equation and Fast Walsh Transform, proposed by Chose et al. and the Multi-pass fast correlation attack proposed by Zhang et al. We guess some bits of initial states of the target LFSR with the same method as previously proposed methods, but we can get one more bits at each passes and we will recover the initial states more efficiently.

• The Journal of Korean Institute of Information Technology
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• v.17 no.10
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• pp.49-55
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• 2019

In this paper, we propose a simple precoding vector design scheme for multi-user multiple-input single-output (MISO) interference channel when there are multiple eavesdroppers. We aim to obtain a mathematical closed-form solution of the secrecy rate optimization problem. For this goal, we design the precoding vector based on the signal-to-leakage plus noise ratio (SLNR). More specifically, the proposed precoding vector is designed to completely eliminate a wiretap channel capacity for refraining the eavesdroppers from detecting the transmitted information, and to maximize the transmitter-receiver link achievable rate. We performed simulation for the performance investigation. Simulation results show that the proposed scheme has better secrecy rate than the conventional scheme over all signal-to-noise ratio (SNR) range even though the special condition among the numbers of transmit antennas, transmitter-receiver links, and eavesdroppers is not satisfied.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.6
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• pp.655-663
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• 2021

In this paper, DFT-Based channel estimation with channel response mirroring is proposed and analyzed. In General, pilot symbols for channel estimation in MIMO(Multi-Input Multi-Output) OFDM(Orthogonal Frequency-Division Multiplexing) Systems have a diamond shape in the time-frequency plane. An interpolation technique to estimate the channel response of sub-carriers between reference symbols is needed. Various interpolation techniques such as linear interpolation, low-pass filtering interpolation, cubic interpolation and DFT interpolation are employed to estimate the non-pilot sub-carriers. In this paper, we investigate the conventional DFT-based channel estimation for noise reduction and channel response interpolation. The conventional method has performance degradation by distortion called "edge effect" or "border effect". In order to mitigate the distortion, we propose an improved DFT-based channel estimation with channel response mirroring. This technique can efficiently mitigate the distortion caused by the DFT of channel response discontinuity. Simulation results show that the proposed method has better performance than the conventional DFT-based channel estimation in terms of MSE.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.11
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• pp.17-26
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• 2003

To reduce the nonlinear distortion of high power amplifier(HPA) in down link OFCDM system to employ time domain spreading, we apply technology which transmits MPSK(Multilevel-PSK) signal after clipping on multilevel input signal of IFFT subcarrier. In case that the nonlinear distortion of HPA is considered in AWGN channel, performacne of clipping OFCDM system using extended m sequence is over 2.2㏈ better than that of OFCDM system using extended m sequence when the number of user is 8 and 16. In case that the nonlinear distortion of HPA is considered in quasi-static channel, performacne of clipping OFCDM system using extended m code is over 2㏈ better than that of OFCDM system using extended m sequence when the number of user is 8 and 16.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.6A
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• pp.965-979
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• 2001

본 논문에서는 OFDM 시스템의 송신기에서 사용되는 선형 필터와 고출력 증폭기의 결합에 의한 \"기억성을 갖는 비선형 왜곡\"을 실제 하드웨어 구현에 적합하게 적은 계산량으로 보상할 수 있는 참조 테이블(look up table; LUT) 기반의 사전왜곡기를 제안한다. LUT를 이용하는 사전왜곡기들은 이미 많이 연구되었으나, 본 논문에서는 다중 입력/단일 출력 형태의 기억성을 갖는 비선형 왜곡을 작은 크기의 LUT를 이용하여 효율적으로 보상한다는 점에서 큰 차이가 있다. 제안 방법에서는 먼저 기억성이 없는 고출력 증폭기만이 존재할 때의 사전왜곡기를 우리가 이미 제안한 고정점 반복 사전왜곡기 알고리즘에 기반하여 LUT로 구현하고, 여기에 선형 역 시스템을 결합하여 기억성을 갖는 비선형 왜곡을 보상한다. 실제 구현 가능성 검토를 위해 제안된 사전왜곡기와 16-QAM, 256-IFFT/FFT OFDM 시스템 기저대역 모뎀을 TMS320C30 DSP를 이용하여 구현하였으며, 실험 결과 작은 크기의 LUT를 이용하여도 원래의 고정점 반복 사전왜곡기에 비해 매우 적은 계산량을 요구하면서 동일한 성능을 얻을 수 있음을 확인하였다.있음을 확인하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.3
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• pp.241-247
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• 2007

This paper presents a new Leading edge modulation Buck converter operating in discontinuous conduction mode (DCM) for the pulse voltage input. In the slave output of the LLC half-bridge multi-resonant converter, to regulate the direct chopper's output voltage, its PWM switch is controlled by the leading edge modulation. The principles of this proposed LEM control method and the fast dynamics in inductor current based on the converter impulse response are studied. The theoretical results are verified through an experimental prototype of the 100W 60inch PDP Address power module.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.79-87
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• 2013

A new modulation technique - correlative encoded FSK (CEFSK) - for use in power and bandwidth limited digital communication system is proposed. CEFSK is free of ISI and generates output signals which have a smooth and continuous phase transition and a reduced envelope fluctuation by keeping correlation between amplitude and phases of two subsequent symbols. In comparison to conventional one-bit differential detected (1DD) GFSK, the performance of the 1DD-CEFSK in a non-linearly amplified (NLA) channel impaired by additive white Gaussian noise (AWGN), ISI and IM, is analyzed via computer simulation. The simulation result shows that, in an NLA single-channel, 1DD-CEFSK provides a signal-to-noise ratio (SNR) advantage of up to 1.2dB and 0.8dB at BER of $1{\times}10^{-4}$ when input back-off (IBO) of HPA is -1.0dB and -3.0dB, respectively. For the same channel environment with multi-channel, 1DD-CEFSK outperforms 1DD-GFSK by 1.1dB in SNR, regardless of the value of IBO.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.5-9
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• 2011

There are technical difficulties in measuring the numerical apertures of multi-mode gradient-index plastic optical fibers (GI-POFs) due to their strong speckle noise originating from dopants, non-uniformity of gradient-index profile, and multi-mode interference. Therefore, we propose a new method of obtaining the numerical aperture by controlling the size of the incident laser beam and measuring the numerical aperture of GI-POF. The results show that we can get a value for the numerical aperture of GI-POF very similar to that measured by the conventional method. We can also obtain the optimum launching condition of input beam and maximum coupling efficiency.

• Communications of Mathematical Education
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• v.9
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• pp.317-325
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• 1999

수식에 의한 컴퓨터 그래픽의 입력과 출력에 관한 프로그램의 개발은 수학의 역동화, 인간화, 보편화에 기여하고 있다. 현실적으로 해결해야할 문제와 수식에 의한 해답이 전부인 현재의 수학을 소프트웨어를 활용하여 그래픽 기능을 첨부하면 움직이는 수학을 가시화 할 수 있다. 컴퓨터 프로그램에 의한 수학의 실현은 수학자들 모두의 염원으로 전세계적으로 활발한 연구가 진행되고 이는 것이다. 수학의 원리와 응용성을 가미한 수학적 그래픽의 발전은 새로운 천년을 장식할 새로운 학문분야로 등장하고 있다. 기초과학의 여러 자료를 분석, 검토하여 그래픽으로 조립하는 작업은 수학적 그래픽의 힘으로 가능하며, 실험과 실습의 양상을 바꾸어 놓고 있다. 건축이나 토목 또는 전기전자 학과의 응용수학은 새로운 소프트웨어의 출현으로 컴퓨터 강의로 전환되고 있으며 수학 그 자체로 전산기능을 강화하는 방향으로 개편되고 있다. 수학 교과 내용의 전산 프로그램화와 컴퓨터 활용 수학 학습은 거부할 수 없는 시대적 요구이다. 이 연구에서는 새로운 천년의 시작은 컴퓨터 프로그램에 의한 완성된 그래픽의 연출이라는 시각에서 수식에 의한 컴퓨터 그래픽의 기본 방향을 제시하고 있다. 2차원 평면이나 3차원 공간에 이와 같은 다변수함수의 역할을 구현함으로써 다양한 그래픽을 영상화할 수 있다. 다중화면의 연출, 다단계화면의 조합, 다단계다중화면의 영상화 등은 수학에 의한 애니메이션의 기초가 된다. 평면도형의 기본동작을 화면에 구체화시키는 Table 기능을 실제로 구현한다. 연습과 실행 그리고 재구성을 반복하여 조형미를 갖춘 수학적 그래픽을 실현한다. 수학의 학습에 적용할 가치가 있는 학습조형물을 개발하고, 프로그램의 단순화에 노력한다. 미분기하학의 여러 공식을 이용하여 숨어 있는 그림을 표출하며 미분방정식의 해가 갖는 그래픽의 묘미를 형상화한다. 수식에 의하여 출력된 그래픽의 여러 효과를 응용수학에 활용할 수 있도록 재조립하는 과정을 걸쳐 완성하는데 이 연구의 참된 의미가 있다.