• Journal of Satellite, Information and Communications
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• v.9 no.3
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• pp.27-32
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• 2014

A doppler shift is generated by moving a transmitter or receiver operated in communication systems. The doppler frequency shift between a transmitter and a receiver or the frequency offset present in transceivers must be removed to get the wanted system performance. FTS is used for preventing an accident from operating abnormally and for guaranteeing public protection. A launching vehicle's initial velocity is very fast in order to escape the earth and the amount of doppler shift is large. Recently many studies to adopt the next generation FTS are ongoing. To introduce new FTS, the effects of doppler shift on the performance of the new FTS must be studied. In this paper the doppler effect caused by launching vehicle's velocity affecting the performance of FTS receiver is investigated into two cases, one is for EFTS as a digital FTS and the other is for FTS using a tone signal. Noncoherent DPSK and noncoherent CPFSK are considered as the modulation methods of EFTS. In the cases of the doppler frequency shift of 200Hz present in EFTS using noncoherent DPSK and noncoherent CPFSK are simulated. Simulation results show that $E_b/N_o$ of 0.5dB deteriorates in the region of near BER of about $10^{-5}$ in RS coding. And there is no performance variation in $E_b/N_o$ or $E_b/N_o$ is worsened about 0.1dB in the same BER region for the case of using convolutional and BCH coding. Quadrature detector used in FTS using tone signals is not influenced by the doppler frequency shift.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.3
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• pp.277-282
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• 2016

Effect of spectral drift in coherent fiber laser was investigated by injecting optical feedback to Fabry-Perot resonance loop. Er+3 doped fiber laser having unilateral optical feedback loop in Fabry-Perot configuration using two FBGs was fabricated. The optical feedback was found to be effective in linewidth reduction of fiber laser compared to the case without any optical feedback. The linewidth of three fiber lasers using above configuration were measured to be within 3kHz which is resolution-limited performance of self-heterodyne linewidth measurement set-up. The frequency drift measurement using Mach-Zehnder measurement set-up having 200m optical delay-line in one arm showed that the frequency drift rate of optical feedback fiber laser was measured as 300kHz/sec which was better than the case without optical feedback.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.699-704
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• 2006

본 논문은 회전 및 천이불변 이미지 텍스처 검색의 새로운 방식을 소개한다. 주파수 영역의 극좌표계에서 동일한 공간 주파수에서 각도 방향으로 투영을 하는 각도 투영법을 제안하며, 제안된 각도 투영법을 이용하여 주파수 영역에서 푸리에 계수이 합과 표준편차를 특징벡터로 이용한다. 각도 투영법을 쉽게 구현하기 위해 극좌표계에서 라돈변환이 수행된다. 실험 시 MPEG-7 데이터를 이용하였으며 그 결과는 여러 텍스처 이미지를 검색하는데 있어서 특징을 잘 구별해 내는 결과를 보여준다. 또한 제안된 회전 및 천이불변 특징 추출 알고리듬은 등방성 텍스처나 국부적인 방향성을 보이는 텍스처 영상 검색에도 효율적인 검색률을 보인다.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.42 no.3
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• pp.39-44
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• 2005

In this paper, we use the 5-ary frequency shift keying method for robust powerline communication. To transmit the data by the 3-ary carrires among 5-ary carrirers and three carriers are 115kHz, 120kHz and 125kHz. Each time of three carrires is 0.33ms and total transmitting time duration from zero crossing point has 1ms. We use the dummy carriers which are 50kHz and 350kHz for monitoring the powerline channel state, dummy signal duration is received during 1ms. Experimentation result is shown that the implemented PLC transceiver has better than chirp transceiver at the capacitive load testing in spite of low transmission power.

• The Journal of the Acoustical Society of Korea
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• v.7 no.2
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• pp.51-64
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• 1988

The frequency synthesizer thar has very short transient time is the key to construct the Fast Frequency Hopping(FFH) system. A Direct Digital Frequency Synthesizer(DDFS) whose transient time is in the nS range has been implemented and the performance of which has been examined through this paper. And by considering the hopping characteristic it is confirmed that the DDFS is suitable for the FFH system. Finally an improvement method which can greatly enhances the SNR with the state-of-the-art techniques and simplifies the system design is presented.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.45-53
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• 2011

This paper is technical review about Direct Sequence Spread Spectrum(DSSS) to apply in launch vehicle system. First, we introduce communication protocol(carrier frequency, code length, process gain, data rate, chip rate etc) about several application system using DSSS. And then, we survey and summarize the effect of doppler shift to the DSSS. The doppler shift is important error factor for PN code tracking in the fast moving system like launch vehicle. So, spread spectrum code acquisition technique for a direct sequence system in the presence of doppler effect must be investigated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.1 s.343
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• pp.25-32
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• 2006

We propose a new M-ary state-transition FSK modulator technique for enhancing demodulator's symbol timing recovery which can be applied to acoustic MODEM. In the previous technique, the demodulator's symbol timing performance can degrade when the sequences of same symbols are transmitted. This proposed method, because the transmission symbol changes in every single symbol period, increases the synchronization performance dramatically and has a simple MODEM and frame structure. On the one hand, we improve modulation-derived synchronization(MDS) which is M-ary FSK's symbol timing recovery scheme, then analyze it. Finally the proposed method is analyzed from the viewpoint of frequency efficiency, which proves this method is appropriate for acoustic MODEM.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.2
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• pp.42-42
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• 2001

본 논문은 주파수 천이를 적용시킨 광무선(fiber-radio)시스템의 광링크부에 대한 성능분석을 한다. 제시된 광링크부는 CS(control station)에서 얻어진 밀리미터파 대역 광파일럿톤(optical pilot tone)이 하향링크뿐 아니라 상향링크에도 공급되도록 하여 BS(base station)의 구조를 간단히 하였다. 광파일럿톤을 얻기 위해 CS의 EOM(electro-optic modulator)을 MAB(maximum bias), MIB(minimum bias), QB(quadrature bias)로 바이어스를 달리할 수 있으며 각각의 경우에 따라 링크의 성능을 분석한다. 분석은 레이저 광원의 전력이 일정한 경우와 PD(photo detector)에 수신되는 광 DC 전력이 일정한 경우에 대해서 행하여지며 각 경우에 대해서 최적의 하향링크 CNR 및 상향링크 SFDR(spurious free dynamic range)을 얻기 위해 효과적인 바이어스 방식을 제시한다

• The Journal of the Korea Contents Association
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• v.5 no.3
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• pp.167-173
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• 2005

In a speech coding system using excitation source of voiced and unvoiced, it would be involved a distortion of speech quality in case coexist with a voiced and unvoiced consonants in a frame. So, I propose TSIUVC(Transition Segment Including Unvoiced Consonant) extraction method by using pitch pulses and Zero Crossing Rate in order to unexistent with a voiced and unvoiced consonants in a frame. And this paper present a TSIUVC approximate-synthesis method by using frequency band division. As a result, this method obtains a high quality approximation-synthesis waveform within TSIUVC by using frequency information of 0.547kHz below and 2.813kHz above. And the TSIUVC extraction rate was $91\%$ for female voice and $96.2\%$ for male voice respectively This method has the capability of being applied to a new speech coding of Voiced/Silence/TSIUVC, speech analysis, and speech synthesis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.2
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• pp.309-314
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• 2002

New grid connected PV(Photovoltaic) system of high-frequency link with soft-switching is proposed to solve problems related to the loss of transformer and switch. The operation of Proposed system using the soft switching that consists of high frequency transformer is confirmed by computer simulation and experiment. It can improve its efficiency and solve the Problems mentioned above.