• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10A
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• pp.807-815
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• 2003

MultiCode-CDMA (MC-CDMA) system of chip level MPSK incorporating with clipper (MP-CDMA)[l] shows constant envelope signal which can mitigate the performance degradation due to nonlinear transmit amplifier. In this paper, modulation is modified to carry out differential encoded MPSK rather than MPSK. The modified system is called DMP-CDMA. DMP-CDMA using differential detection has advantages on receiver complexity and pilot overhead. However, it is inferior to coherent detection by about 4.0dB due to inherent power inefficiency of noncoherent detection and the error propagation. Multiple symbol differential detection is employed in order to improve DMP-CDMA using differential detection. As the result, the performance of DMP-CDMA system is improved about 3.6dB compared to differential detection.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.6
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• pp.443-451
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• 2015

Design formula for estimating the wave loading on the perforated caisson having two wave chambers is yet available. In this study, the analysis results are presented with the experimental data for the wave force acting on such a breakwater model. Based on the experimental results, it was able to clarify the variation of wave action according to five different wave phases that are associated with peak wave loading at the three vertical walls. Then the force adjustment factor for double-chamber caisson was estimated, similarly as Takahashi and Shimosako (1994), which needs to be further validated with subsequent experiments and practical application in the field.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.35.3-35.3
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• 2010

항공용 지역위성항법 보강시스템(Ground Based Augmentation System, GBAS)은 지상에서 위성항법시스템에 대한 위치보정정보와 무결성 정보를 생성 및 제공하여 공항 주변 항공기의 정밀 이착륙을 돕는 지상기반의 시스템이다. 이 시스템은 기본적으로 위성항법신호를 사용하기 때문에 전리층 영향을 받게 되는데 특히 전리층 폭풍(Ionospheric storm)의 경우 공간적으로 급격한 위치오차 차이를 발생시키기 때문에 안정적인 항공기의 정밀이착륙을 위해서는 전리층 폭풍의 영향을 최소화 하는 것이 중요하다. 이를 위하여 현재 항공용 지역위성항법 보강시스템의 지상시스템(Ground Facility)과 항공기 탑재시스템에서의 전리층 폭풍에 대한 정확한 감시와 전리층 폭풍의 지배적 영향을 받는 위상항법신호를 제거하거나 보완하는 방식 등 전리층 폭풍의 영향을 최소화하기 위한 기법들이 계속해서 연구 중이다. 이 논문에서는 2001년과 2003년 미국에서 발생한 전리층 폭풍에 대한 위성항법데이터 분석 결과와 기존의 연구결과를 기반으로 전리층 폭풍에 대한 모델링과 지상시스템과 항공기 간의 공간적 상이현상(Spacial decorrelation)을 고려하여 전리층 폭풍이 항공기 이착륙에 미치는 영향에 대한 분석 결과를 제시한다. 전리층 폭풍에 대한 수학적 모델링을 하기 위해서는 전리층 폭풍의 물리적 특성에 대한 이해와 전리층 폭풍 발생 시 획득한 위성항법 데이터를 이용한 통계학적 분석이 선행되며 이러한 분석결과와 항공기 이착륙에 절차를 반영하여 항공기에 미치는 영향 분석을 위한 수학적 모델을 완성하였다. 완성된 모델을 국내 공항에서 실제 비행시험을 통하여 획득한 위성항법데이터에 적용하여 전리층 폭풍이 국내 공항에서 항공기 이착륙에 어떠한 영향을 미치는지를 분석하였다. 또한, 대표적 전리층 폭풍 감지기법 중 하나인 Code-Carrier Divergence Test 알고리즘을 적용한 결과도 함께 제시하였다. 이 논문의 결과는 항공용 지역위성항법 보강시스템에 대한 전리층 폭풍의 영향을 최소화하기 위한 기법 연구의 기반이 되며 시스템의 성능평가를 위한 다양한 시뮬레이션환경의 하나로서도 활용이 가능할 것이다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.607-610
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• 2006

The Digital Frequency Synthesizer(DFS) that generates the wideband signal with hish speed frequency hopping rate and high frequency resolution characteristics was implemented in this paper. The DFS was applied as local oscillator for direct frequency conversion IF modules of DVB-RCS, which directly generates the transmission immediate frequency signal by using DDS and wideband PLL technologies. The DDS technology provides high speed frequency hopping rate and high frequency resolution characteristics, which ate also the DVB-RCS requirement. The wideband PLL technology also provides the wideband signal generation, which is a necessity for direct frequency conversion modules. The implemented DFS provide the spurious suppression characteristic of -50 dBc, frequency resolution of 0.233 Hz and frequency hopping rate of 125 ns, respectively. Also the DFS represent the amplitude flatness of 3 dB and less in the pass-band and phase noise characteristic of -75 dBc/Hz at 1 kHz frequency offset.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.512-515
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• 2010

SIGINT(SIGnal INTelligence) includes several parameters intercepted by measurement and analysis of the RF(Radio frequency) signal from free space. One of the important parameters is frequency information. Expecially, in order to perform instantaneous frequency measurement of Radar and Missile seeker's RF signals, we use dedicated RF modules as a DFD(Digital Frequency Discriminator) to provide frequency information by measurement of the relative phase difference between signals via intended RF delay lines. It must measure and provide realtime based frequency information on short pulsed RF signal up to 100 nSec or less. This document proposes Ultra wideband DFD consisted of a RF input section of Wideband 4 channel RF delay line and correlator, a digital processing section to measure and provide frequency information from I/Q signal, and a frequency calibration section. Also, it will show design suitability based on test results measured under test condition of very short input pulse signals.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.223-228
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• 2007

The Digital Frequency Synthesizer(DFS) that generates the wideband signal with high speed frequency hopping rate and high frequency resolution characteristics was designed and implemented in this paper The DFS was applied as local oscillator for direct frequency conversion IF modules of DVB-RCS, which directly generates the transmission immediate frequency signal by using DDS and wideband PLL technologies. The DDS technology provides high speed frequency hopping rate and high frequency resolution characteristics, which are also the DVB-RCS requirement. The wideband PLL technology also provides the wideband signal generation, which is a necessity for direct frequency conversion modules. The implemented DFS provides the spurious suppression characteristic of -50 dBc and less, frequency resolution of 0.233 Hz and frequency hopping rate of 125 ns, respectively. Also the DFS represents the amplitude flatness of 3 dB and less in the pass-band, and phase noise characteristic of -75 dBc/Hz at 1 kHz frequency offset.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.17-17
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• 2016

이중편파 레이더는 수평 수직반사도($Z_H{\cdot}Z_V$), 차등반사도($Z_{DR}$), 교차상관계수(${\rho}_{HV}$), 차등위상차(${\Phi}_{DP}$) 등 다양한 변수 산출을 통하여 대기 수상체 구분, 우적분포에 영향이 적은 강우량 추정, 밝은 띠(BB, Bright Band)의 탐지 등이 가능하게 됨으로써 수문기상 및 재해관리 분야에 활용성이 점점 더 커지고 있다. 본 연구는 RHI, PPI에서 생산된 레이더 변수를 이용하여 BB를 탐지하고 그 특성을 평가하였다. BB는 레이더를 이용하여 상층대기를 관측할 때 수직단면에서 강수입자가 눈에서 비로 변하는 구간에서 과대하게 높은 반사도가 나타나는 층을 말한다. BB에서는 QPE가 과대 추정되기 때문에, BB의 특성 파악은 레이더의 관측전략 수립과 QPE 보정에 필수적이다. 본 연구에서는 RHI에 의한 $Z_H$의 연직단면분석, RHI와 PPI의 고도각 경사거리(slant range) 빔의 ${\rho}_{HV}$, $Z_{DR}$, $Z_H$에 의한 분석을 통하여 BB의 상단부($BB_{TOP}$), 최정점($BB_{PEAK}$) 및 하단부($BB_{BOTTOM}$)의 고도를 상호 비교 평가하였다. 분석 자료는 KICT X-밴드 레이더에 의한 관측한 2015년 10월 21일의 층상운에 의한 강우를 이용하였다. RHI에 의한 $Z_H$의 연직단면 분석결과 $BB_{top}$, $BB_{bottom}$ 및 $BB_{peak}$는 KICT 레이더 고도(MSL : 40m)를 기준으로 각각 3.26Km, 2.3Km($BB_{width}$: 0.96km) 및 2.7Km로 나타났다. 이 같은 결과는 다른 2가지 분석방법에서도 유사하게 나타나고 있으며, 이는 BB분석을 위해 다양한 변수를 통한 신뢰성 있는 BB의 특성을 파악할 수 있는 기반을 제공한다.

• Korean Journal of Optics and Photonics
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• v.29 no.1
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• pp.1-6
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• 2018

In this study, ray-tracing software was used to calculate the optical path length of an optical system. Using the optical path length, the optical phase, group delay (GD), group delay dispersion (GDD), and third-order dispersion (TOD) of the optical system were obtained. Pulse compressors using a prism pair or grating pair were designed to compensate the GDD of a real optical system for a femtosecond fiber laser. Also, a pulse stretcher using a grating pair with lenses or mirrors was designed. The results of this study can be used to calculate the dispersion of an optical system and optimize the performance of an ultrashort pulse laser optical system.

• The Journal of Korean Institute of Information Technology
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• v.17 no.10
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• pp.57-63
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• 2019

Motion errors which are caused by several reasons, non-ideal path, errors of navigation systems, and radar system errors, have to be corrected. Motion compensation methods can compensate the motion error, but not exactly. To correct these residual errors, several autofocus methods are invented. A popular method is phase gradient autofocus (PGA). PGA does not assume specific circumstances, such as isolated point targets and shapes of errors. PGA is an iterative and adaptive method, so that the processing time is the main problem for the real time processing. In this paper, the improved method to select targets for PGA is proposed to reduce processing time. The variances of image pixels are used to select targets with high SNR. The processing of PGA with these targets diminishes the processing time and iterations effectively. The processed results with real radar data, obtained by flight tests, show that the proposed method compensates errors well, and reduce working time.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.411-419
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• 2020

The experiment of unsteady rip current generated at the successive ends of breaking wave crests of honeycomb pattern waves was conducted in a laboratory wave basin, and its time-varying evolution was observed by using ortho-rectified images. The present experiment utilized the generation of a quasi nodal line of the honeycomb-pattern waves formed by out-of-phase motion of two piston-type wavemakers arranged in the transverse direction, instead of the original honeycomb pattern waves which are generated when two wave trains propagate with slightly different wave directions. The velocities of rip current were measured by using the LSPIV (Large-Scale Particle Image Velocimetry) technique. As a result, the unsteady rip current was generated between successive ends of wave crests, and evolved with its shear fluctuations in this experiment. Also, the time series of LSPIV velocity of the unsteady rip current showd its short component due to waves and its long component due to wave-induced currents.