• 한국통신학회논문지
• /
• 제36권3A호
• /
• pp.189-197
• /
• 2011

무선 광 통신 시스템에서 고속의 데이터를 전송하기 위한 방법으로 대역 효율이 높은 OFDM(orthogonal frequency division multiplexing) 시스템이 연구되고 있다. OFDM 시스템은 PAPR(peak to average power ratio)이 높고 비선형 에러와 디바이스의 불균형으로 발생하는 ICI(inter channel interference)가 발생한다. 무선 광통신 시스템에서 LED(light emission diode)의 구동 전류에 의하여 구동되는 광 출력 파워는 비선형이며 전송 신호는 왜곡된다. 그러므로 비선형 LED 전달함수와 OFDM 신호에 의한 방사된 광 출력의 수신 성능에 대한 연구가 진행되었다. 비선형 왜곡에 의해 발생하는 효과는 기존의 무선 통신에서 사용되는 OFDM의 비선형 특성과 다르며 BER 성능을 저감시킨다. 본 연구에서는 최근 연구된 LED의 비선형성 전달함수를 적용하며, 비선형 왜곡과 Back-off에 의하여 수신기의 주파수영역에서 진폭 감쇄와 ICI를 발생시키므로, BER 성능을 개선시키기 위한 방법을 제안한다. 먼저 LED의 비선형 왜곡을 감소시키기 위한 새로운 PAPR저감 기법을 제안하며, 또한 수산 성능을 향상시키기 위하여 적응형 채널 추정 방식과 전송된 신호를 사용하여 SNR(signal to power ratio)을 개선하여 BER(bit error rate)을 개선하였다. 제안된 방법들을 시뮬레이션 결과를 통하여 확인한다.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
• /
• pp.540-543
• /
• 2007

The modulation transfer function (MTF) in a camera system is a measurement of how well the system will faithfully reproduce the original scene. The electro-optical camera system consists of optics, an array of pixels, and an electronics which is related to the image signal chain. The system MTF can be cascaded with each element's MTF in the frequency domain. That is to say, the electronics MTF including the detector MTF can be recalculated easily by the acquired system MTF if the well-known test optics is used in the measuring process. A Time-Delay and Integration (TDI) detector can make a signal increase by taking multiple exposures of the same object and adding them. It can be considered the various methods to measure the MTF of the TDI camera system. This paper shows the actual and practical MTF measuring methods for the detector and electronics in the TDI camera. The several methods are described according to the scan direction as well as the TDI stages such as the single line mode and the multiple-lines mode. The measuring is performed in the in the static condition or dynamic condition to get the point spread function (PSF) or the line spread function (LSF). Especially, the dynamic test bench is used to simulate on track velocity to synchronize with TDI read out frequency for the dynamic movement.

• 천문학회보
• /
• 제41권2호
• /
• pp.36.2-36.2
• /
• 2016

In mm-VLBI, the quality of observation data is largely affected by atmospheric effect. The most challenging matter is that the phase of correlator output fluctuates rapidly resulting from a variation of atmospheric propagation delay. Consequently, it is demanding to achieve high Signal-to-Noise ratio by integrating data in time domain before calibrating atmospheric delay. However, Korean VLBI Network (KVN) has a unique system to make a 4-frequency (22/43/86/129 GHz) simultaneous observation in mm-wavelength and Frequency Phase Transfer (FPT) calibration technique has effectively removed atmospheric delay in the simultaneous multi-frequency observation of the KVN. For astrometric and astrophysical studies, we evaluated the FPT performance of KVN in various observing conditions. Using the total 38 bright AGNs, we have compared atmospheric conditions such as ground-based weather information, system temperature, atmospheric delay with the calibration results of FPT at 22/43/86/129 GHz during the five experiments in 2013, and quantified its performance in terms of coherence function and Allan variance. We present the analysis result of the relation between the FPT performance and observing conditions.

• Ocean Systems Engineering
• /
• 제10권3호
• /
• pp.317-332
• /
• 2020

This study examines the behaviors and properties of discharged liquid CO₂ from a long elastic pipe moving with a vessel for the oceanic CO₂ sequestration by considering pipe dynamics and vessel motions. The coupled vessel-pipe dynamic analysis for a typical configuration is done in the frequency and time domain using the ORCAFLEX program. The system's characteristics, such as vessel RAOs and pipe-axial-velocity transfer function, are identified by applying a broadband white noise wave spectrum to the vessel-pipe dynamic system. The frequency shift of the vessel's RAO due to the encounter-frequency effect is also investigated through the system identification method. Additionally, the time histories of the tip-of-pipe velocities, along with the corresponding discharged droplet size and Weber numbers, are generated for two different sea states. The comparison between the stiff non-oscillating pipe with the flexible oscillating pipe shows the effect of the vessel and pipe dynamics to the discharged CO₂ droplet size and Weber number. The pipe's axial-mode resonance is the leading cause of the fluctuation of the discharged CO₂ properties. The significant variation of the discharged CO₂ properties observed in this study shows the importance of considering the vessel-pipe motions when designing oceanic CO₂ sequestration strategy, including suitable sequestration locations, discharge rate, towing speed, and sea states.

• 한국항해항만학회지
• /
• 제46권6호
• /
• pp.471-482
• /
• 2022

본 연구는 심해공학수조의 파 생성 특성을 규명하고, 심해공학수조의 기하학적 특성을 반영한 조파기 전달함수의 근사모델을 개발하는 것을 목적으로 한다. 심해공학수조의 기하학적 특성을 반영한 효율적인 해석을 위해 2차원 주파수영역 경계요소법이 적용되었다. 개발된 수치해석법은 해석해와 비교하여 검증되었다. 다양한 주기와 이동식 바닥판의 위치 변화에 대한 조파기의 경계치 문제의 수치해석이 수행되었다. 수치결과를 통해 심해공학수조의 기하학적 특성이 조파기의 전달함수에 미치는 영향을 조사하였고, 이동식 바닥판의 위치를 변화시켜 파도 생성에 대한 깊이 효과를 확인하였다. 경계요소법의 다양한 결과를 효율적으로 활용하기 위해 박판 스플라인 보간 모델 기반의 조파기 근사모델을 개발하였다. 개발된 근사 모델의 타당성은 모델 테스트 결과 비교를 통해 확인하였다.

• 전자공학회논문지SC
• /
• 제44권1호
• /
• pp.19-24
• /
• 2007

본 논문에서는 주파수 영역뿐만 아니라 시간 영역의 설계 사양을 만족할 수 있는 PID-PD 제어기 동조 방법을 제안한다. 제안한 PID-PD 제어기 동조 방법은 PID 제어기와 PI-PD 제어기를 경계로 볼록형 집합을 형성하도록 선정한다. PID-PD 제어기는 PID 제어기와 PI-PD 제어기 각각에 의한 계단 응답과 보드 선도의 이득 사이에 위치하는 응답을 제어한다. 최적 동조 방법에 의해 센서 잡음 저감도 및 안정 강인성을 변수로 하는 가격함수를 최소화하는 제어기를 설계한다. 제안된 제어기의 유용성을 사례 연구와 분석을 통해 검토한다.

• International Journal of Automotive Technology
• /
• 제7권2호
• /
• pp.155-160
• /
• 2006

This paper presents a vehicle model for analyzing the transient shifting characterisitics of a passenger car with automatic transmission. Then the presented vehicle model was linked with the dynamic model of an automatic transmission. In order to identify the parameters of the vehicle model, we installed a test equipment with an accelerometer in a conventional vehicle and performed road tests. With the proposed vehicle model, we simulated the dynamic characteristics during shifting, and benchmarked with experimental results. Moreover, a modal analysis was carried out to investigate the effect of the vehicle model in the frequency domain and to obtain the transfer function of the vehicle model. In addition, we showed the numerical results in the time domain for analyzing the effect of each stiffness element, such as engine mountings and suspensions.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제48권3호
• /
• pp.131-138
• /
• 1999

Generally, the digital controller has many advantages such as high precision, robustness to electrical noise, capability of flexible programming and fast response to the load variation. In this study, we have established proper mathematical equivalent model of Brushless DC (BLDC) motor and estimated the motor parameter by means of the back-emf measurement as being the step input to the controlled target BLDC motor. And the validity of proposed estimation method is confirmed by the test result of step response. As well, we have designed the reasonable digital controller as a consequence of the root locus method which is obtained from the open-loop transfer function of BLDC motor with hall sensor, and the determination of control gain for variable speed control. Here, revised Ziegler-Nichols tuning method is applied for the proper digital gain establishment, and the system stability is verified by the frequency domain analysis with Bode-plot and experimentation.

• International Journal of Aeronautical and Space Sciences
• /
• 제13권4호
• /
• pp.499-506
• /
• 2012

In this paper, a dynamic modeling for the velocity and position information of a single frequency stand-alone GPS(Global Positioning System) receiver is described. In static condition, the position error dynamic model is identified as a first/second order transfer function, and the velocity error model is identified as a band-limited Gaussian white noise via non-parametric method of a PSD(Power Spectrum Density) estimation in continuous time domain. A Kalman filter is proposed considering both correlated/white measurements noise based on identified GPS error model. The performance of the proposed Kalman filtering method is verified via numerical simulation.

• The Journal of the Acoustical Society of Korea
• /
• 제22권3E호
• /
• pp.133-140
• /
• 2003

A time series simulation is presented by a ray approach for the simulating the received waveform of a broadband acoustical signals interacting with the ocean boundaries. The environment is assumed to be horizontally stratified, and the seafloor is described in terms of homogeneous fluid half-space. The ray approach includes the effects of reflection from the air-water, water-sediment interface and phase shifts due to boundaries interaction. To generate time series, we assume that the acoustic energy propagates from source to receiver along eigenrays and represent the action of the bottom on the incident wave by a linear filter and characterized in the frequency domain by the transfer function. As example application, the time series for an explosive source in a shallow water environment is calculated and analyzed in terms of acoustical process. good agreement with measured time series is demonstrated.