• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.9
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• pp.1753-1759
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• 2009

A weather radar as one of the remote sensing devices to analyze the weather phenomena receives the return echoes which consist of scattered electromagnetic wave signals from rain, cloud and dust particles, etc. These received Doppler weather spectra are analyzed to extract the various characteristic weather information. The mean wind velocity is one of the important weather parameters which can be obtained by a weather radar ed it may be useful in the prevention of weather hazards occurred by the abrupt shift of wind in small geographical scales such as microbursts. It is usually estimated by pulse pair method which is considered to be reliable and very efficient in the computational requirement. However, there are some problems in the accurate estimation of the mean velocity if Doppler spectra of weather signals appear to be asymmetric gaussian or multi-peak spectra. Therefore, in this paper, the problems in the mean estimation of asymmetric Doppler spectra are analyzed and the improved method is suggested.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.6
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• pp.125-133
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• 2016

As one of solutions to pursue the efficient use of spectrum resource, we proposed the methodology for the co-channel multi-site radar operations with the synchronous GPS clock. The proposed algorithm, based on a quasi orthogonal property, find a candidate set of the time shifted linear frequency modulation(TSLFM) signals with the minimum acceptable level of the correlation among selected TSLFM signals. To check suggested algorithm, numerical analysis for several radars operating in the same channel with a sawtooth waveform has been performed by using range-Doppler processing for the given system parameters, and computational results are presented and examined in terms of range profile and doppler shift for a targets with velocity and distance. Simulated results have a good agreement with assumed target distance and its velocity, within the error of resolution.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.11
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• pp.999-1011
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• 2015

In modern electronic warfare, RADAR is under constant threat of ECM(Electronic Counter Measures) signals from nearby jammers. The conventional linear frequency modulated(Linear-FM) waveform is easy to be intercepted to estimate its signal parameters due to its periodical phase transition. Recently, APCN(Advanced Pulse Compression Noise) waveform using random amplitude and phase transition was proposed for LPI(Low probability of Intercept). But random phase code signals such as APCN waveform tend to be sensitive to Doppler frequency shift and result in performance degradation during moving target detection. In this paper, random phase and code rate transition based radar waveform(RPCR) is proposed for Doppler tolerance improvement. Time frequency analysis is carried out through ambiguity analysis to validate the improved Doppler tolerance of RPCR waveform. As a means to measure the vulnerability of the proposed RPCR waveform against LPI, WHT(Wigner-Hough Transform) is adopted to analyze and estimate signal parameters for ECCM(Electronic Counter Counter Measures) application.

• Journal of the Optical Society of Korea
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• v.16 no.2
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• pp.174-180
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• 2012

In this study, the feasibility of spectral domain optical Doppler tomography for measuring blood flow characteristics in a micro-tube was demonstrated through several experiments. The use of an SD-ODT system in blood flow measurement can provide high resolution images (5 microns resolution). We prepared three capillary tubes to reveal the effect of different concentrations of hematocrit ratio (HR). One tube serves as the control. The two other tubes contained different concentrations of HR (5%, 25%). Three different capillary tube inlet flow velocities were tested in the present study. The Reynolds number (Re) which is based on the capillary tube inner diameter ranges from Re=6 to 48. We calculated a Doppler shift of the power spectrum of the temporal interference fringes with Kasai autocorrelation function to achieve the velocity profile of the flow. As a result, SD-ODT systems could not detect the cell depletion layer in the present study due to the limitation of spatial resolution. Nevertheless, these systems were proven to be capable of observing the RBCs of blood.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.10
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• pp.1137-1146
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• 2008

OFDM is very effective for the high speed communication system. However, OFDM has the problems of high PAPR and serious ICI, which is different from the single carrier system. Especially, ICI problem caused by phase noise, Doppler effect and frequency offset is main reason for poor performance since it breaks down the orthogonality between subcarriers in OFDM communication system. Therefore, WFMT modulation scheme is studied and the effect of the carrier frequency offset and phase noise is analyzed. WFMT modulation scheme is based on the wavelet theory and complex filter banks for synthesis and analysis of multichannel signal. WFHT modulation scheme keeps on the advantage of filter banks system and can be easily possible for the implementation of filter banks. In this paper, we compare ISI and ICI distortions of the WFMT and OFDM system due to the carrier frequency offset and phase noise. Also, we analyze the PAPR and BER performances in the HPA and ICI situation caused by the Doppler frequency shift and the frequency offset.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.46 no.2
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• pp.165-172
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• 2010

This study was performed to estimate the swimming velocity of Pacific saury (Cololabis saira) migrated offshore Funka Bay of Hokkaido using an acoustic Doppler current profiler (OceanSurveyor, RDI, 153.6kHz) established in T/S Ushio-maru of Hokkaido University, in September 27, 2003. The ADCP's doppler shift revealed as the raw data that the maximum swimming velocity was measured 163.0cm/s, and its horizontal swimming speed and direction were $72.4{\pm}24.1\;cm/s$, $160.1^{\circ}{\pm}22.3^{\circ}$ while the surrounding current speed and direction were $19.6{\pm}8.4\;cm/s$, $328.1^{\circ}{\pm}45.3^{\circ}$. To calculate the actual swimming speed of Pacific saury in each bins, comparisons for each stratified bins must be made between the mean surrounding current velocity vectors, measured for each stratified bin, and its mean swimming velocity vectors, assumed by reference (threshold > -70dB) and 5dB margin among four beams of ADCP. As a result, the actual averaged swimming velocity was 88.6cm/s and the averaged 3-D swimming velocity was 91.3cm/s using the 3-D velocity vector, respectively.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1E
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• pp.25-30
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• 2001

The unstable signature that is defined as frequency change with respect to the time or frequency modulation, is caused by the external loading variation in specific machinery component and Doppler shift etc. In this study, we analyze the generation mechanism of the unstable signature and apply the Extended Kalman filter (EKF) algorithm for its detection. The performance of Extended Kalman Filter is examined for numerical and measured signals and the results show its validity for unstable signature detection.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.26-29
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• 1998

비정치제도 위성통신링크에서는 지표상의 단말기, 지구국 등에 대한 상대적인 위성의 빠른 이동으로 인하여 도플러천이가 발생하며, 이는 이동위성통신 시스템 수신단의 성능을 약화시킨다. 본 논문은 비정지궤도 위성을 이용하는 통신링크 상에서 발생하는 도플러천이의 특성을 분석한다. 분석된 결과는 도플러천이에 대한 시뮬레이션 모델과 보상 알고리즘의 개발에 활용활 수 있을 것이다.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.287-289
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• 1996

IRIS(International Research on the Interior of the sun) is the name of a worldwide network of 6 stations for whole disc Doppler shift measurements. The network has been operating since 1987 and by now a few series of a hundred days long unbroken (by day/night periodicity) data were received. Analysis of these data allowed to receivesome new results which are discussed in the paper.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.373-377
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• 2006

본 논문에서는 이동위성통신 DS/CDMA 시스템의 상향링크 채널에 대한 이중모드 통신방식을 제안하고, 제안 시스템의 성능을 해석하고 제안 시스템의 유용성도 확인하였다. 또한 이동위성통신 DS/CDMA 시스템에 큰 도플러 옵셋의 해결방안으로 Kajiwara가 제안한 이중채널 방식을 이용하여 이동위성채널에 널리 쓰이는 라이시안 페이딩 모델을 설정하였으며 변조 방식으로는 DCPSK 신호를 이동체의 속도와 전송률 에러의 성능을 비교 분석하였다.