• 한국통신학회논문지
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• 제22권1호
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• pp.116-126
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• 1997

디지털 시스템에서 높은 샘플링 주파수는 방대한 데이터의 처리를 요구하므로, 이러한 시스템은 실시간 처리가 어렵다. 본 연구에서는 비선형 에너지-추적 신호 연산기를 사용하여 표본화 주파수를 낮출 수 있는 undersampling 기법에 의해서 4종류의 AM/FM 복조기들을 설계하여 제안하였다. 특히, 이시스템들을 조절이 가능한 undersampling 주파수 및 3dB 대역폭이 각각 주어지게 된다. 이 설계된 검파기들을 분석한 결과, 특성 및 오차의 측면에서 유용함을 밝혔다.

• 대한전기학회논문지:시스템및제어부문D
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• 제49권7호
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• pp.399-406
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• 2000

We propose an nonlinear demodulation algorithm for undersampled multicomponent AM(Amplitude Modulation), FM(Frequency Modulation) and AM-FM signals. First, we derive respectively undersampling frequency of the AM, FM and AM-FM using undersampling scheme, and separate respectively monocomponent signals from multicomponent signals using periodic algebraic separation algorithm. In this case augmented separation matrix is very regular and sparse, it has a special structure. The proposed demodulation algorithm detects respectively message signals of the IA(Instantaneous Amplitude) and IF(Instantaneous Frequency) from descrete monocomponent AM, FM and AM-FM signals with an undersampling frequency to be controllable. Verifying the RMS(Root Mean Squares) errors of the detected signals, we show that the performance is excellent.

• 대한전기학회논문지:전력기술부문A
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• 제48권5호
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• pp.643-649
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• 1999

In this paper, we proposed that ｉ) noise-tolerant four kinds of AM(Amplitude Modulation)-FM(Frequency Modulation) demodulators are designed, ⅱ) we derived undersampling frequency through the product via energy operator of the monocomponent AM-FM signals separated form two-component AM-FM signals, and ⅲ) these four kinds of AM-FM demodulators detect respectively information signals of the IA(Instantaneous Amplitude) and IF(Instantaneous Frequency) by undersampling frequency to be different each other from the undersampled monocomponet AM-FM signals. Particularly, the proposed algorithm can control undersampling frequency by an integer factor. And these efficient AM-FM demodulators are well worked with the undersampled AM-FM signals.

• Smart Structures and Systems
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• 제25권3호
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• pp.369-384
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• 2020

A wavefield sparse reconstruction technique based on compressed sensing is developed in this work to dramatically reduce the number of measurements. Firstly, a severely underdetermined representation of guided wavefield at a snapshot is established in the spatial domain. Secondly, an optimal compressed sensing model of guided wavefield sparse reconstruction is established based on l₁-norm penalty, where a suite of discrete cosine functions is selected as the dictionary to promote the sparsity. The regular, random and jittered undersampling schemes are compared and selected as the undersampling matrix of compressed sensing. Thirdly, a gradient projection method is employed to solve the compressed sensing model of wavefield sparse reconstruction from highly incomplete measurements. Finally, experiments with different excitation frequencies are conducted on an aluminum plate to verify the effectiveness of the proposed sparse reconstruction method, where a scanning laser Doppler vibrometer as the true benchmark is used to measure the original wavefield in a given inspection region. Experiments demonstrate that the missing wavefield data can be accurately reconstructed from less than 12% of the original measurements; The reconstruction accuracy of the jittered undersampling scheme is slightly higher than that of the random undersampling scheme in high probability, but the regular undersampling scheme fails to reconstruct the wavefield image; A quantified mapping relationship between the sparsity ratio and the recovery error over a special interval is established with respect to statistical modeling and analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.1316-1319
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• 1996

진폭변조(AM) 신호를 검파기하기 위한 디지탈 시스템을 실현하기 위해서는 보통 변조된 신호의 최대주파수의 2배 이상되는 주파수로 샘플링해야만 한다. 이러한 경우에 반송파가 커지면 처리할 데이터가 많아지기 때문에 디지탈 시스템이 복잡해져 실시간 처리가 어렵게 된다. 본 연구에서는 샘플링 주파수를 대역폭을 기준으로 하여 낮출 수 있는 유용한 두 종류의 복조시스템을 제안하였다. 또한 undersampling한 복조회로에 대한 특성 및 오차를 해석하고 검토하였다.

• 대한의용생체공학회:의공학회지
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• 제11권1호
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• pp.89-96
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• 1990

The numerical evaluation of Rayleigh's integral for the sound source reconstruction can be speeded up by the use of angular frequency propagation method and the FFT. However, are several source of errors involved during the reconstruction. Besides the aliasing error due to undersampling in space, the wrap around error. which is caused by undersampling the kernel functionin frequency domain, and windowing effect are present. We found that there is no replicated source problem and the windowing effect is due to the windowing the kernel function In frequency domain, and, xero padding is always required to improve the quality of reconstruction.

• 한국컴퓨터정보학회논문지
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• 제29권9호
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• pp.9-23
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• 2024

본 연구에서는 3차원 보행 데이터 기반 체질량지수(Body Mass Index, BMI) 추정 기술의 분류 정확도를 향상시킬 수 있는 방법을 제안한다. BMI 추정 기술에 관해 기존 연구에서는 BMI 분류 정확도가 약 60%에 불과했다. 이에 본 연구에서는 먼저 BMI 분류 정확도가 낮았던 원인을 규명한다. 본 연구의 분석 결과에 따르면, 그 원인은 보행 데이터 세트의 클래스 불균형(Class Imbalance) 문제를 해결하기 위해 언더샘플링(Undersampling) 기법을 사용한 것에 있었다. 이에 본 연구에서는 언더샘플링 기법 대신 오버샘플링(Oversampling) 기법을 적용해 클래스 불균형 문제를 해결하는 것을 제안한다. 또한, 보행 데이터 기반 BMI 추정 기술에서 인체 측정학(Anthropometric) 특징과 시공간적(Spatiotemporal) 특징의 유용성을 재입증한다. 기존 연구에서는 언더샘플링 기법이 적용된 상태에서 인체 측정학 특징과 시공간적 특징의 유용성이 평가됐고, 두 특징을 함께 사용하면 단독으로 사용했을 때보다 BMI 추정 성능이 낮아진다고 보고됐다. 하지만 본 연구 결과에 따르면, 두 특징을 함께 사용하고 오버샘플링 기법을 적용했을 때 BMI 추정 문제에서 92.92%의 정확도로 SOTA(State-Of-The-Art) 성능을 달성하는 것을 보인다.

• Korean Journal of Radiology
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• 제24권12호
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• pp.1293-1297
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• 2023

• 대한의용생체공학회:의공학회지
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• 제19권2호
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• pp.143-152
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• 1998

In this paper, we present the performances of a Doppler system using single channel RF(Radio Frequency) sampling. This technique consists of undersampling the ultrasonic blood backscattered RF signal on a single channel. Conventional undersampling method in Doppler imaging system have to use a minimum of two identical parallel demodulation channels to reconstruct the multigate analytic Doppler signal. However, this system suffers from hardware complexity and problem of unbalance(gain and phase) between the channels. In order to reduce these problems, we have realized a multigate pulsed Doppler system using undersampling on a single channel, It requires sampling frequency at $4f_o$(where $f_o$ is the center frequency of the transducer) and 12bits A/D converter. The proposed " single-Channel RF Sampling" method aims to decrease the required sampling frequency proportionally to $4f_o$/(2k+1). To show the influence of the factor k on the measurements, we have compared the velocity profiles obtained in vitro and in vivo for different intersequence delays time (k=0 to 10). We have used a 4MHz center frequency transducer and a Phantom Doppler system with a laminar stationary flow. The axial and volumetric velocity profiles in the vessel have been computed according to factor k and have been compared. The influence of the angle between the ultrasonic beam and the flow axis direction, and the fluid viscosity on the velocity profiles obtained for different values of k factor is presented. For experiment in vivo on the carotid, we have used a data acquisition system with a sampling frequency of 20MHz and a dynamic range of 12bits. We have compared the axial velocity profiles in systole and diastole phase obtained for single channel RF sampling factor.ng factor.

• 천문학회보
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• 제38권1호
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• pp.64.1-64.1
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• 2013

The point spread function (PSF) of an optical system is in general defined as a two-dimensional intensity distribution which results from a single point source at infinity. It is an important key for the evaluation of the optical performance of an astronomical telescope. The PSFs of the soft X-ray telescope (SXT) aboard Yohkoh were measured in a wide range of the field-of-view under the in-flight configuration at White Sands Missile Range prior to launching the satellite. It has been known that the SXT PSF has a sharp peak at the core and the intensity drops very fast as it goes distant from the center. Due to the combination of this sharp peak at the PSF core and the effect of undersampling by a large pixel size, a carefully designed method is requested in the examination of the PSF data. The pattern of the SXT PSF is determined by the fitting of a mathematical functional form to the pre-launch experimental data. The elliptical Moffat function has been adopted for the evaluation of the SXT PSF. It is revealed from our study that the SXT PSF shows a peculiar characteristics, and thus a careful consideration on the undersampling effect and also a proper choice of statistics are necessary for the determination of the best fit function of the PSF. Details on the on- and off-axis SXT PSF in the field-of-view will be introduced and discussed in our presentation.