• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.107-114
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• 2001

비검측공 시험법을 현장타설말뚝의 건전도 평가 목적으로 적용함에 있어서 시험법의 적용성을 향상시키기 위한 연구가 진행되어 오고 있다. 본 논문에서는 같은 맥락에서 수행되어 온 일련의 해석적 연구 결과 중 시험법의 해상도에 관한 문제와 말뚝 주변 및 선단지반의 강성이 비검측공 시험결과에 미치는 영향에 관해 다루었다. 본 논문에서 수행한 연구결과에 의하면 충격응답기법의 해상도를 평가하기 위해서는 말뚝재료에 대한 지반의 강성비($V_{s}$ /$V_{c}$)와 말뚝의 길이에 대한 직경의 비(L/D)에 의존하는 기존 평가기준에 부가하여 말뚝의 상대적인 체적변화가 필히 고려되어야 한다는 결론을 얻었다. 한편, 말뚝이 수평으로 층이 진 주변 지반을 통과하여 말뚝선단부를 지지하는 지반(선단지반)에 근입되거나 지지되는 경우에 말뚝의 자유단 혹은 고정단 경계 조건은 주변 지반과 선단 지반의 강성비와 선단 지반에 대한 말뚝의 근입깊이에 따라 변화한다는 사실을 규명하였다. 말뚝의 건전도 평가 시에 사용하게 되는 말뚝의 공진주파수가 이들 조건에 따라 변화하므로 결과적으로 시험결과분석에 있어서 이들 영향이 필히 고려되어야 한다는 결론을 얻었다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.217-222
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• 2004

In this paper, the efficient channel estimation schemes for DRM system(AM band digital radio broadcasting standard) are investigated. In frequency domain, by means of the linear interpolation, the second order interpolation, cubic spline interpolation, and time domain interpolation, the channel impulse response is estimated respectively to compensate the attenuation due to the fading. And in time domain, the frequency channel impulse response is averaged to reduce the attenuation due to the AWGN. By the simulation, the performance of MSE, BER and the complexity of calculation is compared and analyzed for each interpolation scheme.

• Journal of IKEEE
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• v.24 no.1
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• pp.120-126
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• 2020

We present a user recognition method using human body impulse response signals. The body compositions vary from person to person depending on the portion of water, muscle, and fat. In the body communication study, the body has been interpreted circuit models using capacitance and resistances, and its characteristics are determined by the body compositions. Therefore, the individual body channel is unique and can be used for user recognition. In this paper, we applied pseudo impulse signals to the left hand and recorded received signals from the right hand. The empirical mode decomposition (EMD) method removed noise from the received signals and 10 peak values are extracted. We set the differences between peak amplitudes as a key feature to identify individuals. We collected data from 6 subjects and achieved accuracy of 97.71% for the user recognition application.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.27-30
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• 2003

무선 통신 서비스에 대한 수요가 급격히 증가하면서 높은 데이터 전송율을 갖는 무선 통신에 대한 연구가 활발히 진행되고 있다. UWB는 (Ultra Wide Band) 이러한 문제점을 해결할 수 있는 통신 방법 중의 하나로 이 논문에서는 현재 IEEE 802.15.TG3a 표준화 위원회에서 제시하고 있는 채널 모델에 대해서 알아보고, 제시된 채널 모델에 LS (Least Square) 방법을 적용하여 채널의 임펄스 응답을 (Channel Impulse Response) 추정한다. 채널 추정의 성능 지표로 Preamble의 크기에 따른 MSE와 (Mean Square Error) 각각의 채널에 대한 비트 에러율을 사용하여 모의 실험을 본 논문에서 다루는 추정 기법의 성능을 분석한다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.5
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• pp.538-542
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• 2018

Echo generated in digital hearing aid vent give rise to user's discomfort. For cancelling feedback echo in vent, it is required to estimate vent impulse response exactly. The vent impulse response has time varying and sparse characteristics. The IPNLMS has been known a useful adaptive algorithm to estimate vent impulse response with these characteristics. In this paper, subband sparse adaptive filter which applying IPNLMS to subband hearing aid structure is proposed to cancel echo of vent by estimating sparse vent impulse response. In the propose method, the decomposition of input signal to subband can pre-whiten each subband signal, so adaptive filter convergence speed can be improved. And the poly phase component decomposition of adaptive filter increases sparsity of each components, and the better echo cancellation can be possible without additional computation. To derive coefficients update equation of the adaptive filter, by defining the cost function based weight NLMS is defined, and the coefficient update equation of each subband is derived. For verifying performances of the adaptive filter, convergence speed, and steady state error by white signal input, and echo cancelling results by real speech input are evaluated by comparing conventional adaptive filters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.66-78
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• 2002

In this paper, we propose a new symbol offset estimation technique for an orthogonal frequency-division multiplexing (OFDM)-based wireless LAN. When both inter-symbol interference (ISI) and inter-channel interference (ICI) do not exist in an OFDM symbol, symbol offsets cause circular shifts in the estimated channel impulse response (CIR) by the amount of symbol offset. Also, the power delay profile of a typical multipath wireless channel can be modeled by exponentially decaying function, and most energy of multipath channel is concentrated at the beginning part of the CIR. Based on these properties, the proposed symbol offset estimation technique estimates the CIR, which is circularly shifted by the amount of symbol offset, and then calculates the partial mean power from the estimated impulse response by using a moving window with a finite length. And, symbol offset can be estimated from the index of a moving window having the maximal partial mean power. The proposed technique can reduce noise effect in the process of the CIR estimation, and remove ISI and ICI using repetitive training symbol structure in time-domain for minimum training overhead. The performances of the proposed symbol offset estimation technique in typical indoor channels are demonstrated by computer simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.3
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• pp.9-14
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• 2008

In this paper, we propose the channel sounding scheme which is made for ideal communication between some application as well as the short distance of high speed data transmission in MIMO-OFDM system for Wireless PAN. This method is able to perceive the duration of the impulse response through the delaying of power delay profile, modeled a power delay profile which has an attenuate characteristic, and obtained the coefficient of channel response by ML (maximum likelihood). Through the amplitudes, phases and delays associated with each multipath component which were acquired from this channel sounding scheme, we can describe the wave propagation characteristics of channels between the transmitter and receiver so that the receiver could enhance not only the reliability but also the ability of communication link.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.11a
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• pp.106-109
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• 2011

본 논문에서는 연속된 프레임을 갖는 영상의 프레임간 움직임 추정 기법을 응용하여 고해상도 영상을 획득하는 초고 해상도 기법을 제안한다. 기존의 단일 영상을 이용한 초고해상도 기법의 경우 영상에서의 고주파 대역을 찾기 위해 확률 기반의 다양한 방법이 제시되었으나 연산에 사용할 수 있는 정보가 제한적이라는 문제가 존재한다. 이러한 문제를 해결하기 위해 연속된 프레임을 이용한 다양한 초고해상도 기법이 제안되었다. 본 논문에서는 주어진 영상의 전, 후의 다수 프레임을 정하여 6-tap FIR(finite impulse response) 필터를 이용하여 프레임들의 부화소(sub-pixel)를 구한 뒤에, 부화소 정밀도의 움직임 추정을 통하여 보다 정확한 고주파성분을 복원하고자 한다. 실험을 통하여 제안하는 기법이 기존의 고등차수(bi-cubic)보간법 보다 선명한 영상을 획득할 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.6A
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• pp.341-350
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• 2003

In this paper, we evaluate the performance of a moving average (MA) channel estimation filter when space-time block coding transmit diversity (STBC-TD) is applied to the wideband direct sequence code division multiple access (WCDMA) forward link. And we present the infinite impulse response (IIR) filter scheme that can reduce the required memory buffer and the channel estimation delay time. This paper also compares the performance between MA filter scheme and IIR filter scheme in various Rayleigh fading channel environments through the bit error rate (BER) and the frame error rate (FER). Extensive computer simulation results show that transmission with STBC-TD provides a significant gain in performance over no transmit diversity technique, particularly at pedestrian speeds. If STBC-TD technique is employed in the channel estimator based on MA filter, it provides considerable performance gains against Rayleigh fading and reduces the optimum filter tap number. Consequently, the channel estimation delay time and the complexity of the receiver are reduced. In addition, the channel estimator based on IIR filter has the advantages such as little memory requirement and no delay time compared to the MA scheme. However, IIR filter coefficients is very sensitive to the mobile speed change and it exerts a serious influence upon the performance. For that reason, it is important to set uP the optimum IIR filter coefficients.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.774-777
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• 2002

There are various methods to join mechanical structures together. They typically include welding, mechanical joints by bolts and other processes depending on specific needs. Analyses of joints in the mechanical structures are essential in understanding the dynamic characteristics of the structures. In this research an impulse technique is applies to investigate the dynamic behavior of joints produced by bolts. The length overlap in the joints was varied as the number of the bolts in the joins was changed. Also, the torque applied to the bolts were adjusted. Resonance frequencies were determined for the joints to evaluate the relationship between the increase in the applied torque and the increase in the number of bolts used in the joints. The results have demonstrated that the resonance frequencies of the joints increase with the increasing torque.