• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.359-365
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• 2006

Wave-front error(WFE) is the main parameter that determines the optical performance of the opto-mechanical system. In the development of opto-mechanics, WFE due to the main loading conditions are set to the important specifications. The deformation of the optical surface can be exactly calculated thanks to the evolution of numerical methods such as the finite element method(FEM). To calculate WFE from the deformation results of FEM, another approximation of the optical surface deformation is required. It needs to construct additional grid or element mesh. To construct additional mesh is troublesomeand leads to transformation error. In this work, the moving least-squares approximation is used to reconstruct wave front error It has the advantage of accurate approximation with only nodal data. There is no need to construct additional mesh for approximation. The proposed method is applied to the examples of GOCI scan mirror in various loading conditions. The validity is demonstrated through examples.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.245-250
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• 2009

In communications and signal processing area, a number of least mean square adaptive algorithms have been used because of simplicity and robustness. However the LMS algorithm is known to have slow and non-uniform convergence. Various variable step size LMS adaptive algorithms have been introduced and researched to speed up the convergence rate. A variable step size LMS algorithm using the error difference for updating the step size is proposed. Compared with other algorithms, simulation results show that the proposed LMS algorithm has a fast convergence. The theoretical performance of the proposed algorithm is also analyzed for the steady state.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4C
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• pp.254-264
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• 2011

In this paper, we propose two algorithm for improving the performance of wireless localization(Trilateration and Least Square) based on the range based approach method in indoor environment using RSSI for ranging distance. we propose a method to discriminate the case that has relatively large estimation errors in trilateration using Heron''s formula for the volume of a tetrahedron. And we propose the algorithm to process the discriminated types of distance using the absolute value calculated by Heron''s formula. In addition, we propose another algorithm for the case of which the number of anchor nodes larger than three. In this case, Residual Weighting Factor(RWGH) improves the performance of Least Square. However, RWGH requires many number of calculations. In this paper, we propose Iterative Weighted Centroid Algorithm(IWCA) that has better performance and less calculation than RWGH. We show the improvement of performance for two algorithms and the combination of these algorithm by using simulation results.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.11 no.4
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• pp.363-370
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• 2017

In this paper, we proposed a low-complexity speech enhancement algorithm based on a improved minima controlled recursive averaging (IMCRA) and log minimum mean square error (logMMSE). The IMCRA algorithm track the minima value of input power within buffers in local window and identify the speech presence using ratio between input power and its minima value. In this process, many number of operations are required. To reduce the number of operations of IMCRA algorithm, minima value is tracked using time-varying frequency-dependent smoothing based on speech presence probability. The proposed algorithm enhanced speech quality by 2.778%, 3.481%, 2.980% and 2.162% in 0, 5, 10 and 15dB SNR respectively and reduced computational complexity by average 9.570%.

• Proceedings of the Korea Information Processing Society Conference
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• 2001.10b
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• pp.1323-1326
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• 2001

서브네트워크에서 실시간으로 통신 트래픽을 감시하고, 트래픽 정보를 바탕으로 시계열 분석을 이용해 트래픽의 변화추이를 예측할 수 있는 시스템을 설계 및 구현한다. SNMP를 이용한 MIB-II 정보를 바탕으로 하는 분석 방법은 누적 데이터를 기본으로 하는 관리 방법으로 이상 징후의 판단이 실시간 감시에는 적합하지 않은 점이 있다. 따라서, 본 논문에서는 실시간 트래픽 감시를 위해 서브네트워크에 들어오거나 나가는 트래픽의 양을 측정하여 분석하고, 이 정보를 바탕으로 특정 시점 이후의 트래픽 추이를 시계열 분석 방법을 이용하여 미래의 트래픽 양을 예측하는 알고리즘을 시스템으로 구현한다. 예측 알고리즘으로는 AR, MA, ARMA, ARIMA 모델중에 평균 제곱 오차를 최소로 가지는 알고리즘을 선택하여 예측하도록 설계한다. 개발되는 시스템을 망 관리자가 전체 통신 네트워크의 부하 상태를 예상할 수 있게 하여 신속하고 예방적인 대응을 할 수 있다.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.44-45
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• 2000

Shack-Hartmann 센서로부터 얻어진 기울기 정보로부터 파면을 재구성하고 분석하기 위해서는 각각의 점 영상에 대한 위상 구배로부터 파면의 위상을 재구성할 수 있는 수학적인 알고리즘이 필요하다. 파면의 위상을 재구성하기 위한 알고리즘은 Hudgin, Fried, Southwell이 제시한 세 가지 방법에 대한 연구결과가 가장 많이 알려져 있다. 본 연구에서는 CCD 카메라로부터 전송된 디지털 영상에서 각각의 점 영상의 중심점을 추출하여 점 영상의 이동정보로부터 수평과 수직방향의 기울기를 계산하고, 이를 바탕으로 최소제곱법(least-square fitting)을 사용하여 위상을 재구성하였다. 파면의 기울기 정보로부터 파면을 재구성하기 위해 기존의 이론을 바탕으로 행렬계산법을 사용하여 각각의 경우를 일반화하였고, 위상의 복구와 파면의 보정에 따른 해석적인 오차의 관계를 논의하였다. (중략)

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.505-506
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• 2007

일반적으로 저가 장비를 이용한 수신 신호 강도(RSSI)의 측정은 전파의 특성상 다소 부정확한 정보를 제공하고, 이는 최소평균제곱오차(MMSE)를 이용한 위치 추정 방법에 있어 큰 오차 요인으로 작용한다. 따라서 이 논문에서는 수신 신호 강도를 이용한 기존의 위치 추정 방법을 개선하기 위해 센서 네트워크상의 유효 노드선정 알고리즘을 제시한다. 그리고 개선된 방법을 이용하여 센서 네트워크 기반의 실내 위치 추정 시스템을 구현 한다. 끝으로, 개선된 방법의 성능 검증을 위한 실험 결과를 제시 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.139-148
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• 2012

The MLS(Moving Least Squares) Difference Method is a numerical scheme that combines the MLS method of Meshfree method and Taylor expansion involving not numerical quadrature or mesh structure but only nodes. This paper presents an dynamic algorithm of MLS difference method for solving transient solid mechanics problems. The developed algorithm performs time integration by using Newmark method and directly discretizes strong forms. It is very convenient to increase the order of Taylor polynomial because derivative approximations are obtained by the Taylor series expanded by MLS method without real differentiation. The accuracy and efficiency of the dynamic algorithm are verified through numerical experiments. Numerical results converge very well to the closed-form solutions and show less oscillation and periodic error than FEM(Finite Element Method).

• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.206-214
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• 2018

This paper proposes an impact point estimation algorithm of the rifle using microphone sensors. The proposed algorithm resolves the time synchronization problem by expanding the existing ToA (Time of Arrival) method to TDoA (Time Difference of Arrival) method and verifies the performance of the algorithm through the actual shooting experiments. By comparing analysis of the actual and the estimated impact points by the algorithm, it is confirmed that the proposed algorithm has excellent performance by estimating the impact point accurately within the tolerance range.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.19 no.1
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• pp.71-78
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• 1983

A method is given for obtaining low-order models for a linear time-invariant system of high-order by minimizing a functional of the reduction error between the output response of the original system and the low-order model. The method is based on the Astrom's algorithm for the evaluation of complex integrals and the conjugate gradient method of Fletcher-Reeves. An example illustrating the application of this method is given for approximation of a 4-th order system to be used in the load frequency control of generator systems.