• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.198-202
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• 1988

In digital mobile communications received speech data are affected by burst errors as well as random errors. To overcome these errors we propose a bit-selective forward error correction scheme for the speech data which is sub-band coded at 13 kbps and transmitted over a 16 kbps channel. For a few error correcting codes the signal-to-noise ratio of error-corrected speech is obtained and compared through the simulation of mobile communication channels.

• Journal of the Korean Data and Information Science Society
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• 제10권1호
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• pp.193-198
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• 1999

The estimation of parameters in regression models with multiplicative errors is usually based on the gamma or log-normal likelihoods. Under reciprocal misspecification, we compare the small sample efficiencies of two sets of estimators via a Monte Carlo study. We further consider the case where the errors are a random sample from a Weibull distribution. We compute the asymptotic relative efficiency of quasi-likelihood estimators on the original scale to least squares estimators on the log-transformed scale and perform a Monte Carlo study to compare the small sample performances of quasi-likelihood and least squares estimators.

• The Journal of the Acoustical Society of Korea
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• 제14권1E호
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• pp.65-72
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• 1995

어레이 계수나 센서 위치에 일어나는 불규칙 오류가 선형조건이 주어진 센서어레이의 성능에 미치는 영향을 계수 벡터 공간에서 분석한다. 불규칙 오류에 의하여 최적계수 벡터와 방해신호 방향의 벡터사이에 비직교성이 존재한다는 것이 발견되었다. 이비직교성을 보상함으로써 영저화 성능을 개선하는 방법이 제안되었다. 컴퓨터 실험결과를 제시하였다.

• 대한수학회지
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• 제45권6호
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• pp.1753-1767
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• 2008

Consider the nonparametric regression model $Y_{ni}\;=\;g(x_{ni})+{\epsilon}_{ni}$ ($1\;{\leq}\;i\;{\leq}\;n$), where g($\cdot$) is an unknown regression function, $x_{ni}$ are known fixed design points, and the correlated errors {${\epsilon}_{ni}$, $1\;{\leq}\;i\;{\leq}\;n$} have the same distribution as {$V_i$, $1\;{\leq}\;i\;{\leq}\;n$}, here $V_t\;=\;{\sum}^{\infty}_{j=-{\infty}}\;{\psi}_je_{t-j}$ with ${\sum}^{\infty}_{j=-{\infty}}\;|{\psi}_j|$ < $\infty$ and {$e_t$} are negatively associated random variables. Under appropriate conditions, we derive a Berry-Esseen type bound for the estimator of g($\cdot$). As corollary, by choice of the weights, the Berry-Esseen type bound can attain O($n^{-1/4}({\log}\;n)^{3/4}$).

• 경영과학
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• 제19권1호
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• pp.117-128
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• 2002

In this Paper we investigate the performance of the five efficiency estimation methods which include the stochastic frontier model estimated by maximum likelihood (SFML), the stochastic frontier model estimated by corrected ordinary least squares (SFCOLS), the data envelopment analysis (DIA) model, the combined estimation of SFML and DEA (SFML + DEA), and the combined estimation of SFCOLS arid DIA (SFCOLS+ DEA) using Monte Carlo analysis. The results include: 1) SFML provides most accurate efficiency estimates for the sample sloe 150 or over,2) SFML+DEAor SFCOLS + DIA Perform better for the cases with sample sloe 25, 50, and low random errors, 3) SFCOLS performs better for the close with sample sloe 25, 50, and very high random errors.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.47-55
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• 2004

Several interpolations for image deformation in PIV were evaluated. The tested interpolation methods are linear, quadratic, truncated sinc, windowed sinc, cubic, Lagrange, Gaussian $2^{nd}\;and\;6^{th}$ interpolators. Bias errors and random errors were evaluated in the range of $0\~3.0$ pixel uniform displacement using synthetic images. We also measured the time cost of each interpolator with respect to kernel size. The cubic interpolator with $6\times6$ kernel showed the best results in terms of the performance and time cost.

• Structural Engineering and Mechanics
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• 제5권6호
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• pp.839-851
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• 1997

Closed-form solutions are analytically derived for stochastic properties of earthquake ground motion fields, which are conditioned by an observed time series at certain observation sites and are characterized by spectra with uncertainties. The theoretical framework presented here can estimate not only the expectations of such simulated earthquake ground motions, but also the prediction errors which offer important information for the field of engineering. Before these derivations are made, the theory of conditional random fields is summarized for convenience in this study. Furthermore, a method for stochastic interpolation of power spectra is explained.

• 문화기술의 융합
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• 제4권3호
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• pp.299-303
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• 2018

일반적으로 대공화기의 체계 명중률을 예측할 때 오차를 각각 고정편기, 가변편기 및 랜덤오차로 분류한 후 가변편기와 랜덤오차는 각 오차의 값의 제곱의 합의 제곱근으로 나타내고 고정편기의 경우는 오차의 합으로 나타낸다. 이때 각 오차의 단위 값의 변화에 관한 고각방향과 방위각 방향의 변위를 나타내는 변수가 가중치로 작용한다. 그리고 이 오차들을 이용하여 정규분포식의 적분을 통하여 체계 명중률을 예측한다. 본 논문에서는 오차의 상관관계를 고려하여 체계 명중률을 예측하는 방법을 제시한다. 본 접근법이 정밀한 체계 명중률을 예측하는데 도움이 된다는 것을 보인다.

• Journal of Radiation Protection and Research
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• 제36권4호
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• pp.183-189
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• 2011

To quantitatively evaluate how setup errors in conjunction with dose gradients contribute to the error in IMRT dose quality assurance (DQA) measurements. The control group consisted of 5 DQA plans of which all individual field dose differences were less than ${\pm}5%$. On the contrary, the examination group was composed of 16 DQA plans where any individual field dose difference was larger than ${\pm}10%$ even though their total dose differences were less than ${\pm}5%$. The difference in 3D dose gradients between the two groups was estimated in a cube of $6{\times}6{\times}6\;mm^3$ centered at the verification point. Under the assumption that setup errors existed during the DQA measurements of the examination group, a three dimensional offset point inside the cube was sought out, where the individual field dose difference was minimized. The average dose gradients of the control group along the x, y, and z axes were 0.21, 0.20, and 0.15 $cGy{\cdot}mm^{-1}$, respectively, while those of the examination group were 0.64, 0.48, and 0.28 $cGy{\cdot}mm^{-1}$, respectively. All 16 plans of the examination group had their own 3D offset points in the cube. The individual field dose differences recalculated at the offset points were mostly diminished and thus the average values of total and individual field dose differences were reduced from 3.1% to 2.2% and 15.4% to 2.2%, respectively. The offset distribution turned out to be random in the 3D coordinate. This study provided the quantitative data that support the large individual field dose difference mainly stems from possible geometric errors (e.g., random setup errors) under the influence of steep dose gradients of IMRT field.

• 정보보호학회논문지
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• 제30권6호
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• pp.1115-1130
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• 2020

최근 출시된 차량에는 다수의 ECU(Electronic Control Unit)가 탑재되어 있고, 각 ECU들은 CAN(Controller Area Network)을 통해 통신함으로써 차량을 효율적으로 제어할 수 있다. 하지만 CAN 통신에는 암호화 및 인증 기술이 적용되어 있지 않고, 접근 제어가 없는 Broadcast 방식으로 통신이 이루어지므로 보안에 취약하다는 문제점이 존재한다. 이러한 취약점을 이용하여 차량 제어 등의 수많은 차량 해킹 공격이 이루어지고 있으며 그에 대응하기 위한 연구 또한 진행되고 있다. 차량 해킹 대응 기술들 중에는 완성차에 탑재된 ECU의 취약점을 분석할 수 있는 CAN Fuzzing 기술이 존재한다. 하지만 기존의 CAN Fuzzing 기술들은 ECU들이 전송하는 CAN 메시지 구조를 고려하지 않고 Random한 방식으로 Fuzzing을 진행하기 때문에 많은 시간이 소요된다. 또한, 기존 CAN Fuzzing 기술은 Fuzzing 결과를 모니터링하는 방법에도 한계점이 존재한다. 이러한 CAN Fuzzing 기술의 한계를 해결하고자 본 논문에서는 CAN 메시지의 구조를 분석하고, 이를 바탕으로 ECU의 이상 작동 현상을 유발시킬 수 있는 Fuzzing 입력값을 생성하는 Non-Random CAN Fuzzing 기법을 제안한다. Non-Random CAN Fuzzing은 기존 Random CAN Fuzzing에 비해 소요되는 시간을 절약할 수 있고, 이를 통해 SW 구현 오류 혹은 CAN DBC(Database CAN) 설계 오류 등으로 인해 존재할 수 있는 ECU의 이상 작동 현상과 연관된 CAN 메시지들을 빠르게 발견할 수 있다. 제안하는 Non-Random CAN Fuzzing의 성능을 평가하기 위해 제안 기법을 실제 차량에 적용하였으며 ECU에 이상 작동 현상을 일으킬 수 있는 CAN 메시지를 확인하였다.