• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.155-156
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• 2008

This paper provides a general and compact expression for the probability density function (pdf) and the moment-generating function (MGF) of the maximal ratio combiner output over Rayleigh fading channels. It is then used to derive closed form expression outage probability for repetition code problem. A variety of simulations is performed and shows that they match exactly with analytic ones.

• 한국음향학회지
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• 제37권1호
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• pp.31-38
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• 2018

2015년 5월 제주 서남부 해역에서 실시된 SAVEX15(Shallow Water Acoustic Variability EXperiment 2015) 데이터를 기반으로 내부파가 소나의 예상탐지확률(Predictive Probability of Detection, PPD)에 미치는 영향에 대하여 분석하였다. 제주 서남부 해역은 내부파, 수중음파채널 등으로 인하여 복잡한 해수 유동이 존재하는 해역이다. 본 논문에서는 확률적인 접근 방법을 통하여 소나의 성능을 예측하였다. SAVEX15 데이터 중 11 kHz ~ 31 kHz 대역대의 LFM(Linear Frequency Modulation), MLS(Maximum Length Sequence) 신호를 데이터 처리 하여 음원과 수신기가 약 2.8 km 떨어진 지점에서의 전달손실(Transmission Loss, TL)과 소음준위(Noise Level, NL) 값을 산출하였다. TL과 NL의 확률밀도함수(Probability Density Function, PDF)를 합성곱하여 신호이득에 대한 확률밀도 함수를 구하고 음원과 수신기의 수심에 따른 예상탐지확률을 산출하였다. 솔리톤 패킷과 내부조석 등의 내부파가 존재할 때 시간에 따른 예상탐지확률의 변화를 분석한 결과 각각 다른 양상으로 예상탐지확률 값에 영향을 주는 것을 확인하였다.

• 한국통신학회논문지
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• 제36권10B호
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• pp.1210-1215
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• 2011

이 논문에서는 다중경로 특성과 충격성 잡음이 있는 수중 통신 채널에 대해 확률밀도함수 정합 방법에 근거한 적응등화 알고리듬을 소개하고 결정 궤환을 적용한 확률밀도함수 정함 알고리듬을 제안하였다. 기존의 제곱평균오차 기반의 최소평균제곱 (LMS) 알고리듬은 수중통신 채널의 충격성 잡음과 다중경로 채널을 보상하지 못하는 현상을 보였다. 충격성 잡음에 효과적인 면역성을 보인 선형 확률밀도함수 정합 알고리듬도 열악한 다중경로 환경에서는 만족스럽지 못한 성능을 나타났다. 한편, 제안한 결정 궤환 구조의 비선형 확률밀도함수 정합 알고리듬은 수중 통신 채널의 다중경로 특성과 충격성 잡음에 대해 탁월한 강인성을 가짐을 모의실험을 통해 입증되었다.

• 한국해양공학회지
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• 제28권5호
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• pp.396-403
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• 2014

This paper considered the prediction of the tension force in the design of a TLP tendon, particularly focusing on the springing problem. Springing is an important parameter that exerts a large tension in special cases. It is a nonlinear phenomenon and requires the 2nd-order wave loads to solve. In this paper, a new prediction method for springing and the resultant extreme tension on the tendon of a TLP is introduced. Using the 2nd-order response function computed using the commercial program WADAM, the probability density function of the 2nd-order tension is obtained from an eigenvalue analysis using a quadratic transfer function and sea spectra. A new method is then suggested to predict the extreme tension loads with respect to the number of occurrences. It is shown that the PDF suggested in this study properly predicts the extreme tension in comparison with the time histories of the 2nd-order tension. The expected tension force is larger than that from a linear analysis in the same time windows. This supports the use of the present method to predict the tension due to springing.

• Smart Structures and Systems
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• 제21권5호
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• pp.591-600
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• 2018

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, $R^2$. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

• 한국환경보건학회지
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• 제45권5호
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• pp.497-510
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• 2019

Objectives: The aim of this study was to secure the reliability of using the CalTOX model when evaluating LADD (or ADD) and Risk (or HQ) among local residents for the emission of BTEX (Benzene, Toluene, Ethylbenzene, Xylene) and by closely examining the difference in the confidence interval of the assessment outcomes according to the difference in the probability density function of input variables. Methods: The assessment was made by dividing it according to the method ($I^{\dagger}$) of inputting the probability density function in meteorological variables of the model with log-normal distribution and the method of inputting ($II^{\ddagger}$) after grasping the optimal probability density function using @Risk. A T-test was carried out in order to analyze the difference in confidence interval of the two assessment results. Results: It was evaluated to be 1.46E-03 mg/kg-d in LADD of Benzene, 1.96E-04 mg/kg-d in ADD of Toluene, 8.15E-05 mg/kg-d in ADD of Ethylbenzene, and 2.30E-04 mg/kg-d in ADD of Xylene. As for the predicted confidence interval in LADD and ADD, there was a significant difference between the $I^{\dagger}$ and $II^{\ddagger}$ methods in $LADD_{Inhalation}$ for Benzene, and in $ADD_{Inhalation}$ and ADD for Toluene and Xylene. It appeared to be 3.58E-05 for risk in Benzene, 3.78E-03 for HQ in Toluene, 1.48E-03 for HQ in Ethylbenzene, and 3.77E-03 for HQ in Xylene. As a result of the HQ in Toluene and Xylene, the difference in confidence interval between the $I^{\dagger}$ and $II^{\ddagger}$ methods was shown to be significant. Conclusions: The human risk assessment for BTEX was made by dividing it into the method ($I^{\dagger}$) of inputting the probability density function of meteorological variables for the CalTOX model with log-normal distribution, and the method of inputting ($II^{\ddagger}$) after grasping the optimal probability density function using @Risk. As a result, it was identified that Risk (or HQ) is the same, but that there is a significant difference in the confidence interval of Risk (or HQ) between the $I^{\dagger}$ and $II^{\ddagger}$ methods.

• 대한산업공학회지
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• 제13권2호
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• pp.105-115
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• 1987

Although there are many theoretical methods for the transformation of random variables. it is difficult to find probability density functions for the new random variables because of the complexity in mathematics. The author developed a simulation model solving the above difficulties using FBI (Fortran Based Interpreter) routines. The FBI is a kind of language Interpreter analyzing the arithmetic statement in character data forms. In this paper. the FBI routines will be explained and the structure and applications of simulation model will be also demonstrated. Polynomial curve fitting method is applied to define the probability density function which can not be defined by well-known pdf. This program can also be used for instructing mathematical statistics and identifying distribution of the simulated data.

• Journal of Communications and Networks
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• 제14권1호
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• pp.27-33
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• 2012

In this paper, a new blind signal processing scheme for equalization in fading and impulsive-noise channel environments is introduced based on probability density functionmatching method and a set of Dirac-delta functions. Gaussian kernel of the proposed blind algorithm has the effect of cutting out the outliers on the difference between the desired level values and impulse-infected outputs. And also the proposed algorithm has relatively less sensitivity to channel eigenvalue ratio and has reduced computational complexity compared to the recently introduced correntropy algorithm. According to these characteristics, simulation results show that the proposed blind algorithm produces superior performance in multi-path communication channels corrupted with impulsive noise.

• 천문학회지
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• 제53권2호
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• pp.49-57
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• 2020

We present numerical simulations of decaying hydrodynamic turbulence initially driven by solenoidal (divergence-free) and compressive (curl-free) drivings. Most previous numerical studies for decaying turbulence assume an isothermal equation of state (EOS). Here we use a polytropic EOS, P ∝ ρ^γ, with polytropic exponent γ ranging from 0.7 to 5/3. We mainly aim at determining the effects of γ and driving schemes on the decay law of turbulence energy, E ∝ t^-α. We additionally study probability density function (PDF) of gas density and skewness of the distribution in polytropic turbulence driven by compressive driving. Our findings are as follows. First of all, we find that even if γ does not strongly change the decay law, the driving schemes weakly change the relation; in our all simulations, turbulence decays with α ≈ 1, but compressive driving yields smaller α than solenoidal driving at the same sonic Mach number. Second, we calculate compressive and solenoidal velocity components separately and compare their decay rates in turbulence initially driven by compressive driving. We find that the former decays much faster so that it ends up having a smaller fraction than the latter. Third, the density PDF of compressively driven turbulence with γ > 1 deviates from log-normal distribution: it has a power-law tail at low density as in the case of solenoidally driven turbulence. However, as it decays, the density PDF becomes approximately log-normal. We discuss why decay rates of compressive and solenoidal velocity components are different in compressively driven turbulence and astrophysical implication of our findings.

• 한국전자파학회논문지
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• 제9권3호
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• pp.347-358
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• 1998

복잡하고 다양한 전파 환경을 라이시안 채널로 모델링할 수 있는 가능성에 대해서 검토해 보았다. 라이시안 채널에서의 수신 신호를 컴퓨터 시뮬레이터를 제작하여 모의 실험하였고, 모의 실험된 신호의 PDF(포락선 크기의 분포), PSD(Power Spectral Density), LCR(Level Crossing Rate), ADF(Average Duration of Fades), BER(Bit Error Rate)를 이론치와 비교한 결과 매우 잘 일치함을 확인할 수 있었다.