• 대한원격탐사학회지
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• 제21권5호
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• pp.417-423
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• 2005

A fuzzy approach using an EM algorithm for image classification is presented. In this study, a double compound stochastic image process is assumed to combine a discrete-valued field for region-class processes and a continuous random field for observed intensity processes. The Markov random field is employed to characterize the geophysical connectedness of a digital image structure. The fuzzy classification is an EM iterative approach based on mixture probability distribution. Under the assumption of the double compound process, given an initial class map, this approach iteratively computes the fuzzy membership vectors in the E-step and the estimates of class-related parameters in the M-step. In the experiments with remotely sensed data, the MRF-based method yielded a spatially smooth class-map with more distinctive configuration of the classes than the non-MRF approach.

• 한국시뮬레이션학회:학술대회논문집
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• 한국시뮬레이션학회 1999년도 추계학술대회 논문집
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• pp.75-80
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• 1999

This paper presents a new method to find a optimal solution for stochastic system. This method uses Genetic Algorithm(GA) and simulation. GA is used to search for new alternative and simulation is used to evaluate alternative. The stochastic system has one or more random variables as inputs. Random inputs lead to random outputs. Since the outputs are random, they can be considered only as estimates of the true characteristics of they system. These estimates could greatly differ from the corresponding real characteristics for the system. We need multiple replications to get reliable information on the system. And we have to analyze output data to get a optimal solution. It requires too much computation to be practical. We address the problem of reducing computation. The procedure on this paper use GA character, an iterative process, to reduce the number of replications. The same chromosomes could exit in post and present generation. Computation can be reduced by using the information of the same chromosomes which exist in post and present current generation.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.505-508
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• 2000

The success of target reconstruction in SAR(Synthetic Aperture Radar) imaging system is greatly dependent on the coherent detection. Primary causes of incoherent detection are uncompensated target or sensor motion, random turbulence in propagation media, wrong path in radar platform, and etc. And these appear as multiplicative phase error to the echoed signal, which consequently, causes fatal degradations such as fading or dislocation of target image. In this paper, we present iterative phase error estimation scheme which uses echoed data in all temporal frequencies. We started with analyzing wave equation for one point target and extend to overall echoed data from the target scene - The two wave equations governing the SAR signal at two temporal frequencies of the radar signal are combined to derive a method to reconstruct the complex phase error function. Eventually, this operation attains phase error correction algorithm from the total received SAR signal. We verify the success of the proposed algorithm by applying it to the simulated spotlight-mode SAR data.

• Communications for Statistical Applications and Methods
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• 제31권1호
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• pp.65-85
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• 2024

The tail probability of a function of a multivariate random variable is not easy to estimate by the crude Monte Carlo simulation. When the occurrence of the function value over a threshold is rare, the accurate estimation of the corresponding probability requires a huge number of samples. When the explicit form of the cumulative distribution function of each component of the variable is known, the inverse transform likelihood ratio method is directly applicable scheme to estimate the tail probability efficiently. The method is a type of the importance sampling and its efficiency depends on the selection of the importance sampling distribution. When the cumulative distribution of the multivariate random variable is represented by a copula and its marginal distributions, we develop an iterative algorithm to find the optimal importance sampling distribution, and show the convergence of the algorithm. The performance of the proposed scheme is compared with the crude Monte Carlo simulation numerically.

• 한국정보과학회논문지:소프트웨어및응용
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• 제36권6호
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• pp.451-461
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• 2009

적응적 랜덤 테스팅(Adaptive Random Testing, ART)은 테스트 케이스의 효율적인 선택을 통해 순수 랜덤 테스팅(Random Testing, RT)보다 더 적은 수의 테스트 케이스를 이용해 입력 도메인 내의 오류를 찾는 것을 목적으로 한다. ART 기법 중 하나인 입력 도메인 반복 분할 기법(ART through Iterative Partitioning, IP-ART)은 초기 ART 기법의 단점인 많은 연산량을 입력 도메인 분할에 의해 효율적으로 개선되도록 하였으며, 입력 도메인 확장을 이용한 IP-ART(IP-ART with Enlarged Input Domain, EIP-ART)는 IP-ART의 테스트 케이스 분포 특징을 이용하여 추가적인 성능 향상과 확장성을 제공하였다. 하지만 EIP-ART는 입력 도메인 확장에 따라 발생하는 부하로 인해 테스트 케이스 생성에 오랜 시간을 요구하기 때문에 이의 개선이 필요하다. 따라서 본 논문에서는 두 가지의 추가 부하를 유발하지 않는 테스트 케이스 분포 조절 기법을 제안하고, 이들의 성능 개선 가능성을 실험을 통해 확인하였으며, 실험 결과, 제안된 두 기법 중 입력 도메인 타일링 기법이 모든 환경에서 더 우수한 성능 및 확장성을 갖는 것으로 확인되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권12호
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• pp.4567-4583
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• 2021

This study proposes an analytical approximation algorithm based on extreme value theory (EVT) for the inverse of the power of the incomplete Gamma function. First, the Gumbel function is used to approximate the power of the incomplete Gamma function, and the corresponding inverse problem is transformed into the inversion of an exponential function. Then, using the tail equivalence theorem, the normalized coefficient of the general Weibull distribution function is employed to replace the normalized coefficient of the random variable following a Gamma distribution, and the approximate closed form solution is obtained. The effects of equation parameters on the algorithm performance are evaluated through simulation analysis under various conditions, and the performance of this algorithm is compared to those of the Newton iterative algorithm and other existing approximate analytical algorithms. The proposed algorithm exhibits good approximation performance under appropriate parameter settings. Finally, the performance of this method is evaluated by calculating the thresholds of space-time block coding and space-frequency block coding pattern recognition in multiple-input and multiple-output orthogonal frequency division multiplexing. The analytical approximation method can be applied to other related situations involving the maximum statistics of independent and identically distributed random variables following Gamma distributions.

• 전자공학회논문지CI
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• 제46권3호
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• pp.64-76
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• 2009

적응적 랜덤 테스팅 (Adaptive Random Testing, ART) 기법 중 입력 도메인 반복 분할을 이용한 기법(ART through Iterative Partitioning, IP-ART)은 초기 ART 기법이 가지는 단점인 많은 거리 연산량을 입력 도메인 반복 분할 기법을 이용해 효율적으로 개선하였다. 또한 입력 도메인 확장을 이용한 IP-ART 기법(IP-ART with Enlarged Input Domain, EIP-ART)은 IP-ART가 가지는 특징을 효과적으로 이용해 IP-ART에서 보이는 테스트 케이스 분포 불균일 현상을 완화시켰으며, 다양한 환경에서 좋은 성능을 보인다. 하지만 EIP-ART는 입력 도메인 확장에 의해 발생되는 부수적인 부하로 인해 테스트 케이스 선택이 지연된다는 단점을 가진다. 이에 따라 본 논문에서는 입력 도메인의 확장 없이, IP-ART의 변화를 통한 성능 개선가능성 확인을 위해 테스트 케이스 분포에 영향을 줄 수 있는 세 가지 조건을 정의하고 이들 각각이 기법에 미치는 영향을 평가하였으며, 실험을 통해 정의된 세 가지 조건 중 제한 영역 관리 조건이 기법의 성능에 가장 긍정적인 영향을 주는 것을 확인하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제14권4호
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• pp.365-375
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• 2014

This paper proposes an abnormal V-shaped-error-free non-blind deconvolution technique featuring an adaptively segmented forward-problem based iterative deconvolution (ASDCN) process. Unlike the algebraic based inverse operations, this eliminates any operations of differential and division by zero to successfully circumvent the issue on the abnormal V-shaped error. This effectiveness has been demonstrated for the first time with applying to a real analysis for the effects of the Random Telegraph Noise (RTN) and/or Random Dopant Fluctuation (RDF) on the overall SRAM margin variations. It has been shown that the proposed ASDCN technique can reduce its relative errors of RTN deconvolution by $10^{13}$ to $10^{15}$ fold, which are good enough for avoiding the abnormal ringing errors in the RTN deconvolution process. This enables to suppress the cdf error of the convolution of the RTN with the RDF (i.e., fail-bit-count error) to $1/10^{10}$ error for the conventional algorithm.

• 한국통신학회논문지
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• 제35권7C호
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• pp.611-617
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• 2010

본 논문에서는 직렬 연접 길쌈 부호와 LDPC 부호를 이용하여 수직자기기록 채널에서의 성능을 조사하였다. 실험과정에서 기록 밀도는 1.7, 2.0, 2.4, 2.8 일 때를 각각 실험하였다. 직렬 연접 길쌈 부호는 LDPC 부호보다 복호기의 구현 복잡도가 더 낮다. 직렬 연접 부호는 순환 구조적 길쌈 부호의 부호기와 복호기, 그리고 프리코더와 인터리버로 이루어져 있다. 본 실험에서 직렬 연접 길쌈 부호의 복호 알고리즘은 메시지 전달 알고리즘을 이용하였으며, LDPC 부호의 복호 알고리즘은 Sum Product 알고리즘을 이용하였다. 신호 검출기와 오류정정부호 사이에 반복 복호 기법을 적용한 터보등화기 기법을 적용하였고, 기록 밀도가 높아짐에 따라 직렬 연접 길쌈 부호가 LDPC 부호 보다 더 효율 적인 것을 보였다.

• Nuclear Engineering and Technology
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• 제33권1호
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• pp.25-33
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• 2001

To determine the pin power distribution without disassembling, HANARO fuel assemblies are gamma-scanned and then the distribution is reconstructed tv using the tomography method. The iterative least squares method (ILSM and the wavelet singular value decomposition method (WSVD) are chosen to solve the problem. An optimal convergence criterion is used to stop the iteration algorithm to overcome the potential divergence in ILSM. WSVD gives better results than ILSM , and the average values from the two methods give the best results. The RMSE (root mean square errors) to the reference data are 5.1, 6.6, 5.0, 6.5, and 6.4% and the maximum relative errors are 10.2, 13.7, 12.2, 13.6, and 14.3%, respectively. It is found that the effect of random positions of the pins is important. Although the effect can be accommodated by the iterative calculations simulating the random positions, the use of experimental equipment with a slit covering the whole range of the assembly horizontally is recommended to obtain more accurate results. We made a new apparatus using the results of this study and are conducting an experiment in order to obtain more accurate results.