• 한국통신학회논문지
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• 제32권7A호
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• pp.710-716
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• 2007

본 논문에서는 OFDM 셀룰라 네트워크에서 셀 가장자리에 위치한 사용자를 위한 다운링크 동일채널간섭(CCI) 제거 기법을 소개한다. 기지국간의 협력적 심볼 전송은 동일 심볼을 다른 기지국에서 상이한 부반송파를 사용하여 전송함으로서 이루어진다. 단말기에서는 전송된 심볼을 추정하기 위하여 연판정 최대우도 동일채널간섭 제거기(soft decision maximum likelihood CCI canceler)와 수정된 최대비 합성법 (modified maximum ratio combining (M-MRC))을 적용하며, 합성법에 사용된 가중치는 협력 기지국과 단말기 사이의 채널 상수에 의해서 유도된다. 시뮬레이션 결과로부터 제안된 기법이 주파수 선택적 페이딩 채널과 주파수 비선택적 페이딩 채널에서 각기 9 dB와 6dB의 SIR 이득을 보임을 알 수 있다.

• 산업경영시스템학회지
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• 제28권3호
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• pp.26-35
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• 2005

This paper is intended to compare the hazard rate estimations from Bayesian approach and maximum likelihood estimate(MLE) method. Hazard rate frequently involves unknown parameters and it is common that those parameters are estimated from observed data by using MLE method. Such estimated parameters are appropriate as long as there are sufficient data. Due to various reasons, however, we frequently cannot obtain sufficient data so that the result of MLE method may be unreliable. In order to resolve such a problem we need to rely on the judgement about the unknown parameters. We do this by adopting the Bayesian approach. The first one is to use a predictive distribution and the second one is a method called Bayesian estimate. In addition, in the Bayesian approach, the prior distribution has a critical effect on the result of analysis, so we introduce the method using computerized-simulation to elicit an effective prior distribution. For the simplicity, we use exponential and gamma distributions as a likelihood distribution and its natural conjugate prior distribution, respectively. Finally, numerical examples are given to illustrate the potential benefits of the Bayesian approach.

• 한국통신학회논문지
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• 제32권2C호
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• pp.160-165
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• 2007

In this paper, we propose a novel signal detection method that achieves the maximum likelihood (ML) performance but requires much less computational complexity than the ML detection. When the well-known linear decoding method is used for space-time block coded (STBC) OFDM systems in fast-fading channels, co-channel interference (CCI) as well as inter-carrier interference (ICI) occurs. A maximum likelihood (ML) method can be employed to deal with the CCI; however, its computational complexity is very high. In this paper, we propose a signal detection method for orthogonal space-time coded OFDM systems that achieves the similar error performance as the ML method, but requires much less computational complexity.

• Communications for Statistical Applications and Methods
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• 제8권1호
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• pp.219-227
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• 2001

Another approach (multi-parameter measurement method) of interlaboratory studies of test methods is presented. When the unrestricted normal likelihood for the fixed latent variable model is unbounded, we propose a me쇙 of restricting the parameter space by formulating realistic alternative hypothesis under which the likelihood is bounded. A simulation study verified the claim of conservatism of level of significance based on assumptions about central chi-square distributed test statistics and on Bonferroni approximations. We showed a randomization approach that furnished empirical significance levels would be better than a Bonferroni adjustment.

• 한국정보처리학회논문지
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• 제1권4호
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• pp.511-516
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• 1994

본 논문에서는 전송 잡음 환경 하에서 전자파 산란 물체의 식별을 위하여 사용하 는 파라메타 측정 기법에 관한 연구이다. 최대 유사측정(Maximum Likelihood Estimation : MLE)기법은 물체 식별에 변형하여 응용되면 종래 잘 알려져 사용되어온 함수군속(Pencil of Functions) 기법보다 더 좋은 측정결과를 가진다는 것을 본 논문 은 보여주고 있다. MLE 기법을 포함하여 파라메타 식별을 위한 도구로서 지금까지 여러 제안기법들이 있었으나, 본 논문에서는 샘플 데이타의 길이에 관계없이 목표시 스템의 파라메타 양에만 관계하는 최소단위의 메트릭스 연산이 사용됨을 보여주므로 잡음이 상재하는 추출 데이타로부터 목표식별에 가장 강한 강점이 있다.

• 한국인터넷방송통신학회논문지
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• 제8권3호
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• pp.9-14
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• 2008

본 논문에서는 Wireless PAN을 위한 MIMO-OFDM시스템에서 근거리 데이터 전송과 더불어 주변장치간 원활한 통신을 위해 채널 sounding 기법을 제안한다. 제안된 기법은 전력 확산 지연을 통해서 임펄스 응답의 지속시간을 파악하며, 감쇠 특성을 갖는 전력 지연 프로 파일(power delay profile) 모델링 하였고, ML(maximum likelihood) 기법으로 채널 응답 계수를 얻었다. Channel sounding 기법을 통해 측정한 크기, 위상, 지연의 변수 값으로 송신단과 수신단간의 채널 전파 특성이 측정 된다. 이 측정된 채널 정보들이 수신단에서 채널 상태를 파악하며, 수신단에서 이 채널 정보를 근거로 통신 링크 성능 향상과 신뢰성을 증대시킬 수 있는 기법을 제안하였다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제36권4호
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• pp.273-282
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• 2009

소프트웨어 프로젝트 데이터를 이용한 각종 분석 예측 모델 생성시 직면하는 문제 중 하나는 데이터에 포함된 결측값이며 이에 대한 효과적인 방안은 결측값 대치 법이다. 대표적인 결측값 대치법인 K 최근접 이웃 대치법은 대치과정에서 결측값을 포함하는 인스턴스의 관측정보를 활용하지 못한다는 단점이 있다. 본 연구에서는 이러한 단점을 극복하기 위해 K 최근접 이웃 대치법과 최대 우도 추정법을 결합한 새로운 소프트웨어 프로젝트 수치 데이터용 결측값 대치법을 제안한다. 또한 결측값 대치법의 정확도를 비교하기 위한 새로운 측도를 함께 제안한다.

• 대한의용생체공학회:의공학회지
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• 제37권1호
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• pp.21-30
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• 2016

Weibull distribution with two parameters, shape (k) and scale (s) parameters are used to model the fatigue failure analysis due to periodic vortex shedding of the synovial fluid in knee joints. In order to determine the later parameter, a suitable statistical model is required for velocity distribution of synovial fluid flow. Hence, wide applicability of Weibull distribution in life testing and reliability analysis can be applied to describe the probability distribution of synovial fluid flow velocity. In this work, comparisons of three most widely used methods for estimating Weibull parameters are carried out; i.e. the least square estimation method (LSEM), maximum likelihood estimator (MLE) and the method of moment (MOM), to study fatigue failure of bone joint due to periodic vortex shedding of synovial fluid. The performances of these methods are compared through the analysis of computer generated synovial fluidflow velocity distribution in the physiological range. Significant values for the (k) and (s) parameters are obtained by comparing these methods. The criterions such as root mean square error (RMSE), coefficient of determination ($R^2$), maximum error between the cumulative distribution functions (CDFs) or Kolmogorov-Smirnov (K-S) and the chi square tests are used for the comparison of the suitability of these methods. The results show that maximum likelihood method performs well for most of the cases studied and hence recommended.

• Journal of Astronomy and Space Sciences
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• 제28권4호
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• pp.267-271
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• 2011

I developed an enhanced correction method for Ricean bias which occurs in linear polarization measurement. Two known methods for Ricean bias correction are reviewed. In low signal-to-noise area, the method based on the mode of the equation gives better representation of the fractional polarization. But a caution should be given that the accurate estimation of noise level, i.e. ${\sigma}$ of the polarized flux, is important. The maximum likelihood method is better choice for high signal-to-noise area. I suggest a hybrid method which uses the mode of the equation at the low signal-to-noise area and takes the maximum likelihood method at the high signal-to-noise area. A modified correction coefficient for the mode solution is proposed. The impact on the depolarization measure analysis is discussed.

• Communications for Statistical Applications and Methods
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• 제30권4호
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• pp.411-421
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• 2023

This paper provides a new estimation equation based on the concept of a minimum distance between the empirical and theoretical distribution functions under the most widely used progressive Type-II censoring scheme. For illustrative purposes, simulated and real datasets from a three-parameter Weibull distribution are analyzed. For comparison, the most popular estimation methods, the maximum likelihood and maximum product of spacings estimation methods, are developed together. In the analysis of simulated datasets, the excellence of the provided estimation method is demonstrated through the degree of the estimation failure of the likelihood-based method, and its validity is demonstrated through the mean squared errors and biases of the estimators obtained from the provided estimation equation. In the analysis of the real dataset, two types of goodness-of-fit tests are performed on whether the observed dataset has the three-parameter Weibull distribution under the progressive Type-II censoring scheme, through which the performance of the new estimation equation provided is examined.