• 한국통신학회논문지
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• 제33권12C호
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• pp.1082-1087
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• 2008

MIMO 시스템에서 ML 검출 기법은 많은 다른 검출기들보다 우수한 성능을 보인다. 그러나 ML 검출기법은 NP-hard 문제로 인해 실제 시스템에서 사용하기 어려운 단점을 가지고 있다. 이것은 polynomial-time 안에 최적의 해 (optimal solution)를 찾을 수 없음을 의미한다. 본 논문에서는 ML problem을 적용한 SDR (Semi-Definite Relaxation)에 궤환기법을 통한 검출 알고리즘을 제안한다. 이는 SDR에 의해 구한 최적의 해를 spectral decomposition을 이용해 우세한 eigenvector를 찾아 송신 신호의 확률 분포를 구하고, 이를 수신 신호에 궤환 시킨다. 이는 또 다른 ML problem으로써 다시 SDR를 통해 최적의 해를 구하고 우세한 eigenvector에 해당하는 송신 신호 확률을 구한다. 이 확률은 ML problem에 해당하는 최적의 값으로 추정 송신 신호를 검출할 수 있다. 이러한 기법을 통해 최적 성능을 갖는 ML 검출 기법의 성능에 보다 더 가깝게 접근하였다.

• International Journal of Computer Science & Network Security
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• 제22권12호
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• pp.51-56
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• 2022

In space based constellation network, users are allowed to enter or leave the network arbitrarily. Hence, the number, identities and transmitted data of active users vary with time and have considerable impacts on the receiver's performance. The so-called problem of multiuser detection means identifying the identity of each active user and detecting the data transmitted by each active user. Traditional methods assume that the number of active users is equal to the maximum number of users that the network can hold. The model of traditional methods are simple and the performance are suboptimal. In this paper a Maximum A Posteriori Probability (MAP) based multiuser detection method is proposed. The proposed method models the activity state of users as Markov chain and transforms multiuser detection into searching optimal path in grid map with BCJR algorithm. Simulation results indicate that the proposed method obtains 2.6dB and 1dB E_b/N₀ gains respectively when activity detection error rate and symbol error rate reach 10^-3, comparing with reference methods.

• 한국정보과학회논문지:소프트웨어및응용
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• 제32권5호
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• pp.385-395
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• 2005

긴 문장 분석은 높은 분석 복잡도로 인해 기계 번역에서 매우 어려운 문제이다. 구문 분석의 복잡도를 줄이기 위하여 문장 분할 방법이 제안되었으며 본 논문에서는 문장 분할의 적용률과 정확도를 높이기 위한 최대 엔트로피 확률 모델 기반의 문장 분할 방법을 제시한다. 분할 위치의 어휘 문맥적 특징을 추출하여 후보 분할 위치를 선정하는 규칙을 학습을 통해 자동적으로 획득하고 각 후보 분할 위치에 분할 확률 값을 제공하는 확률 모델을 생성한다. 어휘 문맥은 문장 분할 위치가 표시된 말뭉치로부터 추출되며 최대 엔트로피 원리에 기반하여 확률 모델에 결합된다. Wall Street Journal의 문장을 추출하여 학습 데이타를 생성하는 말뭉치를 구축하고 네 개의 서로 다른 영역으로부터 문장을 추출하여 문장 분할 실험을 하였다. 실험을 통해 약 $88\%$의 문장 분할의 정확도와 약 $98\%$의 적용률을 보였다. 또한 문장 분할이 효율적인 파싱에 기여하는 정도를 측정하여 분석 시간 면에서 약 4.8배, 공간 면에서 약 3.6배의 분석 효율이 향상되었음을 확인하였다.

• 전기전자학회논문지
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• 제19권4호
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• pp.583-589
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• 2015

HEVC CABAC에서는 하나의 빈을 부호화한 후 확률 모델을 업데이트하고, 업데이트된 확률 모델로 다음 빈을 부호화한다. 기존 CABAC 부호화기는 매 사이클마다 1개의 빈밖에는 부호화하지 못하여 처리율을 향상시킬 수 없었다. 본 논문에서는 확률 모델의 업데이트가 필요없는 우회 빈을 병렬처리 함으로서 처리율을 높인 HEVC CABAC 부호화기를 제안한다. 설계된 CABAC 부호화기는 매 사이클마다 1개의 정규 빈을 처리하거나 최대 4개의 우회 빈을 처리할 수 있으며, 평균적으로 매 사이클당 1.15~1.92개의 빈을 처리한다. 0.18 um 공정에서 합성한 결과, 게이트 수는 메모리를 포함하여 78,698 게이트, 최대 동작 속도는 136 MHz, 최대 처리율은 261 Mbin/s이다.

• 한국학교ㆍ지역보건교육학회지
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• 제24권4호
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• pp.27-37
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• 2023

Objectives: The purpose of this study was to investigate the effect of handgrip strength level on cognitive impairment in hypertensive patients. Methods: This study used the first to eighth year data of the Korean Longitudinal Study of Aging (KLoSA). Of the 10,254 respondents who participated in the basic survey, respondents were included that they were diagnosed with high blood pressure and had no cognitive impairment. The handgrip strength was based on the highest value of handgrip strength for both hands. Cognitive function using MMSE results and 23 points or less were defined as cognitive impairment. Cox models were conducted to estimate the hazard ratios (HRs) of cognitive impairment in relation to handgrip strength adjusting for covariates. Results: In the case of hypertension patients, the probability of cognitive decline decreased by 3.0% every time the maximum handgrip strength increased by 1 unit. In the analysis by age, under the age of 64 had a 1.8% decrease in the probability of cognitive decline whenever the maximum handgrip strength increased by 1 unit, and a 3.6% decrease in those over the age of 65. In the gender analysis, male had a 3.2% decrease in the probability of cognitive decline for every 1 unit increase in the maximum handgrip strength, and female had a 2.6% decrease. Conclusions: The results of this study are expected to be used as basic data for the development of interventions to prevent cognitive decline in hypertensive patients by identifying the effect of handgrip strength level on cognitive decline. It is also expected to be used as basic data for health education on the necessity of increasing muscle strength for hypertension patients in the community.

• 대한기계학회논문집
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• 제18권4호
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• pp.1039-1049
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• 1994

The intermitternt and transient fuel spray have been investigated from the simultaneous measurement of droplet sizes and velocities by using Phase/Doppler Particle Analyzer(PDPA). Measurement have been done on the spray axis and at the edge of the spray near nozzle at various gas-to-liquid density ratios(.rho./sub g//.rho./sub l/) that ranges from those found in free atmospheric jets to conditions typical of diesel engines. Probability density distributions of the droplet size and velocity were obtained from raw data and mathematical probability density functions which can fit the experimental distribations were extracted using the principle of maximum likelihood. In the near nozzle region on the spray axis, droplet sizes ranged from the lower limit of the measurement system to the order of nozzle diameter for all (.rho./sub g/ /.rho./sub l/) and droplet sizes tended to be small on the spray edge. At the edge of spray, average droplet velocity peaked during needle opening and needle closing. The rms intensity is greatly incresed as the radial distance from the nozzle is increased. The probability density function which can best fit the physical breakage process such as breakup of fuel drops is exponecially decreasing log-hypebolic function with 4 parameters.

• 한국지하수토양환경학회지:지하수토양환경
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• 제23권1호
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• pp.41-53
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• 2018

Comprehensive statistical analysis for the 127 groundwater monitoring stations in Jeju Island during 2005~2015 was carried out for the re-establishment of management groundwater level. Three probability distribution functions such as normal distibution, GEV (General Extreme Value) distribution, and Gumbel distribution were applied and the maximum likelihood method was used for parameter estimation of each distribution. AIC (Akaike information criterion) was calculated based on the estimated parameters to determine the proper probability distribution for all 127 stations. The results showed that normal distribution and Gumble distribution were found in 11 stations. Whereas GEV distribution were found in 105 stations, which covered most of groundwater monitoring stations. Therefore, confidence levels should be established in accord with the proper probability distribution when groundwater level management is determined.

• 한국농공학회논문집
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• 제50권6호
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• pp.37-47
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• 2008

Photovoltaic power generation is currently being recognized as one of the most popular sources for renewable resources over the country. Although it is also being adapted to rural area for may reasons, it is important to estimate the magnitudes of power outputs with reliable statistical methodologies, while applying historical daily solar energy data, for correct feasibility analysis. In this study, one of the well-known statistical methodologies is employed to define the appropriate probability distributions for monthly power outputs for the selected rural area, county of Seo-san, province of Chungnam. The results imply that the assumption of normal distributions for several months may lead to incorrect decision-making and therefore lead to the unreliable feasibility analysis. Generalized beta and triangular distributions were found to be superior to normal distribution, when describing monthly probability distributions for daily photovoltaic power. Based on the appropriate distributions resulted from this study, Monte Carlo simulation technique was also applied to provide additional flexible information for the relevant decision makers. This study found out new finding that the probability distributions should be considered to make planning of the photovoltaic power system in rural village unit, in order to give reasonable economic analysis to the decision makers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5249-5267
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• 2016

Cognitive radio is an efficient technique to improve spectrum efficiency and relieve the pressure of spectrum resources. In this paper, we investigate the spectrum sensing period in cooperative relay cognitive radio networks; analyze the relationship between the available capacity and the signal-to-noise ratio of the received signal of second users, the target probability of detection and the active probability of primary users. Finally, we derive the closed form expression of the optimal spectrum sensing period in terms of maximum throughput. We simulate the probability of false alarm and available capacity of cognitive radio networks and compare optimal spectrum sensing period scheme with fixed sensing period one in these performance. Simulation results show that the optimal sensing period makes the cognitive networks achieve the higher throughput and better spectrum sensing performance than the fixed sensing period does. Cooperative relay cognitive radio networks with optimal spectrum sensing period can achieve the high capacity and steady probability of false alarm in different target probability of detection. It provides a valuable reference for choosing the optimal spectrum sensing period in cooperative relay cognitive radio networks.

• 한국정보과학회논문지:정보통신
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• 제29권2호
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• pp.181-187
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• 2002

Connection admission control(CAC), which decides whether or not to accept a new call request, is one of the most Important preventive congestion control techniques in asynchronous transfer mode(ATM) networks. To develop a practical CAC scheme, first we propose a "Modified Cell Loss Probability MP${\nu}"$, which is based on "Virtual Cell Loss Probability P${\nu}"$, taking into account mean burst duration of input traffic source and buffer size in ATM networks. MP${\nu}"$ computes more accurate cell loss probability than P${\nu}"$ without increasing computational complexity, since P${\nu}"$ is formulated simply form the maximum and the average cell rate of input traffic. P${\nu}"$ is overestimated as compared to the real cell loss probability when the mean burst duration is relatively small to the buffer capacity. Then, we Propose a CAC scheme, based on "Modified Virtual Bandwidth(MVB)" method, which may individualize the cell loss probabilities in heterogeneous traffic environments. For the proposed approach, we define the interference intensity to identify interferences between heterogeneous traffic sources and use it as well as MP${\nu}"$ to compute MVB. Our approach is well suitable for ATM networks since it provides high bandwidth utilization and guarantees simple and real time CAC computation for heterogeneous traffic environments.heterogeneous traffic environments.