• Journal of Communications and Networks
• /
• 제13권3호
• /
• pp.240-249
• /
• 2011

Cooperative diversity protocols have attracted a great deal of attention since they are thought to be capable of providing diversity multiplexing tradeoff among single antenna wireless devices. In the high signal-to-noise ratio (SNR) region, cooperation is rarely required; hence, the spectral efficiency of the cooperative protocol can be improved by applying a proper cooperation selection technique. In this paper, we present a simple "cooperation selection" technique based on instantaneous channel measurement to improve the spectral efficiency of cooperative protocols. We show that the same instantaneous channel measurement can also be used for relay selection. In this paper two protocols are proposed-proactive and reactive; the selection of one of these protocols depends on whether the decision of cooperation selection is made before or after the transmission of the source. These protocols can successfully select cooperation along with the best relay from a set of available M relays. If the instantaneous source-to-destination channel is strong enough to support the system requirements, then the source simply transmits to the destination as a noncooperative direct transmission; otherwise, a cooperative transmission with the help of the selected best relay is chosen by the system. Analysis and simulation results show that these protocols can achieve higher order diversity with improved spectral efficiency, i.e., a higher diversity-multiplexing tradeoff in a slow-fading environment.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권12호
• /
• pp.5898-5916
• /
• 2018

In this paper, the downlink performance of multi-cell distributed antenna systems (DAS) with a single user in each cell is investigated. Assuming the channel state information is available at the transmitter, four transmission modes are formulated as combinations of remote antenna units (RAUs) selection and cooperative transmission, namely, non-cooperative transmission without RAU selection (NCT), cooperative transmission without RAU selection (CT), non-cooperative transmission with RAU selection (NCT_RAUS), and cooperative transmission with RAU selection (CT_RAUS). By using probability theory, the cumulative distribution function (CDF) of a user's signal to interference plus noise ratio (SINR) and the system ergodic capacity under the above four modes are determined, and their closed-form expressions are obtained. Furthermore, the system energy efficiency (EE) is studied by introducing a realistic power consumption model of DAS. An expression for determining EE is formulated, and the closed-form tradeoff relationship between spectral efficiency (SE) and EE is derived as well. Simulation results demonstrate their consistency with the theoretical analysis and reveal the factors constraining system EE, which provide a scientific basis for future design and optimization of DAS.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2022년도 추계학술대회
• /
• pp.15-17
• /
• 2022

볼 베어링 선택조립 시스템에서 잉여부품을 최소화하기 위해서는 각 부품의 치수 분포를 파악하여 선택 확률을 최적화하여야 하지만, 복잡한 시스템은 생산 공정에 지연이 일으킨다. 본 논문에서는 볼 베어링 선택조립 시스템에서 빠르고 간단하게 선택 우선순위를 결정할 수 있는 군집 우선 선택 알고리즘을 제안한다. 그리고 실제 볼 베어링 선택조립 공정에서 수집한 데이터로 모의 상황을 가정하고, 군집 우선 선택 알고리즘과 기존 알고리즘을 시뮬레이션하여 잉여부품 발생률과 연산소요시간을 평가한다. 시뮬레이션 결과, 군집 우선 선택 알고리즘이 기존 알고리즘에 비하여 83.8% 적은 잉여부품을 발생하였고, 연산소요시간도 39.7% 단축되었다.

• 한국건설관리학회논문집
• /
• 제6권1호
• /
• pp.49-57
• /
• 2005

Construction labor productivity, which is the greatest source of variation in overall construction productivity, is the critical factor for determining the project performance in terms of time and cost, especially during scheduled overtime when extra time and cost are invested. The objective of this research is to select an appropriate type of probability distribution function representing the variability of daily labor productivity during overtime. Based on the results of statistical data analysis of labor performance during different weekly work hours, lognormal distribution is selected in order to take advantage of easiness of generating correlated random numbers. The selected lognormal distribution can be used for development of a simulation model in construction scheduling, cost analysis, and other applications areas where representation of the correlations between variables are essential.

• 음성과학
• /
• 제9권2호
• /
• pp.135-146
• /
• 2002

Generally a speaker verification system improves its system recognition ratio by regularizing log likelihood ratio, using a speaker model and its background speaker model that are required to be verified. The speaker-based cohort method is one of the methods that are widely used for selecting background speaker model. Recently, Gaussian-based cohort model has been suggested as a virtually synthesized cohort model, and unlike a speaker-based model, this is the method that chooses only the probability distributions close to basic speaker's probability distribution among the several neighboring speakers' probability distributions and thereby synthesizes a new virtual speaker model. It shows more excellent results than the existing speaker-based method. This study compared the existing speaker-based background speaker models and virtual speaker models and then constructed new virtual background speaker model groups which combined them in a certain ratio. For this, this study constructed a speaker verification system that uses GMM (Gaussin Mixture Model), and found that the suggested method of selecting virtual background speaker model shows more improved performance.

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

• 한국정보통신학회논문지
• /
• 제17권10호
• /
• pp.2259-2264
• /
• 2013

본 논문에서는 듀얼 홉 multiple-input multiple-output(MIMO) 중계 시스템에서 직교시공간블록코드 전송과 송신안테나 선택 전송을 선택적으로 이용하는 선택적 MIMO 전송 기술을 제안한다. 독립적인 레일레이 페이딩 채널을 가정하여 선택적 MIMO 전송 기술 기반의 디코딩 후 전달 중계 시스템에 대한 아웃티지 확률을 분석하고, 수치적 결과를 통해 직교시공간블록코드 전송 또는 송신안테나 선택 전송을 모든 홉에서 동일하게 이용하는 기존 시스템과 아웃티지 성능을 비교한다. 또한, 성능 비교를 통해 제안 기술이 아웃티지 성능의 저하 없이 시스템 오버헤드를 감소시킬 수 있음을 보인다.

• 한국전기전자재료학회논문지
• /
• 제30권9호
• /
• pp.551-557
• /
• 2017

It is extremely important to improve methodologies for the lifetime assessment of porcelain insulators. While there has been a considerable amount of work regarding the phenomena of lifetime distributions, most of the studies assume that aging distributions follow the Weibull distribution. However, the true underlying distribution is unknown, giving rise to unrealistic inferences, such as parameter estimations. In this article, we review several distributions that are commonly used in reliability and survival analysis, such as the exponential, Weibull, log-normal, and gamma distributions. Some properties, including the characteristics of failure rates of these distributions, are presented. We use a Bayesian approach for model selection and parameter estimation procedures. A well-known measure, called the Bayes factor, is used to find the most plausible model among several contending models. The posterior mean can be used as a parameter estimate for unknown parameters, once a model with the highest posterior probability is selected. Extensive simulation studies are performed to demonstrate our methodologies.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제4권3호
• /
• pp.273-288
• /
• 2010

In this paper, we propose a cooperative multi-relay scheme for a secondary system to achieve spectrum access along with a primary system. In the primary network, a primary transmitter (PT) transmits the primary signal to a primary receiver (PR). In the secondary network, N secondary transmitter-receiver pairs (ST-SR) selected by a centralized control unit (CCU) are ready to assist the primary network. In particular, in the first time slot, PT broadcasts the primary signal to PR, which is also received by STs and SRs. At STs, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions of the available power to the primary and secondary signals respectively. The combined signal is then broadcasted by STs in a predetermined order. In order to achieve diversity gain, STs, SRs and PT will combine received replicas of the primary signal, using selection combining technique (SC). We derive the exact outage probability for the primary network as well as the secondary network. The simulation results are presented to verify the theoretical analyses.

• 한국통신학회논문지
• /
• 제29권7C호
• /
• pp.907-914
• /
• 2004

본 논문에서는 적응 변조 시스템에 수신안테나 교환(switching) 기술을 적용한 방식을 제안하고, 해당 방식이 제공하는 평균 비트 전송 속도를 최대로 하는 안테나 교환 임계값을 유도하였으며, 그에 따른 성능을 도출하였다. 아울러 제안한 시스템의 성능을 단일 안테나를 사용하는 적응 변조 시스템 그리고 안테나 선택 다이버시티(selection diversity)를 사용하는 적응 변조 시스템과 레일레이 페이딩 채널 환경에서 심볼 당 평균 비트 수와 송신 중단 확률 측면에서 비교하였다. 성능 비교 결과 심볼 당 평균 2 비트의 정보를 전달한다고 했을 때 제안한 방식은 단일 안테나를 사용하는 방식에 비해 1.4 dB의 SNR 이득이 있으며, 송신 중단 확률이 0.1일때 제안한 방식은 단일 안테나를 사용하는 방식에 비해 약 6 dB의 SNR 이득을 얻을 수 있음을 알 수 있었다.