• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제17권2호
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• pp.103-113
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• 2013

We analyze the queueing model for leaky bucket (LB) scheme with dynamic arrivals and token rates. In other words, in our LB scheme the arrivals and token rates are changed according to the buffer occupancy. In telecommunication networks, the LB scheme has been used as a policing function to prevent congestion. By considering bursty and correlated properties of input traffic, the arrivals are assumed to follow a Markov-modulated Poisson process (MMPP). We derive the distribution of system state, and obtain the loss probability and the mean waiting time. The analysis is done by using the embedded Markov chain and supplementary variable method. We also present some numerical examples to show the effect of our proposed model.

• Journal of Information Processing Systems
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• 제10권1호
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• pp.119-131
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• 2014

In recent literature on traffic scheduling, the combination of the two-dimensional discrete-time Markov chain (DTMC) and the Markov modulated Poisson process (MMPP) is used to analyze the capacity of VoIP traffic in the cognitive radio system. The performance of the cognitive radio system solely depends on the accuracy of spectrum sensing techniques, the minimization of false alarms, and the scheduling of traffic channels. In this paper, we only emphasize the scheduling of traffic channels (i.e., traffic handling techniques for the primary user [PU] and the secondary user [SU]). We consider the following three different traffic models: the cross-layer analytical model, M/G/1(m) traffic, and the IEEE 802.16e/m scheduling approach to evaluate the performance of the VoIP services of the cognitive radio system from the context of blocking probability and throughput.

• Journal of Communications and Networks
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• 제10권3호
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• pp.287-296
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• 2008

The IEEE 802.11 wireless standard uses the carrier sense multiple access with collision avoidance (CSMA/CA) as its MAC protocol (during the distributed coordination function period). This protocol is an adaptation of the CSMA/CD of the wired networks. CSMA/CA mechanism cannot guarantee quality of service (QoS) required by the application because orits random access method. In this study, we propose a new MAC protocol that considers different types of traffic (e.g., voice and data) and for each traffic type different priority levels are assigned. To improve the QoS of IEEE 802.11 MAC protocols over a multi-channel CSMA/CA, we have developed a new admission policy for both voice and data traffics. This protocol can be performed in direct sequence spread spectrum (DSSS) or frequency hopping spread spectrum (FHSS). For voice traffic we reserve a channel, while for data traffic the access is random using a CSMA/CA mechanism, and in this case a selective reject and push-out mechanism is added to meet the quality of service required by data traffic. To study the performance of the proposed protocol and to show the benefits of our design, a mathematical model is built based on Markov chains. The system could be represented by a Markov chain which is difficult to solve as the state-space is too large. This is due to the resource management and user mobility. Thus, we propose to build an aggregated Markov chain with a smaller state-space that allows performance measures to be computed easily. We have used stochastic comparisons of Markov chains to prove that the proposed access protocol (with selective reject and push-out mechanisms) gives less loss rates of high priority connections (data and voices) than the traditional one (without admission policy and selective reject and push-out mechanisms). We give numerical results to confirm mathematical proofs.

• 한국산림과학회지
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• 제94권6호
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• pp.387-396
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• 2005

이 연구는 점봉산 일대 천연활엽수림의 군집 유형별 천이 경향을 보다 합리적으로 추정하기 위하여 Markov chain의 이론을 응용한 추이확률 모델을 이용하여, 중층의 수종구성으로부터 상층의 수종 구성을 추정하였고, 하층의 수종구성으로부터 중층의 수종 구성을 추정하였다. 개체수 비율로 작성된 대치확률행렬에 개개 수종의 광선 흡수 요인, 번식 요인 및 목재의 이학적 성질을 종합적으로 평가한 극성상지수의 제곱을 가중치로 주어 대치확률행렬을 재구성하여 임분의 천이경향을 예측하였다. 분석된 결과에 의한 각 군집별 안정상태 시기와 상층 및 중층 예측 우점수종을 요약하면 다음과 같다. 당단풍과 까치박달은 생활형의 특성 때문에 상층으로 도약하기는 어렵지만, 높은 구성 비율을 유지할 것으로 예측됨으로서 연구대상 산림생태계에서 생태학적으로 차지하는 비중은 대단히 큰 것으로 평가되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.683-701
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• 2012

IEEE 802.11 standard has achieved huge success in the past decade and is still under development to provide higher physical data rate and better quality of service (QoS). An important problem for the development and optimization of IEEE 802.11 networks is the modeling of the MAC layer channel access protocol. Although there are already many theoretic analysis for the 802.11 MAC protocol in the literature, most of the models focus on the saturated traffic and assume infinite buffer at the MAC layer. In this paper we develop a unified analytical model for IEEE 802.11 MAC protocol in ad hoc networks. The impacts of channel access parameters, traffic rate and buffer size at the MAC layer are modeled with the assistance of a generalized Markov chain and an M/G/1/K queue model. The performance of throughput, packet delivery delay and dropping probability can be achieved. Extensive simulations show the analytical model is highly accurate. From the analytical model it is shown that for practical buffer configuration (e.g. buffer size larger than one), we can maximize the total throughput and reduce the packet blocking probability (due to limited buffer size) and the average queuing delay to zero by effectively controlling the offered load. The average MAC layer service delay as well as its standard deviation, is also much lower than that in saturated conditions and has an upper bound. It is also observed that the optimal load is very close to the maximum achievable throughput regardless of the number of stations or buffer size. Moreover, the model is scalable for performance analysis of 802.11e in unsaturated conditions and 802.11 ad hoc networks with heterogenous traffic flows.

• Spatial Information Research
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• 제5권2호
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• pp.177-183
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• 1997

토지이용 분류 체계상에서의 종류라는 개념은 토지이용 변화의 분류 체계성에 그대로 적용시킬 수가 있다. 본 연구에서는 선형 판별 함수를 원용하는 최우법(Maximum likelihood method)으로 산출되는 토지이용분류의 공간적 결과와 Markov 전이 행렬 방법으로 산출되는 정량적 결과가 상호 보완하는 의미에서 합성모형으로 통합되었다. 본 연구에서는 다변수 판별 함수의 계산법과 Markov 연쇄행렬 계산법에 관하여 토의되고 그 합성 모형을 대상 지역에 실제 적용하여 그 결과 '90년, '95년 토지이용도가 예측 작성되었다. 모형화의 문제 및 예측의 정확도 역시 더욱 토의 되어야 하며 추후 개선의 여지를 남긴다.

• 한국국방경영분석학회지
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• 제6권2호
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• pp.151-184
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• 1980

Simple models for a defense consisting of a preinstalled mine field possibly defended by an anti-tank weapon are derived and analyzed. This paper uses a special Poisson process to model the one or two positions of mines in the mine field. The duel between the anti-tank weapon and offensive tanks crossing the field is modeled with a continuous time Markov chain. Some algebraic solutions and numerical results are obtained for specific scenarios.

• 응용통계연구
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• 제14권2호
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• pp.379-391
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• 2001

본 연구에서는 관심거리가 되고 있는 마코프인쇄 몬테칼로(Markov Chain Monte Carlo, MCMC)방법에 근거한 공간 확률난수 (spatial random variate)생성법과 깁스표본추출법(Gibbs sampling)에 의한 베이지안 분석 방법에 대한 기술적 사항들에 관하여 검토하였다. 먼저 기본적인 확률난수 생성법과 관련된 사항을 살펴보고, 다음으로 조건부명시법(conditional specification)을 이용한 공간 확률난수 생성법을 예를 들어 살펴보기로한다. 다음으로는 이렇게 생성된 공간자료를 분석하기 위하여 깁스표본추출법을 이용한 베이지안 사후분포를 구하는 방법을 살펴보았다.

• 산업공학
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• 제15권1호
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• pp.1-9
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• 2002

Tandem AGV system is obtained by partitioning all workstations into multiple zones assigning a single vehicle to each zone. In this paper, we propose an analytical model to design a tandem AGV system with multi-load AGVs. Using simulation, the performance of the proposed model is shown by comparing a conventional multi-load AGV system.

• Communications for Statistical Applications and Methods
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• 제7권3호
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• pp.817-827
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• 2000

In this paper, we investigate the Bayesian approach to random effect binomial regression models with improper prior due to the absence of information on parameter. We also propose a method of estimating the posterior moments and prediction and discuss some general methods for studying model assessment. The methodology is illustrated with Crowder's Seeds Data. Markov Chain Monte Carlo techniques are used to overcome the computational difficulties.