• Journal of Communications and Networks
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• 제9권3호
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• pp.229-235
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• 2007

This paper analyzes the performance of a Bluetooth piconet in error-prone environments. A statistical characterization of a waiting time, an end-to-end delay, and a goodput are derived analytically in terms of the arrival rates, the number of slaves, and the packet error rate (PER). For simplicity, half-symmetric piconet is assumed in this analysis. Both exhaustive and limited scheduling are considered. The analytic results are validated by simulations.

• 제어로봇시스템학회논문지
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• 제18권8호
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• pp.719-724
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• 2012

A traffic detection system is a device that collects traffic information around an intersection. Most existing traffic detection systems provide very limited traffic information for signal control due to the restriction of vehicle detection area. A signal control scheme determines the transition among signal phases and the time that a phase lasts for. However, the existing signal control scheme do not resolve the traffic congestion effectively since they use restricted traffic information. In this paper, a new traffic detection system with a zone division signal control scheme is proposed to provide correct and detail traffic information and decrease the vehicle's waiting time at the intersection. The traffic detection system obtains traffic information in a way of vehicle-to-roadside communication between vehicles and sensor network. A new signal control scheme is built to exploit the sufficient traffic information provided by the proposed traffic detection system efficiently. Simulation results show that the proposed signal control scheme has 121 % and 56 % lower waiting time and delay time of vehicles at an intersection than other fuzzy signal control scheme.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
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• pp.524-529
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• 1989

In this paper, an approximate sojourn time distribution is obtained for cyclic service systems. We consider symmetric and limited service systems in which each queue has an infinite capacity. The combined service time is defined which consists of the frame service time and server waiting time that is approximated by two cases of the uniform and exponential distributions. The approximate sojourn time distribution is obtained from the Pollaczek-Khinchine formula where the combined service time is used for the service time in the M/G/I model. And some numerical examples are given to validate the suggested approximate analysis.

• 대한산업공학회지
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• 제20권4호
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• pp.37-50
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• 1994

The efficiency of production system is mainly considered in the viewpoints of reducing the average flow time of products and increasing the throughput rate. The performance in these viewpoints is very depending on job dispatching of each machine in real time operation, in the case jobs are released dynamically. In this research, a heuristic dynamic dispatching method is suggested for a flow shop case where new jobs with random process times are released by an interarrival time distribution and the number of waiting jobs between each pair of machines are limited. The proposed method has been compared with some priority rule-based dispatching methods by simulation and found to be superior to them.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.895-909
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• 2013

Distributed Denial-of-Service (DDoS) attacks towards name servers of the Domain Name System (DNS) have threaten to disrupt this critical service. This paper studies the vulnerability of the cache server to the flooding DNS query traffic. As the resolution service provided by cache server, the incoming DNS requests, even the massive attacking traffic, are maintained in the waiting queue. The sojourn of requests lasts until the corresponding responses are returned from the authoritative server or time out. The victim cache server is thus overloaded by the pounding traffic and thereafter goes down. The impact of such attacks is analyzed via the model of queuing process in both cache server and authoritative server. Some specific limits hold for this practical dual queuing process, such as the limited sojourn time in the queue of cache server and the independence of the two queuing processes. The analytical results are presented to evaluate the impact of DDoS attacks on cache server. Finally, numerical results are provided for further analysis.

• 한국항해항만학회지
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• 제40권1호
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• pp.35-41
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• 2016

항만 혼잡은 항만의 서비스 경쟁력 및 선화주의 항만 선택 요인으로 중요하게 인식된다. 우리나라 항만의 현행 체선지표인 체선율은 항만별 선박척수 비율로 단순 산정되어 항만의 고객인 선화주의 항만 선택 결정 및 항만관리자의 항만 개발 및 관리 운영 정책 수립 의사결정에 제한적으로 활용된다. 본 연구는 항만운영정보시스템과 해상교통관제시스템 원시자료를 활용하여 우리나라 항만의 선박 입출항 서비스 수준을 측정하고자 약 10년간의 부두별, 선종별 대기율을 산정하였다. 컨테이너선박의 대기율은 4% 미만, 비컨테이너선박의 대기율은 15% 미만으로 UNCTAD, OECD에서 제시한 적정 수준을 만족했다. 대기율 분석 결과, 포항항이 57%로 가장 높았고, 세부 부두별로는 포항 신항의 1부두, 8부두, 4부두, 5부두, 선종별로는 철강재운반선, 일반화물선, 산물선(벌크선) 등의 순으로 높았다. 선박의 접안시간에 대한 묘박지 대기시간의 비율로 측정되는 대기율과 함께 선석점유율, 선박 대기 척수 및 시간 등은 항만 고객의 관점에서 항만별 부두별 서비스 수준을 평가할 수 있는 유용한 지표이고, 나아가 항만관리자의 항만 투자의사결정이나 관리 운영 정책 수립에 중요한 지표로 활용될 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권10호
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• pp.3851-3866
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• 2015

The dynamic nature of opportunistic networks results in long delays, low rates of success for deliveries, etc. As such user experience is limited, and the further development of opportunistic networks is constrained. This paper proposes a prediction-based routing method for opportunistic networks (PB-OppNet). Firstly, using an ARIMA model, PB-OppNet describes the historical contact information between a node pair as a time series to predict the average encounter time interval of the node pair. Secondly, using an optimal stopping rule, PB-OppNet obtains a threshold for encounter time intervals as forwarding utility. Based on this threshold, a node can easily make decisions of stopping observing, or delivering messages when potential forwarding nodes enter its communication range. It can also report different encounter time intervals to the destination node. With the threshold, PB-OppNet can achieve a better compromise of forwarding utility and waiting delay, so that delivery delay is minimized. The simulation experiment result presented here shows that PB-OppNet is better than existing methods in prediction accuracy for links, delivery delays, delivery success rates, etc.

• 한국산학기술학회논문지
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• 제14권5호
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• pp.2368-2374
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• 2013

엘리베이터의 전력은 대기 시에 소모되는 전력과 운행 시에 소모되는 전력으로 분류할 수 있다. 본 논문에서는 변화가 많은 승객의 교통량에 적절한 운행 대수를 계산하고 운행하지 않는 엘리베이터의 전원을 차단하여 엘리베이터의 대기전력을 저감시키는 퍼지제어기를 제안하였다. 또한 엘리베이터의 운행대수 제한에 의한 승객의 평균 대기시간의 증가도 최소화 하도록 퍼지제어기를 설계하였다. 본 논문에서 제안된 퍼지제어기를 그룹 엘리베이터 실험장치에서 실험하였을 때에 승객의 대기시간이 약 7.5%~9.5% 증가하였고, 한 대당 하루 약 675KWh의 대기전력 저감과 한 대당 년 간 약 236.6KWh의 엘리베이터 대기전력의 저감이 예상된다.

• 한국시뮬레이션학회논문지
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• 제25권3호
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• pp.117-123
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• 2016

본 연구는 다중서버 대기행렬시스템의 관측이 제한되어 있는 경우에 시스템 내부 행태를 추론하는 데에 그 목적이 있다. 대기행렬시스템 분석에 있어 도착 및 서비스시간에 자기상관성이 존재하면 이론적으로 모형화하기가 매우 복잡하고 어렵다. 이에 따라 다양한 분석 기법 및 확률과정 모형들이 개발되었다. 본 논문에서는 외부 관측치에 존재하는 자기상관성과 내부 행태를 관측하기 어려운 경우에 대한 추론 방법을 소개한다. 선행연구의 가정을 완화하여 추론 방법을 제시하고 그에 대한 보조정리 및 정리를 제시한다. 제시된 비모수적 방법을 적용하면 서비스시간에 자기상관성이 존재하더라도 외부 관측치만을 사용하여 다중서버 대기행렬의 내부 행태를 추론할 수 있다. 주요 내부 추론 결과로는 대기시간과 서비스시간을 사용하였다. 또한 제시된 방법의 타당성 검증을 위해 실험 결과를 제시하였다.

• 의료ㆍ복지 건축 : 한국의료복지건축학회 논문집
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• 제16권1호
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• pp.35-42
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• 2010

As a functionally complicated facility, it requires rational strategy to accommodate multi-functional needs to plan a hospital. Ambulatory surgery units located in large hospitals have problems such as longer waiting time and congestion for patients due to complicated planning and organization within limited area, which raise needs for independent ambulatory surgery centers to enable smoother medical treatment for patients. To design an independent ambulatory surgery center, understanding of zoning and layout of each unit needs is particularly required. This study focuses on research of efficient zoning/organization of day surgery unit and circulation arrangements of ambulatory surgery centers by analyzing various examples abroad, which will eventually help finding appropriate way of planning domestic ambulatory surgery centers. Specific area of research includes ambulatory surgery process, programmatic requirements, spatial organization of the facility, layout of surgery unit and circulation arrangements of ambulatory surgery centers.