• 대한산업공학회지
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• 제36권4호
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• pp.248-254
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• 2010

In this paper, we survey the parallel machines scheduling problem with GoS eligibility constraints so as to minimize the makespan. Our survey covers off-line, online and semi-online scheduling problems. In the case of online scheduling, we only focus on online scheduling one by one. Hence we give an introduction to the problem and present important results of the problem.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2007년도 추계학술대회 및 정기총회
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• pp.12-15
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• 2007

Online parallel machine scheduling problems have been studied by many researchers and enormous results are appeared in the last 40 years. With the development of scheduling theory and application, new online scheduling problems where the partial information is known in advance, that is, semi-online, gained much interest due to their increased application in practice. So we consider the online scheduling of three machines with general eligibility and its semi-online variant where the total processing time is known in advance. For the online and semi-online problems, we develop algorithms with competitive ratio of 5/2 which are shown to be optimal.

• 한국정보과학회논문지:시스템및이론
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• 제32권2호
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• pp.68-74
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• 2005

마감시한 스케줄링에서 작업들은 수행을 완료해야 하는 마감시한을 가진다 스케줄링 알고리즘은 각 시간에 어떠한 작업이 수행되어야 하는 지 결정한다. 수행이 마감시한 안에 완료된 작업들만이 알고리즘의 처리량 또는 이익에 포함된다. 작업들은 임의의 가중치를 가지고 알고리즘의 이익은 완료된 작업들의 가중치의 합으로 주어진다. 스케줄링 알고리즘의 목표는 이익을 최대화하는 것이다. 본 논문에서 우리는 온라인 비선점 스케줄링을 생각한다. 여기서 작업들은 온라인으로 도착하고, 스케줄링 알고리즘은 앞으로 도착할 작업들의 정보를 미리 알 수 없다. 작업들은 스케줄 되고 나서 수행 도중에 멈출 수 없다. 이 문제에 대해서, 우리는 임의의 온라인 알고리즘의 성능의 하한을 구한다. 또한 이 하한과 일치하는 성능을 가지는 최적의 온라인 알고리즘을 제안하다.

• Journal of Communications and Networks
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• 제16권3호
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• pp.293-300
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• 2014

As energy harvesting communication systems emerge, there is a need for transmission schemes that dynamically adapt to the energy harvesting process. In this paper, after exhibiting a finite-horizon online throughput-maximizing scheduling problem formulation and the structure of its optimal solution within a dynamic programming formulation, a low complexity online scheduling policy is proposed. The policy exploits the existence of thresholds for choosing rate and power levels as a function of stored energy, harvest state and time until the end of the horizon. The policy, which is based on computing an expected threshold, performs close to optimal on a wide range of example energy harvest patterns. Moreover, it achieves higher throughput values for a given delay, than throughput-optimal online policies developed based on infinite-horizon formulations in recent literature. The solution is extended to include ergodic time-varying (fading) channels, and a corresponding low complexity policy is proposed and evaluated for this case as well.

• 한국정보통신학회논문지
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• 제17권8호
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• pp.1934-1939
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• 2013

본 논문은 마감시간을 가진 작업들의 온라인 스케줄링 문제를 다룬다. 작업들이 시간이 지남에 따라 도착하고 스케줄링 알고리즘은 앞으로 도착할 작업들의 정보를 미리 알지 못한다. 작업들은 동일한 수행시간만큼 실행되고 알고리즘의 목표는 마감 시간 안에 수행을 완료한 작업들의 수를 최대화하는 것이다. 온라인 알고리즘의 성능은 모든 작업 정보를 미리 알고 최적의 답을 줄 수 있는 최적 알고리즘의 성능과 비교하는데 두 알고리즘 성능의 비를 경쟁비라고 한다. 일반적으로 정보의 부재로 인해 온라인 알고리즘은 큰 경쟁비를 가진다. 따라서 온라인 알고리즘에 보다 많은 머신 또는 보다 빠른 머신을 제공했을 때의 경쟁비를 계산하는 자원추가 분석을 수행할 수 있다. 본 논문에서는 온라인 알고리즘이 보다 많은 머신들을 이용할 수 있을 때 최적 알고리즘과 같은 성능을 낼 수 있음을 보일 것이다.

• 융합정보논문지
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• 제9권12호
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• pp.124-132
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• 2019

일정계획은 오프라인(offline) 일정계획과 온라인(online) 일정계획으로 구분할 수 있고, 본 논문은 온라인 상황에서 병렬설비의 주기적 일정계획 수립문제를 다룬다. 도착시간(ready time)이 다른 여러 작업들에 대해 makespan을 최소화하기 위한 작업 일정계획 알고리즘 개발이 목적이다. 이를 위해 각 설비에서의 작업처리 순서는 ERD(Earliest Ready Date) 규칙에 따른 순서가 최적임을 밝혔다. 각 설비 별 배정 작업도 결정 해야하는 병렬설비 문제를 위해서는 혼합정수계획모형(MIP)을 이용하는 알고리즘을 제시하였다. 개발한 알고리즘의 유용성과 성능분석을 위해 수치 예를 활용하여 오프라인 일정계획과 비교하였다. 비교분석 결과, 오프라인 일정계획에 비해 매우 빠른 시간에 일정계획을 수립할 수 있음을 보였고, 주기시간의 감소를 통한 makespan의 단축 가능성을 보였다. 본 논문의 주기적 일정계획 방법은 계획수립을 위한 시간이 매우 작으므로, 설비 및 작업의 수가 많은 온라인 환경에서도 활용할 수 있다. 더불어서 스마트공장이나 블록체인 플랫폼에서의 작업일정 수행을 위해 활용될 수 있을 것으로 기대한다.

• Journal of Communications and Networks
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• 제16권1호
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• pp.36-44
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• 2014

Exploiting the energy-delay tradeoff for energy saving is critical for developing green wireless communication systems. In this paper, we investigate the delay-constrained energy-efficient packet transmission. We aim to minimize the energy consumption of multiple randomly arrived packets in an additive white Gaussian noise channel subject to individual packet delay constraints, by taking into account the practical on-off circuit power consumption at the transmitter. First, we consider the offline case, by assuming that the full packet arrival information is known a priori at the transmitter, and formulate the energy minimization problem as a non-convex optimization problem. By exploiting the specific problem structure, we propose an efficient scheduling algorithm to obtain the globally optimal solution. It is shown that the optimal solution consists of two types of scheduling intervals, namely "selected-off" and "always-on" intervals, which correspond to bits-per-joule energy efficiency maximization and "lazy scheduling" rate allocation, respectively. Next, we consider the practical online case where only causal packet arrival information is available. Inspired by the optimal offline solution, we propose a new online scheme. It is shown by simulations that the proposed online scheme has a comparable performance with the optimal offline one and outperforms the design without considering on-off circuit power as well as the other heuristically designed online schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권3호
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• pp.1164-1183
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• 2019

The rapid development of cloud computing and high requirements of operators requires strong support from the underlying Data Center Networks. Therefore, the effectiveness of using resources in the data center networks becomes a point of concern for operators and material for research. In this paper, we discuss the online virtual-cluster provision problem for multiple tenants with an aim to decide when and where the virtual cluster should be placed in a data center network. Our objective is maximizing the total revenue for the data center networks under the constraints. In order to solve this problem, this paper divides it into two parts: online multi-tenancy scheduling and virtual cluster placement. The first part aims to determine the scheduling orders for the multiple tenants, and the second part aims to determine the locations of virtual machines. We first approach the problem by using the variational inequality model and discuss the existence of the optimal solution. After that, we prove that provisioning virtual clusters for a multi-tenant data center network that maximizes revenue is NP-hard. Due to the complexity of this problem, an efficient heuristic algorithm OMS (Online Multi-tenancy Scheduling) is proposed to solve the online multi-tenancy scheduling problem. We further explore the virtual cluster placement problem based on the OMS and propose a novel algorithm during the virtual machine placement. We evaluate our algorithms through a series of simulations, and the simulations results demonstrate that OMS can significantly increase the efficiency and total revenue for the data centers.

• 대한전기학회논문지:시스템및제어부문D
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• 제53권7호
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• pp.501-508
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• 2004

In this paper, a coordinated scheduling algorithm is proposed to reduce end-to-end delay in distributed control of systems. For the algorithm, the analysis of practical end-to-end delay in the worst case is performed priory with considering implementation of the systems. The end-to-end delay is composed of the delay caused by multi-task scheduling of operating systems, the delay caused by network communications, and the delay caused by asynchronous timing between operating systems and network communications. Through some simulation tests based on CAN(Controller Area Network), the proposed worst case end-to-end delay analysis is validated. Through the simulation tests, it is also shown that a real-time distributed control system designed to existing worst case delay cannot guarantee end-to-end time constraints. With the analysis, a coordinated scheduling algorithm is proposed here. The coordinated scheduling algorithm is focused on the reduction of the delay caused by asynchronous timing between operating systems and network communications. Online deadline assignment strategy is proposed for the scheduling. The performance enhancement of the distributed control systems by the scheduling algorithm is shown through simulation tests.

• 대한산업공학회지
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• 제35권3호
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• pp.213-217
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• 2009

We consider the online scheduling problems of three and four machines under eligibility constraint. Respectively for the cases of three and four machines, we prove that AW algorithm has competitive ratios of $\frac{5}{2}$ and 3 which are shown to be optimal. Also, we show that the same results hold for the semi-online cases with prior knowledge of the total and the largest processing time.