• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권1호
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• pp.68-82
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• 2011

Wireless mesh networks (WMNs) provide high-speed backbone networks without any wired cable. Many researchers have tried to increase network throughput by using multi-channel and multi-radio interfaces. A multi-radio multi-channel WMN requires channel assignment algorithm to decide the number of channels needed for each link. Since the channel assignment affects routing and interference directly, it is a critical component for enhancing network performance. However, the optimal channel assignment is known as a NP complete problem. For high performance, most of previous works assign channels in a centralized manner but they are limited in being applied for dynamic network environments. In this paper, we propose a simple flow estimation algorithm and a hybrid channel assignment algorithm. Our flow estimation algorithm obtains aggregated flow rate information between routers by packet sampling, thereby achieving high scalability. Our hybrid channel assignment algorithm initially assigns channels in a centralized manner first, and runs in a distributed manner to adjust channel assignment when notable traffic changes are detected. This approach provides high scalability and high performance compared with existing algorithms, and they are confirmed through extensive performance evaluations.

• Journal of Communications and Networks
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• 제5권3호
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• pp.230-239
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• 2003

In this paper, we propose a framework to study how to route packets efficiently in multipath communication networks. Two traffic congestion control techniques, namely, flow assignment and packet scheduling, have been investigated. The flow assignment mechanism defines an optimal splitting of data traffic on multiple disjoint paths. The resequencing delay and the usage of the resequencing buffer can be reduced significantly by properly scheduling the sending order of all packets, say, according to their expected arrival times at the destination. To illustrate our model, and without loss of generality, Gaussian distributed end-to-end path delays are used. Our analytical results show that the techniques are very effective in reducing the average end-to-end path delay, the average packet resequencing delay, and the average resequencing buffer occupancy for various path configurations. These promising results can form a basis for designing future adaptive multipath protocols.

• 대한교통학회:학술대회논문집
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• 대한교통학회 2002년도 제41회 학술발표회논문집
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• pp.97-139
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• 2002

The aim of the present study is to find a good quality user equilibrium assignments under time varying condition. For this purpose, this study introduces a dynamic network loading method that can maintain correct flow propagation as well as flow conservation, and it develops a novel solution algorithm that does not need evaluation of the objective function by modifying the Schittenhelm (1990)'s algorithm. This novel algorithm turns out to be efficient and convenient compared to the conventional Frank-Wolfe (1956) algorithm because the former finds solutions based on routes rather than links so that it can maintain correct flow propagation intrinsically in the time-varying network conditions. The application of dynamic user equilibrium (DUE) assignment model with this novel solution algorithm to test networks including medium-sized one shows that the present DUE assignment model gives rise to high quality discrete time solutions when we adopt the deterministic queuing model for a link performance function, and we associate flows and costs in a proper way.

• Management Science and Financial Engineering
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• 제15권1호
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• pp.51-69
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• 2009

A network model and a Genetic Algorithm (GA) is proposed to solve the simultaneous estimation of the trip distribution and traffic assignment from traffic counts in the congested networks in a logit-based Stochastic User Equilibrium (SUE). The model is formulated as a problem of minimizing a non-linear objective function with the linear constraints. In the model, the flow-conservation constraints are utilized to restrict the solution space and to force the link flows become consistent to the traffic counts. The objective of the model is to minimize the discrepancies between two sets of link flows. One is the set of link flows satisfying the constraints of flow-conservation, trip production from origin, trip attraction to destination and traffic counts at observed links. The other is the set of link flows those are estimated through the trip distribution and traffic assignment using the path flow estimator in the logit-based SUE. In the proposed GA, a chromosome is defined as a real vector representing a set of Origin-Destination Matrix (ODM), link flows and route-choice dispersion coefficient. Each chromosome is evaluated by the corresponding discrepancies. The population of the chromosome is evolved by the concurrent simplex crossover and random mutation. To maintain the feasibility of solutions, a bounded vector shipment technique is used during the crossover and mutation.

• 한국콘텐츠학회논문지
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• 제6권2호
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• pp.117-126
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• 2006

자바 바이트코드는 많은 장점을 갖지만 수행 속도가 느리고 분석이 어렵다는 단점을 갖는다 이를 극복하기 위해 바이트코드에 대한 분석과 최적화가 수행되어야 한다. 우선 바이트코드에 대한 제어 흐름 분석을 수행한다. 제어 흐름 분석 후 데이터 흐름 분석과 최적화를 위해서 변수가 어디서 정의되고 어디서 사용되는지에 대한 정보가 필요하다. 각 위치에서 변수에 배정되는 값에 따라 동일한 이름의 변수가 다른 위치에서 다른 값을 가지는 경우가 발생한다. 따라서 정적으로 값과 타입을 결정하기 위해서 변수는 배정되는 것에 따라 분리되어야 한다. 이를 위해 단일 배정 형태를 이용하여 표현할 수 있다. 정적 단일 배정형태(SSA Form)로 변경한 후 정적 분석과 최적화를 위해서는 각 변수와 표현식이 나타내는 각각의 노드에 타입 정보를 설정해야 한다. 본 논문은 타입에 대한 기본 정보를 바탕으로 관련된 동등한 노드를 발견하고 강 결합 요소로 설정한 후 각 노드에 타입을 효율적으로 설정하는 방법을 제안한다

• Journal of Information Processing Systems
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• 제3권1호
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• pp.26-32
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• 2007

Although the Java bytecode has numerous advantages, it also has certain shortcomings such as its slow execution speed and difficulty of analysis. In order to overcome such disadvantages, a bytecode analysis and optimization must be performed. The control flow of the bytecode should be analyzed; next, information is required regarding where the variables are defined and used to conduct a dataflow analysis and optimization. There may be cases where variables with an identical name contain different values at different locations during execution, according to the value assigned to a given variable in each location. Therefore, in order to statically determine the value and type, the variables must be separated according to allocation. In order to achieve this, variables can be expressed using a static single assignment form. After transformation into a static single assignment form, the type information of each node expressed by each variable and expression must be configured to perform a static analysis and optimization. Based on the basic type information, this paper proposes a method for finding the related equivalent nodes, setting nodes with strong connection components, and efficiently assigning each node type.

• 대한교통학회지
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• 제8권1호
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• pp.55-71
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• 1990

The behavioral mechanism underlying the traffic assignment model is a choice, or decision-making process of traveling paths between origins and destinations. The deterministic approach to traffic assignment assumes that travelers choose shortest path from their origin-destination pair. Although this assumption seems reasonable, it presumes that all travelers have perfect information regarding travel time, that they make consistently correct decision, and that they all behave in identical fashion. Stochastic user equilibrium assignment relaxes these presumptions by including a random component in traveler's perception of travel time. The objective of this study is to compare "A Model of Deterministic User Equilibrium Assignment" with "Models of Stochastic User Equilibrium Assignment" in the theoretical and practical aspects. Specifically, SUE models are developed to logit and probit based models according to discrete choice functions. The models were applied to sioux Falls net ork consisting of 24 zones, 24 nodes and 76 links. The distribution of perceived travel time was obtained by using the relationship between speed and traffic flow.

• 한국컴퓨터정보학회논문지
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• 제19권4호
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• pp.91-99
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• 2014

본 논문은 2차 할당 문제의 최적 해를 찾을 수 있는 휴리스틱 다항시간 알고리즘을 제안하였다. 일반적으로 선형 할당 문제의 최적 해는 헝가리안 알고리즘으로 구한다. 그러나 2차 할당문제의 최적 해를 찾는 알고리즘은 제안되지 않고 있다. 제안된 알고리즘은 거리행렬의 단위거리로부터 그리드 형태의 배치를 찾아내고, 이 형태에 맞도록 흐름량 행렬의 최대 값부터 내림차순으로 최대흐름을 최소 거리에 배치하는 최대흐름/최소거리 기법을 적용하였다. 제안된 알고리즘을 다양한 그리드형 2차 할당문제에 적용한 결과 2차 할당문제의 해를 다항시간에 구할 수 있는 알고리즘이 존재할 가능성을 보였다.

• 스마트미디어저널
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• 제12권9호
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• pp.72-80
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• 2023

본 논문에서는 다수의 환자가 발생하여 구급차를 통해 병원으로 이송하여야 하는 경우 최소비용 최대유량 알고리즘에 기반하여 병원을 배정 및 재배정하는 기법을 설계하고 성능을 평가한다. 환자의 증상과 병원들까지의 거리에 의해 플로우 그래프를 생성하는 과정, 링크 용량 수정 과정, 구급차와 병원 매칭 과정 등으로 구성되며 알고리즘 수행시간의 효율성으로 인해 추가환자의 발생이나 병원의 수용능력 변경에도 플로우 그래프 재구성에 의해 재배정을 수행할 수 있다. 프로토타입 구현에 의한 성능 평가 결과 주어진 실험 환경에 대해 제안된 기법은 순차 배정 방식에 비해 24%까지 이송요구시간 불만족을 감소시킬 수 있다.

• 대한산업공학회지
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• 제5권1호
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• pp.45-51
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• 1979

This paper presents a heuristic solution procedure for the quadratic assignment problem, ranking procedure, which can handle the case where not all of the facilities have the same size of area. The ranking procedure is found more efficient than two other existing heuristic procedures from results of computational experience. Based on the out-patients flow pattern and the procedure developed, an improved layout of the three existing general hospitals is developed with the objective of minimizing the total distance travelled by patients in the central and the out-patient clinic.