• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.1647-1655
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• 2006

본 연구는 무선 및 사용자요구사항 등 환경의 변화에 따라 부반송파(subcarrier) 할당, 변조방식 및 전력량을 조절하는 적응형 다중사용자 OFDM 시스템을 다룬다. 먼저 사용자별 전송요구 비트수 및 전체 사용가능한 전력량에 대한 제약 조건하에서 총 데이터 전송량(Throughput)을 최대화하는 최적화 문제를 모형화한다. 이 문제는 대부분의 기존 연구들을 포함할 수 있을 정도로 포괄적이지만 미분이 불가능한 비선형 최적화 문제이면서도 빠른 계산시간을 요구한다. 본 연구는 쌍대간격(Duality Gap)이 0이라는 제안 문제의 특성을 바탕으로 하여 Subgradient 쌍대최적화(Dual Optimization) 기법을 적용한다. 또한 이러한 접근법은 사용자 또는 무선환경의 변화에 적극적으로 적응하는 무선자원 할당 메커니즘을 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3B
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• pp.183-198
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• 2006

We define the incomplete medium sharing system as a multi-channel shared medium communication system where constraints are imposed to the set of channels that may be allocated to some transmitter-receiver node pairs. To derive a centralized MAC scheme of a incomplete medium sharing system, we address the problem of optimal channel allocation The optimal channel allocation problem is then translated into a max-flow problem in a multi-commodity flow graph, and it is shown that the optimal solution can then be obtained by solving a linear programming problem. In addition, two suboptimal channel allocation schemes are proposed to bring down the computational complexity to a practical/feasible level; (1) one is a modified iSLIP channel allocation scheme, (2) the other is sequential channel allocation scheme. From the results of a extensive set of numerical experiments, it is found that the suboptimal schemes evaluate channel utilization close to that of the optimal schemes while requiring much less amount of computation than the optimal scheme. In particular, the sequential channel allocation scheme is shown to achieve higher channel utilization with less computational complexity than . the modified iSLIP channel allocation scheme.

• Journal of KIISE:Information Networking
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• v.31 no.2
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• pp.123-130
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• 2004

Routing and wavelength assignment(RWA) problem is an important issue in optical transport networks based on wavelength division multiplexing(WDM) technique. It is typically solved using a combination of linear programming and graph coloring, or path selection based graph algorithms. Such methods are either complex or make extensive use of heuristics. In this paper we propose a novel and efficient approach which basically obtains the maximum edge disjoint paths (EDPs) for each source-destination demand pair. And those EDPs obtained are stored in Lookup Table and used for the update of weight matrix. Routes are determined in order by the weight matrix for the demand set. The comprehensive computer simulation shows that the Proposed algorithm uses similar or fewer wavelengths with significantly less execution time than bounded greedy approach (BGA) for EDP which is currently known to be effective in practice.

• Management & Information Systems Review
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• v.33 no.5
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• pp.85-95
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• 2014

This paper suggested an efficient mathematical model for strategic alliance of liner shipping companies. Even though a few previous research papers proposed the mathematical models for container slot chartering and allocation under liner shipping, those models were nonlinear and very difficult to solve. So their models had limits to apply them to real world problems. On the other hand, the model suggested in this paper is easy to solve and apply to real world problems because it is a integer linear programming model. This paper tried to apply the model to the same example problem as used in existing research paper. Excel add-in program, Premium Solver Platform was used to solve the problem and the optimal allocation and slot chartering for containers were able to be found easily. The result also showed that the total container shipping cost for applying the strategic alliance model was reduced compared to non-strategic alliance model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1452-1460
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• 2000

A series of papers in recent literature on logical topology design for wavelength routed optical networks have proposed mathematical models and solution methods unifying logical topology design wavelength assignment and traffic routing. The most recent one is by Krishnaswamy and Sivarajan which is more unifying and complete than the previous models. Especially the mathematical formulation is an integer linear program and hence regarded in readiness for an efficient solution method compared to the previous nonlinear programming models. The solution method in [7] is however elementary one relying on the rounding of linear program relaxation. When the rounding happens to be successful it tends to produce near-optimal solutions. In general there is no such guarantee so that the obtained solution may not satisfy the essential constraints such as logical -path hop-count and even wavelength number constraints. Also the computational efforts for linear program relaxation seems to be too excessive. In this paper we propose an improved and unifying solution method based on the same to be too excessive. In this paper we propose an improved and unifying solution method based on the same model. First its computation is considerably smaller. Second it guarantees the solution satisfies all the constraints. Finally applied the same instances the quality of solution is fairly competitive to the previous near optimal solution.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.12
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• pp.1458-1467
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• 1999

VLSI 공정 기술이 발달하면서 이웃한 전선 간의 간격이 점점 더 가까워 지고 있으며, 그에 따라 인접 전선 간의 혼신 문제가 심각해지고 있다. 본 논문에서는 3층 그리드 채널 배선에 적용 가능한 혼신을 최소화시키는 배선층 할당 방법을 제안한다. 이 방법은 선형 의사 불린 최적화 기법에 맞도록 고안되었으며, 적절한 변수 선택 휴리스틱과 상한값 추정 방법을 통하여 최적의 결과를 짧은 시간 안에 찾아낸다. 실험 결과를 통하여, 일반적인 0/1 정수 선형 프로그래밍 기법과 비교하여 성능과 수행시간 면에서 우수함을 보인다. Abstract Current deep-submicron VLSI technology appears to cause crosstalk problem severe since it requires adjacent wires to be placed closer and closer. In this paper, we deal with a horizontal layer assignment problem for three layer HVH channel routing to minimize coupling capacitance, a main source of crosstalk. It is formulated in a 0/1 integer linear programming problem which is then solved by a linear pseudo boolean optimization technique. Experiments show that accurate upper bound estimation technique effectively reduces crosstalk in a reasonable amount of running times.

• The Transactions of the Korea Information Processing Society
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• v.4 no.8
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• pp.2143-2151
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• 1997

As inter-wire spacing on a VLSI chip becomes smaller with the evolution of VLSI fabrication technology, coupling capacitance between adjacent wires is increasing rapidly over ground capacitance. Therefore, it becomes necessary to take into account the crosstalk caused mainly by coupling capacitance during the layout design of VLSI systems. This paper deals with layer assignment problem to minimize crosstalk in three layers gridded channel routing. The problem is formulated in 0/1 integer linear programming style. Upper bound for cost function is estimated for the fast termination. Experiment shows the effectiveness of our approach to minimize crosstalk.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.8
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• pp.1393-1400
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• 2006

This paper optimizes the access probabilities (APs) in a network resource allocation scheme based on access probabilities in order that the waiting time and the blocking probability are minimized under the given constraints, and obtains its performance. In order to optimize APs, an infinite number of balance equations is reduced to a finite number of balance equations by applying Neuts matrix geometric method. And the nonlinear programming problem is converted into a linear programming problem. As a numerical example, the performance measures of waiting time and blocking probability for optimal access probabilities and the maximum utilization under the given constraints are obtained. And it is shown that the scheme with optimal APs gives more performance build-up than the strategy without optimization.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.5
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• pp.365-372
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• 2021

This paper deals with an optimal Weapon-Target Assignment (WTA) algorithm for Closed-In Weapon Systems (CIWS), considering variable burst time. In this study, the WTA problem for CIWS is formulated based on Mixed Integer Linear Programming (MILP). Unlike the previous study assuming that the burst time is fixed regardless of the engagement range, the proposed method utilizes the variable burst time based on the kill probability according to the engagement range. Thus, the proposed method can reflect a more realistic engagement situation and reduce the reaction time of CIWS against targets, compared to the existing method. In this paper, we first reformulate the existing MILP-based WTA problem to accommodate the variable burst Time. The proposed method is then validated through numerical simulations with the help of a commercial optimization tool.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.67-75
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• 2013

The advantages of the orthogonal frequency division multiplexing (OFDM) are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. To further utilize vast channel capacity of the multiuser OFDM, one has to find the efficient adaptive subchannel and bit allocation among users. In this paper, we compare the performance of the linear programming dual of the 0-1 integer programming formulation with the existing convex optimization approach for the optimal subchannel and bit allocation problem of the multiuser OFDM. Utilizing tight lower bound provided by the LP dual formulation, we develop a primal heurisitc algorithm based on the LP dual solution. The performance of the primal heuristic is compared with MAO, ESA heuristic solutions, and integer programming solution on MATLAB simulation on a system employing M-ary quadrature amplitude modulation (MQAM) assuming a frequency-selective channel consisting of three independent Rayleigh multi-paths.