Browsing by Author "Bae, Kyung"
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- Dynamic Data Structures for a Direct Search AlgorithmHe, Jian; Watson, Layne T.; Ramakrishnan, Naren; Shaffer, Clifford A.; Verstak, Alex; Jiang, Jing; Bae, Kyung; Tranter, William H. (Department of Computer Science, Virginia Polytechnic Institute & State University, 2001)The DIRECT (DIviding RECTangles) algorithm of Jones, Perttunen, and Stuckman (1993), a variant of Lipschitzian methods for bound constrained global optimization, has proved effective even in higher dimensions. However, the performance of a DIRECT implementation in real applications depends on the characteristics of the objective function, the problem dimension, and the desired solution accuracy. Implementations with static data structures often fail in practice, since it is difficult to predict memory resource requirements in advance. This is especially critical in multidisciplinary engineering design applications, where the DIRECT optimization is just one small component of a much larger computation, and any component failure aborts the entire design process. To make the DIRECT global optimization algorithm efficient and robust on large-scale, multidisciplinary engineering problems, a set of dynamic data structures is proposed here to balance the memory requirements with execution time, while simultaneously adapting to arbitrary problem size. The focus of this paper is on design issues of the dynamic data structures, and related memory management strategies. Numerical computing techniques and modifications of Jones’ original DIRECT algorithm in terms of stopping rules and box selection rules are also explored. Performance studies are done for synthetic test problems with multiple local optima. Results for application to a site-specific system simulator for wireless communications systems (S4W) are also presented to demonstrate the effectiveness of the proposed dynamic data structures for an implementation of DIRECT.
- Globally Optimal Transmitter Placement for Indoor Wireless Communication SystemsHe, Jian; Verstak, Alex; Watson, Layne T.; Stinson, C.A.; Ramakrishnan, Naren; Shaffer, Clifford A.; Rappaport, Theodore S.; Anderson, Christopher R.; Bae, Kyung; Jiang, Jing; Tranter, William H. (Department of Computer Science, Virginia Polytechnic Institute & State University, 2002-08-01)In this paper, a global optimization technique is applied to solve the optimal transmitter placement problem for indoor wireless systems. An efficient pattern search algorithm ---DIRECT (DIviding RECTangles) of Jones, Perttunen, and Stuckman(1993)---has been connected to a parallel 3D radio propagation ray tracing modeler running on a 200-node Beowulf cluster of Linux workstations. Surrogate functions for a parallel WCDMA (wideband code division multiple access) simulator were used to estimate the system performance for the global optimization algorithm. Power converage and BER(bit error rate) are considered as two different criteria for optimizing locations of a specified number of transmitters across the feasible region of the design space. This paper briefly describes the undrelying radio propagation and WCDMA simulations and focuses on the design issues of the optimization loop.
- S4W: Globally Optimized Design of Wireless Communication SystemsHe, Jian; Verstak, Alex; Watson, Layne T.; Stinson, C.A.; Ramakrishnan, Naren; Shaffer, Clifford A.; Rappaport, Theodore S.; Anderson, Christopher R.; Bae, Kyung; Jiang, Jing; Tranter, William H. (Department of Computer Science, Virginia Polytechnic Institute & State University, 2002-07-01)In this paper, a global optimization technique is applied to solve the optimal transmitter placement problem for indoor wireless systems. An efficient pattern search algorithm -- DIRECT (DIviding RECTangles) of Jones,Perttunen, and Stuckman(1993)--has been connected to a parallel 3D radio propagation ray tracing modeler running on a 200 node. Beowulf cluster of Linux workstations. Surrogate functions for a parallel WCDMA (wideband code division multiple access) simulator were used to estimate the system performance for the global optimization algorithm. Power coverage and BER (bit error rate) are considered as two different criteria for optimizing locations of a specified number of transmitters across the feasible region of the design space. This paper briefly describes the underlying radio propagation and WCDMA simulations and focuses on the design issues of the optimization loop.