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Anyang, South Korea

Park S.,Korea Railroad Research Institute | Hong D.,Yonsei University
IEEE Transactions on Wireless Communications | Year: 2014

We consider energy harvesting cognitive radio networks to improve both energy efficiency and spectral efficiency. The goal of this paper is to analyze the theoretically achievable throughput of the secondary transmitter, which harvests energy from ambient sources or wireless power transfer systems while opportunistically accessing the spectrum licensed to the primary network. By modeling the temporal correlation of the primary traffic according to a time-homogeneous discrete Markov process, we derive the upper bound on the achievable throughput as a function of the energy arrival rate, the temporal correlation of the primary traffic, and the detection threshold for a spectrum sensor. The optimal detection threshold is then derived to maximize the upper bound on the achievable throughput under an energy causality constraint and a collision constraint. The energy causality constraint mandates that the total consumed energy should not exceed the total harvested energy, while the collision constraint is required to protect the primary network from secondary transmission. Analytical results show the temporal correlation of the primary traffic to enable efficient usage of the harvested energy by preventing the secondary transmitter from accessing the spectrum that may be occupied by the primary network. © 2002-2012 IEEE.


Park S.,Korea Railroad Research Institute | Hong D.,Yonsei University
IEEE Transactions on Wireless Communications | Year: 2013

We consider energy harvesting cognitive radio networks in which a secondary transmitter harvests energy from ambient sources or wireless power transfer systems while opportunistically accessing the spectrum licensed to the primary network. The primary traffic is modeled as a time-homogeneous discrete Markov process, and the secondary transmitter may not be able to operate continuously due to sporadic and unstable energy sources. At the beginning of each time slot, the secondary transmitter thus needs to determine whether to remain idle so as to conserve energy, or to execute spectrum sensing to acquire knowledge of the current spectrum occupancy state. It also needs to configure the spectrum sensor detection threshold to achieve an effective tradeoff between false alarms and misdetections. This sequential decision-making, done to maximize the expected total throughput, requires the joint design of a spectrum sensing policy and a detection threshold under the energy causality and collision constraints. We formulate this stochastic optimization problem as a constrained partially observable Markov decision process (POMDP), and then convert it to a computationally tractable unconstrained POMDP. Numerical results show that the proposed approach enables efficient usage of the harvested energy by exploiting the temporal correlation of the primary traffic. © 2002-2012 IEEE.


Park C.-W.,Korea Railroad Research Institute | Lee H.-S.,Kyung Hee University
International Journal of Production Economics | Year: 2013

We study a multi-product assembly production system in which individual components are made to meet various order types. We assume that orders arrive according to a Poisson process, but there is a fixed probability that an order requests a particular kit of different components. Under the CONWIP control mechanism, each component is produced by a flow line with several stations. To analyze this system, we develop an approximation algorithm based on a decomposition method. In the algorithm, a product-form approximation technique as well as a matrix-geometric method is used. Numerical results show that the accuracy of the approximation method is acceptable. © 2013 Elsevier B.V. All rights reserved.


Patent
Korea Railroad Research Institute | Date: 2014-12-22

Disclosed is a high frequency transformer for reducing leakage flux, including a voltage transformation unit for transforming a first voltage, which is inputted thereto, into a second voltage, wherein: a primary winding is divided; and a secondary winding is arranged between the divided primary windings.


Patent
Korea Railroad Research Institute | Date: 2013-08-09

The present invention relates to a two-phase, two-column linear pulse motor propulsion system, and more particularly to a two-phase, two-column linear pulse motor propulsion system which can implement high-speed driving, stopping, and switching directions forward/backward through non-adhesive driving characteristics by improving accelerating performance and torque performance. The two-phase, two-column linear pulse motor propulsion system comprises a field unit

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