• Journal of Korean Society of Industrial and Systems Engineering
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• v.28 no.1
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• pp.129-133
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• 2005

Slotted ALOHA(S-ALOHA) is widely used in local wireless network. We analyze the performance of contention-based model in wireless LAN using S-ALOHA protocol. We analyze the performance of binary exponential backoff (BEB) algorithm under the slotted ALOHA protocol: whenever a node's message which tries to reserve a channel is involved in a collision for the ith time, it chooses one of the next $2^i$ frames with equal probability and attempts the reservation again. We derive the expected access delay and throughput which is defined as the expected number of messages that reserve a channel in a frame. A simulation study is performed to verify our method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.6
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• pp.1610-1618
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• 1998

In this paper, we present the FB(Fair Buffering) mechanism for the efficient support of TCP traffic over UBR connections in the subnet ATM model. We show that both throughput and fairness may be improved with the FB mechanism. The FB mechanism is founded on the observation that the performance of TCP over UBR connections is optimal when the buffer space is allocated in proportion to the connection's bandwidth-delay product. We compare through simulation the performance of the existing drop-tail, EB(Equal Buffering) and the proposed FB buffer management schemes, with and without RR(Roung-Robin) scheduling, and demonstrate that the proposed FB mechanism is most effective when used in conjunction with the RR scheduling scheme.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.663-671
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• 2014

LED lamp arrangement is a critical issue in indoor visible light communication (VLC) system. In this paper, we analyze the illumination distribution under the arrangement of $2{\times}3$ and propose a method to find the optimal lamp arrangement. The method, based on the MIMO (Multiple Input/Multiple Output) system model and taking the first order reflection into consideration, enables accurate analysis of the arrangement of the LED lamps for any room. The studies show that under the optimal arrangement the uniformity of illumination is improved from 0.55 to 0.86, which guarantees that users can get almost equal lighting effects, no matter where they locate themselves. At the same time, the RMS delay spread distribution which is used to evaluate the inter-signal-interference (ISI) is analyzed, and the simulation results indicate that the optimal arrangement also can improve the communication quality by reducing the fluctuation of the RMS delay spread.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.56 no.3
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• pp.136-141
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• 2007

In this paper, a new simple control method for active power filter which can realized the complete compensation of the harmonic currents is proposed. In the proposed scheme, a compensating current reference generator employing resonance model implemented by a DSP(Digital Signal Processor) is introduced. Deadbeat control is employed to control the active power filter. The switching pulse width based SVM(Space Vector Modulation) is adopted so that the current of active power filter is been exactly equal to its reference at the next sampling instant. To compensate the computation delay of digital controller, the prediction of current is achieved by the current observer with deadbeat response.

• Journal of Korean Society of Transportation
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• v.33 no.2
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• pp.214-222
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• 2015

Jeju International Airport has become the most delayed airport in Korea, due to increased demand in air passengers and unexpected local weather condition. Observing the demands continuously grow for a decade, the airport is expected to be saturated in the near future. As a part of effort to prepare effective and timely measure for this expected situation, airport planners seeks the annual runway capacity, i.e., the appropriate number of flight operations in a given year with tolerable delay. In practice, the FAA formula is frequently adopted for the capacity estimation. The method, however, has intrinsic issues: 1) the hourly capacity imbedded in the formula is not clearly defined and thus the estimated value is vulnerable to be subjective judgement, and 2) the formula doesn't consider aircraft delay resulted from runway congestion. In this paper, we explain a novel method for estimating the daily runway capacity and then converting to the annual capacity taking into account the aircraft delay. In this paper, average delay of aircraft was measured using microscopic air traffic simulation model. Daily capacity of the runways were analyzed based on the simulation outputs and the method to assess the yearly capacity is introduced. Using a microscopic simulation model named TAAM, we measure the average aircraft delay at various levels of flight demand, and then estimate the practical daily runway capacity. The estimated daily and annual runway capacities of Jeju airport are about 460 operations a day which is equal to 169,000 operations year. The paper discusses how to verify the simulation model, and also suggests potential enhancement of the method.

• Advances in aircraft and spacecraft science
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• v.10 no.2
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• pp.141-158
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• 2023

In current research work, the aerodynamics performance of a newly designed large flying V aircraft is numerically investigated. Three Flying V configurations, with V-angles of 50°, 70° and 90° that represent the minimum, moderate, and maximum configurations respectively, were designed and modeled to assess their aerodynamic performance at cruise flight conditions. The unstructured mesh was developed using ICEM CFD and Ansys-Fluent was used as an aerodynamic solver. The developed models were numerically simulated at cruise flight conditions with a Mach number equal to 0.15. K-ω SST turbulence model was chosen to account for flow turbulence.The authors performed steady flow simulations.The results obtained from the experimentation reveal that the maximum main angle configuration of 90° had the highest C_Lmax value of 0.46 compared to other configurations. While the drag coefficient remained the same for all three configurations, the 50° V-angle configuration achieved the maximum stall angle of 35°. With limited stall delay benefits, the flying V possesses no sufficient stability, due to the flow separation detected at whole elevon and winglet suction side areas at AoA equal and higher than 30°.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.10
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• pp.2419-2424
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• 2013

In a conventional MOG algorithm, a small threshold for background decision causes the background recognition delay in a periodic background and a large threshold makes it recognize passing objects as background in a stationary background. This paper proposes the improved MOG algorithm using adaptive threshold. The proposed algorithm estimates changes of weight in the dominant model of the MOG algorithm both in the short and long terms, classifies backgrounds into the stationary and periodic ones, and assigns proper thresholds to them. The simulation results show that the proposed algorithm decreases the maximum number of frame in background recognition delay from 137 to 4 in the periodic background keeping the equal performance with the conventional algorithm in the stationary background.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.1
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• pp.1-9
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• 2022

The PoN (Proof of Nonce) distributed consensus algorithm basically uses a non-competitive consensus method that can guarantee an equal opportunity for all nodes to participate in the block generation process, and this method was expected to resolve the first trilemma of the blockchain, called the decentralization problem. However, the decentralization performance of the PoN distributed consensus algorithm can be greatly affected by the network transaction transmission delay characteristics of the nodes composing the block chain system. In particular, in the consensus process, differences in network node performance may significantly affect the composition of the congress and committee on a first-come, first-served basis. Therefore, in this paper, we presented a problem by analyzing the decentralization performance of the PoN distributed consensus algorithm, and suggested a fairness control algorithm using a learning-based probabilistic acceptance rule to improve it. In addition, we verified the superiority of the proposed algorithm by conducting a numerical experiment, while considering the block chain systems composed of various heterogeneous characteristic systems with different network transmission delay.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.27-30
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• 2004

This paper has been designed the TDMG(Time Delay Multiple Gaussian) pulse generator for UWB systems and analyzed the characteristics of UWB impulse. Composite two equal Gaussian pulses in a difference time lag, and then investigated TDMG pulse and modeled mathematically. Designed the TDMG pulse generator by ADS(Advanced Design System) to embody by using actual element with such mathematical model. As well as, this paper finally proved an excellence of the TDMG pulse generator by performing analysis through simulation.

• Geomechanics and Engineering
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• v.21 no.1
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• pp.85-93
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• 2020

In this article, the generalized thermoelastic theory with fractional derivative is presented to estimate the variation of temperature, the components of stress, the components of displacement and the changes in volume fraction field in two-dimensional porous media. Easily, the exact solutions in the Laplace domain are obtained. By using Laplace and Fourier transformations with the eigenvalues method, the physical quantities are obtained analytically. The numerical results for all the physical quantities considered are implemented and presented graphically. The results display that the present model with the fractional derivative is reduced to the Lord and Shulman (LS) and the classical dynamical coupled (CT) theories when the fractional parameter is equivalent to one and the delay time is equal to zero and respectively.