• Journal of Communications and Networks
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• v.18 no.3
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• pp.320-326
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• 2016

In existing literature on multiple-input multiple-output (MIMO) relaying communication systems, antenna selection is often implemented by maximizing the channel capacity or the output single-to-noise ratio (SNR). In this paper, we propose an energy-efficient low-complexity antenna selection scheme for MIMO relaying communication systems. The proposed algorithm is based on beamforming and maximizing the Frobenius norm to jointly optimize the transmit power, number of active antennas, and antenna subsets at the source, relaying and destination. We maximize the energy efficiency between the link of source to relay and the link of relay to destination to obtain the maximum energy efficiency of the system, subject to the SNR constraint. Compared to existing antenna selection methods forMIMO relaying communication systems, simulation results demonstrate that the proposed method can save more power in term of energy efficiency, while having lower computational complexity.

• Journal of Power Electronics
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• v.17 no.3
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• pp.733-743
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• 2017

This paper develops a coordinated control strategy of the doubly fed induction generator (DFIG) system based on repetitive control (RC) under generalized harmonic grid voltage conditions. The proposed RC strategy in the rotor side converter (RSC) is capable of ensuring smooth DFIG electromagnetic torque that will enable the possible safe functioning of the mechanical components, such as gear box and bearing. Moreover, the proposed RC strategy in the grid side converter (GSC) aims to achieve sinusoidal overall currents of the DFIG system injected into the network to guarantee satisfactory power quality. The dc-link voltage fluctuation under the proposed control target is theoretically analyzed. Influence of limited converter capacity on the controllable area has also been studied. A laboratory test platform has been constructed, and the experimental results validate the availability of the proposed RC strategy for the DFIG system under generalized harmonic grid voltage conditions.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1486-1495
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• 2019

Dealing with the DC link fault poses a technical problem for an HVDC based on a modular multilevel converter. The fault suppressing mechanisms of several sub-module topologies with DC fault current blocking capacity are examined in this paper. An improved half-bridge sub-module topology with double direction control switch is also designed to address the additional power consumption problem, and a sub-module topology called hybrid double direction blocking sub module (HDDBSM) is proposed. The DC fault suppression characteristics and sub-module capacitor voltage balance problem is also analyzed, and a self-startup method is designed according to the number of capacitors. The simulation model in PSCAD/EMTDC is built to verify the self-startup process and the DC link fault suppression features.

• Journal of the Korea Society of Computer and Information
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• v.24 no.5
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• pp.19-26
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• 2019

In this paper, we consider the D2D Transmitter(Tx) and Receiver(Rx) pair assignment problem in the cellular system. Sharing the resource of the cellular system, D2D users may cause interference to the cellular system, though it is beneficial to improve the D2D user Capacity. Therefore, to protect the cellular users, D2D transmit power should be carefully controlled. Previously, optimal Tx-Rx assignment to minimize the total transmit power of users was investigated. Accordingly, the iterative algorithm to find the optimum Tx-Rx asignment was obtained. In this work, we consider the case where Tx group users becomes Rx group users, and Rx group users become Tx group users. We prove that the Tx-Rx assignment problem has the duality property. We present the numerical examples that show the duality between U-link and D-link.

• Current Optics and Photonics
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• v.3 no.5
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• pp.365-373
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• 2019

This paper investigates the performance of a hybrid single input multiple output radio frequency/free-space optics (SIMO-RF/FSO) communication system. Each SIMO-RF link is modeled as an independent and identically distributed (i.i.d.) Rayleigh distribution, while the FSO link follows a generalized $M{\acute{a}}laga$ (M) distribution. Considering the fixed gain amplify-and-forward (AF) relay and misalignment errors, novel expressions for the outage probability (OP), average bit error rate (ABER) and average capacity are derived. Numerical results show that atmospheric turbulence and misalignment errors can seriously impair the system performance, and the hybrid RF/FSO communication system using SIMO-RF links can greatly improve system performance. We also analyze system performance under different types of modulation schemes. Numerical results are verified by Monte Carlo simulations.

• International Journal of Computer Science & Network Security
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• v.21 no.1
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• pp.207-213
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• 2021

Networks in Mobile ad hoc contain distribution and do not have a predefined structure which practically means that network modes can play the role of being clients or servers. The routing protocols used in mobile Ad-hoc networks (MANETs) are characterized by limited bandwidth, mobility, limited power supply, and routing protocols. Hybrid routing protocols solve the delay problem of reactive routing protocols and the routing overhead of proactive routing protocols. The Ant Colony Optimization (ACO) algorithm is used to solve other real-life problems such as the travelling salesman problem, capacity planning, and the vehicle routing challenge. Bio-inspired methods have probed lethal in helping to solve the problem domains in these networks. Hybrid routing protocols combine the distance vector routing protocol (DVRP) and the link-state routing protocol (LSRP) to solve the routing problem.

• Journal of IKEEE
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• v.25 no.2
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• pp.399-407
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• 2021

This paper proposes the DC-link voltage design method of Type 4 wind turbine that minimizes power loss and satisfies the High Voltage Ride Through(HVRT) function requirements of the transmission system operator. The Type 4 wind turbine used for large-capacity offshore wind turbine consists of the Back-to-Back converter in which the converter linked to the power grid and the inverter linked to the wind turbine share the DC-link. When the grid high voltage fault occurs in the Type 4 wind turbine, if the DC-link voltage is insufficient compared to the fault voltage level, the current controller of the grid-side converter can't operate smoothly due to over modulation. Therefore, to satisfy the HVRT function, the DC-link voltage should be designed based on the voltage level of high voltage fault. However, steady-state switching losses increase further as the DC-link voltage increases. Therefore, the considerations should be included for the loss to be increased when the DC-link voltage is designed significantly. In this paper, the design method for the DC-link voltage considered the fault voltage level and the loss is explained, and the validity of the proposed design method is verified through the HVRT function simulation based on the PSCAD model of the 2MVA Type 4 wind turbine.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.715-723
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• 2007

A displacement-based seismic design procedure was proposed for mid-to-low-rise steel moment frames. The proposed method was totally different from the current R-factor approach in that it directly uses available connection rotation capacity as a primary design variable. To this end, the relationship between available connection rotation capacity and seismic response modification (R factor) was established first; this relationship has been a missing link in current ductility-based design practice. A step-by-step displacement-based iterative design procedure was then proposed and verified using inelastic dynamic analysis.

• Steel and Composite Structures
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• v.2 no.3
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• pp.171-194
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• 2002

In this paper, the behaviour of axially loaded partially encased composite columns made with light welded H steel shapes is examined using ABAQUS finite element modelling. The results of the numerical simulations are compared to the response observed in previous experimental studies on that column system. The steel shape of the specimens has transverse links attached to the flanges to improve its local buckling capacity and concrete is poured between the flanges only. The test specimens included 14 stubcolumns with a square cross section ranging from 300 mm to 600 mm in depth. The transverse link spacing varied from 0.5 to 1 times the depth and the width-to-thickness ratio of the flanges ranged from 23 to 35. The numerical model accounted for nonlinear stress-strain behaviour of materials, residual stresses in the steel shape, initial local imperfections of the flanges, and allowed for large rotations in the solution. A Riks displacement controlled strategy was used to carry out the analysis. Plastic analyses on the composite models reproduced accurately the capacity of the specimens, the failure mode, the axial strain at peak load, the transverse stresses in the web, and the axial stresses in the transverse links. The influence of applying a typical construction loading sequence could also be reproduced numerically. A design equation is proposed to determine the axial capacity of this type of column.

• Knowledge Management Research
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• v.16 no.2
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• pp.139-172
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• 2015

Employee's agility is becoming a primary factor of improving individual work performance. Employee's agility refers to responsiveness or behavior of employees in the context of work environment change. The purpose of this study is to examine the relationship between employee's agility and work performance in the perspective of agility's influence factors(absorptive capacity, IT resource use, readiness to change) and knowledge-oriented leadership, A survey was conducted for gathering data (a total of 262 employees from 35 industrial organizations) to test the relationships. The results of analysis show that employee's agility is a driving force leading to individual work performance, that employee's absorptive capacity, IT resource use, readiness to change, and knowledge-oriented leadership are the significant influential factors of employee's agility, and that knowledge-oriented leadership strengthens the link between employee's absorptive capacity and agility. For theoretical and practical contributions, the research presents the grounds for arguments that employee's agility is employee's dynamic capability for individual work performance under work environment change, and that organizations trying to improve employee's agility need to explore employee's behavioral attitudes under individual, leader, and organizational dimensions. Limitations arisen in the course of the research and suggestions for future research directions are also discussed.