• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권4호
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• pp.1042-1058
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• 2024

Terahertz (THz) communication is becoming a key technology for future 6G wireless networks because of its ultra-wide band. However, the implementation of THz communication systems confronts formidable challenges, notably beam splitting effects and high computational complexity associated with them. Our primary objective is to design a hybrid precoder that minimizes the Euclidean distance from the fully digital precoder. The analog precoding part adopts the delay-phase alternating minimization (DP-AltMin) algorithm, which divides the analog precoder into phase shifters and time delayers. This effectively addresses the beam splitting effects within THz communication by incorporating time delays. The traditional digital precoding solution, however, needs matrix inversion in THz massive multiple-input multiple-output (MIMO) communication systems, resulting in significant computational complexity and complicating the design of the analog precoder. To address this issue, we exploit the characteristics of THz massive MIMO communication systems and construct the digital precoder as a product of scale factors and semi-unitary matrices. We utilize Schatten norm and Hölder's inequality to create semi-unitary matrices after initializing the scale factors depending on the power allocation. Finally, the analog precoder and digital precoder are alternately optimized to obtain the ultimate hybrid precoding scheme. Extensive numerical simulations have demonstrated that our proposed algorithm outperforms existing methods in mitigating the beam splitting issue, improving system performance, and exhibiting lower complexity. Furthermore, our approach exhibits a more favorable alignment with practical application requirements, underlying its practicality and efficiency.

• Journal of Construction Engineering and Project Management
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• 제5권2호
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• pp.11-15
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• 2015

The Last PlannerSystem (LPS) has been implemented on construction projects to increase work flow reliability, a precondition for project performance againstproductivity and progress targets. The LPS encompasses four tiers of planning processes:master scheduling, phase scheduling, lookahead planning, and commitment / weeklywork planning. This research highlights deficiencies in the current implementation of LPS including poor lookahead planning which results in poor linkage between weeklywork plans and the master schedule. This poor linkage undetermines the ability of theweekly work planning process to select for execution tasks that are critical to projectsuccess. As a result, percent plan complete (PPC) becomes a weak indicator of project progress. The purpose of this research is to improve lookahead planning (the bridgebetween weekly work planning and master scheduling), improve PPC, and improve theselection of tasks that are critical to project success by increasing the link betweenShould, Can, Will, and Did (components of the LPS), thereby rendering PPC a betterindicator of project progress. The research employs the case study research method to describe deficiencies inthe current implementation of the LPS and suggest guidelines for a better application ofLPS in general and lookahead planning in particular. It then introduces an analyticalsimulation model to analyze the lookahead planning process. This is done by examining the impact on PPC of increasing two lookahead planning performance metrics: tasksanticipated (TA) and tasks made ready (TMR). Finally, the research investigates theimportance of the lookahead planning functions: identification and removal ofconstraints, task breakdown, and operations design.The research findings confirm the positive impact of improving lookaheadplanning (i.e., TA and TMR) on PPC. It also recognizes the need to perform lookaheadplanning differently for three types of work involving different levels of uncertainty:stable work, medium uncertainty work, and highly emergent work.The research confirms the LPS rules for practice and specifically the need to planin greater detail as time gets closer to performing the work. It highlights the role of LPSas a production system that incorporates deliberate planning (predetermined andoptimized) and situated planning (flexible and adaptive). Finally, the research presents recommendations for production planningimprovements in three areas: process related, (suggesting guidelines for practice),technical, (highlighting issues with current software programs and advocating theinclusion of collaborative planning capability), and organizational improvements(suggesting transitional steps when applying the LPS).

• 예술경영연구
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• 제56호
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• pp.5-38
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• 2020

본 연구는 문화기반 마을공동체가 어떻게 고유의 공동체 문화를 형성하고, 지속가능한 성숙한 공동체가 되는지 파악하기 위해 정책대상자의 인식, 정서, 역량에 대해 살펴보았다. 공동체의 개념, 공동체 성장요인 및 성장단계, 문화활동, 그리고 정책 집행이론에 대한 선행연구를 살펴보고, 문화기반 마을공동체 사업에 적합한 정책집행 분석모형을 도출하였다. 연구방법은 질적사례연구방법을 채택하였고, 연구대상은 안산 사동 '감골주민회', 안산 대부동 '상동공동체', 안동 신세동 '그림애문화마을'로 문화기반 마을공동체의 성공사례를 선정하였다. 심층인터뷰와 문헌분석, 직접관찰을 통해 얻은 자료를 로버트 인(2009)이 제시한 패턴매칭, 사례통합 분석기법을 활용하여 분석하였다. 연구결과는 첫째, 정책대상자는 공동체 활동을 통해 신뢰와 정서적 친밀감, 소속감을 느끼는 정서적 변화를 겪으며, 지역에 대한 애착심이 향상되었다. 둘째, 정책대상자의 공동체 의식과 공동체 역량이 성장에 중요한 요인으로 나타났다. 공동체 활동을 통해 참여유도, 상호교류, 역량강화, 파트너쉽의 단계를 거치며 성장해나가고 있음을 알 수 있었다. 셋째, 다양한 창의적 문화활동을 통해 스스로를 표현하면서 자신을 재발견하고, 타인과 소통하면서 마을공동체의 공통적 고민과 사회적 문제를 해결하는 경험을 하는 것으로 나타났다. 본 연구는 문화기반 마을공동체에 대한 생태학적 접근 연구를 기반으로 정책집행 분석 모형을 도출하였고, 문화기반 마을공동체의 사례를 분석하여 공동체의 성장 방향성과 실천적 함의를 제시하였다.

• 전력전자학회논문지
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• 제7권2호
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• pp.129-136
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• 2002

최근에 전력계통의 안정 및 고품질화에 대한 요구가 증대되기 시작하였고, 이에 따라 향상된 전력변환기술과 대체에너지원을 이용한 계통연계형 시스템에 대한 연구가 활발히 진행되고 있다 이러한 시스템에서의 인버터의 효율은 매우 중요하다. 따라서 본 논문에서는 이러한 계통연계형 시스템을 고효율화 하기 위한 방법으로 소프트-스위칭 기법이 적용 가능한 전류제어형 인버터를 제안하였다. 또한, 소프트-스위칭 기법을 적용할 수 있는 전류제어 알고리즘과 ZVT 동작원리를 이론적으로 해석하였고 이의 유용성을 시뮬레이션과 실험을 통하여 입증하였다.

• Geomechanics and Engineering
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• 제10권4호
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• pp.423-436
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• 2016

Currently, there is a great interest in the coupling between multiphase fluid flow and geomechanical effects in hydrocarbon reservoirs and surrounding rocks. The ideal solution for this coupled problem is to introduce the geomechanical effects through the stress analysis solution and implement an algorithm, which assures that the equations governing the flow and stress analyses are obeyed in each time step. This paper deals with the implementation of a program (FORTRAN90 interface code), which was developed to couple conventional reservoir (ECLIPSE) and geomechanical (ABAQUS) simulators, using a partial coupling algorithm. The explicit coupled hydro-mechanical behavior of Iranian field during depletion and $CO_2$ injection is studied using the soils consolidation procedure available in ABAQUS. Time dependent reservoir pressure fields obtained from three dimensional compositional reservoir models were transferred into finite element reservoir geomechanical models in ABAQUS as multi-phase flow in deforming reservoirs cannot be performed within ABAQUS. The FEM analysis of the reservoir showed no sign of plastic strain under production and $CO_2$ injection scenarios in any part of the reservoir and the stress paths do not show a critical behavior.

• ETRI Journal
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• 제29권3호
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• pp.363-370
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• 2007

In this paper, we propose a flexible turbo decoding algorithm for a high order modulation scheme that uses a standard half-rate turbo decoder designed for binary quadrature phase-shift keying (B/QPSK) modulation. A transformation applied to the incoming I-channel and Q-channel symbols allows the use of an off-the-shelf B/QPSK turbo decoder without any modifications. Iterative codes such as turbo codes process the received symbols recursively to improve performance. As the number of iterations increases, the execution time and power consumption also increase. The proposed algorithm reduces the latency and power consumption by combination of the radix-4, dual-path processing, parallel decoding, and early-stop algorithms. We implement the proposed scheme on a field-programmable gate array and compare its decoding speed with that of a conventional decoder. The results show that the proposed flexible decoding algorithm is 6.4 times faster than the conventional scheme.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.213-216
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• 2004

This paper describes design and implementation of the 5.5 GHz VCO with parallel-branch inductors using 0.8${\mu}m$ SiGe HBT process technology. The proposed parallel-branch inductor shows $12 \%$ improvement in quality factor in comparison with the conventional inductor. A phase noise of -93 dBc/Hz is measured at 100 kHz offset frequency, and the harmonics in the VCO are suppressed less than -23 dBc. The single-sided output power of the VCO is -6.5$\pm$1.5 dBm. The manufactured VCO consumes 15.0 mA with 2.5 V supply voltage. Its chip areas are 1.8mm ${\times}$ 1.2mm.

• 전력전자학회논문지
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• 제22권1호
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• pp.75-81
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• 2017

This paper presents a design and parallel control strategy of 1.8 kW low-voltage DC-DC converter (LDC) for mild hybrid electric vehicles to improve their power density, system efficiency, and operation stability. Topology and control scheme are important on the LDC for mild hybrid electric vehicles to achieve high system efficiency and power density because of their very low voltage and large current in input and output terminals. Therefore, the optimal topological structure and control algorithm are examined, and a detailed design methodology for the power and control stages is presented. A working sample of 1.8 kW LDC is designed and implemented by applying the adopted topology and control strategy. Experimental results indicate 92.45% of the maximum efficiency and 560 W/l of power density.

• Smart Structures and Systems
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• 제14권6호
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• pp.1151-1172
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• 2014

This paper presents a user programmable computational/control platform developed to conduct real-time hybrid simulation (RTHS). The architecture of this platform is based on the integration of a real-time controller and a field programmable gate array (FPGA).This not only enables the user to apply user-defined control laws to control the experimental substructures, but also provides ample computational resources to run the integration algorithm and analytical substructure state determination in real-time. In this platform the need for SCRAMNet as the communication device between real-time and servo-control workstations has been eliminated which was a critical component in several former RTHS platforms. The accuracy of the servo-hydraulic actuator displacement control, where the control tasks get executed on the FPGA was verified using single-degree-of-freedom (SDOF) and 2 degrees-of-freedom (2DOF) experimental substructures. Finally, the functionality of the proposed system as a robust and reliable RTHS platform for performance evaluation of structural systems was validated by conducting real-time hybrid simulation of a three story nonlinear structure with SDOF and 2DOF experimental substructures. Also, tracking indicators were employed to assess the accuracy of the results.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2002년도 학술논문발표회
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• pp.75-80
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• 2002

The purpose of this study is to conduct researches on the aspects of reconstruction and remodeling of low-rise, dilapidated apartment buildings in the provinces, using comparative methodologies, consequently coming up with the findings in the following. 1) Unlike the rebuilding projects in which the movement process tends to be made in a bulk (in a simultaneous manner), it turns out that when it comes to remodeling, it would be advisable to attempt moving the inhabitants as a group either by the size of their residence or by the building. 2) Given the peculiarities of the construction management mechanism, remodeling projects might seem disadvantageous on the part of the management on account of inadequate accumulation of information and experience. Hence, based on the impeccable assessment of the current status of the subject buildings from the phase of planning, its imperative to closely look into and take into consideration a variety of direct and/or indirect factors in advance of the implementation. 3) A series of comparative researches from the perspective of economical efficiency that remodeling projects appear profitable considering the overall costs including financial expenses, varied taxes, and so on that will be eventually brought forth during the reconstruction period, and all the more so when allowing for the consequential effects which they ought to have upon the natural and human resources, environmental and ecological condition, business potentials, etc. Amelioration to be desired on the basis of the findings above.