• 한국통신학회논문지
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• 제29권2A호
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• pp.202-213
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• 2004

본 논문에서는 다중 안테나 OFDM 기반의 최대 200Mbps급 차세대 무선 LAN 시스템의 프리엠블 구조와 이를 이용한 동기/채널 추정 기법을 제안한다. 제안된 프리엠블 구조를 사용할 경우 IEEE 802.11a 시스템과의 하위 호환성을 유지할 수 있을 뿐 아니라 동기 측면에서는 안테나 다이버시티(diversity) 이득으로 인해 단일 안테나 OFDM 시스템에 비해 우수한 성능을 얻을 수 있다. 또한 채널 추정 측면에서는 프리엠블의 오버헤드가 적고, 기존의 채널 추정 기법들을 적용할 경우 발생하는 시간 동기 오차에 의한 성능 저하를 주파수 영역에서의 위상 보정을 통해 최소화할 수 있다. 제안된 프리엠블 구조를 이용한 동기 및 채널 추정단은 Verilog HDL을 이용하여 하드웨어로 설계 및 검증되었으며, 그 결과 4개의 전송 안테나와 4개의 수신 안테나를 갖는 경우 동기단은 약 150K gates, 채널 추정단은 약 12K gates가 소요되었다.

• ETRI Journal
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• 제33권6호
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• pp.831-840
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• 2011

This paper focuses on codebook-based precoding for space-division multiple access/orthogonal frequency-division multiple access (SDMA-OFDMA) systems aiming to guarantee high throughput for their users as well as to mitigate interference to fixed satellite service (FSS). A systematic design of SDMA codebook for subband-based OFDMA is proposed, which forms multiple orthogonal beams with common spatial null in the direction of a victim FSS earth station (ES). The design enables both transmitter and receiver to independently construct identical codebook by sharing only on the direction angle of an FSS ES, which takes fewer overhead bits than Gram-Schmidt process, a general method satisfying our design criterion. A system-level throughput evaluation shows that the proposed precoding provides superior performance over existing spectrum sharing method, that is, subband deactivation. The spectrum sharing analysis shows that the proposed precoding, even with an estimation error of the direction angles of an FSS ES, causes lower interference than existing precoding, knockdown precoding.

• International Journal of Computer Science & Network Security
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• 제24권2호
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• pp.95-100
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• 2024

Cyclic Delay Diversity (CDD) is a diversity scheme used in OFDM-based telecommunication systems, transforming spatial diversity into frequency diversity and thus avoiding intersymbol interference without entailing the receiver to be aware of the transmission strategy making the signal more reliable achieving full diversity gain in cooperative systems. Here the analyzation of the influence of CDD-SC scheme in Cognitive Radio Network (CRN) is done with the challenge of overcoming the complication called channel estimation along with overhead in CNR. More specifically, the closed-form expressions for outage probability and symbol error rate are divided under different frequencies among independent and identically distributed (i.i.d.) frequency selective fading channel model i.e., the signal is divided into different frequencies and transmitted among several narrow band channels of different characteristics. It is useful in the reduction of interference and crosstalk. The results reveal the diversity order of the proposed system to be mainly affected by the number of multipath components that are available in the CNR.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.2051-2057
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• 2008

This paper is a feasibility study on the calculation of operating cost in regards to the overall operation following the completion of a number of LRT lines currently in progress. Owing to the absence of operating experience in driveless LRT system at home, the difficulties lie in the assumption of the optimal operating budget applying domestic real situation. Nevertheless, with 34 years of accumulated operating experience in heavy rail transit system, Seoul Metro, the nation's biggest urban rail transit operator, performs O&M consultancy services for several on-going projects along with every effort to acquire know-how where the appropriateness of the cost estimation as a required deliverable is reviewed and a more efficient way is provided. The main focus of this study is to seek a method to calculate the optimal amount of operating expenses as well as a cost-effective alternative for possible weaknesses from the standpoint of the operator. The body of this paper discusses the five issues such as personnel cost, overhead, maintenance cost, additional purchase price, alternative investment fee from a more macroscopic point of view, and the conclusion deals with the adequacy of the reason for selection of institutions with various operating know-how.

• 전자공학회논문지
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• 제51권6호
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• pp.26-33
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• 2014

LTE-A (Long Term Evolution-Advanced) 이후 무선 통신 시스템에서는, 시스템 전송률의 향상을 위해 증가한 개수의 입출력 안테나를 사용하는 MIMO (multiple-input multiple-output) 시스템이 활용될 것이다. 이러한 증가한 개수의 안테나 어레이를 사용하는 경우, 채널 정보의 궤환에 있어서 과도한 오버헤드가 문제가 될 수 있다. 본 논문에서는 이러한 상황에서 채널 정보의 궤환 오버헤드를 줄이기 위한 방안과, 특히 수신단에서 두 개 혹은 그 이상의 수신 안테나를 사용하는 다중 랭크 전송시의 적용 방안을 제안한다. 수신단에서 송신단으로 일시에 궤환되는 정보의 양을 줄이기 위해 안테나 어레이를 분할하여 추정하는 채널을 기반으로 특이값 분해 (SVD, Singular Value Decomposition)를 활용하는 빔포밍 방안을 제시한다. SVD의 연산과정의 특성 상, 분할된 행렬에 대한 SVD 연산은 원 행렬의 특성을 상실시킬 수 있으므로 이에 대한 대응 방안에 대해서도 설명한다.

• 한국통신학회논문지
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• 제31권3A호
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• pp.291-303
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• 2006

본 논문에서는 현재 진행 중인 IEEE 802.22 WRAN의 Functional Requirements를 분석하고, 제시된 Requirements를 만족시키는 하향링크 프레임 구조를 제안한다. 제안된 하향링크 프레임 구조는 WRAN 각 채널 환경하에서의 상황인식 적응 Traffic Channel에 의한 Rate Control을 수행하여 전송 효율을 극대화시키며, 이를 위한 하항링크와 상향링크의 Signaling Overhead를 계산한다. 그리고, 하링링크의 프리앰블을 이용한 시간, 주파수동기 및 셀 ID 탐색 성능을 분석하고, 프리앰블 또는 Pilot에 의한 환경 적응적 채널 추정 방법과 동적채널할당(Dynamic Channel Allocation)을 결합한 고정 빔형성(Stationary Beamforming) 알고리즘을 제안한다. 또한, 모의실험을 통하여 이와 같이 제안된 무선 채널 환경에서 적응 부채널 할당 기능을 고려한 상황인식 하향링크 프레임구조가 IEEE 802.22 WRAN 시스템의 요구사항을 만족시킴을 검증한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권4호
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• pp.1693-1713
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• 2018

An important technique used by database administrators (DBAs) is to improve performance in decision-support workloads associated with a Star schema is multi-level partitioning. Queries will then benefit from performance improvements via partition elimination, due to constraints on queries expressed on the dimension tables. As the task of multi-level partitioning can be overwhelming for a DBA we are proposing a wizard that facilitates the task by calculating a partitioning scheme for a particular workload. The system resides completely on a client and interacts with the costing estimation subsystem of the query optimizer via an API over the network, thereby eliminating any need to make changes to the optimizer. In addition, since only cost estimates are needed the wizard overhead is very low. By using a greedy algorithm for search space enumeration over the query predicates in the workload the wizard is efficient with worst-case polynomial complexity. The technology proposed can be applied to any clustering or partitioning scheme in any database management system that provides an interface to the query optimizer. Applied to the Teradata database the technology provides recommendations that outperform a human expert's solution as measured by the total execution time of the workload. We also demonstrate the scalability of our approach when the fact table (and workload) size increases.

• 산업경영시스템학회지
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• 제41권2호
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• pp.153-158
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• 2018

At the Bank of Korea, capital stock statistics were created by the PIM (perpetual inventory method) with fixed capital formation data. Asset classifications also included 2 categories in residential buildings, 4 non-residential buildings, 14 constructions, 9 transportation equipment, 28 machinery, and 2 intangible fixed assets. It is the Korean government accounting system which is developed much with the field of the national accounts including the valuation, but until 2008 it was consistent with single-entry bookkeeping. Many countries, including Korea, were single-entry bookkeeping, not double-entry bookkeeping which can be aggregated by government accounting standard account. There was no distinction in journaling between revenue and capital expenditure when it was consistent with single-entry bookkeeping. For example, we would like to appropriately divide the past budget accounts and the settlement accounts data that have been spent on dredging into capital expenditure and revenue expenditure. It, then, tries to add the capital expenditure calculated to FCF (fixed capital formation), because revenue expenditure is cost for maintenance etc. This could be a new direction, especially, in the estimation of capital stock by the perpetual inventory method for infrastructure (SOC, social overhead capital). It should also be noted that there are differences not only between capital and income expenditure but also by other factors. How long will this difference be covered by the difference between the 'new series' and 'old series' methodologies? In addition, there is no large difference between two series by the major asset classification level. If this is treated as a round-off error, this is a problem.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2004년도 추계학술발표회 논문집
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• pp.367-372
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• 2004

Highway have to be constructed under thorough investigation about function, economy, safety of the traffic and environment, because they are needing huge budget for construction and management as important facilities of the social overhead capital in the national economics. Initially the construction of roads becomes effective the plan, the design, construction phase. The design is foundation of accomplishment of the roads operation, the results of the design operation come to much effect a nation when using roads. Especially ancient design methods were not expected for visual effects as attaching weight to 2-dimensional drawing from flat. Therefore, it is difficult to recognize troubles happened during the work operation besides, many troubles are solved by modification of drawings as situations. For solving of those of the problems, it is emphasize on visual effect through introduction of 3-dimensional design from the initial phase. In case of national conditions, limited national land has caused increasing weight for construction of the roads through cities as the urban centered development. thereupon, citizens are increasing concern about the right of the light and the environmental effect, road designs and construction of the structures under agreement with local residents cause to make troubles. The analysis of 3-dimensional design is necessary as intermediation for decision making. In this study, Virtual reality techniques in 3-dimensional roads design are expected to visual effect on the publishing Internet Web, find problems in first phase and make decision between users and people having civil appeal.

• 대한전자공학회논문지SP
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• 제38권5호
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• pp.509-517
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• 2001

전역탐색알고리즘(full-search algorithm, FSA)은 탐색영역의 범위가 커짐에 따라 방대한 양의 계산을 필요로 하기 때문에 이에 따른 알고리듬의 처리시간이 커지고, 하드웨어로 구현했을 때 회로가 복잡해진다는 문제점을 안고 있다. 본 논문에서는 이러한 문제점을 개선하기 위한 방안으로 비트플레인 정합에 의한 움직임 추정기의 VLSI 구조를 제안한다. 제안된 움직임 추정기에서는 비트 플레인 정합기준을 이용하여 기존의 전역 탐색 알고리즘을 하나의 이진영상으로 적용함으로써 움직임 추정에 소요되는 연산의 양을 크게 줄이면 서도 전역탐색 알고리듬과 유사한 움직임 추정 성능을 갖도록 하였으며, 제안된 VLSI 구조에서는 두 개의 프로세싱 코어를 채택하여 데이터 흐름을 시스톨릭 (systolic) 어레이의 형태로 제어하여, 시스템 내부의 SRAM을 제거하여 동작 속도 상의 이득뿐만 아니라, 메모리 공정을 필요로 하지 않는 저가의 공정을 사용 가능하게 함으로써 제작상의 비용을 절감할 수 있는 해결책을 제시하였다. 구현된 하드웨어는 VHDL을 이용하여 설계하고, 기능 검증을 수행한 후 0.6-μm three-metal CMOS 공정을 이용하여 8.15 X 10.84㎟의 크기로 집적하였다.