• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.202-213
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• 2004

In this paper, we propose a preamble structure and synchronization/channel estimation methods for OFDM-based multiple antenna WLAN systems that have 200Mbps transmit rate. With the proposed preamble structure, multiple antenna WLAN systems are backward-compatible with IEEE 802.11a systems which use the same 5㎓ band and synchronization performance is better than that of single antenna OFDM systems. For channel estimation, the preamble overhead is small and performance degradation by timing synchronization error that causes the critical problem of conventional comb-type multiple antenna channel estimation method also can be minimized by frequency domain phase recovery. Synchronizer and channel estimator for proposed preamble structure are implemented and verified using Verilog HDL. For the system with 4 transmit antennas and 4 receive antennas, about 150K gates are needed for synchronizer and 12K gates for channel estimator.

• ETRI Journal
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• v.33 no.6
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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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• v.24 no.2
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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.

• Proceedings of the KSR Conference
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• 2008.11b
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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.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.26-33
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• 2014

For wireless communication systems of (and beyond) LTE-Advanced, multiple-input multiple-output (MIMO) with an increased number of antennas will be utilized for system throughput improvement. When using such an increased number of antenna, an excessive amount of overhead in channel state information (CSI) feedback can be a serious problem. In this paper, we propose methods which reduce the CSI feedback overhead, particularly including application strategies for multi-rank transmission targeted for two or more reception antennas. To reduce the information which is instantaneously transmitted from the reception node to the transmission node, we present a beamforming method utilizing singular value decomposition (SVD) based on channel estimation of partitioned antenna arrays. Since the SVDs for partial matrices of the channel may lose the characteristics of the original unpartitioned matrix, we explain an appropriate scheme to cope with this problem.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.291-303
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• 2006

In this paper, we analyze functional requirements of the IEEE 802.22 WRAN, and propose a downlink 프레임 structure satisfying the requirements. The proposed downlink 프레임 structure maximizes e transmission efficiency by adopting the cognative radio to assign the sub-channel by reflecting the channel environment of WRAN. We also calculate the signalling overhead for both downlink and uplink, and analyze the performances of time synchronization, frequency synchronization and cell identification based on the 프리앰블 in downlink and suggest the channel estimation method tough 프리앰블 or pilot. As a final result, e stationary beamforming (SBF) algorithm with dynamic channel allocation(DCA) is proposed. The proposed OFDMA downlink 프레임 structure with channel adaptive sub-channel allocation for cognitive radio applications is verified to meet the requirements of IEEE 802.22 WRAN, by computer simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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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.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.2
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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.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2004.11a
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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.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.5
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• pp.509-517
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• 2001

Full-search algorithm requires large amount of computation which causes time delay or very complex hardware architecture for real time implementation. In this paper, we propose a fast motion estimator based on bit-plane matching, which reduce the computational complexity and the hardware cost. In the proposed motion estimator, the conventional motion estimation algorithms are applied to the binary images directly extracted from the video sequence. Furthermore, in the proposed VLSI motion estimator, we employ a Pair of processing cores that calculate the motion vector continuously By controlling the data flow in a systolic fashion using the internal shift registers in the processing cores, we avoid using SRAM (local memory) so that we remove the time overhead for accessing the local memory and adopt lower-cost fabrication technology. We modeled and tested the proposed motion estimator in VHDL, and then synthesized the whole system which has been integrated in a 0.6-$\mu$m triple-metal CMOS chip of size 8.15 X 10.84$\textrm{mm}^2$.