• ETRI Journal
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• v.38 no.2
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• pp.291-301
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• 2016

In this paper, we study an optimized block-diagonal zero-forcing (BD-ZF) precoder in a two-tiered cognitive network consisting of a macro cell (MC) and a small cell (SC). By exploiting multiuser multiple-input and multiple-output Vandermonde-subspace frequency-division multiplexing (VFDM) transmission, a cognitive SC can coexist with an MC. We first devise a cross-tier precoder based on the idea of VFDM to cancel the interference from the SC to the MC. Then, we propose an optimized BD-ZF intra-tier precoder (ITP) to suppress multiuser interference and maximize the throughput in the SC. In the case where the dimension of a provided null space is larger than that required by the BD-ZF ITP, the optimized BD-ZF ITP can collect all limited channel gain by optimizing rotating and selecting matrices. Otherwise, the optimized BD-ZF ITP is validated to be equivalent to the conventional BD-ZF ITP in terms of throughput. Numerical results are presented to demonstrate the throughput improvement of the proposed optimized BD-ZF ITP and to discover the impact of imperfect channel state information.

• Applied Microscopy
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• v.25 no.4
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• pp.9-16
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• 1995

Ultrastructure of stemmata(larval eye) of 5th-instar larval in cabbage butterfly, Pieris rapae L, was morphologically investigated with light microscope, scanning electron microscope and transmission electron microscope Six stemmata are on each side of the head. Stemmata V and VI have a Y-shaped sulcus on the surface of their corneal lenses, the others have a columnar shaped process and smooth globular surface. The visual type of stemmata is resembled a single ommatidium of compound eye. The dioptric apparatus are a biconvex shaped cornea and crystalline cone. As a photoreceptor, each stemmata consists of 7 retinular cells arranged into 2 tiers. The first ceil tier of 3 distal retinular cells has formed a V-shaped cup rhabdome and the second cell tier of 4 basal retinular cells has formed a H-shaped fused rhabdome. Each retinular cell filled with pigment granules and contained multivesiclular bodies, coated vesicle and common organelles. The peripheral parts of retinular cells are enveloped by neuroglia cells and retinular cells are surrounded by 3 corneagenous cells. The distal portions of the 3 corneagenous cells contact each other, but the Y-shaped stemmata is separated from each other immediately under the cornea. The 7 axons from each stemma congregate into a bundle and each 7-axon group joins to form a stemmatal nerve, consisting of 42 retinular axons.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.10a
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• pp.41-41
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• 2011

국제해사기구(IMO)에서2016년에 건조되는 선박부터 Tier III 규제를 예고하고 있다. 이 규 제를 만족하기 위하여 엔진 전처리 기술 및 후처리 기술 개발과 실증 연구가 활발히 진행되고 있다. 이중 SCR(Selective Catalytic Reduction) 반응을 이용한 질소산화물 저감기술이 80% 이상의 Tier III NOx 규제치를 만족할 수 있는 유일한 기술이다. 육상 플랜트에서 실증과 검증이 확보된 SCR 기술의 선박 엔진에 대한 적용을 위해서는 선박의 급격한 운전조건 변화와 엔진에 의한 저주파 진동에 대한 촉매 내구성 확보가 중요하다. 본 연구에서 기공 분포면에서 마이크로 기공보다는 메죠 및 매크로 기공쪽으로 구조를 개선함으로써 촉매 사용시 우려되는 배기가스중의 Soot 또는 2차 합성물질에 의한 촉매기공 막힘을 최대한 방지한 상용 SCR 촉매를 개발하였다. 또한 촉매에 대한 내구성 실증을 위하여 현재 운항 선박(한진피츠버그호)에 장착하여 실증 실험을 수행하였다. 기존 corrugate 타입의 촉매보다 40% 정도의 부피 감소와 차압 감소를 달성하였고 이로 인하여 선박내 제한된 공간에 효율적으로 SCR 시스템 설치가 가능할 것으로 생각된다. 그리고 본 연구에서는 가이드 베인 설치 없이 유동 균일화를 달성하여 반응기 전체의 크기 축소가 가능하다. 이는 추가적인 비용 및 압력 손실 저감, 유지 보수 공간 확보 등의 장점이 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.628-649
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• 2017

Security and resource-saving are both demands of the fifth generation (5G) wireless networks. In this paper, we study the secrecy spectrum efficiency (SSE) and secrecy energy efficiency (SEE) of a K-tier massive multiple-input multiple-output (MIMO) enabled heterogeneous cellular network (HetNet), in which artificial noise (AN) are employed for secrecy enhancement. Assuming (i) independent Poisson point process model for the locations of base stations (BSs) of each tier as well as that of eavesdroppers, (ii) zero-forcing precoding at the macrocell BSs (MBSs), and (iii) maximum average received power-based cell selection, the tractable lower bound expressions for SSE and SEE of massive MIMO enabled HetNets are derived. Then, the influences on secrecy oriented spectrum and energy efficiency performance caused by the power allocation for AN, transmit antenna number, number of users served by each MBS, and eavesdropper density are analyzed respectively. Moreover, the analysis accuracy is verified by Monte Carlo simulations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.4
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• pp.768-774
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• 2007

This paper proposes how to reduce the amount of data transmitted in each sensor and cluster head in order to lengthen the lifetime of sensor network. This study proposes hierarchical filtering for reducing the sensor's energy dissipation. Hierarchical filtering is to divide sensor network by two tiers when filtering it. First tier performs filtering when transmitting the data from cluster member to cluster head, and second tier performs filtering when transmitting the data from cluster head to base station. This should increase the efficiency of filtering and decrease the inaccuracy of the data compared to the methods which enlarge the filter width to do more filtering.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.2
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• pp.344-358
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• 2011

Wireless tactical network (WTN) is the most important present-day technology enabling modern network centric warfare. It inherits many features from WMNs, since the WTN is based on existing wireless mesh networks (WMNs). However, it also has distinctive characteristics, such as hierarchical structures and tight QoS (Quality-of-Service) requirements. Little research has been conducted on hierarchical protocols to support various QoS in WMN. We require new protocols specifically optimized for WTNs. Control packets are generally required to find paths and reserve resources for QoS requirements, so data throughput is not degraded due to overhead. The fundamental solution is to adopt topology aggregation, in which a low tier node aggregates and simplifies the topology information and delivers it to a high tier node. The overhead from control packet exchange can be reduced greatly due to decreased information size. Although topology aggregation is effective for low overhead, it also causes the inaccuracy of topology information; thus, incurring low QoS support capability. Therefore, we need a new topology aggregation algorithm to achieve high accuracy. In this paper, we propose a new aggregation algorithm based on star topology. Noting the hierarchical characteristics in military and hierarchical networks, star topology aggregation can be used effectively. Our algorithm uses a limited number of bypasses to increase the exactness of the star topology aggregation. It adjusts topology parameters whenever it adds a bypass. Consequently, the result is highly accurate and has low computational complexity.

• Asia Pacific Journal of Business Review
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• v.4 no.1
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• pp.45-60
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• 2019

Proposing that the main barriers to mini-packaging success in China, in contrast to India and the Philippines, is Chinese consumers' sociocultural values and attitudes toward products in mini packages, this study investigates the factors that potentially make the China market relatively not conducive to buying products in mini packages via a survey of 468 Chinese adults in Shanghai (first-tier city) and Zhuhai (second-tier city). Results show that respondents agree that products in mini packages are difficult to store once opened, are more expensive than are larger-sized products, do not provide good value for money, entail frequent shopping, are harmful to the environment, are not advertised, and are mainly for trying new products and for traveling. They disagree with many possible reasons for the unpopularity of products in mini packages. This study's contributions are (1) providing in-depth quantitative analysis of the possible reasons mini-packaging is not popular in China, (2) offering managerial advice for using mini-packaging to increase brand competitiveness, (3) developing a scale to measure attitudes toward products in mini packages; and (4) being empirical as opposed to merely anecdotal/speculative like some studies in this area.

• The Journal of the Korea Contents Association
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• v.9 no.1
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• pp.30-44
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• 2009

In this paper, we propose the mobile P2P structure supporting content searches for mobile peers efficiently. The proposed mobile P2P structure is a 3-tier structure which consists of a mobile peer, a mobile super peer, and a stationary super peer to reduce the content search cost of mobile P2P service. For content searches, mobile peer searches content in the communication range and performs hierarchical content searches which is using mobile super peer, stationary super peer for expansion of query region. In order to support hierarchial content searches and the continuity of services according to peer mobilities, peer's join/leave processes are explicitly stored by supporting message structures to the upper layer It is shown through experimental evaluation that the proposed structure improves about 32% contents search performance over the existing 2-tier structure. Since it also reduces the messages transferred to the stationary super peers, it reduced about 25% search loads of them.

• Journal of Digital Convergence
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• v.11 no.10
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• pp.169-179
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• 2013

Small and medium-sized firms are increasingly dependent on the knowledge and expertise of the supply chain as a whole to innovate and improve supply chain performance. This research examines the capabilities that enable firms to collaborate successfully, and aims to identify the determinants of SCM performance of the suppliers participating in supply chains managed by Global Korean companies. This study proposes the technology support, the collaboration with tier two companies, incentives and information sharing as major research variables, and collected the survey responses from 58 domestics suppliers. The statistical results indicate that the incentives, technology support and the collaboration with tier two firms influence the level of co-work with the firm leading supply chain, and that information sharing has some impact on SCM performance of the suppliers. But on the contrary to our expectation, the co-work with the firm leading supply chain has only moderate impact on SCM performance with p value just over 5%. We conclude this paper with some suggestions for future research.

• Korean Journal of Remote Sensing
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• v.40 no.2
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• pp.203-217
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• 2024

The Land Use, Land-Use Change and Forestry (LULUCF) sector of the National Greenhouse Gas Inventory is crucial for obtaining data on carbon sinks, necessitating accurate estimations. This study analyzes cases of countries applying the LULUCF sector at the Tier 3 level to propose enhanced methodologies for carbon sink estimation. In nations like Japan and Western Europe, satellite spatial information such as SPOT, Landsat, and Light Detection and Ranging (LiDAR)is used alongside national statistical data to estimate LULUCF. However, in Korea, the lack of land use change data and the absence of integrated management by category, measurement is predominantly conducted at the Tier 1 level, except for certain forest areas. In this study, Space-borne LiDAR Global Ecosystem Dynamics Investigation (GEDI) was used to calculate forest canopy heights based on Relative Height 100 (RH100) in the cities of Icheon, Gwangju, and Yeoju in Gyeonggi Province, Korea. These canopy heights were compared with the 1:5,000 scale forest maps used for the National Inventory Report in Korea. The GEDI data showed a maximum canopy height of 29.44 meters (m) in Gwangju, contrasting with the forest type maps that reported heights up to 34 m in Gwangju and parts of Icheon, and a minimum of 2 m in Icheon. Additionally, this study utilized Ordinary Least Squares(OLS)regression analysis to compare GEDI RH100 data with forest stand heights at the eup-myeon-dong level using ArcGIS, revealing Standard Deviations (SDs)ranging from -1.4 to 2.5, indicating significant regional variability. Areas where forest stand heights were higher than GEDI measurements showed greater variability, whereas locations with lower tree heights from forest type maps demonstrated lower SDs. The discrepancies between GEDI and actual measurements suggest the potential for improving height estimations through the application of high-resolution remote sensing techniques. To enhance future assessments of forest biomass and carbon storage at the Tier 3 level, high-resolution, reliable data are essential. These findings underscore the urgent need for integrating high-resolution, spatially explicit LiDAR data to enhance the accuracy of carbon sink calculations in Korea.