• The KIPS Transactions:PartC
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• v.13C no.5 s.108
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• pp.627-634
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• 2006

Overlay network eliminates the need to change the application-layer tree when the underlying network changes and enables the overlay network to survive in environments where nonmember nodes do not support multicast functionality. An overlay protocol monitors group dynamics, while underlying unicast protocols track network dynamics, resulting in more stable protocol operation and low control overhead even in a highly dynamic environment. But, if overlay multicast protocols does not know the location information of node, this makes it very difficult to build an efficient multicasting tree. So, we propose a Hierarchical Overlay Multicast Architecture (HOMA) with the location information. Because proposed architecture makes static region-based dynamic group by multicast members, it is 2-tired overlay multicasts of application layer that higher layer forms overlay multicast network between members that represent group, and support multicast between multicast members belonging to region at lower layer. This use GPS, take advantage of geographical region, and realizes a region-sensitive higher layer overlay multicast tree which is impervious to the movements of nodes. The simulation results show that our approach solves the efficiency problem effectively.

• Journal of Internet Computing and Services
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• v.12 no.6
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• pp.43-51
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• 2011

The recent development of the technology for wireless mobile computing and applied technology for location-based services has made it possible to support query processing faster than that in the past. However, some technological limitations on hardware and software still exist. The most critical aspects of query processing are accuracy and speed. For improving the accuracy, it is required that detailed information on the data involved in query processing be saved. In this case, the amount of information on the data increases, which decreases the speed. On the other hand, for increasing the speed, it is necessary to reduce the broadcast cycle, which enables rapid data acquisition as desired. In this case, because of insufficient index information, the listen time for the client increases, which may cause unnecessary energy consumption. Therefore, a trade-off occurs between the accuracy and speed. This paper proposes a hierarchical bitmap-based spatial index (HBI) as a solution for the aforementioned problems. HBI describes an object with 0 and 1 on the Hilbert curve map. It reduces the broadcast cycle by decreasing the index size on the basis of bit information and tree structure. Therefore, it is able to shorten the listen time and query processing time. In addition, HBI enables the detection of the locations of all the objects so that it is possible selectively listen to a broadcast. A performance evaluation of the proposed technique demonstrates that it is excellent.

• Journal of Korean Society for Geospatial Information Science
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• v.19 no.3
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• pp.13-21
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• 2011

In mobile environment supporting mobility technologies, user requirements have been increased with respect to utilization of location information. In particular, moving object DBMS has consistently posed in order to efficiently maintain traffic information related to location of vehicle which tents to tremendously change over time. Despite the fact that these sorts of researches must be taken into consideration, empirical studies on moving object in terms of map database for lbs service, spatial attribute of which is continuously changed over time, have rarely performed. Therefore, aim of this paper is to suggest efficient spatial index scheme, which is capable of supporting query processing algorithm and location of moving object over time, by developing new empirical model. As a result, we can come to the conclusion that moving object model based on multi-fixed grid index makes it possible to cut down on the number of entity for retrieving. What's more, this model enables hierarchical data to be accessed through efficient spatial filtering on large-scale lbs data and constraints in accordance with level in order to display map.

• Journal of the Economic Geographical Society of Korea
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• v.1 no.2
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• pp.71-84
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• 1998

Health has been seen as a resource necessary for both maintaining oneself and for living in a society pursuing high quality of life. Therefore, the medicare provision takes place of one of the most significant indexes for evaluating the regional welfare level. The purpose of this study is to investigate the locational characteristics of medicare service facilities. For the purpose, the distribution patterns of the medicare resources are analyzed both at the regional and local scales. The medicare resources are concentrated at the Metropolitan Seoul area in the regional scale, and they are also concentrated at the economic core areas in the local scale. Especially, higher level medicare resources, such as the general hospitals and medical specialists, show more concentration at the economic core areas than lower level services. This means that access to opportunities to receive higher level medicare is poorer in a more socially disadvantaged area. Since medicare service facilities are invested and operated by both private and public sectors, whose locational mechanisms are deferent, we analyzed the distribution patterns. Most medicare facilities are invested and managed by private sector in Korea, which is operated by market mechanism. This is related with the fact that the medicare facilities are concentrated at the economic core areas. The proportion of private sector is higher in the Metropolitan Seoul area, and thus this region shows stronger spatial disparity of medicare provision. In general, the medicare service facilities are located in the hierarchical structure, and thus the services levels and facility scales are differentiated by the hierarchy. We examined the hierarchical structure in the medicare service facilities in Korea. The referral medicare system has been applied with the assumption of the three level hierarchical structures in Korea. However, we could not find any distinct hierarchical structure in the scales of the medical service facilities.

• Convergence Security Journal
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• v.12 no.1
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• pp.3-8
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• 2012

MANET composed wireless nodes without fixed infrastructure provides high flexibility, but it has weak disadvantage to various attack. It has big weakness to DDoS attack because every node perform packet forwarding especially. In this paper, packet transmission information control technique is proposed to reduce damage of DDoS attack in MANET and search location of attacker when DDoS attacks occur. Hierarchical structure using gateway node is adopted for protect a target of attack in this study. Gateway node in cluster is included like destination nodes surely when source nodes route path to destination nodes and it protects destination nodes. We confirmed efficiency by comparing proposed method in this study with CUSUM and measured the quantity consumed memory of cluster head to evaluate efficiency of information control using to location tracing.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.5
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• pp.658-664
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• 2018

In this paper, we propose a group key management scheme for very high confidential information in tactical wireless networks. For the proposed scheme, we consider the tactical networks that has a hierarchical topology and the nature of high confidential information. The leader node, which may have higher probability of good channel state than others, provides some data to all the network member in order to generate a geographical group key and it transmits the encrypted information with minimum transmission power level to others. By this scheme, the security and reliability for sharing confidential information is ensured. The performance of the proposed scheme is validated by mathematical analysis. It shows that the proposed scheme makes nodes to share a high confidential information securely if the proper parameters for network design are selected.

• Proceedings of the Korea Information Processing Society Conference
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• 2004.11a
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• pp.125-128
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• 2004

최근 이동 통신 기술의 급속한 발달로 인해 휴대폰, PDA 등과 같은 휴대용 단말기의 사용이 보편화 되고 있다. 따라서 이동 객체의 시간에 따른 공간적인 위치정보를 활용하여 다양한 서비스를 제공하는 위치 기반 서비스(Location-Based Service)에 관한 많은 연구가 진행되고 있다. 위치 기반 서비스의 효율적 제공을 위하여 시간에 따라 지속적으로 변하는 이동 객체의 대용량 시공간 정보를 신속하게 저장, 관리, 검색할 수 있는 인덱싱 및 질의 처리 기술이 수반되어야 한다. 본 논문에서는 대용량 이동 객체 데이터베이스를 대상으로 한 효율적인 인덱스 구축을 위한 데이터 압축 표현 방식에 대하여 논한다. 이를 위해 본 논문에서는 기존의 주요 연구에서 2 차원 공간 좌표 (X, Y)로 표현되던 이동 객체의 공간 정보를 계층적 구조를 갖는 행정구역에 기반하여 1 차원의 공간 정보로 압축 표현하는 방식을 제안한다. 이를 이용하여 대용량의 공간정보를 저장하고 있는 이동 객체 데이터베이스의 인덱스 크기의 감소 및 질의 처리 시간의 향상 효과를 얻을 수 있다. 또한, 제안된 방식은 2 차원 공간 좌표를 1 차원의 행정구역 기반의 위치정보로 표현하기 때문에 이로 인한 데이터 손실이 발생할 수 있으나, 일정 공간 내의 객체분포를 필요로 하는 교통 상황 파악, 근사적(approximate) 공간 정보를 필요로 하는 사람${\cdot}$차량 위치 추적 서비스와 같은 위치 기반 서비스를 신속하게 처리하는데 유용하게 사용될 수 있다.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.10
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• pp.147-158
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• 2021

Due to COVID-19, the risk of price volatility in commodity and equity markets increases. The research and application of hedging is the most effective way to reduce the market risk. Hedging is a risk management strategy employed to offset losses in investments by taking an opposite position in a related asset. We use K-means and hierarchical clustering methods to cluster companies and futures products respectively, and analyze the relationship between the number of hedging firms, regional distribution, nature of firms, capital distribution, company size, profitability, number of local Futures Commission Merchants (FCMs), regional location, and listing time. The study shows that listed companies with large scale and good profitability invest more money in hedging, while state-owned enterprises' participation in hedging is more likely to be affected by the company size and the number of local futures commission merchants, and private enterprises are more likely to be affected by the company profitability and the regional location. Listed companies are more willing to choose long-listed and mature futures products for hedging. We also provide policy advice based on our conclusion. So far, there is no study on the characteristics of hedging. This paper fills the gap. The results provide a basis and guidance for people's investment and risk management. Using clustering analysis in hedging study is another innovation of this paper.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.544-550
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• 2006

Next-generation wireless/mobile networks are envisioned to have an IP-based infrastructure. One of the research challenges for next-generation all IP-based networks is the design of intelligent mobility management technologies that have a seamless mobility and minimal signaling overhead. Recently, HMIPv6 was proposed by the IETF for efficient mobility management. HMIPv6 reduces the amount of signaling and improves the performance of MIPv6 in terms of handover latency. However the MAP can be a single point of performance bottleneck when there are a lot of local movements. HMIPv6 can cause signaling overhead due to the unnecessary location update of idle mobile nodes. Therefore, in this paper, we propose the dynamic paging Mobile IPv6 that reduces the signaling cost of the unnecessary location updates using IP paging and organizes dynamically optimal MAP area according to user's mobility and traffic. We show performance results that are obtained from the average total location update cost and packet delivery cost.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.28 no.4
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• pp.55-62
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• 2005

This paper describes the experiment that investigated the possibility of design and evaluation of the usability of earcon applied to voice menu. The earcon has functions in providing navigational cue in the hierarchical menu, and also can be applied to voice menu for improving the recall rate and the response time. In this experiment, participants identified their location with the help of earcon applied to the voice menu with the various earcon parameters. In detail some participants listened to the good quality sound of voice menu using the structured earcon, and they recalled the location they heard. Other participants listened to the good quality sound of voice menu without earcon, and they recalled the location they heard in the same manner. And the response times were checked through their answers. On analyzing the results, we found the earcon applied to voice menu showed the increase of recalling rate from what they heard during experiment. That is the performance of task was better with earcon applied to voice menu than with voice menu without earcon. In the earcon applied to voice menu test, it showed the accuracy of 92.50%, but in voice menu without earcon test, people could only recall 66.25% among given questions. The response time was reduced from 4.98 sec to 3.85 sec. In addition, this experiment showed the 87.5% of participants preferred the earcon applied to voice menu.