• Journal of Korea Spatial Information System Society
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• v.6 no.1 s.11
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• pp.73-85
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• 2004

Recently, as the growth of the wireless Internet, PDA and HPC, the focus of research and development related with GIS(Geographic Information System) has been changed to the Real-Time Mobile GIS to service LBS. To offer LBS efficiently, there must be the Real-Time GIS platform that can deal with dynamic status of moving objects and a location index which can deal with the characteristics of location data. Location data can use the same data type(e.g., point) of GIS, but the management of location data is very different. Therefore, in this paper, we studied the Real-Time Mobile GIS using the HBR-tree to manage mass of location data efficiently. The Real-Time Mobile GIS which is developed in this paper consists of the HBR-tree and the Real-Time GIS Platform HBR-tree. we proposed in this paper, is a combined index type of the R-tree and the spatial hash Although location data are updated frequently, update operations are done within the same hash table in the HBR-tree, so it costs less than other tree-based indexes Since the HBR-tree uses the same search mechanism of the R-tree, it is possible to search location data quickly. The Real-Time GIS platform consists of a Real-Time GIS engine that is extended from a main memory database system. a middleware which can transfer spatial, aspatial data to clients and receive location data from clients, and a mobile client which operates on the mobile devices. Especially, this paper described the performance evaluation conducted with practical tests if the HBR-tree and the Real-Time GIS engine respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.187-193
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• 2010

This paper introduces a new mobile advertisement management system (AMS) utilizing on-line music service in communication networks. The developed AMS delivers commercial advertisement through music service that is preferred in communication networks, which enable advertisers to perform a customer based advertisement and listeners to get a discount on their bills for music service. And eventually the proposed AMS can provide the effective commercial service to the advertisers and the effective clients recruit ways to music providers.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.700-702
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• 2001

현재 이동 컴퓨팅 환경의 여러 제약조건을 고려한 클라이언트 캐시에 대한 다양한 연구가 진행되고 있다. 최근에는 캐시 데이터의 일관성 검사를 위하여 서버의 주기적인 무효화보고(Invalidation Report, IR) 기법을 이용한 연구가 활발하게 진행되고 있다. 즉 서버로부터 전송되는 이전 일정 주기($\omega$)동안 수정된 데이터 항목에 대한 정보를 이용하여, 클라이언트는 자신의 캐시 데이터의 일관성을 검사한다. 하지만 클라이언트가 오랜 접속 단절이 발생할 경우 모든 캐시 데이터를 버려야 하므로, 이 경우 성능에 큰 장점을 얻을 수 없게 된다. 이에 본 논문에서는 이동 컴퓨팅 환경에서 빈번한 접속 단절로 인하여 오랫동안 무효화 보고를 받지 못하더라도 유효한 캐시 데이터를 최대한 유지시킬 수 있는 기법들을 제안한다. 먼저 클라이언트가 접속 단절 후 첫 재접속이 되었을 경우, 자신의 이전 접속 단절 시간을 전송하도록 하여 서버가 동적으로 IR에 포함될 이전 일정 주기를 결정하도록 하였다. 이에 반하여 두 번째 기법에서는 서버가 특정 기간 동안의 IR을 저장하도록 하여, 오랜 접속단절 후에도 클라이언트가 직접 캐쉬 데이터의 일관성 검사를 요청할 수 있도록 하였다.

• ETRI Journal
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• v.31 no.3
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• pp.333-335
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• 2009

To match the requirements of heterogeneous mobile devices, video objects may be transcoded, which requires considerable CPU resources. Alternatively, multiple versions of the same video may be stored on servers, but this requires a lot of disk space. We formulate the trade-off between the versions that are stored on disk and the need for transcoding. We propose an optimal solution to this formulation based on dynamic programming. Experiments show that our scheme allows up to 68% more clients to be admitted than conventional schemes when a reasonable amount of storage is available.

• Journal of Communications and Networks
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• v.7 no.4
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• pp.417-428
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• 2005

The Voronoi diagram (VD) is the most suitable mechanism to find the nearest neighbor (NN) for mobile clients. In NN query processing, it is important to reduce the query response time, since a late query response may contain out-of-date information. In this paper, we study the issue of location dependent information services (LDISs) using a VD. To begin our study, we first introduce a broadcast-based spatial query processing methods designed to support NN query processing. In further sections, we introduce a generic method for location-dependent sequential prefetching and caching. The performance of this scheme is studied in different simulated environments. The core contribution of this research resides in our analytical proof and experimental results.

• Proceedings of the Korean Information Science Society Conference
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• 2001.04b
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• pp.241-243
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• 2001

이동 컴퓨팅 환경이 급속하게 발전하면서 GIS 분야에서도 이동 클라이언트를 이용한 다양한 서비스에 대한 연구가 진행되고 있다. 특히, 이동 클라이언트를 이용한 공간 데이터 변경의 경우에 동시성 제어를 수행해야 하는데 기존 클라이언트-서버 환경에서 사용되는 잠금 기법은 잠금 획득을 위한 긴 대기시간 때문에 적합하지 않다. 본 논문에서는 이동 컴퓨팅 환경에서의 공간 데이터 변경을 위한 3-계층 구조를 제시하며 이 구조에서의 대리 트랜잭션 모델을 정의한다. 또한, 이동클라이언트의 공간 데이터 변경 트랜잭션의 동시성 제어를 위해 전통적인 낙관 기법을 확정하여 공간 데이터에 적합한 확인 기법을 제시하며 동시성 제어에서 트랜잭션 직렬화 보장의 예를 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.5
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• pp.1752-1767
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• 2015

As a special type of mobile ad-hoc network, Vehicular Ad-hoc Network (VANET) is considered as an attractive topic by many researchers. In VANETs, vehicles act as routers and clients, which are connected with each other through unreliable wireless links. Due to the dynamic nature of vehicles, developing communication protocols for VANETs is a challenging task. In this paper, we tackle the problem of real-world VANET operations and propose a new dual-level communication scheme through the combination of power and rate control algorithms. Based on the game theoretic approach, the proposed scheme effectively formulates the interactive situation among several vehicles. With a simulation study, it is confirmed that the proposed scheme can achieve better performance than other existing schemes under widely diverse VANET environments.

• The Transactions of the Korea Information Processing Society
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• v.6 no.1
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• pp.49-56
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• 1999

Distributed object Computing, owing to the development of distributed computing, has improved the performance of distributed processing conducted between homogeneous and heterogeneous systems in network. However, it has failed to solve fundamental problems such as network overload and enormous requests demands by servers and clients. In this paper, we propose to design and implement an Object Migration system that uses the java language to tackle the mentioned problems. As the first step of the implementation of the system, we justify the characteristics of t도 mobile object model that keeps codes and states of an object. Implemented Object Migration System would accept objects being migrated to a specific node and support the virtual place in which objects could be executed automatically. Therefore, the Object Migration system we suggest could not only solve problems imposed to traditional distributed computing but also offer transparency of object migration between homogeneous and heterogeneous systems.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.98-106
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• 2009

This paper proposes an optical wireless transfer agent method which realizes the continuous and swift data transfer of optical wireless terminals in optical wireless networks. The unguided wireless channel generally shows frequent link disconnections and propagation delays due to weak wireless links. Specially speaking, optical wireless channels have more vulnerable links and roaming propagation delays relative to the weakness of the previous RF channels due to their low signal connectivity and small geographic coverage. Conventional optical wireless network protocols did not consider any fault models about physical link faults. Consequently, they have shown data transfer inefficiency for both data link control and physical wireless link control. To overcome these optical wireless environmental problems, this paper suggests a new wireless access point (or base station) agent system, which provides wireless or mobile clients with previous link layer protocols compensated.

• Proceedings of the Korea Information Processing Society Conference
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• 2006.11a
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• pp.697-700
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• 2006

오늘날 인터넷 광범위한 보급은 무선 이동 통신 기술로 급발전하고 무선 단말기의 보급과 폭발적인 증가로 인해 m-commerce가 차세대 상거래의 형태가 될 것으로 예상된다. 현재 m-commerce의 컨텐츠는 m-commerce와는 호환되지 않으며, 질적으로나 양적으로 그 내용이 매우 빈약하다. 따라서 m-commerce의 상품정보 컨텐츠를 m-commerce를 위해서 활용하는 방안이 요구되는데, 여기에는 무선 단말기의 제한된 처리 능력이 고려되어야 한다. 논문에서는 먼저 인터넷 상의 방대한 상품정보를 사용자의 선호도에 기반하여 효과적으로 여과시켜서 사용자가 관심있는 정보만을 간추려서 제공할 수 있는 시스템을 설계하고 구현한다. 다음에 구현된 시스템을 인터넷 쇼핑몰에 대해서 적용한다.