• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.167-178
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• 2003

In mobile computing environments, queries based on the location of mobile clients (MCs) may cause different results. We say that the data of these results are location dependent data (LDD). Location-dependent queries to LDD need to be processed in conjunction with the geographical distance. The efficiency of query processing may also be increased by LDD relationship, etc. But there is the problem of fuzziness about how the distance used in location-dependent queries is evaluated and the data regions are organized. In this paper, we quantify the fuzziness of a location-dependent fuery on LDD. And we propose data regions for LDD, called LDD regions, by relationship of accessed data and the degree of distance between data objects and MCs' locations. In simulation studies we show that the number of database access for location-dependent queries, which have several settings on MCs' favor and two granularity of regions, can be smaller in proposed LDD regions than that in geographical regions.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.5
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• pp.544-549
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• 2006

This research is to introduce about Judgment System for Intelligent Movement(JSIM) that can perform assistance work of human brain. JSIM can order autonomous command and also it can be directly controlled by user. This research assumes that control object is limited to Mobile Robot(MR) Mobile robot offers image and ultrasonic sensor information to user carrying JSIM and it performs guide to user. JSIM having PDA and Sensor-box controls velocity and direction of the mobile robot by soft-computing method that inputs user's command and information that is obtained to mobile robot. Also it controls mobile robot to achieve various movement. This paper introduces wearable JSIM that communicates with around devices and that can do intelligent judgment. To verify the possibility of the proposed system, in real environment, the simulation of control and application problem lot mobile robot will be introduced. Intelligent algorithm in the proposed system is generated by mixed hierarchical fuzzy and neural network.

• Annual Conference of KIPS
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• 2002.04b
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• pp.895-898
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• 2002

현재 활발하게 진행되고 있는 편재 컴퓨팅을 위한 기반에 대한 연구들은, 문맥-인식(Context-Aware) 어플리케이션 및 이를 지원하는 서비스 컴포넌트들을 기반으로 하는 능동 공간(Active Spaces, Smart Spaces)[1][2]을 규모 있게 구현할 수 있도록 해준다. 이러한 기반들의 근간에는 편재 컴퓨팅 디바이스들간의 통신을 위한 분산 서비스가 자리잡게 되며, 환경 내에 있는 주체들과 객체들간의 상호 작용이 이러한 분산 서비스를 통하여 이루어진다. 본 논문에서는 능동 공간을 위한 기반에 대한 설명과 이와 관련한 연구들을 소개하고 공간 내에 있는 주체와 객체들 사이에서 일어날 수 있는 보안 문제에 대한 고려사항을 살펴본다. 또한 편재 컴퓨팅 환경 기반의 보안 서비스를 위한 인증 및 접근 통제 컴포넌트를 제안한다.

• The KIPS Transactions:PartC
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• v.13C no.5 s.108
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• pp.651-658
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• 2006

Mobile computing environment is known to be quite difficult to provide user with a stable QoS(Qualify of Service) due to its mobility nature. In order to protect the inherent characteristics of wireless network such as low bandwidth and high transmission delay along with the user's mobility, many works are conducted to apply caching and prefetching methods. This paper presents a novel prefetching technique which is based on user's preference, that is, interest and Uuかity. It tries to improves the effectiveness of prefetching by separating and appling the interest with personal tendency of a given information, and the popularity with general tendency of the information. The proposed scheme shown relatively superior performance in terms of the utilization ratio of prefetched information and the failure ratio of information retrieval than the existing methods.

• Journal of KIISE:Computing Practices and Letters
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• v.7 no.4
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• pp.350-358
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• 2001

최근 이동 무선통신 환경에 대하여 점차 관심이 집중되고 있다. 이동 무선통신 환경을 구축하기 위하여 WAP(Wirelsee Appkication Protocol) 및 WAP 게이트웨이(Gateway)등이 제안되었는데, WAP 게이트웨이는 이동 무선통신 환경에서도 기존의 유선 네트워크를 함께 이용할 수 있도록 하였다. 그런데 이런 시도는 새로이 WML(Wireless Markup Language)로 구축된 웹사이트들에게만 적용될 뿐이며, HTML로 구축된 기존의 많은 웹사이트들을 지원할 수 없다. 본 논문에서는 새로운 WML 웹사이트들뿐만 아니라, 기존의 HTML 웹사이트들의 내용도 이동 무선통신 환경에서 사용될 수 있도록 하기 위하여, HTMl 필트 기능을 갖춘 WAP 게이트웨이 시스템을 설계하고 구현하였다. 이 시스템은 WAP 서버, 웹 클라이언트, 프로토콜 변환기, WML 인코더/디코도, HTML 필터 등으로 구성되어 있다. 이동 무선단말기 에뮬레이터를 사용한 실험에서 이 시스템을 사용한 결과, WML 및 HTML 웹사이트들에 대해서 수동적인 변환 없이도 이동 무선단말기에서 검색이 가능하였다.

• Annual Conference of KIPS
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• 2007.11a
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• pp.755-758
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• 2007

플래시 메모리는 휴대폰, MP3 플레이어, 개인휴대정보단말기(PDA), 휴대용 멀티미디어 플레이어(PMP), 디지털 카메라 및 캠코더와 같은 이동성이 강한 소형기기에서 가장 많이 사용되는 저장 매체이다. 최근 대용량의 값싼 플래시 메모리가 등장하면서 랩톱이나 데스크톱과 같은 일반적인 컴퓨팅 환경을 지닌 기기들에서도 그 사용이 확대되고 있는 추세이다. 플래시 메모리가 보다 범용적인 저장 장치로 사용되기 위해서는 일반 컴퓨팅 환경에서의 복잡한 작업 부하에서도 우수한 성능을 제공할 수 있는 플래시 변환 계층(Flash Translation Layer)이 반드시 필요하다. 아쉽게도 현재까지 연구된 FTL 기법들은 소형기기의 단순한 작업 부하에 알맞도록 설계되어 있으며, 일반 컴퓨팅 환경과 같이 복잡한 작업 부하를 지닌 환경에서는 우수한 성능을 제공하지 못한다는 단점을 가지고 있다. 본 논문에서는 일반 컴퓨팅 환경의 복잡한 작업 부하에 대해서도 우수한 가비지 수집 성능을 제공하는 새로운 로그 블록 교체 기법을 제안하였다. 실험을 통한 평가 결과, 제안한 기법은 기존 기법 대비 평균 35% 정도의 가비지 수집 부하를 감소시키는 것으로 나타났다.

• Journal of KIISE:Databases
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• v.32 no.1
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• pp.56-70
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• 2005

The results of location-dependent queries(LDQ) generally depend on the current locations of query issuers. Many mechanisms, e.g. broadcast scheme, hoarding, or racking policy, have been developed to improve the system peformance and provide better services, which are specialized for LDQs. Considering geographical adjacency of data and characteristics oi target area, caching policy and broadcast scheme affect the overall performance in LDQ. For this reason, we propose both the caching policy and broadcast scheme, which these features are reflected in. Based on the adjacency of data in LDQ, our broadcast scheme use Hilbert curve to cluster data. Moreover, in order to develop the caching policy suitable for LDQ on urban area, we apply the moving distance of a MH(Mobile Host) to our caching policy We evaluate the performance of the caching policy measuring the workload of MHs and the correctness of LDQ results and the performance of the broadcast scheme measuring the average setup-time of MHs in our experiments. Finally, we expect that our caching policy Provides more correct answers when executing LDQ in focal cache and leads significant improvement of the performance of MHs. It also seems quite probable that our broadcast scheme leads improvement of battery life of the MH.

• Journal of KIISE:Information Networking
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• v.32 no.3
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• pp.339-349
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• 2005

For recent years, data broadcast technology has been recognized as a very effective data delivery mechanism in mobile computing environment with a large number of cli;ents. Especially, a hybrid broadcast algorithm in real-time environment, which integrates one-way broadcast and on-demand broadcast, has an advantage of adapting the requests of clients to a limited up-link bandwidth and following the change of data access pattern. However, previous hybrid broadcasting algorithms has a problem in the methods to get a grip on the change of data access Pattern. It is caused by the diminution of requests for the data items which are contained in periodic broadcasting schedule because they are already broadcasted. To solve this problem, existing researches may remove data items in periodic broadcasting schedule over a few cycles multiplying cooling factor or find out the requests of data items with extracting them on purpose. Both of them are the artificial methods not considering the property of data. In this paper, we propose a real-time adaptive hybrid broadcasting based on data type(RTAHB-DT) to broadcast considering data property and analysis the performance of our aigorithm through simulation study.

• Journal of KIISE:Information Networking
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• v.28 no.3
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• pp.289-296
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• 2001

The Election protocol can be used as a building block in many practical problems such as group communication, atomic commit and replicated data management where a protocol coordinator might be useful. The problem has been widely studied in the research community since one reason for this wide interest is that many distributed protocols need an election protocol. However, despite its usefulness, to our knowledge there is no work that has been devoted to this problem in a mobile computing environment. Mobile systems are more prone to failures than conventional distributed system. Solving election in such an environment requires from a set of mobile hosts to choose a mobile host or a fixed host based on the their priority despite failures of both mobile computing and/or fixed hosts. In this paper, we describe a solution to the election problem from mobile computing systems. This solution is based on the Garcia Molina\\`s Bully algorithm.

• Annual Conference of KIPS
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• 2001.04b
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• pp.705-708
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• 2001

최근 이동 네트워크 상에서의 인터넷 서비스가 활성화되고 있으며, 이에 따른 이동 컴퓨터에 대한 인증 및 비밀성이 요구되고 있다. 따라서, 본 논문에서는 이동 컴퓨터가 도메인간을 이동하면서 노출될 수 있는 이동 컴퓨터의 Identity의 보호를 위해 사용자 Alias를 사용하였으며, 원격 도메인에도 Alias를 사용함으로 익명성 보장 및 불추적성을 지원한 안전한 인증 프로토콜을 제시한다. 또한, 본 논문에서는 안전성을 높이기 위해서 Alias 생성 시 공개키 암호 시스템을 이용하였다.