• 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 In NN query processing, it is important to reduce the query response time, since a late query response may contain out-of-date information.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.

• Journal of KIISE:Databases
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• v.32 no.4
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• pp.405-415
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• 2005

Indexing techniques are used to implement selective tuning in wireless environments Indices are broadcast together with data to help mobile clients locate the required information. As a result, clients stay in doze mode most of the time. The drawback of this solution is that broadcast cycles are lengthened due to additional index information. In location-aware mobile services(LAMSs), it is important to reduce the query response time, since a late query response nay contain out-of-date information. In this paper, we present a broadcast-based spatial query processing method (BBS) designed to support k-NN query processing. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients and the size of the service area.

• 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 KIISE:Databases
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• v.34 no.5
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• pp.448-464
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• 2007

Location-Based Services (LBSs) provide results to queries according to the location of the client issuing the query. In LBS, techniques such as caching and prefetching are effective approaches to reducing the data transmission from a server and query response time. However, they can lead to cache inefficiency and network overload due to the client's mobility and query pattern. To solve these drawbacks, we propose a semantic prefetching (SP) scheme using prefetching segment concept and improved cache replacement policies. When a mobile client enters a new service area, called semantic prefetching area, proposed scheme fetches the necessary semantic information from the server in advance. The mobile client maintains the information in its own cache for query processing of location-dependent data (LDD) in mobile computing environment. The performance of the proposed scheme is investigated in relation to various environmental variables, such as the mobility and query pattern of user, the distributions of LDDs and applied cache replacement strategies. Simulation results show that the proposed scheme is more efficient than the well-known existing scheme for range query and nearest neighbor query. In addition, applying the two queries dynamically to query processing improves the performance of the proposed scheme.

• Journal of Communications and Networks
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• v.7 no.4
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• pp.478-488
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• 2005

To conserve the usage of energy, indexing techniques have been developed in a wireless mobile environment. However, the use of interleaved index segments in a broadcast cycle increases the average access latency for the clients. In this paper, we present the broadcast-based location dependent data delivery scheme (BBS) for dynamic range queries. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. Then, we present a data prefetching and caching scheme, designed to reduce the query response time. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients, and the size of the service area.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.1
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• pp.50-58
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• 2007

In this paper, we propose a query-based visual attention algorithm for effective object finding of a vision-based mobile robot. This algorithm is developed by extending conventional bottom-up visual attention algorithms. In our proposed algorithm various conspicuity maps are merged to make a saliency map, where weighting values are determined by query-dependent object properties. The saliency map is then used to find possible attentive location of queried object. To show the validities of our proposed algorithm, several objects are employed to compare performances of our proposed algorithm with those of conventional bottom-up approaches. Here, as one of exemplar query-dependent object property, color property is used.

• 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.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11b
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• pp.73-75
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• 2005

최근에 이동 객체의 위치 정보를 활용한 위치기반서비스(Location-based Services : LBS)에 대한 관심이 급증하고 있고, 다양한 서비스들이 연구되고 있다. 기존의 이동 객체에 대한 위치 의존 질의(Location-dependent Query)들은 단순히 대상 객체와의 거리만을 고려하였고, 스카이라인 질의(Skyline Query)는 질의의 위치와 무관한 대상 객체의 정적인 속성만을 고려하였다. 이동 객체에 대한 스카이라인 질의는 스카이라인 질의의 다중 속성과 이동 객체의 동적인 속성인 대상 객체와의 거리를 고려해야 하기 때문에 이동 객체의 위치 변경에 따른 연속적인 질의가 발생한다. 이 논문에서는 이동 객체의 연속적인 스카이라인 질의를 효율적으로 처리하기 위한 Voronoi Diagram(VD)기반의 스카이라인 영역(Skyline Region)정의와 효율적인 영역 결정 기법을 제안한다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10a
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• pp.241-243
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• 2001

이동 컴퓨팅 환경에서 이동 호스트의 위치가 변함에 따라 그 의미가 달라지는 위치 의존 질의를 효과적으로 처리하기 위해서는 이동 호스트의 캐시 기법이 중요하지만, 위치 의존 질의를 효과적으로 지원할 수 있는 지구국의 브로드캐스팅 기법도 중요하다. 본 논문에서는 지구국이 담당하는 영역을 격자로 나누어 인덱싱한 데이터를 위치 의존 질의에 적합하도록 공간-채움 곡선을 이용해서 선형 클러스터링하여 구성 시간을 줄이는 브로드캐스팅 기법을 제안하고, 구성 시간을 포함시킨 이동 호스트의 활동 시간을 측정하여 그 성능을 비교한다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10a
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• pp.130-132
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• 2001

이동 컴퓨팅 환청에서 이동 사용자는 언제, 어디서나 현재 자신의 지리적 위치에서 유효성을 갖는 위치 기반 데이터를 액세스 하고자 하는 이동 사용자의 요구가 증가하고 있다. 따라서, 이러한 위치기반의 데이타를 얻기 위한 위치 기반 질의를 표현하고, 효율적으로 처리할 수 있는 방법이 필요하다. 본 논문에서는 위치 기반 질의를 효율적으로 처리 하기 위해 이동 사용자의 현재 위치를 중심으로 하는 원의 방정식을 이용하여 질의 탐색 공간을 표현하고, 질의 영역 분말 방법을 이용하여 탐색공간을 최적화하는 위치 기반 질의 처리 기법을 제안하였다. 또한 이동 사용자에게 적응하는 효율적인 부분 질의 통합 방안을 제시하였다.