• Journal of the Korea Society for Simulation
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• v.12 no.2
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• pp.55-62
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• 2003

The explosive Increase of wireless networks and the advancement of mobile devices lead to the expansion of mobile environment. In accordance with the development of mobile environment, the need to use mobile database is increased sharply, and also it accompanies the related problems. The current mobile database system is based on the centralized method from which a synchronized server manages multiple mobile database management system to synchronize. From this mobile system architecture, several kinds of problems can be detected such as the management of synchronization issues between mobile databases and the transaction management issues. Furthermore, the current mobile database management system does not consider any solution on the fault tolerance. To solve those problems, this paper proposes the mobile agent-based mobile database management system. The proposed system provide high confidence and efficiency by enhancing the network efficiency and fault tolerance through the mobile grouping.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2B
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• pp.27-35
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• 2005

As the number of Mobile IP users is expected to grow, the signaling overhead associated with mobility management in the wireless Internet is bound to grow. And since the wireless link has far less bandwidth resources and limited scalability compared to the wired network link, the signaling overhead associated with mobility management has a severe effect on the wireless link. In this paper, we propose IP-Grouping algorithm that can greatly reduce the signaling cost in the wireless link as Access Routers(ARs) with a large rate of handoff are grouped into a Group Zone. Based on the numerical analysis and simulation, we show that the wireless signaling cost in the IP-Grouping is much lower than that of the Hierarchical Mobile IPv6 under various condition.

• Journal of Digital Convergence
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• v.10 no.4
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• pp.199-206
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• 2012

Increment of mobile client's information request in wireless mobile networks requires a new method to manage and serve the streaming media object. This paper proposes a new object segment grouping method for enhancing the performance of streaming media services in wireless mobile networks. The proposed method performs the similarity metric for the partitioned object segments, and it process the disjunction, conjunction, and filtering for these metrics. This paper was to decided the partitioned group of object segments for these operation metrics, and it decided the performance of streaming media services. The simulation result showed that the proposed method has better performance in throughput, average startup latency, and cache hit ratio.

• Journal of Digital Contents Society
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• v.9 no.4
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• pp.533-541
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• 2008

In distributed mobile systems, the congestion control and disconnection problems are current major issues. This paper proposes a grouping-based fuzzy reference streaming method to improve the performance of systems supporting distributed mobile transactions. The proposed method resolves transaction requests issued by mobile clients using the GS interface. In the paper disconnection problems are resolved efficiently using transaction read and update for improved streaming service. Experimental results show that the proposed method outperforms the other existing methods significantly.

• The KIPS Transactions:PartD
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• v.10D no.3
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• pp.375-386
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• 2003

A rapid growth of mobile devices and a proliferation of wireless networks lead to changing the existing environment into a mobile environment. Expansion of mobile environment makes a pressing need of mobile databases, and there are several solutions to achieve it. But they still accompany with some problems. Especially, the current synchronization server that manages consistently many mobile database management systems is based on the centralized method to synchronize data between the mobile database systems. It is the major factor that causes the lower performance of the whole system. Furthermore, the fault tolerance has not been considered in the existing systems. Therefore, we suggest the mobile agent-based mobile database system in order to resolve the problems. The system, we propose in this paper, provides the high-performance of the whole system by mobile grouping, and also may support a fault-tolerance management method.

• Korean Journal of Cognitive Science
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• v.18 no.2
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• pp.193-221
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• 2007

This study explored the efficient hierarchical data structure of mobile interfaces. The first experiment demonstrated the effects of grouping(clear/unclear), depth level(2/3/5), and the number of items(32/64/128) on the search time and the number of errors. The results indicated that participants spent less time and made fewer errors to perform the task when the clear mobile interfaces, low depth level, and fewer items were provided. In addition, the results indicated that there were no effects of the depth level and the number of items on the search time and number of errors in clear mobile interfaces conditions. As depth level and the number of items changed, on the other hand, participants spent longer time to complete the task and made more mistakes in unclear mobile interfaces conditions. The second experiment investigated the effects of grouping(clear/unclear), the number of items(32/64/128), and spacial cues(colors/ windows/ number of cues) on search time and the number of errors in hierarchical data structures which had five depth levels. The results indicated that participants spent less time to complete the task and made less errors in a mobile interface when grouping is clear and the number of items are fewer. The results were identical with the first experiments. In addition, the main effect of spacial cues indicated that providing spacial cues via pictures and numbers can be helpful to reduce errors in search behaviors.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.293-302
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• 2004

Wireless LAN is a rather mature communication technology that connects mobile terminals. A typical wireless LAN system is composed of one AP and more than one terminals, which is called a BSS. Terminals near to an AP can receive high rate data but terminals far from an AP may not receive data with guaranteed high speed rate because received signal strength is weakened. This paper proposes a method to allow high speed data transmission by grouping terminals and using part of wireless terminals as repeaters. We compare and analyze proposed grouping algorithms based on Depth First Search and Breadth First Search via simulations. A grouping algorithm based on Breadth First Search is shown to be more effective in term of efficiency and coverage.

• The KIPS Transactions:PartC
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• v.13C no.3 s.106
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• pp.339-344
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• 2006

Secure delivery of multicast data can be achieved with the use of a group key for data encryption in mobile ad hoc network (MANET) applications based on the group communication. However, for the support of dynamic group membership, the group key has to be updated for each member joining/leaving and, consequently, a mechanism distributing an updated group key to members is required. The two major categories of the group key distribution mechanisms proposed for wired networks are the naive and the tree-based approaches. The naive approach is based on unicast, so it is not appropriate for large group communication environment. On the other hand, the tree-based approach is scalable in terms of the group size, but requires the reliable multicast mechanism for the group key distribution. In the sense that the reliable multicast mechanism requires a large amount of computing resources from mobile nodes, the tree-based approach is not desirable for the small-sized MANET environment. Therefore, in this paper, we propose a new key distribution protocol, called the proxy-based key management protocol (PROMPT), which is based on the naive approach in the small-sized MANET environment. PROMPT reduces the message overhead of the naive through the first-hop grouping from a source node and the last-hop grouping from proxy nodes using the characteristics of a wireless channel.

• Proceedings of the Korean Information Science Society Conference
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• 2000.04a
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• pp.349-351
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• 2000

이동 방송 환경(mobile broadcasting environment)은 정보를 가지고 있는 서버가 다수의 이동 클라이언트에게 모든 데이터를 주기적으로 방송하면 클라이언트가 자신이 원하는 데이터가 방송 채널에 나타날 때 이를 검색하는 환경을 말한다. 이 때 클라이언트는 일관적이면서 가장 최근에 갱신된 데이터를 필요로 하기 때문에, 병행성 제어 기법을 사용하여 이러한 요구 조건을 충족시켜야 한다. 이동 방송 환경에서는 클라이언트가 여러 가지 제약점을 가지고 있기 때문에 서버가 클라이언트의 일관성 검사를 위한 제어 정보를 데이터와 함께 방송해야 한다. 그러나, 매 방송 주기마다 방송해야 하는 제어 정보의 양이 크기 때문에 일관성 검사에 영향을 주지 않는 범위에서 이를 줄일 필요가 있다. 본 논문에서는 제어 정보의 양을 줄이기 위하여 데이터를 그룹화(grouping)하는 기법을 제시하고, 시뮬레이션을 통해 데이터 그룹화가 클라이언트의 트랜젝션 중단(abort)에 미치는 영향을 알아본다. 서로 다른 데이터들을 하나의 그룹으로 묶으면 클라이언트가 일관성을 검사할 때 트랜잭션이 불필요하게 중단되는 경우가 더 많아질 수 있다. 그러나, 실험 결과 전체 데이터 수의 20% 정도 크기로 데이터를 그룹화하면 불필요하게 트랜잭션이 중단되는 경우가 거의 없으면서 제어 정보의 크기를 줄일 수 있다는 사실을 알 수 있었다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.2
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• pp.87-95
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• 2010

A Vehicular Ad-Hoc Network (VANET) is form of the Mobile Ad-hoc Network (MANET) to provide temporary communication among vehicles via wireless links. In VANET, the vehicle is one of the nodes in networks and communicates with each other. However, the wireless links disconnect very frequently, because vehicles have mobility and move freely. The reason why data accessibility degrades is that disconnection occurs frequently. To improve data accessibility, data replica allocation methods that made group to allocate data replica have proposed in MANET. However, those are not suitable because it is difficult to maintain stable links among the nodes moving fast by centralized group. In this paper, we proposed TBG (Tree Based Grouping) to allocate data replica with the distributed grouping method. Each node has own TBG and allocates data replica based on stability of links to improve data accessibility. The experiment demonstrates that the proposed method outperforms traditional methods in term of data accessibility.