• 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:Databases
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• v.32 no.4
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• pp.394-404
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• 2005

Battery capacity of mobile clients in wireless mobile computing environments is one of the important resources that determine the availability of mobile clients. So, data broadcast techniques in mobile computing environments need not only rapid delivery of requested data but also efficient data delivery mechanisms which can reduce battery consumption of mobile clients. This paper proposes organization of an index and broadcast data for on-demand data broadcast. It organizes an index containing broadcast time of each data using some of high-priority data in a broadcast server. By sending such index information prior to the corresponding data, the proposed approach reduces tuning time of mobile clients. It also includes when the next index information will be broadcasted in each data broadcast. This can reduce tuning time of mobile clients waiting for an index to be broadcasted. Experiments show that the proposed approach effectively reduces tuning time of mobile clients.

• Journal of KIISE:Databases
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• v.29 no.4
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• pp.285-296
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• 2002

When a client requests a set of data items at once, it is crucial to reduce the total time elapsed till the client receives all data items requested. This paper describes a data broadcasting technique that reduces access time for multiple data accesses from clients. The impact of the relative position of each data item in a broadcast schedule is dependent on the degree of data replication between data requests from clients. The relative broadcast frequencies for data items are affected by the degree of access skewness from clients. This paper proposes a technique for generation of a hierarchical data broadcast schedule, which can support multiple data accesses effectively by considering the data sharing among client requests and data access skewness together. Simulation results show that the proposed technique consistently performs better than the previous research results in various environments.

• Journal of KIISE:Databases
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• v.31 no.2
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• pp.140-149
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• 2004

Data broadcast has received much attention as a very efficient method for disseminating data items in mobile environment with large number of mobile clients. In this approach, a database server periodically and continuously broadcasts data items through wireless channels and clients perform read-only transactions by accessing necessary data items from the air. While broadcasting, the server must also process update transactions on the database, which raises an obstacle for client's accessing consistent data. In this research, we propose a new algorithm SCDSC(Serialization Checking with DirtySet on Commit) which is an alternative for solving the concurrency control problem efficiently. The SCDSC is a kind of optimistic concurrency control in that a client checks the consistency of data using a DirtySet as a part of data broadcast when it commits its transaction. In each broadcast cycle, the server updates and disseminates the DirtySet with newly changed data items for last few cycles in the sliding window approach. We perform an analysis and a simulation study to evaluate the performance of our SCDSC algorithm in terms of data consistency and data currency.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.4
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• pp.334-348
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• 2005

The goal of next generation digital broadcasting is offering the interaction among consumers and providers as well as variety services. One of the important factors for this new broadcasting environment keeps the interoperability among providers and consumers since the environment is distributed. Therefore a standard metadata for digital broadcasting is required and TV-Anytime metadata is one of the metadata standards for digital broadcasting. The terminal nodes of TV-Anytime metadata are defined by using MPEG-7 metadata. MPEG-7 metadata is standard metadata for describing multimedia content. Therefore, if we use the MPEG-7 metadata for describing broadcasting content can offer multimedia search services like content-based search by the extension of metadata. The efficient management system for these metadata is important for offering the services with high Duality on real broadcasting environment TV-Anytime metadata and MPEG-7 metadata are technically defined using a single XML schema, so its instances are XML data. Currently, a lot of systemsfor managing XML data are proposed in many researchers and we can expect to adapt these systems for managing broadcasting metadata. But the methods used in these systems are not specific methods for managing broadcasting metadata because of methods for general-purpose. In this paper, we find the properties of broadcasting metadata and develop an efficient metadata management system that is based on the found properties. Since our systemis implemented on real broadcasting environment, we expect that the system is most efficient and suitable. Also our system is interoperable since we use XQuery as query language for querying broadcasting metadata.

• The Journal of Information Technology
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• v.5 no.4
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• pp.9-21
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• 2002

In data broadcasting environments, the server periodically broadcasts data items in the database through the broadcast channel. When each client wants to access any data item, it should monitor the broadcast channel and wait for the desired item to arrive. Client data caching is a very effective technique for reducing the time spent waiting for the desired item to be broadcasted. This paper proposes a new client cache management scheme, named 2Q-CF, to reduce this waiting time and evaluate its performance on the basis of a simulation model. The performance results indicate that 2Q-CF scheme shows superior performances over LRU-CF and CF in the average response time.

• Journal of KIISE:Information Networking
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• v.33 no.4
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• pp.324-332
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• 2006

A caching is a useful technique to alleviate performance degradation due to the inherent narrow bandwidth by reducing contention of broadcast requests. In this paper, we propose a caching strategy for pull-based data broadcast system which considers data popularity among clients. In addition, the proposed strategy also reflects recentness of data access based on data broadcast version. Then, we evaluate the performance of proposed strategy through a simulation approach. According to the results, the strategy considering both hit ratio and miss cost shows better performance than the traditional LRU. In addition, the strategy considering data popularity among clients shows better performance in some cases.

• The KIPS Transactions:PartD
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• v.10D no.6
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• pp.961-970
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• 2003

In data broadcasting environments, the server periodically broadcasts data items in the broadcast channel. When each client wants to access any data item, it should monitor the broadcast channel and wait for the desired item to arrive. Client data caching is a very effective technique for reducing the time spent waiting for the desired item to be broadcastted. This paper proposes a new client cache management scheme, named LRU-CFP, to reduce this waiting time ans evaluates its performance on the basis of a simulation model. The performance results indicate that LRU-CFP scheme shows superior performance over LRU, GRAY and CF in the average response time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.99-107
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• 2002

Broadcast disks are suited for disseminating information to a large number of clients in mobile computing environments. In broadcast disks, the server continuously and repeatedly broadcasts all data items in the database to clients without specific requests. The clients monitor the broadcast channel and retrieve data items as they arrive on the broadcast channel. The broadcast channel then becomes a disk from which clients can retrieve data items. In this paper, we propose a cache conscious concurrency control ($C^4$) scheme to preserve the consistency of client transactions, when the values of broadcast data items are updated at the server. $C^4$ scheme is novel in the sense that it can reduce the response time of client transactions with minimal control information to be broadcast from the server. This is achieved by the judicious caching strategy of the clients.

• The Journal of Information Technology
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• v.7 no.1
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• pp.57-67
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• 2004

Data broadcast has attracted a lot of attention as an efficient way of disseminating data to very large client populations. The main motivation of data broadcast systems is that the number of clients that they serve can grow arbitrarily large without any effect on their performance. The performance of broadcast system depends mainly on client caching strategies and on data broadcast scheduling mechanisms. This paper addresses the latter issue and proposes a new broadcast scheduling scheme, named RxW$^{\alpha}$, that is suitable to data broadcast systems. This paper also evaluates the performance of RxW$^{\alpha}$ on the basis of a simulation model. The performance results indicate that RxW$^{\alpha}$ is capable of improving the performance in the variance of response time significantly, showing a reasonable performance in the response time.