Showing papers by "Wang-Chien Lee published in 1999"

A study on channel allocation for data dissemination in mobile computing environments

Abstract: This paper studies channel allocation methods for data dissemination through broadcast and on-demand channels. Analytical models and cost formulae for exclusive broadcast channels and exclusive on-demand channels are provided. Based on the models, we further derive cost models for dynamic channel allocation methods and propose a channel adaptation algorithm for optimizing system performance. The channel adaptation algorithm can be executed in O(n) time, where n is the number of data items in the database. Performance evaluation shows that the channel allocation algorithm produces optimal channel allocation which significantly improves the system performance under various parameter settings.

Indexing techniques for wireless data broadcast under data clustering and scheduling

Abstract: This paper investigates power conserving indexing techniques for data disseminated on a broadcast channel. A hybrid indexing method combining strengths of the signature and the index tree techniques is presented. Different from previous studies, our research takes into consideration two important data organization factors, namely, clustering and scheduling. Cost models for index, signature and hybrid methods are derived by taking into account various data organizations accommodating these two factors. Based on our analytical comparisons, the signature and the hybrid indexing techniques are the best choices for power conserving indexing of various data organizations on wireless broadcast channels.

Performance evaluation of a wireless hierarchical data dissemination system

Abstract: Various techniques have been developed to improve the performance of wireless information services. Techniques such as information broadcasting, caching of frequently accessed data, and point-to-point channels for pull-based data requests are often used to reduce data access time. To efficiently utilize information broadcast, indexing and scheduling schemes are employed for the organization of data broadcast. Most of the studies in the literature focused either on individual technique or a combination of them with some restrictive assumptions. There is no study considering these techniques working together in an integrated manner. In this paper, we propose a dynamic data delivery model for wireless communication environments. An important feature of our model is that data are disseminated through various storage mediums according to the dynamically collected data access patterns. Various results are presented in a set of simulation studies, which give some of the intuitions behind the design of a wireless data delivery system.

Dynamic data delivery in wireless communication environments

Abstract: Information broadcasting, caching of frequently accessed data, and pull-based data delivery are commonly used techniques to reduce data access time of wireless information services. Most of the studies in the literature focused either on individual technique or a combination of them with some restrictive assumptions. In this paper, we propose a dynamic data delivery model where these three techniques work together in an integrated manner. A particular feature of our model is that data are disseminated through various storage mediums according to the dynamically collected data access patterns. Performance evaluation of the model is conducted by simulation studies.

Mobile Data Access

Abstract: Next generation wireless networks are going to use IP capable mobile terminals and support both voice/multimedia and data services. VoIP is a promising technology allowing a converged core network for all services, and provides a service platform for easier and quicker service creation. Application of VoIP in wireless networks, however, is not so straightforward as people may expect. Among other issues, mobility support is perhaps the most challenging one. The different levels of mobility support (terminal, personal and service mobility) highlight the gap between the existing VoIP framework, which is so far focusing on fixed networks, and the requirements in a wireless environment. After analyzing the existing solutions/proposals for this problem, a framework is proposed in which the mobility-related services are decomposed into several levels so that mobility support is made available to many applications. This layered approach would help to lead to a mobility enabled wireless IP infrastructure in which voice service is just an application.

Signature caching techniques for information filtering in mobile enviroments

Abstract: This paper discusses signature caching strategies to reduce power consumption for wireless broadcast and filtering services. The two-level signature scheme is used for indexing the information frames. A signature is considered as the basic caching entity in this paper. Four caching policies are compared in terms of tune-in time and access time. With reasonable access time delay, all of the caching policies reduce the tune-in time for the two-level signature scheme. Moreover, two cache replacement policies are presented and compared by simulation. The result shows that, when the cache size is small, caching only the integrated signatures is recommended. When the size of cache is greater than that of the integrated signatures, caching both of the integrated and simple signatures is better.

On Simulation Modeling of Information Dissemination Systems in Mobile Environments

Abstract: In this paper, we propose dynamic discrete-event based models for information dissemination systems in both single cell and multiple cell mobile environments. We demonstrate that this novel approach can flexibly model channel borrowing and hand-off scenarios. Finally, we implement two simulation systems based on the single cell model. Our simulations show that broadcast channels can effectively alleviate traffic overload in a cell.

Repository Support for Metadata-based Legacy Migration.

Abstract: Migrating legacy systems involves replacing (either wholly or partially) existing systems and databases, and complex transformations between old and new data, processes and systems. Correctly performing these activities depends on descriptions of data, and other aspects of the legacy and new systems, and the relationships between them, i.e., metadata. Metadata repositories provide tools for capturing, transforming, storing, and manipulating metadata. They can also store information for managing the migration process itself and for (re)use in other migrations. This paper discusses some of the issues that arise when migrating legacy systems and examines how repository technology can be used to address these issues.

Summary of panel discussion : Future of mobile computing : Convergence of research and applications

Abstract: In the panel discussion session of International Workshop on Mobile Data Access, an enthusiastic audience was invited to join the panel of experts, Prof. Dik Lun Lee (Hong Kong University of Science and Technology, Hong Kong), Dr. Radhakrishna Pillai (Kent Ridge Digital Labs, Singapore), Dr. Hiroki Takakura (Kyoto University, Japan) and Mr. Stuart Jacobs (GTE Laboratories, USA) to explore several important issues relating to the data access aspect of mobile computing.