Broadcast Strategies to Maintain Cached Data for Mobile Computing System

Kam-yiu Lam, Edward Chan and Joe Chun-Hung Yuen Department of Computer Science City University of Hong Kong 83 Tat Chee Avenue, Kowloon Hong Kong Fax: 852-2788-8614 Email: {cskylam|csedchan|csjyuen}@cityu.edu.hk Abstract. Although data broadcast has been shown to be an efficient data dissemination technique for mobile computing systems, many issues such as selection of broadcast data and caching strategies at the clients are still active research areas. In this paper, by examining the dynamic properties of the data items in mobile computing systems, we define the validity of a data item by its absolute validity interval (avi). Based on the avi of the data items, we propose different broadcast algorithms in which the selection of data items for broadcast will be based on the avi of the data items and their access frequencies. The purpose of the AVI algorithms is to increase the client cache hit probability so that the access delay for a data item will be much reduced. Simulation experiments have been conducted to compare the AVI algorithms with the algorithm which only considers the popularity of the data items. The results indicate that the AVI algorithms can significantly improve the mean response time and reduce the deadline missing requests.