In a mobile computing system, users carrying portable devices can access database services from any location without requiring a fixed position in the networking environment. Some examples of strategies supported by databases in mobile computing include location dependent queries, long-lived transactions that require migration of data into the portable devices, form-based transactions, and online information report. Within a mobile computing environment, the need for a realtime database management model is strong, because one of the basic requirements in mobile data management is to provide real-time response to transactions of the underlying strategies. However, the resource constraints of mobile computing systems make it difficult to satisfy timing requirements of supported strategies. Low bandwidth, unreliable wireless links, and frequent disconnections increase the overhead of communication between mobile hosts and fixed hosts of the system. There are many situations in which we need to incorporate real-time constraints in broadcasting systems for mobile environments. In this paper, we study broadcast scheduling strategies for pushbased broadcast with timing constraints in the form of deadlines. Unlike previously proposed scheduling algorithms for broadcast systems which aim to minimize the mean access time, our goal is to identify scheduling algorithms for broadcast systems that ensure requests meet their deadlines. We present a study of the performance of traditional real-time strategies and mobile broadcasting strategies, and demonstrate that traditional realtime algorithms do not always perform the best in a mobile environment. We propose a multichannel model based on pushbased real-time broadcast system and also provide an efficient scheduling algorithm, called dynamic adjustment with time constraint (DATC), which is designed for timely delivery of data to mobile clients.
['Ding-Jung Chiang', 'Hwei-Jen Lin', 'Timothy K. Shih']
Providing Data Items with Time Constraints in Multi-Channel Broadcasting Environments