ISSN : 1796-217X
Volume : 3    Issue : 8    Date : November 2008

Providing Data Items with Time Constraints in Multi-Channel Broadcasting Environments
Ding-Jung Chiang, Hwei-Jen Lin, and Timothy K. Shih
Page(s): 65-72
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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.

Index Terms
mobile computing,multichannel broadcasting, time constraint