Research On Broadcast Scheduling Strategy In Embedded Mobile Real-Time DBMS

In the embedded mobile real-time database system (EMRTDBMS), Wireless network has the features of low bandwidth, asymmetry and poor quality, in order to support a large number of mobile clients concurrently accessing the content in database servers, and to improve the scalability of the network communication, data broadcast tech., an important data dissemination method, is provided and applied in EMRTDBMS.Broadcast mode, scheduling strategy, and data organization are the main research directions of data broadcast tech. Scheduling strategy is the key direction particularly. This paper emphasizes on scheduling strategy for data broadcast in real-time environment. Firstly, we introduce the progress of research on scheduling strategy in the past few years, and give the qualitative analysis of those provided strategies. Secondly, by analyzing the characters of data in real-time database, we provide a Real-Time Data Broadcast Model based on hybrid broadcast mode. Then, we give a brief description of TC-AHB, a hybrid broadcast scheduling strategy. And based on that strategy, we provide an improved scheduling strategy, named Improved TC-AHB.By taking the information of data requested mode and data deadline into calculation, TC-AHB can dynamically calculate the bandwidth ratio for periodic broadcast and the being-scheduled data, through a novel sample tech., TC-AHB can also efficiently get more valid data-requested mode. Improved TC-AHB not only inherits those merits of TC-AHB, but also extends the strategy to the broadcast based on transaction scheduling. And, it adopts an idea called distributed periodic broadcast, to solve confliction between a long periodic broadcast interval and real-time requirement of data and transactions.At last, we implement a prototype system for measuring the performance of provided scheduling strategy, and for comparative experiment, we implement not only Improved TC-AHB, but also TC-AHB and an on-demand strategy called EDF-T. The conclusions are: those strategies based on hybrid broadcast mode are more suitable for data broadcast application in real-time environment; and Improved TC-AHB has lower transaction failure ratio, and lower uplink load.