Efficient Algorithms for Scheduling XML Data in a Mobile Wireless Broadcast Environment

This paper tackles the key scheduling problem of reducing the overall wait time of mobile clients in wireless data broadcast systems. It is observed that in periodic broadcast, new mobile clients may join in and existing mobile clients may leave anytime; in on-demand broadcast, high uplink communication cost may occur as all clients have to submit their queries every time. These are likely to degrade existing broadcasting approaches. In this work, we study the scheduling problem of XML data broadcast in a hybrid mode, where the system supports both periodic broadcast and on-demand broadcast services at the same. By taking the structural similarity between XML documents into account, only a small portion of mobile clients would be involved in the scheduling process and all mobile clients can be served more effectively. In this way, communication cost at the client side can be reduced greatly. A formal theoretical analysis of the proposed technique is presented. Based on the analysis, a novel clustering-based scheduling algorithm is developed. Moreover, we utilize an aging method to predict the distribution of incoming queries based on small samples of queries from mobile clients. Finally, we evaluate the approach through a set of experiments and the results show that it can significantly improve access efficiency for mobile clients.