Abstract
The data broadcast has become an attractive dissemination method and an elegant solution to compensate for the limited resources in the mobile computing environment. Indexing methods for the broadcast data have been proposed to speedup access time and reduce power consumption. However, the influence of access failures has not been discussed. For the error-prone mobile environment, the occurrence of the access failures is often due to disconnections, handoffs, and communication noises. Based on the distributed indexing scheme, we propose an adaptive access method which tolerates the access failures. The basic idea is to use index replication to recover from the access failures. One mechanism named search range is provided to dynamically record the range where the desired data item may exist. According to the search range, an unfinished search can be efficiently resumed by finding an available index replicate. A performance analysis is given to show the benefits of the method. Also, the concept of version bits is applied to deal with the updates of the broadcast data. Since the mobile units usually have limited battery capacity, the minimization of the access latency for the broadcast data is an important problem. The indexing and scheduling techniques on the broadcast data should be considered. We propose a solution to find the optimal index and data allocation, which minimizes the access latency for any number of broadcast channels. Two approaches are presented. One is to represent all the possible allocations as a tree in which the optimal one is searched. A pruning strategy based on some properties is applied to greatly reduce the search space. The other is to directly generate the optimal allocation for a single broadcast channel. For the multiple broadcast channel case, we provide a procedure to get a heuristic answer from the one for a single broadcast channel. Moreover, we consider the replication issue on the index allocation. The mobile user may not stay in a fixed cell and may roam from one cell to another. It should be decided which cell the user is currently in before returning the result to the corresponding user for the server. We propose a region-based location strategy by taking advantage of the user's movement behavior to improve the performance of the conventional systems. Each mobile user is associated with a set of regions which are derived from the user's movement patterns. The registration processes in the same region can be eliminated such that the cost of location management can be significantly reduced. Several design issues are studied by considering the workload balance and the call-to-mobility ratio for a user. The proposed strategy can be dynamically adjusted based on different system parameters and user behaviors. A performance analysis on the signaling cost is given to justify the benefits of this approach.