由於行動計算環境資源的限制，資料廣播成為一種資料傳輸的有效方案。廣播資料的索引技術相繼被提出，研究方向著重於搜尋的加速與資料存取電力消耗的減少。然而，資料存取的錯誤對索引過程的影響，並未廣泛的討論。在無線通訊環境下諸多的因素會造成此情形發生，例如：電力不足、訊號減弱、訊號干擾、換手等。針對這個問題我們提出加強索引過程的容錯方式。基本原則是利用廣播資料上存在的索引複製，做為錯誤回復的參考資料。我們利用一種稱為搜尋範圍的資訊，記錄所要搜尋的資料在頻道中的可能位置。利用搜尋範圍可以快速地判斷並找到索引複製的存在，以恢復存取錯誤而造成的索引中斷。
行動用戶一般使用電池驅動的可攜式裝置，為了減少電力的消耗，存取廣播資料的時間延遲必須考慮。建立索引與系統地安排廣播資料的內容，可以降低資料存取的時間。對於索引與資料該如何在多個廣播頻道中安排，我們提出尋找最佳解的方式。第一種方式先將所有可能的排法建成一樹狀圖，接著利用一些特質，將樹狀圖中不可能成為最佳排法的部分刪除，然後再逐一搜尋最佳解。第二種方式先從單一廣播頻道著手，因為這種條件下存在對數時間的演算法。接著我們利用線性時間的轉換方式，找到多頻道的排法，這種排法並非最佳解。此外，我們考慮如何在多廣播頻道下複製索引的方式。

行動用戶可能穿梭於不同的地點，對移動的使用者位置的管理是件重要的工作，這些位置資料將有助於伺服端正確地傳送資料。我們提出依據使用者移動行為的區域管理技術，以改進傳統的管理方式。每個行動用戶依據其移動樣式建立一組區域，去除區域內移動所產生的註冊動作，可有效地降低位置管理的花費。基於負荷量與呼叫/移動比值的考量，我們探討數種改進的方式。我們所提出的策略可依據系統參數與使用者行為樣式的改變而動態調整。

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.

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