在行動計算環境中，因為資料廣播具有同時服務大量客戶端的特性，因此利用廣播方式傳送資料給大量客戶端是一個有效的方法。在廣播環境下，如何節省能源以及降低取得資料的等待時間，一直是相當重要的議題。廣播資料索引的方式是一種被廣泛用來節省能源消耗的方式。此外，快取技術也是一種能有效降低能源消耗與等待時間的方式。目前關於快取技術方面的研究，都是只單獨考慮將廣播索引或資料項目放入快取中。我們認為將索引或資料放入快取中都可能增進系統的效益，因此我們提出同時快取資料與快取索引的混合式快取策略。在我們所提出的混合式快取策略中，我們利用下列三個因素來考量一個資料對系統的價值，並利用該價值判斷是否要快取該資料項：這三種因素分別是(1)資料的使用率、(2)資料被重複使用時，所能降低的能源與等待時間、(3)資料異動的機率。我們將這三個因素量化後建立一個效益函式，並使用效益函式來評估把索引或資料放入快取後所帶來的效益，以此做為快取管理的依據。根據實驗顯示，我們所提出的混合式快取策略確實能達到節省能源與降低資料取得時間的目的。

With data broadcasting approach a broadcast server can serve many mobile clients simultaneously. Therefore, data broadcasting is usually adopted for disseminating data in mobile computing environments. In the data broadcasting approach, selective tuning is widely used to reduce energy consumption and caching is used to reduce both energy consumption and access time. The existing caching policies only consider caching either data items or indices. However, it would be beneficial to cache both of them. In this paper, we propose a hybrid caching policy which considers caching both the data items and the indices. In the hybrid cache policy, we use a profit function to measure the value of keeping an item (a data or an index) in the cache. When the cache is full, the item with the lowest value will be dropped from the cache. The profit function considers the following three factors: (1) access probability of an item, (2) how much energy and waiting time can be saved by using the cached item and (3) the update frequency of the data items in the server. The proposed hybrid cache policy can determine the optimal proportion of data items to indices in the cache according to the update frequency of the data items in the server. According to our experiments, the hybrid policy outperforms those policies that caching only data items or indices.

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