在行動計算的環境中，伺服端必須服務大量的客戶端，因此使用廣播的方式傳送資料給客戶端是一個很有效率的方法。在廣播的環境下，如何節省能源和降低資料的等待時間，是個相當重要的議題。有許多方法可以達成上述之目的，其中最常用的方法就是使用快取空間來暫存資料。但是一旦資料項被伺服端更動，客戶端快取的資料項就無法使用，為了讓客戶端能知道快取中的資料項是否可用，我們在廣播方法中加入驗證報告。在本篇論文中，我們修改了封包的表頭，使得客戶端可以得知驗證報告廣播的時間。並且根據廣播環境的特性，使用編號來取代驗證報告中的時間戳記。此外，我們詳細地討論驗證報告的擺放位置。我們發現若將驗證報告擺在索引之前，則客戶端會為了要取得驗證資料而錯失廣播資料。若將驗證報告擺放在每個資料區塊中第一個異動資料之前，並在驗證報告中加入部份資料廣播的時間。如此可以大量降低客戶端的獲取時間。

Since data broadcasting can disseminate data items to large number of mobile clients simultaneously, it is widely used for distributing data items in a mobile computing environment. Two major performance metrics in a mobile computing environment are energy consumption and access latency. In many recent researches, data caching is used to minimize these two metrics. With data caching, one has to maintain the consistency of the cached data items of a mobile client with those of the mobile server. When data items are updated in the server, a client must be informed of these updates and tries to retrieve the new contents of the data items. To do this, we consider broadcasting invalidation reports (IRs) in the broadcast structure. In this paper, we revise the organization of a packet header such that a mobile client is informed about the time when an invalidation report is broadcasted by accessing the header information. According to the characteristic of the broadcast structure, we use numbers to replace timestamps in IR to reduce the IR size. We carefully study the ways to put IRs in a broadcast structure to reduce the access latency. On way to put an IR is to put it before the index segment. In this way a mobile client tends to miss the broadcasted data items due to the need to access an IR before accessing any data items. Another way is to put an IR before the first updated data item in each data segment. Through a simulation, we show that the second method significantly reduces the access latency.

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