在無線網路下的環境架構，資料廣播是一個有效率的資料傳播方式。現今，有很多相關的研究開始探討多個資料項請求(Multi-item Queries )的廣播排程；並且，多個資料項的請求也比較符合現實的情況。在傳統的拉式或請求式(Pull or On-demand)資料廣播排程都假定一個廣播的時間單位(One Time Slot)只包含了一個資料項(Data Item)，因此排程中的一個廣播時間單位只能提供一個資料項的服務。在這裡本研究採用了一個資料編碼的技術(Network Coding)；就是將多個資料項以編碼(Encoding)的方式結合，並安排到一個廣播時間單位上；如此，一個廣播的時間單位就有多個資料項來服務使用者，使用者只要依據已經Cache的資料項來解碼(Decoding)，就可以得到感興趣的資料。根據先前的研究，在此本研究加入了考慮請求長度的因素來改善資料排程；我們從模擬實驗結果得知與先前[3]的研究方法作對照，我們的方法可以減少20%左右的平均存取時間(Average Access Time)。 Data broadcasting is an efficient method of disseminating information in the on-demand wireless network environment. Recently, there are many related papers began to explore multi-item queries of data scheduling. And, users’ queries needed multiple data items in real world. However, traditional on-demand data broadcast scheduling assume that each time slot includes only one data item. Therefore, each broadcast time slot can only include one data item. Using network coding technique, server can broadcast multiple data items in a time slot. In this paper, we propose a new on-demand data broadcast model with modified network coding. We also consider the factor of requests length. Our approach is different from the traditional network coding, each time slot encodes only a subset of data items, which are decided according to identities of the requested and stored data items in client’s cache. Experiment results show that our algorithm can reduce the average access time by 20% compared with [3].
