隨著使用者對傳輸服務品質上的追求，行動通訊的研究朝著高頻譜使用率的方向發展，如何充分掌握並利用時變頻道的特性，成為提升系統效能的關鍵。
在本篇論文，我們針對一個在無線衰弱頻道傳送資訊的系統中，提出一個臨機式廣播排程演算法。我們的系統在以能夠在多用戶分集增益以及廣播增益之間取捨達到良好的平衡點為前提下，來觀察系統中使用者利用頻道的狀況。為了避免系統對單群使用者排程時，遷就頻道狀況較差的使用者而選擇較低的傳輸速率發送資訊，我們把系統中的使用者依照長期信號干擾比分為兩群，再動態的配置時間槽給系統中不同的群組來使用。透過這樣的方式可以提高系統中頻道的利用度。在我們的方法中，我們利用資訊延遲(Information Lag)來控制群組內使用者的資訊進度差距，以維持群組內的廣播增益，另外再利用群組輸出比例改變量(Group Throughput Ratio Variation)來控制群組間的輸出比例，使信號較佳的使用者能夠充分利用頻道的同時，也能讓信號較差的使用者獲得一定的輸出比例。我們的模擬與實驗結果皆顯示透過我們的排程法則，在單群排程法則的可以有效約束使用者的進度條件下，加入雙群的觀點，利用動態配置頻道給不同群組使用者，使系統效能達到比單群更佳的狀態。

In order to support the high quality channel demanded by users, improving bandwidth efficiency becomes the focus of mobile communication research. Taking full knowledge of time varying channel and exploiting those characteristics are now the key to improve system throughput. We propose an opportunistic multicast scheduling algorithm in a system that sends information over wireless fading channel to users. We observe the channel usage of the system users, taking the balance of the multi-user diversity gain and broadcast gain as the prerequisite. To avoid the disadvantage that the system usually chooses the lower peak rate of users to transmit information when the scheduler regards the total users as one group, we divide users into two groups according to long term Signal to Interference plus Noise Ratio(SINR) and then dynamically allocate channels to different groups. The channel would be used more efficiently. In our scheme, we restrict the information lag between users in the same group to keep broadcast gain in each group by the term information lag and force the throughput ratio of groups to be drifted to Expected Throughput Ratio(ETR) by the term Group Throughput Ratio Variation. In this way the users with better channel state could receive data at higher transmit rate and the others with lower channel state could also acquire certain degree of service. The simulation results show that our system with the mechanism for grouping could achieve better throughput than single group system.

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