IEEE 802.16 標準是一種無線寬頻網路通訊標準，屬於無線都會型網路(Wireless Metropolitan Access Network; WMAN)，具有高傳輸速率、長通訊距離低成本等優點。並且為支援各種多媒體服務而設定了服務品質的標準(Quality of Service; QoS)，總共五種服務品質得以夠滿足不同需求；但是，在IEEE 802.16 標準中，並未完整定義頻寬分配的方法，為了有效率地分配有限的頻寬資源，來達成各項即時與非即時服務品質的保證，好的排程演算法的設計就變成了重要議題
即時性的封包內包含著封包的截止期限(deadline)，因為即時的特性，封包若超過了截止期限還未送出，排程器將會將此封包丟棄，進而影響到服務品質。
本篇論文提出了一種方法，考慮到了各個用戶與全部用戶的封包遺失率的差異。首先，我們處理即時性服務的封包，將延伸即時輪詢服務(extended real-time Polling Service; ertPS)與即時輪詢服務(real-time Polling Service; rtPS)的封包，依照截止期限的大小排序，使得較緊急的封包能夠優先被服務並且傳送，再將截止期限超過現在時間的封包丟棄，並且記錄各個延伸即時輪詢服務佇列的封包遺失率，以及延伸即時輪詢服務的總封包遺失率。若個別佇列封包遺失率大於等於總封包遺失率，就分配頻寬給此一佇列來傳送所有的緊急封包，反之，若個別封包遺失率小於總封包遺失率，則先不分配頻寬給此一佇列；然後，以預設優先權的方式來分配頻寬，也就是依照延伸之即時輪詢服務(extended real-time Polling Service; ertPS)、即時輪詢服務(real-time Polling Service; rtPS)、非即時輪詢服務(non- real-time Polling Service; nrtPS)、盡力服務(Best Effort; BE)的順序來分配；其中本演算法設定：即時性的兩個服務流，至多只能分配到90%的頻寬；而非即時性的服務流，則保證了有10%的頻寬的分配量。藉由此演算法，延伸之即時性輪詢服務在重載時能夠傳送更多封包，以及減少封包遺失的數量集中在單一用戶端工作站的情況。

IEEE 802.16 is a standard for Wireless Metropolitan Access Network (WMAN). It has the advantages of low cost, high speed and long distance communication. To ensure the quality of service (QoS) for different applications, the service flows were classified into five classes in IEEE802.16. However, the schemes for distributing bandwidth are not clearly defined in the standard. Because of the needs of various applications and limited bandwidth resource, it is crucial to design an algorithm to satisfy the QoS requirement of every application.
Real-time packets need to be transmitted before their deadlines. Otherwise, they will be discarded. In this paper, a method is proposed that can control the packet loss rate of real-time packets First, the real-time service queues (including ertPS and rtPS) are sorted according to the deadlines of their packets. Then, the packets over their deadlines are discarded. Then, if the loss rate of one real-time queue is greater than the average loss rate of its class, the emergency packets of this queue will be scheduled. Otherwise, the system will not schedule this serve in this round. Finally, the service queues are scheduled according to the priorities of their classes. The priorities are classified as ertPS, rtPS, nrtPS and BE from up to down. In addition, the real-time services can use 90% of bandwidth in one frame at most. It will ensure the non-real-time service have 10% of bandwidth to use. The simulation result shows that the throughput of ertPS is improved at heavy load. The loss rate of ertPS class will be lower. More importantly, the loss rates of different queues of the same class are almost the same.

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