在IEEE 802.16中，排程器會利用排程演算法將頻寬分配給服務流(Service flow)。為了保障各種多媒體應用的服務品質(Quality of Service; QoS)，服務流總共被分成五個類別。然而在IEEE標準中，並沒有定義明確的排程演算法，所以這一直是開放給學者研究及探討的部分。這五種服務流可以更進一步的分為即時性服務流及非即時性服務流，若即時性封包的等待時間超過了該封包的最大延遲時間，則該封包就會被丟棄，在本論文中，我們將為即時性服務流提出一種排程演算法來保障這類型的封包遺失。
在排程的第一階段，我們使用權重巡迴排程演算法(Weight Round Robin; WRR)並以佇列長度的比例當作權重，每個服務流會根據其佇列長度所佔的比例分配到對應的頻寬。之後排程器會檢查即時性服務流佇列中的每個封包並決定要在此次訊框中傳送的封包，以保障此佇列的封包遺失率。由上述步驟，我們可以得到該佇列的所需頻寬，若所需頻寬大於第一階段佇列被分配到的頻寬，超出部分的頻寬將會從盡力傳送(Best-Effort; BE)佇列於第一階段所分配到的頻寬取走。經由模擬結果我們可以看出，除了在非常重的負載下排程器已無法從盡力傳送佇列取得足夠的頻寬的情形時，排程器都能夠藉由此演算法保障即時性服務流的封包遺失率。

In IEEE 802.16, the bandwidth will be allocated to service flows by the scheduler with scheduling algorithm. To ensure the Quality of Service (QoS) of different application, the service flows are classified into five classes. Nevertheless, there is no specific scheduling algorithm defined in the standard. It is kept opened for the researchers to explore. The five classes of service flows can be further divided into real-time and non-real time. If the waiting time is over the maximum latency of a real-time packet, it will be discarded. In this paper, we will propose a scheduling algorithm to ensure this kind of loss for a real-time flow.
In the first stage of scheduling, the allocated bandwidth of each flow will be proportional to its queue length. In other word, a weighted round robin (W.R.R.) is used for this stage and the weight is proportional to queue length. Then, the scheduler will check the packets in the queue of real-time flow and it will decide the sent packets in this frame to ensure the loss rate of this queue. From this, the allocated bandwidth of this queue can be decided. If this allocated bandwidth is larger than the one obtained in the first stage, the exceeded bandwidth will be got from Best Effort (BE) flow. From the simulation result seen, the scheduler can ensure the loss rate of real-time flow with this algorithm unless it cannot get enough bandwidth from the BE flow in very heavy load.

[1] 台灣區電機電子工業同業公會電子報。(民98年2月18日)。WiMAX 與 Wi-Fi 無線寬頻通訊現況分析。(民103年5月24日) 。取自http://www.teema.org.tw/epaper/20090218/industrial004.html
[2] 廖一全，「A scheduling algorithm to insure minimum bandwidth ratio -a scheduling algorithm for WiMAX network」，碩士論文，國立台灣科技大學，台北市(2013)。
[3] J. G. Andrews, A. Ghosh, and R. Muhamed，“WiMAX技術原理與應用-了解寬頻無線網路”，李蔚澤/許家華(譯)，碁峰資訊，2007
[4] 新通訊原件雜誌。(民97年1月)。提升WiMAX效益　802.16j MR標準脫穎而出。(民103年5月20日)取自 http://www.2cm.com.tw/technologyshow_content.asp?sn=0801140010
[5] MIC觀點。(民95年3月29日)。綠燈亮起-談Mobile WiMAX 802.16e標準通過後之觀察。(民103年5月27日)取自 http://mic.iii.org.tw/pop/MicNews2_op.asp?sno=130&cred=2006/3/29
[6] IEEE STD 802.16™-2012, “IEEE Standard for Air Interface for BroadbandWireless Access Systems,” August 2012.
[7] EventHelix。(無日期)。Long Term Evolution (LTE) Tutorials。(民103年6月28日)取自
http://www.eventhelix.com/lte/lte-tutorials.htm
[8] J. Pinola and K. Pentikousis, “Mobile WiMAX”, The Internet Protocol Journal, Volume 11, No. 2, 2008
[9] 劉原銘，「Enhance RED-based Scheduling(ERBS) Scheme for QoS in WiMax Network」，碩士論文，國立台灣科技大學，台北市(2012)。
[10] S.Ben-Guedria, B. Sanso, J. F. Frigon “PolyMAX, a Mobile WiMAX module for the ns-2 simulator with QoS and AMC support, ”Simulation Modeling Practice and Theory, Vol. 19, pp. 2076-2101, 2011
[11] E. Lee and H. K. Park, “Packet Scheduling Scheme for Multiple Services in Mobile WiMAX System”, Second International Conference on Computer and Network Technology, pp. 60-63, 2010
[12] M. Shreedhar and G. Varghese, “Efficient fair queuing using deficit round-robin,” in IEEE/ACM Transactions on Networking, vol.4, no. 3, pp. 375-385,June 1996
[13] 許博涵，「應用於WiMAX網路考慮佇列長度的頻寬分配法」，碩士論文，國立台灣科技大學，台北市(2012)。
[14] T. Kulshrestha and S. Tanwani, “An Improved Maximum Signal to Interference Ratio Scheduler at Base Station for real time services in WiMAX”, IEEE International Advance Computing Conference, pp.292-295, 2013
[15] H.C. Jang and K. C. Yang, “A QoS Aware Multi-Modulation CAC for WiMAX,” in International Symposium on Computer Science and Society, pp. 365-368, 2011.
[16] J. Chen, C. C. Wang, C. D. Tsai, C. W. Chang, S. S. Liu, J. Guo, W. J. Lien, J. H. Sum, and C. H. Huang, “The Design and Implementation of WiMAX Module for ns-2 Simulator”, Proc. of the ACM/ISCT/VALUETOOLS, October 2006.