IEEE 802.16標準是一種無線都會型網路(Wireless Metropolitan Access Network; WMAN)，其具有高傳輸速率、較廣的訊號覆蓋範圍與支援多媒體服務等特點。而為了保障各種多媒體服務的服務品質(Quality of Service; QoS)，服務流總共被分成五個類別。但在IEEE 802.16標準並沒有去定義頻寬分配，因此如何設計一個排程演算法來滿足所有服務類別的服務品質需求就成為了主要探討的議題。
一個即時性的封包必須在封包的截止期限(deadline)之前傳送出去，一旦超過了封包的截止期限並且封包還未被傳送，那麼封包就會被丟棄進而影響到其服務品質，在本論文中，首先，我們按照即時輪詢服務佇列內封包的截止期限來將封包做排序，使得較緊急的封包能夠被優先傳送。再來，我們將佇列在目前為止所有訊框內所分配到的頻寬總合除以佇列累積總長度，定義為其服務比率(Service Ratio)。然後，以服務比率值來決定是否優先分配頻寬給某一即時輪詢服務佇列，若是服務比率值小於服務比率平均值，就分配頻寬給此一佇列的緊急封包；反之，若服務比率值大於服務比率平均值，就先不分配頻寬給此一佇列。最後，若是有剩餘頻寬，我們使用輪詢法來將剩餘頻寬分配給所有佇列直到頻寬用
I
盡。經由模擬結果我們可以看出，在較重的負載下，使用本論文所提的演算法能夠傳送更多的即時輪詢服務封包，有效地降低封包遺失率。

IEEE 802.16 is a standard for Wireless Metropolitan Access Network (WMAN). It has the advantages of broadband, large coverage and multimedia services. To ensure the quality of service (QoS) for different applications, the service flows are classified into five classes in IEEE802.16. However, it does not provide standard for scheduling bandwidth. Therefore, it becomes a major field of exploring to design a bandwidth allocation algorithm to fulfill the QoS requirement of all classes.
A real-time packe has to be transmitted before its deadline. Otherwise, it will be discard. In this paper, we will sort the packets in queues according to their deadline for real-time Polling Service (rtPS). Thus, emergency packets can be transmitted before the deadline. Then, the sum of scheduled bandwidth will be divided by the sum of queue length in all frames. The result will be called as service ratio of this queue. According to service ratio of all queues, the scheduler will decide the priority of each queue in the same class. The sum of scheduled bandwidth for all queues divided by the sum of all queue lengths in all frames is called as the average service ratio. If the service ratio of one queue is below the average service ratio, the emergency packets of this queue will be scheduled. Otherwise, this queue will not be scheduled temporarily. After this stage, round robin (RR) algorithm will be used to schedule bandwidth for all queues if there is bandwidth left in the last stage. The simulation result shows the loss rate of rtPS class will be improved because the emergency packets have more opportunity to be transmitted before their deadlines with our algorithm in heavy load.

[1] TELECOM CLOUD(n.d.). Connected world: a changing wireless paradigm. Retrieved March 2, 2015, from http://www.telecom-cloud.net/connected-world-a-changing-wireless-paradigm
[2] 李聖宏，「Polling according to the bandwidth request for WiMAX nettwork」， 碩士論文，國立台灣科技大學，台北市(2015)。
[3] Ahmed, Z and Hamma, S, “Efficient and fair scheduling of rtPS traffic in IEEE 802.16 point-to-multipoint networks”, Wireless and Mobile Networking Conference (WMNC) 2011 4th Joint IFIP, pp.1 - 7, Oct. 2011.
[4] Point-to-multipoint topology, from http://itlaw.wikia.com/wiki/Point-to-multipoint_topology
[5] Yi-Hsueh Tsai, IEEE 802.16j Multi-hop Relay, Retrieved July 8,2015, from http://www.slideshare.net/yihsuehtsai/p80216j-d8-20081222
[6] D. Kim and A. Ganz, “Fair and efficient multihop scheduling algorithm for IEEE 802.16 BWA”, BroadNets 2005. 2nd International Conference systems, pp.833-839, Oct. 2005.
[7] Mark C. Wood, “An Analysis of the Design and Implementation of QoS over IEEE 802.16”, April 23, 2006.
[8] The Comparison of TDD LTE And FDD LTE, Retrieved July 8,2015, from https://4gltemobilebroadband.wordpress.com/2012/11/30/the-comparison-of-tdd-lte-and-fdd-lte/
[9] Difference Between OFDM and OFDMA, Retrieved July 8,2015, from http://www.differencebetween.com/difference-between-ofdm-and-vs-ofdma/
[10] OHNO. Y, SHIMIZU. T, HIRAGURI. T, and NAKATSUGAWA. M, “Novel Frame Structures to Improve System Capacity and Latency Performance of a Time-Division Duplex Multihop Relay Wireless Access System”, IEEE Wireless Communications and Networking Conference, pp. 1-6, 2009.
[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] IEEE STD 802.16™-2012, “IEEE Standard for Air Interface for Broadband Wireless Access Systems”, August 2012.
[13] Andrews. J. G, Ghosh. A and Muhamed. R, “Fundamentals of WiMAX: Understanding Broadband Wireless Networking”. Prentice Hall, NJ, 2007.
[14] Gupta S, “Comparison of Various Scheduling Algorithms in WiMAX: A Brief Review”, International Conference on Advances in Management and Technology, pp. 34-36, 2013.
[15] 陳政隅，「Bandwidth Allocation according to Queue Length and packet loss rate-a scheduling algorithm for WiMAX network」，碩士論文，國立台灣科技大學，台北市(2013)。
[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.