IEEE 802.16是一種無線寬頻網路標準，具有較高傳輸速率和較長通訊距離，以及能支援語音、影像多媒體服務等特點。在IEEE 802.16中定義了五種服務品質(Quality of Service; QoS)來滿足各種資料的需求。但是，在IEEE 802.16標準中並沒有將排程演算法作明確定義，所以這部分一直是開放給學者及通訊商來研究及探索。因此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，設計一個好的排程演算法就變成了重要議題。
一個即時性的封包內包含了封包的截止期限(deadline)。因為即時的特性，封包必須在其截止期限(deadline)內傳送出去，否則超過其截止期限，排程器就會將該封包丟棄，進而影響服務品質。本論文提出了一種考慮到了各個用戶間的封包遺失率的差異，一個綜合封包遺失率(Packet Loss Rate; PLR)和調變與編碼方式(Modulation and Coding Scheme; MCS)的排程演算法，首先，我們處理即時性服務的封包，將延伸即時輪詢服務(ertPS)與即時輪詢服務(rtPS)的封包，依照截止期限的大小排序，再將截止期限超過現在時間的封包丟棄，並且記錄各個工作站延伸即時輪詢服務與即時輪詢服務佇列的封包遺失率。
然後，我們會先對免經請求之服務(UGS)做排程，剩下的頻寬會根據各服務類別來做最大可分配的頻寬限制，目的是為了保障每個服務類別都有基本的頻寬可使用，接著，即時性服務的佇列先根據調變與編碼方式，讓緊急封包能優先排程。如此，可讓有較佳調變與編碼方式的佇列優先傳送，使得可以使用的總頻寬較大，可降低總封包遺失率。然而，對於那些調變與編碼方式較差的佇列而言，由於排程機會較少，使得封包遺失率變得無法接受。因此，接下來的排程將同時考慮佇列的封包遺失率和調變與編碼方式，讓有較好的調變或者較大封包遺失率的佇列擁有比較優先的權利去做分配，直到所有的可用剩餘頻寬被分配完畢，或是所有佇列中的封包都被排程為止，模擬結果顯示此方能能讓即時性服務類別的封包遺失率有效的降低，並且減少單一工作站封包遺失的數量過大的情況，讓資源能夠公平的分配與利用。

IEEE 802.16 is a standard for wireless communication network. It has the advantages of high transmission rate, long transmission distance and supports various kinds of multimedia services such as voice and video. For these services, IEEE 802.16 defines five classes for quality of service (QoS) which will meet a variety of data service demands. Nevertheless, IEEE 802.16 does not define the scheduling algorithm for these classes. This is left for researchers and communication suppliers to explore. Therefore, it is important to design a good scheduling algorithm to satisfy the requirement of real time and non-real time service.
In real-time packet, a time stamp is included to indicate its deadline. Real-time packets have to be transmitted before their deadlines. Otherwise, they will be discarded. In this paper, an algorithm is proposed that can consider the packet loss rate (PLR) and modulation and coding scheme (MCS) in scheduling. First, the real-time service queues (including ertPS and rtPS) are sorted according to the deadlines of their packets. Then, a packet will be discarded if its deadline is over and the loss rate of the real-time service queues on each subscriber station (SS) will be recorded. The total available bandwidth for each class will be restricted ensure the available bandwidth of non-real time classes. Firstly, the emergency packets of each queue will be scheduled by the priorities according to MCS. Then, the remaining packets in each queue will be scheduled by the priorities according to PLR and MCS. The simulation result shows that the packet loss rate of the real-time service (ertPS and rtPS) can be improved with our scheduling algorithm.

[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104年5月30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] 廖文嘉，「Emergency first MCS algorithm for WiMAX network」，碩士論文，國立台灣科技大學，台北市(2016)。
[4] 李俊杰。(Bandwidth Allocation Using the Mean & Standard deviation of Arrival Process:A Scheduling Algorithm for WiMAX Network)。使用到達程序之平均值與標準差的頻寬分配法：WiMAX網路的一個排程演算法。民104年11月27日 。
[5] IEEE, "Draft Amendment to IEEE Standard for Local and Metropolitan Area Networks Part 16 : Air Interface for Fixed and Mobile Boardband Wireless Access System,” IEEE P802.16m/D6,May 2010
[6] Yi-Hsueh Tsai, IEEE 802.16j Multi-hop Relay, Retrieved July 8,2015, from http://www.slideshare.net/yihsuehtsai/p80216j-d8-20081222L. Nuaymi, WiMAX: Technology for Broadband Wireless Access, John Wiley & Sons, 2007.
[7] “Air Interface for Fixed and Mobile Broadband Wireless Access Systems – Multi-hop Relay Specification,” IEEE 802.16j-06/026r4, June 2007
[8] L. Nuaymi, WiMAX: Technology for Broadband Wireless Access, John Wiley & Sons, 2007
[9] 許獻聰，WiMAX無線網路技術系列，國立中央大學通訊工程系，2009年。.
[10] 黃偉承，「A loss-rate ensured scheduling algorithm for WiMAX network」，碩士論文，國立台灣科技大學，台北市(2014)。
[11] IEEE standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, ISO/IEC 8802-11:1999(E), Aug. 1999
[12] 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。
[13] IEEE STD 802.16™-2012, “IEEE Standard for Air Interface for Broadband Wireless Access Systems,” August 2012。
[14] E. L. Hahne and R. G. Gallager,“Round robin scheduling for fair flow control in Data Communication Networks” , International Conference on Communications, pp. 103-107, June 1986.
[15] V. Sagar and D. Das, “ Modified EDF algorithm and WiMAX architecture to ensure end-to-end delay in multi-hop networks,” IEEE Region 10 Conference TENCON, pp. 1-6, Nov. 2008。
[16] A. Iera, A. Molinaro, S. Pizzi, and R. Calabria, “Channel-aware scheduling for QoS and fairness provisioning in IEEE 802.16/WiMAX broadband wireless access systems,” IEEE Network, pp. 34-41, Oct. 2007
[17] 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)。