IEEE 802.16標準是一種無線都會網路技術，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 802.16標準中並沒有定義頻寬分配的排程演算法，因此，如何設計一個好的排程演算法來滿足所有服務品質類別的需求就成為了主要探討與研究的議題。
　　即時性的封包必須在限制的時間內傳送出去，一旦封包的傳送延遲超過可容忍的最大值，封包就會被丟棄。在「根據封包剩餘時間比率限制排程法(RL) [1]」中，針對延伸之即時輪詢服務(ertPS)，只要封包剩餘時間低於整個服務類別(class)平均封包剩餘時間的0.6倍，這個封包將優先排列；針對即時輪詢服務(rtPS)，設定的剩餘時間的門檻則為0.4倍。在「調適性根據封包剩餘時間比率限制排程法(ARL) [2]」中，rtPS及ertPS所設定的剩餘時間門檻改為x和y。(x,y)的起始值(0.4,0.3)及(0.6,0.4)，隨著即時輪詢服務的封包遺失率變大，x會跟著變小，y會跟著變大，以確保即時輪詢服務的封包遺失率限制在要求的範圍內。然而，當(x,y)的起始值為(0.6,0.4)時，在ARL中的封包遺失率並沒有比RL好，原因是，x的起始值為0.6時，ARL演算法ertPS分配到的頻寬過大，當負載增加時(封包遺失率變大)，即使x值變小，ertPS分配到的頻寬並未明顯變小，使得rtPS可以使用的剩餘頻寬無法增加，因此無法改善rtPS的封包遺失率。
本論文中，提出考慮封包遺失率與剩餘時間之WiMAX網路排程法PLRRT演算法，修改ARL演算法，當rtPS的封包遺失率達到所要求的門檻值，除了減少x值之外，還會限制ertPS可分配的最大頻寬，使得rtPS在本訊框可以分配的最大頻寬會比上一訊框至少多出1%，以此方法改善ARL演算法。模擬結果顯示，不同於ARL演算法，本論文所提出的演算法，可以改善rtPS的封包遺失率。

IEEE 802.16 Standard is a Wireless Metropolitan Area Network (WMAN). To ensure the Quality of Service (QoS) of different application, the service flows are classified into five classes. In IEEE 802.16, the scheduling algorithms for allocating bandwidth is not defined. Therefore, to design an excellent scheduling algorithm satisfying the QoS requirements of all classes become a main research topic.

If the waiting time is over the maximum latency of a real-time packet, it will be discarded. In “A ratio limited scheduling algorithm for WiMAX network according to packet remaining time[1]”,this packet will be scheduled as long as the remaining packet time is less than 0.6 times of the average packet remaining time for ertPS. The threshold for the remaining time set is 0.4 times for rtPS.In “Adaptive Ratio Limited Scheduling Algorithm for WiMAX Network according to Packet Left Time[2]”,set the remaining time threshold to x and y for ertPS and rtPS. The starting values (0.4, 0.3) and (0.6, 0.4). To ensure that the packet loss rate of real-time polling service is limited within the required range,the packet loss rate of real-time polling service becomes larger, x will be smaller and y will be larger. However,the starting value (x,y) is (0.6, 0.4), the packet loss rate in ARL is not better than RL since the ertPS is allocated too large bandwidth when the starting value x 0.6 for the ARL algorithm.As the traffic load is increased (the packet loss rate become larger),the bandwidth’s allocation does not decrease significantly even if the value of x becomes smaller for ertPS.The remaining available bandwidth can not be increased for rtPS, so the packet loss rate of rtPS can not be improved .

In this paper, we modify the ARL algorithm. When rtPS packet loss rate reaches the required threshold value, in addition to reducing the value of x, it also limits the maximum bandwidth that can be allocated so that rtPS can be allocated the maximum in this frame. The ARL algorithm is improved by 1% more bandwidth than the one to the previous frame. Simulation results show that (x,y) is (0.6, 0.4), the algorithm proposed in this paper can improve the packet loss rate of rtPS.

[1]楊舜帆（2014）。根據封包剩餘時間WiMAX網路的比率限制排程法 A ratio limited scheduling algorithm for WiMAX network according to packet remaining time。國立臺灣科技大學電子工程系碩士論文，臺北市。
[2]黃凱翔( 2016 )。調適性根據封包剩餘時間WiMAX網路的比率限制排程法(Adaptive Ratio Limited Scheduling Algorithm for WiMAX Network according to Packet Left Time)。國立臺灣科技大學電子工程系碩士論文，臺北市。
[3]WirelessStandard.RFiDCentre.Retrieved from http://www.rfidc.com/docs/introductiontowireless_standards.htm
[4]IEEE Draft Amendment Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems - Advanced Air Interface. (2010). IEEE P802.16m/D6 May 2010, 1-932.
[5]Oktay, M. & Mantar, H. A. (2011, January). A Real-Time Scheduling Architecture for IEEE 802.16 - WiMAX Systems. Paper presented at the 2011 IEEE 9th International Symposium on Applied Machine Intelligence and Informatics (SAMI).
[6]李俊杰（2016）。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 Bandwidth Allocation Using the Mean & Standard deviation of Arrival Process: A Scheduling Algorithm for WiMAX Network。國立臺灣科技大學電子工程系博士論文，臺北市。
[7]IEEE Standard for Air Interface for Broadband Wireless Access Systems - Redline. (2012). IEEE Std 802.16-2012 (Revision of IEEE Std 802.16-2009) - Redline, 1-2542.
[8]Andrews, J. G., Ghosh, A. & Muhamed, R. (2007). Fundamentals of WiMAX: Understanding Broadband Wireless Networking: Prentice Hall.
[9]Ohrtman, F. (2005). WiMAX HANDBOOK Building 802-16 Wireless Networks: McGraw-Hill Education.
[10]Ohno, Y., Shimizu, T., Hiraguri, T. & Nakatsugawa, M. (2009, April). Novel Frame Structures to Improve System Capacity and Latency Performance of a Time-Division Duplex Multihop Relay Wireless Access System. Paper presented at the 2009 IEEE Wireless Communications and Networking Conference.
[11]4G WIRELESS EVOLUTION COFERENCE. (2009). SlidePlayer.
Retrieved from http://slideplayer.com/slide/4680109/
[12]Nuaymi, L. (2007). WiMAX: Technology for Broadband Wireless Access: Wiley.

[13]許獻聰（2009）。WiMAX無線網路技術系列。國立中央大學通訊工程系，桃園縣。
[14]IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems. (2004). IEEE Std 802.16-2004 (Revision of IEEE Std 802.16-2001), 0_1-857. doi:10.1109/IEEESTD.2004.226664
[15]IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1. (2006). IEEE Std 802.16e-2005 and IEEE Std 802.16-2004/Cor 1-2005 (Amendment and Corrigendum to IEEE Std 802.16-2004), 0_1-822. doi:10.1109/IEEESTD.2006.99107
[16]陳政隅（2013）。應用於WiMAX網路考慮佇列長度與封包遺失率的頻寬分配法 Bandwidth Allocation according to Queue Length and Packet Loss Rate - a Scheduling Algorithm for WiMAX Network。國立臺灣科技大學電子工程系碩士論文，臺北市。
[17]陳麒安（2014）。應用於WiMAX網路考慮封包最後時限的排序法 A scheduling algorithm for WiMAX network by considering the last deadline of packet。國立臺灣科技大學電子工程系碩士論文，臺北市。
[18]李聖宏（2015）。應用於WiMAX網路依頻寬需求調變的輪詢法 Polling according to the bandwidth request for WiMAX network。國立臺灣科技大學電子工程系碩士論文，臺北市。
[19]Hahne, E. L.& Gallager, R. G. (1986, June). Round robin scheduling for fair flow control in Data Communication Networks. International Conference on Communications.
[20]Demers, A., Keshav, S. & Shenker, S. (1989, September). Analysis and simulation of a fair queuing algorithm. SIGCOMM 1989 Symposium proceedings on Communications architectures & protocols.
[21]Cicconetti, C., Erta, A., Lenzini, L. & Mingozzi, E. (2007). Performance Evaluation of the IEEE 802.16 MAC for QoS Support. IEEE Transactions on Mobile Computing, 6(1), 26-38. doi:10.1109/TMC.2007.250669
[22]Zubairi, J. A., Erdogan, E. & Reich, S. (2015, July). Experiments in fair scheduling in 4G WiMAX and LTE. Paper presented at the 2015 International Conference on High Performance Computing & Simulation (HPCS).
[23]Shreedhar, M. & Varghese, G. (1996). Efficient fair queuing using deficit round-robin. IEEE/ACM Transactions on Networking, 4(3), 375-385. doi:10.1109/90.502236
[24]Lu, S., Bharghavan, V. & Srikant, R. (1999). Fair scheduling in wireless packet networks. IEEE/ACM Transactions on Networking, 7(4), 473-489. doi:10.1109/90.793003
[25]Cicconetti, C., Lenzini, L., Mingozzi, E. & Eklund, C. (2006). Quality of service support in IEEE 802.16 networks. IEEE Network, 20(2), 50-55. doi:10.1109/MNET.2006.1607896
[26]Sagar, V. & Das, D. (2008, November). Modified EDF algorithm and WiMAX architecture to ensure end-to-end delay in multi-hop networks. Paper presented at the TENCON 2008 - 2008 IEEE Region 10 Conference.
[27]Wongthavarawat, K. & Ganz, A. (2003, February). Packet scheduling for QoS support in IEEE 802.16 broadband wireless access systems. International Journal of Communication systems, volume 16, issue 1.
[28]Chen, J., Jiao, W. & Wang, H. (2005, May). A service flow management strategy for IEEE 802.16 broadband wireless access systems in TDD mode. Paper presented at the IEEE International Conference on Communications, 2005. ICC 2005. 2005.
[29]Iera, A., Molinaro, A., Pizzi, S. & Calabria, R. (2007). Channel-Aware Scheduling for QoS and Fairness Provisioning in IEEE 802.16/WiMAX Broadband Wireless Access Systems. IEEE Network, 21(5), 34-41. doi:10.1109/MNET.2007.4305171
[30]Chen, J., Wang, C., Tsai, C., Chang, C., Liu, S., Guo, J., Lien, W., Sum, J. & Hung, C. (2006, October). The Design and Implementation of WiMAX Module for ns-2 Simulator. ACM International Conference Proceeding Series, 202. doi:10.1145/1190455.1190458