為了進一步支援無線網路上的服務品質(QoS)，IEEE 802.11e通訊協定目前正在制訂中。其提供兩種媒介存取方式，一為基礎的進階分散存取(EDCA)，另一種是建構在進階分散存取下的混合控制存取(HCCA)。802.11e中，藉由不同的訊框間隔(IFS)與競爭視窗(CW)相關參數的設定以區隔不同的存取等級(AC)。為了在802.11e網路下進一步的發展有效的服務品質管理機制，我們提出了一個數學模型以分析在進階分散存取網路下所使用的頻寬與媒體存取層所延遲的時間。在這個模型下，每個站台可以支援多個不同等級的資料流(聲音/影音與資料)。透過這個數學模型，允入控制與資源管理可以很容易實現，也可以支援不同應用程式的不同需求。

For supporting Quality of Service (QoS) for wireless networks, the IEEE 802.11 Task Group E currently defines enhancements to the IEEE 802.11 MAC, called 802.11e. The IEEE 802.11e provides two mechanisms for the support of applications with QoS requirements, namely, Enhanced Distributed Channel Access (EDCA) and HCF Controlled Channel Access (HCCA). EDCA mechanism defines four access categories (ACs) that provide support for the delivery of traffic with user priorities. Different AC uses various Inter-Frame Space (IFS) and Contention Window (CW) parameters. In order to further develop efficient QoS management for the IEEE 802.11e networks, we propose an analytical model to evaluate throughput and MAC delay of the basic access method of the IEEE 802.11e - EDCA. Our Markov chains consider the situation of different multimedia (voice/video and data) traffic flows in a mobile station. This is improved from previous work, and closer to real usage scenarios. The correctness of our analysis has been validated via simulation results. Throughout our model, call admission control (CAC) and resource management can be easily applied, and thus QoS for hybrid requirements is supported.

[1] IEEE, “Wireless LAN medium access control (MAC) and physical layer (PHY) specification”, IEEE Standard 802.11, June 1999
[2] IEEE, “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specification: High speed Physical Layer (PHY) extension in the 2.4 GHz band”, IEEE Standard 802.11b, September 1999
[3] IEEE, “Wireless LAN medium access control (MAC) and physical layer (PHY) specification: High-speed Physical Layer extension in the 5 GHz band”, IEEE Standard 802.11a, September 1999
[4] IEEE, “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Further Higher-Speed Physical Layer Extension in the 2.4 GHz Band”, IEEE Standard 802.11g, January 2003
[5] IEEE, “Wireless Medium Access Control (MAC) and Physical Layer (PHY) specifications: Medium Access Control (MAC) Quality of Service (QoS) Enhancements”, IEEE Draft 6.0 802.11e, November 2003
[6] Giuseppe Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordination Function” IEEE Journal on Selected Area in Communication, V18, N3, March 2000
[7] HaitaoWu, Yong Peng, Keping Long, Shiduan Cheng, Jian Ma, “Performance of Reliable Transport Protocol over IEEE 802.11 Wireless LAN: Analysis and Enhancement”, IEEE Infocom’02, New York, June 2002
[8] Bo Li, Roberto Battiti, “Achieving Maximum Throughput and Service Differentiation by Enhancing the IEEE 802.11 MAC Protocol”, Wireless On-Demand Network Systems 2004, LNCS 2928, pp. 285-300, January 2004
[9] Jun Zhao, Zihua Guo, Qian Zhang, Wenwu Zhu, “Performance Study of MAC for Service Differentiation in IEEE 802.11” IEEE Globecom’02, November 2002
[10] Hua Zhu, Imrich Chlamtac, “An Analytical Model for IEEE 802.11e EDCF Differential Services”, ICCCN’03, October 2003
[11] Daqing Gu, Jinyun Zhang, “QoS Enhancement in IEEE802.11”, IEEE Wireless Communications, June 2003
[12] Stefan Mangold, Sunghyun Choi, Guido R. Hiertz, Ole Klein, and Bernhard, “Analysis of IEEE 802.11e for QoS Support in Wireless LANs”, IEEE Wireless Communications, December 2003
[13] Pierre Ansel, Qiang Ni, Thierry Turletti, “FHCF: A Fair Scheduling Scheme for 802.11e WLAN”, INRIA, July 2004
[14] Wayne L. Winston, Indiana University, “Operations Research: Applications and Algorithms” 3rd ed. 1994