隨著無線區域網路快速地普及，近來提升無線網路的能力越來越引人注意，為了在無線網路802.11 上提供服務品質保證(Quality of Service) ，IEEE 802.11 Group E 提出了802.11e，用以確保多媒體服務的品質能夠得到保證。
其中提出了混合式協調功能(Hybrid Coordination Function，HCF)，包括了以輪詢為基礎的HCF通道存取機制(HCCA)和以分散競爭為基礎的EDCF 通道存取機制(EDCA)，這些機制的目的在於提供較嚴格的服務品質保證(QoS)給即時資料傳輸。在本論文的主要的探討在以中，我們評估新的IEEE 802.11e 標準中所用來支援服務品質保證的機制，也就是在原本IEEE 802.11 標準中的媒介存取控制層(MAC)的制下延伸討論因IEEE 802.11a/b/g 在不同的編碼調變(Coding Modulation)方式下，會造成不同的傳輸速率與不同的發射功率。高傳輸速度能夠在短時間內將資料傳遞出去，達到較高的頻寬，但相對的其抗干擾能力便比較薄弱。
所以本論文提出一個可以利用IEEE802.11的muti-rate的特性,利用RTS/CTS的機制,當Sender接收到CTS的封包時,CTS封包理面會有關於channel condition的資訊,來了解現在的channel的可以能容納PHY error 傳送的rate按照RBAR(Receiver Based Auto Rate)機制來知道現在此接收端所能容許會成功可以傳輸的頻寬，並在此機制下探討OAR(Opportunistic Auto Rate)對EDCF的機制有多大的效能改變。

The IEEE 802.11 wireless media access standard supports multiple data rates at the physical layer. Moreover, various auto rate adaptation mechanisms at the medium access layer (MAC) have been proposed to utilize this multi-rate capability by automatically adapting the transmission rate to best match the channel conditions. In this paper, we introduce the Opportunistic Auto Rate (OAR) protocol to better exploit durations of high-quality channels conditions. The key mechanism of the OAR protocol is to opportunistically send multiple back-to-back data packets whenever the channel quality is good. We also analytically study OAR and characterize the gains in throughput as a function of the channel conditions. Finally, we perform an extensive set of ns-2 simulations to study on the IEEE 802.11e, and topology on the throughput of OAR , and compared with the a single-rate IEEE 802.11.

B. Sadeghi, V. Kanodia, A. Sabharwal, and E. Knighlty, ``Opportunistic Media Access for Multirate Ad Hoc Networks,'' in Proceedings of ACM MobiCom'02 , Atlanta, Giorgia, September 2002
G. Holland, N. Vaidya, and P. Bahl, ``A Rate-adaptive MAC Protocol for Multi-hop Wireless Networks,'' in Proceedings of ACM MobiCom'01 , Rome, Italy, September 2001
R. Punnoose, P. Nikitin, and D. Stancil, ``Efficient Simulation of Ricean Fading within a Packet Simulator,'' in IEEE Vehicular Technology Conference, pages 764-767, 2000