IEEE 802.11e 為改善服務品質保證的問題，透過改善IEEE 802.11 媒體存取層的協定，並導入兩種新的無線通道存取方式：加強分散式通道存取方式(EDCA)與混合協調控制通道存取方式(HCCA)。因為無線網路通道時變的特性，其可用頻寬與時變的封包傳送速率很容易影響傳送封包的品質。大部份的無線網路產品皆同時提供不同的調變方式與實體層的傳送速度，以適應無線網路環境的需求。一般來說，較低的傳送速率會佔據較長的無線通道傳送時間，並降低系統的性能。這會導致頻寬的浪費與不公平性，且無法提供服務品質保證。本論文應用跨層的觀念並加強EDCAF 協定，提出了加強的 EDCAF 協定稱E2DCAF，同時並提出一個多重速率的離散馬可夫鏈無線通道模型。驗證結果，E2DCAF 能有效改善系統性能與加強封包傳送的公平性。
另外本論文並同時分析與探討 AIFSN 與 CWmin 競爭參數對無線區域網路系統效能的影響。同時並提出一個參數適應性動態調整方案(ACS)以改善系統效能，此方案能相容於現存的 IEEE 80 2.11e EDCAF並透過調整競爭參數的方式能有效的改善系統的性能並提供服務品質的差異化。

IEEE 802.11e provides the guaranteed quality of service (QoS) by proving different transmission priorities. IEEE 802.11e improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two new channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function (HCF) controlled channel access (HCCA). The available bandwidth and transmission rate may be easily affected by the signal quality, because the characteristic of communication channel in wireless environment is in random time-variation manner. Therefore, most devices support different transmission rates in wireless network. Generally a station using a lower transmission rate will occupy communication channel for a longer time and degrade system performance, which causes bandwidth waste and unfairness and cannot provide the guaranteed QoS for the stations with higher transmission rates. We propose an enhancing EDCAF (E2DCAF) by consolidating the cross-layer concept and IEEE 802.11e EDCAF protocol; a multirate discrete Markov chain model is developed and analyzed for the system with multiple transmission rates. According to the obtained results, E2DCAF improves performance especially in throughput and fairness. E2DCAF scheduling also makes the different QoS requirements be processed efficiently and flexibly
This paper also presents a simulation analysis of the influence of the AIFSN and CWmin parameters on the IEEE 802.11 networks and proposes a simple optimal scheme called Adaptive Control Scheme (ACS) which is based on different traffic classes and QoS requirement to improve the WLAN performance. The algorithm is simple and effective in managing QoS WLAN networks. The main objective of this algorithm is to provide an effective and simple tuning mechanism for QoS WLAN, complementary to legend IEEE 802.11e.

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