針對目前 IEEE 802.11 a/b/g 無線系統皆以碰撞避免式載波偵測多重存取(carrier sense multiple access with collision avoidance; CSMA/CA) 以競爭為基礎，其並無法提供完整服務品質(quality of service; QoS)的保證，IEEE因而制定802.11e標準針對中樞協調功能(pointer coordination function; PCF)及分散式協調功能(distributed coordination function; DCF)環境分別做不同的媒介存取控制層協定(medium access control; MAC)設計以提供QoS保證。但在無線的環境中每個節點的執行速率與頻寬隨時都在改變，因此要確實執行QoS保證仍有許多困難，本論文希望能針對無線環境中可變頻寬的特性來加強QoS的保證。
本論文，在IEEE 802.11e EDCA mode多重傳送速率下的無線網路基礎架構中，提出一個適應性速率控制(adaptive rate control algorithm; ARCA)方法，改善因為頻寬與速率變動而下降的產能(throughput) 、降低每個封包碰撞率(per-packet collision rate)及封包丟棄率(dropping rate)，更有效率的使用無線區域網路(wireless local area network；WLAN)資源。ARCA利用頻寬因數(bandwidth factor)與優先權表格(priority table)動態調整EDCA的參數仲裁訊框間間隔(arbitration inter-frame space；AIFS)、競爭視窗(contention window; CW)、持續因數(persistence factor; PF) 等，配合實體層速率上升或下降來組合變化這些參數，來提高整個系統工作效能。使得實體層速率較高之工作站(station; STA)不會受到因通道狀態改變而有較低實體層速率之STA影響。透過模擬的方式，將我們所提出的方法與IEEE 802.11e標準互相比較，從模擬結果顯示，ARCA確實能比IEEE 802.11提供更好的產能。

All based on carrier sense multiple access with collision avoidance (CSMA/CA) contention base to IEEE 802.11 a/b/g wireless system at present. It is unable to offer the assurance of intact quality of service (QoS) , therefore IEEE makes 802.11e standard to offer QoS. IEEE 802.11e does different medium access control (MAC) layer to design separately to pointer coordination function (PCF) and distributed coordination function (DCF). But each nodal execution speed with bandwidth to change at any time among wireless environment, so should really carry out QoS and guarantee that there are a lot of difficulties. This thesis hopes to strengthen the assurance of QoS to the variable and bandwidth characteristic in the wireless environment.
This paper proposes an adaptive rate control algorithm (ARCA) to improve throughput, collision rate and drop rate of each packet in the IEEE 802.11e EDCA mode multi-rate infrastructure wireless networks. It uses more efficient wireless LAN resources. ARCA utilizes the parameter of bandwidth factor and priority table dynamically to adjust the parameter of arbitration inter-frame space (AIFS), contention window (CW) , persistence factor (PF) of EDCA. These parameters are adjusted by ARCA to improve the efficiency of the whole system according to the rising or falling of the data rate in physical layer. Making the 802.11e high data rate of station (STA) don’t be influenced the lower data rate of STA because the channel status changed. By way of simulating, ARCA compares with 802.11e standard. It can offer better throughput than 802.11e.

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