Study of An Enhancement of the IEEE 802.11 DCF via Distributed Reservation

[[abstract]]IEEE 802.11媒介存取控制層提供分散式協調功能(Distributed Coordination Function，簡稱DCF)，使用後退(backoff)機制來避免碰撞發生，分別從控制競爭視窗(Contention Window)中隨機選取傳送時間(backoff time)，錯開不同工作站傳送訊框的時間，避免碰撞的發生，然而隨著工作站的數目增加，碰撞的機率也明顯增多，導致throughput呈現下降的情形。 本篇論文提出Early Backoff Announcement(簡稱EBA)的演算法，是對原本DCF加以調整改善，因此分別使用EBA和DCF的工作站能平穩的存在同一個WLAN，在EBA的方法中，工作站將預定下次傳送資料的時間(next backoff time)並將此資訊存放訊框中進行傳送，其他工作站接收這個資訊，在選取下次資料傳送時就能避開再同一時間進行傳送，避免碰撞發生。透過模擬和數值分析，顯示這套演算法能有效減少碰撞，以提升throughput。[[abstract]]IEEE 802.11 Media Access Control (MAC) layer provide Distributed Coordination Function (DCF), the station which transmit frame have to backoff for a random period of time uniformly chosen within the Contention Window (CW). However the more the station increase, the lower throughput become. The more the station increase, the more probability of collision increase. This thesis improves DCF by using Early Back off Announcement (EBA), and the stations which respectively using EBA and DCF are compatible with each other in the same WLAN. Using EBA algorithm, the station will transmit the data including next backoff time to other stations, so that the others can avoid collision by averting transmit data concurrently in next backoff time. Both simulation results and numerical analysis verify the EBA algorithm leads to high throughput and less collision.[[note]]碩