An Enhanced Backoff Mechanism in IEEE 802.11 Distributed Coordination Function

• Main Authors: Po-Yen Chih, 池柏諺
• Other Authors: 賴飛羆
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/30124747993158405352

碩士 === 國立臺灣大學 === 資訊工程學研究所 === 93 === With a rapid growing rate of wireless requirements, wireless LAN (WLAN) is becoming more and more popular. The main standard which is used today for WLAN is IEEE 802.11 standard. The standard defined two protocol functions in both contention-based and contention-free structures: Distributed Coordination Function (DCF) and Point Coordination Function (PCF). The major coordination way in contention-based structure is using a mechanism called backoff timer. After the channel idle for a period of time plus a backoff time can a mobile station transmit data frame. The backoff time is randomly chosen from a contention window (CW) that defines the range for the backoff time. While a transmission collision happened, the station doubles its CW in order to avoid another collision. But it is not efficient to double the CW every time the channel has collision. So we proposed a new backoff mechanism allowing stations to transmit data with slow increasing CW, use it to enhance the throughput. We use NS-2 to simulate the proposed mechanism, and the results show that the throughput of this new mechanism is the same as DCF when the station number is small, but is better than DCF when the station number becomes larger.