| Summary: | 碩士 === 國防大學中正理工學院 === 資訊科學研究所 === 95 === The backoff mechanism of IEEE802.11 Distributed Coordination Function (DCF) on Medium Access Control (MAC) layer takes advantage of Binary Exponential Backoff (BEB) to control the Contention Window (CW) and avoid collision. To design an efficient backoff algorithm, we have to consider two objectives: (1) To decrease unnecessary bakeoff time delay, and (2) To reduce the probability of collision. If we diminish the CW to decrease the unnecessary backoff time, the collision will increase. On the other hand, if we enlarge the CW to avoid collision, we will increase the unnecessary backoff time. There is a trade-off between the two objectives. Therefore, it is important to choose the appropriate CW.
In the paper, we attempt to improve the BEB by proposing a new backoff algorithm. According to the Fibonacci Series, the ratio of two adjacent numbers is 1.618, so called the Golden Ratio. The CW value that grows with the Golden Ratio won’t increase too fast. And to decrease the unnecessary backoff time delay, we have a CWbalance to balance the network flow and make it more efficient. We simulate infrastructure WLAN and infrastructureless WLAN by using Network Simulator Version 2 (NS2). From the result, our protocol improves the throughput about 13% when there are more than 30 stations, and we decrease delay efficiently. Especially in the area of Battlefield and Calamity, we obtained high performance. Finally, it will help our army deliver the information efficiently in the event of a war.
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