| Summary: | 碩士 === 中興大學 === 電機工程學系所 === 95 === IEEE WLAN work team established IEEE 802.11 standard in 1997. It defined two different operation types of Wireless LAN - Infrastructure Wireless LAN and Ad-Hoc Wireless LAN. Among these systems, what basic media competitive scheme IEEE 802.11 MAC uses is DCF scheme.
DCF can be used in Infrastructure Wireless LAN and Ad-Hoc Wireless LAN simultaneously, and it utilizes Carrier-Sense Multiple Access, Collision Avoidance (can be abbreviated as CSMA/CA), and Random Backoff Scheme to make station to transmit and receive information.
Although DCF uses the techniques mentioned above may avoid some collision during the transmission, it sometimes also causes stations waiting for a long time. Every time when a lot of workstations compete for accessing the channel, it is easy to create the same backoff time which may produce collision; however, after collision, repeatedly, it needs to take a long time to get into the competitive cycle. For this reason, how can we create a compatible contention window to reduce the collisions when facing the great amount of stations is a important study.
In this paper, we provide an approach of generating a new contention window to reduce the opportunities of collisions happened in the systems. The main idea is aiming at that, under the channel condition of heavy load, stations produces the same backoff time and collides easily. After the collision occurs, we may adopt approaches we assumed to lessen the opportunities of it and to promote the performance of whole transmission.
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