Performance Improvement for IEEE 802.11 Distributed Coordination Function (DCF)

Kiyoshi TAKAHASHI  Toshinori TSUBOI  

IEICE TRANSACTIONS on Communications   Vol.E89-B   No.5   pp.1605-1612
Publication Date: 2006/05/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.5.1605
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
MAC protocol,  backoff algorithm,  finish tags,  saturation throughput,  

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The medium access control (MAC) protocol is the main determiner of the system throughput in Wireless Local Area Networks (WLANs). The MAC technique of the IEEE 802.11 protocol is called Distributed Coordination Function (DCF). DCF is based on a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. Each station generates a random backoff interval before transmitting a packet to minimize the probability of collision with packets being transmitted by other stations. However, when the number of stations increases, the system throughput decreases. This paper proposes a new backoff algorithm that uses finish tags. The proposed algorithm uses the finish tag of each station to control the backoff intervals so as to improve system throughput. The finish tag is updated when a packet reaches the front of its flow, and it is attached to the packet just prior to transmission. When a station receives packets with older finish tags, its backoff time interval is increased. For this reason, the more the stations there are, the larger the backoff time becomes. Simulations confirm that the proposal improves system throughput of a IEEE 802.11 network under saturation conditions.