Optimal Contention Window Adjustment for Asymmetry Traffic in Erroneous Channels over IEEE802.11 WLANs

Zhengyong FENG  Guangjun WEN  

IEICE TRANSACTIONS on Communications   Vol.E96-B   No.5   pp.1149-1157
Publication Date: 2013/05/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E96.B.1149
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
Markov Chain,  asymmetry traffic,  saturation throughput,  erroneous channels,  WLANs,  CSMA/CA,  

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IEEE802.11 Wireless Local Area Networks (WLANs) are becoming more and more pervasive due to their simple channel access mechanism, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), but this mechanism provides all nodes including Access Point and other Stations with the same channel access probability. This characteristic does not suit the infrastructure mode which has so many downlink flows to be transmitted at the Access Point that congestion at the Access Point is more likely to occur. To resolve this asymmetry traffic problem, we develop an Optimal Contention Window Adjustment method assuming the condition of erroneous channels over WLANs. This method can be easily implemented and is compatible with the original CSMA/CA mechanism. It holds the ratio of downlink and uplink flows and at the same time achieves the maximum saturation throughput in the WLANs. We use the Markov Chain analytical model to analyze its performance and validate it through the simulations.