On Fairness in Heterogeneous WLAN Environments

Abstract

We analyze the fairness of IEEE 802.11 DCF in heterogeneous wireless LAN environments where users experience unequal channel conditions due to the mobility and fading effects. Previous works [3] [4] show that the 802.11 CSMA/CA can present fairness characteristics in both long- term and short-term. However, the conclusion is only valid under the condition of homogeneous link qualities, which may be impractical. In this paper, we consider heterogeneous channel conditions based on an analytical approach of extending a verified two dimensional Markov chain model of DCF proposed by Bianchi [10]. From our analytical results, it is shown that 802.11 CSMA/CA can present fairness among hosts with identical link qualities regardless of equal or different data rates applied, which is consistent with the observations of previous works. Our analytical results also demonstrate that the presence of heterogeneous channel conditions can pose significant unfairness of channel sharing even with a link adaptation mechanism since the MCSs (modulation and coding schemes) available are limited.