Fairness analysis of throughput and delay in WLAN environments with channel diversities

Chiapin Wang,Shih-Hau Fang,Hao-Kai Lo

doi:10.1186/1687-1499-2011-42

Abstract

The article investigates fairness in terms of throughput and packet delays among users with diverse channel conditions due to the mobility and fading effects in IEEE 802.11 WLAN (wireless local area networks) environments. 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. Our analytical results further demonstrate that the presence of diverse channel conditions can pose significant unfairness on both throughput and packet delays even with a link adaptation mechanism since the MCSs (modulation and coding schemes) available are limited. The simulation results validate the accuracy of our analytical model.

Highlights

IEEE 802.11 based wireless local area networks (WLAN) become increasingly prevailing with their ubiquitous nature and low cost infrastructure
Overview of IEEE 802.11 distributed coordination function (DCF) First we briefly introduce 802.11 DCF based on CSMA/ CA
We provide performance analyses in both cases of stations transmitting at an equal data rate and at different data rates with a link adaptation mechanism

Summary

Introduction

IEEE 802.11 based wireless local area networks (WLAN) become increasingly prevailing with their ubiquitous nature and low cost infrastructure. The work [15] presents a dynamic contention window control scheme based on the number of downlink flows to achieve per-flow fairness It does not consider some dynamics in WLAN environments such as channel conditions and traffic loads that can greatly impact the performance of fairness. Our analytical model can be used to evaluate the statistical performance of DCF in realistic WLAN environments since it takes more factors into account including the finite retransmission limit, the probability that the backoff counter is frozen when the channel is sensed busy, error-prone channels, and multiple data rates. Our analytical results demonstrated that when all the hosts transmit at an equal data rate, 802.11 CSMA/ CA can only present fairness on condition of homogeneous link qualities; the presence of diverse link qualities can cause significant unfairness. The average packet delay of two stations in diverse channel conditions (with equal data rates)

40 IC host

Conclusion