A Distributed Fair Scheduling Scheme With a New Analysis Model in IEEE 802.11 Wireless LANs

Abstract

In this paper, we study the performance of 802.11 wireless local area networks (WLANs) and propose a distributed packet scheduling scheme that improves the short-term fairness among stations in a WLAN. First, we present a completely different analytical model to analyze the performance of 802.11 distributed coordination function (DCF), which models the channel contention dynamics of an IEEE 802.11 system, rather than the individual user perspective adopted by most previous analytical works based on Markov chains. Our model is much simpler than previous Markov chain models that have been used popularly to model the DCF's binary exponential backoff (BEB) procedure. In our model, the backoff stage and the value of the backoff counter are represented as a queueing system and the residual service time at the queue, respectively. Then, we model an entire 802.11 WLAN as a closed queuing network and derive the performance of the 802.11 DCF based on the queueing theory. Next, by exploiting the analytic results, we develop a simple distributed runtime estimation scheme that effectively calculates the number of contending stations. Finally, we propose a distributed packet scheduling scheme that improves the short-term fairness to the IEEE 802.11 network. The scheme utilizes the token bucket mechanism and controls the packet arrival rate sent down to the medium access control (MAC) layer from the logical link control (LLC) layer by adjusting the token-generation rate according to the measured channel contention level. Performance evaluation results show that our scheduling scheme provides a higher degree of short-term fairness as well as throughput improvement.