On the End-to-End Delay Analysis of the IEEE 802.11 Distributed Coordination Function

The IEEE 802.11 protocol is the dominant standard for wireless local area networks (WLANs) and has generated much interests in investigating and improving its performance. The IEEE 802.11 medium access control (MAC) is mainly based on the distributed coordination function (DCF). DCF uses a carrier sense multiple access with collision avoidance (CSMA/CA) protocol in order to resolve contention between wireless stations and to verify successful transmissions. In this paper we present an extensive investigation of the performance of the IEEE 802.11b MAC protocol, in respect of end-to-end delay. The end-to-end delay analysis of the IEEE 802.11b has not been completed, because no adequate queuing delay is provided. Our delay analysis is based on Bianchi's model for the DCF, while a more comprehensive model could be used as well. We use z-transform of backoff duration to get mean value, variance and probability distribution of MAC delay. From the mean value and the variance of the MAC delay we determine the mean queuing delay in each station. Our analysis is validated by simulation results for both the Basic and RTS/CTS access mechanisms of the DCF. The accuracy of the analysis found to be quite satisfactory. We assume data rates of 1, 5.5 and 11 Mbps, in order to highlight the effect of the bit rate on delay performance for both access mechanisms.