Exact distribution of access delay in IEEE 802.11 DCF MAC

This paper presents an analytical framework to calculate the probability mass function (pmf) of channel access delay in IEEE 802.11 distributed coordination function (DCF) medium access control (MAC) mechanism. The access delay is defined as the time between a station chooses a new backoff value and the time it is able to access the channel for data packet transmission. Using a Markov process, the access delay is modeled as having phase-type distribution. Since the back-off is frozen when the channel is sensed busy, the access delay distribution is observed to be composed of non-continuous clusters. The envelope of the pmf as well as the envelope of each cluster resemble hyper-exponential distribution. While the proposed model is flexible enough to accommodate any distribution of MAC data frame length, the numerical results presented in this paper are for the fixed-length data frames. The model would be useful in many aspects such as queueing analysis and/or designing energy-efficient MAC protocols compatible with the IEEE 802.11 DCF standard