Modeling the Short-Term Unfairness of IEEE 802.11 in Presence of Hidden Terminals

IEEE 802.11 exhibits both short-term and long-term unfairness [15]. The short-term fairness automatically gives rise to long-term fairness, but not vice versa [11]. When we thoroughly investigated a simple scenario with hidden terminals, we found it to be unfair on the short-term basis, though it provides fair access on a long-term basis. It implies that the protocol cannot be used to provide fair access for delay sensitive traffic even in a simple scenario. In this paper, we analyze the short-term behavior using the embedded-Markov chain method to answer the following two questions: (i) once a node gets control of the medium, what is the average number of packets this node can transmit consecutively without experiencing any collision, (ii) once a node loses its control of the medium, what is the average time the node has to wait before it gets control of the medium again. The first question reflects on how long a node can capture the medium, whereas the second question reflects on how long a node may be starved. The analytical model is validated by the simulation results. Our work is distinct from most of the work published in the literature in two aspects: we focus on the short-term behavior rather than the long-term, and the analytical method is adopted for the study.