Simplified Probabilistic Modelling and Analysis of Enhanced Distributed Coordination Access in IEEE 802.11

The IEEE 802.11 standard defines access categories (AC) and differentiated medium access control mechanisms for wireless local area networks. The preferential or deferral treatment of frames is achieved using configurable Arbitration Inter-Frame Spaces (AIFS) and customizable Contention Window (CW) sizes. In this paper, we address the problem of determining when a station, being a part of wireless communication, will access the medium. We present an algorithm calculating the probability of winning the contention by a given station, characterized by its AIFS and CW values. The probability of collision is calculated by similar means. The results were verified by simulations in Matlab and OPNET Modeler tools. We also introduce a web applet implementing and interactively demonstrating the results.