Modelling a Contention-Based Wireless MAC Protocol with EDCA Countdown and Constrained Priority Freezing

Abstract

Analytical modelling is an important part of distributed wireless MAC protocol research and analysis. Most of the protocols proposed in the literature are based on a countdown and use one of two different countdown types: DCF or EDCA type, both defined in the IEEE 802.11 group of standards. The difference between the two countdowns is seemingly negligible, but it can lead to remarkable differences in network performance. In this paper, a new model of a simple protocol is developed that uses an EDCA type of countdown and employs a constrained priority freezing mechanism. It is based on a three-dimensional Markov chain that represents the operation of a single observed station. The model is validated by comparing the numerical results with the simulation results and shows a very high degree of accuracy. Therefore, the proposed model should serve as a basis for the development of more complex models of protocols using EDCA countdown with constrained priority freezing.