A simple nonsaturated IEEE 802.11e EDCA model

We model a nonsaturated IEEE 802.11e EDCA network for a small buffer size. Our model is much simpler and more accurate than others that have appeared in the literature. The model is simple because 1) we invoke the Kumar renewal-reward approach for the saturated collision probability rather than the Bianchi Markov-chain approach, as in previous work, and 2) we approximate the nonsaturated attempt rate by scaling the attempt rate of the saturated setting with the probability of a packet arrival. We verify the accuracy of our model using ns-2 simulation and show that the collision probability obtained in our model is the most accurate amongst related work. The collision probability governs all other performance metrics, such as throughputs and delay characteristics; we show that since prior works do not model the nonsaturated collision probabilities accurately, they fail to correctly capture the delay characteristics. Also, our results indicate that if we accurately model the nonsaturated collision probability, the same formulas used for the saturated performance descriptors can produce accurate results for nonsaturated operation, and therefore is unnecessary to construct specific formulas for nonsaturated performance descriptors, as done in previous work.