Performance evaluation for IEEE 802.11e enhanced distributed coordination function

摘要

The IEEE 802.11e working group aims to enhance the current 802.11 medium access control (MAC) to support integrated data and voice (or video) communications. Till now, a draft of the IEEE 802.11e enhanced distributed coordination function (EDCF) has been proposed. In the literature, there is very limited analysis about EDCF since it is a new protocol, and most related work are only confined to simulation or saturation state. In this paper, we evaluate the performance of EDCF by dividing the traffic into two groups, namely real-time packets and non-realtime packets, and use an analytical model to quantify the performance of both IFS priority and contention window (CW) priority in the EDCF. In our analysis, we assume that the traffic arrival is a Poisson process. We provide a queue model for EDCF. Since there are multiple stations contending for one channel in the system, the queue model for EDCF cannot be a regular M/G/1 model. We redefine the service time and the waiting time so that we can still use M/G/1 model in the analysis. To validate the accuracy of our analytical results, we have done extensive simulations and we observed that EDCF does provide service differentiation between different traffic categories. But due to the inherent contention characteristic of carrier sense multiple access with collision avoidance (CSMA/ CA) MAC protocol, the delay cannot be guaranteed, even for the highest priority traffic. A lot more work needs to be done for the MAC protocol to effectively support service differentiation in the future.