A new constrained-send mechanism to enhance the performance of IEEE 802.11 DCF

In this paper, we proposed a modified access mechanism named Constrained-send DCF (CDCF) to improve the performance of IEEE 802.11 DCF protocol. We find that, in DCF, the transmission probability is higher than the reasonable value when the node number is greater than 4 under basic access scheme or than 17 under RTS/CTS scheme, and it results in serious collision. To constrain stations´ transmission, we introduced a constrained-send probability at the end of each backoff procedure. We analyzed the performance of this mechanism based on a 2-Dimension Markov analytical model, after that we derived the optimum constrained-send probability. Numerical results show that the CDCF mechanism has much better performance than DCF with respect to both throughput and average packet delay. And under RTS/CTS scheme, although CDCF slightly improve the throughput performance (due to the natural good throughput performance of RTS/CTS-scheme DCF), it leads to a much better average packet delay performance compared to DCF. The CDCF keeps all the features of the IEEE 802.11 DCF protocol and is quite easy to implement.