Optimization study of the contention window in 802.11 DCF

This paper first introduces the basic principle of IEEE 802.11 DCF and analyses the effect of the two system parameters, network size and minimize contention window, on the performance in terms of saturation throughput and probability of collisions. To overcome the shortcomings of the original 802.11DCF, the influence of the contention window´s size was analyzed. 802.11DCF-SD (Success Decrease) method was proposed on the basis of the analytical results. This paper discusses the improved performance from two aspects - saturation throughput and collision probability. Results indicate that the performance of 802.11 DCF-SD is much better than that of Barakat C´s method, especially the collision probability which has been significantly reduced and maintained at a lower level. Meanwhile we discuss the impact of a continuous number N´ of successful transmissions on the network performance before the contention window size has dropped by half. Experiments show that the overall performance of the network is optimal when N´ takes the value of ten.