Local estimation of collision probabilities in 802.11 WLANs: An experimental study

Current 802.11 networks do not typically achieve the maximum potential throughput despite link adaptation and cross-layer optimization techniques designed to alleviate many causes of packet loss. A primary contributing factor is the difficulty in distinguishing between various causes of packet loss, including collisions caused by high network use, co-channel interference from neighboring networks, and errors due to poor channel conditions. In previous work, we used NS-2 simulations to show that estimating various components of loss probability such as direct collisions, staggered collisions, and physical layer errors, can be used to improve the throughput of 802.11 networks via link adaptation, carrier sense threshold adaptation, and MAC layer packet length adaptation. We have also proposed a method to estimate the various components of loss probability by comparing channel occupancy at a station with that of its access point. In this paper, we use Ath5k open source wireless card driver in an experimental testbed in order to experimentally verify the accuracy of our previously proposed approach to estimating collision probability. We show that our proposed methodology accurately estimates overall collision probability to within 5%. This experimental verification demonstrates the feasibility of our collision probability estimation approach and the resulting throughput gains in practice.