Cross-Layer Optimization of Voice over IP in Wireless Mesh Networks

Optimizing the operation of IEEE 802.11 networks requires estimatingthe load of the wireless channel. The channel busy fraction, which is thefraction of time in which the wireless channel is sensed busy due to suc-cessful or unsuccessful transmissions, can be used as indicator for this pur-pose. It can be obtained from e.g. the IEEE 802.11k channel load reportor hardware-specific interfaces. Previously, the channel busy fraction hasbeen used as a metric for different purposes such as routing and admis-sion control. However, a thorough evaluation of the relationship betweenthe busy fraction and other important characteristics such as the collisionprobability and throughput is missing. In this paper, we present an an-alytical model to study the channel busy fraction in non-saturated IEEE802.11 networks. We validate the model with measurements in a testbed.The predictions from the model match measurements well. Furthermore,we demonstrate how to apply the model to estimate the available link band-width. Using measurements obtained from a testbed operated at 6 Mbit/s,we show that the channel busy fraction allows an accurate prediction of theavailable bandwidth with an error smaller than 70 kbit/s.