Know Your Neighbour: Packet Loss Correlation in IEEE 802.11b/g Multicast

In this paper we present a number of wireless measurements conducted on mobile phones using WLAN IEEE802.11b/g in a multicast scenario. When designing efficient error recovery mechanisms for reliable multicast protocols, it is necessary to have good a understanding how channel errors occur and preferably to have a network model that describes these errors well. The measurement results in this work are not sufficient to create an accurate error model, nevertheless they provide two important results. First, the assumption of independent package loss, commonly assumed in simulations and analytical work, does not hold. In all measurements conducted the packet loss, observed at different devices, indicated some level of correlation. Therefore error models used for simulations and analytical evaluation should take this finding into consideration. Secondly, the packet loss probability observed at mobile devices of the same brand and model, exhibited large differences. A uniform packet error probability will therefore not be a satisfactory error model, even when considering homogeneous networks.