Extending the Ad Hoc Horizon in Dense 802.11 Networks Using Fountain Codes

Ad hoc networks are one operational mode of IEEE802.11 wireless local area networks (WLANs) in which users form themselves the network and act as routers to one another. When the density of such a network is high, capacity becomes limited by the interference resulting from the collisions between simultaneously transmitted packets. Interference gets even worse in the case of reliable transport based on TCP as data packets interfere with the acknowledgements sent back in the reverse direction. In this context, the term ad hoc horizon refers to the number of nodes and hops beyond which TCP performance is no longer satisfactory in terms of throughput. We investigate in this work this horizon in the presence of a transport scheme based on fountain codes instead of TCP. Fountain codes are rate less, low complexity codes, which allow for open-loop reliable transport, without acknowledgements in the reverse direction; this would in turn decrease interference and increase the horizon. Indeed, our results show a horizon almost twice as large as that obtained with TCP.