802.11 has been used well beyond its original intended use of WLANs. Of particular interest to us in this paper is its use in long-distance mesh networks being designed/used for lowcost rural connectivity. We describe in detail a new MAC protocol, called 2P, that is suited for such networks in terms of efficiency. A significant challenge here is the implementation of this protocol on top of off-the-shelf 802.11 hardware, to preserve the cost benefits. We show how this can be achieved, by exploiting the flexibilities available within Prism2-based chipsets. We then present the dependence of 2P on the network topology, and show that it is indeed possible to design in practice, network topologies compatible with 2P. We describe experimental as well as simulationbased evaluations of 2P, and show that 2P achieves significant performance improvement (as much as 20 times more throughput) over 802.11 CSMA/CA in long-distance mesh networks.

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Abstract

The past decade has seen communication revolution in the form of cellular telephony as well as the Internet, but much of it has been restricted to the developed world and metro pockets in the developing world. While the use of cellular technologies can cut down on the time to deploy access networks, the cost economics make this non-viable in growing telecom economies. In the Digital Gangetic Plains (DGP) project, we are exploring the use of 802.11 as a long-distance access technology. 802.11 is currently cost-priced due to competitive mass production and hence is attractive for low cost and rapid deployment in rural areas.We have built an extensive testbed in a rural setting consisting of multi-hop directional 802.11 links, the testbed spanning up to 80km at its longest. To our knowledge such a long-distance, multi-hop testbed based on 802.11 is unique thus far. While 802.11 is attractive in terms of cost economics, it was inherently designed for indoor use. Our novel use of the technology for outdoor, long-distance access links presents several challenges. Our experience with the testbed has brought several research as well as operational issues to the fore. In this paper, we describe the novel technical challenges that lie ahead in using 802.11 to bridge the digital divide.

Abstract-IEEE 802.11 (WiFi) has been used beyond its original intended purpose of a tether-free LAN. In this paper, we are interested in the use of 802.11 in mesh networks. Specifically, we consider those which involve directional antennas and longdistance point-to-point links. In recent work, the 2P MAC protocol has been designed to suit such a network architecture. In this paper, we assume the use of the 2P MAC protocol in the links of the network, and consider the problem of link channel allocation. We first formulate the problem of minimizing the mismatch between link capacities desired by the network operator and that achieved under a channel allocation. We show that this problem is NP-hard. We then explore several heuristics for channel allocation and find a set of heuristics that achieve the optimal allocation in most scenarios.