Multihop connectivity in wireless ad hoc networks

Wireless ad hoc networks have numerous real life applications as they can be instantaneously established, require no infrastructure, and are autonomic and selforganizing. Multihop connectivity is the ability of the multiple-hops-away nodes—nodes which are not directly connected—to communicate with each other. Since wireless ad hoc networks are infrastructure-less, the participating nodes themselves are supposed to establish the service of multihop connectivity by forwarding the messages on behalf of each other. Routing and Relaying are the two approaches to provide multihop connectivity in wireless ad hoc networks. In Relaying, MAC layer is the point in the protocol stack at which the switching or forwarding decision takes place, while Routing schemes perform this decision at a later stage i.e. at Network layer. Routing is a widely researched and practiced solution to the problem of multihop connectivity, whereas Relaying has not been adequately explored in wireless ad hoc networks. This thesis argues that due to the specific nature of the wireless ad hoc networks and the MAC protocols for these networks, Relaying is technically a more suitable option in these networks and has higher prospects. This argument is supported by designing a multihop version of the IEEE 802.11 MAC protocol and comparing its performance with the AODV routing protocol. The analysis shows that a multihop 802.11 MAC can be implemented in a much simpler manner and it can achieve performance comparable with that of AODV. In reactive or on-demand routing—the class of routing protocols widely acclaimed for its lower overhead—the accessibility prediction scheme is introduced which reduces the routing overhead by avoiding routing actions which are possible-tofail. Furthermore, this thesis evaluates the effect of utilizing obsolete routing information—a common approach to optimize the reactive routing protocols. Based on the analysis, it is argued that this act is inconsistent with the nature of the reactive routing and can have limited but unpredictable benefits, mainly when no additional overhead is incurred.