Greedy Algorithms to Determine Stable Paths and Trees in Mobile Ad hoc Networks

Abstract

A mobile ad hoc network (MANET) is a dynamic, resource-constrained, distributed system of independent and arbitrarily moving wireless nodes and bandwidth-constrained links. MANET nodes operate with limited battery charge and use a limited transmission range to sustain an extended lifetime. As a result, MANET routes are often multi-hop in nature and nodes forward the data for others. Based on their primary route selection principle, MANET routing protocols are classified into two categories (Meghanathan & Farago, 2004): minimum-weight based routing and stability-based routing protocols. The minimumweight path among the set of available paths in a weighted network graph is the path with the minimum total weight summed over all its edges. The routing metrics generally targeted include: hop count, delay, energy consumption, node lifetime and etc. The stability-based routing protocols are aimed to minimize the number of route transitions and incur the least possible route discovery and maintenance overhead to the network. A majority of the ad hoc routing protocols are minimum-weight based and are proposed to optimize one or more performance metrics in a greedy fashion without looking at the future. For example, the Dynamic Source Routing (DSR) protocol (Johnson et. al., 2001) instantaneously selects any shortest path that appears to exist and similarly the Ad hoc Ondemand Distance Vector (AODV) protocol (Perkins & Royer, 1999) chooses the route that propagated the Route Request (RREQ) route discovery messages, with the lowest delay. To maintain optimality in their performance metrics, minimum-weight based routing protocols change their paths frequently and incur a huge network overhead. The stability-based routing protocols attempt to discover stable routes based on the knowledge of the past topology changes, future topology changes or a combination of both. Prominent within the relatively smaller class of stability-based routing protocols proposed in the literature include: Associativity-based Routing (ABR) (Toh, 1997), Flow-Oriented Routing Protocol (FORP) (Su et. al., 2001) and the Route-lifetime Assessment Based Routing (RABR) (Agarwal et. al., 2000) protocols. ABR selects paths based on the degree of association stability, which is basically a measure of the number of beacons exchanged between two neighbor nodes. FORP selects the route that will have the largest expiration time since the time of its discovery. The expiration time of a route is measured as the minimum of the predicted expiration time of its constituent links. RABR uses the average change in the received signal strength to predict the time when the received signal strength would fall below a critical O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg