Fault-tolerance in wireless ad hoc networks: Bi-connectivity through movement of removable nodes

Abstract

For a wireless ad hoc network to achieve fault-tolerance, it is desired that the network is bi-connected. This means that each pair of nodes in the network have at least two node-disjoint paths between them, and thus, failure at any single node does not partition the network. In other words, in a bi-connected network, there is no cut-node (defined as a node such that the removal of it partitions the network). To make a connected but not bi-connected network become bi-connected, actions should be taken such that all cut-nodes become non-cut-nodes. In this research, we propose to deal with cut-nodes from a new perspective. Specifically, we first introduce a new concept of removable node, defined as a non-cut-node such that the removal of it does not generate any new cut-node in the network. Then, we propose to move a removable node to a new location around a cut-node. In this way, the cut-node becomes a non-cut-node, that is, the failure of it does not partition the network anymore. Algorithms are provided (i) to identify removable nodes; (ii) to match cut-nodes with a feasible set of removable nodes, in which all nodes can be simultaneously removed from the network without generating any new cut-node in the network; and (iii) to derive the final location of a removable node such that its movement distance is the shortest and the associated cut-node becomes a non-cut-node. The proposed algorithms do not guarantee the final bi-connectivity but have the merits of a large success rate (almost 100% in the simulation), a small number of moved nodes, and a short total movement distance. In addition, the proposed algorithms are shown to be effective even when there are a large portion of fixed nodes in the network. Copyright © 2011 John Wiley & Sons, Ltd. If there is no cut-node in a network, the network is bi-connected, which is desired. In this paper, we introduce a new concept of removable node, defined as a non-cut-node such that the removal of it does not generate any new cut-node in the network. Then, we propose to move a removable node to a new location around a cut-node. In this way, the cut-node becomes a non-cut-node. The network becomes bi-connected after all cut-nodes become non-cut-nodes. Copyright © 2011 John Wiley & Sons, Ltd.