Efficient flooding in Wireless Sensor Networks secured with neighborhood keys

Network flooding is a fundamental communication primitive for Wireless Sensor Networks (WSN). Flooding is used for disseminating code updates and parameter changes, affecting the operation of all nodes in the network. When flooding occurs each node, typically, broadcasts the flooding packet once. The costs for flooding, however, can become significant if neighborhood keys are used for communication (as proposed in recent research on secure localization and key distribution [1]), since, instead of a single broadcast, a node is required to perform several unicast transmissions. In this paper we address the problem of minimizing the number of unicast transmissions required for ensuring 100% network coverage for flooding in WSN secured with neighborhood keys. We show that the problem is NP-hard and propose an approximation algorithm for solving it. Through simulations, we demonstrate that our algorithm ensures 100% network coverage for flooding, while requiring, surprisingly, as low as 0.75 packet transmissions per node.