On the gradient formation incorporating node movement for gradient-based routing in Delay Tolerant Mobile Sensor Networks

Gradient-based routing, where each node calculates a metric that indicates how useful a node might be in relaying messages to a destination node and transmits messages according to the metric, is one of promising approaches for Delay Tolerant Mobile Sensor Networks. However, existing gradient-based routing methods do not consider movement of nodes to form their gradient and this may result in inefficient message relays and degradation in their performance. In this paper, we discuss how node movements affect message delivery in gradient-based routing methods and propose a gradient-based routing method that incorporates node movements into its gradient to remedy inefficient message relays. The idea of our proposal is to identify nodes leaving from the destination node and nodes approaching to the destination node. Since those leaving nodes are less useful to relay messages to the destination node, our proposed method tries to prevent nodes from transmitting messages to nodes leaving from a destination node. Through simulation experiments, we show that our proposal decreases the average message delivery delay under various node mobility models. Our proposal reduces at most 50% of the average message delivery delay in the case that nodes move straight. We also show that our proposal significantly decreases the maximum message delivery delay.