Gradient-based routing in Delay Tolerant Mobile Sensor Networks incorporating node mobility

Gradient-based routing, where each node calculates a metric that indicates how useful a node might be in relaying messages to a sink 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 node mobility to form their gradient and this may result in inefficient message relays and degradation in their performance. In this paper, we discuss how node mobility affects message delivery in gradient-based routing and propose a gradient-based routing method that incorporates node mobility into its gradient to reduce the effect of inefficient message relays. The key idea of our proposal is to distinguish nodes leaving from a sink node from nodes approaching to a sink node. Since those leaving nodes are less useful to relay messages to a sink node, our proposed method prevents nodes from transmitting messages to nodes leaving from a sink node. Through simulations, we show that our proposal decreases the average message delivery delay under various node mobility models. Moreover, our proposal reduces the average message delivery delay by up to 50% in the case that nodes move straightly.