Phero-Trail: a Bio-inspired Location Service for Mobile Underwater Sensor Networks

A SEA Swarm (Sensor Equipped Aquatic Swarm) is a collection of mobile underwater sensors that moves as a group with water current and enables 4D (space and time) monitoring of local underwater events such as contaminants and intruders. For prompt alert reporting, mobile sensors forward events to mobile sinks (i.e., autonomous underwater vehicles) via geographic routing. In order for a packet to be routed towards the destination using geographical routing, it requires to know the location of the destination. This is accomplished by having a location service in the network that returns the location of a requested node. Our goal is to design such location service for SEA Swarm. In this paper, we analyze various design choices to realize an efficient location service in a SEA Swarm. We find that conventional ad hoc network location service protocols cannot be directly used, because the entire swarm moves along water current. We show that maintaining location information in a 2D plane is a better design choice. Given this, we propose a bio-inspired location service called a Phero-Trail location service protocol. In Phero-Trail, location information is stored in a 2D upper hull of a SEA Swarm, and a mobile sink uses its trajectory (` la a pheromone trail of ants) projected to the 2D hull to maintain location information. This a enables mobile sensors to efficiently locate a mobile sink. Our results show that Phero-Trail performs better than existing approaches.