Underwater Acoustic Sensor Networks

The oceans cover approximately 70% of the Earth's surface and are essential to climate regulation, transportation, food production, and oil exploration. All these activities require monitoring of aquatic environments. Nevertheless, the current monitoring techniques, such as remote telemetry and sequential local sensing, cannot satisfy the requirements of the aquatic applications. In order to satisfy these applications underwater acoustic networks are under development. These networks are composed of underwater sensor nodes equipped with acoustic modems. The sensor nodes collect data and transmit it directly or through multihop routing to a surface base station. Autonomous Underwater Vehicles (AUVs) can also cross the network collecting data from sensor nodes. The key differentiating point for underwater networks is the use of an acoustic channel which brings new challenges for the design of this kind of networks. The bandwidth is severely limited and the propagation delay of the underwater channel is five orders of magnitude than in RF terrestrial channels. The underwater channel also suffers with multipath and fading and consequently nodes experience high bit error rates. Furthermore, underwater sensor nodes are supplied by batteries and the recharge are difficult because the solar energy cannot be exploited. Because of these factors, the development of underwater networks becomes a great challenge. In GTA, we are focusing on medium access control and routing protocols. We are working on the design of protocols which takes into account alternative metrics, such as reliability, fairness, quality-of-service, and covertness. The goal is to develop specific protocols in order to optimize the network operation.