Heterogeneous system framework for underwater networking

The integration of Radio Frequency (RF) Command and Control (C2) networks with underwater (UW) networks that are based on acoustic communications requires comprehensive solutions to address several technical challenges and interoperability issues. A major constraint arises from the large capability gap between acoustic and RF communications, the former being characterized by very low data rates and a propagation speed over five orders of magnitude slower (1.5 × 10³ m/s versus 3 × 10⁸ m/s) than the latter. The UW acoustic communications channel is also strongly influenced by environmental conditions and subject to frequent disruption. In such a context, typical assumptions associated with Internet protocols, such as the possibility of assuring an end-to-end path between source and destination and the capacity to provide a small end-to-end error rate, are no longer tenable. These differences are driving UW communications research to develop new protocols (where no standard exists) that are robust and interoperable. In this context the NATO Undersea Research Centre (NURC) is working towards the definition of a heterogeneous network framework based on Disruption Tolerant Networking (DTN) protocols and aligned with the guidance of the NATO Interoperability Standards and Profiles (NISP). This framework will eventually transition to NATO´s Network Enabled Capabilities (NNEC) to support new concepts for underwater surveillance of harbours and critical infrastructures, anti-submarine warfare and environmental monitoring. This paper provides an overview of some key components of the proposed framework, including MAC protocols and beaconing systems specifically adapted to underwater operations, as well as higher-layer protocols characterised by a high degree of cross-layer interaction. Preliminary results from field testing are presented that provide useful guidance for further development of this integrated concept.