An underwater communication network to remote subsea platforms_x000d_ _x000d_

The aim of this project is to provide remote access to underwater sensors deployed for detection of subsea activity through the development of a distributed communication network. To avoid eavesdropping and access of data from intruders, covert transmission between the nodes is required. Also, to avoid a surface expression (for example a buoy) that is easily detected, a gateway buried a few meters below the sea surface will serve to establish a link with a mobile platform above the sea surface.

The subsea network will rely primarily on acoustic propagation to exchange and relay information between the underwater nodes. To extend the range, different network topologies will be studied and a communication protocol will be defined to allow deployment of self-powered nodes for missions that can span several months. The messages will be broken up using short burst to share the network resources among multiple nodes. Also, adaptive modulation techniques that rely on a diverse set of frequency tones will reduce the probability of intercept. Using these modulation techniques, the users will be provided unique signatures that are spread over a wide bandwidth, and constrained by the hardware requirements available on submarine vessels. Specific coding techniques will be used to encrypt the message, and allow a secured and private link.

To forward the data from below the sea surface to a surface vessel, a short-range relay link will be established that crosses the air-water interface. A communication link relying on magnetic induction (MI) will be proposed for this purpose. Although MI has traditionally been used as a short range link on the order of ten meters for diver-to-diver communication, in this work MI will be used at the air-water interface, and the possibility of achieving a few hundred meters will be explored. For this, a priori, an analytical model of the behaviour of the electro-magnetic fields, as it crosses the air-water boundary will be developed. A reconfigurable radio will be used to optimize the capacity of the link, as the distance between the nodes is varied. At the end of the project, the network will be deployed at sea.