Improving the Reliability of Underwater Communication

Telemetry or wireless communication is the obvious choice, but radio does not work under water. As alternative, acoustic signals are prone to disruptions and sometimes complete failure. This highlights some of the major challenges with submarine information and communications technology (ICT).

Under good conditions currently available subsea modems can perform their role satisfactorily. However, when the hydro-acoustic conditions get worse due to interfering noise, varying multi-path propagations and other factors, communications may and often do fail. Even in calm seas, the stratification of the water body can cause severe signal reverberations and dynamic fluctuation of the channel properties, resulting in poor transmissions. Thus, a real innovation was needed to provide reliable wireless communication under varying conditions.

New approaches employ a continuous change of frequencies that not only serves to transmit information, but also to compensate for sources of interference, such as echoes and noise. Acoustic underwater modems that "sing" like whales and dolphins in the ultrasonic range are able to reliably transmit digital data over distances up to several kilometers with no data loss or harm to the environment.

This way, the signal energy is continuously spread over a wide range of frequencies and the signal structure is adapted so that the multi-path components do not interfere with each other. At the receiver side, advanced signal processing collects the energy and converts the received signals into narrow-band signals.

Sweep Spread Carrier (S2C) is a technology that continuously spreads the signal energy over a wide range of frequencies and adapts the signal structure so that the multipath components do not interfere with each other. At the receiver side, advanced signal processing collects the energy and converts the received signals into narrow-band signals. Taking advantage of the ultra-wideband sweep technology the subsea modems continuously determine the signal propagation time and Doppler shift with a high accuracy, which at the same time intrinsically provide the precise distance and relative velocity between modem pairs. Long and short-baseline positioning or tracking mobile systems (AUVs, remotely operated vehicles [ROVs], robots) are simplified.

Complex communication, navigation and monitoring networks can be established. Each modem is able to be individually addressed, and at each connection to another address it calculates the distance and relative velocity and evaluates the acoustic properties of that channel. Sharing these data with other nodes enables optimal traffic planning and routing in the network.