The main objective is to develop the technology for a long to medium range acoustic communication network capable of operating over distances far larger than the water depth. The network would provide greatly increased capability for monitoring, and acquiring data from, a set of unsupervised sub-sea instruments and long range AUVs, via a ship or a surface buoy providing a radio/satellite link to land. Acoustic communication is the only realistic option for such a network since optics and radio waves are too highly attenuated in sea water. The proposed experimental network would achieve a point-to-point link of up to 10 km using an 8 kHz carrier, with target data rates of up to 4 kbits/s on each link using coherent modulation. Scaling for longer ranges will be considered by modelling.
The main technical difficulties arise from the strong, time varying reverberation present in the very shallow channel (causing both fading and intersymbol interference), and from co-channel interference from units transmitting simultaneously. Promising results have been achieved with receivers based on recent signal processing methods that exploit the uncorrelated fading characteristics on all the various signal paths to separate them at the receiver. These innovative multi-access methods, in combination with traditional techniques, will be investigated by using a 3-D array of transducers at the receiver to achieve spatial diversity, with an adaptive combiner optimised for each signal source. The design of the adaptive combiners will be an important part of the investigation in which modern cyclostationary and higher order signal statistics will be exploited.
The concept of a network has several other advantages: (a) by using a number of short hops, much longer ranges can be achieved; (b) if data from an instrument can be obtained by more than one route, this higher level of diversity can be used to improved reliability; and (c) the multiway flow of data can be used to control how the network adapts to changing conditions and requirements. The project is divided into 8 tasks, which include the development of new transducers and the construction of an experimental system to be used in two sea trials to test the principles. The consortium of 7 partners includes 2 universities with many years experience of underwater acoustic communications and modelling, 4 SMEs currently producing acoustic communication equipment and AUVs, and a large oil company representing the end user who will provide free ship time.
Such a communication system would not only be of benefit to ocean science, but could prove to be of enormous commercial and environmental value, improving the safety and efficiency of underwater oil production, enabling new approaches to managing fisheries, enhancing pollution monitoring, and contributing to preservation of the marine environment.
Funding SchemeCSC - Cost-sharing contracts