Distributed MIMO sonar for underwater monitoring

Acoustic waves are the only means for long-range underwater signal transmission. Recent developments in underwater acoustic (UWA) communications, underwater robotics and vehicles make it timely to consider the development of cooperative UWA networks based on the use of static and moving sensor nodes. Such networks can significantly enhance performance and reduce the cost of surveillance operations, especially if UMS sonar and communication systems are jointly designed and optimised to achieve the greatest performance. For UMS, passive and active sensor (sonar) systems are used. Passive systems are typically lower cost, but underwater targets can produce low-level acoustic noise such that they cannot provide high detection performance. Active multiple-input multiple-output (MIMO) sonar systems with joint processing of information from multiple nodes can significantly improve UMS performance. An important task is to develop distributed MIMO target detection techniques across a network of nodes and to understand how the network communication signals can be exploited to further enhance the capability of the system. The acoustic communication channel is limited in capacity. With larger networks, the inherent low data rate of underwater communication systems will also render it necessary to have a co-existing sonar and communication system. With an UMS system processing signals from multiple nodes, joint communication-sonar network protocols are required to prevent mutual interference. The long communication sessions required for transmission of large amounts of data between multiple nodes can significantly limit the target detection performance due to the limited time available for sonar transmission. Existing communication signals can be additionally used to play the role of MIMO sonar signals, thus providing extra potential to improve the target detection. This however poses additional problems, e.g., since communication signals carrying unknown data introduce uncertainty which the MIMO sonar system would have to deal with. A key purpose of this PhD is to undertake a feasibility study of using communication signals transmitted in the network for the purpose of MIMO sonar operation. The benefits and drawbacks of such a combined approach will be analysed in comparison with using separate signals for communications and MIMO sonar. The research will require using mathematical methods as well as methods of signal processing, communications and information theory. The novel designs will be validated using numerical simulation and sea/lake experiments where possible.

This research is most closely aligned with the information and communication technologies (ICT) theme. It will feed into a much larger programme of work on Cooperative Underwater Surveillance Networks (EP/V009591/1) and benefit from sight of developments on this collaborative research programme, which includes a number of academic and industrial project partners.