Full-Duplex for Underwater Acoustic Communications

In recent years, there has been an immense interest in developing underwater acoustic communication (UAC) systems related to remote control and telemetry applications for the off-shore oil & gas industry. In practice, the only feasible method to achieve sub-sea communications is by means of acoustic signals. However, due to the limited bandwidth of the UAC channel, past research concentrated on the half-duplex (HD) mode of operation using time-division duplexing (TDD). Recently, full-duplex (FD) transmission attracted attention in wireless communications due to its potential to nearly double the throughput of single-hop wireless communication links. However, there is an evident absence of equivalent in-depth research in FD for UAC systems, despite the severe bandwidth limitations of the UAC channel. Hence, we outline 3 crucial challenges to be addressed in this research project:
Challenge 1-Understanding the Self Interference (SI) in FD UAC systems: FD comes with the promise of theoretically doubling the throughput. However, in practice, SI induced by the large power difference between the distant and local transmissions will result in signal to interference and noise loss, and in turn throughput performance degradation. For acoustic waveforms and UAC modems little is known with regard to the statistical properties of SI and the impact of non-ideal/non-linear characteristics of hardware components operating in FD mode. In order to design effective self interference cancellation (SIC) methods, a comprehensive understanding and accurate models of SI are required.
Challenge 2-SIC methods: To fully exploit the potential of FD transmission, effective SIC methods are required capable of providing cancellation up to approximately 100 dB. Passive and active SIC methods have been proposed for wireless communications, however, they have not been investigated at all for UAC waveforms, and we believe that there is significant potential in their utilisation, as well as in developing new and improved approaches.
Challenge 3-To realise the benefits of FD in UAC networks: The enhanced physical layer capability offered by FD links can only be fully realised if the medium access control (MAC) layer is suitably designed for simultaneous transmission and reception on the same frequency channel. This calls for highly adaptive scheduling based on varying traffic demands, channel conditions and local interference. The long propagation delays demand efficient assignment of capacity using methods adopted for satellite systems, including free, predictive assignment of capacity, and FD-enabled physical layer network coding.

To address these challenges we propose 5 work packages (WP) at Newcastle University (NU) and University of York (UoY) with the aim to design an FD-enabled UAC system that nearly doubles the throughput of equivalent HD systems under the same power and bandwidth constraints. WP A (NU) will study the effects of SI for UAC waveforms and hardware, and provide analytical models capturing the characteristics of SI. WP B (UoY) will study the performance of joint analog and digital SIC and beamforming methods to enable FD operation of acoustic modems. WP C (NU) and WP D (UoY) will investigate the design and performance of FD single and multi-hop relaying methods at physical layer and efficient MAC protocols. WP E (NU) will be used for experimental validation, refinement and integration of the proposed FD system. Experiments will be carried out in the anechoic water tank at NU and using full-scale sea trials conducted in the North Sea in realistic shallow-water channels using NU's research vessel.

The research in this proposal is potentially transformative and will contribute to the development of FD-based underwater networking and communication capabilities required by applications such as oil & gas exploration, oceanographic data collection, pollution monitoring, disaster prevention, and security.