Full-Duplex For Underwater Acoustic Communications

近年来，人们对开发与海上油气行业远程控制和遥测应用相关的水声通信（UAC）系统产生了极大的兴趣。在实践中，实现海底通信的唯一可行方法是利用声信号。然而，由于UAC信道的带宽有限，以往的研究主要集中在使用时分双工（TDD）的半双工（HD）工作模式上。近年来，全双工（FD）传输由于具有将单跳无线通信链路的吞吐量提高近一倍的潜力，在无线通信领域引起了人们的关注。然而，尽管UAC信道存在严重的带宽限制，但在UAC系统的FD方面显然缺乏相当深入的研究。因此，我们概述了本研究项目中需要解决的3个关键挑战：挑战1-了解FD UAC系统中的自干扰（SI）： FD在理论上有望将吞吐量提高一倍。然而，在实际应用中，由远端和本地传输之间的较大功率差引起的SI将导致信号干扰和噪声损失，进而导致吞吐量性能下降。对于声波波形和UAC调制解调器，人们对SI的统计特性以及在FD模式下运行的硬件组件的非理想/非线性特性的影响知之甚少。为了设计有效的自干扰消除（SIC）方法，需要对自干扰进行全面的理解和精确的建模。挑战2-SIC方法：为了充分利用FD传输的潜力，需要能够提供高达约100 dB的有效SIC方法。无源和有源SIC方法已经被提出用于无线通信，然而，它们根本没有被研究用于UAC波形，我们相信它们的利用以及开发新的和改进的方法都有很大的潜力。挑战3-在UAC网络中实现FD的好处：只有在介质访问控制（MAC）层被适当地设计为在同一频率信道上同时发送和接收时，FD链路提供的增强物理层能力才能完全实现。这需要基于不同的业务需求、信道条件和本地干扰的高度自适应调度。长传播延迟要求使用卫星系统采用的方法进行有效的容量分配，包括自由、预测的容量分配和fd支持的物理层网络编码。为了应对这些挑战，我们在纽卡斯尔大学（NU）和约克大学（UoY）提出了5个工作包（WP），旨在设计一个fd支持的UAC系统，在相同功率和带宽限制下，该系统的吞吐量几乎是同等高清系统的两倍。WP A （NU）将研究SI对UAC波形和硬件的影响，并提供捕捉SI特征的分析模型。WP B （uy）将研究联合模拟和数字SIC的性能以及波束形成方法，以实现声学调制解调器的FD操作。WP C （NU）和WP D （uwey）将研究物理层和高效MAC协议的FD单跳和多跳中继方法的设计和性能。WP E （NU）将用于实验验证、改进和整合提议的FD系统。实验将在北大的消声水箱中进行，并使用北大的研究船在北海的实际浅水通道中进行全尺寸海上试验。该提案中的研究具有潜在的变革性，将有助于开发基于fd的水下网络和通信能力，这些能力适用于石油和天然气勘探、海洋数据收集、污染监测、灾害预防和安全等应用。

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.