Acoustic Intelligent Surface System for Reliable and Efficient Underwater Communications

While acoustic-based underwater communication systems have been widely used for many decades, existing systems still suffer from the low reliability problem due to the severe multipath fading, especially in shallow water environments. It is well known that MIMO and beamforming techniques are among the most effective solutions to address fading challenges. However, not all underwater devices can carry the multiple-transducer system due to cost and size limitations, especially small AUVs and sensors. In this paper, we design and characterize the novel acoustic intelligent surfaces in the underwater environment, which enables the beamforming capability to address the multipath fading problem, without requiring the end-users to equip MIMO components. To the best of our knowledge, although electromagnetic (EM) intelligent surfaces have been intensively investigated for terrestrial communications recently, acoustic intelligent surface has not been explored since it has completely different physical mechanism and hardware structure than that of EM surfaces. Therefore, in this paper, we design a new reconfigurable piezoelectric reflector array that performs as an underwater intelligent surface. Rigorous analytical model is developed to characterize how the designed underwater intelligent surface controls the propagation of acoustic waves in the underwater multipath channel. Based on the new design and model, the underwater intelligent surface-enabled beamforming protocol is provided. Through a hybrid underwater communication simulator based on COMSOL Multiphysics and Bellhop toolbox, we demonstrate the proposed acoustic intelligent surface can effectively form and steer acoustic beams and significantly mitigate the multipath fading in shallow underwater environments.