Time reversal methods for high frequency multiple-input/multiple-output underwater acoustic communication

Abstract

As a sound focusing technique, time reversal has been utilized in underwater acoustic communication since the 1990s. Here, we particularly study the usage of time reversal methods to separate sounds from different sound sources for high frequency transmissions (greater than 10 kHz), in addition to sound focusing. The separation of sounds creates multiple parallel acoustic links between multiple transducers and a receiver array, thus, providing increased data rates between the source and receiver for communication purposes. It is referred to as multiple-input/multiple-output (MIMO) acoustic communication. Multiple at-sea experiments have been conducted to demonstrate high frequency MIMO signaling and their communication performance. A number of signal processing techniques have been developed in the time reversal framework to enhance the sound focusing and separation that are needed in high frequency acoustic MIMO communication. For example, multi-stage interference cancellation methods have been devised to suppress the co-channel interference and to ensure the sound separation. In this talk, we will show their effectiveness in the presence of water column variability based on our experimental data. An acoustic communication channel model will also be used to explain the impact of environmental variability.