Vertical multiuser communication using adaptive time reversal

Time reversal is an attractive solution to achieve channel equalization in a rich multipath environment such as underwater acoustic communication (UAC) channel because of its spatial and temporal focusing effect. Recently, demands for multiuser communication have increased in the field of UAC. In Japan Agency Marine-Earth Science and Technology (JAMSTEC), multiple autonomous underwater vehicles (AUVs) operation is planned to widen observation area. Adaptive time reversal is a method for space division multiplexing (SDM) based on its spatial focusing and nulling effect, and a promising solution for multiuser communication. In previous studies, it has been demonstrated that adaptive time reversal is very effective for “horizontal” multiuser communication, in which signals from multiple sources are received vertical receiver array. In this study, adaptive time reversal is applied for “vertical” multiuser communication, which is between a support vessel and multiple vehicles below the vessel. At-sea experiments were carried out in which signals from two sources near the seabed were measured at the receivers on the bottom of the research vessel. As results, adaptive time reversal is also effective for such vertical multiuser communication and has better performance than orthogonal frequency-division multiplexing (OFDM) with SDM combiners.