High-rate underwater acoustic communication at over 600 kbps $\times$ km for vertical uplink data transmission on a full-depth lander system

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) operates several unmanned and manned underwater vehicles for scientific research in deep water. Recently, we have developed a new high-rate underwater acoustic communication system, or acoustic modem, for vertical uplink data transmission from these vehicles. This acoustic modem uses single-carrier modulation with a decision feedback equalizer (DFE), and it has been demonstrated that the modem's performance is very stable under the Doppler effect and much better than that of orthogonal frequency division multiplexing (OFDM). In 2019, a successor acoustic modem was developed for a lander operable to a depth of 11,000 m. In an at-sea experiment conducted at a depth of 6,180 m, an effective data rate of 98.9 kbps was achieved, using the $\mathbf{18\pm 6.25{kHz}}$ frequency band with 256 quadrature amplitude modulation (QAM). In an experiment at a depth of 9,230 m, an effective data rate of 69.24 kbps was achieved, using the $\mathbf{18\pm 5{kHz}}$ frequency band with 128QAM. Thus, it was demonstrated that the performance of this acoustic modem exceeds 600 kbps $\times$ km with the index of communication data rate $\times$ range.