High-rate acoustic communication at the data rate of 69 kbps over the range of 3,600 m developed for vertical uplink communication

In Japan Agency for Marine-Earth Science and Technology (JAMSTEC), autonomous underwater vehicles (AUVs) and a manned submersible have been operated for various scientific researches in deep water. These vehicles are equipped with vertical acoustic communication systems with the mothership to receive commands or send status information. Last year, a new high-rate uplink communication system using single-carrier modulation was developed by our group for a manned submersible SHINKAI6500 and its performance was verified in an at-sea experiment. As results, in diving to the depth of 3,600 m, the effective data rate of 69.24 kbps with error free was achieved using the frequency band of 10 kHz, that is, with the spectral efficiency of 6.924 bps/Hz. The performance was very stable even under the Doppler effect caused by the fluctuation of the mothership and ascending/descending movement of the submersible, whose velocity was up to 2 knots approximately. In the meantime, communication with multi-carrier modulation, orthogonal frequency division multiplexing (OFDM), was also carried out in this experiment. However, the performance with OFDM was degraded due to the Doppler shift although the techniques of resampling based on the estimated frequency shifts and 1/3 pilot interpolation, in which the data rate is sacrificed, are applied. Thus, it was demonstrated that the performance of the new developed communication system is much better than that of OFDM and is very effective for vertical communication between an underwater vehicle and a mothership. Now, the system is installed in SHINKAI6500 for practical use and utilized for still image transmission from the submergible to the mothership.