This work focuses on the insights from the ocean experiments conducted using an underwater acoustic massive multiple-input multiple-output (MIMO) communication system, carried out in the North Pacific Ocean. A 25-channel acoustic transmitter was developed, utilizing a field-programmable gate array (FPGA) for signal processing, batteries, power management boards, and power amplifiers to drive the transducers, all housed within an aluminium watertight enclosure. The transducers were arranged in a pentose-based geometry for optimised beam patterns, and wideband beamforming was implemented using tap-delay lines on single-carrier coherent modulation. An inertial measurement unit (IMU) was embedded in the transmitter to record it's orientation during deployment. The cage was placed on the seabed at a depth of 100 m, and a 4-element receiver array with GPS antenna was mounted on a vessel to collect data. Signals were captured at radial distances of 100, 200, and 300 m. A GPS unit was also installed on a shore-based building, enabling differential corrections for accurate receiver positioning. Two transmission modes, with and without beamforming, were tested. The results revealed that, although path loss is the main contributor to signal attenuation, beamforming noticeably shapes the spatial pattern of signal strength, with clear dependence on the direction. Sparse data collection points limited full beam-pattern validation, but the findings clearly demonstrate the effectiveness of wideband beamforming in underwater environment.
Khan et al. (Wed,) studied this question.