Underwater Communication Experiments for Transmitting Multiple Data Streams Using a Vector Acoustic MIMO System: OFDM and FSK Modulations

In this paper, we utilize the vector components of the acoustic field in a MIMO setting, to simultaneously transmit multiple independent data streams to increase the communication spectral efficiency in bandlimited underwater channels, while using small-size vector transceivers. In the developed vector MIMO-OFDM system, we use one ring vector transducer to transmit two or three data streams, and two ring vector transducers to transmit four data streams. At the receiver side, we use a sphere vector sensor that provides measurements of the x, y and $z$ components of the acoustic particle velocity, plus six scalar sensors that measure the acoustic pressure - the scalar component of the acoustic field. Additionally, we present a vector MIMO-FSK system that includes one ring vector transmitter and one ring vector receiver. Our results obtained using underwater experiments demonstrate the feasibility of simultaneous transmission and demodulation of multiple data streams using compact vector transceivers, to optimally use the limited bandwidth while using small-size transceivers.