In this paper, we propose a novel underwater acoustic (UWA) communication scheme that achieves energy and spectrum efficiency simultaneously by combining Doppler-resilient orthogonal signal division multiplexing (D-OSDM) and multiple-input-multiple-output (MIMO) signaling. We present both the transmitter processing and the receiver processing for MIMO D-OSDM. We evaluate the performance of MIMO D-OSDM in simulations with a large intersymbol interference of 25 symbols and a Doppler spread with a maximum Doppler shift of 8 Hz. In addition, the sea trial is performed in Suruga Bay, where the receiver is mounted on a barge and a research vessel with the transmitter makes round trips along a line with a speed of 4 kn. In the experiments, we obtain an intersymbol interference of 3.6-29.7 symbols and a Doppler spread of several Hertz (leading to a spread of over two to three subcarrier spacings). The simulation results suggest that MIMO D-OSDM has an advantage over normal D-OSDM, Doppler-resilient MIMO orthogonal frequency division multiplexing (MIMO D-OFDM), and classical OFDM with MIMO signaling (MIMO OFDM) - MIMO D-OSDM achieves better bit error rate performance than the benchmarks. The sea trial results also support the advantage of MIMO D-OSDM - it achieves a coded block error rate of 3.2% while normal D-OSDM and MIMO D-OFDM achieve a coded block error rate of 9.7% and 9.3%, respectively. We conclude that MIMO D-OSDM can become a viable technique that achieves reliable and effective UWA communication.

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Underwater acoustic (UWA) channels are one of the historical mobile ultrawideband channels characterized by large delay and Doppler spreads, but reliable UWA communication remains challenging. Here we performed an initial demonstration of the Doppler-resilient orthogonal signal division multiplexing (D-OSDM) technique in an actual sea environment. D-OSDM spreads data symbols in both time and frequency with guardbands to exploit the time and frequency diversity of UWA channels. The experiment was performed in a challenging scenario: the transmitter was fixed on a floating pier, and the receiver was mounted on a moving remote-controlled boat. The harbor UWA channel had a delay spread of 50 ms and a Doppler spread of up to 4.5 Hz, in the presence of additive Gaussian noise, and the combination of two Rayleigh fading models (a two-path model without Doppler spread and a multi-path model with Doppler spread) was able to successfully model the actual environment. Our results also confirmed that a UWA communication link using D-OSDM will deliver excellent reliability even for a harbor UWA channel with a mobile receiver; D-OSDM achieves better communication quality compared to other communication schemes in both simulations and experiments.

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In this paper, we propose a novel underwater acoustic communication scheme that achieves energy and spectrum efficiency simultaneously by combining Doppler-resilient orthogonal signal division multiplexing (D-OSDM) and multiple-input multiple-output (MIMO) signaling. We present both the transmitter and receiver processing for MIMO D-OSDM. We evaluate the performance of MIMO D-OSDM in simulations with a large inter-symbol interference (60 symbols) and Doppler spread (maximum Doppler shift of 15 Hz). The simulation results show that MIMO D-OSDM achieves almost the same energy efficiency as normal D-OSDM while doubling the spectrum efficiency. We conclude that MIMO D-OSDM can become a viable technique that achieves reliable and effective UWA communication.@en