Performance of OFDM-based massive MIMO OTFS systems for underwater acoustic communication

In this paper multi-user (MU) underwater acoustic (UWA) communication is investigated using massive multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based orthogonal time frequency space modulation (OTFS) systems. The performance of a 4-user scenario is evaluated over a simulated 1 km vertically-configured time-varying underwater acoustic channel (UAC) in terms of bit error rate (BER) and maximum achievable bit rate. Considering 64-QAM and frequency-domain pilot-based channel estimation, it is shown that the underwater vehicles employing the OFDM-based OTFS modulation outperform those using the conventional OFDM modulation in a dynamic UAC. The application of massive MIMO allows the four underwater vehicles to use the same time and frequency resources to transmit their information reliably to a surface station. Furthermore, it is shown that each underwater vehicle in the MU-massive MIMO transmission scenario can achieve an effective bit rate as high as 198.7 kbps over the 1 km UAC using four transmitting transducers