OTFS for Underwater Acoustic Communications: Frame Design and Channel Estimation

Recently, orthogonal time frequency space (OTFS), a two-dimensional modulation technique designed in delay-Doppler domain, has received significant attention. Generally, OTFS modulation is very efficient for the time-varying and doubly-spread channels. It motivates us the use of OTFS into the time-varying and doubly-spread underwater acoustic (UWA) channels. However, the application of OTFS faces the over-spread problems in the UWA communications. In this work, we discuss input and output relationship for the OTFS under the over-spread channels, and provide frame design suggestions for UWA communications. Then three improved channel estimation algorithms in the delay-time domain are proposed. The simulation results show that the proposed OTFS system can be applied in the over-spread UWA channels and improve the communication performance.