The Upper Bound of the OTFS Channel Capacity Under Underwater Acoustic Channels

Recently, Orthogonal Time Frequency Space (OTFS), a two-dimensional modulation technique designed for the delay-Doppler domain, has gained significant attention. Underwater Acoustic (UWA) channels present challenges due to time and frequency spreading. OTFS is highly efficient for time-varying, doubly spread channels, making it a promising solution for UWA communication. In this paper, we derive the upper bound of channel capacity for UWA OTFS systems. The upper bound is determined by accounting for the path loss and noise characteristics of sound propagation in the ocean within the OTFS-based UWA communication system. The simulation results show that the upper bound is influenced by bandwidth and the distance between the transmitter and the receiver. Compared to OFDM, the OTFS UWA communication system performs better in Doppler spread channels, offering higher information rates and improved effectiveness in practical doubly spread UWA channels.