Doppler-Resilient Orthogonal Signal-Division Multiplexing for Underwater Acoustic Communication

Underwater acoustic (UWA) channels are characterized by a severe spread in time and frequency, and are usually labeled as “doubly spread channels.” In this paper, we propose Doppler-resilient orthogonal signal-division multiplexing (D–OSDM), to provide a highly reliable communication environment in doubly spread channels for UWA communication. D–OSDM multiplexes several data vectors in addition to a pilot vector, and preserves orthogonality among them even after propagation through doubly spread channels, under the assumption that the channel can be modeled by a basis expansion model (BEM). We describe the signal processing steps at the transmitter and the receiver for D–OSDM, and evaluate its performance by both simulations and experiments. To generate a doubly spread channel, a test tank with a wave generator is employed. The obtained results suggest that D–OSDM can provide low-power and high-quality UWA communications in channels with large delay and Doppler spreads; for example, D–OSDM succeeds to achieve a block error rate (BLER) of 10$^{-3}$ while BEM-based orthogonal frequency-division multiplexing (OFDM) has a BLER floor of 10$^{-2}$ in the experiments. Equivalently, D–OSDM can reduce the signal power required for communications to achieve the same BER significantly. Overall, it was found that D–OSDM can become a powerful communication tool for underwater operations.