Intellectual Merit: New and ongoing ocean sciences projects, including Long-Term Ecological Research (LTER) sites and the Ocean Observatories Initiative have multiple needs for low-cost, open architecture acoustic modems for underwater networking. This exploratory research determines if single-carrier frequency domain equalization (SC-FDE) is a viable alternative to orthogonal frequency-division multiplexing (OFDM) for high-speed, longer range acoustic communications. SC-FDE has potentially significant advantages over OFDM in terms of lower power variation and lower-complexity coding requirements. The underwater acoustic channel is challenging to the communication systems designer due to its long, sparse multipath characteristics and rapid time-variation (Doppler spread). A robust Matching Pursuits (MP) channel estimator, previously developed for lower data rate direct-sequence acoustic modems by the investigators, is applied here to both SC-FDE and OFDM. Side-by-side comparisons are performed to determine if SC-FDE is feasible in the underwater channel and if its power and complexity advantages over OFDM hold in the acoustic regime. Both SC-FDE and OFDM require error correction coding to communicate over the long range acoustic channel. New iterative decoding and channel estimation techniques combining Matching Pursuits and convolutional coding are investigated for real-time implementation. Existing testbeds are used to evaluate SC-FDE and OFDM modem performance.
Broader Impact: Real-time acoustic communications is required for a broad range of ocean sciences and ecological research projects. The results of this research could be an important first step to off-the-shelf availability of acoustic networking for oceanographic researchers. Research enabled by underwater networking can have broad impacts on our understanding of interactions between the physical undersea environment and marine life, including the critical question of health of coral reefs worldwide. This project also provides cross-training to graduate students in ocean sciences, signal processing and networking research.
