Intellectual Merit: This project investigates a paradigm shift in acoustic underwater communication from single-carrier transmission to multi-carrier modulation in the form of orthogonal frequency division multiplexing (OFDM). OFDM has its unique strength in handling high-rate transmissions over long dispersive channels and has prevailed in recent broadband wireless radio applications. However, underwater acoustic channels are far more challenging than their radio counterparts due to their large bandwidth-to-carrier-frequency ratio, large propagation delay, large multipath spread, and fast channel variations. Incorporating the unique characteristics of underwater acoustic channels, our first task is to make OFDM work in underwater environments with fast-moving platforms. Preliminary experimental results have demonstrated the effectiveness of our proposed approach even when the relative speed between the transmitter and the receiver is up to 10 knots, which is the current state of the art. In our second task, we equip the multi-carrier modem with precise-ranging capability. The key is to develop precise synchronization algorithms that can locate the "first arrival" in the presence of dense multi-path conditions and that can work well in fast-varying underwater channels. In our third task, we develop a standalone modem prototype based on a digital signal processor that integrates the transceiver algorithms developed in this project.
Broader Impact: Providing a multi-carrier acoustic modem with ranging capability, this project has the potential to directly benefit the development of underwater wireless sensor networks for a variety of applications. Due to the large bandwidth-to-carrier-frequency ratio of underwater acoustic channels, the proposed methodology and algorithms may, also, have an impact on wideband and ultra-wideband radio applications. This project integrates research and education to enhance the content of undergraduate and graduate classes and, in particular, provides innovative senior design projects.
