Time reversal-based underwater acoustic communications

Over more than a decade beginning in 1996, we conducted a series of time reversal mirror (TRM) experiments in collaboration with the NATO Undersea Research Centre in coastal waters. The method leverages spatial diversity to achieve both spatial and temporal focusing in complex environments, offering a promising alternative to conventional multichannel equalizers (M-DFE) for underwater communications. Temporal focusing enables self-equalization and mitigation of intersymbol interference (ISI), which can then be followed by an adaptive decision feedback equalizer (DFE), known as TR-DFE. Additionally, spatial focusing facilitates multiuser communications, with adaptive TR further reducing crosstalk among users. Our findings reveal that TR-DFE outperforms M-DFE, particularly when high-order constellations, such as 32-QAM, are employed, significantly enhancing data throughput and spectral efficiency. This presentation will showcase examples inspired by Bill’s invaluable contributions and insights.