Chirp-based analog communication for the underwater acoustic channel

Underwater acoustic communication is characterized by the unique challenges inherent to the medium. Factors such as multipath, Doppler, and refraction can make digital communication prone to errors or unreliable. Often in traditional digital communications, this means a packet of digital bits is either received entirely correctly or discarded, even when only a fraction of the packet bits have errors. However, in many cases—such as real-time AUV telemetry and monitoring—it is acceptable when the received value is close to the transmitted one. To explore these use cases, we propose an analog modulation scheme that encodes continuous-valued data in the unit interval 0, 1 onto circularly shifted chirps, thereby bypassing traditional digital constellation and modulation schemes. By encoding each datum as a continuous value with a single circularly shifted chirp, this scheme enables communication to continue even under severe distortion, albeit with reduced precision. Demodulation and Doppler correction are implemented via time-reversal methods. We will present communication measurements and performance analysis from lake experiments. Work supported by NSF (CNS#2016726 and CNS#2048188) and USGS grants (G23AC00157)