Laser-Acoustic Cross-Medium Communication (LACMC) System: Theoretical Channel Model and Experiments

Recent advancements in acoustic and millimeter-wave technologies have enabled direct communication over water–air interfaces. This cross-medium communication involves three key steps: an underwater transducer emits acoustic waves that create surface vibrations, airborne radars detect these vibrations using millimeter waves, and finally, processed radar signals facilitate communication. However, this scheme suffers from short communication distances (approximately 1 m over water) and low resolution (millimetre level). In this article, a laser-acoustic cross-medium communication (LACMC) system is proposed and validated in anechoic tank experiments with the expectation of addressing the challenges of direct, high-precision, long-range communication across water--air interfaces for integrated air--sea networking. We analyze signal transmission through underwater, water surface, and air mediums and establish a robust LACMC channel model, which was verified by experiments. Experimental results prove that the channel is time-invariant and frequency-selective, with a single direct path and no multipath effects. We further enhance cross-medium communication quality by designing appropriate transmitted signals based on channel characteristics and employing laser Doppler vibrometry for high-precision, noncontact measurements. Our experimental results demonstrate the system's efficacy in long-distance applications, achieving an underwater communication distance of 3.5 m and an above-water distance of 10.8 m. The study is expected to provide a foundation for direct, high-precision, and long-distance communication between underwater nodes and airborne nodes.