Bridging Range and Speed: A Dynamic Acoustic–Optical Underwater Modem

Underwater wireless communication must balance the long-reach reliability of acoustics with the high-speed, short-range advantages of optics. Herein, we introduce a dual-mode modem that continuously measures both optical and acoustic signal-to-noise ratio (SNR) and, based on a pair of predefined target link reliability thresholds, enables an adaptive mechanism for high-rate optical transmission if the environmental conditions are favorable, otherwise for fixed-rate acoustic mode when the channel quality degrades. SNR estimation requires control signaling between the communication ends that, similarly to the data transmission case, suffers from propagation impairments. In this regard, a dual mode mechanism is applied to the feedback signaling as well, so as to optimize the overall communication throughput as a function of the channel state. Simulations results demonstrate seamless, millisecond-scale handovers and significant throughput gains over single-mode modem design.