AquaFlicker : Visible Flicker for Motion-Resilient Underwater Optical Communication

Underwater communication supports a wide range of scientific, industrial, and recreational activities. Most existing solutions rely on specialized acoustic or optical hardware. Recent smartphone-based optical approaches improve accessibility, but they remain highly sensitive to blur, motion, and scattering when static spatial visual codes are used. In this work, we revisit smartphone optical camera communication (OCC) for underwater environments. We make a key observation: small-amplitude or high-frequency luminance variations are rapidly attenuated by scattering and haze. In contrast, strong temporal ON/OFF transitions preserve detectable temporal edges across frames, even under motion and optical degradation. Building on this insight, we present AquaFlicker , a smartphone-only underwater OCC system. The system encodes data through deliberate temporal ON/OFF flickering and decodes it using lightweight, motion-aware temporal processing. AquaFlicker enables continuous data streaming without requiring external optics or synchronization hardware. It is designed to tolerate natural hand motion, off-axis viewing, and contrast loss caused by underwater scattering. Extensive experiments show that AquaFlicker sustains communication up to 7-8 m in clear water and remains stable under moderate turbidity conditions. It supports viewing angles up to ±25° and tolerates handheld motion of approximately 15 px/s. Compared with prior smartphone-based approaches, AquaFlicker achieves higher motion tolerance while maintaining end-to-end latency below 200 ms.