Broadband Millimeter-Wave Communication Under Water

Underwater wireless communication requires flexible solutions that balance transmission range, data rate, and latency, particularly for short-range data exchange. In this work, we experimentally investigate a photonics-assisted 85-GHz millimeter-wave transmission system in a controlled water-loaded configuration. The transmitter and receiver are separated by 3 m, including a 2.3 m free-space section and a 0.7 m interchangeable test section. The received power of a 100 MHz pilot is measured under three configurations: unobstructed air, an empty plastic tank, and a water-filled tank. Relative to the air reference, the empty tank introduces a 4.1 dB received-power penalty, while filling the tank with water produces a further 15.3 dB reduction, resulting in a total penalty of 19.4 dB. Broadband transmission is further evaluated using 10 Gbaud single-carrier QPSK and probabilistically shaped 16QAM (PS-16QAM) signals under the water-filled configuration. Both modulation formats achieve pre-FEC bit-error rates (BER) below the reference 20%-overhead soft-decision FEC threshold at suitable optical input powers. These results provide quantitative experimental insights into broadband W-band signal transmission and recovery in water-loaded environments, supporting further investigation of high-capacity, proximity-oriented wireless communication systems.