A photonics-assisted D-band wireless transmission system employing an in-phase/quadrature (I/Q) mixer and maximum-ratio combining (MRC) is experimentally demonstrated. Two intermediate-frequency (IF) outputs from a single radio-frequency input are digitized and processed separately. After channel estimation and equalization, the recovered complex baseband signals are coherently combined. A 32-Gbaud quadrature phase-shift keying orthogonal frequency-division multiplexing (QPSK-OFDM) signal with an effective payload rate of 38.65 Gb/s is transmitted over a 20 m indoor wireless link with a calculated optical-beat carrier frequency of 138.5 GHz. Across seven input optical power settings from −8 to −2 dBm, MRC provides an average signal-to-noise ratio (SNR) improvement of 1.78 dB and a maximum improvement of 2.32 dB relative to the higher-SNR single branch at each power. Combining also improves constellation convergence and reduces the bit error rate (BER), with the MRC output falling below the 7% hard-decision forward-error-correction threshold of 3.8 × 10⁻³ at the sampled power settings of −5 dBm and above. These results demonstrate improved signal quality through I/Q-branch combining in the investigated D-band link.

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.