8-ary Underwater Optical Wireless Communication Systems Using Blue-Green Color Shift Keying and Multi-Level Intensity Modulation

Inspired by visible light communication, we propose a novel 8-ary underwater optical wireless communication (UOWC) system that combines color shift keying with multi-level intensity modulation. The system employs blue and green LEDs to deliver high throughput while ensuring robust tolerance to transmitter-receiver misalignment. Performance is evaluated through Monte Carlo simulations using commercially available multi-color LEDs, with Lambertian and H-models employed to characterize intensity distribution and spectral behavior. The channel impulse response incorporates absorption and scattering effects, analyzed both with and without the blueshift induced by receiver filters. Key performance metrics, including path loss (PL) and bit error rate (BER), are assessed across a range of transmission rates, link lengths, and fields of view in clean, coastal, and harbor water environments. Results show PL values of approximately 50 dB at link lengths of 6.5, 20, and 40 meters in harbor, coastal, and clean waters, respectively. Relaxing the bandwidth limitation of LEDs, the system achieves error-free data rates of up to 30 Gbps over 20 meters in coastal water and 5 Gbps over 8 meters in harbor water, with blueshift increasing PL by approximately 0.4 dB in harbor conditions. Our results demonstrate that the proposed UOWC system can achieve symbol rates on the order of hundreds of gigasymbols per second over 30 meters in clean water. These findings underscore the fact that extending LED bandwidth limitations toward the gigahertz range could enable high-speed communication that is less sensitive to alignment across diverse aquatic environments.