Performance analysis and optimization of modulation techniques for underwater optical wireless communication in varied aquatic environments.

Underwater Optical Wireless Communication (UOWC) has emerged as a promising technology for enabling high-speed and low-latency data transmission in aquatic environments. However, the performance of UOWC systems is severely affected by absorption, scattering, turbulence, and background noise, making the choice of modulation techniques vital for ensuring reliable and efficient communication. This paper presents a comprehensive performance analysis of six prominent modulation schemes-On-Off Keying (OOK), Pulse Position Modulation (PPM), Quadrature Phase Shift Keying (QPSK), Differential Phase Shift Keying (DPSK), 32-Phase Shift Keying (32-PSK), and 64-Quadrature Amplitude Modulation (64-QAM)-under various underwater conditions. The study utilizes both LED and LD photo-sources (LED-PS and LD-PS) operating at a green wavelength of 520 nm, optimal for coastal and turbid harbor waters due to its lower attenuation characteristics. A silicon photomultiplier (SiPM-PD) with a receiver sensitivity of -53.4 dBm is employed for detecting low-power signals. Extensive numerical simulations evaluate key performance metrics including received power, Bit Error Rate (BER), Signal-to-Noise Ratio (SNR), channel capacity, and link range across different water types-pure, clear, coastal, and turbid-and turbulence intensities. This study offers the advantage of integrating multiple transmitter types, modulation schemes, and environmental factors, providing a comprehensive exploration of the trade-offs between communication range, transmitted power, and channel capacity. Results indicate that OOK enables the longest achievable communication distance (up to 123.73 m in pure seawater at BER = 10⁻⁵ with LD-PS), while high-order schemes such as 64-QAM achieve superior channel capacities (up to 53.23 bps/Hz), albeit at the cost of increased power and SNR requirements. The findings underscore a fundamental trade-off between range and Shannon spectral efficiency, guiding the selection of optimal modulation strategies for varied underwater applications, including environmental monitoring, underwater robotics, and defense communications.