Simulation study on different pulse modulation schemes for efficient underwater optical communication

Abstract Underwater Optical Communication (UWOC) uses visible light (wavelengths around 450–550 nm) to transmit data through water. The system consists of LED/laser transmitters and photodetector receivers that convert electrical signals to light pulses and vice versa. While offering high bandwidth (Gbps) and low latency, the technology is limited by water turbidity, scattering, and absorption, typically restricting effective range to 10–100 m in clear water. The transfer of data from underwater unmanned systems or sensors to a surface vessel or land-based station poses a considerable obstacle in marine surveillance and research. In this work, 4 and 8 quadrature amplitude modulation (QAM) schemes and different pulse modulation techniques namely Pulse Position Modulation (PPM), Differential Pulse Interval Modulation (DPIM), and Dual-Header Pulse Interval Modulation (DH-PIM) are analyzed with Forward Error Correction (FEC) for assessing the performance of underwater optical communication systems for efficient data transmission. An exponential gamma function is used to model the underwater channel, and the performance is estimated for data rates of 100 Mbps, 500 Mbps, 1 Gbps, and 2 Gbps. For 2 Gbps transmission incorporating FEC, 4-QAM performs best among all the modulation technique considered, as it provides maximum transmission range of 34.9 m, for a transmitted power of 5 mW at BER of 10 −15 . In the case of pulse modulation techniques, 8-PPM gives maximum distance of 29.6 m under similar operating conditions.