Non-line-of-sight (NLOS) link budget analysis for underwater wireless optical communications (UWOCs)

Nowadays, Optical Wireless Communications provide high data rates and minimal delay, making them ideal for real-time video and image applications in the Internet of Underwater Things (IoUT). However, Line-of-Sight (LOS) communication may not always be feasible due to misalignment, obstacles, or the random orientation of transceivers, especially for underwater sensor nodes or mobile users, to mitigate this challenge, a non-LOS (NLOS) link configuration is established. This paper conducts a feasibility study of communication links using a link budget approach to determine the feasible NLOS communication range for two types of transmitters: light emitting diode photo source (LED-PS) and laser diode photo source (LD-PS), at two wavelengths. A more realistic power link budget is developed. This paper examines the effects of underwater channel scattering and absorption, LED and LD-PS-based transmitters, and SiPM-PD-based receivers. In addition, it investigates how underwater environments, transmitter, and receiver parameters impact the communication link range. The effect of different water types on communication range was analyzed. Various transmitter parameters such as beam divergence angle and optical power, as well as receiver parameters such as incident angle and PD active area, were explored. The impact of different Lambertian order values was also assessed. The contribution of this paper is knowing the value of the received power used to determine the communication distance, this power is compared to the required receiver sensitivity, and the resulting link margin is used to determine the feasibility of the communication link.