Performance Analysis of Air-to-Water Optical Wireless Communication Using SPADs

Establishing highly reliable optical wireless communication links to submerged receivers exposed to insufficient light requires highly sensitive receivers with the ability to detect each photon carrying information. To this end, single photon avalanche diode (SPAD) receivers can be considered an appropriate option for the optical receiver system as they benefit from active quenching and biasing circuits, and offer a considerably high breaking voltage, providing the optical system with the ability to detect every single received photon in the ideal case. However, the sensitivity and bandwidth of the existing SPAD receivers have been limited by their dead time and limited photon detection efficiency. In this study, the performance of underwater SPAD receivers in detecting transmitted information from an optical transmitter located in the free space above the sea surface was assessed. To this end, the saddle-point approximation was used along with the Birnbaum-Saunders distribution to statistically model the fading coefficient of the air-to-water optical wireless communication channels and the statistical photon counting behavior of SPADs. The performance of the communication link was then assessed by obtaining the analytical relations for bit error rate. Finally, the results of numerical simulations are presented and the negative effects of dead time on information detection in the optical receiver system in various transmission bit rates are studied.