On the Impact of Mobility on the Underwater Optical IoT Architecture for Positioning and Communication

The use of Optical Wireless Communications is largely adopted in both indoor and outdoor applications. Recently, it is also extending to underwater scenarios, as an alternative technology to the acoustic one, which is traditionally adopted. Knowing more precisely the position of artifacts, technical/scientific instruments and operators in the marine environment increases the operational potential and consequently, the interest in the progress of knowledge is guaranteed. Furthermore, the possibility of operating in both shallow and deep waters and the opportunity to be a new underwater navigation system increases the possibility of success of underwater activities, in the context of the Internet of Underwater Things (IoUT). This paper introduces an underwater all-optical IoT network architecture for both communication and positioning tasks. We initially discuss the main issues for data transmission via underwater visible light communications, and present an IoUT schematic based on Light Emitting Diode (LED) devices accordingly deployed on the seabed and illuminating a given space of interest. Then, a simple but accurate fingerprinting-based localization approach is presented, able to estimate the position of an object moving within the space of interest (e.g., a diver or an Autonomous Underwater Vehicle). The positioning error is auto-adjusted in case of variable channel coefficients, mainly due to changes in water turbidity space distribution. The achieved results have been assessed in case of two different paths, where variable distances from the positioning/communication LEDs are assumed.