Minimizing Age of Information for Underwater Optical Wireless Sensor Networks.

In Underwater Optical Wireless Sensor Networks (UOWSNs), the Age of information (AoI) is critical as it manifests information freshness, which is extremely useful for real-time monitoring applications. Prior works extensively focus on improving AoI in single-hop or multi-hop networks with fixed paths. However, the issue of multi-path transmission is overlooked. In this paper, we make the first attempt to address the issue of minimizing AoI through link scheduling in UOWSNs (termed MAKE problem). To minimize AoI, we propose an AoI model and corresponding link constraint model for multi-path and multi-hop UOWSNs. Then, we formalize the MAKE problem into a submodular function maximization problem, and propose a greedy method with an approximation ratio guarantee to solve it. Theoretical analyses are presented to explore the features of our scheme. Finally, to demonstrate the effectiveness of the proposed scheme, extensive simulations are conducted. The results reveal that the proposed scheme has 21.4% lower total average AoI compared with other baseline algorithms. Furthermore, test-bed experiments are carried out to verify the applicability of the proposed scheme in practical applications.