A Routing Protocol for Underwater Acoustic-Optical Hybrid Wireless Sensor Networks Based on Packet Hierarchy and Void Processing

In recent years, with the growing demand for oceanic exploration, underwater wireless sensor networks (UWSNs) have gained intensive research interests. In UWSNs, the prevailing routing algorithms predominantly utilize either acoustic or optical waves for data transmission with some of them employing hybrid acoustic-optical strategies. However, none of these algorithms considers the distinct characteristics of both media for heterogeneous data packets characterized by diverse priority (e.g., importance level), which limits their efficiency. A hybrid acoustic-optical routing algorithm based on packet hierarchy and void processing (PHVP) is proposed to address this challenge. The proposed PHVP algorithm employs a hybrid strategy by delivering the data with high importance via optical waves and the ones with low importance via acoustic waves to reduce transmission delay. Besides, the proposed algorithm also employs a hybrid two-stage void handling mechanism, which utilizes the characteristics of both acoustic and optic waves to realize a two-stage void processing strategy. This mechanism reduces the probability of packet loss in void regions and thereby raises packet delivery rate (PDR). In addition, by comprehensively considering the divergence angle and energy of network nodes during routing, the proposed PHVP algorithm reduces the consumed energy in UWSNs and prolongs their lifetime. Simulation results exhibit that the proposed PHVP algorithm significantly obtains about at least 36% and 73% improvements in PDR and network lifetime when compared to the classical routing algorithms adopted in the simulations.