Underwater Wireless Sensor Networks: Architecture, Communication Challenges, Localization Techniques, Security Issues, and Future Research Directions – A Comprehensive Survey

Abstract

Dependable underwater monitoring technologies are of great importance to the marine environment evaluation, offshore infrastructure surveillance, oceanographic sensing, disaster prediction, and defense applications. Underwater Wireless Sensor Networks (UWSN) constitute the basis of such operations. Contrary to the radio-frequency dominated terrestrial communication, UWSN is inherently challenged by the nature of underwater physical medium. Acoustic signals are generally used in UWSNs, which have limited bandwidth, long propagation delay, high bit error rates, multipath distortions, Doppler shifts, and extremely low power. The positioning of nodes emerges as a critical requirement in UWSNs because of the insufficiency of physical measurements. GPS signals are inaccessible underwater, and alternative techniques should be used for underwater vehicle localization. Positioning can be achieved through acoustic ranges, anchor nodes, utilizing Autonomous Underwater Vehicles (AUV), cooperative localization methods, numerical optimization, and machine learning techniques. In this article, we present a comprehensive survey of the key aspects of UWSN. Specifically, we highlight the importance of localization in UWSNs, and give an in-depth overview of physical layer considerations, networking solutions, and advanced localization algorithms. We classify the localization algorithms based on range-based, range-free, mobile anchor utilization, optimization, and machine learning approaches. Additionally, we discuss the critical system-level impediments such as sound speed profiles, synchronization errors, sparse deployments, and possible security threats. Finally, we provide the insights on the topics of IoUT, edge intelligence, and federated learning, along with considerations on digital twins and energy autonomy.