# Recent Progress on Underwater Wireless Communication Methods and Applications
## 1 Introduction  
The ocean, covering over 70% of the Earth's surface, represents one of the most vast and least explored frontiers of our planet. It harbors a diverse range of natural resources, including fisheries, oil reserves, mineral deposits, and novel biological compounds, many of which are vital to the global economy and scientific research. Consequently, there has been a sustained and growing effort to explore, monitor, and sustainably exploit these oceanic resources. This growing demand has elevated ocean exploration to a strategic priority across both scientific and industrial sectors, with applications spanning from climate research and deep-sea biodiversity studies to offshore energy extraction and national defense [1, 2]. In this context, the development and deployment of robust communication technologies--especially underwater wireless communication systems--have become indispensable. These technologies serve as the backbone for enabling real-time data exchange between underwater platforms and surface control stations, significantly enhancing the operational capacity of oceanographic missions [3; 4]. Underwater wireless communication now plays a critical role in a wide array of applications, including long-term marine environmental monitoring, underwater infrastructure inspection, seabed mapping, and collaborative operations involving multiple autonomous platforms [5; 6]. However, unlike terrestrial or aerial wireless communication systems, underwater wireless communication faces a unique and complex set of environmental challenges. The underwater medium is characterized by high spatial and temporal variability [7; 8], with factors such as salinity, hydrostatic pressure, temperature gradients, suspended particles, and dynamic currents all influencing signal propagation. In particular, seawater's high conductivity and optical scattering properties in both shallow and deep-sea conditions severely attenuate electromagnetic and optical signals. These factors collectively contribute to unstable and low-bandwidth communication links [9; 10], posing substantial obstacles to the reliable transmission of information over long distances. As such, overcoming these limitations necessitates the development of innovative and environment-adaptive communication strategies. At the same time, the rapid evolution of underwater robotic systems--particularly autonomous underwater vehicles (AUVs)--has introduced new and stringent demands for underwater communication infrastructure. Unlike traditional manned submersibles, AUVs operate without human intervention, requiring robust and efficient communication channels for mission-critical tasks such as remote sensing, seabed inspection, collaborative navigation, and adaptive control. As these vehicles are increasingly deployed in heterogeneous and unstructured underwater environments, communication systems must support not only reliable real-time data transfer but also inter-vehicle coordination, energy-aware routing, and dynamic reconfiguration [11; 12]. To this end, there is a growing need for integrated underwater communication architectures that interconnect a wide range of assets--surface buoys, research vessels, AUVs, and static sensor networks--forming a cohesive and intelligent marine information network. Recent progress in underwater wireless communication technologies has primarily concentrated on three modalities: acoustic, radio frequency (RF), and optical wireless communication. Each of these methods addresses different operational ranges and environmental constraints. Acoustic communication remains the dominant technique for long-range transmission, owing to its superior propagation characteristics in water. However, its practical deployment is often limited by low data rates, high latency, and susceptibility to ambient noise and multipath effects [13].