Underwater Distributed Antenna Systems: Design Opportunities and Challenges
Underwater systems for ocean exploration and monitoring consist of a mix of geographically distributed stationary infrastructure and mobile units. The stationary infrastructure could be bottom-anchored nodes and surface buoys that are connected to a control center via cables and in-air radio links. Both the stationary and mobile units can be equipped with acoustic communication modules for underwater wireless data transmission. With the backbone (cable or radio) connection, those acoustic communication modules naturally form an underwater DAS. Similar to the DAS in terrestrial radio networks, the underwater DAS supports larger acoustic communication coverage and higher network throughput compared to the CAS. Furthermore, the characteristics of underwater acoustic channels, such as the frequency-dependent signal absorption loss and the low sound speed in water, lead to unique design challenges and unforeseen opportunities in the underwater DAS. This article examines both theoretical and system design issues pertaining to the underwater DAS, including operation strategies, communication algorithms and mobile node positioning, and pinpoints future research directions to fully realize its potentials.