Abstract
The connectivity of undersea sensors and airborne nodes across the water-air interface has been long sought. This study designs a free-space wireless laser communications system that yields a high net data rate of 850 Mbit/s when perfectly aligned. This system can also be used for an extended coverage of 1963 cm 2 at the receiver while sustaining a net data rate of 9 Mbit/s over 10 m. The utility of this system was verified for direct communications across the water-air interface in a canal of the Red Sea based on a pre-aligned link as well as a diving pool under a mobile signal-searching mode. The canal deployment measured a real-time data rate of 87 Mbit/s when pre-aligned in turbid water over 50 min, which confirms the system robustness in harsh water environments. In the pool deployment, a drone configured with a photodetector flew over the surface of the water and recorded the underwater signals without a structure-assisted alignment. Using a four-quadrature amplitude-modulated orthogonal frequency-division multiplexing (4-QAM-OFDM) modulation scheme provided a net data rate of 44 Mbit/s over a 2.3-m underwater and 3.5-m air link. The results validated the link stability and mitigated problems that arise from misalignment and mobility in harsh environments, which paves the way for future field applications.
Highlights
The concept of the Internet of Underwater Things (IoUT) was proposed in 2012 to satisfy the demands of underwater communication networks [1]
The wide, license-free bandwidth and low energy consumption in such environments promote the consideration of underwater wireless optical communication (UWOC) as a transformative technology compared with conventional marine acoustic and radio-frequency (RF) technologies for high-speed communication activities in the IoUT
A drone-aided diving pool trial showed that the system can facilitate a 44-Mbit/s direct and mobile communication link over a transmission distance of 2.3 m under water and 3.5 m in air, which was free of structureassisted alignment
Summary
The concept of the Internet of Underwater Things (IoUT) was proposed in 2012 to satisfy the demands of underwater communication networks [1]. The difficulty of obtaining precise position, acquisition, and tracking (PAT) information in submerged oceanic environments hampers undersea missions when using optical light A net data rate of 44 Mbit/s with a transmission length at 2.3 m underwater and 3.5 m in the air was achieved for communications between fixed underwater nodes and mobile airborne nodes These results reflect impressive performance for direct communications across a wavy water–air interface in a mobile signal search mode. 0.45A w/ > 1 GHz 0.57A w/ > 1 GHz 0.65A w/ > 1 GHz 0.75A w/ > 1 GHz 0.45A w/o 21 MHz 0.57A w/o 20 MHz 0.65A w/o 15 MHz 0.75A w/o 14 MHz
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