Long-Term and Real-Time High-Speed Underwater Wireless Optical Communications in Deep Sea
Jialiang Zhang, Sujing Wang, Ziqi Ma, Guanjun Gao, Yonggang Guo, Fei Zhang, Shanguo Huang, Jie Zhang
Abstract
The seafloor observation network can perform all-weather, long-term, continuous, real-time, and in-situ observation of the ocean by combining various observation methods including cabled seafloor nodes and self-contained nodes, as well as mobile platforms, where reliable and long-term high-speed underwater wireless communication becomes an essential requirement. Recently, underwater wireless optical communication (UWOC) has emerged as a highly promising solution and is rapidly becoming a research hotspot for meeting this requirement. In this article, we demonstrate an experiment with the application of a high-speed UWOC system for the deep sea seafloor observation network. To the best of our knowledge this is the first long-term real-time deep-sea UWOC link with bitrate as high as 125 Mb/s. Between two nodes of 30 m distance and at a depth of 1650 m, two-way Ethernet UWOC links are achieved with 125 Mb/s direction-adjustable green light link and 6.25 Mb/s nonline-of-sight (NLOS) blue light link. High quality video transmission of 8K 30 FPS and 4K 120 FPS are achieved through a high-speed 125 Mb/s green light link, with 100 percent peak signal-to-noise ratio (PSNR) agreement, showing the capability of transmitting high-quality lossless videos. Our 30-day long-term measurement results show that the BER performance of both 125 Mb/s and 6.25 Mb/s links is lower than 10– <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , proving the stability and reliability of this UWOC system at a depth of 1650 m. By measuring the light attenuation of a deep-sea water sample, the maximum transmission distance for the green and blue light links are estimated to be 117.7 and 128.3 m with geometry loss, which can be extended to 231.6 and 337.5 m without geometry loss. With the first long-term and real-time UWOC system in the deep sea, we believe this demonstration can provide valuable experience for further UWOC studies and converged ocean observation networking with cabled and cable-less observation platforms.