Underwater collaborative work between small mobile platforms (SMP) such as divers, litter submarine or AUV, requires a high data rate communication system which is compact, reliable, affordable and eye-safe.The high bandwidth of LED-based underwater wireless optical communication (UWOC) is an advantage. Artificial, emulated as well as simulated, turbid underwater channel has been studied recently, but no practical nature water. To fully meet the requirements of challenging turbid underwater channel scenarios for SMP, we demonstrated a green LED-based UWOC system up to a bandwidth of 3.4 MHz in a highly-turbid nature lake water.Through a contrast wireless optical communication (WOC) experiment in air, turbid water channel is observed to compensates the receiving signal amplitude attenuates after propagating a longer attenuation length due to multiple-scattered light caused diffusion, and thus to be more like a single-input multi-output (SIMO) system. From our experimental observation, the SIMO channel model could be employed not only in turbulent UWOC, but also in highly turbid UWOC. Moreover, turbid water channel is observed a "frequency selection" effect, thus LED with lower threshold voltage at higher frequency would optimize bandwidth and link range, and a robust pre-code for interference cancellation would be a well-direct choice to constructing different UWOC system in highly turbid water for SMP. Our finding will provide a new reference complementing the current LED-based UWOC systems in realistic water environment.

Cabled ocean observatories (COOs) have enabled real-time in situ ocean observations for decades, thereby facilitating oceanic understanding and exploration. This review discusses typical COOs worldwide in terms of system configurations and state-of-the-art technology, including network structures, power supply modes, and communication capabilities, and provides a comprehensive analysis of their technical routes. The main characteristics of line, ring, star, and grid networks and their applicability in COOs are elucidated, and the advantages and disadvantages of various power supply modes, as well as the opportunities brought by the development of communication technologies, are described. The insights gained from these discussions can inform the implementation of grid structures, optimization of cable routings, expansion of COO scales, application of dual-conductor submarine cables, and upgrading of communication capacity. On this basis, the challenges and future research directions related to COOs are presented.

As underwater platforms become increasingly networked and autonomous, reliable and physically secure links are emerging as critical engineering infrastructure for ocean observation, offshore energy, and maritime security. Underwater wireless optical communication (UWOC) addresses the bandwidth–latency gap left by acoustic systems, yet most existing implementations operate at fixed rates and cannot adapt to dynamic underwater channels. This study presents a real-time multi-rate adaptive bidirectional (time-divided) UWOC system implemented on field-programmable gate arrays (FPGAs). A DC-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) physical layer with four switchable formats (BPSK, 4-QAM, 8-QAM, and 16-QAM) is combined with a pilot-free blind SNR estimation algorithm exploiting virtual carriers and an ACK/NAK stop-and-wait automatic repeat request (ARQ) protocol. The system autonomously adjusts its physical rate between 10 and 100 Mbps across a maximum single-pass water attenuation of 54.8 dB. The narrow line-of-sight beam geometry and tight receiver field of view further offer inherent spatial filtering against eavesdropping, positioning the system as a candidate secure multi-modal component of underwater communication networks. Outdoor-pool experiments with an optical attenuation coefficient of 1.37 dB/m, certified by the China Electronic Product Reliability and Environmental Testing Research Institute (CEPREI, the Fifth Electronics Research Institute of MIIT), demonstrated a mean BER ≤ 1.8 × 10⁻⁶ in all four modes, with every individual certified run below the 10⁻⁵; criterion (worst single run: 5.4 × 10⁻⁶). These results establish a real-time hardware proof of concept validated in an outdoor pool, constituting a step toward field-deployable adaptive underwater optical links in marine engineering scenarios—AUV docking, subsea infrastructure inspection, and underwater sensor networks—and provide a verified platform on which physical-layer security extensions can be built.