New approach for designing an underwater free-space optical communication system

Abstract

Ocean observation system that involves multiple underwater vehicles and seafloor nodes plays an important role in better learning the ocean, where underwater wireless communication is mandatory for massive data interaction. Optical communication that has wide bandwidth and comprehensive working distance is the preferred method compared to acoustic and other methods. However, the presence of directionality makes the optical method difficult to use especially when the transceiver is equipped on a motive vehicle. In this study, an underwater free-space optical communication method of transmitting information is proposed. Characteristics of underwater optical transmission, as well as the photoelectric signal processing and modulation and demodulation algorithms, are studied and modeled. New approach for realizing underwater free-space optical communication is proposed and simulated. A prototype including a free-space optical transmitter and a receiver is developed; tests in different scenarios were carried out, and the results were observed: (1) by using the minimum number of LEDs, the effect of uniform lighting in space is achieved, and the transmitter coverage reaches 160°. (2) When the power of the transmitter is 10 W and the communication rate is 1 Mbps, the maximum communication distance reaches 13 m.

Shannon–Hartley Channel Capacity for Underwater Wireless Optical Communications

“…Figure shows a plot of the channel capacity C max (eq ) in comparison to experimental results drawn from the literature. − These are for underwater optical communication channels as a function of distance, z . While there have been tremendous strides in the past few years in realizing high data rate underwater optical channels, the experimental conditions vary widely across data encoding schemes, optical powers, wavelengths, seawater types, distances, and transmit-receive beam configurations.…”

“…Solid lines are the maximum channel capacity C max (eq ) for various types of seawater. Circles show experimental data harvested from the literature. − The acoustic communications upper limit (dashed line) is an extrapolation of the upper bounds for Deep Sea State 0 developed from ref and shown for comparison.…”

“…Recently, there has been an upsurge in interest in underwater optical wireless communications. ,,− Here “wireless” is interpreted to mean there is no waveguiding of the light and that the communication channel is the water medium itself. Furthermore, in practical applications, the water medium is seawater.…”

“…Although there have been significant advances in demonstrating underwater wireless communications using various data encoding schemes over several distances, − there seems to be no agreed approach to understanding the informational capacity for this mode of communication. In fact, to date, experimental results show little or no alignment with the existing limits on informational capacity.…”

Transmission Characteristics and Spatial Coherence of Partially Coherent Light-Emitting Diode Array in the Ocean

“…The spatial coherence of the beam significantly influences various aspects, including the sensitivity of the optical detection system, requirements for detector size, information transmission capacity, and resistance to interference, rendering it an indispensable consideration. Currently, in the modeling and simulation process of light beams, the spatial coherence lengths of partially coherent laser beams and LEDs are typically considered to range from infinity to millimeters and micrometers, respectively [11][12][13]. Some high-power LEDs or specially designed LEDs modulated by the coherence structure can potentially mitigate the negative effect of the channel [14][15][16].…”