Underwater Optical Communication System Research Articles

Analysis of orbital angular momentum spectra of Hankel-Bessel beams in channels with oceanic turbulence

Beams with different-mode-number (l) orbital angular momenta (OAMs) are mutually orthogonal to each other, which makes it possible to enlarge the channel capacity in an OAM multiplexed underwater optical communication (UOC) system. Nevertheless, the implementation of this strategy is limited by oceanic turbulence. Hankel-Bessel (HB) vortex beams carrying OAM are relatively less affected by atmospheric turbulence due to their ability to propagate without changing the intensity profile (non-diffraction nature) and remarkable ability to be reconstructed after encountering an obstacle (self-healing mechanism). Consequently, HB vortex beams can be used as the carriers to increase the channel capacity of information transmission. In this paper, based on the Rytov approximation theory, the analytical expressions of OAM spectra for HB vortex beams under weak horizontal oceanic turbulent channels are derived. The influences of oceanic turbulence parameters on the OAM spectra of HB vortex beams are investigated via numerical calculations. The results indicate that oceanic turbulence leads to the decline of detection probability of transmitted OAM mode and the broadening of OAM spectra as well. Similarly, the spatial coherence length in oceanic turbulence decreases with increasing propagation distance and the dissipation rate of mean-squared temperature and with decreasing the dissipation rate of turbulent kinetic energy, which lead to the decline of detection probability of transmitted OAM mode for HB vortex beams. On the other hand, beams with larger OAM mode numbers each have a wider beam spreading after propagating in the turbulence, which results in the decrease of the detection probability for transmitted OAM modes of HB vortex beams. And the HB vortex beams are more affected by salinity fluctuation than by temperature fluctuations, which indicates that salinity fluctuations are much more effective than temperature fluctuations in determinating the effect of oceanic turbulence. In addition, for weak turbulence and a distance of several tens of meters, the transmission performance of HB vortex beams is worse than that of Laguerre-Gaussian vortex beams with the optimal waist setting. These results provide references for the realization of optical communication links in the marine environment.

A theoretical study on the impact of particle scattering on the channel characteristics of underwater optical communication system

Scattering by water molecules and particulate matters determines the path and distance of photon propagation in underwater medium. Consequently, photon angle of scattering (given by scattering phase function) requires to be considered in addition to the extinction coefficient of the aquatic medium governed by the absorption and scattering coefficients in channel characterization for an underwater wireless optical communication (UWOC) system. This study focuses on analyzing the received signal power and impulse response of UWOC channel based on Monte-Carlo simulations for different water types, link distances, link geometries and transceiver parameters. A newly developed scattering phase function (referred to as SS phase function), which represents the real water types more accurately like the Petzold phase function, is considered for quantification of the channel characteristics along with the effects of absorption and scattering coefficients. A comparison between the results simulated using various phase function models and the experimental measurements of Petzold revealed that the SS phase function model predicts values closely matching with the actual values of the Petzold’s phase function, which further establishes the importance of using a correct scattering phase function model while estimating the channel capacity of UWOC system in terms of the received power and channel impulse response. Results further demonstrate a great advantage of considering the nonzero probability of receiving scattered photons in estimating channel capacity rather than considering the reception of only ballistic photons as in Beer’s Law, which severely underestimates the received power and affects the range of communication especially in the scattering water column. The received power computed based on the Monte-Carlo method by considering the receiver aperture sizes and field of views in different water types are further analyzed and discussed. These results are essential for evaluating the underwater link budget and constructing different system and design parameters for an UWOC system.

A Compact Autonomous Underwater Vehicle With Cephalopod-Inspired Propulsion

AbstractIn this paper, a bioinspired, compact, cost-effective autonomous underwater vehicle system is presented. Designed to operate in a heterogeneous, multivehicle collaboration hierarchy, the presented vehicle design features 3D printing technology to enable fast fabrication with a complex internal structure. Similar to a previous vehicle prototype, this system generates propulsive forces by expelling unsteady, pulsed jets, inspired by the locomotion of cephalopods and jellyfish. The novel thrusters enable the vehicle to be fully actuated in horizontal plane motions, without sacrificing the low-forward-drag, slender vehicle profile. By successively ingesting water and expelling finite water jets, periodic actuation forces are generated at all possible vehicle velocities, eliminating the need for control surfaces used in many conventional underwater vehicle designs. A semiactive buoyancy control system, inspired by the nautilus, adjusts the vehicle depth by passively allowing water flowing into and actively expelling water out of an internal bladder. A compact embedded system is developed to achieve the control and sensing capabilities necessary for multiagent interactions with the minimum required processing power and at a low energy cost. The new vehicle design also showcases an underwater optical communication system for short-range, high-speed data transmission, supplementing the conventional acoustic communication system. Experimental results show that, with the thruster motors powered at a 60% duty-cycle, the new vehicle is able to achieve a 1/4 zero-radius turn in 3.5 s and one-body-width sway translation in 2.5 s.

Zero‐padding block transmission for underwater optical wireless communications

An underwater optical wireless communication (UOWC) system is considered. For such system, a zero-padding (ZP) block-transmission scheme is presented to reduce the influence of inter-symbol-interference. Simulation results, which are based on the existing experimental data of channel pulse response, show that ZP system is effective especially for serious dispersive channel with high data rates and thus, potentially applicable to the high data rate UOWC systems.

Development of a biomimetic underwater microrobot for a father–son robot system

Conventional underwater intervention tasks are performed by underwater vehicles equipped with rigid multi-link arms. However, the movements of conventional mechanical arms exert reactive force on the vehicle platform due to their enormous bulk. Additionally, they cannot be used for small object recovery. In this paper, an ionic conducting polymer film (ICPF) actuator-based crayfish-inspired microrobot is designed and developed as a son robot for object recovery, which is connected to the amphibious father robot by copper wires. The crayfish-like son robot is used as the mechanical arm of the father---son robot system, which can grasp the small object especially in restricted spaces. The crayfish-inspired son robot actuated by ten ICPF actuators can realize underwater basic motions. The father robot can emit the son robot for object recovery. A proximity sensor is mounted in front of the microrobot between the two ICPF hands to implement the autonomous grasping motion. And we designed a blue LED-based underwater optical communication system to realize the communication between the father robot and the son robot for microrobot recovery. We carried out the experiments to confirm the basic operations of the microrobot, evaluate the performance of the communication system, and verify the blue LED tracking mechanism for microrobot recovery.

The Development of Novel High Speed – Low Noise pHEMT Device for Lossless Underwater Optical Communication

We report the development of two epilayers namely the baseline highly strained channel and enhanced low gate leakage samples. The Hall data shows that the enhanced epilayer portraying higher sheet carrier concentration, but comparable carrier mobility in the 2-DEG layer, as compared to the baseline sample. The WinGreen simulation also conformed the enhanced epilayer advantages where wider Schottky barrier is observed and subsequently double carrier concentration is simulated in the channel. Both samples show low AuGe/Au Ohmic contact resistivity of approximately 0.16 Ω.mm. A tremendous advantage on 1 μm Schottky gate leakage is also recorded on enhanced epilayer where the leakage is more than seven times lower than that of the baseline sample. The resulted characteristics are much better than the reported submicron device, thus this device has find an important application in high-gain lossless transmission, especially in underwater optical communication system.

Cellular Underwater Wireless Optical CDMA Network: Performance Analysis and Implementation Concepts

In this paper, we introduce and investigate a cellular underwater wireless optical code division multiple-access (OCDMA) network based on optical orthogonal codes (OOC). The structures, principles, and performance of the underwater wireless OCDMA network in various water types are presented. Since underwater wireless optical links are considered for high-bandwidth underwater communications at short ranges, we will place a set of optical base transceiver stations (OBTS) each in the center of a hexagonal cell to cover a larger underwater area. The OBTSs are connected via fiber optic to an optical network controller (ONC) which operates as the core of the network. An integral expression for system error probability is obtained for both uplink and downlink schemes under a specific channel model expressed in this paper, among many channel models in underwater optical communication systems. Furthermore, an experimental prototype of underwater an OCDMA system including the OBTS, ONC, transmitters, and receivers are implemented using field programmable gate arrays (FPGA).

Underwater optical communication performance for laser beam propagation through weak oceanic turbulence.

In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case.

블루투스와 연동하는 수중 가시광 통신 시스템의 구현

Abstract: Communication underwater is severely limited when compared to communications in air because water is essentially opaque to electromagnetic radiation except in visible range. Acoustic systems are capable of long range communication, but offer limited data rates and significant latency due to the speed of sound in water. On the other hand, optical wireless communication has been proposed as one of the best alternatives to meet the requirements of the underwater observation and subsea monitoring systems. It will help In this study, we are developing an underwater optical communication system that integrates with a depot ship float-ing on the water. An interface between LED lighting communication system and Bluetooth module is pre-sented to support the underwater-to-air communications. Error free image and text transmission at 3 m of wa-ter were achieved at bit rates of 230.4 kbps. This development effort will enhance infrastructure to efficiently interconnect between underwater wireless systems and command ship networks for underwater monitoring.

Simulating channel losses in an underwater optical communication system.

A Monte Carlo numerical simulation for computing the received power for an underwater optical communication system is discussed and validated. Power loss between receiver and transmitter is simulated for a variety of receiver aperture sizes and fields of view. Additionally, pointing-and-tracking losses are simulated.

Conceptual Design of Future Undersea Unmanned Vehicle (UUV) System for Mine Disposal

A conceptual design is proposed for an effective mine countermeasure (MCM) system, which consists of three unmanned underwater vehicles (UUVs) and 10-20 small charged deliverable vehicles. New underwater optical communication systems are introduced to improve onboard mine reconnaissance and decision making with the key technologies focused on system and communication efficiency, capability of data processing, and cost-effectiveness of MCM systems. The proposed UUV MCM system is cost-effective due to adapting disposable mine neutralization instruments, upgrading data process units, and configuring optical communication systems between heterogeneous underwater and surface vehicle units in operations. At the same time, efficient and reliable underwater optical and electromagnetic wave communication systems are also introduced and analyzed for future system applications.

AquaOptical: A Lightweight Device for High-rate Long-range Underwater Point-to-Point Communication

AbstractThis article describes AquaOptical, an underwater optical communication system. Three optical modems have been developed: a long-range system, a short-range system, and a hybrid system. We describe their hardware and software architectures and highlight trade-offs. We present pool and ocean experiments with each system. In clear water, AquaOptical achieved a data rate of 1.2 Mbit/s at distances up to 30 m. In water with visibility estimated at 3 m, AquaOptical achieved communication at data rates of 0.6 Mbit/s at distances up to 9 m.

Paving the way for a future underwater omni-directional wireless optical communication systems

To lay down the foundation for an underwater omni-directional optical communication system for tele-operation, we tested a point-to-point optical communication system, using laser-emitting diodes (LEDs). The LEDs used in the test emitted light in the green and blue light spectrum and were tested in a pool and in a tank filled with lake water. The primary objective of these tests was to get profiles of the behaviors of such communication systems with respect to water characteristics such as turbidity levels, prior to building the proposed omni-directional optical communication. The results of the tests indicated that turbidity level, viewing angle and separation distance plays a significant role in the behavior of blue light in water. Furthermore, it was possible to graph the profile of the behavior of light with respect to the parameters of interest. The results of the tests and related research are discussed in this paper.