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A Review on Practical Considerations and Solutions in Underwater Wireless Optical Communication
摘要： Underwater wireless optical communication (UWOC) has attracted increasing interest in various underwater activities because of its order-of-magnitude higher bandwidth compared to acoustic and radio-frequency technologies. Testbeds and pre-aligned UWOC links were constructed for physical layer evaluation, which verified that UWOC systems can operate at tens of gigabits per second or close to a hundred meters of distance. This holds promise for realizing a globally connected Internet of Underwater Things (IoUT). However, due to the fundamental complexity of the ocean water environment, there are considerable practical challenges in establishing reliable UWOC links. Thus, in addition to providing an exhaustive overview of recent advances in UWOC, this paper addresses various underwater challenges and offers insights into the solutions for these challenges. In particular, oceanic turbulence, which induces scintillation and misalignment in underwater links, is one key factor in degrading UWOC performance. Novel solutions are proposed to ease the requirements on pointing, acquisition, and tracking (PAT) for establishing robustness in UWOC links. The solutions include light-scattering-based non-line-of-sight (NLOS) PAT-relieving communication modality as well as scintillating-fiber-based photoreceiver and large-photovoltaic cells as the optical signal detectors. Naturally, the dual-function photovoltaic–photodetector device readily offers a means of energy harvesting for powering up future IoUT sensors.
关键词： non-line-of-sight,Underwater wireless optical communication,energy harvesting,turbulence,fiber detector
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) - Istanbul, Turkey (2019.9.8-2019.9.11)] 2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) - Transmit Laser Selection for Underwater Visible Light Communication Systems
摘要： Visible light communication (VLC) has the potential to serve as a high-speed underwater wireless connectivity solution to support real-time image and video transmission. Underwater propagation medium imposes additional challenges on the design of VLC systems which were originally proposed for indoor applications. Temperature and salinity fluctuations result in fluctuations of the refractive index of seawater and eventually introduce turbulence-induced fading. In this paper, to mitigate the effects of fading, we propose transmit laser selection for a diver-to-diver underwater VLC link where the transmitter has multiple laser sources and the receiver has one photodetector. The source with the highest received instantaneous signal-to-noise ratio is selected for transmission while the remaining sources remain idle. We derive a closed-form expression for asymptotical bit error rate over log-normal distributed underwater turbulence channels and derive the achievable diversity order. We further present simulation results to confirm our derivations and diversity gain analysis.
关键词： bit error rate performance,underwater optical turbulence,transmit laser selection,diversity order,Underwater visible light communication
更新于2025-09-16 10:30:52
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Amplification of laser echo signal in a turbulent atmosphere
摘要： Laser beam backscatter in a turbulent atmosphere is analyzed. The mean intensity of radiation scattered in turbulent atmosphere is shown to increase in the backward direction in comparison with the intensity of radiation scattered in the same direction in absence of turbulence, due to the effect of backscatter amplification in random media. As the strength of refractive turbulence increases, the amplification factor first grows, achieves the maximum, and then decreases. The area of manifestation of the backscattering amplification effect in the plane, transverse to the propagation direction, increases in size with intensification of refractive turbulence. It is found that the amplification factor depends on the inner scale of turbulence and the regime of diffraction of optical radiation at the transmitting aperture. It is maximal for spherical wave and grows with an increase of the inner scale. The data on the amplification effect for the mean power of the lidar echo signal as a function of refractive turbulence strength, regime of diffraction at the transmitting aperture, inner scale of turbulence, and size of the receiving aperture are reported for the first time.
关键词： Backscatter amplification,Refractive turbulence,Laser echo signal
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Simultaneous Observation of Turbulence and Spin Glass in a Photonic System: Theory and Experiment
摘要： We report in this communication the coexistence phenomenon relating two of the most challenging behaviors of complex systems: turbulence and spin glass. In 1998, Bohr, Jensen and Paladin [1] conjectured that it would be possible to find a connection between them, although they pointed out that “it could be too early to decide whether it can pave the way to a deeper understanding of intermittency in fully developed turbulence”. Both effects have been widely studied in a diversity of physical systems, including photonic ones, particularly in the field of random lasers and random fiber lasers [2,3]. However, it was only recently that the coexistence of turbulence-like and spin-glass behavior was identified in any experimental system, once again in a photonics system based on a random fiber laser (RFL) [4]. The experimental results were theoretically supported by a newly proposed photonic Pearson coefficient, with which the experimental results could be well fitted to describe both the turbulent and the glassy behavior in the RFL.
关键词： turbulence,Pearson coefficient,photonic system,random fiber laser,spin glass
更新于2025-09-16 10:30:52
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Performance enhancement of high-capacity coherent DWDM free-space optical communication link using digital signal processing
摘要： In this paper, 1.28 Tbps (32 × 40 Gbps) high-capacity DWDM-FSO link has been investigated for performance enhancement using coherent detection and digital signal processing (DSP). The DP-16QAM-modulated proposed DWDM-FSO link has been analyzed for both adverse weather and turbulent atmospheric conditions. It is observed that when link is subjected to strong turbulence along with adverse weather conditions, the DSP-aided coherent DWDM-FSO receiver achieves target bit error rate (BER) of 10?4 at signal-to-noise ratio (SNR) of 36.4 dB, while for similar conditions, the SNR requirements for IM/DD-based DWDM-FSO link shoots by 12.8 dB to 49.2 dB. Also, in terms of operational link range, the proposed link even under strong turbulent conditions serves 1.88 km, whereas IM/DD link was restricted to mere 1.12 km for target of BER of 10?4, thus producing a decent range increment of 760 m. The proposed link has been designed and investigated using OptiSystem? 14.2.
关键词： Atmospheric turbulence,Coherent detection,Digital signal processing,Free-space optical communication,Gamma–Gamma channel modeling,DWDM
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 19th International Conference on Communication Technology (ICCT) - Xi'an, China (2019.10.16-2019.10.19)] 2019 IEEE 19th International Conference on Communication Technology (ICCT) - Fiber-coupling Efficiency for Satellite-to-ground Laser Links with Angle-of-arrival Fluctuations
摘要： In a satellite-to-ground laser communication system, the presence of atmospheric turbulence and residual angle of arrival fluctuations limit the efficiency with which the propagating beam is coupled into a single-mode fiber. Considering the influence of atmospheric turbulence and residual jitter of angle of arrive, the expression of mean-coupling efficiency is handled in the receiver aperture plane in this paper. The optimal design parameter of the optical receiver system in the satellite-to-ground laser links can be obtained by maximize fiber coupling efficiency. Corresponding numerical results based on the expression derived in this paper will be useful in parametric estimation and optimization of optical receiver system.
关键词： fiber coupling,free space optical communication,angle of arrival,atmospheric turbulence
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Numerical Simulation of Ground-to-Satellite Laser Transmission based on Unequal Spacing Phase Screen
摘要： In this paper, the numerical simulation method of multi-layer phase screen step-by-step transmission is used to study the influence of atmospheric turbulence on the satellite-ground optical upstream communication. The model of atmospheric turbulence laser transmission between satellite and ground is established to simulate the laser transmission between ground terminal and Low-Orbit satellite. Unequal spacing phase screen is used to simulate non-uniform turbulence. The simulation calculation of optical transmission under different turbulence conditions with different zenith angles can be realized. The simulation results of the satellite upstream optical communication verified the model.
关键词： ground-to-satellite laser communication,unequal spacing phase screen,turbulence simulation
更新于2025-09-16 10:30:52
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Fast wavefront reconstruction method of reception diversity atmospheric laser communication based on Fractional Brownian motion
摘要： In order to reconstruct the wavefront of reception diversity atmospheric laser communication, the paper first improves the reconstructing modal method of traditional single-input-single-output laser communication based on mutual information. Because the distortion wavefront caused by atmospheric turbulence is a fractal surface of Fractional Brownian motion, a fast wavefront reconstructing method of reception diversity atmospheric laser communication is proposed in this paper. The result shows that the wavefront reconstructing method based on mutual information can optimize the reconstructing performance effectively. Besides, the running time of proposed reconstructing method of reception diversity atmospheric laser communication decreases greatly. Through the comparison of generated wavefront and reconstructed wavefront, the feasibility of the proposed method is demonstrated. It proves that the wavefront reconstructed by proposed method based on Fractional Brownian motion can fit the theory well through the comparison of phase structure function.
关键词： Atmospheric turbulence,Wavefront reconstruction,Fractional Brownian motion,Reception diversity,Mutual information
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Single Shot Axially Resolved Femtosecond Laser Filament Profiles
摘要： An array of synchronized microphones measures energy deposition along the length of laser filament in a single shot. A spread of collapse location positions due to air turbulence and laser energy fluctuations causes a pronounced difference between single shot measurements and conventional multi-shot averaging.
关键词： turbulence,filamentation
更新于2025-09-16 10:30:52
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Generalised statistical distribution for turbulence-induced fading in wireless optical communication systems
摘要： The unified M distribution is recently proposed for analysing turbulence-induced fading effects in wireless optical communication (WOC) systems. In developing this model, the large-scale fluctuations have been approximated by gamma distribution, instead of widely accepted log-normal distribution. However, the accuracy of this approximation decreases when the variance of the log-normal distribution is large. As another approach, the inverse-Gaussian (IG) distribution has been proposed in the literature to model the large-scale fluctuation, results in a new accurate, closed-form distribution termed as S model. To generalise the above results, in this study, the authors propose to approximate the large-scale fluctuations by generalised IG distribution. They show that this new approach results in an accurate, closed-form generalised distribution, called here as H model which includes M and S models as its special cases. To show the applicability of the presented model, they consider a WOC system with heterodyne detection scheme and investigate its bit error rate (BER) performance over H-distributed fading channel. They derive closed-form analytical expression for the BER of the considered system and show that in a special case, it coincides with the results presented in the open technical literature.
关键词： bit error rate,M distribution,turbulence-induced fading,wireless optical communication,H model,inverse-Gaussian distribution
更新于2025-09-16 10:30:52