最新刊期
卷 ， 期 4 ， 2023
- 摘要：High-speed Underwater Optical Wireless Communication (UWOC) can achieve Gbit/s signal transmission rate, which is of great significance for modern underwater applications. This paper first describes the development process of UWOC, and then compares different kinds of UWOC. Finally, we summarize the research status of high speed UWOC system, and discuss three parts of high speed UWOC: light source, receiver and signal processing. It is expected that this paper can bring help to the research and development of high-speed UWOC in the future.关键词：UWOC;optical receiver;digital signal processing;modulation technique
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发布时间：2023-08-14 - 摘要：Non-Line-of-Sight (NLOS) Underwater Wireless Optical Communication (UWOC) is mainly realized through the air-seawater interface reflection or the scattering of light by particles in seawater. It can effectively solve the link alignment issues of Line-of-Sight (LOS) underwater wireless optical communication. This paper summarizes the research progress of NLOS UWOC technology in the aspects of channel model, simulation and experiment. At present, scholars mainly explore the effects of water quality, wave, turbulence, modulation technology, receiving and sending terminal configuration on the performance of NLOS UWOC link. Few scholars have studied the effects of complex hydrodynamic and water quality factors, non-linearity of light source, non-linearity, sensitivity and noise of detector on the performance of NLOS UWOC and effective solutions. Therefore, it is necessary to carry out more in-depth channel model, simulation and experimental research in the future, so as to promote the development of NLOS UWOC technology.关键词：UWOC;NLOS;channel model;Monte Carlo simulation
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发布时间：2023-08-14 - 摘要：Underwater optical communication is a new and feasible underwater communication technology, which has developed rapidly in recent years. To build a high-performance and practical underwater optical communication system, it is necessary to consider and optimize the design from the device to the system, from the internal modulation to the external environment. This paper summarizes the current problems of underwater optical communication from the aspects of underwater optical communication system transmitter and receiver, modulation format and underwater channel. The paper also classifies and summarizes the three key technologies of improving underwater optical communication distance, communication rate and communication stability, and gives the possible solutions. It provides reference for the follow-up system design and experimental research.关键词：underwater optical communication;communications technology;laser communication;single photon detector
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发布时间：2023-08-14 - 摘要：Underwater Wireless Optical Communication (UWOC) has the advantages of large capacity, high speed and etc. However, it suffers from limited communication range and data rate in practice due to the complex underwater environment and the limited bandwidth of optical devices. Multiple-Input Multiple-Output (MIMO) technology has received considerable attention since it converts spatial single-stream data into multiple-stream data for parallel transmission. Therefore it can extend the UWOC range and alleviate the performance degradation caused by underwater absorption, scattering, and turbulence. In this paper, focusing on the MIMO technology in UWOC systems, we analyzed the channel modeling, research progress, experimental setups and prototypes, and the development and future trend of MIMO-UWOC technology.关键词：UWOC;MIMO;spatial diversity;bit error rate;spatial multiplexing
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发布时间：2023-08-14 - 摘要：Underwater Visible Light Communication (UVLC) has great advantages of high transmission rate, large capacity, low latency, and low cost, which has become a feasible and attractive alternative in the field of underwater communication, with broad application prospects. However, UVLC performance is limited by bottleneck issues such as bandwidth limitations and various linear or nonlinear effects. In order to alleviate these problems, we studied geometrically-shaping based Amplitude Phase Shift Keying (APSK) modulation and coding mapping. A waveform-stage post equalizer based on Bidirectional Recurrent Neural Network (BRNN) is also proposed. In addition, a waveform-to-symbol receiver based on Deep Neural Network (DNN) is proposed to replace the traditional matching filtering, down-sampling, post-equalization and other operations. Compared with traditional receiver, the dynamic range of voltage using BRNN based post equalizer is improved by 170 mV(69%) and it is improved by 245 mV(100%) using waveform-to-symbol receiver based on DNN. In the paper, a waveform-stage post equalizer based on BRNN and a waveform-to-symbol receiver based on DNN are experimentally verified to be promising schemes in future UVLC.关键词：UVLC;APSK;BRNN;post-equalization;DNN
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发布时间：2023-08-14 - 摘要：A dual-wavelength transceiver separation method is proposed for the problem of self-interference limiting the system communication performance in Full-Duplex Underwater Wireless Optical Communication (FD-UWOC) systems. Based on the Monte Carlo numerical simulation, the effects of self-interference on the performance of 450 nm single-wavelength, 525 nm single-wavelength and dual-wavelength FD-UWOC systems are analyzed under three typical water qualities of Jerlov I, Jerlov IB and Jerlov II. The simulation results show that the poorer the water quality, the stronger the self-interference. It is also shown that the enhancement of self-interference will significantly reduce the Optical Signal to Noise Ratio (OSNR) of FD-UWOC, which limits the longest transmission distance of the system. The FD-UWOC system using the dual-wavelength transceiver separation method can bring about 60 dB improvement in OSNR compared with the single-wavelength FD-UWOC system, which can achieve a longer transmission distance. An 80 m improvement in Jerlov II water quality, and an effective transmission distance of more than 100 m in Jerlov I and Jerlov IB water quality are achieved. These results provide some reference significance to the design of FD-UWOC system.关键词：FD-UWOC;Monte Carlo method;self-interference;backscattering;dual-wavelength
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发布时间：2023-08-14 - 摘要：The Angle of Arrival (AOA) fluctuation caused by oceanic turbulence is the critical factor affecting the performance of underwater communication and imaging systems. Based on the general Oceanic Turbulence Optical Power Spectrum (OTOPS), this paper derives analytical solutions for the full interval of the Wave Structure Function (WSF) and the AOA fluctuation variance of the Gaussian beam using the Rytov approximation method applicable to weak turbulence conditions. The approximate solutions of the above physical quantities and the Spatial Coherence Radius (SCR) in the asymptotic intervals of large spacing (ρ≫η, where ρ denotes spacing andη denotes Kolmogorov microscale) and small spacing (ρ≪η) are also discussed. The numerical results show that the existing results have a large deviation around the Fresnel ratio Λ0=1 when ρ≫η. On the basis of this, the relationship between AOA fluctuation variance andρ/η is also analyzed. In the asymptotic interval ρ≪η, the AOA fluctuation variance is almost constant. When in the interval ρ≈η, the AOA fluctuation variance decreases sharply. When in the asymptotic interval ρ≫η, the decline of the AOA fluctuation variance becomes gradually flat. The results derived in this paper are more accurate and applicable to a wider range. These results will enable a better study of the propagation properties of Gaussian beams in weak oceanic turbulence.关键词：AOA fluctuation;oceanic turbulence;Gaussian beams;Rytov approximation
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发布时间：2023-08-14 - 摘要：Underwater Wireless Optical Communications (UWOC) is an emerging high-speed underwater communication technology that has gradually attracted widespread attention in academia and industry due to its advantages of high transmission bandwidth, electromagnetic interference resistance, low power consumption, and small size. Although light has a larger attenuation in underwater transmission than acoustic wave, its transmission distance can still reach hundreds of meters, which is sufficient to meet the requirements for sensor data transmission. However, UWOC technology is still in an early stage of development, with most experiments being conducted only in laboratory water tanks. Therefore, unified performance testing models and methodologies are required due to different testing methods for UWOC. In order to objectively evaluate the performance of a UWOC system, this article attempts to propose the general testing method, model and evaluation indicators for UWOC systems, to promote the development of UWOC technology.关键词：UWOC;testing model;evaluation indicators;testing method;underwater testing
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发布时间：2023-08-14 - 摘要：The transmission characteristics of laser in four types of harbor water were studied using Monte Carlo method simulations for the characteristics of strong absorption and high scattering of water in marine harbors. The effects of water quality parameters and transmission distance on the optical signal power, impulse response and spot quality were quantified and analyzed at certain optical wavelengths, optical energies and divergence angles. The analysis shows that the attenuation characteristics of laser remain consistent as the attenuation length increases when the optical signal is transmitted in the four types of harbor waters. The rate of attenuation of the optical power also does not conform to the linear relationship described by Beer's law. Under the same water quality conditions, the width of the optical pulse, the size of the light spot increases with the attenuation length. However, when the attenuation length is transmitted from 20 to 30, the width of the optical pulse is almost unchanged, and the change in the amount of light pulse spreading is less than 1 ns with the size of the light spot increases continuously. In addition, at the same attenuation length, the light pulse and the spreading amount of light spot with the water quality attenuation coefficient increases and decreases.关键词：underwater wireless optical transmission;bule-green light;Monto Carlo;impulse response;light spot change
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发布时间：2023-08-14 - 摘要：In underwater optical communication systems, timely acquisition of distance information with the receiving end and high-speed communication are required. This paper proposes to integrate the monocular ranging function into the underwater blue-green laser communication system to realize the underwater optical communication ranging by integrating short-distance visual ranging and long-distance laser ranging. Using Monte Carlo method simulation, an underwater laser signal channel transmission model is established to simulate underwater laser spot images under different target sizes, distances and water qualities. We analyze the influence of these three factors on the accuracy of underwater monocular ranging. Considering the influence of spot diffusion and contrast reduction in simulated images on ranging accuracy, a monocular ranging algorithm is proposed that combines image enhancement and Zernike moments subpixel edge detection for small-sized underwater light source targets to improve the accuracy of the monocular ranging algorithm. Laboratory pool experiments were conducted to verify that the algorithm accuracy can meet the requirements.关键词：underwater laser communication and ranging;Monte Carlo method;small size target;image enhancement;subpixel edge detection
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发布时间：2023-08-14 - 摘要：In underwater mobile visible light communication systems, the received optical power varies significantly when the transmission distance changes due to the large intrinsic absorption of water. This paper proposes an underwater mobile visible light communication technology based on Gain Feedback Control (GFC), which expands the dynamic range of both communication distance and Field of View (FOV). At a moving speed of 0.13 m/s, we achieved real-time duplex video transmission with adjustable communication distances between 0.9~5.2 m, data rates of 5.0 Mbit/s, video pixels of 800×600, and Frames Per Second (FPS) greater than zero. Compared with the system without GFC, the dynamic range of communication distance and receiving FOV angle has expanded to 5.3 and 2.8 times, respectively. In order to further verify the performance of the system, we measured the average scintillation index, data transmission outage probability, and Bit Error Rate (BER) of the system at different moving speeds. Within the dynamic range of communication distance, as the moving speed increases, the average scintillation index and BER correspondingly increase. However, even when the moving speed reaches 0.83 m/s, which is the maximum speed of the system, communication remains uninterrupted. Our results indicate that the system has good robustness and has good potential underwater mobile communication applications.关键词：visible light communication;mobile communication;video communication;dynamic range
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发布时间：2023-08-14 - 摘要：Visible Light Communication (VLC) has become an effective underwater communication technology due to its advantages such as fast transmission speed and strong confidentiality. When light propagates underwater, it is prone to scattering, resulting in a decrease in the energy of light propagation with the increase of transmission distance. Therefore, improving the responsiveness of the receiving end is the key technology to achieve underwater VLC. This article first designs a new holographic waveguide focusing system for the front end of the detector, which can effectively improve the signal-to-noise ratio of underwater detectors. Then, we construct a low-cost antimony sulfide thin film detector with weak light detection capability. Based on the built VLC system, the experimental results show that the dark current of the receiver detector is only 10-7 A/cm2, with a 3 dB bandwidth of 220 kHz, a response of 0.2 A/W, and an external quantum efficiency of over 70% in the blue green light band. Therefore, the new antimony sulfide thin film detector combined with a holographic waveguide focusing system can achieve weak light detection of visible light, making it a very effective underwater visible light receiving system.关键词：underwater VLC;Sb2S3;detector;holographic grating;optical waveguide
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发布时间：2023-08-14
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