Underwater Communication System Research Articles

Underwater optical wireless communication system based on dual polarization states with optical code division multiple access: performance evaluation

Underwater optical wireless communication system based on dual polarization states with optical code division multiple access: performance evaluation

Energy efficiency optimization in a parallel relay-assisted UWOC system with simultaneous lightwave information and power transfer.

In this paper, we investigate the energy efficiency optimization for a parallel relay-assisted underwater wireless optical communication (UWOC) system with simultaneous lightwave information and power transfer (SLIPT) over an aggregate channel. In this system, relay nodes are equipped with energy harvesting devices, getting energy from the direct current component of the received signal transmitted by the source node. These nodes utilize the harvested energy to transmit the signal to the destination node with the decoding and forwarding strategy. The harvested energy for each relay node is derived by the Gauss-Laguerre quadrature formula and the outage probability is deduced by the Meijer-G function. Then, the system's energy efficiency can be calculated and an energy efficiency maximization problem is built up with respect to the bias current. We propose a three-level-iteration algorithm to solve this problem. In the first level, the Dinkelbach method is used to represent energy efficiency in a parametric subtractive form. In the second level, we use the penalty function method to convert the object function and constraint. In the third level, the objective function is transformed into a quadratic function by using a successive convex approximate method, thereby solving for the bias current. The effects of system parameters on energy efficiency are also analyzed. Theoretical results and Monte Carlo simulations suggest that employing the solved bias current can significantly improve the system's energy efficiency.

Performance analysis of OSSK-UWOC systems considering pointing errors and channel estimation errors.

In this paper, we present the bit error rate (BER) performance of the underwater wireless optical communication (UWOC) systems using the optical space shift keying (OSSK) on the gamma-gamma turbulent fading channel, which also considers pointing errors and channel estimation errors. Firstly, we develop the new expressions for the probability density function (PDF) based on the Gamma-Gamma distribution with error factors. Subsequently, we analyze the statistical characteristic of the difference in attenuation coefficients between two channels in the OSSK system, by which we provide analytical results for evaluating the average BER performance. The results show that the effective improvement of spectral efficiency (SE) and BER performance is achieved by rationally allocating the number of lasers and detectors in the system. The OSSK-UWOC system performs better when a narrow beam waist is used. Furthermore, the presence of channel estimation error brings the BER performance advantage to the system, and the system with a high channel estimation error (ρ = 0.7) shows a 4 dB improvement in signal-to-noise ratio (SNR) gain compared to the system with a low channel estimation error (ρ = 0.95). The findings in this paper can be used for the UWOC system design.

Adaptive double-loop coverage optimization of underwater wireless directional restricted sensor networks

Underwater Wireless Sensor Networks (UWSNs) play a crucial role in underwater communication system, in which node deployment is a complex problem. Most of the previous researches are based on all-direction underwater acoustic sensors. However, most of the sensors are in limited direction in practical systems. The deployment of directional sensors not only needs to consider its position adjustment, but also needs to accurately adjust its direction according to the sensing angle, sensing distance and other parameters in its sensing model, so it is difficult to achieve optimization with traditional algorithms. In this paper, we propose the Adaptive Heuristic Algorithm for UWSNs (AHAU) to solve this problem in underwater communication systems. AHAU features the addition of inner layer of adaptive parameter iteration to outer layer of global iteration. AHAU can more precisely adjust the direction of the sensor to achieve higher target coverage rate. The effectiveness and reliability of the proposed algorithm are verified by designing experiments. The results of experiments show that AHAU can achieve better adjustment effect under different parameter conditions to ensure the spatial coverage of UWSNs.

ОРГАНИЗАЦИЯ ПОДВОДНОЙ БЕСПРОВОДНОЙ СИСТЕМЫ СВЯЗИ

The article discusses underwater wireless communication systems. Research in the field of underwater optical wireless communication system will allow developing science, industry, to find solutions to defense tasks and emergencies, to carry out remote monitoring of environmental pollution of the underwater world and control underwater objects and equipment of oilrigs, to conduct underwater research and much more. The purpose of the work is to develop a classification of the principles of construction and organization of underwater wireless communication, taking into account modern achievements and development of technologies in the field of underwater wireless communication systems, to assess the strengths and weaknesses of underwater acoustic, radio frequency and optical communication systems. It is shown that the underwater optical wireless communication system has a great potential to enhance the traditional underwater acoustic communication system and underwater radio frequency communication system due to the high speed of information transmission, low latency, lower power consumption and compact size. To select the equipment and organize the communication channel, a generalized classification of an underwater optical wireless communication system has been developed, depending on the routing protocols used, on the configuration of the communication channel, on the optical properties of water, on the type of water in which the transmission channel is organized, on the mobility of underwater vehicles and the coverage area, on the type of modulation used, the method of underwater communication and from the factors affecting the organization of the communication channel.

Performance evaluation of a UOWC system based on the FRS/OCDMA code for different types of Jerlov waters.

In this work, the fixed right shift (FRS) code is utilized for the optical code division multiple access (OCDMA) technique in an underwater optical wireless communication (UOWC) system. Additionally, in this system, a 532nm laser diode (LD) source is employed to generate optical signals. The investigation encompasses an analysis of five distinct Jerlov water types, each exhibiting diverse chlorophyll concentrations. The performance of the proposed system is evaluated when each channel that is assigned a unique FRS code sequence carries different data rates (2.5, 5, and 10Gbps). Underwater (UW) ranges, bit error rate (BER), eye diagrams, and quality factor (Q-factor) are the performance metrics used to evaluate the system performance. The proposed UOWC-FRS/OCDMA system is simulated, and the obtained results show that the eye diagram openings close, the BER increases, and the Q-factor decreases as the data rate per each channel increases from 2.5 to 10Gbps, and the attenuation of water becomes higher. Moreover, the lower attenuation values caused by the Jerlov type I (JI) waterbody allow each channel to carry 10Gbps of data to propagate longer UW for a range of 35m with a log(BER) ≤-6.33 and Q-factor greater than 4.9. On the other hand, at the same values of BER and Q-factor, the shortest ranges of 12 and 5.15m are obtained for JII and JIII waters, respectively, where their attenuation coefficient values are 0.5297 (JII) and 1.8998 m -1 (JIII). Furthermore, as our model uses three channels, the overall achieved capacity is 3×10G b p s=30G b p s.

Underwater entanglement propagation of auto-focusing Airy beams.

In underwater wireless optical communication, orbital angular momentum (OAM) states suffer from turbulence distortions. This study aims to investigate the effectiveness of auto-focusing and OAM entanglement of the beams in reducing the turbulence effects. We implement the single-phase approximation and the extended Huygens-Fresnel principle to derive the detection probability of the entangled Airy beams under unstable oceanic turbulence. The results show that auto-focusing can protect the signal OAM mode and suppress modal crosstalks, while entangled OAM states can further enhance the resistance against oceanic turbulence around the focus position. The numerical analysis demonstrates that after the auto-focusing position, the beams evolve in completely opposite directions, indicating that the focal length should be modulated according to the length of a practical link to enhance received signals. These findings suggest that entangled auto-focusing vortex beams may be a desirable light source in underwater communication systems.

Design and experimental demonstration of underwater wireless optical communication system based on semantic communication paradigm.

Underwater wireless optical communication (UWOC) has been widely studied as a key technology for ocean exploration and exploitation. However, current UWOC systems neglect semantic information of transmitted symbols, leading to unnecessary consumption of communication resources for transmitting non-essential data. In this paper, we propose and demonstrate a deep-learning-based underwater wireless optical semantic communication (UWOSC) system for image transmission. By utilizing a deep residual convolutional neural network, the semantic information can be extracted and mapped into the transmitted symbols. Moreover, we design a channel model based on long short-term memory network and employ a two-phase training strategy to ensure that the system matches the underwater channel. To evaluate the performance of the proposed UWOSC system, we conduct a series of experiments on an emulated UWOC experimental platform, in which the effects of different turbidity channel environments and bandwidth compression ratios are investigated. Experimental results show that the UWOSC system exhibits superior performance compared to the conventional communication schemes, particularly in challenging channel environments and low bandwidth compression ratios.

Performance Evaluation of Maximum Ratio Combining Diversity Technology and Traditional System Based on Comprehensive Noise Analysis in Underwater Wireless Optical Communication

The maximum ratio combining (MRC) diversity technology has shown outstanding performance in overcoming the adverse effects of underwater wireless optical communication (UWOC) systems. However, its actual performance gain will be affected by the detection area and noise, which requires an in-depth analysis. In this paper, on the basis of fully considering the noises in the UWOC system, the performance of the MRC diversity technology is fairly and comprehensively studied by comparing it with two single-input–single-output (SISO) systems using a small aperture detection (SAD) scheme or a large-aperture detection (LAD) scheme through a Monte Carlo simulation and a formula analysis. The results show that the traditional belief that the MRC diversity scheme has consistently outperformed SISO systems may be misleading. When the thermal noise is dominant and the background noise is small, the LAD scheme performs better than the MRC diversity scheme with the same detection area. And in other cases, the MRC diversity scheme with the same detection area is always superior to the SISO systems. The conclusions obtained in this paper have a guiding significance for the practical application of UWOC.

Performance analysis of 3 × 10 Gb/s UOWC transmission system based on OCDMA using a DPS code

A new underwater optical wireless communication (UOWC) system utilizing optical code division multiple access (OCDMA) is proposed based on diagonal permutation shift (DPS) code. Different data rates of 2.5 Gb/s, 5 Gb/s, and 10 Gb/s are transmitted simultaneously in this model, where three channels are utilized, each is assigned with a distinct DPS code-sequence. Additionally, laser diodes operating in the green spectrum range are modulated to carry the OCDMA optical signals of each channel. Moreover, attenuation caused by different types of waterbodies are considered. These waterbodies include those who are located near harbors like harbor I (HA I) and harbor II (HA II), near the coast that are known as coastal sea (CS), inside sea water ‘pure sea (PS)’, and in clear oceans (CL). The performance of the UOWC utilizing OCDMA/DPS code system is evaluated through bit error rate (BER), quality factor , and eye diagrams. The accomplished results assure a successful transmission of the three channels underwater for ranges of 13 m for PS, 10 m for CL, 7.2 m for CS, 4.3 m for HA I, and 3 m for HA II with BER below 10-5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${10}^{-5}$$\\end{document} at data rate 10 Gb/s.

Coverage Enhancement of Light-Emitting Diode Array in Underwater Internet of Things over Optical Channels

The construction of the underwater Internet of Things (UIoT) is crucial to marine resource development, environmental observation, and tactical surveillance. The underwater optical wireless communication (UOWC) system with its large bandwidth and wide coverage facilitates the high-capacity information interconnection within the UIoT networks over short and medium ranges. To enhance the coverage characteristics of the UOWC system, an optimized lemniscate-compensated layout of light-emitting diode (LED) array is proposed in this paper, which can ameliorate the received optical power and reliability at the receiving terminal. Compared with traditional circular and rectangular layouts, the received optical power and bit error rate (BER) performance of the proposed system are analyzed based on the Monte Carlo simulation method. The analysis results show that the proposed LED array achieves a smaller peak power deviation and mean square error of the received optical power under three typical seawater environments. Furthermore, the proposed LED-array scheme supports a better BER performance of the UOWC system. For example, in turbid seawater with a transmission depth of 9.5 m, the BER of the proposed LED array layout is 1 × 10−7, which is better than the BER of 3.5 × 10−6 and 1 × 10−4 under the other two traditional light source layouts.

MTU2-Net: Extracting Internal Solitary Waves from SAR Images

Internal Solitary Waves (ISWs) play a pivotal role in transporting energy and matter within the ocean and also pose substantial risks to ocean engineering, navigation, and underwater communication systems. Consequently, measures need to be adopted to alleviate their negative effects and minimize linked risks. An effective method entails extracting ISW positions from Synthetic Aperture Radar (SAR) data for precise trajectory prediction and efficient avoidance strategies. However, manual extraction of ISWs from SAR data is time-consuming and prone to inaccuracies. Hence, it is imperative to develop a high-precision, rapid, and automated ISW-extraction algorithm. In this paper, we introduce Middle Transformer U2-net (MTU2-net), an innovative model that integrates a distinctive loss function and Transformer to improve the accuracy of ISWs’ extraction. The novel loss function enhances the model’s capacity to extract bow waves, whereas the Transformer ensures coherence in ISW’s patterns. By conducting experiments involving 762 image scenes, incorporating ISWs, from the South China Sea, we established a standardized dataset. The Mean Intersection over Union (MIoU) achieved on this dataset was 71.57%, surpassing the performance of other compared methods. The experimental outcomes showcase the remarkable performance of our proposed model in precisely extracting bow wave attributes from SAR data.

Bit error rate performance of underwater optical wireless communication with hybrid modulation

AbstractTurbulence effects can cause performance degradation for underwater optical wireless communication (UOWC) system. In this paper, a hybrid modulation (modulation–modulation, M–M) is presented to resist turbulence‐induced fading and improve the transmission performance of UOWC systems. The proposed differential phase shift keying‐multiple pulse position modulation (DPSK‐mPPM) is adopted as hybrid modulation to improve the bit error rate (BER) performance over UOWC turbulence channel of Gamma–Gamma distribution. Subsequently, the closed‐form average BER expressions of mPPM and hybrid DPSK‐mPPM modulation are derived and investigated, which are related to the oceanic turbulence parameters. The influence of the variation of anisotropy factor of ocean turbulence is analysed for the UOWC system over strong Gamma–Gamma turbulent channels. Finally, the numerical simulation results demonstrate the effectiveness of proposed DPSK‐mPPM to improve the BER performance compared to the traditional single modulation over UOWC channel under the same conditions. Furthermore, the work of this paper improves the practicality of the proposed DPSK‐mPPM scheme for underwater communication in complex oceanic environments.

Reference signal aided self-interference cancellation for in band full duplex underwater wireless optical communication

A novel self-interference cancellation method for in-band full-duplex (IBFD) underwater wireless optical communication (UWOC) system is proposed and experimentally verified. This method reduces the self-interference to its intrinsic noise level using a reference optical signal whose amplitude is opposite to the self-interference signal, together with a deep neural network to compensate for the nonlinear distortion enhanced by increased DC. The bit error rates (BERs) before and after self-interference cancellation at different data rates are tested and compared with the existed polarization-based cancellation scheme. Results presented in this paper show that more than 10 dB self-interference cancellation ratio can be achieved by the proposed scheme at 100 MHz signal rate, and outperforms the polarization-based scheme. With the assistance of the proposed method, a data rate of 100Mbps was achieved simultaneously at the uplink and downlink within IBFD based UWOC.

Bubbles-induced turbulence channel prediction mechanism based on machine vision in underwater wireless optical communication.

Bubbles-induced turbulence poses a significant challenge to the stability of underwater wireless optical communication (UWOC) system. Existing methods for understanding channel characteristics rely on the pilot information from the feed-back channel, which are ineffective and inaccurate due to the rapidly changing nature of the underwater channel. We propose a machine-vision-based channel prediction mechanism which contains three modules of motion judgment module, image processing module and scintillation index (SI) prediction module. The mechanism captures images of bubbles and calculates the bubble density. Subsequently, a relational function is applied to acquire the predicted SI which quantifies the impacts of bubbles on the channel. Experimental results validate the effectiveness of the proposed mechanism.

Study on performance of a relay-assisted UWOC system based on adaptive optics

To improve the performance of underwater wireless optical communication (UWOC) systems, we propose a relay-assisted UWOC system model based on adaptive optics (AO). The closed expressions of the scintillation index, composite channel probability density function, and outage probability of the Gaussian beam before and after AO compensation are derived using the extended Rytov theory and Meijer G-function. The performance variation of an UWOC system with different parameters is analyzed by simulation. The results show that AO correction can compensate for the distorted wavefront and significantly reduce the intensity fluctuation at the receiving end. The proposed system can efficiently alleviate channel fading, improving the outage probability performance of the UWOC system.

FrFT equalization for underwater sweep-spread communication system

In underwater acoustic channels, multipath propagation and Doppler frequency can distort the received signal and reduce system reliability. In order to effectively combat multipath interference, the Sweep-Spread Carrier (SSC) system using frequency swept signal is proposed, however, the SSC receiver performs well only when the maximum delay spread of path arrivals and the Doppler spread are moderate. In this paper, fractional Fourier transform (FrFT) is applied to channel equalization of the SSC system, which improves the ability to resist the Doppler effect and intersymbol interference (ISI). FrFT can simplify the channel characteristics by selecting an appropriate transform order. We analyze the FrFT equalizer in the SSC system under the zero forcing (ZF) criterion and minimum mean squared error (MMSE) criterion. Compared with typical nonlinear Turbo equalization, FrFT equalizer only requires lower complexity to achieve good performance. The numerical simulation results in bellhop and ray tracing channels and the results of the Wu-yuan Bay test channel show the high robustness of the proposed method in doubly dispersive channels.

A Novel Strategy for the Synthesis of High Stability of Luminescent Zero Dimensional-Two Dimensional CsPbBr3 Quantum Dot/1,4-bis(4-methylstyryl)benzene Nanoplate Heterostructures at an Atmospheric Condition.

Perovskite quantum dots (QDs), emerging with excellent bright-green photoluminescence (PL) and a large absorption coefficient, are of great potential for the fabrication of light sources in underwater optical wireless communication systems. However, the instability caused by low formation energy and abundant surface traps is still a major concern for perovskite-based light sources in underwater conditions. Herein, we propose ultra-stable zero dimensional-two dimensional (0D-2D) CsPbBr3 QD/1,4-bis(4-methylstyryl)benzene (p-MSB) nanoplate (NP) heterostructures synthesized via a facile approach at room temperature in air. CsPbBr3 QDs can naturally nucleate on the p-MSB NP toluene solution, and the radiative combination is drastically intensified owing to the electron transfer within the typical type-II heterostructures, leading to a sharply increased PLQY of the heterostructure thin films up to 200% compared with the pristine sample. The passivation of defects within CsPbBr3 QDs can be effectively realized with the existence of p-MSB NPs, and thus the obviously improved PL is steadily witnessed in an ambient atmosphere and thermal environment. Meanwhile, the enhanced humidity stability and a peak EQE of 9.67% suggests a synergetic strategy for concurrently addressing the knotty problems on unsatisfied luminous efficiency and stability of perovskites for high-performance green-emitting optoelectronic devices in underwater applications.

Channel characteristics of underwater optical communication system

Underwater communication technology has seen significant development in recent years, with a focus on finding efficient and secure techniques for exploring the underwater world. While acoustic and electromagnetic waves have limitations in water, the use of optical communication has become a focus of research due to its high bandwidth and low delay. Research has shown that blue and green lights are absorbed less than other wavelengths in water, making them suitable for underwater optical communication. In recent years, people have been working with optical communication in harsh environments. The optical system and the acoustic system have been combined to achieve certain development. Several high-speed underwater laser transmission systems have also been developed, with varying transfer rates and distances. This paper focuses on the theory of underwater optical systems and their communication channel characteristics.

Joint SIC and power allocation for a multi-user paired UWOC-NOMA system in a turbulence environment.

This paper proposes a staircase joint optimization scheme (SJOS) with alternating diagonal interference cancellation and power allocation in an underwater wireless optical communication system based on nonorthogonal multiple access (UWOC-NOMA) with the multi-user paired. The scheme employs the directional iteration to alternatively optimize the subproblems of the interference cancellation and the power allocation. Furthermore, a one-way sorting algorithm based on the alternating diagonal interference cancellation and power allocation subalgorithm based on the conjugate gradient method are presented to solve the two subproblems, respectively. Simulation results show that the algorithm effectively reduces the average outage probability of the system with fast convergence, even with an increase in the number of paired users.