Oceanic Turbulence Parameters Research Articles

Transmission characteristics of partially coherent pin-like optical vortex beams in oceanic turbulence

Based on the Rytov approximation theory, the analytical formulae for the mode detection probability and channel capacity of the partially coherent pin-like optical (PCPO) vortex beams propagating in oceanic turbulence are obtained. The effects of light source parameters and oceanic turbulence parameters on the transmission characteristics of the PCPO vortex beams are analyzed in detail by numerical simulations. According to numerical results, a larger spatial coherence length of the partially coherent source endows the beams with a superior channel capacity performance while accompanied by a decrease in transmission robustness. Meanwhile, PCPO vortex beam with greater phase modulation power parameter and longer wavelength is conducive to enhancing the transmission quality through oceanic turbulence. In addition, the channel capacity of the system can be effectively augmented with the increase of the dissipation rate of kinetic energy per unit mass of fluid, the anisotropy factor, the inner scale radius and the decrease of the mean square temperature dissipation rate, the temperature-salinity contribution ratio. The results also indicate that PCPO vortex beam is a better candidate than Gaussian vortex beam for long-distance transmission. This paper provides a theoretical reference for studying an underwater communication link using PCPO vortex beams as the transmission carrier.

Oceanic turbulence parameters recognition based on convolutional neural network

The distortion induced by ocean turbulence has a substantial impact on the propagation of light in water, posing challenges for applications including underwater wireless optical communications and submarine surveys. Obtaining accurate information about the properties of oceanic turbulence (OT), particularly the parameters describing OT, is crucial for addressing these challenges and enhancing the performance of such applications. In this paper, we propose a convolutional neural network (CNN) and validate its ability to recognize OT parameters. The physical quantities of oceanic turbulence collectively influence the formation and strength of turbulence. We recognize the dissipation rate of temperature variance χ T and the turbulent kinetic energy dissipation rate ɛ, taking into account various balance parameter ω, transmission distance z. Furthermore, in order to simultaneously recognize χ T and ɛ, we enhanced the existing network by modifying the output structure, resulting in a dual-output architecture that facilitates concurrent classification of both χ T and ɛ. Our method for classifying turbulence parameters will contribute to the field of underwater wireless optical communication and promote its further development.

Effects of system pointing error and turbulence media anisotropy on the propagation of a perfect Laguerre-Gaussian vortex beam

We investigate the influences of the system pointing errors, oceanic turbulence, and transceiver parameters on the perfect Laguerre-Gaussian(PLG) in an optical propagation system with M-order quadrature amplitude modulation(M-QAM). The model of the ABER for turbulent seawater propagation systems with pointing errors is created in Rytov approximation. The evolution of ABER under different modulation order M of QAM, signal-to-noise ratio (SNR) of the transceiver systems, and turbulent parameters of seawater shows with the increase of system pointing errors, there is a pointing error value corresponding to the conversion of modulation mode from 4-QAM to256-QAM of the system with the lowest ABER, and this conversion point is related to the aperture value of the transceiver of the system. The propagation systems with high-order modulation QAM and large-aperture optical transceivers have higher tolerance of system pointing error than those of low-order modulation QAM and small-aperture transceivers. The pointing error tolerance of the system with low PLG's radial order, low OAM topological charge, and high SNR of transceiver is larger than that of the system with high PLG's radial order, high OAM topological charge, low SNR of transceiver system. The PLG vortex has a better tolerance to pointing errors than the Bessel Gaussian beam.

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.

Propagation of hollow higher-order cosh-Gaussian beam in oceanic turbulence

The averaged received intensity of hollow higher-order cosh-Gaussian (HHOCG) beam propagating in oceanic turbulence is derived based on extended Huygens–Fresnel integral. In detail, the effect of beam parameters and oceanic turbulence parameters on the received intensity is analyzed. Interestingly, beam has a focusing nature along propagation. Our results indicate that received intensity distribution is not affected from the variation in source field parameters. Beam size at the receiver plane can vary according to the changes in turbulence nature. Accordingly, the provided results will contribute to the improvement of both underwater optical communication and imaging systems.

Propagation of a Lorentz Non-Uniformly Correlated Beam in a Turbulent Ocean

We study the propagation characteristics (spectral intensity and degree of coherence) of a new type of Lorentz non-uniformly correlated (LNUC) beam based on the extended Huygens–Fresnel principle and the spatial power spectrum of oceanic turbulence. The effects of the oceanic turbulence parameters and initial beam parameters on the evolution propagation characteristics of LNUC beams are studied in detail by numerical simulation. The results indicate that such beams exhibit self-focusing propagation features in both free space and oceanic turbulence. Decreasing the dissipation rate of kinetic energy per unit mass of fluid and the Kolmogorov inner scale, or increasing the relative strength of temperature to salinity undulations and the dissipation rate of mean-square temperature of the turbulent ocean tends to increase the negative effects on the beams. Furthermore, we propose a strategy of increasing the beam width and decreasing the coherence length, to reduce the negative effects of the turbulence.

Evolution behavior of the coherent vortex dipole in oceanic turbulence.

The propagation of a Gaussian Schell-model (GSM) beam with a coherent vortex dipole (CVD) through oceanic turbulence is studied in detail. The creation and annihilation of the CVDs occur with propagation, which is similar to the case of atmospheric turbulence. However, the appearance and vanishment of a coherent vortex may occur by varying the propagation distance, oceanic turbulence parameters, or beam parameters, which is different from the case of atmospheric turbulence. The stronger the oceanic turbulence, the faster the evolution process of the CVD carried by GSM beams.

Effect of oceanic turbulence with anisotropy on the propagation of multi-sinc Schell-model beams

Using the extended Huygens-Fresnel principle, the expressions for the cross-spectral density function of both the circular and square multi-sinc Schell-model (MSSM) beams propagating in an anisotropic oceanic turbulent medium have been derived respectively. Based on the expression, the effects of the oceanic turbulence parameters and the anisotropic factor on the intensity and coherence properties of such beams are explored explicitly. By comparative analysis with the case in free space, it is shown that the adjustable multi-ring and square lattice intensity structures of the MSSM beam in ocean are shaped to be circular flat-topped, square flat-topped or Gaussian-like due to different strength of turbulence. The unique intensity patterns can be maintained for a relatively long propagation distance as the anisotropic factor increases. Furthermore, it is found that the turbulent parameters including the salinity and temperature contribution factor, rate of dissipation of turbulent kinetic energy and rate of dissipation of the mean squared temperature have less impacts on the propagation behaviors of the MSSM beam in anisotropic oceanic turbulence in comparison to the corresponding isotropic case. The results presented here have potential applications in oceanic optical telecommunication links.

Multi-Gaussian correlated Hankel-Bessel beam properties in anisotropic oceanic turbulence.

We introduce the model of a multi-Gaussian correlated Hankel-Bessel (MGCHB) beam generated by a multi-Gaussian Shell-model source and investigate the properties of the beam in anisotropic oceanic turbulence. Under Rytov approximation, the detection probability of the MGCHB beam and the channel capacity with MGCHB beams are derived; both the influence of oceanic turbulence and initial beam parameters on them are discussed by numerical simulations. The results show that the increase of the dissipation rate of kinetic energy per unit mass of fluid, the anisotropic coefficient, and the inner scale factor, as well as the decrease of the dissipation rate of mean-squared temperature and the temperature-salinity contribution ratio, can significantly improve the detection probability and the channel capacity. The results also indicate that the MGCHB beam is a better candidate than an Airy vortex beam for mitigating the influence of oceanic turbulence. Furthermore, smaller topological charge and larger orbital angular momentum modes number are beneficial to improve the detection probability and channel capacity, respectively. Moreover, the performance of the MGCHB beam with longer wavelength, smaller beam index, and larger transverse coherence width is conducive to enhancing the transmission quality through oceanic turbulence.

Scintillation and BER analysis of cosine and cosine-hyperbolic-Gaussian beams in turbulent ocean.

Effects of source beam, link, and oceanic turbulence parameters on the scintillation index and bit error rate (BER) performance of cosine (cos) and cosine-hyperbolic (cosh) Gaussian light beams have been investigated in order to improve wireless optical communication link performance in oceanic turbulence. The Nikishov and Nikishov power spectrum of oceanic water and extended Huygens Fresnel principle were used in our evaluations; the results were obtained via MATLAB. The scintillation index and BER were examined versus oceanic turbulence parameters, which are the rate of dissipation of mean-square temperature, the ratio of temperature and salinity contributions to the refractive index spectrum, and the dissipation rate of kinetic energy per unit fluid mass of fluid. Further, the scintillation index and BER are investigated against the source size, propagation distance, and complex displacement parameters of cos- and cosh-Gaussian beams. This study aimed to select the suitable sinusoidal beam to be employed in order to increase the performance of underwater wireless optical communication systems operating in oceanic turbulence.

Research on Hypergeometric-Gaussian Vortex Beam Propagating under Oceanic Turbulence by Theoretical Derivation and Numerical Simulation

In this paper, we use two methods to research the propagation characteristics of a Hypergeometric-Gaussian (HyGG) vortex beam under oceanic turbulence. One is numerical calculation based on the Rytov approximation theory, where the theoretical detection probability equation of the HyGG vortex beam propagating through oceanic turbulence is derived. The other is numerical simulation based on random phase screens model of oceanic turbulence, where the influences generated by oceanic turbulence on the phase and intensity of the propagation beam as well as the propagation of the beam through several independent phase screens, kept at the same distance, have the same effect. The effects of oceanic turbulence parameters and initial beam parameters on the detection probability of the HyGG vortex beam at the receiver are discussed. The results of theoretical derivation are well in agreement with those of numerical simulation, which demonstrated that the numerical simulation method could effectively simulate the complex theoretical derivation. Both results show that with higher dissipation rate of kinetic energy per unit mass of fluid, smaller dissipation rate of mean-squared temperature and lower temperature-salinity contribution ratio comes the better detection probability. Meanwhile, a HyGG vortex beam with smaller topological charge and longer wavelength has a superior turbulent resistance property. It provides a promising way to estimate the propagation characteristics of the optical beams in an underwater environment.

Spectral properties of partially coherent chirped Airy pulsed beam in oceanic turbulence

Spectral shifts and spectral intensities of partially coherent chirped Airy pulsed (PCCAP) beams propagating through oceanic turbulence are studied, where spectral properties of partially coherent chirped Gaussian pulsed (PCCGP) beams are also compared. The effects of optical parameters and oceanic turbulence parameters on spectral shifts at different observation positions are mainly discussed. It is shown that the spectral shift of PCCAP beam is richer than that of PCCGP beam, and there exists some critical positions for PCCAP beams where the spectral red-shift reaches its maximum. The spectral red-shift increases with increasing chirped parameter, correlation length or decreasing pulse duration. However, the increasing of spectral red-shift is accompanied by increasing dissipation rate of turbulence kinetic energy in unit mass liquid or decreasing relative intensity of temperature and salinity fluctuations, mean square temperature dissipation rate. A physical explanation of rapid spectral transition is also made.

Average intensity of astigmatic hyperbolic sinusoidal Gaussian beam propagating in oceanic turbulence

We derive the received intensity of astigmatic hyperbolic sinusoidal Gaussian(AHSG) beam propagating through oceanic turbulence. Huygens–Fresnel integral is evaluated to reach the expression at the receiver side. Effect of variations on turbulence parameters such as the rate of dissipation of the mean square temperature, the rate of dissipation of the turbulent kinetic energy per unit mass of fluid, and relative strength of the temperature and salinity fluctuations are examined. We observe that beam has a view having rings at close range but beam evolves into circular shape at a short/long distance depending on the parameters of oceanic turbulence. This evolution occurs faster when the rate of dissipation of the mean square temperature raises. We hope that our results will be used in underwater communication, imaging or range measurement applications.

Analysis of M-QAM Modulated Underwater Wireless Optical Communication System for Reconfigurable UOWSNs Employed in River Meets Ocean Scenario

In this paper, the bit error rate (BER) performance of underwater wireless optical communication system employing with M-ary quadrature amplitude modulation is proposed for underwater optical wireless sensor networks (UOWSN) in river meets ocean scenario. The underwater channel degradation effects such as absorption, scattering and oceanic turbulence is taken into account. The oceanic turbulence is modelled by the Gamma-Gamma distribution. The first time, we proposed re-configurable UOWSN for the real time scenario of the river meets the ocean and derived the novel closed form analytical BER expressions of the proposed system over Gamma-Gamma turbulence with attenuation effects. The impact of oceanic turbulence parameters such as the variations of temperature, kinetic energy, viscosity, salinity, link range and the water type of system performance is investigated for river water, mixed water (river and ocean water) and ocean water. The proposed system and the related analysis will be highly useful in UOWSN and the Internet of underwater thing (IoUT) applications.

Outage probability and channel capacity of an optical spherical wave propagating through anisotropic weak-to-strong oceanic turbulence with Málaga distribution.

The influence of anisotropic weak-to-strong oceanic turbulence on the performance of underwater optical communication (UWOC) systems is investigated in this paper. The Málaga distribution fading model is used to model the statistical distribution of a spherical wave propagating through anisotropic oceanic turbulence, which is a versatile model of weak-to-strong turbulence. First, the scintillation index for a spherical wave propagating in oceanic turbulence is formulated, and closed-form expressions for the outage probability and average channel capacity of the UWOC systems are then proposed in terms of Meijer's G function. The simulation results demonstrate that both the outage probability and the average channel capacity strongly depend on the parameters of oceanic turbulence, such as the ratio of temperature to the contribution of salinity to the refractive index spectrum, the rate of dissipation of kinetic energy per unit mass of fluid, and the rate of dissipation of mean-squared temperature; they are also related to system parameters such as wavelength and aperture diameter. Numerical results are provided to verify the accuracy of our proposed expressions for outage probability and average channel capacity, and perfect agreement is observed.

Influence of Oceanic Turbulence on the Performance of Underwater Quantum Satellite Communication

Oceanic turbulence is one of the important factors that affect the transmission of quantum optical signals in the seawater medium. However, up to now, none research on the influence of oceanic turbulence on the parameters of quantum communication channel is in progress. In order to fill such vacancies, we simulate in this paper the relationship of oceanic turbulence parameters to the optical wave structure function and the optical wave spatial coherence length to acquire the relationship between the oceanic turbulence intensity and oceanic turbulence parameters. Then, the relationships between the oceanic turbulence parameters and the channel entanglement, the bit-flip channel capacity, and the channel error rate are respectively established and simulated. The simulation results provide a reference for underwater quantum communication with the influence of oceanic turbulence.

Average BER performance of rectangular QAM-UWOC over strong oceanic turbulence channels with pointing error

We theoretically analyze the average bit error rate (ABER) performance of underwater wireless optical communication (UWOC) systems using rectangular quadrature-amplitude modulation (QAM) over strong oceanic turbulence channels with pointing error. The strong oceanic turbulence channel is assumed to be a gamma-gamma model. The close-form expression for the ABER is derived by using the Meijer’s G-function. Based on this expression, various effects of system parameters, including QAM scheme, link distance, diameter aperture, ratio of source beam width to aperture radius, and four oceanic turbulence parameters on ABER performance are taken into account. Simulation results show that applying a smaller rectangular QAM dimension and link distance, or a larger aperture diameter and the ratio of beam width to aperture radius can improve the UWOC quality significantly. The contributions of four oceanic turbulence parameters also need to be considered in practical UWOC applications. The results reported in this paper will be benefit to design UWOC systems.

Application of adaptive optics on bit error rate of M-ary pulse-position-modulated oceanic optical wireless communication systems

An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.

Effect of anisotropy on performance of M-ary phase shift keying subcarrier intensity-modulated optical wireless communication links operating in strong oceanic turbulence

In strong oceanic turbulence, the performance of M-ary phase shift keying subcarrier intensity-modulated optical wireless communication (OWC) links is investigated in terms of the bit-error-rate (BER) by considering the effect of anisotropy of the oceanic channel. To calculate the BER of the OWC link, a gamma–gamma statistical channel model is adopted. The extended Huygens–Fresnel principle and the asymptotic Rytov theory are used to obtain the received optical power and the large-scale and small-scale log-intensity variances, respectively. Our graphical illustrations include the BER versus anisotropic factor for various system parameters such as the modulation order, filter bandwidth, link distance, peak amplitude of each subcarrier and the oceanic turbulence parameters.

Radial phased-locked multi-Gaussian Schell-model beam array and its properties in oceanic turbulence

The radial phased-locked multi-Gaussian Schell-model (MGSM) beam array composed by the N MGSM beamlets is first given to describe a new laser array. The evolution properties of radial phased-locked MGSM beam array in free space and oceanic turbulence are discussed in detail. Based on the extended Huygens-Fresnel principle, the MCF and the effective size of radial phased-locked MGSM beam array in oceanic turbulence are derived. The effects of beam parameters and the oceanic turbulence parameters on the spreading and spectral degree of coherence of radial phased-locked MGSM beam array propagating in oceanic turbulence are investigated by using numerical examples. This research may be useful in underwater optical wireless optical communication.