An underwater optical wireless communication method based on the correlation of the flickering characteristics of the turbulence-attenuation coupling effect

Abstract

The application discloses an underwater optical wireless communication method based on a turbulent flow-decay coupling effect correlation flicker characteristic, and comprises the following steps: combining a decay light field and a spatial distribution model of refractive index fluctuation under no turbulent disturbance, and constructing a unified representation turbulent flow and decay coupling framework; based on the unified representation turbulent flow and decay coupling framework, calculating light field statistical characteristics of an optical signal after propagating in a seawater channel, wherein the light field statistical characteristics comprise a spatial wave structure function and a flicker index; according to the light field statistical characteristics, combining underwater channel characteristics and a detection range of a receiving end, obtaining turbulent channel design parameters and realizing underwater optical wireless communication through the turbulent channel. The application fills the blank of the prior art which ignores the nonlinear coupling effect between seawater turbulent flow and decay effect, and applies the method to the design of key parameters of a UOWC system.

Description

Technical Field

[0001] This invention belongs to the technical field of optical communication, specifically relating to an underwater optical wireless communication method based on the scintillation characteristics associated with the turbulence-attenuation coupling effect. Background Technology

[0002] In recent years, with the deepening of marine activities such as marine exploration, resource development, and environmental monitoring, the demand for high-speed and reliable underwater wireless communication technology has become increasingly urgent. Underwater optical wireless communication (UOWC) technology, with its advantages of high bandwidth, low latency, and resistance to electromagnetic interference, has become a key core technology in the field of marine communication.

[0003] When optical signals propagate in seawater, their transmission performance is simultaneously constrained by the signal scintillation effect caused by ocean turbulence and the attenuation effect of seawater on light energy, posing a significant challenge to the design and deployment of UOWC systems. In the field of turbulence channel modeling, existing research largely draws upon mature turbulence theories from atmospheric optical communication, using statistical models such as the Nikishov model and Oceanic Turbulence Optical Power Spectrum (OTOPS) to analyze the scintillation index and phase perturbation phenomena caused by turbulence. However, these models generally neglect the attenuation effect of seawater when analyzing light intensity scintillation characteristics, failing to consider the nonlinear coupling interaction between the attenuation process and turbulence perturbation. This leads to significant deviations between the channel characteristics calculated by the models and the actual channel characteristics in turbid coastal waters where attenuation effects are significant, thus failing to provide a reliable basis for the parameter design of UOWC systems.

[0004] Among other related prior art, the application No. 2023111771238, entitled "An Analysis Method for the Influence of Gaussian Beam Propagation in Anisotropic Plasma Turbulence," discloses an analysis method for the influence of Gaussian beam propagation in anisotropic plasma turbulence. It addresses the plasma turbulence scenario during the reentry of hypersonic vehicles, solving the "blackout" problem in aerospace communications, but does not consider the coupling effect of seawater attenuation and turbulence. The application No. 2025117368678, entitled "A Turbulence Compensation Method for Atmospheric Laser Communication Based on a Novel Kolmogorov-Zakharov Model," discloses an atmospheric laser communication turbulence compensation method based on the Kolmogorov-Zakharov model. It is designed for atmospheric laser communication scenarios and cannot adapt to the strong attenuation characteristics of seawater. It also does not involve the analysis of the coupling effect between attenuation and turbulence.

[0005] In summary, existing technologies cannot accurately characterize the transmission characteristics of optical signals in complex marine environments, resulting in insufficient communication reliability of the UOWC system when deployed in actual turbid waters. Summary of the Invention

[0006] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide an underwater optical wireless communication method based on the scintillation characteristics associated with the turbulence-attenuation coupling effect. This method fills the gap in the prior art by ignoring the nonlinear coupling effect between seawater turbulence and attenuation, and is applied to the design of key parameters of the UOWC system.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an underwater optical wireless communication method based on the scintillation characteristics associated with the turbulence-attenuation coupling effect, comprising the following steps:

[0009] S1. By combining the spatial distribution model of the attenuated optical field and refractive index fluctuation under turbulent disturbance, a unified framework for characterizing the coupling of turbulence and attenuation is constructed.

[0010] S2. Based on a unified framework for characterizing turbulence and attenuation coupling, calculate the statistical characteristics of the optical field after the optical signal propagates in the seawater channel, wherein the statistical characteristics of the optical field are at least the scintillation index.

[0011] S3. Based on the statistical characteristics of the optical field, combined with the underwater channel characteristics and the detection range of the receiver, obtain the design parameters of the turbulence channel and realize underwater optical wireless communication through the turbulence channel.

[0012] As a preferred technical solution, step S1 includes the following steps:

[0013] Based on the complex amplitude of the optical field of a standard Gaussian beam, the light intensity attenuation model corresponding to the seawater medium with an attenuation coefficient of c is introduced using the Beer-Lamber attenuation law to obtain the attenuated optical field without turbulence disturbance.

[0014] Determine the spatial distribution model of refractive index based on the ocean turbulent power spectrum. ,

[0015] The Rytov approximation of the spatial distribution model of the attenuated optical field and refractive index fluctuations is calculated. Combined with the first-order perturbation of the optical field by the turbulent medium, the optical field statistics at the receiver are calculated, and a unified framework for characterizing the coupling between turbulence and attenuation is constructed, as shown in the following equation:

[0016] ,

[0017] in, For the distance of transmission The radial distance vector from the receiver to the center of the light spot. The random amplitude representing the refractive index fluctuation. Represents the wavenumber of light in a vacuum. Represents the spatial wave vector of turbulence. Let be a two-dimensional coordinate vector on a horizontal plane perpendicular to the z-axis. This represents the complex path amplitude weighting parameter. Let the integral variable describe the distance, and , The substitution parameter represents the integral variable of distance. The distance between two observation points in the three-dimensional light field space.

[0018] As a preferred technical solution, the attenuated optical field under turbulence-free conditions is as follows: .

[0019] As a preferred technical solution, the spatial distribution model of the refractive index As shown in the following formula:

[0020] ,

[0021] in, The random amplitude representing the refractive index fluctuation. It is a two-dimensional coordinate vector on a horizontal plane perpendicular to the z-axis.

[0022] As a preferred technical solution, the optical field statistics on the receiving end include two points in the three-dimensional optical field space. and The two light field statistics between them are as follows:

[0023] ,

[0024] in, For the integral kernel of amplitude fluctuation, For phase fluctuation integration kernel, For attenuation term, The substitution parameter represents the distance integral variable, and c is the attenuation coefficient.

[0025] As a preferred technical solution, the point on the receiving end The flicker index is given by the following formula:

[0026] ,

[0027] Among them, the flicker index Characterized by the distance of light signal propagation The radial distance vector to the center of the light spot is The degree of light intensity fluctuation at a point, and Let represent the received light intensity and its squared expected value, respectively. This indicates the real part operator. and Let be the light field statistics of two points in a three-dimensional light field space. It is the spatial power spectral density of the refractive index fluctuations in an isotropic turbulent medium. and Let F represent the diffraction factor and normalized curvature parameter of the Gaussian light wave, respectively, which are related to the propagation distance. ( ) represents the zeroth-order modified Bessel function. Represents the wavenumber of light in a vacuum. Represents the space wave number of turbulence. The substitution parameter represents the integral variable of distance, where r represents the radial distance from the receiver to the center of the light spot. is the attenuation term, and c is the attenuation coefficient.

[0028] As a preferred technical solution, the scintillation index includes the axial scintillation index of the receiver and the aperture-average scintillation index. The axial scintillation index is the scintillation index at the center of the light spot at the receiver, and the aperture-average scintillation index is the average scintillation index calculated based on the receiver aperture size.

[0029] As a preferred technical solution, a space wave structure function is included to describe the mean square error of phase fluctuations between two different points at the receiver. The calculation process incorporates attenuation and amplification correction terms corresponding to the seawater attenuation effect, resulting in the following formula:

[0030] ,

[0031] in, The distance between two observation points in the three-dimensional light field space. Represents the wavenumber of light in a vacuum. Represents the space wave number of turbulence. Where c is the propagation distance of the optical signal, and c is the attenuation coefficient. It is the spatial power spectral density of the refractive index fluctuations in an isotropic turbulent medium. ( ) represents the zeroth-order modified Bessel function. This represents the amplification correction factor for the effect of seawater attenuation on turbulent light intensity scintillation.

[0032] As a preferred technical solution, step S2 includes calculating the space wave structure function based on the OTOPS turbulent power spectrum to obtain the plane wave expression coupled with the attenuation effect of the OTOPS turbulent power spectrum. The plane wave expression follows a quadratic law in the near field and a 5 / 3 power law in the far field. The near field is... The range that is much smaller than the boundary threshold, the far field is The range is much larger than the dividing threshold.

[0033] As a preferred technical solution, step S3 includes:

[0034] The range of DC bias voltage is determined based on the statistical characteristics of the optical field. The DC bias voltage is used to control the light source to emit a signal. The optical signal is received by the receiving end through the underwater channel. The light intensity range of the optical signal is within the detection range of the receiving end. The receiving end demodulates the optical signal.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) This invention incorporates the optical attenuation phenomenon described by the Beer-Lambert law into the Rytov approximation, and for the first time constructs a system architecture that can uniformly characterize the coupling effect of turbulence and attenuation. This architecture provides a complete technical foundation for accurately analyzing the statistical characteristics of optical fields in complex ocean channels.

[0037] (2) Based on the coupling effect analysis framework, this invention proposes a method for calculating the optical field statistical characteristics of the OTOPS ocean turbulence power spectrum, which can obtain accurate calculation results of axial scintillation index, aperture average scintillation index and space wave structure function. It adapts to the changes of different marine environmental parameters such as temperature, salinity and energy dissipation rate, and provides an efficient and accurate tool for predicting the channel characteristics of UOWC system.

[0038] (3) This invention deeply integrates the coupling effect analysis results with the parameter design of the DCO-OFDM system, and proposes a method for determining the range of DC bias voltage based on the scintillation index. This method can ensure that the received light intensity is always within the safe detection range of the photodetector and effectively resist nonlinear distortion caused by high-intensity signal scintillation. Simulation results show that the method of this invention can significantly reduce the bit error rate of the UOWC system in high-attenuation waters and greatly improve the transmission reliability of communication links in complex marine environments. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart illustrating the analysis of scintillation caused by the turbulence-attenuation coupling effect in an embodiment of the present invention.

[0041] Figure 2This is a flowchart of the DCO-OFDM communication system processing of the DC bias voltage setting method according to an embodiment of the present invention;

[0042] Figure 3 This is a schematic diagram illustrating the variation of the scintillation index with the attenuation coefficient in an embodiment of the present invention;

[0043] Figure 4 This is a schematic diagram illustrating the variation of the scintillation index with propagation distance in an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram illustrating the change of the scintillation index with temperature according to an embodiment of the present invention;

[0045] Figure 6 This is a schematic diagram illustrating the change of scintillation index with salinity in an embodiment of the present invention.

[0046] Figure 7 This is a schematic diagram illustrating the change of scintillation index with temperature dispersion in an embodiment of the present invention;

[0047] Figure 8 This is a schematic diagram illustrating the change of the scintillation index with energy dissipation rate in an embodiment of the present invention;

[0048] Figure 9 The simulation results are for the average scintillation index of the aperture in an embodiment of the present invention;

[0049] Figure 10 The simulation results show the bit error rate (BER) of the system in this embodiment of the invention. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0051] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0052] Please see Figure 1 This embodiment provides an underwater optical wireless communication method based on the scintillation characteristics associated with the turbulence-attenuation coupling effect, including the following steps:

[0053] S1. By combining the spatial distribution model of the attenuated optical field and refractive index fluctuation under turbulent disturbance, a unified framework for characterizing the coupling of turbulence and attenuation is constructed.

[0054] The complex amplitude of the optical field of a standard Gaussian beam is:

[0055]

[0056] in, For transmission distance, Let be the radial distance vector from the receiver to the center of the light spot, and define . , , The imaginary unit, Represents the wave number of light, where For wavelength, and Let represent the initial beam waist radius and the initial wavefront curvature radius of the Gaussian light, respectively, and define the function... .

[0057] According to Beer-Lambert's attenuation law, when light passes through an attenuation coefficient of... When the medium is , its amplitude becomes:

[0058]

[0059] Furthermore, according to the Rytov approximation, the first-order perturbation of the optical field by the turbulent medium can be expressed as:

[0060]

[0061] in, Let be a two-dimensional coordinate vector on a horizontal plane perpendicular to the z-axis. The spatial distribution of refractive index can be expressed in the form of a two-dimensional Riemann-Stilgers integral as follows:

[0062]

[0063] in, The random amplitude representing the refractive index fluctuation. It is the turbulent space wave vector, and the turbulent space wave number is defined. .

[0064] Using formulas (1)-(4), we can obtain:

[0065]

[0066] in, This represents the complex path amplitude weighting parameter.

[0067] Based on equation (5), it can be seen that the receiver receives the statistical quantity of the light field after the light field disturbance, that is, the calculation of two points in the three-dimensional light field space. and The two light field statistics are defined as follows:

[0068]

[0069] in, Represents coordinate points and The inner product, Indicates the conjugate symbol.

[0070] In particular, to simplify the above formula (6), the following two variables are defined:

[0071]

[0072] in, Let the integral variable describe the distance, and .

[0073] Then, proceed from arrive By substitution of variables, we can obtain:

[0074]

[0075] Can and Simplified to:

[0076]

[0077] in, For the integral kernel of amplitude fluctuation, This is the phase fluctuation integral kernel.

[0078]

[0079] in, It is the spatial power spectral density of the refractive index fluctuations in an isotropic turbulent medium. and Let F represent the diffraction factor and normalized curvature parameter of the Gaussian light wave, respectively, which are related to the propagation distance. Represents the zeroth-order modified Bessel function, with centroid coordinates. relative coordinates , .

[0080] S2. Based on a unified framework for characterizing turbulence and attenuation coupling, calculate the statistical characteristics of the optical field after the optical signal propagates in the seawater channel, wherein the statistical characteristics of the optical field are at least the scintillation index.

[0081] In step S2, the point on the receiving end The flicker index is:

[0082]

[0083] in, The operator represents the real part operator, and the exponent is blinked. Characterized by the axial propagation distance of The radial distance vector to the center of the light spot is The degree of light intensity fluctuation at a point, It is the spatial power spectral density of the refractive index fluctuations in an isotropic turbulent medium. and Let F represent the diffraction factor and normalized curvature parameter of the Gaussian light wave, respectively, which are related to the propagation distance. ( ) represents the zeroth-order modified Bessel function.

[0084] when At that time, equation (13) corresponds to the axial scintillation index, the value of which is:

[0085]

[0086] This embodiment introduces an attenuation term. The radius of the receiving end can then be obtained as The aperture-average scintillation index, i.e.:

[0087]

[0088] in, Therefore, under the same conditions, the average scintillation index of the receiver aperture and the axial scintillation index can be converted. When it approaches 0, equation (15) will degenerate into (14).

[0089] Because equations (14) and (15) affect The attenuation term in the integral Since it is always greater than or equal to 1, the attenuation effect significantly increases the scintillation index of turbulence.

[0090] Furthermore, the spatial wave structure function (WSF) can be used to describe two different points at the receiver. and The mean square error of the phase fluctuations between them is defined as:

[0091]

[0092] Among them, the distance between two observation points in the three-dimensional light field space .

[0093] Substituting equation (11) into (16), we can obtain the formula for calculating the plane wave WSF of coupled turbulence and attenuation effect:

[0094]

[0095] Thus, this embodiment is able to calculate the numerical values ​​of light intensity scintillation and phase distortion caused by any form of ocean turbulence power spectrum based on a unified system framework for analyzing the correlation scintillation characteristics of turbulence-attenuation coupling effects.

[0096] Based on the above unified framework for characterizing the coupling of turbulence and attenuation, the optical field fluctuation phenomenon at the receiver end coupled with the coupling turbulence and attenuation effects can be analyzed using the currently mainstream OTOPS turbulence power spectrum.

[0097] The OTOPS turbulent power spectrum can be expressed as:

[0098]

[0099] in, The values ​​represent the effects of temperature, salinity, and their coupling effect on the turbulent power spectrum, respectively. A and B are the weighting factors for the effects of temperature and salinity on the refractive index, respectively. It is the Obukhov-Korsin constant. Energy dissipation rate, For Kolmogorov microscale, These represent the dissipation rates under each mode j. Let be a dimensionless parameter determined by Prandtl's number and Schmidt's number, and It can be calculated using the TEOS-10 toolbox.

[0100] This embodiment substitutes equation (18) into equation (14) based on the OTOPS turbulent power spectrum and calculates the power spectrum related to the OTOPS turbulent power spectrum. Integrating this equation yields the following expression for the axial scintillation exponent:

[0101]

[0102] Furthermore, the following formula can be used to calculate equation (19) with respect to... Integrals:

[0103]

[0104] The receiver axial scintillation index, obtained from the coupled turbulence and attenuation effects, is as follows:

[0105]

[0106] in, , and Let represent the beta function and the bivariate confluence hypergeometric function, respectively.

[0107] In particular, for plane waves and spherical waves The above equation can be simplified as follows:

[0108]

[0109] in: It is a standard confluence hypergeometry function.

[0110] On the other hand, substituting equation (18) into equation (15), we can obtain the aperture-average scintillation index as follows:

[0111]

[0112] , , , ;

[0113] in, This indicates that the signal propagation distance is The receiver aperture is The aperture-average scintillation index associated with mode j, These represent temperature, salinity, and temperature-salinity, respectively. This represents the turbulence coefficient associated with mode j. Indicates the combined diffraction length. This represents the combined curvature difference parameter. This represents the Fresnel parameters of the equivalent lens.

[0114] Furthermore, substituting equation (18) into equation (17), we can obtain the plane wave WSF coupled with the OTOPS turbulent power spectrum and attenuation effect, expressed as:

[0115]

[0116] in:

[0117]

[0118] From the observation of equation (26), we can see that and The values ​​are relatively close, and Related items ( )and Related items ( The forms of ) are very similar, but the signs are opposite, so they can be considered to approximately cancel each other out.

[0119] Based on this, we can then use the following approximation formula:

[0120]

[0121] make Equation (24) can be transformed into:

[0122]

[0123] in, From equation (26), it can be seen that the plane wave WSF in the near field ( ) obeys the quadratic law, in the far field ( It follows a 5 / 3 power law, a result consistent with conclusions drawn in atmospheric turbulent environments.

[0124] It should be noted that this embodiment is effective for isotropic turbulent media that satisfy the Beer-Lambert decay law.

[0125] S3. Based on the statistical characteristics of the optical field, combined with the underwater channel characteristics and the detection range of the receiver, obtain the design parameters of the turbulence channel and realize underwater optical wireless communication through the turbulence channel.

[0126] In this embodiment, as Figure 2 As shown, the DC bias voltage of the DCO-OFDM communication system is determined based on the scintillation index. The value range is determined by using a DC bias voltage to control the light source to emit a signal, which is then transmitted through an underwater channel to the receiving end. The light intensity range of the light signal is within the detection range of the receiving end, and the receiving end demodulates the light signal. The basic setting principle is to ensure that the range of received light intensity is within the detection range of the receiving PD.

[0127] To more fully illustrate the significant impact of the attenuation effect proposed in this invention on the scintillation index, and the necessity of using the scintillation index calculated according to this invention to guide the design of the UOWC system, embodiments employing the method described in this invention are given below. Specifically, firstly, the impact of different attenuation rates on the scintillation index under different marine environmental conditions is analyzed through simulation. Then, a simulation platform for the DCO-OFDM communication system is built to measure the system bit error rate (BER) performance under different attenuation rates and scintillation indices. The parameters used in the simulation are shown in Table 1.

[0128] Table 1. Main parameters used in this embodiment

[0129]

[0130] Figure 3The simulation results demonstrate the relationship between the axial scintillation index and the attenuation coefficient for plane waves, spherical waves, and Gaussian beams at different propagation distances. Simulation results show that the attenuation effect significantly exacerbates light intensity fluctuations: for any wave type and propagation distance, All of these parameters increase monotonically with increasing c. During short-distance propagation, the scintillation characteristics of a Gaussian beam are similar to those of a plane wave; however, as the distance increases, its scintillation index falls between that of a plane wave and a spherical wave, reflecting the influence of beam parameters. and The effect of distance.

[0131] Figure 4 The study revealed the enhancing effect of attenuation coefficient and propagation distance on the scintillation index of Gaussian beams. Simulations show that at high attenuation ( ) in sea water, Follow The growth rate is much faster than in an ideal state with no decay ( The conditions in the seawater. The results in the figure show that... At high attenuation rates, the scintillation index in water bodies is approximately 38.7 times that in the absence of attenuation. This result demonstrates that the attenuation effect drastically shortens the reliable communication distance of the UOWC system, and traditional system models that neglect the turbulence-attenuation coupling effect will severely overestimate the system's performance in turbid waters. Therefore, the impact of the attenuation effect on the scintillation index must be considered when designing UOWC system parameters.

[0132] exist Figure 5 and Figure 6 The simulation results show that this embodiment simulates the effects of seawater temperature and salinity on the scintillation index at different attenuation levels. The results indicate that in turbulent oceans, increases in temperature or salinity lead to increased fluctuations in receiver light intensity. More importantly, the attenuation effect amplifies this environmental sensitivity: at higher attenuation coefficients, the scintillation index changes more significantly with temperature or salinity. This reveals an important value of this embodiment: when designing parameters for communication systems in coastal or estuarine waters with drastic isothermal and salinity variations, often accompanied by high attenuation, the coupling effect of turbulence and attenuation must be comprehensively considered; otherwise, severe distortion of the UOWC signal may occur.

[0133] Figure 7 and Figure 8 Energy dissipation rate was analyzed separately. and temperature dissipation rate The effect on the flicker index. The results show that lower... or higher Both of these factors can cause more significant fluctuations in light intensity. This phenomenon is also affected by the attenuation effect, with more dramatic changes occurring at high attenuation rates.

[0134] Figure 9 The receiver aperture size was evaluated. Average scintillation index of Gaussian beam aperture The simulation shows that increasing the receiver aperture can effectively suppress light intensity fluctuations. Figure 10 Furthermore, the correlation between the channel model and the BER performance of the communication system was established, demonstrating the variation of the BER of the DCO-OFDM communication system with the average scintillation index and attenuation coefficient. The results show that the system's BER performance increases with the scintillation index. attenuation coefficient The attenuation effect worsens with increasing intensity. This quantitatively reveals the dual negative impact of the attenuation effect: it not only directly attenuates the signal optical power (the part described by the traditional Beer-Lambert law), but also further increases the system's BER by exacerbating intensity fluctuations (the coupling effect revealed in this embodiment). Therefore, targeted parameter design is essential for system deployment in waters with high attenuation rates.

[0135] Taking a 95% confidence interval as an example, the 0.975 quantile of the standard normal distribution is 1.96. Under the weak turbulence approximation, i.e., the scintillation index... At time 1, we have:

[0136]

[0137] The determined DC bias range is:

[0138]

[0139] in, Channel attenuation factor, For the electro-optical conversion efficiency of the transmitter, To improve the detection efficiency at the receiving end, [ , [ represents the amplitude range of the transmitted signal] , [ ] represents the detection range of the receiving end.

[0140] In summary, the unified framework for characterizing the coupling of turbulence and attenuation proposed in this embodiment can more accurately depict the performance of UOWC systems in real marine environments. The analytical method proposed in this embodiment is the first to quantitatively reveal the aggravating effect of attenuation on the scintillation index, providing a new perspective for the study of light propagation in turbulent media and a basis for the parameter design of underwater wireless optical communication systems.

[0141] It should be noted that, for the sake of simplicity, the aforementioned method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0143] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for underwater optical wireless communication based on the correlation of the scintillation characteristics associated with the turbulent-decay coupling effect, characterized by, Includes the following steps: S1. Combining the spatial distribution model of the attenuated optical field and refractive index fluctuation under turbulent disturbance, a unified framework for characterizing the coupling of turbulence and attenuation is constructed. S2. Based on a unified framework for characterizing turbulence and attenuation coupling, calculate the statistical characteristics of the optical field after the optical signal propagates in the seawater channel, wherein the statistical characteristics of the optical field are at least the scintillation index. S3. Based on the statistical characteristics of the optical field, combined with the underwater channel characteristics and the detection range of the receiver, obtain the design parameters of the turbulence channel and realize underwater optical wireless communication through the turbulence channel. 2.The method according to claim 1, wherein, Step S1 includes the following steps: Based on the complex amplitude of the optical field of a standard Gaussian beam, the light intensity attenuation model corresponding to the seawater medium with an attenuation coefficient of c is introduced using the Beer-Lamber attenuation law to obtain the attenuated optical field without turbulence disturbance. Determination of spatial distribution model of refractive index according to oceanic turbulent power spectrum , The Rytov approximation of the spatial distribution model of the attenuated optical field and refractive index fluctuations is calculated. Combined with the first-order perturbation of the optical field by the turbulent medium, the optical field statistics at the receiver are calculated, and a unified framework for characterizing the coupling between turbulence and attenuation is constructed, as shown in the following equation: ， in, For the distance of transmission The radial distance vector from the receiver to the center of the light spot. The random amplitude representing the refractive index fluctuation. Represents the imaginary unit. Represents the wavenumber of light in a vacuum. Represents the spatial wave vector of turbulence. Let be a two-dimensional coordinate vector on a horizontal plane perpendicular to the z-axis. This represents the complex path amplitude weighting parameter. Let the integral variable describe the distance, and , The substitution parameter represents the integral variable of distance. The distance between two observation points in the three-dimensional light field space. 3.The method according to claim 2, wherein, the attenuated light field without turbulence disturbance is as follows: . 4.The method according to claim 2, wherein, the spatial distribution model of the refractive index as follows: . 5.The method according to claim 2, wherein, The optical field statistics at the receiving end include two points in the three-dimensional optical field space. and The two light field statistics between them are as follows: ， in, For the integral kernel of amplitude fluctuation, For phase fluctuation integration kernel, For attenuation term, The substitution parameter represents the distance integral variable, and c is the attenuation coefficient. 6.The method according to claim 1, wherein, The point on the receiving end The flicker index of the light source, as follows: ， Among them, the flicker index Characterized by the distance of light signal propagation The radial distance vector to the center of the light spot is The degree of light intensity fluctuation at a point, and Let represent the received light intensity and its squared expected value, respectively. This indicates the real part operator. and Let be the light field statistics of two points in a three-dimensional light field space. It is the spatial power spectral density of the refractive index fluctuations in an isotropic turbulent medium. and Let F represent the diffraction factor and normalized curvature parameter of the Gaussian light wave, respectively, which are related to the propagation distance. ( ) represents the zeroth-order modified Bessel function. Represents the wavenumber of light in a vacuum. Represents the space wave number of turbulence. The substitution parameter represents the integral variable of distance, where r represents the radial distance from the receiver to the center of the light spot. is the attenuation term, and c is the attenuation coefficient.

7. The method according to claim 6, wherein the method is characterized by, The scintillation index includes the axial scintillation index of the receiver and the aperture-average scintillation index. The axial scintillation index is the scintillation index at the center of the receiver spot, and the aperture-average scintillation index is the average scintillation index calculated based on the receiver aperture size. 8.The method according to claim 1, wherein, This includes the space wave structure function, which describes the root mean square error of phase fluctuations between two different points at the receiver. Its calculation incorporates attenuation and amplification correction terms corresponding to the seawater attenuation effect, resulting in the following equation: ， in, The distance between two observation points in the three-dimensional light field space. This represents the wavenumber of light in a vacuum. Represents the space wave number of turbulence. Where c is the propagation distance of the optical signal, and c is the attenuation coefficient. It is the spatial power spectral density of the refractive index fluctuations in an isotropic turbulent medium. ( ) represents the zeroth-order modified Bessel function. This represents the amplification correction factor for the effect of seawater attenuation on turbulent light intensity scintillation.

9. The method according to claim 8, wherein the method is characterized by, Step S2 includes calculating the space wave structure function based on the OTOPS turbulent power spectrum to obtain the plane wave expression coupled with the attenuation effect of the OTOPS turbulent power spectrum. This plane wave expression follows a quadratic law in the near field and a 5 / 3 power law in the far field. The near field is... The range that is much smaller than the boundary threshold, the far field is The range is much larger than the dividing threshold. 10.The method according to claim 1, wherein, Step S3 includes: The range of DC bias voltage is determined based on the statistical characteristics of the optical field. The DC bias voltage is used to control the light source to emit a signal. The optical signal is received by the receiving end through the underwater channel. The light intensity range of the optical signal is within the detection range of the receiving end. The receiving end demodulates the optical signal.

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