A method and system for modeling underwater wireless optical communication channels including bubble scattering

Abstract

This invention belongs to the field of underwater wireless optical communication technology, and discloses a method and system for modeling underwater wireless optical communication channels including bubble scattering. The method sets the parameters required for simulation and determines the initial coordinates and motion angle of photons; simulates the scattering process of photons, calculates the position of photons after each collision, and determines whether a photon reaches the receiving surface; after reaching the receiving surface, it stores the photon's coordinates, transmission time, and weight; after the scattering process of all photons is completed, the stored photon coordinates, transmission time, and weight are statistically analyzed to obtain the light spot, channel impulse response, and received power at the receiving end. The underwater wireless optical communication channel scattering modeling method disclosed in this invention, which includes bubble scattering, accurately simulates the scattering of laser light by particles and bubbles in ocean water, providing a certain reference for underwater wireless optical communication channel modeling and system design.

Description

Technical Field

[0001] This invention belongs to the field of underwater wireless optical communication technology, and particularly relates to an underwater wireless optical communication channel modeling method and system that includes bubble scattering. Background Technology

[0002] Currently, underwater wireless optical communication (UWOC) is an emerging underwater wireless communication technology with advantages such as high transmission bandwidth, high speed, high security, and low cost. However, various particles present in seawater (phytoplankton, suspended sediments, debris, and dissolved organic matter) can affect the performance of UWOC, mainly manifested as beam deflection and spot expansion caused by absorption and scattering. In addition, air bubbles in seawater can also interact with the beam, causing it to diffuse into the spatiotemporal domain, thus deviating from the desired path and reducing the performance of the UWOC system.

[0003] Although several beam scattering attenuation models have been proposed for ocean channels, most of these models only consider particle absorption and scattering, neglecting the influence of bubble swarms on the UWOC (Ultra-Wide Orifice). Therefore, establishing a composite channel model that couples bubble swarm scattering and particle absorption and scattering has significant practical value.

[0004] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0005] (1) The performance of existing UWOC technology is easily affected by various particles present in seawater. The absorption and scattering of particles cause the transmission beam to deflect and the beam to expand.

[0006] (2) The bubbles in the seawater will also interact with the beam, causing the beam to spread into the space-time domain, thus deviating from the desired path and reducing the performance of the UWOC system. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method and system for modeling underwater wireless optical communication channels, including bubble scattering.

[0008] This invention is implemented as follows: an underwater wireless optical communication channel modeling method incorporating bubble scattering, the method comprising:

[0009] S1, Calculate the scattering characteristic parameters of the composite channel based on the scattering efficiency factor of a single bubble, the attenuation coefficient of the bubble group, and the scattering phase function;

[0010] S2, determine the initial coordinates and motion angle of the photon according to the type of light source;

[0011] S3, set the parameters required for simulation, simulate the scattering process of photons: calculate the position of the photon after each collision, and determine whether the photon reaches the receiving surface; after reaching the receiving surface, store its position, time, and weight;

[0012] S4: After the scattering process of all photons is completed, based on the stored data, the transmission time and weight of all photons arriving at the receiving surface are calculated to obtain the signal impulse response of the composite channel; the weight and position of the photons are calculated to obtain the light spot and energy distribution of the light spot at the receiving surface; the weights of all photons arriving at the receiving surface are summed and multiplied by the power of a single photon to obtain the received power.

[0013] By following the above steps, the underwater wireless optical communication channel model incorporating bubble scattering as described in this invention can be established. Specifically, the input parameters are the light source and channel parameters, and the output parameters are the light spot at the receiver, the channel impulse response, and the received power.

[0014] Furthermore, the calculation of the scattering efficiency factor for a single bubble in S1 includes:

[0015] According to Mie scattering theory, the scattering efficiency factor Q of the bubble is... sca As shown below:

[0016]

[0017] Among them, a n and b n Here, denoted as Mie scattering coefficient, n is the order, x is the bubble size factor (x = 2πrn0 / λ), r is the bubble radius, n0 is the refractive index of seawater, and λ is the incident light wavelength.

[0018] The Mie scattering coefficient a n and b n Defined as:

[0019]

[0020] m is the relative refractive index, which is the ratio of the refractive index of the bubble to the refractive index of seawater.

[0021] Where, ψ n (Z) and ξ n (Z) is the Ricatti-Bessel function, calculated by the following recursive formula:

[0022]

[0023] The cutoff order n of the order n stop for:

[0024]

[0025] Furthermore, the calculation of the scattering coefficient and scattering phase function of the bubble swarm in S1 includes:

[0026] The scattering coefficient b of the bubble swarm bub (λ) is:

[0027]

[0028] Where, β bub (θ) is the volume scattering function of the bubble swarm, and the formula is:

[0029]

[0030] Among them, [r min ,r max ] represents the size range of the bubble cluster; Q β (θ,r) is the scattering efficiency factor of a bubble of size r in the θ direction; n(r) is the size distribution of the bubble, and the formula is given.

[0031] n(r) = N0p(r)

[0032] Where N0 is the total number density of air bubbles per unit volume of water, in m³. -3 ;

[0033] The radius distribution p(r) of the bubble is defined using the Junge spectrum, and the formula is:

[0034]

[0035] Wherein, dN(r) is the bubble density of aerosol particles with radii in the range of r to r+dr, and the coefficients A and v are the particle size distribution fitting parameters. A is a constant related to the total mass and physical properties of the particles, and v is the slope of the radius distribution curvature.

[0036] The scattering phase function of the bubble is the normalized volume scattering function, and the formula is:

[0037]

[0038] Furthermore, the calculation of the attenuation coefficient and scattering phase function of the composite channel in S1 includes:

[0039] The attenuation coefficient C(λ) of the composite channel is the scattering coefficient b of the bubble swarm. bub The sum of (λ) and the particle's attenuation coefficient c(λ) is calculated using the following formula:

[0040] C(λ)=b bub (λ)+c(λ)=b bub (λ)+a(λ)+b(λ)

[0041] Where a(λ) and b(λ) are the absorption coefficient and scattering coefficient of the particle, respectively;

[0042] The scattering phase function of the composite channel is a weighted sum of the scattering phase function of the bubble swarm and the scattering phase function of the particles, as shown in the formula:

[0043]

[0044] The particle scattering phase function The calculation formula, expressed by the HG scattering phase function, is as follows:

[0045]

[0046] Where g is an asymmetric factor, usually taken as g = 0.924.

[0047] Furthermore, S2 specifically includes:

[0048] Determine the initial coordinates x0 and y0 of the photon and its initial motion angle μ. x μ y and μ z .

[0049] First, calculate the azimuth angle of the photon. The formula for calculating the azimuth cosine is as follows:

[0050]

[0051] The photon source is a Gaussian source, the beam is centrally symmetrical, and the azimuth angle of the initial motion direction of the beam is... It follows a uniform distribution in [0, 2π], therefore, ε1 is a random number between 0 and 1;

[0052] Then, the initial coordinates x0 and y0 of the photon and the initial motion angle μ are calculated. x μ y and μ z The formula is as follows:

[0053]

[0054] Here, θ0 is the diffusion angle of the beam, which is extremely small when a Gaussian light source is used.

[0055] Furthermore, S3 specifically includes:

[0056] S301, set the number of photons, photon transmission speed, wavelength, number of collisions, initial photon weight, link distance, and water body attenuation coefficient and single scattering rate;

[0057] S302, Calculate the photon step size;

[0058] S303, Determine the direction of motion of the photon and its new coordinates;

[0059] S304, calculates the weights after a photon collision;

[0060] S305, based on the new coordinates of the photon, determine whether it has reached the receiving surface; if the photon has reached the receiving surface, store the new coordinates, time and weight, and calculate the next photon scattering collision; if it has not reached the receiving surface, repeat steps S301-S303 until the photon reaches the receiving surface.

[0061] Furthermore, the photon step size is calculated using a cumulative probability distribution, and the actual step size s

[0062] for:

[0063]

[0064] In the formula, ε2 is a random number between (0,1); c(λ) is the attenuation coefficient of the composite channel.

[0065] Furthermore, the direction of photon motion is determined by the scattering angle θ and the azimuth angle. The direction cosine formula is determined as follows:

[0066]

[0067] Azimuth The scattering angle θ is a random value in the range [0, 2π], and is obtained by sampling the scattering phase function of the composite channel;

[0068] The new coordinates of the photon after scattering are calculated based on the direction cosine and the step size:

[0069]

[0070] Furthermore, the weight after the photon collision is ω0, where ω0 is the single scattering rate of the medium, i.e., the ratio of the energy of the scattered portion to the total attenuated energy, calculated using the following formula:

[0071]

[0072] Furthermore, the transmission time t of the photon is calculated by the following formula:

[0073]

[0074] Where d is the path length of photon transmission, i.e., the sum of the step sizes between each scattering; c is the speed of light in vacuum, taken as 3 × 10⁻⁶. 8 m / s.

[0075] Furthermore, the power P of a single photon in S4 is defined by the following formula:

[0076]

[0077] Where h is Planck's constant, taken as 6.6260693 × 10⁻⁶. -34 λ is the incident light wavelength, taken as 532nm.

[0078] Another object of the present invention is to provide an underwater wireless optical communication channel modeling system incorporating bubble scattering that implements the aforementioned underwater wireless optical communication channel modeling method incorporating bubble scattering, the underwater wireless optical communication channel modeling system incorporating bubble scattering comprising:

[0079] The parameter calculation module is used to calculate the composite channel scattering characteristic parameters;

[0080] The scattering simulation module is used to simulate the absorption and scattering process of each photon;

[0081] The data statistics module is used to statistically analyze various parameters of photons arriving at the receiving surface and obtain the output of the channel model.

[0082] Another object of the present invention is to provide a computer device including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the steps of the underwater wireless optical communication channel modeling method including bubble scattering.

[0083] Another object of the present invention is to provide an information data processing terminal for implementing the underwater wireless optical communication channel modeling system including bubble scattering.

[0084] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0085] The underwater wireless optical communication channel scattering modeling method proposed in this invention, which includes bubble scattering, can accurately simulate the scattering of photons by particles and bubbles in ocean water, and can provide a certain reference for underwater wireless optical communication channel modeling and system design.

[0086] The technical effect of the technical solution to be protected by this invention is that it simultaneously considers the effects of particle absorption and scattering as well as bubble scattering on beam transmission, and can simulate the situation under different channel lengths and different light source types, and the output results can all be expressed in specific numerical values.

[0087] The advantages of the technical solution protected by this invention are: it can simultaneously change multiple parameters to simulate different marine channels, including link distance, bubble density, water attenuation coefficient, and light source parameters, thus overcoming to some extent the difficulty in experimentally simulating underwater wireless optical communication channels. The model is established based on the Monte Carlo method, a probabilistic statistical model commonly used in studying optical signal propagation. In the implementation of this technical solution, the number of photons is relatively large, therefore the output result is close to the optimal solution, meaning accuracy can be guaranteed.

[0088] The expected benefits and commercial value of the technical solution after its transformation are as follows: The technical solution proposed in this invention can be combined with existing software or hardware and applied to specific information processing terminals. For example, it can provide a reference for the design of software and hardware for underwater visible light communication systems. The relevant code of the model described in this invention can be applied to the transmitting and receiving terminals of an underwater visible light communication system, and combined with image processing and water quality detection technologies to obtain the bubble density and water attenuation coefficient in the water. This allows for timely adjustment of the power of the light source at the transmitting end or the position of the photodetector at the receiving end, preventing the degradation of the system's communication performance. This improves the versatility of visible light communication systems in complex marine environments and further enhances the application value of underwater visible light communication systems in various aspects such as marine surveying, underwater search and rescue, marine ecological protection, marine fisheries, and marine transportation.

[0089] The technical solution of this invention fills a technological gap in the industry both domestically and internationally: Underwater wireless optical communication has many advantages, including higher transmission bandwidth, higher data rates, better security, and lower costs. However, the propagation of light underwater is easily affected by the marine environment: gradient changes in seawater temperature and salinity can cause turbulence; various particles (phytoplankton, suspended sediments, debris, and dissolved organic matter) and bubbles in the water can absorb or scatter photons. These factors can interfere with the propagation of optical signals, leading to a decrease in the performance of the UWOC system. While significant progress has been made in both theoretical and experimental studies to assess the impact of these factors on the performance of the UWOC system, research combining marine bubbles with the UWOC system is relatively limited.

[0090] The underwater wireless optical communication channel modeling method with bubble scattering provided by this invention can comprehensively consider the impact of particle absorption and scattering and bubble scattering on seawater channels, thus filling a certain degree of technological gap at home and abroad. Attached Figure Description

[0091] Figure 1 This is a schematic diagram of an ocean channel containing bubble clusters provided in an embodiment of the present invention.

[0092] Figure 2 This is a schematic diagram of the steps in the underwater wireless optical communication channel scattering modeling method including bubble scattering provided in the embodiments of the present invention;

[0093] Figure 3 This is a schematic flowchart of the calculation of composite channel scattering characteristic parameters provided in an embodiment of the present invention;

[0094] Figure 4 This is a schematic flowchart illustrating the calculation of the absorption and scattering process of each photon provided in an embodiment of the present invention;

[0095] Figure 5 A, B, and C are schematic diagrams of three related simulation results of the receiver spot provided in the embodiments of the present invention;

[0096] Figure 6 This is a schematic diagram of the simulation results related to the impulse response of the receiving end provided in an embodiment of the present invention;

[0097] Figure 7 This is a schematic diagram of the simulation results related to the received power at the receiving end provided in an embodiment of the present invention;

[0098] Figure 8 This is an initial position distribution diagram of photons provided in an embodiment of the present invention;

[0099] Figure 9 The bubble density is 2×10 8 m -3 The scattering phase function of the composite channel containing bubble swarms in three typical water bodies. Detailed Implementation

[0100] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0101] To enable those skilled in the art to fully understand how the present invention is specifically implemented, this section provides an explanatory description of the embodiments that expand upon the technical solutions of the claims.

[0102] like Figure 1 The diagram shown is a schematic representation of an ocean channel containing a bubble swarm, provided by an embodiment of the present invention.

[0103] like Figure 2 As shown, the underwater wireless optical communication channel modeling method including bubble scattering provided in this embodiment of the invention includes:

[0104] S101, the scattering characteristic parameters of the composite channel are calculated based on the scattering efficiency factor of a single bubble, the attenuation coefficient of the bubble group, and the scattering phase function.

[0105] S102, determine the initial coordinates and motion angle of the photon according to the type of light source;

[0106] S103: Set the parameters required for simulation and simulate the scattering process of photons. Calculate the position of the photon after each collision and determine whether the photon reaches the receiving surface. After reaching the receiving surface, store its position, time and weight.

[0107] S104: After the scattering process of all photons is completed, based on the stored data, the transmission time and weight of all photons arriving at the receiving surface are calculated to obtain the signal impulse response of the composite channel; the weight and position of the photons are calculated to obtain the light spot and energy distribution of the light spot at the receiving surface; the weights of all photons arriving at the receiving surface are accumulated and multiplied by the power of a single photon to obtain the received power.

[0108] like Figure 3 As shown, in step S1, S101, the scattering characteristic parameters of the composite channel are calculated:

[0109] In this embodiment, the radius r of the bubble is set to range from 10 to 300 μm, and the bubble density N0 = 2 × 10⁻⁶. 8 m -3 Using the following Junge spectral distribution p(r) to sample the bubble radius r, its expression is:

[0110]

[0111] Among them, the coefficients c1, c2, and c3 are determined by the upper and lower limits r of the particle size. b and r a The decision is made, and the possible values ​​are shown in Table 1.

[0112] Table 1 Simulation parameters of the Junge distribution

[0113]

[0114] The bubble size distribution n(r) is calculated by the following formula.

[0115] n(r) = N0p(r)

[0116] Given an incident light wavelength of 532 nm and a relative refractive index m of 0.75 between the bubble and seawater, the bubble's scale factor x is calculated using the following formula:

[0117] x = 2πrn0 / λ

[0118] ψ n (Z) and ξ n (Z) is calculated using the following recursive formula:

[0119]

[0120] The initial values ​​used are as follows:

[0121]

[0122] The Mie scattering coefficient a is calculated using the above parameters. n and b n Since the values ​​calculated by Mie scattering theory are represented by the sum of infinitely many terms of different orders, the contribution of higher-order terms to the calculation results decreases as the order increases. Therefore, in practical calculations, it is necessary to calculate the cutoff order n. stop The formula is as follows:

[0123]

[0124] Furthermore, the scattering efficiency factor Q of the bubble is calculated according to the following formula. sca and scattering coefficient b bub (λ):

[0125]

[0126] The water body is set as nearshore seawater, i.e., absorption coefficient a(λ) = 0.179 and scattering coefficient b(λ) = 0.220. The values ​​in Table 2 can be used to simulate the composite channel under different water bodies.

[0127] The asymmetry factor g of the HG scattering phase function is 0.924. The attenuation coefficient c(λ), single scattering rate ω0, and scattering phase function of the composite channel are calculated using the following formula.

[0128]

[0129] Table 2 Absorption and Scattering Coefficients of Different Types of Water Bodies

[0130]

[0131] Furthermore, in step S102, determining the initial coordinates and motion angle of the photon:

[0132] Considering practical applications, a Gaussian light source with a wavelength of λ = 532 nm is adopted, with a divergence angle θ0 of 0.0075 rad and a beam waist width of 0.0078 m.

[0133] Determine the azimuth angle of the photon The formula for calculating the azimuth cosine is as follows:

[0134]

[0135] Since this embodiment uses a Gaussian light source for simulation, the beam is centrally symmetrical, and the azimuth angle of the initial direction of beam motion is... It follows a uniform distribution in [0, 2π], so ε1 is set to a random number between 0 and 1;

[0136] Calculate the initial coordinates x0 and y0 of the photon and the initial motion angle μ. x μ y and μ z The formula is as follows:

[0137]

[0138] The initial position distribution of photons is as follows Figure 8 As shown:

[0139] like Figure 4 As shown, S103, simulating the scattering process of each photon, specifically includes:

[0140] S10301, Set the parameters required for simulation;

[0141] S10302, Calculate the photon step size;

[0142] S10303, Determine the direction of motion of the photon and its new coordinates;

[0143] S10304, Calculate the weights after photon collision;

[0144] S10305, based on the new coordinates of the photon, determine whether it has reached the receiving surface; if the photon has reached the receiving surface, store the new coordinates, time and weight, and calculate the next photon scattering collision; if it has not reached the receiving surface, repeat steps S10301-S10303 until the photon reaches the receiving surface.

[0145] Furthermore, the photon number parameter was set to 1×102. 6 The initial weight of the photon is W0 = 1, the transmission speed of the photon in seawater is 3 / 4 of the speed of light, and the link distance is set to 2-40m.

[0146] Furthermore, the photon step size is calculated using a cumulative probability distribution, and the actual step size is:

[0147]

[0148] In the formula, ε2 is a random number between (0,1); c(λ) is the attenuation coefficient of the composite channel.

[0149] Furthermore, the direction of photon motion is determined by the scattering angle θ and the azimuth angle. The direction cosine formula is determined as follows:

[0150]

[0151] Azimuth The scattering angle θ is a random value in the range [0, 2π], and is obtained by sampling the scattering phase function of the composite channel;

[0152] The new coordinates of the photon after scattering are calculated based on the direction cosine and the step size:

[0153]

[0154] Furthermore, the weight after the photon collision is ω0, where ω0 is the single scattering rate of the medium, i.e., the ratio of the energy of the scattered portion to the total attenuated energy, calculated using the following formula:

[0155]

[0156] Furthermore, the transmission time t of the photon is calculated by the following formula:

[0157]

[0158] Where d is the path length of photon transmission, i.e., the sum of the step sizes between each scattering; c is the speed of light in vacuum, taken as 3 × 10⁻⁶. 8 m / s.

[0159] Furthermore, after the scattering process of all photons in step S104 is completed, the transmission time and weight of all photons arriving at the receiver are calculated based on the stored text data to obtain the signal impulse response of the composite channel; the weight and coordinate of the photons are calculated to obtain the light spot and energy distribution of the light spot at the receiver; the weights of all photons arriving at the receiver are accumulated and multiplied by the power of a single photon to obtain the received power.

[0160] The power P of a single photon is defined by the following equation:

[0161]

[0162] In the formula, h is Planck's constant, taken as 6.6260693 × 10⁻⁶. -34 λ is the incident light wavelength, taken as 532nm.

[0163] A schematic diagram of the receiver spot correlation simulation results in this embodiment of the invention is shown below. Figure 5 As shown. Figure 5 The bubble density N0 is shown to be 4.5 × 10⁻⁶. 7 2×10 8 1×10 9 m -3 The link distance is 5m, and the receiver spot is observed in three typical water areas (clean seawater, nearshore seawater, and turbid sea area). When the bubble density is high enough, the spot will produce severe dispersion, the number of photons received at the receiving surface will be greatly reduced, the position distribution will be more dispersed, and the energy at the center of the spot will be significantly reduced.

[0164] A schematic diagram of the simulation results of the receiver impulse response in this embodiment of the invention is shown below. Figure 6As shown. Figure 6 This demonstrates that the bubble density N0 = 2 × 10 8 m -3 Channel impulse response in nearshore waters at link distances of 10m, 20m, 30m, and 40m. As the link distance increases, the broadening of the impulse response gradually increases. This is because, with a constant bubble density, the longer the link distance, the more bubbles there are, resulting in more scattering of photons by bubbles in the channel, thus increasing the transmission path length.

[0165] A schematic diagram of the simulation results related to the received power at the receiving end in this embodiment of the invention is shown below. Figure 7 As shown. Figure 7 The bubble density N0 is shown to be 4.5 × 10⁻⁶. 7 m -3 2×10 8 m -3 1×10 9 m -3 The received power curves for nearshore waters with link distances of 2–10 m show that the received power decreases significantly at the same link distance as the bubble density increases. This is because the increased number of particles and bubbles in the channel leads to more photon scattering events. Furthermore, the increased bubble density increases the single scattering rate of the composite channel, resulting in greater energy loss after each scattering event.

[0166] To demonstrate the inventiveness and technical value of the technical solution of this invention, this section provides specific product or related technology application examples of the technical solution claimed.

[0167] The underwater wireless optical communication channel modeling method including bubble scattering provided in the application embodiment of the present invention is applied to a computer device, the computer device including a memory and a processor, the memory storing a computer program, and when the computer program is executed by the processor, the processor performs the steps of the underwater wireless optical communication channel modeling method including bubble scattering.

[0168] The underwater wireless optical communication channel modeling method including bubble scattering provided in the application embodiment of the present invention is applied to an information data processing terminal, which is used to implement the underwater wireless optical communication channel modeling system including bubble scattering.

[0169] The embodiments of the present invention have achieved some positive results during the research and development or use process, and have indeed great advantages compared with the prior art. The following content describes them in conjunction with the data, charts and other information of the experimental process.

[0170] Table 3 shows the attenuation coefficients of composite channels containing bubble swarms of different densities in three typical water areas. Compared with the data in Table 2, the attenuation coefficient of the water body increases to different degrees depending on the density of the bubble swarms. That is, the presence of bubble swarms will exacerbate the attenuation of the light beam when it propagates in the ocean.

[0171] Table 3 Attenuation coefficients of composite channels containing bubble swarms of different densities in three typical water bodies.

[0172]

[0173]

[0174] Figure 9 The bubble density is 2×10 8 m -3 The scattering phase functions of composite channels containing bubble swarms in three typical water bodies were obtained. The results show that increasing the water body attenuation coefficient leads to a decrease in the abrupt change in the composite channel scattering phase function at the critical angle. This is because the increased particle content in the water body reduces the contribution of bubbles to the total scattering, and this abrupt change can also be used to distinguish bubbles from other particles.

[0175] Table 4 shows the single scattering rate of the composite channel for bubble swarms of different densities in three typical water bodies, which is the ratio of the scattered energy to the total attenuated energy. Table 4 shows that the higher the bubble swarm density, the more energy the light beam is scattered.

[0176] Table 4. Single scattering rate of the composite channel for bubble swarms of different densities in three typical water bodies.

[0177]

[0178] It should be noted that embodiments of the present invention can be implemented in hardware, software, or a combination of both. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated-design hardware. Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuitry such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field-programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of the above-described hardware circuitry and software, such as firmware.

[0179] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for modeling underwater wireless optical communication channels including bubble scattering, characterized in that, The underwater wireless optical communication channel modeling method incorporating bubble scattering includes: S1, Calculate the scattering characteristic parameters of the composite channel based on the scattering efficiency factor of a single bubble, the attenuation coefficient of the bubble group, and the scattering phase function; S2, set the parameters required for simulation and determine the initial coordinates and motion angle of the photon; S3 simulates the scattering process of photons, calculates the position of photons after each collision, and determines whether the photons have reached the receiving surface; after reaching the receiving surface, it stores the position, time, and weight. S4: After the scattering process of all photons is completed, based on the stored data, the transmission time and weight of all photons arriving at the receiving surface are calculated to obtain the signal impulse response of the composite channel; the weight and position of the photons are calculated to obtain the light spot and energy distribution of the light spot at the receiving surface; the weights of all photons arriving at the receiving surface are summed and multiplied by the power of a single photon to obtain the received power.

2. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 1, characterized in that, The calculation of the scattering efficiency factor for a single bubble in S1 includes: According to Mie scattering theory, the scattering efficiency factor Q of the bubble is... sca As shown below: Among them, a n and b n Here, denoted as Mie scattering coefficient, n is the order, x is the bubble size factor (x = 2πrn0 / λ), r is the bubble radius, n0 is the refractive index of seawater, λ is the incident light wavelength, and m is the relative refractive index, which is the ratio of the bubble refractive index to the seawater refractive index. The Mie scattering coefficient a n and b n Defined as: Where, ψ n (Z) and ξ n (Z) is the Ricatti-Bessel function, calculated by the following recursive formula: The cutoff order n of the order n stop for:

3. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 1, characterized in that, The calculation of the scattering characteristic parameters of the composite channel based on the scattering efficiency factor of a single bubble, the attenuation coefficient of the bubble swarm, and the scattering phase function in S1 includes the calculation of the scattering coefficient and scattering phase function of the bubble swarm: The scattering coefficient b of the bubble swarm bub (λ) is: Where, β bub (θ) is the volume scattering function of the bubble swarm, and the formula is: Among them, [r min ,r max ] represents the size range of the bubble cluster; Q β (θ,r) is the scattering efficiency factor of a bubble of size r in the θ direction; n(r) is the size distribution of the bubble, and the formula is: n(r) = N0p(r) Where N0 is the total number density of air bubbles per unit volume of water, in m³. -3 ; The radius distribution p(r) of the bubble is defined using the Junge spectrum, and the formula is: Wherein, dN(r) is the bubble density of aerosol particles with radii in the range of r to r+dr, and the coefficients A and v are the particle size distribution fitting parameters. A is a constant related to the total mass and physical properties of the particles, and v is the slope of the radius distribution curvature. The scattering phase function of the bubble is the normalized volume scattering function, and the formula is: The calculation of the attenuation coefficient and scattering phase function of the composite channel in S1 includes: The attenuation coefficient C(λ) of the composite channel is the scattering coefficient b of the bubble swarm. bub The sum of (λ) and the particle's attenuation coefficient c(λ) is calculated using the following formula: C(λ)=b bub (λ)+c(λ)=b bub (λ)+a(λ)+b(λ) Where a(λ) and b(λ) are the absorption coefficient and scattering coefficient of the particle, respectively; The scattering phase function of the composite channel is a weighted sum of the scattering phase function of the bubble swarm and the scattering phase function of the particles, as shown in the formula: The particle scattering phase function The calculation formula, expressed by the HG scattering phase function, is as follows: Where g is an asymmetric factor, usually taken as g = 0.

924.

4. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 1, characterized in that, S2 specifically includes: S201, set the number of photons, photon transmission speed, wavelength, number of collisions, initial photon weight, link distance, and water body attenuation coefficient and single scattering rate; S202, Determine the initial coordinates x0 and y0 of the photon and the initial motion angle μ. x μ y and μ z ; The specific process of S202 is as follows: First, calculate the azimuth angle of the photon. The formula for calculating the azimuth cosine is as follows: The photon source is a Gaussian source, the beam is centrally symmetrical, and the azimuth angle of the initial motion direction of the beam is... It follows a uniform distribution in [0, 2π], therefore, ε1 is a random number between 0 and 1; Then, the initial coordinates x0 and y0 of the photon and the initial motion angle μ are calculated. x μ y and μ z The formula is as follows: Here, θ0 is the diffusion angle of the beam, which is extremely small when a Gaussian light source is used.

5. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 1, characterized in that, S3 specifically includes: S301, Calculate the photon step size; S302, Determine the direction of motion of the photon and its new coordinates; S303, calculates the weights after a photon collision; S304, Based on the new coordinates of the photon, determine whether it has reached the receiving surface; if the photon has reached the receiving surface, store the new coordinates, time and weight, and calculate the next photon scattering collision; if it has not reached the receiving surface, repeat steps S301-S303 until the photon reaches the receiving surface. The photon step size is calculated using a cumulative probability distribution; the actual step size is: In the formula, ε2 is a random number between (0,1); c(λ) is the attenuation coefficient of the composite channel.

6. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 5, characterized in that, The direction of photon motion is determined by the scattering angle θ and the azimuth angle. The direction cosine formula is determined as follows: Azimuth The scattering angle θ is a random value in the range [0, 2π], and is obtained by sampling the scattering phase function of the composite channel; The new coordinates of the photon after scattering are calculated based on the direction cosine and the step size: The weight after the photon collision is ω0, where ω0 is the single scattering rate of the medium, i.e., the ratio of the scattered energy to the total attenuated energy, calculated using the following formula:

7. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 6, characterized in that, The transmission time t of the photon is calculated by the following formula: Where d is the path length of photon transmission, i.e., the sum of the step sizes between each scattering; c is the speed of light in vacuum, taken as 3 × 10⁻⁶. 8 m / s.

8. The underwater wireless optical communication channel modeling method including bubble scattering as described in claim 1, characterized in that, The power P of a single photon in S4 is defined by the following formula: Where h is Planck's constant and c is the speed of light in vacuum, taken as 6.6260693 × 10⁻⁶. -34 λ is the incident light wavelength, taken as 532nm.

9. An underwater wireless optical communication channel modeling system incorporating bubble scattering, implementing the underwater wireless optical communication channel modeling method incorporating bubble scattering as described in any one of claims 1-8, characterized in that, The underwater wireless optical communication channel modeling system incorporating bubble scattering includes: The parameter calculation module is used to calculate the composite channel scattering characteristic parameters; The scattering calculation module is used to calculate the absorption and scattering process of each photon; The scattering simulation module is used to simulate the scattering process of photons; The model building module is used to establish underwater wireless optical communication channel models.

10. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the underwater wireless optical communication channel modeling method including bubble scattering as described in any one of claims 1-8.

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