Underwater wireless optical transmission channel modeling method based on multi-phase screen

Abstract

The invention provides an underwater wireless optical transmission channel modeling method based on a multi-phase screen, which comprises the following steps: A, establishing a three-dimensional coordinate system, and initializing system parameters; b, generating n phase screens according to the ocean turbulence power spectrum; c, creating a variable num, and initializing the variable num as 1; d, initial coordinates, direction vectors and weights of photons are determined, and a photon receiving threshold value is set; e, photon transmission is started, and photon coordinates are updated; f, when num is smaller than or equal to n, whether the z coordinate of the photon is smaller than the znum coordinate of the current phase screen or not is judged, and if z is smaller than znum, the photon coordinate is updated; if z is larger than or equal to znum, the photons are returned to the plane where the phase screen is located, the direction vector of the photons is updated according to the generalized Snell law, the remaining step length is calculated, the photon coordinates are updated, and num is increased; g, when num is larger than the total number of the phase screens, the photons continue to be transmitted until the photons reach the receiving face. According to the invention, accurate simulation of underwater light transmission characteristics is realized by deeply considering the cumulative effect of photons passing through the multi-phase screen.

Description

Technical Field

[0001] The present invention relates to the technical field of channel modeling and simulation of wireless optical transmission, and in particular to a method for modeling underwater wireless optical transmission channels based on a multi-phase screen. Background Art

[0002] Underwater communication, detection and imaging are of great significance in the fields of ocean exploration, seabed resource development and underwater navigation. Traditional underwater communication technology mainly uses electromagnetic waves or sound waves to transmit information. Although sound wave communication is suitable for long-distance transmission, it has limited bandwidth, low rate, high latency and is susceptible to interference. In recent years, with the development of optical technology, underwater wireless optical communication has become a research hotspot due to its high bandwidth, low latency and strong anti-interference ability. Among them, the blue-green light band is widely used in the research of underwater communication, imaging and detection technology due to its excellent penetration performance in seawater.

[0003] When optical signals propagate in water, they are affected by a variety of factors in the complex marine environment, including absorption, scattering, and turbulence effects. These effects can lead to multipath effects and beam expansion. However, it is difficult for the existing underwater channel simulation framework to effectively combine turbulence effects with absorption and scattering models. In recent years, some scholars have proposed a modeling method for underwater wireless optical transmission channels based on multiple phase screens, which equates underwater turbulence effects to phase screens, and integrates turbulence, absorption, and scattering effects into the Monte Carlo simulation framework based on the generalized Snell's law. However, the existing methods still have the following shortcomings: First, the phase screens are assumed to be equally spaced, ignoring the spatial non-uniformity of turbulence intensity, and cannot truly reflect the dynamic changes of turbulence; second, the phase screen is assumed to be of a fixed size, but in fact the phase screen should be set to infinite, so as to more comprehensively reflect the impact of turbulence on optical signal propagation; third, when photons pass through multiple phase screens at one time, only the impact of the last phase screen is considered, ignoring the cumulative effect, which is easy to cause simulation deviations in long-distance transmission, and cannot accurately simulate the underwater optical transmission characteristics. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for modeling an underwater wireless optical transmission channel based on a multi-phase screen, thereby solving the problem that the prior method cannot accurately simulate the underwater optical transmission characteristics.

[0005] The present invention specifically adopts the following solutions to solve the above technical problems:

[0006] A method for modeling underwater wireless optical transmission channels based on a multi-phase screen comprises the following steps:

[0007] Step 1: Establish a three-dimensional coordinate system with the light source as the center and the propagation direction as the Z axis, and initialize the system parameters.

[0008] Set the plane where the light source is located as the XOY plane, and the photon propagation direction as the positive direction of the Z axis; set the underwater transmission distance, the light wavelength λ, the Gaussian beam width w0, and the receiving surface radius; in addition, it is also necessary to set the underwater absorption coefficient a, the scattering coefficient b, and the attenuation coefficient c=a+b;

[0009] Step 2: Generate n phase screens based on the ocean turbulence power spectrum. The distance between each phase screen and the light source plane is z1, z2, ... z n .

[0010] Selected ocean power spectrum Φ(k x ,k y ):

[0011]

[0012] Where ε is the energy dissipation rate per unit volume of seawater, χ T is the mean square temperature dissipation rate, ω is the ratio of ocean turbulence caused by temperature to ocean turbulence caused by salinity, and η is the internal scale of turbulence, where

[0013] A T =1.863×10 -2 , A S =1.9×10 -4 ,

[0014] A TS =9.41×10 -3 At this time, the phase spectrum of seawater on any slice perpendicular to the propagation direction of the light beam should be: F Φ (k x ,k y )=2πk 2 ΔzΦ(k x ,k y ), where Δz is the thickness of the turbulent layer or the propagation distance of the light beam, is the wave number of the beam. Φ (k x ,k y ) for the Gaussian random complex matrix h(k x ,k y ) is filtered and then Fourier transformed to obtain the phase screen

[0015]

[0016] Where C is the constant factor that controls the phase screen variance, Among them, Δκ x , Δκ yis the sampling interval; repeat the above steps and change the value of Δz to generate all phase screens.

[0017] Step 3, create an intermediate variable num, the variable num represents the phase screen number, and initialize num to 1.

[0018] Step 4: Determine the initial coordinates (x0, y0, z0) and initial direction vector of the photon Set the photon weight W, initialize the photon weight W = 1, and set the photon reception threshold W th .

[0019] The initial coordinates of the photon (x0, y0, z0) are generated as follows:

[0020] First, generate random numbers r1 and r2 with values ​​uniformly distributed between (0,1) to determine the radial distance between the photon and the center of the light source. Initial scattering angle of photons and the initial azimuth of the photon

[0021] Then, the initial coordinates (x0, y0, z0) and initial direction (u x0 ,u y0 ,u z0 ):

[0022]

[0023]

[0024] Initialize the photon weight W = 1. Set the photon reception threshold W th =10 -6 .

[0025] Step 5: The photon starts to transmit, generating the free step length d of the photon, and according to the direction vector of the photon transmission and the free step size d to update the photon's coordinates (x i ,y i ,z i ).

[0026] The free step length d of generated photons, ξ is a random number in the range of (0,1), c is the underwater attenuation coefficient, and the free step of a photon refers to the distance between the i-th collision and the i+1-th collision of the photon; the coordinates of the photon when it does not experience a free step (x before ,y before ,z before ),

[0027]

[0028] According to the coordinates (x before ,y before ,z before ) and the direction vector (u xi ,u yi ,u zi ), update the coordinates (x) of the photon after the free step i ,y i ,z i )

[0029]

[0030] Step 6: When num is less than or equal to the total number of phase screens, that is, num≤n: Determine whether the current z coordinate of the photon is less than the z coordinate of the current phase screen. num coordinate:

[0031] (1) If z < z num , indicating that the photon has not yet reached the current phase screen, the direction vector and weight of the photon are updated, and then the free step length of the photon is generated and the photon coordinates are updated according to step 5. At this time, num remains unchanged;

[0032] (2) If z ≥ z num , indicating that the photon has passed through the current phase screen, the photon is retracted to the plane where the phase screen is located, the direction vector of the photon is updated according to the generalized Snell's law, and the remaining step length d is calculated s , d s The original free step length d of the photon minus the distance the photon reaches the phase screen, the new photon coordinates are calculated according to the remaining free step length and the updated direction vector, and the photon weight is updated, and num is increased by 1;

[0033] (3) When num is greater than the total number of phase screens, go to step 7.

[0034] If the photon has not reached the phase screen, the photon's coordinates are updated as follows:

[0035] First, the scattering angle θ and azimuth angle are calculated according to the HG scattering phase function.

[0036]

[0037] Where g is an asymmetric factor, g=0.924, r4 and r5 are random numbers uniformly distributed between (0,1);

[0038] Then the photon direction (u xi+1 ,u yi+1 ,u zi+1 ) is updated as follows:

[0039]

[0040]

[0041] The weight of the photon is updated as follows: Where W i is the i-th weight of the photon, W i+1 is the i+1th weight of the photon, b is the scattering coefficient of seawater, and c is the attenuation coefficient of seawater.

[0042] The free step size and photon coordinates are updated as shown in step 5.

[0043] If the photon has passed through the current phase screen, the retreat process is as follows:

[0044] First calculate k1: Then, the distance d1 from the coordinates of the photon before movement to the phase screen plane is calculated based on k1: Then the photon retreats to the coordinate (x p ,y p ,z p )for:

[0045]

[0046] According to the generalized Snell's law, the direction of the photon (u xi ,u yi ,u zi ):

[0047]

[0048] Calculate the remaining free step length d s :d s =d-d1

[0049] Get the coordinates after passing through the phase screen (x i ,y i ,z i ):

[0050]

[0051] Then update num: num=num+1 and enter the next loop judgment.

[0052] When num is greater than the total number of phase screens, go to step 7.

[0053] Step 7: If the photon reaches the receiving surface and the weight is greater than the threshold, the photon is recorded as a valid received photon and its position is counted; if the photon does not reach the receiving surface, the photon direction and weight are continued to be updated to generate a new random step until the photon reaches the receiving surface.

[0054] The present invention proposes a modeling method for underwater wireless optical transmission channels based on multiple phase screens. This method not only takes into account the non-uniform distribution of phase screens, but also deeply analyzes the situation when photons pass through multiple phase screens at one time on the transmission path, thereby fully capturing the cumulative effect of turbulence on optical signals. Compared with traditional methods, the present invention significantly improves the accuracy and applicability of underwater optical channel modeling, and provides a scientific basis for the design and optimization of underwater optical communication systems.

[0055] Advantages or beneficial effects of the present invention:

[0056] (1) The present invention provides a modeling method for underwater wireless optical transmission channels based on multiple phase screens, which can accurately simulate the behavior of photons during underwater propagation. Existing methods usually only consider the influence of the last phase screen when photons pass through multiple phase screens, and ignore the cumulative effect of photons passing through multiple phase screens. The present invention accurately simulates the cumulative influence of each phase screen on the propagation direction of photons by considering the influence of each phase screen on photons when photons pass through multiple phase screens, thereby more accurately simulating the photon transmission process in a complex underwater environment.

[0057] (2) The underwater wireless optical transmission channel modeling method provided by the present invention can more realistically simulate the actual behavior of photons during underwater propagation. Unlike the existing method that assumes that the phase screen is uniformly distributed, the method of the present invention can adapt to the non-uniformly distributed phase screen, accurately reflect the spatial non-uniformity of turbulence intensity, and realistically simulate the dynamic changes of turbulence effects on optical signal propagation, thereby more accurately simulating the transmission characteristics of underwater channels and the propagation process of photons in complex underwater environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the process of photon propagation underwater in the embodiment;

[0059] Figure 2 It is a flow chart of a method for modeling an underwater wireless optical transmission channel based on a multi-phase screen in an embodiment. DETAILED DESCRIPTION

[0060] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments, examples of which are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0061] The specific implementation of the embodiment of the present disclosure is described in detail below with reference to the accompanying drawings.

[0062] like Figure 2 As shown, a method for modeling underwater wireless optical transmission channels based on a multi-phase screen includes the following steps:

[0063] Step 1: Establish a three-dimensional coordinate system with the light source as the center and the propagation direction as the Z axis, and initialize the system parameters:

[0064] Set the plane where the light source is located to the XOY plane, and the photon propagation direction to the positive direction of the Z axis; set the underwater transmission distance distance = 20m, the light wavelength λ = 532nm, the Gaussian beam width w0 = 2mm, and the receiving surface radius R = 0.5m; in addition, the underwater absorption coefficient a = 0.081m -1 , scattering coefficient b = 0.07m -1 , attenuation coefficient c = a + b;

[0065] Step 2: Generate three phase screens based on the ocean turbulence power spectrum. The distance between each phase screen and the light source plane is z1 = 5m, z2 = 12m, and z3 = 16m. The generated phase screens are as follows: Figure 1 As shown in the middle slice, it should be noted that Figure 1 The gray cylinder on the left side is the transmitting light source, the right side is the receiving end, the three thin sheets in the middle are turbulent phase screens, the small dots represent photons, and the arrowed lines leading from the small dots are the propagation paths of the photons.

[0066] For example, Figure 1 The specific process of generating a phase screen is as follows:

[0067] Selected ocean power spectrum Φ(k x ,k y ):

[0068]

[0069] Where ε is the energy dissipation rate per unit volume of seawater, χ T is the mean square temperature dissipation rate, ω is the ratio of ocean turbulence caused by temperature to ocean turbulence caused by salinity, and η is the internal scale of turbulence, where

[0070] A T =1.863×10 -2 , A S =1.9×10 -4 ,

[0071] A TS =9.41×10 -3 At this time, the phase spectrum of seawater on any slice perpendicular to the propagation direction of the light beam should be: F Φ (k x ,k y )=2πk 2 ΔzΦ(k x ,k y), where Δz is the thickness of the turbulent layer or the propagation distance of the light beam, is the wave number of the beam. Φ (k x ,k y ) for the Gaussian random complex matrix h(k x ,k y ) is filtered and then Fourier transformed to obtain the phase screen

[0072]

[0073] Where C is the constant factor that controls the phase screen variance, Among them, Δκ x , Δκ y is the sampling interval; repeat the above steps and change the value of Δz to 5m, 7m, and 4m to generate all phase screens.

[0074] Step 3, create an intermediate variable num, variable num is the phase screen number, and initialize num to 1.

[0075] Step 4: Determine the initial coordinates (x0, y0, z0) and initial direction vector of the photon Set the photon weight W, initialize the photon weight W = 1, and set the photon reception threshold W th The specific process is as follows:

[0076] The initial coordinates of the photon (x0, y0, z0) are generated as follows:

[0077] First, generate random numbers r1 and r2 with values ​​uniformly distributed between (0,1) to determine the radial distance between the photon and the center of the light source. Initial scattering angle of photons and the initial azimuth of the photon

[0078] Then, the initial coordinates (x0, y0, z0) and initial direction (u x0 ,u y0 ,u z0 ):

[0079]

[0080]

[0081] Initialize the photon weight W = 1. Set the photon reception threshold W th =10 -6 .

[0082] Step 5: The photon starts to transmit, generating the free step length d of the photon and calculating the direction vector (u xi ,u yi ,u zi ) and the free step size d to update the photon's coordinates (x i ,y i ,z i ).

[0083] The free step length d of generated photons, ξ is a random number in the range of (0,1), c is the underwater attenuation coefficient, and the free step of a photon refers to the distance between the i-th collision and the i+1-th collision of the photon; the coordinates of the photon when it does not experience a free step (x before ,y before ,z before ),

[0084]

[0085] According to the coordinates (x before ,y before ,z before ) and the direction vector (u xi ,u yi ,u zi ), update the coordinates (x) of the photon after the free step i ,y i ,z i )

[0086]

[0087] Step 6: When num is less than or equal to the total number of phase screens, that is, num≤n: Determine whether the current z coordinate of the photon is less than the z coordinate of the current phase screen. num coordinate:

[0088] (1) If z < z num , indicating that the photon has not yet reached the current phase screen, the direction vector and weight of the photon are updated, and then the free step length of the photon is generated and the photon coordinates are updated according to step 5. At this time, num remains unchanged;

[0089] (2) If z ≥ z num , indicating that the photon has passed through the current phase screen, the photon is retracted to the plane where the phase screen is located, the direction vector of the photon is updated according to the generalized Snell's law, and the remaining step length d is calculated s , d s The original free step length d of the photon minus the distance the photon reaches the phase screen, and num is increased by 1;

[0090] The specific steps are as follows:

[0091] If the photon has not reached the phase screen, the photon's coordinates are updated as follows:

[0092] First, the scattering angle θ and azimuth angle are calculated according to the HG scattering phase function.

[0093]

[0094] Where g is an asymmetric factor, g=0.924, r4 and r5 are random numbers uniformly distributed between (0,1);

[0095] Then the photon direction (u xi+1 ,u yi+1 ,u zi+1 ) is updated as follows:

[0096]

[0097]

[0098] The weight of the photon is updated as follows: Where W i is the i-th weight of the photon, W i+1 is the i+1th weight of the photon.

[0099] The free step size and photon coordinates are updated as shown in step 5.

[0100] If the photon has passed through the current phase screen, the retreat process is as follows:

[0101] First calculate k1: Then, the distance d1 from the coordinates of the photon before movement to the phase screen plane is calculated based on k1: Then the photon retreats to the coordinate (x p ,y p ,z p )for:

[0102]

[0103] According to the generalized Snell's law, the direction of the photon (u xi ,u yi ,u zi ):

[0104]

[0105] Calculate the remaining free step length d s :d s =d-d1

[0106] Get the coordinates after passing through the phase screen (x i ,yi ,z i ):

[0107]

[0108] Then update num: num=num+1 and enter the next loop judgment.

[0109] (3) When num is greater than the total number of phase screens, go to step 7.

[0110] Step 7: If the photon reaches the receiving surface and the weight is greater than the threshold, the photon is recorded as a valid received photon and its position is counted; if the photon does not reach the receiving surface, the photon direction and weight are continued to be updated to generate a new random step until the photon reaches the receiving surface.

[0111] In summary, the underwater wireless optical transmission channel modeling method based on multiple phase screens provided by the present invention can adapt to the situation of non-uniform distribution of phase screens, and takes into account the cumulative effect of photons passing through multiple phase screens, compared to traditional underwater optical transmission simulation methods. This method can more realistically reflect the impact of turbulence effects and complex underwater environments on optical signals by accurately simulating the actual behavior of photons during underwater propagation. The simulation model of the present invention has higher accuracy and reliability, can provide a scientific basis for the performance analysis of underwater optical communication systems, solves the problem that traditional methods cannot accurately simulate the underwater transmission process of photons, and provides strong technical support for system design and optimization.

[0112] The above description describes the embodiments of the present invention in detail, but the present invention is not limited to these specific embodiments. Various modifications, substitutions and improvements can be made within the knowledge of ordinary technicians in the field without violating the basic principles and core ideas of the present invention. These changes should be deemed to be included in the protection scope of the present invention.

Claims

1. A method for modeling underwater wireless optical transmission channels based on multi-phase screens, characterized in that: Include: Step 1, establish a three-dimensional coordinate system with the light source as the center and the propagation direction as the Z axis, and initialize the system parameters; Step 2: Generate n phase screens based on the ocean turbulence power spectrum. The distance between each phase screen and the light source plane is z1, z2, ... z n ; Step 3, create an intermediate variable num, the variable num represents the phase screen number, and initialize num to 1; Step 4: Determine the initial coordinates (x0, y0, z0) and initial direction vector (u x0 ,u y0 ,u z0 ), set the photon weight W, and initialize the photon weight W = 1, set the photon receiving threshold W th ; Step 5: The photon starts to transmit, generating the free step length d of the photon, and according to the direction vector of the photon transmission and the free step size d to update the photon's coordinates (x i ,y i ,z i ); Step 6: When num is less than or equal to the total number of phase screens, that is, num≤n: Determine whether the current z coordinate of the photon is less than the z coordinate of the current phase screen. num Coordinates: If z < z num , determine that the photon has not reached the current phase screen, then update the direction vector and weight of the photon, and then generate the free step length of the photon and update the photon coordinates according to step 5. At this time, num remains unchanged; If z ≥ z num , determine that the photon has passed through the current phase screen, then move the photon back to the plane where the phase screen is located, update the direction vector of the photon according to the generalized Snell's law, and calculate the remaining step length d s , d s Subtract the distance the photon reaches the phase screen from the original free step d of the photon, calculate the new photon coordinates according to the remaining free step and the updated direction vector, and update the photon weight, while adding 1 to num; if num is greater than the total number of phase screens, go to step 7; Step 7: If the photon reaches the receiving surface and the weight is greater than the threshold, the photon is recorded as a valid received photon and its position is counted; If the photon does not reach the receiving surface, continue to update the photon direction and weight, and generate a new random step size until the photon reaches the receiving surface.

2. The underwater wireless optical transmission channel modeling method based on multi-phase screen according to claim 1 is characterized in that: Step 6 deals with the effect of the phase screen on photon transmission as follows: When it is determined that the photon has not yet reached the current phase screen, the coordinates of the photon are updated as follows: First, the scattering angle θ and azimuth angle are calculated according to the HG scattering phase function. Where g is an asymmetric factor, g=0.924, r4 and r5 are random numbers uniformly distributed between (0,1); Then the photon direction (u xi+1 ,u yi+1 ,u zi+1 ) is updated as follows: The weight of the photon is updated as follows: Where W i is the i-th weight of the photon, W i+1 is the i+1th weight of the photon; When it is determined that the photon has passed through the current phase screen, the backoff process is as follows: First calculate k1: Then, the distance d1 from the coordinates of the photon before movement to the phase screen plane is calculated based on k1: Then the photon retreats to the coordinate (x p ,y p ,z p )for: According to the generalized Snell's law, the direction of the photon (u xi ,u yi ,u zi ): Calculate the remaining free step length d s :d s =d-d1 Get the coordinates after passing through the phase screen (x i ,y i ,z i ): Then update num: num=num+1 and enter the next loop judgment; When num is greater than the total number of phase screens, the effects of all phase screens on photon transmission are processed.

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