Fast Calculation Method for Scattering Channels of Non-Line-of-Sight Ultraviolet Optical Communication under Arbitrary Light Sources

Abstract

The present invention discloses a method for rapidly calculating the scattering channel of non-line-of-sight ultraviolet light communication under any light source. The method includes the following steps: Step 1, modeling the emission direction of the photon during the 0th scattering process according to the light intensity distribution of the light source; Step 2, modeling the scattering direction of the photon during the 1st to N-1th scattering according to the scattering phase distribution; Step 3, selecting the random transmission path of the photons that can be received during the Nth scattering; Step 4, calculating the reception probability of all equivalent scattering points by weighting to obtain the received light intensity of any order of scattering. The method of the present invention is no longer limited by the integration accuracy, can solve the problem of difficult simulation of the existing multi-order scattering model, and the method of the present invention has low complexity and can be practically applied to multi-order scattering scenarios; the method of the present invention has high calculation efficiency, solves the problem of low calculation efficiency of the existing Monte Carlo probability model, and further improves the calculation efficiency of the multi-order scattering channel.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and particularly relates to a fast calculation method for a non-line-of-sight ultraviolet optical communication scattering channel under an arbitrary light source. Background Art

[0002] At present, wireless optical communication is considered to be one of the key candidate technologies for future 6G communication due to its huge spectrum potential. Among them, ultraviolet optical communication can utilize the strong scattering effect in the "sun-blind" ultraviolet band (200-280 nm) to achieve non-line-of-sight communication, and has received extensive attention due to its high confidentiality and non-line-of-sight ability.

[0003] As the communication distance increases, the scattering effect of ultraviolet optical communication changes from single-order scattering to multi-order scattering. Existing ultraviolet multi-order scattering channel models are divided into analytical models and probabilistic models. The analytical models currently only have high accuracy for single-order scattering. For example, the invention patents with application numbers 201610121597.4 and 202010499796.5 are applicable to single-order scattering models; there are only approximate models for analytical multi-order scattering, and it is difficult to apply them to complex scenarios due to the limitation of integral accuracy. The probabilistic models use the Monte Carlo simulation method with high accuracy, but the calculation efficiency is low, which is not conducive to the analysis and design of non-line-of-sight ultraviolet optical communication systems.

[0004] In addition, non-line-of-sight ultraviolet optical communication systems mostly use laser or light-emitting diode (LED) light sources, but current ultraviolet optical communication channel models are mostly based on the assumption of a uniform light source and cannot accurately describe the distribution characteristics of actual laser or LED light sources. The difference between the simulated light source and the actual light source will directly affect the accuracy of ultraviolet channel analysis and further lead to serious performance estimation deviations. Summary of the Invention

[0005] In order to overcome the disadvantage that the light source assumption in the existing channel model does not match the actual situation, the present invention provides a fast calculation method for a non-line-of-sight ultraviolet optical communication scattering channel under an arbitrary light source. The method of the present invention includes the following steps:

[0006] Step 1, set that the ultraviolet optical communication system includes a transmitting end T located at the coordinate (0, r, 0) X and a receiving end R located at the origin of coordinates X , regard the field of view (FOV) of the receiving end R X as a cone, set the communication distance as r, and the direction vector of the axis of the beam of T X is μ T , the direction vector of the axis of the FOV of R X is μ R , and the divergence angle of the FOV of R X is β RNon-line-of-sight ultraviolet optical communication is generally divided into three processes: transmission, scattering, and reception. The transmission process is classified as the 0th scattering in photon-order scattering, and the processes of photon N-order scattering and photon reception calculation are described in detail. In the process of photon N-order scattering, the photon scattering direction and the random transmission path after scattering are determined, and based on this, photon-order scattering is divided into the 0th scattering, the 1st to (N - 1)th scatterings, and the Nth scattering;

[0007] Step 2: Model the emission direction of the photon's 0th scattering process according to the light intensity distribution of the light source. Only sample a finite number of emission directions from an infinite number of possible photon emission directions, and only sample a finite number of transmission points on the random transmission path after photon emission. The modeling objects are the emission, transmission, scattering, and reception processes of photons:

[0008] Step 2.1: Taking the emission light source as a Lambert source, its light intensity distribution satisfies the following formula (1):

[0009]

[0010] where m is the Lambert radiation parameter, the emission light source is located in the spherical coordinate system with T X as the center of the sphere, and the photon emission direction μ0 is described by the direction angles (θ, φ);

[0011] Step 2.2: The set of photon emission directions is a hemisphere with a radius of 1 Divide into K0 spherical zones with equal zenith angles θ0 The first spherical zone is a spherical cap, and the spherical zone corresponds to θ0, as shown in the following formula (2):

[0012]

[0013] Except for the spherical cap area, in the remaining spherical zones, the kth (k ∈ {2, 3,..., K0}) spherical zone is divided into k equal azimuth angles φ zones is proportional to the circumferential length C k of the radial cross-section of the spherical zone and is obtained through the following iterative formula (3):

[0014]

[0015] Step 2.3: Sample the divided zones The first spherical zone is a spherical cap, and the sampling photon emission directions of the spherical cap area are μ T ={μ T,x , μ T,y , μ T,z}, and Central axis is the sampling photon emission direction of the th region in the kth spherical zone, then the sampling photon emission directions are as shown in the following formulas (4) and (5):

[0016]

[0017]

[0018] Step 2.4, convert the sampling photon emission directions in the spherical coordinate system to the photon emission directions in the global Cartesian coordinate system. Among them,

[0019]

[0020]

[0021]

[0022] Step 2.5, determine the random transmission path of the emitted photons. Let be the distance between the starting point of the 0th scattering transmission path and T x , be the distance between the ending point and T x . The starting point of the emitted random transmission path is T x , and the ending point is at infinity. Then

[0023] Step 2.6, sample the random transmission path of the photons. Take M0 points with equal occurrence probabilities on the transmission path as the sampling points. These M0 sampling points are equivalent scattering points, and their position vectors are Use the probability of the sampling points to represent the photon probability in their neighborhoods. Utilize the probability density function of the transmission distance of the photons before being absorbed / scattered, as shown in the following formula (9):

[0024] f(d) = k e exp{-k e d}...(9),

[0025] Solve for the vector coordinates of the equivalent scattering points in the global coordinate system Among them, k e is the atmospheric extinction coefficient. Let the distance between the m0-th equivalent scattering point, where m0 ∈ {1, 2,..., M0}, and T x be Then the photon scattering probability of the m0-th equivalent scattering point can be expressed by the photon scattering probabilities at the starting / ending points of the transmission path, as shown in the following formula (10):

[0026]

[0027] Calculate the distance between the equivalent scattering point and T x as shown in the following formula (11):

[0028]

[0029] When as shown in the following formula (12):

[0030]

[0031] Indicated by T X as shown in the following formula (13):

[0032]

[0033] Step 3: Model the scattering directions of photons for the 1st to N-1th scatterings according to the scattering phase distribution, replace the infinitely possible transmission directions of photons with the typical transmission direction, and replace the random transmission path of photons with the equivalent scattering point:

[0034] Step 3.1: In the 1st to N-1th photon scatterings, the transmission direction of the photon for each scattering is distributed according to the scattering probability density function f P (θ, φ), and the direction angles (θ, φ) are used to describe the photon transmission direction The transmission direction (θ, φ) of photon scattering, θ ∈ [0, 2π], φ ∈ [0, 2π], and the set of transmission directions of the photon for the nth scattering is a sphere with a radius of 1

[0035] Step 3.2: Referring to the photon transmission direction sampling method for the 0th scattering, similarly divide zenith angles θ n into K n spherical zones The first spherical zone is a spherical cap. Except for the spherical cap region, divide the kth ∈ {2, 3,..., E n} spherical zone into equal azimuth angles divide into regions Sample the divided regions using the photon transmission direction before scattering as the sampling photon emission direction for the spherical cap region, and use the central axis of as the n kth The sampling photon emission directions of a region, then the sampling photon emission direction angles are As shown in the following formulas (14)-(15):

[0036]

[0037]

[0038] Step 3.3, convert the n-th scattering direction of the sampled photons in the spherical coordinate system to the photon scattering direction in the coordinate system of the ultraviolet optical communication system As shown in the following formulas (16)-(18):

[0039]

[0040]

[0041]

[0042] Step 3.4, determine the random transmission path of the photons after the n-th scattering. Let d n be the distance between the end point of the n-th scattering transmission path and the photon scattering point q n . Among them, is the starting point distance, is the ending point distance. The starting point of the random transmission path after scattering is q n , and the ending point of the transmission path is at infinity. Then

[0043] Step 3.5, referring to the sampling method of the random transmission path of the photons after the 0-th scattering, similarly take M n scattering points with equal occurrence probabilities as the sampling points of the random transmission path of the photons after the n-th scattering. Using the relationship between the equivalent scattering points and the photon scattering probability densities at the starting and ending points of the photon random transmission path, calculate the distance between the m n ∈{1, 2,..., M n}th equivalent scattering point and the photon scattering point q n as shown in the following formula (19):

[0044]

[0045] Calculate the position vector of the equivalent scattering point in the global coordinate system as shown in the following formula (20):

[0046]

[0047] Step 4: Select the random transmission path of the photons that can be received in the Nth scattering according to the intersection point of the photon transmission direction before the Nth scattering and the cone surface of the Field of View (FOV).

[0048] Step 4.1: In the Nth scattering, the transmission direction of the received photons before scattering needs to have an intersection point p with the FOV cone surface i , to reduce redundant calculations, only consider the random transmission paths of the photons that can be received in the (N - 1)th scattering of the photons, and take p i as the end point of the random transmission path of the received photons, i = 1, 2, where p1 is the starting point and p2 is the intersection point as the end point, s i is the distance between the end point of the random transmission path of the photons before the Nth scattering and the previous-order scattering point q N-1 , i = 1, 2, where s1 is the starting point distance and s2 is the end point distance, and set the position vector of the previous-order scattering point q N-1 to be If only single-order scattering of photons is considered, then take T X as the previous-order scattering point;

[0049] Step 4.2: p i is the starting point and the escaping point of the photon in the FOV. According to the vector positions of the starting point and the escaping point obtain a quadratic equation about s i as shown in the following formula (21):

[0050]

[0051] Use the quadratic formula to solve the equation, and determine the geometric meaning of the solution of the equation according to whether q N-1 is inside the FOV. When q N-1 is inside the receiving field of view FOV, take the starting point as the previous-order scattering point q N-1 , take the end point as the intersection point p2, s1 = 0, s2 = min(s i ), when there is no positive real solution s i , take the end point as infinity, s2 = ∞; when q N-1 is outside the receiving field of view FOV, when there are two positive real solutions, take the starting point as the intersection point p1 and the end point as the intersection point p2, when there is only one positive real solution, take the starting point as the intersection point p1 and the end point as infinity, s1 = s i , s2 = ∞;

[0052] Step 5: Assign corresponding weights to the photons according to the light intensity distribution in the photon sampling direction, and calculate the reception probability of all equivalent scattering points by weighting to obtain the received light intensity of any order of scattering;

[0053] Step 5.1: In the 0th scattering, the emission probability of the sampled photons represents the emission probability of photons passing through its neighborhood. Then, sample the photon emission probability as in the following formula (22):

[0054]

[0055] Step 5.2, during the 1st to N - 1th scattering, the sampled transmission probability of the nth photon scattering can represent the transmission probability of photons passing through its neighborhood. Then, the sampled transmission probability of the nth photon scattering is as in the following formula (23):

[0056]

[0057] Step 5.3, due to the equivalent scattering point of the random transmission path after the nth photon scattering having the characteristic that the photon absorption / scattering probabilities are equal, the photon scattering probability p at the mth sampling point of the random transmission path after the nth photon scattering n , is as in the following formula (24):

[0058]

[0059] During the 0th to N - 2th scattering Then, the photon scattering probability p at the mth sampling point of the random transmission path after the nth photon scattering n , is as in the following formula (25):

[0060]

[0061] The random transmission path of photons that can be received during the N - 1th scattering has the starting point and the escape point of the FOV as endpoints. Then, the photon scattering probability p at the mth sampling point of the random transmission path of photons that can be received during the N - 1th scattering N-1 , is as in the following formula (26):

[0062]

[0063] Step 5.4, the probability P that a photon is scattered and received at the mth equivalent scattering point during the Nth scattering R , is as in the following formula (27):

[0064]

[0065] Where represents the vertical receiving - end component of the received light energy is the angle between μ R and , and the scattering - phase probability density function p s (θ k→m ,0) of θ k→mRefers to the propagation direction of the photon before the Nth scattering and the included angle;

[0066] Step 5.5, the Nth-order scattering reception probability of the photon The following formula (28) is obtained by weighting the reception probability through the equivalent scattering point:

[0067]

[0068] The method described in the present invention has the following beneficial effects:

[0069] 1. The method described in the present invention is an analytical calculation model. Compared with the existing analytical calculation models, the method described in the present invention is no longer limited by the integration accuracy, can solve the deficiencies of the existing multi-order scattering model in simulation difficulties, and the method described in the present invention is simple and can be actually applied to multi-order scattering scenarios;

[0070] 2. Compared with the high-photon-number Monte Carlo simulation method with the same accuracy, the method described in the present invention has high calculation efficiency. The calculation efficiency of the first two-order scattering power is improved by more than two orders of magnitude compared with the Monte Carlo probability model, solving the defect of the low calculation efficiency of the existing Monte Carlo probability model and further improving the calculation efficiency of the multi-order scattering channel;

[0071] 3. The calculation model described in the present invention is applicable to the emission light source with any light intensity distribution, can accurately describe the light intensity distribution characteristics of the actually used light source, is beneficial to promoting the application scenarios of the ultraviolet communication system. The method described in the present invention solves the calculation difficulties of the existing multi-order scattering analytical model and the defect of the low calculation efficiency of the Monte Carlo probability model by replacing the infinite possible propagation directions of the photon with the typical propagation direction and the random propagation path of the photon with the equivalent scattering point. Brief Description of the Drawings

[0072] Figure 1 is a schematic diagram of the ultraviolet communication transceiver channel modeling of the method described in the present invention;

[0073] Figure 2 is a schematic diagram of the photon nth scattering propagation direction modeling of the method described in the present invention;

[0074] Figure 3 is the intersection point schematic diagram of the photon propagation direction and the FOV conical surface at different q N-1 positions of the method described in the present invention;

[0075] Figure 4 is the single-order scattering channel impulse response comparison diagram of the method described in the present invention and the high-photon-number (photon number is 5*10 8 ) Monte Carlo simulation method. Detailed Embodiments

[0076] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0077] The method of the present invention comprises the following steps:

[0078] Step 1, as Figure 1 shown, it is assumed that the ultraviolet optical communication system includes a transmitting end T located at the coordinate (0, r, 0) X and a receiving end R located at the origin of coordinates X . The field of view (Field of View, FOV) of the receiving end R X is regarded as a cone. It is assumed that the communication distance is r, and the direction vector of the axis of the T X light beam is μ T , and the direction vector of the axis of the FOV of the R X is μ R . The divergence angle of the FOV of the R X is β R . Non-line-of-sight ultraviolet optical communication is generally divided into three processes: transmission, scattering, and reception. The transmission process is classified as the 0th scattering in photon-order scattering. The processes of photon N-order scattering and photon reception calculation are described in detail. In the process of photon N-order scattering, the photon scattering direction and the random transmission path after photon scattering are determined, and based on this, photon-order scattering is divided into the 0th scattering, the 1st to N-1th scatterings, and the Nth scattering;

[0079] Step 2, model the emission direction of the photon in the 0th scattering process according to the light intensity distribution of the light source. Only sample a finite number of emission directions from an infinite number of possible photon emission directions, and only sample a finite number of transmission points on the random transmission path after photon emission. The modeling objects are the emission, transmission, scattering, and reception processes of photons:

[0080] Step 2.1, taking the emission light source as a Lambert source, its light intensity distribution satisfies the following formula (1):

[0081]

[0082] where m is the Lambert radiation parameter. The emission light source is located in the spherical coordinate system with T X as the center of the sphere, and the photon emission direction μ0 is described by the direction angles (θ, φ);

[0083] Step 2.2, the set of photon emission directions is a hemisphere with a radius of 1 . Divide it into K0 spherical zones with equal zenith angles θ0 . Among them, the first spherical zone is a spherical cap, and the spherical zone corresponds to θ0, as shown in the following formula (2):

[0084]

[0085] Except for the spherical cap region, in the remaining spherical zones, the k-th spherical zone where k ∈ {2, 3,..., K0} with equal azimuth φ k is divided into zones and is proportional to the circumferential length C of the radial cross-section of the spherical zone, and is obtained through the following iterative formula (3): k It is proportional to the circumferential length C of the radial cross-section of the spherical zone and is obtained through the following iterative formula (3):

[0086]

[0087] Step 2.3, sample the divided zones For the first spherical zone, the sampling photon emission directions for the spherical cap are the axes μ T ={μ T,x , μ T,y , μ T,z}, and taking the central axis as the sampling photon emission direction for the -th zone in the k-th spherical zone, then the sampled photon emission directions are as shown in the following formulas (4) and (5): Such as the following formulas (4) and (5):

[0088]

[0089]

[0090] Step 2.4, convert the sampled photon emission directions in the spherical coordinate system to the photon emission directions in the global Cartesian coordinate system where are as shown in the following formulas (6)-(8):

[0091]

[0092]

[0093]

[0094] Step 2.5, determine the random transmission path of the emitted photons. Let be the distance between the starting point of the 0-th scattering transmission path and T x , be the distance between the ending point and T x , the starting point of the emitted random transmission path is T x , and the ending point is at infinity, then

[0095] Step 2.6, sample the random transmission path of photons, and take M0 points with equal occurrence probabilities on the transmission path as sampling points. These M0 sampling points are equivalent scattering points, and their position vectors are Use the probability of the sampling point to represent the photon probability in its neighborhood, and use the probability density function of the transmission distance before the photon is absorbed / scattered, as shown in the following formula (9):

[0096] f(d) = k e exp{-k e d}……(9),

[0097] Solve the vector coordinates of the equivalent scattering points in the global coordinate system where k e is the atmospheric extinction coefficient. Let the distance between the m0-th equivalent scattering point, where m0 ∈ {1, 2,..., M0}, and T x be Then the photon scattering probability of the m0-th equivalent scattering point can be expressed by the photon scattering probabilities at the start / end points of the transmission path, as shown in the following formula (10):

[0098]

[0099] Calculate the distance between the equivalent scattering point and T x as shown in the following formula (11):

[0100]

[0101] When as shown in the following formula (12):

[0102]

[0103] It is represented by T X as shown in the following formula (13):

[0104]

[0105] Step 3, model the scattering directions of photons for the 1st to (N - 1)-th scatterings according to the scattering phase distribution, replace the infinite possible transmission directions of photons with typical transmission directions, and replace the random transmission path of photons with equivalent scattering points:

[0106] Step 3.1, in the 1st to (N - 1)-th photon scatterings, the transmission direction of the photon for each scattering is distributed according to the scattering probability density function f P (θ, φ), and the direction angles (θ, φ) are used to describe the photon transmission direction The transmission direction (θ, φ) of the photon scattering, where θ ∈ [0, 2π] and φ ∈ [0, 2π], as Figure 2As shown, the set of the transmission directions of the n-th photon scattering is a sphere with a radius of 1

[0107] Step 3.2, referring to the sampling method of the transmission direction of the 0-th scattered photon, similarly zenith angles θ n are divided into K n spherical zones The first spherical zone is a spherical cap. Except for the spherical cap region, for the k-th spherical zone in the remaining spherical zones where k ∈ {2, 3,..., K} n spherical zone equal azimuth angles are divided into zones For the divided zones sampling is performed. Taking the transmission direction of the photon before scattering as the sampling photon emission direction of the spherical cap region, and taking the central axis of as the sampling photon emission direction of the -th zone in the k-th spherical zone, then the sampling photon emission direction angles are k n -th as shown in the following formulas (14)-(15):

[0108]

[0109]

[0110] Step 3.3, convert the n-th scattered direction of the photon sampled in the spherical coordinate system to the scattered direction of the photon in the ultraviolet communication system coordinate system as shown in the following formulas (16)-(18):

[0111]

[0112]

[0113]

[0114] Step 3.4, determine the random transmission path of the photon after the n-th scattering. Let d n be the distance between the end point of the n-th scattering transmission path and the photon scattering point q n . Among them, is the starting point distance, is the end point distance. The starting point of the random transmission path after scattering is q n , and the end point of the transmission path is at infinity. Then

[0115] ​​Step 3.5, referring to the photon random transmission path sampling method after the 0th scattering, similarly take M n scattering points with equal occurrence probabilities as the sampling points of the photon random transmission path after the nth scattering. Using the photon scattering probability density relationship between the equivalent scattering points and the starting and ending points of the photon random transmission path, calculate the distance between the m n ∈{1, 2,..., M n} equivalent scattering points and the photon scattering point q n , as shown in the following formula (19):

[0116]

[0117] Calculate the position vector of the equivalent scattering point in the global coordinate system , as shown in the following formula (20):

[0118]

[0119] Step 4, according to the intersection point of the photon transmission direction before the Nth scattering and the cone surface of the receiving field of view (Field of View, FOV), select the photon random transmission paths that can be received in the Nth scattering:

[0120] Step 4.1, in the Nth scattering, the transmission direction of the received photon before scattering needs to have an intersection point p i with the FOV cone surface. To reduce redundant calculations, only consider the photon random transmission paths that can be received in the (N - 1)th scattering of the photon. Take p i as the end point of the random transmission path of the received photon, i = 1, 2, where p1 is the starting point and p2 is the intersection point as the end point, and s i is the distance between the end point of the photon random transmission path before the Nth scattering and the previous-order scattering point q N-1 , i = 1, 2, where s1 is the starting point distance and s2 is the end point distance. Set the position vector of the previous-order scattering point q N-1 as If only considering single-order photon scattering, then take T X as the previous-order scattering point;

[0121] Step 4.2, p i is the starting point and the escaping point of the photon in the FOV. According to the vector positions of the starting point and the escaping point obtain a quadratic equation about s i , as shown in the following formula (21):

[0122]

[0123] Use the quadratic formula to solve the equation. According to q N-1Determine the geometric meaning of the solution of the equation within the FOV, such as Figure 3 As shown, when q N-1 is within the receiving field of view FOV, take the starting point as the previous-order scattering point q N-1 , take the ending point as the intersection point p2, s1 = 0, s2 = min(s i ). When there is no positive real solution s i , take the ending point as infinity, s2 = ∞; when q N-1 is outside the receiving field of view FOV, when there are two positive real solutions, take the starting point as the intersection point p1 and the ending point as the intersection point p2. When there is only one positive real solution, take the starting point as the intersection point p1 and the ending point as infinity, s1 = s i , s2 = ∞;

[0124] Step 5: Assign corresponding weights according to the light intensity distribution in the photon sampling direction, and calculate the receiving probabilities of all equivalent scattering points through weighted calculation to obtain the received light intensity of any-order scattering;

[0125] Step 5.1: In the 0th scattering, the sampling photon emission probability represents the emission probability of the photon passing through its neighborhood. Then the sampling photon emission probability is as shown in the following formula (22):

[0126]

[0127] Step 5.2: In the 1st to N - 1th scatterings, the sampling transmission probability of the nth photon scattering can represent the transmission probability of the photon passing through its neighborhood. Then the sampling transmission probability of the nth photon scattering is as shown in the following formula (23):

[0128]

[0129] Step 5.3: The equivalent scattering point of the random transmission path after the nth photon scattering has the characteristic that the photon absorption / scattering probabilities are equal. The photon scattering probability p n of the mth sampling point on the random transmission path after the nth photon scattering is as shown in the following formula (24):

[0130]

[0131] In the 0th to N - 2th scatterings, Then the photon scattering probability p n of the mth sampling point on the random transmission path after the nth photon scattering is as shown in the following formula (25):

[0132]

[0133] In the (N - 1)-th scattering, if the random transmission path of the received photon has the starting point and the escape point of the FOV as its endpoints, then the photon scattering probability p at the m-th sampling point of the random transmission path of the receivable photon in the (N - 1)-th scattering N-1 , as shown in the following formula (26):

[0134]

[0135] Step 5.4, the probability P that a photon is scattered and received at the m-th equivalent scattering point in the N-th scattering R , as shown in the following formula (27):

[0136]

[0137] Wherein, represents the vertical receiving end component of the received light energy, is μ R and the included angle of, the scattering phase probability density function p s (θ k→m , 0) of θ k→m refers to the transmission direction of the photon before the N-th scattering and the included angle of;

[0138] Step 5.5, the N-th order scattering reception probability of the photon is obtained by weighting the reception probability through the equivalent scattering point as the following formula (28):

[0139]

[0140] Figure 4 is the single-order scattering channel impulse response of the method described in the present invention and the high-photon-number Monte Carlo simulation method. Among them, the Monte Carlo simulation method takes 285 s, and the fast calculation method only takes 0.0026 s. Under an extremely short calculation time, the simulation results of the method described in the present invention are similar to those of the high-photon-number Monte Carlo simulation method.

[0141] As mentioned above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any change or replacement that can be easily thought of by those skilled in the art within the scope disclosed by the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A fast calculation method for the scattering channel of non-line-of-sight ultraviolet light communication under any light source, characterized in that, Including the following steps: Step 1, set that the ultraviolet communication system includes a transmitting end T located at the coordinate (0, r, 0) X and a receiving end R located at the origin of coordinates X , regard the Field of View (FOV) of the receiving end R X as a cone, set the communication distance as r, the direction vector of the axis of the T X light beam pointing is μ T , the direction vector of the axis of the FOV of R X is μ R , the FOV divergence angle of R X is β R ; Non-line-of-sight ultraviolet communication is usually divided into three processes: transmission, scattering, and reception. The transmission process is classified as the 0th scattering in photon-order scattering. The processes of photon N-order scattering and photon reception calculation are described in detail. In the process of photon N-order scattering, determine the photon scattering direction and the random transmission path after photon scattering, and classify the photon-order scattering into the 0th scattering, the 1st to N-1th scatterings, and the Nth scattering accordingly; Step 2: Model the emission direction of the photon in the 0th scattering process according to the light intensity distribution of the light source. Only sample a finite number of emission directions from an infinite number of possible photon emission directions, and only sample a finite number of transmission points on the random transmission path after the photon is emitted. The modeling object is the emission, transmission, scattering, and reception processes of the photon: Step 2.1: Taking the Lambertian light source as an example for the emission light source, its light intensity distribution satisfies the following formula (1): where m is the Lambert radiation parameter, the emission light source is located in the spherical coordinate system with T X as the center of the sphere, and the photon emission direction μ0 is described by the direction angles (θ, φ); Step 2.2, the photon emission direction set is a hemisphere with a radius of 1 Divide into K0 spherical zones with an equal zenith angle θ0 where the first spherical zone is a spherical cap, and the spherical zone corresponds to θ0 as shown in the following formula (2): Except for the spherical cap region, in the remaining spherical zones, the \(k^{th}\) spherical zone where \(k\in\{2,3,\cdots,K0\}\) equal azimuth angle \(\varphi\) k is divided into zones and is proportional to the circumferential length \(C\) of the radial section of the spherical zone, and is obtained through the following iterative formula (3): k proportional to Step 2.3, for the divided region sample it. The first spherical zone is a spherical cap with the emission beam axis μ T ={μ T,x , μ T，y , μ T，z} as the sampling photon emission direction of the spherical cap region. Taking the central axis as the sampling photon emission direction of the th region in the k-th spherical zone, the sampled photon emission direction is as follows in formulas (4) and (5): Step 2.4, convert the photon emission direction sampled in the spherical coordinate system into the photon emission direction in the global Cartesian coordinate system where as shown in the following formulas (6)-(8): Step 2.5, determine the random transmission path of the emitted photons. Let be the distance between the starting point of the 0th scattering transmission path and T x , be the distance between the ending point and T x . The starting point of the randomly transmitted path of the emitted photons is T x , and the ending point is at infinity. Then Step 2.6, sample the random transmission path of photons, and take M0 points with equal occurrence probabilities on the transmission path as sampling points. These M0 sampling points are equivalent scattering points, and their position vectors are Use the probability of the sampling point to represent the photon probability in its neighborhood, and use the probability density function of the transmission distance before the photon is absorbed / scattered as the following formula (9): f(d) = k e exp{-k e d}……(9), Solve for the vector coordinates of the equivalent scattering points in the global coordinate system where k e is the atmospheric extinction coefficient. Let the distance between the m0-th equivalent scattering point, where m0 ∈ {1, 2,..., M0}, and T x be Then the photon scattering probability of the m0-th equivalent scattering point is expressed in terms of the photon scattering probabilities at the start / end points of the transmission path by the following formula (10): Calculate the distance between the equivalent scattering point and T x as shown in the following formula (11): As shown in the following formula (12): Via T X It is expressed as the following formula (13): Step 3: Model the scattering directions of the photons in the 1st to (N - 1)th scattering processes according to the scattering phase distribution. Replace the infinite possible transmission directions of the photons with typical transmission directions, and replace the random transmission path of the photons with equivalent scattering points: Step 3.1, in the 1 to N - 1 photon scatterings, the propagation direction of the photon in each scattering is distributed according to the scattering probability density function f P (θ, φ), and the propagation direction of the photon is described by the direction angles (θ, φ) The propagation direction (θ, φ) of photon scattering, θ ∈ [0, 2π], φ ∈ [0, 2π], and the set of propagation directions of the photon in the nth scattering is a sphere with a radius of 1 Step 3.2, refer to the sampling method of the 0th scattered photon transmission direction, and similarly Equal zenith angle θ n Divided into K n Ball belt The first spherical zone is the spherical crown. Except for the spherical crown area, the k∈{2, 3, ..., K n } ball belt Equal azimuth Divided into Regions Divide the area Sampling is performed to determine the direction of photon transmission before scattering is the emission direction of the sampled photons in the spherical cap area, central axis For the kth n The first ball The sampling photon emission direction of the region, then the sampling photon emission direction angle is As shown in the following formulas (14)-(15): Step 3.3, convert the n-th scattering direction of the photon sampled in the spherical coordinate system to the photon scattering direction in the coordinate system of the ultraviolet communication system as shown in the following formulas (16)-(18): Step 3.4, determine the random transmission path of the photon after the nth scattering. Let d n be the distance between the endpoint of the transmission path after the nth scattering and the photon scattering point q n , where is the starting point distance, is the ending point distance. The starting point of the random transmission path after scattering is q n , and the endpoint of the transmission path is at infinity. Then Step 3.5, referring to the photon random transmission path sampling method after the 0th scattering, similarly take M n scattering points with equal occurrence probabilities as the sampling points of the photon random transmission path after the nth scattering. Using the relationship between the equivalent scattering points and the photon scattering probability density at the starting and ending points of the photon random transmission path, calculate the distance between the m n ∈ {1, 2,..., M n} equivalent scattering points and the photon scattering point q n as shown in the following formula (19): Calculate the position vector of the equivalent scattering point in the global coordinate system As shown in the following formula (20): Step 4: Select the random transmission path of the photons that can be received in the Nth scattering according to the intersection point of the photon transmission direction before the Nth scattering and the cone surface of the receiving field of view (FOV); Step 5: Assign corresponding weights to the photons according to the light intensity distribution in the sampling direction, and calculate the reception probability of all equivalent scattering points by weighted calculation to obtain the received light intensity of any order of scattering.

2. The rapid calculation method for a non-line-of-sight ultraviolet light communication scattering channel under any light source according to claim 1, characterized in that The said Step 4 includes the following steps: Step 4.1, in the Nth scattering, the propagation direction of the receivable photon before scattering needs to have an intersection point p with the FOV conical surface i , to reduce redundant calculations, only consider the random propagation paths of the receivable photons in the (N - 1)th scattering of the photons, and take p i as the end point of the random propagation path of the receivable photon, i = 1, 2, where p1 is the starting point and p2 is the intersection point as the end point, s i is the distance between the end point of the random propagation path of the photon before the Nth scattering and the previous - order scattering point q N-1 , i = 1, 2, where s1 is the starting - point distance and s2 is the end - point distance. Set the position vector of the previous - order scattering point q N-1 to be If only considering single - order scattering of photons, then take T X as the previous - order scattering point; Step 4.2, p i are the starting point and the escaping point of the photon in the FOV. According to the vector positions of the starting point and the escaping point obtain a quadratic equation about s i as shown in the following formula (21): Solve the equation using the quadratic formula. According to q N-1 inside the FOV determines the geometric meaning of the equation solution. When q N-1 is inside the receiving field of view FOV, take the starting point as the previous-order scattering point q N-1 , take the ending point as the intersection point p2, s1 = 0, s2 = min(s i ). When there is no positive real solution s i , take the ending point as infinity, s2 = ∞; when q N-1 is outside the receiving field of view FOV, when there are two positive real solutions, take the starting point as the intersection point p1 and the ending point as the intersection point p2. When there is only one positive real solution, take the starting point as the intersection point p1 and the ending point as infinity, s1 = s i , s2 = ∞.

3. The fast calculation method for the scattering channel of non-line-of-sight ultraviolet optical communication under any light source according to claim 1, characterized in that The said Step 5 includes the following steps: Step 5.1, in the 0th scattering, the sampling photon emission probability represents the emission probability of a photon passing through its neighborhood, and the sampling photon emission probability is as shown in the following formula (22): Step 5.2, in the 1st to N-1th scattering, the sampling transmission probability of the nth photon scattering represents the transmission probability of the photon passing through its neighborhood, and the sampling transmission probability of the nth photon scattering is as shown in the following formula (23): Step 5.3, equivalent scattering points of the random transmission path after the n-th photon scattering has the characteristic of equal photon absorption / scattering probability, and the photon scattering probability p of the m-th sampling point of the random transmission path after the n-th photon scattering n is as shown in the following formula (24): In the 0th to N-2th scattering, Then, the photon scattering probability p of the mth sampling point of the random transmission path after the nth photon scattering n is as shown in the following formula (25): The random transmission path of photons receivable in the (N - 1)-th scattering has the starting point and the escape point of the FOV as its endpoints. Then, the photon scattering probability p of the m-th sampling point on the random transmission path of photons receivable in the (N - 1)-th scattering N-1 is as shown in the following formula (26): Step 5.4, probability P that the photon is received after scattering at the m-th equivalent scattering point in the N-th scattering R As shown in the following formula (27): Among them, represents the vertical receiving end component of the received light energy, is μ R and the included angle between, the scattering phase probability density function p s (θ k→m , 0) of θ k→m refers to the propagation direction of the photon before the Nth scattering and the included angle; Step 5.5, Photon Nth-Order Scattering Reception Probability The following formula (28) is obtained by weighting the reception probability through the equivalent scattering points:

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