Ray tracing-based channel modeling method directed to low-orbit satellite communication

Abstract

The present invention relates to the technical field of wireless communications. Provided are a ray tracing-based channel modeling method directed to low-orbit satellite communication. Said method mainly solves the current problem of the accuracy of a channel model being low due to not completely considering channel characteristics during low-orbit satellite channel modeling. Said method is achieved by the following steps: generating basic parameters of atmospheric and near-ground end environments, said parameters comprising an ionospheric scintillation parameter, a rainfall parameter, and a near-ground environment parameter; considering a channel model of large-scale fading and near-ground end small-scale fading, comprising ionospheric scintillation, rainfall fade, and ray tracing-based multipath effect modeling; and calculating received power-related parameters, comprising power delay profiles under different near-ground scenarios, and the total received powers under different satellite pitches and rainfall rates. According to the present invention, a low-orbit satellite channel is effectively modeled on the basis of ray tracing, taking into consideration the influences of ionospheric scintillation and rainfall in the atmosphere, which provides high accuracy. Moreover, for low-orbit satellite channel analysis, a simulation result has value as reference.

Description

A ray tracing channel modeling method for low-orbit satellite communications Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a ray tracing channel modeling method for low-orbit satellite communications. Background Art

[0002] With the completion of the first set of standards for fifth-generation (5G) mobile communication systems, initial commercial deployment of 5G wireless networks began in 2019. However, the revolutionary vision of 5G has not been fully realized. Current 5G wireless networks still have many shortcomings in the Internet of Everything (IoE) system, which connects a massive number of users and devices. The goal of sixth-generation (6G) wireless networks is not only to achieve higher transmission rates but also to further expand the boundaries and scope of the IoE based on 5G wireless network services. Satellite communication networks are a key focus of 6G wireless network research. Compared to terrestrial wireless communication systems, satellite communication systems offer advantages such as wide coverage and high communication capacity. Specifically, low-orbit satellites offer lower latency, lower power consumption, lower propagation loss, and more flexible networking compared to high- and medium-orbit satellite communication systems. In recent years, the next-generation internet constellation plan has been gradually implemented, achieving a transition from low-frequency bands such as L (1-2 GHz) and S (2-4 GHz) to high-frequency bands such as Ku (12-18 GHz) and Ka (26-40 GHz). To achieve reliable and effective transmission of low-orbit satellite communication information, a necessary task is to study the propagation characteristics of low-orbit satellite communication channels and model them.

[0003] Low-Earth Orbit (LEO) satellite communication channels are subject to numerous influences, including atmospheric absorption, rainfall attenuation, ionospheric scintillation, and Doppler shift. Consequently, they exhibit significant time-variance, making accurate analysis difficult. Existing LEO satellite channel modeling methods include geometric random channel modeling and ray tracing. Existing research uses geometric random channel modeling, which offers high generalizability. However, given the high accuracy requirements of current 5G mobile communication systems, ray tracing offers higher accuracy than geometric random channel modeling. Some researchers have used ray tracing to model LEO satellite channels in scenarios such as helicopters, cities, and satellite solar panels. However, few have considered influencing factors such as ionospheric scintillation and rainfall in the atmosphere, and the analysis of the characteristics of multipath effects in urban areas has not been fully studied. In summary, an accurate LEO satellite channel model is essential for the development of 6G wireless communication networks.

[0004] Summary of the Invention

[0005] Objective of the Invention: To propose a ray-tracing channel modeling method for low-earth orbit satellite communication to solve the above problems existing in the prior art.

[0006] A ray-tracing channel modeling method for low-earth orbit satellite communication comprises the following steps:

[0007] S1. Generate low-earth orbit satellite system parameters; the low-earth orbit satellite system parameters include basic parameters, atmospheric channel environment parameters, and near-earth end channel environment parameters;

[0008] S2. Model the fading channel of the large-scale part, including ionospheric scintillation fading modeling and rainfall attenuation modeling;

[0009] S3. Model the small-scale fading channel at the near-earth end, including multipath effect modeling based on the ray-tracing method;

[0010] S4. Based on steps S1 to S3, calculate the large-scale fading loss and multipath received power of the low-earth orbit satellite channel;

[0011] S5. Implement a low-earth orbit satellite simulation channel model according to step S4, analyze the channel characteristics, and calculate the total received power and power delay spectrum.

[0012] In a further embodiment, the basic parameters include satellite altitude, elevation angle, operating frequency band, and transmit power;

[0013] The calculation method of the satellite-ground communication link distance L is as follows:

[0014] In the formula, θ is the satellite elevation angle, H is the satellite altitude, and R

[0018] = 6371 km is the radius of the earth.

[0015] The atmospheric channel environment parameters include ionospheric scintillation parameters and rainfall parameters;

[0016] The ionospheric scintillation parameter S is used to describe the intensity of ionospheric scintillation and is calculated as follows:

[0017] In the formula, I is the signal intensity and is proportional to the square root of the signal amplitude; <*> represents averaging the content in the brackets;

[0018] The scintillation index is usually divided into three levels: weak (S < 0.3), medium (0.3 < S < 0.6), and strong (S < 0.6). For the weak and medium levels, S has a fixed relationship with f (GHz) and is defined as: S = f n

[0019] Where f is the operating frequency and n is the flicker index factor. For frequency bands above the S band, the flicker index factor n measured in multiple locations ranges from -1.6 to -1.9, with an average value of -1.7.

[0020] The rainfall parameters include rainfall rate R p (mm / h). Rainfall rate R p The rainfall rate when the system outage rate is p%, usually the average rainfall R with a probability of exceeding 0.01% 0.01 To measure the amount of rainfall in a region.

[0021] The near-ground channel environment parameters are urban building scene parameters, including building edge outline dimensions, building height, and building surface reflection coefficient.

[0022] The building edge outline dimensions include the edge point coordinates of the building and the distance between buildings, which are calculated based on actual scenarios.

[0023] Building height significantly affects electromagnetic wave propagation. Direct beams may be blocked by tall buildings, and the number of reflected beams may vary due to changes in the height of buildings surrounding the receiving point. The building height h proposed in Recommendation ITU-R P.1410 follows a Rayleigh distribution with parameter γ, where γ is the typical building height in urban environments:

[0024] The reflection coefficient of the building surface is r, which depends on the dielectric constant ε of the building surface material r , if the angle between the incident wave and the medium surface is α, then the following relationship is met:

[0025] In a further embodiment, step S2 specifically includes:

[0026] S201, ionospheric scintillation fading modeling, calculate ionospheric scintillation loss PL according to the scintillation index S fluc (dB), calculated as follows: PL fluc =27.5×S 1.26

[0027] S202, Rainfall attenuation modeling, Rainfall on the signal propagation path mainly affects the satellite communication system above 3GHz. When modeling, firstly, the rainfall intensity R 0.01 and the satellite elevation angle θ determine the equivalent path length L(R 0.01 ,θ), the calculation method is as follows:

[0028] Secondly, the fading PL caused by rainfall is estimated according to the rainfall attenuation model proposed in ITU-R P.838.rain : PL rain =K(R 0.01 ) α L(R 0.01 ,θ)

[0029] The parameters K and α are the rain attenuation coefficients related to the operating frequency f, the satellite elevation angle θ, and the polarization tilt, which can be obtained by looking up ITU-R P.838.

[0030] In a further embodiment, step S3 specifically includes:

[0031] S301. Generate a near-ground equivalent transmitting circular array. The near-ground equivalent transmitting circular array specifically includes assuming that the transmitter of the low-orbit satellite is always pointing to the ground terminal. When the transmitted signal propagates over a long distance in the atmosphere, the signal energy is evenly distributed on the cross section of the propagation direction and reaches the sky above the urban buildings. According to the plane wave hypothesis, the electromagnetic wave propagated by the low-orbit satellite through the ionosphere above the city is approximately a radius of R. t A circular plane. The radius depends on the satellite's altitude. The center of the circle lies on the direct path and is a fixed distance from the receiving antenna. The normal vector v to the plane is the vector of the direct path. The plane emits multiple parallel rays of equal energy uniformly along vector v.

[0032] S302, generating multipath based on ray tracing method. The ray tracing method generates multipath, specifically including: when the ray emitted by the equivalent circular array passes through the surface of the building, the corresponding reflection path is calculated according to the mirror method, and at the receiving end, a radius of R is used. r The transmitted rays undergo a single or multiple reflections, and some of them reach the receiving end and are effectively received. These rays that effectively reach the receiving end are calculated one by one to obtain the accurate propagation path.

[0033] In a further embodiment, the large-scale fading loss of the low-orbit satellite channel is calculated as follows: PL = PL fs +PL fluc +PL rain

[0034] Where PL fluc is the ionospheric scintillation loss, PL rain is the rainfall loss, PL fs is the free space path loss;

[0035] The free space path loss PL fs The calculation of PL is as follows: fs =32.44+20log 10 L+20log 10 f

[0036] Where L is the distance between the satellite and the ground; f is the operating frequency.

[0037] The multipath received power P mp (τ i ) is calculated as follows:

[0038] Among them, τ i is the time delay of the i-th reflected path relative to the direct path, l i represents the length of the i-th path, P t is the transmission power, λ is the signal wavelength, r i is the reflection coefficient, Δφ i =2π(l i -l1) / λ is the phase difference of the i-th path relative to the direct path. When the direct path exists, Each signal reflection will cause signal energy loss. The third-order and above reflected signal components can be ignored because they are buried in the noise. Therefore, the multipath reflection model includes direct signal, first-order reflected signal and second-order reflected signal. In the second-order reflected signal, r i is the product of two reflection coefficients.

[0039] The RMS delay spread is calculated as follows:

[0040] in is the second-order moment of PDP. RMS delay spread reflects the dispersion of multipath delay.

[0041] Therefore, the total multipath received power is calculated as follows:

[0042] Total received power P r (dBm), calculated as follows:

[0043] Power delay spectrum P r (τ i )(dBm), calculated as follows:

[0044] Among them, PL rs represents free space path loss; PL fluc stands for ionospheric scintillation loss; PL rain represents rainfall loss; P mp Indicates the total multipath received power; l i represents the length of the i-th path, P t is the transmission power, λ is the signal wavelength, r i is the reflection coefficient, Δφ i=2π(l i -l1) / λ is the phase difference of the ith path relative to the direct path.

[0045] Beneficial effects: The ray tracing-based low-orbit satellite channel modeling method used in the present invention has appropriate complexity and higher accuracy compared to the geometric random channel modeling method. In addition, the present invention can change the location distribution and height distribution of ground buildings, so that it can be applied to a variety of specific scenarios and has higher universality. In addition, the present invention compares the model in 3GPP TR 38.811 and obtains a similar receiving power trend. Therefore, the present invention can accurately model the low-orbit satellite-to-ground communication channel in an urban environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG1 is a flow chart of a ray tracing channel modeling method for low-orbit satellite communications.

[0047] FIG2 is a schematic diagram of transmitting and receiving antennas and ray propagation in a near-ground scenario according to an embodiment of the present invention.

[0048] FIG3 is a schematic diagram of a three-dimensional city model according to an embodiment of the present invention.

[0049] Figure 4(a) shows the power delay spectrum of a dense high-rise building scene.

[0050] Figure 4(b) shows the power delay spectrum of the residential area scenario.

[0051] Figure 5(a) shows the power delay spectrum of a dense high-rise building scene.

[0052] Figure 5(b) shows the power delay spectrum of the residential area scenario.

[0053] FIG6 shows the received power calculated at different rainfall rates according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art have not been described to avoid confusion with the present invention.

[0055] This embodiment discloses details of a ray tracing channel modeling method for low-orbit satellite communications, as shown in FIG1 :

[0056] S1. Generate basic parameters of low-orbit satellite system;

[0057] S101, low-orbit satellite altitude H is 550km, operating frequencies f are 2GHz, 28GHz and 40GHz respectively, and transmission power Pt is 30 dBm, and the radius of the earth R E = 6371 km.

[0058] S102. The distance L from the satellite to the ground receiving end can be calculated from the satellite elevation angle θ, the satellite height H, and the radius of the earth R E as follows:

[0059] S103. The atmospheric channel environment specifically includes: ionospheric scintillation parameters and rainfall parameters.

[0060] The intensity of ionospheric scintillation is usually described by the scintillation index S, and the calculation is as follows:

[0061] The scintillation index is usually divided into three levels: weak (S < 0.3), medium (0.3 < S < 0.6), and strong (S < 0.6). For weak and medium levels, there is a fixed relationship between S and f (GHz): S = f n

[0062] where f is the operating frequency and n is the scintillation index factor. For frequencies above the S band, the average value of the scintillation index factor n from measured results in multiple locations is -1.7.

[0063] The rainfall parameters specifically include the rainfall rate R p (mm / h). The rainfall rate R p is the rainfall rate when the system outage rate is p%, and the average rainfall R with a probability exceeding 0.01% is usually used 0.01 to measure the rainfall rate in a certain area. The rainfall rate R 0.01 is set to 0 - 120 mm / h.

[0064] S104. The near - earth end channel environment parameters are mainly urban building scene parameters, including building edge contour dimensions, building height, and building surface reflection coefficient.

[0065] The building edge contour dimensions specifically include the edge point coordinates of the building and the building spacing, which can be obtained according to specific scene data.

[0066] The building height has an obvious impact on the propagation of electromagnetic waves. The direct path may be blocked by high buildings, and the number of reflected paths may change due to the change in the building height around the receiving point. The building height h proposed in the ITU - R P.1410 recommendation conforms to the Rayleigh distribution of the parameter γ, where γ is the general building height in the urban scene:

[0067] The urban model used for simulation is set as a local urban area consisting of 16 buildings. These buildings are arranged in a 4×4 pattern, as shown in Figure 3. There is a road with a width of d between each building. The vertical edge profile of each building is the same, with a length of a along the x-axis and a length of b along the y-axis.

[0068] The simulations were conducted using a dense high-rise building scenario and a residential area scenario. The road width in the dense high-rise building scenario was d = 10m, the length along the x-axis was a = 40m, the length along the y-axis was b = 25m, and the parameter γ = 100. The road width in the residential area scenario was d = 10m, the length along the x-axis was a = 30m, the length along the y-axis was b = 15m, and the parameter γ = 30.

[0069] The reflection coefficient r of the building surface depends on the dielectric constant ε of the building surface material r In this example, all reflecting surfaces are considered as concrete, whose dielectric constant ε r =6.2. If the angle between the incident wave and the medium surface is α, then the following relationship is met:

[0070] S2. Large-scale fading channel modeling, including ionospheric scintillation fading and rain attenuation;

[0071] S201, ionospheric scintillation loss PL fluc (dB) has the following relationship: PL fluc =27.5×S 1.26

[0072] When the operating frequency is 2GHz, PL fluc =6dB, when the operating frequency is above 10GHz, the ionospheric scintillation loss can be ignored.

[0073] S202, simulate different rainfall conditions from sunny weather to rainy weather. First, according to the rainfall intensity R 0.01 and the satellite elevation angle θ determine the equivalent path length L(R 0.01 ,θ), the calculation method is as follows:

[0074] The rainfall attenuation calculation method is as follows: PL rain =K(R 0.01 ) α L(R 0.01 ,θ)

[0075] According to ITU-R P.838, at 2 GHz, the rainfall coefficient K is 0.0000847 and α is 1.0664; at 28 GHz, the rainfall coefficient K is 0.9679 and α is 0.2051; and at 40 GHz, the rainfall coefficient K is 0.8673 and α is 0.4431.

[0076] S3. Modeling of small-scale fading channels near the ground, specifically including: multipath effect modeling;

[0077] S301. Multipath effect modeling is shown in Figure 2. Assume that the transmitter of a low-orbit satellite is always pointing toward the ground terminal. When the transmitted signal propagates over a long distance in the atmosphere, the signal energy is evenly distributed in the cross section of the propagation direction and reaches the sky above the city buildings. Based on the plane wave hypothesis, the electromagnetic wave propagated by the low-orbit satellite through the ionosphere above the city is approximately equal to a radius of R. t = 5m circular plane. The center of the circle is on the direct path, and its distance from the receiving antenna is fixed at 500m. The normal vector v of this plane is the vector of the direct path. The plane uniformly emits multiple parallel rays of equal energy along vector v.

[0078] S302, generating multipath based on ray tracing method. The ray tracing method generates multipath, specifically including: when the ray emitted by the equivalent circular array passes through the surface of the building, the corresponding reflection path is calculated according to the mirror method, and at the receiving end, a radius of R is used. r =1.5m sphere for reception determination. The transmitted rays undergo single or multiple reflections, and some of them reach the receiving end and are effectively received. These rays that effectively reach the receiving end are calculated one by one to obtain the accurate propagation path.

[0079] S4. Calculate the large-scale fading loss and multipath receiving power of the low-orbit satellite channel;

[0080] S401. The calculation method of large-scale fading is as follows: PL = PL fs +PL fluc +PL rain

[0081] Among them, PL fluc is the ionospheric scintillation loss, PL rain is the rainfall loss, PL fs is the free space path loss, calculated as follows: PL fs =32.44+20log 10 L(km)+20log 10 f(MHz)

[0082] S402, small-scale fading, including multipath received power, is calculated as follows:

[0083] Among them, τ i is the time delay of the i-th reflected path relative to the direct path, l i represents the length of the i-th path, P t is the transmission power, λ is the signal wavelength, r i is the reflection coefficient, Δφ i =2π(l i -l1) / λ is the phase difference of the i-th path relative to the direct path. When the direct path exists, Each signal reflection will cause signal energy loss. The third-order and above reflected signal components can be ignored because they are buried in the noise. Therefore, the multipath reflection model includes direct signal, first-order reflected signal and second-order reflected signal. In the second-order reflected signal, r i is the product of two reflection coefficients.

[0084] The RMS delay spread is calculated as follows:

[0085] in is the second-order moment of PDP. RMS delay spread reflects the dispersion of multipath delay.

[0086] Therefore, the total multipath received power is calculated as follows:

[0087] S5. Calculate the power delay spectrum under different scenarios, the multipath received power at different satellite elevation angles, and the received power at different rainfall rates. Based on the multipath dataset, the multipath power delay spectrum can be obtained based on the multipath received power.

[0088] Combining the ionospheric scintillation loss and the rain loss, the total received power is:

[0089] Changing the satellite pitch angle θ, the rainfall rate R 0.01 and operating frequency, the total received power under different influencing factors can be obtained.

[0090] Figures 4(a) and 4(b) show that in an area with dense buildings, the receiving antenna receives three primary reflection paths, and the direct path is blocked by tall buildings. The RMS delay spread is 1.36 ns, and the total received power is -148.8 dBm. In a residential area, the receiving antenna receives 12 paths, including one direct path, 10 primary reflection paths, and one secondary reflection path. The RMS delay spread is 28.02 ns, and the total received power is -135.5 dBm. Simulation results show that in areas with dense buildings, direct path obstruction may occur at low satellite elevation angles, significantly reducing the total received power. Therefore, antenna placement should minimize obstruction of the direct path. In residential areas, due to the limited presence of buildings and the low height of the receiving antenna, the reflection delay from rooftops is relatively small, while the reflection delay from the sides of buildings is relatively large. Secondary reflection paths are present, and the RMS delay spread is significantly affected by the reflection paths, resulting in a higher total received power.

[0091] Figures 5(a) and 5(b) show that in areas with densely populated buildings, the received power is nonexistent for elevations between 0 and 20° due to building obstruction. For elevations between 0 and 50°, the total received power steadily increases, with only the direct path remaining, due to the absence of reflection paths. When the satellite elevation exceeds 50°, multipath effects due to reflection paths from rooftops cause the total received power to fluctuate significantly with increasing elevation, exhibiting an overall upward trend. Comparing these results with the 3GPP TR 38.811 model standard for satellite-to-ground received power in densely populated urban areas shows that the model generally aligns with the 3GPP model standard. Due to inconsistencies in parameters with the standard, the simulated received power slightly differs from the calculated value. The received power in high-frequency bands differs from the standard value. This is because in the L-band (2 GHz), the total received power is only affected by ionospheric scintillation, which attenuates by approximately 6 dB. In the Ka-band (28 GHz), the total received power is virtually unaffected by ionospheric scintillation, but rain attenuation is significant, reaching approximately 16 dB at an elevation angle of 20° and 5.7 dB at an elevation angle of 75°. Comparing the simulation results in high-rise and residential areas reveals greater fluctuations in received power in residential areas. This is due to the greater number of reflection paths and the stronger multipath effect.

[0092] Figure 6 shows the relationship between received power, rainfall rate, and operating frequency at different rainfall rates. At 2 GHz, received power is barely affected by rain attenuation, but at 40 GHz, it significantly attenuates. The simulation results show that higher frequencies reduce received power, and rain attenuation has a significant impact on millimeter-wave frequencies in low-orbit satellite communication systems. To address rain attenuation, antennas with narrower beamwidths can be used to reduce attenuation caused by rain absorption.

[0093] In summary, the ray tracing channel modeling method for low-orbit satellite communications established in the present invention takes into account the influence of ionospheric scintillation and rainfall in the atmosphere, and adopts a circular transmitting array equivalent method to model the near-ground multipath effect. It has high accuracy, moderate complexity and better universality, enriches the modeling method of low-orbit satellite channels, and the statistical characteristics of the simulation are of reference value for the design of low-orbit satellite communication systems.

[0094] Anything not described in detail in the present invention is well known to those skilled in the art.

[0095] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A ray-tracing channel modeling method for low-earth orbit satellite communication, characterized in that It includes the following steps: S1. Generate low Earth orbit satellite system parameters; the low Earth orbit satellite system parameters include basic parameters, atmospheric channel environment parameters, and near-Earth end channel environment parameters; S2. Model the fading channel of the large-scale part, including ionospheric scintillation fading modeling and rainfall attenuation modeling; S3. Model the small-scale fading channel at the near-Earth end, including multipath effect modeling based on the ray tracing method; S4. Based on steps S1 to S3, calculate the large-scale fading loss and multipath received power of the low Earth orbit satellite channel; S5. Calculate the total received power and power delay spectrum according to the large-scale fading loss and multipath received power calculated in step S4.

2. The ray-tracing channel modeling method for low-earth orbit satellite communication according to claim 1, characterized in that, The basic parameters in step S1 include satellite altitude, pitch angle, operating frequency band, and transmit power; According to the basic parameters, the satellite-ground communication link distance L is calculated as follows: where θ is the satellite pitch angle, H is the satellite altitude, and R E is the radius of the Earth.

3. The ray tracing channel modeling method for low Earth orbit satellite communication according to claim 1, characterized in that The atmospheric channel environment parameters in step S1 include ionospheric scintillation parameters and rainfall parameters; The ionospheric scintillation parameter S is used to describe the intensity of ionospheric scintillation and is calculated as follows: In the formula, I is the signal intensity, which is proportional to the square root of the signal amplitude; <*> represents taking the average of the content in the parentheses; The ionospheric scintillation parameter S satisfies the following relationship with the scintillation frequency of the ionosphere: S = f n ; In the formula, f is the operating frequency and n is the scintillation index factor; The rainfall parameters include rainfall rate; the rainfall rate is the rainfall rate when the system outage rate is a predetermined value.

4. The ray tracing channel modeling method for low earth orbit satellite communication according to claim 1, characterized in that, The near-Earth end channel environment parameters in step S1 are urban building scene parameters; the urban building scene parameters include building edge contour dimensions, building height, and building surface reflection coefficient; The building edge contour dimensions include the edge point coordinates of the building and the building spacing; The height h of the building conforms to the Rayleigh distribution P(h) of parameter γ: In the formula, the parameter γ represents the general building height in the urban scene; The expression of the surface reflectivity r of the building is as follows: where ε r represents the dielectric constant of the building surface material; α represents the angle between the incident wave and the medium surface.

5. The ray tracing channel modeling method for low earth orbit satellite communication according to claim 3, characterized in that, The ionospheric scintillation fading modeling described in step S2 includes calculating the ionospheric scintillation loss based on the scintillation index: PL fluc = 27.5 × S 1.26 ; where, PL fluc represents the ionospheric scintillation loss in dB; S represents the ionospheric scintillation parameter.

6. The ray tracing channel modeling method for low earth orbit satellite communication according to claim 1, characterized in that The rainfall attenuation modeling in step S2 includes: According to the rainfall intensity R 0.01 and the satellite pitch angle θ, determine the equivalent path length L(R 0.01 , θ) that the rainfall area experiences: Calculate the fading PL caused by rainfall rain : PL rain = K(R 0.01 ) α L(R 0.01 , θ); In the formula, the parameters K and α are rainfall attenuation coefficients related to the operating frequency f, satellite pitch angle θ, and polarization tilt angle.

7. The ray tracing channel modeling method for low Earth orbit satellite communication according to claim 1, characterized in that The multipath effect modeling based on the ray tracing method in step S3 includes: S301. Generate an equivalent near-ground emission circular plane array: Assume that the transmitter of the low Earth orbit satellite always points to the ground terminal; when the transmitted signal propagates long distances in the atmosphere, the signal energy is evenly distributed on the cross-section in the propagation direction and reaches above the urban building; According to the plane wave hypothesis, the electromagnetic wave propagated by the low-earth orbit satellite through the ionosphere over the city is approximately a circular plane with a radius of R t ; the radius R t depends on the height of the satellite; The center of the circular plane is located on the direct path, and its distance to the receiving antenna is fixed; the normal vector v of the circular plane is the vector of the direct path; the circular plane uniformly emits multiple parallel rays with the same energy along the vector v; S302. Generate multipaths based on the ray tracing method: When the ray emitted by the equivalent circular planar array passes through the building surface, the corresponding reflection path is calculated according to the mirror image method. At the receiving end, a sphere with a radius of R r is used for reception determination; The transmitted rays are reflected once or multiple times, and some of the rays reach the receiving end and are effectively received. The rays that effectively reach the receiving end will be calculated one by one to obtain the accurate propagation path.

8. The ray tracing channel modeling method for low earth orbit satellite communication according to claim 2, characterized in that, The calculation of the large-scale fading loss PL of the low-earth orbit satellite channel is as follows: PL = PL fs + PL fluc + PL rain ; where, PL fluc is the ionospheric scintillation loss, PL rain is the rainfall loss, PL fs is the free space path loss; The free space path loss PL fs is calculated as follows: PL fs = 32.44 + 20 log 10 L + 20 log 10 f; In the formula, L represents the satellite-near-ground communication link distance; f represents the operating frequency.

9. The ray tracing channel modeling method for low Earth orbit satellite communication according to claim 8, characterized in that, The multipath reception power P mp (τ i ) is calculated by the following formula: where τ i is the time delay of the i-th reflected path relative to the direct path, l i represents the length of the i-th path, P t is the transmit power, λ is the signal wavelength, r i is the reflection coefficient, Δφ i = 2π(l i - l1) / λ is the phase difference of the i-th path relative to the direct path.

10. The ray tracing channel modeling method for low earth orbit satellite communication according to claim 9, characterized in that, The total received power P described in step S5 r is calculated as follows: Wherein, PL fs represents free space path loss; PL fluc represents ionospheric scintillation loss; PL rain represents rainfall loss; P mp represents the total multipath received power; The total multipath received power P mp is calculated as follows: where l i represents the length of the i-th path, P t is the transmission power, λ is the signal wavelength, r i is the reflection coefficient, Δφ i = 2π(l i - l1) / λ is the phase difference of the i-th path relative to the direct path; The power delay profile P r (τ i ) is calculated as follows: where P mp (τ i ) represents the multipath received power; PL fs represents the free space path loss; PL fluc represents the ionospheric scintillation loss; PL rain represents the rainfall loss; f represents the operating frequency.

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