A channel modeling method and device suitable for satellite-to-ground communication

Abstract

This invention provides a channel modeling method and apparatus suitable for satellite-to-ground communication. The method includes: generating a satellite trajectory and setting ground environment parameters and simulation parameters; converting the satellite trajectory from a global coordinate system to a local coordinate system; obtaining the satellite position from the converted trajectory and performing ray tracing calculations based on the plane wave assumption to obtain all effective ray paths between the satellite position and the ground receiver position; for each effective ray path, calculating large-scale fading caused by meteorological conditions and small-scale fading caused by multipath propagation and multi-terminal movement at the ground end; and combining the large-scale and small-scale fading to generate a channel model. This invention models large-scale fading caused by meteorological conditions, considers the impact of meteorological attenuation on multipath reception power, and models small-scale fading caused by multipath propagation and multi-terminal movement at the ground end, thus improving the accuracy of modeling.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to a channel modeling method and apparatus suitable for satellite-to-ground communication. Background Technology

[0002] With the rapid development of communication applications, communication technology has undergone revolutionary changes. To meet the technical and application demands for wider coverage, more connections, and ultra-high positioning accuracy, 6G wireless communication networks will adopt a new paradigm and apply new technologies. The 6G vision can be summarized as "full coverage, full spectrum, full application, full sensory experience, full digitalization, and strong security." 6G will expand from partial terrestrial coverage to deep global coverage based on 5G. Satellite communication is an indispensable part of building an integrated air-space-ground-sea network to achieve deep global coverage. For high-latitude areas such as the polar regions where ground base stations are difficult to cover, communication networks can be established via satellite, thereby achieving true global coverage. Currently, satellite communication is widely used in navigation, broadcasting, and Earth observation due to its advantages such as wide coverage.

[0003] Channel characteristic analysis and modeling are fundamental to system design, theoretical analysis, performance evaluation, optimization, and deployment. To establish a stable and reliable satellite-to-ground communication system, accurate analysis of satellite-to-ground communication channel characteristics and the creation of accurate satellite-to-ground communication channel models are necessary. Currently, various channel models suitable for satellite communication have been proposed. For example, the geometrically stochastic satellite-to-ground channel model introduces the concept of clusters to characterize the multipath effects caused by scatterers in the environment. By adjusting parameters, it can be applied to different scenarios and has good versatility. However, it cannot accurately describe the propagation characteristics of electromagnetic waves in specific environments, and therefore may not meet the high-precision requirements of 6G channels in specific scenarios. Ray-tracing-based channel modeling methods, based on geometrical optics (GO) and uniform diffraction theory (UTD), can accurately describe the propagation characteristics of electromagnetic waves, such as reflection and diffraction. By reconstructing real-world scenarios, simulations of specific scenarios can be achieved, exhibiting high accuracy. Therefore, it is also widely used in satellite-to-ground communication channel modeling. However, this method does not fully consider the characteristics of satellite-to-ground communication channels, resulting in relatively low model accuracy. Summary of the Invention

[0004] This invention provides a channel modeling method and apparatus suitable for satellite-to-ground communication, addressing the problem of low model accuracy caused by existing ray tracing algorithms not fully considering the characteristics of satellite-to-ground communication channels. This method effectively models satellite trajectories and improves model accuracy. The technical solution proposed by this invention is as follows:

[0005] In a first aspect, the present invention provides a channel modeling method suitable for satellite-to-ground communication, comprising:

[0006] Generate satellite trajectory and set ground environment parameters and simulation parameters; wherein, the simulation parameters include the position of the ground receiver;

[0007] Based on ground environmental parameters, the satellite trajectory is transformed from the global coordinate system to the local coordinate system to obtain the transformed satellite trajectory.

[0008] The satellite position is obtained from the converted satellite motion trajectory. Ray tracing calculations are performed based on the plane wave assumption to obtain all valid ray paths between the satellite position and the ground receiver position.

[0009] For each valid ray path, calculate the large-scale fading caused by meteorological conditions;

[0010] For each effective ray path, calculate the small-scale fading caused by multipath propagation and multi-end movement at the ground end;

[0011] A channel model is generated by combining large-scale fading and small-scale fading.

[0012] Optionally, all effective ray paths include line-of-sight paths and non-line-of-sight paths;

[0013] The ray tracing calculation based on the plane wave assumption obtains all valid ray paths between the satellite position and the ground receiver position, including:

[0014] The virtual transmitting surface and the direction of parallel ray propagation are determined based on the satellite position and the ground receiver position.

[0015] Based on the determined virtual transmitting surface and the direction of parallel ray propagation, calculate the line-of-sight path between the satellite and the ground receiver;

[0016] A visibility tree is established with the ground receiver as the root node, and the non-line-of-sight path is calculated by traversing the visibility tree.

[0017] Optionally, the visible tree includes a first visible tree and a second visible tree, and the non-line-of-sight path includes an effective reflection path and an effective diffraction path;

[0018] The process of establishing a visibility tree with the ground receiver as the root node and traversing the visibility tree to calculate the non-line-of-sight path includes:

[0019] Establish the first visible tree based on the maximum allowed number of reflections for ray tracing.

[0020] Establish a second visible tree based on the maximum allowed number of diffractions for ray tracing.

[0021] The effective reflection path and the effective diffraction path are calculated based on the first visible tree and the second visible tree, respectively; wherein the effective reflection path and the effective diffraction path satisfy the following: the starting point of the ray is within the virtual emission surface and the ray propagation direction is the parallel ray propagation direction.

[0022] Optionally, the simulation parameters include the simulation frequency;

[0023] The calculation of large-scale fading caused by meteorological conditions for each effective ray path includes:

[0024] Considering the influence of the atmospheric environment, calculate the atmospheric gas attenuation corresponding to each effective ray path;

[0025] Considering the impact of rainfall, calculate the rainfall attenuation corresponding to each effective ray path;

[0026] Considering the effects of tropospheric scintillation, calculate the tropospheric scintillation attenuation corresponding to each effective ray path;

[0027] Considering the effects of ionospheric scintillation, calculate the ionospheric scintillation fading corresponding to each effective ray path;

[0028] Based on atmospheric gas attenuation, precipitation attenuation, tropospheric scintillation attenuation, ionospheric scintillation fading, and simulation frequency, the total attenuation caused by meteorological environment is calculated, and the large-scale fading is obtained.

[0029] Optionally, small-scale fading of the effective ray path is characterized by received power, Doppler shift, and time delay;

[0030] The calculation of small-scale fading caused by multipath propagation and multi-end movement at the ground end for each effective ray path includes:

[0031] Calculate the power generated by the effective ray path at the receiver, and calculate the received power of each effective ray path based on the power generated by the effective ray path at the receiver and the large-scale fading.

[0032] Calculate the Doppler shift for each effective ray path;

[0033] Calculate the time delay for each valid ray path.

[0034] Optionally, the method of generating a channel model by combining large-scale fading and small-scale fading includes:

[0035] Based on the received power, Doppler shift, and time delay of each effective ray path, the channel impulse response is generated, and the channel model is obtained.

[0036] Secondly, the present invention provides a channel modeling apparatus suitable for satellite-to-ground communication, comprising:

[0037] The trajectory generation module is used to generate satellite motion trajectories and set ground environment parameters and simulation parameters; wherein, the simulation parameters include the position of the ground receiver;

[0038] The coordinate transformation module is used to transform the satellite's motion trajectory from the global coordinate system to the local coordinate system based on ground environment parameters, thus obtaining the transformed satellite motion trajectory.

[0039] The ray tracing module is used to obtain the satellite position from the converted satellite motion trajectory, and to perform ray tracing calculations based on the plane wave assumption to obtain all valid ray paths between the satellite position and the ground receiver position.

[0040] The first calculation module is used to calculate the large-scale fading caused by meteorological conditions for each effective ray path;

[0041] The second calculation module is used to calculate the small-scale fading caused by multipath propagation and multi-end movement at the ground end for each effective ray path;

[0042] The model generation module is used to generate a channel model by combining large-scale fading and small-scale fading.

[0043] Thirdly, the present invention provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the channel modeling method for satellite-to-ground communication as described in the first aspect.

[0044] Fourthly, the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the channel modeling method for satellite-to-ground communication as described in the first aspect.

[0045] Fifthly, the present invention provides a computer program product comprising a computer program that, when executed by a processor, implements the channel modeling method for satellite-to-ground communication as described in the first aspect.

[0046] Based on the above technical solution, the beneficial effects of the present invention compared with the prior art are as follows:

[0047] The channel modeling method for satellite-to-ground communication provided by this invention models the actual satellite trajectory and ground environment. By transforming the satellite trajectory to a local coordinate system and performing ray tracing calculations based on the plane wave assumption, it models large-scale fading caused by meteorological environment, considers the impact of meteorological attenuation on multipath reception power, and models small-scale fading caused by ground-end multipath propagation and multi-end movement. By comprehensively considering multiple factors such as satellite trajectory, meteorological environment, near-ground environment, and multi-end movement, the model can more realistically reflect the complex situation in the channel, thereby improving the accuracy of modeling.

[0048] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description, claims and drawings.

[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0051] Figure 1 This is a flowchart illustrating the channel modeling method for satellite-to-ground communication provided by the present invention.

[0052] Figure 2 This is a schematic diagram of the satellite's motion trajectory in the global coordinate system provided by the present invention.

[0053] Figure 3 This is a schematic diagram of the effective ray path propagation at the near-ground end of satellite-to-ground communication provided by the present invention.

[0054] Figure 4 This is a schematic diagram of the channel modeling device for satellite-to-ground communication provided by the present invention.

[0055] Figure 5 This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0057] Satellites can be classified by orbital altitude into Low Earth Orbit (LEO) satellites, Medium Earth Orbit (MEO) satellites, and Geostationary Earth Orbit (GEO) satellites. LEO satellites, with an altitude range of approximately 500-2000 km, have relatively low transmission latency and power consumption, and are mostly used for Earth observation and space stations. MEO satellites, with an altitude range of 2000-35786 km, are widely used in navigation satellites. GEO satellites, located in a circular orbit at an altitude of 35786 km, have a larger coverage area, and meteorological satellites are typically GEO satellites. Commonly used frequency bands for satellite communication include Ku (12-18 GHz), K (18-26.5 GHz), Ka (26.5-40 GHz), and V (40-75 GHz).

[0058] In satellite communication, wireless signals travel through the ionosphere and troposphere to the ground. The ionospheric effect has a significant impact on the propagation of electromagnetic waves below 10 GHz. In the troposphere, communication channels are greatly affected by weather changes such as clouds, rain, and fog. Therefore, the impact of meteorological conditions must be considered when modeling satellite communication channels. Furthermore, buildings near the ground receiver may obstruct communication signals, requiring consideration of multipath propagation. As the satellite moves, its elevation angle changes continuously, and the multipath propagation near the receiver changes dynamically. The high-speed motion of the satellite will cause significant Doppler shifts and variations, which will severely degrade system performance. Channel characteristic analysis and modeling are fundamental to system design, theoretical analysis, performance evaluation, optimization, and deployment. To establish a stable and reliable satellite-to-ground communication system, accurate analysis of the satellite-to-ground communication channel characteristics and the establishment of an accurate satellite-to-ground communication channel model are necessary.

[0059] This invention provides a channel modeling method and apparatus suitable for satellite-to-ground communication, which can effectively model satellite motion trajectories, fully consider the characteristics of satellite-to-ground communication channels, and support satellite-to-ground multi-terminal mobile communication scenarios.

[0060] The following is combined Figures 1-5 This invention describes a channel modeling method and apparatus suitable for satellite-to-ground communication.

[0061] Figure 1 This is a flowchart illustrating the channel modeling method for satellite-to-ground communication provided by the present invention, as shown below. Figure 1 As shown, the method includes the following:

[0062] Step S101: Generate satellite motion trajectory and set ground environment parameters and simulation parameters.

[0063] Based on the satellite's orbital parameters (including one or more of the semi-major axis, eccentricity, inclination, and right ascension of the ascending node), celestial mechanics principles are used to calculate the satellite's three-dimensional spatial position within a given time range. This position data is typically stored in time series format, representing the satellite's coordinates at different points in time. Satellite parameters are then generated, specifically including the satellite's global coordinates at different times, its instantaneous velocity at different times, sampling time interval, satellite transmit power, and satellite antenna type.

[0064] The near-ground environmental parameters are set, specifically including the global and local coordinates of the ground reference point, the three-dimensional vertex coordinates of the building in the local coordinate system, and the material electromagnetic parameters of the building. The material electromagnetic parameters include one or more of the following: dielectric constant, conductivity, roughness, and thickness.

[0065] The specific simulation parameters to be set include the simulation frequency, the ground receiver's motion trajectory or position coordinates, the ground receiver's antenna type, the maximum allowable number of reflections, diffractions, and transmissions for ray tracing.

[0066] Set meteorological environmental parameters, and select whether to consider ionospheric or tropospheric effects based on the simulation frequency. Tropospheric effects include atmospheric attenuation, precipitation attenuation, and tropospheric scintillation. If ionospheric scintillation is considered, set the scintillation index. If precipitation attenuation is considered, set precipitation intensity, annual precipitation exceedance probability, topographic height above mean sea level, and annual average precipitation height above mean sea level. If tropospheric scintillation is considered, set one or more of the following parameters: antenna efficiency, maximum aperture of the ground-based antenna, and wetted radio refractive index.

[0067] Based on the satellite's orbit and the location of the ground station, the satellite-to-ground communication environment needs to be deployed, including parameters such as the antenna orientation, altitude, and gain of the ground station. At the same time, the impact of environmental factors such as terrain, buildings, and vegetation on signal propagation also needs to be considered.

[0068] Step S102: Based on the ground environment parameters, convert the satellite motion trajectory from the global coordinate system to the local coordinate system to obtain the converted satellite motion trajectory.

[0069] The satellite's trajectory is transformed from a global coordinate system (such as a geocentric inertial coordinate system) to a local coordinate system (such as a coordinate system centered on the ground receiver). This transformation simplifies the ray tracing calculation process and makes the relative positional relationship between the starting point (the satellite's position) and the ending point (the ground receiver's position) of the ray tracing more intuitive.

[0070] Step S103: Obtain the satellite position from the converted satellite motion trajectory, perform ray tracing calculation based on the plane wave assumption, and obtain all valid ray paths between the satellite position and the ground receiver position.

[0071] In ray tracing, it is typically assumed that the signal emitted by the satellite is a plane wave, meaning the wavefront is a plane. Based on this plane wave assumption, the satellite position at each time point in the converted satellite trajectory is selected as the transmission point, and the ground receiver position as the receiving point for ray tracing. Ray tracing algorithms consider factors such as the atmosphere and terrain to simulate the propagation path of electromagnetic waves from the satellite to the ground receiver. Through ray tracing, all possible paths to the ground receiver after reflection and diffraction by the ground environment (such as the ground, buildings, trees, etc.) can be identified, including reflection paths and diffraction paths. These paths are then combined to obtain the effective ray paths, i.e., multipath propagation.

[0072] Step S104: For each effective ray path, calculate the large-scale fading caused by meteorological environment.

[0073] Considering the impact of meteorological conditions on signal propagation, these conditions lead to signal energy attenuation. The aforementioned large-scale fading refers to large-scale fading caused by one or more meteorological phenomena such as rainfall attenuation and cloud / fog absorption. For each effective ray path, the signal attenuation caused by the meteorological environment is calculated based on meteorological environmental parameters and the geometric characteristics of the signal propagation path (including one or more parameters such as path length and propagation angle).

[0074] Step S105: For each effective ray path, calculate the small-scale fading caused by multipath propagation and multi-end movement at the ground end.

[0075] Consider the multipath propagation effects around the ground receiver and the possibility of receiver movement. Multipath propagation leads to signal delay spread and frequency-selective fading, while receiver movement can introduce Doppler shift. The aforementioned small-scale fading refers to the fading mainly caused by near-ground multipath propagation and multi-end movement, such as reflection and diffraction from different scatterers leading to coherent superposition of multipath paths with different time delays at the receiver, and the dynamic changes of a moving receiver. For each effective ray path, considering the complexity of the near-ground environment, and combining the ground environment with the receiver's moving speed and direction, electromagnetic simulation methods are used to calculate the signal fluctuations and fading caused by multipath propagation and movement.

[0076] Step S106: Generate a channel model by combining large-scale fading and small-scale fading.

[0077] This invention models realistic satellite trajectories and ground environments. By transforming the satellite trajectory to a local coordinate system and performing ray tracing calculations based on the plane wave assumption, it models large-scale fading caused by meteorological conditions. The impact of meteorological attenuation on multipath reception power is considered, and small-scale fading caused by ground-end multipath propagation and multi-terminal movement is modeled. By comprehensively considering multiple factors such as satellite trajectory, meteorological environment, near-ground environment, and multi-terminal movement, the model can more realistically reflect complex channel conditions, such as atmospheric attenuation, multipath effects, and Doppler shift, thereby improving the accuracy of the channel model.

[0078] This method supports various application scenarios, including satellites at different orbital altitudes, ground receivers in different geographical locations, and complex and variable weather conditions. By adjusting model parameters, it can flexibly adapt to different communication environments and requirements, providing strong support for the design of space-to-ground communication systems in different application scenarios. Accurate channel models can predict and analyze the performance of space-to-ground communication systems, including key indicators such as signal attenuation. This helps provide a reference for performance optimization during the communication system design phase, thereby improving the overall performance and reliability of the system.

[0079] The step S102 above, which involves converting the satellite's trajectory from a global coordinate system to a local coordinate system based on ground environmental parameters to obtain the converted satellite trajectory, specifically includes the following steps:

[0080] S201, Change the satellite trajectory from the global coordinate system (e.g., Figure 2 (As shown) can be converted to a local coordinate system. Taking the latitude, longitude, and altitude coordinate system as an example, the satellite's trajectory can be transformed from the latitude, longitude, and altitude coordinate system to the Earth-Centered Earth-Fixed (ECEF) coordinate system:

[0081]

[0082]

[0083] in,( , , () represents the satellite coordinates after the initial transformation. Latitude (unit: °) Longitude (°), h is altitude (m), e is ellipsoidal eccentricity, R N Let be the radius of curvature of the ramusoidal circle of the reference ellipsoid, and a be the semi-major axis of the Earth ellipsoid. Figure 2 R in E Where is the Earth's radius, and d is the distance from the satellite to the ground receiving point.

[0084] S202. Transform the satellite's trajectory from the ECEF coordinate system to the East-North-Up (ENU) coordinate system:

[0085]

[0086] in, These are the satellite coordinates after the second transformation. Latitude (in degrees) of the ground reference point. Longitude (in °) of the ground reference point. The ECEF coordinates are the ground reference point.

[0087] In an optional embodiment, all effective ray paths in step S103 above include line-of-sight paths and non-line-of-sight paths;

[0088] The ray tracing calculation based on the plane wave assumption described in step S103 above, which obtains all valid ray paths between the satellite position and the ground receiver position, specifically includes:

[0089] S301. Determine the virtual transmitting surface and the direction of parallel ray propagation based on the satellite position and the ground receiver position.

[0090] To simplify the starting conditions for ray tracing, this invention defines a virtual transmitting surface at the satellite's location. The position and shape of this surface can be determined in three-dimensional space based on the satellite's current position, the ground receiver's current position, and the parameters of the set virtual transmitting surface. Specifically, the height h of the virtual transmitting surface is determined based on the satellite's position and the ground receiver's position. vir Radius size r vir The virtual launch surface center position p vir The virtual emitting surface is a circle with radius r, whose normal vector passes through the directions of the satellite and the ground receiver. The direction of the emitted ray propagation is... ,in, This is the satellite's current position. Current location of the ground receiver. Height h of the virtual transmitting surface mentioned above. vir Users can configure it according to their actual needs.

[0091] S302. Based on the determined virtual transmitting surface and the direction of parallel ray propagation, calculate the line-of-sight path between the satellite and the ground receiver.

[0092] The line-of-sight path (LAS) is the most direct propagation path between a satellite and a ground receiver, without any reflections or diffraction. After determining the positions of the virtual transmitter and the ground receiver, the straight-line distance and direction between them can be directly calculated as the LAS. Specifically, the center of the circle connecting the ground receiver and the virtual transmitter is used. If this path is not obstructed by other buildings in the environment, it indicates that a LAS exists between the satellite and the ground receiver, and this path is recorded; otherwise, the LAS is invalid.

[0093] S303. Establish a visible tree with the ground receiver as the root node, and traverse the visible tree to calculate the non-line-of-sight path.

[0094] The aforementioned non-line-of-sight paths include all paths that are reflected, transmitted, or diffracted. To effectively locate these paths, this invention establishes a visible tree to simulate the propagation of electromagnetic waves in the environment.

[0095] First, the visibility tree is established: The visibility tree is constructed starting with the ground receiver as the root node. Each node in the visibility tree represents a possible reflection or diffraction point (such as the ground, buildings, mountains, etc.). Based on ground environment data, it is determined which nodes are visible, meaning those from which electromagnetic waves can propagate from the satellite to and from the ground receiver.

[0096] Second, traverse the visible tree: starting from the root node, traverse each branch of the visible tree. For each branch, calculate the path from the satellite to the current node, and then from the current node to the ground receiver. Multiple reflections or diffractions need to be considered, the feasibility of each path needs to be evaluated, and all valid non-line-of-sight paths need to be retained.

[0097] This invention, by calculating line-of-sight and non-line-of-sight paths separately and considering various factors such as ground environment and meteorological conditions, can more accurately simulate the characteristics of satellite-to-ground communication channels, thereby improving the accuracy of the channel model. The establishment of a visible tree enables the model to handle complex ground environments, which helps in evaluating the performance of satellite-to-ground communication systems under different conditions. Based on this, an accurate channel model can be established to predict and analyze signal coverage and signal quality under different satellite orbits and ground receiver locations.

[0098] Ray tracing channel modeling methods based on SBR suffer from several drawbacks. Since rays are emitted as point sources at the transmitter, the spacing between adjacent rays increases with propagation distance. In long-distance communication scenarios like satellite-to-ground, effective multipath information cannot be received at the receiver, impacting model accuracy. While optimized SBR algorithms based on the parallel wave assumption address these issues, they require a receiver sphere for reception determination, and the method for determining the parallel wave assumption is unclear, making the model's accuracy highly dependent on the size of the receiver sphere. Existing ray tracing channel modeling methods based on the image method do not support parallel wave propagation and are complex due to the long propagation distances between transmitters and receivers in satellite-to-ground scenarios.

[0099] This invention establishes a virtual transmission plane by determining the transceiver's position and the initial ray propagation direction. By establishing a reverse visible tree and defining the initial ray propagation direction, it ensures that all valid ray paths satisfy the parallel wave propagation assumption. Furthermore, establishing the visible tree reduces unnecessary intersection checks during ray tracing, lowering complexity. The propagation path determined by the visible tree accurately reaches the receiver, solving the problem of not being able to receive effective multipath propagation and avoiding low model accuracy due to improper receiver sphere size settings.

[0100] In an optional embodiment, step S303 above, which involves establishing a visibility tree with the ground receiver as the root node and traversing the visibility tree to calculate the non-line-of-sight path, specifically includes:

[0101] S1031. Set the maximum allowed number of reflections and diffractions for ray tracing. These parameters determine the complexity and accuracy of ray tracing. Load the environment model, including terrain, buildings, vegetation, and other obstacles that may affect ray propagation. By limiting the maximum number of reflections and diffractions, unnecessary computation can be reduced while maintaining a certain level of accuracy, thus improving the computational efficiency of ray tracing.

[0102] Based on the maximum allowed number of reflections n for ray tracing, an n+1 level visibility tree (hereinafter referred to as the first visibility tree) is constructed. Starting with the ground receiver as the root node, potential reflecting surfaces in the environment (such as the ground, building walls, etc.) are traversed. For each reflecting surface, possible reflection paths are recursively calculated according to the law of reflection and the maximum allowed number of reflections for ray tracing.

[0103] Specifically, taking the ground receiver as the initial virtual source, the visible surfaces about the ground receiver are calculated and set as child nodes of the virtual source. The mirror points of the receiver about these visible surfaces are calculated and these mirror points are regarded as secondary virtual sources. The visible surfaces about these secondary virtual sources are searched, and so on, until the maximum number of allowed reflections is reached.

[0104] S1032. Based on the set maximum permissible diffraction number m for ray tracing, establish an m+1 level visible tree (hereinafter referred to as the second visible tree). Again, with the ground receiver as the root node, consider diffraction phenomena, such as electromagnetic waves continuing to propagate around the edge of an obstacle. Using diffraction theory (such as Geometric Diffraction Theory (GTD) or Uniform Diffraction Theory (UTD)) and the set maximum permissible diffraction number, calculate possible diffraction paths.

[0105] Specifically, using the ground receiver as the initial virtual source, the visible cleavages related to the receiver are calculated and added to the child nodes of the current visible tree. Using the two endpoints of the visible cleavages as virtual sources, the union of the visible cleavages at the two endpoints is taken as the next level visible cleavage and added to the corresponding child node, and so on, until the maximum allowed number of diffractions is reached. The aforementioned visible cleavages refer to those reachable by the ray path from the receiver.

[0106] S1033. Calculate the effective reflection path and effective diffraction path based on the first and second visible trees, respectively. Traverse the first and second visible trees to extract the effective reflection path and effective diffraction path. Verify that these paths meet the following conditions: the ray originates within the virtual emitting surface, the ray propagation direction is parallel to the ray propagation direction, and the ray is not obstructed by any obstacles such as buildings during the entire propagation process. Record the effective reflection path and diffraction path obtained from ray tracing, specifically including the position coordinates of all interaction points contained in the path and the information of the face or wedge where the interaction points are located.

[0107] This invention, by constructing a visible tree and separately calculating the effective reflection path and effective diffraction path, can more accurately simulate the propagation process of electromagnetic waves in complex environments, thereby improving the accuracy and reliability of the simulation. The calculation results of non-line-of-sight paths help analyze the impact of multipath effects on signal propagation, providing strong support for signal processing and interference suppression. This method can handle scenes containing various obstacles and complex terrains, and is suitable for ray tracing simulations in various environments such as urban areas and mountainous regions.

[0108] In an optional embodiment, the simulation parameters include the simulation frequency;

[0109] The above step S104, which calculates the large-scale fading caused by meteorological conditions for each effective ray path, specifically includes:

[0110] S401. Atmospheric gases such as oxygen and water vapor have a certain absorption effect on electromagnetic waves. By considering parameters such as atmospheric composition, temperature, and pressure, the attenuation of electromagnetic waves during propagation due to atmospheric gas absorption can be calculated. This invention considers the influence of the atmospheric environment and calculates the atmospheric gas attenuation corresponding to each effective ray path. For example, the atmospheric gas attenuation corresponding to each effective ray path can be calculated according to ITU-R P.618. :

[0111]

[0112] in, The pitch angle corresponding to the path obtained by ray tracing calculation, f represents the operating frequency, i.e., the carrier frequency of the transmitter, and A zenith (f) represents the zenith attenuation, which can be obtained by referring to ITU-R P.618.

[0113] S402. Rainfall is a common meteorological phenomenon in satellite communications and has a significant impact on electromagnetic wave propagation. This invention considers the impact of rainfall and calculates the calculated rainfall attenuation for each effective ray path. Rainfall attenuation can be calculated using the rainfall attenuation model proposed in ITU-R P.838. :

[0114]

[0115] Among them, parameters and All are related to the operating frequency Pitch angle corresponding to the path The rainfall attenuation coefficient related to the polarization tilt angle can be obtained by referring to ITU-R P.838. This represents the equivalent path length experienced by the rainfall area. .

[0116] S403. Turbulence and temperature gradient changes in the troposphere cause random variations in the electromagnetic wave propagation path, resulting in scintillation. This scintillation phenomenon leads to rapid fluctuations in signal strength, affecting communication quality. This invention considers the impact of tropospheric scintillation and calculates the tropospheric scintillation attenuation corresponding to each effective ray path. Tropospheric scintillation attenuation can be calculated using the following formula. :

[0117]

[0118] Where p represents the percentage of time, The standard deviation of the reference signal amplitude, This is the antenna average coefficient; relevant parameters can be found in ITU-R P.618.

[0119] Calculating atmospheric gas attenuation helps assess the performance of high-frequency satellite communication systems. Calculating rainfall attenuation allows for the prediction and evaluation of system performance in areas with frequent rainfall, enabling the implementation of measures to mitigate the impact of rainfall, such as increasing transmission power or using more efficient coding and modulation methods.

[0120] This invention calculates tropospheric scintillation attenuation, which helps assess the performance stability of satellite communication systems under complex weather conditions. By understanding the characteristics of scintillation attenuation, appropriate signal processing techniques can be employed to mitigate the impact of scintillation on communication quality.

[0121] S404. The inhomogeneity of the ionospheric structure leads to ionospheric scintillation, causing changes in signal amplitude and phase. This scintillation phenomenon has a particularly significant impact on satellite communication systems operating below 3 GHz. This invention considers the effects of ionospheric scintillation and calculates the ionospheric scintillation fading corresponding to each effective ray path. :

[0122]

[0123] Where S is the flicker index.

[0124] By calculating ionospheric scintillation fading, we can understand the characteristics of ionospheric scintillation, so as to select appropriate communication frequency bands, polarization methods and modulation methods to mitigate the impact of ionospheric scintillation on communication quality. This is of great significance for the design and optimization of satellite communication systems.

[0125] S405. Calculate the total attenuation caused by meteorological environment based on the simulation frequency and meteorological parameters. The tropospheric effect has a significant impact on electromagnetic waves above 10 GHz, including atmospheric attenuation due to gas absorption in clear air, scintillation due to atmospheric turbulence, and attenuation of electromagnetic waves by condensates in the troposphere. The ionospheric effect has a significant impact on the propagation of electromagnetic waves below 10 GHz, and is particularly pronounced for frequencies below 3 GHz. The total attenuation caused by meteorological environment is the aforementioned large-scale fading. It can be calculated as

[0126]

[0127] in, This represents the total meteorological attenuation corresponding to the i-th path. This indicates attenuation caused by atmospheric gases. Indicates a decrease in rainfall. Indicates tropospheric scintillation attenuation. This indicates ionospheric scintillation attenuation.

[0128] This invention comprehensively considers atmospheric gas attenuation, rainfall attenuation, tropospheric scintillation attenuation, and ionospheric scintillation fading, enabling a complete assessment of the impact of meteorological conditions on satellite communication system performance. This detailed fading calculation not only improves the accuracy and reliability of channel models but also provides crucial data support for system design and optimization. By understanding the fading characteristics under different meteorological conditions, effective countermeasures can be developed to improve the reliability and stability of satellite communication systems, meeting communication needs in various complex environments.

[0129] In an optional embodiment, refer to Figure 3 The diagram shows the effective ray path propagation at the near-ground end of satellite-to-ground communication. The small-scale fading parameters of the effective ray path are characterized by received power, Doppler shift, and time delay. Step S105 above, which calculates the small-scale fading caused by multipath propagation and multi-end movement at the ground end for each effective ray path, includes:

[0130] S501. Considering multipath propagation at the ground end, the signal may reach the receiver via multiple paths such as direct, reflected, diffracted, and transmitted light. These paths have different lengths and attenuations, thus causing amplitude and phase changes when the signals are superimposed at the receiver. The impact of meteorological attenuation (i.e., the aforementioned large-scale fading) on ​​the received power of the effective ray path is also considered. This invention first calculates the power generated by the effective ray path at the receiver, and then calculates the received power of each effective ray path based on the power generated by the effective ray path at the receiver and the aforementioned large-scale fading. :

[0131]

[0132] in, Let be the power generated at the receiving end by the i-th effective ray path. Let be the electric field intensity generated at the receiving end by the i-th effective ray path. For the gain of the receiving antenna, For wavelength, The impedance of free space.

[0133] Taking an effective ray path that undergoes M reflections, N diffractions, and J transmissions as an example, its electric field... It can be calculated using the following formula:

[0134]

[0135] in, Let R be the incident electric field, D be the reflection coefficient, and T be the diffraction coefficient. , , denoted as amplitude diffusion factors for reflected wave, diffracted wave, and transmitted wave, respectively; k is the wave number; and r is the total path length.

[0136] S502. Calculate the Doppler frequency shift for each effective ray path. :

[0137]

[0138] Where c is the propagation speed of electromagnetic waves in free space. For the satellite's velocity, The receiver's speed of movement, The velocity of the object interacting with the ray. Let be the unit direction vector between two points of application along the ray path. This represents the unit direction vector from the transmitter to the first point of action. This represents the unit direction vector from the last point of action to the receiving end.

[0139] S503. Calculate the time delay for each effective ray path. ,in, The total length of the i-th effective ray path is the sum of the distance from the satellite to the center of the virtual transmitting surface and the propagation path length calculated by ray tracing from the virtual transmitting surface to the receiver.

[0140] This invention, by separately considering large-scale fading caused by meteorological conditions and small-scale fading such as Doppler shift due to multipath effects, can more accurately simulate signal propagation characteristics in real-world communication environments. Modeling the effects of multipath propagation caused by ground-based buildings and Doppler shift due to transceiver movement helps communication system designers better understand signal fluctuations at the receiver, including power fluctuations, frequency shifts, and delay variations. In mobile communication systems, receiver movement leads to dynamic changes in signal propagation characteristics. By calculating the Doppler shift and delay of each effective ray path, these changes can be tracked in real time, allowing for adjustments to system parameters or the adoption of corresponding compensation measures to enhance the system's adaptability to dynamic environments.

[0141] In an optional embodiment, multipath propagation of the signal at the ground end is considered. Since the signal may reach the receiver through multiple paths with different lengths and attenuations, this will cause changes in amplitude and phase when the signals are superimposed at the receiver. If the receiver (or transmitter) is in a mobile state, the influence of the Doppler effect on the signal frequency also needs to be considered. The Doppler effect causes a shift in the signal frequency. Therefore, this invention combines large-scale fading caused by meteorological conditions with small-scale fading caused by near-ground multipath propagation and multi-end movement to establish a channel model. The method of generating a channel model by combining large-scale fading and small-scale fading in step S106 above specifically includes:

[0142] Based on the received power of each effective ray path Doppler frequency shift and latency The channel impulse response is generated to obtain the channel model. The calculation formula is:

[0143]

[0144] in, For time, Let be the amplitude of the i-th effective ray path, and the amplitude can be obtained by adjusting the above-mentioned received power. Normalization yields the following: The phase of the i-th effective ray path includes the initial phase and the phase change caused by time delay and Doppler shift. The number of effective ray paths calculated for ray tracing. Impulse function. The calculation method for the phase change caused by time delay and Doppler shift can refer to the description in the prior art, using the phase change caused by time delay. For example:

[0145]

[0146] This invention is based on the received power The amplitude response was calculated, taking into account the phase changes caused by Doppler frequency shift and time delay. The channel impulse response described above was obtained by superimposing the channel impulse responses of all effective ray paths. Specifically, large-scale decay caused by meteorological environment. The main influence is on the overall power level of the signal. This invention applies large-scale fading before generating the channel impulse response. To adjust the power at the receiver end to obtain the received power. That is, the aforementioned large-scale fading. Already implied in the received power In the calculation of the channel impulse response. Amplitude through the effective ray path Phase and latency Generate, where amplitude By analyzing the aforementioned received power Normalization yields the phase. It includes the initial phase and the phase changes caused by time delay and Doppler shift (i.e., small-scale fading parameters). In other words, the channel model of this invention combines large-scale fading caused by meteorological environment with small-scale fading generation caused by near-ground multipath propagation and multi-end movement.

[0147] The ray tracing channel modeling method provided by this invention, applicable to satellite-to-ground communication scenarios, models the real satellite trajectory and ground environment. By transforming the satellite trajectory to a local coordinate system and performing ray tracing calculations based on the plane wave assumption, it models large-scale fading such as rainfall attenuation and ionospheric / tropospheric scintillation, considers the impact of meteorological attenuation on the effective ray path received power, and models the effects of multipath propagation caused by ground-end buildings and Doppler frequency shift caused by the movement of the transceiver end, etc., and has high accuracy.

[0148] This channel model combines large-scale fading caused by meteorological conditions with small-scale fading caused by near-ground multipath propagation and multi-terminal movement, enabling it to more comprehensively reflect the complexities of real-world communication environments. By modeling realistic ground-end deployments and the movement trajectories of satellites and ground receivers, and considering propagation characteristics such as electromagnetic wave reflection and diffraction, as well as the impact of multi-terminal movement on multi-spectral frequency shift, the accuracy of the channel model is improved. An accurate channel model helps communication systems more accurately predict and respond to interference and fading in the channel, thereby improving system transmission efficiency and reliability.

[0149] The channel modeling apparatus for satellite-to-ground communication provided by the present invention will be described below. The channel modeling apparatus for satellite-to-ground communication described below can be referred to in correspondence with the channel modeling method for satellite-to-ground communication described above.

[0150] Reference Figure 4 As shown, the device includes:

[0151] The trajectory generation module 601 is used to generate satellite motion trajectories and set ground environment parameters and simulation parameters; wherein, the simulation parameters include the position of the ground receiver;

[0152] The coordinate transformation module 602 is used to transform the satellite motion trajectory from the global coordinate system to the local coordinate system based on ground environment parameters, so as to obtain the transformed satellite motion trajectory.

[0153] The ray tracing module 603 is used to obtain the satellite position from the converted satellite motion trajectory, perform ray tracing calculations based on the plane wave assumption, and obtain all valid ray paths between the satellite position and the position of the ground receiver.

[0154] The first calculation module 604 is used to calculate the large-scale fading caused by meteorological environment for each effective ray path;

[0155] The second calculation module 605 is used to calculate the small-scale fading caused by multipath propagation and multi-end movement at the ground end for each effective ray path;

[0156] Model generation module 606 is used to generate a channel model by combining large-scale fading and small-scale fading.

[0157] Figure 5 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 5 As shown, the electronic device may include a processor 710, a communications interface 720, a memory 730, and a communication bus 740. The processor 710, communications interface 720, and memory 730 communicate with each other via the communication bus 740. The processor 710 can call logical instructions from the memory 730 to execute channel modeling methods suitable for satellite-to-ground communication.

[0158] Furthermore, the logical instructions in the aforementioned memory 730 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, essentially, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0159] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer is able to execute the channel modeling methods for satellite-to-ground communication provided by the above methods.

[0160] In another aspect, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to perform the channel modeling methods for satellite-to-ground communication provided by the methods described above.

[0161] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0162] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for channel modeling suitable for satellite-to-ground communications, characterized in that, include: Generate satellite trajectory and set ground environment parameters and simulation parameters; wherein, the simulation parameters include the position of the ground receiver; Based on ground environmental parameters, the satellite trajectory is transformed from the global coordinate system to the local coordinate system to obtain the transformed satellite trajectory. The satellite position is obtained from the converted satellite motion trajectory. Ray tracing calculations are performed based on the plane wave assumption to obtain all valid ray paths between the satellite position and the ground receiver position. For each valid ray path, calculate the large-scale fading caused by meteorological conditions; For each effective ray path, calculate the small-scale fading caused by multipath propagation and multi-end movement at the ground end; A channel model is generated by combining large-scale fading and small-scale fading. Among them, all effective ray paths include line-of-sight paths and non-line-of-sight paths; The ray tracing calculation based on the plane wave assumption obtains all valid ray paths between the satellite position and the ground receiver position, including: The virtual transmitting surface and the direction of parallel ray propagation are determined based on the satellite position and the ground receiver position. Based on the determined virtual transmitting surface and the direction of parallel ray propagation, calculate the line-of-sight path between the satellite and the ground receiver; Establish a visibility tree with the ground receiver as the root node, and traverse the visibility tree to calculate the non-line-of-sight path; The non-line-of-sight path includes an effective reflection path and an effective diffraction path; the effective reflection path and the effective diffraction path satisfy the following conditions: the starting point of the ray is within the virtual emission surface and the ray propagation direction is parallel to the ray propagation direction, and it is not blocked by any obstacle during the entire propagation process.

2. The method for channel modeling for satellite-to-ground communication according to claim 1, wherein, The visible tree includes a first visible tree and a second visible tree; The process of establishing a visibility tree with the ground receiver as the root node and traversing the visibility tree to calculate the non-line-of-sight path includes: Establish the first visible tree based on the maximum allowed number of reflections for ray tracing. Establish a second visible tree based on the maximum allowed number of diffractions for ray tracing. The effective reflection path and effective diffraction path are calculated based on the first visible tree and the second visible tree, respectively.

3. The method for channel modeling for satellite-to-ground communication according to claim 1, wherein, The simulation parameters include the simulation frequency; The calculation of large-scale fading caused by meteorological conditions for each effective ray path includes: Considering the influence of the atmospheric environment, calculate the atmospheric gas attenuation corresponding to each effective ray path; Considering the impact of rainfall, calculate the rainfall attenuation corresponding to each effective ray path; Considering the effects of tropospheric scintillation, calculate the tropospheric scintillation attenuation corresponding to each effective ray path; Considering the effects of ionospheric scintillation, calculate the ionospheric scintillation fading corresponding to each effective ray path; Based on atmospheric gas attenuation, precipitation attenuation, tropospheric scintillation attenuation, ionospheric scintillation fading, and simulation frequency, the total attenuation caused by meteorological environment is calculated, and the large-scale fading is obtained.

4. The method for channel modeling for satellite-to-ground communication according to claim 1, wherein, Small-scale fading of the effective ray path is characterized by received power, Doppler shift, and time delay. The calculation of small-scale fading caused by multipath propagation and multi-end movement at the ground end for each effective ray path includes: Calculate the power generated by the effective ray path at the receiver, and calculate the received power of each effective ray path based on the power generated by the effective ray path at the receiver and the large-scale fading. Calculate the Doppler shift for each effective ray path; Calculate the time delay for each valid ray path.

5. The method for channel modeling for satellite-to-ground communications according to claim 4, wherein, The method for generating a channel model by combining large-scale fading and small-scale fading includes: Based on the received power, Doppler shift, and time delay of each effective ray path, the channel impulse response is generated, and the channel model is obtained.

6. A channel modeling device suitable for satellite-to-ground communications, characterized in that, include: The trajectory generation module is used to generate satellite motion trajectories and set ground environment parameters and simulation parameters; wherein, the simulation parameters include the position of the ground receiver; The coordinate transformation module is used to transform the satellite's motion trajectory from the global coordinate system to the local coordinate system based on ground environment parameters, thus obtaining the transformed satellite motion trajectory. The ray tracing module is used to obtain the satellite position from the converted satellite trajectory, perform ray tracing calculations based on the plane wave assumption, and obtain all valid ray paths between the satellite position and the ground receiver position; all valid ray paths include line-of-sight paths and non-line-of-sight paths. The ray tracing calculation based on the plane wave assumption obtains all valid ray paths between the satellite position and the ground receiver position, including: The virtual transmitting surface and the direction of parallel ray propagation are determined based on the satellite position and the ground receiver position. The line-of-sight path between the satellite and the ground receiver is calculated based on the determined virtual transmitting surface and the direction of parallel ray propagation. A visibility tree is established with the ground receiver as the root node, and the non-line-of-sight path is calculated by traversing the visibility tree. The non-line-of-sight path includes an effective reflection path and an effective diffraction path. The effective reflection path and the effective diffraction path satisfy the following conditions: the starting point of the ray is within the virtual transmitting surface, the ray propagation direction is the direction of parallel ray propagation, and it is not obstructed by any obstacles during the entire propagation process. The first calculation module is used to calculate the large-scale fading caused by meteorological conditions for each effective ray path; The second calculation module is used to calculate the small-scale fading caused by multipath propagation and multi-end movement at the ground end for each effective ray path; The model generation module is used to generate a channel model by combining large-scale fading and small-scale fading.

7. An electronic device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the channel modeling method for satellite-to-ground communication as described in any one of claims 1 to 5.

8. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the channel modeling method for satellite-to-ground communication as described in any one of claims 1 to 5.

9. A computer program product comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the channel modeling method for satellite-to-ground communication as described in any one of claims 1 to 5.

Images