A modeling method for high dynamic air-to-ground multipath signals

Abstract

The present invention is applicable to the field of channel modeling technology, and provides a modeling method for high-dynamic air-to-ground multipath signals, including the following steps: measuring the receiving power curve in an actual scenario; digitally reconstructing the actual scenario and extracting effective multipaths; establishing a high-dynamic air-to-ground channel model; simulating and outputting the receiving power curve in a wireless simulation device. When the receiving power curve in the actual scenario is consistent with the distribution trend of the receiving power curve output by the wireless channel simulation device, the established high-dynamic air-to-ground channel model is the real channel in the current actual scenario. The high-dynamic air-to-ground channel model established by the present invention is closer to the actual transmission environment, improves the accuracy of the model, and has high applicability; by iteratively correcting the model, the real high-dynamic multipath signal air-to-ground channel in a certain scenario, as well as channel parameters and multipath fading distribution information of the channel can be obtained, thereby optimizing communication performance and improving communication reliability.

Description

Technical Field

[0001] The invention belongs to the technical field of channel modeling, and in particular relates to a modeling method for high-dynamic air-to-ground multipath signals. Background Art

[0002] In the process of air-to-ground wireless signal propagation, due to the rapid flight of the aircraft, it will pass through a variety of channel scenarios in a short period of time, including cities, suburbs, mountains, jungles, etc. In the rapidly changing channel scenario, affected by factors such as tall buildings and trees, remote mountains, and terrain, the energy of electromagnetic waves is propagated through direct, reflected, diffracted, scattered paths, and some random combinations. The received signal is composed of multiple independent phase reflection waves, generating a multipath channel, which causes the transmitted air-to-ground wireless signal to fade into a highly dynamic air-to-ground multipath signal. The fading caused by the highly dynamic air-to-ground multipath signal is bound to occur in the wireless channel. For digital transmission, fading will lead to an increase in the bit error rate. This fading phenomenon seriously deteriorates the quality of the received signal, thereby affecting the reliability of communication.

[0003] Considering the advantage of ray tracing method is to use various efficient algorithms to digitally reconstruct the signal propagation environment and accurately predict the channel characteristic parameters such as power, two-dimensional angle, propagation path loss, delay, etc. At present, most of the channel modeling methods for air-to-ground wireless signal transmission in academia and industry use ray tracing methods. However, the current research on channel modeling methods based on ray tracing theory is not accurate enough. On the one hand, only the multipath delay, relative amplitude and other delay power spectrum information of the wireless signal passing through the space are calculated, but the accurate multipath fading distribution information cannot be obtained. Only the Rayleigh channel model is used as the multipath fading distribution. The Rayleigh distribution is suitable for scenes with no dominant path, independent multipath components and amplitudes that obey random Gaussian distribution, such as urban blocks, indoors and other non-direct line-of-sight environments, but not suitable for scenes with high-speed movement of aircraft, complex and changeable terrain and rapid switching. On the other hand, only the loss of the signal transmission process is considered, ignoring the loss of related influencing factors generated by the transmitter and the transmitting signal device, such as "beam pointing", "flame attenuation", "polarization mismatch", "attitude occlusion" and other influencing factors. Therefore, how to obtain accurate multipath fading distribution information and how to introduce four influencing factors into the channel model based on ray tracing theory to achieve a complete and accurate modeling method is an urgent problem to be solved. Therefore, a modeling method for high dynamic air-to-ground multipath signals is proposed. Summary of the invention

[0004] The purpose of the present invention is to provide a modeling method for high-dynamic air-to-ground multipath signals, aiming to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A modeling method for high dynamic air-to-ground multipath signals comprises the following steps:

[0007] Step 1: Measure the received power curve in the actual scenario, including:

[0008] S101: Connect the channel measurement airborne unit and the ground receiving unit to the transmitting antenna and the receiving antenna respectively, and place the channel measurement airborne unit and the transmitting antenna on the aircraft, and place the ground receiving unit and the receiving antenna on the ground; in the air-to-ground channel measurement scenario, the height of the transmitting end on the aircraft perpendicular to the sea level is higher than the height of the receiving end on the ground perpendicular to the sea level, and a certain elevation angle is formed between the receiving antenna and the transmitting antenna;

[0009] S102: In the Sub-6G operating frequency band of the channel measurement airborne unit, a single carrier signal, a multi-carrier signal or an m-sequence is selected as a measurement signal and radiated to a ground receiving unit via a transmitting antenna;

[0010] S103: The ground receiving unit sets corresponding channel receiving parameters according to the flight parameters and channel collection parameters set by the channel measurement airborne unit. After the receiving antenna receives the same-frequency signal, it collects and stores it through the data processing unit; the total fading loss of the signal is collected and processed to obtain a function of the received power of the signal arriving at the receiving end changing with time, that is, the received power curve in the actual scenario;

[0011] Step 2: Digitally reconstruct the actual scene and extract the effective multipath, including:

[0012] S104: Collect relevant information of the air-to-ground link propagation scenario and determine the special environmental factors on the propagation path; establish a digital model to describe the signal propagation process based on the collected scenario information, consider environmental influencing factors, model the signal propagation, build a digital map of the simulation area, and realize the digital reconstruction of the transmission and reception link propagation scenario;

[0013] S105: using ray tracing technology to simulate the radio wave propagation scenario between the transmitting position and the receiving position, and clustering the simulation output results to obtain the multipath number, relative delay, and relative amplitude parameters of the actual air-to-ground channel;

[0014] Step 3: Establish a high-dynamic air-ground channel model, including:

[0015] S106: using a telemetry module carried on the aircraft to obtain telemetry data of the aircraft, including GPS coordinates of the current position, altitude and attitude information, and transmitting the obtained telemetry data to a ground receiving unit through wireless communication technology; using the received telemetry data to draw a digital map, mapping the GPS coordinates onto the digital map, and marking the movement trajectory of the aircraft; and continuously updating the digital map according to the movement trajectory of the aircraft and the telemetry data;

[0016] S107: Based on ray tracing and the motion trajectory and telemetry data of the aircraft, the beam pointing, flame attenuation, polarization mismatch and attitude occlusion factors are introduced to establish a high-dynamic air-to-ground channel model;

[0017] S108: Calculate channel model parameters using the established high-dynamic air-ground channel model in combination with the motion trajectory of the aircraft, including the number of multipaths, relative delay, relative amplitude, and multipath fading distribution type;

[0018] Step 4: Simulate and output the received power curve on the wireless simulation device, including:

[0019] S109: using the high-dynamic air-to-ground channel model parameters established in S108, modeling and simulation are performed in a wireless channel simulation device, the wireless channel simulation device simulates signal propagation according to the parameters, collects the received power of the simulated receiving antenna, and outputs a curve of the received power changing with time;

[0020] S110: Compare the receiving power curve in the actual scenario with the receiving power curve output by the wireless channel simulation device. If the trends of the two are inconsistent, repeat steps S107, S108 and S109, match and fit the data calculated by the high-dynamic air-ground channel model with the measured data, adjust the parameters and iteratively optimize the modeling results until the distribution trends of the two curves are consistent. The established high-dynamic air-ground channel model is the real channel in the current actual scenario, and the parameters finally calculated are the real channel parameters and multipath fading distribution information of the channel in the current scenario.

[0021] Furthermore, in S103, within a specific time, the aircraft performs three-dimensional random motion for each measurement, and the position of the ground receiving unit moves randomly after each measurement, and the range of the moving position does not exceed 30m. 2 The receiving antenna position changes no less than 20 times; each time the position changes, the ground receiving unit collects and stores a set of data, and the collection time of each set of data is no less than 5s; the total fading loss of the signal L fading Collect and process P r = P t - L fading ;in, P r is the signal power received at the receiving end, P t is the signal power transmitted by the transmitter; the function of the received power of the signal arriving at the receiving end changing with time is obtained, that is, the received power curve in the actual scenario.

[0022] Furthermore, in S105, the processing method is as follows:

[0023] The multipaths whose absolute value of the difference between the multipaths and the relative delay is less than the delay simulation accuracy of the wireless channel simulation device are clustered into clusters, and the relative amplitude of the multipath with the largest relative amplitude at the relative delay is selected.

[0024] Furthermore, in S107, the steps of establishing the high dynamic air-to-ground channel model are as follows:

[0025] S1071: Calculate the beam pointing mismatch loss; assume that the beam pointing mismatch loss is L beam , the expression is as follows:

[0026] ;

[0027] in, i t and i r are the directional angles of the main beams of the transmitting antenna and the receiving antenna, respectively, , i and ψ are the yaw angle, pitch angle and roll angle respectively, ( x t , y t , z t ) is the position of the transmitting antenna in the aircraft coordinate system, ( x r , y r , z r ) is the position of the receiving antenna in the ground coordinate system;

[0028] S1072: Calculate the flame attenuation loss; suppose the flame attenuation loss is L flame , the expression is as follows:

[0029] ;

[0030] in, d Calculate the propagation distance of the signal in the flame for the motion trajectory of the aircraft in the flame environment. is the absorption coefficient of the flame medium, ( x r , y r , z r ) is the position of the receiving antenna in the ground coordinate system, ( x i , yi , z i ) is the position of the antenna in the inertial coordinate system; x i (t) y i (t) z i (t) represent the x, y, and z axis coordinates of the transmitting antenna in the inertial coordinate system, respectively. x r (t) y r (t) z r (t) respectively represent the x, y, and z axis coordinates of the receiving antenna in the ground coordinate system;

[0031] S1073: Calculate polarization mismatch loss; assume that polarization mismatch loss is L pol , the expression is as follows:

[0032] ;

[0033] in, i t and i r are the directional angles of the main beams of the transmitting antenna and the receiving antenna, respectively, , i and ψ are the yaw angle, pitch angle and roll angle respectively, ( x t , y t , z t ) is the position of the transmitting antenna in the aircraft coordinate system, ( x r , y r , z r ) is the position of the receiving antenna in the ground coordinate system;

[0034] S1074: Calculate the posture occlusion loss; assume that the posture occlusion loss is L block , the expression is as follows:

[0035] ;

[0036] in, A vis is the visible area, A totalis the total surface area, calculated from the position and attitude of the aircraft. The visible area of ​​the aircraft is approximately a cylinder, and we get:

[0037] ;

[0038] ;

[0039] in, is the pitch angle of the aircraft relative to the receiver, r is the radius of the approximate cylinder, h is the height of the approximate cylinder;

[0040] S1075: Calculate the free space path loss. Suppose the free space path loss is L FSPL :

[0041] ;

[0042] in, d is the straight-line distance between the transmitting antenna and the receiving antenna obtained by S1072; f is the signal frequency;

[0043] S1076: Calculate the received power; include the beam pointing mismatch loss, flame attenuation loss, polarization mismatch loss and attitude shielding loss into the total path loss:

[0044] ;

[0045] in, P r is the final received power, P t is the signal power transmitted by the channel measuring airborne unit, G t is the transmit antenna gain, G r is the receiving antenna gain; after superimposing the contributions of all rays, the final received power is obtained, and the image of the received power changing with time is output through the ground receiving unit.

[0046] Furthermore, in S108, for the multipath fading distribution type, the signal amplitude obeys the Nakagami-m distribution:

[0047] ;

[0048] in, p ( r ) is the probability density function of Nakagami-m, r is the signal amplitude, m is the shape parameter, is the average power; by adjusting the shape parameter m , fitting different multipath fading characteristics.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention introduces influencing factors such as beam pointing, flame attenuation, polarization mismatch, and attitude shielding to make the high-dynamic air-to-ground channel model closer to the actual transmission environment and improve the accuracy of the model. The present invention iteratively corrects the model to obtain the real high-dynamic multipath signal air-to-ground channel in a certain scenario, as well as the channel parameters and the multipath fading distribution information of the channel, thereby optimizing communication performance and improving communication reliability. The signal amplitude of the Channa channel model adopted by the present invention obeys the Nakagami-m distribution, and by reasonably selecting the shape parameters m , can fit the actual measurement data more accurately and provide an important basis for the analysis and design of wireless communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the ray tracing technology in the present invention.

[0052] Figure 2 It is an implementation flow chart of the present invention.

[0053] Figure 3 This is a basic flow chart of establishing a high-dynamic air-to-ground channel model based on ray tracing theory in the present invention.

[0054] Figure 4 The present invention provides a flow chart for obtaining accurate multipath fading distribution information. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0056] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0057] like Figure 2 As shown, a modeling method for a high dynamic air-to-ground multipath signal provided by an embodiment of the present invention includes the following steps:

[0058] Step 1: Measure the received power curve in the actual scenario, including S101 to S103;

[0059] Step 2: digitally reconstruct the actual scene and extract effective multipaths, including S104 and S105;

[0060] Step 3: Establish a high dynamic air-ground channel model, including S106~S108;

[0061] Step 4: Simulate and output a receiving power curve on a wireless simulation device, including S109 and S110.

[0062] S101~S110 are as follows:

[0063] S101: Connect the channel measurement airborne unit and the ground receiving unit to the transmitting antenna and the receiving antenna respectively, and place the channel measurement airborne unit and the transmitting antenna on the aircraft, and place the ground receiving unit and the receiving antenna on the ground (such as Figure 1 As shown in the figure, the measurement can be carried out in different scenes such as cities, villages, mountains, jungles, etc. In the air-to-ground channel measurement scenario, the height of the transmitter on the aircraft perpendicular to the sea level is higher than the height of the receiver on the ground perpendicular to the sea level, so that a certain elevation angle is formed between the receiving antenna and the transmitting antenna. The distance between the transmitting antenna and the receiving antenna should ensure that the strength of the received signal is not less than the receiving sensitivity of the ground receiving unit, so as to simulate the propagation process of the ground-to-air communication link.

[0064] S102: In the Sub-6G operating frequency band of the channel measurement airborne unit, a single carrier signal, a multi-carrier signal or an m-sequence is selected as a measurement signal and radiated through a transmitting antenna.

[0065] S103: The ground receiving unit sets the corresponding channel receiving parameters according to the flight parameters and channel collection parameters set by the channel measurement airborne unit. After the receiving antenna receives the signal of the same frequency, it collects and stores it through the data processing unit. In order to increase the randomness of the collected signal, the aircraft needs to make three-dimensional random movements during each measurement within a specific time. The position of the ground receiving unit moves randomly after each measurement, but the range of the moving position does not exceed 30m. 2 The receiving antenna position changes no less than 20 times. Each time the position changes, the ground receiving unit collects and stores a set of data. The collection time of each set of data is no less than 5s. The total fading loss of the signal L fading Collect and process P r = P t - L fading ;in, P r is the signal power received at the receiving end, P t It is the signal power transmitted by the transmitter, and the function of the received power of the signal arriving at the receiver changing with time, that is, the received power curve in the actual scenario.

[0066] S104: Collect relevant information about the air-to-ground link propagation scenario, including antenna position, antenna height, obstacle position, terrain information, signal frequency, etc. Determine special environmental factors on the propagation path, such as signal attenuation, multipath propagation, shadow effect, etc. Based on the collected scenario information, establish a digital model to describe the signal propagation process. Use appropriate mathematical models to represent the propagation characteristics of the signal, such as the free space propagation model, the logarithmic distance loss model, the multipath propagation model, etc. Considering the influencing factors of the environment, such as topography, buildings, vegetation coverage, etc., model the signal propagation. Realize the digital reconstruction of the transmission and reception link propagation scenario Construct a digital map of the simulation area, including information such as terrain, elevation, electrical parameters, etc., to realize the digital reconstruction of the transmission and reception link propagation scenario.

[0067] S105: Use ray tracing technology to simulate the radio wave propagation scenario between the transmitting position and the receiving position, and aggregate the simulation output results into clusters to obtain parameters such as the multipath number, relative delay, and relative amplitude of the actual ground-to-air channel. The processing method is as follows:

[0068] For multipaths with dense relative delays, that is, the multipaths whose absolute value of the difference between the multipaths and the relative delay is less than the delay simulation accuracy of the wireless channel simulation equipment are clustered into clusters. The multipaths at the delay are considered to be indistinguishable paths, and the relative amplitude of the multipath with the largest relative amplitude at the relative delay is selected as the representative of the cluster.

[0069] The S105 includes:

[0070] S1051: The number of multipaths refers to the number of paths such as reflection, refraction, and scattering that a signal experiences during propagation. The number of different multipath components can be determined by analyzing the received signal using methods such as autocorrelation function, power spectrum density, or spectrum analysis.

[0071] S1052: Relative delay refers to the difference in arrival delay of each multipath component relative to the main path. The arrival delay of different multipath components can be estimated by observing the time domain characteristics of the signal, such as the waveform and peak position of the signal, and compared with the main path to calculate the relative delay.

[0072] S1053: The relative amplitude represents the ratio of the signal strength of different multipath components to the signal strength of the main path. The relative amplitude of different multipath components can be determined by analyzing the amplitude information of the received signal (such as received signal strength indicator RSSI) or power spectrum density.

[0073] S1054: The multipath fading distribution type is usually determined based on the statistical characteristics of the multipath components. Common distribution types include Rayleigh fading, Rician fading, Nakagami fading, etc. The distribution type of multipath fading can be determined by analyzing the characteristics of the received signal such as amplitude distribution, correlation or power spectrum density.

[0074] S106: Using the telemetry module on the aircraft, obtain the GPS coordinates, altitude, attitude (such as pitch, roll, yaw angle) and other information of the aircraft's current position through the flight controller or other sensors on the aircraft. The acquired telemetry data can be transmitted to the ground receiving unit through wireless communication technology, such as Wi-Fi, Bluetooth, or dedicated remote control frequency. Use the received telemetry data to draw a digital map, which can be achieved by using map drawing software, such as GIS (Geographic Information System) software or a map drawing library in a programming language. Map the GPS coordinates to the digital map and mark the aircraft's location, track and other information. Continuously update the digital map based on the aircraft's motion trajectory and telemetry data. Ensure that the information displayed on the map is synchronized with the actual aircraft's location and status. In addition to the basic location and track information, other additional information, such as terrain height, obstacle location, wind speed, etc., can be added as needed to improve the practicality and accuracy of the map. Design a user interface so that users can easily view and operate the digital map. Save the drawn digital map to a suitable storage device through a shared file or online platform.

[0075] S107: Using the calculation results of S105 and the motion trajectory and telemetry data of the aircraft in S106, based on ray tracing theory and the collected flight data of the aircraft, introduce factors such as beam pointing, flame attenuation, polarization mismatch, and attitude occlusion to establish a high-dynamic air-to-ground channel model (such as Figure 3 The specific steps are as follows:

[0076] Ray tracing theory is a method commonly used in modeling wireless signal propagation. It is based on the principles of geometric optics and calculates the signal fading characteristics at the receiving end by tracing the multipath effects of reflection, refraction, diffraction, etc. during the propagation of the signal, and considering the influence of the aircraft and antenna array on signal propagation according to the three-dimensional attitude motion model of the aircraft, such as beam pointing mismatch loss, polarization mismatch loss, flame attenuation loss, attitude shielding loss.

[0077] The S107 includes:

[0078] S1071: Calculate the beam pointing mismatch loss; beam pointing refers to the direction of the antenna main beam. In ray tracing, the antenna beam pointing during signal propagation can be calculated based on the position and direction of the antenna and the direction of the propagation path. The deviation of beam pointing will affect the received signal strength and multipath effect, which needs to be considered in the fading model. Assume that the beam pointing mismatch loss is L beam ; According to the directional angle of the main beam of the transmitting antenna i t and the receiving antenna main beam i r The calculation results are:

[0079] ;

[0080] Based on the position and attitude data of the aircraft, including the yaw angle , Pitch angle i , Roll Angle ψ , by using the rotation matrix R( , i , ψ ) will be the location of the transmitting antenna ( x t , y t , z t ) from the aircraft coordinate system and the position of the receiving antenna ( x r , y r , z r ) is converted from the ground coordinate system to the inertial coordinate system to obtain the position of the antenna in the inertial coordinate system ( x i , y i , z i ),( x i , y i , z i ) is as follows:

[0081] ;

[0082] The rotation matrix R( , i , ψ ) is as follows:

[0083] ;

[0084] According to the position of the antenna in the inertial coordinate system ( x i , y i , z i ), calculate the main beam angle of the antenna:

[0085] ;

[0086] ;

[0087] in, i t is the azimuth angle of the transmitting antenna main beam, i r is the directional angle of the main beam of the receiving antenna; i t and i r By measuring the received power of the antenna in different directions, the direction corresponding to the maximum power can be found. This direction is the main beam direction of the antenna.

[0088] Finally calculated L beam The complete expression is:

[0089] ;

[0090] S1072: Calculate flame attenuation loss; flame attenuation loss is the attenuation caused by the absorption and scattering of the signal by thermal molecules and gases in the atmosphere. This attenuation is related to the frequency, propagation distance, and atmospheric conditions. In the ray tracing model, the absorption characteristics and scattering effects of the atmosphere can be considered, and the flame attenuation can be calculated by modeling the atmospheric density and temperature in the signal propagation path. Suppose the flame attenuation loss is L flame , the propagation distance of the signal in the flame is calculated based on the motion trajectory of the aircraft in the flame environment d , according to the absorption coefficient of the flame medium , calculate the flame decay loss:

[0091] ;

[0092] According to the actual situation, determine the position and size of the flame area in the inertial coordinate system. A three-dimensional rectangular area can be used to represent the range of the flame area. x , y , z ) and attitude yaw angle , Pitch angle i , Roll Angle ψData, calculate its motion trajectory in the inertial coordinate system. Determine whether the aircraft has entered the flame area, and if so, record the time of entry and exit. In the ground coordinate system, for each moment the aircraft is in the flame area, calculate the straight-line distance between the transmitting antenna and the receiving antenna. This straight-line distance is the propagation distance of the signal in the flame. d .

[0093] Specifically: Assume that the range of the flame area in the inertial coordinate system is x ∈[ x 1, y 2], y ∈[ y 1, y 2], z ∈[ z 1, z 2], for the position of the aircraft at time t ( x ( t ), y ( t ), z ( t )) and posture( ( t ), i ( t ), ψ ( t )) to determine whether it has entered the flame area: If x 1≤ x ( t )≤ x 2, y 1≤ y ( t )≤ y 2, z 1≤ z ( t )≤ z 2, the aircraft enters the flame area, and the time when the aircraft enters and exits the flame area is recorded respectively. t 1 and t 2. For t ∈[ t 1, t 2], calculate the straight-line distance between the transmitting antenna and the receiving antenna d ( t ):

[0094] ;

[0095] in,( x r , y r , z r) is the position of the receiving antenna in the ground coordinate system, ( x i , y i , z i ) is the position of the transmitting antenna in the ground coordinate system, ( x i , y i , z i ) The specific expression is obtained from S1071;

[0096] Finally calculated L flame The complete expression is:

[0097] ;

[0098] S1073: Calculate polarization mismatch loss; polarization mismatch loss refers to the signal attenuation caused by the mismatch between the polarization direction of the transmitting antenna and the polarization direction of the receiving antenna. Polarization loss occurs when the polarization directions of the transmitting and receiving antennas are inconsistent. In practical applications, due to factors such as antenna installation errors and environmental changes, it is difficult for the polarization states of the transmitting antenna and the receiving antenna to be completely consistent. Therefore, it is necessary to consider the impact of this polarization mismatch loss on signal transmission. In the ray tracing model, the polarization loss can be calculated based on the polarization characteristics of the antenna and the polarization direction in the propagation path. Assume that the polarization mismatch loss is L pol , ( x t , y t , z t ) is the position of the transmitting antenna in the aircraft coordinate system, ( x r , y r , z r ) is the position of the receiving antenna in the ground coordinate system. According to the polarization states of the transmitting antenna and the receiving antenna, the polarization mismatch loss is calculated:

[0099] ;

[0100] in, t and r are the polarization angles of the transmitting antenna and the receiving antenna respectively;

[0101] According to the polarization coordinates of the transmitting antenna in the ground coordinate system ( x i ,y i , z i ) Calculate the polarization angle of the antenna t and r :

[0102] ;

[0103] ;

[0104] in,( x i , y i , z i ) The specific expression is obtained from S1071;

[0105] Finally calculated L pol The complete expression is:

[0106] ;

[0107] S1074: Calculate attitude occlusion loss; attitude occlusion refers to the signal attenuation caused by changes in the position and direction of the radio device. Signal attenuation occurs when the antenna is blocked by an obstacle. In the ray tracing model, the position and direction changes of the radio device, as well as the position and shape of obstacles in the propagation path, can be considered to calculate the attenuation caused by attitude occlusion. These factors can be calculated by the ray tracing model, and combined with the characteristics of the propagation path and environmental conditions to establish a channel model. In the process of model building, the interaction and complexity of these factors are taken into account to improve the accuracy and applicability of the fading model. Assume that the attitude occlusion loss is L block , according to the geometric model and motion posture of the aircraft, calculate the signal blocking loss:

[0108] ;

[0109] in, A vis is the visible area, A total is the total surface area, calculated from the position and attitude of the aircraft:

[0110] Generally, a CAD model needs to be built based on the actual size and structure of the aircraft in order to calculate the visible area and total surface area. The model should include the main components of the aircraft, such as the fuselage, wings, and tail. The total surface area of ​​the aircraft is fixed as A totalThe visible area changes with the 3D attitude angle of the aircraft. In the normal viewing angle, the visible area is approximately the lateral area of ​​a cylinder:

[0111] ;

[0112] At other angles, the visible area will change and needs to be calculated based on the missile's attitude, with the transmitting antenna or receiving antenna as the reference, to construct the line of sight direction in the inertial coordinate system. Check the aircraft model along the line of sight to determine which parts are blocked and which parts are visible. Calculate the surface area of ​​the visible part, which is the visible area:

[0113] ;

[0114] in, is the pitch angle of the aircraft relative to the receiver, r is the radius of the approximate cylinder, h is the height of the approximate cylinder;

[0115] S1075: Calculate the free space path loss (FSPL). Assume that the free space path loss is L FSPL :

[0116] ;

[0117] in, d is the straight-line distance between the transmitting antenna and the receiving antenna obtained by S1072 (unit: km); f is the signal frequency (unit: GHz);

[0118] S1076: Calculate the received power; include the beam pointing mismatch loss, flame attenuation loss, polarization mismatch loss and attitude shielding loss into the total path loss:

[0119] ;

[0120] in, P r is the final received power, P t is the signal power transmitted by the channel measuring airborne unit, G t is the transmit antenna gain, G r is the receiving antenna gain; after superimposing the contributions of all rays, the final received power is obtained, and the image of the received power changing with time is output through the ground receiving unit.

[0121] S108: Combined with the motion trajectory of the aircraft (flight track or ballistic trajectory), the established high-dynamic air-to-ground channel model is used to calculate the channel model parameters including the number of multipaths, relative delay, relative amplitude, and multipath fading distribution type. Based on the ray tracing method, the multipath delay, relative amplitude and other delay power spectrum information of the radio waves passing through space can be calculated, but the multipath fading distribution information cannot be obtained. In a complex channel environment, a single multipath fading distribution model cannot be used. Instead, a multipath fading model with strong versatility that can be used to describe complex wireless signal propagation environments is selected. For the multipath fading distribution type, the signal amplitude of the Channa channel model obeys the Nakagami-m distribution:

[0122] ;

[0123] in, p ( r ) is the probability density function of Nakagami-m, r is the signal amplitude, m is the shape parameter, is the average power;

[0124] m =1 corresponds to Rayleigh distribution;

[0125] m >1 corresponds to a better propagation environment;

[0126] m <1 corresponds to a poor propagation environment;

[0127] The Channer channel model is applicable to complex propagation environments such as cities, suburbs, indoors, mountains, jungles, etc. Compared with using only Rayleigh distribution and Reiss distribution to obtain multipath fading distribution information, the Channer distribution is more flexible and universal.

[0128] Another advantage of Nakagami-m is that the shape parameters can be adjusted m , fitting the multipath fading characteristics under different environments: by reasonably selecting the shape parameters m , can fit the actual measurement data more accurately and provide an important basis for the analysis and design of wireless communication systems.

[0129] Specifically, first, the m parameter of the Nakagami-m distribution is initially set to 1 to simulate the most commonly used Rayleigh distribution. Secondly, the sensor equipment of the channel measurement airborne unit is used to sense the current signal transmission environment and judge the air-to-ground signal propagation scenario, and the m parameter is adjusted accordingly. If the perceived signal transmission environment is good, m is increased, and vice versa, m is reduced. Within a period of measurement time, the m parameter is determined, and the Nakagami-m distribution under this m parameter is output. At the same time, it is matched and fitted with the multipath fading distribution measured in the actual scenario, and the relative error is calculated. If the error is not within the set range, the m parameter is continued to be adjusted to continuously iterate and optimize the Nakagami-m distribution in the current environment until the error is controlled within the set range. The Nakagami-m distribution obtained at this time is the most accurate multipath fading distribution in the current environment.

[0130] S109: Using the high-dynamic air-to-ground channel model parameters established in S108, modeling and simulation are performed on the wireless channel simulation device, the receiving power of the receiving antenna of the wireless channel simulation device is collected, and a curve of the receiving power changing with time is output.

[0131] S110: Compare the receiving power curve in the actual scenario with the receiving power curve output by the wireless channel simulation device. If the trends of the two are inconsistent, repeat steps S107, S108 and S109, continuously match and fit the data calculated by the high-dynamic air-to-ground channel model with the measured data, adjust the parameters to iteratively optimize the modeling results, until the distribution trends of the two curves are consistent, then the established wireless channel simulation model is the real high-dynamic multipath signal air-to-ground channel in this scenario, and finally calculate the channel parameters: multipath number, relative delay, relative amplitude and Nakagami-m distribution m The parameters are the actual channel parameters and the multipath fading distribution information of the channel in this scenario.

[0132] The above are only preferred embodiments of the present invention. It should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These should also be regarded as the protection scope of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A modeling method for high dynamic air-to-ground multipath signals, characterized in that: The following steps are involved: Step 1: Measure the received power curve in the actual scenario, including: S101: Connect the channel measurement airborne unit and the ground receiving unit to the transmitting antenna and the receiving antenna respectively, and place the channel measurement airborne unit and the transmitting antenna on the aircraft, and place the ground receiving unit and the receiving antenna on the ground; in the air-to-ground channel measurement scenario, the height of the transmitting end on the aircraft perpendicular to the sea level is higher than the height of the receiving end on the ground perpendicular to the sea level, and a certain elevation angle is formed between the receiving antenna and the transmitting antenna; S102: In the Sub-6G operating frequency band of the channel measurement airborne unit, a single carrier signal, a multi-carrier signal or an m-sequence is selected as a measurement signal and radiated to a ground receiving unit via a transmitting antenna; S103: The ground receiving unit sets corresponding channel receiving parameters according to the flight parameters and channel collection parameters set by the channel measurement airborne unit. After the receiving antenna receives the same-frequency signal, it collects and stores it through the data processing unit; the total fading loss of the signal is collected and processed to obtain a function of the received power of the signal arriving at the receiving end changing with time, that is, the received power curve in the actual scenario; Step 2: Digitally reconstruct the actual scene and extract the effective multipath, including: S104: Collect relevant information of the air-to-ground link propagation scenario and determine the special environmental factors on the propagation path; establish a digital model to describe the signal propagation process based on the collected scenario information, consider environmental influencing factors, model the signal propagation, build a digital map of the simulation area, and realize the digital reconstruction of the transmission and reception link propagation scenario; S105: using ray tracing technology to simulate the radio wave propagation scenario between the transmitting position and the receiving position, and clustering the simulation output results to obtain the multipath number, relative delay and relative amplitude parameters of the actual air-to-ground channel; Step 3: Establish a high-dynamic air-ground channel model, including: S106: using a telemetry module carried on the aircraft to obtain telemetry data of the aircraft, including GPS coordinates of the current position, altitude and attitude information, and transmitting the obtained telemetry data to a ground receiving unit through wireless communication technology; using the received telemetry data to draw a digital map, mapping the GPS coordinates onto the digital map, and marking the movement trajectory of the aircraft; and continuously updating the digital map according to the movement trajectory of the aircraft and the telemetry data; S107: Based on ray tracing and the motion trajectory and telemetry data of the aircraft, the beam pointing, flame attenuation, polarization mismatch and attitude occlusion factors are introduced to establish a high-dynamic air-to-ground channel model; The steps to establish the high dynamic air-ground channel model include calculating the received power, specifically: incorporating beam pointing mismatch loss, flame attenuation loss, polarization mismatch loss and attitude shielding loss into the total path loss: ； in, P r is the final received power, P t is the signal power transmitted by the channel measuring airborne unit, G t is the transmit antenna gain, G r is the receiving antenna gain; L beam is the beam pointing mismatch loss, L flame is the flame decay loss, L pol is the polarization mismatch loss, L block is the attitude occlusion loss, L FSPL is the free space path loss; Outputting an image of the change of the received power over time through a ground receiving unit; S108: Calculate channel model parameters using the established high-dynamic air-ground channel model in combination with the motion trajectory of the aircraft, including the number of multipaths, relative delay, relative amplitude, and multipath fading distribution type; Step 4: Simulate and output the received power curve on the wireless simulation device, including: S109: using the high-dynamic air-to-ground channel model parameters established in S108, modeling and simulation are performed in a wireless channel simulation device, the wireless channel simulation device simulates signal propagation according to the parameters, collects the received power of the simulated receiving antenna, and outputs a curve of the received power changing with time; S110: Compare the receiving power curve in the actual scenario with the receiving power curve output by the wireless channel simulation device. If the trends of the two are inconsistent, repeat steps S107, S108 and S109, match and fit the data calculated by the high-dynamic air-ground channel model with the measured data, adjust the parameters and iteratively optimize the modeling results until the distribution trends of the two curves are consistent. The established high-dynamic air-ground channel model is the real channel in the current actual scenario, and the parameters finally calculated are the real channel parameters and multipath fading distribution information of the channel in the current scenario.

2. The modeling method of high dynamic air-to-ground multipath signal according to claim 1, characterized in that: In S103, within a specific time, the aircraft performs three-dimensional random motion for each measurement, and the position of the ground receiving unit moves randomly after each measurement, and the range of the moving position does not exceed 30m. 2 The receiving antenna position changes no less than 20 times; each time the position changes, the ground receiving unit collects and stores a set of data, and the collection time of each set of data is no less than 5s; the total fading loss of the signal L fading Collect and process P r = P t -L fading ; in, P r is the signal power received at the receiving end, P t is the signal power transmitted by the transmitter; the function of the received power of the signal arriving at the receiving end changing with time is obtained, that is, the received power curve in the actual scenario.

3. The modeling method of high dynamic air-to-ground multipath signal according to claim 1, characterized in that: In S105, the processing method is as follows: The multipaths whose absolute value of the difference between the multipaths and the relative delay is less than the delay simulation accuracy of the wireless channel simulation device are clustered into clusters, and the relative amplitude of the multipath with the largest relative amplitude at the relative delay is selected.

4. The modeling method of high dynamic air-to-ground multipath signal according to claim 1, characterized in that: In S107, the steps of establishing the high dynamic air-to-ground channel model are as follows: S1071: Calculate the beam pointing mismatch loss; assume that the beam pointing mismatch loss is L beam , the expression is as follows: ； in, θ t and θ r are the directional angles of the main beams of the transmitting antenna and the receiving antenna, respectively, , θ and are the yaw angle, pitch angle and roll angle respectively, ( x t , y t , z t ) is the position of the transmitting antenna in the aircraft coordinate system, ( x r , y r , z r ) is the position of the receiving antenna in the ground coordinate system; S1072: Calculate the flame attenuation loss; suppose the flame attenuation loss is L flame , the expression is as follows: ； in, d is the straight-line distance between the transmitting antenna and the receiving antenna, is the absorption coefficient of the flame medium; x i (t) y i (t) z i (t) respectively represent the x, y, and z axis coordinates of the transmitting antenna in the inertial coordinate system at time t, x r (t) y r (t) z r (t) respectively represent the x-axis, y-axis, and z-axis coordinates of the receiving antenna in the ground coordinate system at time t; S1073: Calculate polarization mismatch loss; assume that polarization mismatch loss is L pol , the expression is as follows: ； S1074: Calculate the posture occlusion loss; assume that the posture occlusion loss is L block , the expression is as follows: ； in, A vis is the visible area, A total is the total surface area, calculated from the position and attitude of the aircraft. The visible area of ​​the aircraft is approximately a cylinder, and we get: ； ； in, is the pitch angle of the aircraft relative to the receiver, r is the radius of the approximate cylinder, h is the height of the approximate cylinder; S1075: Calculate the free space path loss. Suppose the free space path loss is L FSPL : ； in, d is the straight-line distance between the transmitting antenna and the receiving antenna obtained by S1072; f is the signal frequency.

5. The modeling method of high dynamic air-to-ground multipath signal according to claim 1, characterized in that: In S108, for the multipath fading distribution type, the signal amplitude obeys the Nakagami-m distribution: ； in, p ( A ) is the probability density function of Nakagami-m, A is the signal amplitude, m is the shape parameter, is the average power; by adjusting the shape parameter m , fitting different multipath fading characteristics.

Images