Method for calculating multipath time delay of waveguide and scattering mixed channel in different waveguide environments

Abstract

The invention relates to a waveguide and scattering mixed channel multipath time delay calculation method in different waveguide environments, which comprises the following steps of: determining the propagation path length of electric waves in an evaporation waveguide channel according to the height of an evaporation waveguide and the heights of transmitting and receiving antennas of a maritime beyond visual range communication system by utilizing a ray tracing model; calculating the propagation path length of the electric wave in the troposphere scattering channel; the multi-path time delay of the evaporation waveguide and troposphere scattering mixed channel under different elevation angles of the transmitting and receiving antennas is obtained by utilizing the height of the evaporation waveguide, the heights of the transmitting and receiving antennas of the maritime beyond-the-horizon communication system, the propagation path length of electric waves in the evaporation waveguide and troposphere scattering channel and the propagation speed of the electric waves. According to the method, the evaporation waveguide height, the transmitting antenna height and the communication distance are substituted into the ray tracing model, the multipath time delay of the evaporation waveguide and the troposphere scattering mixed channel is calculated, and the multipath time delay of the evaporation waveguide and the troposphere scattering mixed channel under the offshore beyond-visual-range condition can be rapidly calculated.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of wireless communication, in particular to a waveguide and scattering mixed channel multipath delay calculation method under different waveguide environments. BACKGROUND

[0002] The satellite can be used to realize the over-the-horizon communication between the shore-based stations, however, the satellite communication has the defects of low communication rate, high cost and poor anti-interference capability. In addition to the satellite communication, the evaporation waveguide and the tropospheric scattering are two main means to realize the over-the-horizon high-speed communication at sea. The mechanism of the evaporation waveguide is that with the evaporation and diffusion of the sea surface water vapor, the atmospheric humidity above the sea surface will decrease sharply with the increase of the height, so that the atmospheric refractive index presents a negative gradient change, thereby the propagation path of the electric wave in the evaporation waveguide environment is refracted downward, when the refractive curvature is greater than the curvature of the sea surface, the electric wave will be trapped in the evaporation waveguide environment, forming the unique pipe bending effect at sea, and finally realizing the over-the-horizon propagation of more than 100 km across the sea. Therefore, the evaporation waveguide is used for the over-the-horizon communication at sea, which has the advantages of long transmission distance, small path loss, high transmission data rate and strong anti-interference capability.

[0003] At the same time, the tropospheric scattering is another means of over-the-horizon propagation of electric wave at sea. A large number of scatterers are distributed in the troposphere, which are various vortex air masses, cloud layers, warm fronts and cold fronts. These scatterers will cause the refraction and re-radiation of the electric wave of very high frequency and above, especially the C-band (4GHz-8GHz) and X-band (8GHz-12GHz), so that the electric wave of the above frequency bands can be over-the-horizon. The communication distance of the tropospheric scattering is at least 150 km, and the farthest can reach 600-700 km, and has the advantages of high transmission rate, good secrecy and mobility, and is widely used in military and emergency communication.

[0004] However, the two propagation modes of the sea evaporation waveguide and the tropospheric scattering are inseparable: when the evaporation waveguide height is high and the communication distance is short (such as the evaporation waveguide height is greater than 12 m and the communication distance is not more than 150 km), the evaporation waveguide is the main mode of over-the-horizon propagation of electric wave at sea; when the evaporation waveguide height is low and the communication distance is long (such as the evaporation waveguide height is less than 12 m and the communication distance is more than 150 km), the tropospheric scattering will become the main mode of over-the-horizon propagation of electric wave at sea. Therefore, although the evaporation waveguide and the tropospheric scattering have different formation mechanisms, the electric wave will automatically select the propagation mode according to the evaporation waveguide height and the communication distance.

[0005] When the evaporation duct is the main mode of over-the-horizon communication at sea, a small part of the radio waves will leak out of the duct layer and propagate over the horizon through the tropospheric scattering channel; similarly, when the tropospheric scattering is the main mode of over-the-horizon communication at sea, a small part of the radio waves will be trapped in the duct layer and propagate over the horizon through the evaporation duct channel. Therefore, the signal reaching the receiving end of the over-the-horizon communication system at sea is the superimposed signal through the evaporation duct and the tropospheric scattering channel. When the over-the-horizon communication mode at sea switches between the evaporation duct and the tropospheric scattering, the intensity of the radio waves reaching the receiving end of the over-the-horizon communication system through the evaporation duct channel and the tropospheric scattering channel is comparable. Due to the different lengths of the evaporation duct and the tropospheric scattering channel, the time of the radio waves reaching the receiving end through the two channels is different, resulting in multipath delay. When the over-the-horizon communication mode switches between the duct and the scattering, it will cause overlapping and interference between adjacent symbols, increase the probability of inter-symbol interference, and reduce the quality of the received signal, ultimately leading to an increase in the bit error rate.

[0006] Currently, the existing over-the-horizon communication multipath delay calculation method at sea mostly calculates the evaporation duct and the tropospheric scattering as two independent modes, and does not fully consider the switching of the over-the-horizon communication mode between the evaporation duct and the tropospheric scattering, thus not considering the evaporation duct and the tropospheric scattering as a mixed channel. At the same time, the existing multipath delay calculation method does not fully consider the influence of the evaporation duct height and the change of the transmitting and receiving antenna height of the over-the-horizon communication system at sea on the multipath delay, resulting in that the calculation result cannot fully adapt to the change of the evaporation duct environment, the change of the transmitting and receiving antenna height, and the frequent switching of the communication mode between the duct and the scattering, and cannot better match the mixed channel of the evaporation duct and the tropospheric scattering.

[0007] The evaporation duct is a waveguide layer formed by the abnormal gradient of the refractive index near the sea surface, and its height directly affects the propagation mode and delay of electromagnetic waves: when the evaporation duct height increases, the higher waveguide layer can capture more electromagnetic wave energy, further increasing the evaporation duct propagation path length and reducing the time delay caused by multipath effects (such as sea surface reflection, scattering); if the waveguide height is too high, part of the high-angle electromagnetic wave may not be effectively captured by the waveguide layer, and directly penetrate out of the waveguide layer without being limited to propagation. This will result in a decrease in captured energy, and the receiving end will rely more on direct, reflected or scattered paths to compensate for the signal. These alternative paths are usually longer and less stable, which may increase the propagation delay or cause signal fading under certain conditions. When the evaporation duct height is low, the waveguide's ability to capture radio waves is weak, and the tropospheric scattering becomes the main over-the-horizon communication mode. The characteristics of long and random scattering path distance will result in a significant increase in time delay.

[0008] The height of the transmitting antenna determines the coupling efficiency of the electromagnetic wave into the waveguide layer: when the antenna is in the evaporation waveguide layer, the electromagnetic wave energy can be coupled into the waveguide efficiently, which dominates the low-latency waveguide propagation, and the time delay characteristics are stable; if the antenna is higher than the waveguide layer, part of the energy cannot enter the waveguide and needs to rely on the scattering path transmission, which introduces a high time delay component. When the antenna is too low and close to the sea surface, the waveguide coupling efficiency decreases, and the sea surface reflection enhances, producing more multipath propagation. These reflection / diffracted paths are usually longer than the direct path, thus increasing the multipath time delay spread.

[0009] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0010] It should be noted that this section aims to provide background or context for the technical solutions of the present application stated in the claims. The description herein is not admitted to be prior art merely because it is included in this section. SUMMARY

[0011] The purpose of the present application is to provide a waveguide and scattering mixed channel multipath time delay calculation method under different waveguide environments, and to at least solve one or more problems caused by the limitations and defects of the related art.

[0012] The present application provides a waveguide and scattering mixed channel multipath time delay calculation method under different waveguide environments, comprising: S1, when the shore base and the shore base communicate through the evaporation waveguide channel, the ray tracing model is used to determine the propagation path length of the electric wave in the evaporation waveguide channel according to the evaporation waveguide height, the transmitting and receiving antenna height of the sea over-the-horizon communication system; wherein the process of calculating the propagation path length of the electric wave in the evaporation waveguide channel by the ray tracing model includes: discretizing the electric wave propagation trajectory into multiple rays, calculating the positional relationship of the electric wave rays by physical laws, and thus obtaining the propagation path length of the electric wave in the evaporation waveguide channel; S2, when the shore base and the shore base communicate through the tropospheric scattering channel, the distance between the transmitting end and the scattering body of the sea over-the-horizon communication system is obtained through the angle between the connecting lines of the transmitting end and the scattering body and the earth center; similarly, the distance between the receiving end and the scattering body of the over-the-horizon communication system can be obtained, and then the sum of the two distances is obtained to obtain the propagation path length of the electric wave in the tropospheric scattering channel; S3, the evaporation waveguide height, the transmitting and receiving antenna height of the sea over-the-horizon communication system, the propagation path length of the electric wave in the evaporation waveguide and the tropospheric scattering channel, and the electric wave propagation speed are used to obtain the multipath time delay of the evaporation waveguide and the tropospheric scattering mixed channel under different transmitting and receiving antenna elevation angles.

[0013] In the present application, S1 comprises the following steps: S1.1, deriving the atmospheric correction refractive index according to the Snell's law of spherical layered atmosphere, and performing Taylor second order approximation on the correction refractive index to obtain the difference of the correction refractive index of the radio wave propagating in the air at different heights; S1.2, assuming that the atmospheric correction refractive index changes linearly with the height between different heights, obtaining the relationship between the correction refractive index and the height of the radio wave according to the difference of the correction refractive index; S1.3, calculating the propagation path length of the radio wave in the evaporation duct channel according to the relationship between the correction refractive index and the height of the radio wave.

[0014] In the present application, S1.1 comprises the following steps: According to the Snell's law of spherical layered atmosphere, the following generalized law is obtained: (1) Wherein, is the height of the antenna, is the propagation height of the radio wave in the air, and are respectively and the atmospheric refractive index at the height, is the radius of the earth, and are respectively the elevation angle of the radio wave ray at and the height; The curved earth curvature model is changed into a flat model by using the atmospheric correction refractive index, and the relationship between the atmospheric correction refractive index M and the atmospheric refractive index n is as follows: (2) When and , the following relationship is obtained by using formula (1) and formula (2): (3) Since the angle between the radio wave ray and the horizontal boundary of the waveguide is small when the waveguide propagation is formed, and the lower atmospheric correction refractive index is close to 1, the following formula is obtained by performing Taylor second order approximation on formula (3): (4) Wherein, and correspond to the elevation angle of the radio wave ray at and the height, is the difference of the correction refractive index at and the height.

[0015] In the present application, S1.2 comprises the following steps: The formula (4) is arranged to obtain the following formula: (5) Assuming that the atmospheric correction refractive index varies linearly with height between and , we have: (6) wherein, is the linear variation rate, and the formula (4) and the formula (6) can be obtained: (7) The formula (7) is rewritten into a differential form as follows: (8) wherein, is the component of the radio wave ray in the vertical height direction, is the antenna elevation angle; the correction refractive index and have the following relationship: (9) wherein, is the evaporation waveguide height, and the aerodynamic roughness factor is 0.11 m.

[0016] In the present application, S1.3 comprises the following steps: The formula (8) is divided by the component of the radio wave ray in the horizontal direction , and we have: (10) The formula (8) and (10) are obtained as follows: (11) The formula (11) is rewritten into the following form: (12) wherein, x 1, x 2 are the distances of the radio wave ray in the horizontal direction; The formula (7) and (12) are used to obtain the variation relationship of the height and the distance in the horizontal direction of the radio wave ray in the vertical direction with the elevation angle, so that the propagation path length of the radio wave in the evaporation waveguide channel is: (13) wherein, is the propagation path length of the radio wave in the evaporation waveguide channel, is the first ray of the radio wave, is the step number of each ray; wherein, represents the first ray of the radio wave at the first step, represents the first ray of the radio wave at the first step, and the same.

[0017] In the present application, in S2, the distance between the transmitting end of the over-the-horizon communication system and the scatterer is expressed as follows:

[0018] wherein, is the elevation angle of the transmitting antenna of the over-the-horizon communication system, is the elevation angle of the receiving antenna of the over-the-horizon communication system, is the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel; the distance between the receiving end of the over-the-horizon communication system and the scatterer is expressed as follows:

[0019] According to and the propagation path length of the radio wave in the tropospheric scatter channel is as follows: .

[0020] In the present application, in S3, the expression of the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel is:

[0021] wherein, c is the propagation speed of the radio wave.

[0022] In the present application, the channel delay of the tropospheric scatter channel is , and the expression of the evaporation duct multipath delay is:

[0023] wherein, is the shortest propagation path length of the radio wave in the evaporation duct channel.

[0024] In the present application, the expression of the multipath delay of the mixed channel of the evaporation duct and the tropospheric scatter is: The maximum value of the multipath delay difference between the tropospheric scattering and the evaporation duct, the multipath delay of the tropospheric scattering channel itself, and the multipath delay of the evaporation duct channel is: .

[0025] In the present application, The expression is:

[0026] Wherein, The radio communication distance is, The working frequency of the communication system is D, the antenna aperture diameter is, The equivalent radius of the earth is, .

[0027] The technical solution provided by the present application can include the following beneficial effects: In the present application, when the shore base and the shore base perform over-the-horizon communication through the evaporation duct and the tropospheric scattering mixed channel, the present application only substitutes the evaporation duct height, the sea over-the-horizon communication system transmitting antenna height, and the communication distance into the ray tracing model to calculate the evaporation duct and the tropospheric scattering mixed channel multipath delay analytical expression, so that the evaporation duct and the tropospheric scattering mixed channel multipath delay under the sea over-the-horizon condition can be quickly calculated; the evaporation duct environment change and the frequent switching of the waveguide and scattering communication mode can be fully adapted; the calculation result of the present application can better match the evaporation duct and the tropospheric scattering mixed channel, and can be used to guide the waveform design of the sea over-the-horizon communication system; the inter-symbol interference is avoided, the bit error rate is reduced, and the performance of the sea over-the-horizon communication system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present disclosure and, together with the specification, serve to explain the principles of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained from these drawings without creative labor for those skilled in the art.

[0029] Figure 1 is a flowchart of the waveguide and scattering mixed channel multipath delay calculation method under different waveguide environments of the present application embodiment; Figure 2 is a scene diagram of the waveguide and scattering mixed channel multipath delay calculation method under different waveguide environments of the present application embodiment; Figure 3 is the evaporation duct and tropospheric scattering mixed channel multipath delay calculation result when the antenna height is 4m, the evaporation duct height is 8m, and the communication distance is 150km in the present application embodiment. Figure 4 is the calculation result of the evaporation waveguide and tropospheric scatter mixed channel multipath delay of the embodiment of the present application when the antenna height is 4m, the evaporation waveguide height is 15m, and the communication distance is 150km; Figure 5 is the calculation result of the evaporation waveguide and tropospheric scatter mixed channel multipath delay of the embodiment of the present application when the antenna height is 8m, the evaporation waveguide height is 15m, and the communication distance is 150km; Figure 6 is the calculation result of the evaporation waveguide and tropospheric scatter mixed channel multipath delay of the embodiment of the present application when the antenna height is 4m, the evaporation waveguide height is 10m, and the communication distance is 300km; Figure 7 is the calculation result of the evaporation waveguide and tropospheric scatter mixed channel multipath delay of the embodiment of the present application when the antenna height is 4m, the evaporation waveguide height is 18m, and the communication distance is 300km; Figure 8 is the calculation result of the evaporation waveguide and tropospheric scatter mixed channel multipath delay of the embodiment of the present application when the antenna height is 8m, the evaporation waveguide height is 18m, and the communication distance is 300km. DETAILED DESCRIPTION

[0030] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations can be implemented in any

[0031] In addition, the drawings are to be considered in all respects as illustrative and not restrictive; identical reference numerals have been used, where possible, to denote identical or similar features, and thus repetitive descriptions can be omitted. Some of the blocks in the drawings are function blocks, and do not necessarily correspond to physical or logical independent entities.

[0032] A waveguide and scatter mixed channel multipath delay calculation method in different waveguide environments is provided in the present example implementation, which, as shown in FIG. 1, includes the following steps: Figure 1 ​S1, when the shore base and the shore base communicate through the evaporation waveguide channel, the ray tracing model is used to determine the propagation path length of the electric wave in the evaporation waveguide channel by the evaporation waveguide height, the transmitting and receiving antenna height of the sea over horizon communication system; wherein the process of calculating the propagation path length of the electric wave in the evaporation waveguide channel by the ray tracing model comprises: discretizing the electric wave propagation track into multiple rays, calculating the position relationship of the electric wave rays by physical law, so as to obtain the propagation path length of the electric wave in the evaporation waveguide channel; S2, when the shore base and the shore base communicate through the troposphere scattering channel, the distance between the transmitting end and the scattering body of the sea over horizon communication system is obtained through the angle between the connecting lines of the transmitting end and the scattering body and the earth center and the angle between the connecting lines; similarly, the distance between the receiving end and the scattering body of the sea over horizon communication system is obtained, and then the two distances are summed to obtain the propagation path length of the electric wave in the troposphere scattering channel; S3, the evaporation waveguide height, the transmitting and receiving antenna height of the sea over horizon communication system, the propagation path length of the electric wave in the evaporation waveguide and the troposphere scattering channel, and the electric wave propagation speed are used to obtain the multipath delay of the evaporation waveguide and the troposphere scattering mixed channel under different transmitting and receiving antenna elevation angles.

[0033] In the application, when the shore base and the shore base communicate through the evaporation waveguide and the troposphere scattering mixed channel, the application only needs to substitute the evaporation waveguide height, the transmitting antenna height of the sea over horizon communication system and the communication distance into the ray tracing model to calculate the evaporation waveguide and the troposphere scattering mixed channel multipath delay analytical expression, so that the evaporation waveguide and the troposphere scattering mixed channel multipath delay under the sea over horizon condition can be calculated quickly; the application can fully adapt to the frequent switching of the evaporation waveguide environment change and the waveguide and scattering communication mode; the calculation result of the application can better match the evaporation waveguide and the troposphere scattering mixed channel, and can be used to guide the waveform design of the sea over horizon communication system; the code interference is avoided, the bit error rate is reduced, and the performance of the sea over horizon communication system is improved.

[0034] The specific situation of each step in the above embodiment will be described below.

[0035] In S1, please refer to Figure 2 , Figure 2 The scene diagram of the mixed channel multipath delay calculation method of the application.

[0036] If the shore base and the shore base communicate through the evaporation waveguide channel, that is, Figure 2 The continuous arc length track (arc length , that is, the arc The length of the propagation path of the radio wave in the evaporation duct channel is calculated according to formula (13) .

[0037] S1 comprises the following steps: S1.1, deriving the atmospheric correction refractive index according to the Snell's law of the spherical layered atmosphere, and performing Taylor's second-order approximation on the correction refractive index to obtain the difference between the correction refractive indices of the radio wave propagating at different altitudes in the air; S1.2, assuming that the atmospheric correction refractive index changes linearly with the altitude between different altitudes, obtaining the relationship between the correction refractive index and the altitude of the radio wave according to the difference between the correction refractive indices; S1.3, calculating the propagation path length of the radio wave in the evaporation duct channel according to the relationship between the correction refractive index and the altitude of the radio wave.

[0038] The specific calculation process is as follows: According to the Snell's law of the spherical layered atmosphere, the following generalized law is obtained: (1) wherein, is the antenna height, is the propagation altitude of the radio wave in the air, and are the atmospheric refractive indices at the altitudes of and respectively, is the radius of the earth, and are the elevations of the radio wave ray at the altitudes of and respectively.

[0039] In order to better simulate the ray trajectory, the correction refractive index is adopted here, so that the curved earth curvature model becomes a flat model. The relationship between is given by the following formula: (2) When and , the following relationship is obtained by using formula (1) and formula (2): (3) Since the angle between the ray and the horizontal boundary of the waveguide is generally small when the waveguide propagation is formed, and the correction refractive index of the lower atmosphere is close to 1, Taylor's second-order approximation is performed on formula (3) to obtain: (4) wherein, and Corresponding to electromagnetic rays in and The angle of elevation at a given altitude, expressed in radians (rad). for and The difference in corrected refractive index at different altitudes.

[0040] The calculation method is characterized by the following steps in step S1.2: Rearranging equation (4), we obtain the following equation: (5) Assuming the atmospheric corrected refractive index is and If the height varies linearly with altitude, then: (6) in, As a linear rate of change, it can be obtained from equations (4) and (6): (7) make , Then equation (7) can be expressed as:

[0041] when and When the value approaches infinity, the above formula can be expressed as:

[0042] right Expanding, we get: Write it in differential form as follows: (8) in, Let be the component of the radio wave ray in the vertical height direction. This is the antenna elevation angle.

[0043] Corrected refractive index and The following relationship exists: (9) in, Evaporation waveguide height, aerodynamic roughness factor rice.

[0044] Divide both sides of equation (8) by the horizontal component of the electromagnetic radiation. Then we have: (10) From equations (8) and (10), we have the following equation: (11) Equation (11) can be rewritten as follows: (12) wherein, x 1, x 2are the distances of the radio wave ray in the horizontal direction.

[0045] From equations (7) and (12), we have the relationship between the height and the distance of the radio wave ray in the vertical direction and the horizontal direction with respect to the elevation angle. The step length of the vertical height can be set to 0.25 m, and each 0.25 m step length corresponds to a point. The distance increment between each point can be calculated to obtain the propagation path length of the radio wave in the evaporation duct channel : (13) wherein, is the propagation path length of the radio wave in the evaporation duct channel, is the i-th radio wave ray, is the step number of each ray; wherein, represents the horizontal position of the i-th radio wave ray at the j-th step, represents the vertical height of the i-th radio wave ray at the j-th step, and are the same. Similarly.

[0046] In S2, please refer to Figure 2 , an isosceles triangle is drawn with the vertical line on the middle side, intersecting at point E. At this time is the angle bisector of , so , . According to the sine theorem, we have . Therefore, the distance between the transmitting end of the maritime over-the-horizon communication system and the scatterer is: (14) Similarly, the distance between the receiving end of the maritime over-the-horizon communication system and the scatterer is: (15) In a quadrilateral, the following equation holds: (16) ​​​​​in, The elevation angle of the transmitting antenna for a beyond-line-of-sight communication system. The elevation angle of the receiving antenna in a beyond-line-of-sight communication system. The central angle is the arc length corresponding to the path of the radio wave propagation in the evaporating waveguide channel. The angle between the line connecting the transmitting antenna to the Earth's center and the line connecting the transmitting antenna to the scattering object. The angle between the line connecting the receiving antenna to the Earth's center and the line connecting the receiving antenna to the scatterer.

[0047] This allows us to obtain the distance between the transmitter of the maritime over-the-horizon communication system and the scatterer. : (17) Similarly, the distance between the receiver and the scattering object in a maritime over-the-horizon communication system. for: (18) Therefore, the propagation path length of radio waves in the tropospheric scattering channel d for: (19) Alternatively, the height above the sea surface when radio waves scatter can be determined using the Earth's radius, the geocentric angle corresponding to the propagation path of radio waves in the evaporation waveguide channel, and the propagation path length of radio waves in the evaporation waveguide channel. The calculation process is as follows: Distance between the scatterer and the Earth's center AC, The height of the scatterer above the sea surface and Earth's radius satisfy: (20) According to the Law of Cosines: (twenty one) Substituting equation (21) into equation (20), we obtain equation (22) or (23): (twenty two) (twenty three) In S3, the multipath delay difference between the tropospheric scattering channel and the evaporation waveguide channel The expression is: (twenty four) in, This represents the multipath delay difference between the evaporation waveguide channel and the tropospheric scattering channel. This refers to the speed of radio wave propagation.

[0048] It should be noted that in the present application, .

[0049] Considering the tropospheric scatter channel itself delay wherein is the communication distance, is the operating frequency of the communication system, D is the antenna aperture diameter of the over-the-horizon communication system at sea, is the equivalent radius of the earth.

[0050] At the same time, the evaporation duct as an excellent channel for over-the-horizon communication at sea, its delay can also be realized by ray tracing model, so the multipath delay of the evaporation duct channel is: (25) wherein, is the shortest propagation path length of the radio wave ray in the evaporation duct environment.

[0051] Therefore, in analyzing the multipath delay of the evaporation duct and the tropospheric scatter mixed channel, the multipath delay of the mixed channel is the maximum value of the difference between the multipath delay of the evaporation duct and the tropospheric scatter mixed channel, the delay of the tropospheric scatter channel itself and the multipath delay of the evaporation duct channel, that is: (26) Experimental part: When the evaporation duct height is low, the ability of the duct to capture radio waves is weak, and the tropospheric scatter becomes the main over-the-horizon communication mode. The characteristics of long and random propagation distance of the scattering path will lead to a significant increase in delay.

[0052] When the antenna aperture diameter of the over-the-horizon communication system deployed on the shore at sea is 2m, the C-band typical frequency point 4.7GHz is selected, the over-the-horizon communication system transmitting antenna height is set to 4m, the evaporation duct height is 8m, the communication distance is 150km, the transmitting antenna horizontal elevation angle is set to 0°, the beam width is -0.3°~0.3°, the calculation step is 0.25m, and the number of ray is 1200. The results calculated according to formula (26) show that: the single-point delay of the evaporation duct and the tropospheric scatter mixed channel mainly concentrates around 0°, and the average delay is small, about 1.3 left and right; the multipath delay of the evaporation duct and the tropospheric scatter mixed channel is the smallest around 0°, and increasing or decreasing the beam angle will increase the multipath delay; the variance of the multipath delay of the evaporation duct and the tropospheric scatter mixed channel is 2.4489 . The simulation results show that the fluctuation degree of the multipath delay between different angles within the beam width is large. Similarly, the antenna aperture diameter, frequency and beam width and other parameters are consistent with the above, Figures 3 to 8The mixed channel multipath delay calculation results of the method are given under different evaporation waveguide heights, transmitting and receiving antenna heights and communication distances.

[0053] Figure 3 is the evaporation waveguide and tropospheric scattering mixed channel multipath delay calculation result of the embodiment of the application under the condition of evaporation waveguide height 8m, transmitting antenna height 4m and communication distance 150km. Figure 3 It can be seen that under the above parameter conditions, the single-point delay of the evaporation waveguide and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.3 ; the evaporation waveguide and tropospheric scattering mixed channel multipath delay is smallest near 0°, and the increase or decrease of the beam angle will increase the multipath delay; the variance of the evaporation waveguide and tropospheric scattering mixed channel multipath delay is 2.4489 , indicating that the fluctuation degree of the multipath delay between different angles within the beam width is large.

[0054] Figure 4 is the evaporation waveguide and tropospheric scattering mixed channel multipath delay calculation result of the embodiment of the application under the condition of evaporation waveguide height 15m, transmitting antenna height 4m and communication distance 150km. Figure 4 It can be seen that under the above parameter conditions, the single-point delay of the evaporation waveguide and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.05 ; the evaporation waveguide and tropospheric scattering mixed channel multipath delay is most dense near 0°, and the mixed channel delay near 0.03° will be slightly lower than that near 0°, but the overall trend is that the increase or decrease of the beam angle will increase the multipath delay; the variance of the evaporation waveguide and tropospheric scattering mixed channel multipath delay is 1.021 , indicating that the fluctuation degree of the multipath delay between different angles within the beam width is small; and Figure 3 It can be seen from the comparison that under the condition of fixed communication distance and antenna height, increasing the evaporation waveguide height can effectively reduce the multipath delay of the evaporation waveguide and tropospheric scattering mixed channel, because when the evaporation waveguide height is low, the waveguide has weak ability to capture radio waves, and the tropospheric scattering becomes the main over-the-horizon communication mode, and the long propagation distance and strong randomness of the scattering path will lead to significant increase of the delay, and vice versa, when the evaporation waveguide height is high, the delay can be effectively reduced.

[0055] Figure 5 is the evaporation waveguide and tropospheric scattering mixed channel multipath delay calculation result of the embodiment of the application under the condition of evaporation waveguide height 15m, transmitting antenna height 8m and communication distance 150km. Figure 5It can be seen that under the above parameter conditions, the single-point delay of the evaporation duct and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.19 The multipath delay of the evaporation duct and tropospheric scattering mixed channel is most concentrated near 0°, and the overall trend is that increasing or decreasing the beam angle will increase the multipath delay; the variance of the multipath delay of the evaporation duct and tropospheric scattering mixed channel is 2.6744 , indicating that the dispersion degree of the multipath delay between different angles within the beam width is large; and Figure 4 It can be seen that under the above parameter conditions, the single-point delay of the evaporation duct and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.19

[0056] Figure 6 is the multipath delay calculation result of the evaporation duct and tropospheric scattering mixed channel when the evaporation duct height is 10 m, the transmitting antenna height is 4 m, and the communication distance is 300 km. From Figure 6 It can be seen that under the above parameter conditions, the single-point delay of the evaporation duct and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.19 The multipath delay of the evaporation duct and tropospheric scattering mixed channel is most concentrated near 0° and is the smallest, and the overall trend is that increasing or decreasing the beam angle will increase the multipath delay; the variance of the multipath delay of the evaporation duct and tropospheric scattering mixed channel is 1.8417 , indicating that the fluctuation degree of the multipath delay between different angles within the beam width is small.

[0057] Figure 7 is the multipath delay calculation result of the evaporation duct and tropospheric scattering mixed channel when the evaporation duct height is 10 m, the transmitting antenna height is 4 m, and the communication distance is 300 km. From Figure 7 It can be seen that under the above parameter conditions, the single-point delay of the evaporation duct and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.19 The multipath delay of the evaporation duct and tropospheric scattering mixed channel is most dense and large near 0°, which is because when the antenna is close to the sea surface, the coupling efficiency of the waveguide may decrease, and the number of sea surface reflection paths increases, and the multipath delay spreads (the delay difference between the reflection path and the direct path increases). In general, increasing or decreasing the beam angle will increase the multipath delay. The variance of the multipath delay of the evaporation duct and tropospheric scattering mixed channel is 1.2887 , which indicates that the fluctuation degree of the multipath delay between different angles within the beam width is small. Figure 6 It can be seen from the comparison that, under the condition that the communication distance and the antenna height are fixed, increasing the evaporation duct height will reduce the multipath delay of the evaporation duct and tropospheric scattering mixed channel, because when the evaporation duct height is low, the waveguide has weak ability to capture radio waves, and the tropospheric scattering becomes the main over-the-horizon communication mode. The characteristics of long and random scattering path propagation distance will cause the delay to increase significantly, and vice versa, when the evaporation duct height is high, the delay can be effectively reduced.

[0058] Figure 8 is the calculation result of the multipath delay of the evaporation duct and tropospheric scattering mixed channel when the evaporation duct height is 18 m, the transmitting antenna height is 8 m, and the communication distance is 300 km according to the embodiment of the application. It can be seen from Figure 8 that under the above parameter conditions, the single-point delay of the evaporation duct and tropospheric scattering mixed channel is mainly concentrated near 0°, and the average delay is small, about 1.16 . The multipath delay of the evaporation duct and tropospheric scattering mixed channel is most dense near 0°, and in general, increasing or decreasing the beam angle will increase the multipath delay. The variance of the multipath delay of the evaporation duct and tropospheric scattering mixed channel is 3.3558 , which indicates that the fluctuation degree of the multipath delay between different angles within the beam width is large. Figure 7 It can be seen from the comparison that, under the condition that the communication distance and the evaporation duct height are fixed, increasing the antenna height will increase the multipath delay of the evaporation duct and tropospheric scattering mixed channel, because when the antenna height is high, the number of reflection and refraction of radio waves in the evaporation duct layer decreases, but at the same time, the trapping ability of the evaporation duct for radio waves weakens, and the tropospheric scattering becomes the main over-the-horizon communication mode. The characteristics of long and random scattering path propagation distance will cause the delay to increase significantly.

[0059] When the over-the-horizon communication system at sea changes the elevation angle of the transmitting and receiving antennas, the propagation path length of the radio wave in the evaporation duct channel remains unchanged, but the propagation path length in the tropospheric scattering channel will change, because when the elevation angle of the transmitting antenna is changed, the distance between the transmitting end of the over-the-horizon communication system on the shore and the scatterer changes, resulting in the need to adjust the elevation angle of the receiving antenna of the receiving end of the over-the-horizon communication system on the shore to ensure that the over-the-horizon communication effect is optimal, so that the propagation path length of the radio wave in the tropospheric scattering channel changes.

[0060] The multi-path time delay calculation method provided by the application can be used to guide the waveform design of the over-the-horizon communication system at sea, so that sufficient symbol intervals are left, thereby fully adapting to the change of the evaporation duct environment, the frequent switching between the duct and scattering communication modes, and better matching the evaporation duct and tropospheric scattering mixed channel, further reducing the inter-symbol interference, reducing the bit error rate of the over-the-horizon communication system at sea, and ultimately improving the performance of the over-the-horizon communication system at sea.

[0061] It should be understood that in the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0062] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses or adaptive changes of this application following the general principles thereof and including those expressly stated or implied herein. The specification and examples are considered exemplary only, and the true scope and spirit of the application are indicated by the appended claims.

Claims

1. A method for calculating the multipath time delay of a waveguide and scattering mixed channel in different waveguide environments, characterized in that, The method comprises the following steps: S1, when the shore base communicates with the shore base through the evaporation waveguide channel, the ray tracing model is used to determine the propagation path length of the electric wave in the evaporation waveguide channel according to the evaporation waveguide height, the transmitting and receiving antenna height of the sea over-the-horizon communication system; wherein the process of calculating the propagation path length of the electric wave in the evaporation waveguide channel by using the ray tracing model comprises the following steps: the electric wave propagation track is discretized into multiple rays, the positional relationship of the electric wave rays is calculated through physical laws, and thus the propagation path length of the electric wave in the evaporation waveguide channel is obtained; S2, when the shore base communicates with the shore base through the troposphere scattering channel, the distance between the transmitting end and the scattering body of the sea over-the-horizon communication system is obtained through the angle between the connecting lines of the transmitting end and the scattering body of the sea over-the-horizon communication system and the earth center; similarly, the distance between the receiving end and the scattering body of the sea over-the-horizon communication system is obtained, and then the sum of the two distances is obtained to obtain the propagation path length of the electric wave in the troposphere scattering channel; S3, the evaporation waveguide height, the transmitting and receiving antenna height of the sea over-the-horizon communication system, the propagation path length of the electric wave in the evaporation waveguide and the troposphere scattering channel, and the electric wave propagation speed are used to obtain the multipath delay of the evaporation waveguide and the troposphere scattering mixed channel under different transmitting and receiving antenna elevation angles.

2. The method of claim 1, wherein, S1 comprises the following steps: S1.1, the difference between the modified refractive indexes of the electric wave propagating at different heights in the air is obtained according to the Snell's law of the spherical layered atmosphere, and the Taylor second-order approximation is performed on the modified refractive index to obtain the relationship between the modified refractive index and the height of the electric wave; S1.2, the relationship between the modified refractive index and the height of the electric wave is obtained according to the difference between the modified refractive indexes, assuming that the modified refractive index of the atmosphere changes linearly with the height between different heights; S1.3, the propagation path length of the electric wave in the evaporation waveguide channel is calculated according to the relationship between the modified refractive index and the height of the electric wave.

3. The method of claim 2, wherein, S1.1 comprises the following steps: According to the Snell's law of the spherical layered atmosphere, the following generalized form of the law is obtained: （1） wherein is the antenna height, is the height of propagation of the radio wave in air, and are respectively and the atmospheric refractive index at the height, is the earth radius, and are respectively the elevation angles of the radio wave ray at and the height. The atmospheric correction refractive index is used to change the curved earth curvature model into a flat model, and the atmospheric correction refractive index M is related to the atmospheric refractive index n as follows: （2） When and then, using equations (1) and (2), the following relationship is obtained: （3） Since the angle between the electric wave ray and the waveguide horizontal boundary is small when the waveguide propagation is formed, and the modified refractive index of the lower atmosphere is close to 1, the Taylor second-order approximation is performed on formula (3) to obtain the following formula: （4） wherein and correspond to the elevation angles of the radio waves at the heights of and respectively, is and the difference of the corrected refractive indexes at the heights of 4. The method of claim 3, wherein, S1.2 comprises the following steps: Formula (4) is arranged to obtain the following formula: （5） Assuming the atmospheric correction refractive index varies linearly with height between and heights, then: （6） wherein is the linear rate of change, which can be obtained from equation (4) and equation (6): （7） Formula (7) is rewritten in the differential form as follows: （8） wherein is the component of the radio wave ray in the vertical height direction, is the antenna elevation angle; corrected refractive index there is a relationship between there is a relationship between （9） wherein is the evaporation waveguide height, the aerodynamic roughness factor meters.

5. The method of claim 4, wherein, S1.3 comprises the following steps: Dividing both sides of equation (8) by the horizontal component of the radio wave Then, we have: （10） Formula (8) and (10) are used to obtain the following formula: （11） Formula (11) is rewritten in the following form: （12） wherein x 1、 x 2 both are the distance of the radio waves in the horizontal direction; The height in the vertical direction and the distance in the horizontal direction of the radio wave ray are obtained from the equations (7) and (12) respectively, and the change relation of the height in the vertical direction and the distance in the horizontal direction with the elevation angle is obtained, thereby obtaining the propagation path length of the radio wave in the evaporation duct channel is: （13） wherein, is the length of the propagation path of the radio wave in the evaporation duct channel, is the number of steps of the th radio wave ray, is the number of steps of each ray; wherein, represents the horizontal position of the th radio wave ray at the th step, represents the vertical height of the th radio wave ray at the th step, and the same reasoning.

6. The method of claim 5, wherein, In S2, the distance between the transmitting end of the over-the-horizon communication system and the scatterer is represented as follows: wherein, an elevation angle of a transmitting antenna for an over-the-horizon communication system, an elevation angle of a receiving antenna for an over-the-horizon communication system, a central angle corresponding to an arc length of a propagation path of an electromagnetic wave in an evaporation duct channel. Distance between an over-the-horizon communication system receiving end and a scatterer is represented as follows: According to and obtaining the propagation path length of an electric wave in a tropospheric scatter channel as follows: 。 7. The method of claim 6, wherein, In S3, the multipath delay difference between tropospheric scatter channel and evaporation duct channel The expression is: wherein c is the speed of propagation of the electric wave.

8. The method of claim 7, wherein, The channel delay of the tropospheric scattering channel is The expression of the evaporation duct multipath delay is wherein is the shortest propagation path length of the radio waves in the evaporation duct channel.

9. The method of claim 8, wherein, Evaporation duct and tropospheric scatter mixed channel multipath delay The difference between the multipath delay of tropospheric scatter and evaporation duct, the delay of tropospheric scatter channel itself and the maximum of the multipath delay of evaporation duct channel, i.e. 。 10. The method of claim 9, wherein, The expression is: wherein is the radio communication distance, is the operating frequency of the communication system, D is the antenna aperture diameter, is the equivalent radius of the earth, .

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