Evaporation waveguide and scattering channel multipath time delay calculation method under different elevation angles

Abstract

The invention discloses an evaporation waveguide and scattering channel multipath time delay calculation method under different elevation angles, and the method comprises the steps: determining the length of a propagation path in an evaporation waveguide channel according to the radius of the earth and a central angle corresponding to the arc length of the propagation path in the evaporation waveguide channel; obtaining the propagation path length of the electric wave in the troposphere scattering channel according to the included angle between the connecting lines of the transmitting antenna and the circle center, the elevation angle of the transmitting antenna and the receiving antenna, the included angle between the connecting lines of the electric wave receiving antenna and the circle center, and the elevation angle of the transmitting antenna and the receiving antenna; then calculating to obtain the multipath time delay of the mixed channel; and setting a code element interval of radio wave communication according to the multipath time delay, so that the radio wave communication adapts to switching of communication modes. According to the calculation expression of the multipath time delay of the mixed channel, which is obtained by the invention, the multipath time delay of the evaporation waveguide and troposphere scattering mixed channel can be quickly calculated; code element intervals of radio wave communication are set according to multipath time delay, inter-symbol interference is avoided, and the bit error rate is reduced.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular, to a method for calculating the multipath delay of an evaporation duct and a scattering channel at different elevation angles. Background Art

[0002] Satellites can be used to achieve over-the-horizon communication between shore bases. However, there are disadvantages such as low communication rate, high cost, and poor anti-interference ability. In addition to satellite communication, evaporation ducts and tropospheric scattering are two main means to achieve high-speed over-the-horizon communication at sea. Among them, the generation mechanism of evaporation ducts is as follows: as sea surface water vapor evaporates and diffuses, the atmospheric humidity above the sea surface will decrease sharply with the increase in height, resulting in a negative gradient change in the atmospheric refractive index. As a result, the propagation path of radio waves in the evaporation duct environment refracts downward. When the refraction curvature is greater than the sea surface curvature, the radio waves will be trapped in the evaporation duct environment, forming a unique ducting effect at sea, and finally achieving over-the-horizon propagation across the sea for hundreds of kilometers. Therefore, using evaporation ducts for over-the-horizon communication at sea has the advantages of long transmission distance, small path loss, high transmission data rate, and strong anti-interference ability.

[0003] At the same time, tropospheric scattering is another means of over-the-horizon propagation of radio waves at sea. There are a large number of scatterers distributed in the troposphere, manifested as various vortex air masses, clouds, warm fronts, and cold fronts. These scatterers will cause the refraction and re-radiation of radio waves in the frequency bands above very high frequency, especially in the C band (4 GHz - 8 GHz), X band (8 GHz - 12 GHz), and Ku band (12 GHz - 18 GHz), so that radio waves in the above frequency bands can propagate over the horizon. The communication distance of tropospheric scattering can reach at least 150 km and up to thousands of kilometers at most, and the transmission rate is high. Due to the many advantages of tropospheric scattering communication, such as anti-nuclear explosion, not being affected by solar storms and geomagnetic storms, good confidentiality and mobility, it has been widely used in military and emergency communications.

[0004] However, the evaporation duct and tropospheric scattering channels at sea are inseparable: when the evaporation duct height is relatively high and the communication distance is relatively short (such as when the evaporation duct height is greater than 12 m and the communication distance does not exceed 200 km), most radio waves will automatically propagate over the horizon through the evaporation duct channel; when the evaporation duct height is relatively low and the communication distance is relatively long (such as when the evaporation duct height is less than 12 m and the communication distance exceeds 200 km), most radio waves will automatically propagate over the horizon through the tropospheric scattering channel. Therefore, although the formation mechanisms of evaporation ducts and tropospheric scattering are different, radio waves will automatically select the propagation path according to the evaporation duct height.

[0005] When most of the radio waves propagate through the evaporation duct channel, a small part will also leak outside the duct layer and propagate through the tropospheric scatter channel; when most of the radio waves propagate through the tropospheric scatter channel, a small part will also be trapped in the duct layer and propagate through the evaporation duct channel. Therefore, when conducting over-the-horizon communication at sea, the signal received at the receiving end is a superimposed signal that has experienced both the evaporation duct and the tropospheric scatter channels. Due to the different lengths of the evaporation duct and tropospheric scatter channels, there is a time difference in the arrival time of the radio waves at the receiving end after passing through these two channels, resulting in multipath delay, further causing overlap and interference between adjacent symbols, increasing the probability of inter-symbol interference, reducing the quality of the received signal, and ultimately increasing the bit error rate.

[0006] Currently, the technologies for calculating the multipath delay of over-the-horizon communication at sea only consider a single channel of either the evaporation duct or the tropospheric scatter. However, a large amount of experimental data on over-the-horizon communication at sea shows that the height of the evaporation duct changes significantly within a day, resulting in one or more switches between the over-the-horizon communication modes of the evaporation duct and the tropospheric scatter. When the communication distance is relatively short and the height of the evaporation duct is relatively high, the over-the-horizon communication system at sea uses the evaporation duct for communication. At this time, the elevation angle of the transmitting antenna needs to be set near 0°, so that more radio wave energy is trapped in the evaporation duct layer; when the communication distance is relatively long or the height of the evaporation duct is relatively low, the over-the-horizon communication system at sea uses the tropospheric scatter for communication. At this time, the elevation angle of the transmitting antenna is generally set between 0° and 5°. At the same time, the elevation angle of the receiving antenna also needs to be adjusted to ensure the optimal over-the-horizon communication effect.

[0007] Different elevation angles of the transmitting and receiving antennas result in different propagation path lengths of the radio waves in the tropospheric scatter channel, and thus the difference in the propagation path lengths of the radio waves passing through the evaporation duct and the tropospheric scatter channels is also different. Especially when the communication mode switches between the evaporation duct and the tropospheric scatter, the signal intensities of the radio waves reaching the receiving end after passing through the evaporation duct and the tropospheric scatter channels are quite similar, which causes serious inter-symbol interference, making the multipath delay calculated by only considering a single channel of either the evaporation duct or the tropospheric scatter unable to well adapt to the changes in the sea evaporation duct environment and unable to further guide the waveform design of the over-the-horizon communication system at sea.

[0008] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0009] It should be noted that this part aims to provide background or context for the technical solutions of the present disclosure stated in the claims. The description herein is not admitted to be prior art merely because it is included in this part. Summary of the Invention

[0010] The object of the present invention is to provide a method for calculating the multipath time delay of an evaporation duct and a scattering channel at different elevation angles, so as to overcome at least to some extent one or more problems caused by the limitations and defects of the related art.

[0011] The present invention provides a method for calculating the multipath time delay of an evaporation duct and a scattering channel at different elevation angles, and the method includes: When performing radio wave communication through an evaporation duct channel, according to the radius of the earth and the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel, determine the propagation path length of the radio wave in the evaporation duct channel; When performing radio wave communication through a tropospheric scattering channel, according to the included angles between the connecting lines of the radio wave transmitting antenna and the scatterer with the center of the circle respectively, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna, determine the distance between the transmitting antenna and the scatterer; according to the included angles between the connecting lines of the radio wave receiving antenna and the scatterer with the center of the circle respectively, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna, determine the distance between the receiving antenna and the scatterer; where the center of the circle refers to the center of the earth; Sum up the two distances between the transmitting antenna and the scatterer and between the receiving antenna and the scatterer to obtain the propagation path length of the radio wave in the tropospheric scattering channel; According to the elevation angle of the transmitting antenna, the elevation angle of the receiving antenna, the propagation path length of the radio wave in the evaporation duct channel, the propagation path length of the radio wave in the tropospheric scattering channel, and the propagation speed of the radio wave, determine the multipath time delay difference between the tropospheric scattering channel and the evaporation duct channel, and according to the multipath time delay difference and the channel time delay of the tropospheric scattering channel, obtain the multipath time delay of the evaporation duct and tropospheric scattering hybrid channel at different elevation angles; Set the symbol interval of the radio wave communication according to the multipath time delay, so that the radio wave communication adapts to the switching of the communication mode.

[0012] In the present invention, the expression of the propagation path length of the radio wave in the evaporation duct channel is as follows:

[0013] where, is the propagation path length of the radio wave in the evaporation duct channel, is the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel, is the radius of the earth.

[0014] In the present invention, the expression of the distance between the transmitting antenna and the scatterer is as follows:

[0015] where, is the distance between the transmitting antenna and the scatterer, is the elevation angle of the transmitting antenna, is the elevation angle of the receiving antenna.

[0016] In the present invention, the expression for the distance between the receiving antenna and the scatterer is as follows:

[0017] where is the distance between the receiving antenna and the scatterer.

[0018] In the present invention, the expression for the propagation path length of the radio wave in the tropospheric scatter channel is as follows:

[0019] where is the propagation path length of the radio wave in the tropospheric scatter channel.

[0020] In the present invention, the expression for the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel is as follows:

[0021] where is the multipath time delay difference between the evaporation duct channel and the tropospheric scatter channel, c is the propagation speed of the radio wave.

[0022] In the present invention, the channel delay of the tropospheric scatter channel is , and the expression for the multipath time delay of the mixed channel of the evaporation duct and the tropospheric scatter is as follows:

[0023] where is the multipath time delay of the mixed channel of the evaporation duct and the tropospheric scatter.

[0024] In the present invention, the expression for the channel delay of the tropospheric scatter channel is as follows:

[0025] where is the radio wave communication distance, is the operating frequency of the radio wave communication, D is the diameter of the antenna aperture, is the equivalent radius of the earth, .

[0026] The technical solution provided by the present invention may include the following beneficial effects: The present invention obtains the calculation expression of the multipath delay of the evaporation duct and tropospheric scatter hybrid channel at different elevation angles according to the elevation angle of the transmitting antenna, the elevation angle of the receiving antenna, the propagation path length of the radio wave in the evaporation duct channel and the tropospheric scatter channel, the propagation speed of the radio wave, and the channel delay of the tropospheric scatter channel, and can quickly calculate the multipath delay of the evaporation duct and tropospheric scatter hybrid channel under the condition of over-the-horizon (OTH) communication at sea; then sets the symbol interval of the radio wave communication according to the multipath delay, so that the radio wave transmission can fully adapt to the frequent switching between the evaporation duct and tropospheric scatter in the OTH communication mode at sea and the situation where ships or small islands and reefs block within the line of sight of the transmitting end of the OTH communication system, enabling the calculation result of the multipath delay to better match the evaporation duct and tropospheric scatter hybrid channel, and can be used to guide the waveform design of the OTH communication system at sea; avoiding inter-symbol interference, reducing the bit error rate, and improving the performance of the OTH communication system at sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings herein are incorporated into and constitute a part of this specification, showing embodiments consistent with the present disclosure and, together with the specification, are used to explain the principles of the present disclosure. Obviously, the accompanying drawings in the following description are only some embodiments of the present disclosure, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0028] Figure 1 is a flowchart of a method for calculating the multipath delay of an evaporation duct and scatter channel at different elevation angles according to an embodiment of the present invention; Figure 2 is a scenario diagram of a method for calculating the multipath delay of an evaporation duct and scatter channel at different elevation angles according to an embodiment of the present invention; Figure 3 is an evaporation duct and tropospheric scatter hybrid channel multipath delay and tropospheric scatter channel delay comparison diagram when the antenna aperture diameter is 2 m, the operating frequency is 4.7 GHz, the transmitting antenna elevation angle is 0 and the receiving antenna elevation angle is 0 -5 according to an embodiment of the present invention; Figure 4 is an evaporation duct and tropospheric scatter hybrid channel multipath delay and tropospheric scatter channel delay comparison diagram when the antenna aperture diameter is 2 m, the operating frequency is 4.7 GHz, the transmitting antenna elevation angle is 5 and the receiving antenna elevation angle is 0 -5 according to an embodiment of the present invention; Figure 5 is an evaporation duct and tropospheric scatter hybrid channel multipath delay and tropospheric scatter channel delay comparison diagram when the antenna aperture diameter is 4 m, the operating frequency is 4.7 GHz, the transmitting antenna elevation angle is 0 , receiving antenna elevation angle 0 -5 Comparison of the multipath delay of the evaporation waveguide and tropospheric scatter mixed channel and the tropospheric scatter channel delay at ; Figure 6 The antenna aperture diameter is 4m, the operating frequency is 4.7GHz, and the transmitting antenna elevation angle is 5 , receiving antenna elevation angle 0 -5 Comparison of the multipath delay of the evaporation waveguide and tropospheric scatter mixed channel and the tropospheric scatter channel delay at ; Figure 7 The antenna aperture diameter is 6m, the operating frequency is 4.7GHz, and the transmitting antenna elevation angle is 0 according to the embodiment of the present invention. , receiving antenna elevation angle 0 -5 Comparison of the multipath delay of the evaporation waveguide and tropospheric scatter mixed channel and the tropospheric scatter channel delay at ; Figure 8 The antenna aperture diameter is 6m, the operating frequency is 4.7GHz, and the transmitting antenna elevation angle is 5 , receiving antenna elevation angle 0 -5 Comparison of the multipath delay of the evaporation waveguide and tropospheric scatter mixed channel and the tropospheric scatter channel delay at ; Figure 9 The antenna aperture diameter is 2m, the operating frequency is 4.7GHz, 6.2GHz, 10GHz and 12GHz, and the transmitting antenna elevation angle is 2 、Receiving antenna elevation angle 1 , 3 and 5 Comparison of the multipath delay of the evaporation waveguide and tropospheric scatter mixed channel and the tropospheric scatter channel delay at ; Figure 10 The antenna aperture diameter is 4m, the operating frequencies are 4.7GHz, 6.2GHz, 10GHz and 12GHz, and the transmitting antenna elevation angle is 2 、Receiving antenna elevation angle 1 , 3 and 5 Comparison of the multipath delay of the evaporation waveguide and tropospheric scatter mixed channel and the tropospheric scatter channel delay at ; Figure 11 The antenna aperture diameter is 6m, the operating frequencies are 4.7GHz, 6.2GHz, 10GHz and 12GHz, and the transmit antenna elevation angle is 1 、Receiving antenna elevation angle 1 , 3 and 5 Comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay at Figure 12 is the comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay when the antenna aperture diameter is 6m, the operating frequencies are 4.7GHz, 6.2GHz, 10GHz and 12GHz, and the elevation angle of the transmitting antenna is 3 and the elevation angle of the receiving antenna is 1 、3 and 5 according to the embodiments of the present invention; Figure 13 is the comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay when the antenna aperture diameter is 6m, the operating frequencies are 4.7GHz, 6.2GHz, 10GHz and 12GHz, and the elevation angle of the transmitting antenna is 5 and the elevation angle of the receiving antenna is 1 、3 and 5 according to the embodiments of the present invention. Detailed implementation manners

[0029] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more complete and thorough, and will fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0030] In addition, the accompanying drawings are only schematic illustrations of the embodiments of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0031] A method for calculating the multipath delay of an evaporation duct and a scatter channel at different elevation angles is provided in the present example embodiment. Please refer to Figure 1 , and the method may include: S101 - S105. Specifically as follows: S101, when radio wave communication is carried out through an evaporation duct channel, determine the propagation path length of the radio wave in the evaporation duct channel according to the radius of the earth and the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel.

[0032] S102. When performing radio wave communication through a tropospheric scatter channel, determine the distance between the transmitting antenna and the scatterer according to the included angles between the lines connecting the radio wave transmitting antenna and the scatterer to the center of the circle respectively, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna; determine the distance between the receiving antenna and the scatterer according to the included angles between the lines connecting the radio wave receiving antenna and the scatterer to the center of the circle respectively, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna; where the center of the circle refers to the center of the earth.

[0033] S103. Sum the two distances, namely the distance between the transmitting antenna and the scatterer and the distance between the receiving antenna and the scatterer, to obtain the propagation path length of the radio wave in the tropospheric scatter channel.

[0034] S104. Determine the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel according to the elevation angle of the transmitting antenna, the elevation angle of the receiving antenna, the propagation path length of the radio wave in the evaporation duct channel, the propagation path length of the radio wave in the tropospheric scatter channel, and the propagation speed of the radio wave. Obtain the multipath delay of the evaporation duct and tropospheric scatter hybrid channel at different elevation angles according to the multipath delay difference and the channel delay of the tropospheric scatter channel.

[0035] S105. Set the symbol interval of the radio wave communication according to the multipath delay, so that the radio wave communication adapts to the switching of the communication mode.

[0036] In this embodiment, according to the elevation angle of the transmitting antenna, the elevation angle of the receiving antenna, the propagation path lengths of the radio wave in the evaporation duct channel and the tropospheric scatter channel, the propagation speed of the radio wave, and the channel delay of the tropospheric scatter channel, the calculation expression of the multipath delay of the evaporation duct and tropospheric scatter hybrid channel at different elevation angles is obtained, which can quickly calculate the multipath delay of the evaporation duct and tropospheric scatter hybrid channel under the condition of over-the-horizon sea communication; setting the symbol interval of the radio wave communication according to the multipath delay can fully adapt to the frequent switching between the evaporation duct and the tropospheric scatter in the over-the-horizon sea communication mode and the situation where ships or small islands and reefs block within the line of sight of the transmitting end of the over-the-horizon sea communication system, so that the calculation result of the multipath delay can better match the evaporation duct and tropospheric scatter hybrid channel, and can be used to guide the waveform design of the over-the-horizon sea communication system; avoid inter-symbol interference, reduce the bit error rate, and improve the performance of the over-the-horizon sea communication system.

[0037] The specific situations of each step in the above embodiments are described below.

[0038] In S101, when communicating between shore bases through an evaporation duct channel, determine the propagation path length of the radio wave in the evaporation duct channel according to the radius of the earth and the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel.

[0039] Please refer to Figure 2, Figure 2 is a scene diagram of the calculation method for the multipath time delay of the evaporation duct and the scattering channel at different elevation angles. Since the height of the evaporation duct varies from a few meters to twenty or thirty meters, and the heights of the transmitting and receiving antennas of the shore-based over-the-horizon communication system at sea are much smaller than the radius of the earth, when calculating the propagation path length of the radio wave in the evaporation duct channel and the propagation path length of the radio wave in the tropospheric scattering channel, the height of the evaporation duct and the heights of the transmitting and receiving antennas are ignored. When communicating between shore-based stations through the evaporation duct channel, that is Figure 2 the spherical distance centered at the earth's center and with the radius of the earth, that is, the arc length, that is, the arc length , hereinafter, . The expression for the propagation path length of the radio wave in the evaporation duct channel is as follows: (1) where is the propagation path length of the radio wave in the evaporation duct channel, is the central angle corresponding to the arc where the propagation path of the radio wave in the evaporation duct channel is located, is the radius of the earth.

[0040] In S102, please refer to Figure 2 , when communicating between shore-based stations through the tropospheric scattering channel, that is, according to Figure 2 in , the path for propagation, and respectively represent the distances between the transmitting end (transmitting antenna) of the shore-based over-the-horizon communication system deployed at sea and the scatterer, and the distances between the scatterer and the receiving end (receiving antenna) of the shore-based over-the-horizon communication system deployed at sea.

[0041] Determine the distance between the transmitting antenna and the scatterer according to the included angles between the lines connecting the radio wave transmitting antenna and the scatterer with the center of the circle, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna; similarly, the distance between the receiving antenna and the scatterer can also be determined.

[0042] The expression for the distance between the transmitting antenna and the scatterer is as follows: (2) where is the distance between the transmitting antenna and the scatterer, is the elevation angle of the transmitting antenna, is the elevation angle of the receiving antenna.

[0043] The expression for the distance between the receiving antenna and the scatterer is as follows: (3) Among them, is the distance between the receiving antenna and the scatterer.

[0044] In S103, the above two distances are summed to obtain the propagation path length of the radio wave in the tropospheric scatter channel.

[0045] The expression for the propagation path length of the radio wave in the tropospheric scatter channel is as follows: (4) Among them, is the propagation path length of the radio wave in the tropospheric scatter channel, .

[0046] Please refer to Figure 2 , isosceles Draw a perpendicular line from point C to in side, intersecting at point E. At this time, is 's angle bisector. Therefore, , . According to the sine theorem, we can get . Therefore, the distance between the transmitter of the shore-based over-the-horizon communication system and the scatterer: (5) Similarly, the distance between the receiver of the shore-based over-the-horizon communication system and the scatterer can be obtained: (6) In the quadrilateral , the following relationship exists: (7) Among them, is the angle between the line connecting the transmitting antenna and the center of the earth and the line connecting the transmitting antenna and the scatterer, is the angle between the line connecting the receiving antenna and the center of the earth and the line connecting the receiving antenna and the scatterer.

[0047] Using the above relationship, the propagation path length d of the radio wave in the tropospheric scatter channel can be calculated.

[0048] In S104, according to the elevation angle of the transmitting antenna, the elevation angle of the receiving antenna, the propagation path length of the radio wave in the evaporation duct channel, the propagation path length of the radio wave in the tropospheric scatter channel, and the propagation speed of the radio wave, the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel is determined. The expression for the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel is as follows: (8) Wherein, is the multipath time delay difference between the evaporation duct channel and the tropospheric scatter channel, c is the propagation speed of the radio wave.

[0049] The time delay of the tropospheric scatter channel itself is as follows: (9) Wherein, is the radio wave communication distance, is the operating frequency of the radio wave communication, D is the diameter of the antenna aperture, is the equivalent radius of the earth.

[0050] As an excellent channel for over-the-horizon communication at sea, the time delay magnitude of the evaporation duct is in the nanosecond level. Therefore, when analyzing the multipath time delay of the mixed channel of the evaporation duct and the tropospheric scatter, the time delay of the evaporation duct channel itself is ignored. When analyzing the multipath time delay of the mixed channel, it is necessary to consider both the time delay of the tropospheric scatter channel itself and the multipath time delay difference between the evaporation duct channel and the tropospheric scatter channel, and take the maximum value of the two as the multipath time delay of the mixed channel of the evaporation duct and the tropospheric scatter. The expression is as follows: (10) In addition, the height h of the radio wave from the sea surface when scattering occurs can also be determined.

[0051] The height of the radio wave from the sea surface when scattering occurs is: (11) According to the cosine theorem of trigonometric functions, the distance between the scatterer and the center of the earth can be obtained: (12) Substituting Equation (12) into Equation (11), the expression for the height of the radio wave from the sea surface when scattering occurs can be obtained as Equation (13) or Equation (14): (13) (14) Next, the calculation method of this application was used for experiments, and the experimental results are as Figures 3 to 13 shown.

[0052] When the diameter of the antenna aperture of the over-the-horizon communication system deployed on the shore base at sea is 2m, a typical C-band frequency point of 4.7GHz is selected, and the elevation angle of the transmitting antenna of the over-the-horizon communication system at sea is set to 0 , and at the same time, the elevation angle of the receiving antenna is at 0 - 5 vary between. The calculation result of formula (10) shows that when the elevation angle of the receiving antenna is 0 -5 °, the multipath delay of the evaporation duct and tropospheric scattering hybrid channel is the same as that of the scattering channel. Similarly, when the antenna aperture diameter is 2m, 4m, and 6m, and the elevation angle of the transmitting antenna is set to 0 and 5 . Figures 3 to 8 shows the comparison of the multipath delay of the evaporation duct and tropospheric scattering hybrid channel with that of the tropospheric scattering channel when the elevation angle of the receiving antenna is 0 and 5 °, and the antenna aperture diameters are different. 、1 、2、 3 、4 and 5 °.

[0053] Figure 3 is the comparison diagram of the multipath delay of the evaporation duct and tropospheric scattering hybrid channel with that of the tropospheric scattering channel when the antenna aperture diameter is 2m, the operating frequency is 4.7GHz, the elevation angle of the transmitting antenna is 0 °, and the elevation angle of the receiving antenna is 0 -5 °. It can be seen from Figure 3 that under the above parameter conditions, the multipath delay of the evaporation duct and tropospheric scattering hybrid channel is the same as that of the tropospheric scattering channel.

[0054] Figure 4 is the comparison diagram of the multipath delay of the evaporation duct and tropospheric scattering hybrid channel with that of the tropospheric scattering channel when the antenna aperture diameter is 2m, the operating frequency is 4.7GHz, the elevation angle of the transmitting antenna is 5 °, and the elevation angle of the receiving antenna is 0 -5 °. It can be seen from Figure 4 that at the same communication distance, the multipath delay of the evaporation duct and tropospheric scattering hybrid channel increases with the increase of the elevation angle of the receiving antenna; at the same elevation angle of the receiving antenna, the multipath delay of the hybrid channel increases with the increase of the communication distance. In particular, when the elevation angle of the receiving antenna is 0 °, the multipath delay of the evaporation duct and tropospheric scattering hybrid channel is the same as that of the tropospheric scattering channel. In addition, the multipath delay of the hybrid channel is greater than that of the tropospheric scattering channel.

[0055] Figure 5 is the comparison diagram of the multipath delay of the evaporation duct and tropospheric scattering hybrid channel with that of the tropospheric scattering channel when the antenna aperture diameter is 4m, the operating frequency is 4.7GHz, the elevation angle of the transmitting antenna is 0 °, and the elevation angle of the receiving antenna is 0 -5 Comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay at Figure 5 It can be seen that when the elevation angle of the receiving antenna is 0 and 1 and when the elevation angle of the receiving antenna is 2 and the communication distance is less than 420 km, the multipath delay of the evaporation duct and troposcatter mixed channel is the same as that of the troposcatter channel. In addition, the multipath delay of the mixed channel is greater than that of the troposcatter channel.

[0056] Figure 6 is the comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay according to the embodiment of the present invention with an antenna aperture diameter of 4 m, a working frequency of 4.7 GHz, a transmitting antenna elevation angle of 5 , and a receiving antenna elevation angle of 0 -5 It can be seen from Figure 6 that when the elevation angle of the receiving antenna is 0 -5 the multipath delay of the mixed channel is greater than that of the troposcatter channel.

[0057] Figure 7 is the comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay according to the embodiment of the present invention with an antenna aperture diameter of 6 m, a working frequency of 4.7 GHz, a transmitting antenna elevation angle of 0 , and a receiving antenna elevation angle of 0 -5 It can be seen from Figure 7 that when the elevation angle of the receiving antenna is 0 and when the elevation angle of the receiving antenna is 1 and the communication distance is less than 400 km, the multipath delay of the evaporation duct and troposcatter mixed channel is the same as that of the troposcatter channel. In addition, the multipath delay of the mixed channel is greater than that of the troposcatter channel.

[0058] Figure 8 is the comparison diagram of multipath delay of evaporation duct and troposcatter mixed channel and troposcatter channel delay according to the embodiment of the present invention with an antenna aperture diameter of 6 m, a working frequency of 4.7 GHz, a transmitting antenna elevation angle of 5 , and a receiving antenna elevation angle of 0 -5 It can be seen from Figure 8 that when the elevation angle of the receiving antenna is 0 -5 the multipath delay of the mixed channel is greater than that of the troposcatter channel.

[0059] Figure 9 is based on the antenna aperture diameter of 2 m and operating frequency of 4.7 GHz in the embodiment of the present invention ( Figure 9 (a) in Figure 9 (b) in Figure 9 (c) in Figure 9 (d) in , elevation angle of the transmitting antenna is 2 , elevation angle of the receiving antenna is 1 , 3 , and 5 Figure 9 . It is a comparison diagram of the multipath delay of the evaporation duct and troposcatter hybrid channel and the troposcatter channel delay. It can be seen from that when the elevation angle of the receiving antenna is 1 , the multipath delays of the evaporation duct and troposcatter hybrid channel are the same as those of the troposcatter channel at the 4.7 GHz frequency point; while at the 6.2 GHz, 10 GHz, and 12 GHz frequency points, when the elevation angle of the receiving antenna is 1 , 3 , and 5

[0060] Figure 10 is based on the antenna aperture diameter of 4 m and operating frequency of 4.7 GHz in the embodiment of the present invention ( Figure 10 (a) in Figure 10 (b) in Figure 10 (c) in Figure 10 (d) in , elevation angle of the transmitting antenna is 2 , elevation angle of the receiving antenna is 1 , 3 , and 5

[0061] Figure 11 is based on the antenna aperture diameter of 6 m and operating frequency of 4.7 GHz in the embodiment of the present invention ( Figure 11 (a) in Figure 11 (b) in Figure 11 (c) in Figure 11 (d) in , elevation angle of the transmitting antenna is 1 , elevation angle of the receiving antenna is 1 , 3 Comparison diagram of multipath delay of evaporation duct and tropospheric scatter hybrid channel and tropospheric scatter channel at

[0062] Figure 12 is based on the antenna aperture diameter of 6m and operating frequency of 4.7GHz in the embodiment of the present invention ( Figure 12 (a) in Figure 12 (b) in Figure 12 (c) in Figure 12 (d) in , elevation angle of transmitting antenna 3 , elevation angle of receiving antenna 1 , 3 and 5

[0063] Figure 13 is based on the antenna aperture diameter of 6m and operating frequency of 4.7GHz in the embodiment of the present invention ( Figure 13 (a) in Figure 13 (b) in Figure 13 (c) in Figure 13 (d) in , elevation angle of transmitting antenna 5 , elevation angle of receiving antenna 1 , 3 and 5

[0064] From Figures 10 to 13 it can be seen that at the four frequency points of 4.7GHz, 6.2GHz, 10GHz and 12GHz, when the elevation angle of the receiving antenna is 1 , 3 and 5, the multipath delay of the hybrid channel is greater than that of the tropospheric scatter channel. Therefore, when calculating the multipath delay, the multipath delay of the evaporation duct and tropospheric scatter hybrid channel needs to be comprehensively considered; in particular, with the increase of the antenna aperture diameter and the elevation angle of the transmitting antenna, the multipath delay of the evaporation duct and tropospheric scatter hybrid channel increases.

[0065] In the embodiment of the present invention, when the elevation angles of the transmitting and receiving antennas of the over-the-horizon communication system at sea are changed, the propagation path length of the radio wave in the evaporation duct channel remains unchanged. However, the propagation path length in the tropospheric scatter channel will change because when the elevation angle of the transmitting antenna is changed, the distance between the transmitting end of the shore-based over-the-horizon communication system and the scatterer changes, resulting in the need to adjust the elevation angle of the receiving antenna at the receiving end of the shore-based over-the-horizon communication system to ensure that the over-the-horizon communication effect reaches the optimal, thereby changing the propagation path length of the radio wave in the tropospheric scatter channel.

[0066] The multipath delay calculation method proposed by the present invention can be used to guide the waveform design of over-the-horizon communication systems at sea. When designing an over-the-horizon communication system at sea, in order to avoid intersymbol interference, the symbol interval must be greater than the multipath delay of the evaporation duct and tropospheric scatter hybrid channel , therefore, the symbol interval is set to 1.5 - 2 times the multipath delay of the evaporation duct and tropospheric scatter hybrid channel, reserving enough time for the channel so that the energy of the previous symbol decays to a negligible level, leaving sufficient symbol interval, better adapting to the frequent switching of the evaporation duct and tropospheric scatter communication modes and the situation where ships or small islands and reefs block within the line of sight of the transmitter of the over-the-horizon communication system at sea, thereby reducing intersymbol interference and 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.

[0067] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims. All of these fall within the protection scope of the present invention.

Claims

1. Calculation method of evaporation duct and scattering channel multipath time delay at different elevation angles, characterized in that The method includes: When performing radio wave communication through an evaporation duct channel, determining the propagation path length of the radio wave in the evaporation duct channel according to the radius of the earth and the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel; When performing radio wave communication through a tropospheric scatter channel, determining the distance between the transmitting antenna and the scatterer according to the included angles between the connecting lines of the transmitting antenna and the scatterer and the center of the earth respectively, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna; determining the distance between the receiving antenna and the scatterer according to the included angles between the connecting lines of the receiving antenna and the scatterer and the center of the earth respectively, the elevation angle of the transmitting antenna, and the elevation angle of the receiving antenna; wherein, the center of the earth refers to the center of the earth; Summing the two distances, namely the distance between the transmitting antenna and the scatterer and the distance between the receiving antenna and the scatterer, to obtain the propagation path length of the radio wave in the tropospheric scatter channel; Determining the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel according to the elevation angle of the transmitting antenna, the elevation angle of the receiving antenna, the propagation path length of the radio wave in the evaporation duct channel, the propagation path length of the radio wave in the tropospheric scatter channel, and the propagation speed of the radio wave, and obtaining the multipath time delay of the hybrid channel of the evaporation duct and the tropospheric scatter at different elevation angles according to the multipath time delay difference and the channel time delay of the tropospheric scatter channel; Setting the symbol interval of the radio wave communication according to the multipath time delay to enable the radio wave communication to adapt to the switching of the communication mode.

2. The method for calculating the multipath time delay of the evaporation duct and the scattering channel at different elevation angles according to claim 1, wherein The expression of the propagation path length of the radio wave in the evaporation duct channel is as follows: Among them, is the propagation path length of the radio wave in the evaporation duct channel, is the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel, is the radius of the earth.

3. The method for calculating the multipath time delay of the evaporation duct and the scattering channel at different elevation angles according to claim 2, wherein The expression of the distance between the transmitting antenna and the scatterer is as follows: wherein, is the distance between the transmitting antenna and the scatterer, is the elevation angle of the transmitting antenna, is the elevation angle of the receiving antenna.

4. The method for calculating the multipath time delay of the evaporation duct and the scattering channel at different elevation angles according to claim 3, wherein The expression of the distance between the receiving antenna and the scatterer is as follows: Among them, is the distance between the receiving antenna and the scatterer.

5. The method for calculating the multipath time delay of the evaporation duct and the scattering channel at different elevation angles according to claim 4, wherein The expression of the propagation path length of the radio wave in the tropospheric scatter channel is as follows: Among them, is the propagation path length of radio waves in the tropospheric scatter channel.

6. The method for calculating the multipath time delay of an evaporation duct and a scattering channel at different elevation angles according to claim 5, wherein The expression of the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel is as follows: Among them, is the multipath time delay difference between the evaporation duct channel and the tropospheric scatter channel, c is the propagation speed of the radio wave.

7. The method for calculating the multipath time delay of the evaporation duct and the scattering channel at different elevation angles according to claim 6, wherein The channel delay of the tropospheric scatter channel is , and the expression of the multipath delay of the evaporation duct and tropospheric scatter hybrid channel is as follows: wherein, is the multipath time delay of the evaporation duct and tropospheric scatter hybrid channel.

8. The method for calculating the multipath time delay of the evaporation duct and the scattering channel at different elevation angles according to claim 7, wherein, The expression of the channel time delay of the tropospheric scatter channel is as follows: Among them, is the radio wave communication distance, is the operating frequency of radio wave communication, D is the antenna aperture diameter, is the equivalent radius of the earth, .

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