Evaporation waveguide and scattering mixed channel multipath time delay calculation method under different distances

Abstract

The invention discloses a multipath time delay calculation method for an evaporation waveguide and scattering mixed channel under different distances, 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; determining the propagation path length in the troposphere scattering channel according to the positions of the scatterer, the transmitting antenna and the receiving antenna; according to the propagation path length in the evaporation waveguide channel, the propagation path length in the troposphere scattering channel, the propagation speed of the electric wave and the channel time delay of the troposphere scattering channel, determining the multipath time delay of the evaporation waveguide and troposphere scattering mixed channel under different communication distances; 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 method, 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] Embodiments of the present disclosure relate to the field of wireless communication technologies, and in particular, to a method for calculating the multipath delay of an evaporation duct and scattering hybrid channel at different distances. Background Art

[0002] Satellites can be used to achieve over-the-horizon communication between maritime mobile ships and shore-based stations. 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 the 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 electromagnetic waves in the evaporation duct environment refracts downward. When the refraction curvature is greater than the sea surface curvature, the electromagnetic 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 electromagnetic 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 refraction and re-radiation of radio waves in the frequency band 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 electromagnetic waves in the above frequency bands can perform over-the-horizon propagation. 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 electromagnetic 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 electromagnetic 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, electromagnetic waves will automatically select the propagation path according to the evaporation duct height.

[0005] When most electromagnetic 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 electromagnetic 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 performing over-the-horizon communication at sea, the signal received at the receiving end is a superimposed signal that has passed through the evaporation duct and tropospheric scatter channels. Since the lengths of the evaporation duct and tropospheric scatter channels are different, there is a time difference in the arrival time of the communication signal at the receiving end through these two channels, resulting in multipath time 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 methods for calculating the multipath time delay of over-the-horizon communication at sea only consider the influence of a single channel, 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 over-the-horizon communication modes between the evaporation duct and the tropospheric scatter. When the communication mode switches, the signal strengths of the signals arriving at the receiving end through the evaporation duct and tropospheric scatter channels are comparable, and the inter-symbol interference is severe. Therefore, the multipath time delay calculated by only considering a single channel of the evaporation duct or the tropospheric scatter cannot well adapt to and guide the waveform design of the over-the-horizon communication system at sea.

[0007] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0008] 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

[0009] The purpose of the embodiments of the present disclosure is to provide a method for calculating the multipath time delay of a mixed channel of evaporation duct and scatter at different distances, so as to at least overcome one or more problems caused by the limitations and defects of the related technologies to a certain extent.

[0010] The embodiments of the present disclosure provide a method for calculating the multipath time delay of a mixed channel of evaporation duct and scatter at different distances, including: When performing radio wave communication through 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, determine the propagation path length of the radio wave in the evaporation duct channel, where the center of the central angle is the center of the earth; When performing radio wave communication through the tropospheric scatter channel, the angles between the transmitting antenna and the receiving antenna and the sea level are both 0°, and according to the positions of the scatterer, the transmitting antenna, and the receiving antenna, determine the propagation path length of the radio wave in the tropospheric scatter channel; According to the propagation path length of radio waves in the evaporation duct channel, the propagation path length of radio waves in the tropospheric scattering channel, and the propagation speed of radio waves, the multipath time delay difference between the tropospheric scattering channel and the evaporation duct channel is obtained. According to the multipath time delay difference and the channel time delay of the tropospheric scattering channel, the multipath time delay of the evaporation duct and tropospheric scattering hybrid channel at different communication distances is determined. Set the symbol interval of radio wave communication according to the multipath time delay, so that the radio wave communication adapts to the switching of communication modes.

[0011] In one embodiment of the present disclosure, the expression for the propagation path length of radio waves in the evaporation duct channel is as follows:

[0012] Where, is the propagation path length of radio waves in the evaporation duct channel, is the central angle corresponding to the arc length of the propagation path in the evaporation duct channel, is the radius of the earth.

[0013] In one embodiment of the present disclosure, the expression for the propagation path length of radio waves in the tropospheric scattering channel is as follows:

[0014] Where, is the propagation path length of radio waves in the tropospheric scattering channel.

[0015] In one embodiment of the present disclosure, the expression for the multipath time delay difference between the tropospheric scattering channel and the evaporation duct channel is:

[0016] Where, is the multipath time delay difference between the tropospheric scattering channel and the evaporation duct channel, is the propagation speed of radio waves within the over-the-horizon range at sea.

[0017] In one embodiment of the present disclosure, the expression for the channel time delay of the tropospheric scattering channel is:

[0018] Where, is the radio wave communication distance, is the operating frequency of radio wave scattering communication, D is the diameter of the antenna aperture, is the equivalent radius of the earth.

[0019] In one embodiment of the present disclosure, the expression for the multipath time delay of the evaporation duct and tropospheric scattering hybrid channel at different communication distances is:

[0020] Among them, is the multipath delay of the evaporation duct and tropospheric scatter hybrid channel.

[0021] The technical solutions provided by the embodiments of the present disclosure may include the following beneficial effects: Under the condition that the angles between the transmitting and receiving antennas and the sea level are both 0°, the embodiments of the present disclosure determine the propagation path length of the radio wave according to the propagation speed of the radio wave, the scatterer, and the positions of the transmitting and receiving antennas, and can quickly calculate the multipath delay of the evaporation duct and tropospheric scatter hybrid channel under the condition of over-the-horizon communication at sea; set the symbol interval of the radio wave communication according to the multipath delay, so that it can fully adapt to the frequent switching between the evaporation duct and tropospheric scatter in the over-the-horizon communication mode at sea, 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 communication system at sea; avoid inter-symbol interference, reduce the bit error rate, and improve the performance of the over-the-horizon communication system at sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present disclosure, and are used together with the specification to explain the principles of the present disclosure. Obviously, the 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.

[0023] Figure 1 is a flowchart of a method for calculating the multipath delay of an evaporation duct and scatter hybrid channel at different distances 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 hybrid channel at different distances according to an embodiment of the present invention; Figure 3 is a comparison diagram of the multipath delay of the evaporation duct and tropospheric scatter hybrid channel and the scatter channel delay at four typical frequency points in the C and X bands when the antenna aperture diameter is 2m according to an embodiment of the present invention; Figure 4 is a comparison diagram of the multipath delay of the evaporation duct and tropospheric scatter hybrid channel and the scatter channel delay at four typical frequency points in the C and X bands when the antenna aperture diameter is 4m according to an embodiment of the present invention; Figure 5 is a comparison diagram of the multipath delay of the evaporation duct and tropospheric scatter hybrid channel and the scatter channel delay at four typical frequency points in the C and X bands when the antenna aperture diameter is 6m according to an embodiment of the present invention; Figure 6It is a schematic diagram of the multipath delay calculation results of the evaporation duct and tropospheric scatter hybrid channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 2 m according to an embodiment of the present invention; Figure 7 It is a schematic diagram of the multipath delay calculation results of the evaporation duct and tropospheric scatter hybrid channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 4 m according to an embodiment of the present invention; Figure 8 It is a schematic diagram of the multipath delay calculation results of the evaporation duct and tropospheric scatter hybrid channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 6 m according to an embodiment of the present invention. Detailed implementation manners

[0024] 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 comprehensive, and will fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0025] In addition, the 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.

[0026] A method for calculating the multipath delay of the evaporation duct and scatter hybrid channel at different distances is provided in the present example embodiment. Please refer to Figure 1 , and this method may include: S101 - S104. Specifically as follows: S101, when performing radio wave communication through the 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, where the center of the central angle is the center of the earth.

[0027] S102, when performing radio wave communication through the tropospheric scatter channel, the angles between the transmitting antenna and the receiving antenna and the sea level are both 0°, and determine the propagation path length of the radio wave in the tropospheric scatter channel according to the positions of the scatterer, the transmitting antenna, and the receiving antenna.

[0028] S103. Obtain the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel according to 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. Determine the multipath delay of the evaporation duct and tropospheric scatter hybrid channel at different communication distances according to the multipath delay difference and the channel delay of the tropospheric scatter channel.

[0029] S104. 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.

[0030] In this embodiment, when the angles between the transmitting and receiving antennas and the sea level are both 0°, determine the propagation path length of the radio wave according to the propagation speed of the radio wave, the scatterer, and the positions of the transmitting and receiving antennas, so as to quickly calculate the multipath delay of the evaporation duct and tropospheric scatter hybrid channel under the condition of over-the-horizon communication at sea; set the symbol interval of the radio wave communication according to the multipath delay, so that it can fully adapt to the frequent switching between the evaporation duct and tropospheric scatter in the over-the-horizon communication mode at sea, 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 communication system at sea; avoid inter-symbol interference, reduce the bit error rate, and improve the performance of the over-the-horizon communication system at sea.

[0031] The following describes the specific situations of each step in the above embodiments.

[0032] In S101, when the radio wave for communication between a marine ship and a shore base propagates through the 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, where the center of the central angle is the center of the earth.

[0033] Please refer to Figure 2 , Figure 2 is a scenario diagram of the multipath delay calculation method for the evaporation duct and scatter hybrid channel at different distances according to the embodiment of the present invention. Since the height of the evaporation duct varies within the range of several meters to twenty or thirty meters, and the heights of the transmitting and receiving antennas of the scatter communication system are much smaller than the radius of the earth, when calculating the evaporation duct path length and the scatter path length, the height of the evaporation duct and the heights of the transmitting and receiving antennas are ignored. If the radio wave for communication between a marine ship and a shore base propagates through the evaporation duct channel, that is Figure 2 the spherical distance with the center of the earth as the center and the radius of the earth as the radius in, that is, the length of arc BD, that is, the arc length , can be calculated according to the central angle corresponding to the arc length of the propagation path of the communication signal in the evaporation duct channel and the radius of the earth and the calculation formula is as follows: (1) 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 in the evaporation duct channel, is the radius of the earth, .

[0034] In S102, when the radio wave for communication between a marine ship and a shore station propagates through the tropospheric scatter channel, the angles between both the transmitting antenna and the receiving antenna and the sea level are 0°, that is, they are tangent, and the intersection point of the extension lines of the tangents is the location of the scatterer. When the positions of the transmitting end and the receiving end of the over-the-horizon communication system at sea are given, the sum of the distance between the transmitting end (transmitting antenna) of the over-the-horizon communication system installed on the marine mobile ship and the scatterer and the distance between the receiving end (receiving antenna) of the shore-based over-the-horizon communication system and the scatterer can obtain the propagation path length of the communication signal in the tropospheric scatter channel.

[0035] It should be noted that the distance between the transmitting end of the communication system and the scatterer is equal to the distance between the receiving end of the communication system and the scatterer.

[0036] Please refer to Figure 2 , when the radio wave for communication between a marine ship and a shore station propagates through the tropospheric scatter channel, that is Figure 2 it propagates along the paths DA and AB in , where DA and AB respectively represent the distance between the transmitting end of the over-the-horizon communication system installed on the marine mobile ship and the scatterer and the distance between the receiving end of the shore-based over-the-horizon communication system and the scatterer. According to the distance between the transmitting end of the over-the-horizon communication system installed on the marine mobile ship and the scatterer, the distance between the receiving end of the shore-based over-the-horizon communication system and the scatterer, and the half angle of the central angle corresponding to the arc length of the propagation path of the communication signal in the evaporation duct channel, calculate the propagation path length of the tropospheric scatter in the over-the-horizon range at sea, and its expression is as follows: (2) Among them, is the propagation path length of the radio wave in the tropospheric scatter channel.

[0037] In S103, based on the propagation path length of the communication signal in the evaporation duct channel, the propagation path length of the communication signal in the tropospheric scatter channel, and the propagation speed of the radio wave in the over-the-horizon range at sea, the expression of the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel is: (3) Among them, is the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel, It is the propagation speed of radio waves within the over-the-horizon range at sea.

[0038] The expression for the channel delay of the tropospheric scatter channel is: (4) Where, is the radio communication distance, is the operating frequency of radio wave scatter communication, D is the diameter of the antenna aperture, is the equivalent radius of the earth.

[0039] At the same time, as an excellent channel for over-the-horizon communication at sea, the evaporation duct has a time delay order of nanoseconds. Therefore, when analyzing the multipath time delay of the evaporation duct and tropospheric scatter hybrid channel, the time delay of the evaporation duct channel itself is ignored.

[0040] The multipath time delay of the evaporation duct and tropospheric scatter hybrid channel at different communication distances is obtained by comprehensively considering the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel and the channel delay of the tropospheric scatter channel, and taking the maximum value between the two as the multipath time delay of the hybrid channel. The expression is as follows: (5) Where, is the multipath time delay of the evaporation duct and tropospheric scatter hybrid channel.

[0041] In addition, the height of the scatterer from the sea surface can be determined according to the radius of the earth, the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel, and the length of the propagation path of the radio wave in the evaporation duct channel. The calculation process of the height is as follows: First, please refer to Figure 2 , the height h of the scatterer from the sea surface is: (6) Using the trigonometric function relationship, the distance between the scatterer and the center of the earth: (7) Furthermore, the expression for the height of the scatterer from the sea surface is obtained as: (8) Where, is the height of the scatterer from the sea surface, is the half angle of the central angle corresponding to the arc length of the propagation path of the radio wave in the evaporation duct channel.

[0042] Next, the calculation method of this application was used for experiments, and the experimental results are as Figures 3 to 8 shown.

[0043] When the antenna aperture diameter of the over-the-horizon communication system at sea is 2 m, two typical frequency points of 4.7 GHz and 6.2 GHz in the C band, and two typical frequency points of 10 GHz and 12 GHz in the X band are selected, and the communication distance is set to 100 km - 300 km. The calculation results by formula (5) show that the multipath delays of the evaporation duct and tropospheric scatter hybrid channel are the same as those of the scatter channel; similarly, the antenna aperture diameter range is set from 2 m to 6 m with a step of 2 m. Figures 3 to 5 The comparison results of the multipath delays of the evaporation duct and tropospheric scatter hybrid channel and the scatter channel at four typical frequency points in the C and X bands under different antenna aperture diameters are given.

[0044] Figure 3 It is a comparison diagram of the multipath delays of the evaporation duct and tropospheric scatter hybrid channel and the scatter channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 2 m according to the embodiment of the present invention. Among them, Figure 3 (a) in Figure 3 (b) in Figure 3 (c) in Figure 3 (d) in respectively correspond to the frequency points of 4.7 GHz in the C band, 6.2 GHz in the C band, 10 GHz in the X band, and 12 GHz in the X band when the antenna aperture diameter is 2 m. From Figure 3 it can be seen that when the communication distance is 100 km - 300 km, at four typical frequency points in the C and X bands, the multipath delays of the evaporation duct and tropospheric scatter hybrid channel are the same as those of the scatter channel.

[0045] Figure 4 It is a comparison diagram of the multipath delays of the evaporation duct and tropospheric scatter hybrid channel and the scatter channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 4 m according to the embodiment of the present invention. Among them, Figure 4 (a) in Figure 4 (b) in Figure 4 (c) in Figure 4 (d) in respectively correspond to the frequency points of 4.7 GHz in the C band, 6.2 GHz in the C band, 10 GHz in the X band, and 12 GHz in the X band when the antenna aperture diameter is 4 m. From Figure 4 it can be seen that at two typical frequency points in the C band, namely 4.7 GHz and 6.2 GHz, the multipath delays of the evaporation duct and tropospheric scatter hybrid channel are the same as those of the scatter channel. However, at two typical frequency points in the X band, namely 10 GHz and 12 GHz, when the communication distance is greater than 520 km and 440 km respectively, the multipath delays of the evaporation duct and tropospheric scatter hybrid channel will exceed those of the scatter channel. Therefore, the multipath delays of the evaporation duct and tropospheric scatter hybrid channel need to be comprehensively considered when calculating the multipath delay.

[0046] Figure 5It is a comparison diagram of the multipath delay of the evaporation duct and tropospheric scattering mixed channel and the scattering channel delay at four typical frequency points in the C and X bands when the antenna aperture diameter is 6 m according to an embodiment of the present invention. Among them, Figure 5 (a) in Figure 5 (b) in Figure 5 (c) in Figure 5 (d) in respectively correspond to the frequency points of 4.7 GHz in the C band, 6.2 GHz in the C band, 10 GHz in the X band, and 12 GHz in the X band when the antenna aperture diameter is 6 m. It can be seen from Figure 5 that the multipath delay of the evaporation duct and tropospheric scattering mixed channel is the same as the scattering channel delay at the 4.7 GHz frequency point, while at the 6.2 GHz, 10 GHz, and 12 GHz frequency points, when the communication distances are greater than 560 km, 360 km, and 300 km respectively, the multipath delay of the evaporation duct and tropospheric scattering mixed channel will be greater than the scattering channel delay. Therefore, the multipath delay of the evaporation duct and tropospheric scattering mixed channel needs to be comprehensively considered when calculating the multipath delay.

[0047] When the antenna aperture diameter is 2 m, two typical frequency points of 4.7 GHz and 6.2 GHz in the C band, and two typical frequency points of 10 GHz and 12 GHz in the X band are selected, the communication distance is set to 100 km - 300 km, and the multipath delay of the evaporation duct and tropospheric scattering mixed channel decreases with the increase of frequency; similarly, when the antenna aperture diameter range is set from 2 m to 6 m with a step of 2 m, Figures 6 to 8 a schematic diagram of the calculation results of the multipath delay of the evaporation duct and tropospheric scattering mixed channel at four typical frequency points in the C and X bands under different antenna aperture diameters is given.

[0048] Figure 6 It is a schematic diagram of the calculation results of the multipath delay of the evaporation duct and tropospheric scattering mixed channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 2 m according to an embodiment of the present invention. It can be seen from Figure 6 that when the communication distance is 100 km - 300 km, at the same frequency, the multipath delay of the evaporation duct and tropospheric scattering mixed channel increases with the increase of the communication distance; at the same communication distance, the multipath delay of the evaporation duct and tropospheric scattering mixed channel decreases with the increase of frequency.

[0049] Figure 7 It is a schematic diagram of the calculation results of the multipath delay of the evaporation duct and tropospheric scattering mixed channel at four typical frequency points in the C and X bands when the antenna aperture diameter is 4 m according to an embodiment of the present invention. It can be seen from Figure 7It can be seen that at the typical frequency points of the X-band, namely 10 GHz and 12 GHz, when the communication distance is greater than 520 km, the multipath time delays of the two are the same. Therefore, when calculating the multipath time delay, the multipath time delay of the evaporation duct and troposcatter mixed channel needs to be comprehensively considered.

[0050] Figure 8 is a schematic diagram of the calculation results of the multipath time delay of the evaporation duct and troposcatter mixed channel at four typical frequency points of C and X bands with an antenna aperture diameter of 6 m according to an embodiment of the present invention. From Figure 8 It can be seen that at the typical frequency points of the X-band, namely 10 GHz and 12 GHz, when the communication distance is greater than 340 km, the multipath time delays of the two are the same; and when the communication distance is greater than 560 km, at the frequency points of 6.2 GHz, 10 GHz and 12 GHz, the multipath time delay at the 6.2 GHz frequency point is also the same as that at the 10 GHz and 12 GHz frequency points.

[0051] In the case where the angles between the transmitting and receiving antennas and the sea level are both 0°, the present invention can quickly calculate the multipath time delay of the evaporation duct and troposcatter mixed channel under the over-the-horizon communication condition at sea only by substituting the communication distance between the marine ship and the shore base, the operating frequency of the over-the-horizon communication system at sea and the antenna aperture into the analytical expression of the multipath time delay of the evaporation duct and troposcatter mixed channel derived. Therefore, the calculation method of the present invention can fully adapt to the frequent switching between the evaporation duct and troposcatter in the over-the-horizon communication mode at sea, so that the calculation result of the multipath time delay can better match the evaporation duct and troposcatter mixed channel, and can be used to guide the waveform design of the over-the-horizon communication system at sea. When designing the over-the-horizon communication system at sea, in order to avoid inter-symbol interference, the symbol interval must be greater than the multipath time delay of the evaporation duct and troposcatter mixed channel , therefore, the symbol interval is set to 1.5 - 2 times the multipath time delay of the evaporation duct and troposcatter mixed channel, reserving enough time for the channel, so that the energy of the previous symbol decays to a negligible level, thereby effectively avoiding inter-symbol interference and finally reducing the bit error rate and improving the performance of the over-the-horizon communication system at sea.

[0052] The calculation method of the present application significantly optimizes the over-the-horizon communication performance at sea by accurately analyzing the difference in multipath time delay between the evaporation duct and troposcatter paths. By establishing a path time delay calculation model (i.e., formula (5)) at different communication distances, it effectively reduces the inter-symbol interference in the mixed channel transmission, improves the signal reception quality and reduces the bit error rate, avoids the high complexity of traditional numerical simulation, provides an efficient theoretical support for the waveform design of the communication system, and enhances the reliability and engineering applicability of the evaporation duct and troposcatter communication system.

[0053] 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 spirit of the present invention and the scope protected by the claims. All of these are within the protection scope of the present invention.

Claims

1. A multipath delay calculation method for an evaporation duct and scattering hybrid channel at different distances, 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, where the center of the central angle is the center of the earth; When performing radio wave communication through a tropospheric scatter channel, the angles between the transmitting antenna and the receiving antenna and the sea level are both 0°, and determining the propagation path length of the radio wave in the tropospheric scatter channel according to the positions of the scatterer, the transmitting antenna, and the receiving antenna; Obtaining the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel according to 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 determining the multipath delay of the evaporation duct and tropospheric scatter hybrid channel at different communication distances according to the multipath delay difference and the channel delay of the tropospheric scatter channel; Setting 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.

2. The multipath delay calculation method for the evaporation duct and scattering hybrid channel at different distances according to claim 1, characterized in that The expression for the propagation path length of the radio wave in the evaporation duct channel is as follows: Wherein, 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 in the evaporation duct channel, is the radius of the earth.

3. The multipath delay calculation method for an evaporation duct and scattering hybrid channel at different distances according to claim 2, wherein The expression for the propagation path length of the radio wave in the tropospheric scatter channel is as follows: wherein, is the propagation path length of radio waves in the tropospheric scattering channel.

4. The multipath delay calculation method for the evaporation duct and scattering hybrid channel at different distances according to claim 3, characterized in that, The expression for the multipath delay difference between the tropospheric scatter channel and the evaporation duct channel is: wherein, is the multipath time delay difference between the tropospheric scatter channel and the evaporation duct channel, is the propagation speed of radio waves within the over-the-horizon range at sea.

5. The multipath delay calculation method for the evaporation duct and scattering hybrid channel at different distances according to claim 4, characterized in that The expression for the channel delay of the tropospheric scatter channel is: Among them, is the radio wave communication distance, is the operating frequency of radio wave scattering communication, D is the antenna aperture diameter, is the equivalent radius of the earth.

6. The multipath delay calculation method for the evaporation duct and scattering hybrid channel at different distances according to claim 5, wherein The expression for the multipath delay of the evaporation duct and tropospheric scatter hybrid channel at different communication distances is: Among them, is the multipath delay of the evaporation duct and tropospheric scatter hybrid channel.

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