A communication visual field calculation method based on the 3D Fresnel zone

Abstract

The present invention discloses a communication visibility calculation method based on the 3D Fresnel zone, comprising the steps of: S1 scanning and reading the DEM grid data of a pre-prepared target area to obtain the terrain data of the target area; S2 randomly selecting a grid unit in the terrain data as a transmitting unit T, and taking the remaining grid units in the terrain data as receiving units R; S3 sequentially calculating the communication visibility V<subgt;ij< / subgt> from the transmitting unit T to each receiving unit R; S4 the set composed of the communication visibility V<subgt;ij< / subgt> from the transmitting unit T to each receiving unit R is the communication visibility area of the transmitting unit T, denoted as: Viewshed<subgt;T< / subgt> = {V<subgt;ij< / subgt>}. The present invention can be fully applied to applications such as the siting planning of transmission towers and communication relay path planning based on communication visibility areas on terrains with large-scale massive data.

Description

Technical Field

[0001] The present invention relates to the technical field of communication visibility, and in particular to a method for calculating communication visibility based on a 3D Fresnel zone. Background Art

[0002] Terrain visibility refers to the range that can be seen or is visible from a given observation point, and it has a wide range of application fields, such as landscape analysis, ancient village layout, site selection planning, and path planning. Communication visibility refers to the area where a receiving antenna can receive signals at points around a transmitting antenna established on a certain unit of the terrain. Therefore, communication visibility can also be regarded as a type of terrain visibility. Communication visibility is based on the propagation of wireless electromagnetic signals and determines whether it is visible based on whether there are obstacles blocking the line-of-sight propagation path between the transmitting end and the receiving end. Communication visibility can be used to judge applications such as relay communication path planning and transmitting tower site selection planning.

[0003] Electromagnetic waves are generated by electromagnetic oscillations. For example, the signals generated by a high-frequency oscillation circuit are a type of electromagnetic wave, which can be transmitted through an antenna. Obviously, its energy comes from the power supply of this circuit. In the experiment where Hertz discovered electromagnetic waves, the high voltage used to generate the electric spark between the spark gaps was a method of generating electromagnetic oscillations, and its energy also came from the power supply of the device. There are various forms of electromagnetic wave propagation, mainly including space propagation and guided propagation in a waveguide system. The microwave used in wireless communication (such as mobile phones) is transmitted between the base station and the mobile phone through space propagation and is guided propagation in the waveguide after entering the mobile phone. Generally, the wireless transmission distance is much greater than the transmission distance in the guided system. Electromagnetic waves propagate forward through the continuous conversion between electric field energy and magnetic field energy (its law is determined by Maxwell's equations), and can propagate forward without loss in a vacuum, without the need for a medium or the so-called ether substance as its propagation medium.

[0004] However, in the actual propagation space, there are obstacles. As a wave, when electromagnetic waves encounter obstacles during propagation, diffraction will occur, and the vibration direction of the wave itself will change, such as Figure 2As shown, this phenomenon is a 180-degree change in the "phase" of the wave. After the propagation path of the reflected wave reaches the receiving point, it "superimposes" with the original direct wave signal. This superposition can lead to both signal weakening and enhancement. If the extra distance that the reflected wave travels compared to the direct wave is exactly an integer multiple of a wavelength, the phase difference between the direct wave and the reflected wave remains 180 degrees, one at the peak moment and the other at the trough moment, so the two wave signals will attenuate after superposition. If the distance difference after subtracting the direct wave from the path traveled by the reflected wave is exactly an integer multiple of half a wavelength, the 180-degree phase difference formed by the reflected wave is delayed by another 180 degrees generated by the path difference, so that the reflected wave becomes the same phase as the original direct signal. At the receiving point, peak superimposes with peak and trough superimposes with trough, and the acquired signal is enhanced. Therefore, the direct wave and the reflected wave of radio waves sometimes weaken each other and sometimes enhance each other. Ideally, find a wireless transmission path so that the direct signal and the reflected signal do not weaken each other, and the transmission distance can be closer to the theoretical maximum value. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a communication visibility calculation method based on the 3D Fresnel zone.

[0006] To achieve the object of the present invention, a communication visibility calculation method based on the 3D Fresnel zone is provided, including the following steps:

[0007] S1: Scan and read the DEM grid data of the pre-prepared target area to obtain the terrain data of the target area;

[0008] S2: Randomly select a grid cell in the terrain data as the transmitting unit T, and regard the remaining grid cells in the terrain data as the receiving units R;

[0009] S3: Calculate the communication visibility V from the transmitting unit T to each receiving unit R in sequence ij , i = 1, 2, 3,..., N; j = 1, 2, 3,..., N, where i and j respectively represent the abscissa and ordinate of the current receiving unit R, and N 2 represents the total number of receiving units R;

[0010] S4: The set composed of the communication visibility V from the transmitting unit T to each receiving unit R ij is the communication visibility area of the transmitting unit T, denoted as: Viewshed T ={V ij}.

[0011] Further, in the step S3, the communication visibility V from the transmitting unit T to each receiving unit R is calculated one by one in sequence. ij The specific process is as follows:

[0012] a1: Denote each receiving unit R as the receiving cell Cell. ij Then, obtain the coordinate value and elevation value of any one of the receiving cells Cell. ij

[0013] a2: Construct the first Fresnel zone between the transmitting unit T and the receiving cell Cell. ij And obtain the ellipse formed by projecting the first Fresnel zone between the transmitting unit T and the receiving cell Cell onto the terrain grid cells. Then calculate and obtain each grid cell Cell ij contained in the ellipse, where k = 1, 2, 3,..., M. Here, k represents the k-th grid cell passed by a propagation curve, and M represents the number of grid cells passed by a propagation curve. Finally, use the interpolation method to obtain the spatial coordinates (s, t, Cell ijk ijk (Elev)) of the corresponding terrain point of the grid cell Cell, where s and t respectively represent the abscissa and ordinate of the grid cell where the terrain point is located. ijk

[0014] a3: Based on the obtained coordinate value and elevation value of the receiving cell Cell ij and the spatial coordinates (s, t, Cell ijk ijk (Elev)) of the corresponding terrain point of the grid cell Cell, calculate and judge in sequence whether all the propagation curves passing through different grid cells in the first Fresnel zone are blocked by obstacles. If there are n propagation curves not blocked by obstacles, then the communication visibility V from the transmitting unit T to the receiving unit R ij is n, where n is an integer greater than or equal to 0.

[0015] Further, in the step a3, based on the obtained coordinate value and elevation value of the receiving cell Cell ij and the spatial coordinates (s, t, Cell ijk ijk (Elev)) of the corresponding terrain point of the grid cell Cell, the specific process of calculating and judging in sequence whether all the propagation curves passing through different grid cells in the first Fresnel zone are blocked by obstacles is as follows:

[0016] b1: Determine the 60% area ellipsoid formula of the first Fresnel zone as follows:

[0017]

[0018] Among them, λ represents the signal wavelength, SD represents the Euclidean distance from the transmitting end to the current receiving end, α represents the rotation angle of the ellipsoid observed from the positive y-axis, x and y respectively represent the abscissa s and ordinate t of the grid cell where the terrain point is located, and z represents the elevation value Cell ijk (Elev);

[0019] b2: Based on the k-th grid cell Cell passed by a propagation curve passing through different grid cells within the first Fresnel zone ijk The spatial coordinates (s, t, Cell ijk (Elev)) of the terrain point where it is located are calculated and it is determined whether the terrain point is inside or outside the 60% area ellipsoid of the first Fresnel zone. If the terrain point is inside the 60% area ellipsoid of the first Fresnel zone, then the terrain point blocks the communication of the propagation curve where it is located; if the terrain point is outside the 60% area ellipsoid of the first Fresnel zone, then based on the elevation value Cell ijk (Elev), it is further determined whether the terrain point is above or below the 60% area ellipsoid of the first Fresnel zone; if the terrain point is below the 60% area ellipsoid of the first Fresnel zone, it means that the terrain point does not block the communication of the propagation curve where it is located; if the terrain point is above the 60% area ellipsoid of the first Fresnel zone, it means that the terrain point blocks the communication of the propagation curve where it is located;

[0020] b3: Repeat step b2 until each grid cell Cell ijk where the terrain points located are all calculated and determined whether they block the communication of the propagation curve where they are located; if the number of terrain points that block the communication of the propagation curve where they are located is equal to 0, then this propagation curve is not blocked by obstacles; if the number of terrain points that block the communication of the propagation curve where they are located is greater than 0, then this propagation curve is blocked by obstacles.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] 1. The communication visible area calculation method proposed by the present invention combines grid terrain data and constructs the first Fresnel zone based on the line of sight, laying a foundation for the calculation and application of the communication visible area.

[0023] 2. The communication visible area calculation method based on the 3D Fresnel zone proposed by the present invention provides a new idea for applications such as site selection planning and path planning based on the communication visible area.

[0024] 3. The present invention can be applied to the field of digital terrain analysis with large-scale terrain data, such as the problem of communication base station site selection, the problem of path planning based on communication visibility, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flowchart of a method for calculating communication visibility based on the 3D Fresnel zone in an embodiment;

[0026] Figure 2 is a schematic diagram of wave diffraction in an embodiment;

[0027] Figure 3 is a schematic diagram of the reflected path and the direct path in an embodiment;

[0028] Figure 4 is a schematic diagram of the first Fresnel zone in an embodiment;

[0029] Figure 5 is a schematic diagram of the projected ellipse of the first Fresnel zone in an embodiment;

[0030] Figure 6 is a schematic diagram after the first Fresnel zone is projected onto the terrain surface in an embodiment;

[0031] Figure 7 is a schematic diagram of curves passing through different terrain points within the projected ellipse in an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0033] Referring to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0034] The object of the present invention is to solve the analysis method of communication visibility. The present invention calculates the signal strength from the transmitting antenna on the terrain to the receiving antenna at other terrain points through a method based on the line-of-sight and signal reflection or diffraction mechanisms to determine whether the signal is reachable. According to the electromagnetic field propagation mechanism, the first Fresnel zone is constructed between the transmitting antenna and the receiving antenna, and the communication signal attenuation value on each grid cell on the line-of-sight path connecting the transmitting point and the receiving point is gradually calculated. By calculating the total attenuation cumulative value of the signal, it is determined whether communication is possible. Finally, the communication visibility of all grid cells within a given radius centered on the transmitting point on the terrain is completed, thereby obtaining the communication visibility area of the transmitting point.

[0035] Reference Figure 1 shown, Figure 1 is a flowchart of a method for calculating the communication visibility area based on the 3D Fresnel zone in an embodiment, including the following steps:

[0036] S1: Scan and read the DEM grid data of the pre-prepared target area, and obtain the terrain data of the target area;

[0037] S2: Randomly select a grid cell in the terrain data as the transmitting unit T, and then regard the remaining grid cells in the terrain data as the receiving unit R;

[0038] S3: Calculate the communication visibility V from the transmitting unit T to each receiving unit R one by one in sequence ij , i = 1, 2, 3,..., N; j = 1, 2, 3,..., N, where i and j respectively represent the abscissa and ordinate of the current receiving unit R, and N 2 represents the total number of receiving units R;

[0039] S4: The set composed of the communication visibility V from the transmitting unit T to each receiving unit R ij is the communication visibility area of the transmitting unit T, denoted as: Viewshed T ={V ij}.

[0040] In an embodiment, in the step S3, the specific process of calculating the communication visibility V from the transmitting unit T to each receiving unit R one by one in sequence ij includes the following:

[0041] a1: Denote each receiving unit R as the receiving unit Cell ij , and then obtain the coordinate value and elevation value of any one of the receiving units Cell ij ;

[0042] a2: Construct the transmitting unit T and the receiving unit Cellij The first Fresnel zone of the transmitting unit T and the receiving unit Cell are obtained. ij The first Fresnel zone is projected onto an ellipse on the terrain grid cell; then each grid cell contained in the ellipse is calculated and obtained. ijk ,k=1,2,3,…,M, where k represents the kth grid cell that a propagation curve passes through, and M represents the number of grid cells that a propagation curve passes through; finally, the interpolation method is used to obtain the grid cell Cell ijk The spatial coordinates of the corresponding terrain points (s, t, Cell ijk (Elev)), where s and t represent the horizontal and vertical coordinates of the grid cell where the terrain point is located, respectively;

[0043] The ellipsoid of the first Fresnel zone can be regarded as generated by rotating the space ellipse plane based on LOS by 360 degrees. Every time the space ellipse plane rotates by one angle, a projected ellipse will be obtained on the ground. Therefore, countless projected ellipse boundaries constitute the projection plane on the terrain. Each ellipse boundary will pass through a series of grid cells. If there are multiple ellipse boundaries in the projection plane that pass through the same grid cells, these boundaries will be merged and then calculated. Electromagnetic wave transmission is different from line of sight. It encounters obstacles during propagation and produces diffraction. The boundaries passing through different grid cells are regarded as curved lines of sight. The distance between the transmitting unit T and the receiving unit Cell is calculated. ij The grid cell through which each curve passes is contained in the ellipse of the first Fresnel zone projected onto the topographic grid cell. ijk , where the spatial coordinates of these grid cells are obtained by interpolation as (x k ,y k ,z k Within the largest projected ellipse, we can find several curves that pass through different grid cells. We then calculate whether the elevation of each grid cell that the curve passes through intrudes into the 60% area of the first Fresnel zone. If none of the cells on the curve exceed this threshold, the curve is considered unobstructed. Therefore, we need to determine whether each curve within the projected ellipse is obstructed. In addition to using the two boundaries of the largest projected ellipse as the two curves, we subtract half the terrain accuracy from the minor axis of the largest projected ellipse to generate a new ellipse. This new ellipse then has two boundaries, and so on, until the minor axis of the latest ellipse is less than half the terrain accuracy.

[0044] a3: Based on the received receiving unit Cell ij The coordinate value and elevation value of the grid cell ijk The spatial coordinates of the corresponding terrain points (s, t, Cell ijk(Elev)), calculate and determine in sequence whether all propagation curves passing through different grid cells in the first Fresnel zone are blocked by obstacles. If there are n propagation curves not blocked by obstacles, the communication visibility V from the transmitting unit T to the receiving unit R ij is n, where n is an integer greater than or equal to 0.

[0045] Assume that the number of grid cells passed by a curve is M. For the grid cells Cell passed by a propagation curve ijk , k = 1, 2, 3, …, M, and its elevation value is Cell ijk (Elev). Therefore, the spatial coordinates of this terrain point are (s, t, Cell ijk (Elev)), where s and t are the abscissa and ordinate of the grid where the terrain point is located.

[0046] In one embodiment, in step a3, based on the obtained coordinate values and elevation value of the receiving unit Cell ij , the spatial coordinates (s, t, Cell ijk of the corresponding terrain point of the grid cell Cell ijk (Elev)), the specific process of calculating and determining in sequence whether all propagation curves passing through different grid cells in the first Fresnel zone are blocked by obstacles is as follows:

[0047] b1: Determine the 60% area ellipsoid formula of the first Fresnel zone as follows:

[0048]

[0049] where, λ represents the signal wavelength, SD represents the Euclidean distance from the transmitting end to the current receiving end, α represents the rotation angle of the ellipsoid observed from the positive y-axis, x and y respectively represent the abscissa s and ordinate t of the grid cell where the terrain point is located, and z represents the elevation value Cell ijk (Elev);

[0050] In the experiment, the terrain accuracy used is 1 meter, the wavelength is 0.5 meter. Assume that the terrain coordinates of the transmitting end are (0, 0), the terrain elevation value is 30, and the height of the transmitting antenna is 10 meters; the coordinates of the receiving end are (8, 9), the terrain elevation value is 40, and the height of the receiving antenna is 5 meters. Then, the cosine value and sine value of the tilt angle α of the ellipsoid are calculated as: cosα =

[0051] 0.319, sinα = 0.769. Substituting into the formula, the Euclidean distance between the transmitting end and the receiving end can be obtained The length of the short axis of the first Fresnel zone ellipsoid The length of the long axis is The ellipsoid formula for the first Fresnel zone from the current transmitter to the receiver is as follows:

[0052]

[0053] b2: Calculate whether the coordinate point (s, t, Cel ijk (Elev)) is inside or outside the above ellipsoid. If the point is inside the ellipsoid, that is, the value obtained by substituting the coordinate point into the above ellipsoid equation is less than or equal to 1, it means that the elliptical curve passing through this point is blocked by an obstacle; if it is outside the ellipsoid, that is, the value obtained by substituting the coordinate point into the above ellipsoid equation is greater than 1, it is still necessary to further determine whether the point is above or below the ellipsoid. If it is below the ellipsoid, it means that this point does not block the communication of the curve where it is located. If it is above the ellipsoid, this point becomes an obstacle blocking the signal propagation of the curve.

[0054] b3: Repeat step b2 until every grid cell Cell ijk where the terrain points are located has been calculated and judged whether it blocks the communication of the propagation curve where it is located; if the number of terrain points blocking the communication of the propagation curve is equal to 0, then this propagation curve is not blocked by an obstacle; if the number of terrain points blocking the communication of the propagation curve is greater than 0, then this propagation curve is blocked by an obstacle.

[0055] Electromagnetic waves are generated by electromagnetic oscillations. For example, the signal generated by a high-frequency oscillation circuit is a kind of electromagnetic wave, which can be emitted through an antenna. Obviously, its energy comes from the power supply of this circuit; in the experiment where Hertz discovered electromagnetic waves, the high voltage used caused electric sparks to occur between the spark gaps, which is a way to generate electromagnetic oscillations, and its energy also comes from the power supply of this device. There are various forms of electromagnetic wave propagation, mainly including space propagation and guided propagation in a waveguide system. The microwave used in wireless communication (such as mobile phones) is space propagation between the base station and the mobile phone, and it is waveguide guided propagation after entering the mobile phone. Generally, the wireless transmission distance is much greater than the transmission distance in the guided system. Electromagnetic waves propagate forward through the continuous conversion between electric field energy and magnetic field energy (its law is determined by Maxwell's equations), and can propagate forward without loss in a vacuum, without the need for a medium or the so-called ether substance as its propagation medium.

[0056] However, in the actual propagation space, there are obstacles. As a kind of wave, when electromagnetic waves encounter obstacles during propagation, diffraction will occur, and the vibration direction of the wave itself will change, such as Figure 2As shown, this phenomenon is a 180-degree change in the "phase" of the wave. After the propagation path of the reflected wave reaches the receiving point, it "superimposes" with the original direct wave signal. This superposition can lead to both signal weakening and enhancement. If the extra distance that the reflected wave travels compared to the direct wave is exactly an integer multiple of a wavelength, the phase difference between the direct wave and the reflected wave remains 180 degrees, with one at the peak moment and the other at the trough moment. In this case, the superposition of the two wave signals will result in signal attenuation. If the distance difference between the path of the reflected wave and the direct wave after subtracting the direct wave is exactly an integer multiple of half a wavelength, the 180-degree phase difference formed by the reflected wave is delayed by another 180 degrees generated by the path difference, causing the reflected wave to have the same phase as the original direct signal. At the receiving point, the peaks are superimposed on the peaks, and the troughs are superimposed on the troughs, and the acquired signal is enhanced. Therefore, the direct wave and the reflected wave of radio waves sometimes weaken each other and sometimes enhance each other. Ideally, find a wireless transmission path so that the direct signal and the reflected signal do not weaken each other, and the transmission distance can be closer to the theoretical maximum value.

[0057] The first Fresnel zone

[0058] According to the conclusions of Huygens and Fresnel, for wireless transmission to be completed between the transmitter and the receiver, as Figure 3 shown, the difference between the transmission path B of the reflected signal and the transmission path A of the direct signal cannot be greater than 1 times half a wavelength. And if the height of the obstacle increases but does not exceed the height of the direct path A, then the distance difference between the reflected signal path and the direct signal path may be an even multiple of half a wavelength. When the two wave signals are superimposed at the receiving point, the signal will attenuate.

[0059] Therefore, the two scientists Huygens and Fresnel concluded that all path differences between the transmitter and the receiver being exactly an integer multiple of half a wavelength is a necessary condition for line-of-sight transmission. Among them, the path with the shortest distance difference between the reflected wave and the direct wave, which is exactly 1 times half a wavelength, can best ensure the signal strength of line-of-sight transmission.

[0060] Theoretically, there are infinitely many Fresnel zones around the line of sight between the transmitter and the receiver, but the innermost one is the first Fresnel zone. This area is an "ellipsoidal zone" formed by a set of reflection paths with the shortest path difference of only 1 times half a wavelength, as Figure 4 shown. It defines the critical blocking area for unobstructed line-of-sight, thus ensuring the signal strength of line-of-sight transmission. Figure 4The thick black solid line indicates the straight line line-of-sight (LOS) path from the transmitter to the receiver. For obstacles that penetrate the first Fresnel zone but do not block the LOS path, attention needs to be paid to the constructive or destructive interference from the reflected waves. It should be noted that the Fresnel zone constitutes a three-dimensional region, so obstacles can penetrate from above, below, or the side of the LOS path. Penetrating most of the interior of the first Fresnel zone will result in a decrease in the received signal strength or fading. Engineering believes that keeping at least 60% of the radius of the first Fresnel zone obstacle-free can reduce the attenuation of the received signal.

[0061] 3D Fresnel zone

[0062] Since the current judgment methods for the communication visibility based on the Fresnel zone only project the LOS path from the transmitter to the receiver onto the corresponding terrain and judge the position of the elevation value corresponding to the projected terrain point in the first Fresnel zone, if there is a terrain point that penetrates 60% of the first Fresnel zone, then it is considered that the transmitter and the current receiver are not communicable. However, electromagnetic wave signals vibrate and transmit forward in wavefronts one by one. Even if there are obstacles on the LOS path reaching 60% of the first Fresnel zone, the wave can still bypass the obstacle and continue to propagate forward from the side. Therefore, it is unreasonable to only judge the terrain points on the LOS path. Considering that the first Fresnel zone is an ellipsoid, the ellipsoid can be regarded as obtained by rotating an elliptical plane around the LOS, and the projection of the ellipsoid onto the terrain surface is an ellipse. The projection ellipse includes a series of terrain points, and as Figure 4 shown, the two foci where the major axis of the ellipse is located are E1 and E2. As Figure 5 shown, the terrain in the figure is 10*10, the terrain accuracy is 1 meter, and the part with a value of 1 is the terrain points included in the projection ellipse.

[0063] The length of the minor axis of the ellipsoid of the first Fresnel zone can be approximately expressed by formula (1):

[0064]

[0065] where λ is the wavelength of the electromagnetic wave, SD is the Euclidean distance from the transmitter to the current receiver, which can be expressed as formula (2):

[0066]

[0067] T(Elev) and R(Elev) are the terrain elevation values of the transmitter and the receiver respectively, and D is the horizontal distance from the transmitter to the receiver, expressed as formula (3):

[0068]

[0069] Among them, T(x) and T(y) represent the horizontal coordinate points of the transmitting end, R(x) and R(y) are the horizontal coordinate points of the receiving end, and C is the terrain accuracy.

[0070] The major axis length of the ellipsoid of the first Fresnel zone can be expressed by formula (4):

[0071]

[0072] Therefore, the ellipsoid formula for 60% of the first Fresnel zone is expressed as formula (5):

[0073]

[0074] In formula (5), x and y are the coordinates of the cell where the terrain point is located, and z is the elevation value of the terrain at the cell location.

[0075] Since the heights of the transmitting point and the receiving point may not be the same, the ellipsoid of the first Fresnel zone will rotate. Assuming that the ellipsoid rotates around the y-axis by an angle α, then formula (5) is modified to formula (6):

[0076]

[0077] Assume in the Cartesian coordinate system, as Figure 4 shown, the coordinate origin is (0, 0), and the focus closest to the coordinate origin is used as the signal transmitting point position. The ellipse represented by formula (6) needs to be translated, translated along the positive x-axis direction by HMa 3D ×cosα, and translated along the positive z-axis direction by -HMa 3D ×sinα + E1(Elev), where E1(Elev) is the elevation value of the terrain point corresponding to one of the projection ellipse vertex coordinates.

[0078] Due to the special nature of electromagnetic wave transmission, even when encountering obstacles, the wave signal may still bypass the obstacles and continue to propagate forward. Therefore, the transmission within the ellipsoid of the first Fresnel zone can be regarded as a kind of curved line-of-sight transmission. There are theoretically countless such propagation curves, and there are also countless curves corresponding within the ellipse projected onto the terrain. These curves are all composed of countless projection ellipses, as Figure 6 shown. Whether the receiving end can receive the signal from the transmitting end only needs to judge whether all the curves are blocked by obstacles. On the grid terrain data, each curve within the projection ellipse includes some terrain points. Affected by the terrain accuracy, there are multiple curves passing through the same terrain points. Then, the curves passing through the same terrain points can be merged into one curve. Thus, the countless curves within the ellipse are simplified to a finite number of curves, as Figure 7 shown. Figure 7The medium terrain accuracy is 1 meter. Assuming the signal wavelength is 0.5 meter, since the curves are all composed of projected ellipses, and the length of the minor axis of the ellipse determines the terrain points that can be passed by the two boundary curves of an ellipse. Through experiments, it is found that the number of curves passing through different terrain points included in an ellipse is related to the terrain accuracy. Starting from the length of the minor axis of the largest ellipse projected from the first Fresnel zone, subtract half of the terrain accuracy from this length each time as the length of the minor axis of the subsequent projected ellipse until the length of the minor axis is less than half of the terrain accuracy. If the length of the minor axis is less than half of the terrain accuracy, then this ellipse can be approximately regarded as the LOS line of sight. Therefore Figure 6 A total of 5 curves passing through different terrain points are included in

[0079] After obtaining the projection propagation curves by the above method, sequentially determine the position of the elevation value of the terrain points passed by each curve in the first Fresnel zone. If the elevation value invades 60% of the area of the first Fresnel zone, then this curve is regarded as blocked by an obstacle. Finally, if each curve is not blocked, then the communication quality from the transmitter to the receiver is the best; if all curves are blocked by obstacles, then the receiver cannot normally receive the signal sent by the transmitter; if some curves are blocked, then the receiver can receive the signal from the transmitter, but the received signal strength will be affected.

[0080] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0081] It should be noted that the terms "first / second / third" involved in the embodiments of the present application are only used to distinguish similar objects and do not represent a specific order for the objects. It can be understood that "first / second / third" can be interchanged with a specific order or sequence under allowable circumstances. It should be understood that the objects distinguished by "first / second / third" can be interchanged under appropriate circumstances so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here.

[0082] The terms "including" and "having" in the embodiments of the present application and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, device, product, or equipment that includes a series of steps or modules is not limited to the listed steps or modules, but optionally further includes steps or modules not listed, or optionally further includes other steps or modules inherent to these processes, methods, products, or equipment.

[0083] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A communication visual field calculation method based on the 3D Fresnel zone, characterized in that, Including the following steps: S1: Scan and read the DEM grid data of the pre-prepared target area, and obtain the terrain data of the target area; S2: Randomly select a grid cell in the terrain data as the transmitting unit T, and then regard the remaining grid cells in the terrain data as the receiving units R; S3: Calculate the communication visibility V from the transmitting unit T to each receiving unit R one by one in sequence ij , i = 1, 2, 3, …, N; j = 1, 2, 3, …, N, where i and j respectively represent the abscissa and ordinate of the current receiving unit R, and N 2 represents the total number of receiving units R; S4: The communication visibility V from the transmitting unit T to each receiving unit R ij The set composed of them is the communication visibility area of the transmitting unit T, denoted as: Viewshed T ={V ij}; In the step S3, the communication visibility V from the transmitting unit T to each receiving unit R is calculated one by one in sequence. ij The specific process is as follows: a1: Denote each of the receiving units R as receiving cell Cell ij , then obtain the coordinate value and elevation value of any one of the receiving cells Cell ij . a2: Construct the first Fresnel zone of the transmitting unit T and the receiving unit Cell ij and obtain the ellipse formed by projecting the first Fresnel zone of the transmitting unit T and the receiving unit Cell ij onto the terrain grid cells; then calculate and obtain each grid cell Cell ijk , k = 1, 2, 3, …, M, where k represents the k-th grid cell passed by a propagation curve, and M represents the number of grid cells passed by a propagation curve; finally, use the interpolation method to obtain the spatial coordinates (s, t, Cell ijk (Elev)) of the corresponding terrain points, where s and t respectively represent the abscissa and ordinate of the grid cell where the terrain point is located; ijk (Elev)) a3: Based on the obtained coordinate values and elevation values of the receiving unit Cell ij and the spatial coordinates (s, t, Cell ijk (Elev)) of the corresponding terrain points of the grid cell Cell, calculate and determine in sequence whether all propagation curves passing through different grid cells in the first Fresnel zone are blocked by obstacles. If there are n propagation curves not blocked by obstacles, then the communication visibility V ijk from the transmitting unit T to the receiving unit R is n, where n is an integer greater than or equal to 0; ij ​ In the step a3, based on the obtained receiving unit Cell ij coordinate values and elevation values, and the grid unit Cell ijk corresponding spatial coordinates (s, t, Cell ijk (Elev)) of the terrain points, the specific process of sequentially calculating and determining whether all propagation curves passing through different grid cells in the first Fresnel zone are blocked by obstacles is as follows: b1: Determine the 60% area ellipsoid formula of the first Fresnel zone as follows: Among them, λ represents the signal wavelength, SD represents the Euclidean distance from the transmitting end to the current receiving end, α represents the rotation angle of the ellipsoid observed from the positive y-axis, x and y respectively represent the abscissa s and ordinate t of the grid cell where the terrain point is located, and z represents the elevation value Cell iik (Elev); b2: the k-th grid cell Cell passed by a propagation curve passing through different grid cells in the first Fresnel zone ijk The spatial coordinates (s, t, Cell ijk (Elev)) of the terrain point at the location are calculated and it is determined whether the terrain point is inside or outside the 60% regional ellipsoid of the first Fresnel zone. If the terrain point is inside the 60% regional ellipsoid of the first Fresnel zone, the terrain point blocks the communication of the propagation curve where it is located; if the terrain point is outside the 60% regional ellipsoid of the first Fresnel zone, based on the elevation value Cell ijk (Elev), it is further determined whether the terrain point is above or below the 60% regional ellipsoid of the first Fresnel zone; if the terrain point is below the 60% regional ellipsoid of the first Fresnel zone, it means that the terrain point does not block the communication of the propagation curve where it is located; if the terrain point is above the 60% regional ellipsoid of the first Fresnel zone, it means that the terrain point blocks the communication of the propagation curve where it is located; b3: Repeat step b2 until every grid cell Cell ijk where the terrain points are located have been calculated and judged whether they block the communication of the propagation curve passing through them; if the number of terrain points that block the communication of the propagation curve is equal to 0, then this propagation curve is not blocked by obstacles; if the number of terrain points that block the communication of the propagation curve is greater than 0, then this propagation curve is blocked by obstacles.

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