Channel modeling method with horizontal coupling distance and based on surface wave transmission

Abstract

The invention provides a channel modeling method with a horizontal coupling distance and based on surface wave transmission. The channel modeling method comprises the following steps: step 1, setting a transmitting end, a receiving end and a metal tube; 2, carrying out initial measurement; step 3, calculating a path loss value according to the measurement data; 4, changing the distance between the transmitting end and the receiving end and repeating the step 3; 5, changing the height difference between the sending end and the receiving end, and repeating the steps 3-4; step 6, constructing a path loss model with receiving end horizontal coupling distance influence; step 7, obtaining a final path loss model; and step 8, inputting the distance d between the transmitting end and the receiving end and the horizontal coupling distance of the receiving end into the final path loss model to obtain a path loss value of a receiving-transmitting end channel under a corresponding condition. Compared with the prior art, the method is more convenient for guiding optimized layout of signal coverage and working nodes in an industrial Internet of Things environment.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a channel modeling method based on surface wave transmission with a horizontal coupling distance. Background Art

[0002] The Industrial Internet of Things is a system that innovates, transforms and optimizes traditional industrial production processes through digitalization and intelligent means. With the in-depth development of 5G technology and the deep integration of industrialization and informatization, the Industrial Internet of Things has become one of the important application scenarios of 5G and future communication systems, and the wireless channel characteristics and models are the basis and premise for the design and optimization of the Industrial Internet of Things communication system. Therefore, it is of great significance to analyze and model the wireless channel characteristics of the Industrial Internet of Things environment.

[0003] At present, the wireless channel modeling methods for industrial Internet of Things scenarios mainly include statistical models, physical models and semi-statistical models, among which the statistical model describes the signal propagation characteristics by statistically analyzing the channel parameters, the physical model accurately describes the signal propagation process in a complex environment based on the electromagnetic wave propagation characteristics, and the non-statistical model can combine the advantages of the first two to describe the signal propagation characteristics. However, these existing studies all regard the large number of metal bodies or mechanical equipment in the industrial environment as scatterers of interference signals to explore the wireless channel propagation characteristics of the IIoT environment, and whether these metal bodies or mechanical equipment can be converted into transmission media to reduce the number of scatterers is a problem worth exploring. To this end, in order to prevent a large number of dense metal conductors in the industrial Internet of Things scenario from becoming scatterers, Sun J. et al. (a method for modeling indoor wireless channel path loss based on surface wave excitation, patent publication number CN116846499) proposed a channel modeling method based on surface wave transmission. By introducing the surface wave transmission mechanism, the metal conductor is "transformed" into a surface wave transmission line to achieve low-loss wireless propagation characteristics and solve various signal-to-noise ratio degradation problems caused by deep fading of the wireless channel. In addition, Ma et al. (patent publication number XDPCN241424, a channel modeling method, device and storage medium based on surface wave transmission) further explored the influence of the vertical coupling distance of the receiving end on the surface wave excitation effect, and proposed a wireless channel modeling method based on surface wave excitation with the influence of the vertical coupling distance of the receiving end, which laid the foundation for the optimal layout of signal coverage and working nodes in the industrial Internet of Things environment.

[0004] However, in the actual indoor measurement environment, the presence of metal bodies, the different heights of the transmitting and receiving ends, and the different positions will all have a certain impact on the excitation of surface waves. Therefore, in addition to exploring the influence of the vertical coupling distance of the receiving end on the surface wave transmission, it is also of great significance to explore the influence of its horizontal coupling distance on the surface wave excitation and transmission characteristics. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a channel modeling method based on surface wave transmission with horizontal coupling distance in view of the shortcomings of the prior art, comprising the following steps:

[0006] Step 1, setting a transmitting end, a receiving end and a metal pipe, wherein the distance between the transmitting end and the receiving end can be changed;

[0007] Step 2, placing the metal tube directly above the transmitting end and the receiving end, adjusting the horizontal coupling distance of the receiving end, performing initial measurement, and obtaining the range of the boundary value of the horizontal coupling distance of the receiving end;

[0008] Step 3: fix the distance d between the transmitting end and the receiving end, perform channel measurement using a vector network analyzer VNA, adjust the horizontal coupling distance of the receiving end, collect wireless channel measurement data at different horizontal coupling distances of the receiving end, and calculate the path loss value according to the measurement data;

[0009] Step 4, change the distance d between the transmitter and the receiver and repeat step 3;

[0010] Step 5, change the height difference △h between the transmitting end and the receiving end and repeat steps 3 to 4;

[0011] Step 6: Obtain two or more path loss values ​​according to Steps 3 to 5, and construct a path loss model PL (d hc );

[0012] Step 7: Use the constructed path loss model PL(d hc ) The least squares method is used to fit the parameters and the path loss model PL(d hc ) The correction values ​​of each parameter are used to obtain the final path loss model PL (d f );

[0013] Step 8: Input the distance d between the transmitter and the receiver and the horizontal coupling distance of the receiver into the final path loss model PL (d f ), and obtain the path loss value of the transmitting and receiving end channel in the corresponding case.

[0014] In step 1, the transmitting end and the receiving end are both connected to a vector network analyzer VNA via cables, and both the transmitting end and the receiving end are equipped with a surface wave exciter for experiment.

[0015] In step 1, the initial heights of the transmitter and the receiver are adjusted to 1 m, and two height-adjustable brackets are placed on the left side of the transmitter and the right side of the receiver, respectively. The heights of the two brackets are adjusted so that the brackets are higher than the transmitter and the receiver.

[0016] In step 2, the metal tube has a diameter of 2.4 cm and a length of 3 m;

[0017] The adjusting of the horizontal coupling distance of the receiving end refers to: making the horizontal coupling distance range of the receiving end no greater than 1 / 4 wavelength corresponding to the center operating frequency of the vector network analyzer VNA, so as to fully excite the surface wave mode; the horizontal coupling distance of the receiving end refers to the distance that the receiving end moves to the left or right.

[0018] In step 2, during the initial measurement, the receiving end is measured every time it moves 0.05m to the left or right. The corresponding path loss value is extracted and calculated for each measurement. After obtaining the functional relationship between the horizontal coupling distance of the receiving end and the path loss, the range of the receiving end horizontal coupling distance boundary value is obtained according to the curve image fitted by the functional relationship (after the boundary value, the signal is no longer transmitted in the form of surface waves). Through repeated measurements, it is found that when the receiving end moves in the horizontal direction, there is a boundary value for the horizontal coupling distance, and the boundary value is about 0.3m. After preliminarily determining that the boundary value is about 0.3m, in order to more accurately depict the functional relationship between the horizontal coupling distance of the receiving end and the path loss, especially the subtle changes near the boundary value, it is necessary to select a suitable measurement range. The selection of the range needs to balance data density and experimental error: if the range is too large (such as the initial 0.05m), the measured data will be too small, and the detailed features near the boundary value may not be fully revealed; if the range is too small, the experimental operation error may be introduced due to the short moving distance of the receiving end. At the same time, in order to avoid the problem of inaccurate measurement caused by non-integer units moving to the left or right (such as 0.5cm, 1.2cm, etc.), a range that can ensure that the data points are dense enough to reflect subtle changes and reduce the experimental error caused by the small moving distance to the left or right is selected, that is, 0.02m is the most appropriate. This range not only meets the experimental accuracy requirements, but also facilitates experimental operation and data recording.

[0019] In step 3, after determining the demarcation value, the receiving end moves 0.02m to the left or right for a measurement. The horizontal coupling distance of the receiving end is adjusted and measured within the demarcation value range of 0.3m. After obtaining the corresponding path loss value, the average of all path loss values ​​is calculated as the final path loss value corresponding to each measurement.

[0020] Step 4 includes: adjusting the distance d between the transmitting end and the receiving end to 1m, 1.5m, 2m and 2.5m respectively, and repeating step 3. Since the length of the metal tube is 3m, and the transmitting end and the receiving end are both located between two height-adjustable brackets, the distance d between the transmitting end and the receiving end is less than 3m. In addition, selecting too large a range will result in less experimental data, and selecting too small a range will result in large errors in experimental measurements. Since selecting 0.5m as the measurement range can obtain sufficient measurement data and meet the requirements of experimental accuracy, d is adjusted every 0.5m for measurement to ensure the feasibility of the experiment. In addition, through repeated measurements, it is found that the measurement data when d=0.5m and the measurement data when d is other values ​​have too large errors, so the measurement data when d=0.5m is discarded, and d=1m, 1.5m, 2m, 2.5m are selected for measurement.

[0021] Step 5 includes: keeping the height of the transmitting end unchanged, changing the height of the receiving end to change the height difference, and the initial heights of the transmitting end and the receiving end are both 1m. After repeated measurements, it is found that when the receiving end drops by 0.25m, that is, the height of the receiving end is 0.75m, the experimental data has a large error with the experimental data when the height of the receiving end is 0.9m and 0.8m, and the curve fitted by the data is also quite different from the fitting curve in other cases. Therefore, the maximum range of the actual variable height of the receiving end is 0.75m-1m. In addition, the experiment found that when the receiving end is measured once every 0.05m, the experimental data obtained is sufficient, and the height between the receiving end and the transmitting end can be clearly distinguished, which can effectively avoid the experimental error caused by the small height difference, and the experimental data is more accurate. Therefore, the receiving end is measured once every 0.05m, and a total of 4 measurements are made, that is, when the height of the receiving end is 0.95m, 0.9m, 0.85m and 0.8m, a measurement is made, and steps 3 to 4 are repeated. This choice not only meets the requirements of experimental accuracy, but also ensures the efficiency and feasibility of the experiment.

[0022] Step 6 includes: performing parameter fitting on the obtained path loss value, selecting different function models including logarithmic function and cubic function for fitting, and comparing the root mean square error RMSE values ​​corresponding to different function models. If the root mean square error RMSE value of a function model is the smallest, then the function model is the most suitable path loss model, and the one with the highest fitting degree is the constructed path loss model PL (d hc );

[0023] By comparison, it is found that the root mean square error RMSE value is the smallest when the cubic function model is used, so the constructed path loss model PL(d hc )The final expression is:

[0024]

[0025] Among them, d hc is the horizontal coupling distance of the receiving end; a 1 ,a 2 ,a 3 ,a 4 is the coefficient.

[0026] In step 7, the final path loss model PL(d f ) is expressed as:

[0027]

[0028] Among them, d r is the selected reference distance, PL(d r ) indicates that at the reference distance d r The path loss value at d f represents the horizontal coupling distance of the receiving end, β represents the path loss exponent, and Z τ is the shadow fading that obeys a normal distribution with a mean of 0 and a standard deviation of τ.

[0029] The present invention has the following beneficial effects:

[0030] 1. The present invention promotes signal transmission by introducing electromagnetic surface waves propagating on the metal surface, further reduces the dense scattering and multipath effects caused by free propagation, reduces the randomness of the channel, is conducive to alleviating interference between channels, and increases the signal-to-noise ratio, which can fully ensure the reliability of channel transmission and is conducive to flexible deployment and adjustment;

[0031] 2. The present invention further simplifies the channel model and the surface wave transmission mode, which is conducive to guiding the signal coverage in the IIoT environment and optimizing the layout of the constructed channel model;

[0032] 3. Compared with other studies at this stage, the present invention also takes into account the influence of the left and right moving distance of the receiving end, that is, the horizontal coupling distance of the receiving end, on the surface wave transmission characteristics. The influence of the horizontal coupling distance of the receiving end on the large-scale fading characteristics is different. The metal tube with better excitation effect is used for experiment, which can further reduce the path loss and ensure the reliability and safety of signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0034] Figure 1 It is a specific modeling process framework diagram of the present invention.

[0035] Figure 2It is a schematic diagram of the measurement scenario of the present invention.

[0036] Figure 3 It is a schematic diagram of the design of the horizontal coupling distance of the receiving end of the present invention.

[0037] Figure 4 It is a schematic diagram for comparing fitting curves of the path loss model of the horizontal coupling distance of the receiving end under different distances between the transmitting and receiving ends when the receiving end moves to the left under the condition that there is no height difference between the transmitting and receiving ends of the present invention.

[0038] Figure 5 It is a schematic diagram for comparing fitting curves of the path loss model of the horizontal coupling distance of the receiving end under different distances between the transmitting and receiving ends when the receiving end moves to the right under the condition that there is no height difference between the transmitting and receiving ends of the present invention.

[0039] Figure 6 It is a schematic diagram for comparing fitting curves of the path loss model of the horizontal coupling distance of the receiving end under different distances between the transmitting and receiving ends when the receiving end moves to the left under the condition that the height difference between the transmitting and receiving ends is 0.05m.

[0040] Figure 7 It is a schematic diagram for comparing fitting curves of the path loss model of the horizontal coupling distance of the receiving end under different distances between the transmitting and receiving ends when the receiving end moves to the right under the condition that the height difference between the transmitting and receiving ends is 0.05m.

[0041] Figure 8 The left and right comparison diagrams are of the logarithmic distance path loss model of the present invention when there is no height difference between the transmitting and receiving ends and the proposed path loss model and the path loss measurement value.

[0042] Fig. 9 The left and right comparison diagrams are of the logarithmic distance path loss model of the present invention when the height difference between the transmitting and receiving ends is 0.05m and between the proposed path loss model and the path loss measurement value. DETAILED DESCRIPTION

[0043] like Figure 1 As shown, the embodiment of the present invention proposes a channel modeling method based on surface wave transmission with horizontal coupling distance, which is generally used in industrial Internet of Things scenarios. The following steps are performed through experimental equipment:

[0044] Step 1: Construct an indoor surface wave transmission measurement scene, which is equipped with a transmitter Tx, a receiver Rx and a metal pipe. The initial height of both ends of the transmitter and receiver is adjusted to 1m, and two height-adjustable brackets are placed on the left side of the transmitter and the right side of the receiver respectively. The heights of the two brackets are adjusted to be higher than the heights of the two ends of the transmitter and receiver. In the specific implementation process:

[0045] The distance d between the transmitting and receiving ends can be changed;

[0046] Both the transmitting and receiving ends were connected to a vector network analyzer VNA via cables, and both ends were equipped with surface wave exciters for the experiments;

[0047] Specifically, this scenario can refer to Figure 2 The measurement scheme shown in the figure sets up a vector network analyzer VNA and two coaxial cables with the same loss. The surface wave exciters at the transmitting and receiving ends are fixed on a tripod so that their height and position can be adjusted. Both ends are connected to the vector network analyzer VNA through coaxial cables. The metal pipe is fixed with a tripod just above the transmitting and receiving ends. At this point, the measurement scene has been set up.

[0048] Step 2: Place a metal tube with a diameter of 2.4 cm and a length of 3 m above the transmitting and receiving ends, as shown in Figure 3 As shown, the horizontal coupling distance of the receiving end is adjusted, and the range of the coupling distance is not greater than 1 / 4 wavelength corresponding to the central operating frequency, so as to fully excite the surface wave mode operation;

[0049] Step 3: The distance d between the transmitting end and the receiving end and the height of the receiving end and the transmitting end are fixed. At this time, the distance d between the transmitting end and the receiving end is 1m. The horizontal coupling distance of the receiving end is changed. The receiving end starts from being located directly below the metal pipe (that is, starting from 0m), and moves horizontally to the left / right every 0.02m, where the horizontal distance between the receiving end and the metal pipe is the horizontal coupling distance of the receiving end, until the receiving end is 0.3m away from the metal pipe. There are 31 measurement points in total, and 9 measurements are performed at each measurement point. The wireless channel measurement data of the receiving end at the horizontal coupling distance of the receiving end at each measurement point is collected by using the vector network analyzer VNA, and the path loss value is calculated and extracted from the measurement data. Each time the horizontal coupling distance of the receiving end is changed, the corresponding path loss value is extracted by measurement and the average value of all measurements is calculated to obtain the path loss value corresponding to each change in the horizontal coupling distance of the receiving end.

[0050] Step 4: Change the distance d between the transmitter and the receiver to 1.5m, 2m, 2.5m and repeat step 3 above;

[0051] Step 5: Change the height of the receiving end, while keeping the height of the sending end unchanged. Initially, the heights of both ends are 1m. The receiving end is measured every time it descends 0.05m. This is repeated 4 times. Steps 3 and 4 are repeated.

[0052] Step 6: According to the multiple path loss values ​​extracted in the above steps, the obtained path loss values ​​are parameter fitted, and different function models including logarithmic function and cubic function are selected for fitting. The trend of these fitting curves and the actual measurement data is observed, and the root mean square error RMSE values ​​corresponding to different function models are compared. If the root mean square error RMSE value of a function model is the smallest, then the function model is the most suitable path loss model. The one with a high degree of fitting is the constructed path loss model PL (d hc ). By comparison, it is found that the RMSE value of the model using the cubic function is the smallest, so the path loss model PL(d hc ) is expressed as:

[0053]

[0054] Among them, d hc is the distance the receiving end moves left and right, that is, the horizontal coupling distance of the receiving end, a 1 ,a 2 ,a 3 ,a 4 Represent the coefficients of each term in the above expression respectively.

[0055] According to the measurement data related to the horizontal coupling distance of the receiving end collected above, different function models are used to construct the path loss model PL (d hc ), select the model with the smallest root mean square error RMSE. Since the measured data includes the cases with and without the height difference between the transmitter and receiver, it is necessary to fit both cases. The RMSE of different function models fitted without the height difference between the transmitter and receiver are shown in Table 1 below.

[0056] Table 1

[0057]

[0058] The RMSE of different function model fittings under the condition of a height difference of 0.05 m between the transmitting and receiving ends is shown in Table 2.

[0059] Table 2

[0060]

[0061] From the above two tables, we can see that the RMSE of the proposed function fitting is the smallest regardless of whether there is a height difference between the transmitting and receiving ends;

[0062] Step 7: Substitute the path loss model PL(d hc ) The least squares method is used to fit the parameters and the path loss model PL(d hc) The correction values ​​of each parameter are used to obtain the final expression of the established path loss model PL(d f ) is expressed as:

[0063]

[0064] Among them, d r is the selected reference distance, PL(d r ) indicates that at the reference distance d r The path loss value at d f represents the horizontal coupling distance of the receiving end, β represents the path loss exponent, PL(d hc ) is the path loss caused by the horizontal coupling distance when the receiving antenna moves left and right, Z τ is the shadow fading that obeys a normal distribution with a mean of 0 and a standard deviation of τ.

[0065] In addition, the parameters of the parameter fitting of the present invention are shown in Table 3 and Table 4. Table 3 is a table of parameters for fitting using the proposed model under the condition of no height difference between the transmitting and receiving ends, and Table 4 is a table of parameters for fitting using the proposed model under the condition of a height difference between the transmitting and receiving ends of 0.05 m.

[0066] Table 3

[0067]

[0068] Table 4

[0069]

[0070]

[0071] It should be noted that the parameter values ​​in the above two tables are obtained by fitting the actual measured data and the established model. Different scenarios or other variables may result in different parameter values, and these parameter values ​​are only applicable to the above specific scenarios.

[0072] Step 8: Input the distance d between the transmitter and the receiver and the horizontal coupling distance of the receiver into the final path loss model PL(d f ), the channel path loss value of the transmitting and receiving ends in the corresponding situation can be obtained.

[0073] In the specific results, Figures 4 to 7The PL diagram of the metal tube excited surface wave transmission as the horizontal coupling distance of the receiving end changes when the receiving end moves to the left and right under the conditions of no height difference between the transmitting and receiving ends and the height difference of the transmitting and receiving ends being 0.05m is given. From the figure, it can be analyzed that no matter how the height difference between the transmitting and receiving ends and the distance between the two ends change, the PL increases with the increase of the horizontal coupling distance of the receiving end, but it is not a simple linear relationship. The growth rate is large in the front range, but after moving to a certain distance, the growth rate becomes smaller and smaller. Although the growth rate is very small in the final distance range, the PL value still increases instead of tending to a constant value.

[0074] In addition, from Figure 4 , Figure 5 , Figure 6 , Figure 7 It can be seen that no matter what the situation is, before starting a certain distance, the growth rate of PL is relatively large, that is, the greater the change in transmission path loss, the lower the surface wave excitation transmission effect, and the relative free space loss changes steadily within this range, that is, within this range, as the horizontal coupling distance of the receiving end increases, the efficiency of exciting surface wave transmission becomes lower and lower. This section is due to the dominance of surface wave transmission, but when the horizontal coupling distance of the receiving end exceeds a certain value, the growth trend gradually stabilizes. At this time, although surface waves may still exist, the free propagation of signals plays a dominant role, and the change of PL becomes the law of free space signal propagation. At this time, it is no longer surface wave transmission. Therefore, there is a boundary value for the horizontal coupling distance of the receiving end. Before the boundary value, surface wave transmission is dominant, and after this boundary value, free space propagation is dominant.

[0075] also Figure 8 and Fig. 9 Surface comparison diagrams between the logarithmic distance path loss model and the proposed path loss model are given. It can be seen from the figure that the proposed path loss model is closer to the measured data, while there is a large deviation between the logarithmic distance path loss model and the measured value, which indicates that the proposed path loss model can more accurately characterize the path loss values ​​corresponding to different receiving end horizontal coupling distances under the measurement environment.

[0076] The present invention provides a channel modeling method based on surface wave transmission with horizontal coupling distance. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A channel modeling method based on surface wave transmission with horizontal coupling distance, characterized in that: The following steps are involved: Step 1, setting a transmitting end, a receiving end and a metal pipe, wherein the distance between the transmitting end and the receiving end can be changed; Step 2, placing the metal tube directly above the transmitting end and the receiving end, adjusting the horizontal coupling distance of the receiving end, performing initial measurement, and obtaining the range of the boundary value of the horizontal coupling distance of the receiving end; Step 3: fix the distance d between the transmitting end and the receiving end, perform channel measurement using a vector network analyzer VNA, adjust the horizontal coupling distance of the receiving end, collect wireless channel measurement data at different horizontal coupling distances of the receiving end, and calculate the path loss value according to the measurement data; Step 4, change the distance d between the transmitter and the receiver and repeat step 3; Step 5, change the height difference △h between the transmitting end and the receiving end and repeat steps 3 to 4; Step 6: Obtain two or more path loss values ​​according to Steps 3 to 5, and construct a path loss model PL (d hc ); Step 7: Use the constructed path loss model PL(d hc ) The least squares method is used to fit the parameters and the path loss model PL(d hc ) The correction values ​​of each parameter are used to obtain the final path loss model PL (d f ); Step 8: Input the distance d between the transmitter and the receiver and the horizontal coupling distance of the receiver into the final path loss model PL (d f ), and obtain the path loss value of the transmitting and receiving end channel in the corresponding case.

2. The method according to claim 1, characterized in that In step 1, the transmitting end and the receiving end are both connected to a vector network analyzer VNA via cables, and both the transmitting end and the receiving end are equipped with a surface wave exciter for experiment.

3. The method according to claim 2, characterized in that In step 1, the initial heights of the transmitter and the receiver are adjusted to 1 m, and two height-adjustable brackets are placed on the left side of the transmitter and the right side of the receiver, respectively. The heights of the two brackets are adjusted so that the brackets are higher than the transmitter and the receiver.

4. The method according to claim 3, characterized in that In step 2, the metal tube has a diameter of 2.4 cm and a length of 3 m; The adjusting of the horizontal coupling distance of the receiving end means: making the horizontal coupling distance range of the receiving end no greater than 1 / 4 wavelength corresponding to the center operating frequency of the vector network analyzer VNA; the horizontal coupling distance of the receiving end means the distance that the receiving end moves to the left or right.

5. The method according to claim 4, characterized in that In step 2, during the initial measurement, the receiving end is measured every time it moves 0.05m to the left or right. The corresponding path loss value is extracted and calculated for each measurement. After the functional relationship between the horizontal coupling distance of the receiving end and the path loss is obtained, the range of the boundary value of the horizontal coupling distance of the receiving end is obtained according to the curve image fitted by the functional relationship, and the boundary value is 0.3m.

6. The method according to claim 5, characterized in that In step 3, after determining the demarcation value, the receiving end moves 0.02m to the left or right for a measurement. The horizontal coupling distance of the receiving end is adjusted and measured within the demarcation value range of 0.3m. After obtaining the corresponding path loss value, the average of all path loss values ​​is calculated as the final path loss value corresponding to each measurement.

7. The method according to claim 6, characterized in that Step 4 includes: adjusting the distance d between the transmitting end and the receiving end to 1m, 1.5m, 2m and 2.5m respectively, and repeating step 3.

8. The method according to claim 7, characterized in that Step 5 includes: keeping the height of the transmitting end unchanged, changing the height of the receiving end to change the height difference, and the initial heights of the transmitting end and the receiving end are both 1m; measuring once every time the receiving end descends 0.05m, for a total of 4 measurements, that is, measuring once each time the receiving end height is 0.95m, 0.9m, 0.85m and 0.8m, and repeating steps 3 to 4.

9. The method according to claim 8, characterized in that Step 6 includes: fitting the obtained path loss value with parameters, selecting different function models including logarithmic function and cubic function for fitting, and comparing the root mean square error RMSE values ​​corresponding to different function models. It is found that the root mean square error RMSE value is the smallest when the cubic function model is used. Therefore, the constructed path loss model PL(d hc )The final expression is: Among them, d hc is the horizontal coupling distance at the receiving end; a1, a2, a3, a4 are coefficients.

10. The method according to claim 9, characterized in that In step 7, the final path loss model PL(d f ) is expressed as: Among them, d r is the selected reference distance, PL(d r ) indicates that at the reference distance d r The path loss value at d f represents the horizontal coupling distance at the receiving end, β represents the path loss index, and Z τ is the shadow fading that obeys a normal distribution with a mean of 0 and a standard deviation of τ.

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