Measurement and modeling of surface wave transmission channels based on receiving antenna angle variation

Abstract

The present invention provides a surface wave transmission channel measurement and modeling method based on the change of receiving antenna angle, including: step 1, establishing a channel measurement system and setting a measurement scene; step 2, obtaining measurement data; step 3, obtaining the average path loss value of each measurement point; step 4, constructing an initial model of path loss without surface wave angle; step 5, constructing an initial model of path loss with excited surface wave angle; step 6, calculating the path loss attenuation value; step 7, obtaining the final expression of the path loss attenuation value; step 8, obtaining the initial path loss index model; step 9, fitting the model function of the path loss index; step 10, constructing an indoor high-frequency channel path loss model; step 11, performing small-scale fading related characteristics analysis; step 12, path loss analysis. The present invention can effectively optimize the performance of the wireless communication system in the indoor environment of the industrial Internet of Things.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial Internet of Things wireless communications, and in particular to a surface wave transmission channel measurement and modeling method based on receiving antenna angle changes. Background Art

[0002] With the rapid development of IoT technology, the Industrial Internet of Things (IIoT) has emerged and has become an important driver of the intelligent transformation of the industrial system. The Industrial Internet of Things is mainly used in all aspects of the entire life cycle, such as design, production, management and service, and is an important part of the emerging industry. However, the scenarios of the Industrial Internet of Things are diverse and complex. For example, multiple interferences such as multiple refraction points and multiple scattering points between multiple objects make the channel characteristics more complex, and the path loss characteristics of the communication system are also more complex, which has a significant impact on the performance and reliability of the communication system.

[0003] At present, some scholars have achieved some results in the modeling of path loss of wireless channels in industrial Internet of Things, such as ray tracing, Monte Carlo method and method based on geometric optics, etc. However, these methods still have some problems and challenges. For example, ray tracing method is a deterministic modeling method, which is relatively complex and the accuracy of modeling is highly dependent on the accuracy of the reproduction of the original environmental information. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a wireless channel measurement method, device and modeling method in which there is an angle difference between the transmitting antenna and the receiving antenna of the conductor transmitting surface waves in the indoor environment of the industrial Internet of Things. The surface wave is introduced by coupling the antenna with the metal pipe, which effectively reduces the loss of the signal transmission process. It is especially suitable for actual complex scenes, optimizes channel characteristics and effectively overcomes the problem of complex and changeable indoor environment. The antenna angle factor is introduced for accurate modeling and measurement, which provides better guarantee for the optimization of the performance of the indoor wireless communication system of the industrial Internet of Things. At the same time, the present invention provides a simple, easy to implement and low-cost channel measurement method and device, which is suitable for signal measurement and analysis in various indoor environments of the industrial Internet of Things.

[0005] The present invention specifically provides a surface wave transmission channel measurement and modeling method based on the change of receiving antenna angle, comprising the following steps:

[0006] Step 1: Establish a channel measurement system and set up a measurement scenario;

[0007] Step 2: Get the measurement data:

[0008] Step 3, obtaining the average path loss value of each measurement point;

[0009] Step 4, constructing an initial model of path loss without surface wave angle;

[0010] Step 5, constructing an initial model of the angle path loss of the excited surface wave;

[0011] Step 6: Set the distance between the transmitting antenna and the receiving antenna d With distance d The path loss value at the corresponding antenna angle Substitute it into the initial model of path loss without surface wave angle and the initial model of path loss with excited surface wave angle, and calculate the angles of the transmitting antenna and the receiving antenna as θ , the distance between the transmitting antenna and the receiving antenna is d The path loss attenuation value when ;

[0012] Step 7: Use the least squares method to extract parameters and fit the coefficients A 1 , B 1 , A 2 , B 2 ,get Final expression;

[0013] Step 8: Obtain an initial path loss index model based on the path loss index values ​​extracted from the measurements and varying based on different antenna angles. ;

[0014] Step 9, calculating the path loss index values ​​based on different transmitting and receiving antenna angles according to the average path losses at different angles of the transmitting antenna and the receiving antenna and at different transmitting and receiving end distances, and fitting the model function of the path loss index by the least square method;

[0015] Step 10: According to the angles of the transmitting antenna and the receiving antenna θ , the distance d between the transmitting antenna and the receiving antenna, and the model of the path loss index for different transmitting antenna and receiving antenna angles , attenuation values ​​at different antenna angles Construct a path loss model for indoor high-frequency channels;

[0016] Step 11, performing small-scale fading related characteristic analysis;

[0017] Step 12: Path loss analysis.

[0018] Step 1 includes: the channel measurement system includes two wide-beam antennas, a metal pipe and an antenna fixing plate with adjustable coupling distance;

[0019] The two wide beam antennas are used to transmit and receive signals respectively. A wide beam antenna is an antenna with a transmitting and receiving angle greater than 30 degrees. Its main feature is a wider main lobe and smaller side lobe. Wide beam antennas are widely used in wireless communications because they can cover a wider area and increase the coverage area of ​​the signal, while also providing better multipath channel transmission characteristics.

[0020] The metal pipe is used as a medium for signal transmission to connect two wide beam antennas; the adjustable coupling distance antenna fixing plate is used to control the distance between the metal pipe and the two wide beam antennas; the adjustable coupling distance antenna fixing plate adopts an adjustable structure, including two layers of acrylic plates and a knob control system, which has a good fixing effect and will not affect the experimental data measurement. The two wide beam antennas are located between the two layers of acrylic plates, at the diagonal center of the acrylic plates and close to the lower acrylic plate; the two layers of cardboard are fixed with screws at the four corners; the knob control system is used to control the upper and lower distances between the two layers of acrylic plates, thereby changing the distance between the metal pipe and the two wide beam antennas (i.e., the coupling distance); the present invention performs channel measurement and analysis at different angles between the transmitting antenna and the receiving antenna, and further studies the transmission quality and channel characteristics of the signal at different distances. Signal transmission mechanism: In the wireless channel measurement system of the present invention, part of the signal is still propagated through the wireless channel, but most of the signal is transmitted to the receiving end antenna along the metal pipe in the form of surface waves. Metal pipes have good conductivity, are stable and not easy to deform, so the transmission efficiency is higher and the transmission distance is longer, thereby improving the signal reception strength and stability.

[0021] In the scene setting, first fix the transmitting end of the antenna at a preset point to keep the height of the transmitting end of the antenna unchanged; then fix the transmitting antenna and move the receiving antenna. To better fit the actual industrial IoT environment, the distance between the transmitting antenna and the receiving antenna is gradually increased from 0.5m to 3m without loss of generality. The receiving antenna moves along a straight line and measurement points are set every 0.5m for fixed measurement.

[0022] At each transmitting and receiving antenna distance point between the transmitting and receiving antennas (0.5 meters to 3 meters), rotate the receiving antenna counterclockwise around the center of the acrylic plate to 180° (no need to rotate to 360°, because this is equivalent to rotating clockwise to 180°, and the experimental results consistent with clockwise can be obtained), so that there is an angle difference between the transmitting antenna and the receiving antenna, that is, the transmitting antenna and the receiving antenna are not completely facing each other. The transmitting antenna and the receiving antenna facing each other is 0°, and X1 (generally 9) measurements are performed every 15° and saved, and the average path loss is calculated to improve the accuracy of the measurement results.

[0023] In step 2, the measurement data includes the distance between the transmitting antenna and the receiving antenna d, the distance between the transmitting antenna and the receiving antenna d Angle difference between the upper transmitting and receiving antennas θ , and the distances d and the angle of the transmitting and receiving antennas θ The corresponding path loss value.

[0024] Step 3 includes: calculating the average path loss value using the following formula:

[0025] , (1)

[0026] in, is the average path loss value at distance d, M is the total number of measurements, is the number of frequency points measured in the measurement frequency band, n is the frequency point number, is the frequency response of the mth measurement, f is the signal frequency;

[0027] ; and are the amplitude and phase obtained from the mth measurement respectively, i is an imaginary number, e is a natural constant; The frequency domain measurement method is used to obtain the frequency domain response of the entire frequency band by continuously sending a single frequency carrier signal and frequency domain sweeping with a vector network analyzer (VNA). The formula is:

[0028] , (2)

[0029] in, Indicates an equivalent relationship. represents the received signal spectrum function, is the transmitted signal spectrum function, is the scattering parameter of the wireless channel, also in frequency The complex frequency response at .

[0030] Step 4 includes: the initial model of the surface wave-free angle path loss is:

[0031] , (3)

[0032] in Indicates the distance between the transmitting antenna and the receiving antenna d Path loss value at the corresponding antenna angle when ; is the reference distance, which is set to 0.5m here; is the reference antenna angle, set to 0°; At the reference distance and reference antenna angle Path loss value at ; Shadow fading, shadow fading It has a mean of zero and a standard deviation of Normal distribution of is the attenuation value based on different antenna angles and transmitter-receiver distances, where j =1,2, when j=1, it means no surface wave is involved, when j =2 indicates the introduction of surface waves. It indicates the attenuation value based on different antenna angles and transmitter-receiver distances when there is no surface wave involved. Indicates the attenuation value based on different antenna angles and distances between the transmitter and receiver when the surface wave is introduced; Represents the path loss exponent value when there is no surface wave involvement.

[0033] Step 5 includes: the initial model of the excited surface wave angle path loss is:

[0034] , (4)

[0035] , (5)

[0036] in, Indicates the distance between the transmitting antenna and the receiving antenna when exciting surface waves d Path loss value at the corresponding antenna angle when ; , Indicates the wavelength of the wireless carrier signal; and They represent the distribution functions of shadow fading respectively. The variance and mean of Indicates the path loss exponent value when surface waves are introduced.

[0037] Step 6 includes: calculating the angles of the transmitting antenna and the receiving antenna according to the following formula: θ , the distance between the transmitting antenna and the receiving antenna is d The path loss attenuation value when :

[0038] , (6)

[0039] , (7)

[0040] , (8)

[0041] , (9)

[0042] in, , ; Indicates the angles of the transmitting antenna and the receiving antenna when there is no surface wave involved θ The path loss intercept at , Indicates the angles of the transmitting antenna and the receiving antenna when the surface wave is introduced θ The path loss intercept at ;

[0043] Constructed according to the attenuation value changes at different transmitting and receiving antenna angles The initial model:

[0044] , (10)

[0045] in , are the parameters to be fitted.

[0046] Step 7 includes: The final expression is:

[0047] , (11)

[0048] (12).

[0049] Step 8 includes: the initial path loss index model for:

[0050] , (13)

[0051] in, , , , are the parameters to be fitted.

[0052] Step 9 includes: the model function of the path loss index is:

[0053] , (14)

[0054] , (15)

[0055] In step 10, the indoor high-frequency channel path loss model is:

[0056] ,

[0057] ;

[0058] Step 11 includes: The main research parameter of small-scale fading is the root mean square delay spread , It indicates the degree of multipath fading in the wireless channel and can also measure the possibility of inter-code interference of the signal, laying a theoretical foundation for the design of the physical layer algorithm of the communication system.

[0059] The power delay profile (PDP) reflects the change of signal power over time, and can clearly show the multipath phenomenon caused by signal reflection and refraction caused by factors such as floors, walls, ceilings, and pedestrians. In the invention, since the channel measurement is performed in the frequency domain, the measured frequency response data is processed by inverse discrete Fourier transform to obtain the channel impulse response. For a grid point at a location, that is, the X1-order data of the measurement point, the instantaneous power delay profile The calculation formula is:

[0060] , (16)

[0061] in, is the channel impulse response in the time domain, For the channel l A resolvable delay; t i Indicates the measurement time of each set of data;

[0062] Then, by averaging the measured data, the instantaneous power delay spectrum of each grid point is obtained. for:

[0063] , (17)

[0064] in, It is an expectation algorithm; at each measurement point, the instantaneous power delay spectrum PDP data obtained from the X1 group of grid points are averaged to obtain the time dispersion parameters of the measurement point.

[0065] In response to the problems of the prior art, the present invention introduces the concept of surface waves, which becomes a research direction with breakthrough potential. Surface waves are electromagnetic waves that propagate along the surface of a medium and have the characteristic of attenuation along the surface. Surface waves are special coupling modes between electromagnetic waves and the boundary of a medium. For example, magnetic fields and electric fields propagate near the surface of a medium in the form of transverse electric waves (TE waves) and transverse magnetic waves (TM waves), attenuating along the surface. TE waves are waves in which the electric field is perpendicular to the surface, while TM waves have a magnetic field perpendicular to the surface. These waves are widely used in microwave technology and optics, such as antenna design and optical fiber communication. By conducting in-depth measurement and analysis of the propagation of surface waves, the fading, multipath effects and interference of wireless channels can be more accurately understood. In practical applications, different excitation methods can have different effects on the characteristics of surface waves, such as excitation position, polarization direction, wavelength, etc. Therefore, it is necessary to select a suitable surface wave excitation method according to the specific application scenario and requirements, and conduct in-depth research and optimization on it to improve system performance and effect. The surface wave excitation method used in the present invention is to utilize the coupling effect between the metal conductor and the medium.

[0066] The present invention proposes a wireless channel measurement and modeling method based on surface wave excitation of receiving antenna angle change. The method first generates a wired channel that effectively reduces path loss through surface wave excitation, converts pure wireless channel propagation into a quasi-random channel combining wireless and wired, and greatly reduces path loss. Secondly, considering the complex structure and object distribution in the industrial Internet of Things environment, especially in order to make the signal more concentrated for specific scenarios, we will not use omnidirectional antennas as carriers for signal transmission and reception. Usually, semi-directional antennas can be used to undertake the task of signal transmission and reception to achieve more efficient wireless communication. Semi-directional is the direction of half a sphere. In order to communicate more flexibly, or in some special cases, the transmitting antenna and the receiving antenna cannot completely realize face-to-face transmission of signals, and there is an angle difference between the transmitting antenna and the receiving antenna. For the convenience of research, we fix the transmitting end and change the angle of the receiving end antenna, which is also closer to the actual situation. Combined with the propagation characteristics of different frequency bands and frequencies, the accurate modeling of the indoor wireless channel path loss combining wired and wireless in the context of the industrial Internet of Things is realized. Specifically, this method uses the surface wave excitation effect, considers the impact of metal structures, obstacles and reflections on signal propagation, and provides a more accurate path loss estimation in the industrial Internet of Things environment by analyzing different distance characteristics.

[0067] Beneficial effect: The present invention combines wired channels with wireless channels by adding conductors between transmitting and receiving antennas to introduce surface waves, which can effectively reduce the path loss of signal transmission in the indoor environment of the Industrial Internet of Things, and can effectively optimize the performance of the wireless communication system in the indoor environment of the Industrial Internet of Things, thereby helping the design and optimization of the wireless communication system in the indoor environment of the Industrial Internet of Things.

[0068] In order to adapt to actual complex scenarios, optimize channel characteristics and effectively overcome the complex and changeable indoor environment, the antenna angle factor is introduced for precise modeling and measurement, which provides better guarantee for the optimization of the performance of the industrial Internet of Things indoor wireless communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] 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.

[0070] Figure 1 Schematic diagram of the experimental scene setup for indoor channel measurement.

[0071] Figure 2 A partial close-up of the experimental setup for indoor channel measurement.

[0072] Figure 3 Flowchart of the method for modeling path loss of indoor wireless channels.

[0073] Figure 4 A line graph comparing channel path loss when the angles of the transmitting and receiving antennas are changed before and after the introduction of surface waves in indoor channel measurement.

[0074] Figure 5 This is a PDP diagram without surface wave excitation.

[0075] Figure 6 This is a PDP diagram with surface wave excitation.

[0076] Figure 7 RMS delay spread Cumulative distribution plot of . DETAILED DESCRIPTION

[0077] like Figure 3 As shown, in a specific embodiment of the present invention, a surface wave transmission channel measurement and modeling method based on the change of the receiving antenna angle is provided, comprising the following steps:

[0078] Step 1: Establish a channel measurement system and set up a measurement scenario;

[0079] Step 2: Get the measurement data:

[0080] Step 3, obtaining the average path loss value of each measurement point;

[0081] Step 4, constructing an initial model of path loss without surface wave angle;

[0082] Step 5, constructing an initial model of the angle path loss of the excited surface wave;

[0083] Step 6: Set the distance between the transmitting antenna and the receiving antennad With distance d The path loss value at the corresponding antenna angle Substitute it into the initial model of path loss without surface wave angle and the initial model of path loss with excited surface wave angle, and calculate the angles of the transmitting antenna and the receiving antenna as θ , the distance between the transmitting antenna and the receiving antenna is d The path loss attenuation value when ;

[0084] Step 7: Use the least squares method to extract parameters and fit the coefficients A 1 , B 1 , A 2 , B 2 ,get Final expression;

[0085] Step 8: Obtain an initial path loss index model based on the path loss index values ​​extracted from the measurements and varying based on different antenna angles. ;

[0086] Step 9, calculating the path loss index values ​​based on different transmitting and receiving antenna angles according to the average path losses at different angles of the transmitting antenna and the receiving antenna and at different transmitting and receiving end distances, and fitting the model function of the path loss index by the least square method;

[0087] Step 10: According to the angles of the transmitting antenna and the receiving antenna θ , the distance d between the transmitting antenna and the receiving antenna, and the model of the path loss index for different transmitting antenna and receiving antenna angles , attenuation values ​​at different antenna angles Construct a path loss model for indoor high-frequency channels;

[0088] Step 11, performing small-scale fading related characteristic analysis;

[0089] Step 12, path loss analysis: In free space, the angle difference between the transmitting antenna and the receiving antenna will have a significant impact on the wireless communication performance, which cannot be ignored in the industrial Internet of Things environment. According to the preliminary experimental results (such as Figure 4As shown in the figure, it is found that the path loss will gradually increase with the increase of the angle difference between the transmitting antenna and the receiving antenna, and the loss reaches the maximum at 90°. After that, as the antenna angle continues to increase, the loss tends to decrease and reaches a new minimum point at 180°, but the loss value is still larger than that at 0°. According to relevant antenna theory, the reduction in loss may be caused by antenna polarization. Subsequently, after the introduction of surface waves, the path loss can be reduced by about 20dB overall, but the path loss also shows the same trend with angle changes.

[0090] Step 1 includes: Figure 1 As shown, the channel measurement system includes two wide-beam antennas, a metal pipe and an antenna fixing plate with adjustable coupling distance;

[0091] The two wide beam antennas are used to transmit and receive signals respectively. A wide beam antenna is an antenna with a transmitting and receiving angle greater than 30 degrees. Its main feature is a wider main lobe and smaller side lobe. Wide beam antennas are widely used in wireless communications because they can cover a wider area and increase the coverage area of ​​the signal, while also providing better multipath channel transmission characteristics.

[0092] The metal pipe is used as a medium for signal transmission to connect two wide beam antennas; the adjustable coupling distance antenna fixing plate is used to control the distance between the metal pipe and the two wide beam antennas; the adjustable coupling distance antenna fixing plate adopts an adjustable structure, including two layers of acrylic plates and a knob control system, which has a good fixing effect and will not affect the experimental data measurement. The two wide beam antennas are located between the two layers of acrylic plates, at the diagonal center of the acrylic plates and close to the lower acrylic plate; the two layers of cardboard are fixed with screws at the four corners; the knob control system is used to control the upper and lower distances between the two layers of acrylic plates, thereby changing the distance between the metal pipe and the two wide beam antennas (i.e., the coupling distance); the present invention performs channel measurement and analysis at different angles between the transmitting antenna and the receiving antenna, and further studies the transmission quality and channel characteristics of the signal at different distances. Signal transmission mechanism: In the wireless channel measurement system of the present invention, part of the signal is still propagated through the wireless channel, but most of the signal is transmitted to the receiving end antenna along the metal pipe in the form of surface waves. Metal pipes have good conductivity, are stable and not easy to deform, so the transmission efficiency is higher and the transmission distance is longer, thereby improving the signal reception strength and stability.

[0093] like Figure 2As shown, in the scene setting, the transmitting end of the antenna is first fixed at a preset point to keep the height of the transmitting end of the antenna unchanged; then the transmitting antenna is fixed and the receiving antenna is moved. To better fit the actual industrial Internet of Things environment, the distance between the transmitting antenna and the receiving antenna is gradually increased from 0.5m to 3m without loss of generality. The receiving antenna moves along a straight line and measurement points are set every 0.5m for fixed measurement.

[0094] At each transmitting and receiving antenna distance point between the transmitting and receiving antennas (0.5 meters to 3 meters), rotate the receiving antenna counterclockwise around the center of the acrylic plate to 180° (no need to rotate to 360°, because this is equivalent to rotating clockwise to 180°, and the experimental results consistent with clockwise can be obtained), so that there is an angle difference between the transmitting antenna and the receiving antenna, that is, the transmitting antenna and the receiving antenna are not completely facing each other. The transmitting antenna and the receiving antenna facing each other is 0°. Take 9 measurements every 15° and save them, and calculate the average path loss to improve the accuracy of the measurement results.

[0095] In step 2, the measurement data includes the distance between the transmitting antenna and the receiving antenna d , the distance between the transmitting antenna and the receiving antenna d Angle difference between the upper transmitting and receiving antennas θ , and the distances d and the angle of the transmitting and receiving antennas θ The corresponding path loss value.

[0096] Step 3 includes: calculating the average path loss value using the following formula:

[0097] , (1)

[0098] in, is the average path loss value at distance d, M is the total number of measurements, is the number of frequency points measured in the measurement frequency band, n is the frequency point number, is the frequency response of the mth measurement, f is the signal frequency;

[0099] ; and are the amplitude and phase obtained from the mth measurement respectively, i is an imaginary number, e is a natural constant; The frequency domain measurement method is used to obtain the frequency domain response of the entire frequency band by continuously sending a single frequency carrier signal and frequency domain sweeping with a vector network analyzer (VNA). The formula is:

[0100] , (2)

[0101] in, Indicates an equivalent relationship. represents the received signal spectrum function, is the transmitted signal spectrum function, is the scattering parameter of the wireless channel, also in frequency The complex frequency response at .

[0102] Step 4 includes: the initial model of the surface wave-free angle path loss is:

[0103] , (3)

[0104] in Indicates the distance between the transmitting antenna and the receiving antenna d Path loss value at the corresponding antenna angle when ; is the reference distance, which is set to 0.5m here; is the reference antenna angle, set to 0°; At the reference distance and reference antenna angle Path loss value at ; Shadow fading, shadow fading It has a mean of zero and a standard deviation of Normal distribution of is the attenuation value based on different antenna angles and transmitter-receiver distances, where j =1,2, when j=1, it means no surface wave is involved, when j =2 indicates the introduction of surface waves. It indicates the attenuation value based on different antenna angles and transmitter-receiver distances when there is no surface wave involved. Indicates the attenuation value based on different antenna angles and distances between the transmitter and receiver when the surface wave is introduced; Represents the path loss exponent value when there is no surface wave involvement.

[0105] Step 5 includes: the initial model of the excited surface wave angle path loss is:

[0106] , (4)

[0107] , (5)

[0108] in, Indicates the distance between the transmitting antenna and the receiving antenna when exciting surface waves d Path loss value at the corresponding antenna angle when ; , Indicates the wavelength of the wireless carrier signal; and They represent the distribution functions of shadow fading respectively. The variance and mean of Indicates the path loss exponent value when surface waves are introduced.

[0109] Step 6 includes: calculating the angles of the transmitting antenna and the receiving antenna according to the following formula: θ , the distance between the transmitting antenna and the receiving antenna is d The path loss attenuation value when :

[0110] , (6)

[0111] , (7)

[0112] , (8)

[0113] , (9)

[0114] in, , ; Indicates the angles of the transmitting antenna and the receiving antenna when there is no surface wave involved θ The path loss intercept at , Indicates the angles of the transmitting antenna and the receiving antenna when the surface wave is introduced θ The path loss intercept at ;

[0115] Constructed according to the change of attenuation value at different transmitting antenna and receiving antenna angles The initial model:

[0116] , (10)

[0117] in , are the parameters to be fitted.

[0118] Step 7 includes: The final expression is:

[0119] , (11)

[0120] (12).

[0121] Step 8 includes: the initial path loss index model for:

[0122] , (13)

[0123] in, , , , are the parameters to be fitted.

[0124] Step 9 includes: the model function of the path loss index is:

[0125] , (14)

[0126] , (15)

[0127] In step 10, the indoor high frequency band channel path loss model is:

[0128] ,

[0129] ;

[0130] Step 11 includes: the power delay profile (PDP) reflects the change of signal power over time, and can clearly show the multipath phenomenon caused by signal reflection and refraction caused by factors such as floors, walls, ceilings and pedestrians. In the invention, since the channel measurement is performed in the frequency domain, the measured frequency response data is processed by inverse discrete Fourier transform to obtain the channel impulse response. For a grid point at a location, that is, 9 times the data of the measurement point, the instantaneous power delay profile The calculation formula is:

[0131] , (16)

[0132] in, is the channel impulse response in the time domain, For the channel l A resolvable delay; t i Indicates the measurement time of each set of data;

[0133] Then, by averaging the measured data, the instantaneous power delay spectrum of each grid point is obtained. for:

[0134] , (17)

[0135] in, It is an expectation algorithm; at each measurement point, the instantaneous power delay spectrum PDP data obtained from 9 groups of grid points are averaged to obtain the time dispersion parameter of the measurement point.

[0136] Figure 5 , Figure 6 The delay power spectra of different antenna angles under two conditions (with or without surface wave excitation) with a transmitter-receiver distance of 1m are given, and three typical angles (0°, 90°, 180°) are selected. Figure 5 , Figure 6 It can be seen that regardless of whether there is surface wave excitation or not, the main path and the secondary path are clearly distinguished when the antenna angle is 0°. This is because this is the closest to free space, and most of the electromagnetic waves are direct paths; when the antenna angle is 90° and 180°, the multipath effect is enhanced, the proportion of direct paths of electromagnetic waves decreases, and the signal is mainly propagated through reflection, refraction, diffraction, scattering, etc., so the multipath is richer at this time. In addition, it can be seen that when there is surface wave excitation, the power of the signal received by the receiving end is significantly higher than the received signal power of wireless communication when there is no surface wave, which further verifies that surface waves are of great significance in optimizing wireless communication performance.

[0137] RMS Delay Spread The cumulative distribution of Figure 7 The corresponding mean and standard deviation are given in Table 1. It can be seen from the chart that when there is surface wave excitation, The mean and standard deviation are both smaller than those without surface waves, and the mean changes gently with the increase of antenna angle, indicating that when surface wave excitation is present, the system performance can be optimized while the system stability can be increased, and it is not easily affected by external factors. In addition, regardless of whether there is surface wave excitation or not, the mean and standard deviation are the smallest when the antenna angle is 0°, because at this time most of the electromagnetic waves are direct paths; while at other angles The mean and standard deviation are significantly larger because the direct path ratio is reduced after partial or even complete occlusion, which means that the multipath propagation effect is more significant. This shows that different antenna angles produce different degrees of multipath.

[0138] Table 1

[0139]

[0140] By introducing surface wave excitation, the method proposed in the present invention can more comprehensively capture channel characteristics, including multi-dimensional information in space, frequency and time. Compared with traditional methods, this multi-dimensional channel measurement is more accurate and provides a more stable data basis for system design. Secondly, the uniqueness of the method of the present invention lies in its reduction of loss. After the surface wave is introduced, the quasi-random channel combining the wired channel and the wireless channel can greatly reduce the path loss and improve the quality and reliability of signal transmission. By introducing the surface wave, the fading effect in signal transmission can also be effectively reduced, and the stability and reliability of signal propagation are enhanced. In addition, the surface wave excitation mode of the present invention is relatively simple. It only needs to place the metal conductor on the antenna surface to achieve zero coupling distance excitation of the surface wave. There are a large number of metal conductors in the industrial Internet of Things environment, such as metal pipes, tracks and power lines, which can be used as media for exciting surface waves. Finally, the environment in the industrial Internet of Things environment is complex. In order to achieve more effective and reliable communication, or for more flexible communication, there is an angle difference between the receiving antenna and the transmitting antenna. At this time, it is very necessary to model the path loss of the wireless channel based on the surface wave excitation of the receiving antenna angle change. Its transmission characteristics need to be accurately modeled and measured in order to achieve the best transmission effect in practical applications.

[0141] The present invention provides a surface wave transmission channel measurement and modeling method based on the change of the receiving antenna angle. 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 surface wave transmission channel measurement and modeling method based on the change of receiving antenna angle, characterized in that: The following steps are involved: Step 1, establish a channel measurement system and set a measurement scene; in the scene setting, first fix the transmitting end of the antenna at a preset point and keep the height of the transmitting end of the antenna unchanged; then fix the transmitting antenna and move the receiving antenna. The receiving antenna moves along a straight line and sets measurement points at intervals for fixed measurement; Step 2: Get the measurement data: Step 3, obtaining the average path loss value of each measurement point; Step 4, constructing an initial model of path loss without surface wave angle; Step 5, constructing an initial model of the angle path loss of the excited surface wave; Step 6: Substitute the distance d between the transmitting antenna and the receiving antenna and the path loss value PL(d,θ) at the antenna angle corresponding to the distance d into the initial model of the path loss without surface wave angle and the initial model of the path loss with excited surface wave angle, and calculate the path loss attenuation value J when the angle difference between the transmitting antenna and the receiving antenna is θ and the distance between the transmitting antenna and the receiving antenna is d. j (θ); Step 7: Use the least squares method to extract parameters and fit the coefficients A1, B1, A2, B2 to get J j (θ) Final expression; Step 8: Obtain an initial path loss index model n according to the path loss index value extracted from the measurement that varies based on different antenna angles. j (θ); Step 9, calculating the path loss index values ​​based on different transmitting and receiving antenna angles according to the average path losses at different angles of the transmitting antenna and the receiving antenna and at different transmitting and receiving end distances, and fitting the model function of the path loss index by the least square method; Step 10: according to the angle difference θ between the transmitting antenna and the receiving antenna, the distance d between the transmitting antenna and the receiving antenna, and the model n of the path loss index at different transmitting antenna and receiving antenna angles j (θ), attenuation value J at different antenna angles j (θ) Constructing indoor high frequency channel path loss model; Step 11, performing small-scale fading related characteristic analysis; Step 12: path loss analysis; Step 3 includes: calculating the average path loss value using the following formula: in, is the average path loss value at distance d, M is the total number of measurements, N f is the number of frequency points measured in the measurement frequency band, n is the frequency point number; |H m (f,d,θ)| 2 is the frequency response of the mth measurement, f is the signal frequency, |H m (f,d,θ)|=|H(ω)|e iθ(ω) ,|H(ω)| and θ(ω) are the amplitude and phase obtained from the mth measurement, i is an imaginary number, and e is a natural constant; |H m (f, d, θ)| is obtained by frequency domain measurement. By continuously sending a single frequency carrier signal and frequency domain sweeping with a vector network analyzer, the frequency domain response of the entire frequency band can be obtained. The formula is: S 21 (ω)∝H(ω)=Y(ω) / X(ω)=|H(ω)|e iθ(ω) (2) Where ∝ represents an equivalent relationship, Y(ω) represents the received signal spectrum function, X(ω) represents the transmitted signal spectrum function, S 21 (ω) is the scattering parameter of the wireless channel, which is also the complex frequency response at frequency ω; Step 4 includes: the initial model of the surface wave-free angle path loss is: Where PL(d,θ) represents the path loss value at the corresponding antenna angle difference θ when the distance between the transmitting antenna and the receiving antenna is d; d0 is the reference distance, which is set to 0.5m here; θ0 is the reference antenna angle difference, which is set to 0°; PL(d0,θ0) is the path loss value at the reference distance d0 and the reference antenna angle difference θ0; X σ θ is shadow fading, shadow fading X σ θ It obeys a normal distribution with a mean of zero and a standard deviation of σ; J j (θ) is the attenuation value based on different antenna angles and transceiver distances, where j = 1, 2. When j = 1, it means no surface wave is involved. When j = 2, it means the surface wave is introduced. J1(θ) represents the attenuation value based on different antenna angles and transceiver distances when no surface wave is involved. J2(θ) represents the attenuation value based on different antenna angles and transceiver distances when the surface wave is introduced. n1(θ) represents the path loss index value when no surface wave is involved. Step 5 includes: the initial model of the excited surface wave angle path loss is: Among them, PL s (d,θ) represents the path loss value at the antenna angle difference θ corresponding to the distance d between the transmitting antenna and the receiving antenna when the surface wave is excited; d0>10λ, λ represents the wavelength of the wireless carrier signal; n2(θ) represents the path loss exponent value when the surface wave is introduced; Step 6 includes: calculating the path loss attenuation value J when the angle difference θ between the transmitting antenna and the receiving antenna and the distance d between the transmitting antenna and the receiving antenna are calculated according to the following formula: j (θ): J1(θ)=G1(θ)-PL(d0,θ0) (8) J2(θ)=G2(θ)-PL s (d0,θ0) (9) Among them, PL(d0,θ0)=37.2232, PL s (d0,θ0)=22.8639; G1(θ) represents the path loss intercept at the angle difference θ between the transmitting antenna and the receiving antenna when there is no surface wave involved, and G2(θ) represents the path loss intercept at the angle θ between the transmitting antenna and the receiving antenna when the surface wave is introduced; According to the attenuation value changes of different transmitting antenna and receiving antenna angles, J is constructed. j The initial model of (θ): J j (θ)=θ 4 e^(A j θ+B j ) (10) Among them A j , B j is the parameter to be fitted; Step 8 includes: the initial path loss index model n j (θ) is: n j (θ)=a j +b j cos(θd j )+c j sin(θd j ) (13) Among them, a j , b j 、c j d j are the parameters to be fitted.

2. The method according to claim 1, characterized in that Step 1 includes: the channel measurement system includes two wide beam antennas, a metal pipe and an antenna fixing plate with adjustable coupling distance; The two wide-beam antennas are used for transmitting and receiving signals respectively, and the wide-beam antenna is an antenna with a transmitting and receiving angle greater than 30 degrees; the metal pipe is used as a medium for signal transmission, connecting the two wide-beam antennas; the adjustable coupling distance antenna fixing plate is used to control the distance between the metal pipe and the two wide-beam antennas; the adjustable coupling distance antenna fixing plate adopts an adjustable structure, including upper and lower layers of acrylic plates and a knob control system, and the two wide-beam antennas are located between the two layers of acrylic plates, at the diagonal center of the acrylic plates and close to the lower acrylic plate; the knob control system is used to control the upper and lower distance between the two layers of acrylic plates, thereby changing the distance between the metal pipe and the two wide-beam antennas; At each transmitting and receiving antenna distance point between the transmitting and receiving antennas, rotate the receiving antenna counterclockwise around the center of the acrylic plate to 180° so that there is an angle difference between the transmitting antenna and the receiving antenna, that is, the transmitting antenna and the receiving antenna are not completely facing each other. The transmitting antenna and the receiving antenna facing each other is 0°. Perform X1 measurements every 15° and save them, and calculate the average path loss.

3. The method according to claim 2, characterized in that In step 2, the measurement data includes the distance d between the transmitting antenna and the receiving antenna, the angle difference θ between the transmitting antenna and the receiving antenna at the distance d between the transmitting antenna and the receiving antenna, and the path loss values ​​corresponding to each distance d and the angle difference θ between the transmitting antenna and the receiving antenna.

4. The method according to claim 3, characterized in that Step 7 includes: j (θ) The final expression is: J1(θ)=θ 4 e^(-0.037θ-12.6067) (11), J2(θ)=θ 4 e^(-0.0358θ-12.5346) (12).

5. The method according to claim 4, characterized in that Step 9 includes: the model function of the path loss index is: n1(θ)=0.78+0.0462cos(0.0325θ)+0.0268sin(0.0325θ) (14) n2(θ)=0.2148-0.1304cos(0.0301θ)-0.0734sin(0.0301θ) (15) In step 10, the indoor high frequency band channel path loss model is: PL(d,θ)=37.2232+[0.78+0.0462cos(0.0325θ)+0.0268sin(0.0325θ)]log 10 (2d)+θ 4 e^(-0.037θ-12.6067)+X σ θ , PL s (d,θ)=22.8639+[0.2148-0.1304cos(0.0301θ)-0.0734sin(0.0301θ)]log 10 (2d)+θ 4 e^(-0.0358θ-12.5346)+X σ θ ; Step 11 includes: performing inverse discrete Fourier transform processing on the measured frequency response data to obtain the channel impulse response. For a grid point at a location, that is, the X1-order data of the measurement point, the instantaneous power delay spectrum PDP (t i ,τ l ) is calculated as: PDP(t i ,t l )=|h(t i ,t l )| 2 (16) Among them, h(t i ,τ l ) is the time domain channel impulse response, τ l is the lth resolvable delay in the channel; t i Indicates the measurement time of each set of data; Then, by averaging the measured data, the instantaneous power delay profile PDP (τ l )for: PDP(t l )=E t {PDP(t i ,t l )} (17) Among them, E t {·} is an expectation algorithm; at each measurement point, the instantaneous power delay profile PDP data obtained from the X1 group of grid points are averaged to obtain the time dispersion parameter of the measurement point.

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