Short-wave broadcast antenna channel evaluation and prediction method and system

Abstract

The invention discloses a short-wave broadcast antenna channel evaluation and prediction method, which comprises the following steps: step 1, accessing equipment: accessing channel evaluation equipment 5 into a broadcast system, connecting a short-wave broadcast transmitter 1, a radio frequency transmission system 3 and the channel evaluation equipment 5 to a radio frequency change-over switch 2, and connecting the output end of the radio frequency transmission system 3 to an antenna feeder 4; step 2, rotating the antenna to a specified orientation: rotating the antenna array plane of the broadcasting system to the specified orientation through antenna rotating equipment according to the area needing channel assessment; step 3, setting an equipment state: setting a radio frequency change-over switch 2 to a channel evaluation mode, setting a radio frequency transmission system 3, and setting a detection mode of channel evaluation equipment 5 to be a fixed frequency point detection mode or a sweep frequency detection mode according to specific task requirements; and 4, carrying out detection and channel evaluation. According to the invention, an active ionosphere oblique return type detection mode is adopted, and support is provided for broadcast frequency optimization selection, transmitting power control, antenna mode selection and broadcast effect evaluation.

Description

Technical Field

[0001] The present invention relates to the field of ionospheric sounding and short-wave broadcasting, and particularly to a method and system for evaluating and predicting short-wave broadcast antenna channels. Background Art

[0002] Short-wave broadcasting refers to signal coverage using electromagnetic waves with frequencies ranging from 3 to 30 MHz. Short-wave propagation has a series of advantages such as strong penetration ability, being less susceptible to interference, being safe, convenient, and fast, and is welcomed and loved by people and is widely used in international broadcasting.

[0003] There are two ways of short-wave propagation: ground-wave propagation and sky-wave propagation. Among them, sky-wave propagation is the main propagation method, and sky-wave propagation mainly relies on the reflection effect of the ionosphere on electromagnetic waves.

[0004] The short-wave broadcast coverage effect is mainly affected by the changes in the ionosphere. The changes in the ionosphere have a great impact on the quality and propagation distance of short-wave broadcasting. When the ionosphere changes violently, short-wave broadcasting may even be interrupted, affecting normal communication. The signal field strength coverage situation after the short-wave broadcast is reflected by the ionosphere can be predicted based on a certain ionospheric model (such as ITU-REC533). However, the coverage prediction of electromagnetic waves is an extremely complex project, and there may be a large error between the prediction accuracy and the actual broadcast situation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to improve the prediction accuracy of short-wave broadcast coverage effect.

[0006] The present invention solves the above technical problem by the following technical means: A method for evaluating and predicting short-wave broadcast antenna channels, characterized by comprising the following steps:

[0007] Step 1, access equipment: Connect the channel evaluation equipment (5) to the broadcast system, where the short-wave broadcast transmitter (1), the RF transmission system (3), and the channel evaluation equipment (5) are all connected to the RF switch (2), and the output end of the RF transmission system (3) is connected to the antenna feeder (4);

[0008] Step 2, rotate the antenna to a specified azimuth: According to the area where channel evaluation is required, rotate the antenna array of the broadcast system to the specified azimuth through the antenna rotation equipment;

[0009] Step 3, set the equipment state: Set the RF switch (2) to the channel evaluation mode, set the RF transmission system (3), and according to specific task requirements, set the detection mode of the channel evaluation equipment (5) to the fixed frequency point detection mode or the frequency sweep detection mode;

[0010] Step 4, conduct detection and conduct channel evaluation;

[0011] Among them, the process of channel evaluation includes data processing, and the data processing includes:

[0012] S441. Return scatter ionogram interpretation;

[0013] S442. Ionospheric inversion;

[0014] S443. Regional ionospheric reconstruction;

[0015] S444. Coordinate transformation. Since the group path P' of signal propagation is actually obtained in return scatter detection, to obtain the ground distance D of the detected object, to achieve this P-D transformation, the return scatter energy estimation formula is as follows:

[0016]

[0017] Among them, the extended ground scatter cross-section

[0018]

[0019] Among them, σ 0 (α) is the ground scatter coefficient, which is related to the incident angle α, c is the speed of light, δ t is the pulse width, D is the ground distance, θ is the direction angle of the antenna, A is the area of the irradiated ground; f is the operating frequency; L α is the ionospheric absorption loss, which is related to α and f, L p is the system transmission loss; R is the skywave path length, which is related to the ionospheric reflection height, G r , G t are the gains of the receiving antenna and the transmitting antenna, which are related to α and f, and the transmitting power P of the channel evaluation device t ;

[0020] According to the return scatter energy estimation formula, given the return scatter emission average power, skywave path length, transmitting antenna gain, received power, and operating frequency, calculate the absorption loss, system transmission loss, and path loss. The three together are called the total loss L ∑ ;

[0021] For return scatter, since the path scatter is two-way, assuming the group path is the same, therefore, the two-way free space transmission loss is twice that of the one-way free space transmission loss. The radio wave passes through the ionosphere twice, so the ionospheric absorption needs to be calculated twice, and the system transmission loss also passes through twice:

[0022]

[0023] Channel assessment is the round-trip loss that is returned. The radiation of the broadcast system is the one-way loss. To obtain the total one-way loss, take half of all the total losses. This loss is a function of distance and needs to be divided by the receiving antenna gain. Combining the estimated backscattered energy received, estimate the power S of the detection signal reaching the ground and sea surface of the target area. 0 (α):

[0024]

[0025] Substitute the power P of the broadcast transmitter radio to obtain the radiation field strength S of the broadcast signal in the service area. radio (α), determine the coverage effect based on the radiation field strength:

[0026]

[0027] As a further optimized technical solution, when the fixed frequency point detection mode is selected, the processes of step 4, detection and channel assessment are as follows:

[0028] S41, in the channel assessment device (5), set the working parameters of the channel assessment, and control the automatic tuning unit 31 to match the working frequency point;

[0029] S42, after confirming that the RF link status is normal, perform fixed frequency point detection and receive the echo signal;

[0030] S43, process the received echo signal. The processing methods are single frequency point signal processing and Doppler processing, respectively realizing pulse compression and time accumulation:

[0031] S44, generate the ionogram and then perform the data processing.

[0032] As a further optimized technical solution, the backscattered ionogram interpretation in S441 includes successively performing: interference suppression signal recognition, image preprocessing, echo energy calculation, leading edge extraction, pattern recognition, MOF extraction, so as to obtain the characteristic parameter data of the ionogram;

[0033] Interference suppression signal recognition includes recognizing and removing co-frequency interference and performing full-noise data judgment and recognition;

[0034] Image preprocessing is mainly divided into noise removal and signal compensation after noise removal. Noise removal includes channel noise mean denoising, clearing range side lobes, removing random noise, clearing meteor trails, clearing direct wave signals. Signal compensation includes distance correlation compensation signal, linear compensation of co-frequency interference channels, and eight-neighborhood method compensation signal;

[0035] Echo energy calculation is to calculate the energy mean of different frequencies and different distance segments to obtain the echo energy;

[0036] Frontier extraction refers to sequentially extracting the bottom frontier and the F-layer frontier for the echo energy. Among them, extracting the bottom frontier includes initially extracting the bottom frontier, removing frontier singularities, and performing least-squares fitting on the frontier. Extracting the F-layer frontier includes segmentally extracting the F-layer frontier, correcting the frontier value, gradient-weighted extraction of the frontier, and adaptive-order fitting of the frontier;

[0037] Pattern recognition refers to determining the number of patterns and the signal propagation mode for the echo energy after frontier extraction;

[0038] MOF extraction includes calculating the MOF according to the frontier for the distance segment below the frontier cut-off point and extracting the MOF by finding the right boundary for the distance segment above the frontier cut-off point.

[0039] As a further optimized technical solution, the ionospheric inversion in S442 includes: performing ionospheric inversion based on the detection and processing results of the receiving channel;

[0040] The regional ionospheric reconstruction in S443 includes: reconstructing the ionospheric electron concentration profile, obtaining the two-dimensional electron concentration profile in the azimuth direction through the reconstruction technology, and performing interpolation calculation on the two-dimensional electron concentration profile.

[0041] As a further optimized technical solution, when the swept-frequency detection mode is selected, the processes in steps 4, detection, and channel evaluation are as follows:

[0042] S45, set the working parameters for channel evaluation;

[0043] S46, send down the starting frequency working parameters to control the automatic tuning unit to match the working frequency point;

[0044] S47, perform detection after confirming that the RF link status is normal and receive the echo signal;

[0045] S48, after completing the detection of the starting frequency, send down the next frequency parameter according to the frequency step to control the automatic tuning unit to match the working frequency point;

[0046] S49, perform detection after confirming that the RF link status is normal and receive the echo signal; and so on until the detection of the end frequency is completed;

[0047] S50, for the detection of each frequency, repeat the processes of steps S43 to S44 for processing the received echo signal and data processing.

[0048] As a further optimized technical solution, it further includes step 5, which is plotted by using a method where the horizontal axis is frequency, the vertical axis is distance, and the echo signal intensities at different frequencies and distances are marked with different colors. The signal intensities are represented by different levels of colors from weak to strong, namely blue - green - yellow - red.

[0049] As a further optimized technical solution, the single-frequency signal processing: Pulse compression is implemented through correlation processing. Taking the one-transmission-one-reception mode at equal intervals as an example, the receiver samples an echo every t b After collecting an echo sample, after processing, a column of impulse response data vectors of the ionospheric channel represented by complex numbers is obtained for each received cycle of echo samples. The impulse response data vectors obtained from multiple consecutive detections are sorted by time to form a complex matrix, and this matrix is the ionospheric double-time response matrix;

[0050] Doppler processing: The amplitudes of adjacent rows in the same column of the double-time response matrix are the same, and there is a phase difference. This phase difference only contains Doppler information. Fourier transform is performed on the signals of each column of the double-time response matrix to obtain the corresponding scattering function matrix.

[0051] The present invention also provides a system adopting the short-wave broadcast antenna channel evaluation and prediction method described in any one of the above, including a short-wave broadcast transmitter (1), a radio frequency switch (2), a radio frequency transmission system (3), an antenna feeder (4), and a channel evaluation device (5). Among them, the short-wave broadcast transmitter (1), the radio frequency transmission system (3), and the channel evaluation device (5) are all connected to the radio frequency switch (2), and the output end of the radio frequency transmission system (3) is connected to the antenna feeder (4).

[0052] As a further optimized technical solution, the radio frequency transmission system (3) includes an automatic tuning unit (31), a balun (32), a program switch (33), and a phase shifter switch (34) connected in sequence. Among them, the radio frequency switch (2) is connected to the automatic tuning unit (31), and the output end of the phase shifter switch (34) is connected to the antenna feeder (4).

[0053] As a further optimized technical solution, the channel evaluation device (5) adopts a high-performance general bus control computer and receives information using network and serial port data interfaces.

[0054] The advantages of the present invention are as follows:

[0055] A proactive ionospheric sounding method is proposed. By using the existing radio frequency transmission and antenna feeder equipment of short-wave broadcasts and adopting a time-sharing working mode with the broadcast transmission, ionospheric sounding, information processing, evaluation, and display are carried out to realize the evaluation of the coverage range, field strength, and ionospheric state of short-wave broadcasts, timely obtain the ionospheric channel state from the short-wave broadcast transmitting station to the service area, visually predict the field strength coverage and transmission distance of the radio station, more accurately and intuitively understand the short-wave broadcast field strength coverage in the target area, and provide guidance for optimizing the working parameters of the broadcast system. The prediction accuracy of the short-wave broadcast coverage effect is improved,

[0056] Adopting the active ionospheric return detection method also provides support for the optimal selection of broadcast frequencies, transmission power control, antenna mode selection, and broadcast effect evaluation. Description of the Drawings

[0057] Figure 1 It is the schematic composition diagram of the shortwave broadcast antenna channel evaluation system according to the embodiment of the present invention;

[0058] Figure 2 It is the flowchart of the shortwave broadcast antenna channel evaluation method according to the embodiment of the present invention;

[0059] Figure 3 It is the flowchart of the evaluation process of the fixed frequency point detection mode in the embodiment of the present invention;

[0060] Figure 4 is Figure 3 the specific flowchart of data processing in

[0061] Figure 5 It is the flowchart of the evaluation process of the frequency sweep detection mode in the embodiment of the present invention. Detailed Embodiments

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0063] As Figure 1 shown, a shortwave broadcast antenna channel evaluation and prediction system of the present invention includes a shortwave broadcast transmitter 1, a radio frequency switch 2, a radio frequency transmission system 3, an antenna feeder 4, and a channel evaluation device 5. Among them, the shortwave broadcast transmitter 1, the radio frequency transmission system 3, and the channel evaluation device 5 are all connected to the radio frequency switch 2, and the output end of the radio frequency transmission system 3 is connected to the antenna feeder 4. The radio frequency transmission system 3 includes a sequentially connected automatic tuning unit 31, a balun 32, a program switch 33, and a phase shifter switch 34. Among them, the radio frequency switch 2 is connected to the automatic tuning unit 31, and the output end of the phase shifter switch 34 is connected to the antenna feeder 4.

[0064] The channel evaluation device 5 adopts a high-performance general bus control computer, and receives information of relevant devices such as the antenna rotation system, the program switch 33, and the phase shifter switch 34 through data interfaces such as the network and serial port, which is used for the identification of detection data and the display of detection results. The device realizes the functions of transmitting standing wave warning and standing wave protection in a software and hardware interlocking manner, as well as the state interlocking protection functions with the RF switch 2, the program switch 33, etc. When the RF status is not confirmed to be available, the user operation is automatically blocked and corresponding status prompts are given, and it is saved in the form of a log file.

[0065] This system multiplexes the broadcast system for signal transmission and reception.

[0066] As Figure 2 shown, a shortwave broadcast antenna channel evaluation and prediction method provided by the present invention includes the following steps:

[0067] Step 1, access the device: Connect the channel evaluation device 5 to the broadcast system, and form an active return channel evaluation system with the shortwave broadcast transmitter 1, the RF transmission system 3, and the antenna feeder 4 of the broadcast system;

[0068] Step 2, rotate the antenna to the specified azimuth: According to the area where channel evaluation is required, rotate the antenna array of the broadcast system to the specified azimuth through the antenna rotation device;

[0069] Step 3, set the device status: Set the RF switch 2 to the channel evaluation mode, set the RF transmission system 3 (balun 32, program switch 33, and phase shifter switch 34), and according to specific task requirements, set the detection mode of the channel evaluation device 5 to the fixed frequency point detection mode or the frequency sweep detection mode. When it is necessary to determine the coverage effect of the fixed frequency point, the fixed frequency point detection mode is adopted; when it is not certain which frequency point has a better coverage effect, the frequency sweep detection mode is adopted to select the working frequency point by optimizing the frequency sweep detection results;

[0070] Step 4, perform detection and channel evaluation.

[0071] When the fixed frequency point detection mode is selected, the detection and channel evaluation process is as follows:

[0072] S41, in the channel evaluation device 5, set working parameters such as the frequency value, pulse width, signal bandwidth, repetition period, number of pulses, radiation power, etc. of channel evaluation, and control the automatic tuning unit 31 to match the working frequency point;

[0073] S42, perform fixed frequency point detection after confirming that the RF link status is normal, and receive the echo signal;

[0074] S43. Process the received echo signals. The processing methods are single-frequency signal processing and Doppler processing, which respectively achieve pulse compression and time integration:

[0075] Single-frequency signal processing: Pulse compression is implemented through correlation processing. Taking the equal-interval one-transmission-and-one-reception mode as an example, the receiver samples an echo every t b (the width of the transmitted symbol). After receiving one cycle of echo samples, a column vector of impulse response data of the ionospheric channel represented by complex numbers can be obtained through correlation processing. The impulse response data vectors obtained from multiple consecutive detections are sorted by time to form a complex matrix, which is the ionospheric two-time response matrix;

[0076] Doppler processing: The amplitudes of adjacent rows in the same column of the two-time response matrix are the same, and there is a phase difference. This phase difference only contains Doppler information. Perform Fourier transform on the signals of each column of the two-time response matrix to obtain the corresponding scattering function matrix;

[0077] The above single-frequency signal processing and Doppler processing methods are existing and mature signal processing technologies, which will not be elaborated here.

[0078] S44. Generate an ionogram and then perform data processing. The data processing includes the interpretation of the backscatter ionogram S441, ionospheric inversion S442, regional ionospheric reconstruction S443, and coordinate transformation S444, to obtain information such as the coverage area and field strength calculation results, regional ionospheric inversion results, etc., so as to realize the evaluation and auxiliary decision-making of the shortwave broadcast channel.

[0079] The mechanism of backscatter sounding: The channel evaluation device 5 transmits shortwave signals obliquely into the air at a certain elevation angle through the broadcast system. The signals are reflected by the ionosphere and propagated to the distant ground and sea surfaces. The unevenness and electrical property inhomogeneity of the ground and sea surfaces cause the radio signals to scatter in all directions, and a part of the radio waves will be reflected back to the transmitter along the original path through the ionosphere again and be received.

[0080] The distance of backscatter sounding is the group delay of radio wave propagation, that is, the time for the electromagnetic wave to be transmitted from the transmitter, refracted and reflected by the ionosphere to reach the ground, scattered by the ground, and then refracted and reflected by the ionosphere to reach the receiver. Multiplying this propagation time by the speed of electromagnetic wave propagation in free space gives the so-called group path. Therefore, what is actually obtained by backscatter sounding is the group path of radio wave propagation rather than the real ground distance (great circle distance), and it is necessary to perform the conversion between group delay and ground distance, which is usually called P-D transformation. After P-D transformation, a backscatter ionogram of frequency-ground distance-echo amplitude is formed, and data processing, parameter extraction, ionospheric inversion, regional reconstruction, and propagation field strength prediction are performed on the ionogram.

[0081] Among them, the interpretation of the scattered ionization diagram returned by S441 includes the following steps carried out in sequence: interference suppression signal recognition, image preprocessing, echo energy calculation, front extraction, pattern recognition, and MOF extraction, so as to obtain the characteristic parameter data of the ionization diagram.

[0082] Interference suppression signal recognition includes identifying and removing co-frequency interference and performing full-noise data judgment and recognition.

[0083] Image preprocessing is mainly divided into noise removal and signal compensation after noise removal. Noise removal includes channel noise mean denoising, removing range side lobes, removing random noise, removing meteor trails, and removing direct wave signals. Signal compensation includes distance correlation compensation signal, linear compensation of co-frequency interference channels, and octal neighborhood method compensation signal.

[0084] Echo energy calculation is to calculate the energy mean values of different frequencies and different distance segments to obtain the echo energy.

[0085] Front extraction refers to sequentially extracting the bottom front and F-layer front for the echo energy. Among them, extracting the bottom front includes initially extracting the bottom front, removing front singular points, and least-squares fitting of the front. Extracting the F-layer front includes segmentally extracting the F-layer front, correcting the front value, gradient-weighted extraction of the front, and adaptive order fitting of the front.

[0086] Pattern recognition refers to judging the number of patterns and determining the signal propagation mode for the echo energy after front extraction.

[0087] MOF (Maximum Observable Frequency) extraction includes calculating MOF according to the front for the distance segment below the front cut-off point and extracting MOF by finding the right boundary for the distance segment above the front cut-off point.

[0088] Ionospheric inversion in S442 includes: performing ionospheric inversion according to the detection and processing results of the receiving channel.

[0089] Regional ionospheric reconstruction in S443 includes: reconstructing the ionospheric electron concentration profile. Through the reconstruction technology, a two-dimensional electron concentration profile in the azimuth direction is obtained. To obtain a three-dimensional electron concentration profile, interpolation calculation needs to be performed on the two-dimensional electron concentration profile. In this project, linear interpolation operation is adopted.

[0090] Coordinate transformation in S444: Since the group path P' of signal propagation is actually obtained in the backscatter detection, and people are more concerned about the ground distance D of the detected object. To achieve this P-D transformation, the short-wave three-dimensional ray tracing technology is used to form a complete ray trace and find the transformation relationship between the group delay of radio wave propagation and the ground distance. Using the International Reference Ionosphere (IRI) model as the background ionosphere, this transformation is carried out by combining the IRI model and the detection results of the backscatter detection equipment itself, including:

[0091] In engineering, the method for estimating the returned scattered energy is as follows:

[0092]

[0093] Among them, the extended ground scattering cross-section

[0094]

[0095] Among them, σ 0 (α) is the ground scattering coefficient, which is related to the incident angle α.

[0096] c is the speed of light, δ t is the pulse width, D is the ground distance, θ is the direction angle of the antenna, A is the area of the illuminated ground; f is the operating frequency; L α is the ionospheric absorption loss, which is related to α and f, L p is the system transmission loss; R is the skywave path length, which is related to the ionospheric reflection height, G r , G t are the gains of the receiving antenna and the transmitting antenna, which are related to α and f, and the transmitting power P of the channel evaluation device t .

[0097] According to the formula for estimating the returned scattered energy, given the average power of the returned scattered emission, the skywave path length, the transmitting antenna gain, the received power, and the operating frequency, the absorption loss, the system transmission loss, and the path loss can be calculated. The three together are called the total loss L ∑ .

[0098] For the returned scatter, since the path scatter is two-way and assuming the group path is the same, therefore, the two-way free space transmission loss is twice that of the one-way free space transmission loss; the radio wave passes through the ionosphere twice, so the ionospheric absorption needs to be calculated twice; the system transmission loss also passes through twice.

[0099]

[0100] The channel evaluation is the two-way loss of the return type, and the broadcast system radiation is the one-way loss. To obtain the one-way total loss, take half of all the total losses This loss is a function of the distance and needs to be divided by the receiving antenna gain. Combining with the estimated returned scattered energy received, the power S 0 (α) of the detection signal reaching the ground and sea surface of the target area can be predicted:

[0101]

[0102] Substitute the power P radio of the broadcast transmitter, and the radiation field strength S of the broadcast signal in the service area can be obtained radio(α) Determine the coverage effect according to the radiation field strength:

[0103]

[0104] When the frequency sweep detection mode is selected, the detection and channel evaluation process is as follows:

[0105] S45. Set the working parameters such as the start frequency, end frequency, frequency step, pulse width, signal bandwidth, repetition period, number of pulses, radiation power, etc. for channel evaluation;

[0106] S46. Send down the start frequency working parameters to control the automatic tuning unit to match the working frequency point;

[0107] S47. After confirming that the RF link status is normal, perform detection and receive the echo signal;

[0108] S48. After completing the detection at the start frequency, send down the next frequency parameter according to the frequency step to control the automatic tuning unit to match the working frequency point;

[0109] S49. After confirming that the RF link status is normal, perform detection and receive the echo signal; and so on until the detection at the end frequency is completed;

[0110] S50. For the detection at each frequency, repeat the process of processing the received echo signal and data processing in steps S43 to S44. The amplitude values of the echoes at different group distances can be extracted from the scattering function matrix detected at each frequency point. These data are arranged in ascending order of frequency points to obtain the echo amplitude matrix. According to this matrix, a frequency sweep ionization diagram with the horizontal axis representing the working frequency and the vertical axis representing the group delay distance can be drawn, so as to obtain the field strength values of broadcast signals at different frequency points and different distances within the frequency sweep range;

[0111] Step 5. Draw using the method of using the horizontal axis as the frequency and the vertical axis as the distance, and different echo signal intensities at different frequencies and distances are marked with different colors. The signal intensities are represented by different levels of colors from weak to strong, namely blue - green - yellow - red.

Claims

1. A shortwave broadcast antenna channel estimation and prediction method, characterized in that: The steps include: Step 1, access equipment: connect the channel assessment device (5) to the broadcasting system, wherein the shortwave broadcasting transmitter (1), the radio frequency transmission system (3) and the channel assessment device (5) are all connected to the radio frequency switching switch (2), and the output end of the radio frequency transmission system (3) is connected to the antenna feed line (4); Step 2: Rotate the antenna to a specified position: Rotate the antenna array of the broadcasting system to a specified position by using an antenna rotation device according to the area where channel assessment needs to be performed; Step 3, setting the device status: setting the radio frequency switch (2) to the channel assessment mode, setting the radio frequency transmission system (3), and setting the detection mode of the channel assessment device (5) to a fixed frequency detection mode or a sweep frequency detection mode according to specific task requirements; Step 4: perform detection and channel assessment; The channel assessment includes a data processing process, and the data processing includes: S441, backscatter ionization pattern interpretation; S442, ionospheric inversion; S443, Regional ionospheric reconstruction; S444, coordinate transformation, since the backscatter detection actually obtains the group path P' of signal propagation, in order to obtain the ground distance D of the detected object, to achieve this PD transformation, the backscatter energy estimation formula is as follows: Among them, the extended ground scattering cross section Among them, σ0(α) is the ground scattering coefficient, which is related to the incident angle α, c is the speed of light, δ t is the pulse width, D is the ground distance, θ is the direction angle of the antenna, A is the area of ​​the ground illuminated; f is the operating frequency; L α is the ionospheric absorption loss, which is related to α, f, and L p is the system transmission loss; R is the sky wave path length, which is related to the ionospheric reflection height, G r , G t is the gain of the receiving antenna and the transmitting antenna, which is related to α, f, and the transmitting power P of the channel assessment device t ; According to the backscatter energy estimation formula, the average backscatter transmission power, sky wave path length, transmitting antenna gain, receiving power, and operating frequency are known. The absorption loss, system transmission loss, and path loss are calculated. The three together are called the total loss L ∑ ; For return scattering, since the path scattering is two-way, assuming that the group paths are the same, the two-way free space transmission loss is twice the one-way free space transmission loss. The radio wave passes through the ionosphere twice, so the ionospheric absorption needs to be calculated twice, and the system transmission loss also passes through twice: Channel evaluation is the return two-way loss, and broadcast system radiation is the one-way loss. To obtain the total one-way loss, take half of the total loss. This loss is a function of distance and needs to be divided by the receiving antenna gain. Combined with the received backscatter energy estimate, the power S0(α) of the detection signal reaching the sea surface in the target area is estimated: The power of the broadcast transmitter P radio Bring it in, that is, obtain the radiation field strength S of the broadcast signal in the service area radio (α), the coverage effect is determined according to the radiation field strength:

2. A shortwave broadcast antenna channel estimation prediction method according to claim 1, characterized in that: When the fixed frequency detection mode is selected, the detection and channel assessment process in step 4 is as follows: S41, in the channel assessment device (5), setting the working parameters of the channel assessment and controlling the automatic tuning unit 31 to match the working frequency point; S42, after confirming that the radio frequency link is in a normal state, a fixed frequency point detection is performed and an echo signal is received; S43, processing the received echo signal by single frequency signal processing and Doppler processing, respectively realizing pulse pressure and time accumulation: S44, performing the data processing after the ionization diagram is generated.

3. A shortwave broadcast antenna channel estimation prediction method according to claim 1, characterized in that: The S441 backscatter ionization image interpretation includes the following steps: interference suppression signal recognition, image preprocessing, echo energy calculation, front extraction, pattern recognition, and MOF extraction, so as to obtain characteristic parameter data of the ionization image; Interference suppression signal identification includes identifying and removing co-frequency interference and performing full noise data judgment and identification; Image preprocessing is mainly divided into noise removal and signal compensation after noise removal. Noise removal includes channel noise mean denoising, range sidelobe removal, random noise removal, meteor trail removal, and direct wave signal removal. Signal compensation includes range correlation compensation signal, linear compensation for co-frequency interference channels, and eight-neighborhood compensation signal. The echo energy calculation is to calculate the energy average of different frequencies and distance segments to obtain the echo energy; Frontier extraction refers to extracting the bottom layer frontier and F layer frontier in sequence according to the echo energy, wherein the bottom layer frontier extraction includes preliminary extraction of the bottom layer frontier, removal of frontier singular points, and least squares fitting of the frontier, and the F layer frontier extraction includes segmented extraction of the F layer frontier, correction of the frontier value, gradient weighted extraction of the frontier, and adaptive order fitting of the frontier; Pattern recognition refers to judging the number of patterns and determining the signal propagation mode based on the echo energy after front extraction; MOF extraction includes calculating MOF based on the frontier for the distance segment below the frontier cutoff point and extracting MOF by finding the right boundary for the distance segment above the frontier cutoff point.

4. A shortwave broadcast antenna channel estimation prediction method according to claim 3, characterized in that: S442 ionospheric inversion includes: performing ionospheric inversion according to the receiving channel detection processing result; The S443 regional ionosphere reconstruction includes: reconstructing the ionosphere electron concentration profile, obtaining the azimuthal two-dimensional electron concentration profile through reconstruction technology, and performing interpolation calculation on the two-dimensional electron concentration profile.

5. The shortwave broadcast antenna channel estimation prediction method according to claim 2, characterized in that: When the sweep detection mode is selected, the detection and channel assessment process in step 4 is as follows: S45, setting working parameters of channel assessment; S46, sending the starting frequency working parameters to control the automatic tuning unit to match the working frequency point; S47, after confirming that the radio frequency link state is normal, detection is performed again and the echo signal is received; S48, after completing the starting frequency detection, the next frequency parameter is sent according to the frequency step to control the automatic tuning unit to match the working frequency point; S49, after confirming that the radio frequency link is in a normal state, detection is performed again and the echo signal is received; this is done until the detection is completed at the end frequency; S50, for each frequency detection, repeat the process of processing the received echo signal and data processing from step S43 to S44.

6. A shortwave broadcast antenna channel estimation prediction method according to claim 1, characterized in that: The method also includes step 5, wherein the horizontal axis is the frequency and the vertical axis is the distance, and the echo signal strength at different frequencies and distances is plotted by marking with different colors, and the signal strength is represented from weak to strong by different levels of blue, green, yellow and red.

7. A shortwave broadcast antenna channel estimation and prediction method according to claim 1, characterized in that: The single frequency signal processing: pulse compression is performed through correlation processing. Taking the equal interval one transmission and one reception mode as an example, the receiver transmits every t b Collect an echo sample. After receiving one cycle of echo samples, a column of complex-numbered impulse response data vectors of the ionospheric channel is obtained after processing. Multiple impulse response data vectors obtained by continuous detection are sorted in time to form a complex matrix, which is the ionospheric dual-time response matrix. Doppler processing: The amplitudes of adjacent rows in the same column of the dual-time response matrix are the same, and there is a phase difference. This phase difference only contains Doppler information. Fourier transform is performed on each column signal of the dual-time response matrix to obtain the corresponding scattering function matrix.

8. A system using the shortwave broadcast antenna channel estimation and prediction method according to any one of claims 1 to 7, characterized in that: The invention comprises a shortwave broadcast transmitter (1), a radio frequency switching switch (2), a radio frequency transmission system (3), an antenna feed line (4) and a channel evaluation device (5), wherein the shortwave broadcast transmitter (1), the radio frequency transmission system (3) and the channel evaluation device (5) are all connected to the radio frequency switching switch (2), and the output end of the radio frequency transmission system (3) is connected to the antenna feed line (4).

9. The system for shortwave broadcast antenna channel estimation and prediction according to claim 8, characterized in that: The radio frequency transmission system (3) comprises an automatic tuning unit (31), a balanced-unbalanced converter (32), a program switch (33), and a phase shift switch (34) which are connected in sequence, wherein the radio frequency switching switch (2) is connected to the automatic tuning unit (31), and the output end of the phase shift switch (34) is connected to the antenna feed line (4).

10. The system for shortwave broadcast antenna channel estimation and prediction according to claim 8, characterized in that: The channel assessment device (5) adopts a high-performance universal bus control computer and receives information via a network and a serial port data interface.

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