Method and system for interference rejection transmission of data links for high-speed aircraft

Abstract

This invention relates to the field of data link anti-interference transmission technology, specifically to a method and system for anti-interference transmission of data links for high-speed aircraft. The method involves transforming the digital baseband received signal of the high-speed aircraft to obtain a two-dimensional time-frequency energy distribution map, identifying the interfering signal, and extracting its received power value. It then performs spatial spectrum estimation on the interfering signal to obtain its direction of arrival (AOA), and calculates the estimated distance of the interfering source by combining this with terrain elevation data. The method also calculates the AOA and transmission distance of the useful signal. Based on the estimated distance of the interfering source, the transmission distance of the useful signal, and the received power value, it calculates the current interference-to-signal ratio (ISR) estimate. Finally, it processes the digital baseband received signal to obtain the current transmission frame bit error rate (BER). Based on the BER and the current IRR estimate, it adjusts the spreading factor and coding rate of the next transmission frame. This method improves the anti-interference capability of data link transmission for high-speed aircraft in low-altitude flight scenarios such as mountainous valleys.

Description

Technical Field

[0001] This invention relates to the field of data link anti-interference transmission technology, specifically to a method and system for anti-interference transmission of data links for high-speed aircraft. Background Technology

[0002] In scenarios where high-speed aircraft fly at low altitudes over mountainous and canyon terrain, their data link communication faces extremely severe challenges. The target often leverages the terrain's high altitude advantage to deploy strong interference sources around the high-speed aircraft's flight path, implementing high-power interference at close range. Simultaneously, the distance between the user's control platform and the high-speed aircraft is vast, requiring long-distance signal transmission for control and information exchange. This creates an asymmetrical situation of "strong interference at close range and weak signal at long range," resulting in an extremely harsh electromagnetic environment for data link communication.

[0003] In such extreme electromagnetic environments, traditional anti-jamming methods struggle to effectively suppress strong, close-range interference. Strong interference can severely overwhelm useful signals, making it difficult for the receiver to accurately extract and identify useful information. This can lead to data link communication interruptions or a significant increase in error rates, compromising reliable data transmission. This not only affects information exchange between the high-speed aircraft and its control platform, reducing the accuracy and timeliness of mission execution, but may also cause mission failure due to the inability to receive timely and accurate instructions.

[0004] Therefore, there is an urgent need for a reliable data link transmission mechanism that can enable high-speed aircraft to fly at low altitudes in mountainous and canyon environments, so as to ensure normal communication of high-speed aircraft in complex electromagnetic environments. Summary of the Invention

[0005] (1) Technical problems to be solved

[0006] The purpose of this invention is to provide a method and system for anti-interference transmission of data links for high-speed aircraft, in order to solve the problem of unreliable data link transmission caused by the asymmetric pattern formed when high-speed aircraft fly at low altitudes in mountainous and canyon environments, where the target uses the terrain's high-altitude advantage to carry out close-range strong interference, while the control platform's signal needs to be transmitted over long distances.

[0007] (2) Technical solution

[0008] To achieve the above objectives, in one aspect, the present invention provides a method for anti-interference transmission of data links in high-speed aircraft, the method comprising:

[0009] S1. Acquire the radio frequency signal in the current time slot of the high-speed aircraft and convert it to obtain the digital baseband received signal; acquire the current three-dimensional position coordinates and three-dimensional velocity vector of the high-speed aircraft, the three-dimensional position coordinates of the control platform, and the terrain elevation data within the flight corridor.

[0010] S2. Perform time-frequency transformation on the digital baseband received signal to obtain a time-frequency two-dimensional energy distribution map. Identify concentrated energy regions in the time-frequency two-dimensional energy distribution map whose energy values ​​exceed a preset multiple of the background noise as interference signals, and extract the received power value of the interference signals.

[0011] S3. Based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft, determine the surrounding mountain area above the current flight altitude as the high elevation angle search constraint area for the interference source; within the high elevation angle search constraint area for the interference source, perform spatial spectrum estimation on the interference signal to obtain the direction of arrival angle of the interference signal, and calculate the estimated distance of the interference source in combination with the terrain elevation data; calculate the direction of arrival angle and transmission distance of the useful signal based on the current three-dimensional position coordinates of the high-speed aircraft and the three-dimensional position coordinates of the control platform; calculate the current interference-to-signal ratio estimate based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal.

[0012] S4. Adjust the beam weight of the airborne receiving antenna array according to the arrival angle of the interference signal and the arrival angle of the useful signal, and perform spatial filtering on the digital baseband received signal according to the beam weight to obtain a first intermediate signal; calculate the Doppler frequency shift value of the useful signal according to the three-dimensional velocity vector of the high-speed aircraft and the arrival angle of the useful signal, and perform bandpass filtering on the first intermediate signal with the Doppler frequency shift value of the useful signal as the center frequency to obtain a second intermediate signal; obtain the current transmission frame bit error rate by data processing on the second intermediate signal, and adjust the spreading factor and coding rate of the next transmission frame according to the current transmission frame bit error rate and the current interference-to-signal ratio estimate.

[0013] Furthermore, the method for determining the surrounding mountainous areas above the current flight altitude as the high-angle search constraint region for interference sources based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft includes:

[0014] Centered on the current three-dimensional position coordinates of the high-speed aircraft, the terrain search range is determined according to the maximum detection range of the airborne receiving antenna array; within the terrain search range, the terrain elevation data within the flight corridor is sampled in a grid to obtain a set of terrain elevation sampling points, and each sampling point in the set of terrain elevation sampling points contains horizontal position coordinates and elevation values.

[0015] The elevation values ​​of each sampling point in the terrain elevation sampling point set are compared with the height component in the current three-dimensional position coordinates of the high-speed aircraft, and sampling points with elevation values ​​greater than the height component are selected to form a candidate occlusion point set.

[0016] Based on the current three-dimensional position coordinates of the high-speed aircraft and the horizontal position coordinates and elevation values ​​of each candidate shielding point in the candidate shielding point set, the azimuth and elevation angles of each candidate shielding point relative to the high-speed aircraft are calculated to obtain the candidate shielding point angle set; adjacent azimuth and elevation angles in the candidate shielding point angle set are merged into a continuous angle interval, and the continuous angle interval is determined as the high elevation angle search constraint region of the interference source.

[0017] Furthermore, the method for calculating the azimuth and elevation angles of each candidate shielding point relative to the high-speed aircraft based on the current three-dimensional position coordinates of the high-speed aircraft and the horizontal position coordinates and elevation values ​​of each candidate shielding point in the candidate shielding point set includes:

[0018] The horizontal position difference vector is calculated based on the horizontal position coordinates of each candidate shielding point and the horizontal position component in the current three-dimensional position coordinates of the high-speed aircraft. The horizontal distance and azimuth of each candidate shielding point relative to the high-speed aircraft are calculated based on the horizontal position difference vector. The altitude difference is calculated based on the elevation value of each candidate shielding point and the altitude component in the current three-dimensional position coordinates of the high-speed aircraft. The elevation angle of each candidate shielding point relative to the high-speed aircraft is calculated based on the altitude difference and the horizontal distance. The azimuth and elevation angles corresponding to each candidate shielding point are combined into angle pairs, and all angle pairs constitute the angle set of candidate shielding points.

[0019] Furthermore, the method of obtaining the arrival direction angle of the interference signal by spatial spectrum estimation of the interference signal within the high elevation angle search constraint area of ​​the interference source, and calculating the estimated distance of the interference source by combining the terrain elevation data includes:

[0020] The azimuth and elevation search ranges for spatial spectrum estimation are determined based on the high elevation angle search constraint region of the interference source. An angle search grid is constructed within the azimuth and elevation search ranges. A steering vector matrix is ​​constructed based on the element positions of the airborne receiving antenna array and the azimuth and elevation angles corresponding to each grid point in the angle search grid.

[0021] The received signal covariance matrix is ​​calculated based on the received digital baseband signal; the spatial spectral energy distribution is obtained by calculating the spatial spectral function value corresponding to each grid point based on the received signal covariance matrix and the steering vector matrix; energy peak points are searched in the spatial spectral energy distribution, and the azimuth and elevation angles corresponding to the energy peak points are determined as the arrival direction angles of the interference signal; a spatial ray is constructed along the direction determined by the arrival direction angle of the interference signal, starting from the current three-dimensional position coordinates of the high-speed aircraft; the intersection point of the spatial ray and the terrain surface represented by the terrain elevation data within the flight path corridor is calculated, and the distance between the current three-dimensional position coordinates of the high-speed aircraft and the intersection point is determined as the estimated distance of the interference source.

[0022] Furthermore, the method for constructing the steering vector matrix based on the azimuth and elevation angles corresponding to each grid point in the search grid according to the element positions and angles of the airborne receiving antenna array includes:

[0023] The process involves: obtaining the three-dimensional position coordinates of each element in the airborne receiving antenna array relative to the array reference point to obtain the element position set; traversing each grid point in the angle search grid and calculating the signal arrival unit vector corresponding to the current grid point based on the azimuth and elevation angles; for each element in the element position set, calculating the dot product of the current element position coordinates and the signal arrival unit vector to obtain the spatial phase delay of the current element relative to the array reference point; calculating the phase factor corresponding to the current element based on the spatial phase delay and the carrier wavelength of the received signal; arranging the phase factors corresponding to all elements in the element order to form the steering vector corresponding to the current grid point; and traversing all grid points in the completed angle search grid and arranging the steering vectors corresponding to all grid points to form a steering vector matrix.

[0024] Furthermore, the method for obtaining the spatial spectral energy distribution by calculating the spatial spectral function value corresponding to each grid point based on the received signal covariance matrix and steering vector matrix includes:

[0025] The received signal covariance matrix is ​​decomposed into eigenvalue set and corresponding eigenvector set. The eigenvalue set is sorted in descending order of numerical value. The eigenvectors corresponding to the remaining eigenvalues ​​after descending sorting (excluding the first preset number of eigenvalues ​​from the signal source) form a noise subspace matrix. Each grid point in the angle search grid is traversed to extract the steering vector corresponding to each grid point in the steering vector matrix. The projection energy of the steering vector corresponding to each grid point and the noise subspace matrix is ​​calculated. The reciprocal of the projection energy is used as the spatial spectrum function value corresponding to the grid point. The spatial spectrum function values ​​corresponding to all grid points are arranged according to azimuth and elevation angles to form a spatial spectrum energy distribution.

[0026] Furthermore, the method for calculating the current interference-to-signal ratio estimate based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal includes:

[0027] The path loss index under the current propagation environment is calculated based on the received power value of the interference signal and the estimated distance of the interference source; the path transmission loss value of the useful signal is calculated based on the path loss index and the transmission distance of the useful signal; the preset transmit power and transmit antenna gain of the control platform are obtained, and the equivalent omnidirectional radiated power of the control platform is calculated based on the preset transmit power and transmit antenna gain.

[0028] The receiver gain of the airborne receiving antenna array along the direction of arrival of the useful signal is obtained. Based on the equivalent isotropic radiated power of the self-control platform, the path transmission loss of the useful signal, and the receiver gain, the estimated value of the received power of the useful signal is calculated. The ratio of the received power of the interference signal to the estimated value of the received power of the useful signal is determined as the current interference-to-signal ratio estimate.

[0029] Further, the method of obtaining the current transmission frame bit error rate by data processing of the second intermediate signal, and adjusting the spreading factor and coding rate of the next transmission frame based on the current transmission frame bit error rate and the current interference-to-signal ratio estimate includes:

[0030] The second intermediate signal is despread according to the spreading factor of the current transmission frame to obtain the despread signal; the despread signal is channel decoded according to the coding rate of the current transmission frame to obtain the decoded bit sequence; the training bits in the decoded bit sequence are compared bit by bit with the preset local training sequence, the number of bits with matching errors is counted, and the bit error rate of the current transmission frame is calculated according to the ratio of the number of bits with matching errors to the total number of training bits.

[0031] Based on the current interference-to-signal ratio (ISR) estimate, a preset ISR-to-transmission parameter mapping table is consulted to obtain a set of candidate spreading factors and a set of candidate coding rates. If the current transmission frame bit error rate (BER) is higher than a preset target BER threshold, a spreading factor greater than the current transmission frame spreading factor is selected from the candidate spreading factor set, and a coding rate less than the current transmission frame coding rate is selected from the candidate coding rate set. If the current transmission frame BER is not higher than the preset target BER threshold, a spreading factor less than the current transmission frame spreading factor is selected from the candidate spreading factor set, and a coding rate greater than the current transmission frame coding rate is selected from the candidate coding rate set. The selected spreading factor and coding rate are determined as the spreading factor and coding rate for the next transmission frame.

[0032] On the other hand, based on the same inventive concept, this invention also provides a high-speed aircraft data link anti-interference transmission system, the system comprising: a signal and data acquisition module, an interference signal determination and received power value extraction module, an interference-to-signal ratio estimation calculation module, and a signal processing and parameter adjustment module, wherein each module is sequentially connected in communication.

[0033] The signal and data acquisition module is used to acquire the radio frequency signal in the current time slot of the high-speed aircraft and convert it into a digital baseband received signal; acquire the current three-dimensional position coordinates and three-dimensional velocity vector of the high-speed aircraft, the three-dimensional position coordinates of the control platform, and the terrain elevation data within the flight corridor.

[0034] The interference signal determination and received power value extraction module is used to perform time-frequency transformation on the digital baseband received signal to obtain a time-frequency two-dimensional energy distribution map, determine the concentrated energy region in the time-frequency two-dimensional energy distribution map whose energy value exceeds a preset multiple of the background noise as an interference signal, and extract the received power value of the interference signal.

[0035] The interference-to-signal ratio (CNR) estimation module is used to determine the surrounding mountainous areas above the current flight altitude as the interference source high-angle search constraint area based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft; within the interference source high-angle search constraint area, the spatial spectrum of the interference signal is estimated to obtain the direction of arrival (ROA) of the interference signal, and the estimated distance of the interference source is calculated by combining the terrain elevation data; the useful signal ROA and useful signal transmission distance are calculated based on the current three-dimensional position coordinates of the high-speed aircraft and the three-dimensional position coordinates of the control platform; and the current CNR estimate is calculated based on the estimated distance of the interference source, the useful signal transmission distance, and the received power value of the interference signal.

[0036] The signal processing and parameter adjustment module is used to adjust the beam weight of the airborne receiving antenna array according to the arrival direction angle of the interference signal and the arrival direction angle of the useful signal; to perform spatial filtering on the digital baseband received signal according to the beam weight to obtain a first intermediate signal; to calculate the Doppler frequency shift value of the useful signal according to the three-dimensional velocity vector of the high-speed aircraft and the arrival direction angle of the useful signal; to perform bandpass filtering on the first intermediate signal with the Doppler frequency shift value of the useful signal as the center frequency to obtain a second intermediate signal; to obtain the current transmission frame bit error rate by data processing on the second intermediate signal; and to adjust the spreading factor and coding rate of the next transmission frame according to the current transmission frame bit error rate and the current interference-to-signal ratio estimate.

[0037] (3) Beneficial effects

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. By utilizing terrain elevation data within the flight corridor and the current position information of the high-speed aircraft, the surrounding mountainous areas above the current flight altitude are identified as the high elevation angle search constraint area for interference sources. This reduces the search range of spatial spectrum estimation from the entire airspace to a limited angular interval constrained by terrain, significantly reducing the computational complexity of interference source localization and improving the estimation accuracy and real-time performance of the arrival direction angle of interference signals. This lays an accurate spatial information foundation for subsequent anti-interference processing.

[0040] 2. By adjusting the beam weight of the airborne receiving antenna array according to the arrival angles of the interference signal and the useful signal, spatial filtering is achieved. In addition, the Doppler frequency shift value of the useful signal is calculated in combination with the motion state of the high-speed aircraft for bandpass filtering. Through the joint processing mechanism of spatial filtering and frequency filtering, interference energy from the direction of the interference source is suppressed in the spatial domain, and the Doppler frequency band of the useful signal is extracted in the frequency domain. This achieves effective suppression of strong interference signals at close range and effective extraction of weak useful signals at long range.

[0041] 3. Based on the current bit error rate and the current interference-to-signal ratio estimate, the spreading factor and coding rate of the next transmission frame are adaptively adjusted. When the interference intensity is high or the bit error rate increases, the spreading factor is increased and the coding rate is decreased to enhance transmission reliability. When the interference intensity is low or the bit error rate decreases, the spreading factor is decreased and the coding rate is increased to improve transmission efficiency. This achieves real-time matching between transmission parameters and the dynamically changing electromagnetic environment, maximizing transmission efficiency while ensuring transmission reliability. Attached Figure Description

[0042] Figure 1 This is a flowchart of the high-speed aircraft data link anti-interference transmission method according to Embodiment 1 of the present invention.

[0043] Figure 2 This is a schematic diagram of the module composition of the high-speed aircraft data link anti-interference transmission system according to Embodiment 2 of the present invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Before providing examples, it is necessary to describe the application scenarios of the present invention. The present invention is a data link anti-interference transmission method and system for high-speed aircraft, which is applied to the anti-interference transmission of data links in the low-altitude flight scenarios of high-speed aircraft in mountainous canyons.

[0046] Example 1: As Figure 1 As shown, this embodiment provides a method for anti-interference transmission of data links in high-speed aircraft, the method including:

[0047] S1. Acquire the radio frequency signal of the high-speed aircraft in the current time slot and convert it to obtain the digital baseband received signal; acquire the current three-dimensional position coordinates and three-dimensional velocity vector of the high-speed aircraft, the three-dimensional position coordinates of the control platform, and the terrain elevation data within the flight path corridor; in the scenario where the high-speed aircraft communicates with the control platform via data link during low-altitude flight in mountainous canyons, the high-speed aircraft flies at low altitude in the valleys along a pre-planned flight path corridor, while the control platform is located in a safe rear position far from the flight area, sending control commands to the high-speed aircraft via data link and receiving the status information returned by the high-speed aircraft. The target party utilizes the terrain characteristics of the mountainous canyons to deploy jamming equipment at high altitudes on the mountains surrounding the flight path corridor, implementing close-range high-power jamming on the high-speed aircraft's data link reception. Because the jamming source is deployed at high altitudes on the mountains, it exhibits a high elevation angle characteristic relative to the low-altitude high-speed aircraft, while the control platform is located at a distance, and the useful signal usually exhibits a low elevation angle or horizontal incidence characteristic relative to the high-speed aircraft. At the start of each communication time slot, the high-speed aircraft's onboard receiving system first acquires the radio frequency (RF) signal within that time slot. This RF signal is a mixed signal received by each element of the onboard receiving antenna array, containing useful signals from the control platform, interference signals from high-altitude sources on the mountainside, and background noise. The onboard receiving system down-converts, samples, and quantizes the RF signal, converting it from the RF band to the baseband band to obtain the digital baseband received signal. The digital baseband received signal is a multi-channel signal, with each channel corresponding to an element in the antenna array. Subsequent signal processing is based on this digital baseband received signal.

[0048] The high-speed aircraft obtains its current three-dimensional position coordinates through a combination of onboard inertial navigation and satellite navigation systems. These coordinates are typically represented using a geocentric coordinate system or a local northeast-sky coordinate system, containing longitude, latitude, and altitude components, or as eastward, northward, and celestial positions. Simultaneously, the high-speed aircraft acquires its current three-dimensional velocity vector, which describes its motion in three-dimensional space, including velocity magnitude and direction. The three-dimensional position coordinates of the control platform are pre-loaded into the high-speed aircraft during the mission planning phase and remain unchanged during flight or are updated according to a predetermined pattern. Terrain elevation data within the flight path corridor is also pre-loaded during mission planning. This data is stored in the form of a digital elevation model, covering terrain information within a certain range on both sides of the high-speed aircraft's planned flight path. Each data point includes horizontal position coordinates and the corresponding ground elevation value.

[0049] S2. The digital baseband received signal is subjected to time-frequency transformation to obtain a two-dimensional time-frequency energy distribution map. Concentrated energy regions in the time-frequency two-dimensional energy distribution map whose energy values ​​exceed a preset multiple of the background noise are identified as interference signals, and the received power value of the interference signal is extracted. The purpose of time-frequency transformation is to convert the signal from a time-domain representation to a time-frequency joint domain representation, so that the energy distribution characteristics of the signal in both time and frequency dimensions are presented. Commonly used time-frequency transformation methods include short-time Fourier transform and wavelet transform. Taking short-time Fourier transform as an example, it divides the digital baseband received signal into multiple overlapping short time periods. A Fourier transform is performed on the signal within each time period to obtain the spectrum corresponding to that time period. Arranging the spectra of all time periods in chronological order constitutes the two-dimensional time-frequency energy distribution map. In the two-dimensional time-frequency energy distribution map, the horizontal axis represents time, and the vertical axis represents frequency. The value of each time-frequency point represents the energy intensity of the signal at that frequency at that moment.

[0050] In a two-dimensional energy distribution map of time and frequency, background noise typically manifests as a low-energy background noise uniformly distributed across the entire time-frequency plane. Interference signals, due to their concentrated energy and often exhibiting certain time-frequency structural characteristics, form concentrated regions on the time-frequency plane with significantly higher energy than the background noise. By setting a preset multiple of the background noise as a detection threshold, concentrated energy regions in the two-dimensional energy distribution map whose energy values ​​exceed this threshold are identified as interference signals. For example, if the average energy of the background noise is N and the preset multiple is 10, then concentrated regions with energy values ​​exceeding 10N are identified as the region containing interference signals. After determining the presence of interference signals, the received power value of the interference signal is extracted. The received power value can be obtained by integrating the energy within the time-frequency region identified as interference signals or by taking the peak value, characterizing the power intensity of the interference signal when it reaches the receiver of the high-speed aircraft.

[0051] S3. Based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft, determine the surrounding mountain areas above the current flight altitude as the high elevation angle search constraint area for the interference source. Within the high elevation angle search constraint area, perform spatial spectrum estimation on the interference signal to obtain the direction of arrival (DOA) of the interference signal, and calculate the estimated distance of the interference source by combining it with the terrain elevation data. Calculate the DOA and transmission distance of the useful signal based on the current three-dimensional position coordinates of the high-speed aircraft and the three-dimensional position coordinates of the friendly control platform. Calculate the current interference-to-signal ratio (ISR) estimate based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal. The DOA of the useful signal is obtained by calculating the spatial vector direction from the friendly control platform to the high-speed aircraft; this DOA describes the spatial direction from which the useful signal is incident on the high-speed aircraft. The transmission distance of the useful signal is the straight-line distance between the high-speed aircraft and the friendly control platform, which can be directly calculated using the three-dimensional coordinates of two points. Since the friendly control platform is located far from the battlefield, the transmission distance of the useful signal is usually much greater than the estimated distance of the interference source.

[0052] S4. Adjust the beam weights of the airborne receiving antenna array according to the arrival angles of the interference signal and the useful signal. Perform spatial filtering on the digital baseband received signal according to the beam weights to obtain a first intermediate signal. Calculate the Doppler frequency shift of the useful signal based on the three-dimensional velocity vector of the high-speed aircraft and the arrival angle of the useful signal. Use the Doppler frequency shift as the center frequency to perform bandpass filtering on the first intermediate signal to obtain a second intermediate signal. Process the second intermediate signal to obtain the current transmission frame bit error rate. Adjust the spreading factor and coding rate of the next transmission frame according to the current transmission frame bit error rate and the current interference-to-signal ratio estimate. Beam weights are complex weighting coefficients applied to the received signal of each array element. By rationally designing the beam weights, the antenna array can form a main lobe of receiving gain in the direction of arrival of the useful signal, while simultaneously forming a null or low sidelobe of receiving gain in the direction of arrival of the interference signal. Applying the designed beam weights to the digital baseband received signal and performing weighted summation completes the spatial filtering process to obtain the first intermediate signal. Spatial filtering utilizes the spatial differences between the useful signal and the interference signal to suppress interference energy from the direction of the interference source while maintaining the receiving gain of the useful signal. Because the high-speed aircraft is in a high-speed motion state, the useful signal from the friendly control platform will experience a frequency shift due to the Doppler effect. This frequency shift is related to the speed of the high-speed aircraft and the incident direction of the useful signal. The Doppler frequency shift value of the useful signal is calculated based on the three-dimensional velocity vector of the high-speed aircraft and the arrival angle of the useful signal. Specifically, the radial velocity component is obtained by projecting the velocity vector of the high-speed aircraft onto the arrival direction of the useful signal, and then the frequency shift is calculated using the Doppler frequency shift formula. Using the calculated Doppler frequency shift value of the useful signal as the center frequency, a bandpass filter is designed to perform bandpass filtering on the first intermediate signal, filtering out frequency components other than the center frequency to obtain the second intermediate signal. Bandpass filtering utilizes the specific Doppler frequency shift characteristics of the useful signal caused by the motion of the high-speed aircraft to further suppress interference and noise components that do not match the frequency characteristics of the useful signal. Spreading factor and coding rate are key parameters affecting transmission reliability and efficiency: a larger spreading factor and lower coding rate provide stronger anti-interference and error correction capabilities, but reduce the effective data transmission rate; a smaller spreading factor and higher coding rate improve transmission efficiency, but relatively weaken anti-interference capabilities. Based on the current interference-to-signal ratio estimate, a range of candidate parameters suitable for the current interference environment is determined. Then, specific parameters are selected from the candidate range based on the comparison between the current transmitted frame bit error rate and the target bit error rate threshold. Through this adaptive adjustment mechanism, transmission parameters can be optimized in real time in dynamically changing interference environments, achieving a balance between transmission reliability and efficiency, and ensuring reliable data link communication for high-speed aircraft in complex electromagnetic environments.

[0053] The method for determining the surrounding mountainous areas above the current flight altitude as interference source high-angle search constraint areas based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft includes:

[0054] Centered on the current three-dimensional position coordinates of the high-speed aircraft, the terrain search range is determined based on the maximum detection range of the airborne receiving antenna array. Within this search range, terrain elevation data within the flight corridor is gridded to obtain a set of terrain elevation sampling points. Each sampling point in this set contains horizontal position coordinates and an elevation value. In low-altitude flight scenarios involving mountainous valleys, the target's jamming equipment is deployed at high elevations on the mountains surrounding the flight path. These jamming sources will inevitably exhibit a positive elevation angle relative to the low-altitude high-speed aircraft, meaning their elevation is greater than the high-speed aircraft's flight altitude. By analyzing the pre-loaded terrain elevation data, it is determined which surrounding areas have elevations higher than the high-speed aircraft's current flight altitude, thus confining the potential locations of jamming sources to these high elevation angle directions and avoiding blind searches across the entire airspace. The terrain search range is determined by the maximum detection range of the airborne receiving antenna array, and jamming sources beyond this range have limited interference effects due to excessive signal attenuation and can be disregarded. The maximum detection range of an airborne receiving antenna array is related to parameters such as antenna gain, receiver sensitivity, and operating frequency, which are known parameters determined during system design. For example, if the maximum detection range of the airborne receiving antenna array is 20 kilometers, then the circular area with the current position of the high-speed aircraft as the center and a radius of 20 kilometers is the terrain search range. Terrain elevation data within the flight path corridor is pre-loaded in the form of a digital elevation model. Its raw data typically has a certain spatial resolution, such as recording an elevation value every 30 or 90 meters. Grid sampling extracts terrain elevation data points within the terrain search range according to a preset sampling interval to form a terrain elevation sampling point set. The selection of the sampling interval requires a trade-off between computational efficiency and spatial resolution: too small a sampling interval will result in too many sampling points and excessive computational burden; too large a sampling interval may miss important terrain features. Each sampling point in the terrain elevation sampling point set contains two types of information: horizontal position coordinates describing the point's location on the horizontal plane, and an elevation value describing the point's ground elevation.

[0055] The elevation values ​​of each sampling point in the terrain elevation sampling point set are compared with the altitude component of the high-speed aircraft's current three-dimensional position coordinates. Sampling points with elevation values ​​greater than the altitude component are selected to form a candidate shielding point set. The altitude component of the high-speed aircraft's current three-dimensional position coordinates represents its current flight altitude, usually expressed as altitude. For each sampling point in the terrain elevation sampling point set, if its elevation value is greater than the high-speed aircraft's current flight altitude, the terrain position corresponding to the sampling point is higher than the high-speed aircraft, and from the high-speed aircraft's perspective, this direction presents a positive elevation angle, suggesting that an interference source may be deployed at this location. If its elevation value is less than or equal to the high-speed aircraft's current flight altitude, the terrain position corresponding to the sampling point is not higher than the high-speed aircraft, and from the high-speed aircraft's perspective, this direction presents a zero or negative elevation angle, making it unlikely that an interference source will effectively interfere from this direction. Through this comparison and selection process, all sampling points with elevation values ​​greater than the high-speed aircraft's current flight altitude are retained to form a candidate shielding point set. Each point in the candidate shielding point set represents a high-level terrain location where an interference source may be deployed.

[0056] Based on the current three-dimensional position coordinates of the high-speed aircraft and the horizontal position coordinates and elevation values ​​of each candidate shielding point in the candidate shielding point set, the azimuth and elevation angles of each candidate shielding point relative to the high-speed aircraft are calculated to obtain a set of candidate shielding point angles. Adjacent azimuth and elevation angles in the candidate shielding point angle set are merged into continuous angle intervals, which are then defined as the high elevation angle search constraint region for the interference source. Since the candidate shielding points originate from continuous mountain terrain, adjacent candidate shielding points are usually adjacent in angle space, forming several continuous angle intervals. Adjacent azimuth and elevation angles in the candidate shielding point angle set are merged to aggregate scattered angle pairs into continuous angle intervals. For example, if the candidate shielding point angle set contains multiple angle pairs with azimuth ranging from 45 to 60 degrees and elevation ranging from 10 to 25 degrees, these angle pairs can be merged into a continuous angle interval, which describes the angular coverage range of a certain mountain range surrounding the high-speed aircraft relative to the high-speed aircraft. All merged continuous angle intervals are defined as the high elevation angle search constraint region for the interference source. The high-elevation angle search constraint region for interference sources may contain one or more discontinuous angle intervals, corresponding to one or more mountains above the flight altitude around the high-speed aircraft. Subsequent spatial spectrum estimation will be performed within these angle intervals, rather than searching the entire airspace, thereby significantly reducing computational complexity and improving the accuracy of interference source localization.

[0057] The method for calculating the azimuth and elevation angles of each candidate shielding point relative to the high-speed aircraft based on the current three-dimensional position coordinates of the high-speed aircraft and the horizontal position coordinates and elevation values ​​of each candidate shielding point in the candidate shielding point set includes:

[0058] A horizontal position difference vector is calculated based on the horizontal position coordinates of each candidate shielding point and the horizontal position component of the high-speed aircraft's current three-dimensional position coordinates. The horizontal distance and azimuth of each candidate shielding point relative to the high-speed aircraft are then calculated based on this horizontal position difference vector. An altitude difference is calculated based on the elevation value of each candidate shielding point and the altitude component of the high-speed aircraft's current three-dimensional position coordinates. The elevation angle of each candidate shielding point relative to the high-speed aircraft is calculated based on the altitude difference and the horizontal distance. The azimuth and elevation angles corresponding to each candidate shielding point are then paired to form angle pairs, and all angle pairs constitute the candidate shielding point angle set. The horizontal position coordinates of the candidate shielding points include eastward and northward components, and the horizontal position component of the high-speed aircraft's current three-dimensional position coordinates also includes eastward and northward components. The horizontal position difference vector is obtained by subtracting the horizontal position coordinates of the candidate shielding point from the horizontal position component of the high-speed aircraft. This vector describes the direction and distance from the high-speed aircraft to the candidate shielding point on the horizontal plane. Its eastward component represents the east-west offset of the candidate shielding point relative to the high-speed aircraft, and its northward component represents the north-south offset. The horizontal distance is the magnitude of the horizontal position difference vector, which is the square root of the sum of the squares of the eastward and northward components. It represents the distance between the projection points of the high-speed aircraft and the candidate shielding point on the horizontal plane. The azimuth is the angle between the horizontal position difference vector and true north, and can be calculated using the arctangent function. Specifically, with true north as the zero-degree reference, if the horizontal position difference vector points northeast, the azimuth is an acute angle between 0 and 90 degrees; if it points southeast, the azimuth is between 90 and 180 degrees; if it points southwest, the azimuth is between 180 and 270 degrees; and if it points northwest, the azimuth is between 270 and 360 degrees. In practical calculations, the four-quadrant arctangent function is typically used to correctly handle various directional situations. The altitude difference is obtained by subtracting the elevation value of the candidate obscured point from the altitude component of the high-speed aircraft's current three-dimensional position coordinates. Since the points in the candidate obscured point set are selected points with elevation values ​​greater than the high-speed aircraft's flight altitude, the altitude difference is necessarily positive, indicating the vertical distance between the candidate obscured point and the high-speed aircraft. The elevation angle is the angle between the line of sight from the high-speed aircraft and the horizontal plane, calculated using the arctangent function; that is, the elevation angle equals the altitude difference divided by the arctangent of the horizontal distance. For example, if a candidate obscured point is 500 meters above the high-speed aircraft and the horizontal distance is 2 kilometers, the elevation angle is approximately 14 degrees. A larger elevation angle indicates a steeper relative to the high-speed aircraft, typically corresponding to nearby peaks with significant elevation differences. After calculating the azimuth and elevation angles, the azimuth and elevation angles corresponding to each candidate obscured point are paired. Each angle pair contains two values: the first is the azimuth angle and the second is the elevation angle. Together, they describe the spatial orientation of the candidate shielding point relative to the high-speed aircraft.The angle pairs corresponding to all candidate occlusion points in the candidate occlusion point set are gathered together to form the candidate occlusion point angle set.

[0059] The method for obtaining the direction of arrival angle of the interference signal by spatial spectrum estimation within the high elevation angle search constraint area of ​​the interference source, and calculating the estimated distance of the interference source by combining the spatial spectrum estimation of the interference signal with terrain elevation data includes:

[0060] The azimuth and elevation search ranges for spatial spectrum estimation are determined based on the high elevation angle search constraint region of the interference source. An angle search grid is then constructed within these ranges. A steering vector matrix is ​​constructed based on the element positions of the airborne receiving antenna array and the azimuth and elevation angles corresponding to each grid point in the angle search grid. Spatial spectrum estimation utilizes the spatial filtering characteristics of the antenna array to estimate the direction of the incident signal. When a signal is incident on the antenna array from a certain direction, the path length of the signal to each element differs due to their different spatial positions, resulting in a phase difference in the signals received by each element. This phase difference has a definite mathematical relationship with the incident direction of the signal. By analyzing the phase relationship between the received signals of each element, the incident direction of the signal can be deduced. The high elevation angle search constraint region of the interference source is one or more continuous angular intervals, each containing an azimuth range and an elevation range. Using these angular intervals as the search range for spatial spectrum estimation, instead of searching the entire airspace (azimuth 0 to 360 degrees, elevation -90 to +90 degrees), can significantly reduce the number of angle points searched. The angle search grid is a grid structure formed by discretizing samples along the azimuth and elevation dimensions according to a certain angular step. Each grid point corresponds to a combination of an azimuth value and an elevation value. The size of the angular step determines the angular resolution of the spatial spectrum estimation: a smaller step results in higher angular resolution but also higher computational cost; a larger step results in lower computational cost but may reduce the accuracy of angle estimation. For example, if the azimuth search range is 45 to 60 degrees, the elevation search range is 10 to 25 degrees, and the angular step is 1 degree, then the angle search grid contains 256 grid points (16 x 16).

[0061] The received signal covariance matrix is ​​calculated based on the received digital baseband signal; the spatial spectral energy distribution is obtained by calculating the spatial spectral function value corresponding to each grid point based on the received signal covariance matrix and the steering vector matrix; energy peak points are searched in the spatial spectral energy distribution, and the azimuth and elevation angles corresponding to the energy peak points are determined as the arrival direction angles of the interference signal; a spatial ray is constructed along the direction determined by the arrival direction angle of the interference signal, starting from the current three-dimensional position coordinates of the high-speed aircraft; the intersection point of the spatial ray and the terrain surface represented by the terrain elevation data within the flight path corridor is calculated, and the distance between the current three-dimensional position coordinates of the high-speed aircraft and the intersection point is determined as the estimated distance of the interference source.

[0062] The received signal covariance matrix describes the statistical correlation characteristics among the received signals of each element in the antenna array and is the core input data for spatial spectrum estimation. Specifically, the digital baseband received signal is divided into multiple snapshots over time. Each snapshot contains the received sample values ​​of all elements at a certain moment. Each snapshot is represented as a column vector. The product of this column vector and its conjugate transpose is calculated, and the average of the products of all snapshots is used to obtain the received signal covariance matrix. The received signal covariance matrix is ​​a square matrix with dimensions equal to the number of elements in the antenna array. Energy peak points are searched in the spatial spectrum energy distribution. Due to the presence of interference signals, the spatial spectrum function value will show a significant peak at the angular position corresponding to the incident direction of the interference signal. By searching for the maximum value or local maximum point in the spatial spectrum energy distribution, the location of the energy peak point is determined, and the azimuth and elevation angles corresponding to this energy peak point are determined as the arrival direction angle of the interference signal. If multiple interference sources exist, multiple energy peak points will appear in the spatial spectrum energy distribution, each peak point corresponding to the arrival direction angle of an interference source.

[0063] Since the interference source is deployed on the mountain surface, the direction indicated by the arrival angle of the interference signal must point to a certain location on the mountain. Starting from the current three-dimensional position coordinates of the high-speed aircraft, a spatial ray is constructed along the direction determined by the arrival angle of the interference signal. This spatial ray extends outward from the high-speed aircraft's position along the three-dimensional direction determined by the azimuth and elevation angles. The intersection point of this spatial ray with the terrain surface represented by the terrain elevation data within the flight path corridor is calculated. The terrain surface is a three-dimensional surface composed of terrain elevation data, and the intersection point of the spatial ray and the terrain surface is the estimated transmission location of the interference signal. The three-dimensional Euclidean distance between the current three-dimensional position coordinates of the high-speed aircraft and this intersection point is determined as the estimated distance of the interference source.

[0064] The method for constructing a steering vector matrix based on the azimuth and elevation angles corresponding to each grid point in the search grid according to the element positions and angles of the airborne receiving antenna array includes:

[0065] The process involves obtaining the three-dimensional position coordinates of each element in the airborne receiving antenna array relative to the array reference point to obtain the element position set; traversing each grid point in the angle search grid, calculating the signal arrival unit vector corresponding to the current grid point based on the azimuth and elevation angles; for each element in the element position set, calculating the inner product of the current element's position coordinates and the signal arrival unit vector to obtain the spatial phase delay of the current element relative to the array reference point; calculating the phase factor corresponding to the current element based on the spatial phase delay and the carrier wavelength of the received signal; arranging the phase factors corresponding to all elements in the element order to form the steering vector corresponding to the current grid point; traversing all grid points in the completed angle search grid, and arranging the steering vectors corresponding to all grid points to form a steering vector matrix. The array reference point is typically chosen as the geometric center of the antenna array or the position of a specific element as the coordinate origin, and the position coordinates of each element are described with reference to this origin. The element position set contains the three-dimensional coordinates of all elements, and the coordinates of each element include x, y, and z components, corresponding to the element's offset relative to the array reference point in three orthogonal directions. The number of antenna elements and their spatial arrangement are known parameters determined during system design. Common array configurations include uniform linear arrays, uniform area arrays, and circular arrays. For the current grid point, the signal arrival unit vector is calculated based on its corresponding azimuth and elevation angles. The signal arrival unit vector is a three-dimensional unit vector describing the propagation direction of the signal from that direction. Let the azimuth angle be φ and the elevation angle be θ. Then the three components of the signal arrival unit vector are: the x-component equals cosine θ multiplied by sine φ, the y-component equals cosine θ multiplied by cosine φ, and the z-component equals sine θ. The magnitude of the signal arrival unit vector is one, pointing in the direction of the signal's origin. The spatial phase delay describes the phase difference caused by the difference in path length between the signal reaching the current element and reaching the array reference point. The projection distance of the current element relative to the array reference point in the signal propagation direction is obtained by performing an inner product operation on the position coordinate vector of the current element and the signal arrival unit vector. This projection distance is the spatial phase delay. If the projection distance is positive, it means the signal arrives at the array reference point first, then at the current element; if the projection distance is negative, it means the signal arrives at the current element first, then at the array reference point. The phase factor is a complex number with a magnitude of one. The phase angle is equal to the spatial phase delay divided by the carrier wavelength and then multiplied by twice pi. The carrier wavelength is equal to the speed of light divided by the carrier frequency, and is a known parameter after the system's operating frequency is determined. Let the spatial phase delay be d and the carrier wavelength be λ, then the phase factor is exp(j×2π×d÷λ), where j is the imaginary unit. The phase factor describes the phase offset of the signal from the current direction at the current element relative to the array reference point. The steering vector is a complex vector with a dimension equal to the number of elements in the antenna array; each component is the phase factor of the corresponding element.The steering vector fully describes the phase response characteristics of the signal from the direction corresponding to the current grid point across the entire antenna array. By traversing all grid points in the completed angle search grid, the steering vectors corresponding to all grid points are obtained. These steering vectors are then arranged in columns to form a steering vector matrix. The number of rows in the steering vector matrix equals the number of elements in the antenna array, and the number of columns equals the number of grid points in the angle search grid. Each column corresponds to the steering vector in the direction of one grid point.

[0066] The method for calculating the spatial spectral energy distribution based on the received signal covariance matrix and steering vector matrix to determine the spatial spectral function value corresponding to each grid point includes:

[0067] The received signal covariance matrix is ​​eigenvalued to obtain a set of eigenvalues ​​and a corresponding set of eigenvectors. The eigenvalues ​​are sorted in descending order of value, and the eigenvectors corresponding to the remaining eigenvalues ​​after descending sorting (excluding the first preset number of eigenvalues ​​from the signal source) form a noise subspace matrix. Each grid point in the angle search grid is traversed to extract the steering vector corresponding to each grid point in the steering vector matrix. The projected energy of the steering vector corresponding to each grid point and the noise subspace matrix is ​​calculated, and the reciprocal of the projected energy is used as the spatial spectrum function value corresponding to the grid point. The spatial spectrum function values ​​corresponding to all grid points are arranged according to azimuth and elevation angles to form a spatial spectrum energy distribution. Let the dimension of the received signal covariance matrix be M x M, where M is the number of elements in the antenna array. Then, eigenvalue decomposition yields M eigenvalues ​​and M corresponding eigenvectors. The eigenvalues ​​are real numbers representing the energy intensity in the direction of the corresponding eigenvector; the eigenvectors are M-dimensional complex vectors representing a principal direction of the covariance matrix. All eigenvalues ​​are combined into an eigenvalue set, and all eigenvectors are combined into an eigenvector set. The preset number of signal sources is a system parameter representing the expected number of incident signals. It can be estimated and set in advance according to the task scenario. In this embodiment, interference signals and useful signals are mainly considered. After sorting in descending order, the first few larger eigenvalues ​​of the preset number of signal sources correspond to signal components, and the remaining smaller eigenvalues ​​correspond to noise components. For the current grid point, the steering vector corresponding to the grid point is extracted from the steering vector matrix. The steering vector is an M-dimensional complex vector that describes the theoretical phase response of the signal from the direction corresponding to the grid point on each array element. The projection energy is calculated by left-multiplying the steering vector by the conjugate transpose of the noise subspace matrix, then right-multiplying it by the noise subspace matrix, and finally left-multiplying it by the conjugate transpose of the steering vector to obtain a scalar value, which is the projection energy of the steering vector on the noise subspace. If the direction corresponding to the current grid point is exactly the incident direction of a signal, then the steering vector in that direction is orthogonal to the noise subspace, and the projection energy is close to zero; if the direction corresponding to the current grid point is not the incident direction of the signal, then the projection energy is larger. The reciprocal of the projected energy is used as the spatial spectrum function value corresponding to the current grid point. Since the projected energy corresponding to the signal direction is close to zero, its reciprocal tends to infinity, forming a sharp peak in the spatial spectrum. The projected energy corresponding to non-signal directions is larger, and its reciprocal is smaller, appearing as a lower value in the spatial spectrum. In this way, by searching for the peak position of the spatial spectrum function, the incident direction of the signal can be estimated. After traversing all grid points in the angle search grid, the spatial spectrum function values ​​corresponding to all grid points are obtained. These spatial spectrum function values ​​are arranged according to the azimuth and elevation coordinates of the grid points to form the spatial spectrum energy distribution. The spatial spectrum energy distribution is a two-dimensional distribution map, with the horizontal axis representing the azimuth and the vertical axis representing the elevation, and the value at each position representing the spatial spectrum function value in the corresponding direction.

[0068] The method for calculating the current interference-to-signal ratio estimate based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal includes:

[0069] The path loss index under the current propagation environment is calculated based on the received power value of the interference signal and the estimated distance of the interference source. The path transmission loss value of the useful signal is calculated based on the path loss index and the transmission distance of the useful signal. The preset transmit power and transmit antenna gain of the control platform are obtained, and the equivalent isotropic radiated power of the control platform is calculated based on the preset transmit power and transmit antenna gain. The interference-to-signal ratio (ISR) is the ratio of the interference signal power to the useful signal power, and it is a core indicator for measuring the severity of the current electromagnetic environment. In an asymmetric pattern where interference is close and strong, and the signal is far and weak, the ISR is usually very high. However, because the useful signal is overwhelmed by strong interference, it needs to be estimated using link budgeting. By using the measured data of the interference signal (received power and distance) to infer the attenuation characteristics of the current propagation environment, and then applying these attenuation characteristics to the useful signal link for power estimation, it is possible to adapt to the current actual propagation environment. The path loss exponent is a key parameter describing the attenuation characteristics of electromagnetic wave propagation. In the logarithmic distance path loss model, the relationship between received power and transmission distance is: received power (dB / mW) equals transmitted power (dB / mW) minus the path loss exponent multiplied by ten times the logarithmic distance, minus other fixed losses. Different propagation environments have different path loss exponents: the path loss exponent is two in free space, typically three to four in urban environments, and may be even higher in mountainous and canyon environments due to multipath effects and obstruction. By using the received power value of the interfering signal and the estimated distance of the interfering source, assuming the transmitted power of the interfering source is within a certain range, the path loss exponent in the current propagation environment can be deduced. Substituting the path loss exponent into the logarithmic distance path loss model, using the useful signal transmission distance as a parameter, the power attenuation of the useful signal along the propagation path, i.e., the useful signal path transmission loss value, is calculated. Since the useful signal transmission distance is usually much larger than the estimated distance of the interfering source, the useful signal path transmission loss value is usually much larger than the path loss of the interfering signal, which is the main reason for the high interference-to-signal ratio.

[0070] The receiver gain of the airborne receiving antenna array along the direction of arrival of the useful signal is obtained. Based on the equivalent isotropic radiated power of the control platform, the path transmission loss of the useful signal, and the receiver gain, an estimated value of the received power of the useful signal is calculated. The ratio of the received power of the interference signal to the estimated received power of the useful signal is determined as the current interference-to-signal ratio estimate. The preset transmit power and transmit antenna gain of the control platform are obtained, and the equivalent isotropic radiated power of the control platform is calculated based on these two values. The preset transmit power is the output power of the transmitter of the control platform, and the transmit antenna gain is the gain value of the transmit antenna of the control platform in the direction pointing towards the high-speed aircraft. Both are known parameters pre-programmed to the high-speed aircraft during the mission planning phase. The equivalent isotropic radiated power equals the transmit power multiplied by the transmit antenna gain, representing the effective radiation capability of the control platform in the direction pointing towards the high-speed aircraft. The receiver gain of the airborne receiving antenna array along the direction of arrival of the useful signal is obtained. The airborne receiving antenna array has different receiver gains in different directions, and the receiver gain along the direction of arrival of the useful signal determines the antenna array's ability to receive the useful signal.

[0071] The method for calculating the useful signal received power estimate is to subtract the useful signal path transmission loss from the equivalent isotropic radiated power and then add the receiving gain to obtain the power estimate of the useful signal reaching the high-speed aircraft receiver. The ratio of the received power of the interference signal to the estimated received power of the useful signal is determined as the current interference-to-signal ratio estimate, usually expressed in decibels, reflecting the interference intensity faced by the high-speed aircraft at the current moment.

[0072] The method for obtaining the current transmission frame bit error rate by data processing of the second intermediate signal, and adjusting the spreading factor and coding rate of the next transmission frame based on the current transmission frame bit error rate and the current interference-to-signal ratio estimate, includes:

[0073] The second intermediate signal is despread according to the spreading factor of the current transmission frame to obtain the despread signal; the despread signal is then channel-decoded according to the coding rate of the current transmission frame to obtain the decoded bit sequence; the training bits in the decoded bit sequence are compared bit-by-bit with a preset local training sequence, the number of bits with matching errors is counted, and the bit error rate of the current transmission frame is calculated based on the ratio of the number of bits with matching errors to the total number of training bits; the second intermediate signal is a signal that has undergone joint processing of spatial domain filtering and frequency domain filtering, in which interference components have been significantly suppressed. The purpose of data processing on the second intermediate signal is twofold: first, to recover the information bits transmitted by the transmitting end and complete the data reception of the current frame; second, to evaluate the transmission quality of the current frame and provide a basis for parameter adjustment for the next frame. Spread spectrum communication is an anti-interference transmission technology. The transmitting end multiplies the narrowband information signal with a wideband spreading code, spreading the signal energy over a wider frequency band for transmission. The receiving end despreads the received signal using the same spreading code, refocusing the signal energy back onto the narrowband while spreading out interference signals that do not match the spreading code, thus achieving spreading gain. The spreading factor is the length of the spreading code; a larger spreading factor results in higher spreading gain and stronger anti-interference capability, but a lower data transmission rate. Despreading involves performing correlation operations between the second intermediate signal and the locally generated spreading code to output the despread signal. The spreading factor of the current transmission frame is a parameter pre-agreed between the transmitting and receiving ends, or determined by adjusting the parameters of the previous frame. Channel decoding is performed on the despread signal according to the coding rate of the current transmission frame to obtain the decoded bit sequence. Channel coding is another technique to improve transmission reliability. The transmitting end adds redundant check bits to the information bits, enabling the receiving end to detect and correct errors generated during transmission. The coding rate is the ratio of the number of information bits to the total number of bits after encoding. A lower coding rate indicates higher redundancy and stronger error correction capability, but lower transmission efficiency. Commonly used channel coding methods include convolutional codes and low-density parity-check codes. Channel decoding involves recovering the most probable sequence of transmitted bits based on the coding rules and the soft or hard information of the received signal. The coding rate of the current transmission frame is also pre-agreed upon by the sender and receiver or determined through parameter adjustments.

[0074] The decoded bit sequence consists of two parts: information bits and training bits. Training bits are a pre-agreed, known bit sequence embedded in the transmission frame for purposes such as channel estimation, synchronization, and transmission quality assessment. The training bits are extracted from the decoded bit sequence and compared bit-by-bit with a pre-set local training sequence. The local training sequence is a bit sequence pre-stored at the receiver that is identical to the sender's training bits. Bit-by-bit comparison involves comparing the decoded training bits with the corresponding bits in the local training sequence, counting the number of inconsistent bits, i.e., the number of bits with misalignment. The bit error rate (BER) is a standard indicator of digital communication transmission quality, representing the proportion of received bits that contain errors. A lower BER indicates better transmission quality, while a higher BER indicates worse transmission quality.

[0075] Based on the current interference-to-signal ratio (ISR) estimate, a preset ISR-to-transmission parameter mapping table is consulted to obtain a set of candidate spreading factors and a set of candidate coding rates. If the current transmission frame's bit error rate (BER) is higher than a preset target BER threshold, a spreading factor greater than the current transmission frame's spreading factor is selected from the candidate spreading factor set, and a coding rate less than the current transmission frame's coding rate is selected from the candidate coding rate set. If the current transmission frame's BER is not higher than the preset target BER threshold, a spreading factor less than the current transmission frame's spreading factor is selected from the candidate spreading factor set, and a coding rate greater than the current transmission frame's coding rate is selected from the candidate coding rate set. The selected spreading factor and coding rate are then determined as the spreading factor and coding rate for the next transmission frame. The ISR-to-transmission parameter mapping table is established during the system design phase through theoretical analysis or simulation experiments, describing the range of spreading factor and coding rate combinations that can meet transmission quality requirements under different ISR conditions. For example, when the interference-to-signal ratio (ISR) is 20 decibels, the candidate spreading factor set might include options such as 64, 128, and 256, while the candidate coding rate set might include options such as one-third, one-half, and two-thirds. When the ISR is 30 decibels, due to stronger interference, the candidate spreading factor set might only include larger values ​​such as 256 and 512, while the candidate coding rate set might only include lower values ​​such as one-quarter and one-third. The target bit error rate (BER) threshold is a transmission quality indicator determined during system design based on task requirements; for example, it could be set to 0.1% or 0.01%. If the BER of the current transmission frame is higher than the target BER threshold, it indicates insufficient transmission reliability under the current parameter configuration, requiring enhanced anti-interference capabilities. Therefore, a spreading factor greater than the current transmission frame's spreading factor is selected from the candidate spreading factor set, and a coding rate less than the current transmission frame's coding rate is selected from the candidate coding rate set. Increasing the spreading factor can improve the spreading gain, and decreasing the coding rate can increase error correction redundancy; both contribute to reducing the BER. If the current transmission frame's bit error rate (BER) is not higher than the target BER threshold, it indicates that the current parameter configuration has a certain margin, and transmission efficiency can be appropriately improved. Therefore, a spreading factor smaller than the current transmission frame's spreading factor is selected from the candidate spreading factor set, and a coding rate larger than the current transmission frame's coding rate is selected from the candidate coding rate set. Reducing the spreading factor and increasing the coding rate can improve data transmission rate while ensuring transmission quality. The selected spreading factor and coding rate are determined as the spreading factor and coding rate for the next transmission frame, and the sending end is notified via the reverse link, enabling the sending end to use the updated parameters for transmission in the next transmission frame.

[0076] Example 2: Based on the same inventive concept, such as Figure 2As shown, this embodiment also provides a high-speed aircraft data link anti-interference transmission system, which includes: a signal and data acquisition module, an interference signal determination and received power value extraction module, an interference-to-signal ratio estimation calculation module, and a signal processing and parameter adjustment module, with each module being connected in a sequential communication manner;

[0077] The signal and data acquisition module is used to acquire the radio frequency signal in the current time slot of the high-speed aircraft and convert it into a digital baseband received signal; acquire the current three-dimensional position coordinates and three-dimensional velocity vector of the high-speed aircraft, the three-dimensional position coordinates of the control platform, and the terrain elevation data within the flight corridor.

[0078] The interference signal determination and received power value extraction module is used to perform time-frequency transformation on the digital baseband received signal to obtain a time-frequency two-dimensional energy distribution map, determine the concentrated energy region in the time-frequency two-dimensional energy distribution map whose energy value exceeds a preset multiple of the background noise as an interference signal, and extract the received power value of the interference signal.

[0079] The interference-to-signal ratio (CNR) estimation module is used to determine the surrounding mountainous areas above the current flight altitude as the interference source high-angle search constraint area based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft; within the interference source high-angle search constraint area, the spatial spectrum of the interference signal is estimated to obtain the direction of arrival (ROA) of the interference signal, and the estimated distance of the interference source is calculated by combining the terrain elevation data; the useful signal ROA and useful signal transmission distance are calculated based on the current three-dimensional position coordinates of the high-speed aircraft and the three-dimensional position coordinates of the control platform; and the current CNR estimate is calculated based on the estimated distance of the interference source, the useful signal transmission distance, and the received power value of the interference signal.

[0080] The signal processing and parameter adjustment module is used to adjust the beam weight of the airborne receiving antenna array according to the arrival direction angle of the interference signal and the arrival direction angle of the useful signal; to perform spatial filtering on the digital baseband received signal according to the beam weight to obtain a first intermediate signal; to calculate the Doppler frequency shift value of the useful signal according to the three-dimensional velocity vector of the high-speed aircraft and the arrival direction angle of the useful signal; to perform bandpass filtering on the first intermediate signal with the Doppler frequency shift value of the useful signal as the center frequency to obtain a second intermediate signal; to obtain the current transmission frame bit error rate by data processing on the second intermediate signal; and to adjust the spreading factor and coding rate of the next transmission frame according to the current transmission frame bit error rate and the current interference-to-signal ratio estimate.

[0081] It should be noted that the specific methods by which each module performs operations in the system described in the above embodiments have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0082] Finally, it should be noted that although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for anti-interference transmission of data links in high-speed aircraft, characterized in that, The method includes: Acquire the radio frequency signal of the high-speed aircraft in the current time slot and convert it to obtain the digital baseband received signal; acquire the current three-dimensional position coordinates and three-dimensional velocity vector of the high-speed aircraft, the three-dimensional position coordinates of the control platform, and the terrain elevation data within the flight corridor; The digital baseband received signal is transformed by time and frequency to obtain a time-frequency two-dimensional energy distribution map. The concentrated energy region in the time-frequency two-dimensional energy distribution map whose energy value exceeds a preset multiple of the background noise is identified as an interference signal, and the received power value of the interference signal is extracted. Based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft, a surrounding mountain area higher than the current flight altitude is determined as the high elevation angle search constraint area for the interference source. Within the high elevation angle search constraint area, the spatial spectrum of the interference signal is estimated to obtain the direction of arrival angle of the interference signal, and the estimated distance of the interference source is calculated by combining the terrain elevation data. Based on the current three-dimensional position coordinates of the high-speed aircraft and the three-dimensional position coordinates of the friendly control platform, the direction of arrival angle and the transmission distance of the useful signal are calculated. Based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal, the current interference-to-signal ratio estimate is calculated. The beam weights of the airborne receiving antenna array are adjusted based on the arrival angles of the interference signal and the arrival angle of the useful signal. The digital baseband received signal is then spatially filtered according to the beam weights to obtain a first intermediate signal. The Doppler frequency shift of the useful signal is calculated based on the three-dimensional velocity vector of the high-speed aircraft and the arrival angle of the useful signal. The first intermediate signal is then bandpass filtered using the Doppler frequency shift of the useful signal as the center frequency to obtain a second intermediate signal. The bit error rate of the current transmission frame is obtained through data processing on the second intermediate signal. The spreading factor and coding rate of the next transmission frame are adjusted based on the current bit error rate and the current interference-to-signal ratio estimate. The method for obtaining the direction of arrival angle of the interference signal by spatial spectrum estimation within the high elevation angle search constraint area of ​​the interference source, and calculating the estimated distance of the interference source by combining the spatial spectrum estimation of the interference signal with terrain elevation data includes: The azimuth and elevation search ranges for spatial spectrum estimation are determined based on the high elevation angle search constraint region of the interference source. An angle search grid is constructed within the azimuth and elevation search ranges. A steering vector matrix is ​​constructed based on the element positions of the airborne receiving antenna array and the azimuth and elevation angles corresponding to each grid point in the angle search grid. The received signal covariance matrix is ​​calculated based on the received digital baseband signal; the spatial spectral energy distribution is obtained by calculating the spatial spectral function value corresponding to each grid point based on the received signal covariance matrix and the steering vector matrix; energy peak points are searched in the spatial spectral energy distribution, and the azimuth and elevation angles corresponding to the energy peak points are determined as the arrival direction angles of the interference signal; a spatial ray is constructed along the direction determined by the arrival direction angle of the interference signal, starting from the current three-dimensional position coordinates of the high-speed aircraft; the intersection point of the spatial ray and the terrain surface represented by the terrain elevation data within the flight path corridor is calculated, and the distance between the current three-dimensional position coordinates of the high-speed aircraft and the intersection point is determined as the estimated distance of the interference source.

2. The high-speed aircraft data link anti-interference transmission method according to claim 1, characterized in that, The method for determining the surrounding mountainous areas above the current flight altitude as interference source high-angle search constraint areas based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft includes: Centered on the current three-dimensional position coordinates of the high-speed aircraft, the terrain search range is determined according to the maximum detection range of the airborne receiving antenna array; within the terrain search range, the terrain elevation data within the flight corridor is gridded to obtain a set of terrain elevation sampling points, and each sampling point in the set of terrain elevation sampling points contains horizontal position coordinates and elevation values; The elevation values ​​of each sampling point in the terrain elevation sampling point set are compared with the height component in the current three-dimensional position coordinates of the high-speed aircraft, and sampling points with elevation values ​​greater than the height component are selected to form a candidate occlusion point set. Based on the current three-dimensional position coordinates of the high-speed aircraft and the horizontal position coordinates and elevation values ​​of each candidate shielding point in the candidate shielding point set, the azimuth and elevation angles of each candidate shielding point relative to the high-speed aircraft are calculated to obtain the candidate shielding point angle set; adjacent azimuth and elevation angles in the candidate shielding point angle set are merged into a continuous angle interval, and the continuous angle interval is determined as the high elevation angle search constraint region of the interference source.

3. The high-speed aircraft data link anti-interference transmission method according to claim 2, characterized in that, The method for calculating the azimuth and elevation angles of each candidate shielding point relative to the high-speed aircraft based on the current three-dimensional position coordinates of the high-speed aircraft and the horizontal position coordinates and elevation values ​​of each candidate shielding point in the candidate shielding point set includes: The horizontal position difference vector is calculated based on the horizontal position coordinates of each candidate shielding point and the horizontal position component in the current three-dimensional position coordinates of the high-speed aircraft. The horizontal distance and azimuth of each candidate shielding point relative to the high-speed aircraft are calculated based on the horizontal position difference vector. The altitude difference is calculated based on the elevation value of each candidate shielding point and the altitude component in the current three-dimensional position coordinates of the high-speed aircraft. The elevation angle of each candidate shielding point relative to the high-speed aircraft is calculated based on the altitude difference and the horizontal distance. The azimuth and elevation angles corresponding to each candidate shielding point are combined into angle pairs, and all angle pairs constitute the angle set of candidate shielding points.

4. The high-speed aircraft data link anti-interference transmission method according to claim 1, characterized in that, The method for constructing a steering vector matrix based on the azimuth and elevation angles corresponding to each grid point in the search grid according to the element positions and angles of the airborne receiving antenna array includes: The process involves: obtaining the three-dimensional position coordinates of each element in the airborne receiving antenna array relative to the array reference point to obtain the element position set; traversing each grid point in the angle search grid and calculating the signal arrival unit vector corresponding to the current grid point based on the azimuth and elevation angles; for each element in the element position set, calculating the dot product of the current element position coordinates and the signal arrival unit vector to obtain the spatial phase delay of the current element relative to the array reference point; calculating the phase factor corresponding to the current element based on the spatial phase delay and the carrier wavelength of the received signal; arranging the phase factors corresponding to all elements in the element order to form the steering vector corresponding to the current grid point; and traversing all grid points in the completed angle search grid and arranging the steering vectors corresponding to all grid points to form a steering vector matrix.

5. The high-speed aircraft data link anti-interference transmission method according to claim 1, characterized in that, The method for calculating the spatial spectral energy distribution based on the received signal covariance matrix and steering vector matrix to determine the spatial spectral function value corresponding to each grid point includes: The received signal covariance matrix is ​​decomposed into eigenvalue set and corresponding eigenvector set. The eigenvalue set is sorted in descending order of numerical value. The eigenvectors corresponding to the remaining eigenvalues ​​after descending sorting (excluding the first preset number of eigenvalues ​​from the signal source) form a noise subspace matrix. Each grid point in the angle search grid is traversed to extract the steering vector corresponding to each grid point in the steering vector matrix. The projection energy of the steering vector corresponding to each grid point and the noise subspace matrix is ​​calculated. The reciprocal of the projection energy is used as the spatial spectrum function value corresponding to the grid point. The spatial spectrum function values ​​corresponding to all grid points are arranged according to azimuth and elevation angles to form a spatial spectrum energy distribution.

6. The high-speed aircraft data link anti-interference transmission method according to claim 1, characterized in that, The method for calculating the current interference-to-signal ratio estimate based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal includes: The path loss index under the current propagation environment is calculated based on the received power value of the interference signal and the estimated distance of the interference source; the path transmission loss value of the useful signal is calculated based on the path loss index and the transmission distance of the useful signal; the preset transmit power and transmit antenna gain of the control platform are obtained, and the equivalent omnidirectional radiated power of the control platform is calculated based on the preset transmit power and transmit antenna gain. The receiver gain of the airborne receiving antenna array along the direction of arrival of the useful signal is obtained. Based on the equivalent omnidirectional radiated power of the self-control platform, the path transmission loss of the useful signal, and the receiver gain, the estimated value of the received power of the useful signal is calculated. The ratio of the received power of the interference signal to the estimated value of the received power of the useful signal is determined as the current interference-to-signal ratio estimate.

7. The high-speed aircraft data link anti-interference transmission method according to claim 1, characterized in that, The method for obtaining the current transmission frame bit error rate by data processing of the second intermediate signal, and adjusting the spreading factor and coding rate of the next transmission frame based on the current transmission frame bit error rate and the current interference-to-signal ratio estimate, includes: The second intermediate signal is despread according to the spreading factor of the current transmission frame to obtain the despread signal; the despread signal is channel decoded according to the coding rate of the current transmission frame to obtain the decoded bit sequence; the training bits in the decoded bit sequence are compared bit by bit with the preset local training sequence, the number of bits with matching errors is counted, and the bit error rate of the current transmission frame is calculated according to the ratio of the number of bits with matching errors to the total number of training bits. Based on the current interference-to-signal ratio (ISR) estimate, a preset ISR-to-transmission parameter mapping table is consulted to obtain a set of candidate spreading factors and a set of candidate coding rates. If the current transmission frame bit error rate (BER) is higher than a preset target BER threshold, a spreading factor greater than the current transmission frame spreading factor is selected from the candidate spreading factor set, and a coding rate less than the current transmission frame coding rate is selected from the candidate coding rate set. If the current transmission frame BER is not higher than the preset target BER threshold, a spreading factor less than the current transmission frame spreading factor is selected from the candidate spreading factor set, and a coding rate greater than the current transmission frame coding rate is selected from the candidate coding rate set. The selected spreading factor and coding rate are determined as the spreading factor and coding rate for the next transmission frame.

8. A high-speed aircraft data link anti-interference transmission system, characterized in that, The system includes: a signal and data acquisition module, an interference signal determination and received power value extraction module, an interference-to-signal ratio estimation calculation module, and a signal processing and parameter adjustment module, with each module being connected in a sequential communication manner. The signal and data acquisition module is used to acquire the radio frequency signal in the current time slot of the high-speed aircraft and convert it into a digital baseband received signal; acquire the current three-dimensional position coordinates and three-dimensional velocity vector of the high-speed aircraft, the three-dimensional position coordinates of the control platform, and the terrain elevation data within the flight corridor. The interference signal determination and received power value extraction module is used to perform time-frequency transformation on the digital baseband received signal to obtain a time-frequency two-dimensional energy distribution map, determine the concentrated energy area in the time-frequency two-dimensional energy distribution map whose energy value exceeds a preset multiple of the background noise as an interference signal, and extract the received power value of the interference signal. The interference-to-signal ratio (CNR) estimation module is used to determine, based on the terrain elevation data and the current three-dimensional position coordinates of the high-speed aircraft, a surrounding mountain area above the current flight altitude as a high-angle search constraint region for the interference source; within the high-angle search constraint region, spatial spectrum estimation of the interference signal is performed to obtain the direction of arrival (AOA) of the interference signal, and the estimated distance of the interference source is calculated by combining the terrain elevation data; the AAO and transmission distance of the useful signal are calculated based on the current three-dimensional position coordinates of the high-speed aircraft and the three-dimensional position coordinates of the control platform; and the current CNR estimate is calculated based on the estimated distance of the interference source, the transmission distance of the useful signal, and the received power value of the interference signal. The signal processing and parameter adjustment module is used to adjust the beam weight of the airborne receiving antenna array according to the arrival angle of the interference signal and the arrival angle of the useful signal; to perform spatial filtering on the digital baseband received signal according to the beam weight to obtain a first intermediate signal; to calculate the Doppler frequency shift value of the useful signal according to the three-dimensional velocity vector of the high-speed aircraft and the arrival angle of the useful signal; to perform bandpass filtering on the first intermediate signal with the Doppler frequency shift value of the useful signal as the center frequency to obtain a second intermediate signal; to obtain the current transmission frame bit error rate by data processing on the second intermediate signal; and to adjust the spreading factor and coding rate of the next transmission frame according to the current transmission frame bit error rate and the current interference-to-signal ratio estimate. The method for obtaining the direction of arrival angle of the interference signal by spatial spectrum estimation within the high elevation angle search constraint area of ​​the interference source, and calculating the estimated distance of the interference source by combining the spatial spectrum estimation of the interference signal with terrain elevation data includes: The azimuth and elevation search ranges for spatial spectrum estimation are determined based on the high elevation angle search constraint region of the interference source. An angle search grid is constructed within the azimuth and elevation search ranges. A steering vector matrix is ​​constructed based on the element positions of the airborne receiving antenna array and the azimuth and elevation angles corresponding to each grid point in the angle search grid. The received signal covariance matrix is ​​calculated based on the received digital baseband signal; the spatial spectral energy distribution is obtained by calculating the spatial spectral function value corresponding to each grid point based on the received signal covariance matrix and the steering vector matrix; energy peak points are searched in the spatial spectral energy distribution, and the azimuth and elevation angles corresponding to the energy peak points are determined as the arrival direction angles of the interference signal; a spatial ray is constructed along the direction determined by the arrival direction angle of the interference signal, starting from the current three-dimensional position coordinates of the high-speed aircraft; the intersection point of the spatial ray and the terrain surface represented by the terrain elevation data within the flight path corridor is calculated, and the distance between the current three-dimensional position coordinates of the high-speed aircraft and the intersection point is determined as the estimated distance of the interference source.

Images