A method and system for resisting satellite navigation spoofing using array antennas based on integrated navigation

Abstract

This invention relates to a method and system for resisting satellite navigation spoofing using an array antenna based on integrated navigation, belonging to the field of integrated navigation technology. It can improve system robustness and solve the problem of satellite navigation receiver terminals being susceptible to external spoofing interference. The method includes: S1, calculating the current carrier attitude based on the angular rate, specific force information, and magnetic flux information output by the inertial measurement unit; S2, calculating the projection of the true direction vector of the currently visible satellite in the geographic system, then projecting it onto the array antenna coordinate system according to the carrier attitude, and calculating the elevation angle and azimuth angle of the visible satellite relative to the array antenna coordinate system; S3, sampling and down-converting the satellite signal of the current epoch using digital frequency storage technology, and continuously adjusting the zero-point direction using array antenna directional nulling technology to detect whether a spoofing signal enters; S4, determining the direction of arrival of the spoofing signal; S5, shaping the array antenna radiation pattern; S6, adjusting the beam pointing to suppress the entry of spoofing signals.

Description

Technical Field

[0001] This invention relates to the field of integrated navigation technology, and in particular to a method for resisting satellite navigation spoofing using an array antenna based on integrated navigation. Background Technology

[0002] Integrated navigation systems achieve complementarity between individual navigation systems by fusing data from multiple sensors, resulting in high positioning accuracy and strong stability. Therefore, they are widely used in both military and civilian fields. However, satellite navigation systems, as a crucial component of integrated navigation systems, also suffer from weak signal strength and are highly susceptible to interference and deception. Without corresponding measures, these weaknesses could pose significant risks to various sectors of my country's military and civilian industries. Therefore, anti-spoofing technology for satellite signals is extremely important.

[0003] Therefore, it is necessary to study an array antenna anti-satellite navigation spoofing method and system based on integrated navigation to address the shortcomings of existing technologies and solve or mitigate one or more of the above-mentioned problems. Summary of the Invention

[0004] In view of this, the present invention provides a method and system for resisting satellite navigation spoofing using an array antenna based on integrated navigation. By combining hardware and software, the robustness of the integrated navigation system is improved, which can solve the problem that satellite navigation receiver terminals are susceptible to external spoofing and interference.

[0005] On one hand, the present invention provides a method for resisting satellite navigation spoofing using an array antenna based on integrated navigation, characterized in that the method includes the following steps:

[0006] S1. Calculate the current carrier attitude based on the angular rate and specific force information output by the inertial measurement unit and / or the magnetic flux information output by the magnetic intensity measurement device.

[0007] S2. Calculate the true orientation vector of all visible satellites in the geographic system, and then project the true orientation vector into the array antenna coordinate system according to the carrier attitude obtained in S1. Calculate the elevation angle and azimuth angle of the visible satellites relative to the array antenna coordinate system.

[0008] S3. The satellite signal of the current epoch is sampled and down-converted using digital frequency storage technology and stored. The zero-point direction is continuously adjusted using the directional zeroing technology of the array antenna to detect whether any deception signals are entering. If no deception signal is detected, the anti-deception operation ends; otherwise, proceed to the next step.

[0009] S4. Determine the direction of the incoming wave of the deception signal;

[0010] S5. Shape the radiation pattern of the array antenna;

[0011] S6. Adjust the beam direction based on the antenna pattern obtained in S5 to suppress the entry of deceptive signals.

[0012] In addition to the aspects and any possible implementations described above, a further implementation is provided in which step S4 includes: using the signal obtained after forming a null region in the direction of the real signal source, the phase comparison method is used to measure the direction of arrival of the deceptive signal.

[0013] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the magnetic strength measuring device is specifically a magnetometer.

[0014] As described above, and in accordance with any possible implementation, a further implementation is provided, wherein step S1 includes:

[0015] S11. Determine whether the criteria are met. in, β1 is the acceleration output by the accelerometer in the inertial measurement unit, g is the local gravity, and β1 is the preset acceleration threshold. If the conditions are met, the carrier is determined to be in a low-acceleration maneuver state, and the carrier attitude is calculated based on this state; otherwise, proceed to the next step.

[0016] S12. Determine whether the horizontal acceleration satisfies criterion f. H <β2, where f H β1 is the horizontal acceleration magnitude, and β2 is the preset horizontal acceleration threshold. If the threshold is met, the vehicle is determined to be in a low-acceleration maneuver state, and the vehicle attitude is calculated based on this state; otherwise, proceed to the next step.

[0017] S13. Based on the output of the gyroscope in the inertial measurement unit, determine whether the carrier is undergoing continuous turning or hovering motion. If there is no turning or hovering, it is considered that the misalignment angle error is large and the attitude needs to be corrected.

[0018] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the attitude correction in step S13 includes: correcting the horizontal misalignment angle based on the horizontal specific force, and correcting the azimuth misalignment angle based on the magnetic flux information.

[0019] In addition to the aspects and any possible implementations described above, a further implementation is provided, in which the azimuth misalignment is corrected based on magnetic flux information, specifically by replacing the azimuth angle with magnetic heading.

[0020] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the calculation of the projection of the true direction vector of the visible satellite in the geographic system in step S2 is specifically as follows: the current visible satellite number is determined based on the current carrier position information output by the integrated navigation system, the current time maintained by the local clock, and the pre-loaded satellite almanac; then the projection of the true direction vector of all currently visible satellites in the geographic system is calculated based on the satellite position information calculated from the almanac.

[0021] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the specific content of determining the direction of arrival of the deception signal in step S4 includes: selecting a real signal, performing a nulling operation in its source direction, and determining the direction of arrival of the deception signal based on the information obtained from the nulling operation and using the phase comparison method.

[0022] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the selected real signal is the satellite signal of the current epoch.

[0023] In addition to the aspects described above and any possible implementation, a further implementation is provided in which step S5 includes shaping the array antenna pattern based on the elevation angle and azimuth angle of the satellite signal at the current epoch in step S3 and the elevation angle and azimuth angle of the spoofing signal in step S4.

[0024] In addition to the aspects and any possible implementations described above, a further implementation is provided, wherein step S6 includes: applying a null constraint condition to the array pattern, forcing the array pattern to always form a null in a certain fixed incoming wave direction, thereby suppressing the deception signal;

[0025] The specific steps include:

[0026] S61. Calculate the array steering vector of the interference based on the direction of arrival of the deception signal;

[0027] S62. Construct a virtual correlation matrix from the array steering vectors; if there are multiple incoming wave directions, sum the virtual correlation matrices formed by each array steering vector.

[0028] S63. Calculate the static direction coefficient of the zero-point constraint;

[0029] S64. Apply the static orientation coefficient as a constraint to the array orientation pattern.

[0030] On the other hand, the present invention provides an array antenna anti-satellite navigation spoofing system based on integrated navigation, characterized in that the system includes an inertial measurement unit, a magnetometer, and a processing module, wherein the inertial measurement unit and the magnetometer are both connected to the processing module;

[0031] The processing module includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of any of the methods described above.

[0032] Compared with the prior art, one of the above technical solutions has the following advantages or beneficial effects: The present invention adopts a combination of software and hardware, and improves performance by combining various resources on the basis of traditional array antenna anti-spoofing. It can make full use of the data of other airborne sensors and the maneuverability of the carrier itself to identify possible spoofing signals. At the algorithm level, it uses a tightly coupled Kalman filter algorithm and adopts sequential filtering technology, which makes it easier for the system to eliminate the satellite channels that are currently being spoofed.

[0033] Another technical solution in the above-mentioned technical solution has the following advantages or beneficial effects: The method of the present invention makes full use of reliable data provided by other sensors in the integrated navigation system to assist the satellite receiver in detecting and eliminating spoofing signals, and has high practical value.

[0034] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of a method for resisting satellite navigation spoofing using an array antenna based on integrated navigation, provided in one embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of phase difference measurement under two-dimensional planar conditions for an array antenna anti-satellite navigation spoofing method based on integrated navigation provided in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of phase difference measurement under three-dimensional plane conditions for an array antenna anti-satellite navigation spoofing method based on integrated navigation provided in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of an array antenna adaptive filtering model for an array antenna anti-satellite navigation spoofing method based on integrated navigation, provided in one embodiment of the present invention.

[0040] Figure 5 This is a structural diagram of a uniformly distributed square grid array antenna of an array antenna anti-satellite navigation spoofing method based on integrated navigation provided in an embodiment of the present invention;

[0041] Figure 6This is a schematic diagram of the array antenna signal incident in an embodiment of the method for resisting satellite navigation spoofing based on integrated navigation array antennas provided by the present invention;

[0042] Figure 7 This is a flowchart of a zero-point shaping method for an array antenna based on integrated navigation to resist satellite navigation spoofing, provided in an embodiment of the present invention. Detailed Implementation

[0043] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0044] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0045] Satellite signal deception techniques are mainly divided into two types: relay-based and generation-based. Based on the implementation method, they can be further divided into single-antenna deception and multi-antenna deception. Anti-deception techniques for satellite signals include both detection and elimination of deception interference signals. To address the vulnerability of satellite navigation receiver terminals to external deception interference, this invention proposes a method for combating satellite navigation deception based on an array antenna in integrated navigation. This method comprises two parts: detection and elimination of deceptive interference signals. From the receiver signal processing perspective, the direction of arrival of the deceptive signal is detected using an array antenna and spatial filtering technology. From the navigation and positioning layer perspective, the correct direction of the satellite signal is estimated using airborne sensor data, and the beam pointing is adjusted, thus achieving anti-satellite navigation deception at two levels.

[0046] According to a specific embodiment of the present invention, the array antenna anti-satellite navigation spoofing method based on integrated navigation is as follows: Figure 1 As shown, the steps include:

[0047] Step 1: Calculate the current attitude of the carrier by fusing the angular rate and specific force information output from the IMU with the magnetic flux information output from the magnetometer. Details are as follows:

[0048] Based on Newton's principle of inertia, the angular rate and specific force information output by the IMU cannot be disturbed; similarly, the magnetic flux measured by the magnetometer comes from the Earth's magnetic field and is generally difficult to interfere with. Therefore, maneuver decisions can be made based on the accelerometer output. When the vehicle is hovering, moving at a constant speed, or experiencing low acceleration, attitude reference technology can be used to correct the vehicle's attitude, thus maintaining the stability and usability of the integrated navigation system for an extended period and providing the vehicle with a relatively accurate attitude reference. The IMU, or Inertial Measurement Unit, mainly consists of a gyroscope and an accelerometer.

[0049] First, compare the specific force output of the accelerometers. The modulus and the local gravity g, if they satisfy the criterion (β1 is a preset acceleration threshold), so it can be preliminarily assumed that there is no acceleration maneuver. To reduce the influence of accelerometer measurement noise, under stable vehicle motion, the average value of the accelerometer over a period of time is generally used instead of the instantaneous value for judgment. Then, in the criterion... Based on this, the magnitude of the horizontal acceleration is then calculated. To make further judgments:

[0050] (1) When f H When the acceleration is less than β2 (β2 is a preset horizontal acceleration threshold), it can be determined that there is no acceleration maneuver, and the specific force can be used. Solve or estimate the misalignment angle φ b .

[0051] (2) When f H When ≥β2, there may be two cases: one is to calculate the misalignment angle φ in the attitude matrix. b The magnitude is relatively large, and secondly, the carrier does indeed exhibit significant horizontal acceleration maneuvering. Further judgment based on condition f... H If ≥β2 only occurs within a short period of time, it is considered that there is a short-term high-acceleration maneuver, and only the gyroscope output is used to maintain the attitude. If the condition occurs continuously for a long time, exceeding the preset time threshold, it is necessary to check whether the carrier has a continuous turning or circling motion in conjunction with the gyroscope output. If there is turning or circling, no further processing is required. If there is no turning or circling, it is considered that the root cause is a large misalignment angle error, and the attitude needs to be quickly corrected.

[0052] Under low-acceleration maneuvering conditions, the inertial navigation specific force equation and its error equation are approximated as follows:

[0053]

[0054]

[0055] Under steady-state conditions, acceleration and acceleration error have the same meaning. Setting the above equations to be equal, we get...

[0056]

[0057] At low maneuverability, the right side of the equation is It can be approximated as Rewritten in fractional form, we have

[0058]

[0059] Right now

[0060]

[0061] in, g n =[0 0 -g] T ; φ = [φ E φ N φ U ] T The above formula shows that the horizontal specific force only provides information on the horizontal misalignment angle correction, and cannot be used to calculate the azimuth misalignment φ. U However, the azimuth angle can be approximated by the magnetic heading given by the magnetometer. Let's assume the azimuth correction factor φ for now. U =0, therefore we have

[0062]

[0063] Right now

[0064]

[0065] in, This represents the specific force modulus at low maneuverability; e3 = [0 0 1] T Let z be the unit vector along the z-axis. Multiply both sides of the equation by the left side. And record achievable

[0066]

[0067] C3 is the attitude array. The third row vector. Therefore, it can be seen that the two unit vectors... and The included angle between them is the projection φ of the horizontal misalignment angle in the b-frame. b .

[0068] The calculated value of the misalignment angle φ b The quaternion attitude update algorithm, combined with the gyroscope angle increment output, is as follows:

[0069]

[0070] in

[0071]

[0072] It is in the time period [t] m-1 ,t m The gyroscope angle increment output within ]; Δθ′ m This represents the angular increment after misalignment correction and has a modulus Δθ′. m =|Δθ′ m |;α∈[0 ,[1] is the misalignment angle correction coefficient. The smaller α is, the stronger the ability to resist short-term acceleration interference, but the slower it will recover after the misalignment angle error occurs. Using the above attitude update algorithm, it can quickly respond to and track the angular motion changes of the vehicle, and continuously correct the misalignment angle, thereby achieving high-precision horizontal attitude navigation and obtaining relatively accurate pitch angle θ and roll angle γ.

[0073] Within a small area, the geomagnetic field vector H can be treated as a constant vector, and a magnetic field coordinate system (ox) can be established. m y m z m The magnetic field coordinate system (abbreviated as m-system) is used. When the magnetic field coordinate system coincides with the geographic coordinate system, the output of the magnetometer's three axes is M. n =[M N 0M D ] T Under the load system, the magnetometer output is according to Substitute the pitch angle θ and roll angle γ output by the integrated navigation system into the direction cosine matrix. After that, we can obtain

[0074]

[0075] Thus, the components of the geomagnetic field vector on the X and Y axes are obtained as follows:

[0076]

[0077] Thus, the magnetic heading is obtained.

[0078]

[0079] Step 2: Determine the currently visible satellite number based on the current vehicle position information output by the inertial / terrain matching / magnetic / barometric altimeter integrated navigation system, the current time maintained by the local clock, and the pre-loaded satellite almanac. Then, calculate the projection of the true direction vector of all currently visible satellites in the geographic frame using the satellite position information calculated from the almanac. Finally, based on the current vehicle attitude information calculated in Step 1, project this direction vector into the array antenna coordinate system, and use this to calculate the elevation angle and azimuth angle of the visible satellites relative to the array antenna coordinate system. Details are as follows:

[0080] For integrated navigation systems, the inertial navigation system relies on inertial information and can provide reliable position information without depending on any external information. The barometric altimeter, which measures changes in external air pressure to obtain the current altitude, is also resistant to spoofing or interference. Furthermore, the terrain matching system can also determine the current position by matching it with the current terrain, thus correcting position divergence caused by long-term operation of the inertial navigation system. Therefore, for integrated navigation systems, the current position information of the carrier is a known quantity. The high-precision clock on the integrated navigation system can also maintain accurate UTC time for a considerable period; the satellite almanac has a validity period of up to six months and can be pre-loaded into the integrated navigation system before receiver use. In summary, the visible satellite numbers and their positions in the ECEF coordinate system at the current receiver location can be calculated using Kepler's equations, thereby eliminating spoofing signals from invisible satellites.

[0081] For the true orientation vectors of all visible satellites, firstly, calculate the projection of the vector between the currently tracked satellite and the carrier in the ECEF coordinate system; secondly, use the transformation matrix from the ECEF coordinate system to the geographic system to project this vector into the geographic system. The calculation method is as follows:

[0082]

[0083] Wherein, [Δe Δn Δu] T Let [Δx Δy Δz] be the vector between the currently tracked satellite and the carrier in a geographic coordinate system with the carrier's location as the origin. T S is the projection of the observation vector from the carrier to the satellite into the ECEF coordinate system, and S is the transformation matrix between the ECEF coordinate system and the geographic system.

[0084]

[0085] [XYZ] T The satellite's position in the ECEF coordinate system is calculated by the satellite receiver based on the almanac. [x yz] T The position of the vehicle in the ECEF coordinate system is output by the integrated navigation system. L and λ represent the latitude and longitude of the vehicle, respectively.

[0086] The array antenna coordinate system is defined as a Cartesian coordinate system, with the origin at the geometric center of the array antenna. The X-axis points to the right of the array antenna, the Y-axis points forward, and the Z-axis points upward. The horizontal plane of the array antenna has an elevation angle of 0 degrees, and the zenith direction has an elevation angle of +90 degrees. Assume the attitude transition matrix from the spatial coordinate system (p-frame) to the geographic coordinate system (n-frame) is... Let the pitch angle, roll angle, and yaw angle (positive for north by east) be [θ γ ψ]T The sequence of the three rotations from the p-frame to the n-frame is: yaw-pitch-roll. At this point, we have...

[0087]

[0088] Then we can obtain the coordinates of the visible satellite relative to the array antenna coordinate system [X]. P Y P Z P ] T for:

[0089]

[0090] Based on the formulas for calculating altitude and azimuth:

[0091]

[0092]

[0093] θ、 Let θ be the elevation angle and azimuth angle, respectively. Where θ ∈ (0, π / 2).

[0094] Step 3: Using digital frequency storage technology, the satellite signal of the current epoch is sampled, down-converted, and stored in the integrated navigation system; the nulling technology of the array antenna is used to continuously adjust the zero-point direction and detect whether any deceptive signals are entering. Details are as follows:

[0095] (1) Due to the large number of satellite signals within the same epoch and the wide range of zero-point formation directions, it is difficult to complete the detection of deception signals within a single epoch, and it places an excessive burden on the processor. Digital frequency storage technology stores the digital signals obtained by high-speed A / D signal sampling in the device, enabling the integrated navigation system to store and reproduce radio frequency and microwave signals.

[0096] A spatial filter is a filter that outputs a weighted sum of the signals received from each channel of an array. Assume a uniform linear array composed of N omnidirectional antenna elements, with a spacing of d between adjacent elements. Let N×1 vector W represent the weighting vector, i.e.

[0097] W = [w1 … w] N ] T

[0098] The output signal can then be expressed as:

[0099] G(θ)=W H ·a(θ)

[0100] a(θ) is the N-dimensional direction vector of the array antenna:

[0101]

[0102] in, Where λ is the satellite signal wavelength, and θ is the angle between the signal direction and the array normal.

[0103] Nullification is the simplest spatial filtering technique, where the initial antenna pattern is determined by the beam vector. An adaptive algorithm corrects the antenna weights to minimize the output power of the weighted signal, thus creating a null in the direction of interference. Essentially, null formation aims to make the sum of the signal energy contributions received by each antenna element in a specified direction approach zero. To achieve this, a constraint must be imposed to ensure that the power of the antenna pattern in this specified spatial region is sufficiently small, while maintaining as much consistency as possible with the original antenna pattern in other directions. Therefore, the problem of finding a null in a specific direction reduces to minimizing the change in weights under the null power constraint in that direction.

[0104] For the output signal G(θ) of the array antenna, the squared gain |G(θ)| is used. 2 =W H a(θ)Wa(θ) H By constraining it to be less than a given constant ε, the above minimization optimization problem can be expressed as follows:

[0105] obj:minf(W)=||W-W0|| 2

[0106] STW H QW≤ε

[0107] In the formula, W0 is the initial weight vector of the array, which is Chebyshev magnitude weighted in this paper; W is the weight vector to be optimized; the constant ε controls the null depth in the null formation direction; Q is an N×N dimensional Hermitian matrix with values ​​of

[0108]

[0109] In the formula, θ m To form the center of the zero-depression region, Δθ m It is the width of m zero-depressions.

[0110] Eigenvalue decomposition of Q can be expressed as:

[0111] Q=ΓΛΓ H

[0112] Λ=diag(λ1,λ2,…λ1)

[0113] In the formula, Γ is the unitary matrix formed by the eigenvectors of Q, and Λ is the diagonal matrix of eigenvalues ​​of Q.

[0114] The aforementioned minimization optimization problem involves finding a weight vector W that is closest to the initial weight vector W0, under the constraint that the power integral in the direction of the null formation is less than a certain constant ε. Since the larger eigenvalues ​​of matrix Q are related to the number of nulls M, choosing a suitable n such that M ≤ n ≤ N ensures that the array has an approximately zero response in the spatial region. By constraining a set of eigenvectors of matrix Q to achieve a zero response within a certain width of interest, the optimization problem is transformed into...

[0115] obj:minf(W)=||W-W0|| 2

[0116] STW H e i =0, i=1,2,3…n, M≤n≤N

[0117] In the formula, e i It is the i-th eigenvalue of Q. Since W is a real number, the weight W can be obtained by solving the Lagrange multiplier method.

[0118] Step 3.1 The satellite signal is weighted by processing the signal in the device through a spatial filter, thereby forming a null in the desired direction to shield the signal in that direction, so as to detect whether there is a spoofing signal.

[0119] (2) Based on the current carrier attitude information calculated in step 1, obtain the attitude transfer matrix from the array antenna coordinate system to the geographic coordinate system. After transforming the regions with different azimuth and elevation angles in the geographic coordinate system to the antenna coordinate system, use the method in (1) to perform null scans in various directions of space. If the satellite signal can still be received after the elevation and azimuth angles calculated in step 2 form null regions, it indicates that there are deception signals entering in other directions.

[0120] (3) The array antenna needs to be controlled to point towards the direction of the strongest satellite signal based on the integrated navigation information to form a null, and the null area must maintain accurate pointing towards the satellite at all times during the carrier's movement. This is the most critical indicator of this method. During the tracking process, factors such as the accuracy of sensors and actuators can cause the antenna to not point accurately to the theoretical position, resulting in the antenna pointing away from the satellite and causing the null area to fail. Therefore, in actual operation, a conical scanning tracking method can be used to continuously adjust the pointing of the null area to align with the satellite.

[0121] The principle of the conical scanning tracking method is as follows: Assume the antenna is offset from the central axis OO' by a small angle ε and rotates around the axis at a constant speed. OS' is the antenna beam axis, T is the trajectory of the antenna's circular motion, and S is the actual direction of the satellite. If the antenna is not aligned, the magnitude of θ and the received satellite signal strength will continuously change within one scan cycle. The satellite's position is determined based on these changes in θ and satellite signal strength, and the antenna is adjusted accordingly. When the antenna is aligned with the satellite, the axes OS and OO' coincide, at which point θ no longer changes and the satellite signal strength is strongest.

[0122] The signal level received by the antenna at its maximum gain (within the half-power beamwidth) satisfies the following equation:

[0123]

[0124] Where P0 is the maximum signal level received at the antenna's maximum gain, θ 1 / 2 Let be the half-power beamwidth, θ be the angle at which the antenna deviates from its maximum gain, P(θ) be the signal level at θ, and a be a constant coefficient related to the antenna aperture and the frequency of the received signal.

[0125]

[0126] Where λ is the wavelength of the signal received by the antenna, f is the frequency of the satellite signal, D is the antenna aperture, and c is the speed of electromagnetic wave propagation in space.

[0127] Let the relationship between the voltage output by the array antenna and the received signal power be:

[0128] U=b·(P (θ) -P m )

[0129] Where b is the slope between the array antenna output voltage and the signal level, and Pm is the minimum level that the receiver can detect.

[0130] make achievable

[0131]

[0132] Where U is the voltage output by the antenna at a point θ away from the maximum gain point; Um is the maximum voltage output by the antenna at the point of maximum gain; the other parameters are existing fixed parameters. It can be seen that the level fading at the maximum gain point of the antenna is only related to the angle at which the antenna is pointing away from the maximum gain point.

[0133] The conical scanning of an array antenna can be decomposed into azimuth and elevation directions. The antenna undergoes cosine motion in the azimuth direction and sinusoidal motion in the elevation direction. The null region resulting from the combination of these two motions represents the circular motion. The equations of motion for the azimuth and elevation directions are shown below:

[0134]

[0135]

[0136] n = 1, 2, 3…N

[0137] Where N is the number of points dividing the circle; P AZ P EL Let P be the center of the circular motion. AZ(n) P AZ(n) Let be any point on the circular motion of the antenna during the conical scanning process.

[0138] Let S be the satellite position; O be the current antenna pointing position, and the deviation angle between point O and the satellite be θ; ε be the circular scan radius. Um is the angle between the antenna's offset from the satellite's position and the horizontal direction; Um is any point on the circular trajectory T of the beam, where the signal level is U. AGC ; Let AZ be the angle between the plane and the horizontal direction during its motion; AZ is the horizontal direction, and EL is the direction perpendicular to the horizontal; in triangle ΔSOU M In the middle, we can obtain from the Law of Cosines

[0139]

[0140] Based on the fundamental principle of conical scanning, the signal level equation at any point on the circular motion trajectory of the beam can be obtained:

[0141]

[0142] The equation exhibits only one maximum and one minimum value within a single scan cycle; and the maximum and minimum values ​​occur at the two intersections of the line connecting the center of the circumference and the satellite's position with the circumference; based on this, a new tracking adjustment method can be derived:

[0143] Suppose that the voltage measured by the receiver at the point closest to the satellite during the scanning process is U. max The voltage value measured by the receiver at the farthest point is U. min The adjustment amount of the antenna in the azimuth angle can be obtained as follows:

[0144]

[0145] Substitute θ and After that, there was

[0146]

[0147] The magnitude of the minimum voltage level detected by the receiver within one scan cycle determines whether the satellite falls within or outside the circular scan range. When the satellite is exactly on the circular scan trajectory, the voltage output by the receiver is:

[0148] U th =b·(P (2·ε) -P m ).

[0149] In summary, the formula for adjusting the antenna in the azimuth direction is as follows:

[0150]

[0151]

[0152] Similarly, the adjustment amount in the pitch angle direction can be obtained as follows:

[0153]

[0154]

[0155] Using the above technology, in actual operation, the conical scanning tracking method can be used to continuously adjust the zero-depression area to align with the satellite to ensure that the signal is stably blocked, which facilitates subsequent steps to process and judge the signal.

[0156] Step 4: If deceptive signals are detected in other directions in Step 3, the direction of arrival of the deceptive signal is measured using the phase comparison method, based on the signal obtained after forming a null region in the direction of the true signal source. Specifically:

[0157] First, based on the integrated navigation information and satellite position and velocity information, null techniques are used to create a null in the direction of the real satellite signal, shielding the signal in that direction and preventing interference that the real signal may cause to the deceptive signal.

[0158] Next, the direction of arrival of the spoofing signal is detected. This can be achieved using an array antenna attitude measurement method. This method utilizes carrier phase difference measurement. For ease of explanation, we will begin with the analysis of a two-dimensional plane. The principle of direction finding using phase difference measurement in a two-dimensional plane is as follows: Figure 2 As shown.

[0159] Figure 2The direction-finding baseline is formed between antenna elements A and B, with a straight-line distance of d. Since the distance between the satellite and the receiver is much greater than d, the angle between the direction of arrival of the navigation signal and the normal to the baseline can be considered to be θ. If the signal wavelength is λ, and a perpendicular line is drawn from antenna element B, the phase difference φ between the same signal reaching antenna elements A and B is expressed by the following formula:

[0160] φ = 2πd·sinθ / λ.

[0161] The phase difference φ ranges from [-π, π). If d >> λ / 2, then the above formula suffers from phase ambiguity, meaning that multiple different θ values ​​correspond to the same φ value, causing ambiguity in the direction finding results. Therefore, after obtaining the phase difference measurement, the method for calculating the direction of arrival is as follows:

[0162]

[0163] To further solve the above equation, we can use the short-baseline recursive method for the long baseline: According to the above equation, if d < ±λ / 2, it is obvious that |2πd·sinθ / λ| < π, which ensures that there is no phase ambiguity problem. Considering the existence of measurement noise, the baseline length should be smaller. Generally, the peak-to-peak value of carrier phase measurement noise is 0.1 cycles, and the signal wavelength is about 20cm. Therefore, the short baseline length can be set to 6cm. At this time, according to the above equation, the error of the incoming wave direction can be calculated to be about 19.5°. And n+1 antennas on the same straight line can construct n baselines. When the baseline length exceeds 24cm, the error of the incoming wave direction is about 4.8°, which can meet the angle discrimination requirements. In summary, the following ambiguity recursive relationship can be obtained:

[0164]

[0165] In the formula, N k D represents the phase ambiguity corresponding to the baseline length from the first antenna to the (k+1)th antenna. k φ is the baseline length from the first antenna to the (k+1)th antenna. k This is the phase difference between the same signal received by the first antenna and the (k+1)th antenna.

[0166] Therefore, if the phase ambiguity N k-1 Given that, in order to obtain N k The following conditions must be met:

[0167]

[0168] Δφ k This represents the phase measurement error between the signals received by the first antenna and the (k+1)th antenna. Finally, we obtain...

[0169]

[0170] Extending the above method to three-dimensional situations: Measurements are performed by setting up two mutually perpendicular baselines on a platform, such as... Figure 3 As shown. Figure 3 In the diagram, AB and CD are two perpendicular baselines. The line-of-sight vectors MA, MB, MC, and MD of the satellite signal reaching the antenna can be approximated as parallel. MA, MB, and AB are coplanar (and similarly for MC, MD, and CD), simplifying the problem to the two-dimensional direction finding scenario described above. In the antenna array coordinate system defined in step 3, the projections of the unit line-of-sight vectors onto the X and Y axes can be calculated using the two-dimensional direction finding principle. Then, the azimuth and elevation angles of the satellite signal can be obtained using trigonometric functions.

[0171] Step 5: Compare the elevation and azimuth angles of the real and spoofed signals calculated in Steps 3 and 4, and shape the radiation pattern of the array antenna. Specifically:

[0172] Because navigation satellites move continuously according to constellation diagrams, their positions are constantly changing. To achieve position calculation, the receiver needs to stably track the signals of at least four navigation satellites. Therefore, the satellite navigation array antenna needs to form a multi-beam pointing pattern, with each beam pointing towards a navigation satellite. Simultaneously, it needs to track the satellite's azimuth changes in real time and adjust the beam pointing accordingly to improve the ground navigation receiver's reception of satellite signals.

[0173] Adaptive beamformers are the main physical hardware components of spatial adaptive filtering. The topology of planar array antennas is one of the key technologies for signal processing in adaptive beamformers; the equivalent area of ​​the antenna array, array spacing, and array boundary distribution determine the characteristics of digital beamforming; different array topologies have different spatial angular resolutions and symmetries. Common planar arrays include square arrays, circular arrays, and hexagonal arrays.

[0174] Without loss of generality, the working principle of an adaptive beamformer is studied using a uniform linear array as an example. Its model is shown in the attached figure. Figure 4 As shown. Assume all array elements are isotropic, the element spacing is d, and each element is followed by a receiving element. A spatial incident signal s(t) enters the antenna array at an angle θ and is received, x1(t), x2(t), ..., x... N (t) represents the output signals of the N array element channels, w1, w2, ..., w N These are the weighted values ​​of the outputs of the N array element channels, and the weighted sum is the output y(t) of the array antenna.

[0175] Due to the different spatial positions of the array elements, the incident signal arrives at each element at different times, resulting in different signals x1(t), x2(t), ..., x... received by the array. N (t) have a phase delay between them, let the phase delay of x2(t) compared to x1(t) be . x3(t) also has a phase delay compared to x2(t). ...and so on, where the delay phase angle β is

[0176] β=2πd·sinθ / λ

[0177] Where λ is the wavelength of the incident signal, and d is the spacing between array elements. Then the signals received by the array are x1(t), x2(t), ..., x... N The relationship between (t) and the incident signal s(t) is as follows:

[0178]

[0179] Let N×1 vectors X(t) and a(θ) represent the signal received by the array and the delay phase of each array element, respectively. a(θ) is also called the array's steering vector. That is:

[0180] X(t)=[x1(t),x2(t),...,x N (t)] T

[0181]

[0182] In the case of multiple incident signals, M spatial incident signals s1(t), s2(t), ..., s M (t) are given by angles θ1, θ2, ..., θ M Entering the antenna array and being received,

[0183] S(t)=[s1(t), s2(t),...,s M (t)] T

[0184] A=[a1(t), a2(t),...,a M (t)] T

[0185] Among them, there are M guiding vectors a1(t), a2(t), ..., a M The matrix A formed by (t) is called the manifold matrix of the array. At this point, we have...

[0186] X(t) = A·S(t)

[0187] Furthermore, if the incident signal contains multiple signals, including both desired signals and unwanted interference signals, and the quantities of the desired and interference signals can be determined beforehand—for example, if the quantity of the desired signals is M and the quantity of the interference signals is P—then the above formula can be expressed as:

[0188] X(t) = A·S(t) + B·J(t)

[0189] B is the steering vector of P interference signals. M+1 (t), a M+2 (t), ..., a M+P The popular matrix is ​​composed of P interference signals s(t), where J(t) is the number of interference signals s. M+1 (t), s M+2 (t), ..., s M+P The matrix formed by (t).

[0190] The adaptive filter outputs a weighted sum of the signals received from each channel of the array. Let the N×1 vector W represent the weighting vector, i.e.

[0191] W = [w1, w2, ..., w N ] T

[0192] Then the array output signal y(t) can be rewritten as

[0193] y(t)=W H ·X(t)

[0194] By finding a suitable weighting vector (optimal weighting vector) that maximizes the amount of the desired signal component in the output signal, the interference and noise components can be minimized. The effect can be measured by the radiation pattern. The radiation pattern is defined as the array response to signals at different angles given the array weighting vector, and measures the amplification factor of the array for incident signals from various directions in space.

[0195] F(θ)=W H ·a(θ)

[0196] This method extends the one-dimensional array scenario described above to a multi-dimensional case. Firstly, the topology used in this method is a square array antenna. A uniformly distributed square lattice structure is shown in the attached figure. Figure 5As shown, the array elements are uniformly distributed at equal intervals along the X and Y axes. Without loss of generality, we assume the array antenna has a total of K elements, with a spacing of d between elements, the geometric center of the array as the reference origin, and all array elements are isotropic. We define the array antenna spatial coordinate system as a spherical coordinate system with its origin at the geometric center of the array antenna, the X-axis pointing to the right of the array antenna, the Y-axis pointing forward, and the Z-axis pointing upward. Then, for the k-th element antenna with row number m and column number n, let its coordinates in the array antenna spatial coordinate system be (r... k θ k 0), then its polar coordinates on the array distribution plane are as follows: Figure 6 As shown, it can be represented as:

[0197]

[0198] For the m-th incident satellite signal, its direction cosine depends only on the incident signal angle, and its elevation angle and azimuth angle are defined as follows: Then the direction cosine is...

[0199]

[0200] In summary, the delay τ for array element k to receive the signal from the m-th satellite is... mk It can be represented as a function of direction cosines.

[0201]

[0202] Therefore, for narrowband incident signals, the delay of the signal received by the array element can be approximated as the phase of the carrier:

[0203]

[0204] definition Let m be the steering vector of signal m, then The dimension is K:

[0205]

[0206] Let W be the array weight coefficient matrix, and ω be the complex weight coefficients. mn Let be the element in the m-th row and n-th column.

[0207] And there are

[0208]

[0209] In summary, the synthesized beam pattern function of the antenna array is:

[0210]

[0211] Therefore, the beam pattern can be calculated based on the obtained elevation and azimuth angles, and spoofing signals from other directions can be suppressed.

[0212] Step 6: Adjust the beam direction based on the antenna pattern calculated in Step 5 to suppress spoofing signals. Details are as follows:

[0213] For deception jamming using a single antenna transmission mode, all interfering satellite signals calculated in step 4 originate from the same direction; however, for deception jamming using a multi-antenna transmission mode, the direction of the satellite signals originates differs from that calculated in step 3. Therefore, this method can effectively detect deception signals transmitted by a single antenna and suppress them by using optimal beamforming techniques to create null points.

[0214] Null constraints are applied to the array beam pattern, forcing it to always form nulls along a fixed incoming wave direction. The null constraint is a predetermined, fixed constraint, and the null direction is calculated in step 4. The null constraint algorithm implementation steps are as follows:

[0215] 1) Calculate the array steering vector of the interference based on the deception signal obtained in step 4.

[0216] The calculation formula is as follows:

[0217]

[0218] 2) Construct a virtual correlation matrix from the steering vectors, calculated using the following formula:

[0219]

[0220] If there are multiple beam pointing directions, the virtual correlation matrix formed by each guiding vector needs to be summed.

[0221] The number of beam pointing must be less than the number of antenna array elements.

[0222]

[0223] To avoid ill-conditioned matrix inversion, an identity matrix can be loaded onto the virtual correlation matrix.

[0224] R′ b =R b +δI

[0225] 3) Calculate the static direction coefficient of the zero-point constraint, and use the direction coefficient to obtain the zero-point constraint matrix filter. This allows the interference to be synthesized and canceled with the signal received by the reference antenna element after delay matching, amplitude weighting and phase weighting, thereby achieving the purpose of eliminating the deception signal.

[0226]

[0227] in This is a K*1 dimensional constant vector, with the first element being 1 and all other elements being 0. The block diagram for implementing the zero-point shaping constraint is shown below. Figure 7 As shown, the interference received by the auxiliary antenna element is combined with the signal received by the reference antenna element after delay matching, amplitude weighting, and phase weighting to cancel it out. By adjusting the delay matching and amplitude and phase weighting coefficients, the deception signals are mutually canceled, thereby ensuring the normal operation of the receiver.

[0228] This invention utilizes redundant information from a combined navigation system and integrates array antenna hardware to implement an anti-satellite navigation spoofing method from the perspectives of improving the receiver signal processing layer and navigation and positioning layer algorithms. This method can detect and eliminate deceptive interference signals, improving the navigation system's adaptability to complex environments and showing broad application prospects.

[0229] The foregoing has provided a detailed description of a method and system for resisting satellite navigation spoofing based on an array antenna using integrated navigation, as provided in the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and its core ideas; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0230] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system including said element. "Substantially" means within an acceptable margin of error, indicating that a person skilled in the art can resolve the technical problem and substantially achieve the technical effect within a certain margin of error.

[0231] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. In the above embodiments, implementation may be achieved wholly or partially by software, hardware, firmware, or any combination thereof. When implemented in the form of a computer program product, which includes one or more computer instructions, when loaded or executed on a computer, all or part of the processes or functions described in the embodiments of this invention are generated. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another, for example, the computer instructions may be transmitted from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL) or wireless (e.g., infrared, wireless, microwave, etc.) means). The computer-readable storage medium may be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid state disks (SSDs)).

Claims

1. A method for resisting satellite navigation spoofing using an array antenna based on integrated navigation, characterized in that, The steps of the method include: S1. Based on the angular rate and specific force information output by the inertial measurement unit and the magnetic flux information output by the magnetic intensity measurement device, calculate the current carrier attitude. S2. Calculate the true orientation vector of all visible satellites in the geographic system, and then project the true orientation vector into the array antenna coordinate system according to the carrier attitude obtained in S1. Calculate the elevation angle and azimuth angle of the visible satellites relative to the array antenna coordinate system. S3. The satellite signal of the current epoch is sampled and down-converted using digital frequency storage technology and stored. The signal stored in the device is processed by a spatial filter to weight the satellite signal, thereby forming a null trap in the desired direction to shield the signal in that direction, so as to detect whether there is a spoofing signal. If not, the anti-spoofing operation ends; otherwise, proceed to the next step. S4. Determine the direction of the incoming wave of the deception signal; S5. Shape the radiation pattern of the array antenna; S6. Adjust the beam pointing according to the antenna pattern obtained in S5 to suppress the entry of spoofing signals. Specifically, calculate the array steering vector of the interference based on the direction of the incoming wave of the spoofing signal obtained in S4; construct a virtual correlation matrix using the steering vector; calculate the static directional coefficient of the null constraint, and use the directional coefficient to obtain the null constraint matrix filter, so that the interference is combined with the signal received by the reference antenna element after delay matching, amplitude weighting and phase weighting to cancel it out, thereby achieving the purpose of eliminating the spoofing signal.

2. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 1, characterized in that, Step S4 includes: using the signal obtained after forming a null region in the direction of the real signal source, the phase comparison method is used to measure the direction of arrival of the deception signal.

3. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 1, characterized in that, Step S1 includes: S11. Determine whether the criteria are met. ,in, The acceleration output by the accelerometer in the inertial measurement unit. Due to local gravity, The preset acceleration threshold is used; if it is met, the carrier is determined to be in a low-acceleration maneuver state, and the carrier attitude is calculated based on this state; otherwise, proceed to the next step. S12. Determine whether the horizontal acceleration meets the criteria. ,in, The horizontal acceleration magnitude, The preset horizontal acceleration threshold is used; if it is met, the vehicle is determined to be in a low-acceleration maneuver state, and the vehicle attitude is calculated based on this state; otherwise, proceed to the next step. S13. Based on the output of the gyroscope in the inertial measurement unit, determine whether the carrier is undergoing continuous turning or hovering motion. If there is no turning or hovering, it is considered that the misalignment angle error is large and the attitude needs to be corrected.

4. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 3, characterized in that, The attitude correction in step S13 includes: correcting the horizontal misalignment angle based on the horizontal specific force, and correcting the azimuth misalignment angle based on the magnetic flux information.

5. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 4, characterized in that, The correction of the azimuth angle based on magnetic flux information is specifically done by replacing the azimuth angle with magnetic heading.

6. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 1, characterized in that, The specific steps for calculating the projection of the true direction vector of the visible satellites in the geographic system in step S2 are as follows: determine the current visible satellite number based on the current carrier position information output by the integrated navigation system, the current time maintained by the local clock, and the pre-loaded satellite almanac; then calculate the projection of the true direction vector of all currently visible satellites in the geographic system based on the satellite position information calculated from the almanac.

7. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 1, characterized in that, The specific steps for determining the direction of arrival of the deception signal in step S4 include: selecting a real signal, performing a nulling operation on its source direction, and determining the direction of arrival of the deception signal based on the information obtained from the nulling operation and using the phase comparison method.

8. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 7, characterized in that, The selected real signal is the satellite signal of the current epoch.

9. The method for resisting satellite navigation spoofing using array antennas based on integrated navigation according to claim 1, characterized in that, Step S5 includes shaping the array antenna pattern based on the elevation and azimuth angles of the satellite signal at the current epoch in step S3 and the elevation and azimuth angles of the spoofing signal in step S4.

10. A satellite navigation spoofing anti-array antenna system based on integrated navigation, characterized in that, The system includes an inertial measurement unit, a magnetic field measurement device, and a processing module, wherein both the inertial measurement unit and the magnetic field measurement device are connected to the processing module. The processing module includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method as described in any one of claims 1-9.

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