A joint processing method for GNSS suppression and deception interference

Abstract

The present invention discloses a joint processing method for GNSS suppression and deception interference. The method comprises the following steps: receiving a signal, converting the signal into a digital zero intermediate frequency signal, taking the signal as an input signal vector, performing a power inversion operation, taking the inverse matrix of the autocorrelation matrix as a projection matrix, outputting a multi-channel signal, performing a multi-channel tracking operation, synchronously extracting a carrier phase observation quantity and a signal amplitude observation quantity, calculating the carrier phase single difference and the signal amplitude ratio between each channel and a reference channel as a basis for estimating a signal steering vector, calculating the square sum of the carrier phase double difference as a statistic for deception detection, and comparing the result with a preset detection threshold. If the statistic is less than the detection threshold, the signal is determined to be deception interference, and the projection matrix is ​​calculated using the steering vector. The process is repeated until the deception interference disappears. Otherwise, the signal is determined to be a real satellite signal, and the steering vector is made to participate in beamforming, and a positioning operation is performed.

Description

Technical Field

[0001] The present invention belongs to the field of satellite navigation technology, and in particular relates to an interference processing technology. Background Art

[0002] Faced with an increasingly complex electromagnetic environment, Global Navigation Satellite System (GNSS) user-side receivers may encounter various forms of interference during use. Intentional jamming against GNSS receivers can be broadly categorized into two types: suppression jamming and deceptive jamming. Suppression jamming is simple to implement and increasingly mature. Its basic principle is to transmit high-power electromagnetic signals, rendering the target receiver inoperable. Deceptive jamming, a newer and more subtle type of jamming, broadcasts false navigation signals to induce the target receiver to produce erroneous positioning and timing results, making it even more threatening. The differences in the mechanisms and signal characteristics of these two types of jamming have led to relatively independent research.

[0003] High-power suppressive jamming is eliminated through time-domain filtering, frequency-domain filtering, and spatial-domain filtering. Spatial-domain adaptive processing technology based on array antennas is currently the most effective anti-interference measure. Lower-power deceptive jamming requires detecting anomalies in signal characteristics or positioning results at each stage of navigation signal reception and processing, such as signal power monitoring, Doppler monitoring, and receiver autonomous integrity monitoring. Even if a conventional single-antenna receiver is equipped with a deception detection module, it cannot eliminate the deceptive signal after detecting it. Array antenna technology can not only identify any two deceptive signals with the same incident direction based on the spatial characteristics of the signal, but also eliminate deceptive interference through spatial-domain filtering, restoring the receiver's positioning and timing functions.

[0004] With the increasing application of satellite navigation systems in both military and civilian sectors, the interference environments GNSS receivers may face are becoming increasingly complex. With the advancement of anti-spoofing technology, various new spoofing methods are emerging. For example, to successfully implement deceptive jamming, the enemy first broadcasts a high-power suppression signal, causing the target receiver to lose lock and enter a reacquisition state, allowing the spoofing signal to successfully enter the receiver's tracking loop. For example, continuously and simultaneously broadcasting both suppression and spoofing jamming signals can significantly impact receiver performance and positioning results, as most receivers have implemented countermeasures against suppression jamming. Currently, there are few methods that can jointly address these complex scenarios where both suppression and spoofing jamming exist. A common countermeasure involves cascading traditional anti-spoofing jamming algorithms, such as SAP, STAP, and SFAP, with single-antenna spoofing detection methods, without leveraging the spatial processing techniques of array antennas for spoofing detection and suppression. Summary of the Invention

[0005] In order to solve the problem of the coexistence of suppression and deception interference in the prior art, the present invention proposes a joint processing method for GNSS suppression and deception interference. Each antenna array element receives an electromagnetic signal, and after preprocessing, a power-inverted subspace projection method is adopted to eliminate high-power suppression interference signals. Multi-channel tracking is used to obtain carrier phase observations, and deception detection and suppression are performed to ensure the safe application of satellite navigation systems in various complex environments. In order to achieve the above purpose, the present invention adopts the following technical solutions.

[0006] Step 1: Each antenna array element receives the signal, which is filtered, amplified and frequency-converted through the RF channel and converted into an analog intermediate frequency signal. After analog-to-digital conversion and synchronous sampling, it is converted into a digital intermediate frequency signal. After digital down-conversion, it is converted into a digital zero intermediate frequency signal.

[0007] Step 2: Take multiple digital zero-IF signals as input signal vectors, perform power inversion operation, calculate the autocorrelation matrix of the input signal vectors, use the inverse matrix of the autocorrelation matrix as the projection matrix, project the input signal vectors, and output multiple signals.

[0008] Principle of Step 2: Suppressive jamming has high signal power. The power of real satellite signals and spoofing signals is often less than that of noise. The inverse matrix of the autocorrelation matrix can be approximated as the orthogonal complement space of the interference subspace. Projecting using the orthogonal complement space can effectively filter out high-power suppressive jamming.

[0009] Step 3: Multi-channel tracking is performed on multiple signals. A tracking channel is assigned to the multiple outputs of each satellite PRN number. The carrier phase observations and signal amplitude observations are extracted synchronously. The carrier phase single difference and signal amplitude ratio between each channel and the reference channel are calculated as the basis for estimating the signal steering vector. The carrier phase single difference observations of any two PRNs are subtracted in turn, and the sum of the squares of the carrier phase double differences is calculated as the statistic for deception detection.

[0010] Step 4: Compare the spoofing detection statistic with the preset detection threshold. If the statistic is less than the detection threshold, the signal is determined to be spoofing interference. The projection matrix is ​​calculated using the steering vector, and step 3 is repeated until the spoofing interference disappears. Otherwise, the signal is determined to be a real satellite signal, the steering vector is used to participate in beamforming, and the positioning operation is performed.

[0011] Principle of Step 4: Deception suppression and beamforming operations are performed on multi-path signals. The decision on whether to perform deception suppression or beamforming is made based on the results of the previous deception detection. If deception exists, projection is used to eliminate the deception signal. Otherwise, beamforming technology is used to amplify the real satellite signal.

[0012] The beneficial effects of the present invention include:

[0013] It is effective against both suppression jamming and deception jamming, or both, significantly expanding the application scenarios of GNSS receivers and enabling the safe application of satellite navigation systems in various complex scenarios.

[0014] Leveraging the spatial processing advantages of array antennas, the system detects and suppresses two types of interference, resolving the technical issues of single-antenna anti-spoofing methods, which can only detect the presence of spoofing but cannot eliminate it or restore the receiver's positioning capabilities. The fact that jammers transmit two or more spoofing signals from the same antenna is the only prerequisite for spoofing detection and suppression based on array multi-channel tracking. This approach has a wide range of applications and can address most spoofing threats.

[0015] The irrational characteristics of each antenna array element, the amplitude and phase inconsistency of the RF channel, and the amplitude and phase offsets of the spoofing signal caused by the suppression interference cancellation module are already included in the carrier phase observations and signal amplitude observations extracted from each tracking channel in the spoofing detection and suppression algorithm based on multi-channel tracking. This relaxes the requirements of the anti-spoofing module for antenna design and processing and RF channel calibration, and has great practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the system architecture for implementing this method, Figure 2 are different probability distribution functions. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0018] In step 1: Assume that two interference signals exist at any time, and use N antenna elements to receive the signal. After processing, use the formula Represents the intermediate frequency sampling signal, where j q [k], Indicates M J A suppression jamming signal and its guidance vector, Indicates M S A deceptive jamming signal and its guidance vector, Indicates M A real satellite signals and their steering vectors, and n[k] represents the N-dimensional noise vector.

[0019] In the field of array signal processing, the formula represents the steering vector, where λ represents the signal wavelength, p k =[x k ,y k ,z k ] T k (k=1,…,N) represents the position coordinates of the kth antenna array element in the local coordinate system, represents the direction vector of the incident signal, θ represents the pitch angle, Indicates the azimuth.

[0020] Algorithm principle: The steering vector of the array signal reflects the phase difference between the signals reaching each antenna. Incident signals from the same direction have the same phase difference and steering vector. Most deceptive jammers use the same antenna to transmit deceptive signals for all satellites. However, the spatial distribution of real satellites is relatively dispersed, and navigation signals cannot come from the same direction. The presence of deceptive jammers from the same direction can be determined by determining whether the phase differences of different tracking signals are the same.

[0021] In step 2: Suppose there are K sampling points, use the formula Estimate the autocorrelation matrix of the array signal and use its inverse matrix As the projection matrix, use the formula Calculate the output signal, where μ represents a fixed coefficient that controls the signal amplitude and does not affect the output signal-to-noise ratio. Denote the steering vector and noise vector of the deceptive or true signal after subspace projection, and use Represents the direction of the incident signal, using the formula Calculate the steering vector of the incident signal, where They represent the amplitude change and phase shift caused by the influence of the subspace projection on the kth (k=1,…,N) incident signal.

[0022] Algorithm principle: The power of the suppression jamming signal is relatively high. The power of the real satellite signal and the spoofing signal is generally less than the noise power. The inverse matrix of the autocorrelation matrix is ​​approximately the orthogonal complement of the interference subspace. Using it to project the input signal can eliminate the suppression jamming. The impact of the subspace projection on subsequent spoofing detection and suppression processing is mainly reflected in the changes in the signal guidance vector, including amplitude changes and phase offsets. Although suppression jamming suppression will cause carrier phase offsets, the offsets caused by signals from the same direction are the same, and spoofing detection based on carrier phase difference remains effective.

[0023] In step 3: Assume that the N output signals of each PRN number track M navigation signals. The carrier phase observation extracted by the i-th (i=1,…,M) tracking channel in the k-th (k=1,…,N) signal is expressed as (i=1,…,M,k=1,…,N) Calculate the single difference of the carrier phase extracted from each channel of each navigation signal and the reference channel (k=1), using the formula (i, j = 1, ..., M, k = 1, ..., N) to calculate the carrier phase double difference between any two navigation signals, using the formula The sum of squares of the carrier phase double differences is calculated as the spoofing detection statistic.

[0024] Algorithm principle: The tracking loop of a general GNSS receiver can extract signal carrier phase observations. The detection statistic for the presence of deception satisfies the chi-square distribution with N degrees of freedom, while the detection statistic for the absence of deception satisfies the non-central chi-square distribution with N degrees of freedom.

[0025] When deception exists, the angle between the two signals is 0°, and the probability distribution function is as follows: Figure 2 As shown in a, when deception does not exist, the probability distribution functions of the angles between the two signals are 10°, 30°, and 50° respectively. Figure 2 As shown in b, c, and d, the detection threshold can be determined based on the probability distribution function of the chi-square distribution and the false alarm probability requirement.

[0026] In step 4: Based on the carrier phase single difference and signal amplitude ratio, use the formula Calculate the steering vector of the tracked i-th (i=1,…,M) signal, where Indicates the signal amplitude ratio between each channel and the reference channel, and They represent the output results of the in-phase and quadrature correlators of the i-th (i=1,…,M) signal in the k-th (k=1,…,N) tracking channel, respectively. coh represents the coherent integration time, Indicates the signal power. If there is a deceptive signal, The steering vector of the deceptive signal is represented by the formula Calculate the output signal. If there is no deception signal, use Beam the real satellite signal to improve the signal-to-noise ratio gain, using the formula Calculate the output signal, where i=1,…,M,k=1,…,N.

[0027] The above are embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A method for jointly processing GNSS suppression and deception interference, characterized in that: include: Step 1: Each antenna array element receives the signal, which is filtered, amplified and frequency-converted through the RF channel and converted into an analog intermediate frequency signal. After analog-to-digital conversion and synchronous sampling, it is converted into a digital intermediate frequency signal. After digital down-conversion, it is converted into a digital zero intermediate frequency signal. Step 2: Take multiple digital zero-IF signals as input signal vectors, perform power inversion operation, calculate the autocorrelation matrix of the input signal vectors, use the inverse matrix of the autocorrelation matrix as the projection matrix, project the input signal vectors, and output multiple signals; Step 3: Multi-channel tracking is performed on the multi-path signals. Each satellite PRN number is assigned a tracking channel to the multi-path output. The carrier phase observations and signal amplitude observations are extracted synchronously. The carrier phase single difference and signal amplitude ratio of each channel to the reference channel are calculated as the basis for estimating the signal steering vector. The carrier phase single difference observations of any two PRNs are subtracted in sequence, and the sum of the squares of the carrier phase double differences is calculated as the statistic for spoofing detection. Step 4: Compare the spoofing detection statistic with the preset detection threshold. If the statistic is less than the detection threshold, the signal is determined to be spoofing interference. The projection matrix is ​​calculated using the steering vector, and step 3 is repeated until the spoofing interference disappears. Otherwise, the signal is determined to be a real satellite signal, the steering vector is used to participate in beamforming, and the positioning operation is performed.

2. The method for jointly processing GNSS suppression and deception interference according to claim 1, characterized in that: The step 1 includes: assuming that two interference signals exist at any time, using N antenna array elements to receive the signal, and after processing, using the formula Represents the intermediate frequency sampling signal, where j q [k], Indicates M J Suppression jamming signals and their steering vectors, where q = 1, ... M J ; Indicates M S Deceptive jamming signals and their steering vectors, where p = 1, ... M S ; Indicates M A real satellite signals and their steering vectors, where p = 1, ... M A ; n[k] represents the N-dimensional noise vector; in the field of array signal processing, the formula is used represents the steering vector, where λ represents the signal wavelength, p k =[x k ,y k ,z k ] T represents the position coordinates of the kth antenna array element in the local coordinate system, where k = 1,…,N; represents the direction vector of the incident signal, θ represents the pitch angle, Indicates the azimuth.

3. The method for jointly processing GNSS suppression and deception interference according to claim 2, characterized in that: The second step includes: setting K sampling points, using the formula Estimate the autocorrelation matrix of the array signal and use its inverse matrix As the projection matrix, use the formula Calculate the output signal, where μ represents a fixed coefficient that controls the signal amplitude and does not affect the output signal-to-noise ratio. Denote the steering vector and noise vector of the deceptive or true signal after subspace projection, and use Represents the direction of the incident signal, using the formula Calculate the steering vector of the incident signal, where They represent the amplitude change and phase shift caused by the influence of the subspace projection on the k-th incident signal, where k = 1,…,N.

4. The method for jointly processing GNSS suppression and deception interference according to claim 3, characterized in that: The step 3 includes: assuming that N output signals of each PRN number are tracked to M navigation signals, It represents the carrier phase observation extracted by the ith tracking channel in the kth signal, using the formula Calculate the single difference of the carrier phase extracted from each channel of each navigation signal and the reference channel, using the formula Calculate the carrier phase double difference between any two navigation signals using the formula The sum of squares of the carrier phase double differences is calculated as the spoofing detection statistic, where i, j = 1, ..., M, k = 1, ..., N.

5. The method for jointly processing GNSS suppression and deception interference according to claim 4, characterized in that: The fourth step includes: using the formula according to the carrier phase single difference and the signal amplitude ratio Calculate the steering vector of the tracked i-th signal, where Indicates the signal amplitude ratio between each channel and the reference channel, and They represent the output results of the in-phase and quadrature correlators of the i-th signal in the k-th tracking channel, T coh represents the coherent integration time, Indicates the signal power. If there is a deceptive signal, The steering vector of the deceptive signal is represented by the formula Calculate the output signal; if there is no deception signal, use Beam the real satellite signal to improve the signal-to-noise ratio gain, using the formula Calculate the output signal, where i=1,…,M,k=1,…,N.

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