An anti-jamming method for extracting GNSS useful signals in a strong interference environment

Abstract

The present invention discloses an anti-jamming method for extracting GNSS useful signals in a strong interference environment, which relates to the field of satellite navigation technology and specifically includes the following steps: monitoring the gain value of the AGC, and if the gain value changes significantly, interference is detected; calculating the power ratio of the interference signal to the GNSS useful signal by using the monitored AGC gain value; down-converting the signal received by the GNSS receiver to the base frequency and filtering out high-frequency signals and noise; processing the base-frequency signal by using PCA to remove part of the interference; transforming the signal processed by PCA to the Doppler-delay domain to determine the frequency of the GNSS useful signal; transforming the signal processed by PCA to the time-frequency domain to solve the phase of the GNSS useful signal; and extracting the GNSS useful signal from the interfered signal by using the power ratio, frequency and phase. The present invention can accurately recover the GNSS useful signal in a strong interference environment, improve the positioning accuracy in an interference environment, and provide precise positioning for various applications requiring positioning.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite navigation, and particularly to an anti-jamming method for extracting GNSS useful signals in a strong interference environment. Background Art

[0002] The Global Navigation Satellite System (GNSS) provides all-weather, all-day high-precision position, speed, and time information for user terminal devices in various fields of sea, land, air, and space through radio signals transmitted by space navigation satellites, and can provide accurate positioning for users. However, since the power of GNSS signals is small when propagating from space to the ground, and the internal structure of GNSS receivers is relatively clear, GNSS receivers are easily subjected to malicious electromagnetic interference against GNSS signals during operation.

[0003] When a navigation system using GNSS signals enters an interference environment from an environment without electromagnetic interference against GNSS signals, the positioning performance of the system is severely threatened. When the interference signal power is much stronger than the GNSS signal, it will affect the reception of real GNSS signals, cause serious distortion, and even lose signals. Summary of the Invention

[0004] Aiming at the defects of the prior art, the present invention provides an anti-jamming method for extracting GNSS useful signals in a strong interference environment, which can extract GNSS useful signals without distortion in a strong interference environment.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An anti-jamming method for extracting GNSS useful signals in a strong interference environment specifically includes the following steps:

[0007] S1 Monitor the AGC gain value of the RF front end in real time. When the AGC gain value changes significantly, interference is detected;

[0008] S2 Calculate the power ratio a of the interference signal to the GNSS useful signal using the AGC gain value g1 when not interfered and the AGC gain value g2 when interfered by the interference signal source. a is obtained by the following formula:

[0009]

[0010] S3 Down-convert the signal to the baseband frequency and filter out high-frequency signals and noise therein, where the signal includes one or more weak useful signal parts related to GNSS satellites and a strong interference part from the interference signal source;

[0011] S4 Obtain the covariance matrix of the baseband time-domain signal, calculate the eigenvalues and eigenvectors. The strong interference signals correspond to larger eigenvalues, but the eigenvalue thresholds of the GNSS useful signals cannot be accurately determined. Only select and discard the larger eigenvalues among them. There are still interference signals in the remaining signals, but with less energy;

[0012] S5 Transform the baseband time-domain signal to the Doppler-delay domain representation through symplectic Fourier transform; the basis function selection of the symplectic Fourier transform takes into account the maximum Doppler frequency shift present;

[0013] S6 Determine the Doppler delay of the GNSS useful signal in the Doppler-delay domain according to the signal energy magnitude, and then determine the frequency ω of the GNSS useful signal received by the receiver;

[0014] S7 Transform the baseband time-domain signal through short-time Fourier transform to the time-frequency domain representation. Using the frequency obtained in step S6, with this frequency as the center, extract the time-frequency diagram within a certain frequency range, convolve it with a convolution kernel of appropriate size, calculate the energy magnitude around this frequency, determine the interference-free time point according to the energy magnitude, and solve the phase of the GNSS useful signal with the phase at this moment

[0015] S8 Transform the received time-domain signal s(t) to the frequency-domain representation using Fourier transform, i.e., s(ω). Obtain the power ratio a of the GNSS useful signal to the interference signal in step S2, obtain the frequency ω of the GNSS useful signal in step S6, and obtain the phase of the GNSS useful signal in step S7 The GNSS useful signal needs to satisfy constraints in terms of energy and phase, and the specific expressions are as follows:

[0016]

[0017] In the formula, I ω represents the real part of the GNSS useful signal u(ω) at frequency ω, and R ω represents the real part of the GNSS useful signal u(ω) at frequency ω.

[0018] Under the constraint conditions of formula (2), the method for solving the GNSS useful signal from the composite signal of the GNSS useful signal and the interference signal is specifically expressed as;

[0019] minimize||u(ω)+i(ω)-s(ω)|| 2 (3)

[0020] subject to (2)

[0021] Obtain the GNSS useful signal by solving formula (3). Description of the Drawings

[0022] Figure 1 is the flow chart of the present invention;

[0023] Figure 2 is the Doppler-delay domain image without PCA processing obtained by using the present invention in a specific embodiment;

[0024] Figure 3 is the Doppler-delay domain image with PCA processing obtained by using the present invention in a specific embodiment;

[0025] Figure 4 is the time-frequency domain image obtained by using the present invention in a specific embodiment.

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] In an exemplary embodiment, the global satellite navigation system selects the Global Positioning System (GPS). In an exemplary embodiment of GPS, the L1 signal (operating at approximately 1575.42 MHz) is implemented, the interference signal selects a chirp interference, and the signal-to-interference ratio is -15 dB.

[0028] Figure 1 is the flow chart of an anti-jamming method for extracting GNSS useful signals in a strong interference environment provided by the present invention. As shown in the figure, it includes the following steps:

[0029] S1 Monitor the AGC gain value of the RF front end in real time. When the AGC gain value changes significantly, interference is detected;

[0030] S2 After confirming interference, calculate the power ratio a of the interference signal to the GNSS useful signal by using the AGC gain value g1 when not interfered and the AGC gain value g2 when interfered by the interference signal source. a is obtained by the following formula:

[0031]

[0032] S3 Down-convert the signal received by the GNSS receiver to the baseband frequency, and filter out the high-frequency signals and noise therein for processing;

[0033] S4 Convert the baseband time-domain signal to the Doppler-delay domain representation by using the symplectic Fourier transform, where the basis function is determined according to the approximate value of the Doppler frequency shift of the signal received by the GNSS receiver;

[0034] S5 Determine the Doppler delay of the GNSS useful signal according to the signal energy magnitude in the Doppler-delay domain, and then determine the frequency ω of the GNSS useful signal received by the receiver;

[0035] S6 transforms the baseband time-domain signal into the time-frequency domain representation through the short-time Fourier transform, uses the frequency obtained in step S5, extracts the time-frequency diagram within a certain frequency range centered on this frequency, convolves it with a convolution kernel of an appropriate size, sets all the values of the convolution kernel to 1, calculates the energy magnitude around this frequency, determines the undisturbed time point according to the energy magnitude, and solves the phase of the GNSS useful signal with the phase at this moment.

[0036] S7 transforms the received time-domain signal s(t) into the frequency-domain representation by using the Fourier transform, that is, s(ω). Obtains the power ratio a of the GNSS useful signal and the interference signal in step S2, obtains the frequency ω of the GNSS useful signal in step S5, and obtains the phase of the GNSS useful signal in step S6. The GNSS useful signal needs to satisfy constraints in terms of energy and phase, and the specific expressions are as follows:

[0037]

[0038] In the formula, I ω represents the real part of the GNSS useful signal u(ω) at the frequency ω, and R ω represents the real part of the GNSS useful signal u(ω) at the frequency ω. Formula (2) indicates that the power of the GNSS useful signal and the interference signal needs to satisfy the power ratio a and the phase of the GNSS useful signal needs to be equivalent to the phase obtained in step S6.

[0039] Under the constraint conditions of formula (2), the method for solving the GNSS useful signal from the composite signal of the GNSS useful signal and the interference signal, the specific expression is;

[0040] minimize||u(ω + i(ω - s(ω)|| 2 (3)

[0041] subject to (2)

[0042] Figure 2 and Figure 3 are respectively the Doppler-delay domain images without PCA processing and the Doppler-delay domain images after PCA processing obtained by transforming the baseband signal obtained by the method of the present invention, Figure 4 is the time-frequency domain image obtained by transforming the baseband signal obtained by the method of the present invention. In this embodiment, the interference signal is selected as the chirp interference, and the signal-to-interference ratio is -15 dB.

[0043] From Figure 2 and Figure 3It can be seen that after eliminating part of the interference by PCA, the signals can be more clearly resolved in the Doppler-delay domain. The color depth in the figure represents the energy magnitude. The useful GNSS signal is delayed by 3 kHz compared to the standard carrier signal frequency. Figure 4 It can be seen that when the useful GNSS signal is not interfered, this can be used to solve the phase of the useful GNSS signal.

[0044] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An anti-jamming method for extracting GNSS useful signals in a strong interference environment, characterized in that, It includes the following steps: S1 Monitor the AGC gain value of the RF front-end in real time. When the AGC gain value changes significantly, interference is detected; S2 Use the gain values of the AGC of the RF front-end when it is interfered and when it is not interfered to solve the power ratio between the GNSS useful signal and the interference signal; S3 Down-convert the signal to the baseband frequency and filter out the high-frequency signals and noise therein, where the signal includes one or more weak useful signal parts related to GNSS satellites and a strong interference part from an interference signal source; S4 Use PCA to eliminate part of the interference in the baseband time-domain signal; S5 Convert the baseband time-domain signal to the Doppler-delay domain representation through the symplectic Fourier transform; S6 In the Doppler-delay domain, solve the frequency ω of the down-converted GNSS useful signal; S7 converts the baseband time-domain signal into a time-frequency domain representation through short-time Fourier transform, and uses the frequency obtained in step S6 to analyze and obtain the phase of the GNSS useful signal in the time-frequency domain. S8 Use the GNSS useful signal extraction algorithm to solve and extract the GNSS useful signal in the signal; The method for extracting the GNSS useful signal specifically includes the following steps: The signal received by the GNSS receiver can be expressed by the following formula: s(t) = u(t) + i(t) (2); In the formula, u(t) represents the GNSS useful signal, and i(t) represents the interference signal; perform a Fourier transform on the signal s(t) to convert it to the frequency-domain representation s(ω) = u(ω) + i(ω) (3); In step S2, the power ratio a of the GNSS useful signal to the interference signal is obtained. In step S6, the frequency ω of the GNSS useful signal is obtained. In step S7, the phase of the GNSS useful signal is obtained The GNSS useful signal needs to satisfy constraints in terms of energy and phase, which are specifically expressed as follows Wherein, I ω represents the real part of the GNSS useful signal u(ω) at frequency ω, and R ω represents the imaginary part of the GNSS useful signal u(ω) at frequency ω; Under the constraint conditions of formula (4), the method for solving the GNSS useful signal from the composite signal of the GNSS useful signal and the interference signal, the specific expression is Obtain the GNSS useful signal u(ω) by solving formula (5), and perform an inverse transform on it to the time domain to finally obtain the GNSS useful signal u(t).

2. The anti-jamming method for extracting GNSS useful signals according to claim 1, characterized in that, In step S2, calculate the power ratio a of the interference signal to the GNSS useful signal according to the AGC gain value g1 when not interfered and the AGC gain value g2 when interfered by an interference signal source. a is obtained by the following formula:

3. The anti-jamming method for extracting GNSS useful signals according to claim 1, characterized in that, In step S4, the selection of the eigenvalues discarded by the PCA transform is discarded.

4. The anti-jamming method for extracting GNSS useful signals according to claim 1, characterized in that, In step S5, the design of the basis function of the symplectic Fourier transform is carried out.

5. The anti-jamming method for extracting GNSS useful signals according to claim 1, characterized in that, In step S6, in the Doppler-delay domain, determine the Doppler delay of the GNSS useful signal according to the signal energy magnitude, and then determine the frequency ω of the GNSS useful signal received by the receiver.

6. The anti-jamming method for extracting GNSS useful signals according to claim 1, characterized in that, In step S7, according to the energy distribution in the time-frequency diagram, solve the phase of the GNSS useful signal

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