Improved GPS spoofing signal ranging and velocity measurement method with carrier synchronization loop compensation Doppler

Abstract

The application proposes a GPS spoofing signal ranging and velocity measurement method for improving carrier synchronization loop compensation Doppler, which firstly uses square spectrum to perform Doppler coarse estimation on intermediate frequency echo signal; then uses phase-locked loop to obtain accurate Doppler frequency, estimates target velocity and performs Doppler compensation before matched filtering, thereby avoiding the influence of autocorrelation loss caused by Doppler sensitivity on matched filtering effect; finally, the interpolation method is used to improve the ranging accuracy of matched filtering. Simulation experiments show that the method can effectively improve the ranging and velocity measurement accuracy without improving the sampling rate.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to an improved GPS spoofing signal ranging and speed measurement method using carrier synchronization loop compensation Doppler. Background Technology

[0002] With the continuous development of aircraft system technology, the number of various low-altitude aircraft is growing exponentially, and cases of unauthorized drone flights causing safety hazards are occurring frequently. To address the threats to public safety and personal privacy posed by the illegal use of drones, the development of counter-drone systems has become a very important research area.

[0003] Jamming the GNSS navigation systems of unmanned aerial vehicles (UAVs) has always been a research hotspot in UAV countermeasures. GNSS jamming mainly includes suppression jamming and deception jamming. Suppression jamming primarily transmits high-power jamming signals, directly causing the target receiver to "lose lock," preventing it from performing normal acquisition, tracking, and positioning calculations. Deception jamming mainly relays satellite navigation signals or generates counterfeit satellite navigation signals, making it impossible for the target receiver to distinguish between real and jammed signals. It then uses its power advantage to mislead the target receiver into obtaining incorrect position information based on the deceptive jamming signal. Suppression jamming is easily detected because of its high signal transmission power and direct loss of receiver lock. In contrast, deception jamming is more covert.

[0004] In integrated navigation and jamming detection systems based on GNSS spoofing signals, target detection is primarily achieved by receiving and processing the echoes of the spoofing signals. Since GNSS signals are not designed for radar detection, ranging and velocity measurement algorithms suitable for GNSS spoofing signal target detection need to be developed. In low-altitude detection scenarios, strong clutter interference is common, and targets often move slowly with weak echoes. Therefore, clutter suppression algorithms suitable for detecting slow, weak targets under low signal-to-clutter ratio conditions need to be studied.

[0005] When using GNSS spoofing signals for ranging and velocity measurement, the accuracy is primarily limited by the signal sampling rate. Furthermore, if the moving target is moving at a high speed, it can lead to significant autocorrelation loss and matched filter mismatch, resulting in inaccurate ranging. In practical engineering applications, due to limitations in hardware performance and computational load, it is often difficult to improve accuracy simply by increasing the sampling rate. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes an improved GPS spoofing signal ranging and velocity measurement method with carrier synchronization loop compensation Doppler. This method can improve ranging and velocity measurement accuracy without increasing the sampling rate, and the ranging and velocity measurement errors are significantly smaller than those of conventional methods.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An improved method for ranging and velocity measurement using GPS spoofing signals with carrier synchronization loop compensation Doppler is proposed, and the specific steps are as follows:

[0009] (1) Receive the echo signal, perform down-conversion processing on the echo, and strip the modulated carrier to obtain the intermediate frequency signal S(t);

[0010] (2) The intermediate frequency signal is divided into two channels for processing, which are used for speed measurement and distance measurement respectively. The speed measurement channel is first estimated using the square spectrum frequency to obtain , yes again A rough Doppler estimate is performed to obtain the valuation. ;

[0011] (3) Determine whether Doppler coarse compensation is needed based on the Doppler coarse estimation result. If the Doppler coarse estimation value is greater than or equal to 1000Hz, then perform Doppler coarse compensation and then use a phase-locked loop to perform Doppler frequency fine estimation. Otherwise, directly use a phase-locked loop to perform Doppler fine estimation, and use the phase-locked loop to obtain the accurate Doppler frequency, thereby estimating the target velocity v.

[0012] (4) Perform Doppler compensation on the intermediate frequency echo signal based on the accurate Doppler frequency obtained in the speed measurement channel, and perform frequency domain zero-fill operation before matched filtering;

[0013] (5) Finally, the pseudocode phase is estimated by matched filtering, the time delay is obtained and the target distance R is calculated.

[0014] Furthermore, in step (1), the intermediate frequency echo signal after down-conversion... for:

[0015] .

[0016] Furthermore, in step (2), .

[0017] Furthermore, step (3) specifically includes:

[0018] (3.1) If the coarse Doppler estimate is greater than or equal to 1000Hz, then construct a coarse Doppler frequency offset compensation function based on this estimate: Multiplying the compensation function by the signal, we get:

[0019] ;

[0020] in, , representing the Doppler frequency estimation error; This represents the residual phase after compensation.

[0021] (3.2) Further construct a carrier synchronization loop based on a phase-locked loop to accurately estimate the echo Doppler frequency. The compensated signal can be expressed using Euler's formula as follows: in, ;

[0022] (3.3) In order to further improve the signal energy, respectively... and conduct The integral over time, then the first... The integral results are as follows:

[0023] ;

[0024] ;

[0025] (3.4) If the phase detector uses the four-quadrant arctangent algorithm for phase identification, then: ,in, It is the arctangent function in the four quadrants;

[0026] (3.5) Based on the carrier synchronization results of the phase-locked loop, the Doppler frequency estimation result of the phase-locked loop can be obtained as follows: The final intermediate frequency echo signal Doppler frequency estimation ;

[0027] (3.6) If the coarse Doppler estimate is less than 1000 Hz, then FFT Doppler coarse compensation is not required, and the Doppler frequency estimation is performed directly using a phase-locked loop. In this case, the final intermediate frequency echo signal Doppler frequency estimate is obtained. This is the result of the phase-locked loop Doppler frequency estimation. .Right now The expression is:

[0028] ;

[0029] (3.7) Target velocity estimation results The calculation formula is: .

[0030] Furthermore, step (4) specifically includes:

[0031] (4.1) Perform Doppler compensation on the received intermediate frequency echo signal, and the compensated signal Represented as:

[0032] ;

[0033] (4.2) Assume the intermediate frequency echo signal after Doppler compensation Discretization is expressed as Perform FFT operation on it, and then perform zero-padding in the frequency domain. Zero-padding in the frequency domain is equivalent to interpolating the middle of the original sampling interval in the time domain.

[0034] Let the discretized matched filter coefficient signal be... After performing FFT processing, the same frequency domain zero-padding is applied to ensure that the input signal and the matched filter length are consistent. The transformed data are then multiplied accordingly, and an inverse Fourier transform is performed to obtain the matched filtering result. ,and;

[0035] ;

[0036] in, and The input signals are respectively and matched filter coefficients To further improve the signal-to-noise ratio, the Fourier transform of multiple matched filter outputs is performed. The results are then summed after modulo operation for incoherent accumulation. Finally, peak detection is performed on the incoherent accumulation result to obtain the pseudo-code phase. Based on the pseudo-code phase, a relatively accurate time delay is obtained. .

[0037] Furthermore, in step (5), .

[0038] Beneficial Effects: Compared with existing technologies, the significant advantages of this invention are: the ranging accuracy of traditional matched filtering methods depends on the sampling rate, and the velocity accuracy of traditional FFT methods depends on the sampling rate and the number of sampling points. Furthermore, when the target's speed is high, the correlation peak of the matched filter output drops sharply due to the Doppler sensitivity of the GNSS spoofing signal. To address these shortcomings, this invention proposes a GPS spoofing signal ranging and velocity measurement method based on improved carrier synchronization loop compensation for Doppler. This method first uses squared spectrum estimation to obtain a coarse estimate of the echo's Doppler frequency, then uses a phase-locked loop to obtain a precise Doppler frequency estimate and calculate the target velocity, while simultaneously performing precise Doppler compensation. Finally, interpolation is used to improve ranging accuracy. Under the same sampling rate and number of sampling points, the ranging and velocity measurement accuracy of this method is significantly improved compared to conventional matched filtering ranging methods and FFT velocity measurement methods. Attached Figure Description

[0039] Figure 1 This is a flowchart of an embodiment of the present invention;

[0040] Figure 2 This is the flowchart for the distance measurement section. Detailed Implementation

[0041] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0042] The algorithm first needs to down-convert the echo to obtain the intermediate frequency (IF) signal by stripping the modulated carrier. Then, the IF signal is...

[0043] The signal is processed through two channels: one for speed measurement and the other for distance measurement. The speed measurement channel first uses a square...

[0044] The spectrum is used to perform a coarse Doppler estimation of the intermediate frequency echo signal, and then the need for Doppler is determined based on the coarse Doppler estimation results.

[0045] Coarse compensation is performed, followed by the use of a phase-locked loop to obtain the precise Doppler frequency, thereby estimating the target velocity. This is done before ranging.

[0046] Doppler compensation needs to be performed on the intermediate frequency echo signal based on the precise Doppler frequency obtained from the speed measurement channel, in order to avoid...

[0047] To improve ranging accuracy while increasing the sampling rate, a frequency domain zero-filling operation is performed before matched filtering, and finally, the ranging accuracy is improved by matching.

[0048] The algorithm filters and estimates the pseudocode phase, obtains the time delay, and calculates the target distance. The overall flowchart is as follows: Figure 1 As shown. The specific algorithm flow is as follows:

[0049] (1) Receive the echo signal, generate a local carrier signal with the same modulation carrier frequency as the transmitted signal, and downconvert the RF echo signal to an intermediate frequency signal through mixing and filtering for subsequent processing. Assume the downconverted intermediate frequency echo signal... for:

[0050]

[0051] in, For the received signal amplitude, For delayed pseudocode, This represents the Doppler frequency value. This represents the initial phase of the received signal.

[0052] (2) The intermediate frequency signal is divided into two channels for processing, one for speed measurement and the other for distance measurement. The speed measurement channel first uses the square spectrum frequency estimation to obtain... Yes, yes again. A rough Doppler estimate is performed to obtain the valuation. .

[0053] Step (2) specifically includes:

[0054] (2.1) First, perform squared-spectrum frequency estimation. For After squaring the pseudocode, all values ​​become 1, so we get: .

[0055] (2.2) Estimation using FFT The Doppler frequency can be used to obtain a rough estimate of the Doppler frequency of the intermediate frequency echo. Based on the obtained Doppler rough estimate Size determines whether coarse Doppler compensation is needed.

[0056] (3) Determine whether coarse Doppler compensation is needed based on the coarse Doppler estimation results. If the coarse Doppler estimation value is greater than or equal to 1000Hz, perform coarse Doppler compensation and then use a phase-locked loop (PLL) for fine Doppler frequency estimation; otherwise, use a PLL directly for fine Doppler estimation. Use the PLL to obtain the accurate Doppler frequency, thereby estimating the target velocity v.

[0057] Step (3) specifically includes:

[0058] (3.1) If the coarse Doppler estimate is greater than or equal to 1000Hz, then construct a coarse Doppler frequency offset compensation function based on this estimate: .

[0059] Multiplying the compensation function by the signal, we get: ,in, , representing the Doppler frequency estimation error; This represents the residual phase after compensation.

[0060] (3.2) To further reduce the error, a carrier synchronization loop based on a phase-locked loop needs to be constructed to accurately estimate the echo Doppler frequency. The compensated signal can be expressed using Euler's formula as follows: .in, .

[0061] (3.3) In order to further improve the signal energy, respectively... and conduct The integral over time, then the first... The integral results are as follows:

[0062]

[0063] (3.4) If the phase detector uses the four-quadrant arctangent algorithm for phase identification, then: ,in, It is the arctangent function in the four quadrants.

[0064] (3.5) Based on the carrier synchronization results of the phase-locked loop, the Doppler frequency estimation result of the phase-locked loop can be obtained as follows: The final intermediate frequency echo signal Doppler frequency estimation .

[0065] (3.6) If the coarse Doppler estimate is less than 1000Hz, then there is no need to perform FFT Doppler coarse compensation. Doppler frequency estimation can be performed directly using a phase-locked loop. In this case, the final intermediate frequency echo signal Doppler frequency estimate is obtained. This is the result of the phase-locked loop Doppler frequency estimation. .Right now The expression is:

[0066]

[0067] (3.7) After obtaining a more accurate Doppler frequency estimate f, the target velocity estimate v can be obtained, calculated using the following formula: .

[0068] (4) Perform Doppler compensation on the intermediate frequency echo signal based on the accurate Doppler frequency obtained in the speed measurement channel, and perform frequency domain zero-fill operation before matched filtering.

[0069] Step (4) specifically includes:

[0070] (4.1) To avoid the target motion affecting the matched filtering effect, it is necessary to first perform Doppler compensation on the received intermediate frequency echo signal. The compensated signal Represented as: .

[0071] (4.2) Assume the intermediate frequency echo signal after Doppler compensation Discretization is expressed as The sample is then subjected to an FFT operation, and then zero-padding is performed in the frequency domain. Zero-padding in the frequency domain is equivalent to interpolating the original sampling interval in the time domain.

[0072] Let the discretized matched filter coefficient signal be... After performing FFT processing, the same frequency domain zero-padding is applied to ensure that the input signal and the matched filter length are consistent. Multiplying the transformed data and performing an inverse Fourier transform yields the matched filtering result. The above ranging procedure is as follows: Figure 2 As shown.

[0073]

[0074] in, and The input signals are respectively and matched filter coefficients The Fourier transform is then performed. To further improve the signal-to-noise ratio, the modulo values ​​of the outputs from multiple matched filters are summed for incoherent accumulation. Finally, peak detection is performed on the incoherent accumulation result to obtain the pseudo-code phase, and a relatively accurate time delay is obtained based on the pseudo-code phase. .

[0075] (5) Finally, the pseudocode phase is estimated by matched filtering, the time delay is obtained, and the target distance is calculated. .

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. An improved GPS spoofing signal ranging and velocity measurement method using carrier synchronization loop compensation Doppler, characterized in that, The specific steps are as follows: (1) Receive the echo signal, perform down-conversion processing on the echo, and strip the modulation carrier to obtain the intermediate frequency signal S(t); (2) The intermediate frequency signal is divided into two channels for processing, which are used for speed measurement and distance measurement respectively. The speed measurement channel is first estimated using the square spectrum frequency to obtain , yes again A rough Doppler estimate is performed to obtain the valuation. ; (3) Determine whether Doppler coarse compensation is needed based on the Doppler coarse estimation result. If the Doppler coarse estimation value is greater than or equal to 1000Hz, then perform Doppler coarse compensation and then use a phase-locked loop to perform Doppler frequency fine estimation. Otherwise, directly use a phase-locked loop to perform Doppler fine estimation, and use the phase-locked loop to obtain the accurate Doppler frequency, thereby estimating the target velocity v. Step (3) specifically includes: (3.1) If the coarse Doppler estimate is greater than or equal to 1000Hz, then construct a coarse Doppler frequency offset compensation function based on this estimate: Multiplying the compensation function by the signal, we get: ； in, , representing the Doppler frequency estimation error; This represents the residual phase after compensation; (3.2) Further construct a carrier synchronization loop based on a phase-locked loop to accurately estimate the echo Doppler frequency. The compensated signal can be expressed using Euler's formula as follows: in, ; (3.3) In order to further improve the signal energy, respectively... and conduct The integral over time, then the first... The integral results are as follows: ； ； (3.4) If the phase detector uses the four-quadrant arctangent algorithm for phase identification, then: ,in, It is the arctangent function in the four quadrants; (3.5) Based on the carrier synchronization results of the phase-locked loop, the Doppler frequency estimation result of the phase-locked loop can be obtained as follows: The final intermediate frequency echo signal Doppler frequency estimation ; (3.6) If the coarse Doppler estimate is less than 1000 Hz, then FFT Doppler coarse compensation is not required, and the Doppler frequency estimation is performed directly using a phase-locked loop. In this case, the final intermediate frequency echo signal Doppler frequency estimate is obtained. This is the result of the phase-locked loop Doppler frequency estimation. ,Right now The expression is: ； (3.7) Target velocity estimation results The calculation formula is: ; (4) Perform Doppler compensation on the intermediate frequency echo signal based on the accurate Doppler frequency obtained in the speed measurement channel, and perform frequency domain zero-fill operation before matched filtering; Step (4) specifically includes: (4.1) Perform Doppler compensation on the received intermediate frequency echo signal, and the compensated signal Represented as: ； (4.2) Assume the intermediate frequency echo signal after Doppler compensation Discretization is expressed as Perform FFT operation on it, and then perform zero-padding in the frequency domain. Zero-padding in the frequency domain is equivalent to interpolating the middle of the original sampling interval in the time domain. Let the discretized matched filter coefficient signal be... After performing FFT processing, the same frequency domain zero-padding is applied to ensure that the input signal and the matched filter length are consistent. The transformed data are then multiplied accordingly, and an inverse Fourier transform is performed to obtain the matched filtering result. ,and; ； in, and The input signals are respectively and matched filter coefficients The Fourier transform is performed, and finally, peak detection is performed on the incoherent accumulation result to obtain the pseudo-code phase. The relatively accurate time delay is obtained based on the pseudo-code phase. ; (5) Finally, the pseudocode phase is estimated by matched filtering, the time delay is obtained and the target distance R is calculated.

2. The improved GPS spoofing signal ranging and velocity measurement method with carrier synchronization loop compensation Doppler as described in claim 1, characterized in that: In step (1), the intermediate frequency echo signal after down-conversion for: 。 3. The improved GPS spoofing signal ranging and velocity measurement method with carrier synchronization loop compensation Doppler as described in claim 1, characterized in that: In step (2), .

4. The improved GPS spoofing signal ranging and velocity measurement method with carrier synchronization loop compensation Doppler as described in claim 1, characterized in that: In step (5), .

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