A Tracking Channel Implementation Method for GNSS Anti-Repeatable Spoofing Interference

Abstract

The present invention relates to the field of satellite navigation anti-jamming technology, and particularly relates to a method for implementing a tracking channel for GNSS anti-repeat-spoofing interference, including: preprocessing the radio frequency front-end signal to obtain an intermediate frequency signal; after successful acquisition, entering the tracking channel for normal tracking processing, and at the same time delaying the intermediate frequency signal by multiple preset steps to obtain multiple delayed signals; determining whether the carrier phase and code phase of the tracking channel are synchronized, and after the carrier phase and code phase are synchronized, performing a correlation operation on the replicated carrier sequence and pseudo-code sequence in the tracking channel to obtain a mixed sequence, and performing a correlation accumulation on the mixed sequence and the multiple delayed signals to obtain an energy sequence; obtaining the peak value in the energy sequence and comparing it with a threshold value, and when the peak value is greater than the threshold value, recording the position where the peak value is located, and accordingly adjusting the code numerically controlled oscillator in the tracking channel so that the tracking channel tracks the real signal. The present invention improves the effectiveness of the tracking channel in rejecting spoofing signals.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite navigation anti-jamming, and particularly relates to a method for implementing a tracking channel for GNSS anti-repeater spoofing interference. Background Art

[0002] The Global Navigation Satellite System (GNSS) is one of the four major satellite navigation systems, which can provide services such as positioning, speed measurement, and timekeeping for global users, and has been deeply applied to various aspects of the military and civilian fields. Currently, an important factor threatening the security of GNSS is repeater spoofing interference, and the repeater spoofing interference of GNSS has seriously affected the use of GNSS. Due to its relatively low complexity and low cost, the repeater spoofing interference technology has become the main threat to interfering with users' use of GNSS. Especially in the military aspect, because the repeater signal is generally more powerful than the normal signal, and the time to reach the user device is later after delay forwarding, the user receiver is more likely to capture the powerful repeater signal during the acquisition stage, and the calculated pseudorange will be longer, resulting in incorrect user positioning. Once the spoofing interference signal is captured and positioning or speed measurement is performed based on the spoofing interference signal, the measurement result will deviate from the actual target, which may cause immeasurable losses. This also illustrates the necessity of a receiver with anti-repeater spoofing interference.

[0003] For repeater spoofing interference, currently, it is generally eliminated during the signal acquisition stage. Specifically, the repeater spoofing signal is eliminated according to the power and arrival time of the captured signal. However, when the power of the real signal is weak, there is a certain probability of capturing the repeater spoofing signal at this stage and locking the repeater spoofing signal during the tracking stage. Especially in a complex environment, if the real signal is blocked by buildings or mountains at the beginning of the acquisition stage while the repeater signal is visible, the spoofing signal will be captured and tracked. After tracking the spoofing signal, the repeater spoofing signal is mistakenly regarded as the real signal, so that the repeater spoofing signal cannot be eliminated, resulting in deviation in the final positioning. Summary of the Invention

[0004] The present invention aims to provide a method for implementing a tracking channel for GNSS anti-repeater spoofing interference to identify and eliminate the spoofing signal.

[0005] The method for implementing a tracking channel for GNSS anti-repeater spoofing interference in this solution includes the steps:

[0006] Step 1: Preprocess the radio frequency front-end signal to obtain an intermediate frequency signal, capture the intermediate frequency signal, and transfer it to the tracking channel for tracking after successful capture;

[0007] It further includes the steps:

[0008] Step 2: Send the intermediate-frequency signal into multiple tracking channels for normal tracking processing, and at the same time delay the intermediate-frequency signal according to multiple preset step lengths respectively to obtain multiple delayed signals;

[0009] Step 3: Determine whether the carrier phase and code phase of the tracking channel are synchronized. After the carrier phase and code phase are synchronized, perform a correlation operation on the copied carrier sequence and pseudo-code sequence in the tracking channel to obtain a mixed sequence, and perform a correlation accumulation on the mixed sequence and the multiple delayed signals to obtain an energy sequence;

[0010] Step 4: Obtain the peak value in the energy sequence and compare it with the threshold value. When the peak value is greater than the threshold value, adjust the code numerically controlled oscillator in the tracking channel according to the peak value so that the tracking channel tracks the real signal.

[0011] The beneficial effect of this solution is:

[0012] Preprocess the radio frequency front-end signal to obtain an intermediate-frequency signal, capture the intermediate-frequency signal, and after successful capture, perform a delay to obtain multiple delayed signals. At the same time, perform a correlation on the copied carrier sequence and pseudo-code sequence in the tracking channel, and then perform a correlation accumulation with the multiple delayed signals to obtain an energy sequence. Compare the peak value in the energy sequence with the threshold value, and when the peak value is greater than the threshold value, adjust the code numerically controlled oscillator in the tracking channel to eliminate the transponder spoofing signal in the tracking channel and make the tracking channel track the real signal. It can detect in real time whether the current channel is a spoofing signal, improve the effectiveness of the tracking channel in eliminating spoofing signals, and prevent the user from positioning incorrectly.

[0013] Further, in the step 2, delay is performed respectively with Δτ, 2Δτ,..., mΔτ as the preset step lengths to obtain m delayed signals, where: Δτ is less than or equal to half of a pseudo-code chip.

[0014] The beneficial effect is: Delay the intermediate-frequency signal according to an arithmetic progression so as to be able to find out the spoofing signal in the energy sequence obtained after correlation and eliminate it, and improve the accuracy of spoofing signal recognition.

[0015] Further, in the step 4, when the peak value is greater than the threshold value, record the serial number k when the peak value is greater than the threshold value, and adjust the limit of the code numerically controlled oscillator to be k Δτ chips ahead.

[0016] The beneficial effect is: Adjust the chips of the code numerically controlled oscillator in advance with the serial number when the peak value is greater than the threshold value to accurately eliminate the spoofing signal and accurately track the real signal.

[0017] Further, preset a linear feedback shift register that is not related to all GNSS pseudo-codes, and let the linear feedback shift register generate an output sequence.

[0018] The beneficial effects are as follows: By separately presetting a linear feedback shift register, an output sequence that is uncorrelated with all GNSS pseudo-codes is generated, which will not interfere with the normal use of the tracking channel.

[0019] Further, obtain the output sequence of the linear feedback shift register, perform correlation accumulation on the output sequence and the intermediate frequency signal in Step 1 to obtain a correlation accumulation energy value, perform weighted calculation on the correlation accumulation energy value to obtain a noise energy P_noise, and multiply the noise energy P_noise by a coefficient a to obtain a threshold value, where the coefficient a > 2.

[0020] The beneficial effects are as follows: By obtaining the threshold value in the way of this solution, spoofing signals can be accurately identified, the correlation accumulation values of each time of the noise channel can be smoothed, the threshold value can be made stable, and external interference during the tracking process can be excluded.

[0021] Further, when performing weighted calculation, sum the product of the current correlation accumulation energy value multiplied by the first weight and the product of the previous correlation accumulation energy value multiplied by the second weight to obtain the noise energy, and then use this noise energy for the next weighted calculation.

[0022] The beneficial effects are as follows: Through this weighted calculation method, the problem of noise floor energy spikes caused by external factors during the tracking process can be excluded, excessive jitter caused by noise can be reduced, a smoothing effect can be achieved, and the stability of the noise floor energy can be maintained.

[0023] Further, the first weight is (L - b) / L, and the second weight is b / L, where L ≥ 2 and b < L / 2.

[0024] The beneficial effects are as follows: By calculating the noise energy using two weights for the current and previous correlation accumulation ability values, the weight of the previous value is not more than 0.5, and the current correlation accumulation energy has a higher weight, so as to exclude the interference of external factors and maintain the stability of the noise floor energy. Description of the Drawings

[0025] Figure 1 It is the principle block diagram of the first embodiment of the method for realizing the tracking channel of the GNSS anti-repeater spoofing interference of the present invention;

[0026] Figure 2 It is the schematic diagram of the correlation process of the multi-path delay signal and the replicated carrier mixed sequence in the first embodiment of the method for realizing the tracking channel of the GNSS anti-repeater spoofing interference of the present invention;

[0027] Figure 3 It is the schematic diagram of the principle of calculating the threshold value in the first embodiment of the method for realizing the tracking channel of the GNSS anti-repeater spoofing interference of the present invention. Detailed Embodiment

[0028] The following is a further detailed description through specific embodiments.

[0029] Embodiment 1

[0030] Implementation method of tracking channel for GNSS anti-repeat transponder spoofing interference, as Figure 1 shown, includes the steps of:

[0031] Step 1: Preprocess the RF front-end signal to obtain an intermediate-frequency signal. The preprocessing is down-conversion and A / D conversion. The technology of down-converting the received signal is an existing technology and will not be elaborated here. Capture the intermediate-frequency signal. After successful capture, transfer it to the tracking channel for tracking. The process of signal capture is as follows: Enter the capture stage. After successful capture of the satellite signal, transfer it to the tracking channel. The roughly estimated values of the Doppler frequency and code phase obtained by capture are sent to the tracking channel together. Adjust the carrier numerically controlled oscillator and code numerically controlled oscillator of the tracking channel. Then the tracking channel continuously tracks this satellite. After successfully capturing one satellite, transfer to tracking. The capture module then captures the next satellite, and so on in a cycle. This signal capture technology is existing and will not be elaborated here.

[0032] Step 2: Send the intermediate-frequency signal into multiple tracking channels for normal tracking processing. For example, send the intermediate-frequency signal into n tracking channels. Since the capture module of GNSS captures a certain satellite signal and then transfers it to the tracking channel to continuously track this satellite signal, and in the actual process, many satellite signals will be captured, so there are multiple tracking channels, and each channel operates independently. At the same time, delay the intermediate-frequency signal according to multiple preset step lengths respectively to obtain multiple delayed signals. The multiple preset step lengths form an arithmetic sequence with a tolerance of Δτ, that is, the intermediate-frequency signal is delayed by Δτ, 2Δτ,..., mΔτ respectively to obtain m delayed signals, and the tolerance Δτ is less than or equal to half of the pseudo-code chip.

[0033] Step 3: Judge whether the carrier phase and code phase of the tracking channel are synchronized. Judge whether they are synchronized according to the information obtained from the tracking channel. Synchronization can be judged by the existing carrier-to-noise ratio and will not be elaborated here. After the carrier phase and code phase are synchronized, perform a correlation operation on the carrier sequence and pseudo-code sequence copied by the tracking channel to obtain a mixed sequence, and perform a correlation accumulation on the mixed sequence and the multiple delayed signals to obtain an energy sequence.

[0034] Step 4: Obtain the peak in the energy sequence and compare it with the threshold value. When the peak is greater than the threshold value, record the serial number k when the peak is greater than the threshold value as the position of the peak. Adjust the code numerically controlled oscillator in the tracking channel according to the serial number k of the peak, and adjust the limit of the code numerically controlled oscillator to lead by k Δτ chips, that is, K * Δτ chips. For example, when making 5 delayed signals and performing correlation accumulation with the mixed signal, an energy sequence of 5 correlation accumulation values is obtained, which are 100, 102, 98, 1000, 105 respectively. Then, for the peak of 1000, the corresponding position is the 4th. When adjusting the code numerically controlled oscillator, it is necessary to lead by 4 Δτ chips to make the tracking channel track the real signal. The leading amount of the code numerically controlled oscillator is determined according to the signal delay Δτ. For example, if the received signal delay is a half-chip delay, then here it is to lead by k half-chips. If the received signal delay is a 1 / 4-chip delay, then here it is to lead by k 1 / 4-chips. Here, the leading amount is equal to the delay amount of the intermediate frequency signal when obtaining the correlation accumulation peak.

[0035] Since the intermediate frequency sequence received by the tracking channel contains the real signal and the retransmitted signal, when the current tracking channel is tracking the retransmitted signal, both the channel carrier numerically controlled oscillator and the code numerically controlled oscillator are copying the information of the retransmitted signal. At this time, the received signal is delayed in multiple paths to Figure 2 take the example shown. When the delay amount is 10Δτ, the correlation accumulation of the delayed signal and the copied mixed sequence will exceed the threshold. At this time, the serial number is k = 10. Then, the code numerically controlled oscillator of the tracking channel needs to be adjusted to lead by 10Δτ phases to restore to the tracking of the normal signal. Figure 1 The PVT solution in

[0036] such as Figure 3 shown is the positioning solution performed after removing the retransmitted spoofing interference signal in the later stage. It is an existing technology and will not be elaborated here.

[0037] When performing weighted calculation, the noise energy is obtained by summing the product of the current relevant cumulative energy value multiplied by the first weight and the product of the previous relevant cumulative energy value multiplied by the second weight. The first weight is (L - b) / L, and the second weight is b / L, where L ≥ 2 and b < L / 2. During this iterative process, if L is taken too small, the influence of the previous relevant cumulative energy value on the local relevant cumulative value is relatively large. Taking L ≥ 2 and b < L / 2 is to ensure that the weight of the previous relevant cumulative energy value does not exceed 0.5, so as to reduce the influence of the previous relevant cumulative energy value on the current relevant cumulative energy value. For example, when L = 5, b = 1, the previous relevant cumulative energy value is 5, and the current relevant cumulative energy value is 6. After smoothing, the output is 6*(4 / 5) + 5*(1 / 5) = 5.8, so the output value is 5.8. During the next smoothing, 5.8 will be used as the "previous relevant cumulative energy value".

[0038] Record the sequence number k when the peak value is greater than the threshold value, and adjust the chips of the code numerically controlled oscillator with k. This can accurately eliminate the spoofing signal. The reason is that in the tracking channel, if the spoofing signal is delayed by k Δτ chips compared to the real signal, when the channel tracks the spoofing signal, the pseudo-code sequence replicated by the tracking channel is delayed by k Δτ chips compared to the real signal. When the received intermediate frequency sequence is delayed by k Δτ chips, at this time, the starting phase of the normal signal is the same as the phase of the pseudo-code sequence replicated by the tracking channel. At this time, the mixed sequence replicated by the tracking channel will have the maximum relevant cumulative value with the received sequence delayed by k Δτ chips, and this value will exceed the set threshold value. If a value exceeding the threshold is found after relevant accumulation with m delayed sequences, it indicates that the current channel is tracking a spoofing signal. Record the sequence number k exceeding the threshold value, and adjust the code numerically controlled oscillator in the normal tracking channel to be advanced by k Δτ chips; when the tracking channel tracks a normal signal and no cumulative value exceeding the threshold value is found after relevant accumulation after delay, it indicates that the normal signal is being tracked at this time, and there is no need to adjust the channel code numerically controlled oscillator (i.e., code NCO). When k = 10, as Figure 2 shown in the relevant cumulative process, it can be seen that when the tracking and retransmission signal is in the channel, the local mixed sequence is consistent with the spoofing code sequence in the received intermediate frequency sequence. After delaying the intermediate frequency signal, the real code of the received signal is consistent with the spoofing signal. At this time, a value exceeding the threshold will be obtained through relevant accumulation with the mixed sequence.

[0039] In this embodiment, the radio frequency front-end signal is processed into an intermediate frequency signal, and the intermediate frequency signal is delayed to obtain multiple delayed signals. At the same time, the carrier sequence and the pseudo-code sequence copied in the tracking channel are correlated, and then correlated and accumulated with the multiple delayed signals to obtain an energy sequence. The peak value in the energy sequence is compared with a threshold value. When the peak value is greater than the threshold value, the code-controlled oscillator in the tracking channel is adjusted to eliminate the retransmitted spoofing signal in the tracking channel, so that the tracking channel can track the real signal. Since in a static environment or a low-dynamic environment, the Doppler frequency of the retransmitted signal is not much different from the Doppler frequency of the real signal. When the difference is less than the pulling range of the carrier loop in the tracking channel, the solution of this embodiment can, through correlation accumulation, and judge the retransmitted spoofing signal greater than the threshold value with the designed threshold value, can effectively detect and eliminate the retransmitted spoofing signal, can detect in real time whether the current channel is a spoofing signal, improve the effectiveness of the tracking channel to eliminate the spoofing signal, and prevent the user from positioning errors.

[0040] The above are only the embodiments of the present invention. Specific structures and characteristics and other common knowledge well known in the art are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners and other records in the specification can be used to explain the content of the claims.

Claims

1. A method for implementing a tracking channel of GNSS anti-repeater spoofing interference, comprising the steps: Step 1: Preprocess the radio frequency front-end signal to obtain an intermediate frequency signal, capture the intermediate frequency signal, and transfer it to the tracking channel for tracking after successful capture; It is characterized in that It further includes the steps: Step 2: Send the intermediate frequency signal into multiple tracking channels for normal tracking processing, and at the same time delay the intermediate frequency signal according to multiple preset step lengths to obtain multiple delayed signals; Step 3: Determine whether the carrier phase and code phase of the tracking channel are synchronized. After the carrier phase and code phase are synchronized, perform a correlation operation on the carrier sequence and pseudo-code sequence copied by the tracking channel to obtain a mixed sequence, and perform a correlation accumulation on the mixed sequence and the multiple delayed signals to obtain an energy sequence; Step 4: Obtain the peak in the energy sequence and compare it with the threshold value. When the peak is greater than the threshold value, adjust the code numerically controlled oscillator in the tracking channel according to the position of the peak so that the tracking channel tracks the real signal; Preset a linear feedback shift register that is not related to all GNSS pseudo-codes, let the linear feedback shift register generate an output sequence, obtain the output sequence of the linear feedback shift register, perform a correlation accumulation on the output sequence and the intermediate frequency signal in Step 1 to obtain a correlation accumulation energy value, perform a weighted calculation on the correlation accumulation energy value to obtain the noise energy P_noise, and multiply the noise energy P_noise by a coefficient a to obtain the threshold value, where the coefficient a > 2.

2. The method for implementing a tracking channel of GNSS anti-repeat spoofing interference according to claim 1, characterized in that: In the second step, delays are respectively performed with as the preset step lengths to obtain channels of delayed signals, where: is less than or equal to half of a pseudo-code chip.

3. The tracking channel implementation method for GNSS anti-repeater spoofing interference according to claim 2, wherein: In the fourth step, when the peak value is greater than the threshold value, record the sequence number k when the peak value is greater than the threshold value, and adjust the limit of the code-controlled oscillator to lead by k chips.

4. The tracking channel implementation method for GNSS anti-repeater spoofing interference according to claim 1, wherein: When performing the weighted calculation, sum the product of the current correlation accumulation energy value multiplied by the first weight and the product of the previous correlation accumulation energy value multiplied by the second weight to obtain the noise energy, and then use this noise energy for the next weighted calculation.

5. The method for implementing a tracking channel of GNSS anti-repeater spoofing interference according to claim 4, wherein: The first weight is (L - b) / L, and the second weight is b / L, where L ≥ 2 .

Images