JP6943084B2 - Signal tracking program, signal tracking method and information processing device - Google Patents

Description

The present invention relates to a signal tracking program, a signal tracking method and an information processing apparatus.

A GNSS (Global Navigation Satellite System) that performs position positioning based on a signal received from a GNSS satellite is known (see, for example, Patent Document 1 and Patent Document 2). Deception (spoofing, spoofing) causes misidentification of positioning information such as time information and position information obtained from a real signal transmitted by a GNSS satellite by disguising it. Therefore, it is necessary to prevent deception in GNSS, but in Patent Document 1 and Patent Document 2, it is not possible to determine whether the signal received by the receiver is a deception signal or a genuine signal.

As protection against fraud, there are a method of signal authentication, encryption, and a method of invalidating (null steering) the signal in the direction of arrival of the fraudulent signal by using a plurality of receiving antennas. However, these methods require changes such as multi-antenna in existing systems and hardware, and it is not possible to prevent fraudulent attacks without making these changes.

The power used to carry a deceptive signal is higher than the power used to carry a real signal. Therefore, the deception signal causes deterioration of the C / N (Carria to Noise) value of the real signal. When the C / N value deteriorates until the real signal cannot be tracked, the signal is recaptured, and the tracking of the signal is restored.

Japanese Unexamined Patent Publication No. 2011-433655 Japanese Unexamined Patent Publication No. 2001-153942

However, when the signal is reacquired, the receiver captures the higher power received signal. Therefore, in signal reacquisition, the receiver has a problem that it cannot track a correct signal because it acquires a deceptive signal carried with a power higher than that of a real received signal.

Therefore, in one aspect, the present invention aims to improve the reliability of signal tracking.

In one embodiment, a signal including satellite identification information is received, the signal identified by the satellite identification information is tracked according to a change in the frequency of the signal, and the signal is not tracked at a predetermined cycle. When it is determined whether the signal is possible and it is determined that the signal cannot be tracked, the estimated value of the frequency change when the signal is re-tracked is estimated, and the estimated value of the frequency change is estimated. Based on the above, a signal tracking program for causing a computer to perform processing is provided, which re-tracks a signal according to a determination result of a fraudulent attack.

In one aspect, the present invention can improve the reliability of signal tracking.

The figure which shows an example of the hardware configuration of the receiver which concerns on one Embodiment. A flowchart for explaining a conventional signal tracking method. The figure which shows an example of the functional structure of the receiver which concerns on one Embodiment. The flowchart which shows an example of the signal tracking processing which concerns on one Embodiment. The figure for demonstrating the estimation of the carrier frequency and the code phase which concerns on one Embodiment. The flowchart which shows an example of the update cycle monitoring process which concerns on one Embodiment. The figure for demonstrating the monitoring of the frame number and the update cycle which concerns on one Embodiment. The flowchart which shows an example of the correlation value monitoring processing which concerns on one Embodiment. The figure for demonstrating the re-tracking of a signal which concerns on one Embodiment. The flowchart which shows an example of the signal tracking processing which concerns on the modification of one Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals to omit duplicate explanations.

[Receiver hardware configuration]
FIG. 1 shows an example of a hardware configuration of a GNSS (Global Navigation Satellite System) receiver (hereinafter, referred to as “receiver”) 10 according to an embodiment of the present invention. The receiver 10 receives and demodulates a positioning signal from the GNSS satellite 1 which is a positioning satellite arranged in the orbit around the earth, and obtains the current position, speed, and the like of the mounted moving object based on the result. This is an example of an information processing apparatus having a function of executing a calculation operation, that is, a positioning operation.

The receiver 10 includes an antenna unit 11, a frequency conversion circuit 101, an A / D conversion circuit 102, a correlator 103, a code and carrier generator 104, a CPU 105, a calculation circuit 106, a clock generator 107, a memory 108, and an inertial measurement unit 109. Has.

The receiver 10 receives the signal transmitted from the GNSS satellite 1 in orbit around the earth by using the antenna unit 11, amplifies the received signal, and converts the frequency by the frequency conversion circuit 101. The frequency-converted signal is converted from an analog signal to a digital signal by the A / D conversion circuit 102 and supplied to the correlator 103.

A cord and carrier generator 104 are provided corresponding to the correlator 103. The code and the carrier generator 104 operate with reference to the clock supplied from the clock generator 107, and generate a carrier and correlation detection spreading code (hereinafter referred to as “diffusion code”) under the control of the CPU 105. It is supplied to the correlator 103. In the correlator 103, the carrier from the code and carrier generator 104 and the carrier in the received signal are frequency and phase-locked, and the spreading code from the code and carrier generator 104 and the spreading code related to the received signal are phase-locked. Then, the correlation value obtained in the correlator 103 becomes a peak. The CPU 105 controls the code and carrier generator 104 so that the correlation value in the correlator 103 peaks for the GNSS satellite 1 used for the positioning operation (signal acquisition). In addition, the code and carrier generator 104 are controlled so that the correlation value continues to peak (signal tracking).

An example of a spreading code, for example, a C / A spreading code is composed of 1023 chips, and therefore the code phase can be represented by the number of this chip. Therefore, in FIG. 1, the code phase is referred to as the chip number. show. The reception frequency indicates the carrier frequency of the signal transmitted from the GNSS satellite 1.

The signal transmitted from the GNSS satellite 1 is transmitted using, for example, a carrier frequency of 1575.42 MHz. Further, these signals are spread-modulated using a spreading code defined for each GNSS satellite 1 and then transmitted from the GNSS satellite 1. In this way, the GNSS satellite 1 transmits a signal including a diffusion code which is an example of satellite identification information capable of identifying its own satellite.

As the spreading code, there are a plurality of spreading codes such as a C / A spreading code having a chip rate of 1.023 MHz. Therefore, in the receiver 10, a spreading code for correlation detection corresponding to the spreading code related to the GNSS satellite 1 is generated, and the received signal is despread by establishing and maintaining synchronization between the spreading code and the received signal. ..

Due to this despreading, the code and carrier generator 104 generates a spreading code for correlation detection. The correlator 103 obtains the correlation value between the spreading code and the received signal. The CPU 105 uses the calculation circuit 106 to sweep and change the code phase in the spreading code to determine the correlation value. The CPU 105 captures the code phase in the received signal from the GNSS satellite 1 by detecting the appearance of a peak in the correlation value (code phase search), and establishes the synchronization of the code phase. This captures the signal.

After capturing the signal once, the CPU 105 tracks the change in the code phase in the received signal from the GNSS satellite 1 by controlling the code phase in the diffusion code for correlation detection so that the correlation value continues to maintain its peak. , Keep the code phase in sync. As a result, the signal is tracked.

In the signal tracking state, the receiver 10 receives information such as information contained in the despreaded received signal and code phase (and carrier phase) obtained by synchronization of code phases (and carrier phase). Use it to perform positioning operations.

The CPU 105 stores in the memory 108 a reception frame counter value that counts the number of frames of the signal received by capturing the signal and tracking the signal. The inertial measurement unit 109 measures the moving speed and the moving direction of the receiver 10. The moving speed and the moving direction are examples of information indicating the moving status of the receiver 10. Another example of the information indicating the movement status of the receiver 10 is the acceleration of the receiver 10. The inertial measurement unit 109 may measure the acceleration of the receiver 10.

(Conventional signal tracking method)
Explaining the conventional signal tracking method with reference to FIG. 2, first, the CPU 105 captures the signal transmitted from the GNSS satellite 1 (step S1). Next, the CPU 105 adjusts the PLL (Phase Locked Loop / PLL (Delay Locked Loop)) based on the captured signal information (carrier phase and code phase), and synchronizes the code phase (and carrier phase). The signal is tracked (step S2, step S3). At this time, the CPU 105 controls the signal acquisition and the signal tracking by using the calculation circuit 106, the code and carrier generator 104, and the correlator 103.

Next, the CPU 105 determines whether or not the signal can be tracked (step S4). When the C / N (Carria to Noise) value is below a predetermined threshold value, the CPU 105 determines that the signal cannot be tracked because the C / N value has deteriorated, returns to step S1, and returns to the signal. Recapture.

On the other hand, in step S4, when the C / N value is equal to or higher than a predetermined threshold value, the CPU 105 determines that the signal can be tracked because the C / N value has not deteriorated, and proceeds to step S5 to proceed to the received signal. Is back-spread and the navigation data (navigation data) is decoded. After that, the process returns to step S2 to continue tracking the signal.

When conducting a spoofing attack, the power level used to carry the deceptive signal is usually higher than the power level used to carry the real signal. Therefore, in the real signal transmitted from the GNSS satellite 1, the deception signal causes deterioration of the C / N value. As a result, in the example of FIG. 2, when the C / N value falls below a predetermined threshold value and the signal cannot be tracked, the signal is recaptured (step S1). Since the same spreading code is used for the diffusion modulation of the deceptive signal and the real signal, it is indistinguishable between the two signals, and the power level of the deceptive signal is higher than that of the real signal. Therefore, when recapture occurs, the receiver 10 is more likely to capture the deceptive signal than the real signal.

In order to avoid such an event, the receiver 10 according to the present embodiment does not recapture the signal when the real signal cannot be tracked due to the influence of the fraudulent attack. That is, in the receiver 10 according to the present embodiment, even if the real signal cannot be tracked, recapture is performed to avoid capturing the deceptive signal. Instead of recapturing, the receiver 10 according to the present embodiment estimates the amount of change in the carrier frequency during a fraudulent attack in consideration of the influence of the Doppler frequency. Then, the receiver 10 estimates the start position of the code, that is, the code phase from the peak of the correlation value based on the estimated value of the amount of change in the carrier frequency when returning to the normal state. This makes it possible to restore the tracking of the signal without reacquiring the signal. Hereinafter, an example of the functional configuration and operation of the receiver 10 according to the present embodiment will be described in order.

[Receiver function configuration]
An example of the functional configuration of the receiver 10 according to the present embodiment will be described with reference to FIG. FIG. 3 shows an example of the functional configuration of the receiver 10 according to the embodiment. The receiver 10 according to the present embodiment includes an antenna unit 11, a frequency conversion unit 12, an A / D conversion unit 13, a capture unit 14, a tracking unit 15, a navigation data decoding unit 16, a frame number / update cycle monitoring unit 17, and an IMU. It has an Inertial Measurement Unit 18, a carrier frequency estimation unit 19, a PLL (Phase Locked Loop) / PLL (Delay Locked Loop) adjustment unit 20, a determination unit 21, and a storage unit 22.

The signal is transmitted from the GNSS satellite 1 after being diffusion-modulated using a diffusion code which is an example of satellite identification information capable of identifying the GNSS satellite 1. The antenna unit 11 receives the signal transmitted from the GNSS satellite 1. The antenna unit 11 is an example of a receiving unit that receives a signal including satellite identification information that can identify the GNSS satellite 1.

The frequency conversion unit 12 frequency-converts the received signal. For example, the frequency conversion unit 12 converts a signal having a frequency of 1.5 GHz into a code having a code frequency of about several MHz. For example, when receiving a signal that is diffusion-modulated with a C / A diffusion code, the frequency conversion unit 12 transmits a signal having a carrier frequency of 1575.42 MHz shown in FIG. 5 (a), and the C / A diffusion code is a 1023 chip. Converts to a code with a code frequency of 1.023 MHz.

The A / D conversion unit 13 converts the signal (analog signal) converted to the code frequency into a digital signal.

The capture unit 14 correlates the digital signal after A / D conversion with each diffusion code for correlation detection (an example of identification information of each GNSS satellite 1 and information unique to each GNSS satellite 1). The signal is captured by taking it. The capturing unit 14 obtains the correlation value between the diffusion code for correlation detection and the received signal, and determines the correlation value while sweeping and changing the code phase in the diffusion code for correlation detection. When it is detected that a peak appears in the correlation value, the capture unit 14 captures the code phase in the received signal from the GNSS satellite 1 and establishes the synchronization of the code phase. As a result, the capture unit 14 captures the signal.

After capturing the signal, the tracking unit 15 controls the synchronization of the code phase in the spreading code so that the correlation value continues to maintain the peak by the PLL / DLL adjusting unit 20. As a result, the tracking unit 15 tracks the change in the code phase in the received signal from the GNSS satellite 1, maintains the synchronization of the code phase, and tracks the signal.

The PLL / DLL adjusting unit 20 adjusts so as to maintain the synchronization of the code phase based on the information (carrier phase and code phase) of the captured signal. The determination unit 21 determines whether or not a deceptive attack is being performed on the determined correlation value from the number of peaks while sweeping and changing the code phase in the diffusion code for correlation detection. That is, the determination unit 21 confirms whether or not there are a plurality of correlation value peaks within a predetermined time, and if there are a plurality of correlation value peaks, it is determined that a fraudulent attack is in progress. In this case, in the present embodiment, the tracking return of the signal is not performed, and the process of estimating the amount of change in the carrier frequency by the carrier frequency estimation unit 19 is continued. As a result, after the deceptive attack is eliminated, the signal tracking can be restored without performing the signal reacquisition operation. The carrier frequency estimation unit 19 is an example of an estimation unit that estimates the amount of frequency change when the signal is re-tracked after the deception attack is eliminated when it is determined that the signal cannot be tracked.

The navigation data decoding unit 16 despreads the signal by the spreading code and decodes the navigation data.

A real signal has periodicity. For example, frames of a signal received in an update cycle of t seconds are given a continuous frame number for each frame according to the order of reception. The frame number / update cycle monitoring unit 17 counts up the frame number of the received frame according to a predetermined update cycle, and stores it in the storage unit 22 as a received frame counter value 24.

The frame number / update cycle monitoring unit 17 confirms the frame number and update cycle of the signal after the tracking return, and there is a difference between the continuity from the frame number of the signal received before the deception attack and the update cycle. Check if there is any. If the frame number / update cycle monitoring unit 17 determines that there is a difference between the continuity of the signal received before the deception attack from the frame number and the update cycle, it is possible that the deception signal has been received. high. Therefore, in this case, the frame number / update cycle monitoring unit 17 does not determine that the real signal is being received, and the carrier frequency estimation unit 19 continues and re-estimates the amount of change in the carrier frequency. ..

When the receiver 10 is moving, the IMU unit 18 acquires information indicating the movement status such as the movement speed and the movement direction of the receiver 10 and gives it to the carrier frequency estimation unit 19. The carrier frequency estimation unit 19 corrects the amount of change in the carrier frequency based on the information indicating the movement status of the receiver 10. As a result, even when the receiver 10 is moving, it is possible to accurately estimate the amount of change in the carrier frequency during a deceptive attack.

The functions of each part of the receiver 10 according to the present embodiment described above can be realized by the hardware configuration of the receiver 10 shown in FIG. Specifically, among the functions of each part of the receiver 10 described above, the frequency conversion unit 12 can be realized by, for example, the frequency conversion circuit 101 shown in FIG. The A / D conversion unit 13 can be realized by, for example, the A / D conversion circuit 102. The functions of the capture unit 14, the tracking unit 15, the navigation data decoding unit 16, the frame number / update cycle monitoring unit 17, the carrier frequency estimation unit 19, the PLL / PLL adjustment unit 20, and the determination unit 21 are stored in the storage unit 22. The signal tracking program can be realized by the processing to be executed by the CPU 105 and the calculation circuit 106, the code and carrier generator 104, and the correlator 103. The function of the IMU unit 18 can be realized by, for example, the inertial measurement unit 109. The function of the storage unit 22 can be realized by, for example, a storage device on the cloud connected to the receiver 10 via the memory 108 or the network.

[Signal tracking process]
Next, an example of the signal tracking process according to the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing an example of the signal tracking process according to the embodiment.

When this process is started, the capture unit 14 captures the received signal from the GNSS satellite 1 (step S10). Specifically, the capture unit 14 obtains the correlation value between the spread code and the received signal, and detects that a peak appears in the correlation value while sweeping and changing the code phase in the spread code, thereby detecting the code phase in the received signal. Is captured (signal capture) and code phase synchronization is established.

After capturing the signal once, the tracking unit 15 tracks the signal by controlling the code phase in the spreading code so that the correlation value continues to maintain its peak (step S12).

The PLL (Phase Locked Loop and PLL (Delay Locked Loop) adjusting unit 20) adjusts the code phase so as to maintain the synchronization based on the captured signal information (carrier phase and code phase) (step S14). The code is a different value for each GNSS satellite 1. Therefore, the peak of the correlation value can be calculated for each GNSS satellite 1 by performing reverse diffusion using the correct diffusion code. Even if the reverse spreading is performed using the wrong spreading code, the peak of the correlation value does not appear and the synchronization of the code phase cannot be maintained.

For example, as a result of reverse diffusion of the received signal, a peak of the correlation value appears at a predetermined cycle. When the peak of the correlation value appears, it can be seen that the diffusion modulation and the inverse diffusion can be matched by the diffusion code used for the inverse diffusion. The peak of the correlation value at this time is the beginning position of the code (code phase), and by detecting where the beginning of the code is in a predetermined cycle, the synchronization of the code phase of the captured signal is maintained. , Signal tracking becomes possible.

FIG. 5A shows the influence of the carrier Doppler frequency on the code frequency. As shown in FIG. 5B, in the code phase (the beginning position of the code), the code phase changes according to the change in the carrier frequency. Since the navigation data cannot be restored unless the correlation value is obtained, the PLL / DLL adjustment unit 20 controls to maintain the synchronization of the code phases. The graph of FIG. 5C is an example showing that the carrier frequency of the GNSS satellite 1 changes linearly mainly under the influence of the Doppler frequency when the receiver is stationary. The inclination of the carrier frequency differs depending on each GNSS satellite 1 and the date and time. The PLL / DLL adjusting unit 20 calculates the inclination of the carrier frequency when the signal is normally received, and stores it in the storage unit 22 together with the carrier frequency.

Returning to FIG. 4, the determination unit 21 then determines whether or not the signal cannot be tracked (step S16). The determination unit 21 determines that the signal can be tracked when the C / N value is equal to or higher than a predetermined threshold value, and the navigation data decoding unit 16 back-diffuses the received signal and calculates it based on the correlation value. Decoding the navigation data (step S18).

Next, the frame number / update cycle monitoring unit 17 executes the update cycle monitoring process (step S20), and determines whether the frame number of the received signal and the update cycle are normal based on the result (step S22). ). When the frame number / update cycle monitoring unit 17 determines that the frame number and the update cycle are normal, the process returns to step S12, and the tracking unit 15 continues tracking the signal. The update cycle monitoring process in step 20 will be described later with reference to FIG.

If the frame number / update cycle monitoring unit 17 determines in step S22 that the frame number and update cycle are not normal, the process proceeds in step S24.

Further, in step S16, when the determination unit 21 determines that the C / N value is below a predetermined threshold value, it determines that the signal cannot be tracked because the C / N value has deteriorated, and in step S24. Proceed to.

In step S24, the carrier frequency estimation unit 19 calculates an estimated value of the amount of change in the carrier frequency during the period when the real signal could not be received due to the deception attack from the inclination of the carrier frequency when the signal is normally received. do. The slope of the carrier frequency indicates the degree of influence of the Doppler frequency, and differs depending on each GNSS satellite 1 and the date and time.

When the receiver 10 is stationary, the carrier frequency of the GNSS satellite 1 changes linearly, as shown in FIG. 5 (c). Therefore, the carrier frequency estimation unit 19 multiplies the slope of the carrier frequency immediately before the deception attack by the time estimated that the real signal could not be received due to the deception attack to obtain an estimated value of the amount of change in the carrier frequency. calculate. The amount of change in the code phase can be predicted based on the estimated value of the amount of change in the carrier frequency. As a result, as shown in FIG. 5D, the amount of change in the code phase at the time of normal return can be estimated from the estimated value of the amount of change in the carrier frequency, and the synchronization of the code phase can be controlled.

In step S14 of FIG. 4 described above, the PLL / DLL adjusting unit 20 normally receives a real signal (for example, the time from (1) to (2) in FIG. 5 (c)). ), The slope of the carrier frequency is calculated based on the peak of the correlation value, and is stored in the storage unit 22. Therefore, in step S24, the carrier frequency estimation unit 19 multiplies the inclination of the carrier frequency stored in the storage unit 22 by the time estimated that the real signal could not be received due to the deception attack, thereby performing the carrier. An estimated value of the amount of change in frequency can be calculated.

Next, the determination unit 21 executes the correlation value monitoring process (step S26), and determines whether the fraudulent attack has been eliminated according to the result (step S28). The correlation value monitoring process in step 28 will be described later with reference to FIG.

If the determination unit 21 determines that the deceptive attack is in progress, that is, the deceptive attack has not been eliminated, the processes of steps S24 to S28 are repeated until the deceptive attack is eliminated. When the determination unit 21 determines that the deceptive attack has been eliminated, the determination unit 21 returns to step S14.

When returning from step S28 to step S14, the PLL / DLL adjusting unit 20 estimates the amount of change in the code phase at the time of tracking return from the calculated estimated value of the amount of change in the carrier frequency, and determines the start position of the code, that is, the code phase. Estimate (see FIGS. 5 (c) and 5 (d)). Next, the process proceeds to step S12, and the tracking unit 15 re-tracks the signal based on the estimated code phase. Next, when the determination unit 21 determines that the C / N value has not deteriorated and the signal can be tracked (step S16), the navigation data decoding unit 16 is calculated by adjusting the PLL / DLL. The navigation data is decoded based on the correlation value (step S18). After that, the update cycle monitoring process is executed again (step S20).

(Update cycle monitoring process)
Next, the update cycle monitoring process called in step S20 will be described with reference to FIGS. 6 and 7. FIG. 6 is a flowchart showing an example of the update cycle monitoring process according to the embodiment. FIG. 7 is a diagram for explaining monitoring of the frame number and the update cycle according to the embodiment.

FIG. 7A shows an example of the frame number assigned to the frame (received frame) of the received signal in the normal state. The received frame has periodicity, and the frame number is incremented by one every predetermined update cycle (for example, t seconds). In the example of FIG. 7A, frame numbers n, n + 1, n + 2, ... Are assigned to the received frames in order. n is an integer.

The frame number / update cycle monitoring unit 17 monitors the received signal, counts up the received frame counter value 24 by one for each update cycle, which is the frame switching timing of the signal before receiving the deception signal, and stores it in the storage unit 22. do.

In the update cycle monitoring process of FIG. 6, first, the frame number / update cycle monitoring unit 17 determines whether or not the frame numbers are continuous (step S201). For example, as shown in FIG. 7B, it is assumed that normal signals to which frame numbers n, n + 1, n + 2, and n + 3 are assigned are sequentially received in a t second cycle. After receiving the deception signal with the frame number n + 5 with a delay of + α with respect to the cycle after the next t seconds, the deception signal with the frame numbers n + 6, n + 7, ... Is received in the t second cycle. Suppose you did.

At this time, the reception frame counter value 24 is counted up at each frame switching timing of the signal before the reception of the deception signal, that is, every t-second update cycle. Therefore, the received frame counter value 24 corresponding to the deceptive signal whose frame number is n + 5 received at a time delayed by α from t seconds is n + 5. In this case, the frame number / update cycle monitoring unit 17 determines that the received frame counter value 24 is discontinuous between n + 3 and n + 5.

As a result, the frame number / update cycle monitoring unit 17 detects that there is a possibility of a fraudulent attack because the frame number is abnormal, outputs an alarm (step S203), and ends this process.

On the other hand, in step S201, when the frame number / update cycle monitoring unit 17 determines that the frame numbers have continuity, it determines whether the frame update cycles do not match (step S205). When the frame number / update cycle monitoring unit 17 determines that the frame update cycles do not match, it detects that there is a possibility of a fraudulent attack, outputs an alarm (step S203), and ends this process.

On the other hand, in step S205, when the frame number / update cycle monitoring unit 17 determines that the frame update cycles match, it determines that the frame number and the frame update cycle are normal (step S207), and this process To finish.

For example, as shown in FIG. 7C, after receiving a frame of a real signal to which frame numbers n, n + 1, n + 2, and n + 3 are assigned in a t second cycle, a deception signal is received and the frame number is n + 4, It is assumed that the reception frame of the real signal of n + 5, ..., N + 8 cannot be received. After that, it is assumed that the normal state is restored and a frame of a real signal with frame numbers n + 9, n + 10, ... Is received.

In this case, the frame number / update cycle monitoring unit 17 predicts the frame number of the received frame during the deceptive attack from the received frame counter value 24 before the deceptive attack for each t second update cycle even during the deceptive attack. As a result, the frame number / update cycle monitoring unit 17 can predict the frame number of the real signal when the normal reception state is restored. In the example of FIG. 7C, the frame number / update cycle monitoring unit 17 predicts that the frame number of the received signal at the time of returning to the normal state is n + 9 from the received frame counter value 24, and the frame of the actually received signal. If it matches the number, it is determined that the frame update cycle is normal. On the other hand, when the frame number / update cycle monitoring unit 17 does not match the frame number of the received signal at the time of returning to the normal state predicted from the received frame counter value 24, the frame number of the actually received signal does not match. It is determined that the frame update cycle is abnormal.

In the determination of the continuity of the frame numbers in step S201, the number of error continuities for determining the continuity of the frame numbers may be arbitrarily set in advance. For example, when 5 is set for the number of error continuities, even if the frame numbers of the received frames are discontinuous, the number of consecutive frame numbers of the received frames before and after the discontinuous frames is 6 or more. For example, it may be determined that the frame numbers have continuity. In this case, if the number of consecutive frame numbers of the received frames is 5 or less before or after the discontinuous frames, it is determined that the frame numbers are not continuous.

Further, in the determination of the frame update cycle in step S205, a threshold value indicating an abnormality in the frame update cycle may be arbitrarily set in advance. For example, when 2 is set to the threshold value indicating an abnormality in the frame update cycle, the frame number of the received signal at the time of returning to the normal reception state matches the frame number predicted at that timing from the received frame counter value 24. Even if it is not, if the difference is less than 2, it may be determined that the frame update cycle is normal. In this case, if the difference is 2 or more, it is determined that the frame update cycle is normal.

According to the update cycle monitoring process described above, the frame number / update cycle monitoring unit 17 confirms the frame number of the signal after the tracking return and the update cycle of the frame, and the frame of the signal received before the deception attack. Check if there is a difference between the continuity from the number and the update cycle. If the frame number / update cycle monitoring unit 17 determines that there is a difference between the continuity of the signal received before the deception attack from the frame number and the update cycle, there is a possibility of being deceived. Therefore, the process proceeds from step S22 in FIG. 4 to step S24.

In FIG. 4, even when it is impossible to track the real signal (deterioration of the C / N value) in step S16, it is determined that there is a possibility of being attacked by deception, and the process proceeds to step S24. In step S24, the carrier frequency estimation unit 19 calculates an estimated value of the amount of change in the carrier frequency required for tracking.

That is, in the present embodiment, when it is determined that a fraudulent attack is in progress, the process returns to step S10 and the recapture operation is not performed. That is, the receiver 10 according to the present embodiment estimates the amount of change in the carrier frequency required for tracking in consideration of the Doppler frequency even if the real signal cannot be tracked, and the change in the carrier frequency. The amount of fluctuation in the code phase is estimated based on the estimated value of the amount. As a result, it is possible to restore the tracking of the signal based on the fluctuation amount of the code phase without performing recapturing after eliminating the fraudulent attack. Hereinafter, the details of the correlation value monitoring process in step S26, which determines whether or not a fraudulent attack is in progress based on the estimated value of the amount of change in the carrier frequency calculated in step 24, will be described.

(Correlation value monitoring process)
The correlation value monitoring process called in step S26 will be described with reference to FIGS. 8 and 9. FIG. 8 is a flowchart showing an example of the correlation value monitoring process according to the embodiment. FIG. 9 is a diagram for explaining the re-tracking of the signal according to the embodiment.

In the correlation value monitoring process of FIG. 8, first, the capture unit 14 captures the signal (step S281). The signal captured at this time is used only for confirming the number of peaks of the correlation value.

Next, the determination unit 21 determines whether the peak of the detected correlation value is 2 or more (step S283). When the determination unit 21 determines that the peak of the correlation value is 2 or more, it determines that the deception signal is received because there are a plurality of received signals from the same GNSS satellite 1, and the deception attack is in progress. It detects that there is, and outputs an alarm (step S285). The acquisition unit 14 determines whether it is the confirmation time of signal reacquisition (step S287), and when it is determined that it is the confirmation time of signal reacquisition, returns to step S281 to confirm the number of peaks of the correlation value. The signal is captured again, and the processing after S283 is repeated. On the other hand, in step S283, when the determination unit 21 determines that the peak of the correlation value is not 2 or more, it determines that no deception attack has been performed (step S289), and ends this process.

As described above, according to the receiver 10 according to the present embodiment, the determination unit 21 confirms whether or not a plurality of received signals from the same GNSS satellite 1 exist in order to determine whether or not a fraudulent attack is in progress. When a real signal and a deception signal are received from the same GNSS satellite 1, there are two peaks of the correlation value within a predetermined time. In this case, the determination unit 21 determines that it has been attacked by deception. When it is determined that the board has been attacked, the internal operation of the PLL adjustment is stopped and the carrier frequency at the time of the PLL stop is stored in the storage unit 22 as shown in FIG.

After that, when only the real signal is received from the same GNSS satellite 1, the peak of the correlation value becomes one. If there is only one peak of the correlation value, the determination unit 21 determines that the user has not been attacked by deception. In this case, the determination unit 21 determines that the signal can be tracked normally. At this time, as shown in FIG. 9, the carrier frequency estimation unit 19 calculates a value obtained by adding an estimated value of the amount of change in the carrier frequency indicating the change in the carrier frequency due to the Doppler frequency to the carrier frequency stored in the storage unit 22. do. That is, the carrier frequency estimation unit 19 calculates an estimated value of the amount of change in the carrier frequency by multiplying the slope of the carrier frequency shown in FIG. 5 (c) by the time during the deception attack.

The PLL / DLL adjusting unit 20 estimates the amount of change in the code phase at the time of normal return from the estimated value of the amount of change in the carrier frequency, and controls the synchronization of the code phase. As a result, the signal can be re-tracked without re-capturing the signal, and the navigation data can be decoded based on the correlation value calculated by the re-tracking of the signal.

[Signal tracking process related to modified example]
Next, an example of the signal tracking process according to the modified example of the present embodiment will be described with reference to FIG. FIG. 10 is a flowchart showing an example of signal tracking processing according to a modified example of the present embodiment. The signal tracking process according to the modification of the present embodiment is different from the signal tracking process according to the present embodiment in that the receiver 10 is moving, which is based on the premise that the receiver 10 is not moving. Therefore, the signal tracking process according to the modified example will be described focusing on the above differences. The same process steps as the signal tracking process according to the present embodiment shown in FIG. 4 are given the same step numbers to simplify the description.

When this process is started, signal acquisition, signal tracking and PLL / DLL adjustment are performed in steps S10 to S16, and if the signal can be tracked normally, the navigation data is decoded in step S18. , The update cycle monitoring process is executed. If it is determined that the frame number and the update cycle are normal as a result of executing the update cycle monitoring process, the processes of steps S12 to S22 are repeated.

If it is determined in step S16 that the signal cannot be tracked due to the deterioration of the C / N value, the process proceeds to step S34. If it is determined in step S22 that the frame number or the update cycle is not normal, the process proceeds to step S34.

In step S30, the IMU unit 18 acquires information (IMU information) indicating the movement status of the receiver 10 from the acceleration sensor and the gyro sensor attached to the receiver 10. The IMU unit 18 calculates the moving speed and moving direction of the receiver 10 based on the IMU information (step S32).

In step S34, the carrier frequency estimation unit 19 calculates an estimated value of the amount of change in the carrier frequency during the period when the real signal could not be received due to the deception attack from the inclination of the carrier frequency when the signal is normally received. do. When the receiver 10 is moving, the estimated value of the change in carrier frequency is affected by the Doppler frequency and the movement of the receiver 10. Therefore, in this modification, the carrier frequency estimation unit 19 acquires information (IMU information) indicating the movement status of the receiver 10 from the IMU unit 18, and based on the acquired IMU information, an estimated value of the amount of change in the carrier frequency. To correct. As a result, the PLL / DLL adjustment unit 20 can estimate the amount of change in the code phase at the time of normal return from the estimated value of the amount of change in the corrected carrier frequency, and control the synchronization of the code phase.

Next, the determination unit 21 executes the correlation value monitoring process (step S26), and determines whether the fraudulent attack has been eliminated according to the result (step S28). If the determination unit 21 determines that the deception attack is in progress, the process returns to step S34 until the deception attack is eliminated, and the processes of steps S34, S26, and S28 are repeated. When the determination unit 21 determines that the deceptive attack has been eliminated, the determination unit 21 returns to step S14.

In step S14, the PLL / DLL adjusting unit 20 estimates the amount of change in the code phase at the time of tracking return from the estimated value of the amount of change in the corrected carrier frequency, and estimates the head position of the code. The tracking unit 15 re-tracks the signal (step S12), and when the signal tracking is normal (step S16), the navigation data decoding unit 16 decodes the navigation data based on the calculated correlation value (step S18). ). After that, the update cycle monitoring process is executed again (step S20).

As described above, in the signal tracking process according to the modified example, when the receiver 10 is moving, the carrier frequency is based on the information (IMU information) indicating the movement status of the receiver 10 calculated by the IMU unit 18. Correct the estimated value of the amount of change in. This makes it possible to obtain a more accurate estimate of the amount of change in the carrier frequency. As a result, even when the receiver 10 is moving, after the deceptive attack is eliminated, the signal tracking can be restored without performing the signal recapture operation, and the reliability of the signal tracking is improved. Can be made to.

As described above, according to the present embodiment and its modification, the PLL control value at the time when the signal cannot be tracked due to the deception attack, paying attention to the relationship between the change amount of the carrier frequency and the change amount of the code phase of the GNSS satellite 1. (Carrier frequency, carrier frequency gradient, etc.) are saved. Then, the amount of change in the carrier frequency is estimated from the slope of the carrier frequency in consideration of the change in the Doppler frequency while the real signal cannot be received during the deception attack. Then, the receiver 10 estimates the amount of change in the code phase at the time of return to tracking from the estimated value of the amount of change in the carrier frequency when returning to the tracking state after the deception signal is eliminated, and controls the synchronization of the code phase. .. Further, the receiver 10 can improve the reliability of tracking the signal at the time of tracking / returning by confirming the continuity of the frame number of the received signal at the time of tracking / returning and the frame update cycle.

By the above operation, in the present embodiment and its modified example, the receiver 10 can obtain the effect of preventing fraudulent attacks without the need to change the hardware of the GNSS system or the receiver 10.

Although the signal tracking program, the signal tracking method, and the information processing device have been described above by the above-described embodiment, the signal tracking program, the signal tracking method, and the information processing device according to the present invention are not limited to the above-described embodiment. Various modifications and improvements are possible within the scope of the invention. Further, when a plurality of the above-described embodiments and modifications exist, they can be combined within a consistent range.

With respect to the above description, the following sections will be further disclosed.
(Appendix 1)
Receives a signal containing satellite identification information
The signal identified by the satellite identification information is tracked according to the change in the frequency of the signal, and it is determined whether the signal cannot be tracked in a predetermined cycle.
When it is determined that the signal cannot be tracked, the estimated value of the frequency change when the signal is re-tracked is estimated.
Based on the estimated value of the amount of change in the frequency, the signal is re-tracked according to the judgment result of the fraudulent attack.
A signal tracking program that lets a computer perform processing.
(Appendix 2)
When it is determined that the deception attack of the signal is eliminated, the signal is re-tracked based on the estimated value of the change amount of the frequency.
The signal tracking program according to Appendix 1.
(Appendix 3)
The frame number of the received signal is counted, and the frame number is counted.
When the value obtained by counting the frame numbers does not satisfy the condition regarding the continuity of the frames of the received signal, or the condition regarding the predetermined period of the frames of the received signal, the amount of change in the frequency. Based on the estimated value, it is determined whether the fraudulent attack of the signal is eliminated.
The signal tracking program according to Appendix 1 or 2.
(Appendix 4)
The estimated value of the amount of change in the frequency is corrected according to the information indicating the movement status of the receiver that receives the signal.
The signal tracking program according to any one of Appendix 1 to 3.
(Appendix 5)
Receives a signal containing satellite identification information
The signal identified by the satellite identification information is tracked according to the change in the frequency of the signal, and it is determined whether the signal cannot be tracked in a predetermined cycle.
When it is determined that the signal cannot be tracked, the estimated value of the frequency change when the signal is re-tracked is estimated.
Based on the estimated value of the amount of change in the frequency, the signal is re-tracked according to the judgment result of the fraudulent attack.
A signal tracking method in which a computer performs processing.
(Appendix 6)
When it is determined that the deception attack of the signal is eliminated, the signal is re-tracked based on the estimated value of the change amount of the frequency.
The signal tracking method according to Appendix 5.
(Appendix 7)
The frame number of the received signal is counted, and the frame number is counted.
When the value obtained by counting the frame numbers does not satisfy the condition regarding the continuity of the frames of the received signal, or the condition regarding the predetermined period of the frames of the received signal, the amount of change in the frequency. Based on the estimated value, it is determined whether the fraudulent attack of the signal is eliminated.
The signal tracking method according to Appendix 5 or 6.
(Appendix 8)
The estimated value of the amount of change in the frequency is corrected according to the information indicating the movement status of the receiver that receives the signal.
The signal tracking method according to any one of Appendix 5 to 7.
(Appendix 9)
A receiver that receives signals containing satellite identification information,
A determination unit that tracks the signal identified by the satellite identification information according to a change in the frequency of the signal and determines whether or not the signal cannot be tracked in a predetermined cycle.
When it is determined that the signal cannot be tracked, the estimation unit that estimates the estimated value of the frequency change when the signal is re-tracked, and the estimation unit.
Based on the estimated value of the amount of change in the frequency, the tracking unit that re-tracks the signal according to the judgment result of the deception attack, and
Information processing device with.
(Appendix 10)
When it is determined that the deceptive attack of the signal is eliminated, the tracking unit re-tracks the signal based on the estimated value of the change amount of the frequency.
The information processing device according to Appendix 9.
(Appendix 11)
It has a frame number / update cycle monitoring unit that counts the frame number of the received signal.
When the value obtained by counting the frame numbers does not satisfy the condition regarding the continuity of the frames of the received signal, or when the determination unit does not satisfy the condition regarding the predetermined period of the frames of the received signal, the determination unit said. Based on the estimated value of the amount of change in frequency, it is determined whether the fraudulent attack of the signal is eliminated.
The information processing device according to Appendix 9 or 10.
(Appendix 12)
The estimation unit corrects the estimated value of the amount of change in the frequency according to the information indicating the movement status of the receiver that receives the signal.
The information processing device according to any one of Appendix 9 to 11.

11 Antenna unit 12 Frequency conversion unit 13 A / D conversion unit 14 Capture unit 15 Tracking unit 16 Navigation data decoding unit 17 Frame number / update cycle monitoring unit 18 IMU unit 19 Carrier frequency estimation unit 20 PLL / PLL adjustment unit 21 Judgment unit 22 Storage 101 Frequency conversion circuit 102 A / D conversion circuit 103 Correlator 104 Code and carrier generator 105 CPU
106 Calculation circuit 107 Clock generator 108 Memory 109 Inertial measurement unit

Claims (6)

Receives a signal containing satellite identification information
The signal identified by the satellite identification information is tracked according to the change in the frequency of the signal, and it is determined whether the signal cannot be tracked in a predetermined cycle.
When it is determined that the signal cannot be tracked, the estimated value of the amount of change in frequency when the signal is re-tracked is estimated.
Based on the estimated value of the amount of change in the frequency, the signal is re-tracked according to the judgment result of the fraudulent attack.
A signal tracking program that lets a computer perform processing. The signal tracking program according to claim 1, wherein when it is determined that the deception attack of the signal is eliminated, the signal is re-tracked based on the estimated value of the change amount of the frequency, and the processing is executed by the computer. The frame number of the received signal is counted, and the frame number is counted.
When the value obtained by counting the frame numbers does not satisfy the condition regarding the continuity of the frames of the received signal, or when the condition regarding the predetermined period of the frames of the received signal is not satisfied, the amount of change in the frequency The signal tracking program according to claim 1 or 2, which causes a computer to perform a process of determining whether or not a fraudulent attack on the signal has been eliminated based on an estimated value. The signal according to any one of claims 1 to 3, wherein the estimated value of the amount of change in the frequency is corrected according to the information indicating the movement status of the information processing apparatus that receives the signal, and the processing is executed by the computer. Tracking program. Receives a signal containing satellite identification information
The signal identified by the satellite identification information is tracked according to the change in the frequency of the signal, and it is determined whether the signal cannot be tracked in a predetermined cycle.
When it is determined that the signal cannot be tracked, the estimated value of the frequency change when the signal is re-tracked is estimated.
Based on the estimated value of the amount of change in the frequency, the signal is re-tracked according to the judgment result of the fraudulent attack.
A signal tracking method in which a computer performs processing. A receiver that receives signals containing satellite identification information,
A determination unit that tracks the signal identified by the satellite identification information according to a change in the frequency of the signal, and determines whether or not the signal cannot be tracked in a predetermined cycle.
When it is determined that the signal cannot be tracked, the estimation unit that estimates the estimated value of the frequency change when the signal is re-tracked, and the estimation unit.
Based on the estimated value of the amount of change in the frequency, the tracking unit that re-tracks the signal according to the judgment result of the deception attack, and
Information processing device with.

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