A multipath signal detection apparatus and method

Abstract

The application relates to a multi-path signal detection device and method, which comprises a radio frequency processing module, a carrier tracking loop, a code tracking loop and a multi-path detector connected in sequence. The radio frequency processing module receives satellite signals and sends the signals to the carrier tracking loop after radio frequency processing. The carrier tracking loop sends the received signals to the code tracking loop after stripping the carrier. The code tracking loop outputs the received signals to the multi-path detector after stripping the pseudo code. The multi-path detector is used for detecting whether the received satellite signals are multi-path signals. The application can effectively detect multi-path signals.

Description

Technical Field

[0001] This invention relates to the field of signal reception and detection technology, and in particular to a multipath signal detection device and method. Background Technology

[0002] Satellite navigation and positioning devices receive signals transmitted by satellites, perform distance measurements, and achieve three-dimensional positioning through multiple distance measurements. However, in complex environments such as urban buildings, when receiving signals, there is a chance of receiving signals reflected by buildings. This type of signal causes a larger error in the distance measurement value, which is called multipath propagation. Multipath errors can lead to positioning errors of tens or even hundreds of meters.

[0003] Satellite navigation and positioning devices are affected by multipath signals in the following three ways:

[0004] One scenario is that during the tracking of a normal direct signal, a reflected signal is suddenly received. In this case, the loop tracking frequency is normal, and two peaks will be superimposed in the autocorrelation result of the code loop, which has a significant impact on the code loop and reduces the carrier-to-noise ratio.

[0005] The second scenario is that during the tracking of the direct signal, the signal enters an obstructed environment, causing the energy of the direct signal to decrease. During this process, a reflected signal is suddenly received. In the autocorrelation result of the code ring, two peaks will be superimposed, further weakening the energy of the direct signal, resulting in the reflected signal having higher energy than the direct signal.

[0006] In three scenarios, during the tracking process where the direct signal is lost, a reflected signal is suddenly received, resulting in only one peak in the code ring autocorrelation result, where the peak energy is weaker than that of the direct signal.

[0007] In all three scenarios, a common characteristic is that the satellite signal energy decreases after receiving a multipath signal. If the normal signal energy can be accurately predicted, it will be possible to detect satellite observations subjected to multipath interference in these three scenarios. For the second scenario, the results of the correlation branches before and after the code ring can also be used for judgment.

[0008] It's easy to see that traditional methods, due to the inherent differences in carrier-to-noise ratios (CNR) among satellites, inevitably lead to false multipath detections or low success rates when using the CNR of other satellites to determine multipath propagation. Furthermore, traditional multipath detection methods rely on the CNR of other satellites to determine if a satellite is affected by multipath propagation, rarely using methods that predict the CNR of normal satellites to assess multipath influence. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a multipath signal detection device and method that can effectively detect multipath signals.

[0010] The technical solution adopted by the present invention to solve its technical problem is as follows: a multipath signal detection device is provided, comprising a radio frequency processing module, a carrier tracking loop, a code tracking loop, and a multipath detector connected in sequence. The radio frequency processing module receives satellite signals and performs radio frequency processing before sending them to the carrier tracking loop. The carrier tracking loop strips the carrier from the received signal and sends it to the code tracking loop. The code tracking loop strips the pseudocode from the received signal and outputs it to the multipath detector. The multipath detector is used to detect whether the received satellite signal is a multipath signal.

[0011] The carrier tracking loop includes a mixer, a low-pass filter, a discriminator, and a carrier loop filter connected in sequence, with the carrier loop filter and the mixer connected together.

[0012] The code tracking loop includes an E-branch correlator, an L-branch correlator, a P-branch correlator, a code loop discriminator, a code loop filter, and a shift register;

[0013] The output signal from the carrier tracking loop is fed into the E-branch correlator, L-branch correlator, and P-branch correlator to remove pseudo-code. The P-branch correlator outputs the current carrier-to-noise ratio to the multipath detector. The E-branch correlator outputs the difference between the carrier-to-noise ratios of the E-branch and P-branch to the multipath detector. The L-branch correlator outputs the difference between the carrier-to-noise ratios of the L-branch and P-branch to the multipath detector.

[0014] The P branch inputs the coherent integral of the satellite signal and the local pseudocode to the code loop discriminator, passes through the code loop filter to the shift register, and then forms a closed code loop tracking with the E branch correlator, L branch correlator, and P branch correlator.

[0015] The technical solution adopted by this invention to solve its technical problem is: to provide a multipath signal detection method, comprising:

[0016] Step (1): Receive satellite signals, perform radio frequency processing on the satellite signals, and strip the carrier from the radio frequency processed signals;

[0017] Step (2): Calculate the lead carrier-to-noise ratio of the signal after carrier stripping;

[0018] Step (3): Calculate the delay-to-noise ratio of the signal after carrier stripping;

[0019] Step (4): Calculate the current carrier-to-noise ratio of the signal after carrier stripping;

[0020] Step (5): Compare the current carrier-to-noise ratio of the signal after carrier stripping with the leading carrier-to-noise ratio and the delayed carrier-to-noise ratio respectively to determine whether the received satellite signal is a multipath signal.

[0021] Step (5) includes: determining whether the leading carrier-to-noise ratio and the delayed carrier-to-noise ratio are both greater than 0. If both are greater than 0, the received signal is a multipath signal; if both are less than 0, the current carrier-to-noise ratio is compared with the preset carrier-to-noise ratio.

[0022] The comparison between the current carrier-to-noise ratio and the preset carrier-to-noise ratio specifically involves: if the current carrier-to-noise ratio is less than the preset carrier-to-noise ratio, then the received signal is a multipath signal; if the current carrier-to-noise ratio is greater than the preset carrier-to-noise ratio, then the received signal is determined to be a multipath signal based on the preset carrier-to-noise ratio.

[0023] The step of determining whether the received signal is a multipath signal based on the preset carrier-to-noise ratio specifically means: if the preset carrier-to-noise ratio is the normal carrier-to-noise ratio of the satellite, then the received signal is not a multipath signal; if the preset carrier-to-noise ratio does not reach the normal carrier-to-noise ratio of the satellite, then it is impossible to determine whether the received signal is a multipath signal.

[0024] It also includes updating the preset carrier-to-noise ratio by taking a weighted average of the preset carrier-to-noise ratio and the current carrier-to-noise ratio. Specifically, the weighting method for the preset carrier-to-noise ratio and the current carrier-to-noise ratio during the weighted averaging is as follows:

[0025] If the current carrier-to-noise ratio is equal to the preset carrier-to-noise ratio, then both the current carrier-to-noise ratio weight and the preset carrier-to-noise ratio weight are set to 0.5;

[0026] If the current carrier-to-noise ratio is greater than the preset carrier-to-noise ratio, then the weight of the current carrier-to-noise ratio is set to 1, and the weight of the preset carrier-to-noise ratio is set to 0.

[0027] If the preset carrier-to-noise ratio is 3dB greater than the current carrier-to-noise ratio, then the preset carrier-to-noise ratio weight is set to 1 and the current carrier-to-noise ratio weight is set to 0.

[0028] If the preset carrier-to-noise ratio is greater than the current carrier-to-noise ratio but does not exceed 3dB, then the preset carrier-to-noise ratio weight is set to 29 / 30, and the current carrier-to-noise ratio weight is set to 1 / 30.

[0029] Beneficial effects

[0030] By adopting the above-mentioned technical solutions, this invention has the following advantages and positive effects compared with the prior art: This invention proposes to predict the satellite carrier-to-noise ratio to determine multipath signals, and to update the satellite carrier-to-noise ratio during use. In addition, it combines the baseband lead-delay branch results to achieve the best multipath detection effect; This invention achieves the best effect by increasing the use of the correlation results of the lead and delay branches to determine multipath signals; This invention can eliminate the influence of multipath on receiver positioning in complex environments and improve positioning accuracy. Attached Figure Description

[0031] Figure 1This is a diagram showing the correlation calculation results between the received signal and the locally copied C / A code in an embodiment of the present invention;

[0032] Figure 2 This is a flowchart of the multipath detection method according to an embodiment of the present invention;

[0033] Figure 3 This is a flowchart of the preset carrier-to-noise ratio update logic in an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the structure of the multipath signal detection device according to an embodiment of the present invention. Detailed Implementation

[0035] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] Before detailing this implementation method, let's first introduce some basic theories:

[0037] Figure 1 This represents the result of the correlation operation between the received signal and the locally copied C / A code. A normal signal is as follows: Figure 1 As shown in (a), an ideal correlation curve with an isosceles triangle shape will be formed. The correlation result reaches its peak at chip 0 and gradually decreases towards the positive and negative coordinates with chip 0 as the center, finally reaching a value of 0 at chips -1 and 1. The presence of multipath signals will result in... Figure 1 As shown in (b), it will randomly superimpose a multipath signal near the normal signal, that is, an isosceles triangle will appear again centered at the -1 chip and superimposed on the original pattern.

[0038] from Figure 1 The results show that: (1) The correlation results of the normal signal form an isosceles triangle. The instantaneous P branch of the code ring (i.e., the code tracking loop) has the highest correlation gain and the largest carrier-to-noise ratio (CN0). The correlation results of the E branch (one chip ahead) and the L branch (one chip delayed) of the code ring are the lowest, and CN0 is the smallest. The CN0 of the E branch and the L branch is smaller than that of the P branch. (2) The correlation results of the multipath signal form two superimposed isosceles triangles. The correlation results have two peaks, namely the maximum peak value of the multipath signal of the -1 chip and the second largest peak value of the normal signal of the 0 chip. The correlation result of the E branch (one chip ahead) of the code ring is the highest, and CN0 is the largest. The correlation result of the instantaneous P branch of the code ring is the second largest, and CN0 is the second largest. The correlation result of the L branch (one chip delayed) of the code ring is the smallest, and CN0 is the smallest.

[0039] from Figure 1The results show that: (1) The correlation gain of the leading E branch and the delayed L branch of a normal signal is less than that of the timely P branch, and the CN0 of both the E branch and the L branch is less than that of the P branch. (2) The correlation gain of the leading E branch or the delayed L branch of a multipath signal is greater than that of the P branch (note that the leading E branch and the delayed L branch are in an OR relationship). Figure 1 The diagram only shows one case where the leading E branch gain is greater than the P branch gain. In this case, either E branch CN0 or L branch CN0 will be greater than P branch CN0.

[0040] Embodiments of the present invention relate to a multipath signal detection device, such as... Figure 4 As shown, the system includes a radio frequency (RF) processing module, a carrier tracking loop, a code tracking loop, and a multipath detector connected in sequence. The RF processing module receives satellite signals, performs RF processing, and then sends the signals to the carrier tracking loop (i.e., provides the carrier tracking loop with an intermediate frequency signal). The carrier tracking loop strips the carrier from the received signals and sends them to the code tracking loop. The code tracking loop strips the pseudocode from the received signals and outputs them to the multipath detector. The multipath detector is used to detect whether the received signals are multipath signals.

[0041] Furthermore, the carrier tracking loop includes a mixer, a low-pass filter, a discriminator, and a carrier loop filter connected in sequence. The carrier loop filter is connected to the mixer. The function of the carrier tracking loop is to receive the intermediate frequency signal, output the carrier-stripped signal to the code tracking loop, and form a loop itself to maintain signal tracking.

[0042] Furthermore, the code tracking loop includes an E-branch correlator, an L-branch correlator, a P-branch correlator, a code loop discriminator, a code loop filter, and a shift register. After receiving the baseband signal output from the carrier tracking loop, the code tracking loop enters the E-branch correlator, L-branch correlator, and P-branch correlator respectively to remove pseudo-code. The P-branch correlator outputs the current carrier-to-noise ratio to the multipath detector, the E-branch correlator outputs the difference between the E-branch and P-branch carrier-to-noise ratios to the multipath detector, and the L-branch correlator outputs the difference between the L-branch and P-branch carrier-to-noise ratios to the multipath detector. The P-branch also inputs the coherent integration result of the satellite signal and the local pseudo-code to the code loop discriminator, passes through the code loop filter to the shift register, and then forms a closed code loop tracking with the E-branch correlator, L-branch correlator, and P-branch correlator.

[0043] Furthermore, the timely copy code of the P-branch correlator is correlated with the signal from the carrier tracking loop. The E-branch correlator advances the copy code of the P-branch correlator by one chip and then correlates it with the signal output from the carrier tracking loop, outputting the CN0 difference between the E-branch correlator and the P-branch correlator. The L-branch correlator delays the copy code of the P-branch correlator by one chip and then correlates it with the signal output from the carrier tracking loop, outputting the CN0 difference between the L-branch correlator and the P-branch correlator.

[0044] This embodiment relates to a multipath signal detection method, including:

[0045] Step (1): Receive satellite signals through the radio frequency processing module, and send the satellite signals to the carrier tracking loop after radio frequency processing. The carrier tracking loop strips the carrier of the received signal and sends it to the code tracking loop.

[0046] Step (2): The code tracking loop calculates the lead carrier-to-noise ratio of the signal after carrier stripping through the E-branch correlator;

[0047] Step (3): The code tracking loop calculates the delay-to-noise ratio of the signal after carrier stripping through the L-branch correlator;

[0048] Step (4): The code tracking loop calculates the current carrier-to-noise ratio of the signal after carrier stripping using the P-branch correlator;

[0049] Step (5): The current carrier-to-noise ratio of the signal after carrier stripping is compared with the leading carrier-to-noise ratio and the delayed carrier-to-noise ratio by a multipath detector to determine whether the received satellite signal is a multipath signal.

[0050] The following provides a detailed explanation of how step (5) determines whether the received satellite signal is a multipath signal:

[0051] Figure 2 This is a flowchart of a multipath detection method, where CN0 represents the current carrier-to-noise ratio (CNR), early gap CN0 represents the leading CNR, and late gap CN0 represents the delayed CNR. The method acquires the CN0, early gap CN0, and late gap CN0 values ​​of the code ring. First, it checks if both early gap CN0 and late gap CN0 values ​​are greater than zero. If both are greater than zero, it is determined to be multipath; if both are less than zero, it checks if the current CNR is less than a stored preset CNR (i.e.,...). Figure 2The CN0 GAP threshold (i.e., the storage carrier-to-noise ratio) is used to determine the signal. If the current carrier-to-noise ratio is less than the preset carrier-to-noise ratio, the received signal is a multipath signal. If the current carrier-to-noise ratio is greater than the preset carrier-to-noise ratio, there are two cases: if the preset carrier-to-noise ratio is already the normal carrier-to-noise ratio of the satellite, it means that there is indeed no multipath; if the preset carrier-to-noise ratio has not yet reached the normal carrier-to-noise ratio of the satellite, multipath cannot be determined.

[0052] Considering that the carrier-to-noise ratio (CNR) of a normal satellite signal is stronger than that of a multipath signal, this embodiment further includes updating the preset CNR by taking a weighted average of the preset CNR (i.e., the stored CNR) and the current CNR, in order to record the preset CNR as the normal satellite signal CNR. Specifically, the method for setting the weights of the preset CNR and the current CNR during the weighted averaging is as follows: Figure 3 As shown, there are four cases:

[0053] (1) If the current carrier-to-noise ratio is equal to the preset carrier-to-noise ratio, then the weight of the current carrier-to-noise ratio and the weight of the preset carrier-to-noise ratio are both set to 0.5;

[0054] (2) If the current carrier-to-noise ratio is greater than the preset carrier-to-noise ratio, then the weight of the current carrier-to-noise ratio is set to 1 and the weight of the preset carrier-to-noise ratio is set to 0.

[0055] (3) If the preset carrier-to-noise ratio is greater than the current carrier-to-noise ratio by more than 3dB, then the preset carrier-to-noise ratio weight is set to 1 and the current carrier-to-noise ratio weight is set to 0.

[0056] (4) If the preset carrier-to-noise ratio is greater than the current carrier-to-noise ratio but does not exceed 3dB, then the preset carrier-to-noise ratio weight is set to 29 / 30 and the current carrier-to-noise ratio weight is set to 1 / 30.

[0057] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A multipath signal detection device, characterized in that, The system includes a radio frequency processing module, a carrier tracking loop, a code tracking loop, and a multipath detector connected in sequence. The radio frequency processing module receives satellite signals, performs radio frequency processing, and then sends the signals to the carrier tracking loop. The carrier tracking loop strips the carrier from the received signals and sends them to the code tracking loop. The code tracking loop strips the pseudocode from the received signals and then outputs them to the multipath detector. The multipath detector is used to detect whether the received satellite signals are multipath signals. The code tracking loop includes an E-branch correlator, an L-branch correlator, a P-branch correlator, a code loop discriminator, a code loop filter, and a shift register. The output signal from the carrier tracking loop enters the E-branch correlator, L-branch correlator, and P-branch correlator respectively to remove pseudocode. The P-branch inputs the coherent integral of the satellite signal and the local pseudocode to the code loop discriminator, passes through the code loop filter to the shift register, and then forms a closed code loop tracking with the E-branch correlator, L-branch correlator, and P-branch correlator. The timely copy code of the P-branch correlator is correlated with the output signal of the carrier tracking loop, and the current carrier-to-noise ratio of the resulting carrier-stripped signal is transmitted to the multipath detector. The E-branch correlator advances the copy code of the P-branch correlator by one chip, then performs a correlation operation with the output signal of the carrier tracking loop, outputting the CN0 difference between the E-branch correlator and the P-branch correlator. This CN0 difference is then transmitted to the multipath detector as the lead carrier-to-noise ratio of the carrier-stripped signal. Similarly, the L-branch correlator delays the copy code of the P-branch correlator by one chip, then performs a correlation operation with the output signal of the carrier tracking loop, outputting the CN0 difference between the L-branch correlator and the P-branch correlator. This CN0 difference is then transmitted to the multipath detector as the delay carrier-to-noise ratio of the carrier-stripped signal. The multipath detector determines whether the received satellite signal is a multipath signal based on the current carrier-to-noise ratio, leading carrier-to-noise ratio, and delayed carrier-to-noise ratio of the signal after carrier stripping. Specifically, it determines whether the leading carrier-to-noise ratio and the delayed carrier-to-noise ratio are both greater than 0. If both are greater than 0, the received signal is a multipath signal. If both are less than 0, the current carrier-to-noise ratio is compared with a preset carrier-to-noise ratio. If the current carrier-to-noise ratio is less than the preset carrier-to-noise ratio, the received signal is a multipath signal. If the current carrier-to-noise ratio is greater than the preset carrier-to-noise ratio, then if the preset carrier-to-noise ratio is the normal carrier-to-noise ratio of the satellite, the received signal is not a multipath signal; if the preset carrier-to-noise ratio does not reach the normal carrier-to-noise ratio of the satellite, it is impossible to determine whether the received signal is a multipath signal.

2. The multipath signal detection device according to claim 1, characterized in that, The carrier tracking loop includes a mixer, a low-pass filter, a discriminator, and a carrier loop filter connected in sequence, with the carrier loop filter and the mixer connected together.

3. The multipath signal detection device according to claim 1, characterized in that, The preset carrier-to-noise ratio is updated by taking a weighted average of the preset carrier-to-noise ratio and the current carrier-to-noise ratio. Specifically, the weights of the preset carrier-to-noise ratio and the current carrier-to-noise ratio are set as follows: If the current carrier-to-noise ratio is equal to the preset carrier-to-noise ratio, then both the current carrier-to-noise ratio weight and the preset carrier-to-noise ratio weight are set to 0.5; If the current carrier-to-noise ratio is greater than the preset carrier-to-noise ratio, then the weight of the current carrier-to-noise ratio is set to 1, and the weight of the preset carrier-to-noise ratio is set to 0. If the preset carrier-to-noise ratio is 3dB greater than the current carrier-to-noise ratio, then the preset carrier-to-noise ratio weight is set to 1 and the current carrier-to-noise ratio weight is set to 0. If the preset carrier-to-noise ratio is greater than the current carrier-to-noise ratio but does not exceed 3dB, then the preset carrier-to-noise ratio weight is set to 29 / 30, and the current carrier-to-noise ratio weight is set to 1 / 30.

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