CN114624736A - Anti-interference method of Beidou time synchronization receiver - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/21—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/35—Constructional details or hardware or software details of the signal processing chain
- G01S19/37—Hardware or software details of the signal processing chain
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- G—PHYSICS
- G04—HOROLOGY
- G04R—RADIO-CONTROLLED TIME-PIECES
- G04R20/00—Setting the time according to the time information carried or implied by the radio signal
- G04R20/02—Setting the time according to the time information carried or implied by the radio signal the radio signal being sent by a satellite, e.g. GPS
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Abstract
The invention discloses an anti-interference method of a Beidou time synchronization receiver, which comprises the following steps: 1) inputting a baseband digital intermediate frequency signal output by a radio frequency front-end processing module of a receiver into an interference suppression module; 2) the interference suppression module adopts a frequency domain interference suppression algorithm to suppress interference in the signal; 3) before time service resolving, eliminating forwarding type interference in an output signal of an interference suppression module; 4) in the time service resolving process, the undetected forwarding type interference signals are filtered by using a Kalman filtering algorithm. The anti-interference method of the Beidou time synchronization receiver can effectively inhibit narrow-band interference and forwarding interference and can improve the accuracy of the time synchronization device for outputting time information.
Description
Technical Field
The invention relates to the technical field of satellite navigation time service application, in particular to an anti-interference method of a Beidou time synchronization receiver.
Background
With the development of satellite navigation technology and the continuous expansion of the application field thereof, the satellite time service technology is widely applied to the industries of electric power, traffic, communication, banking, finance and the like. The satellite time service is utilized to realize high-precision clock synchronization in a wide area range, the cost is low, especially, the Beidou satellite navigation system in China is put into operation formally, the satellite time service-based synchronization technology plays an increasingly important role in China, and the safety of the satellite time service receiver is increasingly prominent. However, due to the limited wave power of the satellite, the electromagnetic interference of the transmission channel is complex, the format of the signal frame is open, and the signals of the satellite navigation system are extremely vulnerable to the deceptive interference. The deception jamming can cause the time synchronization device to output wrong time information, which can pose a serious threat to the safety of production operation.
Disclosure of Invention
In view of this, the present invention aims to provide an anti-interference method for a beidou time synchronization receiver, so as to solve the technical problem that electromagnetic interference affects the accuracy of time information output by a time synchronization device.
The anti-interference method of the Beidou time synchronization receiver comprises the following steps of:
1) inputting a baseband digital intermediate frequency signal output by a radio frequency front-end processing module of a receiver into an interference suppression module;
2) the interference suppression module adopts a frequency domain interference suppression algorithm to suppress the interference in the signal, and the method further comprises the following steps:
2a) performing serial-to-parallel conversion on an input signal;
2b) performing windowing processing on the signals subjected to serial-parallel conversion;
2c) performing FFT processing on the windowed signal, and transforming the time domain data to a frequency domain;
2d) one path of the signal after FFT processing is sent to a weighting vector generating unit to update the frequency domain weighting vector generated in the previous period, and the other path of the signal is weighted with the generated frequency domain weighting vector;
2f) performing IFFT processing on the weighted signals to recover time domain data;
2g) performing parallel-serial conversion on the signal after IFFT processing and then outputting the signal, and keeping the data rate of input and output unchanged;
3) before time service resolving, eliminating forwarding interference in an output signal of an interference suppression module, and further comprising the following steps:
3a) detecting the power of the signals, and rejecting the signals with the power exceeding a set range;
3b) detecting the arrival time of the signals, and rejecting the signals with the arrival time exceeding a set range;
3c) detecting the message information, and rejecting abnormal message information signals;
4) and in the time service resolving process, filtering undetected forwarding type interference signals by using a Kalman filtering algorithm.
Further, the step 2d) of generating the frequency domain weighting vector by the weighting vector generating unit comprises the following steps:
2d1) taking an absolute value of the signal after FFT processing and then squaring the signal;
2d2) averagely dividing the signal into a plurality of sections;
2d3) calculating the periodic diagram of each segment, and taking the average of each periodic diagram as a power spectrum;
2d4) and comparing the amplitude of the power spectrum with a decision threshold to generate a frequency domain weighting vector.
Further, in step 2d), a path of signal weighted by the frequency domain weighting vector is subjected to whitening filtering processing, and the whitening filter is:
wherein N is0And NJNoise power spectral density and interference power spectral density, respectively, f is the signal frequency, fIIs the interference center frequency, B is the noise bandwidth, alpha is the ratio of the interference bandwidth to the noise bandwidth, and j is the narrowband interference signal;
when the dry-to-noise ratio is much larger than 1, the whitening filter is approximated as
Wherein f is0' is the interference frequency;
or in step 2d), one path of signal which is subjected to weighting operation with the frequency domain weighting vector is input into a frequency domain remover, and interference spectral lines with the amplitude exceeding an interference removal threshold are zeroed, wherein the frequency domain remover is provided with attenuation factors equal to or larger than the interference removal threshold
The attenuator of (2) is cascaded with the whitening filter in the formula (2), and the transfer function of the frequency domain rejector is:
the invention has the beneficial effects that:
the anti-interference method of the Beidou time synchronization receiver can effectively inhibit narrow-band interference and forwarding type interference and can improve the accuracy of the time synchronization device for outputting time information.
Drawings
FIG. 1 is a diagram of a receiver system framework; it can be seen from the figure that the receiver system mainly comprises three major parts, namely a radio frequency front-end processing module, an interference suppression module and a time service module. The antenna collects the received navigation signals mixed with noise interference and transmits the navigation signals to the radio frequency front end. When the radio frequency module receives signals, the functions of filtering, signal amplification, down-conversion and the like are realized. The received high frequency signal is down converted to an intermediate frequency analog signal by frequency conversion processing. The frequency-reduced signal is processed by a multistage band-pass filter to remove out-of-band noise, and then is sampled by DSP software or other signal processors A/D to reduce the data flow rate and become a baseband digital intermediate frequency signal.
FIG. 2 is a schematic block diagram of a frequency domain interference suppression algorithm;
FIG. 3 is a diagram of a frequency domain weighting vector generation structure;
fig. 4 is a flow chart of a satellite navigation system receiver repeater interference suppression algorithm.
Detailed Description
The invention is further described below with reference to the figures and examples.
The anti-interference method of the Beidou time synchronization receiver in the embodiment mainly solves the problems of narrow-band interference resistance and forwarding type deception interference resistance. The anti-interference method of the Beidou time synchronization receiver in the embodiment comprises the following steps:
1) and inputting the baseband digital intermediate frequency signal output by the radio frequency front-end processing module of the receiver into an interference suppression module.
2) The interference suppression module adopts a frequency domain interference suppression algorithm to suppress the interference in the signal, and the method further comprises the following steps:
2a) the input signal is converted from serial to parallel.
2b) And performing windowing processing on the signals after serial-parallel conversion to reduce frequency spectrum leakage caused by data truncation. In this step, a data window with a small side lobe level is adopted to reduce the spectrum leakage. From the time domain perspective, windowing (a conventional FFT uses a rectangular window) is to perform window function weighting on input data; the window function is gradually attenuated from the center to two ends, so that the continuity of the data of the front section and the rear section can be ensured, and the purpose of reducing the frequency spectrum leakage is achieved.
2c) The windowed signal is subjected to FFT (fast Fourier transform) processing, and the time domain data is transformed into the frequency domain.
2d) One path of the signal after FFT processing is sent to a weighting vector generating unit to update the frequency domain weighting vector generated in the previous period, and the other path of the signal is weighted with the generated frequency domain weighting vector.
The frequency domain weighting vector is used for determining the position of an interference frequency band according to the power spectral density of an input signal and carrying out weighting processing on the interfered signal spectrum, so that the purpose of interference suppression is achieved.
In this step, the step of generating the frequency domain weighting vector by the weighting vector generating unit includes the steps of:
2d1) taking an absolute value of the signal after FFT processing and then squaring the signal;
2d2) averagely dividing the signal into a plurality of sections;
2d3) calculating the periodic diagram of each segment, and taking the average of each periodic diagram as a power spectrum;
2d4) and comparing the amplitude of the power spectrum with a decision threshold to generate a frequency domain weighting vector.
In this step, a path of signal weighted by the frequency domain weighting vector is subjected to whitening filtering processing, and the whitening filter is:
wherein N is0And NJNoise power spectral density and interference power spectral density, respectively, f is the signal frequency, fIIs the interference center frequency, B is the noise bandwidth, α is the ratio of the interference bandwidth to the noise bandwidth, and j is the narrowband interference signal.
When the dry-to-noise ratio is much larger than 1, the whitening filter is approximated as
Wherein f is0' is the interference frequency.
In this case, the whitening filter is equivalent to completely spectrally filtering out interference, noise, and signals in the interference band, and normalizing the noise power spectrum outside the interference band. The whitening filter is placed before the matched filter of the receiver.
Or in step 2d), the signal subjected to weighting operation with the frequency domain weighting vector is input into a frequency domain remover, and interference spectral lines with amplitudes exceeding an interference removal threshold are zeroed, wherein the frequency domain remover is provided with attenuation factors equal to
The attenuator of (2) is cascaded with the whitening filter in the formula (2), and the transfer function of the frequency domain rejector is:
the frequency domain eliminator specifically utilizes a large spectral line return-to-zero principle to return interference spectral lines with amplitudes exceeding an interference elimination threshold to zero, and other spectral lines are kept unchanged, so that the purpose of interference suppression is achieved. From the perspective of the filter, the frequency domain interference rejection algorithm is equivalent to an ideal band elimination filter with zero phase response, the algorithm time delay is equal to 0, and the time delay estimation process can be omitted.
2f) The weighted signal is subjected to IFFT (Inverse Fast Fourier Transform) processing to restore time domain data.
2g) And performing parallel-serial conversion on the signals after the IFFT processing, and outputting the signals, wherein the data rate of input and output is kept unchanged.
The suppression of the narrow-band interference can be realized through a frequency domain interference suppression algorithm, and the spurious-free dynamic range can reach 88 dB.
3) Before time service resolving, eliminating forwarding interference in an output signal of an interference suppression module, and further comprising the following steps:
3a) and detecting the power of the signal, and rejecting the signal with the power exceeding a set range. Although the strength of the interference signal is comparable to that of the satellite signal and is very high in concealment, the strength of the interference signal is slightly higher than that of the real satellite signal, because only this makes the interference signal dominant in the acquisition process of the receiver. The power of the satellite signal received by the receiver has a normal and reasonable working range, namely-110 dBm to-133 dBm, under the influence of the on-satellite transmitting power range, so that if the power of the received navigation satellite signal exceeds the range, the signal can be considered as a forwarding interference signal.
The estimation of the power of the navigation satellite signal is mainly determined according to the magnitude of an integral value of a relevant channel, namely the output power of the relevant channel. That is, the power (sum of squared integral values) of the current branch in the three-way integrating branches (leading, lagging, and current) is divided by the noise power. The noise power calculation method is as follows:
because there is an AGC automatic gain control function at the front end of an a/D analog-to-digital conversion device in a general navigation receiver, the strength of an input signal can be basically kept unchanged, and if the a/D adopts 3-bit quantization, the probability distribution of signal amplitude maintenance after quantization of the analog input signal can be set as:
the local carrier wave adopted by the local carrier wave recovery also uses 3bit quantization, and the quantization method is as follows:
branch I or branch Q: +2+2+1-1-2-2-1+1
Under the condition of no signal input, calculating the product result of the local carrier signal and the input signal, and under the condition that the amplitude of the input signal is as follows:
(i) input signal amplitude: +3
Multiplication with the local carrier signal results in: +6+6+3-3-6-6-3+3
Product result mean square value: 22.5
(ii) Input signal amplitude: +1
Multiplication with the local carrier signal results in: +2+2+1-1-2-2-1+1
Product result mean square value: 2.5
Because a single calculation is influenced by noise and has larger fluctuation, the average value of the single calculation can be calculated by adopting multiple times of statistics, thereby obtaining more accurate signal power estimation. In addition, the signal can be filtered by a low-pass filter in a single pass, so that an accurate signal power estimation value can be obtained.
3b) And detecting the arrival time of the signals, and rejecting the signals of which the arrival time exceeds a set range. Due to different constellation layouts and different arrival Times (TOAs) of signals of different satellites, the range of the arrival time of the signals cannot be effectively limited by considering the deviation between the satellite and the ground receiver clock, so that whether the received signals are the repeater interference or not is judged. However, since the constellation model is fixed, the difference between the arrival times of different satellite signals, i.e. the relative value of the arrival times, has a reasonable range, so that the constellation model can be established through simulation to obtain the relative value range of the arrival times between the satellites, and when the received signal exceeds the range, the received signal can be regarded as a repeater interference signal.
How to set a reasonable range of this satellite arrival time difference is described below. For the simulation of the Beidou system, the orbit radius of the satellite is about 26561.750 km, and the earth radius is about 6378 km. When the receiver is at different longitudes (0-360 °) and latitudes (0-180 °) (the altitude is 0 °), in one orbit period (0-360 °), it is simulated that the maximum value of the difference at the time of arrival of the satellite does not change significantly with the longitude but changes significantly with the latitude, and the larger the latitude is, the smaller the maximum value of the difference at the time of arrival is, and the maximum value of the difference at the time of arrival of different satellites is 17.7 ms. The receiver with different application backgrounds corresponds to an altitude range, and when the altitude of the receiver changes, the maximum value of the difference between the arrival times of the satellites at all the longitude and latitude positions of the receiver is simulated, so that the higher the altitude of the receiver is, the larger the maximum value of the difference between the arrival times of the satellites is, and the maximum value of the difference between the arrival times of the satellites is increased by 0.22ms every 100km of the altitude. Since the judgment is simply and effectively carried out in one step, the obvious low-quality retransmission type interference signal is aimed at, and the altitude range of the near-earth receiver is several hundred kilometers, the maximum value judgment threshold of the satellite arrival time difference is set to be 20ms, the preliminary judgment and judgment are carried out, and when the arrival time difference between the received satellite signal and other visible satellite signals exceeds the range, the signal can be considered as the retransmission type interference signal.
3c) And detecting the message information and rejecting abnormal signals of the message information. The navigation message information errors introduced by the repeater interference signals comprise satellite ephemeris errors and satellite clock correction errors aiming at causing satellite position errors and pseudo range correction errors (comprising ionospheric delay error correction) aiming at causing satellite pseudo range value deviations. The satellite ephemeris, the satellite clock correction value and the ionosphere delay error correction value are calculated from corresponding parameters in the navigation message, and the parameters have experience magnitude and experience range, so that the forwarding type interference signal with the obvious interference characteristic can be eliminated before positioning and resolving by adopting a message information monitoring and judging method.
4) And in the time service resolving process, filtering undetected forwarding type interference signals by using a Kalman filtering algorithm. In step 3b), the decision threshold cannot be identified for the interference signal within the ambiguity range, and the step filters the interference signal by using an anti-forwarding interference Kalman filtering algorithm in the information processing stage of the receiver.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.
Claims (3)
1. An anti-interference method of a Beidou time synchronization receiver is characterized in that: the method comprises the following steps:
1) inputting a baseband digital intermediate frequency signal output by a radio frequency front-end processing module of a receiver into an interference suppression module;
2) the interference suppression module adopts a frequency domain interference suppression algorithm to suppress the interference in the signal, and the method comprises the following steps:
2a) performing serial-to-parallel conversion on an input signal;
2b) performing windowing processing on the signals subjected to serial-parallel conversion;
2c) performing FFT processing on the windowed signal, and transforming the time domain data to a frequency domain;
2d) one path of the signal after FFT processing is sent to a weighting vector generating unit to update the frequency domain weighting vector generated in the previous period, and the other path of the signal is weighted with the generated frequency domain weighting vector;
2f) performing IFFT processing on the weighted signals to recover time domain data;
2g) performing parallel-serial conversion on the IFFT processed signals and then outputting the signals, and keeping the data rate of input and output unchanged;
3) before time service resolving, eliminating forwarding interference in an output signal of an interference suppression module, and further comprising the following steps:
3a) detecting the power of the signals, and rejecting the signals with the power exceeding a set range;
3b) detecting the arrival time of the signals, and rejecting the signals with the arrival time exceeding a set range;
3c) detecting the message information, and rejecting abnormal message information signals;
4) and in the time service resolving process, filtering undetected forwarding type interference signals by using a Kalman filtering algorithm.
2. The anti-interference method of the Beidou time synchronous receiver according to claim 1, wherein: the step 2d) of generating the frequency domain weighting vector by the weighting vector generating unit comprises the following steps:
2d1) taking an absolute value of the signal after FFT processing and then squaring the signal;
2d2) averagely dividing the signal into a plurality of sections;
2d3) calculating the periodic diagram of each segment, and taking the average of each periodic diagram as a power spectrum;
2d4) and comparing the amplitude of the power spectrum with a decision threshold to generate a frequency domain weighting vector.
3. The anti-interference method of the Beidou time synchronous receiver according to claim 1, wherein: in step 2d), a path of signal weighted by the frequency domain weighted vector is subjected to whitening filtering processing, and the whitening filter is as follows:
wherein N is0And NJNoise power spectral density and interference power spectral density, respectively, f is the signal frequency, fIIs the interference center frequency, B is the noise bandwidth, alpha is the ratio of the interference bandwidth to the noise bandwidth, and j is the narrowband interference signal;
when the dry-to-noise ratio is much larger than 1, the whitening filter is approximated as
Wherein f'0Is the interference frequency;
or in step 2d) will be weighted with the frequency domain weight vectorOne path of signal for weighting operation is input into a frequency domain eliminator, and interference spectral lines with the amplitude exceeding an interference elimination threshold are zeroed, wherein the frequency domain eliminator is formed by that attenuation factors are equal to
The attenuator of (2) is cascaded with the whitening filter in the formula (2), and the transfer function of the frequency domain rejector is:
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116068586A (en) * | 2023-04-06 | 2023-05-05 | 武汉大学 | GNSS time service receiver LQG clock controller parameter design method |
| CN117215172A (en) * | 2023-08-17 | 2023-12-12 | 辽宁天衡智通防务科技有限公司 | Satellite time service method and device, satellite time service system and storage medium |
| CN117215172B (en) * | 2023-08-17 | 2024-03-19 | 辽宁天衡智通防务科技有限公司 | Satellite time service method and device, satellite time service system and storage medium |
| CN116755319A (en) * | 2023-08-18 | 2023-09-15 | 青岛鼎信通讯股份有限公司 | Electric energy meter clock system, control method and device, computer equipment and medium |
| CN116755319B (en) * | 2023-08-18 | 2023-11-21 | 青岛鼎信通讯股份有限公司 | Electric energy meter clock system, control method and device, computer equipment and medium |
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