A method and system for extracting information of a very low frequency station signal based on a phase-locked loop

Abstract

The present application belongs to the technical field of very low frequency fluctuation detection, and discloses a very low frequency station signal information extraction method and system based on a phase-locked loop. The present application amplifies and samples a wide frequency signal containing a very low frequency station transmitting signal, sets local MSK demodulation parameters, uses phase-locked loop technology to respectively perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring very low frequency station, extracts a baseband synchronization signal and a carrier synchronization signal from the phase-locked loops of the upper and lower frequencies, respectively, calculates the amplitude information of the upper and lower frequencies using the baseband synchronization signal, and further obtains the amplitude information of the target monitoring very low frequency station. The carrier synchronization signals of the upper and lower frequencies are used to extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station, and further extract the phase offset information of the target monitoring very low frequency station. The present application can improve the accuracy of very low frequency station signal information extraction.

Description

Technical Field

[0001] This invention belongs to the field of very low frequency (VLF) wave detection technology, and more specifically, relates to a method and system for extracting VLF station signal information based on a phase-locked loop (PLL). Background Technology

[0002] Very Low Frequency (VLF) waves are electromagnetic waves with frequencies ranging from 3 kHz to 30 kHz. VLF waves can be divided into two categories: natural signals and signals from artificial stations. Human-made VLF signals from stations around the world cover different frequencies within this band and are widely used in scientific research and communications. VLF waves play an important role in geophysics, space environment monitoring, communications, and navigation, especially in solar activity monitoring, ionospheric exploration, and maritime communications.

[0003] VLF signal detection equipment is typically equipped with a high-sensitivity receiving system, combined with signal processing methods to demodulate the signal and extract key features. However, in complex electromagnetic environments, VLF signals are often affected by various noise sources, such as interference from ground power lines, industrial facilities, and other man-made electromagnetic sources, making accurate signal extraction difficult. Improving the accuracy of VLF station signal information extraction is a technical problem of concern and needs to be solved in this field. Summary of the Invention

[0004] This invention provides a method and system for extracting very low frequency (VLF) station signal information based on a phase-locked loop (PLL), thereby solving the problem of low accuracy in the extraction of VLF station signal information in the prior art.

[0005] This invention provides a method for extracting very low frequency (VLF) station signal information based on a phase-locked loop (PLL), comprising the following steps:

[0006] S1 amplifies and samples the broadband signal containing the very low frequency station's transmitted signal to obtain sampled information;

[0007] S2, set the local MSK demodulation parameters based on the modulation information of the target monitoring very low frequency station signal;

[0008] S3, combining the local MSK demodulation parameters, the sampled information is used as the input of the phase-locked loop, and the phase-locked loop technology is used to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring very low frequency station.

[0009] S4. After synchronization is achieved using a phase-locked loop, the baseband synchronization signal and carrier synchronization signal are extracted from the phase-locked loops of the upper and lower frequencies, respectively.

[0010] S5, using the baseband synchronization signal obtained in S4, calculate the amplitude information of the upper and lower frequencies respectively;

[0011] S6, combine the amplitude information of the upper and lower frequencies obtained from S5 to obtain the amplitude information of the target monitoring very low frequency station;

[0012] S7. Using the upper and lower frequency carrier synchronization signals obtained in S4, extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station.

[0013] S8. Based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station obtained in S7, the phase offset information of the target monitoring VLF station is extracted.

[0014] Preferably, in S2, the local MSK demodulation parameters set include the carrier frequency of the target monitoring very low frequency station. MSK modulated baseband signal baud rate And the data sampling rate and ADC bit depth of the local receiving device.

[0015] Preferably, in S3, a Costas phase-locked loop is used for carrier synchronization; the Costas phase-locked loop includes a mixer, a low-pass filter, a phase detector, a loop filter, and a voltage-controlled oscillator.

[0016] Preferably, the initial frequency of the voltage-controlled oscillator is [high frequency]. The initial frequency of the voltage-controlled oscillator at a lower frequency Determined by the following formula:

[0017]

[0018]

[0019] in, It is the carrier frequency of the target monitoring very low frequency station signal. It is the baud rate of the MSK modulated baseband signal.

[0020] Preferably, in S4, the extracted baseband synchronization signal includes: a baseband in-phase synchronization signal at an upper frequency and a baseband in-phase synchronization signal at a lower frequency, as well as a baseband quadrature synchronization signal at an upper frequency and a baseband quadrature synchronization signal at a lower frequency.

[0021] Preferably, in S5, the amplitude information of the upper frequency and the amplitude information of the lower frequency are represented as follows:

[0022]

[0023]

[0024] In the formula, and These are the amplitude information for the upper frequency and the amplitude information for the lower frequency, respectively. and These are the phases of the baseband synchronization signal at the upper frequency and the lower frequency, respectively.

[0025] The upper frequency baseband synchronization signal includes the upper frequency baseband in-phase synchronization signal and the upper frequency baseband quadrature synchronization signal, and the lower frequency baseband synchronization signal includes the lower frequency baseband in-phase synchronization signal and the lower frequency baseband quadrature synchronization signal.

[0026] Preferably, in S6, the amplitude information of the target monitoring very low frequency station is represented as follows:

[0027]

[0028] In the formula, The amplitude information of the target very low frequency station is monitored.

[0029] Preferably, specifically, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station is represented as follows:

[0030]

[0031] In the formula, It is the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station. It is the frequency of the carrier synchronization signal extracted from the upper frequency. It is the frequency of the carrier synchronization signal extracted from the lower frequency.

[0032] Preferably, in S8, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station is... The local mixer signal, used as the frequency, is multiplied by the received MSK modulated signal transmitted by the target monitoring VLF station, and then passed through a low-pass filter to obtain the baseband signal.

[0033]

[0034] In the formula, The baseband signal is obtained after passing through a low-pass filter. Indicates low-pass filtering. It is the MSK modulated signal received from the target monitoring very low frequency station. It is the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station;

[0035] The amplitude information of the target monitoring VLF station is obtained by dividing the baseband signal obtained after passing through the low-pass filter by S6. This yields baseband phase information with a constant unit amplitude; the squared baseband phase information is then compared with... and Multiply them, then integrate them over time, with an integration step of 1 second. The integration results are denoted as follows: and :

[0036]

[0037]

[0038] right and Let the angles be denoted as follows: and Adding them together and dividing by 2 gives the phase shift information with a time resolution of 1 second. , means as follows:

[0039]

[0040] In the formula, To monitor the phase shift information of very low frequency (VLF) stations. From the first angle, For the second angle, Indicates to Take the angle, Indicates to Take the angle.

[0041] On the other hand, the present invention provides a very low frequency (VLF) station signal information extraction system based on a phase-locked loop, comprising:

[0042] The receiving and processing module is used to amplify and sample broadband signals containing very low frequency (VLF) station transmission signals to obtain sampled information;

[0043] The demodulation setting module is used to set the local MSK demodulation parameters based on the modulation information of the target monitoring very low frequency station signal;

[0044] The carrier synchronization module is used to combine the local MSK demodulation parameters, take the sampling information as the input of the phase-locked loop, and use phase-locked loop technology to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring VLF station.

[0045] The synchronization signal extraction module is used to extract the baseband synchronization signal and the carrier synchronization signal from the upper and lower frequency phase-locked loops respectively after synchronization is achieved using a phase-locked loop;

[0046] The amplitude information calculation module is used to calculate the amplitude information of the upper and lower frequencies using the obtained baseband synchronization signal, and to combine the amplitude information of the upper and lower frequencies to obtain the amplitude information of the target monitoring very low frequency station.

[0047] The phase offset calculation module is used to obtain the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station using the upper and lower frequency carrier synchronization signals, and to extract the phase offset information of the target monitoring VLF station based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station.

[0048] The phase-locked loop-based very low frequency (VLF) station signal information extraction system is used to perform the steps in the phase-locked loop-based VLF station signal information extraction method described above.

[0049] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0050] This invention first amplifies and samples the broadband signal containing the very low frequency (VLF) station's transmitted signal to obtain sampled information. Based on the modulation information of the target VLF station's signal, local MSK demodulation parameters are set. Then, combining the local MSK demodulation parameters, the sampled information is used as the input to a phase-locked loop (PLL), and PLL technology is used to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target VLF station. After synchronization using the PLL, baseband synchronization signals and carrier synchronization signals are extracted from the upper and lower frequency PLLs, respectively. Then, using the obtained baseband synchronization signals, the amplitude information of the upper and lower frequencies is calculated. The amplitude information of the upper and lower frequencies is combined to obtain the amplitude information of the target VLF station. Using the obtained upper and lower frequency carrier synchronization signals, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target VLF station is extracted. Finally, based on the obtained frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target VLF station, the phase offset information of the target VLF station is extracted. This invention targets the field of Very Low Frequency (VLF) research. To meet the needs of VLF signal extraction and detection, it combines phase-locked loop (PLL) technology to solve the problem of the impact of carrier frequency offset of received VLF station signals on information extraction, thereby improving the accuracy of VLF station signal information extraction. This invention maintains high sensitivity and stability in complex electromagnetic environments, and is particularly suitable for conditions with high noise backgrounds and weak signals, ensuring the acquisition of accurate amplitude and phase information. Attached Figure Description

[0051] Figure 1 This is a flowchart of a method for extracting very low frequency (VLF) station signal information based on a phase-locked loop, provided in Embodiment 1 of the present invention.

[0052] Figure 2 This is a schematic diagram illustrating the extraction of amplitude information, baseband synchronization signal, and carrier synchronization signal based on a Kostas phase-locked loop in a very low frequency station signal information extraction method based on a phase-locked loop provided in Embodiment 1 of the present invention.

[0053] Figure 3 This is a schematic diagram of the loop filter used in the Costas ring in the very low frequency station signal information extraction method based on phase-locked loop provided in Embodiment 1 of the present invention.

[0054] Figure 4 This is a schematic diagram illustrating the extraction of phase offset information using the frequency of the extracted carrier synchronization signal as the frequency of the local mixing signal in a very low frequency station signal information extraction method based on a phase-locked loop provided in Embodiment 1 of the present invention.

[0055] Figure 5 This is a comparison diagram of the input signal amplitude and the output signal amplitude in a very low frequency station signal information extraction method based on a phase-locked loop provided in Embodiment 1 of the present invention.

[0056] Figure 6 This is a comparison diagram of the input phase offset and the output phase offset (i.e., the output phase offset without frequency offset) in a very low frequency station signal information extraction method based on phase-locked loop provided in Embodiment 1 of the present invention.

[0057] Figure 7 A comparison diagram of the input phase offset and the phase offset (i.e., the output phase offset with frequency offset) extracted without using the very low frequency station signal information extraction method based on phase-locked loop provided in Embodiment 1 of the present invention. Detailed Implementation

[0058] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0059] Example 1:

[0060] Example 1 provides a method for extracting very low frequency (VLF) station signal information based on a phase-locked loop (PLL). See [link / reference]. Figure 1 This includes the following steps:

[0061] S1 amplifies and samples the broadband signal containing the very low frequency (VLF) station's transmitted signal to obtain sampled information.

[0062] Specifically, two orthogonal magnetic loop antennas are used to receive very low frequency (VLF) fluctuation signals. According to Faraday's law of electromagnetic induction, the change in magnetic field strength is represented by a current. This weak current signal is amplified by an amplifier, sampled by an ADC, and the sampled information is then uploaded to a computer for storage via a data transmission line.

[0063] S2, set the local MSK demodulation parameters based on the modulation information of the target monitoring very low frequency station signal.

[0064] The local MSK demodulation parameters set include the carrier frequency of the target monitoring very low frequency station. MSK modulated baseband signal baud rate And the data sampling rate and ADC bit depth of the local receiving device.

[0065] Specifically, firstly, the modulation information of the target monitoring very low frequency (VLF) station signal is determined. This invention designs an information extraction method for MSK (Minimum Shift Keying) modulated signals. It can be written as:

[0066]

[0067] In the formula, It is amplitude information. It is the carrier angular frequency. It is code element information. It is the duration of the symbol. It is the phase constant within one symbol period in MSK modulation.

[0068] In practice, the received target monitoring signal is the MSK modulated signal transmitted by the very low frequency (VLF) station. It often manifests in the following forms:

[0069]

[0070] In the formula, For the amplitude information of the received signal, The carrier frequency offset is caused by the propagation path or hardware device. It is the phase offset of the signal from that station.

[0071] The observer needs to extract from the received signal and Both of these are of great significance for the study of the lower ionosphere. Currently, extraction... and Methods rarely consider carrier frequency offset The impact, but for For extraction The presence of [this element] can cause significant interference. This invention utilizes phase-locked loop (PLL) carrier synchronization technology to offset the carrier frequency. Eliminate, thereby improving The accuracy.

[0072] After determining the carrier frequency and baud rate of the target monitoring very low frequency (VLF) station signal, it is also necessary to determine the sampling rate and ADC bit depth of the observation equipment. Although the frequency range of VLF waves is 3kHz to 30kHz, MSK-modulated station signals around the world cover a wider frequency range. Therefore, to satisfy the Nyquist sampling theorem, the sampling rate is generally above 100kHz. The bit depth of the ADC affects the accuracy of the acquired signal, but excessively high bit depths sometimes do not effectively improve the accuracy of information extraction; instead, they increase the burden on data processing and storage. Generally, a 16-bit ADC is sufficient for observation requirements.

[0073] S3, combining the local MSK demodulation parameters set in S2, the sampling information obtained in S1 is used as the input of the phase-locked loop, and the phase-locked loop technology is used to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring very low frequency station.

[0074] For details, see Figure 2 Carrier synchronization is achieved using a Costas phase-locked loop (PLL), which includes a mixer, a low-pass filter, a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The mixer multiplies the VCO's output signal by the input signal, shifting the input signal's frequency range closer to the baseband through spectrum shifting. The low-pass filter's cutoff frequency is related to the MSK modulation parameters of the VLF station and is typically half the baseband signal baud rate. The phase detector obtains the phase error using the baseband signals from the in-phase and quadrature branches. After passing through the phase detector, this phase error enters the loop filter, generating the control signal for the VCO.

[0075] Among them, see Figure 3 The loop filter is designed using a first-order digital circuit architecture, consisting of two branches. The design parameters of the two branches are determined by the following formula:

[0076]

[0077]

[0078] In the formula, For the parameters of the 0th order branch, For the parameters of a first-order branch (containing one accumulator), For voltage-controlled oscillator gain, For phase detector gain, The damping coefficient is... For natural frequency, The time period of the phase-locked loop.

[0079] After passing through the loop filter, the voltage-controlled oscillator (VCO) changes the frequency of its output sine wave according to the control signal. After a period of time, the frequency of the VCO's output signal will be the same as the frequency of the PLL's input signal, and the phase difference between the input and output signals will remain stable, approximately zero.

[0080] Among them, the initial frequency of the voltage-controlled oscillator of the phase-locked loop is... The initial frequency of the voltage-controlled oscillator with a low-frequency phase-locked loop. Determined by the following formula:

[0081]

[0082]

[0083] in, It is the carrier frequency of the target monitoring very low frequency station signal. It is the baud rate of the MSK modulated baseband signal.

[0084] For different very low frequency stations Often different, Most are 200Hz.

[0085] S4. After synchronization is achieved using a phase-locked loop, the baseband synchronization signal and carrier synchronization signal are extracted from the upper and lower frequency phase-locked loops, respectively.

[0086] The extracted baseband synchronization signals include: baseband in-phase synchronization signals at higher frequencies and baseband in-phase synchronization signals at lower frequencies, as well as baseband quadrature synchronization signals at higher frequencies and baseband quadrature synchronization signals at lower frequencies.

[0087] That is, the baseband synchronization signal extracted by the Costas ring includes: the baseband synchronization signal of the in-phase branch and the baseband synchronization signal of the quadrature branch. Since there are upper and lower frequencies, there are a total of four baseband synchronization signals: the baseband in-phase synchronization signal of the upper frequency, the baseband quadrature synchronization signal of the upper frequency, the baseband in-phase synchronization signal of the lower frequency, and the baseband quadrature synchronization signal of the lower frequency.

[0088] Once the Costas ring is locked, the sinusoidal signal output by the voltage-controlled oscillator will be synchronized with the upper and lower frequency carriers of the input MSK signal. Therefore, the upper and lower frequency carrier synchronization signals can be extracted.

[0089] S5 uses the baseband synchronization signal obtained from S4 to calculate the amplitude information of the upper and lower frequencies respectively.

[0090] For details, see Figure 2 The obtained baseband in-phase synchronization signal and baseband quadrature synchronization signal are squared and then added together to obtain the squared amplitude value. The square root of this squared value is then used to obtain the amplitude information of the upper and lower frequencies.

[0091] The amplitude information for the upper frequency and the amplitude information for the lower frequency are represented as follows:

[0092]

[0093]

[0094] In the formula, and These are the amplitude information for the upper frequency and the amplitude information for the lower frequency, respectively. and These represent the phases of the baseband synchronization signal at the upper frequency and the lower frequency, respectively.

[0095] The upper frequency baseband synchronization signal includes the upper frequency baseband in-phase synchronization signal and the upper frequency baseband quadrature synchronization signal, and the lower frequency baseband synchronization signal includes the lower frequency baseband in-phase synchronization signal and the lower frequency baseband quadrature synchronization signal.

[0096] S6 combines the amplitude information of the upper and lower frequencies obtained from S5 to obtain the amplitude information of the very low frequency station for target monitoring.

[0097] Specifically, the amplitude information of the signal from the upper and lower frequencies is averaged to obtain the amplitude information of the station's signal. That is, the amplitude information of the target monitoring very low frequency station is represented as follows:

[0098]

[0099] In the formula, The amplitude information of the target very low frequency station is monitored.

[0100] S7 uses the upper and lower frequency carrier synchronization signals obtained in S4 to extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station.

[0101] Specifically, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station is represented as follows:

[0102]

[0103] In the formula, It is the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station. It is the frequency of the carrier synchronization signal extracted from the upper frequency. It is the frequency of the carrier synchronization signal extracted from the lower frequency.

[0104] S8, see S8. Figure 4Based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station obtained in S7, the phase offset information of the target monitoring VLF station is extracted.

[0105] Specifically, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station is... The local mixer signal, used as the frequency, is multiplied by the received MSK modulated signal transmitted by the target monitoring VLF station, and then passed through a low-pass filter to obtain the baseband signal.

[0106]

[0107] In the formula, The baseband signal is obtained after passing through a low-pass filter. Indicates low-pass filtering. It is the MSK modulated signal received from the target monitoring very low frequency station. It is the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station.

[0108] The amplitude information of the target monitoring VLF station is obtained by dividing the baseband signal obtained after passing through the low-pass filter by S6. This yields baseband phase information with a constant unit amplitude; the squared baseband phase information is then compared with... and Multiply them, then integrate them over time, with an integration step of 1 second. The integration results are denoted as follows: and :

[0109]

[0110]

[0111] right and Let the angles be denoted as follows: and Adding them together and dividing by 2 gives the phase shift information with a time resolution of 1 second. , means as follows:

[0112]

[0113] In the formula, To monitor the phase shift information of very low frequency (VLF) stations. From the first angle, For the second angle, Indicates to Take the angle, Indicates to Take the angle.

[0114] The present invention will be further illustrated below with reference to parameters.

[0115] In S1, two orthogonal magnetic loop antennas are used to receive very low frequency (VLF) fluctuation signals. According to Faraday's law of electromagnetic induction, the change in magnetic field strength is represented by a current. This weak current signal is amplified by an amplifier, sampled by a 16-bit ADC, and the sampled information is uploaded to a computer for storage via a data transmission line.

[0116] In S2, the NWC very low frequency station is used as the target monitoring station, and the carrier frequency for MSK demodulation is set to 19.8kHz, with a baud rate of 200Hz. In this embodiment, the sampling rate of the data acquisition system is 250kHz, with some oversampling; the ADC bit depth is 16 bits.

[0117] In S3, the cutoff frequency of the low-pass filter is related to the MSK modulation parameters of the very low frequency station, and is set to 100Hz here. It is 19.8kHz. For 200Hz, the calculated value is... , .

[0118] In S4, see Figure 2 The difference between the in-phase and quadrature branches of the Costas phase-locked loop (PLL) lies in the phase of the voltage-controlled oscillator (VCO) output signal. For the in-phase branch, the VCO output signal does not pass through a phase shifter; for the quadrature branch, the VCO output signal passes through a 90° phase shifter. It should be noted that after the input signal passes through the PLL, the VCO output signal will have a 90° phase difference with the input signal; therefore, the VCO output only becomes in phase with the input signal after passing through the phase shifter. Baseband in-phase and quadrature synchronization signals are extracted at the low-pass filter outputs of the in-phase and quadrature branches. Since there are upper and lower frequencies, there are four baseband synchronization signals output: the upper frequency in-phase synchronization signal, the upper frequency quadrature synchronization signal, the lower frequency in-phase synchronization signal, and the lower frequency quadrature synchronization signal. The carrier synchronization signal is extracted at the in-phase output of the VCO.

[0119] S5 uses the baseband synchronization signal obtained from S4 to calculate the amplitude information of the upper and lower frequencies respectively.

[0120] S6 combines the amplitude information of the upper and lower frequencies obtained from S5 to obtain the amplitude information of the very low frequency station for target monitoring.

[0121] S7 uses the upper and lower frequency carrier synchronization signals obtained in S4 to extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station.

[0122] S8. Based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station obtained in S7, the phase offset information of the target monitoring VLF station is extracted.

[0123] In this embodiment, an MSK modulated signal transmitted by an NWC very low frequency station was simulated, with a carrier frequency of 19.8 kHz, a baud rate of 200 Hz, a frequency offset of 100 MHz, and a phase offset of 45°. This simulated signal was used as... Figure 2 The input to the phase-locked loop (PLL) is used to extract the baseband in-phase synchronization signal, baseband quadrature synchronization signal, and carrier synchronization signal at the upper and lower frequencies after the PLL is locked. By processing the upper and lower frequency baseband synchronization signals, the amplitude information of the station signal can be obtained. For example... Figure 5 As shown, the "-" line represents the amplitude of the input MSK signal. As a standard value, the "-." line represents the station signal amplitude obtained using the method of this invention. The station amplitude information extracted using the method of this invention has an error of less than 0.01% compared to the standard value. Figure 4 The steps shown involve using the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station as the frequency of the local mixer signal. The input MSK signal is then mixed and low-pass filtered using the local mixer signal to obtain the baseband signal. The baseband signal is then squared and multiplied by... and Then, the two results are integrated separately with a step size of 1 second; after merging, the phase shift information with a time resolution of 1 second is finally obtained. The phase shift information finally obtained in this embodiment is as follows: Figure 6 As shown, the "-" line represents the phase offset of the input MSK signal, i.e., the standard value; the "." line represents the phase offset information obtained using the method of this invention, with an error within 0.3°. For comparison, Figure 7 The "-" line represents the phase offset of the input MSK signal, i.e., the standard value, while the "-." line represents the phase offset information obtained without using the method of this invention, exhibiting a linear relationship over time, i.e., there is a phase offset. Interference from the items prevents the extraction of the required data. .

[0124] Furthermore, to ensure precise synchronization of the phase-locked loop (PLL) and minimize the output frequency fluctuation range of the voltage-controlled oscillator (VCO), the design parameters of the loop filter can be further optimized. Optimized design can effectively reduce system frequency fluctuations and improve signal synchronization accuracy. However, changing the filter's design parameters increases the time required for the PLL to reach synchronization. Therefore, in practical applications, a trade-off must be struck between the design requirements: how to achieve synchronization quickly while maintaining accuracy to meet the needs of real-time signal processing.

[0125] In summary, Example 1 demonstrates a method for extracting very low frequency (VLF) station signals based on a phase-locked loop (PLL). Through precise synchronization and signal processing, it can effectively extract phase shift information from complex VLF signals. The method provided by this invention has significant advantages in extracting weak signals, significantly improving the signal-to-noise ratio and enhancing synchronization accuracy. It can provide reliable data support for fields such as geophysical monitoring, ionospheric exploration, and maritime communications.

[0126] Example 2:

[0127] Example 2 provides a very low frequency (VLF) station signal information extraction system based on a phase-locked loop, comprising:

[0128] The receiving and processing module amplifies and samples the broadband signal containing the very low frequency station's transmitted signal to obtain sampled information;

[0129] The demodulation setting module is used to set the local MSK demodulation parameters based on the modulation information of the target monitoring very low frequency station signal;

[0130] The carrier synchronization module is used to combine the local MSK demodulation parameters, take the sampling information as the input of the phase-locked loop, and use phase-locked loop technology to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring VLF station.

[0131] The synchronization signal extraction module is used to extract the baseband synchronization signal and the carrier synchronization signal from the upper and lower frequency phase-locked loops respectively after synchronization is achieved using a phase-locked loop;

[0132] The amplitude information calculation module is used to calculate the amplitude information of the upper and lower frequencies using the obtained baseband synchronization signal, and to combine the amplitude information of the upper and lower frequencies to obtain the amplitude information of the target monitoring very low frequency station.

[0133] The phase offset calculation module is used to extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station using the upper and lower frequency carrier synchronization signals, and to extract the phase offset information of the target monitoring VLF station based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station.

[0134] The phase-locked loop-based very low frequency (VLF) station signal information extraction system is used to perform the steps in the phase-locked loop-based VLF station signal information extraction method as described in Example 1.

[0135] Since the functions of each module in the system provided in Embodiment 2 correspond to the steps in the method provided in Embodiment 1, they can be understood by referring to the description of Embodiment 1, and will not be repeated here.

[0136] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can 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 such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for extracting very low frequency (VLF) station signal information based on a phase-locked loop (PLL), characterized in that, Includes the following steps: S1 amplifies and samples the broadband signal containing the very low frequency station's transmitted signal to obtain sampled information; S2, set the local MSK demodulation parameters based on the modulation information of the target monitoring very low frequency station signal; S3, Combining the local MSK demodulation parameters, the sampled information is used as the input of the phase-locked loop, and the phase-locked loop technology is used to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring very low frequency station. S4. After synchronization is achieved using a phase-locked loop, the baseband synchronization signal and carrier synchronization signal are extracted from the phase-locked loops of the upper and lower frequencies, respectively. S5, using the baseband synchronization signal obtained in S4, calculate the amplitude information of the upper and lower frequencies respectively; S6, combine the amplitude information of the upper and lower frequencies obtained from S5 to obtain the amplitude information of the target monitoring very low frequency station; S7. Using the upper and lower frequency carrier synchronization signals obtained in S4, extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station. S8. Based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station obtained in S7, the phase offset information of the target monitoring VLF station is extracted. In S2, the local MSK demodulation parameters set include the carrier frequency of the target monitoring very low frequency station. MSK modulated baseband signal baud rate And the data sampling rate and ADC bit depth of the local receiving device; In S3, a Costas phase-locked loop is used for carrier synchronization; the Costas phase-locked loop includes a mixer, a low-pass filter, a phase detector, a loop filter, and a voltage-controlled oscillator. In S8, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station is... The local mixer signal is multiplied by the received MSK modulated signal transmitted by the target monitoring VLF station, and then passed through a low-pass filter to obtain the baseband signal. In the formula, The baseband signal is obtained after passing through a low-pass filter. Indicates low-pass filtering. It is the MSK modulated signal received from the target monitoring very low frequency station. It is the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station; The amplitude information of the target monitoring VLF station is obtained by dividing the baseband signal obtained after passing through the low-pass filter by S6. This yields baseband phase information with a constant unit amplitude; the squared baseband phase information is then compared with... and Multiply them, then integrate them over time, with an integration step of 1 second. The integration results are denoted as follows: and : right and Let the angles be denoted as follows: and Adding them together and dividing by 2 gives the phase shift information with a time resolution of 1 second. , means as follows: In the formula, To monitor the phase shift information of very low frequency (VLF) stations. From the first angle, For the second angle, Indicates to Take the angle, Indicates to Take the angle.

2. The method for extracting very low frequency station signal information based on a phase-locked loop according to claim 1, characterized in that, Initial frequency of the voltage-controlled oscillator at the upper frequency The initial frequency of the voltage-controlled oscillator at a lower frequency Determined by the following formula: in, It is the carrier frequency of the target monitoring very low frequency station signal. It is the baud rate of the MSK modulated baseband signal.

3. The method for extracting very low frequency station signal information based on a phase-locked loop according to claim 1, characterized in that, In S4, the extracted baseband synchronization signals include: baseband in-phase synchronization signals at the upper frequency and baseband in-phase synchronization signals at the lower frequency, as well as baseband quadrature synchronization signals at the upper frequency and baseband quadrature synchronization signals at the lower frequency.

4. The method for extracting very low frequency station signal information based on a phase-locked loop according to claim 3, characterized in that, In S5, the amplitude information of the upper frequency and the amplitude information of the lower frequency are represented as follows: In the formula, and These are the amplitude information for the upper frequency and the amplitude information for the lower frequency, respectively. and These are the phases of the baseband synchronization signal at the upper frequency and the lower frequency, respectively. The upper frequency baseband synchronization signal includes the upper frequency baseband in-phase synchronization signal and the upper frequency baseband quadrature synchronization signal, and the lower frequency baseband synchronization signal includes the lower frequency baseband in-phase synchronization signal and the lower frequency baseband quadrature synchronization signal.

5. The method for extracting very low frequency station signal information based on a phase-locked loop according to claim 4, characterized in that, In S6, the amplitude information of the target monitoring very low frequency station is represented as follows: In the formula, The amplitude information of the target very low frequency station is monitored.

6. The method for extracting very low frequency station signal information based on a phase-locked loop according to claim 1, characterized in that, In S7, the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station is represented as follows: In the formula, It is the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring very low frequency station. It is the frequency of the carrier synchronization signal extracted from the upper frequency. It is the frequency of the carrier synchronization signal extracted from the lower frequency.

7. A very low frequency (VLF) station signal information extraction system based on a phase-locked loop (PLL), characterized in that, include: The receiving and processing module is used to amplify and sample broadband signals containing very low frequency (VLF) station transmission signals to obtain sampled information; The demodulation setting module is used to set the local MSK demodulation parameters based on the modulation information of the target monitoring very low frequency station signal; The carrier synchronization module is used to combine the local MSK demodulation parameters, take the sampling information as the input of the phase-locked loop, and use phase-locked loop technology to perform carrier synchronization on the upper and lower frequencies of the MSK modulated signal transmitted by the target monitoring very low frequency station. The synchronization signal extraction module is used to extract the baseband synchronization signal and the carrier synchronization signal from the upper and lower frequency phase-locked loops respectively after synchronization is achieved using a phase-locked loop; The amplitude information calculation module is used to calculate the amplitude information of the upper and lower frequencies using the obtained baseband synchronization signal, and to combine the amplitude information of the upper and lower frequencies to obtain the amplitude information of the target monitoring very low frequency station. The phase offset calculation module is used to extract the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station using the upper and lower frequency carrier synchronization signals, and to extract the phase offset information of the target monitoring VLF station based on the frequency of the carrier synchronization signal of the MSK modulated signal transmitted by the target monitoring VLF station. The phase-locked loop-based very low frequency (VLF) station signal information extraction system is used to perform the steps in the phase-locked loop-based VLF station signal information extraction method as described in any one of claims 1-6.

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