A beidou signal demodulation system based on envelope detection

Abstract

The application relates to a Beidou signal demodulation system based on envelope detection, and belongs to the technical field of Beidou signal demodulation. In the system, a signal preprocessing unit is used to capture a Beidou common network radiation signal, adjust an amplitude parameter, filter out high-frequency pulse clutter, and generate a pretreated Beidou mixed signal; a carrier frequency screening unit is used to perform spectrum scanning, carrier frequency parameter extraction and filter passband adjustment on the pretreated signal, screen and calibrate the carrier frequency bearing signal, and generate a Beidou modulation intermediate signal; an envelope detection unit is used to adjust parameters based on a passive adaptive envelope detection technology, rectify, filter and extract the envelope of the carrier frequency bearing signal, and generate a Beidou signal envelope sketch; and a calibration demodulation unit is used to filter, calibrate the amplitude and time sequence of the envelope sketch, and finally generate a Beidou demodulation positioning reference signal. Through the cooperative operation of the units, the application realizes accurate demodulation of the Beidou common network radiation signal, and improves the stability and accuracy of the demodulated signal.

Description

Technical Field

[0001] This invention belongs to the field of BeiDou signal demodulation technology, specifically relating to a BeiDou signal demodulation system based on envelope detection. Background Technology

[0002] With its advantages of high precision, wide coverage, and all-weather operation, BeiDou positioning technology has been widely used in various positioning and navigation scenarios. As spectrum resources become increasingly scarce, the co-transmission of BeiDou positioning signals and mobile communication signals has become the mainstream trend in the industry. This mode can effectively save spectrum resources and reduce equipment deployment costs, and is especially suitable for BeiDou signal coverage in enclosed scenarios such as underground garages, tunnels, and inside buildings.

[0003] The BeiDou shared network radiated signal is a hybrid signal generated after BeiDou modulation signals and mobile communication signals are transmitted through the shared network. The BeiDou modulation signal is obtained by modulating the original BeiDou positioning signal onto a carrier frequency signal, and the frequency of the carrier frequency signal is a preset multiple of the frequency of the original BeiDou positioning signal. In closed scenarios, after transmission through the transmission link, the BeiDou shared network radiated signal is easily affected by multiple factors such as environmental obstruction, link attenuation, and external electromagnetic interference, ultimately forming a hybrid signal with deep mixing of BeiDou modulation signals and mobile communication signals. This hybrid signal not only suffers from problems such as random amplitude fluctuations, high-frequency pulse clutter, and carrier frequency offset, but may also exhibit signal spectrum overlap and phase distortion, posing a significant challenge to the accurate demodulation of BeiDou signals. Existing BeiDou signal demodulation technologies lack targeted processing solutions for hybrid signals after shared network transmission, and each demodulation stage has obvious deficiencies, making it difficult to meet the needs of practical applications.

[0004] The signal preprocessing stage can only use a fixed threshold filtering method to simply filter out some low-frequency noise. It cannot dynamically adjust the gain parameters according to the amplitude fluctuations of the BeiDou network radiated signal, resulting in excessively large signal amplitude fluctuations. In the subsequent demodulation process, problems such as detection threshold failure, signal saturation, or weak signals that cannot be identified are prone to occur, which seriously affects the demodulation stability. The carrier frequency selection stage lacks a precise spectrum scanning and parameter calibration mechanism and mostly uses a single frequency scanning mode. It cannot quickly lock the carrier frequency spectrum range of the BeiDou modulated signal and it is difficult to effectively distinguish the spectrum overlap area between the BeiDou carrier frequency signal and the mobile communication signal. As a result, it is impossible to accurately select the carrier frequency carrying signal of the BeiDou modulated signal from the mixed signal. It is susceptible to strong interference from mobile communication signals and external low-frequency noise, which leads to inaccurate carrier frequency parameter extraction. Envelope detection process In China, existing technologies mostly employ fixed-parameter detection methods. The detection parameters cannot adaptively adjust according to changes in the amplitude of the BeiDou modulation signal. When the signal amplitude fluctuates, problems such as detection distortion and incomplete envelope extraction are easily encountered, leading to the loss or distortion of the envelope features of the original BeiDou positioning signal and making it impossible to accurately restore the core information of the BeiDou positioning signal. At the same time, the demodulation process lacks an integrated filtering and calibration mechanism. The filtering stage can only filter out single types of clutter and cannot specifically handle harmonic signals, spurious signals, and residual carrier frequency components generated during the detection process. Amplitude calibration and timing calibration are independent of each other and cannot work together to correct signal deviations. Ultimately, this results in unstable amplitude and disordered timing of the demodulated BeiDou signal, which cannot meet the usage requirements of various positioning terminals and may even lead to serious problems such as inaccurate terminal positioning and positioning delay.

[0005] The existing demodulation technology operates independently, lacking a collaborative mechanism. The parameters of each stage—signal preprocessing, carrier frequency selection, envelope detection, and calibration demodulation—cannot be matched or dynamically coordinated. This not only reduces demodulation efficiency but also exacerbates the instability of the demodulated signal. It is difficult to adapt to the complex signal environment after BeiDou network co-transmission and cannot cope with the differences in signal transmission under different closed scenarios. This greatly limits the promotion and application of BeiDou positioning technology and mobile communication co-transmission mode. Therefore, a BeiDou signal demodulation system that can solve the above-mentioned technical pain points is needed. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a BeiDou signal demodulation system based on envelope detection. The objective of this invention can be achieved through the following technical solutions: A BeiDou signal demodulation system based on envelope detection includes: a signal preprocessing unit, a carrier frequency screening unit, an envelope detection unit, and a calibration and demodulation unit; The signal preprocessing unit acquires the amplitude data of the BeiDou shared network radiation signal, calculates the amplitude fluctuation range, and adjusts the gain adjustment parameters; it identifies and filters out high-frequency pulse clutter in the BeiDou shared network radiation signal by setting a clutter identification threshold, and generates a preprocessed BeiDou hybrid signal. The carrier frequency filtering unit performs a spectrum scan on the preprocessed BeiDou mixed signal to obtain the carrier frequency spectrum characteristics of the BeiDou modulation signal, extracts the carrier frequency component parameters, adjusts the start and end frequency parameters of the bandpass filter passband, and generates the carrier frequency carrying signal in the BeiDou modulation signal; the mobile communication signal and low-frequency noise are filtered out through the filter passband, and the BeiDou modulation intermediate signal is generated after spectrum calibration. The envelope detection unit, based on passive adaptive envelope detection technology, acquires the amplitude variation data of the BeiDou modulation intermediate signal, adjusts the filter capacitance and load resistance parameters, performs half-wave rectification on the carrier frequency signal, filters and smooths the pulsating DC signal to remove high-frequency pulsating components, extracts the envelope of the modulation components of the carrier frequency signal, demodulates and separates the envelope features of the original BeiDou positioning signal, and generates a preliminary BeiDou signal envelope. The calibration and demodulation unit performs low-pass filtering on the prototype BeiDou signal envelope, calculates the amplitude deviation, adjusts the amplitude adjustment coefficient, and calibrates the signal amplitude to a preset target amplitude. Based on the actual timing data of the prototype BeiDou signal envelope, it identifies the timing deviation and calculates the deviation amount, corrects the signal timing deviation, and generates a BeiDou demodulation positioning reference signal.

[0007] Specifically, the process of adjusting the gain adjustment parameter includes: acquiring amplitude samples at fixed intervals based on the BeiDou network radiation signal, and removing instantaneous abnormal amplitude data; performing statistical calculations on the filtered amplitude samples, taking the difference between the maximum and minimum values ​​of the amplitude samples as the amplitude fluctuation range, comparing it with the preset amplitude stability range judgment standard, and adjusting the gain adjustment parameter.

[0008] Specifically, the process of generating the preprocessed BeiDou hybrid signal includes: calling a preset clutter identification and judgment standard, performing a filtering operation on the selected clutter components based on the spectrum data of the BeiDou network radiation signal, integrating the remaining effective signal components and performing spectrum consistency verification, and generating the preprocessed BeiDou hybrid signal.

[0009] Specifically, the process of extracting carrier frequency component parameters includes: performing a spectrum scanning operation on the preprocessed BeiDou hybrid signal, capturing spectrum features point by point, generating the spectrum range corresponding to the carrier frequency, extracting the core feature parameters of the carrier frequency components, including the center spectrum position, amplitude variation range, and phase characteristics of the carrier frequency; comparing the core feature parameters with the preset carrier frequency parameter judgment range one by one, eliminating abnormal information, retaining valid carrier frequency parameters and classifying and storing them to establish a carrier frequency parameter archive.

[0010] Specifically, the process of the carrier frequency carrying signal includes: comparing the center spectrum position and amplitude variation range in the carrier frequency parameter file with the preset carrier frequency band determination criteria to generate the adjustment direction and adjustment amplitude of the start and end frequencies of the filter passband, and adjusting the start and end frequency parameters of the bandpass filter passband; connecting the preprocessed BeiDou mixed signal to the adjusted bandpass filter passband, and filtering out the carrier frequency carrying signal in the BeiDou modulated signal through filtering operations.

[0011] Specifically, the process of generating the BeiDou modulation intermediate signal after spectrum calibration includes: using the adjusted bandpass filter passband to perform a secondary filtering operation on the selected carrier frequency signal, gradually filtering out mobile communication signals and low-frequency noise components mixed in; starting spectrum calibration, identifying the offset of carrier frequency parameters, calculating the offset amplitude, formulating a parameter correction scheme based on the offset amplitude, and correcting the offset of carrier frequency parameters according to the correction scheme; and performing spectrum smoothing processing on the integrated signal to eliminate instantaneous signal fluctuations generated during the calibration process, thereby generating the BeiDou modulation intermediate signal.

[0012] Specifically, the passive adaptive envelope detection technology includes the following steps: based on the passive adaptive envelope detection technology, acquiring the amplitude information of the BeiDou modulated intermediate signal, recording amplitude data at fixed time intervals to generate an amplitude change sequence; tracking and monitoring the change trend of amplitude information through the amplitude change sequence to form an amplitude change law, generating the amplitude characteristics of the signal, including amplitude fluctuation amplitude, stable duration, and instantaneous change rate; and adjusting the filtering and load adjustment parameters according to the amplitude characteristics.

[0013] Specifically, the half-wave rectification process includes: connecting the carrier frequency signal to the detection process, retaining the positive amplitude signal component in the carrier frequency signal, performing the half-wave rectification on the carrier frequency signal to convert the high-frequency carrier frequency component into a pulsating DC signal; and performing layered filtering and smoothing on the pulsating DC signal to filter out the high-frequency pulsating component in layers.

[0014] Specifically, the process of generating the preliminary BeiDou signal envelope includes: identifying the modulation component in the carrier frequency signal through spectrum identification, separating the modulation component from the carrier frequency component, performing envelope extraction on the separated modulation component, pre-setting the sampling interval and duration of envelope extraction, collecting the amplitude peak value of the modulation component point by point, connecting all amplitude peak values ​​to form a preliminary envelope curve, demodulating and separating the envelope features of the original BeiDou positioning signal through the extraction process; performing preliminary processing on the envelope features, calling the preset spurious feature judgment criteria, removing spurious features in the envelope, smoothing the envelope curve after removing spurious features, filling in the missing points in the envelope curve, integrating the processed envelope information to form an envelope waveform, and generating the preliminary BeiDou signal envelope.

[0015] Specifically, the process of low-pass filtering the prototype BeiDou signal envelope includes: inputting the prototype BeiDou signal envelope into the low-pass filtering process, performing spectrum analysis on the prototype BeiDou signal envelope, gradually adjusting the cutoff frequency parameters of the low-pass filter based on the various clutter spectrum characteristics obtained from the spectrum analysis, and generating a targeted filtering suppression threshold; applying the adjusted low-pass filter parameters to the filtering process to perform low-pass filtering on the prototype BeiDou signal envelope.

[0016] Specifically, the process of calibrating the signal amplitude to a preset target amplitude includes: capturing the actual amplitude after low-pass filtering, continuously collecting actual amplitude samples at fixed intervals, calculating the average amplitude as the actual amplitude data; calling the preset target amplitude judgment standard, formulating an amplitude adjustment scheme based on the deviation data, adjusting the amplitude adjustment coefficient, and linking the signal amplitude with the amplitude adjustment coefficient to adjust the signal amplitude to reach the target amplitude judgment standard, and maintaining the amplitude fluctuation within a preset stable range, and fixing the current amplitude adjustment coefficient.

[0017] Specifically, the process of generating the BeiDou demodulation positioning reference signal includes: based on the actual timing information of the BeiDou signal envelope prototype, recording the timing data of each signal node according to the signal transmission order to generate an actual timing sequence; calling a preset timing judgment standard to mark the deviation nodes, and correcting the timing deviation of the deviation nodes according to the timing deviation direction and duration according to the signal transmission order; integrating the amplitude, timing and envelope characteristics of the corrected signal to generate the BeiDou demodulation positioning reference signal.

[0018] The beneficial effects of this invention are as follows: The signal preprocessing unit continuously captures the amplitude data of the BeiDou network radiation signal, eliminates abnormal amplitudes and adjusts the gain parameters to keep the signal amplitude within a stable range. At the same time, it filters out high-frequency pulse clutter through preset clutter identification and judgment criteria, retains the effective components of the BeiDou modulation signal, and provides a stable and clean input signal for subsequent carrier frequency screening and detection operations, reducing the impact of clutter and amplitude fluctuations on the subsequent demodulation process.

[0019] The carrier frequency screening unit adopts a spectrum scanning method that combines coarse and fine scanning. It can lock the carrier frequency spectrum range of the Beidou modulation signal, extract and verify the core parameters of the carrier frequency, and achieve accurate screening of the carrier frequency-carrying signal by dynamically adjusting the passband parameters of the bandpass filter. After secondary filtering and spectrum calibration, mobile communication signals and residual low-frequency noise are filtered out, and the carrier frequency parameter offset is corrected to ensure the integrity and accuracy of the carrier frequency-carrying signal.

[0020] The envelope detection unit is based on passive adaptive envelope detection technology. It can adaptively adjust the filtering and load-related parameters according to the amplitude variation law of the BeiDou modulation intermediate signal, so that the detection parameters are accurately matched with the signal amplitude characteristics. Combined with rectification, layered filtering smoothing and envelope extraction operations, it can separate the envelope features of the original BeiDou positioning signal, eliminate stray features, avoid detection distortion, and ensure the integrity of the BeiDou signal envelope.

[0021] The calibration and demodulation unit dynamically adjusts the low-pass filter parameters by analyzing the clutter spectrum characteristics, specifically filtering out harmonics, spurious signals and residual carrier frequency components generated during the detection process. At the same time, through amplitude comparison, deviation calculation and adjustment coefficient adjustment, the signal amplitude is calibrated to the preset standard. Combined with timing deviation identification, calculation and correction, the unit integrates the core features of the signal to generate the BeiDou demodulation positioning reference signal.

[0022] The envelope detection unit uses passive adaptive adjustment logic, which does not require external control signals. It can trigger parameter adjustment through changes in the signal amplitude itself, adapt to the dynamic fluctuations of the signal amplitude, improve the system's adaptability to complex BeiDou network radiation signals, and expand the system's application scenarios. Attached Figure Description

[0023] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 This is an architecture diagram of a BeiDou signal demodulation system based on envelope detection according to the present invention. Figure 2 This is a schematic diagram illustrating the envelope detection and calibration / demodulation steps in this invention. Detailed Implementation

[0025] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0026] Please see Figures 1-2 A BeiDou signal demodulation system based on envelope detection includes: a signal preprocessing unit, a carrier frequency screening unit, an envelope detection unit, and a calibration and demodulation unit; The signal preprocessing unit acquires the amplitude data of the BeiDou shared network radiation signal, calculates the amplitude fluctuation range, and adjusts the gain adjustment parameters; it identifies and filters out high-frequency pulse clutter in the BeiDou shared network radiation signal by setting a clutter identification threshold, and generates a preprocessed BeiDou hybrid signal. The carrier frequency filtering unit performs a spectrum scan on the preprocessed BeiDou mixed signal to obtain the carrier frequency spectrum characteristics of the BeiDou modulation signal, extracts the carrier frequency component parameters, adjusts the start and end frequency parameters of the bandpass filter passband, and generates the carrier frequency carrying signal in the BeiDou modulation signal; the mobile communication signal and low-frequency noise are filtered out through the filter passband, and the BeiDou modulation intermediate signal is generated after spectrum calibration. The envelope detection unit, based on passive adaptive envelope detection technology, acquires the amplitude variation data of the BeiDou modulation intermediate signal, adjusts the filter capacitance and load resistance parameters, performs half-wave rectification on the carrier frequency signal, filters and smooths the pulsating DC signal to remove high-frequency pulsating components, extracts the envelope of the modulation components of the carrier frequency signal, demodulates and separates the envelope features of the original BeiDou positioning signal, and generates a preliminary BeiDou signal envelope. The calibration and demodulation unit performs low-pass filtering on the prototype BeiDou signal envelope, calculates the amplitude deviation, adjusts the amplitude adjustment coefficient, and calibrates the signal amplitude to a preset target amplitude. Based on the actual timing data of the prototype BeiDou signal envelope, it identifies the timing deviation and calculates the deviation amount, corrects the signal timing deviation, and generates a BeiDou demodulation positioning reference signal.

[0027] Specifically, the process of adjusting the gain adjustment parameters includes: continuously capturing BeiDou network radiation signals, recording the amplitude information of the signals one by one, continuously collecting multiple sets of amplitude samples at fixed intervals, calling the preset abnormal amplitude judgment standard, comparing the collected amplitude samples with the judgment standard one by one, and eliminating instantaneous abnormal amplitude data that exceed the judgment standard range to avoid abnormal data affecting the calculation results; statistically calculating the effective amplitude samples after screening, sorting out the maximum and minimum amplitude values ​​of all samples, calculating the difference between the two as the amplitude fluctuation range, comparing the calculated fluctuation range with the preset amplitude stability range judgment standard, and if the fluctuation range exceeds the stability range, gradually adjusting the gain adjustment parameters, re-capturing amplitude data and calculating the fluctuation range after each adjustment, repeatedly comparing and adjusting until the amplitude fluctuation range falls into the preset stability range, stopping parameter adjustment and maintaining the current gain adjustment parameter state to ensure the stability of subsequent signal amplitude.

[0028] Specifically, the process of generating the preprocessed BeiDou hybrid signal includes: calling a preset clutter identification and judgment standard, which includes core judgment elements such as the spectral range, amplitude threshold, and duration of high-frequency pulse clutter; capturing the complete spectral information of the BeiDou network radiation signal in real time; comparing the captured spectral information with each element of the clutter identification and judgment standard in spectral frequency order; filtering out signal components whose spectral range, amplitude, and duration all conform to the characteristics of high-frequency pulse clutter and exceed the judgment standard range; performing targeted filtering operations on the filtered clutter components; continuously monitoring the changes in the signal spectrum in segments during the filtering process; comparing the signal spectrum before and after each segment of clutter filtering to confirm that the effective components of the BeiDou modulated signal have not been damaged, thus avoiding the erroneous filtering of effective signals; and after all high-frequency pulse clutter has been filtered out, integrating all remaining effective signal components and performing spectral consistency verification on the integrated signal to ensure that the signal components are complete and without missing parts, ultimately forming the preprocessed BeiDou hybrid signal.

[0029] Specifically, the process of extracting carrier frequency component parameters includes: performing a comprehensive spectrum scan on the preprocessed BeiDou mixed signal; first, starting the coarse scan mode to perform a preliminary scan of the signal spectrum at a relatively wide frequency interval, quickly locking the approximate spectrum range corresponding to the BeiDou modulation signal, and excluding spectrum regions that obviously do not belong to the BeiDou modulation signal; then switching to the fine scan mode, performing a precise scan at a narrow frequency interval within the approximate spectrum range locked by the coarse scan, capturing spectrum features point by point, locking the precise spectrum range corresponding to the carrier frequency, and extracting the core feature parameters of the carrier frequency components from the locked precise spectrum range, including the center spectrum position of the carrier frequency, amplitude variation range, and phase characteristics; verifying each extracted core parameter individually, comparing each parameter with the preset carrier frequency parameter judgment range one by one, eliminating abnormal information that exceeds the judgment range or does not conform to the carrier frequency characteristics, retaining all valid carrier frequency parameters that meet the standards and classifying and storing them to establish a carrier frequency parameter archive, providing accurate and reliable parameter basis for subsequent filter passband adjustment.

[0030] Specifically, the process of the carrier frequency carrying signal includes: retrieving all valid carrier frequency parameters from the stored carrier frequency parameter file, focusing on extracting the center spectrum position and amplitude variation range of the carrier frequency, comparing these two core parameters with the preset carrier frequency band judgment standard in real time, calculating the deviation between the two item by item, and determining the adjustment direction and adjustment range of the start and end frequencies of the filter passband; based on the calculated deviation and adjustment range, gradually adjusting the start and end frequency related parameters of the bandpass filter passband, and after each adjustment, comparing the adaptability of the valid carrier frequency parameters with the adjusted filter passband to check whether the filter passband can completely cover the carrier frequency spectrum range, and repeatedly adjusting the adaptability until the filter passband accurately corresponds to the carrier frequency spectrum of the BeiDou modulation signal; inputting the pre-processed BeiDou mixed signal into the adjusted bandpass filter passband, filtering out the carrier frequency carrying signal in the BeiDou modulation signal through filtering operations, comprehensively detecting the selected carrier frequency carrying signal, checking the carrier frequency component and the modulation component of the original BeiDou positioning signal in the signal point by point, confirming that both components are complete, without missing or distorted, and ensuring that the carrier frequency carrying signal meets the requirements of subsequent detection processing.

[0031] Specifically, the process of generating the BeiDou modulation intermediate signal after spectrum calibration includes: using the adjusted bandpass filter passband, performing a secondary filtering operation on the selected carrier frequency signal to clarify the spectral characteristics of the mobile communication signal and residual low-frequency clutter, setting targeted filtering suppression parameters, focusing on suppressing signal components that conform to the spectral characteristics of these two types of clutter, and gradually filtering out the mobile communication signal and residual low-frequency clutter components mixed in; after filtering, starting the spectrum calibration mechanism, performing comprehensive and detailed spectrum detection on the filtered signal, checking the accuracy of each core parameter of the carrier frequency component point by point, comparing it with the stored effective carrier frequency parameters, identifying the offset of the carrier frequency parameters, calculating the offset amplitude, formulating a parameter correction scheme based on the offset amplitude, and gradually correcting the offset of the carrier frequency parameters according to the correction scheme until the carrier frequency component parameters are restored to the effective range, ensuring that the carrier frequency components remain stable; after calibration, integrating all effective components in the signal, performing spectrum smoothing processing on the integrated signal, eliminating instantaneous signal fluctuations generated during the calibration process, ensuring that the signal spectrum is coherent and stable, and finally forming the BeiDou modulation intermediate signal.

[0032] Specifically, the passive adaptive envelope detection technology includes the following steps: activating the passive adaptive envelope detection technology, establishing an amplitude change tracking mechanism, continuously capturing the amplitude information of the BeiDou modulated intermediate signal, recording amplitude data at fixed time intervals to form a complete amplitude change sequence; tracking and monitoring the change trend of amplitude information through the amplitude change sequence, identifying the rise and fall patterns and fluctuation periods of the amplitude, forming a complete amplitude change pattern; combining the identified amplitude change pattern, analyzing the amplitude characteristics of the signal, including amplitude fluctuation amplitude, stability duration, and instantaneous change rate; based on the analyzed amplitude characteristics, gradually adjusting the filtering and load-related adjustment parameters, monitoring the change in the amplitude change pattern after each adjustment, verifying the adaptation effect of parameter adjustments on the signal amplitude characteristics, continuously adjusting and repeatedly adapting until the detection-related parameters completely match the amplitude characteristics of the BeiDou modulated intermediate signal, ensuring stable and accurate subsequent detection operations.

[0033] Specifically, the half-wave rectification process includes: connecting the carrier frequency signal to the detection processing flow, clarifying the half-wave rectification processing standard, retaining only the positive amplitude signal component of the carrier frequency signal, removing the negative amplitude signal component, performing a complete half-wave rectification operation on the carrier frequency signal to convert the high-frequency carrier frequency component into a pulsating DC signal; performing layered filtering and smoothing processing on the converted pulsating DC signal, first filtering out the high-frequency pulsating component with a large amplitude through preliminary filtering, then filtering out the residual high-frequency pulsating component with a small amplitude through fine filtering, and gradually filtering out all high-frequency pulsating components in the signal layer by layer; during the filtering process, continuously monitoring the change in signal amplitude, recording amplitude data point by point, checking the stability of the signal amplitude, and continuing filtering until the signal amplitude tends to be stable. After each layered filtering is completed, checking the modulation characteristics of the original BeiDou positioning signal in the signal to ensure that the signal after filtering out the high-frequency pulsating component can completely retain the modulation characteristics of the original BeiDou positioning signal without the loss or distortion of modulation characteristics.

[0034] Specifically, the process of generating the preliminary BeiDou signal envelope includes: for the filtered and smoothed signal, locking the modulation component in the carrier frequency signal through spectrum identification, clarifying the spectrum range and timing characteristics of the modulation component, separating the modulation component from the carrier frequency component, and extracting the modulation component separately; performing envelope extraction operation on the separated modulation component using an envelope extraction algorithm, setting the sampling interval and duration of envelope extraction, collecting the amplitude peak value of the modulation component point by point, connecting all amplitude peak values ​​to form a preliminary envelope curve, and demodulating and separating the envelope features of the original BeiDou positioning signal through the extraction process; performing preliminary processing on the separated envelope features, calling the preset spurious feature judgment criteria, identifying spurious points in the envelope curve that do not conform to the envelope features of the original BeiDou positioning signal, removing spurious features in the envelope, smoothing the envelope curve after removing spurious features, filling in the missing points in the envelope curve, and retaining the complete envelope information of the original BeiDou positioning signal; integrating the processed envelope information to form a coherent and complete envelope waveform, and finally generating the preliminary BeiDou signal envelope.

[0035] Specifically, the low-pass filtering process for the BeiDou signal envelope prototype includes: first, inputting the BeiDou signal envelope prototype into the low-pass filtering process; second, performing spectral analysis on the BeiDou signal envelope prototype to clarify the spectral characteristics of harmonic signals, spurious signals, and residual carrier frequency components generated during detection, including the spectral range, amplitude, and phase characteristics of each spurious signal; third, gradually adjusting the cutoff frequency parameters of the low-pass filter based on the analyzed spectral characteristics of various spurious signals, setting targeted filtering suppression thresholds to ensure that the low-pass filter can accurately suppress various spurious signals and residual carrier frequency components while avoiding damage to the BeiDou signal envelope characteristics; fourth, applying the adjusted low-pass filter parameters to the filtering process to perform low-pass filtering on the BeiDou signal envelope prototype; fifth, continuously monitoring the signal waveform segment by segment during the filtering process, comparing the waveform changes before and after filtering segment by segment to confirm that various spurious signals and residual carrier frequency components have been effectively filtered out, while ensuring that the envelope characteristics of the filtered signal are not destroyed and are completely preserved, until all spurious signals and residual carrier frequency components have been filtered out, and then stopping the filtering operation.

[0036] Specifically, the process of calibrating the signal amplitude to a preset target amplitude includes: capturing the actual amplitude of the low-pass filtered signal; continuously collecting multiple sets of actual amplitude samples at fixed intervals; calculating the average amplitude of the samples as the final actual amplitude data; calling the preset target amplitude judgment standard to clarify the specific range and stability requirements of the target amplitude; comparing the calculated actual amplitude data with the target amplitude judgment standard item by item to calculate the deviation between the two and clarify the direction and specific magnitude of the deviation; formulating an amplitude adjustment scheme based on the deviation; gradually adjusting the amplitude adjustment coefficient; after each adjustment, re-collecting the actual signal amplitude, calculating the amplitude deviation after adjustment, and verifying the adjustment effect; and linking the signal amplitude with the amplitude adjustment coefficient, repeatedly comparing and continuously calibrating until the signal amplitude reaches the target amplitude judgment standard and the amplitude fluctuation remains within the preset stable range, fixing the current amplitude adjustment coefficient to ensure signal amplitude stability.

[0037] Specifically, the process of generating the BeiDou demodulation and positioning reference signal includes: capturing the actual timing information of the initial BeiDou signal envelope; recording the timing data of each signal node according to the signal transmission order to form a complete actual timing sequence; calling the preset timing judgment standard to clarify the standard timing range and timing interval requirements of each signal node; comparing the actual timing sequence with the timing judgment standard one by one to identify the timing deviation between the two for each node and marking the deviation nodes; analyzing the marked deviation nodes separately to calculate the specific degree of timing deviation of each deviation node and clarify the direction and duration of the deviation; formulating a targeted timing correction scheme according to the degree of deviation of each deviation node; gradually correcting the timing deviation of each deviation node according to the signal transmission order; after each correction, checking the timing data of the corrected node to verify the correction effect; after all timing deviations are corrected, integrating the amplitude, timing, and envelope characteristics of the signal, and comprehensively verifying the integrated signal to ensure that all signal characteristics meet the preset standard, ultimately forming the BeiDou demodulation and positioning reference signal.

[0038] This embodiment discloses a BeiDou signal demodulation system based on envelope detection, applicable to signal demodulation after BeiDou and mobile communication signals are transmitted on a shared network in enclosed environments such as underground garages and utility tunnels. The signal converter adopts a 1-input 1-output architecture, and the core implements a complete process of filtering, passive envelope detection, and clutter filtering, working together to demodulate the BeiDou shared network radiated signal. The preset amplitude stability range is [M1, M2], the preset clutter identification amplitude threshold is M3, the spectrum range is [f1, f2], the original BeiDou positioning signal frequency is f0, the carrier signal frequency is f_c (f_c = k × f0, k is a preset multiple and k ≥ 3), and the preset carrier frequency band parameters are [f_c]. - ,f_c + The preset target amplitude is M0, and the preset time standard interval is T0.

[0039] The system input signal described in this embodiment is a mixed signal radiated by the BeiDou network (a mixture of BeiDou modulation signal and mobile communication signal, the BeiDou modulation signal being obtained by modulating the original BeiDou positioning signal f0 onto the carrier frequency f_c), and the output signal is the BeiDou demodulated positioning reference signal after calibration and demodulation. The signal preprocessing unit corresponds to the initial clutter filtering and signal amplitude preprocessing of the signal converter, the carrier frequency screening unit corresponds to the bandpass filtering frequency selection stage of the signal converter, the envelope detection unit corresponds to the passive detection stage of the signal converter, and the calibration and demodulation unit corresponds to the clutter filtering and signal recovery output stage of the signal converter. The units are linked in sequence to realize the complete function of "filtering-detection-clutter filtering" of the signal converter.

[0040] (I) Specific Implementation of the Signal Preprocessing Unit The signal preprocessing unit receives the mixed signals radiated by the BeiDou network. Its core functions include signal amplitude stabilization and high-frequency pulse clutter filtering, generating a preprocessed BeiDou mixed signal. The specific implementation process is as follows: 1. Amplitude Data Acquisition and Anomaly Removal: Continuously capture the mixed radiation signal from the BeiDou network, and collect amplitude samples at fixed time intervals t, for a total of n sets of amplitude samples, denoted as A1, A2, A3, ..., A n (n is the preset number of acquisition groups, t is the preset acquisition interval); call the preset abnormal amplitude judgment standard and set the abnormal amplitude threshold to [M 1- M 2+ ] (M 1- <M1, M 2+ >M2), compare each group of amplitude samples with this threshold. If a certain group of samples A i (i=1,2,...,n) satisfying A i <M 1- Or A i >M 2+ If the sample is an instantaneous abnormal amplitude, it is determined to be discarded; after screening, the valid amplitude samples are obtained and denoted as A'1, A'2, ..., A' m (m≤n, where m is the number of valid sample groups).

[0041] 2. Amplitude fluctuation calculation and gain parameter adjustment: Statistical verification is performed on the effective amplitude samples. First, the maximum value A' in the effective samples is calculated. max and minimum value A' min The formula for calculating the amplitude fluctuation ΔA is: ΔA = A' max -A' min The calculated ΔA is compared with the fluctuation threshold ΔA0 (ΔA0=M2-M1) corresponding to the preset amplitude stability range, and the gain adjustment parameter G (G is the initial preset gain parameter) is adjusted in two cases: (1) If ΔA≤ΔA0, it means that the amplitude fluctuation meets the stability requirements, and there is no need to adjust the gain parameter. Keep the current gain G unchanged. 0(2) If ΔA>ΔA0, it means that the amplitude fluctuation exceeds the stable range and the gain parameter needs to be adjusted step by step. The formula for calculating the gain adjustment amount ΔG is: ΔG=G×(ΔA-ΔA0) / ΔA0 (the adjustment coefficient is (ΔA-ΔA0) / ΔA0 to ensure that the adjustment amplitude is positively correlated with the fluctuation deviation). After each adjustment, n sets of amplitude samples are collected again, and the above abnormal elimination, fluctuation amplitude calculation and comparison steps are repeated until the calculated ΔA'≤ΔA0, and the adjustment is stopped. The gain parameter at this time is recorded as G', G'=G+ΣΔG (ΣΔG is the sum of the gain adjustment amount of multiple adjustments). After adjustment, the amplitude of the signal is maintained in the range of [M1,M2].

[0042] 3. High-frequency pulse clutter identification and filtering calculation: A preset clutter identification criterion is invoked, which includes the spectral range [f1, f2] of the high-frequency pulse clutter, the amplitude threshold M3 (M3 < M1), and the duration threshold t0. The spectral information of the mixed signals radiated by the BeiDou network is captured in real time. The signal's spectral frequency is denoted as f, and the corresponding amplitude is A(f). The [f, A(f)] of each frequency point is compared with the clutter identification criterion. If a frequency point satisfies f ∈ [f1, f2], A(f) ≥ M3, and the signal duration t0 corresponding to that frequency point is within the specified range, then the clutter is removed. i If ≥t0, then the signal component corresponding to that frequency point is determined to be high-frequency pulse noise; During the clutter filtering process, a filtering suppression coefficient K is set (K is a preset suppression coefficient, 0 < K < 1). The amplitude of the signal component identified as clutter is calculated as follows: A''(f) = A(f) × K. This calculation is used to suppress the amplitude of the clutter. During the filtering process, the signal spectrum changes are continuously monitored. After each clutter suppression is completed, the amplitude deviation ΔA'' = A(f) - A''(f) is calculated to ensure that ΔA'' ≥ A(f) × (1 - K0) (K0 is the preset minimum suppression coefficient) to avoid clutter not being effectively filtered out. After all high-frequency pulse clutter is filtered out, the remaining effective signal components are integrated to generate a pre-processed BeiDou hybrid signal, denoted as S1(t) (t is a time variable).

[0043] (II) Specific Implementation of Carrier Frequency Screening Unit The carrier frequency screening unit receives the preprocessed BeiDou mixed signal S1(t) and performs core tasks such as spectrum scanning, carrier frequency parameter extraction, filter passband adjustment, clutter filtering, and spectrum calibration to generate the BeiDou modulated intermediate signal. The specific implementation process is as follows: 1. Spectrum Scanning and Carrier Frequency Spectrum Locking: A combined coarse and fine spectrum scan is performed on the preprocessed BeiDou hybrid signal S1(t). First, the coarse scan mode is started, and the coarse scan frequency interval Δf1 is set (Δf1 is the preset coarse scan interval). The scan frequency range is [f0×k]. - ,f0×k + ](k - <k<k + k - k + (with preset multiple boundaries), the approximate spectral range of the BeiDou modulation signal is quickly determined through coarse scanning [f'_c - ,f'_c + ]; Then switch to fine scan mode, set the fine scan frequency interval Δf2 (Δf2 < Δf1, Δf2 is the preset fine scan interval), in [f'_c - ,f'_c + A precise scan is performed within the range, capturing spectral features point by point to pinpoint the precise spectral range [f_c] corresponding to the carrier frequency f_c. - ',f_c + '](f_c - '≥f_c - f_c + '≤f_c + ).

[0044] 2. Carrier frequency parameter extraction and verification calculation: From the locked precise spectrum range [f_c - ',f_c + In the image, the core parameters of the carrier frequency component are extracted, including the carrier center frequency f'_c and the carrier amplitude range [A_c]. min ,A_c max The specific calculations for each parameter, including the carrier frequency phase φ_c, are as follows: (1) Carrier center frequency f'_c: Collect all frequency points f within the precise spectrum range i (i=1,2,...,p, where p is the number of fine-scan frequency points), the corresponding amplitude is A_c i The amplitude-weighted average value is calculated, which is the center frequency of the carrier frequency. The formula is: f'_c=(Σf i ×A_c i ) / (ΣA_c i (i=1,2,...,p, where Σ is the summation symbol); (2) Carrier frequency amplitude range [A_c min A_c max ]: For all A_c i Sort the data and take the minimum value A_c. min The maximum value is A_c max That is, the amplitude range is between the two; (3) Carrier frequency phase φ_c: Based on spectrum phase detection, the phase data corresponding to the center frequency f'_c of the carrier frequency is collected and denoted as φ_c1, φ_c2, ..., φ_c q (q is the preset number of phase acquisition groups), calculate the average value to obtain the final carrier frequency phase, the calculation formula is: φ_c=(φ_c1+φ_c2+...+φ_c q ) / q.

[0045] Parameter validation: Extract f'_c, [A_c min A_c max ] and φ_c are compared with the preset carrier frequency parameters respectively. The preset carrier frequency center frequency threshold is [f_c -0 ,f_c +0 ](f_c -0 =f_c-Δf0,f_c +0 =f_c+Δf0, where Δf0 is the preset frequency deviation threshold), and the preset carrier frequency amplitude threshold is [A_c]. -0 A_c +0 The preset carrier frequency phase threshold is [φ_c]. -0 ,φ_c +0 If all parameters are within the corresponding preset threshold range, they are determined to be valid carrier frequency parameters and stored for later use; if a parameter exceeds the threshold, such as f'_c < f_c -0 Or f'_c > f_c +0 If the spectrum scan and parameter extraction are repeated, the process continues until all parameters are valid.

[0046] 3. Bandpass Filter Passband Adjustment Calculation: Based on the stored effective carrier frequency parameters, adjust the start and end frequency parameters of the bandpass filter passband. Let the passband before adjustment be [f_t]. - ,f_t + The adjusted passband is [f_t']. - ,f_t' + The specific adjustments and calculations are as follows: (1) Passband start frequency f_t' - Calculation of f_t' - =f'_c-(f_c + '-f'_c) ensures that the passband start frequency is lower than the carrier center frequency and covers the lower limit of the carrier frequency; (2) Passband termination frequency f_t' + Calculation of f_t' + =f'_c+(f'_c-f_c - '), ensuring that the passband termination frequency is higher than the carrier center frequency and covers the upper limit of the carrier frequency; After adjustment, calculate the passband width Δf_t'=f_t'+ -f_t' - , and the carrier frequency spectral width Δf_c'=f_c + '-f_c - A comparison is performed to ensure that Δf_t' = Δf_c' + 2Δf_b (Δf_b is a preset redundant bandwidth used to avoid missing carrier frequency signals). If this condition is not met, the start and end frequencies of the passband are recalculated and adjusted until they meet the requirements. After the adjustment is completed, the preprocessed BeiDou mixed signal S1(t) is connected to the passband filter to filter out the carrier frequency carrying signal S2(t) (which includes the carrier frequency component and the modulation component of the original BeiDou positioning signal).

[0047] 4. Clutter Filtering and Spectrum Calibration Calculation: Using the adjusted bandpass filter passband, a secondary filter is performed on the carrier frequency signal S2(t) to filter out mobile communication signals and residual low-frequency clutter. The clutter suppression threshold is set to A_z (A_z < A_c). m ᵢ n ), components in the signal with amplitude A≤A_z are identified as noise and filtered out; after filtering, the signal S2'(t) is obtained; Spectrum calibration: Collect the carrier frequency parameters of S2'(t), denoted as f''_c and A''_c. max 、A''_c min φ''_c, and φ''_c are respectively related to the stored effective carrier frequency parameters f'_c and A_c. max A_c min By comparing φ_c, the deviations of each parameter are calculated: (1) Frequency deviation Δf_c = |f''_c - f'_c|; (2) Amplitude deviation ΔA_c max =|A''_c max -A_c max |,ΔA_c min =|A''_c min -A_c min |; (3) Phase deviation Δφ_c = |φ''_c - φ_c|; Let the allowable deviation values ​​for the parameters be Δf_c0, ΔA_c0, and Δφ_c0, respectively. If all deviations satisfy Δf_c ≤ Δf_c0 and ΔA_c max ≤ΔA_c0、ΔA_c minIf ΔA_c0 and Δφ_c ≤ Δφ_c0, the calibration is qualified. If there is a deviation that exceeds the allowable value, such as Δf_c > Δf_c0, the start frequency of the bandpass filter is adjusted by adjusting Δf_t = Δf_c × k_f (k_f is the preset frequency calibration coefficient). After adjustment, the parameters are re-acquired and the deviation is calculated until all deviations meet the requirements. After calibration, the signal is subjected to spectrum smoothing to generate the Beidou modulation intermediate signal S3(t), which is output to the envelope detection unit.

[0048] (III) Specific implementation and calculation of envelope detection unit The envelope detection unit receives the BeiDou modulated intermediate signal S3(t). Based on passive adaptive envelope detection technology, it performs core tasks such as detection parameter adjustment, half-wave rectification, filtering and smoothing, and envelope extraction to generate a preliminary BeiDou signal envelope. The specific implementation process is as follows: 1. Amplitude Variation Data Acquisition and Pattern Analysis: Establish an amplitude variation tracking mechanism, and collect amplitude data of S3(t) at time intervals t' (t' is the preset tracking interval), for a total of p sets of data, denoted as B1, B2, ..., B p By analyzing the amplitude variation patterns using this set of data, the amplitude variation rate v can be calculated. i (i=1,2,...,p-1), the calculation formula is: v i =(B i+1 -B i ) / t', according to v i The positive or negative change of the amplitude determines the upward or downward trend of the amplitude, and at the same time, the average rate of change of amplitude v_avg=(Σv i ) / (p-1), which serves as the basis for parameter adjustment.

[0049] 2. Adaptive Adjustment Calculation of Detector Parameters: The core adjustable parameters of the envelope detector unit are the filter capacitance-related parameter C and the load-related parameter R. The initial parameters are C0 and R0, respectively. Based on the amplitude variation law and average variation rate v_avg summarized above, C and R are adjusted. The specific calculation is as follows: (1) Adjustment of filter capacitance parameter C: Set capacitance adjustment coefficient k_c (k_c is a preset coefficient, which is positively correlated with the amplitude change rate), and adjust the amount ΔC = C0 × |v_avg| × k_c; if v_avg > 0 (amplitude is generally on the rise), then the adjusted capacitance C' = C0 + ΔC; if v_avg < 0 (amplitude is generally on the fall), then the adjusted capacitance C' = C0 - ΔC; if v_avg = 0 (amplitude is stable), then C' = C0; (2) Adjustment of load-related parameters R: Set the load adjustment coefficient k_r (k_r is a preset coefficient, which is negatively correlated with the rate of change of amplitude), and the adjustment amount ΔR = R0 × |v_avg| × k_r; if v_avg > 0, then the adjusted load parameter R' = R0 - ΔR; if v_avg < 0, then the adjusted load parameter R' = R0 + ΔR; if v_avg = 0, then R' = R0; After adjustment, the output amplitudes B'1, B'2, ..., B' of the adjusted detector are collected. p Calculate the adjusted amplitude fluctuation range ΔB'=B' max -B' min The parameters are compared with the preset detection amplitude fluctuation threshold ΔB0. If ΔB' ≤ ΔB0, the parameter adjustment is qualified, and C' and R' are determined as the final detection parameters. If ΔB' > ΔB0, the above adjustment calculation steps are repeated until the requirements are met.

[0050] 3. Half-wave rectification and filtering smoothing calculation: The carrier frequency signal S2(t) is connected to the adjusted detector link, and half-wave rectification is performed. The rectification threshold B0' (B0' is the preset rectification threshold, slightly greater than 0) is set to rectify the amplitude B(t) of S2(t). The formula for calculating the rectified amplitude B_rect(t) is: if B(t)≥B0', then B_rect(t)=B(t); if B(t)<B0', then B_rect(t)=0. Through this calculation, the high-frequency carrier frequency component is converted into a pulsating DC signal S4(t).

[0051] The S4(t) is subjected to hierarchical filtering and smoothing, which consists of two steps: preliminary filtering and fine filtering. (1) Preliminary filtering: Set the preliminary filtering coefficient k_f1 (k_f1 is a preset coefficient, 0 < k_f1 < 1), and calculate the amplitude B_f1(t) after filtering as follows: B_f1(t) = B_rect(t) × (1 - k_f1) + B_rect(t - t'') × k_f1 (t'' is the preliminary filtering time constant), which is used to filter out high-frequency pulsation components with large amplitude; (2) Fine filtering: Set the fine filtering coefficient k_f2 (k_f2 is a preset coefficient, 0 < k_f2 < k_f1), and calculate the amplitude B_f2(t) after filtering as follows: B_f2(t) = B_f1(t) × (1-k_f2) + B_f1(t-t''') × k_f2 (t''' is the fine filtering time constant, t''' < t''), which is used to filter out residual small-amplitude high-frequency pulsation components; After filtering, calculate the amplitude deviation before and after filtering: ΔB_f = B_rect(t) - B_f2(t), ensuring that ΔB_f ≤ B_rect(t) × k_f max (k_f) max(This is a preset maximum filter amplitude loss coefficient) to avoid excessive loss of effective signal amplitude.

[0052] 4. Envelope Extraction and Calculation: The modulation component in the carrier frequency signal is locked, and an envelope extraction algorithm is used, calculated according to the sampling interval t. s (t) s The peak amplitudes of B_f2(t) are collected at preset sampling intervals and denoted as P1, P2, ..., P. q (q is the number of peak acquisition groups); connect all the peak values ​​to form a preliminary envelope curve, smooth and correct the preliminary envelope curve, and the formula for calculating the corrected envelope amplitude P'i (i=1,2,...,q) is: P'i=(Pᵢ -1 +2Pᵢ+Pᵢ +1 ) / 4 (i=2,3,...,q-1), with peak values ​​at both ends P'1=P1, P' q =P q The envelope features of the original BeiDou positioning signal are separated by this calculation and demodulation. The corrected envelope information is integrated to generate a preliminary BeiDou signal envelope S5(t), which is then transmitted to the calibration and demodulation unit.

[0053] (iv) Specific implementation of the calibration and demodulation unit The calibration and demodulation unit receives the initial BeiDou signal envelope S5(t), performs low-pass filtering, amplitude calibration, and timing calibration, and generates a BeiDou demodulated positioning reference signal. The specific implementation process is as follows: 1. Low-pass filtering and clutter removal calculation: For S5(t), low-pass filtering is performed. First, the spectral characteristics of harmonic signals, spurious signals and residual carrier frequency components generated during the detection process are analyzed. The clutter spectrum range is set as [f_z1, f_z2]. Based on this spectrum range, the cutoff frequency f_L of the low-pass filter is adjusted. The formula for calculating the cutoff frequency is: f_L = f_z1 - Δf_z (Δf_z is the preset cutoff frequency redundancy). Connecting S5(t) to the adjusted low-pass filter link, the formula for calculating the amplitude B_L(t) of the filtered signal is: B_L(t) = S5(t) × [1 - (f / f_L)] 2 (f is the current frequency of the signal). When f ≥ f_L, B_L(t) ≈ 0, achieving targeted filtering of clutter. During the filtering process, the signal waveform is continuously monitored, and the clutter filtering efficiency η is calculated. The calculation formula is: η = (total clutter amplitude - total clutter amplitude after filtering) / total clutter amplitude × 100%. Ensure that η ≥ η0 (η0 is the preset minimum filtering efficiency). If it is not satisfied, the cutoff frequency f_L is readjusted until it meets the requirements. After filtering, the signal S6(t) is obtained.

[0054] 2. Amplitude Calibration and Calculation: Capture the actual amplitude of S6(t), and collect r sets of actual amplitude samples at time intervals t_c (t_c is the preset calibration interval), denoted as C1, C2, ..., C6. r Calculate the actual average amplitude C_avg using the formula: C_avg = (C1 + C2 + ... + C r Compare C_avg with the preset target amplitude M0, calculate the amplitude deviation ΔC = C_avg - M0, and adjust the amplitude adjustment coefficient K_A (K_A is the initial preset adjustment coefficient) according to ΔC. The specific adjustment calculation is as follows: (1) If ΔC=0, it means that the amplitude meets the requirements and there is no need to adjust the adjustment coefficient. Keep K_A unchanged. (2) If ΔC>0, it means that the actual amplitude is higher than the target amplitude. The adjusted adjustment coefficient K'_A=K_A×(1-ΔC / M0) and the adjusted signal amplitude C'_avg=C_avg×K'_A; (3) If ΔC < 0, it means that the actual amplitude is lower than the target amplitude. The adjusted adjustment coefficient K'_A = K_A × (1 + |ΔC| / M0) and the adjusted signal amplitude C'_avg = C_avg × K'_A; After adjustment, recollect samples, calculate C'_avg, compare it with M0, and calculate the deviation ΔC' = |C'_avg - M0|. If ΔC' ≤ ΔC 00 (ΔC0 is the preset allowable deviation for amplitude calibration), then the amplitude calibration is qualified; if ΔC' > ΔC0, repeat the above adjustment calculation steps until the requirements are met, and the signal S7(t) is obtained after calibration.

[0055] 3. Timing Calibration and Calculation: Capture the actual timing data of S7(t), record the timing of each signal node according to the signal transmission order, denoted as T1, T2, ..., Tᵢ (Tᵢ is the actual timing of the i-th node), and preset the standard timing of each node as T. 01 T 02 ... T 0i (T) 0i =T0×i, where T0 is the preset time series standard interval); calculate the time series deviation ΔT for each node. i =T i -T 0i (i=1,2,...,i), timing correction is performed in two cases: (1) If ΔTᵢ>0 (actual time lag), the correction amount ΔT' i =ΔT i ×k_t (k_t is the preset lag correction coefficient, 0 < k_t < 1), the corrected time series T' i =T i -ΔT' iᵢ; (2) If ΔTᵢ<0 (actual timing is ahead), the correction amount ΔT' i =|ΔT i |×k_t' (k_t' is the preset lead correction coefficient, 0 < k_t' < 1), the corrected timing T' i =T i +ΔT' i ; After correction, calculate the correction deviation ΔT'' for each node. i =|T' i -T 0i |, Set the allowable deviation ΔT0 for timing calibration, if all ΔT'' i If ≤ΔT0, then the timing calibration is qualified; if ΔT'' exists... i >ΔT0, repeat the above correction calculation steps until the requirements are met; After timing calibration is completed, the amplitude, timing and envelope characteristics of signal S7(t) are integrated to generate BeiDou demodulation positioning reference signal S8(t), which can be directly used by various positioning terminals.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A BeiDou signal demodulation system based on envelope detection, characterized in that, include: Signal preprocessing unit, carrier frequency screening unit, envelope detection unit, and calibration and demodulation unit; The signal preprocessing unit acquires the amplitude data of the BeiDou network radiation signal, calculates the amplitude fluctuation range, and adjusts the gain adjustment parameters. By setting a clutter identification threshold, high-frequency pulse clutter in the BeiDou shared network radiation signal is identified and filtered out to generate a pre-processed BeiDou hybrid signal. The carrier frequency filtering unit performs a spectrum scan on the preprocessed BeiDou mixed signal to obtain the carrier frequency spectrum characteristics of the BeiDou modulation signal, extracts the carrier frequency component parameters, adjusts the start and end frequency parameters of the bandpass filter passband, and generates the carrier frequency carrying signal in the BeiDou modulation signal; the mobile communication signal and low-frequency noise are filtered out through the filter passband, and the BeiDou modulation intermediate signal is generated after spectrum calibration. The envelope detection unit, based on passive adaptive envelope detection technology, acquires the amplitude variation data of the BeiDou modulation intermediate signal, adjusts the filter capacitance and load resistance parameters, performs half-wave rectification on the carrier frequency signal, filters and smooths the pulsating DC signal to remove high-frequency pulsating components, extracts the envelope of the modulation components of the carrier frequency signal, demodulates and separates the envelope features of the original BeiDou positioning signal, and generates a preliminary BeiDou signal envelope. The calibration and demodulation unit performs low-pass filtering on the BeiDou signal envelope prototype, calculates the amplitude deviation value, adjusts the amplitude adjustment coefficient, and calibrates the signal amplitude to the preset target amplitude. Based on the actual timing data of the BeiDou signal envelope prototype, timing deviations are identified and the deviation amount is calculated. The signal timing deviations are corrected, and a BeiDou demodulation positioning reference signal is generated.

2. The system according to claim 1, characterized in that, The specific process of adjusting the gain adjustment parameter includes: acquiring amplitude samples at fixed intervals based on the BeiDou network radiation signal, and removing instantaneous abnormal amplitude data; performing statistical calculations on the filtered amplitude samples, taking the difference between the maximum and minimum values ​​of the amplitude samples as the amplitude fluctuation range, comparing it with the preset amplitude stability range judgment standard, and adjusting the gain adjustment parameter.

3. The system according to claim 1, characterized in that, The specific process of generating the preprocessed BeiDou hybrid signal includes: calling a preset clutter identification and judgment standard, performing a filtering operation on the selected clutter components based on the spectrum data of the BeiDou network radiation signal, integrating the remaining effective signal components and performing spectrum consistency verification to generate the preprocessed BeiDou hybrid signal.

4. The system according to claim 1, characterized in that, The specific process of extracting carrier frequency component parameters includes: performing a spectrum scanning operation on the preprocessed BeiDou hybrid signal, capturing spectrum features point by point, generating the spectrum range corresponding to the carrier frequency, extracting the core feature parameters of the carrier frequency components, including the center spectrum position, amplitude variation range and phase characteristics of the carrier frequency; comparing the core feature parameters with the preset carrier frequency parameter judgment range one by one, eliminating abnormal information, retaining the valid carrier frequency parameters and classifying and storing them to establish a carrier frequency parameter archive.

5. The system according to claim 1, characterized in that, The specific process of the carrier frequency carrying signal includes: comparing the center spectrum position and amplitude variation range in the carrier frequency parameter file with the preset carrier frequency band determination criteria to generate the adjustment direction and adjustment amplitude of the start and end frequencies of the filter passband, and adjusting the start and end frequency parameters of the bandpass filter passband; connecting the preprocessed BeiDou mixed signal to the adjusted bandpass filter passband, and filtering out the carrier frequency carrying signal in the BeiDou modulated signal through filtering operations.

6. The system according to claim 1, characterized in that, The specific process of generating the BeiDou modulation intermediate signal after spectrum calibration includes: using the adjusted bandpass filter passband to perform a secondary filtering operation on the selected carrier frequency signal, gradually filtering out mobile communication signals and low-frequency noise components mixed in; starting spectrum calibration, identifying the offset of carrier frequency parameters, calculating the offset amplitude, formulating a parameter correction scheme based on the offset amplitude, and correcting the offset of carrier frequency parameters according to the correction scheme; and performing spectrum smoothing processing on the integrated signal to eliminate instantaneous signal fluctuations generated during the calibration process, thereby generating the BeiDou modulation intermediate signal.

7. The system according to claim 1, characterized in that, The specific process of the passive adaptive envelope detection technology includes: acquiring the amplitude information of the Beidou modulated intermediate signal based on the passive adaptive envelope detection technology, recording amplitude data at fixed time intervals to generate an amplitude change sequence; tracking and monitoring the change trend of amplitude information through the amplitude change sequence to form an amplitude change law and generate the amplitude characteristics of the signal, including amplitude fluctuation amplitude, stable duration and instantaneous change rate; and adjusting the filtering and load adjustment parameters according to the amplitude characteristics.

8. The system according to claim 1, characterized in that, The specific process of the half-wave rectification includes: connecting the carrier frequency signal to the detection process, retaining the positive amplitude signal component in the carrier frequency signal, performing the half-wave rectification on the carrier frequency signal to convert the high-frequency carrier frequency component into a pulsating DC signal; and performing layered filtering and smoothing on the pulsating DC signal to filter out the high-frequency pulsating component in layers.

9. The system according to claim 1, characterized in that, The specific process for generating the preliminary envelope shape of the BeiDou signal includes: identifying the modulation component in the carrier frequency signal through spectrum identification, separating the modulation component from the carrier frequency component, performing envelope extraction on the separated modulation component, setting the sampling interval and duration for envelope extraction, collecting the amplitude peak value of the modulation component point by point, connecting all amplitude peak values ​​to form a preliminary envelope curve, demodulating and separating the envelope features of the original BeiDou positioning signal through the extraction process; performing preliminary processing on the envelope features, calling the preset spurious feature judgment criteria, removing spurious features in the envelope, smoothing the envelope curve after removing spurious features, filling in the missing points in the envelope curve, integrating the processed envelope information to form an envelope waveform, and generating the preliminary envelope shape of the BeiDou signal.

10. The system according to claim 1, characterized in that, The specific process of low-pass filtering the prototype BeiDou signal envelope includes: inputting the prototype BeiDou signal envelope into the low-pass filtering process, performing spectrum analysis on the prototype BeiDou signal envelope, gradually adjusting the cutoff frequency parameters of the low-pass filter based on the various clutter spectrum characteristics obtained from the spectrum analysis, and generating a targeted filtering suppression threshold; applying the adjusted low-pass filter parameters to the filtering process to perform low-pass filtering on the prototype BeiDou signal envelope.

11. The system according to claim 1, characterized in that, The specific process of calibrating the signal amplitude to the preset target amplitude includes: based on the actual amplitude of the BeiDou signal envelope after low-pass filtering, continuously collecting actual amplitude samples at fixed intervals, calculating the average amplitude as the actual amplitude data; calling the preset target amplitude judgment standard, formulating an amplitude adjustment scheme based on the deviation data, adjusting the amplitude adjustment coefficient, and linking the signal amplitude with the amplitude adjustment coefficient to adjust the signal amplitude to reach the target amplitude judgment standard, and maintaining the amplitude fluctuation within the preset stable range, and fixing the current amplitude adjustment coefficient.

12. The system according to claim 1, characterized in that, The specific process of generating the BeiDou demodulation and positioning reference signal includes: based on the actual timing information of the BeiDou signal envelope prototype, recording the timing data of each signal node according to the signal transmission order to generate an actual timing sequence; calling the preset timing judgment standard to mark the deviation nodes, and correcting the timing deviation of the deviation nodes according to the timing deviation direction and duration according to the signal transmission order; integrating the amplitude, timing and envelope characteristics of the corrected signal to generate the BeiDou demodulation and positioning reference signal.

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