Satellite navigation baseband digital signal capturing method and device based on code Doppler compensation

Abstract

The invention provides a satellite navigation baseband digital signal capturing method and device based on code Doppler compensation, and relates to the technical field of satellite navigation signal processing. The method mainly comprises the following steps: preprocessing to obtain data to be captured; coherent integration stripping pseudo codes; performing DFT frequency sweeping to extract multi-frequency point features; the Doppler offset of each frequency point code is calculated, and a result is obtained through offset incoherent dislocation accumulation; and performing peak searching to obtain a signal peak. According to the process, the code Doppler frequency shift influence is processed in a targeted mode, coherent and incoherent processing is integrated, pseudo codes are effectively stripped, frequency point features are extracted, the precision and efficiency of signal capturing are improved, and the suppression capacity for the Doppler effect is enhanced.

Description

Technical Field

[0001] This invention relates to the field of satellite navigation signal processing technology, specifically to a method and apparatus for acquiring satellite navigation baseband digital signals based on code Doppler compensation. Background Technology

[0002] With the continuous development of satellite communication, satellite motion has a significant impact on the frequency of its signals, known as Doppler shift. Doppler shift is a frequency change caused by satellite motion; when a satellite moves towards the receiver, the signal frequency increases, and when the satellite moves away from the receiver, the signal frequency decreases.

[0003] Satellite navigation systems use pseudo-random codes (PRN codes) to distinguish different satellite signals and perform functions such as ranging. Each satellite transmits a unique pseudo-random code, and ground receivers acquire and track the corresponding satellite signal by matching this code.

[0004] When there is relative motion between the satellite and the receiver, not only will the signal carrier undergo a Doppler shift, but the pseudo-random code will also experience a frequency change, i.e., a code Doppler shift. This is because the relative motion between the receiver and the satellite alters the signal propagation time, causing the rate of phase change of the pseudo-random code to differ from that during transmission, thus resulting in a shift in the code rate.

[0005] Code Doppler shift is a phenomenon in satellite navigation, wireless communication and other fields where the signal frequency changes due to the relative motion between the signal source and the receiver. It has a great impact on signal acquisition performance, mainly manifested in reduced signal correlation, increased acquisition difficulty, decreased detection probability and extended acquisition time. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method and apparatus for acquiring satellite navigation baseband digital signals based on code Doppler compensation, which addresses the shortcomings of the prior art.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A satellite navigation baseband digital signal acquisition method based on code Doppler compensation, comprising the following steps:

[0008] S1. Preprocess the received satellite navigation baseband digital signal to obtain the data to be acquired;

[0009] S2. Perform coherent integration on the data to be captured to obtain the coherent integration result after removing the pseudocode;

[0010] S3. Perform DFT frequency sweeping on the coherent integral result after stripping the pseudocode to obtain the signal characteristics of multiple frequency points.

[0011] S4. Calculate the code Doppler offset of the signal characteristics of each frequency point based on the preset DFT base frequency point to obtain the code Doppler offset of each frequency point.

[0012] S5. Perform incoherent misalignment accumulation calculation based on the preset number of incoherent steps and the code Doppler offset of each frequency point to obtain the accumulation result;

[0013] S6. Perform a peak search on the accumulated result to obtain the peak value of the satellite navigation baseband digital signal.

[0014] Another technical solution of the present invention to solve the above-mentioned technical problems is as follows: A satellite navigation baseband digital signal acquisition device based on code Doppler compensation, comprising:

[0015] The signal preprocessing module is used to preprocess the received satellite navigation baseband digital signals to obtain the data to be acquired;

[0016] The coherent integration processing module is used to perform coherent integration processing on the data to be captured to obtain the coherent integration result after removing the pseudocode.

[0017] The code Doppler compensation processing module is used to: perform DFT frequency sweep processing on the coherent integration result after stripping the pseudocode to obtain signal characteristics at multiple frequency points;

[0018] Based on the preset DFT base frequency, the code Doppler offset of each frequency point is calculated to obtain the code Doppler offset of each frequency point.

[0019] Based on the preset number of incoherent iterations and the code Doppler offset at each frequency point, an incoherent misalignment accumulation calculation is performed to obtain the accumulation result;

[0020] The signal search module is used to perform peak search on the accumulated results to obtain the peak value of the satellite navigation baseband digital signal.

[0021] The beneficial effects of this invention are: through a complete process of preprocessing, coherent integration, DFT frequency sweeping, code Doppler shift calculation, incoherent misalignment accumulation, and peak search, the influence of code Doppler frequency shift is specifically addressed. By integrating coherent and incoherent processing, pseudo-codes are effectively removed and frequency features are extracted, improving the accuracy and efficiency of satellite navigation signal acquisition and enhancing the ability to suppress the Doppler effect. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the satellite navigation baseband digital signal acquisition method provided in an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of code Doppler shift provided in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the structure of a satellite navigation baseband digital signal acquisition device provided in an embodiment of the present invention. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] Example 1: As Figure 1 As shown, this embodiment of the invention provides a satellite navigation baseband digital signal acquisition method based on code Doppler compensation, comprising the following steps:

[0027] S1. Preprocess the received satellite navigation baseband digital signal to obtain the data to be acquired;

[0028] S2. Perform coherent integration on the data to be captured to obtain the coherent integration result after removing the pseudocode;

[0029] S3. Perform DFT frequency sweeping on the coherent integral result after stripping the pseudocode to obtain the signal characteristics of multiple frequency points.

[0030] S4. Calculate the code Doppler offset of the signal characteristics of each frequency point based on the preset DFT base frequency point to obtain the code Doppler offset of each frequency point.

[0031] S5. Perform incoherent misalignment accumulation calculation based on the preset number of incoherent steps and the code Doppler offset of each frequency point to obtain the accumulation result;

[0032] S6. Perform a peak search on the accumulated result to obtain the peak value of the satellite navigation baseband digital signal.

[0033] In the above embodiments, the influence of code Doppler frequency shift is specifically addressed through a complete process of preprocessing, coherent integration, DFT frequency sweeping, code Doppler shift calculation, incoherent misalignment accumulation, and peak search.

[0034] A complete acquisition process, from signal preprocessing to peak search, was constructed to specifically address the impact of code Doppler shift on signal acquisition. Preprocessing yields standardized data to be acquired, laying the foundation for subsequent processing; coherent integration effectively removes pseudo-codes while retaining key signal components; DFT frequency sweeping accurately extracts multi-frequency features, providing a basis for frequency domain analysis; code Doppler shift calculation quantifies frequency shifts, and incoherent misalignment accumulation enhances signal energy; finally, peak search locates the effective signal. The synergistic effect of each step, integrating the advantages of coherent and incoherent processing, significantly improves the accuracy and efficiency of satellite navigation signal acquisition and enhances the ability to suppress the Doppler effect.

[0035] Preferably, the method further includes step S7:

[0036] After obtaining the peak value of the satellite navigation baseband digital signal, it is determined whether the peak value exceeds the peak value threshold. If it does, the peak value is determined to be valid and the acquisition is completed. If it does not exceed the threshold, a valid peak value has not been acquired. The code phase is jumped according to the preset code phase jump step size parameter, that is, the number of chips (or phase interval) that the relevant code phase needs to be skipped after the current peak value search is completed, which is used to expand the code phase range of subsequent searches. Return to S2 and re-perform coherent integration processing until the obtained peak value is determined to be valid.

[0037] In the above embodiments, a new peak threshold judgment and code phase switching mechanism is added. The validity of the peak value is verified by the threshold to avoid false positives; if the threshold is not met, the code phase is switched for reprocessing to ensure that no valid signal is missed, significantly improving the acquisition success rate and reducing the risk of missed detections. This mechanism forms a closed-loop verification and iterative search logic, significantly improving the reliability and success rate of signal acquisition, and effectively solving the problem of false positives or missed detections that are prone to occur with single searches.

[0038] Preferably, in step S1, the received satellite navigation baseband digital signal is preprocessed to obtain the data to be acquired, including:

[0039] The received satellite navigation baseband digital signal is filtered by a filter, and the gain parameter of the filtered satellite navigation baseband digital signal is adjusted to a preset quantization range to obtain the baseband data stream.

[0040] Data blocks are extracted from the baseband data stream according to a preset coherent integration length to obtain the data to be captured.

[0041] In the above embodiments, filtering the received signal effectively removes noise and interference, improving the purity of the baseband signal. Adjusting the gain parameter of the filtered signal to a preset quantization range ensures the amplitude stability and consistency of the baseband data stream, preventing gain fluctuations from affecting the accuracy of subsequent integration and other processing steps. Extracting data blocks according to a preset coherent integration length provides standardized and adaptable data input for subsequent coherent integration steps, reducing the impact of data redundancy or insufficiency on processing results. These operations optimize data quality from the source, laying a reliable foundation for the efficient and accurate operation of the entire signal acquisition process.

[0042] Preferably, in step S2, performing coherent integration processing on the data to be captured to obtain the coherent integration result after removing the pseudocode includes:

[0043] A pseudo-random code is obtained from the received satellite navigation baseband digital signal, and a reference local pseudo-code of the same origin as the satellite navigation baseband digital signal is generated. Specifically, based on the pseudo-random code (PRN code) characteristics of the target satellite system (such as BDB3I, GPS L1), a local pseudo-code sequence corresponding to the received signal is generated. The pseudo-code length and code rate are consistent with the target satellite signal (e.g., the pseudo-code length of the BDB3I signal is 10230 chips, and the code rate is 1.023 Mcps).

[0044] The reference local pseudocode is phase-shifted by a preset correlator array to obtain the code phase offset corresponding to each correlator in the correlator array. Specifically, the offset interval is set according to the acquisition accuracy requirements (e.g., the correlation interval is 2 chips). For example, the offsets of 16 correlators can be 0 chips, 2 chips, 4 chips, ..., 30 chips in sequence, covering the 32-chip code phase range (16×2 chips) within the current search window.

[0045] The data to be captured is simultaneously input into each correlator in the correlator array. Each correlator multiplies the data to be captured with its corresponding code phase offset at the same time point, and outputs a new sequence corresponding to each correlator. Specifically, the buffered data to be captured is input into the correlator array (e.g., 16 parallel correlators), each correlator corresponding to a different code phase offset. Through the sliding correlation operation between the data to be captured and the local pseudocode, the initial alignment and stripping of the pseudocode is achieved.

[0046] The new sequence output by each correlator is subjected to coherent integration of a preset length to remove pseudo-code, resulting in a coherent integral result after pseudo-code removal. Specifically, the correlation result output by the correlator is coherently integrated for a preset length (e.g., the coherence time is set to 4ms, and the number of integration points = sampling rate × coherence time). Noise is further suppressed by accumulating signal energy to obtain the coherent integral result after pseudo-code removal. During the integration process, the local pseudo-code and the received signal must be kept in phase synchronization to ensure effective accumulation of integration energy.

[0047] In the above embodiments, the accuracy of pseudocode stripping is improved through refined coherent integration processing. It generates a reference local pseudocode that originates from the same source as the satellite signal, ensuring the consistency of the reference benchmark; phase shifting of the local pseudocode is performed using a correlator array, covering multi-dimensional code phase shifts to achieve comprehensive capture of signals with different phases; the data to be captured is synchronously multiplied with the code phase shifts corresponding to each correlator at the same time point, reducing time misalignment errors and ensuring the accuracy of correlation calculations; then, pseudocode is effectively stripped through coherent integration of a preset length, retaining key signal components. This process, through precise phase matching and synchronization processing, significantly improves the reliability of the coherent integration results, laying a high-quality data foundation for subsequent frequency point feature extraction.

[0048] Preferably, in step S3, the coherent integration result after removing the pseudocode is subjected to DFT frequency sweep processing to obtain signal features at multiple frequency points, including:

[0049] Based on the frequency resolution of the satellite navigation signal, the number of DFT points for the DFT sweep frequency is configured, and the calculation formula is as follows: Where N is the number of DFT points, f s Δf is the sampling rate of the coherent integral result, and Δf is the frequency resolution;

[0050] The actual frequency f corresponding to the frequency index value k is determined based on the frequency resolution and the number of DFT points. k , where f k = (kN / 2)·Δf;

[0051] By performing an N-point DFT sweep on the coherent integral result after removing the pseudocode using the DFT points N, multiple complex results at various frequency points are obtained. The calculation formula is as follows:

[0052]

[0053] Where S(k) is the complex result of the k-th frequency point in the frequency domain, s(n) is the coherent integration result, k is the frequency index value, and n is the time index value in the time domain, n = 0, 1, ..., N-1, e -j2πkn / N It is a complex exponential phase factor;

[0054] The amplitude and phase information of the complex result S(k) for each frequency point are extracted according to the frequency index value k, wherein the amplitude information is represented as:

[0055]

[0056] Where Re(S(k)) is the real part and Im(S(k)) is the imaginary part; the larger the amplitude value, the closer the Doppler frequency corresponding to that frequency point is to the actual frequency offset of the received signal, and the more concentrated the signal energy.

[0057] The phase information is represented as follows:

[0058] Phase(k)=arg(S(k))=arctan2(Im(S(k)),Re(S(k))),

[0059] The calculated amplitude and phase information are associated with preset DFT base frequencies to obtain the actual frequency f of the corresponding frequency index value k for each DFT base frequency. k The amplitude information (Amplitude(k)) and phase information (Phase(k)) are used to obtain the signal characteristics at multiple frequency points.

[0060] In the above embodiments, by configuring the number of DFT points based on frequency resolution, the accuracy of frequency analysis is ensured to meet the requirements; the actual frequency corresponding to the frequency point index value is accurately calculated, and the frequency point is accurately located; the complex result of the frequency point is obtained by scanning the frequency with N-point DFT, and the amplitude and phase information are extracted, so as to fully capture the frequency domain characteristics of the signal; and this information is associated with the preset DFT base frequency point, so as to provide high-precision, multi-dimensional frequency point feature data for subsequent code Doppler offset calculation, which significantly improves the accuracy and reliability of frequency domain analysis and lays a solid data foundation for the entire signal acquisition process.

[0061] Preferably, in step S4, the code Doppler offset is calculated based on the preset DFT base frequency to obtain the code Doppler offset of each frequency point, including:

[0062] Based on the code Doppler offset calculation formula and the preset DFT base frequency and the actual frequency f in the frequency signal characteristics. k The code Doppler offset is calculated based on the correspondence, and the formula for calculating the code Doppler offset is expressed as follows:

[0063]

[0064] Among them, f d_code (k) is the code Doppler offset, f d-carrier (k)=f k f code f is the pseudocode rate. carrier For carrier frequency.

[0065] In the above embodiments, by establishing a quantitative conversion relationship between carrier Doppler and code Doppler, the carrier frequency offset (i.e., the actual frequency of the frequency point) is correlated with the pseudo-code rate and the carrier frequency, thus achieving accurate quantification of the code Doppler offset. This provides accurate offset parameters for subsequent incoherent misalignment accumulation, ensures targeted compensation for code Doppler frequency shift, effectively reduces problems such as reduced signal correlation caused by frequency offset, and improves the processing accuracy of the code Doppler effect during signal acquisition.

[0066] Preferably, in step S5, the incoherent misalignment accumulation calculation is performed based on a preset number of incoherent iterations and the code Doppler offset at each frequency point, including:

[0067] The number of noncoherent cycles is set to N based on the signal strength requirements, and the offset direction and offset magnitude of each frequency point are determined. The offset direction can be positive or negative.

[0068] For a single frequency point, perform N rounds of incoherent misaligned accumulation calculations for each frequency point within the accumulation window:

[0069] Take the phase of the frequency signal characteristic of the current accumulation period i, 1≤i≤N, according to the code Doppler offset f d_code (k) Calculate the shift step size. The calculation process for the shift step size is as follows: If it is a positive shift, the phase of the current accumulation period i shifts to the left relative to the data of the previous round; if it is a negative shift, the phase of the current accumulation period i shifts to the right relative to the data of the previous round. The shift amount is related to f. d_code (k)×T is proportional, where T is the duration of the coherence period;

[0070] The current data is superimposed with the accumulated result of the previous round according to the staggered step size.

[0071] When performing code Doppler compensation processing in the noncoherent phase, a single code Doppler offset is used for m consecutive frequency points (m = 4 or 8), reducing the code Doppler offset calculation logic by a factor of m. This saves hardware resource consumption.

[0072] In the above embodiments, the incoherent accumulation process is optimized to achieve dynamic compensation for code Doppler shift. It flexibly sets the number of incoherent accumulations based on signal strength requirements, adapting to different signal scenarios; the frequency division point determines the offset direction and magnitude, and each frequency point is processed separately to avoid errors from uniform accumulation; the misalignment step size is calculated using the code Doppler shift, with positive / negative offsets corresponding to left / right phase adjustments respectively, and the offset is proportional to the product of the offset and the coherent period duration, ensuring compensation accuracy; the current data is superimposed with the previous round's result according to the step size, effectively accumulating signal energy. This mechanism improves the adaptability of incoherent accumulation to code Doppler frequency shift, enhances weak signal detection capabilities, and optimizes accumulation efficiency and effectiveness.

[0073] Finally, a peak search is performed on the accumulated results to obtain the peak value of the satellite navigation baseband digital signal: traversing the two-dimensional energy matrix of "code phase-Doppler frequency" formed after incoherent misaligned accumulation, the point with the largest amplitude value in the matrix is ​​located by sliding window or point-by-point comparison; this point is the peak value of the satellite navigation baseband digital signal, and its corresponding code phase and Doppler frequency parameters reflect the location where the signal energy is most concentrated.

[0074] Since the number of correlators is limited, assuming the number of correlators n=16, the edge part cor data generated by the offset is not fully accumulated, so additional storage units (or storage areas) are needed to save it. In the next coherent and incoherent set, the saved previous offset data is read again for misaligned accumulation to achieve phase continuity. The storage depth and the number of correlators determine the maximum number of code phase offsets.

[0075] Preferably, step S5 further includes the following step:

[0076] A storage area is set up to cache edge coherent data whose offset exceeds the preset length of the correlator array;

[0077] When the next accumulation cycle begins, the edge coherent data of the previous accumulation cycle is read from the storage area, the phase is aligned with the phase of the current frequency signal characteristics according to the phase of the edge coherent data, and then the data is filled into the current accumulation window according to the misalignment step size.

[0078] After completing N rounds of incoherent misalignment accumulation calculations, output the accumulation result.

[0079] Specifically, phase alignment refers to, such as Figure 2 As shown in the positive frequency offset (left figure), when the signal exhibits positive code Doppler offset:

[0080] The current segment cor: the vertical sequence is [0,1,2,...,n-1] (each row represents the coherent result at a time).

[0081] Historical cumulative values: The vertical sequence is also [0,1,2,...,n-1].

[0082] Misalignment logic: The i-th result of the historical accumulated value is aligned with the (i+1)-th result of the current segment (e.g., the historical 0 corresponds to the current 1, the historical 1 corresponds to the current 2, and so on).

[0083] The actual output cor: The effective overlapping accumulation intervals are [1,2,...,n-1] (current segment) and [0,1,...,n-2] (history). By misaligning, the current segment, which is "leading" in phase, is aligned with the history segment, which is "lagging" in phase, thus achieving coherent superposition.

[0084] In the negative frequency offset (right figure), when the signal exhibits negative code Doppler offset:

[0085] The current segment cor has a vertical sequence of [0,1,2,...,n-1].

[0086] Historical cumulative values: The vertical sequence is [0,1,2,...,n-1].

[0087] Misalignment logic: The i-th result of the historical accumulated value is aligned with the (i-1)-th result of the current segment (e.g., the historical 1 corresponds to the current 0, the historical 2 corresponds to the current 1, and so on).

[0088] The actual output cor: The effective overlapping accumulation intervals are [0,1,...,n-2] (current segment) and [1,2,...,n-1] (history). By misaligning, the current segment, which is "lagging" in phase, is aligned with the history segment, which is "leading" in phase, thus achieving coherent superposition.

[0089] Code Doppler causes phase misalignment of coherent results at different times. By aligning the misalignment in opposite directions, the historical and current coherent results are superimposed at the same phase position, maximizing the gain of coherent accumulation, improving the signal-to-noise ratio, and assisting in signal acquisition.

[0090] The above embodiments solve the problem of edge data loss in incoherent misaligned accumulation, ensuring the integrity and continuity of the accumulation. By allocating a storage area to cache edge coherent data with offsets exceeding the length of the correlator array, critical data truncation due to offset is avoided. After reading the cached edge data in the next accumulation cycle, phase alignment is performed to match the signal characteristics of the current frequency point, and then the data is padded to the current accumulation window according to the misalignment step size. This ensures the coherent connection of data from different cycles and reduces accumulation errors caused by incomplete data. Ultimately, this makes the N-round incoherent misaligned accumulation results more reliable, improves the accuracy of signal energy accumulation, provides more complete signal feature data for subsequent peak search, and further optimizes acquisition performance.

[0091] Taking the BD B3I signal as an example, assuming 16 correlators and a correlation interval of 2, and with 4 x 16 ms of coherent and incoherent acquisition times, a two-chip offset is calculated, meaning the maximum offset is 2. Acquiring the B3I signal at a signal strength of -143 dBm, with the acquisition parameters adjusted to a coherent time of 4 and an incoherent time of 16, and using code Doppler compensation compared to not using it, within a fixed time window, the number of successful acquisitions can be increased by 10% based on the two-and-a-half-chip offset.

[0092] Example 2: Figure 3 As shown, this embodiment of the invention also provides a satellite navigation baseband digital signal acquisition device based on code Doppler compensation, comprising:

[0093] The signal preprocessing module is used to preprocess the received satellite navigation baseband digital signals to obtain the data to be acquired;

[0094] The coherent integration processing module is used to perform coherent integration processing on the data to be captured to obtain the coherent integration result after removing the pseudocode.

[0095] The code Doppler compensation processing module is used to: perform DFT frequency sweep processing on the coherent integration result after stripping the pseudocode to obtain signal characteristics at multiple frequency points;

[0096] Based on the preset DFT base frequency, the code Doppler offset of each frequency point is calculated to obtain the code Doppler offset of each frequency point.

[0097] Based on the preset number of incoherent iterations and the code Doppler offset at each frequency point, an incoherent misalignment accumulation calculation is performed to obtain the accumulation result;

[0098] The signal search module is used to perform peak search on the accumulated results to obtain the peak value of the satellite navigation baseband digital signal.

[0099] Preferably, the coherent integration processing of the data to be captured to obtain the coherent integration result after removing the pseudocode includes:

[0100] Obtain pseudo-random codes from the received satellite navigation baseband digital signals and generate reference local pseudo-codes that are of the same origin as the satellite navigation baseband digital signals;

[0101] The reference local pseudocode is phase-shifted by a preset correlator array to obtain the code phase shift amount corresponding to each correlator in the correlator array.

[0102] The data to be captured is simultaneously input into each correlator in the correlator array. Each correlator multiplies the data to be captured with its corresponding code phase offset at the same time point and outputs a new sequence corresponding to each correlator.

[0103] The new sequence output by each correlator is subjected to a coherent integral of a preset length to remove the pseudocode, and the coherent integral result after removing the pseudocode is obtained.

[0104] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0105] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0106] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for acquiring baseband digital signals for satellite navigation based on code Doppler compensation, characterized in that, Includes the following steps: S1. Preprocess the received satellite navigation baseband digital signal to obtain the data to be acquired; S2. Perform coherent integration on the data to be captured to obtain the coherent integration result after removing the pseudocode; S3. Perform DFT frequency sweeping on the coherent integral result after stripping the pseudocode to obtain the signal characteristics of multiple frequency points. S4. Calculate the code Doppler offset of the signal characteristics of each frequency point based on the preset DFT base frequency point to obtain the code Doppler offset of each frequency point. S5. Perform incoherent misalignment accumulation calculation based on the preset number of incoherent steps and the code Doppler offset of each frequency point to obtain the accumulation result; S6. Perform a peak search on the accumulated result to obtain the peak value of the satellite navigation baseband digital signal.

2. The satellite navigation baseband digital signal acquisition method according to claim 1, characterized in that, It also includes step S7: After obtaining the peak value of the satellite navigation baseband digital signal, it is determined whether the peak value exceeds the peak value threshold. If it does, the peak value is determined to be valid, and the acquisition is completed. If the threshold is not exceeded, no valid peak value is captured. The code phase is then switched according to the preset code phase switching step size parameter, and the process returns to S2 to re-perform coherent integration until the obtained peak value is determined to be valid.

3. The satellite navigation baseband digital signal acquisition method according to claim 1, characterized in that, In step S1, the received satellite navigation baseband digital signal is preprocessed to obtain the data to be acquired, including: The received satellite navigation baseband digital signal is filtered by a filter, and the gain parameter of the filtered satellite navigation baseband digital signal is adjusted to a preset quantization range to obtain the baseband data stream. Data blocks are extracted from the baseband data stream according to a preset coherent integration length to obtain the data to be captured.

4. The satellite navigation baseband digital signal acquisition method according to claim 1, characterized in that, In step S2, coherent integration processing is performed on the data to be captured to obtain the coherent integration result after removing the pseudocode, including: Obtain pseudo-random codes from the received satellite navigation baseband digital signals and generate reference local pseudo-codes that are of the same origin as the satellite navigation baseband digital signals; The reference local pseudocode is phase-shifted by a preset correlator array to obtain the code phase shift amount corresponding to each correlator in the correlator array. The data to be captured is simultaneously input into each correlator in the correlator array. Each correlator multiplies the data to be captured with its corresponding code phase offset at the same time point and outputs a new sequence corresponding to each correlator. The new sequence output by each correlator is subjected to a coherent integral of a preset length to remove the pseudocode, and the coherent integral result after removing the pseudocode is obtained.

5. The satellite navigation baseband digital signal acquisition method according to claim 1, characterized in that, In step S3, the coherent integration result after removing the pseudocode is subjected to DFT frequency sweep processing to obtain signal features at multiple frequency points, including: Based on the frequency resolution of the satellite navigation signal, the number of DFT points for the DFT sweep frequency is configured, and the calculation formula is as follows: Where N is the number of DFT points, f s Δf is the sampling rate of the coherent integral result, and Δf is the frequency resolution; The actual frequency f corresponding to the frequency index value k is determined based on the frequency resolution and the number of DFT points. k , where f k = (kN / 2)·Δf; By performing an N-point DFT sweep on the coherent integral result after removing the pseudocode using the DFT points N, multiple complex results at various frequency points are obtained. The calculation formula is as follows: Where S(k) is the complex result of the k-th frequency point in the frequency domain, s(n) is the coherent integration result, k is the frequency index value, and n is the time index value in the time domain, n = 0, 1, ..., N-1, e -j2πkn / N It is a complex exponential phase factor; The amplitude and phase information of the complex result S(k) for each frequency point are extracted according to the frequency index value k, wherein the amplitude information is represented as: Where Re(S(k)) is the real part and Im(S(k)) is the imaginary part; The phase information is represented as follows: Phase(k)=arg(S(k))=arctan2(Im(S(k)),Re(S(k))), The calculated amplitude and phase information are associated with preset DFT base frequencies to obtain the actual frequency f of the corresponding frequency index value k for each DFT base frequency. k The amplitude information (Amplitude(k)) and phase information (Phase(k)) are used to obtain the signal characteristics at multiple frequency points.

6. The satellite navigation baseband digital signal acquisition method according to claim 5, characterized in that, In step S4, the code Doppler offset of each frequency point is calculated based on the preset DFT base frequency point to obtain the code Doppler offset of each frequency point, including: Based on the code Doppler offset calculation formula and the preset DFT base frequency and the actual frequency f in the frequency signal characteristics. k The code Doppler offset is calculated based on the correspondence, and the formula for calculating the code Doppler offset is expressed as follows: Among them, f d_code (k) is the code Doppler offset, f d_carrier (k)=f k f code f is the pseudocode rate. carrier For carrier frequency.

7. The satellite navigation baseband digital signal acquisition method according to claim 6, characterized in that, In step S5, incoherent misalignment accumulation calculation is performed based on a preset number of incoherent iterations and the code Doppler offset at each frequency point, including: The number of noncoherent cycles is set to N based on the signal strength requirements, and the offset direction and offset magnitude of each frequency point are determined. The offset direction can be positive or negative. For a single frequency point, perform N rounds of incoherent misaligned accumulation calculations for each frequency point within the accumulation window: Take the phase of the frequency signal characteristic of the current accumulation period i, 1≤i≤N, according to the code Doppler offset f d_code (k) Calculate the shift step size. The calculation process for the shift step size is as follows: If it is a positive shift, the phase of the current accumulation period i shifts to the left relative to the data of the previous round; if it is a negative shift, the phase of the current accumulation period i shifts to the right relative to the data of the previous round. The shift amount is related to f. d_code (k)×T is proportional, where T is the duration of the coherence period; The current data is superimposed with the accumulated result of the previous round according to the staggered step size.

8. The satellite navigation baseband digital signal acquisition method according to claim 7, characterized in that, S5 further includes the following steps: A storage area is set up to cache edge coherent data whose offset exceeds the preset length of the correlator array; When the next accumulation cycle begins, the edge coherent data of the previous accumulation cycle is read from the storage area, the phase is aligned with the phase of the current frequency signal characteristics according to the phase of the edge coherent data, and then the data is filled into the current accumulation window according to the misalignment step size. After completing N rounds of incoherent misalignment accumulation calculations, output the accumulation result.

9. A satellite navigation baseband digital signal acquisition device based on code Doppler compensation, characterized in that, include: The signal preprocessing module is used to preprocess the received satellite navigation baseband digital signals to obtain the data to be acquired; The coherent integration processing module is used to perform coherent integration processing on the data to be captured to obtain the coherent integration result after removing the pseudocode. The code Doppler compensation processing module is used to: perform DFT frequency sweep processing on the coherent integration result after stripping the pseudocode to obtain signal characteristics at multiple frequency points; Based on the preset DFT base frequency, the code Doppler offset of each frequency point is calculated to obtain the code Doppler offset of each frequency point. Based on the preset number of incoherent iterations and the code Doppler offset at each frequency point, an incoherent misalignment accumulation calculation is performed to obtain the accumulation result; The signal search module is used to perform peak search on the accumulated results to obtain the peak value of the satellite navigation baseband digital signal.

10. The satellite navigation baseband digital signal acquisition device according to claim 9, characterized in that, The process of performing coherent integration on the data to be captured to obtain the coherent integration result after removing the pseudocode includes: Obtain pseudo-random codes from the received satellite navigation baseband digital signals and generate reference local pseudo-codes that are of the same origin as the satellite navigation baseband digital signals; The reference local pseudocode is phase-shifted by a preset correlator array to obtain the code phase shift amount corresponding to each correlator in the correlator array. The data to be captured is simultaneously input into each correlator in the correlator array. Each correlator multiplies the data to be captured with its corresponding code phase offset at the same time point and outputs a new sequence corresponding to each correlator. The new sequence output by each correlator is subjected to a coherent integral of a preset length to remove the pseudocode, and the coherent integral result after removing the pseudocode is obtained.

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