A multi-mode GNSS signal acquisition method and device based on segmented cyclic correlation

Abstract

The present invention provides a multi-mode GNSS signal acquisition method and device based on piecewise cyclic correlation. The method comprises: performing spread spectrum code processing; performing intermediate frequency down-conversion, resampling and piecewise processing on satellite data; performing Doppler down-conversion to obtain zero Doppler satellite data; performing piecewise cyclic correlation operation to obtain piecewise cyclic correlation result R i,j ; According to the capture sensitivity requirements, R i,j Perform coherent integration to obtain RC n According to RC n Perform capture judgment; when capture fails, perform Doppler update calculation. This method reduces the number of FFT points by segment processing, reduces the hardware resources, and meets the characteristics of being compatible with multiple types of satellite capture.

Description

Technical Field

[0001] The present invention relates to the field of satellite navigation technology, and in particular to a multi-mode GNSS signal acquisition method and device based on segmented cyclic correlation. Background Art

[0002] In the design of GNSS receiver chips, the control of hardware resource usage is not only about cost control, but also affects the chip size and power consumption. Generally, the part that consumes the most resources is the capture module. Usually, GNSS receiver hardware uses code phase parallel frequency serial search (i.e., cyclic correlation algorithm) to capture satellite signals. Its fast algorithm requires FFT-IFFT operation. The length of FFT will determine the number of registers required by the hardware, the hardware area and cost, so it is necessary to select the appropriate number of FFT operation points.

[0003] In the design of multi-mode and multi-frequency GNSS receiver chips, since the spread spectrum code lengths of satellite signals in different frequency modes are inconsistent, if multiple FFT modules are considered to be compatible with calculations of different lengths, the requirements for hardware resources will increase dramatically. For example, considering the frequency modes of GPS L1 / L5, Galileo E1 and Beidou B1I, the spread spectrum code lengths are 1023 / 10230, 4096 and 2046 respectively. In order to implement cyclic correlation search for spread spectrum codes of different lengths, the FFT length will be different, and at least 4 FFT modules of different lengths need to be designed. Although the FFT module with the longest number of points (L5) can be considered for compatible calculations, the FFT length is too large for other frequency modes, which is a waste of resources and computing time.

[0004] How to achieve compatibility of signal capture in multiple frequency modes and reduce hardware resource costs is a problem that needs to be solved in hardware implementation. Summary of the invention

[0005] In view of this, the present invention provides a multi-mode GNSS signal acquisition method and device based on segmented cyclic correlation to solve the deficiencies of the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] An embodiment of the present invention provides a multi-mode GNSS signal acquisition method based on piecewise cyclic correlation, comprising:

[0008] Performing spread spectrum code processing;

[0009] The satellite data is down-converted to intermediate frequency, resampled and segmented;

[0010] Doppler down-conversion is performed to obtain zero-Doppler satellite data;

[0011] Perform the segmented cyclic correlation operation to obtain the segmented cyclic correlation result R i,j ;

[0012] According to the capture sensitivity requirements, R i,j Perform coherent integration to obtain RC n ;

[0013] Make a capture decision;

[0014] Perform Doppler update calculations.

[0015] Furthermore, performing the spread spectrum code processing specifically includes:

[0016] According to the acquisition mode, the possible satellite signal type is selected as one of the GPS L5 / L1, Beidou B1C / B1I / B3I / B2A / B2B and Galileo E1 / E5A / E5B signals, and the corresponding spread spectrum code is generated according to the satellite number, and its length is set to M.

[0017] The spreading code is extended to twice its original length, and the code length becomes 2M after extension; the extension is to repeatedly insert the own code chip after each code chip; one code chip becomes two identical code chips; each data of the spreading code sequence before extension represents one code chip, while each data of the sequence after extension represents half a code chip;

[0018] The extended local spreading code sequence is divided into N segments, each segment is L half-chips long, and the sequence data of each segment are: P1,…,P N , the P1 sequence content is: The P2 sequence content is: The same goes for other sequences;

[0019] L spreading code data P j Fill 0 to N fft length, perform FFT and take conjugate to get FP j ; Among them, the number of FFT points N fft ≥2L, and N fft is an integer power of 2;

[0020] Furthermore, for different frequency modes, the selection of L should follow the following principles:

[0021] In order to be compatible with the same FFT module in hardware implementation, the length of L is fixed; at the same time, L should be divisible by M, that is, N should be an integer. In all the above frequency modes, the code length of GPS L1 is 2M=2046, the code length of Beidou B1I is 2M=4092, and the code length of Galileo E1 is 2M=8184. In other modes, the code length is 2M=20460. L=2046 can be set, and the corresponding N is 1, 2, 4 and 10 respectively.

[0022] Furthermore, the satellite data is subjected to intermediate frequency down-conversion, resampling and segmentation processing, specifically including:

[0023] Mixing satellite data with a local intermediate frequency carrier to obtain zero intermediate frequency data;

[0024] Accumulating zero intermediate frequency data belonging to the same half chip according to the spreading code rate to generate half chip resampled data;

[0025] Then the half-chip resampled data is segmented into L data segments. Let the resampled data be {d1, d2, …, d i ,…}, the segmented data is D={D1,D2,…,D i ,…}, where data D i For the sequence {d (i-1)L+1 ,d (i-1)L+2 ,…,d iL}.

[0026] Furthermore, in order to achieve coherent integration of one spreading cycle after segmentation, the satellite data length should contain 2 spreading code cycles: the Beidou B1C signal length is greater than 20 milliseconds, the Galileo E1 is greater than 8 milliseconds, and the other satellite data lengths are greater than 2 milliseconds.

[0027] Further, Doppler down-conversion includes:

[0028] Generate a local carrier whose frequency is a certain Doppler value f0, and update D to the complex product of the local carrier and D.

[0029] Furthermore, a segmented cyclic correlation operation is performed, and the correlation matching process of the i-th and i+1-th segment data and the j-th segment spread spectrum code is:

[0030] The continuous 2 segments, i.e. 2L zero Doppler satellite data D i D i+1 Fill 0 to N fft Length FFT to get FD i ;

[0031] FP j and FD i Multiply the complex numbers to get FDP ij;

[0032] About FDP ij Perform IFFT operation to obtain the cyclic correlation result R of the i-th and i+1-th segment data and the j-th segment spread spectrum code i,j .

[0033] Furthermore, for R i,j The coherent integration specifically includes:

[0034] Perform coherent integration according to capture sensitivity requirements: When sensitivity needs to be increased, the cyclic correlation result R i,j Perform coherent integration accumulation, coherent integration RC n It is expressed as: When there is no need to improve the sensitivity, no coherent accumulation is performed and RC is taken n =R 1,n ,1≤n≤N;

[0035] Furthermore, the capture decision process is:

[0036] About RC n The modulus is calculated and the maximum value is searched. If the maximum value exceeds the preset threshold, it is determined that the capture is successful, and the satellite signal code phase CP is calculated according to the position where the maximum value appears. Otherwise, it is determined that the current preset Doppler frequency value capture has failed, and the next preset Doppler frequency value search is entered until all Doppler values ​​are searched.

[0037] Furthermore, the satellite type number phase is calculated as follows:

[0038] Let's assume that the maximum value appears at RC n The position m (0≤m≤L-1) is:

[0039] CP=mod(L(n-1)-m+2M,2M)

[0040] Where mod(x,y) is the modulo-y operation, and the CP unit is half a chip.

[0041] Further, the Doppler update is calculated as follows:

[0042] f0=f0+f step

[0043] where f step is the Doppler search step. Determine whether f0 exceeds the Doppler search range. If not, continue the above search process. Otherwise, determine that the current satellite capture fails.

[0044] The capture method provided by the present invention takes into account the design of FFT module length and capture under various spread spectrum code lengths. After selecting a fixed length of FFT points, a period of spread spectrum code is split into N segments, each segment is L in length, and satellite data is also segmented according to the same length, using a cyclic correlation code phase capture method, and each segment of data may correspond to N segments of spread spectrum code, so each segment of data is subjected to N cyclic correlation code phase searches. In this process, segmented cyclic correlation reduces the number of FFT calculation points, which can reduce the requirements for hardware resources. At the same time, due to the reduction in correlation length, the signal-to-noise ratio will inevitably be lost during the capture process. If only one segment of spread spectrum code is used for search, better results can be obtained under strong signals.

[0045] During the search process, if the Doppler value and code phase can match, a peak will appear at a certain position in the multiple correlation results. i,j If the jth segment spreading code matches the ith and i+1th segment data successfully, and the peak value appears at position m, then R i+1,j+1 ,…,R i+N-1,j+N-1 A peak will also appear at position m, so the cyclic correlation result data of each segment can be coherently integrated, which is equivalent to a correlation of one cycle, which can improve the signal-to-noise ratio during capture and obtain higher capture sensitivity, which is suitable for capturing weaker signals.

[0046] When performing correlation operations on a complete period of spread spectrum code, segmentation can reduce the number of FFT points, but multiple segments need to be searched, which reduces hardware resources but increases calculation time.

[0047] The embodiment of the present invention provides a multi-mode GNSS signal acquisition device based on segmented cyclic correlation, including: a spread spectrum code generation module, a spread spectrum code preprocessing module, a data preprocessing module, a Doppler stripping module, a cyclic correlation module, a coherent integration module, a capture decision module, and a Doppler calculation module.

[0048] The spread spectrum code generation module generates a spread spectrum code with a length of M according to the external input signal frequency point pattern and the satellite number;

[0049] The spread spectrum code preprocessing module is used to perform half-chip resampling and expansion; divide 2M spread spectrum code chips into N segments, each segment is L in length; perform FFT operation on each segment, and calculate conjugate to obtain the spread spectrum code conjugate spectrum;

[0050] The data preprocessing module is used to perform intermediate frequency down-conversion, resampling and segment processing on the satellite data;

[0051] The Doppler stripping module is used to mix the processed satellite data with a local carrier of a preset Doppler frequency to complete Doppler down-conversion to obtain zero Doppler satellite data;

[0052] The cyclic correlation module performs FFT operation, complex multiplication and IFFT operation on the satellite data to obtain the cyclic correlation result R i,j ;

[0053] The coherent integration module is used to perform coherent integration according to the capture sensitivity. When the sensitivity needs to be improved, the coherent integration RC n It is expressed as: When there is no need to improve the sensitivity, no coherent accumulation is performed and RC is taken n =R 1,n ,1≤n≤N;

[0054] The capture decision module is used to perform coherent integration RC n The module is found and the maximum value is searched. If the maximum value exceeds the preset threshold, it is determined that the capture is successful, and the satellite signal code phase CP is calculated according to the position where the maximum value appears; otherwise, it is determined that the current preset Doppler frequency value capture fails, and the next preset Doppler frequency value search is entered;

[0055] The Doppler calculation module is used to calculate the next preset Doppler frequency value and determine whether the Doppler value exceeds the capture range. If it does not exceed the range, the above capture process is repeated. If it exceeds the range, the capture of the satellite is terminated.

[0056] Furthermore, the cyclic correlation module includes: an FFT module, a multiplication module and an IFFT module;

[0057] The FFT module is used to transform L spread spectrum code data P j Fill 0 to N fft length, perform FFT and take conjugate to get FP j ; Among them, the number of FFT points N fft ≥2L, and N fft is an integer power of 2;

[0058] The FFT module is also used to convert two consecutive segments, i.e., 2L zero-frequency satellite data D i D i+1 Fill 0 to N fft Length FFT to get FD i ;

[0059] The multiplication module is used to convert FP j and FD i Multiply the complex numbers to get FDP ij ;

[0060] The IFFT module is used to ij Perform IFFT operation to obtain the circular correlation result Ri,j .

[0061] An embodiment of the present invention further provides a computer storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are implemented.

[0062] The technical solution provided by the present invention realizes compatible capture of satellite signals in multiple frequency point modes by segmenting and cyclically calculating the spread spectrum code; the segment processing reduces the number of FFT points, thereby reducing the requirements for hardware resources. The capture sensitivity can be improved by coherent integration of the segmented results. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0064] Figure 1 A schematic flow chart of a multi-mode GNSS signal acquisition method based on segmented cyclic correlation provided by an embodiment of the present invention;

[0065] Figure 2 A schematic diagram of the structure of a multi-mode GNSS signal acquisition device based on piecewise cyclic correlation provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] Figure 1 The figure is a flow chart of a multi-mode GNSS signal acquisition method based on segmented cyclic correlation provided by an embodiment of the present invention. The method comprises the following steps:

[0068] S101. Generate a spread spectrum code with a code length of M according to different frequency point modes and satellite numbers.

[0069] S102, performing half-chip resampling, expansion and segmentation processing on the spread spectrum code with a code length of M.

[0070] The spread spectrum code is extended to twice its original length. The satellite signal spread spectrum code length is M, and the code length becomes 2M after extension. During the extension, the code chip itself is repeatedly inserted after each code chip, and one code chip is turned into two identical code chips.

[0071] The extended local spreading code sequence is divided into N segments, each segment is L half-chips long, and the sequence data of each segment are: P1,…,P N , the P1 sequence content is: The P2 sequence content is: The same goes for other sequences.

[0072] The spread spectrum code data P j Fill 0 to N fft length, perform FFT and take conjugate to get FP j .

[0073] S103, performing intermediate frequency down-conversion, resampling and segmentation processing on the satellite data.

[0074] Generate a local complex signal whose carrier frequency is the signal intermediate frequency f i , multiply the local carrier signal and the satellite signal to generate zero intermediate frequency data. According to the spread spectrum code rate, the zero intermediate frequency signals belonging to the same half code chip are accumulated to generate a half code chip resampled signal, which is then segmented into L data segments to generate data S1.

[0075] S104, performing Doppler down-conversion on the segmented satellite data S1.

[0076] According to the given preset Doppler value (f0), a local complex signal carrier is generated, multiplied with the S1 data, and the Doppler value in the signal is stripped. Signal S2 is generated. Let S2 contain data segments D1,…,D i ,…, the length of each data segment is L.

[0077] S105, performing cyclic correlation operations.

[0078] The two consecutive segments of zero Doppler satellite data D i D i+1 Fill 0 to N fft Length FFT to get FD i ; FP j and FD i Multiply the complex numbers to get FDP ij ; for FDP ij Perform IFFT operation to obtain the circular correlation result R i,j .

[0079] The local spread spectrum code and zero frequency data are selected as follows: the first data is D1D2, the second data is D2D3, ..., the i-th data is D i D i+1 ,…; get data D i D i+1 When P1,…,P N Perform N cycles of correlation, and the results are R i,1 ,…,R i,j ,…,R i,N .

[0080] S106, coherently integrate the cyclic correlation result according to the capture sensitivity requirement to obtain RC n .

[0081] The capture sensitivity requirement is determined by external inputs.

[0082] When there is no need to improve the sensitivity, no coherent accumulation is performed and R 1,n (1≤n≤N) directly outputs RC n .

[0083] If you need to increase the sensitivity, you need to adjust R i,j Performing coherent accumulation gives:

[0084]

[0085] S107: Capture decision.

[0086] About RC n (1≤n≤N) finds the modulus and searches for the maximum value in it. If the maximum value exceeds the preset threshold, it is considered that the capture is successful. At this time, the maximum value appears in RC k If the code phase is calculated to be CP, then the capture is considered to have failed at the current given Doppler value, and the next Doppler value search is required.

[0087] S108: Update preset Doppler value

[0088] Assuming that the initial preset Doppler value is f0, after completing the code phase search for f0, if the capture fails, f0 is accumulated with a step value, and the process jumps to S104 until the capture is successful or the Doppler value is out of range.

[0089] Segmented cyclic correlation can achieve compatible capture of satellite signals in multiple frequency modes; segmentation can divide a long-period spread spectrum code into multiple parts for cyclic correlation, thereby reducing the number of FFT points and the requirements of the capture operation on hardware resources; coherent integration can effectively complete the long-period spread spectrum code satellite signal capture function under weak signal strength.

[0090] like Figure 2 As shown, an embodiment of the present invention provides a multi-mode GNSS signal acquisition device based on segmented cyclic correlation, including: a spread spectrum code generation module 100, a spread spectrum code preprocessing module 101, a data preprocessing module 102, a Doppler stripping module 103, a cyclic correlation module 104, a coherent integration module 105, a capture decision module 106 and a Doppler calculation module 107.

[0091] The spread spectrum code generating module 100 is used to select a satellite signal mode according to an external input and generate a corresponding spread spectrum code according to a satellite number.

[0092] The spread spectrum code preprocessing module 101 is used to perform half-chip resampling expansion and segmentation processing on the spread spectrum code with a code length of M; when segmenting, the length of each segment is controlled to be L, 2M=N×L; where N is the number of segments; and output data to the 104 module.

[0093] The data preprocessing module 102 is used to perform intermediate frequency down-conversion, resampling and segment processing on the satellite data; and output it to the module 103.

[0094] The Doppler stripping module 103 is used to mix the processed satellite data with a local carrier of a preset Doppler frequency to complete Doppler down-conversion to obtain zero-Doppler satellite data; and output it to the module 104 .

[0095] The cyclic correlation module 104 is used to perform FFT operation, complex multiplication and IFFT operation on the zero Doppler satellite data to obtain the cyclic correlation result R i,j .

[0096] The circular correlation module 104 includes: an FFT module 104_1 , a multiplication module 104_2 and an IFFT module 104_3 .

[0097] The FFT module 104_1 is used to transform the L spread spectrum code data P j Fill 0 to N fft length, perform FFT and take conjugate to get FP j ; Among them, the number of FFT points N fft ≥2L, and N fft The FFT module 104_1 is also used to convert 2 consecutive segments, i.e. 2L zero-frequency satellite data D i D i+1 Fill 0 to N fft Length FFT to get FD i ; Multiplication module 104_2 is used to convert FP j and FD i Multiply the complex numbers to get FDP ij IFFT module 104_3 is used for FDP ij Perform IFFT operation to obtain the circular correlation result Ri,j .

[0098] The coherent integration module 105 is used to perform coherent integration on the cyclic correlation result according to the external input sensitivity requirement; when the external signal is weak, the coherent integration RC n It is expressed as: When the external signal is strong, no coherent accumulation is performed and RC is taken n =R 1,n ,1≤n≤N.

[0099] The acquisition decision module 106 is used to perform coherent integration RC n The module is found and the maximum value is searched. If the maximum value exceeds the preset threshold, it is determined that the capture is successful, and the satellite signal code phase CP is calculated according to the position where the maximum value appears; otherwise, it is determined that the current preset Doppler frequency value capture fails, and the next preset Doppler frequency value search is entered;

[0100] The Doppler calculation module 107 is used to calculate the next preset Doppler frequency value and determine whether to end the current satellite capture. If the capture continues, it is output to the module 103; otherwise, the capture of the satellite is ended.

[0101] It should be noted that: the multi-mode GNSS signal acquisition device based on segmented cyclic correlation provided in the above embodiment only uses the division of the above program modules as an example when performing acquisition. In actual applications, the above processing can be assigned to different program modules as needed, that is, the internal structure of the device is divided into different program modules to complete all or part of the processing described above. In addition, the multi-mode GNSS signal acquisition device based on segmented cyclic correlation provided in the above embodiment belongs to the same concept as the acquisition method embodiment. The specific implementation process is detailed in the method embodiment. The beneficial effects are the same as the method embodiment and will not be repeated here.

[0102] The embodiment of the present invention further provides a computer storage medium, which is a computer-readable storage medium, on which a computer program is stored, and the above-mentioned computer program can be executed by a processor of a multi-mode GNSS signal acquisition device based on segmented cyclic correlation to complete the steps of the aforementioned multi-mode GNSS signal acquisition method based on segmented cyclic correlation. The computer-readable storage medium can be a magnetic random access memory (FRAM), a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a flash memory, a magnetic surface memory, an optical disk, or a compact disc read-only memory (CD-ROM) and the like.

[0103] In the several embodiments provided by the present invention, it should be understood that the disclosed methods and intelligent devices can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as: multiple units or components can be combined, or can be integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the components shown or discussed can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0104] The units described above as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units; some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0105] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A multi-mode GNSS signal acquisition method based on piecewise cyclic correlation, characterized in that: include: Performing spread spectrum code processing; Specifically, the method includes: selecting the satellite signal type according to the acquisition mode, and generating the corresponding spread spectrum code according to the satellite number, assuming that the spread spectrum code length is M; extending the spread spectrum code to twice the original length, and the code length becomes 2M after the extension; the extension is to repeatedly insert the own code chip after each code chip; one code chip becomes two identical code chips; each data of the spread spectrum code sequence before the extension represents one code chip, and each data of the sequence after the extension represents half a code chip; the local spread spectrum code sequence after the extension is divided into N segments, each segment is L half code chips in length, and each segment sequence data is: P1,…,P N , the P1 sequence content is: {chip 1 chip 1…chip }, P2 sequence content is: {chip Chip ... code chip L}; other sequences are analogous; L spreading code data P j Fill 0 to N fft length, perform FFT and take conjugate to get the code FFT result FP j ; Among them, the number of FFT points N fft ≥2L, and N fft is an integer power of 2; The satellite data is down-converted to intermediate frequency, resampled and segmented; Doppler down-converting the segmented satellite data to obtain zero-Doppler satellite data; Perform the segmented cyclic correlation operation to obtain the segmented cyclic correlation result R i,j Specifically include: 2 consecutive segments, i.e. 2L zero Doppler satellite data D i D i+1 Fill 0 to N fft Length FFT to get FD i ; FP j and FD i Multiply the complex numbers to get FDP ij ; for FDP ij Perform IFFT operation to obtain the cyclic correlation result R of the i-th and i+1-th segment data and the j-th segment spread spectrum code i,j ; According to the capture sensitivity requirements, R i,j Perform coherent integration to obtain RC n ; According to RC n Make a capture decision; Doppler update calculation is performed when acquisition fails.

2. The method according to claim 1, characterized in that The value of L is 2046; the corresponding value of N for GPS L1 is 1; the corresponding value of N for Beidou B1I is 2; the corresponding value of N for Galileo E1 is 4; and the corresponding value of N for others is 10.

3. The method according to claim 1, characterized in that The satellite data is processed by down-converting, resampling and segmenting the intermediate frequency, including: Mixing satellite data with a local intermediate frequency carrier to obtain zero intermediate frequency data; Accumulating zero intermediate frequency data belonging to the same half chip according to the spreading code rate to generate half chip resampled data; Then the half-chip resampled data is segmented into segments of L data.

4. The method according to claim 3, characterized in that The satellite data length meets the following conditions: the Beidou B1C signal length is greater than 20 milliseconds; the Galileo E1 is greater than 8 milliseconds; the GPS L5 / L1, Beidou B1I / B3I / B2A / B2B and GalileoE5A / E5B signal lengths are greater than 2 milliseconds.

5. The method according to claim 1, characterized in that According to the capture sensitivity requirements, R i,j Perform coherent integration to obtain RC n Specifically include: Perform coherent integration according to capture sensitivity requirements: When sensitivity needs to be increased, the cyclic correlation result R i,j Perform coherent integration accumulation, coherent integration RC n It is expressed as: When there is no need to improve the sensitivity, no coherent accumulation is performed and RC is taken n =R 1,n ,1≤n≤N.

6. The method according to claim 1, characterized in that The capture decision process is: About RC n The modulus is calculated and the maximum value is searched. If the maximum value exceeds the preset threshold, it is determined that the capture is successful, and the satellite signal code phase CP is calculated according to the position where the maximum value appears. Otherwise, it is determined that the current preset Doppler frequency value capture has failed, and the next preset Doppler frequency value search is entered until all Doppler values ​​are searched.

7. The method according to claim 6, characterized in that The satellite signal code phase CP is calculated as follows: Assume that the maximum value occurs at RC n The position m, 0≤m≤L-1, then: CP=mod(L(n-1)-m+2M,2M) Wherein mod(x,y) is the modulo y operation, the CP unit is half a chip, 1≤n≤N.

8. A multi-mode GNSS signal acquisition device based on piecewise cyclic correlation, characterized in that: include: Spread spectrum code generation module, spread spectrum code preprocessing module, data preprocessing module, Doppler stripping module, cyclic correlation module, coherent integration module, capture decision module, Doppler calculation module; The spread spectrum code generation module generates a spread spectrum code with a length of M according to the external input signal frequency point pattern and the satellite number; Specifically, the method includes: generating a corresponding spread spectrum code according to the satellite signal mode and satellite number selected by the acquisition mode, and setting the spread spectrum code length to M; extending the spread spectrum code to twice the original length, and the code length becomes 2M after extension; the extension is to repeatedly insert the own code chip after each code chip; converting one code chip into two identical code chips; each data of the spread spectrum code sequence before extension represents one code chip, and each data of the sequence after extension represents half a code chip; dividing the extended local spread spectrum code sequence into N segments, each segment is L half code chips in length, and each segment sequence data is: P1,…,P N , the P1 sequence content is: {chip 1 chip 1…chip }, P2 sequence content is: {chip Chip ... code chip L}; other sequences are analogous; L spreading code data P j Fill 0 to N fft length, perform FFT and take conjugate to get the code FFT result FP j ; Among them, the number of FFT points N fft ≥2L, and N fft is an integer power of 2; The spread spectrum code preprocessing module is used to perform half-chip resampling and expansion; divide 2M spread spectrum code chips into N segments, each segment is L in length; perform FFT operation on each segment, and calculate conjugate to obtain the spread spectrum code conjugate spectrum; The data preprocessing module is used to perform intermediate frequency down-conversion, resampling and segment processing on the satellite data after segment processing; The Doppler stripping module is used to mix the processed satellite data with a local carrier of a preset Doppler frequency to complete Doppler down-conversion to obtain zero Doppler satellite data; The cyclic correlation module performs FFT operation, complex multiplication and IFFT operation on the satellite data to obtain the cyclic correlation result R i,j Specifically include: 2 consecutive segments, i.e. 2L zero Doppler satellite data D i D i+1 Fill 0 to N fft Length FFT to get FD i ; FP j and FD i Multiply the complex numbers to get FDP ij ; for FDP ij Perform IFFT operation to obtain the cyclic correlation result R of the i-th and i+1-th segment data and the j-th segment spread spectrum code i,j ; The coherent integration module is used to perform coherent integration according to the capture sensitivity. When the sensitivity needs to be improved, the coherent integration RC n It is expressed as: When there is no need to improve the sensitivity, no coherent accumulation is performed and RC is taken n =R 1,n ,1≤n≤N; The capture decision module is used to perform coherent integration RC n The module is found and the maximum value is searched. If the maximum value exceeds the preset threshold, it is determined that the capture is successful, and the satellite signal code phase CP is calculated according to the position where the maximum value appears; otherwise, it is determined that the current preset Doppler frequency value capture fails, and the next preset Doppler frequency value search is entered; The Doppler calculation module is used to calculate the next preset Doppler frequency value and determine whether the Doppler value exceeds the capture range. If it does not exceed the range, the above capture process is repeated. If it exceeds the range, the capture of the satellite is terminated.

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