Beidou Navigation System BDS Secondary Differential Coherent Data Bit Synchronization Method and System

Abstract

The present invention belongs to the field of navigation data synchronization technology, and discloses a Beidou navigation system BDS secondary differential coherent data bit synchronization method and system, using a data preprocessing module to preprocess the original Beidou radio frequency input signal to obtain 1ms complex coherent data; using a 20ms interval differential module to perform complex conjugate differential of 1ms complex coherent data at intervals of 20ms to obtain differential data at intervals of 20ms; using a 1ms interval differential module to perform complex conjugate differential of differential data at intervals of 1ms to obtain differential data at intervals of 1ms; using a storage folding solution module to perform data storage and folding coherent accumulation of differential data at intervals of 1ms, and give a bit synchronization output position. The present invention performs data bit synchronization based on a differential coherent method, can avoid being affected by NH codes, directly performs bit synchronization in a weak signal environment, improves the data bit synchronization effect, and at the same time has low resource consumption and is less affected by signal Doppler.

Description

Technical Field

[0001] The present invention belongs to the technical field of navigation data synchronization, and in particular relates to a Beidou navigation system (BDS) secondary differential coherent data bit synchronization method and system. Background Art

[0002] At present, the BeiDou Navigation System (BDS) is a global satellite navigation system independently built and operated by China, which can provide global users with all-weather, all-day, high-precision positioning, navigation and timing services. In 2020, the last networking satellite of my country's BeiDou-3 global satellite navigation system was launched into space, completing the global networking of BeiDou satellites. The BeiDou Navigation System has as many as 47 satellites in orbit to provide services. BeiDou navigation is widely used in aviation and maritime navigation, earthquake relief positioning, and even space satellite positioning and orbit determination.

[0003] In the Beidou signal, the navigation message may flip every 20ms. The data bit synchronization of the navigation message is an important step in signal processing in the Beidou navigation signal receiver. It is a prerequisite for parsing the ephemeris data in the signal and is used to find the edge position of the navigation message modulated on the carrier. In many application scenarios of Beidou navigation, the signal power is low and the strength is weak in some environments. The secondary modulated NH code (Neumann-Hoffman code, fixed sequence is 00000100110101001110, length 20, and its starting point is aligned with the navigation message) in the Beidou navigation system signal will be intertwined with the noise under weak signals, resulting in a large number of unknown symbol flips, and data bit synchronization in weak signal environments becomes difficult.

[0004] For the bit synchronization of Beidou signals, the sliding matching NH code and signal data symbols are generally used for bit synchronization, but this method has poor effect under weak signals and cannot reliably and accurately find the data bit synchronization position. Maximum likelihood bit synchronization is a navigation signal bit synchronization method commonly used in weak signal environments. The paper "A new bit synchronization method for a GPS receiver" applies it to GPS signals, which is also applicable to Beidou signals. By stripping off the NH code from twenty possible data bit starting points at the same time and then accumulating data, comparing the accumulated values, and taking the maximum value position as the bit synchronization position, this method needs to store multiple groups of accumulated values ​​at the same time, consumes a lot of storage resources, and is sensitive to signal Doppler. The patent "A Beidou satellite navigation receiver bit synchronization method" uses group matching to achieve Beidou data bit synchronization, but this method consumes a lot of resources and needs to be stabilized after the tracking loop is stable before bit synchronization can be performed. Bit synchronization cannot be performed directly in a weak signal environment.

[0005] Through the above analysis, the problems and defects of the prior art are as follows:

[0006] (1) The existing method of using sliding matching NH code and signal data symbols for bit synchronization has a problem of poor effect under weak signals and cannot reliably and accurately find the data bit synchronization position.

[0007] (2) Maximum likelihood bit synchronization is a navigation signal bit synchronization method commonly used in weak signal environments. This method requires storing multiple sets of accumulated values ​​at the same time, consumes a lot of storage resources, and is sensitive to signal Doppler.

[0008] (3) The existing method of using group matching to achieve Beidou data bit synchronization consumes a lot of resources and cannot directly perform bit synchronization in a weak signal environment. Summary of the invention

[0009] In view of the problems existing in the prior art, the present invention provides a Beidou navigation system (BDS) secondary differential coherent data bit synchronization method and system, aiming to solve the problem of Beidou data bit synchronization difficulty under weak signals caused by secondary modulation NH code.

[0010] The present invention is implemented in this way: a Beidou navigation system BDS secondary differential coherent data bit synchronization system, the Beidou navigation system BDS secondary differential coherent data bit synchronization system comprising:

[0011] The data preprocessing module is used to preprocess the original Beidou RF input signal to obtain 1ms complex coherent data and send it to the 20ms interval differential module;

[0012] The 20ms interval differential module is used to perform complex conjugate differential of the 1ms complex coherent data output by the data preprocessing module at an interval of 20ms to obtain differential data at an interval of 20ms and send the differential data to the 1ms interval differential module;

[0013] The 1 ms interval difference module is used to perform complex conjugate difference at intervals of 1 ms on the difference data output by the 20 ms interval difference module to obtain 1 ms interval difference data and send it to the storage folding solution module;

[0014] The storage folding solution module is used to store and fold the differential data at intervals of 1ms and coherently accumulate the data, and give a bit-synchronous output position.

[0015] Furthermore, the data preprocessing module includes:

[0016] The analog-to-digital conversion unit is used to perform analog-to-digital conversion on the intermediate frequency BDS signal after RF processing to obtain complex BDS baseband data;

[0017] A carrier stripping unit, used for stripping and removing the carrier signal in the complex baseband data by multiplying the local carrier signal to obtain a carrier-free signal;

[0018] The complex baseband data includes two signal components, I and Q, where I is the real part and Q is the imaginary part;

[0019] In the 1ms coherent integrator, the 1ms carrier-free signal is multiplied and accumulated with the local C / A code data to obtain 1ms complex coherent data.

[0020] Further, the 20ms interval differential module includes:

[0021] The 20ms delay unit is used to delay the 1ms complex coherent data by 20ms before outputting it;

[0022] A complex conjugate unit is used to perform complex conjugate processing on the 1 ms coherent accumulation data after the 20 ms delay unit to obtain conjugate delayed 20 ms coherent accumulation data;

[0023] The multiplier multiplies the real-time 1 ms coherent accumulation data and the conjugate delayed 20 ms coherent accumulation data, removes the NH code in the signal, and obtains differential data with an interval of 20 ms.

[0024] Further, the 1 ms interval differential module includes:

[0025] The 1ms delay unit is used to delay the 20ms differential data by 1ms before outputting it.

[0026] A complex conjugate unit is used to perform complex conjugate processing on the 20ms interval differential data after the 1ms delay unit to obtain the conjugate delayed 1ms coherent accumulation data;

[0027] The multiplier multiplies the real-time 1 ms coherent accumulation data and the conjugate delayed 1 ms coherent accumulation data to obtain differential data with an interval of 1 ms.

[0028] Further, the storage folding solution module includes:

[0029] A storage folding unit is used to accumulate differential data at intervals of 1 ms;

[0030] A modulo unit, used for performing a modulo operation on 20 results of the storage folding unit;

[0031] The minimum value unit is used to find the minimum value of the 20 results after modulo taking, and output the position of the minimum value in the 20 results as the last output bit synchronization position.

[0032] Another object of the present invention is to provide a Beidou navigation system BDS secondary differential coherent data bit synchronization method using the Beidou navigation system BDS secondary differential coherent data bit synchronization system, the Beidou navigation system BDS secondary differential coherent data bit synchronization method comprising the following steps:

[0033] Step 1: Use the data preprocessing module to preprocess the original Beidou RF input signal to obtain 1ms complex coherent data, and send it to step 2 for 20ms difference interval;

[0034] Step 2: Use the 20ms interval differential module to perform complex conjugate differential of the output 1ms complex coherent data at intervals of 20ms to obtain 20ms interval differential data, and send it to step 3 for 1ms interval differential;

[0035] Step 3: Use the 1ms interval difference module to perform complex conjugate difference at intervals of 1ms on the differential data output from step 2 to obtain 1ms interval differential data, and send it to step 4 for storage folding and solution;

[0036] Step 4: Use the storage folding solution module to store and fold the 1ms interval differential data output in step 3 for coherent accumulation, and give a bit-synchronous output position.

[0037] Furthermore, the conjugate operation in step 2 is in the form of (I+jQ) * =I-jQ;

[0038] The conjugate operation in step 3 is in the form of (I+jQ) * =I-jQ;

[0039] In step 4, the differential data at intervals of 1 ms are accumulated according to the following formula:

[0040]

[0041] Among them, Z(t) is the t-th data after two conjugate difference operations to achieve the coherence of the difference results. After folding and storage, 20 results are obtained.

[0042] Another object of the present invention is to provide a computer device, the computer device comprising a memory and a processor, the memory storing a computer program, and when the computer program is executed by the processor, the processor performs the following steps:

[0043] The original Beidou RF input signal is preprocessed by the data preprocessing module to obtain 1ms complex coherent data, and sent to the 20ms interval differential module; the 20ms interval differential module is used to perform complex conjugate differential of the 1ms complex coherent data at an interval of 20ms to obtain 20ms interval differential data, and sent to the 1ms interval differential module; the 1ms interval differential module is used to perform complex conjugate differential of the differential data at an interval of 1ms to obtain 1ms interval differential data, and sent to the storage folding solution module; the storage folding solution module is used to store and fold coherently accumulate the 1ms interval differential data, and give the in-place synchronous output position.

[0044] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the following steps:

[0045] The original Beidou RF input signal is preprocessed by the data preprocessing module to obtain 1ms complex coherent data, and sent to the 20ms interval differential module; the 20ms interval differential module is used to perform complex conjugate differential of the 1ms complex coherent data at an interval of 20ms to obtain 20ms interval differential data, and sent to the 1ms interval differential module; the 1ms interval differential module is used to perform complex conjugate differential of the differential data at an interval of 1ms to obtain 1ms interval differential data, and sent to the storage folding solution module; the storage folding solution module is used to store and fold coherently accumulate the 1ms interval differential data, and give the in-place synchronous output position.

[0046] Another object of the present invention is to provide an information data processing terminal, which is used to implement the Beidou navigation system BDS secondary differential coherent data bit synchronization system.

[0047] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0048] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, the technical solutions to be protected by the present invention and the results and data during the research and development process are closely combined to analyze in detail and deeply how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about after solving the problems. The specific description is as follows:

[0049] The present invention uses two differentials and performs coherent accumulation to avoid the influence of NH code on bit synchronization and improve the bit synchronization accuracy under weak signals.

[0050] The present invention adopts a two-time differential coherence method to perform data bit synchronization, which can avoid the influence of NH code on Beidou data bit synchronization and reduce the influence of Doppler on bit synchronization.

[0051] The present invention uses a storage folding method to accumulate data, occupies less space, and can infinitely extend the length of data involved in differential processing without increasing the storage resources consumed by the invention.

[0052] The present invention can not only effectively perform data bit synchronization in a weak signal environment, but also meet the need for data bit synchronization in a strong signal environment.

[0053] Second, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0054] The Beidou navigation system BDS secondary differential coherence data bit synchronization method provided by the present invention performs data bit synchronization based on a differential coherence method, can avoid being affected by NH codes, directly performs bit synchronization in a weak signal environment, improves the data bit synchronization effect, and has low resource consumption and is less affected by signal Doppler.

[0055] Third, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0056] (1) The technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0057] The present invention can perform data bit synchronization on the received Beidou navigation signal in a weak signal environment without signal tracking processing, and has low storage resource occupancy, thus filling the gap in a data bit synchronization processing method with low resource consumption in a weak Beidou navigation signal environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. 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 creative work.

[0059] Figure 1 It is a flow chart of a method for secondary differential coherent data bit synchronization of the Beidou navigation system BDS provided by an embodiment of the present invention;

[0060] Figure 2 It is a schematic diagram of the system structure of the Beidou navigation system BDS secondary differential coherent data bit synchronization provided by an embodiment of the present invention;

[0061] Figure 3 It is a schematic diagram of the complex conjugate difference principle with an interval of 20ms provided by an embodiment of the present invention;

[0062] Figure 4 It is a schematic diagram of storage folding provided by an embodiment of the present invention;

[0063] Figure 5 This is a result diagram of comparing storage resource occupancy of different algorithms provided by an embodiment of the present invention;

[0064] Figure 6 It is a comparison diagram of different Doppler residual performances of the secondary differential coherence provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0066] In view of the problems existing in the prior art, the present invention provides a Beidou navigation system (BDS) secondary differential coherent data bit synchronization method and system. The present invention is described in detail below with reference to the accompanying drawings.

[0067] 1. Explanatory Examples In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an illustrative example that expands and describes the technical solution of the claims.

[0068] like Figure 1 As shown, the Beidou navigation system BDS secondary differential coherent data bit synchronization method provided by the embodiment of the present invention includes the following steps:

[0069] S101, using the data preprocessing module to preprocess the original Beidou radio frequency input signal to obtain 1ms complex coherent data, and send it to S102 for 20ms interval differentiation;

[0070] S102, using a 20ms interval differential module to perform complex conjugate differential of the output 1ms complex coherent data at intervals of 20ms, to obtain differential data at intervals of 20ms, and send the data to S103 for differential data at intervals of 1ms;

[0071] S103, using a 1 ms interval differential module to perform complex conjugate differential on the differential data output by S102 at intervals of 1 ms, to obtain differential data at intervals of 1 ms, and send the data to S104 for storage folding and solving;

[0072] S104, using the storage folding solution module to perform data storage and folding coherent accumulation on the 1 ms interval differential data output from S103, and give a bit-synchronous output position.

[0073] like Figure 2As shown, the Beidou navigation system BDS secondary differential coherent data bit synchronization system provided by the embodiment of the present invention includes a data preprocessing unit, a 20ms interval differential unit, a 1ms interval differential unit, and a storage folding solution unit. The data preprocessing unit performs analog-to-digital conversion on the received Beidou navigation signal to obtain a digital intermediate frequency signal, multiplies it with the local carrier, strips off the carrier part of the original signal, and then passes through a 1ms coherent integration module. By multiplying and accumulating the signal with the local C / A code (a pseudo-random code of the Beidou navigation system used for coarse ranging and capturing and tracking Beidou satellites, it is actually a Gold code), 1ms coherent accumulated data is calculated. The 20ms interval differential unit performs a 20ms interval complex conjugate differential operation on the 1ms coherent accumulated data to achieve the stripping and removal of the modulated NH code in the data, thereby avoiding the influence of the NH code on subsequent processing. The 1ms interval differential unit performs a 1ms interval complex conjugate differential on the 20ms interval differential data to achieve the calculation of the symbol jump point of the navigation message. The storage folding solution unit folds and accumulates the data processed by two differential calculations to improve the signal-to-noise ratio of the signal, and then obtains the bit synchronization position output by finding the minimum value position in the folded accumulated value through modulo and minimum value processing.

[0074] like Figure 3 As shown, for the 20ms interval differential unit, the sign of the 1ms coherent integration value is jointly determined by the navigation message symbol and the NH code symbol of the Beidou signal. The 20ms interval complex conjugate differential method is adopted, and the characteristics of the NH code cyclic modulation in the Beidou navigation signal are utilized. The NH code data symbol of the Nth 1ms integration result must be the same as the NH code data symbol of the N+20 1ms integration results. N is the data position. The 20ms interval complex conjugate differential is performed, and the 1ms sign bit flip caused by the modulation of the NH code can be eliminated, and the data containing only the sign bit flip caused by the navigation message flip can be obtained.

[0075] like Figure 4 As shown, for the storage folding solution unit, the coherent accumulation processing of the differential results is realized through the storage folding module to improve the sensitivity performance of the secondary differential processing in a weak signal environment. The specific process of storage folding is as follows: the result of the secondary complex conjugate difference is stored in a storage area M with a length of 20, Z(t) is the tth differential result, and is stored in the storage area according to the rules that satisfy the following formula, then the corresponding position data will be folded to the same position.

[0076]

[0077] Through data folding, a small amount of symbol flipping caused by noise will be offset in the process of folding accumulation, and the length of data involved in folding can be extended infinitely. If the original differential result data is longer during the data folding process, the coherent gain will be higher, and the probability of the correct bit synchronization position that can be finally obtained will be higher.

[0078] 2. Application Examples: In order to prove the creativity and technical value of the technical solution of the present invention, this section provides application examples of the technical solution of the claims on specific products or related technologies.

[0079] The present invention can be applied to the data bit synchronization of receivers in unassisted extremely weak signal environments such as high-orbit Beidou receivers or deep-space exploration Beidou receivers. If applied to high-orbit Beidou receivers, the Beidou navigation system signal in the receiver's environment is weak, and because it is in orbital space, it cannot rely on other external signals for assistance.

[0080] In a high-orbit weak signal environment, after completing high-sensitivity capture of the signal, the data bit edge of the signal is in an unknown state. Since the signal is weak, conventional signal tracking is impossible. High-sensitivity tracking requires a known data bit edge as a prerequisite, so data bit synchronization is required first.

[0081] The following takes a high-orbit spacecraft onboard receiver as an example to describe in detail the specific implementation method of the present invention in actual application.

[0082] In a high-orbit environment, the spacecraft is located in an environment that is higher than the Beidou navigation satellite and is blocked by the earth. It can only receive signals from Beidou navigation satellites that are orbiting opposite the earth. The receiver receives the Beidou signal and performs high-sensitivity capture and measurement of the signal to obtain the real-time code phase and rough Doppler information of the signal. Since the rough Doppler information is not accurate, there is a certain Doppler frequency difference, and the received signal is weak, conventional signal tracking cannot be performed.

[0083] The received Beidou signal is preprocessed in the data preprocessing module according to the signal code phase and coarse Doppler, the signal intermediate frequency carrier and coarse Doppler are removed, the signal C / A code is stripped and accumulated to obtain a 1ms coherent cumulative value. At this time, the 1ms coherent cumulative value obtained may have erroneous symbol flips due to factors such as residual Doppler and signal noise.

[0084] Two differential processings are performed in the 20ms interval differential module and the 1ms interval differential module to remove the NH code in the signal and extract the possible jump positions of the Beidou navigation message in the differential process.

[0085] In the data folding solution module, the data that has been differentially processed for a long time is folded and stored. During the data storage folding process, the signal noise is offset in the folding process due to its Gaussian noise characteristics, while the symbol changes caused by the navigation data jumps are continuously accumulated, and the signal-to-noise ratio is improved. The sensitivity performance of the algorithm is improved through the folding process, and the data bit synchronization position is output after the minimum value is obtained.

[0086] By utilizing the output data bit synchronization position, the signal integration time is extended, so that the coherent integration time is extended from 1ms to 10ms, or 20ms or longer, and based on this, high-sensitivity signal tracking is performed to reduce the existing Doppler error, achieve signal lock, and then perform frame synchronization and telegram analysis, and participate in the receiver positioning solution.

[0087] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0088] 3. Evidence of the effects of the embodiments. The embodiments of the present invention have achieved some positive effects during the development or use process, and indeed have great advantages over the prior art. The following content is described in conjunction with the data, charts, etc. of the test process.

[0089] By implementing different Beidou data bit synchronization algorithms on the same platform, the storage resource usage of different algorithms is compared, such as Figure 5 As shown, when the same Beidou signal data length is used for data bit synchronization calculation and processing, the storage space occupied by the present invention is significantly reduced compared with other algorithms, and only a fraction of other algorithms is required to achieve basic data bit synchronization functions.

[0090] The satellite data acquisition card is used to collect BeiDou signals of navigation satellite simulators at different powers, and simulation is performed. Different Doppler residuals are added to the signal simulation, and the data bit synchronization probability under different signal strengths and different Doppler residuals is calculated, such as Figure 6 As shown, the present invention can perform effective data bit synchronization processing in a weak signal environment when the Doppler residual is low, and can still maintain a certain bit synchronization effect in the case of a Doppler residual.

[0091] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A BeiDou Navigation System (BDS) secondary differential coherent data bit synchronization system, characterized in that: The Beidou navigation system BDS secondary differential coherent data bit synchronization system includes: The data preprocessing module is used to preprocess the original Beidou RF input signal to obtain 1ms complex coherent data and send it to the 20ms interval differential module; The 20ms interval differential module is used to perform complex conjugate differential of the 1ms complex coherent data output by the data preprocessing module at an interval of 20ms to obtain differential data at an interval of 20ms and send the differential data to the 1ms interval differential module; The 1 ms interval difference module is used to perform complex conjugate difference at intervals of 1 ms on the difference data output by the 20 ms interval difference module to obtain 1 ms interval difference data and send it to the storage folding solution module; The storage folding solution module is used to store and fold the differential data at intervals of 1ms and coherently accumulate the data, and give a bit-synchronous output position.

2. The BeiDou navigation system BDS secondary differential coherent data bit synchronization system as claimed in claim 1, characterized in that: The data preprocessing module comprises: The analog-to-digital conversion unit is used to perform analog-to-digital conversion on the intermediate frequency BDS signal after RF processing to obtain complex BDS baseband data; A carrier stripping unit, used for stripping and removing the carrier signal in the complex baseband data by multiplying the local carrier signal to obtain a carrier-free signal; The complex baseband data includes two signal components, I and Q, where I is the real part and Q is the imaginary part; In the 1ms coherent integrator, the 1ms carrier-free signal is multiplied and accumulated with the local C / A code data to obtain 1ms complex coherent data.

3. The BeiDou navigation system BDS secondary differential coherent data bit synchronization system as claimed in claim 1, characterized in that: The 20ms interval differential module includes: The 20ms delay unit is used to delay the 1ms complex coherent data by 20ms before outputting it; A complex conjugate unit is used to perform complex conjugate processing on the 1 ms coherent accumulation data after the 20 ms delay unit to obtain conjugate delayed 20 ms coherent accumulation data; The multiplier multiplies the real-time 1 ms coherent accumulation data and the conjugate delayed 20 ms coherent accumulation data, removes the NH code in the signal, and obtains differential data with an interval of 20 ms.

4. The BeiDou navigation system BDS secondary differential coherent data bit synchronization system as claimed in claim 1, characterized in that: The 1ms interval differential module includes: The 1ms delay unit is used to delay the 20ms differential data by 1ms before outputting it. A complex conjugate unit is used to perform complex conjugate processing on the 20ms interval differential data after the 1ms delay unit to obtain the conjugate delayed 1ms coherent accumulation data; The multiplier multiplies the real-time 1 ms coherent accumulation data and the conjugate delayed 1 ms coherent accumulation data to obtain differential data with an interval of 1 ms.

5. The BeiDou Navigation System (BDS) secondary differential coherent data bit synchronization system as claimed in claim 1, characterized in that: The storage folding solution module comprises: A storage folding unit is used to accumulate differential data at intervals of 1 ms; A modulo unit, used for performing a modulo operation on 20 results of the storage folding unit; The minimum value unit is used to find the minimum value of the 20 results after modulo taking, and output the position of the minimum value in the 20 results as the last output bit synchronization position.

6. A BeiDou navigation system BDS secondary differential coherent data bit synchronization method using the BeiDou navigation system BDS secondary differential coherent data bit synchronization system as claimed in any one of claims 1 to 5, characterized in that: The Beidou navigation system BDS secondary differential coherent data bit synchronization method comprises the following steps: Step 1: Use the data preprocessing module to preprocess the original Beidou RF input signal to obtain 1ms complex coherent data, and send it to step 2 for 20ms difference interval; Step 2: Use the 20ms interval differential module to perform complex conjugate differential of the output 1ms complex coherent data at intervals of 20ms to obtain 20ms interval differential data, and send it to step 3 for 1ms interval differential; Step 3: Use the 1ms interval difference module to perform complex conjugate difference at intervals of 1ms on the differential data output from step 2 to obtain 1ms interval differential data, and send it to step 4 for storage folding and solution; Step 4: Use the storage folding solution module to store and fold the 1ms interval differential data output in step 3 for coherent accumulation, and give a bit-synchronous output position.

7. The BeiDou Navigation System (BDS) secondary differential coherent data bit synchronization method as claimed in claim 6, characterized in that: The conjugate operation in step 2 is in the form of (I+jQ) * =I-jQ; The conjugate operation in step 3 is in the form of (I+jQ) * =I-jQ; In step 4, the differential data at intervals of 1 ms are accumulated according to the following formula: Among them, Z(t) is the t-th data after two conjugate difference operations to achieve the coherence of the difference results. After folding and storage, 20 results are obtained.

8. A computer device, characterized in that: The computer device includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the following steps: The original Beidou RF input signal is preprocessed by the data preprocessing module to obtain 1ms complex coherent data, and sent to the 20ms interval differential module; the 20ms interval differential module is used to perform complex conjugate differential of the 1ms complex coherent data at an interval of 20ms to obtain 20ms interval differential data, and sent to the 1ms interval differential module; The differential data is subjected to complex conjugate differential at intervals of 1 ms using a 1 ms differential module to obtain differential data at intervals of 1 ms and sent to a storage folding solution module; the differential data at intervals of 1 ms is subjected to data storage and folding coherent accumulation using the storage folding solution module and a synchronous output position is given.

9. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the following steps: The original Beidou RF input signal is preprocessed by the data preprocessing module to obtain 1ms complex coherent data, and sent to the 20ms interval differential module; the 20ms interval differential module is used to perform complex conjugate differential of the 1ms complex coherent data at an interval of 20ms to obtain 20ms interval differential data, and sent to the 1ms interval differential module; the 1ms interval differential module is used to perform complex conjugate differential of the differential data at an interval of 1ms to obtain 1ms interval differential data, and sent to the storage folding solution module; the storage folding solution module is used to store and fold coherently accumulate the 1ms interval differential data, and give the in-place synchronous output position.

10. An information data processing terminal, characterized in that: The information data processing terminal is used to implement the Beidou navigation system BDS secondary differential coherent data bit synchronization system as described in any one of claims 1 to 5.

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