Frame synchronization method and system suitable for deep space GNSS weak signals

Abstract

The present invention relates to a frame synchronization method and system suitable for deep space GNSS weak signals. By analyzing and processing captured signals, corresponding weak signal message subframe information is obtained, including at least the accumulated values ​​of the I and Q paths of the message bits. At the same time, navigation message frames are analyzed and processed to obtain synchronization header information. The position of the message frame header is then confirmed based on the message subframe information and the synchronization header information. The present invention can solve the problem that existing weak signal processing methods in deep space environments cannot achieve message frame synchronization, avoid the situation where navigation positioning anomalies caused by the inability to synchronize message frames are conducive to achieving frame synchronization processing when the carrier phase is not locked. It can be applied to pure frequency-locked tracking with higher tracking sensitivity. By achieving deep space GNSS weak signal message frame synchronization, the signal transmission time can be obtained, and then the pseudorange and other observation information can be calculated to achieve the positioning of the detector.

Description

Technical Field

[0001] The present invention relates to the field of satellite signal applications, and in particular to a frame synchronization method and system applicable to deep space GNSS weak signals. Background Art

[0002] With the increasing adoption of navigation systems, more and more aircraft and flight equipment are using satellite navigation systems for single-point positioning and velocity measurement. Deep space exploration aircraft, driven by breakthroughs in high-sensitivity signal processing technology, are gradually adopting satellite navigation-based positioning methods. In deep space applications, where signals are extremely weak and message demodulation is impossible, navigation messages are transmitted to the aircraft receiver via ground-based tracking and control stations. High-sensitivity receivers require message frame synchronization to determine the signal transmission time, thereby achieving pseudorange and positioning. However, in extremely weak signal conditions, pure frequency-locked tracking is employed, rendering traditional frame synchronization techniques inadequate. Summary of the Invention

[0003] The purpose of the present invention is to provide a frame synchronization method and system suitable for deep space GNSS weak signals, so as to realize message frame synchronization in weak signal scenarios.

[0004] To achieve the above-mentioned object, the present invention provides a frame synchronization method applicable to deep space GNSS weak signals, comprising:

[0005] S10 analyzes and processes the captured signal to obtain telegram subframe information;

[0006] S20 analyzes and processes the navigation message frame to obtain synchronization header information;

[0007] S30. Confirm the position of the message frame header according to the message subframe information and the synchronization header information.

[0008] The above technical solution also includes:

[0009] S40 repeats steps S10-S30, recording the number of times the position of the message frame header appears;

[0010] S50: Determine the corresponding position where the position of the telegram frame header appears the most times, and use it as the position of the telegram frame header.

[0011] In the above technical solution, the analysis and processing of the captured signal to obtain the message subframe information specifically includes:

[0012] S11 obtains the accumulated value of I and Q paths representing the message bits;

[0013] S12. Sequentially, the accumulated value of the corresponding message bits in the N consecutive message subframes is differentiated from the accumulated value of the previous message bits to obtain a differential value;

[0014] S13. Perform coherent accumulation on the differential results of the N electronic message subframes to obtain a coherent accumulation value.

[0015] In the above technical solution, in step S30, confirming the position of the message frame header according to the message subframe information and the synchronization header information includes:

[0016] S31. Differentiate the synchronization header of the navigation message frame to obtain the synchronization header differential value;

[0017] S32. Accumulate the coherent accumulated value of the message bits sequentially by the synchronization header differential value to obtain the differential accumulated value;

[0018] S33. Confirm the maximum value of the differential accumulated values. The position immediately preceding the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header.

[0019] In the above technical solution, in step S12, the accumulated values ​​of the corresponding message bits in the consecutive N message subframes are sequentially differentiated from the accumulated value of the previous message bits to obtain a differential value, which specifically includes:

[0020]

[0021] in, It is expressed as the complex form of the accumulated value of the i-th message bit of the j-th subframe, represents the accumulated value of the i-th message bit I in the j-th subframe, represents the accumulated value of the Q path of the i-th message bit of the j-th subframe; It is expressed as the conjugate of the accumulated value of the i-1th message bit of the jth subframe; It is expressed as the i-th differential value of the j-th subframe; the value range of i is 1ˉM, where M is the number of navigation messages in a subframe; the value range of j is 1ˉN, where N is the number of message subframes used for frame synchronization judgment.

[0022] In the above technical solution, in step S13, coherent accumulation is performed on the differential results of the N message subframes to obtain a coherent accumulation value, including:

[0023]

[0024] Among them, V i represents the i-th coherent accumulation result in a subframe.

[0025] In the above technical solution, in S31, the synchronization header of the navigation message frame is differentiated to obtain the synchronization header differential value, which specifically includes:

[0026] S311. Perform XOR processing on the synchronization headers of the navigation message frame in sequence, and perform XOR processing on the current synchronization header bit and the previous synchronization header bit;

[0027] S312. Perform a result conversion on the obtained XOR result to obtain a differential value;

[0028] Among them, when the XOR result is 0, the difference value is 1; when the XOR result is 1, the difference value is -1;

[0029] S313. When the length of the synchronization header is L, obtain L-1 fixed known differential values ​​F1:F L-1 .

[0030] In the above technical solution, in step S32, the coherent accumulation value of the message bit is accumulated in sequence by the synchronization header differential value to obtain the differential accumulation value S i (i=1~M), specifically including:

[0031] S1=F1V1+F2V2+L+F L-1 V L-1

[0032] S2=F1V2+F2V3+L+F L-1 V L

[0033] …

[0034] S M-1 =F1V M-1 +F2V M +L+F L-1 V L+M-4 +F L V L+M-3

[0035] S M =F1V M +F2V1+L+F L-1 V L+M-3 +F L V L+M-2 .

[0036] In the above technical solution, in step S33, the maximum value of the differential accumulated value is confirmed, and the previous position of the corresponding position of the maximum value of the differential accumulated value is the position of the message frame header, which specifically includes:

[0037] S331. Obtained differential accumulated value S i (i=1~M) is a complex number, find its amplitude;

[0038] S332. Compare M differential accumulated values ​​S i The magnitude of the amplitude;

[0039] S333. Take S i The position before the position of the maximum amplitude value is the frame synchronization position.

[0040] Another object of the present invention is a frame synchronization system suitable for deep space GNSS weak signals, which is applied to the frame synchronization method suitable for deep space GNSS weak signals described in any one of the above technical solutions, including an acquisition module, a first calculation module, a second calculation module, a third calculation module, a fourth calculation module and a confirmation module;

[0041] The acquisition module is used to analyze and process the captured signal to obtain the accumulated values ​​of the I path and the Q path representing the message bits;

[0042] The first calculation module is configured to sequentially perform a differential operation on the accumulated values ​​of corresponding message bits in N consecutive message subframes and the accumulated value of the previous message bits to obtain a differential value;

[0043] The second calculation module is configured to perform coherent accumulation on the differential results of the N electronic message subframes to obtain a coherent accumulation value;

[0044] The third calculation module is used to differentiate the synchronization header of the navigation message frame to obtain a synchronization header differential value;

[0045] The fourth calculation module is configured to sequentially accumulate the coherent accumulated values ​​of the message bits using the synchronization header differential values ​​to obtain a differential accumulated value;

[0046] The confirmation module is used to confirm the maximum value of the differential accumulated values, and the previous position of the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header.

[0047] The present invention provides a frame synchronization method and system for deep space GNSS weak signals. The method and system analyze and process the captured signals to obtain the corresponding weak signal message subframe information, including at least the accumulated values ​​of the I and Q paths of the message bits. The method also analyzes and processes the navigation message frame to obtain the synchronization header information. The method then confirms the position of the message frame header based on the message subframe information and the synchronization header information. The method solves the problem that the existing weak signal processing method cannot achieve message frame synchronization in a deep space environment, avoids the abnormal navigation positioning caused by the inability to synchronize the message frame, and is conducive to achieving frame synchronization processing when the carrier phase is not locked. The method can be applied to pure frequency-locked tracking with higher tracking sensitivity. By achieving deep space GNSS weak signal message frame synchronization, the signal emission time can be obtained, and then the pseudorange and other observation information can be calculated, and finally the positioning of the detector is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1A flowchart schematically illustrating a frame synchronization method applicable to deep space GNSS weak signals according to an embodiment of the present invention;

[0049] Figure 2 A flowchart schematically illustrating a frame synchronization method applicable to deep space GNSS weak signals according to another embodiment of the present invention;

[0050] Figure 3 A block diagram schematically illustrates the steps of a frame synchronization method applicable to deep space GNSS weak signals according to one embodiment of the present invention;

[0051] Figure 4 The figure schematically shows a frame synchronization system suitable for deep space GNSS weak signals according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0053] Combine Figure 1 and Figure 2 As shown, according to one embodiment of the present invention, a frame synchronization method applicable to deep space GNSS weak signals of the present invention includes:

[0054] S10 analyzes and processes the captured signal to obtain telegram subframe information;

[0055] S20 analyzes and processes the navigation message frame to obtain synchronization header information;

[0056] S30. Confirm the position of the message frame header according to the message subframe information and synchronization header information.

[0057] In this embodiment, by analyzing and processing the captured signal, the corresponding weak signal telegram subframe information is obtained, including at least the accumulated values ​​of the I and Q paths of the telegram bits, and at the same time, the navigation telegram frame is analyzed and processed to obtain the synchronization header information, and then the position of the telegram frame header is confirmed based on the telegram subframe information and the synchronization header information. This can solve the problem that the existing weak signal processing method in the deep space environment cannot achieve telegram frame synchronization, avoid the abnormal navigation positioning caused by the inability to synchronize the telegram frame, and is conducive to achieving frame synchronization processing when the carrier phase is not locked. It can be applied to pure frequency-locked tracking with higher tracking sensitivity, and by achieving deep space GNSS weak signal telegram frame synchronization, the signal transmission time can be obtained, and then the observation information such as pseudorange can be calculated, and finally the positioning of the detector is achieved.

[0058] Specifically, after capturing the weak GNSS signal, the terminal analyzes and processes the signal to obtain the accumulated values ​​of the I and Q paths of the message bits, then differentiates the accumulated values ​​of the message bits in N consecutive message subframes from the accumulated values ​​of the previous message bits to obtain the differential value, and then coherently accumulates the differential results of the N subframes to obtain the coherent accumulated value, thereby completing the acquisition of the message subframe information; the terminal differentiates the synchronization header of the navigation message frame to obtain the synchronization header differential value, thereby completing the acquisition of the synchronization header information, wherein the navigation message can be injected into the aircraft receiver through the ground measurement and control station; then the synchronization header differential value is used to accumulate the coherent accumulated values ​​of the message bits in sequence to obtain the differential accumulated value, and the maximum value in the differential accumulated value is found, and the position before the position of the maximum value is the position of the message frame header.

[0059] In one embodiment of the present invention, preferably, it further includes:

[0060] S40 repeats steps S10-S30, recording the number of times the position of the message frame header appears;

[0061] S50. Determine the corresponding position where the position of the message frame header appears the most times, and use it as the position of the message frame header.

[0062] In this embodiment, by repeatedly executing steps S10-S30, the consistency of the frame synchronization judgment result is checked, the number of times the position of the telegram frame header appears is recorded, and the corresponding position where the position of the telegram frame header appears the most times is determined as the position of the telegram frame header, which is beneficial to improving the accuracy and reliability of the position of the telegram frame header, that is, improving the reliability of frame synchronization.

[0063] Specifically, the signal captured by the navigation terminal is easily affected by noise, which affects the frame synchronization judgment result. Therefore, the navigation terminal calculates multiple frame synchronizations to obtain the positions of multiple telegram frame headers. If the positions of multiple frame synchronizations are consistent, it is determined that the navigation terminal has completed the frame synchronization processing of the current satellite, and then performs positioning solution to obtain the location of the navigation terminal; if the positions of multiple frame synchronizations are inconsistent, the next round of frame synchronization of the current satellite is re-performed.

[0064] For example, the navigation terminal performs 10 rounds of frame synchronization judgment, among which at least 8 rounds of frame synchronization positions are consistent, then it is determined that the navigation terminal has completed the frame synchronization processing of the current satellite; if the results of all 10 rounds are inconsistent, the 11th round of frame synchronization judgment is performed.

[0065] like Figure 2 As shown, in one embodiment of the present invention, preferably, analyzing and processing the captured signal to obtain the message subframe information specifically includes:

[0066] S11 obtains the accumulated value of I and Q paths representing the message bits;

[0067] S12. Sequentially perform differential calculations on the accumulated value of the corresponding message bits in N consecutive message subframes and the accumulated value of the previous message bits to obtain a differential value;

[0068] S13. Perform coherent accumulation on the differential results of the N message subframes to obtain a coherent accumulation value.

[0069] like Figure 2 As shown, in one embodiment of the present invention, preferably, in step S30, confirming the position of the message frame header according to the message subframe information and the synchronization header information includes:

[0070] S31. Differentiate the synchronization header of the navigation message frame to obtain the synchronization header differential value;

[0071] S32. Accumulate the coherent accumulated value of the message bits sequentially by the synchronization header differential value to obtain the differential accumulated value;

[0072] S33. Confirm the maximum value of the differential accumulated values. The position immediately preceding the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header.

[0073] In one embodiment of the present invention, preferably, in step S12, the accumulated values ​​of corresponding message bits in N consecutive message subframes are sequentially differentiated from the accumulated values ​​of the previous message bits to obtain a differential value, which specifically includes:

[0074]

[0075] in, It is expressed as the complex form of the accumulated value of the i-th message bit of the j-th subframe, represents the accumulated value of the i-th message bit I in the j-th subframe, represents the accumulated value of the Q path of the i-th message bit of the j-th subframe; It is expressed as the conjugate of the accumulated value of the i-1th message bit of the jth subframe; It is expressed as the i-th differential value of the j-th subframe; the value range of i is 1ˉM, where M is the number of navigation messages in a subframe; the value range of j is 1ˉN, where N is the number of message subframes used for frame synchronization judgment.

[0076] In one embodiment of the present invention, preferably, in step S13, coherent accumulation is performed on the differential results of the N message subframes to obtain a coherent accumulation value, including:

[0077]

[0078] Among them, V i represents the i-th coherent accumulation result in a subframe.

[0079] In one embodiment of the present invention, preferably, in S31, performing differentiation on the synchronization header of the navigation message frame to obtain a synchronization header differential value specifically includes:

[0080] S311. Perform XOR processing on the synchronization headers of the navigation message frame in sequence, and perform XOR processing on the current synchronization header bit and the previous synchronization header bit;

[0081] S312. Perform a result conversion on the obtained XOR result to obtain a differential value;

[0082] Among them, when the XOR result is 0, the difference value is 1; when the XOR result is 1, the difference value is -1;

[0083] S313. When the length of the synchronization header is L, obtain L-1 fixed known differential values ​​F1:F L-1 .

[0084] In one embodiment of the present invention, preferably, in step S32, the coherent accumulation values ​​of the message bits are accumulated in sequence by using the synchronization header differential value to obtain the differential accumulation value S i (i=1~M), specifically including:

[0085] S1=F1V1+F2V2+L+F L-1 V L-1

[0086] S2=F1V2+F2V3+L+F L-1 V L

[0087] …

[0088] S M-1 =F1V M-1 +F2V M +L+F L-1 V L+M-4 +F L V L+M-3

[0089] S M =F1V M +F2V1+L+F L-1 V L+M-3 +F L V L+M-2 .

[0090] In one embodiment of the present invention, preferably, in step S33, the maximum value of the differential accumulated values ​​is confirmed, and the previous position of the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header, which specifically includes:

[0091] S331. Obtained differential accumulated value Si (i=1~M) is a complex number, find its amplitude;

[0092] S332. Compare M differential accumulated values ​​S i The magnitude of the amplitude;

[0093] S333. Take S i The position before the position of the maximum amplitude value is the frame synchronization position.

[0094] like Figure 4 As shown, according to another embodiment of the present invention, a frame synchronization system applicable to deep space GNSS weak signals of the present invention is applied to the frame synchronization method applicable to deep space GNSS weak signals in any of the above embodiments, including an acquisition module, a first calculation module, a second calculation module, a third calculation module, a fourth calculation module and a confirmation module;

[0095] The acquisition module is used to analyze and process the captured signal to obtain the accumulated values ​​of the I and Q channels representing the message bits;

[0096] A first calculation module is used to sequentially perform a differential operation on the accumulated value of corresponding message bits in N consecutive message subframes and the accumulated value of the previous message bits to obtain a differential value;

[0097] The second calculation module is used to perform coherent accumulation on the differential results of the N message subframes to obtain a coherent accumulation value;

[0098] a third calculation module, configured to perform a differential operation on the synchronization header of the navigation message frame to obtain a synchronization header differential value;

[0099] a fourth calculation module, configured to sequentially accumulate the coherent accumulated values ​​of the message bits using the synchronization header differential values ​​to obtain a differential accumulated value;

[0100] The confirmation module is used to confirm the maximum value of the differential accumulated value, and the previous position of the corresponding position of the maximum value of the differential accumulated value is the position of the telegram frame header.

[0101] In this embodiment, by setting an acquisition module, a first calculation module, a second calculation module, a third calculation module, a fourth calculation module and a confirmation module, the corresponding weak signal telegram subframe information is obtained, at least including the accumulated values ​​of the I path and Q path of the telegram bits, and at the same time, the navigation telegram frame is analyzed and processed to obtain the synchronization header information, and then the position of the telegram frame header is confirmed based on the telegram subframe information and the synchronization header information. This can solve the problem that the existing weak signal processing method in the deep space environment cannot achieve telegram frame synchronization, avoid the abnormal navigation positioning caused by the inability to synchronize the telegram frame, and is conducive to achieving frame synchronization processing when the carrier phase is not locked. It can be applied to pure frequency-locked tracking with higher tracking sensitivity, and by achieving deep space GNSS weak signal telegram frame synchronization, the signal transmission time can be obtained, and then the pseudorange and other observation information can be solved to finally achieve the positioning of the detector.

[0102] According to another embodiment of the present invention, a computer storage medium of the present invention stores a computer program, and when the computer program is executed by a processor, the frame synchronization method applicable to deep space GNSS weak signals of any one of the above embodiments is implemented.

[0103] According to another embodiment of the present invention, a terminal of the present invention includes: a memory and a processor, wherein a computer program is stored in the memory;

[0104] The processor is configured to execute the computer program in the memory;

[0105] When the computer program is executed by a processor, the frame synchronization method applicable to deep space GNSS weak signals of any one of the above-mentioned embodiments is implemented.

[0106] like Figure 3 As shown, an implementation example of the present invention is a frame synchronization method applicable to deep space GNSS weak signals, and the processing process of the GPS navigation terminal includes:

[0107] Step S201: The navigation terminal captures and tracks the GPS L1CA signal and obtains the accumulated values ​​representing the I and Q paths of the message bits through a correlator.

[0108] Step S202: The navigation terminal determines the number N of message subframes used for frame synchronization determination based on the current signal power;

[0109] Step S203: The navigation terminal sequentially performs a differential operation on the accumulated message bit values ​​in N consecutive message subframes and the accumulated message bit value of the previous message to obtain a differential value.

[0110] Step S204: The navigation terminal performs coherent accumulation on the differential results of the N message subframes to obtain a coherent accumulation value;

[0111] Step S205: The navigation terminal performs a differential operation on the synchronization header of the navigation message frame according to the synchronization header information known in the GPS L1CA interface control file to obtain a synchronization header differential value.

[0112] Step S206: The navigation terminal uses the synchronization header differential value to sequentially accumulate the coherent cumulative value of the message bits to obtain a differential cumulative value;

[0113] Step S207: The navigation terminal starts searching for the maximum value in the differential accumulated value. The position before the maximum value is the position of the message frame header, and the frame header position is recorded.

[0114] Step S208: The navigation terminal checks the consistency of the multiple frame synchronization judgment results. If the frame synchronization positions are consistent in the multiple judgment results, execute S209; if the frame synchronization positions are inconsistent in the multiple judgment results, re-perform the next round of frame synchronization judgment for the current satellite and execute S202.

[0115] Step S209: The navigation terminal completes the frame synchronization processing of the current satellite, and then performs positioning calculation to obtain the location of the navigation terminal.

[0116] The above contents are merely examples of specific solutions of the present invention. For devices and structures not described in detail, it should be understood that they can be implemented by adopting general devices and methods available in the art.

[0117] The above description is merely one embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A frame synchronization method suitable for deep space GNSS weak signals, characterized in that: include: S10. Analyze and process the captured signal to obtain message subframe information, including: S11 obtains the accumulated value of I and Q paths representing the message bits; S12 sequentially performing differential calculations on the N consecutive subframes of the message bit corresponding to the message bit accumulated value and the previous message bit accumulated value of the message subframe to obtain a differential value; S13 performs coherent accumulation of the differential results of the N subframes of the message to obtain a coherent accumulated value; S20 analyzes and processes the navigation message frame to obtain synchronization header information; S30. According to the message subframe information and the synchronization header information, confirm the position of the message frame header, including: S31. Differentiate the synchronization header of the navigation message frame to obtain a synchronization header differential value, specifically including: S311. Perform XOR processing on the synchronization headers of the navigation message frame in sequence, and perform XOR processing on the current synchronization header bit and the previous synchronization header bit; S312. Perform a result conversion on the obtained XOR result to obtain a differential value; Among them, when the XOR result is 0, the difference value is 1; when the XOR result is 1, the difference value is -1; S313. When the length of the synchronization header is L, obtain L-1 fixed known differential values ​​F1~F L ; S32. Accumulate the coherent accumulated value of the message bits sequentially by the synchronization header differential value to obtain the differential accumulated value; S33. Confirm the maximum value of the differential accumulated values. The position immediately preceding the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header.

2. The frame synchronization method for deep space GNSS weak signals according to claim 1, characterized in that: Also includes: S40 repeats steps S10-S30, recording the number of occurrences of the position of the message frame header; S50: Determine the corresponding position where the position of the telegram frame header appears the most times, and use it as the position of the telegram frame header.

3. The frame synchronization method applicable to deep space GNSS weak signals according to claim 1, characterized in that: In step S12, the accumulated values ​​of the corresponding message bits in the consecutive N message subframes are sequentially differentiated from the accumulated value of the message bits in the previous message subframe to obtain a differential value, which specifically includes: in, It is expressed as the complex form of the accumulated value of the i-th message bit of the j-th subframe, represents the accumulated value of the i-th message bit I in the j-th subframe, represents the accumulated value of the Q path of the i-th message bit of the j-th subframe; It is expressed as the conjugate of the accumulated value of the i-1th message bit of the jth subframe; It is represented as the i-th differential value of the j-th subframe; the value range of i is 1 to M, where M is the number of navigation messages in a subframe; the value range of j is 1 to N, where N is the number of message subframes used for frame synchronization judgment.

4. The frame synchronization method applicable to deep space GNSS weak signals according to claim 3, characterized in that: In step S13, coherent accumulation is performed on the differential results of the N message subframes to obtain a coherent accumulation value, including: Among them, V i represents the i-th coherent accumulation result in a subframe.

5. The frame synchronization method applicable to deep space GNSS weak signals according to claim 4, characterized in that: In step S32, the coherent accumulation value of the message bits is accumulated in sequence by the synchronization header differential value to obtain the differential accumulation value S i (i=1~M), specifically including: S1=F1V1+F2V2+…+F L-1 V L-1 +F L V L <h2 style=";text-align:left;direction:ltr">S2=F1V2+F2V3+…+F<h2 style=";text-align:left;direction:ltr"> L-1 <h2 style=";text-align:left;direction:ltr"> V<h2 style=";text-align:left;direction:ltr"> L <h2 style=";text-align:left;direction:ltr"> +F<h2 style=";text-align:left;direction:ltr"> L <h2 style=";text-align:left;direction:ltr"> V<h2 style=";text-align:left;direction:ltr"> L+1 … S M-1 =F1V M-1 +F2V M +…+F L-1 V L-3 +F L V L-2 S M =F1V M +F2V1+…+F L-1 V L-2 +F L V L-1 。 6. The frame synchronization method applicable to deep space GNSS weak signals according to claim 1, characterized in that: In step S33, the maximum value of the differential accumulated values ​​is confirmed, and the previous position of the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header, which specifically includes: S331. Obtained differential accumulated value S i (i=1~M) is a complex number, find its amplitude; S332. Compare M differential accumulated values ​​S i The magnitude of the amplitude; S333. Take S i The position before the position of the maximum amplitude value is the frame synchronization position.

7. A frame synchronization system suitable for deep space GNSS weak signals, characterized in that: A frame synchronization method for deep space GNSS weak signals as described in any one of claims 1 to 6, comprising an acquisition module, a first calculation module, a second calculation module, a third calculation module, a fourth calculation module, and a confirmation module; The acquisition module is used to analyze and process the captured signal to obtain the accumulated values ​​of the I path and the Q path representing the message bits; The first calculation module is configured to sequentially perform a differential operation on the accumulated values ​​of corresponding message bits in N consecutive message subframes and the accumulated value of message bits in the previous message subframe to obtain a differential value; The second calculation module is configured to perform coherent accumulation on the differential results of the N electronic message subframes to obtain a coherent accumulation value; The third calculation module is used to differentiate the synchronization header of the navigation message frame to obtain a synchronization header differential value; The fourth calculation module is configured to sequentially accumulate the coherent accumulated values ​​of the message bits using the synchronization header differential values ​​to obtain a differential accumulated value; The confirmation module is used to confirm the maximum value of the differential accumulated values, and the previous position of the corresponding position of the maximum value of the differential accumulated values ​​is the position of the message frame header.

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