阅读说明：本技术 一种北斗b1c信号导航电文帧同步及解码方法 (Beidou B1C signal navigation message frame synchronization and decoding method ) 是由 罗凯 许睿 陈佳林 曾庆化 熊智 张煜曦 于 2021-08-17 设计创作，主要内容包括：本发明公开了一种北斗B1C信号导航电文帧同步及解码方法；来自北斗B1C信号接收机天线的数字中频信号经过捕获得到卫星捕获的伪随机码编号、码相位及多普勒频率初值,获得捕获结果可根据接收机需求对单数据分量进行跟踪或对数据分量和导频分量双分量进行跟踪选择设置参数。设置完跟踪分量,接收机对选择分量进行跟踪获得跟踪分量同相支路即时值的输出值。此时的输出同相支路即时值的信号,对导频分量表示含有子码信息的信号,对数据分量表示编码后的导航数据信息的信号。本发明在接收机实时解码导航电文的情况下可以减少解码电文的复杂度,提高解码电文的效率,为北斗B1C接收机解码导航电文提供了有效方案,具有实际工程意义。(The invention discloses a Beidou B1C signal navigation message frame synchronization and decoding method; the digital intermediate frequency signals from the Beidou B1C signal receiver antenna are captured to obtain pseudo-random code numbers, code phases and Doppler frequency initial values captured by the satellite, and the captured results can be used for tracking single data components or tracking double components of the data components and pilot frequency components according to the requirements of the receiver to select setting parameters. And after the tracking component is set, the receiver tracks the selected component to obtain the output value of the in-phase branch immediate value of the tracking component. In this case, the signal of the in-phase branch immediate value is output, the signal containing the subcode information is represented by the pilot component, and the signal of the encoded navigation data information is represented by the data component. The invention can reduce the complexity of the decoded message and improve the efficiency of the decoded message under the condition that the receiver decodes the navigation message in real time, provides an effective scheme for the Beidou B1C receiver to decode the navigation message, and has practical engineering significance.)

1. A Beidou B1C signal navigation message frame synchronization and decoding method is characterized by comprising the following steps:

step (1), the Beidou receiver B1C converts the Beidou satellite signals received by the antenna into digital intermediate frequency signals after radio frequency front end processing, and provides the digital intermediate frequency signals for a receiver input signal source;

the receiver acquires the visible satellites existing at the present time, and the acquisition code phase and Doppler frequency of the visible satellites through an acquisition algorithm, so that the visible satellites are convenient to follow-up tracking and use;

step (3), the receiver selects to track the data component or pilot frequency component contained in the Beidou satellite according to the user requirement and the carrier-to-noise ratio of the captured signal, when the carrier-to-noise ratio of the captured signal is more than or equal to 40dB-Hz or only the data component is selected to be tracked according to the user requirement, and the parameter of the tracking component is set to be 1; when the carrier-to-noise ratio of the captured signal is less than 40dB-Hz or the running time is not considered, selecting a tracking pilot frequency component and a data component, and setting a tracking component parameter to be 2;

after acquiring tracking component parameters, the receiver performs a tracking process according to the acquired PRN number, code phase and Doppler frequency;

step (5), the PRN number, the tracking component I branch value and the tracking component parameter value are transmitted into a double-component frame synchronization module, and single data component frame synchronization or pilot frequency component auxiliary data component frame synchronization is selected through the tracking component parameter value; when the tracking component parameter is 1, generating a data component synchronization head sequence through the PRN number to synchronize the head of the data component with more than 18s to obtain the position P of the sub-frame 1_df1Simultaneously deducing the starting positions of sub-frames 2 and 3 of the nth complete frameAndwhen the tracking component parameter is 2; obtaining data of pilot frequency component in 6s for correlation to obtain a frame data initial position P corresponding to the current data_pnCalculating the starting and stopping positions of the sub-frames 1, 2 and 3 of the nth complete frame period of the data component at the moment And

step (6), the multi-satellite joint debugging decoding module obtains the initial position of the subframe 1, when the external SOH value is judged to be 999, the decoding is judged to be the first satellite decoding, the data of the subframe 1 is resolved through BCH decoding to obtain SOH information, and the SOH information is stored to the external storage; when the external SOH value is judged not to be 999, namely the decoding of other star subframes 1 is completed, an SOH coding lead-lag sequence can be generated according to the external stored SOH information of other stars and is related to the current SOH value, the SOH value of the maximum peak value judgment coding sequence is obtained, the BCH decoding process is reduced, and the subframe 1 decoding process is completed;

step (7), the deinterlacing module of the sub-frames 2 and 3 obtains the starting and ending positions of the sub-frame 2, and the obtained data block interlaced with the sub-frames 2 and 3 is separated into the coded messages corresponding to the sub-frames 2 and 3, so that each sub-frame can be processed independently; transmitting the encoded telegraph text of the sub-frames 2 and 3 after de-interleaving into an LPDC removing module, and respectively removing redundant data of the sub-frames 2 and 3 bits by the LPDC removing module to leave decoded sub-frame 2 and 3 telegraph text data;

step (8), a CRC (cyclic redundancy check) module is carried out on the subframe 2 and subframe 3 decoded message data in the step (7), if the check is successful, the decoded message data is decoded into correct message data, and if the check is incorrect, the starting and stopping positions of the new message subframes 1, 2 and 3 in the next period are calculated again in the step (5);

and (9) repeating the circulation steps (2) to (8), continuously obtaining the real-time synchronous message frame head and the decoded message signal of the receiver, storing the navigation message contained in the subframe, and updating the message information.

2. The beidou B1C signal navigation message frame synchronization and decoding method of claim 1, wherein in step (5), the dual component frame synchronization module uses the read tracking parameter and PRN information to select single data component frame synchronization or pilot component auxiliary data component frame synchronization by determining whether the tracking parameter is 1; when the parameter is 1, performing polarity conversion and storage on the acquired 36-second tracking data component, reading a locally generated synchronous frame header matrix F, selecting a 21-bit frame header sequence in the matrix F according to a satellite PRN (pseudo random number), and performing correlation integral operation on the tracking data component to obtain a correlation function of the tracking data component; for the time length of the tracking data component is longer than the time of two continuous frames, namely the frame head sequence of the occurrence of the correlation function obtains a plurality of 21 maximum correlation values with 18s intervals; determining the first maximum correlation value as the first whole frame start position P_df1Calculating the starting positions of sub-frames 2 and 3 of the nth complete frameAndwhen the tracking parameter is not 1, the data component and the pilot frequency component content are obtained, the polarity is converted and stored, then the pilot frequency component subcode synchronization algorithm is carried out on the data of the pilot frequency component 6s after the polarity conversion and the one-cycle complete 1800 bit subcode, and the synchronization bit P is obtained_pnSynchronizing to calculate the start and stop positions of sub-frames 1, 2 and 3 of the nth complete frame periodAnd

3. the method for synchronizing and decoding frame of Beidou B1C signals according to claim 1, wherein in the step (5), the local data component synchronization frame header matrix F is as follows, each row is separated by a semicolon, and 1 to 45 rows correspond to the synchronization frame headers of PRN19 to PRN63 respectively:

F＝[010010011001011000001；010011001011000001010；010100100110010110000；010101110100001111011；010110000010100100110；010111010000111101101；011000001010010011001；011001011000001010010；011010101110100001111；011011111100111000100；011100010001101111110；011101000011110110101；011110110101011101000；011111100111000100011；100000101001001100101；100001111011010101110；100010001101111110011；100011011111100111000；100100110010110000010；100101100000101001001；100110010110000010100；100111000100011011111；101000011110110101011；101001001100101100000；101010111010000111101；101011101000011110110；101100000101001001100；101101010111010000111；101110100001111011010；101111110011100010001；110000010100100110010；110001000110111111001；110010110000010100100；110011100010001101111；110100001111011010101；110101011101000011110；110110101011101000011；110111111001110001000；111000100011011111100；111001110001000110111；111010000111101101010；111011010101110100001；111100111000100011011；111101101010111010000；111110011100010001101]。

4. the beidou B1C signal navigation message frame synchronization and decoding method according to claim 1, wherein in step (5), the calculation formula in the two-component frame synchronization module is as follows:

5. the Beidou B1C signal navigation message frame synchronization and decoding method according to claim 1, characterized in that, in the pilot frequency component subcode synchronization algorithm, the local subcode generator NCO output is multiplied by the local input 6s data signal which is subjected to FFT and conjugate after being subjected to FFT, the output result is converted into a time domain signal through IFFT, and the modulus value output by IFFT represents the correlation integral result of the input data and the local subcode; if a peak is present, the peak will,the sync bit P, which represents the beginning of the input 6s data in the 18s full period subcode_pn。

6. The Beidou B1C signal navigation message frame synchronization and decoding method according to claim 1, wherein in the step (6), after the multi-satellite joint tone subframe 1 decoding module acquires the starting position of the subframe 1, PRN encoded information in the message is removed, and the remaining SOH encoded sequences representing SOH count values in the subframe 1 are decoded.

7. The Beidou B1C signal navigation message frame synchronization and decoding method according to claim 6, wherein the specific steps of the step (6) are firstly, after reading external SOH count, judging; since the range of the SOH count value is 0 to 256, the SOH count value is initialized before the method starts, and the SOH count value initialization value is 999, so that subsequent judgment and updating are facilitated; secondly, when the SOH count value is equal to 999, the first satellite starts to decode the SOH count value, correlation is carried out on the obtained SOH coding sequence value in the telegraph and all sequences generated locally to obtain 256 maximum correlation values, peak point detection is carried out on the correlation values, the maximum peak point represents the SOH count value corresponding to the current SOH coding sequence, and the decoded SOH count value is stored to locally assist other satellites to carry out combined decoding of the SOH value; when the SOH value is not equal to 999, the current value is represented by the latest SOH counting value of other star decoding in the previous period, the current value is respectively extracted according to the SOH value of the criminal, and the difference value of the counting values before and after the current value is the SOH sequence represented by 1; and finally, carrying out correlation on the received SOH message coding sequence to obtain a maximum peak value, judging the SOH value, and updating the SOH value to the local.

8. The beidou B1C signal navigation message frame synchronization and decoding method according to claim 1, wherein in step (7), according to the obtained starting positions of subframes 2 and 3 of the complete frame, 1728-bit data formed by interleaving subframes 2 and 3 are deinterleaved to obtain subframe 2 data of 1200 bits and subframe 3 data of 528 bits respectively, and then redundant bits of subframes 2 and 3 are truncated by the property of LDPC coding to leave information bits.

9. The Beidou B1C signal navigation message frame synchronization and decoding method according to claim 1, wherein in the step (7), for a 2k length 64 system LDPC (2k, k) row sequence m_1×2kSequence m 'after removal of redundant bits'_1×kAnd the redundant bit sequence m ″)_1×kAnd original m_1×2kThe relationship of (1) is:

m_1×2k＝[m′_1×k,m″_1×k]

wherein: m'_1×kIs a decoded sequence vector of length k, m ″)_1×kRedundancy with length k is a row vector; LDPC (2k, k) means that an information codeword with length k is encoded to obtain an information codeword with length 2k, and each codeword represents a 64-ary sequence by 6 binary numbers.

10. The beidou B1C signal navigation message frame synchronization and decoding method of claim 1, wherein in step (8), CRC check is performed on the content of the information bits, if the check output is 1, the decoding error is found, and the start positions of sub-frames 2 and 3 of the next whole frame are reckoned to perform the above operations; if the check output is 0, the decoding message is correct, and the decoding message is stored so as to read ephemeris data in the following process.

Technical Field

The invention belongs to the technical field of Beidou B1C baseband signal positioning navigation and control, and particularly relates to a Beidou B1C signal navigation message frame synchronization and decoding method.

Background

With the increasing demand of military and civil fields for Navigation applications, each country has recently implemented a modernized upgrade plan of Global positioning System (GNSS), wherein in the aspect of civil signals, a new System signal of L1C is added to the GPS at the L1 frequency band, a beidou three-number B1C signal is added to the beidou Navigation System, and an E1OS signal is added to the galileo System. In the process of using a new system signal, a plurality of linear error correction codes are introduced into a B-CNAV1 message of a Beidou B1C signal data component part, and a frame structure without a fixed synchronization head is used, so that a brand new challenge is brought to frame synchronization and navigation message decoding of the Beidou message. Therefore, the problem of frame synchronization of the Beidou message, the decoding of the navigation message and the reduction of the complexity of the decoding message become an important part of satellite software receivers in the field of satellite navigation, and the method has important engineering significance for Beidou No. three receivers.

The beidou B1C signal is one of the signals of the modernization of the navigation system, and the signal thereof is composed of a data signal and a pilot signal. The period of one frame of text message of B1C is 18s, and the frame structure of text message data includes: subframe 1 information of 72 bits after BCH (21,6) + BCH (51,8) coding; subframe 2 and subframe 3 of 1728-bit text after LDPC (1200, 600) and LDPC (528, 264) coding and CRC check and then block interleaving. The subframe 1 information is changed at any time, which indicates that the text data has no fixed frame header, the frame synchronization can not be completed by using the traditional method, the text error correction coding mode is various, and the decoding complexity is high.

Multi-component data does not exist in the most traditional Beidou and GPS navigation signal systems, the value of an I branch output from a tracking loop is directly binary into 1 and-1, the initial position of a subframe is obtained through an 8bit or 11bit synchronization head, and then the data of a navigation message is directly read according to a message structure; meanwhile, the Beidou and Galileo systems in later newly-released second-generation signals add bit interleaving and BCH (15,11,1) coding and hard decision decoding of a small amount of data on a text structure. The new system signal does not use data component and pilot frequency component, and uses a large amount of linear error correction coding and thousands of bits of block interleaving coding on the navigation text. Therefore, a strategy method for subframe synchronization and message decoding of the Beidou B1C signal navigation message is designed, the complexity of message decoding can be effectively reduced, and the efficiency of message decoding is improved.

Disclosure of Invention

The invention provides a Beidou B1C signal navigation message frame synchronization and decoding method, which aims to solve the problems in the prior art.

In order to achieve the purpose, the invention adopts the technical scheme that:

a Beidou B1C signal navigation message frame synchronization and decoding method comprises the following steps:

step (1), the Beidou receiver B1C converts the Beidou satellite signals received by the antenna into digital intermediate frequency signals after radio frequency front end processing, and provides the digital intermediate frequency signals for a receiver input signal source;

the receiver acquires the visible satellites existing at the present time, and the acquisition code phase and Doppler frequency of the visible satellites through an acquisition algorithm, so that the visible satellites are convenient to follow-up tracking and use;

step (3), the receiver selects to track the data component or pilot frequency component contained in the Beidou satellite according to the user requirement and the carrier-to-noise ratio of the captured signal, when the carrier-to-noise ratio of the captured signal is more than or equal to 40dB-Hz or only the data component is selected to be tracked according to the user requirement, and the parameter of the tracking component is set to be 1; when the carrier-to-noise ratio of the captured signal is less than 40dB-Hz or the running time is not considered, selecting a tracking pilot frequency component and a data component, and setting a tracking component parameter to be 2;

after acquiring tracking component parameters, the receiver performs a tracking process according to the acquired PRN number, code phase and Doppler frequency;

step (5), the PRN number, the tracking component I branch value and the tracking component parameter value are transmitted into a double-component frame synchronization module, and single data component frame synchronization or pilot frequency component auxiliary data component frame synchronization is selected through the tracking component parameter value; when the tracking component parameter is 1, the signal is outputGenerating data component synchronous head sequence by passing PRN number, synchronizing frame head of data component more than 18s to obtain position P of sub-frame 1_df1Simultaneously deducing the starting positions of sub-frames 2 and 3 of the nth complete frameAndwhen the tracking component parameter is 2; obtaining data of pilot frequency component in 6s for correlation to obtain a frame data initial position P corresponding to the current data_pnCalculating the starting and stopping positions of the sub-frames 1, 2 and 3 of the nth complete frame period of the data component at the moment And

step (6), the multi-satellite joint debugging decoding module obtains the initial position of the subframe 1, when the external SOH value is judged to be 999, the decoding is judged to be the first satellite decoding, the data of the subframe 1 is resolved through BCH decoding to obtain SOH information, and the SOH information is stored to the external storage; when the external SOH value is judged not to be 999, namely the decoding of other star subframes 1 is completed, an SOH coding lead-lag sequence can be generated according to the external stored SOH information of other stars and is related to the current SOH value, the SOH value of the maximum peak value judgment coding sequence is obtained, the BCH decoding process is reduced, and the subframe 1 decoding process is completed;

step (7), the deinterlacing module of the sub-frames 2 and 3 obtains the starting and ending positions of the sub-frame 2, and the obtained data block interlaced with the sub-frames 2 and 3 is separated into the coded messages corresponding to the sub-frames 2 and 3, so that each sub-frame can be processed independently; transmitting the encoded telegraph text of the sub-frames 2 and 3 after de-interleaving into an LPDC removing module, and respectively removing redundant data of the sub-frames 2 and 3 bits by the LPDC removing module to leave decoded sub-frame 2 and 3 telegraph text data;

step (8), a CRC (cyclic redundancy check) module is carried out on the subframe 2 and subframe 3 decoded message data in the step (7), if the check is successful, the decoded message data is decoded into correct message data, and if the check is incorrect, the starting and stopping positions of the new message subframes 1, 2 and 3 in the next period are calculated again in the step (5);

and (9) repeating the circulation steps (2) to (8), continuously obtaining the real-time synchronous message frame head and the decoded message signal of the receiver, storing the navigation message contained in the subframe, and updating the message information.

Further, in the step (5), the dual component frame synchronization module selects single data component frame synchronization or pilot component auxiliary data component frame synchronization by determining whether the tracking parameter is 1 by using the read tracking parameter and PRN information; when the parameter is 1, performing polarity conversion and storage on the acquired 36-second tracking data component, reading a locally generated synchronous frame header matrix F, selecting a 21-bit frame header sequence in the matrix F according to a satellite PRN (pseudo random number), and performing correlation integral operation on the tracking data component to obtain a correlation function of the tracking data component; for the time length of the tracking data component is longer than the time of two continuous frames, namely the frame head sequence of the occurrence of the correlation function obtains a plurality of 21 maximum correlation values with 18s intervals; determining the first maximum correlation value as the first whole frame start position P_df1Calculating the starting positions of sub-frames 2 and 3 of the nth complete frameAndwhen the tracking parameter is not 1, the data component and the pilot frequency component content are obtained, the polarity is converted and stored, then the pilot frequency component subcode synchronization algorithm is carried out on the data of the pilot frequency component 6s after the polarity conversion and the one-cycle complete 1800 bit subcode, and the synchronization bit P is obtained_pnSynchronizing to calculate the start and stop positions of sub-frames 1, 2 and 3 of the nth complete frame periodAnd

further, in step (5), the local data component synchronization frame header matrix F is as follows, where each row is separated by a semicolon, and rows 1 to 45 correspond to synchronization frame headers of PRN19 to PRN63, respectively:

F＝[010010011001011000001；010011001011000001010；010100100110010110000；010101110100001111011；010110000010100100110；010111010000111101101；011000001010010011001；011001011000001010010；011010101110100001111；011011111100111000100；011100010001101111110；011101000011110110101；011110110101011101000；011111100111000100011；100000101001001100101；100001111011010101110；100010001101111110011；100011011111100111000；100100110010110000010；100101100000101001001；100110010110000010100；100111000100011011111；101000011110110101011；101001001100101100000；101010111010000111101；101011101000011110110；101100000101001001100；101101010111010000111；101110100001111011010；101111110011100010001；110000010100100110010；110001000110111111001；110010110000010100100；110011100010001101111；110100001111011010101；110101011101000011110；110110101011101000011；110111111001110001000；111000100011011111100；111001110001000110111；111010000111101101010；111011010101110100001；111100111000100011011；111101101010111010000；111110011100010001101]。

further, in the step (5), the calculation formula in the two-component frame synchronization module is as follows:

in the pilot frequency component subcode synchronization algorithm, the output of a local subcode generator NCO is multiplied by a local input 6s data signal which is subjected to FFT and conjugate after being subjected to FFT, the output result is converted into a time domain signal through IFFT, and a modulus value output by the IFFT represents a correlation integral result of the input data and the local subcode; if the peak occurs, it represents the sync bit P of the input 6s data starting in the 18s whole period sub-code_pn。

Further, in the step (6), after the multi-satellite joint debugging subframe 1 decoding module acquires the starting position of the subframe 1, the PRN code information in the text is removed, and the remaining SOH code sequences representing the SOH count value in the subframe 1 are decoded.

Further, the specific step of the step (6) is to read the external SOH count and then to determine; since the range of the SOH count value is 0 to 256, the SOH count value is initialized before the method starts, and the SOH count value initialization value is 999, so that subsequent judgment and updating are facilitated; secondly, when the SOH count value is equal to 999, the first satellite starts to decode the SOH count value, correlation is carried out on the obtained SOH coding sequence value in the telegraph and all sequences generated locally to obtain 256 maximum correlation values, peak point detection is carried out on the correlation values, the maximum peak point represents the SOH count value corresponding to the current SOH coding sequence, and the decoded SOH count value is stored to locally assist other satellites to carry out combined decoding of the SOH value; when the SOH value is not equal to 999, the current value is represented by the latest SOH counting value of other star decoding in the previous period, the current value is respectively extracted according to the SOH value of the criminal, and the difference value of the counting values before and after the current value is the SOH sequence represented by 1; and finally, carrying out correlation on the received SOH message coding sequence to obtain a maximum peak value, judging the SOH value, and updating the SOH value to the local.

Further, in the step (7), according to the obtained starting positions of the subframes 2 and 3 of the complete frame, the 1728-bit data formed by interleaving the subframes 2 and 3 is deinterleaved to obtain the subframe 2 data of 1200 bits and the subframe 3 data of 528 bits respectively, and then the redundant bits of the subframes 2 and 3 are truncated by the property of LDPC coding to leave information bits.

Further, in the step (7), for a 64-system LDPC (2k, k) row sequence m with a length of 2k_1×2kSequence m 'after removal of redundant bits'_1×kAnd the redundant bit sequence m ″)_1×kAnd original m_1×2kThe relationship of (1) is:

m_1×2k＝[m′_1×k，m″_1×k]

wherein: m'_1×kIs a decoded sequence vector of length k, m ″)₁×_kRedundancy with length k is a row vector; LDPC (2k, k) means that an information codeword with length k is encoded to obtain an information codeword with length 2k, and each codeword represents a 64-ary sequence by 6 binary numbers.

Further, in the step (8), CRC check is performed on the content of the information bit, if the check output is 1, decoding is erroneous, and the start positions of the sub-frames 2 and 3 of the next whole frame are calculated again, so as to perform the above operation; if the check output is 0, the decoding message is correct, and the decoding message is stored so as to read ephemeris data in the following process.

Compared with the prior art, the invention has the following beneficial effects:

the invention can reduce the complexity of the decoded message and improve the efficiency of the decoded message under the condition that the receiver decodes the navigation message in real time, provides an effective scheme for the Beidou B1C receiver to decode the navigation message, and has practical engineering significance.

Drawings

FIG. 1 is a flow chart of frame synchronization and decoding of Beidou B1C signal navigation messages in the present invention;

FIG. 2 is a flow chart of a two component frame synchronization module method of the present invention;

FIG. 3 is a flow chart of a pilot component subcode synchronization algorithm in the present invention;

FIG. 4 is a flowchart of a method for decoding a multi-satellite coherent tone subframe 1 according to the present invention;

FIG. 5 is a flow chart of the subframe 2, 3 message decoding in the present invention;

FIG. 6 is a two-component data synchronization test of the present invention, wherein: FIG. 6(a) is a single data component frame sync; FIG. 6(b) is a pilot component assisted data component frame synchronization;

FIG. 7 is a schematic diagram of the estimated position of the experimental data chip according to the present invention;

fig. 8 illustrates the fast late data determination for sub-frame 1 in the present invention.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1

A Beidou B1C signal navigation message frame synchronization and decoding module comprises a double-component frame synchronization module, a subframe 1 multi-satellite joint modulation decoding module, a subframe 2 and subframe 3 decoding module,

the digital intermediate frequency signals from the Beidou B1C signal receiver antenna are captured to obtain pseudo-random code numbers (PRN numbers), code phases and Doppler frequency initial values captured by the satellite, and the captured results can be used for tracking single data components or tracking double components of the data components and pilot frequency components according to the requirements of the receiver to select set parameters. After setting the tracking component, the receiver tracks the selected component to obtain the output value (I branch) of the instantaneous value of the in-phase branch of the tracking component. In this case, the signal of the in-phase branch immediate value is output, the signal containing the subcode information is represented by the pilot component, and the signal of the encoded navigation data information is represented by the data component. In order to further facilitate obtaining the initial bit position of the navigation message information, the PRN number and the output value of the tracking component I branch are input into a double-component frame synchronization module.

And the double-component frame synchronization module selects frame header synchronization of a data component or pilot frequency component auxiliary data component for frame synchronization according to the PRN, the I branch value of the tracking component and the tracking parameter. And performing the operation of a text decoding module at the frame header starting positions of the sub-frames 1, 2 and 3 obtained by the frame synchronization module. Transmitting the starting and ending positions of the subframe 1 into a multi-satellite joint debugging decoding module to decode and obtain the telegraph text data of the subframe 1; after the subframe 1 is decoded, transmitting the starting and ending positions of the subframes 2 and 3 and the binary navigation message into the subframe 2 and 3 modules for de-interleaving to obtain messages coded by the subframe 2 and the subframe 3; and stripping the LDPC codes of the coded messages of the subframes 2 and 3 through an LDPC redundancy bit removing module, and directly carrying out decoding verification through a CRC (cyclic redundancy check) module to obtain the decoded message information of the subframes 2 and 3.

A Beidou B1C signal navigation message frame synchronization and decoding method comprises the following steps:

step (1), the Beidou receiver B1C converts the Beidou satellite signals received by the antenna into digital intermediate frequency signals after radio frequency front end processing, and provides the digital intermediate frequency signals for a receiver input signal source;

the receiver acquires the visible satellites existing at the present time, and the acquisition code phase and Doppler frequency of the visible satellites through an acquisition algorithm, so that the visible satellites are convenient to follow-up tracking and use;

step (3), the receiver selects to track the data component or pilot frequency component contained in the Beidou satellite according to the user requirement and the carrier-to-noise ratio of the captured signal, when the carrier-to-noise ratio of the captured signal is more than or equal to 40dB-Hz or only the data component is selected to be tracked according to the user requirement, and the parameter of the tracking component is set to be 1; when the carrier-to-noise ratio of the captured signal is less than 40dB-Hz or the running time is not considered, selecting a tracking pilot frequency component and a data component, and setting a tracking component parameter to be 2;

after acquiring tracking component parameters, the receiver performs a tracking process according to the acquired PRN number, code phase and Doppler frequency;

step (5), the PRN number, the tracking component I branch value and the tracking component parameter value are transmitted into a double-component frame synchronization module, and single data component frame synchronization or pilot frequency component auxiliary data component frame synchronization is selected through the tracking component parameter value; when the tracking component parameter is 1, a data component synchronization header sequence pair is generated by the PRN number for 18s or moreFrame header synchronization of data component to obtain sub-frame 1 position P_df1Simultaneously deducing the starting positions of sub-frames 2 and 3 of the nth complete frameAndwhen the tracking component parameter is 2; obtaining data of pilot frequency component in 6s for correlation to obtain a frame data initial position P corresponding to the current data_pnCalculating the starting and stopping positions of the sub-frames 1, 2 and 3 of the nth complete frame period of the data component at the moment And

in particular: in the step (5), the dual component frame synchronization module selects single data component frame synchronization or pilot frequency component auxiliary data component frame synchronization by judging whether the tracking parameter is 1 or not by using the read tracking parameter and PRN information; when the parameter is 1, performing polarity conversion and storage on the acquired 36-second tracking data component, reading a locally generated synchronous frame header matrix F, selecting a 21-bit frame header sequence in the matrix F according to a satellite PRN (pseudo random number), and performing correlation integral operation on the tracking data component to obtain a correlation function of the tracking data component; for the time length of the tracking data component is longer than the time of two continuous frames, namely the frame head sequence of the occurrence of the correlation function obtains a plurality of 21 maximum correlation values with 18s intervals; determining the first maximum correlation value as the first whole frame start position P_df1Calculating the starting positions of sub-frames 2 and 3 of the nth complete frameAndwhen the tracking parameter is not 1, the data component and the pilot frequency component content are obtained, the polarity is converted and stored, then the pilot frequency component subcode synchronization algorithm is carried out on the data of the pilot frequency component 6s after the polarity conversion and the one-cycle complete 1800 bit subcode, and the synchronization bit P is obtained_pnSynchronizing to calculate the start and stop positions of sub-frames 1, 2 and 3 of the nth complete frame periodAnd

in step (5), the local data component synchronization frame header matrix F is as follows, each line is separated by a semicolon, and 1 to 45 lines correspond to the synchronization frame headers of PRN19 to PRN63, respectively:

F＝[010010011001011000001；010011001011000001010；010100100110010110000；010101110100001111011；010110000010100100110；010111010000111101101；011000001010010011001；011001011000001010010；011010101110100001111；011011111100111000100；011100010001101111110；011101000011110110101；011110110101011101000；011111100111000100011；100000101001001100101；100001111011010101110；100010001101111110011；100011011111100111000；100100110010110000010；100101100000101001001；100110010110000010100；100111000100011011111；101000011110110101011；101001001100101100000；101010111010000111101；101011101000011110110；101100000101001001100；101101010111010000111；101110100001111011010；101111110011100010001；110000010100100110010；110001000110111111001；110010110000010100100；110011100010001101111；110100001111011010101；110101011101000011110；110110101011101000011；110111111001110001000；111000100011011111100；111001110001000110111；111010000111101101010；111011010101110100001；111100111000100011011；111101101010111010000；111110011100010001101]。

in the step (5), the calculation formula in the two-component frame synchronization module is as follows:

in the pilot frequency component subcode synchronization algorithm, the output of a local subcode generator NCO is multiplied by a local input 6s data signal which is subjected to FFT and conjugate after being subjected to FFT, the output result is converted into a time domain signal through IFFT, and a modulus value output by the IFFT represents a correlation integral result of the input data and the local subcode; if the peak occurs, it represents the sync bit P of the input 6s data starting in the 18s whole period sub-code_pn。

Step (6), the multi-satellite joint debugging decoding module obtains the initial position of the subframe 1, when the external SOH value is judged to be 999, the decoding is judged to be the first satellite decoding, the data of the subframe 1 is resolved through BCH decoding to obtain SOH information, and the SOH information is stored to the external storage; when the external SOH value is judged not to be 999, namely the decoding of other star subframes 1 is completed, an SOH coding lead-lag sequence can be generated according to the external stored SOH information of other stars and is related to the current SOH value, the SOH value of the maximum peak value judgment coding sequence is obtained, the BCH decoding process is reduced, and the subframe 1 decoding process is completed;

specifically, in the step (6), after the multi-satellite joint tone subframe 1 decoding module acquires the starting position of the subframe 1, PRN code information in the text is removed, and the remaining SOH code sequences representing SOH count values in the subframe 1 are decoded.

The specific step of the step (6) is firstly to read the external SOH count and then to judge; since the range of the SOH count value is 0 to 256, the SOH count value is initialized before the method starts, and the SOH count value initialization value is 999, so that subsequent judgment and updating are facilitated; secondly, when the SOH count value is equal to 999, the first satellite starts to decode the SOH count value, correlation is carried out on the obtained SOH coding sequence value in the telegraph and all sequences generated locally to obtain 256 maximum correlation values, peak point detection is carried out on the correlation values, the maximum peak point represents the SOH count value corresponding to the current SOH coding sequence, and the decoded SOH count value is stored to locally assist other satellites to carry out combined decoding of the SOH value; when the SOH value is not equal to 999, the current value is represented by the latest SOH counting value of other star decoding in the previous period, the current value is respectively extracted according to the SOH value of the criminal, and the difference value of the counting values before and after the current value is the SOH sequence represented by 1; and finally, carrying out correlation on the received SOH message coding sequence to obtain a maximum peak value, judging the SOH value, and updating the SOH value to the local.

Step (7), the deinterlacing module of the sub-frames 2 and 3 obtains the starting and ending positions of the sub-frame 2, and the obtained data block interlaced with the sub-frames 2 and 3 is separated into the coded messages corresponding to the sub-frames 2 and 3, so that each sub-frame can be processed independently; transmitting the encoded telegraph text of the sub-frames 2 and 3 after de-interleaving into an LPDC removing module, and respectively removing redundant data of the sub-frames 2 and 3 bits by the LPDC removing module to leave decoded sub-frame 2 and 3 telegraph text data;

specifically, in the step (7), based on the obtained starting positions of subframes 2 and 3 of the complete frame, 1728-bit data formed by interleaving subframes 2 and 3 are deinterleaved to obtain subframe 2 data of 1200 bits and subframe 3 data of 528 bits, respectively, and then redundant bits of subframes 2 and 3 are truncated to leave information bits.

In the step (7), the64-ary LDPC (2k, k) line sequence m of 2k length_1×2kSequence m 'after removal of redundant bits'_1×kAnd the redundant bit sequence m ″)_1×kAnd original m_1×2kThe relationship of (1) is:

m_1×2k＝[m′1_×k，m″_1×k]

wherein: m'_1×kIs a decoded sequence vector of length k, m ″)_1×kRedundancy with length k is a row vector; LDPC (2k, k) means that an information codeword with length k is encoded to obtain an information codeword with length 2k, and each codeword represents a 64-ary sequence by 6 binary numbers.

Step (8), a CRC (cyclic redundancy check) module is carried out on the subframe 2 and subframe 3 decoded message data in the step (7), if the check is successful, the decoded message data is decoded into correct message data, and if the check is incorrect, the starting and stopping positions of the new message subframes 1, 2 and 3 in the next period are calculated again in the step (5);

specifically, in the step (8), CRC check is performed on the content of the information bits, if the check output is 1, decoding is erroneous, and the start positions of the sub-frames 2 and 3 of the next whole frame are estimated again, so that the above operation is performed; if the check output is 0, the decoding message is correct, and the decoding message is stored so as to read ephemeris data in the following process.

And (9) repeating the circulation steps (2) to (8), continuously obtaining the real-time synchronous message frame head and the decoded message signal of the receiver, storing the navigation message contained in the subframe, and updating the message information.

Description of the simulation

(1) Fig. 6(a) is a correlation result of the frame synchronization of the experimental data component, and fig. 6(b) is an experimental result of the pilot frequency component correlation algorithm. Fig. 6(a) shows that when the 60s data components are synchronized by using the frame headers, 3 maximum correlation peak values with correlation values of 21 are obtained, the interval is 18s, 1524 bits in the data can be judged to be the head of the first complete frame and also the start position of the subframe 1, and the positions of the subframes 2 and 3 can be found to be 1596 bits and 2796 bits respectively by calculation formulas. Fig. 6(b) can obtain 278 bits (i.e. 2.78 seconds) at the start position of the whole sub-code period, i.e. calculate 1524 bits, 1596 bits, 2796 bits at the positions of the whole sub-frames 1, 2, 3 respectively as shown in fig. 7.

Fig. 7 shows the position of the subcode corresponding to the experimental data in fig. 6 (a). The real position of the data corresponds to the 278 th bit of the sub-code of the whole period, and the 1524 th bit of the data corresponds to the beginning position of the sub-frame 1, so that it can be seen that the 6s data at the beginning of the data can accurately judge that the pilot data corresponds to the beginning of the 278 th bit of the sub-code at this moment. According with the experimental result.

(2) The method for decoding the multi-satellite joint modulation subframe 1 is characterized in that the experimental use data can acquire and track the satellites as prn38, 20, 29, 39, 19, 30 and 35. According to the principle of multi-satellite tune, the hour second data of the text of subframe 1 of the satellite prn38 which is tracked for the first time is stored as the current hour second. The SOH count value of this experiment is 115, and when the SOH count value is taken as a reference, the code sequence of BCH (51,8) corresponding to the count values 114 and 116 and the code text sequence corresponding to the current SOH value are respectively obtained, and are correlated with the sub-frame 1SOH data corresponding to the frame header which is synchronized. For the convenience of observation, as shown in fig. 8, the data of count values 2 before and after are selected as the analysis chart, and it can be known that the SOH value of subframe 1 of the satellite to be captured and tracked at this moment has the maximum correlation value with prn38 at the same SOH.

(3) Comparing the decoding method with the traditional correlation method, wherein the decoding method comprises the steps of extracting data for more than 36s in the traditional way, obtaining a frame head through a correlation pilot frequency subcode, and then decoding the subframe 1, and the decoding method comprises the steps of performing traditional de-interleaving, removing LDPC and CRC check on the subframes 2 and 3, and both the decoding methods can decode correct messages. Compared with the traditional decoding method, the multi-satellite joint modulation method omits the PRN number decoding and the SOH calculation in the subframe 1, a group of data is completely decoded from the beginning of the first satellite in each experiment, then the obtained SOH value is stored, and the difference value of the previous and next 18s and the SOH value of the captured satellite at the moment are quickly decoded to improve the speed. 5, 10, 20, 50, 100, 1000 complete experiments were performed, respectively, to obtain the time comparisons as shown in the following table.

It can be found that when the number of experiments becomes longer, namely the running time of the real-time receiver is side length, the multi-satellite joint debugging algorithm can obviously show advantages, and the time is shortened by about 53.6%.

TABLE 1 Algorithm elapsed time detection

At present, methods for synchronizing navigation message frames of new signals and coding in decoded messages are fewer, and research on the aspect of reducing complexity of decoded messages is less. Therefore, the invention can reduce the complexity of the decoded message and improve the efficiency of the decoded message under the condition that the receiver decodes the navigation message in real time, provides an effective scheme for the Beidou B1C receiver to decode the navigation message, and has practical engineering significance.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.