A fast acquisition method of low earth orbit navigation enhancement MCSK signal

Abstract

The application discloses a kind of low orbit navigation enhancement MCSK signal fast acquisition method, MCSK signal includes high-speed message signal and low-speed message signal, the total number of code period of the MCSK signal is N, the number of code period of the low-speed message signal is nlow;N>nlow;Specifically includes the following steps: step one, initialization frequency search index, frequency search carrier NCO control information and the satellite number to be captured, and initialization processing is carried out to the acquisition and storage of baseband signal based on MBZP scheme;Step two, acquisition, storage and reading baseband signal;Acquisition baseband signal, baseband signal is stored and read according to MBZP scheme;Step three, baseband signal frequency adjustment: from MCSK signal system characteristics, by setting local time domain signal, can guarantee that sampling time and Doppler does not exist under any combination of peak problem, and coherent correlation loss, guarantee the accuracy of acquisition result.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of satellite navigation, and relates to a fast acquisition method of a low-orbit navigation enhanced MCSK signal. BACKGROUND

[0002] With the vigorous development of low-orbit satellite constellations, especially the proposal of a low-orbit giant Internet constellation plan represented by Starlink, positioning, navigation and timing (PNT) services based on low-orbit satellite constellations have gradually become a research hotspot. Low-orbit satellite constellations and medium-high-orbit navigation satellite constellations can form an advantage complementation, providing a new idea for breaking through the performance bottleneck of PNT services. The PNT service based on a low-orbit satellite constellation mainly utilizes the fast geometric configuration change of a low-orbit satellite to broadcast a special low-orbit navigation enhanced signal, so as to realize the improvement of the PPP convergence speed. Unlike a traditional satellite navigation signal, a star network low-orbit navigation enhancement designs and uses a new signal system, i.e., a multiplexed code shift keying (MCSK), in orbit.

[0003] The MCSK adopts two components: one component mainly supports high-precision carrier measurement (measurement component), and the other component mainly supports high-information-rate broadcasting (data component). For the ranging component, no data is modulated or only low-speed messages are modulated, and a direct spread spectrum modulation mode same as GNSS is adopted. For the data component, a CSK modulated signal is adopted. The CSK is a multi-ary information modulated signal, and different code initial phases are used to modulate information, which is generally denoted as CSK(U, R), U represents the number of bits modulated by each CSK symbol, therefore, the number of different code initial phases used is 2U, and R represents the number of code periods lasting for each CSK symbol. The MCSK signal is a signal generated by adopting code period time division multiplexing of the above measurement component and data component.

[0004] The capture is a rough estimation of code phase and carrier frequency of the navigation signal, is the first synchronization process of the receiver and the navigation signal, and is a prerequisite for the receiver to position. The traditional navigation capture algorithm includes serial code phase capture and parallel code phase capture. The former can realize accurate phase estimation by correlating the input signal with the locally reproduced target signal, but its code phase dimension is serial calculation, time overhead is large, and is gradually replaced by parallel code phase capture in the traditional GNSS scene. When applied to the low-orbit navigation scene, the number of target satellites increases sharply, the satellite visible time shortens, and the availability of serial code phase capture is further reduced. The parallel code phase capture is based on the corresponding relationship between the time domain correlation process and the spectrum multiplication, and uses FFT operation to realize parallel output of code phase correlation results. The patent "GPS signal capture method and system" (application number: CN20121012835) and the like propose to eliminate the correlation loss caused by data bit flipping by extending the length and form of the locally reproduced signal based on double block zero padding (DBZP) and its variant, but the above method is only applicable to traditional GNSS signals, and when applied to MCSK signals, not only there is correlation loss, but also in the extreme case, a stable peak error is introduced, which makes the MCSK signal unable to be correctly synchronized, and the receiver loses the positioning ability. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to provide a fast capture method for low-orbit navigation enhanced MCSK signals, so as to solve the technical problems of slow capture speed and low accuracy of capture results in the prior art when capturing signals in the low-orbit navigation enhanced scene.

[0006] In order to solve the above technical problems, the technical scheme is adopted as follows:

[0007] A fast capture method for low-orbit navigation enhanced MCSK signals, the MCSK signal includes high-speed message signal and low-speed message signal, the total number of code periods of the MCSK signal is N, and the number of code periods of the low-speed message signal is nlow; nlow

[0008] Step one, initializing the frequency search index, the frequency search carrier NCO control information and the satellite number to be captured, and initializing the acquisition and storage of the baseband signal based on the MBZP scheme;

[0009] Step two, acquiring, storing and reading the baseband signal;

[0010] Acquiring the baseband signal, and storing and reading the baseband signal according to the MBZP scheme;

[0011] Step three, frequency adjustment of the baseband signal:

[0012] The baseband signal read in step two is down-converted by using the frequency search carrier NCO control information provided by the capture control module to obtain a frequency-adjusted baseband signal S base_I_i (n) and S base_Q_i (n);

[0013] Step four, generating local frequency domain signals SI(n) and SQ(n) of the satellite to be captured according to the MBZP scheme;

[0014] Step five, performing correlation operation on the frequency-adjusted baseband signal S base_I_i (n) and S base_Q_i (n) obtained in step three and the MBZP-based local frequency domain signals SI(n) and SQ(n) obtained in step four to obtain a correlation result S corr_I_i (n) and

[0015] Step six, performing two-level correlation result processing on the correlation result S corr_I_i (n) and obtained in step five to obtain a first-level correlation result Sncorr1(n) and a second-level correlation result S NCcorr2 (n);

[0016] Step seven, comparing a decision threshold V TH2 with the second-level correlation result S NCcorr2 (n) obtained in step six to determine the capture result;

[0017] The capture result includes satellite number, satellite frequency Doppler, capture signal start time information, capture signal code phase M index2 and capture signal cycle start bit estimation value M index1 *f s *T+

[0018] M index2 .

[0019] Step two specifically includes the following steps:

[0020] Step 2.1, sampling and storing the baseband signal according to the stored instructions, taking the local millisecond pulse as the start, and recording the time information Tstamp corresponding to the sampling start time;

[0021] The baseband signal storage length is not less than [N×N n +1]f s T;

[0022] Wherein:

[0023] N nrepresents the number of accumulations;

[0024] f s represents the sampling rate;

[0025] T represents the code period;

[0026] Step 2.2, continuously read the baseband signal of length N C according to the reading instruction;

[0027] N C ≥ [N+1]f s T

[0028] (i-1)Nf s T+1≥N n ;

[0029] wherein:

[0030] (i-1)Nf s T+1 represents the starting position of the i-th reading data.

[0031] Step three specifically comprises the following steps:

[0032] Step 3.1, generating a sine sequence and a cosine sequence based on the frequency search carrier NCO control information of step one;

[0033] The length of the sine sequence and the cosine sequence is not less than N C ;

[0034] Step 3.2, multiplying the sine sequence and the cosine sequence obtained in step 3.1 with the baseband signal read in step 2 respectively, to obtain the frequency-adjusted baseband signal S base_I_i (n) and S base_Q_i (n).

[0035] Step four specifically comprises the following steps:

[0036] Step 4.1, generating a local time domain signal C'(n);

[0037] The length of the local time domain signal C'(n) is N C =2x, wherein

[0038] Step 4.2, segmenting [N+1]f s T of the local time domain signal of step 4.1 with f s T as the segmentation length, to obtain N+1 local time domain signal segments;

[0039] Step 4.3, adding a code period of the pseudo code sequence C m (nm ), the rest of the local time domain signal segment is zero, to get the local time domain signal c(n), wherein c1(n1) ~ c N+1 (n N+1 ) cannot have two identical non-zero sequences and at least one non-zero sequence;

[0040] The pseudo code sequence C m (n m ) is generated by satellite number and pseudo code NCO control information control;

[0041]

[0042] Wherein:

[0043] n m = n - (m-1)f s T;

[0044] Step 4.4, the local time domain signal c(n) obtained in step 4.3 is subjected to fast Fourier transform, to generate the local frequency domain signal SI(n) and SQ(n) based on MBZP;

[0045] SI(n)+jSQ0(n)=FFT[c(n)]

[0046] SQ(n)=-SQ0(n)。

[0047] Step five specifically includes the following steps:

[0048] Step 5.1, the frequency adjusted baseband signal S base_l_i (n) and S base_Q_i (n) obtained in step three are subjected to fast Fourier transform, to obtain the frequency domain sequence Sib_i(n) and SQb_i(n) of the frequency adjusted baseband signal;

[0049] Sib_i(n)+jSQb_i(n)=FFT[S base_I_i (n)+S base_Q_i (n)]

[0050] Step 5.2, the frequency domain sequence Sib_i(n) and SQb_i(n) of the frequency adjusted baseband signal obtained in step 5.1 are subjected to correlation operation with the local frequency domain signal SI(n) and SQ(n) based on MBZP obtained in step four, to obtain the frequency domain information SIR_i(n) and SQR_i(n) of the correlation result:

[0051] SIR_i(n)=SIb_i(n)×SI(n)-SQb_i(n)×SQ(n)

[0052] SQR_i(n) = SIB_i(n) x SQ(n) + SQB_i(n) x SI(n)

[0053] Step 5.3, inverse Fourier transform the frequency domain information of the correlation result obtained in step 5.2 to obtain the correlation result S corr_I_i (n) and jS corr_Q_i (n) ;

[0054] S corr_l_i (n) + jS corr_Q_i (n) = IFFT [SIR_i(n) + j SQR_i(n)].

[0055] Step six specifically comprises the following steps:

[0056] Step 6.1, perform first level correlation result processing on the correlation result S corr_I_i (n) and jS corr_Q_i (n) obtained in step five according to the following formula to obtain the first level correlation result Sncorr1(n) ;

[0057]

[0058] T n1 represents the number of accumulations;

[0059] Step 6.2, determine whether the value of nlow of the MCSK signal to be captured is 1, if yes, proceed to step six, if no, proceed to step 6.3;

[0060] Step 6.3, perform second level correlation result processing on the first level correlation processing result Sncorr1(n) obtained in step 6.1 according to the following formula to obtain the second level correlation result S NCcorr2 (n) ;

[0061]

[0062] wherein:

[0063] T n2 represents the number of accumulations, T n2 = N + 1;

[0064] Step seven specifically comprises the following steps:

[0065] Step 7.1, record and store S NCcorr2 (n), determine whether the current frequency search index has completed all searches, if yes, proceed to step 7.2, if no, update the current frequency search index, update the frequency search carrier NCO control information based on the current frequency search index, and return to step one;

[0066] Step 7.2, determine S NCcorr2 Is the maximum value of (n) greater than V? TH2 If yes, the capture is successful, and the capture result is obtained. Proceed to step one. If no, proceed directly to step one.

[0067] The acquisition results include satellite number, satellite frequency Doppler, acquisition signal start time information, and acquisition signal code phase M. index2 and the start bit M of the capture signal period index1 *f s *T+M index2 ;

[0068] In step 7.2, the capture result obtained includes the start bit M of the capture signal period. index1 *f s *T+M index2 The acquisition method includes the following steps:

[0069] S1, with f s T represents the spacing pair S NCcorr2 The maximum value corresponds to the Sncorr1 value corresponding to the frequency search index, which is then segmented. The maximum value of each Sncorr1 segment is related to the decision threshold V. TH1 By comparison, the symbol sequence S is obtained. S (q):

[0070]

[0071] S2, for the symbol sequence S S (q) and its first term S S(1) Processing yields S S1 (q);

[0072]

[0073] S2, for S S1 (q) Calculate the estimated value Mindex1 of the start position of the acquisition signal period using the following formula, which is the start position M of the acquisition signal period. index1 *f s *T+M index2 ;

[0074] M index1 =find(S S1 (m+1)=1and S S1 (m)=0)-1.

[0075] Compared with the prior art, the beneficial technical effects of this invention are:

[0076] (I) The present application is based on MCSK signal system characteristics, through setting local time domain signal, the sampling time and Doppler can be guaranteed without missing peak problem in any combination, and coherent correlation loss, the accuracy of the acquisition result is guaranteed.

[0077] (II) The present application introduces the correlation result of local time domain signal, so that the acquisition can not only output the acquisition signal code phase and satellite frequency Doppler, but also output the acquisition signal cycle start bit estimate value, speed up the conversion of capture and tracking, and improve the acquisition speed. BRIEF DESCRIPTION OF DRAWINGS

[0078] Figure 1 The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0079] Figure 2 The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0080] Figure 3 The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0081] Figure 4 The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0082] Figure 5 The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0083] The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme. DETAILED DESCRIPTION

[0084] It should be noted that all the components in the present application, in the absence of special instructions, are known components in the art.

[0085] The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0086] The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0087] The present application discloses a low-orbit navigation enhanced MCSK signal fast acquisition scheme.

[0088] Collecting the baseband signal, and storing and reading the baseband signal according to the MBZP scheme;

[0089] Step three, frequency adjustment of the baseband signal:

[0090] The baseband signal read in step two is subjected to frequency down conversion processing by using the frequency search carrier NCO control information provided by the capture control module, so as to obtain the frequency-adjusted baseband signal S base_I_i (n) and S base_Q_i (n);

[0091] Step four, generating the local frequency domain signals SI(n) and SQ(n) of the satellite to be captured according to the MBZP scheme;

[0092] Step five, performing correlation operation on the frequency-adjusted baseband signal S base_I_i (n) and S base_Q_i (n) obtained in step three and the MBZP-based local frequency domain signals SI(n) and SQ(n) obtained in step four, so as to obtain the correlation results S corr_I_i (n) and

[0093] Step six, performing two-level correlation result processing on the correlation results S corr_I_i (n) and obtained in step five, so as to obtain the first-level correlation result Sncorr1(n) and the second-level correlation result S NCcorr2 (n);

[0094] Step seven, comparing the decision threshold V TH2 with the second-level correlation result S NCcorr2 (n) obtained in step six, so as to obtain the capture result;

[0095] The capture result includes satellite number, satellite frequency Doppler, capture signal start time information, capture signal code phase M index2 and capture signal cycle start bit estimation value M index1 *f s *T+M index2 .

[0096] In the above technical scheme, starting from the MCSK signal system characteristics, the local time domain signal is set, so that the sampling time and Doppler do not exist the problem of missing peaks under any combination, and the coherent correlation loss is guaranteed, so that the accuracy of the capture result is guaranteed.

[0097] The correlation result of the local time domain signal is introduced, so that the capture can not only output the capture signal code phase and satellite frequency Doppler, but also output the capture signal cycle start bit estimation value, so as to accelerate the capture conversion and improve the capture speed.

[0098] Step two specifically comprises the following steps:

[0099] Step 2.1, according to the storage instruction, taking the local millisecond pulse as the starting point, sampling and storing the baseband signal, and recording the time information Tstamp corresponding to the sampling starting time;

[0100] The length of the baseband signal storage is not less than [N x N n + 1]f s T;

[0101] Wherein:

[0102] N n represents the number of accumulations;

[0103] f s represents the sampling rate;

[0104] T represents the code period;

[0105] Step 2.2, according to the read instruction, continuously reading the baseband signal with a length of N C ;

[0106] N C ≥ [N + 1]f s T

[0107] (i-1)Nf s T+1≥N n ;

[0108] Wherein:

[0109] (i-1)Nf s T+1 represents the starting position of the i-th reading data.

[0110] Step three specifically comprises the following steps:

[0111] Step 3.1, based on the frequency search carrier NCO control information of step one, generating sine sequence and cosine sequence;

[0112] The length of the sine sequence and the cosine sequence is not less than N C ;

[0113] Step 3.2, multiplying the sine sequence and cosine sequence obtained in step 3.1 with the baseband signal read in step 2 respectively, to obtain the frequency adjusted baseband signal S base_I_i (n) and S base_Q_i (n).

[0114] Step four, specifically comprising the following steps:

[0115] Step 4.1, generating a local time domain signal C'(n);

[0116] The length of the local time-domain signal C'(n) is N C =2x, where

[0117] Step 4.2, with f s T is the segmentation length for the [N+1]f of the local time-domain signal in step 4.1. s T is segmented to obtain N+1 local time domain signal segments;

[0118] Step 4.3: Add a pseudo-code sequence C of the satellite to be acquired for one code period to at least one local time-domain signal segment obtained in step 4.2. m (n m The remaining local time domain signal segments are set to zero to obtain the local time domain signal c(n), where c1(n1)~c N+1 (n N+1 A sequence cannot have two identical non-zero sequences and must have at least one non-zero sequence.

[0119] Pseudocode sequence C m (n m It is generated under the control of satellite number and pseudocode NCO control information;

[0120]

[0121] in:

[0122] n m =n-(m-1)f s T;

[0123] Step 4.4: Perform a Fast Fourier Transform on the local time domain signal c(n) obtained in Step 4.3 to generate local frequency domain signals SI(n) and SQ(n) based on MBZP.

[0124] SI(n) + jSQ0(n) = FFT[c(n)]

[0125] SQ(n) = -SQ0(n).

[0126] Step five specifically includes the following steps:

[0127] Step 5.1, adjust the frequency of the baseband signal S obtained in step three. base_l_i (n) and S base_Q_i Perform a fast Fourier transform on (n) to obtain the frequency domain sequences Sib_i(n) and SQb_i(n) of the baseband signal after frequency adjustment;

[0128] Sib_i(n) + jSQb_i(n) = FFT[S base_I_i (n)+S base_Q_i (n)]

[0129] Step 5.2, correlating the frequency domain sequences Sib_i(n) and SQb_i(n) of the frequency adjusted baseband signal obtained in step 5.1 with the MBZP based local frequency domain signals SI(n) and SQ(n) obtained in step four to obtain the frequency domain information of the correlation results SIR_i(n) and SQR_i(n) :

[0130] SIR_i(n) = SIb_i(n) * SI(n) - SQb_i(n) * SQ(n)

[0131] SQR_i(n) = SIb_i(n) * SQ(n) + SQb_i(n) * SI(n)

[0132] Step 5.3, performing inverse Fourier transform on the frequency domain information of the correlation results obtained in step 5.2 to obtain the correlation results S corr_I_i (n) and jS corr_Q_i (n) ;

[0133] S corr_I_i (n) + jS corr_Q_i (n) = IFFT [SIR_i(n) + j SQR_i(n)].

[0134] Step six specifically comprises the following steps:

[0135] Step 6.1, performing first level correlation result processing on the correlation results S corr_I_i (n) and jS corr_Q_i (n) obtained in step five according to the following formula to obtain the first level correlation results Sncorr1(n) :

[0136]

[0137] T n1 represents the number of accumulations;

[0138] Step 6.2, judging whether the value of nlow of the MCSK signal to be captured is 1, if yes, entering step six, if no, entering step 6.3;

[0139] Step 6.3, performing second level correlation result processing on the first level correlation processing results Sncorr1(n) obtained in step 6.1 according to the following formula to obtain the second level correlation results S NCcorr2 (n) ;

[0140]

[0141] wherein:

[0142] T n2 represents the number of accumulations, Tn2 =N+1.

[0143] Step seven specifically includes the following steps:

[0144] Step 7.1, record and store S NCcorr2 (n), determine whether the current frequency search index has completed the entire search. If yes, proceed to step 7.2. If no, update the current frequency search index, update the frequency search carrier NCO control information based on the current frequency search index, and return to step one.

[0145] Step 7.2, determine S NCcorr2 Is the maximum value of (n) greater than V? TH2 If yes, the capture is successful, the capture result is obtained, and the process proceeds to step one; otherwise, proceed directly to step one.

[0146] The acquisition results include satellite number, satellite frequency Doppler, acquisition signal start time information, and acquisition signal code phase M. index2 and the start bit M of the capture signal period index1 *f s *T+M index2 ;

[0147] In step 7.2, the capture result obtained includes the start bit M of the capture signal period. index1 *f s *T+M index2 The acquisition method includes the following steps:

[0148] S1, with f s T represents the spacing pair S NCcorr2 The maximum value corresponds to the Sncorr1 value corresponding to the frequency search index, which is then segmented. The maximum value of each Sncorr1 segment is related to the decision threshold V. TH1 By comparison, the symbol sequence S is obtained. S (q):

[0149]

[0150] S2, for the symbol sequence S S (q) and its first term S S(1) Processing yields S S1 (q);

[0151]

[0152] S2, for S S1 (q) Calculate the estimated value Mindex1 of the start position of the acquisition signal period using the following formula, which is the start position M of the acquisition signal period. index1 *f s *T+M index2 ;

[0153] M index1 = find(S S1 (m+1) = 1 and S S1 (m) = 0) - 1.

[0154] Embodiment:

[0155] This embodiment uses the above-mentioned fast acquisition method of low-orbit navigation enhancement MCSK signal to acquire MCSK(U, 2, 1) signal, as shown in the following formula: Figure 5 Figure 5 The corresponding relationship between the local reference signal and each sampling time is depicted taking MCSK(U, 2, 1) as an example. It can be seen that the signal local recurrence 1 code period low-speed measurement component is used for correlation with the target low-speed measurement component in the input signal to form a correlation peak, recurrence nlow code period 0 is used to eliminate the correlation loss introduced by the low-speed message flip of the measurement component, and further N-nlow code period 0 is used for the correlation between the high-speed message component and the local low-speed measurement component to eliminate the correlation loss. It is based on the above process that the accuracy of the correlation peak is guaranteed regardless of the sampling time, and no coherent correlation loss is introduced. The present application realizes fast acquisition based on the fft framework, and further by selecting N+1 signals to be acquired and adding them to N+1 local signals, parallel search of different satellites can be realized, further improving the acquisition speed.​

Claims

1. A fast acquisition method of a low earth orbit navigation augmentation MCSK signal, characterized in that, The MCSK signal includes high-speed text signal and low-speed text signal, the total number of code periods of the MCSK signal is N, and the number of code periods of the low-speed text signal is nlow; nlow Step one, initialize the frequency search index, the frequency search carrier NCO control information and the satellite number to be captured, and initialize the acquisition and storage of the baseband signal based on the MBZP scheme; Step two, acquire, store and read the baseband signal; Acquire the baseband signal, and store and read the baseband signal according to the MBZP scheme; Step three, frequency adjustment of the baseband signal: The frequency search carrier NCO control information obtained in step one is used to down-convert the baseband signal read in step two, and a baseband signal S after frequency adjustment is obtained base_I_i (n) and S base_Q_i (n); Step four, generate the local frequency domain signals SI(n) and SQ(n) of the satellite to be captured according to the MBZP scheme; Step 4.1, generate the local time domain signal C'(n); The length of the local time domain signal C'(n) is N C = 2x, where N C is the length of the baseband signal; Step 4.2, f s T is the segment length of the [N+1]f s T local time domain signal in step 4.1, and the N+1 local time domain signal segments are obtained by segment processing. f s denotes the sampling rate; T denotes the code period; Step 4.

3. Adding a code period of the pseudo-code sequence C of the satellite to be captured in at least one of the local time domain signal segments obtained in step 4.2 m (n m ), and the rest of the local time domain signal segments are set to zero, obtaining the local time domain signal c(n), wherein c1(n1) ~ c N+1 (n N+1 ) cannot have two identical non-zero sequences and at least one non-zero sequence; The pseudo code sequence C m (n m ) is generated by satellite number and pseudo code NCO control information control; Wherein: n m = n - (m - 1)f s T; Step 4.4, perform fast Fourier transform on the local time domain signal c(n) obtained in step 4.3 to generate the local frequency domain signals SI(n) and SQ(n) based on MBZP; SI(n)+jSQ0(n)=FFT[c(n)] SQ(n)=-SQ0(n); Step five, the frequency adjusted baseband signal S obtained in step three is used base_I_i (n) and S base_Q_i (n) and corr_I_i (n) and Step six, the correlation results S corr_I_i (n) and Two levels of correlation results are processed to obtain first level correlation results Sncorr1(n) and second level correlation results S NCcorr2 (n); Step seven, a decision threshold V is adopted TH2 the second level related result S obtained in step six NCcorr2 (n) comparison judgment, capture result is obtained; The capture result includes satellite number, satellite frequency Doppler, capture signal start time information, capture signal code phase M index2 and capture signal cycle start bit M index1 *f s *T+M index2 ; where f s represents a sampling rate; T represents a code period; M index1 represents a signal period start bit estimate.

2. The method for fast acquisition of low earth orbit navigation augmentation MCSK signals as recited in claim 1 wherein, Step two specifically includes the following steps: Step 2.1, according to the storage instruction, taking the local millisecond pulse as the starting point, sampling and storing the baseband signal, and recording the time information Tstamp corresponding to the sampling starting time; The baseband signal storage length is not less than [N x N n +1]f s T; Wherein: N n represents the number of accumulations; f s denotes the sampling rate; T represents the code period; Step 2.2, continuously read the baseband signal of length N according to the read instruction; C ; N C ≥[N+1]f s T (i-1) Nf s T+1≥N n ; Wherein: (i-1) Nf s T+1 indicates the start position of the i-th reading data.

3. The method for fast acquisition of low earth orbit navigation augmentation MCSK signals as recited in claim 2 wherein, Step three specifically includes the following steps: Step 3.1, generate sine and cosine sequences based on the frequency search carrier NCO control information in step one; The length of the sine sequence and the cosine sequence are both not less than N C ; Step 3.2, the sine sequence and the cosine sequence obtained in step 3.1 are multiplied with the baseband signal read in step 2 respectively, to obtain the frequency-adjusted baseband signal S base_I_i (n) and S base_Q_i (n).

4. The method for fast acquisition of low earth orbit navigation augmentation MCSK signals as recited in claim 1 wherein, Step five specifically includes the following steps: Step 5.1, adjust the frequency of the baseband signal S obtained in step three. base_I_i (n) and S base_Q_i Perform a fast Fourier transform on (n) to obtain the frequency domain sequences Sib_i(n) and SQb_i(n) of the baseband signal after frequency adjustment; Sib_i(n) + jSQb_i(n) = FFT[S base_I_i (n) + S base_Q_i (n)] Step 5.2, perform correlation operation on the frequency domain sequences Sib_i(n) and SQb_i(n) of the frequency-adjusted baseband signal obtained in step 5.1 and the local frequency domain signals SI(n) and SQ(n) based on MBZP obtained in step four, to obtain the frequency domain information SIR_i(n) and SQR_i(n) of the correlation result: SIR_i(n)=SIb_i(n)×SI(n)-SQb_i(n)×SQ(n) SQR_i(n)=SIb_i(n)×SQ(n)+SQb_i(n)×SI(n) Step 5.

3. Inverse Fourier transform is performed on the frequency domain information of the correlation result obtained in step 5.2 to obtain the correlation result S corr_l_i (n) and jS corr_Q_i (n); S corr_I_i (n)+jS corr_Q_i (n) = IFFT[SIR_i(n) + j SQR_i(n)].

5. The method for fast acquisition of low earth orbit navigation augmentation MCSK signals as recited in claim 1, wherein, Step six specifically includes the following steps: Step 6.

1. The correlation results S obtained in step five are processed in a first level correlation process according to the following equation to obtain first level correlation results Sncorr1(n) corr_I_i (n) and jS corr_Q_i (n) are processed in a first level correlation process according to the following equation to obtain first level correlation results Sncorr1(n) T n1 represents the number of accumulations; Step 6.2, judge whether the value of nlow of the MCSK signal to be captured is 1, if yes, go to step six, if not, go to step 6.3; Step 6.

3. The first level correlation processing result Sncorr1(n) obtained in step 6.1 is processed to obtain a second level correlation result Sncorr2(n) according to the following equation: NCcorr2 (n); Wherein: T n2 denotes the number of accumulations, T n2 = N + 1.

6. The method for fast acquisition of low earth orbit navigation augmentation MCSK signals as recited in claim 1 wherein, Step seven specifically includes the following steps: Step 7.1, record and store S NCcorr2 (n), determine if the current frequency search index has completed all searches, if so, proceed to step 7.2, if not, update the current frequency search index, update the frequency search carrier NCO control information based on the current frequency search index, and return to step one; Step 7.2, judging S NCcorr2 (n) is greater than V TH2 , if yes, the capture is successful, the capture result is obtained, and step 1 is entered, if no, step 1 is directly entered; The capture result includes satellite number, satellite frequency Doppler, capture signal start time information, capture signal code phase M index2 and capture signal cycle start bit M index1 *f s *T+M index2 .

7. The method for fast acquisition of low earth orbit navigation augmentation MCSK signals as recited in claim 6 wherein, In the capture result obtained in Step 7.2, the capture signal cycle start bit M index1 *f s *T+M index2 The acquisition method comprises the following steps: S1, with f s T is the spacing on S NCcorr2 The maximum value of each segment of Sncorr1 is compared with the decision threshold V TH1 The symbol sequence S S (q): S2, the symbol sequence S S (q) and the first item S S(1) is processed to obtain S S1 (q); S2, to S S1 (q) performing a calculation according to the following equation to obtain an estimated value Mindexl of the acquisition signal period start bit, i.e. the acquisition signal period start bit M index1 *f s *T+M index2 ; M index1 = find(S S1 (m+1) = 1 and S S1 (m) = 0) - 1.

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