GNSS satellite signal recapturing method and device

Abstract

The invention provides a GNSS satellite signal recapture method and device, and the method comprises the steps: storing a satellite signal parameter in real time when satellite signal tracking completes bit synchronization and a carrier-to-noise ratio is greater than a preset threshold; the satellite signal parameters comprise a storage time value t0, a carrier Doppler value f0 and a bit boundary value b0; wherein t0 and b0 are count values, t0 represents the sampling point count from starting of the GNSS receiver to parameter storage, and b0 represents the sampling point count of the known bit boundary closest to the t0 moment; when the satellite signal is recovered after the satellite signal is unlocked, predicting Doppler and bit boundaries; performing bit boundary accurate search by using the predicted value; and performing Doppler accurate search by using a bit boundary accurate search result. According to the method, by predicting the bit boundary, satellite signal lock losing recapturing is rapidly achieved, bit synchronization is completed at the same time, and conditions are provided for rapid repositioning.

Description

Technical Field

[0001] The present invention relates to the field of GNSS technology, and in particular to a GNSS satellite signal recapture method and device. Background Art

[0002] With the development of satellite navigation technology, GNSS receivers have been widely used in various industries, and at the same time, higher requirements have been placed on the real-time performance and rapid response capabilities of receivers. During operation, the receiver will frequently pass through obstacles such as urban canyons, woods, and the bottom of viaducts, which may cause the signal to be temporarily lost. Even when passing through tunnels, all satellite signals will be completely lost. The loss repositioning time is an important performance indicator of the receiver. The loss repositioning time is mainly composed of the capture time and the telegram bit synchronization time. Therefore, how to quickly recapture the satellite signal after the loss of lock and quickly achieve bit synchronization is one of the difficult problems that GNSS receivers need to solve.

[0003] The satellite signal received by the receiver is a spread spectrum signal with Doppler. The capture module captures the signal in the two-dimensional plane of spread spectrum code phase and Doppler. Bit synchronization is the process of searching for the message bit phase. The general processing process is to first perform a two-dimensional capture search, establish a tracking channel, and then perform a bit synchronization search, which takes a long time.

[0004] The recapture algorithm generally predicts the future code phase and Doppler based on the existing spread spectrum code phase and carrier Doppler frequency values, and uses the predicted Doppler to search near the predicted code phase (such as no more than ±2 chips). The speed is fast, provided that the loss of lock time is short. However, after a long period of loss of lock (such as more than 100 seconds or even longer), the above prediction will fail.

[0005] How to provide a fast and efficient acquisition method to reduce hardware resource usage and improve the first positioning time is a problem that urgently needs to be solved. Summary of the invention

[0006] In view of this, the present invention provides a fast capture method, device and computer storage medium to solve the deficiencies of the prior art.

[0007] The embodiment of the present invention provides a GNSS signal lock recapture method, comprising real-time saving of satellite signal parameters when satellite signal tracking completes bit synchronization and the carrier-to-noise ratio is greater than a preset threshold; the satellite signal parameters include: saving time value t 0 , carrier Doppler value f 0 and bit boundary value b 0 ; where t 0 and b 0 is the count value, t 0represents the sampling point count from when the GNSS receiver is powered on to when the parameters are saved, and b 0 represents the sampling point count of the nearest known bit boundary to the moment of t 0 ;

[0008] When the satellite signal recovers after the satellite signal is lost, the Doppler and bit boundary are predicted;

[0009] Use the predicted value to perform an accurate search for the bit boundary;

[0010] Use the result of the accurate search for the bit boundary to perform an accurate search for the Doppler.

[0011] Furthermore, a bit refers to a bit. For example, a bit of the GPS L1 signal contains 20 spreading cycles and the time is 20 milliseconds (ms). Some satellite signals are modulated with other codes on the bit. For example, the NH code is modulated on the bit of B1I of Beidou, and the NH code is modulated on the L5 pilot channel, the code sequence length is 20, and the length of each chip is 1 ms; the sub - code is modulated on the pilot channel of B1C, the code sequence length is 1800, and the length of each chip is 10 ms; the sub - code is modulated on the E1 pilot channel, the code sequence length is 25, and the length of each chip is 4 ms. When there is coding, these codes are uniformly called sub - codes; at the same time, the "bit" is defined as: when there is no coding modulation, a bit refers to the length of a navigation bit, such as the L1 bit length is 20 ms; when there is coding modulation, a bit refers to a coding cycle, such as the B1I bit length is 20 ms, and the E1 bit length is 100 ms. Define the sub - code sequence as sc i (0 ≤ i < n, n is the sequence length), and the maintenance time length of a single chip of the sub - code is l milliseconds. The bit boundary refers to the sampling point count of the first bit, and at the same time, it is also the first sampling point of the satellite signal spreading code cycle.

[0012] Furthermore, the specific prediction of the Doppler is to use the saved Doppler f 0 as the predicted Doppler value f 1 ; the prediction of the bit boundary refers to predicting the first bit boundary b 1 coming after the specified moment t 1 ; the calculation process is as follows:

[0013] Assign t s = b 0 , calculate the time difference Δt, with the unit of seconds:

[0014] Δt = (t 1 - t s ) / f s

[0015] where f s is the sampling frequency. Continue to update the time difference to an integer multiple of the bit length:

[0016]

[0017] Among them, t b It is the time length of a bit or a subcode period in seconds. fix(·) indicates rounding operation.

[0018] Calculate the ratio r of carrier Doppler and spreading code Doppler:

[0019] r = f Carry / f Code

[0020] Among them, f Code is the spread spectrum code transmission frequency, that is, the spread spectrum code standard code rate, f Carry The satellite signal carrier transmission frequency.

[0021] Calculate the Doppler value f of the spreading code dc :

[0022] f dc =f 1 / r

[0023] Calculate the number of standard sampling points d corresponding to the Δt time 1 :

[0024] d 1 =Δt*f s

[0025] Calculate the correction value Δd of the number of sampling points caused by the spreading code Doppler value:

[0026]

[0027] make

[0028]

[0029] Then we have:

[0030] Δd=f 0 *r 0

[0031] The number of sampling points d corresponding to the predicted time Δt is:

[0032] d=d 1 -Δd

[0033] The prediction results are:

[0034] b 1 =t s +d

[0035] The predicted value d is calculated from the standard value d 1and correction value Δd. The former is proportional to the time Δt. When Δt is determined, d 1 is also certain; the value of Δd is inaccurate because f 1 is a predicted value. Assume that f is allowed 1 The actual value of changes within the time Δt is [f 0 -500,f 0 +500], taking its extreme value as f 0 ±500 and assuming that it changes uniformly, the average Doppler value within Δt time is f 0 ±250, then b 1 The variation range is [ t s+d-250r 0 ,t s +d+250r 0 ].

[0036] Furthermore, performing a precise search for the bit boundary refers to re-searching the bit boundary based on the predicted value.

[0037] Obviously, due to f 1 The predicted value has an error, the bit boundary predicted value b 1 There is also an error in the predicted value of , and it will become larger as Δt increases. Therefore, when Δt is large, it is necessary to adjust the bit boundary b 1 .

[0038] According to the principle of difference and cyclic correlation, as long as the satellite signal bit boundary is guaranteed to exist in the first ms interval of the signal, the subcode can be accurately stripped and the satellite signal can be captured. 1 Should be within 1ms before the actual bit boundary.

[0039] set up Indicates the number of sampling points within 1 millisecond, Δd x =d 1 / 8, represents the number of sampling points in 1 / 8 millisecond, take b s0 =b 1 -Δd x is the starting point of the data, and the Doppler is f 0 , perform parallel search for the spread spectrum code and obtain the spread spectrum code phase.

[0040] Furthermore, the spreading code parallel search process is:

[0041] Strip the satellite sampling data of the carrier frequency f = f i +f 0 , where f i The satellite sampling data center frequency is 2 times the spreading code rate f c (fc =f Code +f dc ) is resampled, the sampling data length is 2 milliseconds, and then FFT operation is performed to obtain the resampled data spectrum s d ; Get the 1 millisecond chip data s before the satellite spread spectrum code that needs to be recaptured c , also perform 2 times code rate sampling, perform FFT and take conjugate to obtain code spectrum data; multiply the two spectrum data and perform IFFT to obtain the correlation result R 0 .

[0042] Here, the 1 millisecond code chip data before the spread spectrum code may be 1023 data, such as L1, B1C, E1, etc., or it may be 2046 data, such as B1I, or it may be 10230 data, such as L5, B3I, E5A, etc.

[0043] Furthermore, when the GNSS satellite signal is lower than a preset value, a differential correlation operation is used to improve the signal-to-noise ratio of signal detection; it is assumed that N differential correlations are performed.

[0044] Calculate the i-th correlation result R i :The starting point of the data is b si =b s0 +i*d 1 , take 2 milliseconds of data, repeat R 0 The calculation process of R i In this process, the last 1 millisecond of the i-1th resampled satellite data is used as the first 1 millisecond of the i-th resampled data; if the satellite code period is m milliseconds, then s c The obtained code chip sequence is the kth 1 millisecond sequence in the code period sequence, mod(i,m) represents the remainder of i modulo m.

[0045] R i Subcode stripping results for:

[0046]

[0047] When the satellite signal does not have a subcode, R i Directly assign to

[0048] The N-times differential coherence calculation is as follows:

[0049]

[0050] Where conj(·) means taking conjugate.

[0051] Furthermore, the parallel search of spreading codes also includes acquisition decision.

[0052] When the maximum value in dR exceeds the preset threshold value Th r When the capture is successful, the code phase C is calculated. r ; Otherwise, the capture is judged as failed.

[0053] Furthermore, performing Doppler precise search specifically includes:

[0054] Assume that the data length used in the precise search of the position boundary is n s Sampling points, let N 0 = l*n is the number of milliseconds contained in a secondary code cycle, and the next upcoming boundary value b is calculated x :

[0055]

[0056] From b x Click to start sampling satellite data, using carrier frequency f and code rate f c The carrier and spread spectrum code are stripped off respectively, and resampled with a resampling frequency of 1000 Hz to obtain the resampled data s i (0≤i <N 0 ).

[0057] Subcode stripping is performed on the resampled data to obtain:

[0058]

[0059] right Perform N f Point FFT operation is performed, the result is modulo and the maximum value is searched, and the frequency value is calculated based on the maximum value position. x , then the precise value of the satellite signal Doppler f 2 for:

[0060] f 2 =f 0 +f x .

[0061] Furthermore, N f Determined by the frequency error; let f 2 The error is not greater than Δf, then:

[0062] 1000 / N f ≤2Δf.

[0063] An embodiment of the present invention provides a GNSS satellite signal recapture device, comprising: a real-time storage unit, a prediction unit and a precise search unit;

[0064] The real-time storage unit is used to save satellite signal parameters in real time when the satellite signal tracking completes bit synchronization and the carrier-to-noise ratio is greater than a preset threshold; the satellite signal parameters include: the storage time value t 0 , carrier Doppler value f 0 and bit boundary value b 0 ; where t 0 and b 0 is the count value, t 0 represents the sampling point count from the time the GNSS receiver is powered on to the time the parameters are saved, and b 0 Indicates distance from 0 The sampling point count of the nearest known bit boundary at the instant;

[0065] The prediction unit is used to predict the Doppler and bit boundaries when the satellite signal is restored after the satellite signal is lost;

[0066] The precise search unit is used to perform a precise bit boundary search using the predicted value and to perform a precise Doppler search using the result of the precise bit boundary search.

[0067] The present invention predicts the bit boundary of the satellite within a certain period of time after losing lock by using the known satellite tracking bit boundary and Doppler value; further adjusts the boundary value so that the prediction ensures that the 0th millisecond of the acquired data must contain the bit boundary; then uses the circular correlation and differential method to accurately search the spread spectrum code boundary with a certain sensitivity; finally uses FFT to accurately calculate the satellite Doppler. The present invention quickly realizes satellite signal loss and recapture by predicting the bit boundary, and simultaneously completes the bit synchronization, providing conditions for rapid repositioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0069] Figure 1 A schematic diagram of a process flow of a rapid capture method provided by an embodiment of the present invention;

[0070] Figure 2 A schematic structural diagram of a rapid capture device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0071] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] The following is an example of a B1I satellite. The embodiment of the present invention provides a method for recapture after a loss of lock, including the following steps:

[0073] S101, when the satellite is in tracking state, when CNR ≥ Th c When t is saved, the satellite parameters are saved. 0 , f 0 , b 0 .

[0074] Satellite signal tracking has completed bit synchronization, and the carrier-to-noise ratio (CNR) is greater than the preset threshold value Th c , real-time save satellite signal parameters t 0 , f 0 , b 0 The satellite signal parameters include: saving time value t 0 , carrier Doppler value f 0 and bit boundary value b 0 ; where t 0 and b 0 is the count value, t 0 represents the sampling point count from the time the GNSS receiver is powered on to the time the parameters are saved, and b 0 Indicates distance from 0 The sampling point count of the nearest known bit boundary at the time. Unless otherwise specified, the sampling point count described below refers to the sampling point count value from the start of the GNSS receiver to the specified time.

[0075] Saving satellite signal parameters means updating and saving satellite signal parameters in real time, that is, as long as the carrier-to-noise ratio (CNR) is greater than the preset threshold value Th c If the conditions are met, save the parameters again.

[0076] S102, check whether the unlock recapture command is received, if not, continue to wait; otherwise, proceed to the next step.

[0077] When the satellite signal is restored after losing the satellite signal lock, the Doppler and position boundaries can be predicted after receiving the lost lock recapture command;

[0078] S103, read the current sampling point count value t according to the instruction 1 , and calculate them in order to predict the Doppler and bit boundaries:

[0079] Doppler prediction is used to save the Doppler f 0 as the predicted Doppler value.

[0080] Bit boundary prediction refers to predicting the specified time t 1 The first bit boundary b that comes after 1 The calculation process is as follows:

[0081] Update time length:

[0082] t s =b 0

[0083] Δt=(t 1 -t s ) / f s

[0084]

[0085] Calculate code Doppler:

[0086] r = f Carry / f Code

[0087] f dc =f 0 / r

[0088] Calculate the count value of the sampling points from the time when the parameters are saved to the predicted bit boundary:

[0089] d=Δt*f s

[0090] Calculate the correction value Δd of the number of sampling points caused by the spreading code Doppler value:

[0091]

[0092] d=d-Δd

[0093] b 1 =t s +d

[0094] The predicted value d is calculated from the standard value d 1 and correction value Δd. The former is proportional to the time Δt. When Δt is determined, d 1 is also certain; the value of Δd is inaccurate because f 1 is a predicted value. Assume that f is allowed 1 The actual value of changes within the time Δt is [f 0 -500,f 0 +500], taking its extreme value as f 0 ±500 and assuming that it changes uniformly, the average Doppler value within Δt time is f0 ±250, then b 1 The variation range is [t s +d-250r 0 ,t s +d+250r 0 ].

[0095] S104, searching the spread spectrum codes in parallel and calculating the precise value of the bit boundary.

[0096] Obviously, due to f 1 The predicted value has an error, the bit boundary predicted value b 1 There is also an error in the predicted value of , and it will become larger as Δt increases. Therefore, when Δt is large, it is necessary to adjust the bit boundary b 1 .

[0097] According to the principle of difference and cyclic correlation, as long as the satellite signal bit boundary is guaranteed to exist in the first ms interval of the signal, the subcode can be accurately stripped and the satellite signal can be captured. 1 Should be within 1ms before the actual bit boundary.

[0098] We advance the bit boundary prediction value by 1 / 8ms.

[0099] set up Indicates the number of sampling points within 1 millisecond, Δd x =d 1 / 8, which means the number of sampling points in 1 / 8 millisecond. is the starting point of the data, and the Doppler is f 0 , perform parallel search for the spread spectrum code and obtain the spread spectrum code phase.

[0100] Set the number of differences to N.

[0101] From b s0 Get the sampled data, use f to strip the carrier frequency of the sampled data, and use f c =f Code +f dc The data is resampled by half a chip, that is, twice the spreading code rate, and the resampled data is used to perform cyclic correlation calculation with the local spreading code to obtain the cyclic correlation result R i (0≤i≤N); In this process, the number of sampling data used is n s ;

[0102] Calculate the i-th (1≤i≤N) correlation result R i :The starting point of the data is b si =b s0 +i*d 1 , take 2 milliseconds of data, repeat R 0The calculation process of R i In this process, the last 1 millisecond of the i-1th resampled satellite data is used as the first 1 millisecond of the i-th resampled data; if the satellite code period is m milliseconds, then s c The obtained code chip sequence is the kth 1 millisecond sequence in the code period sequence, mod(i,m) represents the remainder of i modulo m.

[0103] R i To strip subcodes:

[0104]

[0105] Perform differential coherence calculations:

[0106]

[0107] Search for the maximum value in dR and compare it with the given threshold value Th r If the code phase exceeds the threshold, the capture is considered successful and the code phase value is calculated as C. r ; Otherwise, the capture is considered to have failed and the capture is exited.

[0108] S105. Calculate the accurate Doppler value.

[0109] Calculate the next upcoming bit boundary value b x :

[0110]

[0111] From b x Click to start sampling satellite data, using carrier frequency f and code rate f c The carrier and spread spectrum code are stripped off respectively, and resampled with a resampling frequency of 1000 Hz to obtain the resampled data s i (0≤i <N 0 ).

[0112] Subcode stripping is performed on the resampled data to obtain:

[0113]

[0114] right Perform N f Point FFT operation is performed, the result is modulo and the maximum value is searched, and the frequency value is calculated based on the maximum value position. x , then the precise value of the satellite signal Doppler f 2 for:

[0115] f 2 =f 0 +f x .

[0116] like Figure 2 As shown, an embodiment of the present invention further provides a GNSS satellite signal recapture device, comprising: a real-time storage unit, a prediction unit and a precise search unit;

[0117] The real-time storage unit is used to save satellite signal parameters in real time when the satellite signal tracking completes bit synchronization and the carrier-to-noise ratio is greater than a preset threshold; the satellite signal parameters include: the storage time value t 0 , carrier Doppler value f 0 and bit boundary value b 0 ; where t 0 and b 0 is the count value, t 0 represents the sampling point count from the time the GNSS receiver is powered on to the time the parameters are saved, and b 0 Indicates distance from 0 The prediction unit is used to predict the Doppler and bit boundary when the satellite signal is restored after the satellite signal is lost; the precise search unit is used to use the predicted value to perform a precise bit boundary search and use the result of the precise bit boundary search to perform a precise Doppler search.

[0118] It should be noted that: the GNSS satellite signal recapture device provided in the above embodiment only uses the division of the above program modules as an example when performing capture. In actual applications, the above processing can be assigned to different program modules as needed, that is, the internal structure of the device is divided into different program modules to complete all or part of the processing described above. In addition, the GNSS satellite signal recapture device and the GNSS satellite signal recapture method embodiment provided in the above embodiment belong to the same concept. The specific implementation process is detailed in the method embodiment. The beneficial effects are the same as the method embodiment and will not be repeated here.

[0119] The embodiment of the present invention further provides a computer storage medium, which is a computer-readable storage medium, on which a computer program is stored, and the computer program can be executed by a processor of a GNSS satellite signal recapture device to complete the steps of the aforementioned GNSS satellite signal recapture method. The computer-readable storage medium can be a ferromagnetic random access memory (FRAM), a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a flash memory, a magnetic surface memory, an optical disk, or a compact disc read-only memory (CD-ROM).

[0120] In the several embodiments provided by the present invention, it should be understood that the disclosed methods and intelligent devices can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as: multiple units or components can be combined, or can be integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the components shown or discussed can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0121] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A GNSS satellite signal recapture method, characterized in that: include: When the satellite signal tracking completes bit synchronization and the carrier-to-noise ratio is greater than the preset threshold, the satellite signal parameters are saved in real time; The satellite signal parameters include: a saving time value t0, a carrier Doppler value f0 and a bit boundary value b0; wherein t0 and b0 are count values, t0 represents a sampling point count from when the GNSS receiver is turned on to when the parameters are saved, and b0 represents a sampling point count of a known bit boundary closest to time t0; When the satellite signal is restored after the satellite signal is lost, the Doppler and bit boundaries are predicted; Use the predicted value to perform accurate bit boundary search; The result of the bit boundary precise search is used to perform Doppler precise search.

2. The method according to claim 1, characterized in that The bit boundary refers to the count of the first sampling point of a bit and is also the first sampling point of the satellite signal spreading code period; when there is no coding modulation in the satellite signal, a bit refers to the length of a navigation bit; when there is coding modulation in the satellite signal, a bit refers to a coding period; when there is coding modulation, these codings are uniformly referred to as sub-codes; the sub-code sequence is defined as sc i , where 0 ≤ i < n, n is the sequence length, the duration of a single chip of the sub-code is l seconds, and a sub-code period is t b = l * n.

3. The method according to claim 1, characterized in that The Doppler prediction is to use the saved Doppler f0 as the predicted Doppler value f1; the bit boundary prediction is to predict the first bit boundary b1 that arrives after the specified time t1; the calculation process is as follows: Assign t s = b0, calculate the time difference Δt, in seconds: Δt = (t1-t s ) / f s Among them, f s is the sampling frequency; the time difference continues to be updated to be an integer multiple of the bit length: Among them, t b is the time length of a bit or a subcode period in seconds, and fix(·) indicates rounding operation; Calculate the ratio r of carrier Doppler and spreading code Doppler: r=f Carry / f Code Among them, f Code is the spread spectrum code transmission frequency, that is, the spread spectrum code standard code rate, f Carry is the satellite signal carrier transmission frequency; Calculate the Doppler value f of the spreading code dc : f dc =f1 / r Calculate the number of standard sampling points d1 corresponding to the Δt time: d1=Δt*f s Calculate the correction value Δd of the number of sampling points caused by the spreading code Doppler value: make Then we have: Δd=f0*r0 The number of sampling points d corresponding to the predicted time Δt is: d=d1-Δd The prediction results are: b1=t s +d The predicted value d consists of the standard value d1 and the corrected value Δd. The former is proportional to the time Δt. When Δt is determined, d1 is also determined. The value of Δd is inaccurate because f1 is a predicted value. When the actual value of f1 is allowed to vary within the Δt time range [f0-L, f0+L], its extreme value is f0±L and it is assumed to vary uniformly, then the average Doppler value within the Δt time is Then the range of b1 is 4. The method according to claim 1, characterized in that The use of the predicted value to perform accurate bit boundary search specifically includes: Advance the bit boundary prediction value by 1 / 8ms: Indicates the number of sampling points within 1 millisecond, Δd x =d1 / 8, which means the number of sampling points in 1 / 8 millisecond, take b s0 =b1-Δd x Take f0 as the starting point of the sampling data, take the Doppler as f0, perform parallel search for the spread spectrum code, and obtain the spread spectrum code phase.

5. The method according to claim 4, characterized in that The parallel search of the spreading codes specifically includes: Strip the satellite sampling data of the carrier frequency f = f i +f0, where f i The satellite sampling data center frequency is 2 times the spreading code rate f c Resample, where f c =f Code +f dc , the sampling data length is 2 milliseconds, and then FFT operation is performed to obtain the resampled data spectrum s d ; Get the 1 millisecond chip data s before the satellite spread spectrum code that needs to be recaptured c , similarly perform 2 times code rate sampling, perform FFT and take conjugate to obtain code spectrum data; multiply the two spectrum data and perform IFFT to obtain the correlation result R0.

6. The method according to claim 5, characterized in that When the GNSS satellite signal is lower than the preset value, differential correlation operation is used to improve the signal-to-noise ratio of signal detection; The differential correlation operation process is as follows: Calculate the i-th correlation result R i :The starting point of the data is b si =b s0 +i*d1, take 2 milliseconds of data, repeat the calculation process of R0, and get R i ; In this process, the last 1 millisecond of the i-1th resampled satellite data is used as the first 1 millisecond of the i-th resampled data; if the satellite code period is m milliseconds, then s c The obtained chip sequence is the kth = mod(i,m)+1 1 millisecond sequence in the code period sequence, where mod(i,m) represents the remainder of i modulo m; R i Subcode stripping results for: When the satellite signal does not have a subcode, sc k Take 1 and directly change R i Directly assign to N times differential coherence calculation results Where conj(·) means taking conjugate.

7. The method according to claim 6, characterized in that The parallel search of the spreading codes also includes acquisition decision; When the maximum value in dR exceeds the preset threshold value Th r When the capture is successful, the code phase C is calculated. r ; Otherwise, the capture is judged as failed.

8. The method according to claim 1, characterized in that The Doppler precise search specifically includes: Assume that the data length used in the precise search of the position boundary is n s Sampling points, let N0 = l*n be the number of milliseconds contained in a secondary code cycle, calculate the next upcoming boundary value b x : From b x Click to start sampling satellite data, using carrier frequency f and code rate f c The carrier and spread spectrum code are stripped off respectively, and resampled with a resampling frequency of 1000 Hz to obtain the resampled data s i (0≤i <N0); Subcode stripping is performed on the resampled data to obtain: right Perform N f Point FFT operation is performed, the result is modulo and the maximum value is searched, and the frequency value is calculated based on the maximum value position. x , then the satellite signal Doppler precise value f2=f0+f x .

9. The method according to claim 8, characterized in that N f Determined by the frequency error; assuming the error of f2 is not greater than Δf, then: 1000 / N f ≤2Δf.

10. A GNSS satellite signal recapture device, characterized in that: include: Real-time storage unit, prediction unit and precise search unit; The real-time storage unit is used to save satellite signal parameters in real time when satellite signal tracking completes bit synchronization and the carrier-to-noise ratio is greater than a preset threshold; the satellite signal parameters include: a saving time value t0, a carrier Doppler value f0 and a bit boundary value b0; wherein t0 and b0 are count values, t0 represents a sampling point count from when the GNSS receiver is turned on to when the parameters are saved, and b0 represents a sampling point count of a known bit boundary closest to time t0; The prediction unit is used to predict the Doppler and bit boundaries when the satellite signal is restored after the satellite signal is lost; The precise search unit is used to perform a precise bit boundary search using the predicted value and to perform a precise Doppler search using the result of the precise bit boundary search.

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