CN113009522A - Long-time coherent integration capturing algorithm module for Doppler frequency residual error correction - Google Patents

Long-time coherent integration capturing algorithm module for Doppler frequency residual error correction Download PDF

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CN113009522A
CN113009522A CN202110170670.8A CN202110170670A CN113009522A CN 113009522 A CN113009522 A CN 113009522A CN 202110170670 A CN202110170670 A CN 202110170670A CN 113009522 A CN113009522 A CN 113009522A
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CN113009522B (en
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高法钦
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Zhejiang University of Technology ZJUT
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/254—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to Doppler shift of satellite signals

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Abstract

The invention relates to a signal coarse synchronization module of a satellite receiving device. The long-time pre-coherent integration acquisition algorithm for Doppler frequency residual error correction and carrier phase alignment is provided, and the usability of the receiver in a weak signal environment is improved. The technical scheme is as follows: a long-time coherent integration capturing algorithm module for Doppler frequency residual correction comprises a Doppler frequency offset correction module (comprising a block superposition and phase compensation module, a spectral peak detection module and a storage and table look-up module which are connected in sequence), a residual correction module, a bit flip estimation module, a storage module, a table look-up module and a text removal module which are connected in sequence; meanwhile, after being connected with the local carrier generation adjusting module, the residual error correcting module is connected with the text removing module in parallel and then is connected to the multiplier module for processing, and then enters the FFT module.

Description

Long-time coherent integration capturing algorithm module for Doppler frequency residual error correction
Technical Field
The invention relates to a signal coarse synchronization module of a satellite receiving device, namely a long-time coherent integration acquisition algorithm module with Doppler frequency residual error correction.
Background
Global navigation satellite positioning system (GNSS) is a satellite-based radio navigation system that provides all-weather real-time navigation and positioning services, and has been applied to various fields of national economy. At present, the GPS system which is the earliest global positioning system to be researched and developed and applied in the global scope is widely applied in China, and the Beidou system which is independently researched and developed in China is built in 6 months in 2020 and provides global navigation positioning service.
The GNSS satellite transmitted signals are weak enough to reach a ground GNSS receiver, for example, the GPS signals are about-130 dBmW, which is 20-30 dB lower than the internal thermal noise of the receiver. In particular, in complex environments such as indoors, cities, forests, etc., GNSS reception signal-to-noise ratios are lower, and these are just the main environments for human activities.
Local decoding of a GNSS receiver requires a local carrier signal having the same frequency and phase as the received signal and a pseudo-random spreading code (pseudo code for short) signal. Due to the influence of factors such as doppler effect, the frequency of the GNSS signal actually received and its pseudo code phase have uncertainty. Therefore, the local signal needs to be synchronized with the received signal through a synchronization process such as acquisition and tracking. GNSS signal acquisition is a two-dimensional search of the pseudo-code phase space and the carrier frequency space. The longer the coherent accumulation time, the smaller the doppler frequency search step. The frequency search step size is usually required to be satisfied
Figure BDA0002938821330000011
The search step of the pseudo code phase is less than 1/2 chips, where TcohThe duration is accumulated for the pre-coherent integration of the acquisition algorithm.
When the pre-coherent integration accumulation time of the acquisition algorithm exceeds 20ms, the carrier frequency search step cannot be larger than 50Hz, and for the Doppler frequency variation range of about +/-10 kHz in satellite signals, a smaller search step means that the search frequency is increased, and the time consumption of the search algorithm is remarkably increased.
The results of literature investigations show that: estimating and removing the bit reversal and compressing the Doppler frequency variation range is the key for realizing long-time pre-coherent integration capture, and accurately correcting carrier phase drift caused by factors such as local carrier frequency error is the key for improving the sensitivity of the long-time pre-coherent integration capture.
Literature investigations have shown that long term pre-coherent integration is the preferred method to further improve the gain of the acquisition process. At present, although relevant documents already exist at home and abroad to research a high-sensitivity acquisition algorithm of a GNSS signal, certain research work has been done on the aspects of high-sensitivity acquisition, rapid acquisition algorithm modeling and the like, if a double-Division Block Zero Padding (DBZP) algorithm and a multi-stage coherent accumulation acquisition algorithm are proposed in the documents, the accumulation time is sufficiently prolonged, but the algorithm consumes a lot of time and is difficult to popularize and apply, square loss and doppler frequency residual errors are still main factors influencing the acquisition performance in an environment with an extremely low signal-to-noise ratio, and the two aspects of the acquisition sensitivity and the acquisition efficiency are difficult to be considered simultaneously.
Disclosure of Invention
The invention aims to overcome the defects of the background technology, provides a long-time pre-coherent integration acquisition algorithm for Doppler frequency residual error correction and carrier phase alignment, and improves the usability of a receiver in a weak signal environment.
The technical scheme provided by the invention is as follows:
a long-time coherent integration capturing algorithm module for Doppler frequency residual correction comprises a Doppler frequency offset correction module (comprising a block superposition and phase compensation module, a spectral peak detection module and a storage and table look-up module which are connected in sequence), a residual correction module, a bit flip estimation module, a storage module, a table look-up module and a text removal module which are connected in sequence; meanwhile, after the residual error correction module is connected with the local carrier generation adjustment module, the residual error correction module and the text removal module are connected in parallel to the multiplier module for processing and then enter the FFT module;
the local pseudo code generating module is connected with the conjugate FFT module in sequence and then is connected with the output of the FFT module in parallel to be accessed into the multiplier module for processing; and after the processing result is output, the processing result sequentially enters an IFFT module and a threshold judgment module, then the captured signal is output, and the processing result is accessed to a local carrier generation and adjustment module.
The output end of the Doppler frequency offset correction module group is also connected with the input end of the bit flipping estimation module, and the Doppler frequency estimation value is used for assisting in predicting the pseudo code phase; on the basis, the bit reversal estimation module estimates and eliminates the influence of the bit reversal of the navigation message, and finally, the capture sensitivity is improved in a mode of obtaining signal processing gain through long-time coherent accumulation.
The Doppler frequency offset correction module group and the bit flipping estimation module only operate once in the GNSS receiver capturing process.
When the GNSS signal is very weak and the pre-coherent integration time is more than 20 milliseconds, the residual correction module operates the Doppler frequency residual correction algorithm, so that the Doppler frequency estimation precision is further improved, the processing gain of the pre-coherent integration is improved, and the capture sensitivity is finally improved.
The doppler frequency residual error correction algorithm is:
dividing a GNSS intermediate frequency input signal with the time length of T milliseconds into M subblocks with the length of N after being squared, and dividing a local carrier squared signal considering the Doppler frequency into M subblocks with the length of N. Then, the squared input signal and the local signal are subjected to a correlation operation by using fast Fourier transform, and the correlation result is set as YkFor M correlation results YkDifferential accumulation is performed and the maximum of the following calculations is searched:
Figure BDA0002938821330000031
| | represents the modulo operation, and for the maximum value, the doppler frequency error is calculated as follows:
Figure BDA0002938821330000032
using the result to estimate the carrier Doppler frequency
Figure BDA0002938821330000033
And (3) correcting:
Figure BDA0002938821330000034
when the GNSS signal is very weak and the pre-coherent integration time is longer than 20 milliseconds, a carrier phase alignment algorithm is operated to improve the processing gain of the pre-coherent integration.
The carrier phase alignment algorithm is as follows:
estimating error signals using doppler frequency
Figure BDA0002938821330000035
Calculating carrier phase shift caused by Doppler frequency shift in long-time coherent integration accumulation time:
I) experiment and simulation analysis: firstly, estimating the Doppler frequency f of the tracking loop of the GNSS receivertraAs the true Doppler frequency in the signal, the true frequency f of the input GNSS intermediate frequency sampling signal IGIFS can be calculatedIGIFS，fIGIFS＝fIF+ftra+nerr1Doppler frequency estimated by the algorithm of the invention
Figure BDA0002938821330000041
Calculating to obtain the carrier frequency of the local signal
Figure BDA0002938821330000042
Then, the frequency error between the input signal and the local carrier signal is calculated, and the carrier phase error Pha is calculated by the following formuladif；
Figure BDA0002938821330000043
II) carrier phase error analysis modeling; the change of the carrier phase error has an obvious trend, and a function relation curve of the local carrier phase error changing along with Doppler frequency estimation error and time length is obtained through a polynomial fitting modeling method;
III) carrier Doppler frequency estimation error obtained by residual error correction algorithm of Doppler frequency
Figure BDA0002938821330000044
And as input, estimating and correcting the phase error of the carrier, aligning the input signal with the local signal in a mode of inserting/removing a local signal sampling point, and realizing the function by a local carrier generation and adjustment module.
Aiming at a GNSS navigation user end receiver system, the efficiency of a capture algorithm is improved through an algorithm of Doppler frequency estimation and correction (realized by a Doppler frequency offset correction module group), the limit of coherent integration time is broken through the algorithm of navigation message bit flip estimation and correction, the signal processing gain of the capture algorithm is improved through the algorithm of Doppler frequency residual error correction and carrier phase alignment, and finally a long-time coherent integration capture algorithm module is designed. The invention can adaptively adjust the coherent integration time according to the signal environment, improve the sensitivity performance of the receiver and simultaneously consider the efficiency of the acquisition algorithm. When the signal is shielded, the environmental noise is large and the receiver is in a motion state, the GNSS receiver using the method can also stably give a positioning result.
The invention overcomes the defects of Doppler frequency, pseudo code phase drift and motion in long-time coherent integration accumulation, which causes pseudo code correlation peak envelope broadening and reduction, and the like, and can enable a GNSS receiver to automatically estimate the Doppler frequency and correct the residual error, estimate and correct the influence of navigation message bit overturning, correct carrier phase drift and improve the usability of the receiver under weak signals. The performance of the receiver is obviously improved compared with the common high-sensitivity GNSS receiver no matter in low signal-to-noise ratio or dynamic application.
The long-time coherent integration capturing algorithm module for Doppler frequency residual error correction provided by the invention has the beneficial effects that the GNSS signals can be normally received under the condition that the signals are shielded or certain environmental interference is caused, and the efficiency and the sensitivity of GNSS signal high-sensitivity GNSS signal capturing are improved through algorithms such as Doppler frequency estimation and correction, Doppler frequency estimation residual error correction, carrier phase alignment and the like; by designing a navigation message bit-flipping estimation and correction algorithm (realized by combining a bit-flipping estimation module, a storage module, a search module, a message removal module and the like), the time length of pre-coherent integration is increased, the weak signal capturing sensitivity of the GNSS is further improved, the performance of the GNSS receiver is obviously improved compared with that of a common high-sensitivity GNSS receiver, and the GNSS receiver can keep normal work in a dynamic application environment with low signal-to-noise ratio.
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FIG. 1 is a constitutional structural view of the present invention.
Fig. 2 is a schematic diagram of a phase compensation adjustment frequency scheme according to the present invention.
Fig. 3 is a schematic diagram of carrier phase deviation caused by doppler frequency estimation error in the present invention.
Fig. 4a1 and 4a2 are schematic diagrams of the pre-coherent integration output and captured detection amount using the present invention.
Fig. 4B1 and 4B2 are schematic diagrams of the output of pre-coherent integration and the captured detection amount without the present invention.
FIG. 5 is a block diagram of a GNSS receiver.
Fig. 6 is a flowchart of a specific algorithm for acquiring a satellite signal.
Detailed Description
The following further description is made with reference to the embodiments shown in the drawings.
The invention realizes a capture algorithm which can estimate the bit reversal of the navigation message and only adopts coherent addition to realize long-time accumulation; firstly, a carrier Doppler frequency offset estimation and correction algorithm is designed, and the search range of the carrier Doppler frequency offset is compressed, so that the complexity of a capture algorithm is reduced. Then, the estimation of the navigation message bit reversal is realized by utilizing a grouping coherent calculation method, and the influence of the navigation message bit reversal on the signal accumulation gain is cancelled. Secondly, when the coherent integration is accumulated and exceeds the bit length of the navigation message, the influence of the accumulated data phase synchronization error caused by small frequency drift on the accumulated gain cannot be ignored; the invention discloses a scheme for estimating the residual error by using the information according to the phase difference information of adjacent data blocks which is certainly contained in the grouping difference accumulation result, improves the coherent accumulation gain and the capturing sensitivity of the GNSS signals, reduces the coherent loss and improves the signal processing gain of the coherent integration accumulation. And finally, designing a long-time coherent accumulation algorithm to complete the acquisition of the signal. The functional block diagram of the present invention is shown in fig. 1.
In a mode of adopting a Doppler frequency estimation-compressed carrier frequency search space-fast acquisition algorithm, the calculation process of the GNSS signal acquisition assisted by the Doppler frequency offset correction module group comprises the following steps: the GNSS intermediate frequency sampling signal is used as an input signal, and the input data is subjected to block superposition (block superposition and phase compensation module) according to the time-frequency transformation relation of the time domain broadening corresponding to the frequency domain compression) Compressing the Doppler frequency fdSearching a range, estimating Doppler frequency and storing the result in a lookup table Acqb; when capturing satellite signals, a record is taken from the table Acqb, and the Doppler frequency is obtained from the record
Figure BDA0002938821330000061
(or the frequency of the IGIFS) estimate, two quadrature local carriers of different phases are generated, multiplied by the input signal (represented by the circled plus x in the multiplication block diagram) to produce the I branch signal and the Q branch signal, which is orthogonal to it. Then the I branch and the Q branch are combined into a complex input signal and are subjected to Fourier transform (FFT module), the complex input signal is multiplied by the result of the local C/A code after the complex input signal is subjected to conjugate Fourier transform (conjugate FFT module), the result is converted into a time domain through inverse Fourier transform (IFFT module), an absolute value is obtained, a correlation value between the input signal and the local signal is obtained, and finally whether the signal is captured or not is judged by searching a maximum correlation value. The method is the same as a common GNSS signal code domain parallel acquisition algorithm except that the frequency uncertainty range is reduced to 20Hz from +/-10 KHz and the navigation message bit jumps. The process flow shown in fig. 1 completes the GNSS signal acquisition calculation.
The Doppler frequency offset correction module group estimates the Doppler frequency and compresses the scheme of frequency search space. Firstly, the block superposition operation is carried out, on one hand, the signal-to-noise ratio of the signal can be improved, on the other hand, the block superposition is carried out on the input data based on the signal processing correlation theory of the time domain expansion corresponding to the frequency domain compression, the operation widens the time domain, the frequency domain is compressed, and therefore the Doppler frequency fdIs narrowed, compressing the range of acquisition algorithm frequency search. Then, a set of adjusting frequencies delta f is selected to obtain a set of phase compensation sequences
Figure BDA0002938821330000071
Wherein, TsFor a sampling period, n is an integer, and the input GNSS intermediate frequency sampling data r (-) is multiplied by the sequence β (n), and the result is represented by r% (-). And dividing the frequency search space at equal intervals by a phase compensation method, and further compressing the frequency search space. E.g. selecting 20 equally spaced tuning frequencies, forIn response to the different result r% (-), the frequency corresponding to the maximum responder is the estimated doppler frequency offset, and the frequency uncertainty range is further reduced, as shown in fig. 2.
A basic scheme for navigation message bit flip estimation. Selecting the data length as TIStarting from the first pseudo-code period signal, the data of (T) is calculated with the interval of 1 pseudo-code period and the duration of TI-1) correlation calculations. And then, processing and analyzing the calculation result, and obtaining the moment when the telegraph text bit jumps based on a mode of searching the minimum value point. When the bit reversal occurs at the middle position participating in coherent accumulation calculation data, the numerical value of the coherent accumulation result is minimum (obviously smaller than the average value), and accordingly, a data block with the bit reversal is found out, and the subsequent data block is correspondingly processed according to the reversal condition, so that the influence of the bit reversal of the navigation message is eliminated.
In order to improve the GNSS signal capturing sensitivity by increasing the method of the pre-coherent integration time CIT, the invention discloses a Doppler frequency residual error correction algorithm and a carrier phase alignment algorithm.
The doppler frequency residual error correction algorithm is:
when long-time coherent accumulation is performed, the influence of accumulated data phase synchronization errors caused by small frequency drift on the accumulated gain cannot be ignored. Based on the inference that the grouping difference accumulation result contains the phase difference information of the adjacent data blocks, the invention discloses a scheme for estimating the Doppler frequency estimation residual error by using the information so as to improve the coherent accumulation gain and the capture sensitivity, and the scheme idea is as follows:
dividing a GNSS intermediate frequency input signal with the time length of T milliseconds into M subblocks with the length of N after being squared, and dividing a local carrier squared signal considering the Doppler frequency into M subblocks with the length of N. Then, the squared input signal and the local signal are subjected to a correlation operation by using fast Fourier transform, and the correlation result is set as YkFor M correlation results YkDifferential accumulation is performed and the maximum of the following calculations is searched:
Figure BDA0002938821330000081
| | represents the modulo operation, and for the maximum value, the doppler frequency error is calculated as follows:
Figure BDA0002938821330000082
using the result to estimate the carrier Doppler frequency
Figure BDA0002938821330000083
And (3) correcting:
Figure BDA0002938821330000084
the corrected result reduces the influence of the Doppler frequency estimation residual on the acquisition performance and improves the accuracy of the Doppler frequency estimation.
See fig. 3; estimating error signals using doppler frequency
Figure BDA0002938821330000088
And calculating the carrier phase drift caused by the Doppler frequency shift in the long-time coherent integration accumulation time, and reducing the error by a modeling correction method (running a carrier phase alignment algorithm).
The carrier phase alignment algorithm is as follows:
simulation analysis: setting the Doppler frequency f of the tracking loop estimatetraThe true Doppler frequency of the signal is obtained by calculating the true frequency f of the signalIGIFS，fIGIFS＝fIF+ftra+nerr1Doppler frequency estimated by the algorithm of the invention
Figure BDA0002938821330000085
Calculating the frequency of the local signal
Figure BDA0002938821330000086
Then, the frequency error between the input signal and the local carrier signal is calculated by the following formulaOut-of-carrier phase error Phadif。
Figure BDA0002938821330000087
The simulation is performed according to the method described in the above formula, and the phase error curve of the local carrier is described with reference to fig. 3.
In fig. 3, the abscissa represents the coherent integration accumulation time CIT, and the ordinate represents the carrier phase deviation. It can be seen that the variation of the carrier phase error has a significant trend. The function relation curve of the local carrier phase error changing along with the Doppler frequency estimation error and the time length can be obtained by a polynomial fitting modeling method, namely the Doppler frequency shift residual error estimated from the function relation curve
Figure BDA0002938821330000091
As input, carrier phase error is estimated and corrected, and input (GNSS intermediate frequency) signals are aligned with local signals by inserting/removing local signal sampling points, improving coherent integration accumulation gain.
The influence of the doppler frequency estimation accuracy on the coherent integration accumulation duration and the acquisition sensitivity is shown in fig. 4a1, 4a2, 4B1 and 4B2 as a simulation analysis result.
The simulation analysis result of the influence of the Doppler frequency estimation precision and the coherent integration accumulation time length on the pre-coherent integration accumulation is shown in the figure. The abscissa is the coherent integration accumulation time CIT, and the ordinate is the carrier phase deviation (where the ordinate in fig. 4a2 is the captured detected quantity ADV: defined as the ratio of the maximum value to the second largest value of the correlation output result); each curve corresponds to the simulation results of a different PRN encoded satellite signal.
The two graphs of fig. 4a1 and fig. 4a2 correspond to an acquisition algorithm using frequency domain search, the doppler frequency estimation accuracy is high, and the frequency error between the input signal IGIFS and the local signal is less than 1.8Hz, for example, when acquiring a satellite signal with PRN being 18, the frequency error is less than 0.5Hz (compared with the tracked carrier frequency). The smaller the frequency error is, the lower the rate of the phase error increasing with time is, the longer the coherent integration output (coherent integration output) can be kept rising, and further the sensitivity of GNSS signal acquisition can be improved as much as possible by increasing the coherent integration time CIT. As can be seen from these two graphs, the satellite signal coherent integration output (coherent integration output) and the acquisition decision ADV of PRN 18,22 keep rising when CIT is less than 250 ms.
The corresponding capturing algorithms of fig. 4B1 and fig. 4B2 do not use a frequency domain searching method, that is, the estimated carrier doppler frequency value is directly used to generate the local carrier signal, the correction accuracy of the corresponding carrier doppler frequency is low, and the frequency error between the IGIFS and the local signal is more than 2Hz in many cases. When CIT >120ms, the coherent integration accumulation output may drop as CIT rises, meaning that increasing CIT cannot continue to improve acquisition sensitivity.
The position of the GNSS signal acquisition algorithm module of the present invention in the GNSS receiver (prior art, structure see fig. 5) is shown in fig. 5; the GNSS receiver consists of a radio frequency front end, a baseband signal processing module and a navigation positioning resolving module. The baseband signal processing module comprises signal capturing, tracking, decoding, navigation message extraction and other sub-modules. The GNSS signal captures and roughly estimates the pseudo code phase and the carrier Doppler frequency, and the signal tracking module realizes accurate estimation of the pseudo code phase and the carrier Doppler frequency so as to realize despreading and demodulation of the GNSS signal. The decoding and message extracting module obtains navigation messages through Viterbi decoding, satellite ephemeris information and pseudorange measurement information at the current moment are obtained, and the navigation positioning resolving module uses the ephemeris information and the measured pseudorange and pseudorange rate information to achieve navigation positioning resolving.
Referring to fig. 6, the calculation process for capturing a GNSS satellite signal is: after Doppler frequency estimation and residual error compensation, generating a local carrier signal, multiplying the local carrier signal by the input signal without the navigation message, and then performing Fourier transform FFT to obtain a result Pa; adjusting the pseudo code rate by using the Doppler frequency estimation value, generating a local C/A code and carrying out conjugate Fourier transform, and recording the result as Pb; and converting the result of multiplying Pa by Pb into a time domain through inverse Fourier transform IFFT to obtain a correlation b value between the input signal and the local signal. It is decided whether or not the signal is captured by searching for the maximum correlation value.
Except for the residual error correction module and the local carrier generation adjustment module, all other modules (such as a block superposition and phase compensation module, a spectral peak detection module, a storage module, a table look-up module, a storage and table look-up module, a bit flipping estimation module, a text removal module and the like) adopted in the invention are the prior art. In the local carrier generation adjusting module, a carrier phase alignment algorithm is added on the basis of the prior art such as carrier generation.

Claims (7)

1. A long-time coherent integration capturing algorithm module for Doppler residual error correction comprises a Doppler frequency offset correction module group, a residual error correction module, a bit flip estimation module, a storage module, a table look-up module and a message removal module which are sequentially connected; meanwhile, after the residual error correction module is connected with the local carrier generation adjustment module, the residual error correction module and the text removal module are connected in parallel to the multiplier module for processing and then enter the FFT module;
the local pseudo code generating module is connected with the conjugate FFT module in sequence and then is connected with the output of the FFT module in parallel to be accessed into the multiplier module for processing; the processing result sequentially enters an IFFT module and a threshold judgment module after being output, then the captured signal is output, and the local carrier generation and adjustment module is accessed;
the Doppler frequency offset correction module comprises a block superposition and phase compensation module, a spectral peak detection module and a storage and table look-up module which are sequentially connected.
2. The Doppler residual error corrected long-term coherent integration acquisition algorithm module according to claim 1, wherein the output end of the Doppler frequency offset correction module group is further connected to the input end of the bit flipping estimation module, and the Doppler frequency estimation value is used for auxiliary prediction of the pseudo code phase; on the basis, the bit flipping estimation module estimates and eliminates the influence of the bit flipping of the navigation message; and finally, the acquisition sensitivity is improved in a mode of acquiring signal processing gain through long-time coherent accumulation.
3. The doppler residual corrected long time coherent integration acquisition algorithm module of claim 2, wherein: the Doppler frequency offset correction module group and the bit flipping estimation module only operate once in the GNSS receiver capturing process.
4. The Doppler residual corrected long time coherent integration acquisition algorithm module of claim 3, wherein: when the GNSS signal is very weak and the pre-coherent integration time is more than 20 milliseconds, the residual correction module operates the Doppler frequency residual correction algorithm, so that the Doppler frequency estimation precision is further improved, the processing gain of the pre-coherent integration is improved, and the capture sensitivity is finally improved.
5. The Doppler residual corrected long time coherent integration acquisition algorithm module of claim 4, wherein: the doppler frequency residual error correction algorithm is:
dividing a GNSS intermediate frequency input signal with the time length of T milliseconds into M subblocks with the length of N after being squared, and dividing a local carrier squared signal considering the Doppler frequency into M subblocks with the length of N. Then, the squared input signal and the local signal are subjected to a correlation operation by using fast Fourier transform, and the correlation result is set as YkFor M correlation results YkDifferential accumulation is performed and the maximum of the following calculations is searched:
Figure FDA0002938821320000021
| | represents the modulo operation, and for the maximum value, the doppler frequency error is calculated as follows:
Figure FDA0002938821320000022
using the result to estimate the carrier Doppler frequency
Figure FDA0002938821320000023
And (3) correcting:
Figure FDA0002938821320000024
6. the Doppler residual corrected long time coherent integration acquisition algorithm module of claim 5, wherein: when the GNSS signal is very weak and the pre-coherent integration time is longer than 20 milliseconds, a carrier phase alignment algorithm in the local carrier generation adjusting module is operated to improve the processing gain of the pre-coherent integration.
7. The doppler residual corrected long term coherent integration acquisition algorithm module of claim 6, wherein: the carrier phase alignment algorithm is as follows:
estimating error signals using doppler frequency
Figure FDA0002938821320000025
Calculating carrier phase shift caused by Doppler frequency shift in long-time coherent integration accumulation time:
I) experiment and simulation analysis: firstly, estimating the Doppler frequency f of the tracking loop of the GNSS receivertraAs the true Doppler frequency in the signal, the true frequency f of the input GNSS intermediate frequency sampling signal IGIFS can be calculatedIGIFS，fIGIFS＝fIF+ftra+nerr1Doppler frequency estimated by the algorithm of the invention
Figure FDA0002938821320000026
Calculating to obtain the carrier frequency of the local signal
Figure FDA0002938821320000027
Then, the frequency error between the input signal and the local carrier signal is calculated, and the carrier phase error Pha is calculated by the following formuladif；
Figure FDA0002938821320000031
II) carrier phase error analysis modeling; the change of the carrier phase error has an obvious trend, and a function relation curve of the local carrier phase error changing along with Doppler frequency estimation error and time length is obtained through a polynomial fitting modeling method;
III) carrier Doppler frequency estimation error obtained by residual error correction algorithm of Doppler frequency
Figure FDA0002938821320000032
And as input, estimating and correcting the phase error of the carrier, aligning the input signal with the local signal in a mode of inserting/removing a local signal sampling point, and realizing the function by a local carrier generation and adjustment module.
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CN114553656A (en) * 2022-02-21 2022-05-27 西安电子科技大学 Weak signal capturing method based on unequal-length double-block zero-filling algorithm
CN115144877A (en) * 2022-06-23 2022-10-04 上海德寰通信技术有限公司 Satellite signal acquisition method and device, ground terminal and medium

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