CN113009522B - Long-time coherent integration capturing algorithm module for Doppler frequency residual error correction - Google Patents

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 acquisition algorithm module for Doppler frequency residual correction

Technical Field

The invention relates to a signal coarse synchronization module of a satellite receiving device, namely a long-time coherent integration capture algorithm module with Doppler frequency residual error correction.

Background Art

The Global Navigation Satellite System (GNSS) is a satellite-based radio navigation system that can provide all-weather real-time navigation and positioning services and has been applied to various fields of the national economy. At present, the GPS system, the earliest global satellite positioning system developed and applied in the world, has been widely used in my country. my country's independently developed global satellite positioning system Beidou system was completed in June 2020 and provides global navigation and positioning services.

The GNSS satellite transmission signal is already quite weak when it reaches the ground GNSS receiver. For example, the GPS signal is about -130dBmW, which is 20-30dB lower than the internal thermal noise of the receiver. In particular, the GNSS reception signal-to-noise ratio is even lower in complex environments such as indoors, cities, and forests, which are precisely the main environments for human activities.

伪码相位的搜索步长小于1/2码片，其中，T_coh为捕获算法的预相干积分累加时长。The local decoding of the GNSS receiver requires a local carrier signal and a pseudo-random spread spectrum code (pseudo-code for short) signal with the same frequency and phase as the received signal. Due to the influence of factors such as the Doppler effect, the frequency of the actual received GNSS signal and its pseudo-code phase are uncertain. Therefore, it is necessary to synchronize the local signal with the received signal through synchronization processes such as capture and tracking. GNSS signal capture is a two-dimensional search process of pseudo-code phase space and carrier frequency space. The longer the coherent accumulation time, the smaller the Doppler frequency search step size. The frequency search step size is usually required to meet

The search step of the pseudo code phase is less than 1/2 chip, where T _coh is the pre-coherent integration accumulation time of the acquisition algorithm.

When the pre-coherent integration accumulation time of the acquisition algorithm exceeds 20ms, the carrier frequency search step cannot be greater than 50Hz. For the Doppler frequency variation range of about ±10kHz in the satellite signal, a smaller search step means an increase in the number of searches and a significant increase in the time spent on the search algorithm.

The results of literature survey show that estimating and removing bit flips and compressing the Doppler frequency variation range are the key to achieving long-term pre-coherent integration capture, and accurately correcting the carrier phase drift caused by factors such as local carrier frequency error is the key to improving the sensitivity of long-term pre-coherent integration capture.

Literature research shows that long-term pre-coherent integration is the preferred method to further improve the acquisition processing gain. At present, although there are relevant literatures at home and abroad that study the high-sensitivity acquisition algorithm of GNSS signals, and some research work has been done in high-sensitivity acquisition and fast acquisition algorithm modeling, such as the double block zero padding (DBZP) algorithm and the multi-level coherent accumulation acquisition algorithm proposed in some literatures, which fully extend the accumulation time, the algorithm is time-consuming and difficult to promote and apply. The square loss and Doppler frequency residual are still the main factors affecting the acquisition performance in extremely low signal-to-noise ratio environments, and it is difficult to take into account both the capture sensitivity and the capture efficiency at the same time.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a long-term pre-coherent integration capture algorithm for Doppler frequency residual correction and carrier phase alignment to improve the availability of the receiver in a weak signal environment.

The technical solution provided by the present invention is:

A long-time coherent integration capture algorithm module for Doppler frequency residual correction comprises a Doppler frequency deviation correction module (including a block superposition and phase compensation module, a spectrum peak detection module, and a storage and table lookup module connected in sequence), a residual correction module, a bit flip estimation module, a storage module, a table lookup module, and a message removal module; at the same time, after the residual correction module is connected to a local carrier generation adjustment module, it is connected in parallel with the message removal module to a multiplier module for processing and then enters an FFT module;

The local pseudo code generation module is connected in sequence to the conjugate FFT module and then connected to the multiplier module in parallel with the output of the FFT module for processing; after the processing result is output, it enters the IFFT module and the threshold judgment module in sequence, outputs the captured signal, and is connected to the local carrier generation adjustment module.

The output end of the Doppler frequency offset correction module group is also connected to the input end of the bit flip estimation module, and the Doppler frequency estimation value is used to assist in predicting the pseudo code phase; on this basis, the bit flip estimation module estimates and eliminates the influence of the navigation message bit flip, and finally, the capture sensitivity is improved by obtaining the signal processing gain through long-term coherent accumulation.

The Doppler frequency offset correction module group and the bit flip estimation module are only run once during the GNSS receiver acquisition process.

When the GNSS signal is very weak and the pre-coherent integration time is greater than 20 milliseconds, the residual correction module runs the Doppler frequency residual correction algorithm to further improve the Doppler frequency estimation accuracy, increase the processing gain of the pre-coherent integration, and ultimately improve the capture sensitivity.

The Doppler frequency residual correction algorithm is:

The GNSS intermediate frequency input signal with a duration of T milliseconds is squared and divided into M sub-blocks of length N. The local carrier squared signal after considering the Doppler frequency is also divided into M sub-blocks of length N. Then, the squared input signal and the local signal are correlated using the fast Fourier transform. Let the correlation result be Y _k . The M correlation results Y _k are differentially accumulated and the maximum value of the following calculation is searched:

|| represents a modulo operation. For the maximum value, the Doppler frequency error is calculated as follows:

进行校正：

The carrier Doppler frequency estimate is calculated using the above results.

To make a correction:

When the GNSS signal is very weak and the pre-coherent integration time is greater than 20 milliseconds, the carrier phase alignment algorithm is run to improve the processing gain of the pre-coherent integration.

The carrier phase alignment algorithm is:

计算多普勒频移在长时间相干积分累加时间内引起的载波相位飘移：Using Doppler frequency to estimate the error signal

Calculate the carrier phase drift caused by Doppler frequency shift during long coherent integration accumulation time:

计算得到本地信号的载波频率

然后，计算输入信号与本地载波信号的频率误差，并由下式计算出载波相位误差Pha_dif；I) Experimental and simulation analysis: First, the Doppler frequency f _tra estimated by the GNSS receiver tracking loop is used as the real Doppler frequency in the signal, thereby calculating the real frequency f IGIFS of the input GNSS intermediate frequency sampling signal _IGIFS , f _IGIFS = f _IF + f _tra + n _err1 . The Doppler frequency estimated by the algorithm of the present invention is

Calculate the carrier frequency of the local signal

Then, the frequency error between the input signal and the local carrier signal is calculated, and the carrier phase error Pha _dif is calculated by the following formula:

II) Carrier phase error analysis modeling; The above carrier phase error has a clear trend in change, and a functional relationship curve of the local carrier phase error changing with the Doppler frequency estimation error and duration is obtained by a polynomial fitting modeling method;

做为输入，估计并校正载波相位误差，通过插入/剔除本地信号采样点的方式将输入信号与本地信号对齐，此功能由本地载波生成调整模块实现。III) The carrier Doppler frequency estimation error obtained by the Doppler frequency residual correction algorithm

As input, the carrier phase error is estimated and corrected, and the input signal is aligned with the local signal by inserting/removing local signal sampling points. This function is implemented by the local carrier generation and adjustment module.

The present invention is directed to a GNSS navigation user-end receiver system, and improves the efficiency of the capture algorithm through a Doppler frequency estimation and correction algorithm (implemented by a Doppler frequency offset correction module group), breaks through the limitation of the coherent integration time through a navigation message bit flip estimation and correction algorithm, and improves the signal processing gain of the capture algorithm through a Doppler frequency residual correction and carrier phase alignment algorithm, and finally designs a long-term coherent integration capture algorithm module. The present invention can adaptively adjust the coherent integration time according to the signal environment, improve the sensitivity performance of the receiver, and take into account the efficiency of the capture algorithm. When the signal is blocked, the environmental noise is large, and the receiver is in motion, the GNSS receiver using the present invention can also stably give positioning results.

The present invention overcomes the drawbacks of Doppler frequency and pseudo code phase drift and movement in long-term coherent integration accumulation, which leads to broadening and reduction of pseudo code correlation peak envelope. The present invention enables the GNSS receiver to automatically estimate the Doppler frequency and correct its residual, estimate and correct the influence of navigation message bit flipping, correct carrier phase drift, and improve the receiver's availability under weak signals. Whether in low signal-to-noise ratio or in dynamic applications, the performance of the receiver of this solution is significantly improved compared with ordinary high-sensitivity GNSS receivers.

The beneficial effect of the present invention is that the long-term coherent integration capture algorithm module with Doppler frequency residual correction provided by the present invention can maintain normal reception of GNSS signals when the signals are blocked or subject to certain environmental interference, and improve the efficiency and sensitivity of high-sensitivity GNSS signal capture through algorithms such as Doppler frequency estimation and correction, Doppler frequency estimation residual correction, and carrier phase alignment; by designing a navigation message bit flip estimation and correction algorithm (combined by a bit flip estimation module, storage, search, message removal, and other modules), the pre-coherent integration time is increased, and the GNSS weak signal capture sensitivity is further improved. The performance of the GNSS receiver of this scheme is significantly improved compared to ordinary high-sensitivity GNSS receivers, and can maintain normal operation in a low signal-to-noise ratio and dynamic application environment.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a composition structure diagram of the present invention.

FIG. 2 is a schematic diagram of a frequency adjustment scheme for phase compensation in the present invention.

FIG. 3 is a schematic diagram of a carrier phase deviation caused by a Doppler frequency estimation error in the present invention.

4A1 and 4A2 are schematic diagrams of the pre-coherent integration output and the captured detection quantity according to the present invention.

FIG. 4B1 and FIG. 4B2 are schematic diagrams of pre-coherent integration output and captured detection quantity without adopting the present invention.

FIG5 is a structural diagram of a GNSS receiver.

FIG6 is a flow chart of a specific algorithm for capturing a satellite signal.

DETAILED DESCRIPTION

The following is a further description with reference to the embodiments shown in the accompanying drawings.

The present invention realizes a capture algorithm that can estimate the bit flip of the navigation message and only uses the coherent accumulation method to realize long-term accumulation; first, a carrier Doppler frequency deviation estimation and correction algorithm is designed to compress the search range of the carrier Doppler frequency deviation, thereby reducing the complexity of the capture algorithm. Then, the estimation of the navigation message bit flip is realized by using the group coherent calculation method, and the influence of the navigation message bit flip on the signal accumulation gain is eliminated. Secondly, since the coherent integral accumulation exceeds the navigation message bit length, the influence of the accumulated data phase synchronization error caused by the slight frequency drift on the accumulation gain cannot be ignored; based on the phase differential information of adjacent data blocks that must be contained in the group differential accumulation result, the present invention discloses a scheme for estimating the Doppler frequency estimation residual using this information, thereby improving the coherent accumulation gain and capture sensitivity of the GNSS signal, reducing the coherent loss, and improving the signal processing gain of the coherent integral accumulation. Finally, a long-term coherent accumulation algorithm is designed to complete the signal capture. The functional structure diagram of the present invention is shown in Figure 1.

(或IGIFS的频率)估计值，生成不同相位的两路正交本地载波，与输入信号相乘(乘法模块图中用圆圈中加×表示)，产生I支路信号和与其正交的Q支路信号。然后I支路和Q支路合为一路复输入信号并进行傅立叶变换(FFT模块)，与本地C/A码经过共轭傅立叶变换(共轭FFT模块)结果相乘，其结果通过反傅立叶变换(IFFT模块)转换到时域，再取绝对值，得到输入信号与本地信号间的相关值，最后通过搜索最大相关值判断是否捕获到信号。除频率不确定度范围由±10KHz降低到20Hz、以及导航电文比特跳变外，其余步骤与普通的GNSS信号码域并行捕获算法一样。如图1所述流程完成GNSS信号捕获计算。The calculation process of the Doppler frequency deviation correction module group to assist GNSS signal acquisition by adopting the Doppler frequency estimation-compressed carrier frequency search space-fast acquisition algorithm is as follows: taking the GNSS intermediate frequency sampling signal as the input signal, according to the time-frequency transformation relationship between time domain broadening and frequency domain compression, the input data is block-superimposed (block superposition and phase compensation module), the Doppler frequency f _d search range is compressed, the Doppler frequency is estimated and the result is stored in the lookup table Acqb; when capturing the satellite signal, a record is taken from the table Acqb, and the Doppler frequency is obtained from the record.

(or the frequency of IGIFS) estimate, generate two orthogonal local carriers with different phases, multiply with the input signal (indicated by a circle with × in the multiplication module diagram), generate I branch signal and Q branch signal orthogonal to it. Then I branch and Q branch are combined into a complex input signal and Fourier transform (FFT module), multiplied with the result of conjugate Fourier transform (conjugate FFT module) of local C/A code, and the result is converted to time domain by inverse Fourier transform (IFFT module), and then the absolute value is taken to obtain the correlation value between the input signal and the local signal, and finally the maximum correlation value is searched to determine whether the signal is captured. Except that the frequency uncertainty range is reduced from ±10KHz to 20Hz, and the navigation message bit jumps, the remaining steps are the same as the ordinary GNSS signal code domain parallel capture algorithm. The process described in Figure 1 completes the GNSS signal capture calculation.

其中，T_s为采样周期，n为整数，输入的GNSS中频采样数据r(·)与序列β(n)相乘，结果用r％(·)表示。通过相位补偿的方法将频率搜索空间进行等间隔划分，进一步压缩频率搜索空间。如选20个等间隔的调整频率，对应不同的结果r％(·)，取最大响应者对应的频率即为估计出的多普勒频偏，频率不确定范围进一步减少，如图2所示。The Doppler frequency offset correction module estimates the Doppler frequency and compresses the frequency search space. First, a block superposition operation is performed. On the one hand, the signal-to-noise ratio of the signal can be improved. On the other hand, based on the signal processing theory that time domain expansion corresponds to frequency domain compression, the input data is superimposed in blocks. This operation widens the time domain and compresses the frequency domain. Therefore, the Doppler frequency _fd is reduced, compressing the frequency search range of the capture algorithm. Then, a set of adjustment frequencies δf is selected to obtain a set of phase compensation sequences

Where _Ts is the 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%(·). The frequency search space is divided into equal intervals by the phase compensation method to further compress the frequency search space. If 20 equally spaced adjustment frequencies are selected, corresponding to different results r%(·), the frequency corresponding to the maximum responder is taken as the estimated Doppler frequency deviation, and the frequency uncertainty range is further reduced, as shown in Figure 2.

The basic scheme for estimating the bit flip of the navigation message. Select data with a data length of _TI , start from the first pseudo code period signal, and calculate (TI _- 1) correlation calculations with an interval of 1 pseudo code period and a duration of t. Then, the calculation results are processed and analyzed, and the moment when the message bit jump occurs is obtained based on the method of searching for the minimum point. When the bit flip occurs in the middle position of the data participating in the coherent accumulation calculation, the value of the coherent accumulation result is the smallest (significantly smaller than the average value), and the data block with bit flip is found based on this, and the subsequent data blocks are processed accordingly according to the flip situation to eliminate the impact of the navigation message bit flip.

In order to improve the GNSS signal acquisition sensitivity by increasing the pre-coherence integration time CIT, the present invention discloses a Doppler frequency residual correction algorithm and a carrier phase alignment algorithm.

The Doppler frequency residual correction algorithm is:

During long-term coherent accumulation, the influence of the phase synchronization error of the accumulated data caused by the slight frequency drift on the accumulated gain cannot be ignored. Based on the inference that the group differential accumulation result contains the phase differential information of adjacent data blocks, the present invention discloses a scheme for estimating the Doppler frequency estimation residual using this information, so as to improve the coherent accumulation gain and capture sensitivity. The scheme idea is as follows:

The GNSS intermediate frequency input signal with a duration of T milliseconds is squared and divided into M sub-blocks of length N. The local carrier squared signal after considering the Doppler frequency is also divided into M sub-blocks of length N. Then, the squared input signal and the local signal are correlated using the fast Fourier transform. Let the correlation result be Y _k . The M correlation results Y _k are differentially accumulated and the maximum value of the following calculation is searched:

|| represents a modulo operation. For the maximum value, the Doppler frequency error is calculated as follows:

进行校正：

The carrier Doppler frequency estimate is calculated using the above results.

To make a correction:

The corrected result reduces the influence of Doppler frequency estimation residual on acquisition performance and improves the accuracy of Doppler frequency estimation.

计算多普勒频移在长时间相干积分累加时间内引起的载波相位飘移，通过建模校正的方法(运行载波相位对齐算法)降低这部分误差。See Figure 3; using Doppler frequency to estimate the error signal

The carrier phase drift caused by the Doppler frequency shift during the long coherent integration accumulation time is calculated, and this part of the error is reduced by the modeling correction method (running the carrier phase alignment algorithm).

The carrier phase alignment algorithm is:

计算得到本地信号的频率

然后，计算输入信号与本地载波信号的频率误差，由下式计算出载波相位误差Pha_dif。Simulation analysis: Assuming that the Doppler frequency f _tra estimated by the tracking loop is the real Doppler frequency in the signal, the real frequency f _IGIFS of the signal can be calculated, f _IGIFS = f _IF + f _tra + n _err1 , and the Doppler frequency estimated by the algorithm of the present invention is

Calculate the frequency of the local signal

Then, the frequency error between the input signal and the local carrier signal is calculated, and the carrier phase error Pha _dif is calculated by the following formula.

According to the method described in the above formula, simulation is performed, and the phase error curve of the local carrier is shown in FIG3 .

做为输入，估计并校正载波相位误差，通过插入/剔除本地信号采样点的方式将输入(GNSS中频)信号与本地信号对齐，提高相干积分累加增益。In Figure 3, the horizontal axis is the coherent integration accumulation time CIT, and the vertical axis is the carrier phase deviation. It can be seen that the change of the carrier phase error has an obvious trend. The functional relationship curve of the local carrier phase error changing with the Doppler frequency estimation error and duration can be obtained by the polynomial fitting modeling method, which can be obtained from the Doppler frequency shift residual estimated above.

As input, the carrier phase error is estimated and corrected, and the input (GNSS intermediate frequency) signal is aligned with the local signal by inserting/removing local signal sampling points to improve the coherent integration and accumulation gain.

The influence of Doppler frequency estimation accuracy on the coherent integration accumulation time and capture sensitivity, the simulation analysis results are shown in Figures 4A1, 4A2, 4B1, and 4B2.

The figure shows the simulation analysis results of the influence of Doppler frequency estimation accuracy and coherent integration accumulation time on pre-coherent integration accumulation. The horizontal axis is the coherent integration accumulation time CIT, and the vertical axis is the carrier phase deviation (where the vertical axis in Figure 4A2 is the capture detection 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 different PRN coded satellite signals.

The two figures in Figure 4A1 and Figure 4A2 correspond to the acquisition algorithm that uses 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 capturing the satellite signal of PRN=18, the frequency error is less than 0.5Hz (compared with the tracked carrier frequency). The smaller the frequency error, the lower the rate at which the phase error increases over time, and the coherent integration output can keep rising for a longer time, and the GNSS signal acquisition sensitivity can be increased as much as possible by increasing the pre-coherent integration time CIT. It can be seen from these two figures that the coherent integration output signal (coherent integration output) and the acquisition decision amount ADV of the satellite signal of PRN=18,22 keep an upward trend when CIT is less than 250 milliseconds.

The corresponding acquisition algorithms in Figures 4B1 and 4B2 do not use the frequency domain search method, that is, they directly use the estimated carrier Doppler frequency value to generate the local carrier signal. The corresponding carrier Doppler frequency correction accuracy is low, and the frequency error between IGIFS and the local signal is greater than 2Hz in many cases. When CIT>120ms, as CIT increases, the coherent integration accumulation output may decrease, which means that increasing CIT cannot continue to improve the acquisition sensitivity.

The position of the GNSS signal acquisition algorithm module of the present invention in the GNSS receiver (prior art, structure see FIG5 ) is shown in FIG5 ; the GNSS receiver is composed of a radio frequency front end, a baseband signal processing module, and a navigation positioning solution module. Among them, the baseband signal processing module includes submodules such as signal acquisition, tracking, decoding, and navigation message extraction. The GNSS signal capture roughly estimates the pseudo-code phase and carrier Doppler frequency, and the signal tracking module realizes accurate estimation of the pseudo-code phase and carrier Doppler frequency in order to realize the despreading and demodulation of the GNSS signal. The decoding and message extraction module obtains the navigation message through Viterbi decoding, obtains the satellite ephemeris information and pseudorange measurement information at the current moment, and the navigation positioning solution module uses the ephemeris information and the measured pseudorange and pseudorange rate information to realize navigation positioning solution.

Referring to Figure 6, the calculation process for capturing a GNSS satellite signal is as follows: after Doppler frequency estimation and residual compensation, a local carrier signal is generated, which is multiplied with the input signal without the navigation message and then subjected to Fourier transform FFT, the result is recorded as Pa; the pseudo code rate is adjusted using the Doppler frequency estimation value, a local C/A code is generated and a conjugate Fourier transform is performed, the result is recorded as Pb; the result of the multiplication of Pa and Pb is converted to the time domain through inverse Fourier transform IFFT to obtain the correlation b value between the input signal and the local signal. Whether the signal is captured is determined by searching for the maximum correlation value.

Except for the residual correction module and the local carrier generation adjustment module, all other modules used in the present invention (such as the block superposition and phase compensation module, the spectrum peak detection module, the storage module, the table lookup module, the storage and table lookup module, the bit flip estimation module, the message removal module, etc.) are all prior art. Among them, in the local carrier generation adjustment module, a carrier phase alignment algorithm is added on the basis of the prior art such as carrier generation.

Claims (6)

1. A long-term coherent integration capture algorithm module for Doppler residual correction, comprising a Doppler frequency offset correction module group, a residual correction module, a bit flip estimation module, a storage module, a table lookup module, and a message removal module connected in sequence; at the same time, after the residual correction module is connected to the local carrier generation adjustment module, it is connected in parallel with the message removal module to the multiplier module for processing and then enters the FFT module; The local pseudo code generation module is sequentially connected to the conjugate FFT module and then connected to the multiplier module in parallel with the output of the FFT module for processing; after the processing result is output, it sequentially enters the IFFT module and the threshold judgment module to output the captured signal and is connected to the local carrier generation adjustment module; The Doppler frequency offset correction module includes a block superposition and phase compensation module, a spectrum peak detection module and a storage and table lookup module connected in sequence; The Doppler frequency residual correction algorithm adopted by the residual correction module is: The GNSS intermediate frequency input signal with a duration of T milliseconds is squared and divided into M sub-blocks of length N. The local carrier square signal after considering the Doppler frequency is also divided into M sub-blocks of length N. Then, the squared input signal and the local signal are correlated using the fast Fourier transform. Let the correlation result be Y _k . The M correlation results Y _k are differentially accumulated and the maximum value of the following calculation is searched:

|| represents a modulo operation. For the maximum value, the Doppler frequency error is calculated as follows:

The carrier Doppler frequency estimate is calculated using the above results.

To make a correction:

2. According to the long-time coherent integration capture algorithm module for Doppler residual correction in claim 1, it is characterized in that the output end of the Doppler frequency offset correction module group is also connected to the input end of the bit flip estimation module, and the Doppler frequency estimation value is used to assist in predicting the pseudo code phase; on this basis, the bit flip estimation module estimates and eliminates the influence of navigation message bit flips; finally, the capture sensitivity is improved by obtaining the signal processing gain through long-time coherent accumulation. 3. The long-term coherent integration acquisition algorithm module for Doppler residual correction according to claim 2 is characterized in that the Doppler frequency offset correction module group and the bit flip estimation module are only run once during the GNSS receiver acquisition process. 4. The long-term coherent integration acquisition algorithm module for Doppler residual correction according to claim 3 is characterized in that: when the GNSS signal is very weak and the pre-coherent integration time is greater than 20 milliseconds, the residual correction module runs the Doppler frequency residual correction algorithm to further improve the Doppler frequency estimation accuracy, improve the processing gain of the pre-coherent integration, and ultimately improve the capture sensitivity. 5. The long-term coherent integration acquisition algorithm module for Doppler residual correction according to claim 4 is characterized in that: when the GNSS signal is very weak and the pre-coherent integration time is greater than 20 milliseconds, the carrier phase alignment algorithm in the local carrier generation adjustment module is run to improve the processing gain of the pre-coherent integration. 6. The long-term coherent integration acquisition algorithm module for Doppler residual correction according to claim 5, characterized in that: the carrier phase alignment algorithm is: Using Doppler frequency to estimate the error signal

Calculate the carrier phase drift caused by Doppler frequency shift during long coherent integration accumulation time: I) Experimental and simulation analysis: First, the Doppler frequency f _tra estimated by the GNSS receiver tracking loop is used as the real Doppler frequency in the signal, thereby calculating the real frequency f IGIFS of the input GNSS intermediate frequency sampling signal _IGIFS , f _IGIFS = f _IF + f _tra + n _err1 . The Doppler frequency estimated by the algorithm is

Calculate the carrier frequency of the local signal

Then, the frequency error between the input signal and the local carrier signal is calculated, and the carrier phase error Pha _dif is calculated by the following formula:

II) Carrier phase error analysis modeling; The above carrier phase error has a clear trend, and the functional relationship curve of the local carrier phase error with the Doppler frequency estimation error and duration is obtained by polynomial fitting modeling method; III) The carrier Doppler frequency estimation error obtained by the Doppler frequency residual correction algorithm

As input, the carrier phase error is estimated and corrected, and the input signal is aligned with the local signal by inserting/removing local signal sampling points. This function is implemented by the local carrier generation and adjustment module.

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