CN106526633B - A kind of GNSS baseband signal acquisition method and device - Google Patents

Abstract

The invention discloses the catching methods and device of a kind of GNSS baseband signal, the catching method includes simultaneously scanning for same by multiple correlators first not capture satellite, after this, which does not capture satellite, is captured, other three are captured according to same method and does not capture satellite；Then the satellite number of other all Observable satellites is got according to the satellite navigation message of aforementioned four captured satellites；The corresponding frequency for not capturing satellite is obtained according to literary asterisk again, and satellite is not captured to other by N number of correlator and is successively scanned for, until all are not captured satellite capture, that is to say that GNSS baseband signal completes capture.By the present invention in that being scanned for multiple correlators to same satellite, capture time of the system to capture satellite-signal when is greatly reduced, the treatment effeciency of system is improved.

Description

A kind of GNSS baseband signal acquisition method and device

technical field

The present invention relates to the processing of GNSS baseband signals, in particular to a method and device for acquiring GNSS baseband signals.

Background technique

With the rapid development of technology, a variety of navigation systems have emerged. It is difficult for a single navigation system to meet the navigation needs in the global, all-weather, and various complex environments. The integrated navigation system composed of two or more systems has become a research hotspot in various countries.

However, what the satellite transmits to the ground is only a high-frequency carrier that modulates the information. In order to obtain useful information such as the satellite's ranging code and navigation message, the satellite signal must be processed. Although the structures and methods of signals transmitted by Beidou, GPS and GLONASS satellites are different from each other, their signal processing methods are similar.

The processing of satellite signals is generally to first analyze, capture and track the signal structure, and finally obtain the navigation message. With the disclosure of the domestic Beidou navigation system, a processing system for GNSS baseband signals in the Beidou navigation system is required. In addition, for the existing satellite signal processing, its processing speed is slow, especially when capturing signals, it cannot support multi-channel data capture.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art, one of the objectives of the present invention is to provide a method for acquiring GNSS baseband signals, which can realize multi-channel and fast acquisition of GNSS baseband signals.

One of the objects of the present invention adopts the following technical solutions to realize:

The present invention provides a method for acquiring a GNSS baseband signal, comprising the following steps:

S1: Divide the frequency of the currently unacquired satellites into M first frequency bands and assign a corresponding correlator to each first frequency band, and search for satellite signals through the correlator in each first frequency band. Do a search and get the output of each correlator;

S2: Determine whether the currently uncaptured satellite is captured according to all the output results. If so, mark the currently uncaptured satellite as the captured satellite, switch to the next satellite and record it as the currently uncaptured satellite, and execute S1; When there are four satellites, execute S3;

S3: Obtain the satellite numbers of all currently observable satellites according to the satellite navigation messages of the above four satellites;

S4: Obtain the frequencies of all unacquired satellites according to the satellite numbers, divide the frequencies of each unacquired satellite into N second frequency bands, and assign a corresponding correlator to each second frequency band, in each second frequency band The method of searching satellite signals through the correlator searches each uncaptured satellite in turn, and judges whether each uncaptured satellite has been captured, if so, the corresponding uncaptured satellite is recorded as the captured satellite;

S5: GNSS baseband signal acquisition is completed when all satellites are marked as acquired satellites.

Preferably, it also includes dividing the frequency of each captured satellite into one third frequency band, and in each third frequency band, the method of searching for satellite signals by a correlator sequentially performs secondary capture on each captured satellite until the Complete secondary acquisition of all captured satellites.

Preferably, the I=10.

Preferably, the method for the correlator to search for satellite signals specifically includes the following steps:

S11: Convert the signal received through the GNSS antenna into an intermediate frequency digital signal s(t), which can be expressed by formula (1):

Among them, P is the signal power; D(t) is the navigation message bit; C(t) is the C/A code; τ is the time delay in the transmission process of the satellite signal from the satellite to the receiver; f _d is the Doppler frequency t is the observation time; f _IF = f _nominal + f _d , which is the intermediate frequency signal of carrier down-conversion; f _nominal represents the nominal frequency of the intermediate frequency digital signal; φ is the initial carrier phase; n(t) is the white Noise, its power spectral density is constant; f _L1 represents the frequency of the intermediate frequency digital signal in the L1 frequency band;

S12: Multiply the intermediate frequency digital signal s(t) by the local carrier signal to obtain the in-phase component I(t) and the positive-phase component Q(t);

The local carrier signal is expressed as in is the estimated Doppler shift during acquisition, f _loc represents the actual frequency of the IF digital signal, Q _loc (t) represents the signal of the in-phase component of the local carrier signal, I _loc (t) represents the signal of the in-phase component of the local carrier signal, φ _loc represents the initial phase of the intermediate frequency digital signal;

After mixing (1) and (2), the in-phase component I(t) and the positive-phase component Q(t) are obtained, which can be expressed by formula (3):

S13: After processing the signal of formula (3) through a low-pass filter, formula (4) is obtained:

in, Estimate residual for Doppler shift;

S14: Assume that the local pseudocode sequence can be expressed as By correlating and integrating it with formula (4), the in-phase component integral _{IP and the positive-phase component integral Q P can} be obtained, which are specifically expressed by formula (5):

where T is the pre-detection integration time, Represents the propagation time of the satellite signal from the satellite to the receiver;

S15: Simplify formula (5) to obtain formula (6):

The in-phase component integral IP and the positive-phase component integral _QP are _finally obtained, that is, the output result of the correlator.

Preferably, T is 1 ms, 2 ms, 5 ms or 10 ms.

Preferably, M=N+4.

Preferably, M=32 and N=28.

In order to overcome the deficiencies of the prior art, the second purpose of the present invention is to provide a device for acquiring GNSS baseband signals, which can realize multi-channel and fast acquisition of GNSS baseband signals.

The second purpose of the present invention adopts the following technical solutions to realize:

The present invention also provides a device for capturing a GNSS baseband signal, comprising:

The first satellite acquisition module is used to divide the frequency of the currently unacquired satellite into M first frequency bands and assign a corresponding correlator to each first frequency band, and search for satellite signals through the correlator in each first frequency band The method searches for the currently unacquired satellites and obtains the output of each correlator;

The capture completion marking module is used to determine whether the currently uncaptured satellite is captured according to all the output results. If so, mark the currently uncaptured satellite as the captured satellite, switch to the next satellite and record it as the currently uncaptured satellite, and execute The first satellite acquisition module; until four satellites are captured, execute the satellite number acquisition module;

The satellite number acquisition module is used to acquire the satellite numbers of all currently observable satellites according to the satellite navigation messages of the above four satellites;

The other satellite acquisition modules are used to obtain the frequencies of all unacquired satellites according to the satellite number, divide the frequency of each unacquired satellite into N second frequency bands, and assign a corresponding correlator to each second frequency band. The method of searching satellite signals by correlators in each second frequency band searches for each unacquired satellite in turn, and judges whether each unacquired satellite has been acquired, if so, the corresponding unacquired satellite is recorded as an acquired satellite ;

The acquisition completion module is used to complete the acquisition of GNSS baseband signals when all satellites are marked as acquired satellites.

Compared with the prior art, the beneficial effects of the present invention are: the present invention greatly reduces the acquisition time of the system for capturing satellite signals by using multiple correlators to search for the same satellite, and improves the processing efficiency of the system; in addition, The present invention also performs secondary acquisition, further positioning the satellite signal in a more accurate frequency band, and provides more accurate data for the subsequent processing.

Description of drawings

1 is a flow chart of a method according to an embodiment provided by the present invention;

FIG. 2 is a block diagram of a device according to an embodiment of the present invention.

Detailed ways

Below, in conjunction with accompanying drawing and specific embodiment, the present invention is further described:

As shown in Figure 1, for a receiver, its position is determined according to satellites, that is, when determining the position of the receiver, the satellite signals of all satellites need to be received first, that is, the satellite signals need to be received. Search and capture. Generally speaking, there are 32 satellites, and the frequencies of the satellite signals of each satellite are different. When the satellite signals of the 32 satellites are captured, in order to improve the capture time, the present invention provides a method for capturing GNSS baseband signals. It can quickly capture satellite signals of all satellites, and the method includes the following steps:

S1: Divide the frequency of the currently unacquired satellites into M first frequency bands and assign a corresponding correlator to each first frequency band, and search for the unacquired satellites by using the method of searching satellite signals by the correlator in each frequency band, And get the output of each correlator.

First of all, when the satellite signal is not known, the frequency of an unacquired satellite is generally set based on empirical values, that is, the frequency band of the satellite signal of a satellite is estimated. A plurality of correlators are set in the receiver, and the correlator is an instrument that extracts the useful signal from the interference and noise by using the correlation characteristics of the signal. The number of correlators in the present invention is set to 32. When searching for the same satellite, 32 correlators are used to perform parallel processing at the same time, so that the satellite search can be completed quickly. Since the frequency range of each unacquired satellite may be very large, it is firstly divided into a plurality of first frequency bands, and a corresponding correlator is allocated to each first frequency band, so as to pass the correlator in each frequency band The method of searching for satellite signals searches for unacquired satellites, so that multiple correlators run simultaneously, which greatly reduces the search time. The method for the correlator to search for satellite signals specifically includes the following steps:

S11: Convert the signal received through the GNSS antenna into an intermediate frequency digital signal s(t), which can be expressed as:

Among them, P is the signal power; D(t) is the navigation message bit; C(t) is the C/A code; τ is the time delay in the transmission process of the satellite signal from the satellite to the receiver; f _d is the Doppler frequency t is the observation time; f _IF = f _nominal + f _d , which is the intermediate frequency signal of carrier down-conversion; f _nominal represents the nominal frequency of the intermediate frequency digital signal; φ is the initial carrier phase; n(t) is the white Noise, its power spectral density is constant; f _L1 represents the frequency of the intermediate frequency digital signal in the L1 frequency band.

S12: Multiply the intermediate frequency digital signal s(t) by the local carrier signal to obtain the in-phase component I(t) and the positive-phase component Q(t);

The local carrier signal is expressed as in is the estimated Doppler shift at the time of acquisition, f _loc represents the actual frequency of the IF digital signal, Q _loc (t) represents the signal of the in-phase component of the local carrier signal, I _loc (t) represents the signal of the in-phase component of the local carrier signal, φ _loc represents the initial phase of the intermediate frequency digital signal.

Assumption In order to estimate the residual error for the Doppler frequency shift, when capturing satellite signals, only by making Δf as close to 0 as possible, the corresponding satellite signals can be captured.

Preferably, in the acquisition of the signal in the present invention, generally, if the value of Δf is set to be less than a certain threshold, it is considered that the acquisition of the satellite is completed.

After mixing (1) and (2), the in-phase component I(t) and the positive-phase component Q(t) are obtained, that is:

S13: Formula (4) is obtained after processing the in-phase component I(t) and the positive-phase component Q(t) through a low-pass filter:

S14: Assume that the local pseudocode sequence can be expressed as Correlate it with equation (4) and integrate it, the in-phase component integral I _P and the positive-phase component integral Q _P can be obtained, which can be expressed by equation (5):

Among them, T is the pre-detection integration time, and T<20ms; for C/A code, it is generally an integer multiple of the chip period of 1ms, Represents the propagation time of the satellite signal from the satellite to the receiver.

S15: Since D(t) is a navigation message bit with a bit rate of 50 bps, it can be considered that D(t) does not change during the integration time T, so it can be referred to outside the integral sign, and formula (5) can be simplified as Formula (6):

That is to say, after each correlator searches the satellite signal, it outputs a set of data of the in-phase component integral IP and the positive-phase component _{integral QP} , that is, the output result of the correlator.

S2: Determine whether the currently uncaptured satellite has been captured according to all the output results. If so, the uncaptured satellite will record the currently uncaptured satellite as the captured satellite, switch to the next satellite and record it as the currently uncaptured satellite, and execute S1 ; Until four satellites are captured, perform S3.

When searching for each unacquired satellite, in the present invention, multiple correlators are used to search for the same unacquired satellite in different frequency bands at the same time, so that the correlators in each frequency band will have an output result. That is to say, the integral IP of the in-phase component obtained in each frequency band and the integral _QP of the positive-phase component are compared with the values obtained by the square and calculation, and the frequency band corresponding to the maximum value is selected as the satellite signal of the _uncaptured satellite. The frequency band, that is, the currently unacquired satellites are captured. When the capture of one satellite is completed, continue to capture other uncaptured satellites according to the same method until the capture of four satellites is completed.

S3: Obtain the satellite numbers of all currently observable satellites according to the satellite navigation messages of the above four satellites.

Generally speaking, as long as there are four satellites, the positioning result can be generated, and the satellite numbers of all observable satellites can be obtained according to the navigation messages in the satellite signals of the above four satellites. Since each satellite has a corresponding satellite number, information such as the position and frequency of the corresponding satellite can be obtained according to the satellite number. In this way, when searching for other unacquired satellites, the frequency range of the search is also determined, so that the search time for other unacquired satellites can be greatly reduced.

S4: Obtain the frequencies of all unacquired satellites according to the satellite numbers, divide the frequencies of each unacquired satellite into N second frequency bands, and assign a corresponding correlator to each second frequency band, in each second frequency band The method of searching satellite signals through the correlator searches each unacquired satellite in turn, and judges whether each unacquired satellite has been acquired. If so, the corresponding unacquired satellite is recorded as the acquired satellite.

Since the satellite number of each unacquired satellite is obtained, the search frequency of the unacquired satellite can be determined. The uncaptured satellites here refer to other satellites except the four satellites that have been captured. Since there are a total of 32 correlators used in the present invention, 4 of which have completed the acquisition of the above four satellites, there are still 28 correlators left. In this way, in order to ensure the search time, 28 correlators can be The detector also searches for an unacquired satellite at the same time. That is, the same method of searching satellite signals by the correlator is used to search for each unacquired satellite. When an uncaptured satellite is captured, it is recorded as a captured satellite, and the other uncaptured satellites continue; until all the uncaptured satellites are captured, that is, all satellites are marked as captured satellites.

S5: GNSS baseband signal acquisition is completed when all satellites are marked as acquired satellites.

When all satellites are captured, that is to say, the satellite signals of all satellites are determined in the corresponding frequency band, so that when the satellite signals are tracked in the next step, the satellite signals of each satellite can be determined within the known In the frequency band, the location information of the receiver can be quickly obtained.

Preferably, when the correlator searches for satellite signals, since the satellite signals have to pass through the ionosphere, the troposphere, etc. before reaching the ground, there is a large energy loss. The received signal energy is strong or weak. For strong signals, the correlator can capture the corresponding signal in a short time; for weak signals, it is difficult for the correlator to capture the corresponding signal in a short time. Therefore, when the satellite signal is searched by the correlator, the pre-detection integration time is set in a round-robin manner. The pre-detection integration times selected in the present invention are 1 ms, 2 ms, 5 ms and 10 ms. That is to say, for example, for strong signals, the pre-detection integration time that can be taken is 1ms, 2ms, and 5ms; and for weak signals, the pre-detection integration time that can be adopted is 10ms. For satellite signals, it generally includes PRN codes and satellite navigation messages; when capturing signals, the local carrier signal is continuously adjusted by mixing the local carrier signal with the satellite signal, so that the local carrier signal is close to the PRN code in the satellite signal. , it means that the satellite signal has been searched, and the PRN code of the satellite signal is changed every once in a while, that is to say, when the signal is acquired, the PRN code of the satellite line must be converted once within the time. Once a search is completed, if it cannot be completed, the local carrier needs to be readjusted to search for the satellite signal again, which will cause a lot of waste of time. For strong signals, it only takes a short time to search for satellite signals. Therefore, the search can be completed by setting the integration time of the search to be shorter, thus saving more time. For weak signals, in a very short time It is difficult to search for the corresponding satellite signal in time, so when searching for the satellite signal, the integration time can be gradually increased until the satellite signal is searched. Of course, the pre-detection integration time will not exceed the change time of the PRN code of the satellite signal. In the present invention, when capturing satellites, an adaptive capturing method is adopted, and a rotation method is adopted to capture satellites. First, set the pre-detection integration time to 1ms. If any satellites cannot be captured under this integration time, the pre-detection integration time will be automatically set to 2ms. In the same way, set the pre-detection integration time to 5ms and 10ms until it is possible to Capture satellites.

In addition, the strength of the judgment signal is also related to the altitude angle of the satellite, and the altitude angle of the satellite can be calculated according to the position of the satellite. That is, the larger the altitude angle of the satellite, the stronger the corresponding signal strength; and the smaller the satellite altitude angle, the weaker the corresponding signal strength. When the position of the satellite is obtained, it can also be determined whether the satellite signal corresponding to the satellite is a strong signal or a weak signal, and then the integration time can be set to further quickly capture the satellite.

Further, it also includes secondary acquisition, which means that all satellites have been acquired for S1 to S4, and the satellite signal of each satellite has been determined in a fixed frequency band, such as the first searched 4 satellites The satellite signals of 28 satellites will be determined in the corresponding first frequency band, and the satellite signals of the next 28 satellites will be determined in the corresponding second frequency band. In order to further make the frequency band of each satellite's satellite line more accurate, the above determined frequency band is divided again, and then all satellites are captured by the above acquisition method, so that the frequency of the satellite signal of each satellite can be obtained. of precision. For example, after using the above S1 to S4 to complete the acquisition of all satellites, the frequency range of the satellite signal is determined to be 500Hz, and then the above 500Hz frequency is divided into multiple frequency bands, for example, it is divided into 10 frequency bands The frequency band, that is, the frequency of each frequency band is 50Hz; then all satellites are captured according to the above acquisition method, so that the final frequency accuracy of the satellite signals of all satellites is 50Hz, which means that the accuracy of the GNSS baseband signal is greatly improved. Increase.

As shown in FIG. 2 , the present invention also provides a device for capturing a GNSS baseband signal, including:

The first satellite acquisition module is used to divide the frequency of the currently unacquired satellite into M first frequency bands and assign a corresponding correlator to each first frequency band, and search for satellite signals through the correlator in each first frequency band The method searches for the currently unacquired satellites and obtains the output of each correlator;

The capture completion marking module is used to determine whether the currently uncaptured satellite is captured according to all the output results. If so, mark the currently uncaptured satellite as the captured satellite, switch to the next satellite and record it as the currently uncaptured satellite, and execute The first satellite acquisition module; until four satellites are captured, execute the satellite number acquisition module;

The satellite number acquisition module is used to acquire the satellite numbers of all currently observable satellites according to the satellite navigation messages of the above four satellites;

The other satellite acquisition modules are used to obtain the frequencies of all unacquired satellites according to the satellite number, divide the frequency of each unacquired satellite into N second frequency bands, and assign a corresponding correlator to each second frequency band. The method of searching satellite signals by correlators in each second frequency band searches for each unacquired satellite in turn, and judges whether each unacquired satellite has been acquired, if so, the corresponding unacquired satellite is recorded as an acquired satellite ;

The acquisition completion module is used to complete the acquisition of GNSS baseband signals when all satellites are marked as acquired satellites.

For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims (7)

1. the acquisition method of a GNSS baseband signal, is characterized in that, comprises the following steps: S1: Divide the frequency of the currently unacquired satellites into M first frequency bands and assign a corresponding correlator to each first frequency band, and search for satellite signals through the correlator in each first frequency band. Do a search and get the output of each correlator; S2: Determine whether the currently uncaptured satellite is captured according to all the output results. If so, mark the currently uncaptured satellite as the captured satellite, switch to the next satellite and record it as the currently uncaptured satellite, and execute S1; When there are four satellites, execute S3; S3: Obtain the satellite numbers of all currently observable satellites according to the satellite navigation messages of the above four satellites; S4: Obtain the frequencies of all unacquired satellites according to the satellite numbers, divide the frequencies of each unacquired satellite into N second frequency bands, and assign a corresponding correlator to each second frequency band, in each second frequency band The method of searching satellite signals through the correlator searches each uncaptured satellite in turn, and judges whether each uncaptured satellite has been captured, if so, the corresponding uncaptured satellite is recorded as the captured satellite; S5: When all satellites are marked as acquired satellites, GNSS baseband signal acquisition is completed; The method for the correlator to search for satellite signals specifically includes the following steps: S11: Convert the signal received through the GNSS antenna into an intermediate frequency digital signal s(t), which can be expressed by formula (1): Among them, P is the signal power; D(t) is the navigation message bit; C(t) is the C/A code; τ is the time delay in the transmission process of the satellite signal from the satellite to the receiver; f _d is the Doppler frequency t is the observation time; f _IF = f _nominal + f _d , which is the intermediate frequency signal of carrier down-conversion; f _nominal represents the nominal frequency of the intermediate frequency digital signal; φ is the initial carrier phase; n(t) is the white Noise, its power spectral density is constant; f _L1 represents the frequency of the intermediate frequency digital signal in the L1 frequency band; S12: Multiply the intermediate frequency digital signal s(t) by the local carrier signal to obtain the in-phase component I(t) and the positive-phase component Q(t); The local carrier signal is expressed as in is the estimated Doppler shift at the time of acquisition, f _loc represents the actual frequency of the IF digital signal, Q _loc (t) represents the signal of the in-phase component of the local carrier signal, I _loc (t) represents the signal of the in-phase component of the local carrier signal, φ _loc represents the initial phase of the intermediate frequency digital signal; After mixing (1) and (2), the in-phase component I(t) and the positive-phase component Q(t) are obtained, which can be expressed by formula (3): S13: After processing the signal of formula (3) through a low-pass filter, formula (4) is obtained: in, Estimate residual for Doppler shift; S14: Assume that the local pseudocode sequence can be expressed as By correlating and integrating it with formula (4), the in-phase component integral _{IP and the positive-phase component integral Q P can} be obtained, which are specifically expressed by formula (5): where T is the pre-detection integration time, Represents the propagation time of the satellite signal from the satellite to the receiver; S15: Simplify formula (5) to obtain formula (6): The final obtained in-phase component integral IP and positive-phase component integral _QP are the output _results of the correlator. 2. the acquisition method of GNSS baseband signal as claimed in claim 1, is characterized in that, also comprises that the frequency of each captured satellite is divided into 1 3rd frequency band, in each 3rd frequency band, searches satellite signal by correlator The method performs secondary acquisition for each captured satellite in turn until the secondary acquisition is completed for all captured satellites. 3 . The method for acquiring a GNSS baseband signal according to claim 2 , wherein the I=10. 4 . 4. The method for acquiring a GNSS baseband signal according to claim 1, wherein T is 1 ms, 2 ms, 5 ms or 10 ms. 5. The method for acquiring a GNSS baseband signal according to claim 1, wherein M=N+4. 6 . The method for acquiring GNSS baseband signals according to claim 5 , wherein M=32 and N=28. 7 . 7. A device for capturing a GNSS baseband signal, comprising: The first satellite acquisition module is used to divide the frequency of the currently unacquired satellite into M first frequency bands and assign a corresponding correlator to each first frequency band, and search for satellite signals through the correlator in each first frequency band The method searches for the currently unacquired satellites and obtains the output of each correlator; The capture completion marking module is used to determine whether the currently uncaptured satellite is captured according to all the output results. If so, mark the currently uncaptured satellite as the captured satellite, switch to the next satellite and record it as the currently uncaptured satellite, and execute The first satellite acquisition module; until four satellites are captured, execute the satellite number acquisition module; The satellite number acquisition module is used to acquire the satellite numbers of all currently observable satellites according to the satellite navigation messages of the above four satellites; The other satellite acquisition modules are used to obtain the frequencies of all unacquired satellites according to the satellite number, divide the frequency of each unacquired satellite into N second frequency bands, and assign a corresponding correlator to each second frequency band. The method of searching satellite signals by correlators in each second frequency band searches for each unacquired satellite in turn, and judges whether each unacquired satellite has been acquired, if so, the corresponding unacquired satellite is recorded as an acquired satellite ; The acquisition completion module is used to complete the acquisition of GNSS baseband signals when all satellites are marked as acquired satellites; The correlator searches for satellite signals by: S11: Convert the signal received through the GNSS antenna into an intermediate frequency digital signal s(t), which can be expressed by formula (1): Among them, P is the signal power; D(t) is the navigation message bit; C(t) is the C/A code; τ is the time delay in the transmission process of the satellite signal from the satellite to the receiver; f _d is the Doppler frequency t is the observation time; f _IF = f _nominal + f _d , which is the intermediate frequency signal of carrier down-conversion; f _nominal represents the nominal frequency of the intermediate frequency digital signal; φ is the initial carrier phase; n(t) is the white Noise, its power spectral density is constant; f _L1 represents the frequency of the intermediate frequency digital signal in the L1 frequency band; S12: Multiply the intermediate frequency digital signal s(t) by the local carrier signal to obtain the in-phase component I(t) and the positive-phase component Q(t); The local carrier signal is expressed as in is the estimated Doppler shift during acquisition, f _loc represents the actual frequency of the IF digital signal, Q _loc (t) represents the signal of the in-phase component of the local carrier signal, I _loc (t) represents the signal of the in-phase component of the local carrier signal, φ _loc represents the initial phase of the intermediate frequency digital signal; After mixing (1) and (2), the in-phase component I(t) and the positive-phase component Q(t) are obtained, which can be expressed by formula (3): S13: After processing the signal of formula (3) through a low-pass filter, formula (4) is obtained: in, Estimate residual for Doppler shift; S14: Assume that the local pseudocode sequence can be expressed as By correlating and integrating it with formula (4), the in-phase component integral _{IP and the positive-phase component integral Q P can} be obtained, which are specifically expressed by formula (5): where T is the pre-detection integration time, Represents the propagation time of the satellite signal from the satellite to the receiver; S15: Simplify formula (5) to obtain formula (6): The final obtained in-phase component integral IP and positive-phase component integral _QP are the output _results of the correlator.