A high-orbit Beidou signal capture method and capture device

Abstract

The present invention relates to a high-orbit Beidou signal capture method and capture device. The capture method includes: converting a Beidou satellite signal into a digital intermediate frequency signal, determining the number of sampling points of a 1-millisecond signal; determining Fourier transform compensation data and inverse Fourier transform compensation data; mixing the 1-millisecond digital intermediate frequency signal with a local carrier to strip the carrier; performing Fourier transform compensation on the carrier stripping signal and then Fourier transforming it; performing Fourier transform compensation on a 1-millisecond local ranging code sequence and then Fourier transforming it; conjugate multiplying the two Fourier transform results; performing inverse Fourier transform on the conjugate multiplication result and then performing inverse Fourier transform compensation; delaying the inverse Fourier transform compensation result by one code phase and then performing a differential coherence operation; and using the cumulative sum of the differential coherence results to perform peak value judgment. When the peak value is greater than or equal to a threshold, the signal is successfully captured. This method saves storage and computing resources, is less affected by noise, and has high signal capture sensitivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of satellite signal processing, and in particular relates to a high-orbit Beidou signal capture method and capture device. Background Art

[0002] With the continuous development of space exploration, the number of high-orbit spacecraft is increasing. Accurately acquiring their position and velocity is crucial. Relying solely on ground station resources cannot meet practical needs. Therefore, using navigation satellite systems to achieve autonomous navigation for high-orbit spacecraft has become a key research focus. In high-orbit environments, the received Beidou signal is weak due to Earth obstruction and long-distance propagation. Therefore, capturing Beidou signals is crucial for autonomous navigation of high-orbit spacecraft.

[0003] During the capture process, if the received signal's millisecond data symbols differ, the coherent integration process will cause data to cancel each other out, resulting in no clear peak in the capture result. To obtain a 1-millisecond IF signal coherence value that is unaffected by data cancellation, existing Beidou signal capture methods require Fourier transforming the 2-millisecond digital IF signal. Specifically, the 1-millisecond local ranging code is supplemented with a 1-millisecond zero value for Fourier transforming. The Fourier transform results of the two are conjugate multiplied together. The result is inverse Fourier transformed, preserving the correlation result from the previous 1 millisecond. Inter-symbol differential processing is used to avoid the effects of Newman-Hoffman code transitions and navigation data transitions, generating coherent data of varying durations through step-by-step coherence and incoherence. The peak value is used to determine if data has been captured, and capture is complete.

[0004] When this capture method obtains a 1-millisecond complete coherence value, it is necessary to supplement the 2-millisecond digital intermediate frequency signal and the 1-millisecond local ranging code with a 1-millisecond zero value to perform a Fourier transform with a data length of 2 milliseconds, and after conjugate multiplication, a 2-millisecond inverse Fourier transform is required. Therefore, when this method calculates the 1-millisecond complete coherence value, it is necessary to use 2 milliseconds of data for Fourier transform and inverse Fourier transform, which wastes computing resources and storage resources and increases the capture time. The 1-millisecond complete coherence value obtained from the 2-millisecond digital intermediate frequency signal is greatly affected by the noise signal, resulting in large errors in the subsequent accumulated coherence results and low signal capture sensitivity. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a high-orbit BeiDou signal acquisition method and acquisition device. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] An embodiment of the present invention provides a method for capturing high-orbit BeiDou signals, comprising the steps of:

[0007] Convert BeiDou satellite signals into digital intermediate frequency signals and determine the number of sampling points of the 1 millisecond digital intermediate frequency signal;

[0008] Determining Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points;

[0009] Mixing the 1 millisecond digital intermediate frequency signal with a local carrier, stripping the carrier including the Doppler shift, and obtaining a carrier-stripped signal;

[0010] Performing Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a first Fourier transform result;

[0011] Performing Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a second Fourier transform result;

[0012] multiplying the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result;

[0013] Performing an inverse Fourier transform on the conjugate multiplication result, and performing inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result;

[0014] Performing a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result;

[0015] The peak value is judged by using the cumulative sum of the differential coherence results within a preset time period. When the peak value of the cumulative sum is greater than or equal to a threshold, the signal is captured successfully.

[0016] In one embodiment of the present invention, converting the Beidou satellite signal into a digital intermediate frequency signal includes:

[0017] The Beidou satellite signal is filtered, amplified, mixed and down-converted, and analog-to-digital converted in sequence to obtain the digital intermediate frequency signal.

[0018] In one embodiment of the present invention, mixing the 1 millisecond digital intermediate frequency signal with a local carrier, stripping the carrier including the Doppler shift, and obtaining a carrier-stripped signal includes:

[0019] The 1 millisecond digital intermediate frequency signal is mixed with a sine carrier and a cosine carrier respectively, and the carrier containing the Doppler shift is stripped to obtain the carrier stripped signal:

[0020] y i,N (nT s )=a+jb

[0021] Among them, y i,N (nT s ) is the signal after the digital intermediate frequency signal is stripped of the carrier, a is the signal after the digital intermediate frequency signal is mixed with the sine carrier, and b is the signal after the digital intermediate frequency signal is mixed with the cosine carrier.

[0022] In one embodiment of the present invention, the Fourier transform compensation data is:

[0023] z(n)=exp(-j(π / N)n)

[0024] Wherein, z(n) is the Fourier transform compensation data, N is the number of sampling points of the 1 millisecond digital intermediate frequency signal, and n=0, 1, ..., N-1.

[0025] In one embodiment of the present invention, performing Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a first Fourier transform result, includes:

[0026] The Fourier transform compensation data is bit-multiplied by the carrier stripping signal to obtain a first Fourier transform compensation result:

[0027] y i ' ,N (nT s )=y i,N (nT s )z(n)

[0028] Among them, y i ' ,N (nT s ) is the first Fourier transform compensation result, y i,N (nT s ) is the signal after the carrier is stripped off the digital intermediate frequency signal of the i-th millisecond, z(n) is the Fourier transform compensation data, T s is the sampling time, N is the number of sampling points of the 1 millisecond digital intermediate frequency signal, n=0,1,...,N-1;

[0029] Perform Fourier transform on the first Fourier transform compensation result to obtain the first Fourier transform result FFT(y i ' ,N (nT s )).

[0030] In one embodiment of the present invention, Fourier transform compensation is performed on a 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and Fourier transform is performed on the compensation result to obtain a second Fourier transform result, including:

[0031] Multiply the Fourier transform compensation data by the local ranging code sequence bit by bit to obtain a second Fourier transform compensation result:

[0032] c i ' ,N (nT s )=c i,N (nT s )z(n)

[0033] Among them, c i ' ,N (nT s ) is the second Fourier transform compensation result, c i,N (nT s ) is the 1 millisecond positive ranging code sequence generated locally, z(n) is the Fourier transform compensation data, T s is the sampling time, N is the number of sampling points of the 1 millisecond digital intermediate frequency signal, n=0,1,...,N-1, i is the i-th millisecond;

[0034] Perform Fourier transform on the second Fourier transform compensation result to obtain the second Fourier transform result FFT (c i ' ,N (nT s )).

[0035] In one embodiment of the present invention, the inverse Fourier transform compensation data is:

[0036] i(r)=exp(j(π / N)r)

[0037] Wherein, i(r) is the inverse Fourier transform compensation data, r=0, 1, ..., N-1.

[0038] In one embodiment of the present invention, performing an inverse Fourier transform on the conjugate multiplication result, and performing inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result, includes:

[0039] Perform inverse Fourier transform on the conjugate multiplication result to obtain an inverse Fourier transform result:

[0040] co′(r)=IFFT{FFT(y i ' ,N (nT s ))[FFT(c i ' ,N (nT s ))] *}

[0041] Where co′(r) is the inverse Fourier transform result, N is the number of sampling points of the 1 millisecond digital intermediate frequency signal, i is the i-th millisecond, p=0,1,...,N-1, r=0,1,...,N-1, FFT(y′ i,N (nT s )) is the first Fourier transform result of each sampling point, FFT(c i ' ,N (nT s )) is the second Fourier transform result of each point;

[0042] The inverse Fourier transform compensation data is multiplied bit by bit by the inverse Fourier transform result to obtain the inverse Fourier transform compensation result:

[0043] co(r)=i(r)co′(r)

[0044] Among them, co(r) is the inverse Fourier transform compensation result, and i(r) is the inverse Fourier transform compensation data.

[0045] In one embodiment of the present invention, performing a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result includes:

[0046] Delaying the current 1 millisecond inverse Fourier transform compensation result by a code phase to obtain a delayed signal;

[0047] The delayed signal is bit-multiplied by the inverse Fourier transform compensation result, and the last bit of the inverse Fourier transform compensation result is multiplied by the first bit of the inverse Fourier transform compensation result of the next millisecond to obtain the differential coherence result.

[0048] Another embodiment of the present invention provides a high-orbit BeiDou signal acquisition device, comprising:

[0049] The RF front-end processing module is used to convert Beidou satellite signals into digital intermediate frequency signals and determine the number of sampling points of the 1 millisecond digital intermediate frequency signal;

[0050] A carrier stripping module is used to mix the 1 millisecond digital intermediate frequency signal with the local carrier, strip the carrier containing the Doppler shift, and obtain a carrier stripped signal;

[0051] a compensation data determination module, configured to determine Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points;

[0052] a first Fourier transform module, configured to perform Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a first Fourier transform result;

[0053] a second Fourier transform module, configured to perform Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a second Fourier transform result;

[0054] a conjugate multiplication module, configured to multiply the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result;

[0055] an inverse Fourier transform module, configured to perform an inverse Fourier transform on the conjugate multiplication result, and perform inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result;

[0056] A code phase delay difference module is used to perform a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result;

[0057] The peak value judgment module is used to perform peak value judgment using the cumulative sum of the differential coherence results within a preset time period. When the peak value of the cumulative sum is greater than or equal to a threshold, the signal is captured successfully.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The present invention obtains a 1-millisecond carrier-stripped signal from a 1-millisecond digital intermediate frequency signal, performs Fourier transform compensation and then Fourier transform on both the 1-millisecond carrier-stripped signal and a 1-millisecond local ranging code sequence, then performs inverse Fourier transform and then inverse Fourier transform compensation on the conjugate multiplication result of the second Fourier transform result and the first Fourier transform result, and finally performs differential coherence. Only the 1-millisecond digital intermediate frequency signal and the 1-millisecond local ranging code sequence are required to obtain a 1-millisecond complete coherence value. Compared with the existing method that requires 2-millisecond digital signals to obtain a 1-millisecond complete coherence integral value, the need for digital intermediate frequency signals is reduced, the capture time is shortened, and storage resources are saved. In addition, the 1-millisecond complete coherence value obtained using the 1-millisecond digital intermediate frequency signal is less affected by noise, has smaller errors, and has higher signal capture sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 A schematic diagram of a flow chart of a high-orbit BeiDou signal acquisition method provided by an embodiment of the present invention;

[0061] Figure 2 A flowchart of another high-orbit BeiDou signal acquisition method provided by an embodiment of the present invention;

[0062] Figure 3 A schematic diagram of a method for capturing high-orbit BeiDou signals provided in an embodiment of the present invention;

[0063] Figure 4 A schematic diagram of Fourier transform compensation provided by an embodiment of the present invention;

[0064] Figure 5 A schematic diagram of inverse Fourier transform compensation provided by an embodiment of the present invention;

[0065] Figure 6 A schematic diagram of differential coherence results provided by an embodiment of the present invention;

[0066] Figure 7 A simulation diagram of the BeiDou-11 satellite signal capture results using the method provided in this invention at a received signal strength of -178 decibel watts using a 201 millisecond received signal;

[0067] Figure 8 A simulation diagram of the BeiDou-11 satellite signal code phase search result obtained by applying the method of this invention to a 201 millisecond received signal at a received signal strength of -178 decibel watts, provided by an embodiment of the present invention;

[0068] Figure 9 This is a simulation diagram of the search results for Doppler shift of BeiDou-11 satellite signals using the method of this article using a 201 millisecond received signal at a received signal strength of -178 decibel watts, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0069] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0070] Example 1

[0071] See Figure 1 and Figure 2 , Figure 1 A flowchart of a method for capturing high-orbit BeiDou signals according to an embodiment of the present invention is provided. Figure 2 A flowchart of another high-orbit Beidou signal acquisition method provided by an embodiment of the present invention.

[0072] The high-orbit BeiDou signal acquisition method provided in this embodiment includes the following steps:

[0073] S1. Convert the BeiDou satellite signal into a digital intermediate frequency signal and determine the number of sampling points of the 1 millisecond digital intermediate frequency signal;

[0074] S2. Determine Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points;

[0075] S3, mixing the 1 millisecond digital intermediate frequency signal with the local carrier, stripping the carrier including the Doppler shift, and obtaining a carrier stripped signal;

[0076] S4. Performing Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a first Fourier transform result;

[0077] S5. Perform Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a second Fourier transform result;

[0078] S6. Multiplying the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result;

[0079] S7. performing an inverse Fourier transform on the conjugate multiplication result, and performing inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result;

[0080] S8, performing a differential coherence operation on the signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result;

[0081] S9. Peak value judgment is performed using the accumulated sum of the differential coherence results within a preset time period. When the peak value of the accumulated sum is greater than or equal to a threshold, the signal is captured successfully.

[0082] See Figure 3 , Figure 3 This is a schematic diagram of the principle of the high-orbit Beidou signal acquisition method provided by an embodiment of the present invention. The principle of the high-orbit Beidou signal acquisition method of this embodiment is as follows:

[0083] The 1-millisecond received signal consists of a positive ranging code period (1 millisecond) and a negative ranging code period (1 millisecond). To maximize the correlation value from this 1-millisecond received signal, a 1-millisecond positive ranging code sequence and a 1-millisecond negative ranging code sequence (2 milliseconds in length) are generated locally. To enable parallel code phase operations without affecting the maximum correlation value, a 1-millisecond zero value is added to the 1-millisecond received signal. The parallel code phase search and capture method requires a 2-millisecond data length for Fourier transform and inverse transform. When the phases are aligned, the maximum correlation value can be achieved.

[0084] Specifically, a 1-millisecond zero value is added to the 1-millisecond digital intermediate frequency signal, and the added signal is Fourier transformed. Then, a 1-millisecond positive ranging code signal and a 1-millisecond negative ranging code signal are generated locally. The 1-millisecond positive ranging code signal and the 1-millisecond negative ranging code signal are combined and Fourier transformed. The two Fourier transform results are conjugate multiplied, and the first 1-millisecond value of the multiplication result is taken to obtain a 1-millisecond complete coherent result. Through the properties of the Fourier transform, according to the number of sampling points N of the 1-millisecond intermediate frequency digital signal, the Fourier transform compensation data block and the Fourier inverse transform compensation data block are pre-determined. Then, a 1-millisecond complete coherent value can be obtained through the 1-millisecond digital intermediate frequency signal and the 1-millisecond positive ranging code sequence. The specific principle is as follows:

[0085] The signal after the digital intermediate frequency signal is stripped of the carrier at millisecond i is y i,N (nT s ), then the digital intermediate frequency signal of the ith millisecond is supplemented with a 1-millisecond zero value and can be recorded as y i,2N (nT s ):

[0086]

[0087] Where N is the number of sampling points of the 1 millisecond digital intermediate frequency signal, T s is the sampling time, n=0,1,...,2N-1.

[0088] The ranging code sequence of the Beidou signal has a period of 1 millisecond. The locally generated 1 period, i.e., a 1 millisecond positive ranging code sequence, is denoted as c i,N (nT s ), and the 1 millisecond positive ranging code sequence is supplemented with a 1 millisecond negative ranging code sequence, and the ranging code c after combining the 1 millisecond positive ranging code sequence and the 1 millisecond negative ranging code sequence i,2N (nT s ) is recorded as:

[0089]

[0090] Where N is the number of sampling points of the 1 millisecond digital intermediate frequency signal, T s is the sampling time, n=0,1,...,2N-1. i,2N (nT s ) and c i,2N (nT s ) can be recorded as co(r):

[0091]

[0092] Where r = 0, 1, ..., 2N-1, Y i,2N (K) is y i,2N (nT s) is obtained by Fourier transform, C i,2N (K) is c i,2N (nT s ) is obtained by Fourier transform, * Indicates conjugation.

[0093] Formula (3) shows that y i,2N (nT s ) and c i,2N (nT s ) in the time domain, which is equivalent to their discrete Fourier transform Y i,2N (K) and The product operation in the frequency domain, that is, the product The inverse discrete Fourier transform of is exactly the correlation value co(r) at each code phase that the receiver needs to detect.

[0094] For obtaining a complete coherent integral of 1 millisecond, only the first N points are useful, and the Fourier transform of 2N points here results in a waste of resources. To solve this problem, the properties of Fourier transform are used to calculate Y. i,2N (K) and C i,2N (K) can be rewritten as:

[0095]

[0096] Where p = 0, 1, ..., N-1.

[0097] From equations (4) and (5), we can get that if the Fourier transform compensation data is recorded as z(n):

[0098] z(n)=exp(-j(π / N)n) (6)

[0099] Where n = 0, 1, ..., N-1;

[0100] Then, record y i ' ,N (nT s )for:

[0101] y i ' ,N (nT s )=y i,N (nT s )z(n) (7)

[0102] Where n = 0, 1, ..., N-1;

[0103] Note c i ' ,N (nT s )for:

[0104] ci ' ,N (nT s )=c i,N (nT s )z(n) (8)

[0105] Where n = 0, 1, ..., N-1.

[0106] Equations (7) and (8) represent the Fourier transform compensation results of the 1 millisecond digital intermediate frequency signal and the 1 millisecond local ranging code, respectively.

[0107] From the definition of Fourier transform, we can know that Y i,2N (K) and C i,2N (K) is:

[0108]

[0109]

[0110] Where p = 0, 1, ..., N-1.

[0111] Equations (9) and (10) represent the Fourier transform results of the 2 millisecond digital intermediate frequency signal and the Fourier transform results of the 2 millisecond local ranging code, respectively.

[0112] Furthermore, formula (3) can be expressed as:

[0113]

[0114] Where r = 0, 1, ..., N-1.

[0115] Furthermore, according to formula (11), if the inverse Fourier transform compensation data is recorded as i(r), then co′(r) is recorded as:

[0116] i(r)=exp(j(π / N)r) (12)

[0117]

[0118] Among them, Y i,2N (2p+1) and C i,2N (2p+1) is the expression of the formula derivation process and has no practical significance. FFT(y i ' ,N (nT s )) is the first Fourier transform result of each sampling point, FFT(c i ' ,N (nT s)) is the second Fourier transform result of each point, r = 0, 1, ..., N-1, p = 0, 1, ..., N-1. Equation (13) represents the inverse Fourier transform result co′(r) of a 1 millisecond signal.

[0119] Combining equations (11), (12), and (13), the inverse Fourier transform compensation result is:

[0120] co(r)=i(r)co′(r) (14)

[0121] Combining equations (9), (10), (11), (12), (13), and (14), it can be seen that the useful coherent integration in the 2-millisecond coherent integration result is only the first 1 millisecond. The retained coherent integration of the first 1 millisecond can be compensated and expressed by performing inverse Fourier transform on the Fourier transform result after 1 millisecond compensation.

[0122] From this, we can get that when the number of sampling points N of the 1 millisecond digital intermediate frequency signal is determined, the value of z(n) can be determined and stored in the register. When the 1 millisecond digital intermediate frequency signal is received, the value of the digital intermediate frequency signal is multiplied bit by bit with the value of the Fourier transform compensation z(n), as shown in the following example: Figure 4 As shown, Figure 4 This is a schematic diagram of Fourier transform compensation provided by an embodiment of the present invention. In this case, only a 1mm digital intermediate frequency signal is needed to obtain a 1ms digital intermediate frequency signal to supplement the 1ms zero value Fourier transform result, avoiding the need for a 2N-point Fourier transform. When a 1ms ranging code sequence is generated locally, its value can be bitwise multiplied by the Fourier transform compensation z(n), as shown in the following example: Figure 4 As shown, the Fourier transform result of the locally generated 1 millisecond positive ranging code supplementing the 1 millisecond negative ranging code can be obtained. When the number of sampling points N of the 1 millisecond digital intermediate frequency signal is determined, the value of i(r) can be determined and stored in the register. After obtaining the inverse Fourier transform result, its value is bit-wise multiplied with the inverse Fourier transform compensation to obtain the complete coherent value of 1 millisecond, as shown in Figure 5 As shown, Figure 5 A schematic diagram of inverse Fourier transform compensation provided by an embodiment of the present invention.

[0123] Based on the above principles, the high-orbit BeiDou signal acquisition method of this embodiment specifically includes:

[0124] S1. Convert BeiDou satellite signals into digital intermediate frequency signals.

[0125] Specifically, the receiving antenna receives Beidou satellite signals, and then uses the RF front-end processing module to filter, amplify, mix and down-convert the Beidou satellite signals, and perform analog-to-digital conversion on the Beidou satellite signals in sequence to obtain a digital intermediate frequency signal. The RF front-end module includes a prefilter, a preamplifier, a down-converter, and an analog-to-digital converter. The RF front-end filters and amplifies the signal received by the antenna through the prefilter and preamplifier, and then mixes it with a sinusoidal wave signal generated by the local device. After mixing, the received high-frequency signal is down-converted to an intermediate frequency signal. The analog-to-digital converter samples the intermediate frequency signal, converting it into a digital intermediate frequency signal. The digital intermediate frequency signal with a length of 1 millisecond is stored in the first register according to the first-in-first-out principle. At the same time, the number of sampling points is determined according to the sampling frequency of the analog-to-digital converter.

[0126] S2. Determine Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points.

[0127] Specifically, according to the above principle, the Fourier transform compensation data is formula (6), and the inverse Fourier transform compensation data is formula (12). From formulas (6) and (12), it can be seen that when the number of sampling points N of the 1 millisecond digital intermediate frequency signal is determined, the values ​​of the Fourier transform compensation data z(n) and the inverse Fourier transform compensation data i(r) can be determined, and the values ​​of z(n) and i(r) are stored in the second register and the third register respectively.

[0128] S3. Mix the 1 millisecond digital intermediate frequency signal with the local carrier, strip the carrier including the Doppler frequency shift, and obtain a carrier stripped signal.

[0129] Specifically, the local carrier search range is set to 15000 Hz, the local carrier search bandwidth is set to 500 Hz (that is, the frequencies of the sine carrier and the cosine carrier are taken from 4092500 Hz to 4107500 Hz at intervals of 500 Hz), and the local carrier numerically controlled oscillator is used to generate the local carrier, which includes the sine carrier (sine table) and the cosine carrier (cosine table); the 1 millisecond digital intermediate frequency signal is mixed with the sine carrier and the cosine carrier respectively, and the digital intermediate frequency signal is reduced to near zero frequency through mixing, and the carrier including the Doppler frequency shift is stripped to obtain the carrier stripping signal. The carrier stripping signal is a complex number formed by the sine carrier branch mixing result a and the cosine carrier branch mixing result b:

[0130] y i,N (nT s )=a+jb

[0131] Among them, y i,N (nT s ) is the signal after the digital intermediate frequency signal is stripped of the carrier, a is the signal after the digital intermediate frequency signal is mixed with the sine carrier, and b is the signal after the digital intermediate frequency signal is mixed with the cosine carrier.

[0132] It can be understood that when searching for the same satellite signal in different frequency bands, the phases of the sine and cosine carriers can remain unchanged. Accordingly, their Fourier transforms and their conjugates also remain unchanged. When searching for another satellite signal, the local carrier numerically controlled oscillator generates the corresponding sine and cosine carriers for the other satellite signal, and then the signal search process in the different frequency band is repeated.

[0133] S4. Perform Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a first Fourier transform result. Specifically including:

[0134] S41 . Multiply the Fourier transform compensation data and the carrier stripping signal bit by bit to obtain a first Fourier transform compensation result.

[0135] Specifically, the Fourier transform compensation value of each sampling point is multiplied by the data of each sampling point of the carrier stripping signal to obtain the first Fourier transform compensation result of each sampling point, that is, formula (7): i ' ,N (nT s )=y i,N (nT s )z(n).

[0136] S42, perform Fourier transform on the first Fourier transform compensation result to obtain a first Fourier transform result FFT(y i ' ,N (nT s )).

[0137] S5. Perform Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a second Fourier transform result. Specifically including:

[0138] S51. Multiply the Fourier transform compensation data and the local ranging code sequence bit by bit to obtain a second Fourier transform compensation result.

[0139] Specifically, first, a local ranging code generator generates a 1 millisecond local ranging code. Exemplarily, the code period of the ranging code is 1 millisecond, and each period includes 2046 code elements.

[0140] Then, the Fourier transform compensation value of each point is multiplied by each local ranging code to obtain the second Fourier transform compensation result of each point, that is, formula (8): i ' ,N (nT s )=c i,N (nT s )z(n).

[0141] S52, perform Fourier transform on the second Fourier transform compensation result to obtain a second Fourier transform result FFT (c i ' ,N (nT s )).

[0142] S6. Multiply the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result.

[0143] Specifically, the second Fourier transform result is complex conjugated to obtain a conjugate value, and then the conjugate value is multiplied by the first Fourier transform result to obtain a conjugate multiplication result.

[0144] S7. Perform inverse Fourier transform on the conjugate multiplication result, and perform inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result. Specifically including:

[0145] S71. Perform inverse Fourier transform on the conjugate multiplication result to obtain the inverse Fourier transform result co′(r), which is formula (13).

[0146] S72. Multiply the inverse Fourier transform compensation data and the inverse Fourier transform result bit by bit to obtain the inverse Fourier transform compensation result.

[0147] Specifically, the inverse Fourier transform compensation value of each point is multiplied bit by bit with the inverse Fourier transform value of each point to obtain the inverse Fourier transform compensation result, that is, formula (14): co(r)=i(r)co′(r).

[0148] S8. Perform a differential coherence operation on the signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result.

[0149] To reduce the impact of Beidou secondary modulation, the correlation result of the previous code phase is multiplied by the correlation result of the next code phase. There are 2046 code elements in one period of ranging code, and only one code element may have a negative result for differential multiplication (located at the symbol jump of the Newman-Hoffman code), while the other multiplication results are positive. Therefore, the signal can be differentially coherently integrated for a long time to eliminate the influence of the Newman-Hoffman code and the navigation data code.

[0150] Specifically, the current 1 millisecond inverse Fourier transform compensation result is delayed by one code phase to obtain a delayed signal; the delayed signal is bit-wise multiplied with the inverse Fourier transform compensation result, and the last bit of the inverse Fourier transform compensation result is multiplied with the first bit of the inverse Fourier transform compensation result of the next millisecond to obtain a differential coherence result.

[0151] See Figure 6 , Figure 6 Schematic diagram of differential coherence results provided by an embodiment of the present invention. Exemplarily, the inverse Fourier transform compensation result includes phase 0, phase 1, ..., phase 2045, and the delayed signal delayed by one phase includes phase 1, ..., phase 2045. Phase 1 of the delayed signal is multiplied by phase 0 of the inverse Fourier transform compensation result, and phase 2 of the delayed signal is multiplied by phase 1 of the inverse Fourier transform compensation result, and so on. Finally, phase 2045 of the inverse Fourier transform compensation result is multiplied by phase 0 of the inverse Fourier transform compensation result of the next millisecond to obtain a differential coherence result, and the differential coherence result of 1 millisecond is stored in the fourth register.

[0152] S9. Peak value judgment is performed using the accumulated sum of the differential coherence results within a preset time period. When the peak value of the accumulated sum is greater than or equal to a threshold, the signal is captured successfully.

[0153] Specifically, steps S3-S8 are repeated every millisecond, the new differential coherence result is bitwise added to the coherence result in the fourth register, and the added result is stored in the fourth register. Specifically, a differential coherence operation is performed on the inverse Fourier transform compensation result according to a code phase. When the fourth register is full after storing the differential coherence result for 1 millisecond, a differential coherence operation is performed on the new inverse Fourier transform compensation result for 1 millisecond according to a code phase. The new code phase differential coherence result is added to the differential coherence result already stored in the fourth register and then stored in the fourth register.

[0154] Specifically, the preset time period can be 200 milliseconds. Because the differential coherence operation requires delaying the inverse Fourier transform compensation result by one code phase, calculating the 200-millisecond differential coherence result requires 201 milliseconds of inverse Fourier transform compensation results. After the 200-millisecond differential coherence results are stored in the fourth register, the value of each position stored in the fourth register is compared with a preset threshold. If the peak value exceeds the threshold, the signal is successfully captured, and the capture result is output. If the peak value does not exceed the threshold, the Beidou satellite signal was not captured. For example, the threshold is set to 3e20.

[0155] This embodiment adds a 1-millisecond zero value to the 1-millisecond digital intermediate frequency signal, then locally generates a 1-millisecond positive ranging code signal and a 1-millisecond negative ranging code signal. A parallel code phase search and acquisition method is used for these two signals. By retaining the correlation value of the previous 1-millisecond, the maximum correlation value can be obtained. This method uses 201-millisecond differential coherent integration, and can capture weak signals 2 decibels better than similar methods in this paper, improving capture sensitivity. Furthermore, this embodiment multiplies the 1-millisecond digital intermediate frequency signal and the 1-millisecond ranging code signal by Fourier transform compensation data before Fourier transforming them, and then multiplies the inverse Fourier transform compensation data after inverse Fourier transforming them to obtain a 1-millisecond correlation integral. This reduces the computational complexity of Fourier function operations and reduces storage and computing resources.

[0156] Furthermore, this embodiment further illustrates the effectiveness of the above-mentioned high-orbit Beidou signal acquisition method through simulation. In the simulation, the intermediate frequency (IF) is 4100000 Hz, and the carrier frequency search range is 15000 Hz. Centered around the IF frequency of 4100000 Hz, the search range is 4092500 Hz to 4107500 Hz with intervals of 500 Hz. A ranging code cycle has 2046 code elements, and when sampled at the sampling frequency, the number of sampling points in one ranging code cycle is 16400.

[0157] See Figure 7 , Figure 7 The embodiment of the present invention provides a simulation diagram of the BeiDou-11 satellite signal capture result using the method of this invention at a received signal strength of -178 decibel watts using a 201 millisecond received signal. The Z-axis coherence value is 1-30, which is the Doppler frequency shift index interval of 500 Hz, and 1-1.6e4 is the code phase. Figure 6 It can be obtained that the maximum peak is 4.54e20. At its location, the carrier index of the ranging code is 14, and the code phase at the sampling frequency is 14485; that is, the searched carrier frequency is 4,099,500 Hz; the code phase is 1807.

[0158] See Figure 8 , Figure 8 The embodiment of the present invention provides a simulation diagram of the BeiDou-11 satellite signal code phase search result using the method of this invention for a 201 millisecond received signal at a received signal strength of -178 decibel watts; the y-axis is the coherence value, and the x-axis is the code phase. Figure 8 It can be obtained that the maximum peak is 4.54e20, and the code phase at the sampling frequency at its location is 14485; that is, the searched code phase is 1807.

[0159] See Figure 9 , Figure 9The embodiment of the present invention provides a simulation diagram of the search results of the Doppler frequency shift of the BeiDou-11 satellite signal using the method of this invention at a received signal strength of -178 decibel watts using a 201 millisecond received signal; the y-axis is the coherence value, and the x-axis is the Doppler frequency shift index. Figure 9 It can be obtained that the maximum peak is 4.54e20, and the carrier index of the ranging code at its location is 14; that is, the searched carrier frequency is 4,099,500 Hz.

[0160] The present invention only requires a 1-millisecond digital intermediate frequency signal and a 1-millisecond local ranging code sequence to obtain a 1-millisecond complete coherent value. Compared with the existing method that requires a 2-millisecond digital signal to obtain a 1-millisecond complete coherent integration value, the need for a digital intermediate frequency signal is reduced, the capture time is reduced, and storage resources are saved. In addition, the use of a 1-millisecond digital intermediate frequency signal to obtain a 1-millisecond complete coherent value is less affected by noise, and can capture Beidou signals of -178 decibel watts, with smaller errors and higher signal capture sensitivity. It is suitable for capturing Beidou signals in a high-orbit environment.

[0161] Example 2

[0162] Based on the first embodiment, this embodiment provides a high-orbit Beidou signal acquisition device, which includes:

[0163] The RF front-end processing module is used to convert Beidou satellite signals into digital intermediate frequency signals and determine the number of sampling points of the 1 millisecond digital intermediate frequency signal;

[0164] A carrier stripping module is used to mix the 1 millisecond digital intermediate frequency signal with the local carrier, strip the carrier containing the Doppler shift, and obtain a carrier stripped signal;

[0165] A compensation data determination module, used to determine Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points;

[0166] a first Fourier transform module, configured to perform Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a first Fourier transform result;

[0167] a second Fourier transform module, configured to perform Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a second Fourier transform result;

[0168] a conjugate multiplication module, configured to multiply the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result;

[0169] an inverse Fourier transform module, configured to perform inverse Fourier transform on the conjugate multiplication result, and perform inverse Fourier transform compensation on the inverse Fourier transform result according to inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result;

[0170] A code phase delay difference module is used to perform a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result;

[0171] The peak decision module is used to perform peak decision using the cumulative sum of the differential coherence results within a preset time period. When the peak value of the cumulative sum is greater than or equal to the threshold, the signal is captured successfully.

[0172] For the specific execution steps and beneficial effects of the high-orbit Beidou signal acquisition device of this embodiment, please refer to Example 1, which will not be repeated in this embodiment.

[0173] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A high-orbit BeiDou signal acquisition method, characterized in that: Including steps: Convert BeiDou satellite signals into digital intermediate frequency signals and determine the number of sampling points of the 1 millisecond digital intermediate frequency signal; Determining Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points; Mixing the 1 millisecond digital intermediate frequency signal with a local carrier, stripping the carrier including the Doppler shift, and obtaining a carrier-stripped signal; Performing Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a first Fourier transform result; Performing Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a second Fourier transform result; multiplying the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result; Performing an inverse Fourier transform on the conjugate multiplication result, and performing inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result; Performing a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result; The peak value is judged by using the cumulative sum of the differential coherence results within a preset time period. When the peak value of the cumulative sum is greater than or equal to a threshold, the signal is captured successfully.

2. The high-orbit BeiDou signal acquisition method according to claim 1, characterized in that: Convert BeiDou satellite signals into digital intermediate frequency signals, including: The Beidou satellite signal is filtered, amplified, mixed and down-converted, and analog-to-digital converted in sequence to obtain the digital intermediate frequency signal.

3. The high-orbit BeiDou signal acquisition method according to claim 1, characterized in that: Mixing the 1 millisecond digital intermediate frequency signal with a local carrier, stripping the carrier including the Doppler shift, and obtaining a carrier-stripped signal, comprising: The 1 millisecond digital intermediate frequency signal is mixed with a sine carrier and a cosine carrier respectively, and the carrier containing the Doppler shift is stripped to obtain the carrier stripped signal: in, It is the signal after the digital intermediate frequency signal is stripped of the carrier. represents the i-th millisecond, Indicates the number of sampling points of a 1 millisecond digital intermediate frequency signal. Indicates by sampling time Sampling a continuous signal sampling points, represents the sampling time, is the signal after the digital intermediate frequency signal is mixed with the sinusoidal carrier. It is the signal after mixing the digital intermediate frequency signal and the cosine carrier.

4. The high-orbit BeiDou signal acquisition method according to claim 3, characterized in that: The Fourier transform compensation data is: in, is the Fourier transform compensation data, is the number of sampling points of the 1 millisecond digital intermediate frequency signal, .

5. The high-orbit BeiDou signal acquisition method according to claim 4, characterized in that: Performing Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a first Fourier transform result, including: The Fourier transform compensation data is bit-multiplied by the carrier stripping signal to obtain a first Fourier transform compensation result: in, is the first Fourier transform compensation result, For the The signal after the millisecond digital intermediate frequency signal is stripped of the carrier, is the Fourier transform compensation data, is the sampling time, is the number of sampling points of the 1 millisecond digital intermediate frequency signal, ; Performing Fourier transform on the first Fourier transform compensation result to obtain the first Fourier transform result .

6. The high-orbit BeiDou signal acquisition method according to claim 4, characterized in that: Performing Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and performing Fourier transform on the compensation result to obtain a second Fourier transform result, including: Multiply the Fourier transform compensation data by the local ranging code sequence bit by bit to obtain a second Fourier transform compensation result: in, is the second Fourier transform compensation result, is a 1 millisecond positive ranging code sequence generated locally, is the Fourier transform compensation data, is the sampling time, is the number of sampling points of the 1 millisecond digital intermediate frequency signal, , For the millisecond; Perform Fourier transform on the second Fourier transform compensation result to obtain the second Fourier transform result .

7. The high-orbit BeiDou signal acquisition method according to claim 6, characterized in that: The inverse Fourier transform compensation data is: in, is the inverse Fourier transform compensation data, .

8. The high-orbit BeiDou signal acquisition method according to claim 7, characterized in that: Performing an inverse Fourier transform on the conjugate multiplication result, and performing inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result, including: Perform inverse Fourier transform on the conjugate multiplication result to obtain an inverse Fourier transform result: in, is the inverse Fourier transform result, is the number of sampling points of the 1 millisecond digital intermediate frequency signal, For the millisecond, , , is the first Fourier transform result of each sampling point, is the second Fourier transform result of each point; The inverse Fourier transform compensation data is multiplied bit by bit by the inverse Fourier transform result to obtain the inverse Fourier transform compensation result: in, is the inverse Fourier transform compensation result, is the inverse Fourier transform compensation data.

9. The high-orbit BeiDou signal acquisition method according to claim 1, characterized in that: Performing a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result, including: Delaying the current 1 millisecond inverse Fourier transform compensation result by a code phase to obtain a delayed signal; The delayed signal is bit-multiplied by the inverse Fourier transform compensation result, and the last bit of the inverse Fourier transform compensation result is multiplied by the first bit of the inverse Fourier transform compensation result of the next millisecond to obtain the differential coherence result.

10. A high-orbit Beidou signal acquisition device, characterized in that: include: The RF front-end processing module is used to convert Beidou satellite signals into digital intermediate frequency signals and determine the number of sampling points of the 1 millisecond digital intermediate frequency signal; A carrier stripping module is used to mix the 1 millisecond digital intermediate frequency signal with the local carrier, strip the carrier containing the Doppler shift, and obtain a carrier stripped signal; a compensation data determination module, configured to determine Fourier transform compensation data and inverse Fourier transform compensation data according to the number of sampling points; a first Fourier transform module, configured to perform Fourier transform compensation on the carrier stripping signal according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a first Fourier transform result; a second Fourier transform module, configured to perform Fourier transform compensation on the 1 millisecond local ranging code sequence according to the Fourier transform compensation data, and perform Fourier transform on the compensation result to obtain a second Fourier transform result; a conjugate multiplication module, configured to multiply the conjugate value of the second Fourier transform result by the first Fourier transform result to obtain a conjugate multiplication result; an inverse Fourier transform module, configured to perform an inverse Fourier transform on the conjugate multiplication result, and perform inverse Fourier transform compensation on the inverse Fourier transform result according to the inverse Fourier transform compensation data to obtain an inverse Fourier transform compensation result; A code phase delay difference module is used to perform a differential coherence operation on a signal after the inverse Fourier transform compensation result is delayed by one code phase and the inverse Fourier transform compensation result to obtain a differential coherence result; The peak value judgment module is used to perform peak value judgment using the cumulative sum of the differential coherence results within a preset time period. When the peak value of the cumulative sum is greater than or equal to a threshold, the signal is captured successfully.

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