High-orbit Beidou signal capturing method and capturing device

Abstract

The invention relates to a high-orbit Beidou signal capturing method and device, and the method comprises the steps: converting a Beidou satellite signal into a digital intermediate frequency signal, and determining the number of sampling points of a 1-millisecond signal; fourier transform compensation data and inverse Fourier transform compensation data are determined; mixing the 1 millisecond digital intermediate frequency signal with a local carrier to strip the carrier; fourier transform compensation is carried out on the carrier stripping signal, and then Fourier transform is carried out; fourier transform compensation is carried out on the 1-millisecond local ranging code sequence, and then Fourier transform is carried out; carrying out conjugate multiplication on the two Fourier transform results; inverse Fourier transform is carried out on a conjugate multiplication result, and then inverse Fourier transform compensation is carried out; delaying an inverse Fourier transform compensation result by a code phase and then performing differential coherent operation; and performing peak value judgment by using the accumulated sum of the differential coherence results, and determining that the signal is successfully captured when the peak value is greater than or equal to a threshold value. According to the method, storage resources and computing resources are saved, the influence of noise is small, and the signal capturing sensitivity is high.

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 has gradually increased. It is very important to accurately obtain their position and speed. Relying solely on ground station resources cannot meet actual needs. Therefore, the use of navigation satellite systems to achieve autonomous navigation of high-orbit spacecraft has become a key research object for researchers. In the high-orbit environment, the received Beidou signal is weak due to the influence of the earth's obstruction and long-distance propagation. Realizing the capture of Beidou signals has become the key to autonomous navigation of high-orbit spacecraft.

[0003] During the capture process, if the data symbols of the received signal in milliseconds are different, the data will cancel each other out during the coherent integration process of the capture process, resulting in no obvious peak in the capture result. In order to obtain the coherent value of the 1 millisecond intermediate frequency signal that is not affected by the data cancellation, the existing Beidou signal capture method needs to Fourier transform the 2 millisecond digital intermediate frequency signal, that is: supplement the 1 millisecond local ranging code with a 1 millisecond zero value for Fourier transform; conjugate multiply the results of the Fourier transform of the two; perform inverse Fourier transform on the result and save the previous 1 millisecond related results; use inter-code differential processing to avoid the influence of Newman-Hoffman code jumps and navigation data jumps, and obtain coherent data of different lengths through step-by-step coherence and step-by-step incoherence; determine whether the data is captured by the peak value, and end when the capture is completed.

[0004] When the 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 a 2-millisecond inverse Fourier transform is required after conjugate multiplication; therefore, the method calculates the 1-millisecond complete coherence value and needs 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 capture method and capture device. The technical problem to be solved by the present invention is achieved by the following technical solutions:

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

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

[0008] Determine 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 frequency 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 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 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.

[0016] In one embodiment of the present invention, converting Beidou satellite signals into digital intermediate frequency signals 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, the 1 millisecond digital intermediate frequency signal is mixed with a local carrier, and the carrier including the Doppler frequency shift is stripped to obtain a carrier stripped signal, including:

[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 frequency 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 Fourier transform compensation data, N is the number of sampling points of 1 millisecond digital intermediate frequency signal, n=0, 1, ..., N-1.

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

[0026] The Fourier transform compensation data is bit-multiplied with 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 from 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 a 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] The Fourier transform compensation data is bit-multiplied with the local ranging code sequence 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 a 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 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 the inverse Fourier transform compensation result, includes:

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

[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 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 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 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;

[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 frequency shift, and obtain a carrier stripping signal;

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

[0052] A first Fourier transform module, used for 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;

[0053] A second Fourier transform module is used 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, used for 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;

[0056] A code phase delay difference module, used for 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;

[0057] The peak value judgment module is used to perform peak value judgment using the cumulative sum of 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 stripping signal from a 1 millisecond digital intermediate frequency signal, performs Fourier transform compensation and then Fourier transform on the 1 millisecond carrier stripping 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 a 1 millisecond digital intermediate frequency signal and a 1 millisecond local ranging code sequence are needed to obtain a 1 millisecond complete coherence value. Compared with the existing method that requires 2 milliseconds of digital signals to obtain a 1 millisecond complete coherence integral value, the need to use 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 coherence value is less affected by noise, has a smaller error, and has a 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 high-orbit BeiDou signal acquisition method provided by 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 a differential coherence result provided by an embodiment of the present invention;

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

[0067] Figure 8 A simulation diagram of the code phase search result of the BeiDou-11 satellite signal provided by the embodiment of the present invention when the received signal strength is -178 decibel watts and the method of the present invention is applied to a 201 millisecond received signal;

[0068] Fig. 9 The embodiment of the present invention provides a simulation diagram of the Doppler frequency shift search result of the BeiDou-11 satellite signal using the method of the present invention at a received signal strength of -178 decibel watts using a 201 millisecond received signal. DETAILED DESCRIPTION

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

[0070] Embodiment 1

[0071] See also Figure 1 and Figure 2 , Figure 1 A flowchart of a method for capturing high-orbit BeiDou signals provided by 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, determining 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 frequency shift, and obtaining a carrier stripping 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 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 also Figure 3 , Figure 3 The principle diagram of the high-orbit Beidou signal acquisition method provided in the embodiment of the present invention. The principle of the high-orbit Beidou signal acquisition method in this embodiment is:

[0083] The 1 millisecond received signal is composed of a positive ranging code of one period (1 millisecond) and a negative ranging code of one period (1 millisecond). In order to obtain the maximum correlation value based on the 1 millisecond received signal, a 1 millisecond positive ranging code sequence and a 1 millisecond negative ranging code sequence (with a length of 2 milliseconds) are generated locally; in order to be able to perform parallel code phase operations without affecting the maximum correlation value, a 1 millisecond zero value is supplemented to the 1 millisecond received signal; when using the parallel code phase search and capture method, a data length of 2 milliseconds is required for Fourier transform and inverse transform; when the phases are aligned, the maximum correlation value can be obtained.

[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 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, and the 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 following is the specific principle idea:

[0085] The signal after the digital intermediate frequency signal is stripped of the carrier at the i-th millisecond 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 local generated 1 period, i.e., 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 obtain 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, let 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] Remember 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 result of the 1 millisecond digital intermediate frequency signal and the Fourier transform compensation result of 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 result of the 2 millisecond digital intermediate frequency signal and the Fourier transform result 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 milliseconds coherent integration result is only the first 1 millisecond, and 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] It can be concluded 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), such as Figure 4 As shown, Figure 4 Schematic diagram of Fourier transform compensation provided by an embodiment of the present invention. In this case, only a 1-millisecond digital intermediate frequency signal is needed to obtain a 1-millisecond digital intermediate frequency signal to supplement a 1-millisecond zero value Fourier transform result, thereby avoiding the need to perform a 2N-point Fourier transform. When a 1-millisecond ranging code sequence is generated locally, its value can be bitwise multiplied by the Fourier transform compensation z(n), such as 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 the inverse Fourier transform result is obtained, its value is multiplied bit by bit with the inverse Fourier transform compensation to obtain the 1 millisecond complete coherent value, 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 principle introduction, 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 Beidou satellite signal is received by the receiving antenna, and then the Beidou satellite signal is filtered, amplified, mixed and down-converted, and analog-to-digital converted by the RF front-end processing module to obtain a digital intermediate frequency signal. Among them, the RF front-end module includes a pre-filter, a pre-amplifier, a down-converter, and an analog-to-digital converter; the RF front-end mixes the signal received by the antenna with the sine wave signal generated by the local machine after filtering and amplification by the pre-filter and the pre-amplifier. After mixing, the received high-frequency signal is down-converted into an intermediate frequency signal, and the analog-to-digital converter samples the intermediate frequency signal, converts the intermediate frequency signal into a digital intermediate frequency signal, and stores the digital intermediate frequency signal with a length of 1 millisecond 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 Fourier inverse 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 Fourier inverse transform compensation data is formula (12). It can be seen from formula (6) and formula (12) 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 Fourier inverse 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, and strip the carrier including the Doppler frequency shift to 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 is generated by a local carrier digitally controlled oscillator. The local carrier includes a sine carrier (sine table) and a cosine carrier (cosine table); a 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 a carrier stripping signal. The carrier stripping signal is a complex number formed by the mixing result a of the sine carrier branch and the mixing result b of the cosine carrier branch:

[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 carrier and the cosine carrier can remain unchanged, and accordingly, their Fourier transform and their conjugate values ​​also remain unchanged. When searching for another satellite signal, the local carrier numerically controlled oscillator generates the sine carrier and cosine carrier corresponding to the other satellite signal, and then performs the signal search process in different frequency bands.

[0133] 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. Specifically including:

[0134] S41, multiplying 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, performing 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. 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, multiplying 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 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] In order 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 operation (located at the sign 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 impact 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 also Figure 6 , Figure 6 Schematic diagram of differential coherence results provided for an embodiment of the present invention. Exemplarily, the inverse Fourier transform compensation result includes phase 0, phase 1, ..., phase 2045, the delayed signal delayed by one phase includes phase 1, ..., phase 2045, the phase 1 of the delayed signal is multiplied by the phase 0 of the inverse Fourier transform compensation result, the phase 2 of the delayed signal is multiplied by the phase 1 of the inverse Fourier transform compensation result, and so on, and finally the phase 2045 of the inverse Fourier transform compensation result is multiplied by the 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 addition result is stored in the fourth register. Specifically, the differential coherence operation is performed on the inverse Fourier transform compensation result according to a code phase, and when the fourth register is full after the 1 millisecond differential coherence result is stored, the new 1 millisecond inverse Fourier transform compensation result is differentially coherently operated according to a code phase, and 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. Since the differential coherence operation needs to delay the Fourier inverse transform compensation result by one code phase, the calculation of the 200 millisecond differential coherence result requires the 201 millisecond Fourier inverse transform compensation result. 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 the preset threshold. If the peak value exceeds the threshold, the signal is captured successfully and the capture result is output; if the peak value does not exceed the threshold, the Beidou satellite signal is not captured. Exemplarily, the threshold is set to 3e20.

[0155] This embodiment adds a 1-millisecond zero value to the 1-millisecond digital intermediate frequency signal, and then locally generates a 1-millisecond positive ranging code signal and a 1-millisecond negative ranging code signal. The parallel code phase search capture method is used for the two signals. By retaining the previous 1-millisecond correlation value, the maximum correlation value can be obtained. The method uses 201-millisecond differential coherent integration, and the weak signal that can be captured is 2 decibels higher than the method similar to this article, thereby improving the capture sensitivity. In addition, this embodiment multiplies the Fourier transform compensation data before Fourier transforming the 1-millisecond digital intermediate frequency signal and the 1-millisecond ranging code, and then multiplies the Fourier inverse transform compensation data after Fourier inverse transforming, so as to obtain a 1-millisecond correlation integral, reduce the amount of Fourier function calculation, and reduce storage resources and computing resources.

[0156] Furthermore, this embodiment further illustrates the effect of the above-mentioned high-orbit Beidou signal acquisition method through simulation. In the simulation, the intermediate frequency is 4100000 Hz, the carrier frequency search range is 15000 Hz, with the intermediate frequency of 4100000 Hz as the center and 500 Hz as the interval, the search range is 4092500 Hz to 4107500 Hz; one period of ranging code has 2046 code elements, and it is sampled according to the sampling frequency, so the number of sampling points of one period of ranging code is 16400.

[0157] See also Figure 7 , Figure 7 The embodiment of the present invention provides a simulation diagram of the BeiDou-11 satellite signal capture result using a 201 millisecond received signal under a received signal strength of -178 decibel watt, wherein the Z-axis coherence value, 1-30 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 which 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 also Figure 8 , Figure 8 The embodiment of the present invention provides a simulation diagram of the BeiDou-11 satellite signal code phase search result when the received signal strength is -178 decibel watts and the method of the present invention is applied to a 201 millisecond received signal; 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 also Fig. 9 , Fig. 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 the present 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. Fig. 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 needs 1 millisecond of digital intermediate frequency signal and 1 millisecond of local ranging code sequence to obtain 1 millisecond of complete coherence value. Compared with the existing method that needs 2 milliseconds of digital signal to obtain 1 millisecond of complete coherence integration value, the need to use digital intermediate frequency signal is reduced, the capture time is reduced, and storage resources are saved. In addition, the use of 1 millisecond of digital intermediate frequency signal to obtain 1 millisecond of complete coherence value is less affected by noise, and the Beidou signal of -178 decibel watt can be captured, the error is smaller, and the signal capture sensitivity is higher, which is suitable for capturing Beidou signals in a high-orbit environment.

[0161] Embodiment 2

[0162] On the basis of the first embodiment, this embodiment provides a high-orbit Beidou signal acquisition device, and the high-orbit Beidou signal acquisition device includes:

[0163] The RF front-end processing module is used to 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;

[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 frequency shift, and obtain a carrier stripping signal;

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

[0166] A first Fourier transform module, used for 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;

[0167] A second Fourier transform module is used 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, used for multiplying 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 is used to 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;

[0170] A code phase delay difference module is used to perform 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 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.

[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 contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A high-orbit Beidou signal acquisition method, characterized in that: Includes steps: Convert Beidou satellite signals into digital intermediate frequency signals and determine the number of sampling points of 1 millisecond digital intermediate frequency signals; Determine 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 frequency 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 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 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.

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 frequency shift, and obtaining a carrier stripped signal, including: The 1 millisecond digital intermediate frequency signal is mixed with a sine carrier and a cosine carrier respectively, and the carrier containing the Doppler frequency shift is stripped to obtain the carrier stripped signal: y i,N (nT s )=a+jb 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.

4. The high-orbit Beidou signal acquisition method according to claim 1, characterized in that: The Fourier transform compensation data is: z(n)=exp(-j(π / N)n) Wherein, z(n) is Fourier transform compensation data, N is the number of sampling points of 1 millisecond digital intermediate frequency signal, n=0, 1, ..., N-1.

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 with the carrier stripping signal to obtain a first Fourier transform compensation result: y′ i,N (nT s )=y i,N (nT s )z(n) 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 from 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 a 1 millisecond digital intermediate frequency signal, n=0,1,...,N-1; Perform Fourier transform on the first Fourier transform compensation result to obtain the first Fourier transform result FFT(y′ i,N (nT s )).

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: The Fourier transform compensation data is bit-multiplied with the local ranging code sequence to obtain a second Fourier transform compensation result: c′ i,N (nT s )=c i,N (nT s )z(n) 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 a 1 millisecond digital intermediate frequency signal, n=0,1,...,N-1, i is the i-th millisecond; Perform Fourier transform on the second Fourier transform compensation result to obtain the second Fourier transform result FFT(c′ i,N (nT s )).

7. The high-orbit Beidou signal acquisition method according to claim 1, characterized in that: The inverse Fourier transform compensation data is: i(r)=exp(j(π / N)r) Wherein, i(r) is the inverse Fourier transform compensation data, r=0, 1, ..., N-1.

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 the inverse Fourier transform result: co′(r)=IFFT{FFT(y′ i,N (nT s ))[FFT(c′ i,N (nT s ))] * } 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; 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: co(r)=i(r)co′(r) Among them, co(r) is the inverse Fourier transform compensation result, and i(r) is the inverse Fourier transform compensation data.

9. The high-orbit Beidou signal acquisition method according to claim 1, characterized in that: The method further comprises: 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 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 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 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; 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 frequency shift, and obtain a carrier stripping signal; A compensation data determination module, used to determine Fourier transform compensation data and Fourier inverse transform compensation data according to the number of sampling points; A first Fourier transform module, used for 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; A second Fourier transform module is used 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, used for 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; A code phase delay difference module, used for 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 judgment module is used to perform peak value judgment using the cumulative sum of 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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