CN114690217A - GPS L1 rapid and accurate capturing method and device and computer storage medium - Google Patents
GPS L1 rapid and accurate capturing method and device and computer storage medium Download PDFInfo
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- CN114690217A CN114690217A CN202011621027.4A CN202011621027A CN114690217A CN 114690217 A CN114690217 A CN 114690217A CN 202011621027 A CN202011621027 A CN 202011621027A CN 114690217 A CN114690217 A CN 114690217A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/246—Acquisition or tracking or demodulation of signals transmitted by the system involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
Abstract
The invention provides a rapid and accurate acquisition method of a GPS L1, which comprises the following steps: performing half-chip sampling and spreading on a spreading code; carrying out intermediate frequency down-conversion and resampling on satellite data; performing frequency mixing on a carrier signal obtained by accumulating a plurality of local carrier sequences corresponding to a preset Doppler frequency group and the processed satellite data to complete Doppler down-conversion to obtain zero Doppler data; segmenting the 2T (T is less than or equal to 10) millisecond zero Doppler data by taking 1 millisecond as a length, and respectively carrying out coherent accumulation on the former T millisecond data and the latter T millisecond data to obtain 2 segments of 1 millisecond length satellite data; performing FFT (fast Fourier transform) operation, complex multiplication and IFFT (inverse fast Fourier transform) operation on the processed spread spectrum codes and satellite data to obtain a cyclic correlation result; respectively solving the module of the 2-section cyclic correlation results and searching the maximum value in the module, if the maximum value exceeds a preset threshold, judging that the coarse acquisition is successful, and calculating the corresponding satellite signal code phase at the moment; if the maximum value does not exceed the preset threshold, updating the preset Doppler frequency group to carry out the next group of Doppler acquisition; and determining the section of the 2T millisecond satellite data in which the maximum value appears, and selecting the section of the satellite data for Doppler accurate acquisition. The method improves the Doppler acquisition precision while accelerating the search speed.
Description
Technical Field
The invention relates to the technical field of satellite navigation, in particular to a method and a device for quickly and accurately capturing GPS L1.
Background
How to perform fast acquisition and realize accurate acquisition of doppler based on fast acquisition is a problem to be solved by modern GPS receiver design.
The acquisition of the satellite signal is realized by correlation search, a circular correlation algorithm is usually used, and the Doppler frequency is required to be searched one by one in the whole frequency search range according to a certain frequency interval; especially when the acquisition signal-to-noise ratio needs to be improved by increasing the coherent integration time, the frequency search interval needs to be reduced, which further increases the frequency search times. Therefore, the rapid capture can be realized by reducing the frequency searching times; while decreasing the number of frequency searches requires increasing the frequency search interval, which means a decrease in the doppler acquisition accuracy. Therefore, the capture speed and the capture accuracy are generally in a pair of contradiction.
How to achieve faster search and improve doppler accuracy, especially for how the GPS L1 signal is implemented in hardware, is a problem that needs to be solved by current GPS receiver designs.
Disclosure of Invention
In view of the above, the present invention provides a method, an apparatus and a computer storage medium for fast and accurate acquisition of GPS L1, so as to solve the deficiencies of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the embodiment of the invention provides a rapid and accurate acquisition method of GPS L1, which comprises the following steps:
performing half-chip sampling and spreading on a spreading code;
carrying out intermediate frequency down-conversion and resampling on satellite data;
performing frequency mixing on a carrier signal obtained by accumulating a plurality of local carrier sequences corresponding to a preset Doppler frequency group and the processed satellite data to complete Doppler down-conversion to obtain zero Doppler data;
segmenting the 2T (T is less than or equal to 10) millisecond zero Doppler data by taking 1 millisecond as a length, and respectively carrying out coherent accumulation on the former T millisecond data and the latter T millisecond data to obtain 2 segments of 1 millisecond length satellite data;
performing FFT (fast Fourier transform) operation, complex multiplication and IFFT (inverse fast Fourier transform) operation on the processed spread spectrum codes and satellite data to obtain a cyclic correlation result;
respectively solving the module of the 2-section cyclic correlation results and searching the maximum value in the module, if the maximum value exceeds a preset threshold, judging that the coarse acquisition is successful, and calculating the corresponding satellite signal code phase at the moment; if the maximum value does not exceed the preset threshold, updating the preset Doppler frequency group to carry out the next group of Doppler acquisition;
and determining the section of the 2T millisecond satellite data in which the maximum value appears, and selecting the section of the satellite data for Doppler accurate acquisition.
Further, the half-chip sampling and spreading of the spreading code specifically includes:
repeatedly inserting the chip after each chip; changing 1 chip to the same 2 chips; spreading code sequence each data represents a chip before spreading and each data represents a half chip after spreading;
repeating the spreading code sequence 2 times spreads the spreading code into 2 spreading periods.
Further, the satellite data intermediate frequency down-conversion and resampling specifically comprises:
mixing satellite data with local intermediate frequency carrier waves to obtain zero intermediate frequency data;
accumulating zero intermediate frequency data belonging to the same half chip according to the spreading code rate to generate half chip resampling data;
the half-chip resampled data is then divided into 2T segments, where each segment of 1 millisecond data represents 1 spreading period.
Further, the predetermined Doppler frequency set comprises a plurality of Doppler values { f }1，f2，…，fi，…，fxIn which fi+1-fiIs a fixed value; i is 0,1, … …, x-1. The search for x doppler is completed each time a cyclic correlation acquisition is completed.
Further, performing FFT operation, complex multiplication, and IFFT operation on the processed spreading code and satellite data to obtain a cyclic correlation result specifically includes:
complementing the processed spread spectrum code with 0 to length NfftAnd performing FFT operationCalculating to obtain a spread spectrum code frequency spectrum; respectively complementing the 2 satellite data with 0 to the length NfftPerforming FFT operation, and taking conjugation to obtain 2 sections of satellite data frequency spectrums; multiplying the spectrum of the spread spectrum code with the spectrum of 2 satellite data respectively; and performing IFFT operation on the multiplication result to obtain a 2-section cyclic correlation result.
Further, the preset Doppler frequency set { f is updated1，f2，…，fi，…，fxThe same step value f is added to each Doppler value in the pairstep(ii) a Updating the formula: f. ofi＝fi+fstep(ii) a Where i is 1,2, … …, x.
Further, determining which segment of the 2T ms length satellite the maximum value occurs in, and selecting the segment of satellite data for doppler accurate acquisition specifically includes:
selecting first or second T millisecond satellite data according to the section with maximum value, calculating the initial position of satellite data spread spectrum code according to code phase, stripping spread spectrum code with T periods from the initial position, and stripping the data with length nxCoherent accumulation of points, followed by NfftAnd point FFT, searching the maximum value of the FFT result module value, and calculating and capturing the Doppler frequency accurate value according to the maximum value position.
The embodiment of the invention also provides a device for quickly and accurately capturing the GPSL1, which comprises: the device comprises a spread spectrum code processing module, a data resampling module, a Doppler stripping module, a coherent accumulation module, an FFT module, a multiplication module, an IFFT module, a capture judgment module, a Doppler configuration module and a Doppler fine capture module;
the spread spectrum code preprocessing module is used for carrying out half chip sampling and spreading on the spread spectrum code;
the data resampling module is used for carrying out intermediate frequency down conversion and resampling on satellite data;
the Doppler stripping module is used for mixing a carrier signal obtained by accumulating a plurality of local carrier sequences corresponding to a preset Doppler frequency group with the satellite data processed by the data resampling module to complete Doppler down-conversion to obtain zero Doppler data;
the coherent accumulation module is used for segmenting the 2T (T is less than or equal to 10) millisecond zero Doppler data by taking 1 millisecond as a length, and respectively carrying out coherent accumulation on the former T millisecond data and the latter T millisecond data to obtain 2 segments of satellite data with the length of 1 millisecond;
the FFT module is used for carrying out N on input datafftPerforming point FFT operation; complementing input data by 0 to NfftPoint; the input data comprises 2 types of spread spectrum codes and satellite data, and are respectively output to the multiplication module after FFT is finished;
the multiplication module firstly takes conjugation to the satellite data frequency spectrum, then carries out complex multiplication on the conjugated data and the spread spectrum code frequency spectrum, and outputs the result to the IFFT module;
the IFFT module carries out IFFT transformation on input data to obtain a cyclic correlation result and outputs the cyclic correlation result to the capture judgment module;
the acquisition judging module is used for solving the modulus of the cyclic correlation result, searching the maximum value in the cyclic correlation result, judging that coarse acquisition is successful if the maximum value exceeds a preset threshold, calculating the code phase of the corresponding satellite signal at the moment, recording the number of sections with the maximum value, and outputting the sections to the Doppler fine acquisition module; if the maximum value does not exceed the preset threshold, judging that the current Doppler value is failed to capture, and outputting a failure mark to the Doppler configuration module;
the Doppler configuration module is used for calculating and updating a set Doppler frequency set so as to carry out the next set of Doppler acquisition;
the Doppler precise acquisition module is used for determining which section of the satellites with the length of 2T milliseconds the maximum value appears in and selecting the data of the section of satellites to carry out Doppler precise acquisition.
Embodiments of the present invention also provide a computer storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the method as described above.
The principle of selecting parameters in the above-described processing procedure is analyzed below.
It can be derived from theory that the amplitude A and the integration time T of the correlation result are obtained during the searchcoh(TcohT/1000) and frequency errorfeIn connection with, namely:
A∝Tcohsinc(feTcoh)
the frequency search is performed using x doppler, which is equivalent to using them to perform correlation separately and then accumulating the correlation results. Suppose that in a certain search, fiThe value of the Doppler frequency closest to the true Doppler of the satellite in the Doppler search range is the difference f from the true DopplereiAt this time, there is feTcohClose to 0, a peak will appear in the search result; but because of other x-1 Doppler values and f in the searchiWith an integer number of frequency intervals Δ f between them and the true dopplereIs large so that feTcohThe value of (a) is larger, so that the attenuation of the sinc function is larger, and the acquisition results corresponding to other x-1 Doppler values are equal to noise, therefore, the noise is increased when the acquisition results corresponding to the x Doppler values are accumulated, the signal-to-noise ratio of the related results is reduced, the detection probability is reduced, and the reduction of x is favorable for improving the acquisition detection probability.
As can be seen from the above formula, T is increasedcohIs taken into account, but f is guaranteedeTcohThe coherent integration result can be improved without change, and the capture sensitivity and the detection probability can be improved. To ensure TcohThe validity of the millisecond length data coherence divides 2T periods into 2 parts and performs coherent accumulation in the processing process, because the navigation bit duration of the GPS L1 signal is 20 milliseconds, the division into 2 parts can ensure that at least one section of data T periods can not span 2 navigation bits, so that the problem of symbol jump caused by navigation data modulation does not exist in the coherent accumulation process, namely that the coherent accumulation of at least one section is valid.
Doppler search time step value f is analyzed as followsstepThe values should follow the principle.
Without loss of generality, feNot equal to 0. To guarantee the integral gain and detection probability, f should be guaranteed in generaleTcohSufficiently small, i.e. sinc (f)eTcoh) Attenuation is small, assuming sinc (f)eTcoh) Greater than a certain value α, and feTcohShould be less than a fixed value beta (derived from alpha), then there is | feThe | is less than or equal to 1000 beta/T. Typically, the Doppler step value is fstepShould be set to | fe2 times the maximum value of l.
From the correlation result, if the sinc function gain required to be guaranteed is not changed, increasing T means | feThe upper limit of | is decreased, that means fstepI.e. an increase in the number of searches.
The strategy for doppler search can be set as: let Doppler search range be [ -F, F]And satisfies the condition 2F ═ x Δ F; f. of1Has an initial value of-F andi-F + (i-1) Δ F; let Doppler step N times, and satisfy Δ f ═ Nfstep. If a single Doppler frequency search is used, Nx searches are needed to cover [ -F, F]The search range of (2). As can be seen from the above-described parallel frequency search method, x Doppler frequencies can be searched for each search, where the frequencies are [ -F, F]In the search range of (2), the number of searches is changed from Nx to N, and is reduced to 1/x.
Therefore, x, f should be determined comprehensively according to the acquisition speed, acquisition Doppler error and acquisition sensitivity requirementsstepAnd T.
In essence, the process of frequency accurate calculation using FFT is still a process of one-time coherent integration, and the integration result is also proportional to sinc (f)eTcoh) Therefore, T iscohAnd feThe foregoing relationship still needs to be satisfied. The following analyzes the parameter configuration in the fine capture.
In order to save hardware cost, the number of FFT points in fine capture is still NfftN is performed on the signal after stripping the spreading codexAnd (4) point accumulation. If the original data sampling rate is fsThe accumulated resampling frequency should be fsr＝fs/nxThe frequency resolution after FFT is fd＝fsr/Nfft. Assuming that the maximum allowable error of the Doppler search is feMaxHas f ofd＝fs/(nxNfft)≤2feMaxIt should be: n isx≥fs/2NfftfeMaxAt this time have
It can be seen that n is increasedxNfftCan reduce Doppler acquisition error, at NfftWhen determined, n can be increasedxThe reduction of Doppler error is realized, and the essence of the reduction is that the data sampling rate of resampling is reduced so as to achieve the purpose of improving frequency resolution and reducing frequency error; however, if f is consideredsrShould satisfy the sampling theorem, so nxCan not be increased infinitely, and the value thereof is determined according to the integral duration T and the Doppler capture error feAnd the number of FFT points NfftDetermined by comprehensive consideration.
According to the technical scheme provided by the invention, a plurality of Doppler values of the satellite signal are simultaneously stripped, so that parallel cyclic correlation acquisition of partial Doppler frequencies is realized, the acquisition estimation value of the code phase is obtained, the computation amount in the acquisition process is reduced, and the rapid acquisition is favorably completed; the Doppler frequency value is accurately calculated by using the acquired code phase, so that a tracking loop can quickly finish a traction process; meanwhile, coherent integration of T periods is carried out in the capturing process, so that the capturing sensitivity is improved to a certain extent.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic flowchart of a method for quickly and accurately capturing GPS L1 according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a fast and accurate GPS L1 capturing device according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic flowchart of a method for quickly and accurately capturing GPS L1 according to an embodiment of the present invention. The method comprises the following steps:
and S101, performing half-chip sampling and spreading on the spreading codes.
The sample length of the spreading code is changed to 2 times of the original length by repeatedly inserting the chip after each chip, and the length after sampling is assumed to be 2M.
And repeating the sampled local spreading code sequence for 2 times to enable the spreading code to be 2 spreading periods.
The spread spectrum code data after the processing is complemented to length N by 0fftAnd performing FFT to obtain spread spectrum code spectrum data.
And S102, carrying out intermediate frequency down-conversion and resampling on the satellite data.
Taking the satellite data length of GPS L1 as 2T milliseconds, generating a local complex carrier signal with the frequency of the signal intermediate frequency fi0And mixing and multiplying the local carrier signal and the satellite signal to generate zero intermediate frequency data. Accumulating zero intermediate frequency data belonging to the same half chip according to the chip rate to generate half chip resampling data, dividing the data into 2T sections according to 2M data as one section, wherein each section is 1 millisecond data, namely representing 1 spread spectrum period, generating data S1。
And S103, accumulating a plurality of local carrier sequences corresponding to the preset Doppler frequency group to obtain a carrier signal.
Setting Doppler search range to [ -F, F]Presetting the Doppler frequency set { f1，f2，…，fi，…，fxX Doppler values are taken1Has an initial value of f1Is ═ F and hasi+1-fi＝Δf，Δf＝2F/x。
x Doppler values { f1，f2，…，fi，…，fxProduce sequences s corresponding to x local carriers1，s2，…，si，…，sxIs added up to a carrier signal
S104, pair S1And performing a plurality of Doppler down-conversions to complete Doppler stripping.
Will S1Multiplying the sum by S to obtain a zero Doppler signal S2。
And S105, carrying out coherent accumulation.
For 2T (T is less than or equal to 10) millisecond S2The data is segmented by taking 1 millisecond as the length, and the data of the first T milliseconds and the data of the second T milliseconds are accumulated to respectively generate 2 segments of satellite data with the length of 1 millisecond.
And S106, performing FFT operation.
Respectively zero-filling 2 satellite data segments into NfftPerforming FFT operation, and taking conjugation to generate 2 sections of satellite data frequency spectrums;
and S107, multiplying the spectrum of the spread spectrum code by the spectrum of 2 satellite data respectively.
And S108, performing IFFT operation on the multiplication result to obtain a cyclic correlation result.
S109, capturing judgment and calculating capturing code phase
Respectively solving the modulus of the 2-section correlation results, searching the maximum value in the modulus, judging that coarse acquisition is successful if the maximum value exceeds a preset threshold, calculating the code phase of the corresponding satellite signal at the moment, and jumping to the step S111 to accurately acquire the Doppler value; if the maximum value does not exceed the preset threshold, the current given Doppler value is considered to be failed to be captured, and the next step S110 is skipped.
And S110, updating the Doppler frequency group.
If the capture fails, update { f1，f2，…，fi，…，fxIs fi＝fi+fstepAnd determine fxIf the maximum acquisition range is exceeded, the current satellite acquisition fails, and the acquisition is finished; otherwise, the step S104 is skipped to perform the next Doppler acquisition judgment calculation.
S111, accurate acquisition of Doppler value
Selecting one section of satellite signal with maximum value in 2 sections of T millisecond length satellite, shifting a certain length (calculating satellite data length needing shifting by capturing code phase), stripping spread spectrum code in T periods, and every nxThe points are accumulated and then 0 is added to the length NfftAnd performing FFT to calculate an accurate Doppler value.
In the whole searching process, a plurality of Doppler frequencies are used for parallel searching at the same time, so that the operation amount is reduced, the rapid acquisition is facilitated, and the signal to noise ratio of the acquisition detection is reduced; coherent integration capture is carried out for a plurality of periods, so that the signal-to-noise ratio of capture detection can be improved; meanwhile, the Doppler frequency is accurately captured, so that the tracking loop can be quickly pulled.
As shown in fig. 2, an embodiment of the present invention provides a fast and accurate GPS L1 acquisition apparatus, including: the system comprises a spread spectrum code processing module 101, a data resampling module 102, a doppler stripping module 103, a coherent accumulation module 104, an FFT module 105, a multiplication module 106, an IFFT module 107, an acquisition decision module 108, a doppler configuration module 109 and a doppler fine acquisition module 110.
The spreading code processing module 101 is configured to perform half-chip sampling and spreading on a spreading code. Sequentially repeating the spread spectrum codes according to the sequence, and changing one chip into the same 2 chips; then repeating for 2 cycles; output to the FFT module 105.
The data resampling module 102 is configured to perform intermediate frequency down-conversion and resampling on the satellite data. The local carrier is generated at an intermediate frequency, satellite data is down-converted to 0 intermediate frequency, and then the data is packed into half chip data according to a spreading code rate and output to the doppler stripping module 103.
The doppler stripping module 103 is configured to perform frequency mixing on a carrier signal obtained by accumulating a plurality of local carrier sequences corresponding to a preset doppler frequency group and the satellite data processed by the data resampling module to complete doppler down-conversion, so as to obtain zero doppler data. And performing carrier Doppler stripping on the half-chip packaged data. The module generates a plurality of local carriers according to a plurality of input Doppler values, accumulates the local carriers into a carrier signal, performs complex multiplication with half-chip satellite data, completely strips the carrier from the satellite signal, changes the carrier into 0 Doppler data, and outputs the 0 Doppler data to the coherent accumulation module 104.
The coherent accumulation module 104 accumulates zero doppler data with 2T periods into 2 segments, wherein the first T periods are accumulated into 1 period as 1 segment, and the last T periods are accumulated into 1 period as another 1 segment. 2 segments of 1 millisecond length satellite data are obtained.
The FFT module 105 is for performing N on the input datafftAnd (6) point FFT. Complementing input data by 0 to NfftAnd (4) point. The input data comprises 2 kinds of spread spectrum codes and satellite data, and the data are respectively output to the multiplication module 106 after finishing FFT.
The multiplication module 106 firstly takes conjugate of the satellite data spectrum, then performs complex multiplication on the conjugate data and the spread spectrum code spectrum, and outputs the result to the IFFT module 107.
The IFFT module 107 performs IFFT transformation on the input data to obtain a cyclic correlation result, and outputs the result to the capture decision module 108.
The acquisition decision module 108 calculates the modulus of the correlation result, searches the maximum value in the correlation result, and if the maximum value exceeds a preset threshold, the acquisition is decided to be successful, the satellite signal code phase is calculated according to the position where the maximum value appears, the number of sections where the maximum value appears is recorded, and the section number is output to the doppler fine acquisition module 110; if the current doppler value fails to exceed the preset threshold, it is determined that the current doppler value acquisition fails, and a failure flag is output to the doppler configuration module 109.
The Doppler configuration module 109 calculates the Doppler value, the next Doppler value being fi＝fi+fstepAnd judge fxWhether the Doppler search range is exceeded; if not, updating { f1，f2，…，fi，…，fxOutputting the Doppler signals to a Doppler stripping module 103 to continue the next group of Doppler acquisition; if the range is exceeded, declaring the capture failure and ending the capture。
The doppler fine acquisition module 110, which can obtain a section of the maximum value appearing in the 2-section T millisecond length satellite from the acquisition decision module 108, selects the satellite signal of the section, shifts a certain length (calculating the satellite data length needing shifting from the acquisition code phase), performs spreading code stripping for T periods, and performs every n periodsxThe points are accumulated and then 0 is added to the length NfftAnd performing FFT to calculate an accurate Doppler value.
It should be noted that: the GPS L1 fast and accurate capturing device provided in the above embodiments is only illustrated by the above division of the program modules when performing capturing, and in practical applications, the above processing allocation may be completed by different program modules according to needs, that is, the internal structure of the device is divided into different program modules to complete all or part of the above described processing. In addition, the GPS L1 fast and accurate capturing apparatus and the capturing method provided by the above embodiments belong to the same concept, and the specific implementation process is described in detail in the method embodiments, and the beneficial effects thereof are the same as the method embodiments and are not described herein again.
An embodiment of the present invention further provides a computer storage medium, which is a computer-readable storage medium, and a computer program is stored thereon, where the computer program is executable by a processor of a GPS L1 fast and accurate acquisition apparatus to perform the steps of the aforementioned GPS L1 fast and accurate acquisition method. The computer-readable storage medium may be a magnetic random access Memory (FRAM), a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable Programmable Read-Only Memory (EPROM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a Flash Memory (Flash Memory), a magnetic surface Memory, an optical disk, or a Compact Disc Read-Only Memory (CD-ROM), among other memories.
In the embodiments provided in the present invention, it should be understood that the disclosed method and intelligent device may be implemented in other ways. The above-described device embodiments are merely illustrative, for example, the division of the unit is only a logical functional division, and there may be other division ways in actual implementation, such as: multiple units or components may be combined, or may be integrated into another system, or some features may be omitted, or not implemented. In addition, the coupling, direct coupling or communication connection between the components shown or discussed may be through some interfaces, and the indirect coupling or communication connection between the devices or units may be electrical, mechanical or other forms.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed on a plurality of network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (10)
1. A rapid accurate acquisition method of a GPS L1 is characterized by comprising the following steps:
performing half-chip sampling and spreading on a spreading code;
carrying out intermediate frequency down-conversion and resampling on satellite data;
performing frequency mixing on a carrier signal obtained by accumulating a plurality of local carrier sequences corresponding to a preset Doppler frequency group and the processed satellite data to complete Doppler down-conversion to obtain zero Doppler data;
segmenting the 2T (T is less than or equal to 10) millisecond zero Doppler data by taking 1 millisecond as a length, and respectively carrying out coherent accumulation on the former T millisecond data and the latter T millisecond data to obtain 2 segments of 1 millisecond length satellite data;
performing FFT (fast Fourier transform) operation, complex multiplication and IFFT (inverse fast Fourier transform) operation on the processed spread spectrum codes and satellite data to obtain a cyclic correlation result;
respectively solving the module of the 2-section cyclic correlation results and searching the maximum value in the module, if the maximum value exceeds a preset threshold, judging that the coarse acquisition is successful, and calculating the corresponding satellite signal code phase at the moment; if the maximum value does not exceed the preset threshold, updating the preset Doppler frequency group to carry out the next group of Doppler acquisition;
and determining the section of the 2T millisecond satellite data in which the maximum value appears, and selecting the section of the satellite data for Doppler accurate acquisition.
2. The method of claim 1, wherein half-chip sampling and spreading the spreading code specifically comprises:
repeatedly inserting the chip after each chip; changing 1 chip to the same 2 chips; spreading code sequences each data represents a chip before spreading and each data represents a half chip after spreading;
repeating the spreading code sequence 2 times spreads the spreading code into 2 spreading periods.
3. The method of claim 1, wherein down-converting and resampling the intermediate frequency of the satellite data specifically comprises:
mixing satellite data with local intermediate frequency carrier waves to obtain zero intermediate frequency data;
accumulating zero intermediate frequency data belonging to the same half chip according to the spreading code rate to generate half chip resampling data;
the half-chip resampled data is then divided into 2T segments, where each segment of 1 millisecond data represents 1 spreading period.
4. The method of claim 1 wherein the predetermined set of doppler frequencies comprises a plurality of doppler values { f }1,f2,…,fi,…,fxIn which fi+1-fiIs a fixed value; i is 0,1, … …, x-1.
5. The method as claimed in claim 1, wherein performing FFT operation, complex multiplication and IFFT operation on the processed spreading codes and satellite data to obtain the cyclic correlation result specifically comprises:
complementing the processed spread spectrum code with 0 to length NfftPerforming FFT operation to obtain a spread spectrum code frequency spectrum; respectively complementing the 2 satellite data with 0 to the length NfftPerforming FFT operation, and taking conjugation to obtain 2 sections of satellite data frequency spectrums; multiplying the spectrum of the spread spectrum code with the spectrum of 2 satellite data respectively; and performing IFFT operation on the multiplication result to obtain a 2-section cyclic correlation result.
6. The method of claim 1, wherein the predetermined set of doppler frequencies { f } is updated1,f2,…,fi,…,fxThe same step value f is added to each Doppler value in the pairstep(ii) a The update formula is: f. ofi＝fi+fstep(ii) a Where i is 1,2, …, x.
7. The method of claim 1, wherein determining which segment of the 2T millisecond length satellite the maximum occurs in, selecting the segment of satellite data for doppler precision acquisition comprises:
selecting first or second T millisecond satellite data according to the section with maximum value, calculating the initial position of satellite data spread spectrum code according to code phase, stripping spread spectrum code with T periods from the initial position, and stripping the data with length nxCoherent accumulation of points, followed by NfftAnd point FFT, searching the maximum value of the FFT result module value, and calculating and capturing the Doppler frequency accurate value according to the maximum value position.
8. The method of claim 7, wherein n isxThe value is selected to satisfy nx≥fs/2NfftfeMaxWherein f issAs the original data sampling rate, feMaxSearch for the maximum allowable error, N, for DopplerfftThe number of points of the FFT.
9. A GPS L1 fast precision acquisition device, comprising: the device comprises a spread spectrum code processing module, a data resampling module, a Doppler stripping module, a coherent accumulation module, an FFT module, a multiplication module, an IFFT module, a capture judgment module, a Doppler configuration module and a Doppler fine capture module;
the spread spectrum code preprocessing module is used for carrying out half chip sampling and spreading on the spread spectrum code;
the data resampling module is used for carrying out intermediate frequency down conversion and resampling on satellite data;
the Doppler stripping module is used for mixing a carrier signal obtained by accumulating a plurality of local carrier sequences corresponding to a preset Doppler frequency group with the satellite data processed by the data resampling module to complete Doppler down-conversion to obtain zero Doppler data;
the coherent accumulation module is used for segmenting the 2T (T is less than or equal to 10) millisecond zero Doppler data by taking 1 millisecond as a length, and respectively carrying out coherent accumulation on the former T millisecond data and the latter T millisecond data to obtain 2 segments of satellite data with the length of 1 millisecond;
the FFT module is used for carrying out N on input datafftPerforming point FFT operation; complementing input data by 0 to NfftPoint; the input data comprises 2 types of spread spectrum codes and satellite data, and the data are respectively output to the multiplication module after FFT;
the multiplication module firstly takes conjugation to the satellite data frequency spectrum, then carries out complex multiplication on the conjugated data and the spread spectrum code frequency spectrum, and outputs the result to the IFFT module;
the IFFT module carries out IFFT transformation on input data to obtain a cyclic correlation result and outputs the cyclic correlation result to the capture judgment module;
the acquisition judging module is used for solving the modulus of the cyclic correlation result, searching the maximum value in the cyclic correlation result, judging that coarse acquisition is successful if the maximum value exceeds a preset threshold, calculating the code phase of the corresponding satellite signal at the moment, recording the number of sections with the maximum value, and outputting the sections to the Doppler fine acquisition module; if the maximum value does not exceed the preset threshold, judging that the current Doppler value is failed to capture, and outputting a failure mark to the Doppler configuration module;
the Doppler configuration module is used for calculating and updating a set Doppler frequency set so as to carry out the next set of Doppler acquisition;
the Doppler precise acquisition module is used for determining a section of the satellite with the length of 2T milliseconds in which the maximum value appears and selecting the data of the section of satellite for Doppler precise acquisition.
10. A computer storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, performs the steps of the method of any of claims 1-8.
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| CN115291258A (en) * | 2022-10-08 | 2022-11-04 | 成都星航时空科技有限公司 | GNSS baseband capturing method |
| CN115987326A (en) * | 2022-12-12 | 2023-04-18 | 成都飞机工业（集团）有限责任公司 | Efficient capturing method suitable for spread spectrum communication system |
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| CN115291258A (en) * | 2022-10-08 | 2022-11-04 | 成都星航时空科技有限公司 | GNSS baseband capturing method |
| CN115291258B (en) * | 2022-10-08 | 2022-12-13 | 成都星航时空科技有限公司 | GNSS baseband capturing method |
| CN115987326A (en) * | 2022-12-12 | 2023-04-18 | 成都飞机工业（集团）有限责任公司 | Efficient capturing method suitable for spread spectrum communication system |
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