CN112987045A - GNSS satellite signal capturing method and device and computer storage medium - Google Patents

Abstract

The invention provides a GNSS satellite signal capturing method, a GNSS satellite signal capturing device and a computer storage medium. The method comprises the following steps: mixing the satellite signals and the local intermediate frequency signals to generate IQ two-path data; resampling is carried out according to the code rate, and data belonging to the same half chip are accumulated to obtain resampled data with 2 times of the code rate; mixing the resampled data with a local carrier of a specified Doppler frequency; performing coherent accumulation on the first half section and the second half section in the data which completes the Doppler down-conversion and has the length of 1 bit cycle according to the corresponding spread spectrum code phase; performing FFT on the two sections of data after coherent accumulation to obtain a data frequency spectrum and taking conjugation; carrying out fast Fourier transform on the local 2-cycle spread spectrum code after 2-time code rate sampling is input to obtain a spread spectrum code frequency spectrum; and carrying out complex multiplication and IFFT, then outputting a result, carrying out modulus taking, searching for a maximum value, and judging whether the acquisition is successful. The method combines 2 times of capture into 1 time of capture, reduces the amount of calculation, and shortens the capture time.

Description

GNSS satellite signal capturing method and device and computer storage medium

Technical Field

The invention relates to the technical field of satellite navigation, in particular to a GNSS satellite signal capturing method, a GNSS satellite signal capturing device and a computer storage medium, and particularly relates to a GPS L1/CA and GLONASS G1 satellite signal capturing method.

Background

In GNSS receiver cold start, a multi-period spreading code coherent integration mode is generally adopted to improve the acquisition sensitivity, such as GPS L1/CA and GLONASS G1 receiver systems. However, since navigation message information is modulated in the signal, there is symbol jump, so that the length of coherent integration is limited. When signal data with a time length of 2T (a symbol modulation maintaining time is set to be 2T) is selected, since a symbol hopping position is unknown, the data is required to be divided into 2 segments for coherent acquisition (namely 2 times of acquisition), so that symbol hopping does not exist in the data in one segment in the coherent integration process, and coherent integration with the time of T is ensured to be acquired in one segment. Therefore, 2 acquisitions are required to obtain coherent integration time of sufficient length. The use of 2 captures results in a large amount of computation and an excessively long capture time.

Disclosure of Invention

In view of the above, the present invention provides a GNSS satellite signal capturing method, apparatus and computer storage medium for solving 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 GNSS satellite signal capturing method, which is characterized by comprising the following steps:

mixing an input satellite signal and a local intermediate frequency signal to complete intermediate frequency down-conversion and generate IQ two-path data;

resampling IQ two paths of data according to code rate, and directly accumulating the sampled data belonging to the same half chip to obtain resampled data with the resampling frequency being 2 times of the code rate;

mixing the resampled IQ data with a local carrier wave with a preset Doppler frequency to finish Doppler down-conversion;

performing coherent accumulation on the first half section of the data with the modulation period of 1 bit symbol after Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section of data with the length of 1 millisecond; processing the second half data in the same way to obtain the 2 nd data with the length of 1 millisecond;

merging the 2 sections of data into 1 section of data, performing fast Fourier transform to obtain a data frequency spectrum, and conjugating the data frequency spectrum;

carrying out fast Fourier transform on the local 2-cycle spread spectrum code after 2-time code rate sampling is input to obtain a spread spectrum code frequency spectrum;

carrying out complex multiplication operation on the conjugate data and the local spread spectrum code frequency spectrum, and carrying out fast Fourier inverse transformation on the product;

and performing modulus extraction on the output result after the fast Fourier inverse transformation, searching the maximum value, judging that the acquisition is successful if the maximum value is greater than a preset threshold, finishing the acquisition of the satellite and outputting the acquisition result.

Further, the fast fourier transform adopts a radix-8 FFT algorithm, and the number of FFT points is 4096.

Furthermore, the local 2-period spread spectrum code data is arranged in a mode that a first period and a second period are continuously arranged.

Further, still include: judging the type of the input satellite signal:

when the type of the input satellite signal is judged to be GPS L1/CA, the local 2-period spread spectrum code data are arranged in a mode that one period of local spread spectrum code data is stored from the 0 th unit bit to the 2045 th unit bit, the other period of local spread spectrum code data is stored from the 2046 th unit bit to the 4091 th unit bit, and all the stored data from the 4092 th unit bit to the 4095 th unit bit are 0;

when the type of the input satellite signal is determined to be GLONASS G1; the local 2-period spread spectrum code data is arranged in a way that the 0 th unit bit to the 1021 th unit bit store one period of local spread spectrum code data, the 1022 th unit bit to the 2043 th unit bit store another period of local spread spectrum code data, and the 2044 th unit bit to the 4095 th unit bit store data which are all 0.

Further, still include: judging the type of the input satellite signal;

when the type of the input satellite signal is judged to be GPS L1/CA, the 1 st data are stored in the 0 th unit bit to the 2045 th unit bit, and the 2 nd data are stored in the 2048 th unit bit to 4093 rd unit bit; the data stored in the 2046 th cell bit to the 2047 th cell bit and the 4094 th cell bit to the 4095 th cell bit are all 0;

when it is determined that the type of the input satellite signal is GLONASS G1 and 1 doppler frequency is searched for at a time; the 1 st data is stored in the 0 th unit bit to the 1021 th unit bit, and the 2 nd data is stored in the 2048 th unit bit to the 3069 th unit bit; the data stored in the unit bit 1022 to the unit bit 2047 and the unit bit 3070 to the unit bit 4095 are all 0;

when the type of the input satellite signal is judged to be GLONASS G1, 2 Doppler frequencies are searched each time, and the difference value between the 2 Doppler frequency values is larger than or equal to a preset difference value, 2 data sequences with different Doppler values and the length of 10 milliseconds are obtained by performing Doppler down-conversion on the 2 Doppler frequencies, the 2 data sequences with the length of 10 milliseconds are divided into 2 data sequences with the length of 5 milliseconds respectively for coherent accumulation, and 4 sections of data with the length of 1 millisecond are obtained; respectively placing 2 sections of data corresponding to the first Doppler frequency from a 0 th unit bit to a 1021 th unit bit and from a 2048 th unit bit to a 3069 th unit bit, and respectively placing 2 sections of data corresponding to the second Doppler frequency from a 1024 th unit bit to a 2045 th unit bit and from a 3072 th unit bit to a 4093 th unit bit; the data stored in the unit bit 1022 to the unit bit 1023, the unit bit 2046 to the unit bit 2047, the unit bit 3070 to the unit bit 3071, and the unit bit 4094 to the unit bit 4095 are all 0.

Further, the preset difference is 200 Hz.

Further, if the maximum value is not greater than the preset threshold, the next preset doppler frequency is selected to continue to be captured until the capturing is successful or the searching of the preset doppler frequency is completed.

The embodiment of the invention provides a GNSS satellite signal capturing device, which comprises: the device comprises a first down-conversion module, a resampling module, a second down-conversion module, a coherent accumulation module, a first FFT module, a conjugate taking module, a second FFT module, a multiplication module, an IFFT module and a capture judgment module;

the first down-conversion module is used for mixing an input satellite signal and a local intermediate frequency signal to complete intermediate frequency down-conversion and generate IQ two-path data;

the resampling module is used for resampling IQ two paths of data according to the code rate, and directly accumulating the sampled data belonging to the same half chip to obtain the resampled data with the resampling frequency of 2 times the code rate;

the second down-conversion module is used for mixing the resampled IQ data with a local carrier with a preset Doppler frequency to complete Doppler down-conversion;

the coherent accumulation module is used for performing coherent accumulation on the first half section of the data with the long modulation period of 1 bit symbol after Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section of data with the length of 1 millisecond; processing the second half data in the same way to obtain the 2 nd data with the length of 1 millisecond;

the first FFT module is used for merging the data of 2 sections into data of 1 section and then carrying out fast Fourier transform to obtain a data frequency spectrum;

the conjugate taking module is used for taking conjugate to the data frequency spectrum;

the second FFT module is used for carrying out fast Fourier transform on the local 2-period spread spectrum code after the 2-time code rate sampling is input to obtain a spread spectrum code frequency spectrum;

the multiplication module is used for carrying out complex multiplication operation on the conjugate data and the local spread spectrum code spectrum;

the IFFT module is used for performing inverse fast Fourier transform on the product;

the acquisition judging module is used for judging whether the acquisition is successful or not, performing modulus taking on the output result of the IFFT module, searching for the maximum value, if the maximum value exceeds a threshold, considering that the acquisition is successful, finishing the acquisition of the satellite and outputting the acquisition result.

Embodiments of the present invention also provide a computer storage medium having a computer program stored thereon, where the computer program is executed by a processor to implement the steps of the above GNSS satellite signal capturing method.

The technical scheme provided by the invention combines at least 2 times of capture into 1 time of capture by processing before FFT based on cyclic correlation processing, reduces the calculated amount and shortens the capture time by at least half of the original time.

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 flowchart illustrating a GNSS satellite signal capturing method according to an embodiment of the present invention;

FIG. 2 is a diagram of an arrangement of circular correlation data provided by an embodiment of the present invention;

FIG. 3 is a schematic diagram of a cyclic shift algorithm according to the present invention;

FIG. 4 is a diagram of a circular correlation 2-cycle satellite data constellation provided in accordance with an embodiment of the present invention;

FIG. 5 is a schematic diagram of a cyclic shift related to the cycle of 2-cycle satellite data according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of a GNSS satellite signal capturing apparatus 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.

Aiming at the problem of 2-time capture of data with one bit time length, the invention combines multiple captures into 1 capture by processing the data by utilizing the principle of cyclic convolution, reduces the times of FFT and IFFT, obviously reduces the overall computation amount of capture and reduces the capture time. The principle of circular convolution is as follows: the cyclic correlation is performed by cyclically moving satellite data (or local code) and local code (or satellite data); fast algorithms can be implemented using FFT and IFFT, which are in principle equivalent. In the hardware implementation process, in order to implement a fast algorithm, an FFT is required; meanwhile, in order to improve the processing speed, a radix-8 FFT algorithm is used in hardware, and the number of FFT points of the radix-8 FFT algorithm can only be an integral power of 8. The fast Fourier transform of the invention adopts radix 8FFT algorithm, and the number of FFT points is 4096.

Taking GPS L1/CA acquisition as an example, the time length of one code period of GPS L1/CA is 1 ms, and after performing intermediate frequency and doppler down-conversion on the signal and half chip sampling on the satellite signal, 0 if satellite data is obtained, and the local code also performs half chip sampling, thus forming 2 sets of data, as shown in fig. 2. In fig. 2, the first group of data is satellite data, and the effective data length of the satellite data is 2046, that is, 2 times the chip period length of the CA code, where cp refers to the code phase of the satellite data, and x represents that the data is 0, that is, the first group of data is satellite data of one code period length 2046. The second group is a local code, comprising chip values of 2 periods in length. Circularly moving satellite data, moving once data, performing a correlation operation on the satellite data and a local code, and obtaining a maximum value of a correlation operation result when the satellite data and the local code are aligned in phase, as shown in fig. 3. The cyclic correlation process is essentially a satellite signal despreading process, and the maximum value is obtained only by phase matching.

When coherent integration is required, two approaches are possible. For 10 ms coherent integration, the first method is to perform the above process calculation every 1 ms (i.e. capture 1 ms of data), and then perform coherent accumulation on 10 ms correlation results (capture results); the second method is that after the satellite data is resampled, the resampled data is first coherently accumulated for 10 ms to 1 ms, and then is circularly correlated with the local (spread spectrum) code. Both implementations are equivalent, and obviously the second approach is less computationally intensive.

The fast algorithm is usually implemented by using FFT-IFFT, and considering that the number of FFT points of radix-8 FFT algorithm should be an integer power of 8, and then considering that the period length of CA code after half chip sampling is 2046, the length of FFT is determined to be 4096. The length of the data participating in the FFT operation is 4096 for each of the 2 sets. After the satellite data is resampled by half chip, FFT is carried out to the satellite data and the local code, conjugation is taken, the satellite data and the local code FFT data are multiplied, IFFT is carried out, and the cyclic correlation process is completed. If coherent integration is required, before FFT, coherent accumulation can be carried out on data after 10 milliseconds of resampling according to corresponding code phases; generally, 20 ms data is divided into 2 10 ms data and then the 2 captures are performed to effectively complete the capture.

In fig. 2, since the second half of the first group of data is set to 0, only one period of data for performing correlation operation is valid in the cyclic correlation process, thereby reducing the influence of noise generated when other positions are correlated on the correlation result; if a code period data is put into the second half section, the data processing of 2 periods can be completed together in the FFT and IFFT processing processes, and meanwhile, it needs to be ensured that when 2046 half chip sample data are separated, they have different code phases, so that only when the second half section data is put, it is required to put 2 half chips after the first half section data, as shown in fig. 4. When the data is circularly moved for cp times, the phase of the first satellite data is matched with the phase of the local code, the correlation result in the correlation window reaches the maximum value, and outside the correlation window, the correlation result can be regarded as noise due to phase mismatch, and the influence on the maximum value is small, as shown in fig. 5; continuing to move the data, the second phase of the satellite data matches the local code phase when moving through 2046+ cp +2 cycles, and similar to the first phase of the data, the maximum correlation result is also obtained. After circular correlation, 4096 correlation results are generated, the first 2046 results are circular correlation results of the first section of data, the 2048 th to 4094 th data correspond to circular correlation results of the second section of data, the maximum value of the amplitude is detected in the two sections of data with the length of 2046, and when the maximum value exceeds a threshold value, the capture can be considered to be successful.

However, since one segment of data is added and 2 bit units (1 chip) are spaced between two segments of data, some influence is caused to the correlation result during the shifting process. When the cp-1 round correlation is carried out, the phase of the whole data of the first section leads the phase of the local code by half a chip, the round correlation result of the first section is half of that of the matched phase, the second section of data is aligned with the phase of cp +1 to 2045 of the 2 nd period of the local code from cp to 2044, namely lags by half a chip, the correlation result of the section is superposed on the result of the first section, when the cp value is smaller, the correlation result value of the 2 nd section is larger, and the superposed value is larger; for example, when the cp-2 cyclic shift is performed, the phase of the first segment of data differs from the local code by 2 phases (1 chip), and the correlation result is equivalent to noise, but the phases cp to 2045 of the 2 nd segment of data are aligned with the corresponding phase of the 2 nd period of the local code, and similarly, if the cp value is small, the correlation result is large. Therefore, there may be 3 continuous large values near cp in the circular correlation result of the 1 st segment data, the correlation peak main lobe width is expanded, and the code phase obtained by the maximum value search is blurred, but in this case, the positional relationship can be analyzed to obtain the correct code phase, and the same may be true for the result of the 2 nd segment data. Of course, when 10 ms coherent integration is performed, there may be a piece of data in 2 pieces of data, which weakens the signal strength after coherent integration due to bit jump, so that the amplitude of the correlation result at 2 phases other than the true phase is reduced. On the other hand, when 1 segment of data is used, the satellite data outside the correlation window is 0 (as shown in fig. 3), and when two segments of data are used (as shown in fig. 5), the satellite data outside the correlation window is not 0, and the correlation accumulation result may increase the amplitude of the correlation result when the phases are not aligned, so that the noise power is increased, and the signal-to-noise ratio at the time of acquisition is decreased, but when the signal is strong and the coherent integration is performed for 10 milliseconds, the decrease in the acquisition signal-to-noise ratio is acceptable in order to obtain a faster acquisition rate.

In a word, 2 sections of data are used simultaneously, 2 times of capture can be completed on the basis of performing FFT and IFFT once, the capture times are reduced, and the capture rate is improved; because 2 satellite data are used, the width of a main lobe of a peak value of a cyclic correlation result can be increased, but a correct code phase can be obtained through processing, and an acquisition result is not influenced; meanwhile, the use of 2 segments of satellite data can cause the signal to noise ratio of the acquisition to be reduced, but can be ignored when the signal is acquired strongly.

Fig. 1 is a flowchart illustrating a GNSS satellite signal capturing method according to an embodiment of the present invention. The method comprises the following steps:

s101, mixing an input satellite signal and a local intermediate frequency signal to complete intermediate frequency down-conversion and generate IQ two-path data.

S102, resampling the IQ two paths of data according to the code rate, and directly accumulating the sampled data belonging to the same half chip to obtain the resampled data with the resampling frequency of 2 times the code rate.

S103, mixing the resampled IQ data with a local carrier wave with a preset Doppler frequency to finish Doppler down-conversion.

S104, performing coherent accumulation on the first half section of the data with the modulation period of 1 bit symbol after Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section of data with the length of 1 millisecond; the second half of the data is processed in the same way, and the 2 nd data with the length of 1 millisecond is obtained.

For the GPS L1/CA signal, one navigation bit of L1 is maintained for 20 ms, i.e., the bit symbol modulation period is 20 ms. Performing coherent accumulation on the first 10 milliseconds in the 20-millisecond data after the Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section data with the length of 1 millisecond; processing the next 10 milliseconds of data by the same method to obtain the 2 nd data with the length of 1 millisecond, and arranging the data of the 1 st data and the 2 nd data according to the mode of figure 4; the 1 st data is stored in the 0 th unit bit to the 2045 th unit bit, and the 2 nd data is stored in the 2048 th unit bit to the 4093 th unit bit; the 2046 th cell bit to 2047 th cell bit and 4094 th cell bit to 4095 th cell bit store data all of 0. After Doppler down-conversion is completed, coherent accumulation of 20 milliseconds of data is carried out, data of each millisecond is correspondingly accumulated on a corresponding code phase, the data of each millisecond becomes 1 millisecond in length after every 10 milliseconds of data accumulation, 2 sections of data can be generated, the 1 st section corresponds to the first 10 milliseconds of data accumulation, and the 2 nd section corresponds to the second 10 milliseconds of data accumulation. One navigation bit of L1 is maintained for 20 ms, and there may be sign inversion between each bit, so that the data is taken to ensure that after consecutive 20 ms data are accumulated into 2 segments, 1 segment of 10 ms data is not sign inverted during the accumulation process, i.e. the coherent accumulation is an effective 10 ms accumulation.

For the GLONASS G1 signal, since the symbol modulation period is 10 ms, coherent accumulation should be performed by dividing 10 ms data into 2 pieces of 5 ms data and generating 2 pieces of data each having a length of 1 ms. The 1-cycle length of the GLONASS G1 code is 511, the 1-cycle length after half-chip resampling becomes 1022, because the number of points of 1-cycle data is 1022, the interval between the 1 st segment and the 2 nd segment of 2-cycle data can be 1026 when the data is prepared, i.e. the 1 st segment of data is stored in the 0 th unit bit to the 1021 th unit bit, and the 2 nd segment of data is stored in the 2048 th unit bit to 3069 th unit bit. The 1022 th cell bit through the 2047 th cell bit and the 3070 th cell bit through the 4095 th cell bit store data all of 0. When the data outside the correlation window are correlated, the correlation results are all 0, the 1 st and 2 nd data do not influence the correlation results, the correlation peak is not expanded, and the phase corresponding to the maximum value does not have ambiguity. Therefore, when two pieces of generated data are prepared for coherent accumulation, the 2 nd piece of data is placed 1026 units of start placement data after the 1 st piece of data ends.

For the GLONASS G1 signal, in order to more effectively utilize FFT and IFFT, 4 pieces of data may be put in the data at the time of data preparation, each piece of data being separated by 2 phase units; in order to reduce the correlation of the data outside the correlation window, the doppler values between the adjacent 2 segments of data are considered, such as the doppler difference is more than 200 Hz. If the satellite data in the correlation window has a correct Doppler value (namely the carrier frequency of the data after Doppler down-conversion is 0), the Doppler values of the data on the left and the right are larger (200Hz and above), the data have high-frequency characteristics relatively, and the influence of the result after correlation on the correlation result in the correlation window is reduced; meanwhile, the local code outside the correlation window aligned with the 2 nd segment data with 0 doppler value is corresponding to 0, and has no influence on the correlation result inside the correlation window. Thus the doppler down-conversion inputs 2 doppler values with a difference of 200 Hz; the output is 2 data sequences of length 10 ms with different doppler values.

Coherent accumulation divides 2 data sequences of 10 milliseconds into 2 data sequences of 5 milliseconds respectively for coherent accumulation to generate 4 sections of data with the length of 1 millisecond; in the data preparation process, 2 pieces of data corresponding to doppler 1 are placed at the positions where cell 0 and cell 2048 start, respectively, and 2 pieces of data corresponding to doppler 2 are placed at the positions where cell 1024 and cell 3072 start, respectively. When the difference value between 2 Doppler frequencies is greater than the preset difference value of 200Hz, 2 groups of Doppler frequencies are subjected to Doppler down-conversion to obtain 2 data sequences with the length of 10 milliseconds and different Doppler values, and the 2 data sequences with the length of 10 milliseconds are divided into 2 data sequences with the length of 5 milliseconds respectively to be subjected to coherent accumulation to obtain 4 sections of data with the length of 1 millisecond; respectively placing 2 sections of data corresponding to the first Doppler frequency from a 0 th unit bit to a 1021 th unit bit and from a 2048 th unit bit to a 3069 th unit bit, and respectively placing 2 sections of data corresponding to the second Doppler frequency from a 1024 th unit bit to a 2045 th unit bit and from a 3072 th unit bit to a 4093 th unit bit; the data stored in the unit bit 1022 to the unit bit 1023, the unit bit 2046 to the unit bit 2047, the unit bit 3070 to the unit bit 3071, and the unit bit 4094 to the unit bit 4095 are all 0.

And S105, combining the 2-segment data into 1-segment data, performing fast Fourier transform to obtain a data frequency spectrum, and conjugating the data frequency spectrum.

And combining the 2 sections of data subjected to coherent accumulation for 1 millisecond into 1 section of data, performing fast Fourier transform to obtain a data frequency spectrum, and conjugating the data frequency spectrum.

Compared with the traditional method of performing FFT on 2 sections of data for 2 times respectively, the method has the innovative point that 2 sections of data are combined into 1 section, and the FFT is performed simultaneously, so that the FFT can be performed for 1 time less, the calculation amount can be reduced, and the capturing time can be shortened.

And S106, carrying out fast Fourier transform on the local 2-cycle spread spectrum code after the 2-time code rate sampling is input to obtain a spread spectrum code frequency spectrum.

The local 2-period spread spectrum code data are arranged in a mode that a first period and a second period are continuously arranged.

As shown in fig. 2, the local 2-cycle GPS spread spectrum code data is arranged in such a manner that the local spread spectrum code data of one cycle is stored in the unit bit 0 to the unit bit 2045, the local spread spectrum code data of another cycle is stored in the unit bit 2046 to the unit bit 4091, and all the stored data in the unit bit 4092 to the unit bit 4095 are 0.

For GLONASS G1, the 2-cycle local spread spectrum code data is arranged in such a way that the 0 th unit bit to the 1021 th unit bit store one cycle of local spread spectrum code data, the 1022 th unit bit to the 2043 th unit bit store another cycle of local spread spectrum code data, and the 2044 th unit bit to 4095 th unit bit store all data of 0.

And S107, carrying out complex multiplication operation on the conjugate data and the local spread spectrum code spectrum, and carrying out inverse fast Fourier transform on the product.

And S108, performing modulus extraction on the output result after the fast Fourier inverse transformation, searching the maximum value, judging that the acquisition is successful if the maximum value is greater than a preset threshold, finishing the acquisition of the satellite and outputting an acquisition result.

And if the maximum value is not greater than the preset threshold, selecting the next preset Doppler frequency to continue capturing until capturing is successful or searching of the preset Doppler frequency is finished.

Apparatus item example 1

As shown in fig. 6, an embodiment of the present invention further provides a GNSS satellite signal capturing apparatus, which is used for capturing GPS L1/CA. The device includes: the device comprises a first down-conversion module I, a resampling module II, a second down-conversion module III, a coherent accumulation module IV, a first FFT module V, a conjugate taking module VI, a second FFT module X, a multiplication module VII, an IFFT module VIII and a capture judgment module IX.

The first down-conversion module I is used for mixing the input satellite signals and the local intermediate frequency signals to complete intermediate frequency down-conversion and generate IQ two-path data.

And the resampling module II is used for resampling IQ two paths of data according to the code rate, and directly accumulating the sampled data belonging to the same half chip to obtain the resampled data with the resampling frequency of 2 times the code rate.

And the second down-conversion module III is used for mixing the resampled IQ data with a local carrier wave with a preset Doppler frequency to finish Doppler down-conversion.

The coherent accumulation module IV is used for performing coherent accumulation on the first half section of the data with the modulation period of 1 bit symbol after Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section of data with the length of 1 millisecond; the second half of the data is processed in the same way, and the 2 nd data with the length of 1 millisecond is obtained. The 1 st and 2 nd pieces of data are arranged as shown in fig. 4.

And the coherent accumulation module IV completes the coherent accumulation of 20 milliseconds of data after down conversion, correspondingly accumulates the data of each millisecond on the same code phase, and changes the data of each millisecond into the length of 1 millisecond after the data of each 10 milliseconds are accumulated, so that 2 sections of data can be generated, wherein the 1 st section corresponds to the data accumulation of the first 10 milliseconds, and the 2 nd section corresponds to the data accumulation of the last 10 milliseconds. One navigation bit of L1 is maintained for 20 ms, and there may be sign inversion between each bit, so that the data is taken to ensure that after consecutive 20 ms data are accumulated into 2 segments, 1 segment of 10 ms data is not sign inverted during the accumulation process, i.e. the coherent accumulation is an effective 10 ms accumulation.

And the first FFT module V is used for merging the data of the 2 sections into the data of the 1 section and then carrying out fast Fourier transform to obtain a data frequency spectrum.

And the conjugation module VI is used for conjugating the data frequency spectrum.

The second FFT module x is configured to perform fast fourier transform on the local 2-cycle spreading code sampled at the input 2-fold code rate to obtain a spreading code spectrum. The local 2-period spreading code arrangement is shown in the lower half of fig. 2.

And the multiplication module VII is used for carrying out complex multiplication operation on the conjugate data and the local spread spectrum code spectrum.

The IFFT block viii is used to perform an inverse fast fourier transform on the product.

And the acquisition judging module IX is used for judging whether the acquisition is successful or not, performing modulus selection on the result output by the IFFT module, searching for the maximum value, if the maximum value exceeds a threshold, judging that the acquisition is successful, finishing the acquisition of the satellite and outputting an acquisition result. If the Doppler value does not exceed the threshold, the next Doppler value needing to be searched is given, and the acquisition of the process is continued.

Apparatus item example 2

As shown in fig. 6, an embodiment of the invention further provides a GNSS satellite signal capturing apparatus, which is used for capturing GLONASS G1. The function of which is substantially identical to that of embodiment 1 of the apparatus, and only the differences will be described here.

The GLONASS G1 code 1 period length is 511, the 1 period length after half chip resampling becomes 1022, so the local CA code 2 period length is 2044, and the FFT point number is still 4096 according to the requirement of radix 8FFT for the operation point number.

The GLONASS G1 symbol modulation period is 10 ms, so the coherent accumulation module 504 should coherently accumulate 10 ms of data into 2 pieces of data with length of 1 ms, and generate 2 pieces of data with length of 5 ms.

Because the point number of the 1-period data is 1022, when the data of fig. 4 is prepared, the interval between the 1 st segment and the 2 nd segment of the 2-period data can be 1026, so that when the data outside the correlation window of fig. 5 is correlated, the correlation results are both 0, the 1 st segment and the 2 nd segment of the data do not affect the correlation results, the correlation peak is not expanded, and the phase corresponding to the maximum value does not appear ambiguity. Therefore, when the coherent accumulation module IV prepares for the two-stage data generated, the 2 nd data placement starts placing data 1026 units after the 1 st data placement ends.

It can be seen that by combining 2 captures into 1 capture, the number of FFT and IFFT is reduced, so that the overall computation of capture is significantly reduced, reducing the capture time.

Apparatus item example 3

As shown in fig. 6, an embodiment of the invention further provides a GNSS satellite signal capturing apparatus, which is used for capturing GLONASS G1. The function of which is substantially identical to that of embodiment 2 of the apparatus, and only the inconsistencies are described here.

To make more efficient use of FFT and IFFT, 4 pieces of data, each separated by 2 phase units, may be put into the data at the time of data preparation of fig. 4; in order to reduce the correlation of the data outside the correlation window in fig. 5, it can be considered that the adjacent 2 segments of data have different doppler values, such as doppler difference more than 200 Hz. If the satellite data in the correlation window has a correct Doppler value (namely the carrier frequency of the data after Doppler down-conversion is 0), the Doppler values of the data on the left and the right are larger (more than 200 Hz), the data have high frequency characteristics relatively, and the influence of the result after correlation on the correlation result in the correlation window is reduced; meanwhile, the local code outside the correlation window aligned with the 2 nd segment data with 0 doppler value is corresponding to 0, and has no influence on the correlation result inside the correlation window.

Therefore, the second down-conversion module III inputs 2 Doppler values, and the difference is 200 Hz; the output is 2 data sequences of length 10 ms with different doppler values.

The coherent accumulation module IV divides 2 data sequences of 10 milliseconds into 2 data sequences of 5 milliseconds respectively to carry out coherent accumulation, and 4 sections of data with the length of 1 millisecond are generated; in the data preparation process, 2 pieces of data corresponding to doppler 1 are placed at the positions where cell 0 and cell 2048 start, respectively, and 2 pieces of data corresponding to doppler 2 are placed at the positions where cell 1024 and cell 3072 start, respectively.

It can be seen that by combining 4 captures into 1 capture, the number of FFTs and IFFTs is reduced, so that the overall computation amount of the capture is significantly reduced, and the capture time is reduced.

It should be noted that: in the GNSS satellite signal capturing apparatus provided in the above embodiment, only the division of the above program modules is taken as an example for performing the capturing, and in practical applications, the above processing distribution may be completed by different program modules according to needs, that is, the internal structure of the apparatus is divided into different program modules to complete all or part of the above-described processing. In addition, the GNSS satellite signal capturing apparatus and the GNSS satellite signal capturing method provided by the above embodiments belong to the same concept, and specific implementation processes thereof are described in detail in the method embodiments, and 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 GNSS satellite signal capturing apparatus to perform the steps of the GNSS satellite signal capturing 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 (9)

1. A GNSS satellite signal acquisition method, comprising:

mixing an input satellite signal and a local intermediate frequency signal to complete intermediate frequency down-conversion and generate IQ two-path data;

resampling IQ two paths of data according to code rate, and directly accumulating the sampled data belonging to the same half chip to obtain resampled data with the resampling frequency being 2 times of the code rate;

mixing the resampled IQ data with a local carrier wave with a preset Doppler frequency to finish Doppler down-conversion;

performing coherent accumulation on the first half section of the data with the modulation period of 1 bit symbol after Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section of data with the length of 1 millisecond; processing the second half data in the same way to obtain the 2 nd data with the length of 1 millisecond;

merging the 2 sections of data into 1 section of data, performing fast Fourier transform to obtain a data frequency spectrum, and conjugating the data frequency spectrum;

carrying out fast Fourier transform on the local 2-cycle spread spectrum code after 2-time code rate sampling is input to obtain a spread spectrum code frequency spectrum;

carrying out complex multiplication operation on the conjugate data and the local spread spectrum code frequency spectrum, and carrying out fast Fourier inverse transformation on the product;

and performing modulus extraction on the output result after the fast Fourier inverse transformation, searching the maximum value, judging that the acquisition is successful if the maximum value is greater than a preset threshold, finishing the acquisition of the satellite and outputting the acquisition result.

2. The method of claim 1, wherein the fast fourier transform employs a radix-8 FFT algorithm with 4096 FFT points.

3. The method of claim 1 wherein the local 2-period spread spectrum code data is arranged in a first period and a second period consecutively.

4. The method of claim 3, further comprising: judging the type of the input satellite signal:

when the type of the input satellite signal is judged to be GPS L1/CA, the local 2-period spread spectrum code data are arranged in a mode that one period of local spread spectrum code data is stored from the 0 th unit bit to the 2045 th unit bit, the other period of local spread spectrum code data is stored from the 2046 th unit bit to the 4091 th unit bit, and all the stored data from the 4092 th unit bit to the 4095 th unit bit are 0;

when the type of the input satellite signal is determined to be GLONASS G1; the local 2-period spread spectrum code data is arranged in a way that the 0 th unit bit to the 1021 th unit bit store one period of local spread spectrum code data, the 1022 th unit bit to the 2043 th unit bit store another period of local spread spectrum code data, and the 2044 th unit bit to the 4095 th unit bit store data which are all 0.

5. The method of claim 1, further comprising: judging the type of the input satellite signal;

when the type of the input satellite signal is judged to be GPS L1/CA, the 1 st data are stored in the 0 th unit bit to the 2045 th unit bit, and the 2 nd data are stored in the 2048 th unit bit to 4093 rd unit bit; the data stored in the 2046 th cell bit to the 2047 th cell bit and the 4094 th cell bit to the 4095 th cell bit are all 0;

when it is determined that the type of the input satellite signal is GLONASS G1 and 1 doppler frequency is searched for at a time; the 1 st data is stored in the 0 th unit bit to the 1021 th unit bit, and the 2 nd data is stored in the 2048 th unit bit to the 3069 th unit bit; the data stored in the unit bit 1022 to the unit bit 2047 and the unit bit 3070 to the unit bit 4095 are all 0;

when the type of the input satellite signal is judged to be GLONASS G1, 2 Doppler frequencies are searched each time, and the difference value between the 2 Doppler frequency values is larger than or equal to a preset difference value, 2 data sequences with different Doppler values and the length of 10 milliseconds are obtained by performing Doppler down-conversion on the 2 Doppler frequencies, the 2 data sequences with the length of 10 milliseconds are divided into 2 data sequences with the length of 5 milliseconds respectively for coherent accumulation, and 4 sections of data with the length of 1 millisecond are obtained; respectively placing 2 sections of data corresponding to the first Doppler frequency from a 0 th unit bit to a 1021 th unit bit and from a 2048 th unit bit to a 3069 th unit bit, and respectively placing 2 sections of data corresponding to the second Doppler frequency from a 1024 th unit bit to a 2045 th unit bit and from a 3072 th unit bit to a 4093 th unit bit; the data stored in the unit bit 1022 to the unit bit 1023, the unit bit 2046 to the unit bit 2047, the unit bit 3070 to the unit bit 3071, and the unit bit 4094 to the unit bit 4095 are all 0.

6. The method of claim 5, wherein the predetermined difference is 200 Hz.

7. The method of claim 1, wherein if the maximum value is not greater than the predetermined threshold, then selecting a next predetermined Doppler frequency to continue the acquisition until the acquisition is successful or the search for the predetermined Doppler frequency is completed.

8. A GNSS satellite signal acquisition apparatus, comprising: the device comprises a first down-conversion module, a resampling module, a second down-conversion module, a coherent accumulation module, a first FFT module, a conjugate taking module, a second FFT module, a multiplication module, an IFFT module and a capture judgment module;

the first down-conversion module is used for mixing an input satellite signal and a local intermediate frequency signal to complete intermediate frequency down-conversion and generate IQ two-path data;

the resampling module is used for resampling IQ two paths of data according to the code rate, and directly accumulating the sampled data belonging to the same half chip to obtain the resampled data with the resampling frequency of 2 times the code rate;

the second down-conversion module is used for mixing the resampled IQ data with a local carrier with a preset Doppler frequency to complete Doppler down-conversion;

the coherent accumulation module is used for performing coherent accumulation on the first half section of the data with the long modulation period of 1 bit symbol after Doppler down-conversion according to the corresponding spread spectrum code phase to generate 1 st section of data with the length of 1 millisecond; processing the second half data in the same way to obtain the 2 nd data with the length of 1 millisecond;

the first FFT module is used for merging the data of 2 sections into data of 1 section and then carrying out fast Fourier transform to obtain a data frequency spectrum;

the conjugate taking module is used for taking conjugate to the data frequency spectrum;

the second FFT module is used for carrying out fast Fourier transform on the local 2-period spread spectrum code after the 2-time code rate sampling is input to obtain a spread spectrum code frequency spectrum;

the multiplication module is used for carrying out complex multiplication operation on the conjugate data and the local spread spectrum code spectrum;

the IFFT module is used for performing inverse fast Fourier transform on the product;

the acquisition judging module is used for judging whether the acquisition is successful or not, performing modulus taking on the output result of the IFFT module, searching for the maximum value, if the maximum value exceeds a threshold, considering that the acquisition is successful, finishing the acquisition of the satellite and outputting the acquisition result.

9. 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 one of claims 1 to 7.

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