CN112764063A - Method for realizing capture processing and receiver - Google Patents
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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
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
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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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- G01S19/01—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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Abstract
A method and a receiver for realizing acquisition processing comprise: carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping; performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result; a second DFT result obtained based on a local coarse acquisition (C/A) code; determining whether the capturing is successful or not according to the first DFT result and the second DFT result; and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed. The embodiment of the invention simplifies the operation of the capturing process.
Description
Technical Field
The present disclosure relates to, but not limited to, satellite navigation technologies, and more particularly, to a method and a receiver for performing an acquisition process.
Background
In recent years, Global Navigation Satellite Systems (GNSS) have been rapidly developed under the demand of a large number of engineering applications; the GNSS receiver comprises a satellite positioning system (GPS) in the United states, a Beidou (BD) system in China, a global navigation satellite positioning system (GLONASS) in Russia and a Galileo (Galileo) system in Europe, wherein the internal structure of the GNSS receiver can be generally divided into an antenna, a Radio Frequency (RF) front end, a baseband digital signal processing part, a positioning navigation operation part and the like according to the working process of the GNSS receiver, firstly, the antenna senses electromagnetic field signals including all satellite signals, outputs digital intermediate frequency signals including all satellite signals through the radio frequency front end processing part, acquires, tracks, synchronizes bits, synchronizes frames, demodulates messages and the like for the digital intermediate frequency signals through the baseband digital signal processing part, obtains a GNSS measured value and a navigation message, and performs the positioning navigation operation to output a positioning and navigation result.
Acquisition is a maximum likelihood estimation process, and the basic idea is to take different parameters to maximize the correlation value between the input signal and the local signal. The acquisition is an important link in the baseband digital signal processing, and the performance of the acquisition directly influences the positioning and navigation performance of the GNSS receiver. The acquisition of the GNSS signal is a three-dimensional search process, and the three-dimensional search comprises the following steps: pseudo-random noise code (PRN) (different satellites correspond to different C/a codes), doppler frequency, and coarse acquisition (C/a) code phase; FIG. 1 is a diagram illustrating a related art acquisition search, as shown in FIG. 1, by first determining PRNs for the satellite numbers to be acquired; then, according to the frequency range to be searched, the Doppler frequency is equally divided into N parts, and each part of frequency bandwidth is fbin(ii) a Then, the code phase is set to M parts, and the code band width tbin(ii) a Forming M × N search units through the processing, wherein each search unit is formed by a frequency band and a code band; the satellite signals can be captured through the parameters corresponding to the search units; if the correlation value of the acquired satellite signals is greater than a preset threshold, the acquisition is successful; the frequency point and the code phase corresponding to the search unit are the targetA plot point and a code phase.
Common capture methods include: serial sliding correlation acquisition and Discrete Fourier Transform (DFT) -based parallel code phase acquisition; these two capture methods are briefly described below:
1. the serial sliding correlation acquisition is a basic signal searching and acquiring method, and mainly performs searching estimation on all possible signal units by continuously adjusting code phase and local carrier frequency to maximize a correlation value so as to determine whether a satellite signal exists. The serial sliding correlation acquisition is simple to realize, only one digital correlator is needed, and the cost is very low; but usually the frequency bandwidth f selected for searchingbinTypically a few hundred hertz, code band width tbinThe acquisition efficiency of the serial sliding correlation acquisition is very low for half a chip, so that a long time is needed to acquire enough satellites for navigation positioning, and the requirement on the Time To First Fix (TTFF) of a receiver in practical engineering is difficult to meet. An improved solution is to use multiple correlators executing in parallel to speed up the search, but this increases the required hardware resources. To improve the acquisition sensitivity of the signal, longer coherent integration and non-coherent integration times should be used, but this further increases the time required for acquisition. The reasons include: longer coherent integration and non-coherent integration times require longer data information, which requires more processing, increasing acquisition time; frequency bandwidth f of searchbinInverse relation to coherent integration time, i.e. if coherent integration time increases, fbinThe number of cells to be searched for is reduced, and for a fixed frequency search range, the number of cells to be searched for is captured is increased, so that the capture time is increased; in addition, since the frequency precision obtained by the acquisition is coarse (generally greater than 100 hertz (hz)), and a relatively fine frequency (generally less than 100hz, even more than ten hertz) is required for entering the tracking link, frequency fine processing is required before the acquisition is carried out to the tracking, which also increases the complexity of the system to a certain extent.
2. The problem of long capturing time is solved to a certain extent by parallel code phase capturing based on DFT; the core of the DFT-based parallel code phase capturing method is that time domain searching on a code phase domain is converted into parallel searching of a frequency domain, so that the code phase searching frequency only needs one time, and finally, the whole two-dimensional capturing only needs to be carried out for a plurality of times (related to a frequency range to be searched and a frequency step length) on a carrier frequency; assuming x (N) and y (N) are digital signals of length N, their discrete fourier transforms are:
and the cyclic correlation values of x (n) and y (n) are:
performing discrete Fourier transform on the correlation value z (n), wherein the discrete Fourier transform Z (k) of z (n) is as follows:
in the formula, Y*(k) Is the conjugate of Y (k). This is a multiplication process for converting the cyclic correlation operation in the time domain to the frequency domain, and when z (k) is calculated, the correlation result z (n) in the time domain can be obtained through inverse discrete fourier transform.
Fig. 2 is a block diagram illustrating a DFT-based parallel code phase acquisition apparatus in the related art, as shown in fig. 2, two carriers, Sine (SIN) and Cosine (COS), are generated locally by a Numerically Controlled Oscillator (NCO); the two paths of carriers are respectively mixed with the input intermediate frequency signal through corresponding mixers, and the carriers are stripped; performing DFT conversion on the two paths of signals subjected to carrier stripping to obtain a frequency domain value; meanwhile, the DFT conversion is carried out on the locally generated coarse capture code (C/A code) and complex conjugation is taken to obtain a conjugate value; multiplying the obtained conjugate value and the frequency domain value by a multiplier; performing inverse DFT processing on the output result of the multiplier to obtain a time domain signal; performing modulus extraction on the obtained time domain information to obtain a correlation value; performing non-coherent integration on the obtained correlation value; comparing the maximum value of the non-coherent integration result with a preset threshold; when the frequency is larger than the preset threshold, determining that the acquisition is successful, and obtaining the frequency and the code phase of the intermediate frequency signal; if the maximum value of the non-coherent integration result is not larger than the preset threshold, determining that the acquisition fails, continuing to perform acquisition search of the next frequency until the satellite is acquired by searching or all frequency points are searched, and then performing search of the next satellite.
Compared with serial sliding correlation acquisition, the parallel code phase acquisition based on DFT has faster search speed and can greatly reduce acquisition time, but when each frequency band is searched, two discrete Fourier transforms and one inverse discrete Fourier transform are required, and the required operation amount is very large. If more coherent integration gain is required, a longer input intermediate frequency signal is required, which results in a larger point DFT operation and more search frequency bands, and finally results in a surge of operation amount to affect the acquisition time of the whole system. The related art adopts FFT to replace DFT for calculation, but the reduction of the operation amount brought by the related art is limited; in addition, parallel code phase acquisition based on DFT also has the problem that the frequency needs to be further refined as that of serial sliding correlation acquisition.
Disclosure of Invention
The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.
The embodiment of the invention provides a method for realizing capture processing and a receiver, which can simplify the operation of a capture process and finely capture the frequency.
The embodiment of the invention provides a method for realizing capture processing, which comprises the following steps:
carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping;
performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result;
a second DFT result obtained based on the local coarse acquisition C/A code;
determining whether the capturing is successful or not according to the first DFT result and the second DFT result;
and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed.
Optionally, the determining whether the capturing is successful according to the first DFT result and the second DFT result includes:
performing point-to-point multiplication on the obtained first DFT result and the second DFT result based on element sorting to obtain a point-to-point product;
performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phase positions;
performing second discrete Fourier transform of a second preset point on a time domain correlation result of the same code phase obtained by one or more inverse discrete Fourier transforms;
performing differential coherent accumulation on the result of the second fourier transform;
a maximum value of the differential coherent accumulation is determined and it is determined whether the acquisition is successful according to the determined maximum value.
Optionally, the second DFT result obtained based on the local coarse acquisition C/a code includes:
and carrying out first DFT transformation of a first preset point on the local coarse capture C/A code, and taking complex conjugate to obtain the second DFT result.
Optionally, the second DFT result is pre-stored.
Optionally, the determining whether the acquisition is successful includes:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and determining capture failure when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold.
In another aspect, an embodiment of the present invention further provides a receiver, including: the device comprises a stripping unit, a first conversion unit, a second conversion unit and a judgment unit; wherein,
the peeling unit is used for: carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping;
the first transformation unit is configured to: performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result;
a second transformation unit to: a second DFT result obtained based on the local coarse acquisition C/A code;
the judgment unit is used for: determining whether the capturing is successful or not according to the first DFT result and the second DFT result;
the shift processing unit is used for: and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed.
Optionally, the determining unit includes a dot product module, an inverse transform module, a differential coherent accumulation module, and a determining module; wherein,
the dot product module is to: performing point-to-point multiplication on the obtained first DFT result and the second DFT result based on element sorting to obtain a point-to-point product;
the inverse transform module is to: performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phases;
the transform module is to: performing second discrete Fourier transform of a second preset point on a time domain correlation result of the same code phase obtained by one or more inverse discrete Fourier transforms;
the differential coherent accumulation module is used for: performing differential coherent accumulation on the result of the second fourier transform;
the judgment module is used for: a maximum value of the differential coherent accumulation is determined and it is determined whether the acquisition is successful according to the determined maximum value.
Optionally, the second transformation unit is specifically configured to: performing first DFT transformation of a first preset point on the local coarse capture C/A code, and taking complex conjugation to obtain a second DFT result; or, the second DFT result is stored in advance.
Optionally, the determining module is specifically configured to:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and determining capture failure when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold.
In still another aspect, an embodiment of the present invention further provides a computer storage medium, where computer-executable instructions are stored in the computer storage medium, and the computer-executable instructions are configured to perform the foregoing method.
Compared with the related art, the technical scheme of the application comprises the following steps: carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping; performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result; a second DFT result obtained based on a local coarse acquisition (C/A) code; determining whether the capturing is successful or not according to the first DFT result and the second DFT result; and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed. The embodiment of the invention simplifies the operation of the capturing process.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the example serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is a diagram illustrating a related art acquisition search;
FIG. 2 is a block diagram illustrating an apparatus for DFT-based parallel code phase acquisition in the related art;
FIG. 3 is a flow chart of a method for implementing the capture process according to an embodiment of the present invention;
FIG. 4 is a flow chart of a method for implementing the capture process according to another embodiment of the present invention;
fig. 5 is a block diagram of a receiver according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the present application, the embodiments and features of the embodiments may be arbitrarily combined with each other without conflict.
The steps illustrated in the flow charts of the figures may be performed in a computer system such as a set of computer-executable instructions. Also, while a logical order is shown in the flow diagrams, in some cases, the steps shown or described may be performed in an order different than here.
Fig. 3 is a flowchart of a method for implementing the capture process according to an embodiment of the present invention, as shown in fig. 3, including:
optionally, the stripping intermediate frequency processing performed in the embodiment of the present invention includes:
generating Sine (SIN) carrier and Cosine (COS) carrier by a Numerically Controlled Oscillator (NCO);
and respectively mixing the sine carrier and the cosine carrier with the intermediate frequency signal to perform down-conversion processing on the intermediate frequency signal so as to realize intermediate frequency stripping.
it should be noted that the first preset point may be determined according to the number of searched code phases, and assuming that the number of searched code phases is 2046, the first preset point may be an integer multiple of 2046.
in addition, taking as an example that the first DFT result includes elements with sequence numbers 1, 2, and 3 … … N, and the second DFT result includes elements with sequence numbers 1, 2, and 3 … … N, the point-to-point multiplication includes: multiplying the element of the first DFT result number 1 by the element of the second DFT result number 1; multiplying the element of the first DFT result number 2 by the element of the second DFT result number 2; multiplying the element of the first DFT result sequence number 3 by the element of the second DFT result sequence number 3; … …, respectively; the element of the first DFT result number N is multiplied by the element of the second DFT result number N.
Optionally, the second DFT result obtained based on the local C/a code in the embodiment of the present invention includes:
performing first DFT transformation of a first preset point on a local coarse capture C/A code, and taking complex conjugation to obtain a second DFT result; or,
the second DFT result is pre-stored.
Step 304, performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phases;
it should be noted that, in the embodiment of the present invention, performing the second discrete fourier transform on the time domain correlation result obtained by one or more inverse discrete fourier transforms by using the second preset point includes:
and performing second discrete Fourier transform of a second preset point on the time domain correlation result with the same code phase obtained by one or more inverse discrete Fourier transforms.
Optionally, the determining whether the capturing is successful in the embodiment of the present invention includes:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold, determining that the capturing fails.
Optionally, after determining whether the acquisition is successful, the method according to the embodiment of the present invention further includes:
and performing cyclic shift on the first DFT result and the second DFT result to perform acquisition search of the next frequency.
It should be noted that, in the embodiment of the present invention, after the intermediate frequency is stripped, the adjustment of the doppler search frequency may be completed by cyclic shift after DFT conversion, which avoids the operation of performing DFT after performing down-conversion for each frequency adjustment, and reduces a large amount of calculation. And after the cyclic shift of the first DFT result and the second DFT result is completed, continuing to execute the capturing process of the steps 303-307.
Compared with the related art, the technical scheme of the application comprises the following steps: stripping the input intermediate frequency signal; performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result; performing point-to-point multiplication on the obtained first DFT result and a second DFT result obtained based on the local coarse capture C/A code based on element sorting to obtain a point-to-point product; performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phases; performing second Fourier transform of a second preset point on a time domain correlation result obtained by one or more inverse discrete Fourier transforms; performing differential coherent accumulation on the result of the second fourier transform; the maximum value of the differential coherent accumulation is determined, and whether acquisition is successful is determined according to the determined maximum value. The embodiment of the invention simplifies the operation of the capturing process and refines the capturing frequency.
Fig. 4 is a flowchart of a method for implementing the capture process according to another embodiment of the present invention, as shown in fig. 4, including:
optionally, the second DFT result obtained based on the local C/a code in the embodiment of the present invention includes:
and carrying out first DFT transformation of a first preset point on the local C/A code, and taking complex conjugate to obtain the second DFT result.
Optionally, the second DFT result may be pre-stored in the embodiment of the present invention.
Optionally, the determining, according to the embodiment of the present invention, whether the capturing is successful according to the first DFT result and the second DFT result includes:
performing point-to-point multiplication on the obtained first DFT result and the second DFT result based on element sorting to obtain a point-to-point product;
performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phase positions;
performing second discrete Fourier transform of a second preset point on a time domain correlation result of the same code phase obtained by one or more inverse discrete Fourier transforms;
performing differential coherent accumulation on the result of the second fourier transform;
a maximum value of the differential coherent accumulation is determined and it is determined whether the acquisition is successful according to the determined maximum value.
optionally, the determining whether the capturing is successful in the embodiment of the present invention includes:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold, determining that the capturing fails.
And 405, when the acquisition is determined to fail, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition and search, and performing acquisition and search of the next frequency until the search of the current satellite is completed.
It should be noted that, the implementation of the present invention for completing search and acquisition of a current satellite includes: successfully acquiring satellite signals before searching and acquiring all frequencies to complete satellite searching; or, the acquisition search of all frequencies of the current satellite is completed without successfully acquiring the satellite signal, and the search of the current satellite is finished according to the related technology. When acquisition is successful, the next satellite is selected for acquisition search processing with reference to the correlation technique.
Compared with the related art, the technical scheme of the application comprises the following steps: carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping; performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result; a second DFT result obtained based on a local coarse acquisition (C/A) code; determining whether the capturing is successful or not according to the first DFT result and the second DFT result; and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed. The embodiment of the invention simplifies the operation of the capturing process.
Fig. 5 is a block diagram of a receiver according to an embodiment of the present invention, as shown in fig. 5, including: the device comprises a stripping unit, a first conversion unit, a second conversion unit and a judgment unit; wherein,
the peeling unit is used for: carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping;
optionally, the stripping unit in the embodiment of the present invention includes: the device comprises a carrier generation module and a frequency mixing module; wherein,
the carrier generation module is used for: generating a sine SIN carrier and a cosine COS carrier by a numerically controlled oscillator NCO;
the mixing module is used for: and mixing the sine carrier and the cosine carrier with the intermediate frequency signal respectively to perform down-conversion processing on the intermediate frequency signal so as to realize intermediate frequency stripping.
The first transformation unit is configured to: performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result;
a second transformation unit to: a second DFT result obtained based on the local coarse acquisition C/A code;
optionally, the second transformation unit in the embodiment of the present invention is specifically configured to: performing first DFT transformation of a first preset point on a local coarse capture C/A code, and taking complex conjugate to obtain a second DFT result; or, the second DFT result is stored in advance.
The judgment unit is used for: determining whether the capturing is successful or not according to the first DFT result and the second DFT result;
optionally, the determining unit in the embodiment of the present invention includes a dot product module, an inverse transform module, a differential coherent accumulation module, and a determining module; wherein,
the dot product module is to: performing point-to-point multiplication on the obtained first DFT result and the second DFT result based on element sorting to obtain a point-to-point product;
the inverse transform module is to: performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phases;
the transform module is to: performing second discrete Fourier transform of a second preset point on a time domain correlation result of the same code phase obtained by one or more inverse discrete Fourier transforms;
the differential coherent accumulation module is used for: performing differential coherent accumulation on the result of the second fourier transform;
the judgment module is used for: a maximum value of the differential coherent accumulation is determined and it is determined whether the acquisition is successful according to the determined maximum value.
The shift processing unit is used for: and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed.
Optionally, the determining module is specifically configured to:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold, determining that the capturing fails.
The embodiment of the invention also provides a computer storage medium, wherein the computer storage medium stores computer executable instructions, and the computer executable instructions are used for executing the method.
The method of the embodiment of the present invention is described below by using application examples, which are only used for illustrating the present invention and are not used for limiting the protection scope of the present invention.
The present application example takes the acquisition of a GPS signal as an example for explanation:
firstly, the C/A code period of the CPS satellite is 1023, the time duration is 1 millisecond, and 2046 code phases need to be searched if a half chip is captured each time; therefore, the present application example uses at least DFT of points where N is an integer multiple of 2046; assuming that N is 2046, the frequency bandwidth f is searchedbin1KHz and sampling frequency fs2.046 MHz. Thus, 2046 data samples per input is exactly one C/A period. The intermediate frequency signal of the GNSS receiver after A/D sampling is as follows:
s(n)＝Axndnsin[2π(fIF+fd)tn+θ] (5)
wherein A is the amplitude of the signal, xnIs the sampled value of the C/A code, dnFor navigation data, fIFAnd fdRespectively, intermediate frequency and Doppler frequency, tnFor the sampling instant, θ is the initial phase. According to the DFT-based parallel code phase acquisition algorithm described above, the down-conversion and fourier transform of the input intermediate frequency signal may obtain a first DFT result, expressed as equation (6); in the formula (6), fbinIs the frequency of the current acquisition search, which is also the search step we assume, fsIs the sampling frequency, tn＝1/fs，N＝fs/fbin。
Performing point-to-point multiplication on the obtained first DFT result and a second DFT result obtained based on the local coarse capture C/A code based on element sorting to obtain a point-to-point product;
performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phase positions;
in the application example, the results corresponding to the same code phase in 2046 time domain correlation results obtained by different millisecond processing at the same frequency point are combined into a new sequence (for example, the 1 st code phase result in each millisecond correlation result), and 2046 sequences are in total.
And performing second discrete Fourier transform of a second preset point on each sequence to generate a result on a second preset frequency point. Therefore, the frequency is fine, the coherent integration time is increased, and the capture sensitivity is improved; the coherent integration results obtained were:
where k is ± 1, ± 3, ± 5, …, Δ f is the final frequency resolution, controlled by different integration times, and Δ f is generally required to be less than
By TcohFor example, 1ms and M8, the total integration time is 8ms, and Δ f should be less than 125 Hz.
In the related technology, after the coherent integration result, non-coherent integration is performed again to further obtain a certain signal gain and improve the capture sensitivity. While the non-coherent integration is to add the amplitudes of the coherent integration results, the amplitude calculation will result in noise energy increase, i.e. square loss. The present application illustrates differential coherent accumulation instead of non-coherent accumulation. Differential coherent accumulation is to multiply the conjugate of adjacent coherent integration results and then accumulate them, although some square loss may exist, there is a gain improvement of 1-2 dB compared to non-coherent integration. The mathematical expression of the method is as follows,
in the formula, U is the number of incoherent accumulation, and the approximate number is because I is assumedu+1Qu-Qu+1IuAnd the output is approximately equal to 0, z (u +1) and z (u) are adjacent correlation integral outputs, the conjugate multiplication of the two is adopted to reduce the noise amplification, but the influence of bit jump of the navigation message is considered, and the adjacent z is adjacent to the bit jump*In addition, (u +1) z (u), the sign may be different to cause cancellation, so the above equation can be written as:
for the cyclic shift processing, the present application example first considers that the search frequency is 2fbinThe conditions of intermediate frequency stripping processing and first DFT conversion of a first preset point on the signals after the intermediate frequency is stripped are carried out:
it can be seen by a pair of equations (6) and (10): after the intermediate frequency is stripped, the adjustment of the Doppler search frequency can be completed through cyclic shift after DFT conversion, thereby avoiding the operation of performing down-conversion and then DFT for each frequency adjustment and reducing a large amount of calculation.
The same method can also be used for navigation systems such as BD, GLONASS, etc., which are not illustrated here.
It will be understood by those skilled in the art that all or part of the steps of the above methods may be implemented by a program instructing associated hardware (e.g., a processor) to perform the steps, and the program may be stored in a computer readable storage medium, such as a read only memory, a magnetic or optical disk, and the like. Alternatively, all or part of the steps of the above embodiments may be implemented using one or more integrated circuits. Accordingly, each module/unit in the above embodiments may be implemented in hardware, for example, by an integrated circuit to implement its corresponding function, or in software, for example, by a processor executing a program/instruction stored in a memory to implement its corresponding function. The present invention is not limited to any specific form of combination of hardware and software.
Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the form and details of the present invention without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A method of implementing an acquisition process, comprising:
carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping;
performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result;
a second DFT result obtained based on the local coarse acquisition C/A code;
determining whether the capturing is successful or not according to the first DFT result and the second DFT result;
and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition and search, and performing acquisition processing according to the obtained frequency until the search of the current satellite is completed.
2. The method of claim 1, wherein the determining whether the acquisition is successful or not through the first DFT result and the second DFT result comprises:
performing point-to-point multiplication on the obtained first DFT result and the second DFT result based on element sorting to obtain a point-to-point product;
performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phases;
performing second discrete Fourier transform of a second preset point on a time domain correlation result of the same code phase obtained by one or more inverse discrete Fourier transforms;
performing differential coherent accumulation on the result of the second fourier transform;
a maximum value of the differential coherent accumulation is determined and it is determined whether the acquisition is successful according to the determined maximum value.
3. The method of claim 1 or 2, wherein the second DFT results obtained based on the local coarse acquisition C/a code comprise:
and carrying out first DFT transformation of a first preset point on the local coarse capture C/A code, and taking complex conjugate to obtain the second DFT result.
4. The method according to claim 1 or 2,
the second DFT result is pre-stored.
5. The method of claim 2, wherein the determining whether acquisition was successful comprises:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold, determining that the capturing fails.
6. A receiver, comprising: the device comprises a stripping unit, a first conversion unit, a second conversion unit and a judgment unit; wherein,
the peeling unit is used for: carrying out down-conversion processing on an input intermediate frequency signal to realize intermediate frequency stripping;
the first transformation unit is configured to: performing first Discrete Fourier Transform (DFT) of a first preset point on the signal stripped from the intermediate frequency to obtain a first DFT result;
a second transformation unit to: a second DFT result obtained based on the local coarse acquisition C/A code;
the judgment unit is used for: determining whether the capturing is successful or not according to the first DFT result and the second DFT result;
the shift processing unit is used for: and when the acquisition failure is determined, performing cyclic shift on the first DFT result and the second DFT result to obtain the next frequency for acquisition search, and performing acquisition search of the next frequency until the search of the current satellite is completed.
7. The receiver of claim 6, wherein the decision unit comprises a dot product module, an inverse transform module, a differential coherent accumulation module, and a decision module; wherein,
the dot product module is to: performing point-to-point multiplication on the obtained first DFT result and the second DFT result based on element sorting to obtain a point-to-point product;
the inverse transform module is to: performing inverse discrete Fourier transform of a first preset point on the obtained point product to obtain time domain correlation results of all code phases;
the transform module is to: performing second discrete Fourier transform of a second preset point on a time domain correlation result of the same code phase obtained by one or more inverse discrete Fourier transforms;
the differential coherent accumulation module is used for: performing differential coherent accumulation on the result of the second fourier transform;
the judgment module is used for: a maximum value of the differential coherent accumulation is determined and it is determined whether the acquisition is successful according to the determined maximum value.
8. The receiver according to claim 6 or 7, wherein the second transform unit is specifically configured to: performing first DFT transformation of a first preset point on a local coarse capture C/A code, and taking complex conjugation to obtain a second DFT result; or, the second DFT result is stored in advance.
9. The receiver of claim 7, wherein the determining module is specifically configured to:
when the determined maximum value of the differential coherent accumulation is larger than a preset threshold, determining that the capturing is successful;
and when the determined maximum value of the differential coherent accumulation is less than or equal to a preset threshold, determining that the capturing fails.
10. A computer storage medium having computer-executable instructions stored therein for performing the method of any one of claims 1-5.
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