CN104993844A - Method and device for searching frequency domain - Google Patents
Method and device for searching frequency domain Download PDFInfo
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Abstract
The invention provides a method and a device for searching a frequency domain. The method comprises the steps as follows: performing first-order down-conversion to a sampling point sequence according to a frequency domain search range; segmenting a coherent integration time according to a first preset value so as to obtain sub coherent integration times; calculating a first-order correlation value, corresponding to each sub coherent integration time, of a first result,; performing second-order down-conversion to each first order correlation value; performing second-order coherent integration calculation to each obtained second result; performing discrete Fourier transform DFT to each obtained second-order correlation value; and determining the frequency of a capturing moment according to each frequency value obtained after performing the DFT transformation. According to the technical solution, the first-order serial search is finished by performing the first-order down-conversion to the sampling point sequence according to the frequency domain search range, and the second-order serial search is finished by performing the second-order down-conversion, and the third-order parallel search is finished by using the DFT, so that the method and the device of the invention could be used for accurately and fast searching the frequency domain in wide range.
Description
Technical Field
The present invention relates to satellite navigation technologies, and in particular, to a frequency domain searching method and apparatus based on a spread spectrum receiver.
Background
In a direct sequence spread spectrum communication system, the acquisition of a spreading code by a receiver is a precondition for realizing signal demodulation. Due to the relative motion of the transmitting and receiving parties, a doppler frequency offset exists between the received signal and the local signal. Theoretical research shows that, during time domain search, the existence of doppler frequency offset affects the correlation detection amplitude, as shown in formula (1):
wherein Z is the correlation detection amplitude without frequency deviation, fdIs Doppler frequency offset (hereinafter referred to as frequency offset), ZdAt a frequency offset of fdAmplitude of time-dependent detection, L being the spreading ratio, TcIs the duration of each chip. As can be seen from equation (1), in the presence of frequency offset, the correlation detection amplitude decays.
When the frequency offset is small, the attenuation of the relevant detection amplitude value can be ignored, and the receiver can complete the acquisition of the spread spectrum code by pure time domain search. However, a large frequency offset causes a significant loss of the time-domain correlated signal-to-noise ratio, and therefore, two-dimensional search in the frequency domain and the time domain is required to acquire the spreading code.
The time domain searching is to align the phase of the local spreading code generator with the phase of the spreading code in the received signal to realize the capture of the spreading code; the frequency domain searching is to estimate the doppler frequency offset and compensate the received signal, so as to reduce the signal-to-noise ratio loss caused by the frequency offset of the received signal and ensure the success of the time domain searching.
In a Global Navigation Satellite System (GNSS), a Global Positioning System (GPS) and a beidou Satellite System use a code division multiple access technology to distinguish different satellites by different pseudo random codes, and a GLONASS (GLONASS) System uses a frequency division multiple access technology to distinguish different satellites by different carrier frequencies. In practice, these systems spread the modulated data using direct sequence spreading. In order to receive the navigation data of a certain satellite, pseudo-random codes for modulating the data must be reproduced, and the reproduced pseudo-codes and the input pseudo-codes are subjected to correlation operation on different phase errors to synchronize the reproduced pseudo-codes and the input pseudo-codes, so that the despreading of the navigation data is completed, and the process is called pseudo-code acquisition. On the other hand, due to the radial movement between the GNSS satellite moving at high speed and the receiver, the carrier wave generates the doppler shift effect. Therefore, after analog down-conversion (radio frequency module) and digital down-conversion of the satellite signal, the frequency value is not zero, but a doppler shift is added on the basis of zero intermediate frequency. In order to demodulate navigation data of a certain satellite, the value of the doppler shift generated by the corresponding satellite must be searched, and the process is called carrier acquisition or frequency domain search.
The existing frequency domain searching method has two different methods of serial and parallel. The advantage of serial search is that the algorithm is simple to implement, has low requirements for system resources, but has a slow capture speed, and is not suitable for application in a long-period code and high-dynamic environment. The parallel search method generally uses a Fast Fourier Transform (FFT) parallel search method, which has a fast acquisition speed, but the search frequency range is limited, which results in a higher signal-to-noise ratio loss due to an excessively large frequency interval.
Disclosure of Invention
In order to solve the technical problem, the invention provides a frequency domain searching method and a frequency domain searching device, which can realize large-range, accurate and quick searching of a frequency domain.
In order to achieve the object of the present invention, the present invention provides a frequency domain searching method, comprising:
performing first-stage down-conversion on the sampling point sequence according to the frequency domain searching range;
segmenting the coherent integration time according to a first preset value to obtain sub-coherent integration time; respectively calculating first-stage correlation values of the first results corresponding to the sub-coherent integration time;
performing second-stage down-conversion on each calculated first-stage correlation value; performing second-stage coherent integration operation on each obtained second result;
performing Discrete Fourier Transform (DFT) on each obtained second-stage correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion.
Further, the performing a first stage down-conversion on the sampling point sequence according to the frequency domain search range includes:
determining a first center frequency of the frequency domain searching range according to the frequency domain searching range;
performing first-stage down-conversion on the sampling point sequence according to the determined first central frequency to obtain a first result;
wherein the first center frequency is a center frequency value corresponding to the frequency domain search range.
Further, the performing of the second-stage down-conversion on each calculated first-stage correlation value includes:
segmenting the determined frequency domain searching range according to a first preset value;
respectively determining second center frequencies of the sub-frequency domain search ranges obtained after segmentation;
performing second-stage down-conversion on each first-stage correlation value according to each determined second center frequency to obtain a second result;
wherein each second center frequency is a center frequency value corresponding to each first sub-frequency domain search range.
Further, the performing a second-stage coherent integration operation on the obtained second result includes:
and respectively carrying out second-stage coherent integration operation on each obtained second result according to a second sub-coherent integration time to obtain each second-stage correlation value, wherein the second sub-coherent integration time is sub-coherent integration time L, and L is a positive integer.
Further, the performing DFT on each obtained second-stage correlation value includes:
segmenting each sub-frequency domain searching range according to a second preset value; to obtain each second sub-frequency domain search range;
determining a third center frequency of each obtained second sub-frequency domain searching range;
performing DFT on each obtained second-stage correlation value according to each determined third center frequency;
wherein each third center frequency is a center frequency value corresponding to the each second sub-frequency domain search range.
Further, the determining the frequency at the capturing time according to the obtained frequency values after DFT conversion includes:
judging each frequency value obtained after DFT conversion and a judgment threshold;
and when the frequency value after DFT conversion is larger than the judgment threshold, determining the frequency value after DFT conversion as the frequency of the capture moment.
The invention also provides a frequency domain searching method, which is characterized by comprising the following steps: the device comprises a first module, a calculation module, a second module and a determination module; wherein,
the first module is used for carrying out first-stage down-conversion on the sampling point sequence according to the frequency domain searching range;
the calculation module is used for segmenting the coherent integration time according to a first preset value so as to obtain sub-coherent integration time; respectively calculating first-stage correlation values of the first results corresponding to the sub-coherent integration time;
the second module is used for carrying out second-stage down-conversion on each calculated first-stage correlation value; performing second-stage coherent integration operation on each obtained second result;
the determining module is used for performing Discrete Fourier Transform (DFT) on each obtained second-stage correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion.
Further, the first module is specifically configured to:
determining a first center frequency of the frequency domain searching range according to the frequency domain searching range;
performing first-stage down-conversion on the sampling point sequence according to the determined first central frequency to obtain a first result;
wherein the first center frequency is a center frequency value corresponding to the frequency domain search range.
Further, the second module is specifically configured to:
segmenting the determined frequency domain searching range according to a first preset value;
respectively determining second center frequencies of the sub-frequency domain search ranges obtained after segmentation;
performing second-stage down-conversion on each first-stage correlation value according to each determined second center frequency to obtain a second result;
wherein each second center frequency is a center frequency value corresponding to each first sub-frequency domain search range.
Further, the second module is further specifically configured to:
and respectively carrying out second-stage coherent integration operation on each obtained second result according to a second sub-coherent integration time to obtain each second-stage correlation value, wherein the second sub-coherent integration time is sub-coherent integration time L, and L is a positive integer.
Further, the determining module is specifically configured to:
segmenting each sub-frequency domain searching range according to a second preset value; to obtain each second sub-frequency domain search range;
determining a third center frequency of each obtained second sub-frequency domain searching range;
performing DFT on each obtained second-stage correlation value according to each determined third center frequency;
wherein each third center frequency is a center frequency value corresponding to the each second sub-frequency domain search range.
Further, the determining module is further specifically configured to:
judging each frequency value obtained after DFT conversion and a judgment threshold;
and when the frequency value after DFT conversion is larger than the judgment threshold, determining the frequency value after DFT conversion as the frequency of the capture moment.
The technical scheme of the invention comprises the following steps: performing first-stage down-conversion on the sampling point sequence according to the frequency domain searching range; segmenting the coherent integration time according to a first preset value to obtain sub-coherent integration time; respectively calculating first-stage correlation values of the first results corresponding to the sub-coherent integration time; performing second-stage down-conversion on each calculated first-stage correlation value; performing second-stage coherent integration operation on each obtained second result; performing Discrete Fourier Transform (DFT) on each obtained second-stage correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion. In the technical scheme of the invention, the first-stage down-conversion is carried out on the sampling point sequence through the frequency domain searching range to complete the first-stage serial search, the second-stage serial search is completed through the second-stage down-conversion, and the third-stage parallel search is completed through DFT, so that the large-range, accurate and rapid search of the frequency domain is realized.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a flow chart of a frequency domain searching method of the present invention;
fig. 2 is a schematic structural diagram of the frequency domain searching apparatus according to 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 the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
Fig. 1 is a flowchart of a frequency domain searching method of the present invention, as shown in fig. 1, including the following steps:
step 101: and carrying out first-stage down-conversion on the sampling point sequence according to the frequency domain searching range. The method specifically comprises the following steps:
determining a first center frequency of the frequency domain searching range according to the frequency domain searching range;
performing first-stage down-conversion on the sampling point sequence according to the determined first central frequency to obtain a first result;
wherein the first center frequency is a center frequency value corresponding to the frequency domain search range.
For example, when the search range is ± 5KHz, the first center frequency is a center frequency value of 0KHz of ± 5KHz, and when the search range is 0KHz to 20KHz, the first center frequency is 10 KHz. The following calculation methods of the second center frequency and the third center frequency are the same as the calculation method of this step, and will not be described again.
The step also includes determining the frequency domain search range before the step, and the specific implementation is well known to those skilled in the art, and is not used to limit the protection scope of the present invention, and will not be described herein again.
It should be noted that how to perform the down-conversion is a conventional technical means known to those skilled in the art, and is not intended to limit the present invention, and will not be described herein.
Step 102: segmenting the coherent integration time according to a first preset value to obtain sub-coherent integration time; first-stage correlation values of the first results corresponding to the respective sub-coherent integration times are respectively calculated.
The first result is the result of performing the first stage down-conversion on the sampling point sequence according to the first center frequency.
For example, the coherent integration time is known as TcohAssuming that each sub-coherent integration time to be acquired is T1Then can be divided intoSub-coherent integration time, the first preset value in step 102 may be M, where M is a positive integer greater than or equal to 1, and M first-stage correlation values may be obtained in this step and may be recorded as x0，x1，..，xM-1。
It should be noted that how to perform the coherent integration operation on the first result to obtain the first-order correlation value belongs to the conventional technical means known to those skilled in the art, and is not described herein again.
Step 103: performing second-stage down-conversion on each calculated first-stage correlation value; and carrying out second-stage coherent integration operation on each obtained second result.
And the second result is the result of carrying out second-stage down-conversion on each calculated first-stage correlation value.
Performing a second-stage down-conversion on each calculated first-stage correlation value comprises:
segmenting the determined frequency domain searching range according to a first preset value;
respectively determining second center frequencies of the sub-frequency domain search ranges obtained after segmentation;
performing second-stage down-conversion on each first-stage correlation value according to each determined second center frequency to obtain a second result;
wherein each second center frequency is a center frequency value corresponding to each first sub-frequency domain search range.
And performing a second stage of coherent integration operation on the obtained second result comprises:
and respectively carrying out second-stage coherent integration operation on each obtained second result according to a second sub-coherent integration time to obtain each second-stage correlation value, wherein the second sub-coherent integration time is sub-coherent integration time L, and L is a positive integer.
For example, the second result can be obtained by using equation (2):
wherein M is 0, 1, M-1, f2Is the second center frequency, T1For the sub-coherent integration time, j is an imaginary unit, e.g., in complex number a + bi, a is the real part and bi is the imaginary part. And performing second-stage coherent integration operation on the second result according to the second sub-coherent integration time (i.e. accumulating each L points into one point) to obtain N-M/L second-stage correlation values which are recorded as y0，y1，...，yN-1。
Step 104: performing Discrete Fourier Transform (DFT) on each obtained second-stage correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion.
Performing DFT on each obtained second-level correlation value includes:
segmenting each sub-frequency domain searching range according to a second preset value; to obtain each second sub-frequency domain search range;
determining a third center frequency of each obtained second sub-frequency domain searching range;
performing DFT on each obtained second-stage correlation value according to each determined third center frequency;
wherein each third center frequency is a center frequency value corresponding to each second sub-frequency domain search range.
And the number of the first and second groups,
determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion, comprising:
judging each frequency value obtained after DFT conversion and a judgment threshold;
and when the frequency value after DFT conversion is larger than the judgment threshold, determining the frequency value after DFT conversion as the frequency of the capture moment.
By way of example, following the above example, y is plotted according to equation (3)0，y1，...，yN-1The DFT is performed and the result is obtained,
wherein N is 0, 1, N-1, k is 0, 1, N-1f3Is the third center frequency, T2Is the sub-coherent integration time, the second sub-coherent integration time, T2＝T1XL, j is the unit of imaginary number.
In the method, the first-stage down-conversion is carried out on the sampling point sequence through the frequency domain searching range to complete the first-stage serial search, the second-stage serial search is completed through the second-stage down-conversion, and the third-stage parallel search is completed through DFT, so that the wide-range, accurate and quick search of the frequency domain is realized.
Fig. 2 is a schematic structural diagram of the frequency domain searching apparatus of the present invention, as shown in fig. 2, including: the device comprises a first module, a calculation module, a second module and a determination module. Wherein,
and the first module is used for carrying out first-stage down-conversion on the sampling point sequence according to the frequency domain searching range.
Wherein, the first module is specifically configured to:
determining a first center frequency of the frequency domain searching range according to the frequency domain searching range;
performing first-stage down-conversion on the sampling point sequence according to the determined first central frequency to obtain a first result;
wherein the first center frequency is a center frequency value corresponding to the frequency domain search range.
The calculation module is used for segmenting the coherent integration time according to a first preset value so as to obtain sub-coherent integration time; first-stage correlation values of the first results corresponding to the respective sub-coherent integration times are respectively calculated.
The first result is the result of performing the first stage down-conversion on the sampling point sequence according to the first center frequency.
The second module is used for carrying out second-stage down-conversion on each calculated first-stage correlation value; and carrying out second-stage coherent integration operation on the obtained second result.
Wherein, the second module is specifically configured to:
segmenting the determined frequency domain searching range according to a first preset value;
respectively determining second center frequencies of the sub-frequency domain search ranges obtained after segmentation;
performing second-stage down-conversion on each first-stage correlation value according to each determined second center frequency to obtain a second result;
wherein each second center frequency is a center frequency value corresponding to each first sub-frequency domain search range.
The second module is further specifically configured to:
and respectively carrying out second-stage coherent integration operation on each obtained second result according to a second sub-coherent integration time to obtain each second-stage correlation value, wherein the second sub-coherent integration time is sub-coherent integration time L, and L is a positive integer.
A determining module, configured to perform a Discrete Fourier Transform (DFT) on each obtained second-level correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion.
The determining module is specifically configured to:
segmenting each sub-frequency domain searching range according to a second preset value; to obtain each second sub-frequency domain search range;
determining a third center frequency of each obtained second sub-frequency domain searching range;
performing DFT on each obtained second-stage correlation value according to each determined third center frequency;
wherein each third center frequency is a center frequency value corresponding to each second sub-frequency domain search range.
And the determining module is further specifically configured to:
judging each frequency value obtained after DFT conversion and a judgment threshold;
and when the frequency value after DFT conversion is larger than the judgment threshold, determining the frequency value after DFT conversion as the frequency of the capture moment.
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 instructing the relevant hardware through a program, 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 the form of hardware, and may also be implemented in the form of a software functional module. The present application is not limited to any specific form of hardware or software combination.
The above description is only a preferred example of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (12)
1. A frequency domain searching method, comprising:
performing first-stage down-conversion on the sampling point sequence according to the frequency domain searching range;
segmenting the coherent integration time according to a first preset value to obtain sub-coherent integration time; respectively calculating first-stage correlation values of the first results corresponding to the sub-coherent integration time;
performing second-stage down-conversion on each calculated first-stage correlation value; performing second-stage coherent integration operation on each obtained second result;
performing Discrete Fourier Transform (DFT) on each obtained second-stage correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion.
2. The method of claim 1, wherein the first stage down-converting the sequence of sample points according to the frequency domain search range comprises:
determining a first center frequency of the frequency domain searching range according to the frequency domain searching range;
performing first-stage down-conversion on the sampling point sequence according to the determined first central frequency to obtain a first result;
wherein the first center frequency is a center frequency value corresponding to the frequency domain search range.
3. The method of claim 1, wherein said second down-converting each calculated first-stage correlation value comprises:
segmenting the determined frequency domain searching range according to a first preset value;
respectively determining second center frequencies of the sub-frequency domain search ranges obtained after segmentation;
performing second-stage down-conversion on each first-stage correlation value according to each determined second center frequency to obtain a second result;
wherein each second center frequency is a center frequency value corresponding to each first sub-frequency domain search range.
4. The method of claim 1, wherein performing a second stage coherent integration operation on the obtained second result comprises:
and respectively carrying out second-stage coherent integration operation on each obtained second result according to a second sub-coherent integration time to obtain each second-stage correlation value, wherein the second sub-coherent integration time is sub-coherent integration time L, and L is a positive integer.
5. The method of claim 1, wherein performing a DFT on each obtained second-stage correlation value comprises:
segmenting each sub-frequency domain searching range according to a second preset value; to obtain each second sub-frequency domain search range;
determining a third center frequency of each obtained second sub-frequency domain searching range;
performing DFT on each obtained second-stage correlation value according to each determined third center frequency;
wherein each third center frequency is a center frequency value corresponding to the each second sub-frequency domain search range.
6. The method according to any one of claims 1 to 5, wherein determining the frequency at the time of capture from the obtained DFT-transformed individual frequency values comprises:
judging each frequency value obtained after DFT conversion and a judgment threshold;
and when the frequency value after DFT conversion is larger than the judgment threshold, determining the frequency value after DFT conversion as the frequency of the capture moment.
7. A frequency domain searching apparatus method, comprising: the device comprises a first module, a calculation module, a second module and a determination module; wherein,
the first module is used for carrying out first-stage down-conversion on the sampling point sequence according to the frequency domain searching range;
the calculation module is used for segmenting the coherent integration time according to a first preset value so as to obtain sub-coherent integration time; respectively calculating first-stage correlation values of the first results corresponding to the sub-coherent integration time;
the second module is used for carrying out second-stage down-conversion on each calculated first-stage correlation value; performing second-stage coherent integration operation on each obtained second result;
the determining module is used for performing Discrete Fourier Transform (DFT) on each obtained second-stage correlation value; and determining the frequency of the capturing moment according to the obtained frequency values after DFT conversion.
8. The apparatus of claim 7, wherein the first module is specifically configured to:
determining a first center frequency of the frequency domain searching range according to the frequency domain searching range;
performing first-stage down-conversion on the sampling point sequence according to the determined first central frequency to obtain a first result;
wherein the first center frequency is a center frequency value corresponding to the frequency domain search range.
9. The apparatus of claim 7, wherein the second module is specifically configured to:
segmenting the determined frequency domain searching range according to a first preset value;
respectively determining second center frequencies of the sub-frequency domain search ranges obtained after segmentation;
performing second-stage down-conversion on each first-stage correlation value according to each determined second center frequency to obtain a second result;
wherein each second center frequency is a center frequency value corresponding to each first sub-frequency domain search range.
10. The apparatus of claim 9, wherein the second module is further specifically configured to:
and respectively carrying out second-stage coherent integration operation on each obtained second result according to a second sub-coherent integration time to obtain each second-stage correlation value, wherein the second sub-coherent integration time is sub-coherent integration time L, and L is a positive integer.
11. The apparatus of claim 7, wherein the determining module is specifically configured to:
segmenting each sub-frequency domain searching range according to a second preset value; to obtain each second sub-frequency domain search range;
determining a third center frequency of each obtained second sub-frequency domain searching range;
performing DFT on each obtained second-stage correlation value according to each determined third center frequency;
wherein each third center frequency is a center frequency value corresponding to the each second sub-frequency domain search range.
12. The apparatus according to any one of claims 7 to 11, wherein the determining module is further specifically configured to:
judging each frequency value obtained after DFT conversion and a judgment threshold;
and when the frequency value after DFT conversion is larger than the judgment threshold, determining the frequency value after DFT conversion as the frequency of the capture moment.
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| CN104601512A (en) * | 2015-01-05 | 2015-05-06 | 江苏指南针导航通信技术有限公司 | Method and system for detecting carrier frequency offset of phase-modulated signals |
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| CN106998586A (en) * | 2017-06-01 | 2017-08-01 | 电子科技大学 | The synchronization acquiring method of wireless communication system in a kind of high dynamic environment |
| CN113820731A (en) * | 2021-11-24 | 2021-12-21 | 湖南跨线桥航天科技有限公司 | Method and system for capturing non-periodic long code signal of satellite navigation receiver |
| CN113820731B (en) * | 2021-11-24 | 2022-06-10 | 湖南跨线桥航天科技有限公司 | Method and system for capturing non-periodic long code signal of satellite navigation receiver |
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