CN102087361A - Method and device for acquiring satellite navigation signal - Google Patents
Method and device for acquiring satellite navigation signal Download PDFInfo
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Abstract
The invention discloses a method and device for acquiring a satellite navigation signal, belonging to the technical field of communication. The method comprises the following steps of: acquiring an in-phase component and a quadrature component, wherein the in-phase component contains a C/A code; respectively carrying out correlation operation on the acquired in-phase component containing the C/A code, and the quadrature component with a local C/A code; carrying out FFT (Fast Fourier Transform) on obtained correction operation results; carrying out differential coherent accumulation on the FFT results; judging according to the results of the differential coherent accumulation, wherein if the results are larger than a threshold value, the satellite signal is successfully acquired, or else, the satellite signal is failed to acquire. The method solves the problem that navigation signals with high symbol hopping ratio cannot be integrated and accumulated for a long time; and the differential coherent accumulation method is adopted, thus the signal to noise ratio is increased and the satellite signals are successfully acquired.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for capturing a satellite navigation signal.
Background
The acquisition technology is a key part in signal processing of a GPS (Global Positioning System) receiver. The quality of the acquisition method is one of the main criteria for evaluating the receiver.
Two highly sensitive GPS signal acquisition methods that are commonly used are coherent integration and non-coherent integration. Coherent integration means that correlation values of received C/A code signals and local C/A code signals in different periods are correspondingly superposed, so that noise can be offset and signals can be enhanced more, and the signal-to-noise ratio is improved. The length of the coherent integration is limited by the doppler shift and the hopping of the navigation data bits. For GPS signals, there may be a data bit transition every 20ms, so if the coherent integration time exceeds 20ms, energy is lost, and the signal-to-noise ratio is reduced. The non-coherent integration is to accumulate the correlation result of each period after taking the modulus, so that the noise intensity is correspondingly accumulated while the signal intensity is superposed, and the improvement of the signal-to-noise ratio is not obvious.
Therefore, the preferred solution to improve the sensitivity of the receiver is to increase the coherent accumulation time as much as possible, but since the navigation signal modulates the navigation Data, the coherent accumulation time is limited by the Data bit jump, so how to avoid the Data bit jump from affecting the coherent accumulation without any auxiliary information becomes a hot point of research of high-sensitivity receivers, and a circular correlation with Multiple Data Bits (CCMDB) acquisition algorithm (as shown in fig. 1) is widely used at present. Wherein in each coherent integration interval, the most reliable combination of data bits is estimated; it is then used to remove the sign effect of the data bits before combining the coherent accumulation into a non-coherent accumulation. Assuming equal probabilities for each combination of data bits, the worst case average equivalent integration time is shown in equation (1):
wherein,
is equivalent integration time, NtIs the number of integrals,. epsilon.is the number of transitions, TIFor total integration time, since only N is searchedbThe integral loss caused by each edge is shown in equation (2):
thus, for the C/A code of GPS, when N isbAt 4, it is substituted into the equations (1) and (2), and finally the integral loss can be calculated to be 10%. But for navigation signals with very high symbol jump rate, NbThe selection of (a) is limited, and thus the integration loss of the above method becomes large.
The inventor finds that the prior art has at least the following disadvantages in the process of implementing the invention: for navigation signals with very high symbol jump rate, long-time integral accumulation cannot be carried out, the signal-to-noise ratio cannot be well improved, and weak signals cannot be well captured.
Disclosure of Invention
In order to prolong the time of integral accumulation, improve the signal-to-noise ratio of a received signal and realize successful acquisition of a weak signal, the embodiment of the invention provides a method for acquiring a satellite navigation signal, and the technical scheme is as follows:
in one aspect, an embodiment of the present invention provides a method for acquiring a satellite navigation signal, where the method includes:
obtaining an in-phase component and a quadrature component containing C/A codes;
respectively carrying out correlation operation on the obtained in-phase component and orthogonal component of the C/A code and a local C/A code;
performing FFT on the result of the correlation operation;
carrying out differential coherent accumulation on the result of FFT conversion;
judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, successfully capturing the satellite signal; otherwise, the acquisition of the satellite signal fails.
The step of performing correlation operation on the obtained in-phase component and quadrature component of the C/a code and the local C/a code respectively specifically includes:
step A: segmenting the 2L millisecond receiving data by taking 2 milliseconds as a unit;
and B: obtaining a locally generated L millisecond replica code, adding 1 millisecond zero after each millisecond replica code;
and C: performing correlation operation on the received data in the step A and the data obtained in the step B to obtain data corresponding to 1 st millisecond of each section after the correlation operation;
step D: judging whether the data with the maximum absolute value in the data corresponding to the 1 st millisecond of each section is less than 0 or not, and if the data is less than 0, performing sign inversion correction; otherwise, executing step E;
step E: and correspondingly adding the L sections of 1 millisecond data, and outputting the 1 millisecond data obtained after the addition.
The step of judging whether the data with the largest absolute value in the data corresponding to the 1 st millisecond of each segment is smaller than 0, and if so, performing the sign inversion correction specifically includes: each value in the piece of data is multiplied by-1.
The step of performing differential coherent accumulation on the FFT result specifically includes:
and carrying out differential coherent accumulation on the orthogonal component and the in-phase component of the nth time and the orthogonal component and the in-phase component of the (n-1) th time respectively.
Judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, successfully capturing the satellite signal; otherwise, the step of failing to acquire the satellite signal further comprises:
if the value is larger than the threshold value, the code phase and the carrier frequency of the C/A code are output after the satellite signal is successfully captured; accordingly, the number of the first and second electrodes,
if the signal is smaller than the preset threshold value, after the signal acquisition fails, the phase and the carrier frequency of the local code are adjusted, and the search is carried out again.
In another aspect, an embodiment of the present invention provides an apparatus for acquiring a satellite navigation signal, where the apparatus includes:
an obtaining module for obtaining an in-phase component and a quadrature component comprising a C/A code;
the operation module is used for respectively carrying out correlation operation on the in-phase component and the orthogonal component of the C/A code obtained by the obtaining module and a local C/A code;
the FFT conversion module is used for carrying out FFT conversion on the result of the correlation operation;
a differential coherent accumulation module, configured to perform differential coherent accumulation on a result transformed by the FFT transformation module;
the judgment module is used for judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, the satellite signal is successfully captured; otherwise, the acquisition of the satellite signal fails.
The operation module specifically comprises:
a segmenting unit for segmenting 2L-millisecond received data in units of 2 milliseconds;
an adding unit for obtaining a locally generated L millisecond replica code, adding 1 millisecond zero after each millisecond replica code;
the acquisition unit is used for carrying out correlation operation on the received data in the segmentation unit and the data obtained in the adding unit, and acquiring data corresponding to the 1 st millisecond of each segment after the correlation operation;
the judging unit is used for judging whether the data with the largest absolute value in the data corresponding to the 1 st millisecond of each section obtained by the obtaining unit is smaller than 0 or not, and if the data is smaller than 0, the sign inversion correction is carried out; otherwise, executing the first output unit;
and the first output unit is used for correspondingly adding the L sections of 1 millisecond data and outputting the 1 millisecond data obtained after the addition.
The judging unit further includes: a calculation subunit for multiplying each value in the segment of data by-1.
The differential coherent accumulation module is specifically configured to perform differential coherent accumulation on the orthogonal component and the in-phase component of the nth time and the orthogonal component and the in-phase component of the (n-1) th time respectively.
The decision module specifically includes:
the judgment unit is used for judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, the satellite signal acquisition is successful; otherwise, the satellite signal acquisition is failed;
a second output unit for outputting a code phase and a carrier frequency of the C/a code; and the adjusting unit is used for adjusting the phase and the carrier frequency of the local code.
The technical scheme provided by the embodiment of the invention has the beneficial effects that:
the method comprises the steps of increasing the time for carrying out correlation operation on the in-phase component and the orthogonal component of the C/A code and the local C/A code respectively, carrying out FFT (fast Fourier transform) conversion on the result of the correlation operation, carrying out differential coherent accumulation on the result of the FFT conversion, and judging according to the result of the differential coherent accumulation, solves the problem that long-time integral accumulation cannot be carried out on a navigation signal with very high symbol jump rate, adopts the method of the differential coherent accumulation, improves the signal-to-noise ratio, and realizes the successful acquisition of a satellite signal.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic diagram of a method for acquiring satellite navigation signals provided by the prior art;
fig. 2 is a schematic diagram of a method for acquiring a satellite navigation signal according to embodiment 1 of the present invention;
fig. 3 is a flowchart of a method for acquiring a satellite navigation signal according to embodiment 1 of the present invention;
FIG. 4 is a schematic diagram of a correlation calculation method provided in embodiment 1 of the present invention;
FIG. 5 is a flow chart of a correlation calculation method provided in embodiment 1 of the present invention;
fig. 6 is a flowchart of an apparatus for acquiring a satellite navigation signal according to embodiment 2 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 with reference to the accompanying drawings.
Example 1
Referring to fig. 2 and fig. 3, an embodiment of the present invention provides a method for acquiring a satellite navigation signal, and the specific flow is described in detail below:
step 101: and carrying out down-conversion on the analog signal received by the GPS receiver to obtain an intermediate frequency signal.
Wherein, the analog signal received by the GPS receiver comprises: carrier signal, text, C/a code. For example: the analog signal received by the GPS receiver is 16MHz, and the intermediate frequency signal of 4MHz is obtained through down-conversion processing.
Step 102: and converting the intermediate frequency signal obtained in the step 101 into an intermediate frequency digital signal through an analog-to-digital converter.
Step 103: and taking the frequency of the intermediate frequency digital signal as a carrier frequency, multiplying the intermediate frequency digital signal by the in-phase component and the quadrature component of the local carrier respectively, stripping the carrier, and obtaining an I path in-phase component and a Q path quadrature component containing C/A codes.
The purpose of multiplying the intermediate frequency digital signal by the in-phase component SIN and the orthogonal component COS of the local carrier is to obtain a text message and a C/A code and strip the carrier.
Step 104: the code NCO generates a local C/a code.
Step 105: and respectively carrying out correlation operation on the local C/A code and the I path in-phase component and the Q path quadrature component of the C/A code obtained in the step 103.
Wherein, a coherent accumulation method is adopted to perform correlation operation, for example: and performing coherent accumulation for 20 milliseconds, dividing the 20 milliseconds into 20 segments, wherein each segment is 1 millisecond, and adding the local C/A code to the data of the corresponding phase of the I path in-phase component and the Q path quadrature component of the C/A code obtained in the step 103 in each segment, namely obtaining the data of 20 segments and 1 millisecond in total. The embodiment of the present invention takes 20 milliseconds as an example for description, and when the embodiment of the present invention is implemented specifically, the embodiment of the present invention does not limit this.
Step 106: the result of the correlation operation in step 105 is FFT transformed from the time domain to the frequency domain.
Step 107: and carrying out differential coherent accumulation on the orthogonal component and the in-phase component of the nth time and the orthogonal component and the in-phase component of the (n-1) th time respectively according to the result of FFT transformation.
The method comprises the steps of carrying out differential coherent accumulation on an nth M-segment 20-millisecond orthogonal component and an nth-1 th M-segment 20-millisecond orthogonal component, and carrying out differential coherent accumulation on an nth M-segment 20-millisecond in-phase component and an nth-1 th M-segment 20-millisecond in-phase component, so as to eliminate noise and enhance signals and improve signal-to-noise ratio, wherein n is the number of capture times. The embodiment of the present invention takes M-segment 20ms data as an example for description, and if M takes a value of 5, differential coherent accumulation of 100 ms is performed, and when the embodiment of the present invention is specifically implemented, the embodiment of the present invention does not limit this.
Step 108: and judging the result after the differential coherent accumulation and a preset threshold value.
Wherein, specifically include: obtaining I + Q or from the in-phase component and the quadrature component after the differential coherent accumulation
Finding the point I with the maximum amplitude value according to the calculation result1、Q1And the point I of second largest amplitude2、Q2Finding a post-calculation (| I)1|+|Q1|)/(|I2|+|Q2I) or
Judging the calculation result and a preset threshold value, if the calculation result is greater than the preset threshold value, indicating that the satellite signal is successfully captured, and executing step 109; otherwise, the acquisition fails, and step 110 is performed.
The preset threshold value set in the embodiment of the present invention is 2.5, and in a specific implementation, the preset threshold value is different according to a difference between fixed empirical values or noise magnitudes, which is not limited in this embodiment of the present invention.
Step 109: and outputting the code phase and the carrier frequency of the C/A code.
Step 110: the phase of the local code is adjusted and steps 103-108 are re-executed until the acquisition is successful.
If the acquisition is not successful and the phase is shifted by 0.5, 1023/0.5 times 2046 times (wherein 1023 is the code length of the C/a code), and no signal is acquired after 2046 times of search, then changing a carrier frequency, i.e. shifting the local carrier frequency by ± 500Hz, plus or minus 10 times, i.e. shifting 21 times, and repeating the above processes until the signal acquisition is successful. If all code phases and carrier frequencies are searched completely and no signal is acquired, the signal acquisition in the period fails.
The correlation operation in step 105 may also adopt other operation manners, see fig. 4 and fig. 5, and the following description is described in detail:
step 201: the 2L millisecond reception data is segmented into L segments in units of 2 milliseconds.
In this case, the received data of 20ms is taken as an example, and is divided into 10 segments.
Step 202: a locally generated L millisecond replica code is obtained.
Step 203: a 1 millisecond zero is added after each millisecond of the replica code.
Wherein, add 1 ms of zero through zero padding device, copy code of every ms becomes 2 ms of data after zero padding through zero padding device, get L2 ms of data of section totally locally.
Step 204: and performing correlation operation on the 2 ms received data of the L segment and the 2 ms zero-padded data of the L segment obtained in step 203 in a one-to-one correspondence manner.
For example: the value of L is 4, namely 1, 2, 3 and 4, and the 2 millisecond received data of the 1 st section and the 2 millisecond zero-filled data of the 1 st section are subjected to correlation operation; carrying out correlation operation on the 2-millisecond received data of the 2 nd section and the 2-millisecond zero-filled data of the 2 nd section; carrying out correlation operation on the 2 millisecond received data of the 3 rd section and the 2 millisecond zero-filled data of the 3 rd section; correlating the 2 ms received data of the 4 th segment with the 2 ms zero-padded data of the 4 th segment
Step 205: and acquiring data corresponding to the 1 st millisecond of each section after the correlation operation.
I.e. the data corresponding to the first millisecond of the L segment is available.
Step 206: judging whether the data with the maximum absolute value in each section of data is less than 0, if so, executing a step 207, and performing sign inversion correction; otherwise, step 208 is performed.
Wherein, if the data with the maximum absolute value in each segment of data is negative, the sign of the segment of data is negative; if the data having the largest absolute value in each piece of data is positive, the sign indicating that the piece of data is positive. For example, if the data corresponding to the 3 rd segment is 3 or-4, the data with the largest absolute value is-4, and since-4 < 0, step 207 is executed.
Step 207: sign inversion correction is performed to multiply each value in the segment of data by-1.
The main purpose of multiplying each value in the piece of data by-1 is to eliminate symbol jumps, such as: there are four segments of data, each segment has 3 data, the 1 st segment is 1, 2, 3, 10, i.e. the sign is positive, the 2 nd segment is 1, -2, 3, 20, i.e. the sign is positive, the 3 rd segment is 4, 5, 6, 15, i.e. the sign is positive, the 4 th segment is 4, -5, -6, -25, i.e. the sign is negative, i.e. there is no sign jump between the 1 st segment of data, the 2 nd segment of data and the 3 rd segment of data, and there is sign jump between the 3 rd segment of data and the 4 th segment of data. That is, it is only necessary to multiply each value in the 4 th data by-1 so that the sign of the 4 th data is positive, thereby eliminating the sign jump between the 3 rd and 4 th data.
Step 208: the L segments of 1 millisecond data are correspondingly added.
Adding the 1 st data in the 1 st data, the 1 st data in the 2 nd data, the 1 st data in the 3 rd data and the 1 st data in the 4 th data; similarly, the 2 nd bit data in the 1 st data, the 2 nd bit data in the 2 nd data, the 2 nd bit data in the 3 rd data, and the 2 nd bit data in the 4 th data are added, that is, the signal gain of each bit is increased.
Step 209: the 1 millisecond data obtained after the addition is output.
The above steps are equivalent to extending the correlation integration time to L milliseconds, accumulating the data with the length of L milliseconds corresponding to the phase, and changing the data into data with 1 millisecond, so that the gain of the signal is increased, and the gain of the signal is 101 gL.
Wherein, the various loss estimates of the receiver are as follows: system noise factor reduction2dB, about 0.9dB of data boundary misalignment, about 2.5dB of incomplete PN code alignment, 1dB of attenuation caused by Doppler frequency shift, 2dB of signal-to-noise ratio if 2 milliseconds of coherent accumulation is carried out, loss is reduced, and the signal-to-noise ratio is changed into SNRL-4.4dB (i.e., 2-2-0.9-2.5-1 ═ 4.4).
Wherein, if the method in step 201-step 209 is adopted, the L-segment 1 ms coherent accumulation is performed first, the SNR is changed to 101gL, the loss listed above is reduced by 6.4dB, and the SNR at this time is changed to SNRL＝101gL-6.4dB。
If the L-segment 1 ms coherent accumulation is performed and then the N-segment L ms differential coherent accumulation is performed, the total snr becomes: SNRtotalThe Loss of differential coherent accumulation is represented by Loss (-6.4+10lgL +10lgN + Loss (-6.4+10lgL), and the values of N and L are reasonably set, for example, L is set to 20 milliseconds, and N is set to 4 or 5, so that the signal-to-noise ratio can be improved to about 15dB, and satellite signals can be successfully acquired.
In conclusion, the method solves the problem that the navigation signal with very high symbol jump rate cannot be subjected to long-time integral accumulation due to the limitation of the integral time of the navigation signal, and realizes the long-time integral accumulation of the navigation signal, thereby improving the signal-to-noise ratio of the received signal and realizing the successful acquisition of the weak signal.
Example 2
Referring to fig. 6, an embodiment of the present invention provides an apparatus for acquiring a satellite navigation signal, where the apparatus mainly includes:
an obtaining module 201, configured to obtain an in-phase component and a quadrature component including a C/a code;
an operation module 202, configured to perform correlation operation on the in-phase component and the orthogonal component of the C/a code obtained by the obtaining module 201 and the local C/a code respectively;
an FFT module 203, configured to perform FFT on the result of the correlation operation;
a difference coherent accumulation module 204, configured to perform difference coherent accumulation on the result transformed by the FFT module 203; the method is particularly used for performing differential coherent accumulation on the quadrature component and the in-phase component of the nth time and the quadrature component and the in-phase component of the (n-1) th time respectively.
The decision module 205 is configured to perform decision according to a result of the differential coherent accumulation, and if the result is greater than a threshold value, the satellite signal acquisition is successful; otherwise, the acquisition of the satellite signal fails.
The obtaining module 201 specifically includes:
a conversion unit 201A, configured to convert an analog signal received by the GPS receiver into an intermediate frequency digital signal;
an obtaining unit 201B is configured to obtain an in-phase component and an orthogonal component including a C/a code according to the intermediate frequency digital signal and the in-phase component and the orthogonal component of the local carrier.
The operation module 202 specifically includes:
a segmenting unit 202A, configured to segment the 2L millisecond received data by using 2 milliseconds as a unit;
an adding unit 202B for obtaining a locally generated L-ms replica code, adding 1 ms zeros after each ms replica code;
an obtaining unit 202C, configured to perform correlation operation on the received data in the segmenting unit 202A and the data obtained in the adding unit 202B, and obtain data corresponding to the 1 st millisecond of each segment after the correlation operation;
the judging unit 202D is configured to judge whether data with the largest absolute value in the data corresponding to the 1 st millisecond of each segment obtained by the obtaining unit 202C is less than 0, and perform symbol inversion correction if the data is less than 0; otherwise, executing the first output unit 202E;
and a first output unit 202E, configured to correspondingly add the L segments of 1 millisecond data, and output the 1 millisecond data obtained after the addition.
The determining unit 202D further includes:
and the calculating subunit is used for multiplying each numerical value in the segment of data by-1.
Wherein, the decision module 205 further includes:
a determining unit 205A, configured to perform a decision according to a result of the differential coherent accumulation, and if the result is greater than a threshold value, it indicates that the satellite signal is successfully captured; otherwise, the satellite signal acquisition is failed;
a second output unit 205B for outputting the code phase and the carrier frequency of the C/a code after the acquisition of the satellite signal is successful;
the adjusting unit 205C is configured to adjust the phase and carrier frequency of the local code after the satellite signal acquisition fails, and to perform the search again.
If the acquisition is not successful and the phase is shifted by 0.5, 1023/0.5 times 2046 times (wherein 1023 is the code length of the C/a code), and no signal is acquired after 2046 times of search, then changing a carrier frequency, i.e. shifting the local carrier frequency by ± 500Hz, plus or minus 10 times, i.e. shifting 21 times, and repeating the above processes until the signal acquisition is successful. If all code phases and carrier frequencies are searched completely and no signal is acquired, the signal acquisition in the period fails.
In summary, the device solves the problem that the navigation signal with very high symbol jump rate cannot be subjected to long-time integration and accumulation due to the limitation of the integration time of the navigation signal, and realizes the long-time integration and accumulation of the navigation signal, thereby improving the signal to noise ratio of the received signal and realizing the successful acquisition of the weak signal.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for acquiring a satellite navigation signal, the method comprising:
obtaining an in-phase component and a quadrature component containing C/A codes;
respectively carrying out correlation operation on the obtained in-phase component and orthogonal component of the C/A code and a local C/A code;
performing FFT on the result of the correlation operation;
carrying out differential coherent accumulation on the result of FFT conversion;
judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, successfully capturing the satellite signal; otherwise, the acquisition of the satellite signal fails.
2. The method of claim 1, wherein the step of correlating the obtained in-phase and quadrature components of the C/a code with the local C/a code comprises:
step A: segmenting the 2L millisecond receiving data by taking 2 milliseconds as a unit;
and B: obtaining a locally generated L millisecond replica code, adding 1 millisecond zero after each millisecond replica code;
and C: performing correlation operation on the received data in the step A and the data obtained in the step B to obtain data corresponding to 1 st millisecond of each section after the correlation operation;
step D: judging whether the data with the maximum absolute value in the data corresponding to the 1 st millisecond of each section is less than 0 or not, and if the data is less than 0, performing sign inversion correction; otherwise, executing step E;
step E: and correspondingly adding the L sections of 1 millisecond data, and outputting the 1 millisecond data obtained after the addition.
3. The method according to claim 2, wherein the step of determining whether the data with the largest absolute value in the data corresponding to the 1 st millisecond of each segment is less than 0, and if the data with the largest absolute value is less than 0, the step of performing the sign inversion correction specifically includes: each value in the piece of data is multiplied by-1.
4. The method of claim 1, wherein the step of differentially coherently accumulating the results of the FFT specifically comprises:
and carrying out differential coherent accumulation on the orthogonal component and the in-phase component of the nth time and the orthogonal component and the in-phase component of the (n-1) th time respectively.
5. The method of claim 1, wherein the decision is made based on a result of the differential coherent accumulation, and the acquisition of the satellite signal is successful if the result is greater than a threshold value; otherwise, the step of failing to acquire the satellite signal further comprises:
if the value is larger than the threshold value, the code phase and the carrier frequency of the C/A code are output after the satellite signal is successfully captured; accordingly, the number of the first and second electrodes,
if the signal is smaller than the preset threshold value, after the signal acquisition fails, the phase and the carrier frequency of the local code are adjusted, and the search is carried out again.
6. An apparatus for acquiring a satellite navigation signal, the apparatus comprising:
an obtaining module for obtaining an in-phase component and a quadrature component comprising a C/A code;
the operation module is used for respectively carrying out correlation operation on the in-phase component and the orthogonal component of the C/A code obtained by the obtaining module and a local C/A code;
the FFT conversion module is used for carrying out FFT conversion on the result of the correlation operation;
a differential coherent accumulation module, configured to perform differential coherent accumulation on a result transformed by the FFT transformation module;
the judgment module is used for judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, the satellite signal is successfully captured; otherwise, the acquisition of the satellite signal fails.
7. The apparatus of claim 6, wherein the operation module specifically comprises:
a segmenting unit for segmenting 2L-millisecond received data in units of 2 milliseconds;
an adding unit for obtaining a locally generated L millisecond replica code, adding 1 millisecond zero after each millisecond replica code;
the acquisition unit is used for carrying out correlation operation on the received data in the segmentation unit and the data obtained in the adding unit, and acquiring data corresponding to the 1 st millisecond of each segment after the correlation operation;
the judging unit is used for judging whether the data with the largest absolute value in the data corresponding to the 1 st millisecond of each section obtained by the obtaining unit is smaller than 0 or not, and if the data is smaller than 0, the sign inversion correction is carried out; otherwise, executing the first output unit;
and the first output unit is used for correspondingly adding the L sections of 1 millisecond data and outputting the 1 millisecond data obtained after the addition.
8. The apparatus of claim 7, wherein the determining unit further comprises:
a calculation subunit for multiplying each value in the segment of data by-1.
9. The apparatus of claim 6, wherein the differentially coherent accumulation module is specifically configured to differentially coherently accumulate the quadrature component and the in-phase component of the nth time and the quadrature component and the in-phase component of the (n-1) th time, respectively.
10. The apparatus of claim 6, wherein the decision module specifically comprises:
the judgment unit is used for judging according to the result of the differential coherent accumulation, and if the result is greater than a threshold value, the satellite signal acquisition is successful; otherwise, the satellite signal acquisition is failed;
a second output unit for outputting a code phase and a carrier frequency of the C/a code;
and the adjusting unit is used for adjusting the phase and the carrier frequency of the local code.
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| Publication number | Priority date | Publication date | Assignee | Title |
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