CN108205145B - GPS frequency tracking method and device and GPS receiver - Google Patents
GPS frequency tracking method and device and GPS receiver Download PDFInfo
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- CN108205145B CN108205145B CN201611179896.XA CN201611179896A CN108205145B CN 108205145 B CN108205145 B CN 108205145B CN 201611179896 A CN201611179896 A CN 201611179896A CN 108205145 B CN108205145 B CN 108205145B
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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
Abstract
The invention provides a GPS frequency tracking method and device and a GPS receiver. The method comprises the following steps: integrating the despread signals; taking L integral lengths as L points, and performing M-point fast Fourier transform to obtain an M-point fast Fourier transform spectrogram; respectively taking a modulus value of a complex number in the M-point fast Fourier transform spectrogram and then squaring the complex number to obtain a real number; repeating the fast Fourier transform K times, and performing incoherent summation on the real number of the same frequency in the spectrogram after the M-point fast Fourier transform; dividing the result after the incoherent integration into an outer ring and an inner ring to calculate a frequency offset value; screening and determining the inner ring frequency offset value and the outer ring frequency offset value; the corresponding sine and cosine waveforms are generated by the digital control oscillator and then sent to the intermediate frequency sampling signal to be mixed so as to eliminate the frequency deviation. The invention can ensure that the GPS receiver can still obtain a more accurate frequency offset value when sudden large frequency offset exists, and improves the stability of the GPS receiver.
Description
Technical Field
The present invention relates to the GPS (global positioning system) technology field, and in particular, to a GPS frequency tracking method, apparatus, and GPS receiver.
Background
The navigation positioning signal sent by the GPS satellite is an information resource which can be shared by countless users. A wide range of users on land, sea and space can receive, track, transform and measure GPS signals through GPS receivers so as to be able to know the longitude, latitude and altitude (or similar measurement information) of the position where the user is located.
The design of the carrier tracking loop is a very important link in the GPS receiver, and the performance of the carrier tracking loop directly affects the sensitivity of the GPS receiver.
The existing carrier tracking loop mainly adopts a mode as shown in fig. 1, a GPS receiver acquires intermediate frequency sampling data after completing signal capture and digital-to-analog conversion, despreads the intermediate frequency sampling data according to a C/a code after code phase adjustment, sends the despread signal to an integrator for integration, sends the integrated signal quantity to a cross point frequency discriminator, divides the integration result into an I path and a Q path for calculation, and calculates a frequency error by using a calculation formula as follows;
Dot＝I(k-1)I(k)+Q(k-1)Q(k)
Cross＝Q(k)I(k-1)-I(k)Q(k)
df＝atan2(cross,dot)/T
wherein d isfAs a frequency error, I(k)Data representing the output of the I path of the frequency discriminator at time k, I(k-1)Representing data output by way I after a delay time T, Q(k)Data representing the Q-path output of the frequency discriminator at time k, Q(k-1)Representing the data output by the Q path after the delay time T;
and sending the frequency error obtained by the frequency discriminator into a frequency-locked loop filter for filtering, removing noise to obtain a more accurate frequency error, sending the more accurate frequency error into a numerical control oscillator to generate a corresponding sine and cosine waveform, and multiplying the sine and cosine waveform by an intermediate-frequency sampling signal to eliminate frequency deviation.
In the process of implementing the invention, the inventor finds that at least the following technical problems exist in the prior art:
when a high dynamic scene occurs in a GPS receiver or the short-term stability of a clock source of the GPS receiver is affected by external environment factors and becomes worse, a larger frequency deviation occurs in a signal received by the GPS receiver, at the moment, a signal-to-noise ratio is ensured by a longer integration time of a GPS carrier tracking loop, so that the larger frequency deviation is corrected, but after the integration time of the GPS carrier tracking loop becomes longer, a positive and negative cancellation condition occurs in a sine and cosine signal for integration, so that errors occur in frequency deviation calculation, and finally the GPS receiver cannot complete positioning.
Disclosure of Invention
The GPS frequency tracking method, the GPS frequency tracking device and the GPS receiver provided by the invention can enable the GPS receiver to still obtain a relatively accurate frequency offset value in the presence of sudden large frequency offset, thereby ensuring that the GPS receiver has good tracking performance and improving the stability of the GPS receiver.
In a first aspect, the present invention provides a GPS frequency tracking method, including:
integrating the despread signals, wherein the integration length of the integration is the amount of the received signals within Nms;
taking L integration lengths of the integrated signals as L points, and performing M-point fast Fourier transform to obtain an M-point fast Fourier transform spectrogram, wherein M > is L;
step three, respectively taking the modulus values of the complex numbers in the frequency spectrogram of the M-point fast Fourier transform, and then squaring to obtain real numbers;
step four, repeating the step two and the step three K times, and carrying out incoherent summation on the K real numbers with the same frequency of the M-section fast Fourier transform, wherein K is a natural number;
fifthly, sending the result after incoherent integration into an outer ring to calculate an outer ring frequency offset value, and sending the result after incoherent integration into an inner ring to calculate an inner ring frequency offset value;
step six, the outer ring frequency offset value and the inner ring frequency offset value are sent to a carrier frequency controller to determine that the result of the final frequency offset value is one of the outer ring frequency offset value or the inner ring frequency offset value;
and seventhly, generating a corresponding sine-cosine waveform by the finally determined outer ring frequency offset value or one of the inner ring frequency offset values through a digital control oscillator, and sending the sine-cosine waveform into an intermediate frequency sampling signal to eliminate frequency offset.
Optionally, before the taking L integration lengths of the integrated signal as L points and performing M-point fast fourier transform to obtain the M-point fast fourier transform spectrogram, the method further includes:
judging whether the time of the L integral lengths exceeds a navigation bit time;
and when the time of the L integration lengths exceeds one navigation bit time, carrying out positive and negative adjustment on the integration result in the residual navigation bit time in the L according to the integration result in the first navigation bit time.
Optionally, the performing positive and negative adjustment on the integration result in the remaining navigation bit time of the time with L integration lengths according to the integration result in the first navigation bit time includes:
when the navigation bit is unknown, 0/1 blind detection is carried out on the navigation bit, wherein the navigation bit is encoded in a binary form;
carrying out positive and negative adjustment on the integral result in the remaining navigation bit time in the L integral length time according to the blind detection result;
when the navigation bit is known, the original value of the sequence of the navigation bit corresponding to the remaining navigation bit time in the time of the L integration lengths is the same as the navigation bit corresponding to the first navigation bit time; and for a sequence that the navigation bits corresponding to the navigation bit time left in the time of L integration lengths are different from the navigation bit corresponding to the first navigation bit time, multiplying the integration result in the navigation bit time left in the time of L integration lengths by-1.
Optionally, the performing 0/1 blind detection on the navigation bit when the navigation bit is unknown includes:
listing possible navigation bit conditions for the rest navigation bit bytes in the L integral lengths according to 0/1 traversal one by one;
performing fast Fourier transform on all integration results in the traversed navigation bit byte time and the integration results in the first navigation bit time in the time of L integration lengths respectively according to the original value and the value multiplied by-1 to obtain a plurality of groups of fast Fourier transform spectrograms;
and taking the peak value of the fast Fourier transform in the multiple groups of fast Fourier transform frequency spectrums to obtain a plurality of peak values, further comparing the plurality of peak values, and taking the navigation bit corresponding to the largest peak value in the plurality of peak values as a navigation bit blind detection result.
Optionally, the sending the result of the incoherent integration to the outer loop to calculate the outer loop frequency offset value includes:
taking a peak value in the result after the incoherent integration, and carrying out peak value verification by setting a threshold value;
and when the peak value verification is correct, calculating a frequency offset value according to the spectrogram, otherwise, setting the frequency offset value to be 0.
Optionally, the performing peak verification on the spectrogram includes: and when the peak value verification result simultaneously meets the following two conditions, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect.
The method comprises the following steps that 1, the ratio of a main peak value to a secondary peak value in a frequency spectrogram is larger than a threshold 1, and the threshold 1 is determined according to system configuration;
and 2, determining that the ratio of the main peak value to the mean value in the spectrogram is greater than a threshold 2, wherein the threshold 2 is determined according to system configuration.
Optionally, when the peak verification is correct, calculating a frequency offset value according to the spectrogram includes:
calculating the outer ring frequency offset value according to the spectrogram by the following formula;
delta_f＝fFFT*[Idx_Pmax+(Pmax+1-Pmax-1)/(Pmax+1+Pmax-1)]
wherein, PmaxIs the energy of the position corresponding to the maximum spectral line, Pmax-1Energy, P, representing the corresponding position to the left of the maximum spectrummax+1Delta _ f represents the frequency offset value, f, for the energy of the corresponding position to the right of the maximum spectral lineFFTA frequency interval representing each spectral line of said fast fourier transform output; idx _ PmaxRepresenting the index to which the largest spectral line corresponds.
Optionally, the sending the result of the incoherent integration to the inner loop to calculate an inner loop frequency offset value includes:
taking the result of the incoherent accumulation and carrying out inner loop frequency offset interpolation calculation at three positions with the abscissa of the spectrogram being 0/1/-1 according to the following formula;
delta_f＝fFFT*(P1-P-1)/(P1+P-1)
wherein, P0/P1/P-1 are respectively the energies corresponding to three spectrum indexes with the abscissa of 0/1/-1 in the spectrum.
In a second aspect, the present invention provides a GPS frequency tracking device, comprising:
the integration unit is used for integrating the despread signals, wherein the integration length of the integration is the received signal quantity within N milliseconds;
the first processing unit is used for taking L integration lengths of the integrated signals as L points, and performing M-point fast Fourier transform to obtain an M-point fast Fourier transform spectrogram, wherein M > is L;
the second processing unit is used for respectively taking the modulus values of the complex numbers in the M-section fast Fourier transform spectrogram and then squaring the complex numbers to obtain real numbers;
a third processing unit, configured to perform incoherent summation on the real numbers of the same frequency of the K M-segment fast fourier transforms obtained by repeating the first processing unit and the second processing unit K times, where K is a natural number;
a calculating unit, configured to send the result after incoherent integration to an outer loop to calculate an outer loop frequency offset value, and send the result after incoherent integration to an inner loop to calculate an inner loop frequency offset value;
a determining unit, configured to send the outer ring frequency offset value and the inner ring frequency offset value to a carrier frequency controller, and determine that a result of the final frequency offset value is one of the outer ring frequency offset value and the inner ring frequency offset value;
and the fourth processing unit is used for generating a corresponding sine-cosine waveform by the finally determined outer ring frequency offset value or one of the inner ring frequency offset values through the digital control oscillator and then sending the sine-cosine waveform into the intermediate frequency sampling signal to eliminate frequency offset.
Optionally, the apparatus further comprises:
a judging unit, configured to judge whether time of the L integration lengths exceeds a navigation bit time before the first processing unit takes L integration lengths of the integrated signal as L points and performs M-point fast fourier transform to obtain an M-point fast fourier transform spectrogram;
and the adjusting unit is used for carrying out positive and negative adjustment on the integration result in the residual navigation bit time in the L according to the integration result in the first navigation bit time when the time of the L integration lengths exceeds one navigation bit time.
Optionally, the adjusting unit includes:
a blind detection module, configured to perform 0/1 blind detection on the navigation bit when the navigation bit is unknown, where the navigation bit is encoded in a binary form;
the first adjusting module is used for carrying out positive and negative adjustment on the integral result in the remaining navigation bit time in the time of the L integral lengths according to the blind detection result;
a second adjusting module, configured to, when the navigation bit is known, leave the original value unchanged for a sequence in which the navigation bit corresponding to the remaining navigation bit time in the time of the L integration lengths is the same as the navigation bit corresponding to the first navigation bit time; and for the sequences that the navigation bits corresponding to the navigation bit time left in the time with the L integration lengths are different from the navigation bits corresponding to the first navigation bit time, multiplying the integration result in the navigation bit time left in the time with the L integration lengths by-1.
Optionally, the blind detection module includes:
the traversal submodule is used for traversing and listing possible navigation bit conditions for the residual navigation bit bytes in the L integration lengths according to 0/1 one by one;
the Fourier transform submodule is used for performing fast Fourier transform on all the integration results in the traversed navigation bit byte time and the integration results in the first navigation bit time in the time of L integration lengths respectively according to the original value and the value multiplied by-1 to obtain a plurality of groups of fast Fourier transform spectrograms;
and the determining submodule is used for obtaining a plurality of peak values by taking the peak value of the fast Fourier transform in the plurality of groups of fast Fourier transform frequency spectrums, further comparing the plurality of peak values, and taking the navigation bit corresponding to the largest peak value in the plurality of peak values as a navigation bit blind detection result.
Optionally, the computing unit comprises:
the outer ring verification module is used for taking a peak value in the result after the incoherent summation and carrying out peak value verification by setting a threshold value;
and the outer loop calculation module is used for calculating a frequency offset value according to the spectrogram of the peak value when the peak value is verified correctly, and otherwise, setting the frequency offset value to be 0.
Optionally, the outer loop verification module includes: and when the peak value verification result simultaneously meets the following two conditions, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect.
The method comprises the following steps that 1, the ratio of a main peak value to a secondary peak value in a frequency spectrogram is larger than a threshold 1, and the threshold 1 is determined according to system configuration;
optionally, the outer loop calculation module is configured to:
calculating the outer ring frequency offset value according to the spectrogram by the following formula;
delta_f＝fFFT*[Idx_Pmax+(Pmax+1-Pmax-1)/(Pmax+1+Pmax-1)]
wherein, PmaxIs the energy of the position corresponding to the maximum spectral line, Pmax-1Energy, P, representing the corresponding position to the left of the maximum spectrummax+1Delta _ f represents the frequency offset value, f, for the energy of the corresponding position to the right of the maximum spectral lineFFTA frequency interval representing each spectral line of said fast fourier transform output; idx _ PmaxRepresenting the index to which the largest spectral line corresponds.
Optionally, the computing unit further comprises:
an inner-loop frequency interpolation calculation module, configured to perform inner-loop frequency offset interpolation calculation according to the following formula at three positions on the abscissa of the spectrogram, which is 0/1/-1, according to the result of the incoherent accumulation;
delta_f＝fFFT*(P1-P-1)/(P1+P-1)
wherein, P0/P1/P-1 are respectively the energies corresponding to three spectrum indexes with the abscissa of 0/1/-1 in the spectrum.
In a third aspect, the present invention provides a GPS receiver comprising the above GPS frequency tracking device.
According to the GPS frequency tracking method, the GPS frequency tracking device and the GPS receiver provided by the embodiment of the invention, the integrated signal is subjected to fast Fourier transform to obtain the Fourier transform spectrogram, the inner loop calculation and the outer loop calculation are carried out on the frequency offset value through the spectrogram, and the peak value is verified, so that the GPS receiver can still obtain a relatively accurate frequency offset value when sudden large frequency offset exists, the GPS receiver is ensured to have good tracking performance, and the stability of the GPS receiver is improved.
Drawings
FIG. 1 is a flow chart of a GPS frequency tracking method according to the prior art;
FIG. 2 is a flowchart of a GPS frequency tracking method according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a fast Fourier transform signal selection result according to the present invention;
FIG. 4 is a block diagram of a GPS frequency tracking method of the present invention;
FIG. 5 is a flowchart of a GPS frequency tracking method according to another embodiment of the present invention;
FIG. 6 is a schematic structural diagram of a GPS frequency tracking device according to an embodiment of the present invention;
FIG. 7 is a schematic structural diagram of a GPS frequency tracking device according to another embodiment of the present invention;
FIG. 8 is a schematic structural diagram of the adjusting unit 19 in FIG. 7;
fig. 9 is a schematic structural diagram of the blind detection module 191 in fig. 8;
fig. 10 is a schematic structural diagram of the calculation unit 15 in fig. 7;
FIG. 11 is a diagram illustrating the peak verification result of the spectrogram after fast Fourier transform;
FIG. 12 is a diagram illustrating the invalid peak verification result of the fast Fourier transformed spectrogram.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a GPS frequency tracking method, as shown in FIG. 2, the method includes:
s11, integrating the despread signals, wherein the integration length of the integration is the amount of signals received within N milliseconds;
optionally, the value of N depends on the range of frequency offset that the frequency discriminator can discriminate;
optionally, before the signal is integrated, after down-converting the received intermediate frequency sampling signal, the de-spreading processing on the down-converted signal is completed by using the C/a code after the code phase adjustment.
S12, taking L integration lengths of the integrated signals as L points, and performing M-point fast Fourier transform to obtain an M-point fast Fourier transform spectrogram, wherein M > is L;
in particular, the input signal due to the fast fourier transform must be 2nSo that when the input L point signal is not 2nAnd then, carrying out zero filling operation on the L point signal to obtain an M point signal, and then carrying out fast Fourier transform.
Specifically, as shown in fig. 3, a navigation bit time is 20ms, and a fft length is 40ms, for example, to represent the fft signal selection process.
S13, respectively taking the modulus values of the complex numbers in the M-section fast Fourier transform spectrogram, and then squaring to obtain real numbers;
s14, repeating the second step and the third step for K times, and carrying out incoherent summation on the K real numbers with the same frequency of the M-section fast Fourier transform, wherein K is a natural number;
s15, sending the result after incoherent integration to an outer ring to calculate an outer ring frequency offset value, and sending the result after incoherent integration to an inner ring to calculate an inner ring frequency offset value;
s16, sending the outer and inner frequency offset values to a carrier frequency controller to determine that a final frequency offset value is one of the outer or inner frequency offset values;
and S17, generating a corresponding sine-cosine waveform by the finally determined outer ring frequency offset value or one of the inner ring frequency offset values through a digital control oscillator, and sending the sine-cosine waveform into an intermediate frequency sampling signal to eliminate frequency offset.
Specifically, as shown in fig. 4, it is a processing block diagram of the GPS frequency tracking method;
according to the GPS frequency tracking method provided by the embodiment of the invention, the integrated signal is subjected to fast Fourier transform to obtain the Fourier transform spectrogram, and the inner loop calculation and the outer loop calculation are carried out on the frequency deviation value through the spectrogram, and the peak value verification mode is adopted, so that the GPS receiver can still obtain a more accurate frequency deviation value in the presence of sudden large frequency deviation, the GPS receiver is ensured to have good tracking performance, and the stability of the GPS receiver is improved.
Optionally, as shown in fig. 5, before the taking L integration lengths of the integrated signal as L points and performing M-point fast fourier transform to obtain the M-point fast fourier transform spectrogram, the method further includes:
s18, judging whether the time of the L integral lengths exceeds a navigation bit time;
and S19, when the time of the L integration lengths exceeds one navigation bit time, carrying out positive and negative adjustment on the integration result in the remaining navigation bit time in the time of the L integration lengths according to the integration result in the first navigation bit time.
Optionally, the performing positive and negative adjustment on the integration result in the remaining navigation bit time of the time with L integration lengths according to the integration result in the first navigation bit time includes:
when the navigation bit is unknown, 0/1 blind detection is carried out on the navigation bit, wherein the navigation bit is encoded in a binary form;
carrying out positive and negative adjustment on the integral result in the remaining navigation bit time in the L integral length time according to the blind detection result;
when the navigation bit is known, the original value of the sequence of the navigation bit corresponding to the remaining navigation bit time in the time of the L integration lengths is the same as the navigation bit corresponding to the first navigation bit time; and for the sequences that the navigation bits corresponding to the navigation bit time left in the time with the L integration lengths are different from the navigation bits corresponding to the first navigation bit time, multiplying the integration result in the navigation bit time left in the time with the L integration lengths by-1.
Optionally, the performing 0/1 blind detection on the navigation bit when the navigation bit is unknown includes:
listing possible navigation bit conditions for the rest navigation bit bytes in the L integral lengths according to 0/1 traversal one by one;
performing fast Fourier transform on all integration results in the traversed navigation bit byte time and the integration results in the first navigation bit time in the time of L integration lengths respectively according to the original value and the value multiplied by-1 to obtain a plurality of groups of fast Fourier transform spectrograms;
and taking the peak value of the fast Fourier transform in the multiple groups of fast Fourier transform frequency spectrums to obtain a plurality of peak values, further comparing the plurality of peak values, and taking the navigation bit corresponding to the largest peak value in the plurality of peak values as a navigation bit blind detection result.
Optionally, the sending the result of the incoherent integration to the outer loop to calculate the outer loop frequency offset value includes:
taking a peak value in the result after the incoherent integration, and carrying out peak value verification by setting a threshold value;
and when the peak value verification is correct, calculating a frequency offset value according to the spectrogram, otherwise, setting the frequency offset value to be 0.
Optionally, the performing peak verification on the spectrogram includes: and when the peak value verification result simultaneously meets the following two conditions, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect.
The method comprises the following steps that 1, the ratio of a main peak value to a secondary peak value in a frequency spectrogram is larger than a threshold 1, and the threshold 1 is determined according to system configuration;
and 2, determining that the ratio of the main peak value to the mean value in the spectrogram is greater than a threshold 2, wherein the threshold 2 is determined according to system configuration.
Optionally, when the peak verification is correct, calculating a frequency offset value according to the spectrogram includes:
calculating the outer ring frequency offset value according to the spectrogram by the following formula;
delta_f＝fFFT*[Idx_Pmax+(Pmax+1-Pmax-1)/(Pmax+1+Pmax-1)]
wherein, PmaxIs the energy of the position corresponding to the maximum spectral line, Pmax-1Energy, P, representing the corresponding position to the left of the maximum spectrummax+1Delta _ f represents the frequency offset value, f, for the energy of the corresponding position to the right of the maximum spectral lineFFTA frequency interval representing each spectral line of said fast fourier transform output; idx _ PmaxRepresenting the index to which the largest spectral line corresponds.
Optionally, the sending the result of the incoherent integration to the inner loop to calculate an inner loop frequency offset value includes:
taking the result of the incoherent accumulation and carrying out inner loop frequency offset interpolation calculation at three positions with the abscissa of the spectrogram being 0/1/-1 according to the following formula;
delta_f＝fFFT*(P1-P-1)/(P1+P-1)
wherein, P0/P1/P-1 are respectively the energies corresponding to three spectrum indexes with the abscissa of 0/1/-1 in the spectrum.
An embodiment of the present invention further provides a GPS frequency tracking device, as shown in fig. 6, the device includes:
an integrating unit 11, configured to integrate the despread signal, where an integration length of the integration is a signal amount received within N milliseconds;
a first processing unit 12, configured to take L integration lengths of the integrated signal as L points, and perform M-point fast fourier transform to obtain an M-point fast fourier transform spectrogram, where M > is L;
a second processing unit 13, configured to perform modulus value extraction on the complex numbers in the M-segment fast fourier transform spectrogram, and then square the complex numbers to obtain real numbers;
a third processing unit 14, configured to perform incoherent summation on the K real numbers of the same frequency of the M-segment fast fourier transform obtained by repeating the first processing unit and the second processing unit K times, where K is a natural number;
a calculating unit 15, configured to send the result after incoherent integration to an outer loop to calculate an outer loop frequency offset value, and send the result after incoherent integration to an inner loop to calculate an inner loop frequency offset value;
a determining unit 16, configured to send the outer ring frequency offset value and the inner ring frequency offset value to a carrier frequency controller to determine that a result of the final frequency offset value is one of the outer ring frequency offset value and the inner ring frequency offset value;
a fourth processing unit 17, configured to generate a corresponding sine-cosine waveform from the finally determined outer loop frequency offset value or one of the inner loop frequency offset values through a digitally controlled oscillator, and send the generated sine-cosine waveform to an intermediate frequency sampling signal to remove frequency offset.
According to the GPS frequency tracking device provided by the embodiment of the invention, the integrated signal is subjected to fast Fourier transform to obtain the Fourier transform spectrogram, and the inner loop calculation, the outer loop calculation and the peak verification are carried out on the frequency offset value through the spectrogram, so that the GPS receiver can still obtain a relatively accurate frequency offset value in the presence of sudden large frequency offset, the GPS receiver is ensured to have good tracking performance, and the stability of the GPS receiver is improved.
Optionally, as shown in fig. 7, the apparatus further includes:
a judging unit 18, configured to judge whether time of the L integration lengths exceeds a navigation bit time before the first processing unit takes L integration lengths of the integrated signal as L points and performs M-point fast fourier transform to obtain an M-point fast fourier transform spectrogram;
and the adjusting unit 19 is configured to, when the time of the L integration lengths exceeds one navigation bit time, perform positive and negative adjustment on the integration result in the remaining navigation bit time in L according to the integration result in the first navigation bit time.
Alternatively, as shown in fig. 8, the adjusting unit 19 includes:
a blind detection module 191, configured to perform 0/1 blind detection on the navigation bit when the navigation bit is unknown, where the navigation bit is encoded in a binary form;
a first adjusting module 192, configured to perform positive and negative adjustment on the integration result in the remaining navigation bit time in the time with the L integration lengths according to the blind detection result;
a second adjusting module 193, configured to, when the navigation bit is known, leave the original value unchanged for a sequence in which the navigation bit corresponding to the remaining navigation bit time in the time of the L integration lengths is the same as the navigation bit corresponding to the first navigation bit time; and for a sequence that the navigation bits corresponding to the navigation bit time left in the time with the L integration lengths are different from the navigation bits corresponding to the navigation bit time for the first time, multiplying the integration result in the navigation bit time left in the L by-1.
Optionally, as shown in fig. 9, the blind detection module 191 includes:
a fourier transform submodule 1912, configured to perform fast fourier transform on all integration results within the traversed navigation bit byte time according to the original value and a value obtained by multiplying the original value by-1, and the integration result within the first navigation bit time in the time of L integration lengths, respectively, to obtain multiple groups of fast fourier transform spectrograms;
the determining sub-module 1913 is configured to obtain multiple peak values by taking a peak value of fast fourier transform in the multiple groups of fast fourier transform frequency spectrums, further compare the multiple peak values, and take a navigation bit corresponding to a largest peak value of the multiple peak values as a navigation bit blind detection result.
Alternatively, as shown in fig. 10, the calculation unit 15 includes:
an outer loop verification module 151, configured to take a peak in the result after the incoherent summation, and perform peak verification by setting a threshold;
and an outer loop calculating module 152, configured to calculate a frequency offset value according to the spectrogram of the peak value when the peak value is correctly verified, and otherwise, set the frequency offset value to 0.
Optionally, the outer ring verification module 151 is further configured to:
and when the peak value verification result simultaneously meets the following two conditions, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect.
The method comprises the following steps that 1, the ratio of a main peak value to a secondary peak value in a frequency spectrogram is larger than a threshold 1, and the threshold 1 is determined according to system configuration;
specifically, as shown in fig. 11, the diagram is a schematic diagram of a peak verification valid result of the fast fourier transformed spectrogram, where a product of the secondary peak and a threshold 1 is smaller than the primary peak; the mean multiplied by the threshold 2 is also smaller than the main peak.
Where the red line represents the maximum of the spectrum, the height of the line represents the energy of the corresponding frequency, and the horizontal axis number represents the index of the fast fourier transform.
And when the two conditions are simultaneously met, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect.
Specifically, as shown in fig. 12, the graph is a schematic diagram of a peak validation invalid result of the fast fourier transformed spectrogram, and the secondary peak multiplied by a threshold 1 is greater than the primary peak; the mean multiplied by the threshold 2 is also larger than the main peak.
Optionally, the outer loop calculation module 152 is further configured to:
calculating the outer ring frequency offset value according to the spectrogram by the following formula;
delta_f＝fFFT*[Idx_Pmax+(Pmax+1-Pmax-1)/(Pmax+1+Pmax-1)]
wherein, PmaxIs the energy of the position corresponding to the maximum spectral line, Pmax-1Represents the maximumEnergy of the corresponding position on the left side of the spectrum, Pmax+1Delta _ f represents the frequency offset value, f, for the energy of the corresponding position to the right of the maximum spectral lineFFTA frequency interval representing each spectral line of said fast fourier transform output; idx _ PmaxRepresenting the index to which the largest spectral line corresponds.
Optionally, as shown in fig. 10, the calculating unit 15 further includes:
an inner-loop frequency interpolation calculation module 153, configured to take the result of the incoherent accumulation and perform inner-loop frequency offset interpolation calculation according to the following formula at three positions on the abscissa of the spectrogram, which is 0/1/-1;
delta_f＝fFFT*(P1-P-1)/(P1+P-1)
wherein, P0/P1/P-1 are respectively the energies corresponding to three spectrum indexes with the abscissa of 0/1/-1 in the spectrum.
The embodiment of the invention also provides a GPS receiver which comprises the GPS frequency tracking device.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (17)
1. A GPS frequency tracking method, comprising:
integrating the despread signals, wherein the integration length of the integration is the amount of signals received within N milliseconds;
taking L integration lengths of the integrated signals as L points, and performing M-point fast Fourier transform to obtain an M-point fast Fourier transform spectrogram, wherein M > is L;
step three, respectively taking the modulus values of the complex numbers in the M-point fast Fourier transform spectrogram, and then squaring the complex numbers to obtain real numbers;
step four, repeating the step two and the step three K times, and carrying out incoherent summation on the real numbers of the same frequency in the spectrogram after K M-point fast Fourier transform, wherein K is a natural number;
fifthly, sending the result after incoherent integration into an outer ring to calculate an outer ring frequency offset value, and sending the result after incoherent integration into an inner ring to calculate an inner ring frequency offset value;
step six, the outer ring frequency offset value and the inner ring frequency offset value are sent to a carrier frequency controller to determine that the result of the final frequency offset value is one of the outer ring frequency offset value or the inner ring frequency offset value;
and seventhly, generating a corresponding sine-cosine waveform by the finally determined outer ring frequency offset value or one of the inner ring frequency offset values through a digital control oscillator, and sending the sine-cosine waveform into an intermediate frequency sampling signal to eliminate frequency offset.
2. The method according to claim 1, wherein before taking L integration lengths of the integrated signal as L points and performing M-point fast fourier transform to obtain the M-point fast fourier transform spectrogram, the method further comprises:
judging whether the time of the L integral lengths exceeds a navigation bit time;
and when the time of the L integration lengths exceeds one navigation bit time, carrying out positive and negative adjustment on the integration result in the remaining navigation bit time in the time of the L integration lengths according to the integration result in the first navigation bit time.
3. The method of claim 2, wherein the adjusting the integration result in the remaining navigation bit time of the L integration length times to positive or negative according to the integration result in the first navigation bit time comprises:
when the navigation bit is unknown, 0/1 blind detection is carried out on the navigation bit, wherein the navigation bit is encoded in a binary form;
carrying out positive and negative adjustment on the integral result in the remaining navigation bit time in the L integral length time according to the blind detection result;
when the navigation bit is known, the original value of the sequence of the navigation bit corresponding to the remaining navigation bit time in the time of the L integration lengths is the same as the navigation bit corresponding to the first navigation bit time; and for a sequence that the navigation bits corresponding to the navigation bit time left in the time of L integration lengths are different from the navigation bit corresponding to the first navigation bit time, multiplying the integration result in the navigation bit time left in the time of L integration lengths by-1.
4. The method of claim 3, wherein the 0/1 blind detection of the navigation bits when the navigation bits are unknown comprises:
listing possible navigation bit conditions for the rest navigation bit bytes in the L integral lengths according to 0/1 traversal one by one;
performing fast Fourier transform on all integration results in the traversed navigation bit byte time and the integration results in the first navigation bit time in the time of L integration lengths respectively according to the original value and the value multiplied by-1 to obtain a plurality of groups of fast Fourier transform spectrograms;
and taking the peak value of the fast Fourier transform in the multiple groups of fast Fourier transform frequency spectrums to obtain a plurality of peak values, further comparing the plurality of peak values, and taking the navigation bit corresponding to the largest peak value in the plurality of peak values as a navigation bit blind detection result.
5. The method of claim 1, wherein said feeding the result of said non-coherent accumulation into an outer loop to calculate an outer loop frequency offset value comprises:
taking a peak value in the result after the incoherent integration, and carrying out peak value verification by setting a threshold value;
and when the peak value verification is correct, calculating a frequency offset value according to the spectrogram, otherwise, setting the frequency offset value to be 0.
6. The method of claim 5, wherein the peak verification by setting a threshold value comprises: when the peak value verification result meets the following two conditions, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect;
the method comprises the following steps that 1, the ratio of a main peak value to a secondary peak value in a frequency spectrogram is larger than a threshold 1, and the threshold 1 is determined according to system configuration;
and 2, determining that the ratio of the main peak value to the mean value in the spectrogram is greater than a threshold 2, wherein the threshold 2 is determined according to system configuration.
7. The method of claim 5, wherein calculating a frequency offset value from the spectrogram when the peak verification is correct comprises:
calculating the outer ring frequency offset value according to the spectrogram by the following formula;
delta_f＝fFFT*[Idx_Pmax+(Pmax+1-Pmax-1)/(Pmax+1+Pmax-1)]
wherein, PmaxIs the energy of the position corresponding to the maximum spectral line, Pmax-1Energy, P, representing the corresponding position to the left of the maximum spectrummax+1Delta _ f represents the frequency offset value, f, for the energy of the corresponding position to the right of the maximum spectral lineFFTA frequency interval representing each spectral line of said fast fourier transform output; idx _ PmaxRepresenting the index to which the largest spectral line corresponds.
8. The method of claim 1, wherein feeding the incoherently summed result into an inner loop to calculate an inner loop frequency offset value comprises:
taking the result of the incoherent accumulation and carrying out inner loop frequency offset interpolation calculation at three positions with the abscissa of the spectrogram being 0/1/-1 according to the following formula;
delta_f＝fFFT*(P1-P-1)/(P1+P-1)
wherein, P0/P1/P-1 are respectively the energies corresponding to three spectrum indexes with the abscissa of 0/1/-1 in the spectrum.
9. A GPS frequency tracking device, comprising:
the integration unit is used for integrating the despread signals, wherein the integration length of the integration is the received signal quantity within N milliseconds;
the first processing unit is used for taking L integration lengths of the integrated signals as L points, and performing M-point fast Fourier transform to obtain an M-point fast Fourier transform spectrogram, wherein M > is L;
the second processing unit is used for respectively taking the modulus values of the complex numbers in the M-point fast Fourier transform spectrogram and then squaring the complex numbers to obtain real numbers;
a third processing unit, configured to perform incoherent summation on the real numbers of the same frequency of the K M-point fast fourier transforms obtained by repeating the first processing unit and the second processing unit K times, where K is a natural number;
a calculating unit, configured to send the result after incoherent integration to an outer loop to calculate an outer loop frequency offset value, and send the result after incoherent integration to an inner loop to calculate an inner loop frequency offset value;
a determining unit, configured to send the outer ring frequency offset value and the inner ring frequency offset value to a carrier frequency controller, and determine that a result of the final frequency offset value is one of the outer ring frequency offset value and the inner ring frequency offset value;
and the fourth processing unit is used for generating a corresponding sine-cosine waveform by the finally determined outer ring frequency offset value or one of the inner ring frequency offset values through the digital control oscillator and then sending the sine-cosine waveform into the intermediate frequency sampling signal to eliminate frequency offset.
10. The apparatus of claim 9, further comprising:
a judging unit, configured to judge whether time of the L integration lengths exceeds a navigation bit time before the first processing unit takes L integration lengths of the integrated signal as L points and performs M-point fast fourier transform to obtain an M-point fast fourier transform spectrogram;
and the adjusting unit is used for carrying out positive and negative adjustment on the integration result in the navigation bit time left in the L integration length time according to the integration result in the first navigation bit time when the L integration length time exceeds one navigation bit time.
11. The apparatus of claim 10, wherein the adjusting unit comprises:
a blind detection module, configured to perform 0/1 blind detection on the navigation bit when the navigation bit is unknown, where the navigation bit is encoded in a binary form;
the first adjusting module is used for carrying out positive and negative adjustment on the integral result in the remaining navigation bit time in the time of the L integral lengths according to the blind detection result;
a second adjusting module, configured to, when the navigation bit is known, leave the original value unchanged for a sequence in which the navigation bit corresponding to the remaining navigation bit time in the time of the L integration lengths is the same as the navigation bit corresponding to the first navigation bit time; and for the sequences that the navigation bits corresponding to the navigation bit time left in the time with the L integration lengths are different from the navigation bits corresponding to the first navigation bit time, multiplying the integration result in the navigation bit time left in the time with the L integration lengths by-1.
12. The apparatus of claim 11, wherein the blind detection module comprises:
the traversal submodule is used for traversing and listing possible navigation bit conditions for the residual navigation bit bytes in the L integration lengths according to 0/1 one by one;
the Fourier transform submodule is used for performing fast Fourier transform on all the integration results in the traversed navigation bit byte time and the integration results in the first navigation bit time in the time of L integration lengths respectively according to the original value and the value multiplied by-1 to obtain a plurality of groups of fast Fourier transform spectrograms;
and the determining submodule is used for obtaining a plurality of peak values by taking the peak value of the fast Fourier transform in the plurality of groups of fast Fourier transform frequency spectrums, further comparing the plurality of peak values, and taking the navigation bit corresponding to the largest peak value in the plurality of peak values as a navigation bit blind detection result.
13. The apparatus of claim 9, wherein the computing unit comprises:
the outer ring verification module is used for taking a peak value in the result after the incoherent summation and carrying out peak value verification by setting a threshold value;
and the outer loop calculation module is used for calculating a frequency offset value according to the spectrogram when the peak value verification is correct, and otherwise, setting the frequency offset value to be 0.
14. The apparatus of claim 13, wherein the outer loop validation module comprises: when the peak value verification result meets the following two conditions, the frequency offset value is considered to be correct, otherwise, the frequency offset value is considered to be incorrect;
the method comprises the following steps that 1, the ratio of a main peak value to a secondary peak value in a frequency spectrogram is larger than a threshold 1, and the threshold 1 is determined according to system configuration;
and 2, determining that the ratio of the main peak value to the mean value in the spectrogram is greater than a threshold 2, wherein the threshold 2 is determined according to system configuration.
15. The apparatus of claim 9, wherein the outer loop calculation module is configured to:
calculating the outer ring frequency offset value according to the spectrogram by the following formula;
delta_f＝fFFT*[Idx_Pmax+(Pmax+1-Pmax-1)/(Pmax+1+Pmax-1)]
wherein, PmaxIs the energy of the position corresponding to the maximum spectral line, Pmax-1Energy, P, representing the corresponding position to the left of the maximum spectrummax+1Delta _ f represents the frequency offset value, f, for the energy of the corresponding position to the right of the maximum spectral lineFFTA frequency interval representing each spectral line of said fast fourier transform output; idx _ PmaxRepresenting the index to which the largest spectral line corresponds.
16. The apparatus of claim 9, wherein the computing unit further comprises:
an inner-loop frequency interpolation calculation module, configured to perform inner-loop frequency offset interpolation calculation according to the following formula at three positions on the abscissa of the spectrogram, which is 0/1/-1, according to the result of the incoherent accumulation; delta _ f ═ fFFT*(P1-P-1)/(P1+P-1)
Wherein, P0/P1/P-1 are respectively the energies corresponding to three spectrum indexes with the abscissa of 0/1/-1 in the spectrum.
17. A GPS receiver, characterized in that it comprises a GPS frequency tracking device according to any one of claims 9 to 16.
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