CN101666869A - Method and device for secondary capturing weak satellite navigation signals - Google Patents
Method and device for secondary capturing weak satellite navigation signals Download PDFInfo
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Abstract
The invention discloses a method and a device for secondary capturing weak satellite navigation signals. A capturing module of a satellite navigation receiver finishes more coarse evaluation on a pseudo code phase and Doppler frequency shift. In high sensitivity satellite navigation receiver, long-time coherent integral is carried out to improve tracking sensitivity, which requires knowing the overturn position of navigation message bit and smaller surplus Doppler frequency shift. After capturing, secondary capturing is performed on data output by a correlation tracker, secondary search is performed on frequency points in the surplus frequency shift range to find the initial positions of the overturn position and secondary coding of the message bit. Frequency shift compensation, correlation integral and square are performed on data output by the correlation tracker after target frequency points and the initial positions of the overturn position and the secondary coding of the modulating message data are found, and a spectrum analysis method is used for performing refined evaluation on the surplus frequency shift after frequency shift compensation. The invention is suitable for thesatellite navigation receivers of multiple systems such as GPS, GLONASS and the like.
Description
Technical field
The present invention relates to a kind of secondary capturing weak satellite navigation signals method and apparatus.
Background technology
Along with the development of radiotelegraphy and space technology, in the past 30 years of satellite-based navigator fix technology have obtained developing rapidly.The NAVSTAR of having built up at present and having come into operation has GPS (GPS) and GPS (Global Position System) (GLONASS), have more NAVSTAR future and come into operation, as Galileo (Galileo) satellite navigation system and the Big Dipper (BeiDou) satellite navigation system; These systems are generically and collectively referred to as the GNSS system sometimes.Navigation neceiver is by receiving the signal of abundant satellite, and picked up signal travel-time information and satellite position information obtain the position, time, speed of receiver etc. according to these information calculations.
In order to resolve by navigator fix, navigation neceiver must receive the signal of at least 4 satellites; Navigation neceiver generally has a plurality of parallel receiving cables, and each passage receives the signal of a satellite.Navigation neceiver is at first caught satellite-signal by these parallel channels, and acquisition procedure is the search procedure of a bidimensional in fact: pseudo-random code phases and Doppler frequency deviation.With GPS is example, and every different length of satellites transmits is 1023, and the cycle is 1 millisecond a pseudo-random sequence; There is relative motion in satellite with receiver is middle, thereby Doppler frequency also is unknown.When catching, navigation neceiver produces different local pseudo-random sequence and carrier frequencies at different satellites and carries out relevant with input signal, when local pseudo-random sequence and list entries phase approximation synchronously and during the frequency approximately equal, relevant output valve can surpass detection threshold.Generally speaking, pseudo-random code phases search stepping is a half-chip when catching, and the Doppler frequency deviation stepping is (1/2T) Hz, and T is the coherent integration time, is generally 1 pseudo-random code cycle.Under weak signal environment,, carry out long-time coherent integration or non-coherent integration behind the related operation usually and obtain enough big processing gain in order accurately to catch chip phase and Doppler frequency deviation.
The navigation neceiver trapping module has been finished the rough estimate of signal, in order to obtain the accurate estimated value of pseudo-random code phases, carrier frequency/phase place, need carry out real-time follow-up to navigation signal.Tracking loop commonly used has delay lock loop (DLL), FLL (FLL) and phaselocked loop (PLL); Delay lock loop (DLL) is used for following the tracks of pseudo-random code phases, and FLL (FLL) and phaselocked loop (PLL) are used for following the tracks of carrier frequency and phase place.Under weak signal environment, it is narrow that above-mentioned loop bandwidth is provided with usually, and when loop bandwidth was narrow, the inherent spurious frequency deviation of initialization loop can not be too big, and catch finish after remaining Doppler frequency deviation not in the capture zone of loop, need carry out meticulous estimation to frequency deviation.At outdoor open field, satellite-signal is more intense, is example with the C/A sign indicating number of GPS, the satellite-signal carrier-to-noise ratio (C/N that navigation neceiver receives
0) be approximately 44dB/Hz, such signal intensity, the intact data of despreading are used for following the tracks of enough; Under weak signal environment, need carry out long-time coherent integration obtaining sufficiently high signal to noise ratio (S/N ratio) to the intact data of despreading, maximum coherence integral time is 20 milliseconds when modulating data is unknown, and need know the moment of modulating data upset.In some modern GNSS signals, handling modulation has outside pseudo-random code, navigation message data, the carrier wave, also there is secondary coding, as just modulating on the L5 frequency range of GPS the Neumann-Hoffman sign indicating number is arranged, in order to carry out long-time coherent integration and demodulation text, must finish the synchronous of secondary coding phase place.At the problems referred to above, satellite navigation receiver carries out pre-service to following the tracks of the correlator output data usually before loop tracks, obtain navigation message bit upturned position, the isoparametric estimated value of meticulous Doppler frequency deviation, with these estimated value initialization track loop.
Summary of the invention
The objective of the invention is to overcome the deficiencies in the prior art, a kind of secondary capturing weak satellite navigation signals method and apparatus is provided.
The method of secondary capturing weak satellite navigation signals comprises the steps:
1) under the control of control module, to store one group and follow the tracks of the correlator output data to memory module, each follows the tracks of the corresponding memory module of passage;
2) after the correlator output data is followed the tracks of in the memory module storage, control module control store module, frequency-variable module, matched filtering module and quadrature detector block will be caught the remaining Doppler frequency deviation scope in back and be divided into a plurality of frequencies; Frequency is searched for, found target frequency and modulation telegraph text data upturned position/secondary coding reference position;
3), the tracking correlator output data of storage is carried out the frequency deviation correction according to the target frequency; According to modulation telegraph text data upturned position/secondary coding reference position, to carrying out coherent integration through the revised data of overdeviation, coherent integration is carried out in same modulation telegraph text data, and the coherent integration time can divide exactly the modulated telegraph text data duration;
4) data after the coherent integration are carried out square operation, eliminate the influence of modulation text data polarity; Data behind the square operation obtain meticulousr frequency deviation with spectrum analysis, and spectrum analysis is carried out in the Frequency Estimation module.
Described under the control of control module, store one group of output data of following the tracks of correlator to memory module, each is followed the tracks of the corresponding memory module step of passage and comprises:
1) following the tracks of the correlator output data is complex signal, and sampling interval is 1 millisecond, and promptly sampling rate is 1KHz, and each modulation telegraph text data has 20 sampled points;
2) memory module storage data volume is 19+20*M, M＞0, the carrier-to-noise ratio decision that the value of M is estimated by acquisition phase;
3) when memory module storage data volume reaches requirement, send the secondary capturing enabling signal to control module.
After the correlator output data is followed the tracks of in described memory module storage, control module control store module, frequency-variable module, matched filtering module and quadrature detector block will be caught the remaining Doppler frequency deviation scope in back and be divided into a plurality of frequencies; Frequency is searched for, is found target frequency and modulation telegraph text data upturned position/secondary coding reference position step to comprise:
1) catch back residue Doppler frequency deviation scope for-(1/4T) Hz～+ (1/4T) Hz, T is the acquisition phase coherent integration time, it is 1 millisecond, residue Doppler frequency deviation scope is cut apart, be spaced apart 1/ (2Td) Hz, wherein Td is 20 milliseconds for the modulation telegraph text data duration, and N=Td/T+1 frequency arranged;
2) for each frequency, the local carrier module in the control module control of conversion module produces local carrier; Control module reads follows the tracks of the correlator output data in the memory module, carry out frequency conversion with the local carrier conjugate multiplication;
3) data after the frequency conversion are through the matched filtering module, and matched filter progression is 20, and tap coefficient is respectively: for the C/A coded signal of GPS be: 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, for the quadrature branch signal of the L5 wave band of GPS be :-1 ,-1 ,-1 ,-1,-1,1 ,-1 ,-1,1,1,-1,1 ,-1,1 ,-1 ,-1,1,1,1 ,-1, for the C/A sign indicating number of GLONASS be: 1,1,1,1,1,1,1,1,1,1 ,-1 ,-1 ,-1 ,-1,-1 ,-1 ,-1 ,-1 ,-1 ,-1;
4) for each frequency, total 19+20*M the input data of matched filtering module, there is 20*M output data M＞0.Per 20 output datas are divided into 1 group, total M group data;
5) for each frequency, to the M group data delivery of matched filtering module output, the 0th group of No. 0 data, the 1st group of No. 0 data are up to No. 0 data addition of M-1 group behind the delivery; The 0th group of No. 1 data, the 1st group of No. 1 data are up to No. 1 data addition of M-1 group; And the like, the 0th group of No. 19 data, the 1st group of No. 19 data are up to No. 19 data additions of M-1 group; Common property is given birth to 20 non-coherent integration data;
6) N total 20*N non-coherent integration data of frequency, the non-coherent integration data are delivered to peak detection block; Peak detection block finds peak value, and the peak value frequency points corresponding is exactly the target frequency, is designated as
The numbering of peak value correspondence is exactly to modulate telegraph text data upturned position/secondary coding reference position, is designated as
Described for each frequency, total 19+20*M the input data of matched filtering module, there is 20*M output data M＞0.Per 20 output datas are divided into 1 group, and total M group data step comprises:
Preceding 19 data of 1) matched filtering module input data are filled up preceding 19 of matched filtering module shift register, and since the 20th input data, data of every input are just exported data, total 20*M output data, M＞0;
2) matched filtering module output data the 0th～19 is divided into the 0th group, and the 20th～39 is divided into the 1st group, and the like the 20*M-20～20*M-1 be divided into M-1 group.
Described according to the target frequency, the tracking correlator output data of storage is carried out the frequency deviation correction; Reference position according to modulation telegraph text data upturned position/secondary coding, to carrying out coherent integration through the revised data of overdeviation, coherent integration is carried out in same modulation telegraph text data, and the coherent integration time can the modulated telegraph text data duration be divided exactly step and be comprised:
1) according to the target frequency
Local carrier generation module in the control module control of conversion module produces frequency
The complex carrier signal signal of respective frequencies.Control module reads the data in the memory module, with local complex carrier signal signal conjugate multiplication, finishes the frequency deviation correction;
2) according to modulation telegraph text data upturned position/secondary coding reference position
Coherent integration is from frequency deviation revised
Individual data begin to carry out, and the coherent integration time is 1 millisecond, 2 milliseconds, 4 milliseconds, 5 milliseconds or 10 milliseconds.
Data after the described coherent integration are carried out square operation, eliminate the influence of modulation text data polarity; Data behind the square operation obtain meticulousr frequency deviation with spectrum analysis, and spectrum analysis is carried out step and comprised in the Frequency Estimation module:
1) square operation is eliminated the variation of modulation text positive-negative polarity, and inherent spurious frequency deviation also becomes original twice simultaneously;
2) the inherent spurious frequency deviation scope is-1/ (4Td) Hz～1/ (4Td) Hz behind the compensate of frequency deviation, square frequency deviation region is doubled, and becomes-1/ (2Td) Hz～1/ (2Td) Hz; Td is 20 milliseconds, and frequency deviation region is-25Hz～25Hz behind the compensate of frequency deviation; Remaining Doppler frequency deviation behind the Spectral Analysis Method estimation compensate of frequency deviation.
The device of secondary capturing weak satellite navigation signals comprises as lower module: follow the tracks of correlator, memory module, frequency-variable module, matched filtering module, non-coherent integration module, peak detection block, coherent integration module, square module, Frequency Estimation module and control module; Following the tracks of correlator, memory module, frequency-variable module links to each other successively; Frequency-variable module links to each other with matched filtering module, coherent integration module respectively; Matched filtering module, non-coherent integration module, peak detection block link to each other successively; Coherent integration module, square module, Frequency Estimation module link to each other successively.Control module control is followed the tracks of the correlator output data and is stored memory module into, and memory module is sent the secondary capturing enabling signal to control module; Control module control store module output data, data find target frequency and modulation telegraph text data upturned position/secondary coding reference position through matched filtering module, non-coherent integration module, peak detection block; After finding target frequency and modulation telegraph text data upturned position/secondary coding reference position, control module control store module output data, data are carried out the frequency deviation correction through frequency-variable module, revised data are through coherent integration module, square module, and square module output data is carried out the fine estimation of frequency deviation through the Frequency Estimation module.
Described frequency-variable module comprises conjugate multiplication module, the local carrier module that is connected.
After the present invention stores one group of tracking correlator output data, can carry out cutting apart once more of frequency deviation to following the tracks of the correlator output data with the mode that piece is handled, by matched filtering module, non-coherent integration module and peak detection block, obtain the accumulated value of different frequent points and different modulating telegraph text data upturned position/secondary coding reference position; Detect the frequency that can find modulation telegraph text data upturned position/secondary coding reference position and search by peak value.According to searching to such an extent that frequency carries out the compensation of frequency deviation to the tracking correlator output data of storage, carry out coherent integration according to the data after finding modulation telegraph text data upturned position/secondary coding reference position to compensate of frequency deviation, coherent integration is carried out in same modulation telegraph text data.Coherent integration result square eliminates the influence of modulation text data polarity, then the estimated value by the meticulousr Doppler frequency deviation of the method acquisition of spectrum analysis.
Description of drawings
Fig. 1 is whole module of the present invention and connects block diagram;
Fig. 2 is the circuit block diagram of frequency-variable module among the present invention;
Fig. 3 is three kinds of coupling waveforms of matched filtering module among the present invention.
Embodiment
The method of secondary capturing weak satellite navigation signals comprises the steps:
1) under the control of control module, to store one group and follow the tracks of the correlator output data to memory module, each follows the tracks of the corresponding memory module of passage;
2) after the correlator output data is followed the tracks of in the memory module storage, control module control store module, frequency-variable module, matched filtering module and quadrature detector block will be caught the remaining Doppler frequency deviation scope in back and be divided into a plurality of frequencies; Frequency is searched for, found target frequency and modulation telegraph text data upturned position/secondary coding reference position;
3), the tracking correlator output data of storage is carried out the frequency deviation correction according to the target frequency; According to modulation telegraph text data upturned position/secondary coding reference position, to carrying out coherent integration through the revised data of overdeviation, coherent integration is carried out in same modulation telegraph text data, and the coherent integration time can divide exactly the modulated telegraph text data duration;
4) data after the coherent integration are carried out square operation, eliminate the influence of modulation text data polarity; Data behind the square operation obtain meticulousr frequency deviation with spectrum analysis, and spectrum analysis is carried out in the Frequency Estimation module.
Under the control of control module, store one group of output data of following the tracks of correlator to memory module, each is followed the tracks of the corresponding memory module step of passage and comprises:
1) following the tracks of the correlator output data is complex signal, and sampling interval is 1 millisecond, and promptly sampling rate is 1KHz, and each modulation telegraph text data has 20 sampled points, output data x
iExpression formula is:
x
i＝Ad
in
ie
j(2πiΔfT+θ)+N
i(1)
I is the data subscript in the formula (1), and A represents the amplitude of signal, d
iExpression modulation telegraph text data, n
iThe secondary coding (secondary coding) that expression exists, Δ f is for having caught the residue Doppler frequency deviation, and T is 1 millisecond here for following the tracks of the correlator output sampling interval time, and θ is an initial phase, N
iBe noise; The upturned position of modulation telegraph text data and the reference position of secondary coding are identical.For the C/A sign indicating number of GPS, n
iPerseverance is a high level; N for the L5 wave band quadrature branch signal of GPS
iFor :-1 ,-1 ,-1 ,-1 ,-1,1 ,-1 ,-1,1,1 ,-1,1 ,-1,1 ,-1 ,-1,1,1,1 ,-1, the cycle is 20 milliseconds; N for the C/A sign indicating number of GLONASS
iFor: 1,1,1,1,1,1,1,1,1,1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1, the cycle is 20 milliseconds;
2) memory module storage data volume is 19+20*M, M＞0, the carrier-to-noise ratio decision that the value of M is estimated by acquisition phase.Acquisition phase is divided into four sections with signal intensity, and segmentation limit and corresponding M value are: as (a) 25dB/Hz＜C/N
0During＜=30dB/Hz, M=80 is as (b) 30dB/Hz＜C/N
0During＜=35dB/Hz, M=60 is as (c) 35dB/Hz＜C/N
0During＜=40dB/Hz, M=40 is as (d) 40dB/Hz＜C/N
0The time, M=20;
3) when memory module storage data volume reaches requirement, send the secondary capturing enabling signal to control module.
After the correlator output data is followed the tracks of in the memory module storage, control module control store module, frequency-variable module, matched filtering module and quadrature detector block will be caught the remaining Doppler frequency deviation scope in back and be divided into a plurality of frequencies; Frequency is searched for, is found target frequency and modulation telegraph text data upturned position/secondary coding reference position step to comprise:
1) catch back residue Doppler frequency deviation scope for-(1/4T) Hz～+ (1/4T) Hz, T is the acquisition phase coherent integration time, it is 1 millisecond, residue Doppler frequency deviation scope is cut apart, be spaced apart 1/ (2Td) Hz, wherein Td is 20 milliseconds for the modulation telegraph text data duration, and N=Td/T+1 frequency arranged.For example when having caught the residue Doppler frequency deviation for-250Hz～250Hz, having 21 frequencies needs search; When inherent spurious frequency deviation be-during 100Hz～100Hz, having 9 frequencies needs search.
2) for each frequency, the local carrier module in the control module control of conversion module produces local carrier; Control module reads follows the tracks of the correlator output data in the memory module, carry out frequency conversion with the local carrier conjugate multiplication;
3) data after the frequency conversion are through the matched filtering module, and matched filter progression is 20, and tap coefficient is respectively: for the C/A coded signal of GPS be: 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, as 301 among Fig. 3; For the quadrature branch signal of the L5 wave band of GPS be :-1 ,-1 ,-1 ,-1 ,-1,1 ,-1 ,-1,1,1 ,-1,1 ,-1,1 ,-1 ,-1,1,1,1 ,-1, as 302 among Fig. 3; For the C/A sign indicating number of GLONASS be: 1,1,1,1,1,1,1,1,1,1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1 ,-1, as 303 among Fig. 3;
4) for each frequency, total 19+20*M the input data of matched filtering module, there is 20*M output data M＞0.Total M group data, every group of 20 data, numbering is respectively 0～19, corresponding possible modulation telegraph text data upturned position/secondary coding reference position of data of identical numbering in every group.Matched filtering module output data expression formula is z
M, δ, n, wherein m represents group number, scope is 0～M-1; δ is possible modulation telegraph text data upturned position/secondary coding reference position, and scope is 0～19, represents the frequency point number of current search with 0～No. 19 corresponding n of data in every group of data, and scope is 0～N-1;
5) for each frequency, to the M group data delivery of matched filtering module output, the 0th group of No. 0 data, the 1st group of No. 0 data are up to No. 0 data addition of M-1 group behind the delivery; The 0th group of No. 1 data, the 1st group of No. 1 data are up to No. 1 data addition of M-1 group; And the like, the 0th group of No. 19 data, the 1st group of No. 19 data are up to No. 19 data additions of M-1 group; Common property is given birth to 20 non-coherent integration data.Date expression after the accumulation is:
6) N total 20*N non-coherent integration data of frequency, non-coherent integration data H
δ, nDeliver to peak detection block; Peak detection block finds peak value, and the peak value frequency points corresponding is exactly the target frequency, is designated as
The numbering of peak value correspondence is exactly to modulate telegraph text data upturned position/secondary coding reference position, is designated as
For each frequency, total 19+20*M the input data of matched filtering module, there is 20*M output data M＞0.Per 20 output datas are divided into 1 group, and total M group data step comprises:
Preceding 19 data of 1) matched filtering module input data are filled up preceding 19 of matched filtering module shift register, and since the 20th input data, data of every input are just exported data, total 20*M output data, M＞0;
2) matched filtering module output data the 0th～19 is divided into the 0th group, and the 20th～39 is divided into the 1st group, and the like the 20*M-20～20*M-1 be divided into M-1 group.
According to the target frequency, the tracking correlator output data of storage is carried out the frequency deviation correction; Reference position according to modulation telegraph text data upturned position/secondary coding, to carrying out coherent integration through the revised data of overdeviation, coherent integration is carried out in same modulation telegraph text data, and the coherent integration time can the modulated telegraph text data duration be divided exactly step and be comprised:
1) according to the target frequency
Local carrier generation module in the control module control of conversion module produces frequency
The complex carrier signal signal of respective frequencies.Control module reads the data in the memory module, with local complex carrier signal signal conjugate multiplication, finishes the frequency deviation correction;
2) according to modulation telegraph text data upturned position/secondary coding reference position
Coherent integration is from frequency deviation revised
Individual data begin to carry out, and the coherent integration time is 1 millisecond, 2 milliseconds, 4 milliseconds, 5 milliseconds or 10 milliseconds.When signal intensity is in scope a, carry out 5 milliseconds of coherent integrations; When signal intensity is in scope b, carry out 4 milliseconds of coherent integrations;
When signal intensity is in scope c, carry out 2 milliseconds of coherent integrations; When signal intensity is in scope d, carry out 1 millisecond of coherent integration.
Data after the coherent integration are carried out square operation, eliminate the influence of modulation text data polarity; Data behind the square operation obtain meticulousr frequency deviation with spectrum analysis, and spectrum analysis is carried out step and comprised in the Frequency Estimation module:
1) square operation is eliminated the variation of modulation text positive-negative polarity, and inherent spurious frequency deviation also becomes original twice simultaneously;
2) the inherent spurious frequency deviation scope is-1/ (4Td) Hz～1/ (4Td) Hz behind the compensate of frequency deviation, square frequency deviation region is doubled, and becomes-1/ (2Td) Hz～1/ (2Td) Hz; Td is 20 milliseconds, and frequency deviation region is-25Hz～25Hz behind the compensate of frequency deviation; Spectral Analysis Method is estimated remaining Doppler frequency deviation behind the compensate of frequency deviation, can carry out the fine estimation of frequency deviation with 256 FFT.
As shown in Figure 1, the device of secondary capturing weak satellite navigation signals comprises as lower module: follow the tracks of correlator, memory module, frequency-variable module, matched filtering module, non-coherent integration module, peak detection block, coherent integration module, square module, Frequency Estimation module and control module; Following the tracks of correlator, memory module, frequency-variable module links to each other successively; Frequency-variable module links to each other with matched filtering module, coherent integration module respectively; Matched filtering module, non-coherent integration module, peak detection block link to each other successively; Coherent integration module, square module, Frequency Estimation module link to each other successively; Control module control is followed the tracks of the correlator output data and is stored memory module into, and memory module is sent the secondary capturing enabling signal to control module; Control module control store module output data, data find target frequency and modulation telegraph text data upturned position/secondary coding reference position through matched filtering module, non-coherent integration module, peak detection block; After finding target frequency and modulation telegraph text data upturned position/secondary coding reference position, control module control store module output data, data are carried out the frequency deviation correction through frequency-variable module, revised data are through coherent integration module, square module, and square module output data is carried out the fine estimation of frequency deviation through the Frequency Estimation module.
As shown in Figure 2, frequency-variable module comprises conjugate multiplication module, the local carrier module that is connected.
Embodiment
Initial acquisition finished pseudo-code phase and Doppler frequency deviation thicker synchronously, in our embodiment, acquisition phase carries out 1 millisecond coherent integration, pseudo-code is spaced apart 0.5 chip.Caught, residue chip phase deviation in-/+0.25 chip, the residue Doppler spread is-/+250Hz.Acquisition phase is finished the initial synchronisation of signal, has also obtained the guestimate of signal intensity, determines the signal carrier-to-noise ratio is below in which scope;
a)25dB/Hz＜C/N
0＜＝30dB/Hz；
b)30dB/Hz＜C/N
0＜＝35dB/Hz；
c)35dB/Hz＜C/N
0＜＝40dB/Hz；
d)40dB/Hz＜C/N
0。
When the signal carrier-to-noise ratio was in scope a, it was the individual tracking correlator of 1619 (M=80) output data, the i.e. data of 1.619s that secondary capturing uses data volume; When the signal carrier-to-noise ratio was in scope b, it was the individual tracking correlator of 1219 (M=60) output data, the i.e. data of 1.219s that secondary capturing uses data volume; When the signal carrier-to-noise ratio was in scope c, it was the individual tracking correlator of 819 (M=40) output data, the i.e. data of 0.819s that secondary capturing uses data volume; When the signal carrier-to-noise ratio was in scope d, it was the individual tracking correlator of 419 (M=20) output data, the i.e. data of 0.419s that secondary capturing uses data volume.The secondary capturing of unlike signal carrier-to-noise ratio scope uses data volume to obtain according to emulation, through the actual measurement checking.
During actual measurement, the signal carrier-to-noise ratio is 27dB/Hz, and Doppler frequency deviation is 1156Hz, and signal format is the C/A sign indicating number of GPS, and the modulation telegraph text data upturned position of the tracking correlator output data of storage is the 3rd data.Catch finish after, the chip phase near-synchronous, the residue Doppler frequency deviation is 156Hz, and the scope that estimates the signal intensity place is a.The search frequency is-250Hz, 225Hz, 200Hz......220Hz, 225Hz, 250Hz during secondary capturing, have 21 frequencies, the non-coherent integration module has 21 groups of output datas, every group of corresponding frequency, every group of data have 20 data, the corresponding a kind of possible modulation telegraph text data upturned position/secondary coding reference position of each data.It is the 3rd data of the 17th group of data that peak detection block finds the position of peak value, shows that the target frequency is 150Hz, and modulation telegraph text data upturned position/secondary coding reference position is the 3rd data of input data.Control module is according to target frequency 150Hz, and control local carrier module produces the complex carrier signal signal of 150Hz, and the tracking correlator output data and the complex carrier signal signal conjugate multiplication that read in the memory module realize compensate of frequency deviation.The inherent spurious frequency deviation of data is 6Hz behind the compensate of frequency deviation.According to modulation telegraph text data upturned position/secondary coding reference position, since the 3rd data, per 5 data are carried out coherent integration, and the data after the coherent integration are carried out square operation.The equivalent sampling rate of the data behind the square operation is 200Hz, and inherent spurious frequency deviation is 12Hz, and these data are carried out 256 FFT computing, and the peak that finds FFT result is 16.The accurate estimated value of inherent spurious frequency deviation is 5.86Hz behind the compensate of frequency deviation according to calculating.
Claims (8)
1. the method for a secondary capturing weak satellite navigation signals is characterized in that comprising the steps:
1) under the control of control module, to store one group and follow the tracks of the correlator output data to memory module, each follows the tracks of the corresponding memory module of passage;
2) after the correlator output data is followed the tracks of in the memory module storage, control module control store module, frequency-variable module, matched filtering module and quadrature detector block will be caught the remaining Doppler frequency deviation scope in back and be divided into a plurality of frequencies; Frequency is searched for, found target frequency and modulation telegraph text data upturned position/secondary coding reference position;
3), the tracking correlator output data of storage is carried out the frequency deviation correction according to the target frequency; According to modulation telegraph text data upturned position/secondary coding reference position, to carrying out coherent integration through the revised data of overdeviation, coherent integration is carried out in same modulation telegraph text data, and the coherent integration time can divide exactly the modulated telegraph text data duration;
4) data after the coherent integration are carried out square operation, eliminate the influence of modulation text data polarity; Data behind the square operation obtain meticulousr frequency deviation with spectrum analysis, and spectrum analysis is carried out in the Frequency Estimation module.
2. the method for a kind of secondary capturing weak satellite navigation signals according to claim 1, it is characterized in that, described under the control of control module, store one group of output data of following the tracks of correlator to memory module, each is followed the tracks of the corresponding memory module step of passage and comprises:
1) following the tracks of the correlator output data is complex signal, and sampling interval is 1 millisecond, and promptly sampling rate is 1KHz, and each modulation telegraph text data has 20 sampled points;
2) memory module storage data volume is 19+20*M, M＞0, the carrier-to-noise ratio decision that the value of M is estimated by acquisition phase;
3) when memory module storage data volume reaches requirement, send the secondary capturing enabling signal to control module.
3. the method for a kind of secondary capturing weak satellite navigation signals according to claim 1, it is characterized in that, after the correlator output data is followed the tracks of in described memory module storage, control module control store module, frequency-variable module, matched filtering module and quadrature detector block will be caught the remaining Doppler frequency deviation scope in back and be divided into a plurality of frequencies; Frequency is searched for, is found target frequency and modulation telegraph text data upturned position/secondary coding reference position step to comprise:
1) catch back residue Doppler frequency deviation scope for-(1/4T) Hz～+ (1/4T) Hz, T is the acquisition phase coherent integration time, it is 1 millisecond, residue Doppler frequency deviation scope is cut apart, be spaced apart 1/ (2Td) Hz, wherein Td is 20 milliseconds for the modulation telegraph text data duration, and N=Td/T+1 frequency arranged;
2) for each frequency, the local carrier module in the control module control of conversion module produces local carrier; Control module reads follows the tracks of the correlator output data in the memory module, carry out frequency conversion with the local carrier conjugate multiplication;
3) data after the frequency conversion are through the matched filtering module, and matched filter progression is 20, and tap coefficient is respectively: for the C/A coded signal of GPS be: 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, for the quadrature branch signal of the L5 wave band of GPS be :-1 ,-1 ,-1 ,-1,-1,1 ,-1 ,-1,1,1,-1,1 ,-1,1 ,-1 ,-1,1,1,1 ,-1, for the C/A sign indicating number of GLONASS be: 1,1,1,1,1,1,1,1,1,1 ,-1 ,-1 ,-1 ,-1,-1 ,-1 ,-1 ,-1 ,-1 ,-1;
4) for each frequency, total 19+20*M the input data of matched filtering module, there is 20*M output data M＞0.Per 20 output datas are divided into 1 group, total M group data;
5) for each frequency, to the M group data delivery of matched filtering module output, the 0th group of No. 0 data, the 1st group of No. 0 data are up to No. 0 data addition of M-1 group behind the delivery; The 0th group of No. 1 data, the 1st group of No. 1 data are up to No. 1 data addition of M-1 group; And the like, the 0th group of No. 19 data, the 1st group of No. 19 data are up to No. 19 data additions of M-1 group; Common property is given birth to 20 non-coherent integration data;
6) N total 20*N non-coherent integration data of frequency, the non-coherent integration data are delivered to peak detection block; Peak detection block finds peak value, and the peak value frequency points corresponding is exactly the target frequency, is designated as
The numbering of peak value correspondence is exactly to modulate telegraph text data upturned position/secondary coding reference position, is designated as
4. the method for a kind of secondary capturing weak satellite navigation signals according to claim 3 is characterized in that, and is described for each frequency, total 19+20*M the input data of matched filtering module, and there is 20*M output data M＞0.Per 20 output datas are divided into 1 group, and total M group data step comprises:
Preceding 19 data of 1) matched filtering module input data are filled up preceding 19 of matched filtering module shift register, and since the 20th input data, data of every input are just exported data, total 20*M output data, M＞0;
2) matched filtering module output data the 0th～19 is divided into the 0th group, and the 20th～39 is divided into the 1st group, and the like the 20*M-20～20*M-1 be divided into M-1 group.
5. the method for a kind of secondary capturing weak satellite navigation signals according to claim 1 is characterized in that, and is described according to the target frequency, and the tracking correlator output data of storage is carried out the frequency deviation correction; Reference position according to modulation telegraph text data upturned position/secondary coding, to carrying out coherent integration through the revised data of overdeviation, coherent integration is carried out in same modulation telegraph text data, and the coherent integration time can the modulated telegraph text data duration be divided exactly step and be comprised:
1) according to the target frequency
Local carrier generation module in the control module control of conversion module produces frequency
The complex carrier signal signal of respective frequencies.Control module reads the data in the memory module, with local complex carrier signal signal conjugate multiplication, finishes the frequency deviation correction;
2) according to modulation telegraph text data upturned position/secondary coding reference position
Coherent integration is from frequency deviation revised
Individual data begin to carry out, and the coherent integration time is 1 millisecond, 2 milliseconds, 4 milliseconds, 5 milliseconds or 10 milliseconds.
6. the method for a kind of secondary capturing weak satellite navigation signals according to claim 1 is characterized in that, the data after the described coherent integration are carried out square operation, eliminates the influence of modulation text data polarity; Data behind the square operation obtain meticulousr frequency deviation with spectrum analysis, and spectrum analysis is carried out step and comprised in the Frequency Estimation module:
1) square operation is eliminated the variation of modulation text positive-negative polarity, and inherent spurious frequency deviation also becomes original twice simultaneously;
2) the inherent spurious frequency deviation scope is-1/ (4Td) Hz～1/ (4Td) Hz behind the compensate of frequency deviation, square frequency deviation region is doubled, and becomes-1/ (2Td) Hz～1/ (2Td) Hz; Td is 20 milliseconds, and frequency deviation region is-25Hz～25Hz behind the compensate of frequency deviation; Remaining Doppler frequency deviation behind the Spectral Analysis Method estimation compensate of frequency deviation.
7. device of the secondary capturing weak satellite navigation signals of method design according to claim 1, it is characterized in that, comprise: follow the tracks of correlator, memory module, frequency-variable module, matched filtering module, non-coherent integration module, peak detection block, coherent integration module, square module, Frequency Estimation module and control module as lower module; Following the tracks of correlator, memory module, frequency-variable module links to each other successively; Frequency-variable module links to each other with matched filtering module, coherent integration module respectively; Matched filtering module, non-coherent integration module, peak detection block link to each other successively; Coherent integration module, square module, Frequency Estimation module link to each other successively.Control module control is followed the tracks of the correlator output data and is stored memory module into, and memory module is sent the secondary capturing enabling signal to control module; Control module control store module output data, data find target frequency and modulation telegraph text data upturned position/secondary coding reference position through matched filtering module, non-coherent integration module, peak detection block; After finding target frequency and modulation telegraph text data upturned position/secondary coding reference position, control module control store module output data, data are carried out the frequency deviation correction through frequency-variable module, revised data are through coherent integration module, square module, and square module output data is carried out the fine estimation of frequency deviation through the Frequency Estimation module.
8. the device as the secondary capturing weak satellite navigation signals of method design as described in the claim 7 is characterized in that described frequency-variable module comprises conjugate multiplication module, the local carrier module that is connected.
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