CN103605139B - Carrier frequency and phase estimation method and carrier frequency and phase estimation system applicable to GNSS (global navigation satellite system) receiver - Google Patents

Abstract

The invention discloses a carrier frequency and phase estimation method and a carrier frequency and phase estimation system applicable to a GNSS (global navigation satellite system) receiver. The method comprises the following steps: performing frequency domain sampling on a satellite intermediate frequency signal, and acquiring N-frequency point carrier frequency domain sampling values with equal frequency intervals, wherein N is more than or equal to 3, and the N-frequency point carrier frequency domain sampling values accord with the sinc function characteristics; establishing a trigonometric identity among the N-frequency point carrier frequency domain sampling values based on the sinc function characteristics, and estimating the carrier frequency and carrier phase according to the established trigonometric identity. The estimated accuracy of the carrier frequency and phase in a capturing or tracking link of the GNSS receiver can be effectively improved under the condition that extra data and computing resources are not increased.

Description

Be applicable to the carrier frequency of GNSS receiver and phase estimation method and system

Technical field

The invention belongs to GLONASS (Global Navigation Satellite System) field, particularly one is applicable to GNSS(Global Navigation Satellite System, GLONASS (Global Navigation Satellite System)) carrier frequency of receiver and phase estimation method and system.

Background technology

The Base-Band Processing of satellite navigation receiver mainly comprises catches, follows the tracks of and resolves three major parts.Catch link and realize the carrier frequency of satellite-signal and the thick synchronous of code phase mainly through the various method such as relevant; Following the tracks of link, mainly to utilize the technology such as phaselocked loop to realize the carrier frequency of satellite-signal synchronous with the essence of phase place, and make the dynamic change of local carrier tracking satellite signal; Resolve the position that the observed quantity partly then utilizing tracking phase to export calculates receiver antenna.In Practical Project, the frequency information that acquisition phase obtains often error is comparatively large, and magnitude is often at hundreds of hertz, and this is too coarse for tracking loop.Therefore, between acquisition and tracking, often adopt the modes such as FLL to increase a traction stage, its objective is and reduce Frequency Estimation scope rapidly, thus make frequency error meet the phase-locked loop operation scope of following the tracks of link.But the mode of this traction needs extra time and data, cause TTFF(primary positioning time) index decline.Other method is in catching, adopt the mode of FFT to obtain carrier frequency, and improves frequency estimation accuracy by the mode of interpolation.This mode is FFT to improve after frequency sampling interval needs to carry out zero padding to data, and this will cause the remarkable increase of calculated amount, and utilizing works does not realize.

In order to improve the tracking sensitivity of receiver under weak signal environment, the most effective mode adopts the mode of FLL to carry out frequency-tracking.Therefore, how fine estimation to go out carrier frequency significant equally for tracking phase.The most effective mode is that the method in catching of copying adopts the modes such as FFT to obtain the estimated value of multiple frequency at present, then the fine estimation of frequency is realized by the mode of Interpolation across frequency or curve, but these methods often degree of accuracy is not high, and calculation of complex, performance is superior not.

Summary of the invention

Not high and need the problem such as excessive data and computational resource for existing GNSS receiver acquisition and tracking stage estimating carrier frequencies precision, the invention provides a kind of precision is high, calculated amount is little carrier frequency and phase estimation method and system, be applicable to GNSS receiver acquisition and tracking link.

The carrier frequency sampled value that the present invention is based on output meets sinc function characteristic at frequency domain, utilizes sinc function characteristic estimating carrier frequency and carrier phase.Under desirable noise-free case, the evaluated error of carrier frequency and carrier phase is zero.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

One, the carrier frequency estimating method of GNSS receiver is applicable to, the method carries out frequency domain sample to satellite intermediate frequency carrier signal, obtain the N frequency carrier wave frequency domain sampled value with equifrequent interval, N >=3, described N frequency carrier wave frequency domain sampled value meets sinc function characteristic, the a linear equation of reflection carrier wave frequency domain sampled value and carrier frequency mathematics relation to be estimated is set up based on sinc function characteristic, solve a linear equation and obtain estimating carrier frequencies formula, according to N frequency carrier wave frequency domain sampled value and estimating carrier frequencies formula estimating carrier frequency.

Above-mentioned N frequency carrier wave frequency domain sampled value obtains by correlator, fourier transform method (DFT) or fast fourier transform method (FFT).

Two, be applicable to the estimating carrier frequencies system of GNSS receiver, comprise:

Code stripper, is used for peeling off a yard information from satellite intermediate frequency signal;

Multifrequency point carrier wave frequency domain sampling system, is used for sampling at frequency domain to the carrier signal that code stripper exports, to obtain the N frequency carrier wave frequency domain sampled value with equifrequent interval;

Frequency Estimation system, is used for carrying out estimating carrier frequencies according to the N frequency carrier wave frequency domain sampled value that multifrequency point carrier wave frequency domain sampling system exports.

Above-mentioned multifrequency point carrier wave frequency domain sampling system comprises N road parallel correlator.

Above-mentioned multifrequency point carrier wave frequency domain sampling system comprises chronotron and the Fourier transform module of the serial of N road, and the chronotron of N road serial all connects Fourier transform module.

Said frequencies estimating system comprises the parallel delivery module in N road, and the delivery module that N road walks abreast all connects frequency discriminator.

Three, be applicable to the carrier phase estimation method of GNSS receiver, the method estimates carrier phase according to the N frequency carrier wave frequency domain sampled value and estimating carrier frequencies value with equifrequent interval, is specially:

According to the estimating carrier frequencies value that the frequency interval between N frequency carrier wave frequency domain sampled value and claim 1 obtain, arctan function is adopted to carry out phase demodulation, to obtain carrier phase estimated value to N frequency carrier wave frequency domain sampled value.

Four, be applicable to the carrier phase estimating system of GNSS receiver, comprise:

Code stripper, is used for peeling off a yard information from satellite intermediate frequency signal;

Multifrequency point carrier wave frequency domain sampling system, is used for sampling at frequency domain to the carrier signal that code stripper exports, to obtain the N frequency carrier wave frequency domain sampled value with equifrequent interval;

Frequency Estimation system, is used for carrying out estimating carrier frequencies according to the N frequency carrier wave frequency domain sampled value that multifrequency point carrier wave frequency domain sampling system exports;

Phase estimating device, is used for carrying out carrier phase estimation according to the estimating carrier frequencies value that N frequency carrier wave frequency domain sampled value and the Frequency Estimation system of the output of multifrequency point carrier wave frequency domain sampling system export.

Compared with prior art, major advantage of the present invention is as follows:

1. directly utilizing adopts the correlation output values of multiple frequency as input quantity, extremely meet the fast Acquisition algorithm based on FFT or parallel correlator in GNSS receiver, do not need extra data and computing time relative to the mode of drawing based on FLL etc., existing observed quantity can be utilized rapidly to carry out essence frequently.

2. relative to existing smart frequency method, the interval between multifrequency point correlator output value of the present invention can be arbitrary value, therefore possesses advantage adjustable flexibly, does not need additionally to do interpolation.

3. carrier frequency estimating method of the present invention utilizes the output of the correlator of different frequent points to present sinc function characteristic, sets up a linear equation of frequency estimation, have structure simple, estimate advantage accurately based on sinc function mathematical characteristic.Ideally, the evaluated error namely during signal noiseless is zero, and this method of estimation itself does not bring any error.

4. the present invention is except effective estimating carrier frequency, and interval and Given information between each frequency can also be utilized effectively to estimate carrier phase, when the conversion capturing tracking, effectively can arrange the phase place initial value of track loop.

5. only need 3 when integrator output valve of the present invention is minimum, calculated amount is little and applicablely realize in software, is particularly useful for track loop.

Accompanying drawing explanation

Fig. 1 is a kind of concrete structure block diagram of present system;

Fig. 2 is the multifrequency point carrier wave frequency domain sampling system structural representation based on parallel correlator;

Fig. 3 is the multifrequency point carrier wave frequency domain sampling system structural representation based on DFT/FFT;

Fig. 4 is the amplitude-frequency response figure that multifrequency point carrier wave frequency domain sampling system exports;

Fig. 5 is the concrete structure block diagram of Frequency Estimation system;

Fig. 6 is estimating carrier frequencies principle schematic of the present invention.

Embodiment

Specific embodiment of the invention is described in detail below in conjunction with accompanying drawing.

Fig. 1 is a kind of concrete structure figure of present system, comprise a yard stripper (101), multifrequency point carrier wave frequency domain sampling system (102), Frequency Estimation system (103) and phase estimating device (104), wherein, multifrequency point carrier wave frequency domain sampling system exports the carrier wave frequency domain sampled value arranged side by side being no less than 3; Frequency Estimation system comprises frequency estimator and smoother.

Code stripper (101) carries out relevant by the local pseudo-code producing correspondence to GNSS intermediate-freuqncy signal, thus peels off the code information in GNSS intermediate-freuqncy signal.During the invention process, no matter be catching link or following the tracks of link, first should peel off the code information in satellite-signal, then carry out frequency domain sample, estimating carrier frequency for carrier wave and estimate carrier phase, the single frequency sinusoidal ripple that namely the present invention be directed to without modulation intelligence is estimated.When not considering noise, the plural form of the above-mentioned single frequency sinusoidal ripple without modulation intelligence can be expressed as wherein, f _eand φ _ebe respectively carrier frequency to be estimated and carrier phase; A represents maximum amplitude; T represents the moment.

Multifrequency point carrier wave frequency domain sampling system is used for sampling to carrier wave, to obtain the multifrequency point frequency domain sample value at equifrequent interval.A kind of embodiment of multifrequency point carrier wave frequency domain sampling system is shown in Fig. 2, and form by the identical correlator in N road (N >=3) is parallel, the frequency interval between the correlator of each road presets.In the correlator of each road, local carrier (201,202) mutually orthogonal two paths of signals is all exported, the two paths of signals that local carrier exports is multiplied with input signal (105) respectively and transports to corresponding integration washer (203,204,205,206) respectively in multiplier, the integration that integration washer realizes input signal adds up, and periodically reset, the plural integrated value that each road correlator exports is multifrequency point carrier wave frequency domain sampled value (106).

The another kind of embodiment of multifrequency point carrier wave frequency domain sampling system is shown in Fig. 3, and this embodiment realizes based on Fourier transform.Input signal (105) is successively through N number of chronotron (301,302,303) of serial connection, and the output signal of N number of chronotron all inputs DFT module or FFT module (304) carries out Fourier transform, exports N frequency carrier wave frequency domain sampled value (106).In Practical Project, for improving frequency sampling value, before Fourier transform, zero padding operation can be carried out to chronotron output signal.

If the leap time that correlator resets cycle or DFT/FFT module input signal is T _coh, then the frequency domain of multifrequency point carrier wave frequency domain sampling system exports and can be expressed as wherein, A represents maximum amplitude; T represents the moment; f _efor carrier frequency to be estimated; φ _efor carrier phase to be estimated; Sinc function is defined as sinc (x)=sin (x)/x, sinc function curve and sees Fig. 4.Therefore, the multifrequency point carrier wave frequency domain sampled value that multifrequency point carrier wave frequency domain sampling system exports is equivalent to different f on sinc function curve _ethe amplitude that place is corresponding, sampling interval is identical with correlator set of frequency interval, also relevant with zero padding number with chronotron parameter.

Frequency Estimation system architecture is shown in Fig. 5, the parallel delivery module (401,402,403) in N road is adopted to eliminate the phase information of N frequency carrier wave frequency domain sampled value (106) respectively, it is complete in curve that the amplitude-frequency response eliminated after phase information in Fig. 4 becomes in Fig. 6, supposes that carrier wave frequency domain sampled value that delivery module exports is the A in Fig. 6 _s, A _p, A _f.Utilize the trigonometric identity relation on sinc function between each sampled value, to A _s, A _p, A _fset up with frequency f after configuration coefficients _efor a linear equation of unknown quantity.

Below will with three multifrequency point carrier wave frequency domain sampled value C _s, C _p, C _ffor example, a kind of concrete grammar of estimating carrier frequencies is described.

Suppose three sampled value C _s, C _p, C _ffrequency interval is △ f, and sampled value symbol is identical, sampled value C _s, C _p, C _fdistinguish corresponding A in figure 6 _s, A _p, A _f.Then A _pcorresponding horizontal ordinate frequency f _ecan be expressed as:

$f_e=\mathrm{\Δf}\frac{A_s-A_f}{A_s-2\cos \left(\mathrm{\π\Δf}{T}_{\mathrm{coh}}\right)A_p+A_f}---\left(1\right)$

According to these class methods, also A can be tried to achieve _s, A _fcorresponding frequency.Identical for ensureing the symbol of three sampled values corresponding sampled value in the diagram, to improve the reach of frequency discriminator, by operating with under type:

Step 1: utilize following formulae discovery C _swith C _p, and C _swith C _fconjugate product and rotatable phase:

$\begin{array}{c}{C}_{\mathrm{sp}}=C_s^{*}*C_p*e^{j*2\mathrm{\π}*\frac{\mathrm{\Δf}}{f_s}*(N-1)}\\ C_{\mathrm{pf}}=C_p^{*}*C_f*e^{j*2\mathrm{\π}*\frac{\mathrm{\Δf}}{f_s}*(N-1)}\end{array}---\left(2\right)$

Wherein, subscript * represents and gets conjugation, and N is sampled value quantity, and this is concrete implements, N=3.

Step 2: judge C _spand C _pfthe sign of real part, by C _spand C _pfreal part is designated as S respectively _spand S _pf, adopt S _spand S _pfcorrect A _sand A _fsymbol obtain corrected value A respectively _ss, A _fs, method is as follows:

A _ss=A _s*S _sp

（3）

A _fs=A _f*S _pf

Step 3: by corrected value A _ssand A _fssubstitute in formula (1) and estimate the frequency that sampled value is corresponding, with A _pfor example, the horizontal ordinate frequency f of its correspondence _eas follows:

$f_e=\mathrm{\Δf}\frac{A_{\mathrm{ss}}-A_{\mathrm{fs}}}{A_{\mathrm{ss}}-2\cos \left(\mathrm{\π\ΔfT}\right)A_p+A_{\mathrm{fs}}}---\left(4\right)$

Based on same mode, the frequency domain sample value more than 3 can be utilized to carry out frequency discrimination, different frequency domain sample value frequency discrimination result input smoothers also can be utilized to be averaged or filtering, thus improve estimated accuracy.

Phase estimating device utilizes the carrier frequency value of multifrequency point carrier wave frequency domain sampled value and Frequency Estimation system estimation to estimate carrier phase.Still for 3 carrier wave frequency domain sampled values, phase estimation process is described below:

Step 1: the parity judging each sampling place secondary lobe number, method is as follows:

In formula (5), P _s, P _p, P _fbe respectively A _s, A _p, A _fthe parity of sampled value place secondary lobe number; f _efor the carrier frequency value estimated; Mod (g) is mod, represent and round downwards.

Step 2: the symbol calculating each frequency domain sample value amplitude according to the parity of sampling place secondary lobe number, and correction acquisition corrected value C is carried out to the symbol of frequency domain sample value amplitude _ss, C _ps, C _fs:

C _ss=C _s*(1-2P _s)

C _ps=C _p*(1-2P _p) （6）

C _fs=C _f*(1-2P _f)

Step 3: utilize corrected value C _ss, C _ps, C _fsestimate carrier phase, any one that can adopt in following four kinds of methods carries out phase estimation:

Method 1: utilize corrected value C _ss, C _ps, C _fsin arbitrary value be input quantity, if input quantity is C _ss, directly utilize arctan function to carry out phase demodulation, obtain carrier phase estimated value φ _e:

${\mathrm{\φ}}_e=a\tan \left(\frac{\mathrm{Imag}\left(C_{\mathrm{ss}}\right)}{\mathrm{Real}\left(C_{\mathrm{ss}}\right)}\right)---\left(7\right)$

In formula (7), Imag (g) and Real (g) represents imaginary part and real part respectively.

Method 2: by three corrected value C _ss, C _ps, C _fsphase rotating after being multiplied, utilizes arctan function to carry out phase demodulation, obtains carrier phase estimated value φ _e:

$C_{\mathrm{sum}}=C_{\mathrm{ss}}*C_{\mathrm{ps}}*C_{\mathrm{fs}}*e^{j*6\mathrm{\π}*f_e*T_{\mathrm{coh}}}$

${\mathrm{\φ}}_e=\frac{a\tan \left(\frac{\mathrm{Imag}\left(C_{\mathrm{sum}}\right)}{\mathrm{Real}\left(C_{\mathrm{sum}}\right)}\right)}{3}---\left(8\right)$

In formula (8), Imag (g) and Real (g) represents imaginary part and real part respectively.

Method 3: to three corrected value C _ss, C _ps, C _fscarry out phase rotating and obtain C _sR, C _pR, C _fR, phase rotating formula is as follows:

$C_{\mathrm{sR}}=C_{\mathrm{ss}}*e^{j*2\mathrm{\π}*f_e*T_{\mathrm{coh}}}*e^{-j*2\mathrm{\π}*\frac{\mathrm{\Δf}}{f_s}*(N-1)}$

$C_{\mathrm{pR}}=C_{\mathrm{ps}}*e^{j*2\mathrm{\π}*f_e*T_{\mathrm{coh}}}---\left(9\right)$

$C_{\mathrm{fR}}=C_{\mathrm{fs}}*e^{j*2\mathrm{\π}*f_e*T_{\mathrm{coh}}}*e^{j*2\mathrm{\π}*\frac{\mathrm{\Δf}}{f_s}*(N-1)}$

Relatively 3 sampled value amplitude orders of magnitude, utilize the phase rotating post-sampling value C of the sampled value of amplitude maximum absolute value _mRcarry out phase estimation, obtain carrier phase estimated value φ _e:

${\mathrm{\φ}}_e=a\tan \left(\frac{\mathrm{Imag}\left(C_{\mathrm{MR}}\right)}{\mathrm{Real}\left(C_{\mathrm{MR}}\right)}\right)---\left(10\right)$

In formula (10), Imag (g) and Real (g) represents imaginary part and real part respectively.

Method 4: to three corrected value C _ss, C _ps, C _fscarry out phase rotating, phase rotating formula is shown in formula (9), adopt formula (10) to carry out phase estimation to the sampled value after phase rotating respectively, and to get phase estimation mean value is phase estimation result:

${\mathrm{\φ}}_e=\frac{a\tan \left(\frac{\mathrm{Imag}\left(C_{\mathrm{sR}}\right)}{\mathrm{Real}\left(C_{\mathrm{sR}}\right)}\right)+a\tan \left(\frac{\mathrm{Imag}\left(C_{\mathrm{pR}}\right)}{\mathrm{Real}\left(C_{\mathrm{pR}}\right)}\right)+a\tan \left(\frac{\mathrm{Imag}\left(C_{\mathrm{fR}}\right)}{\mathrm{Real}\left(C_{\mathrm{fR}}\right)}\right)}{3}---\left(11\right)$

In formula (11), be respectively sampled value A _s, A _p, A _fcorresponding phase estimation value; Imag (g) and Real (g) represents imaginary part and real part respectively.

The same with frequency discriminator, multiple frequency domain sample value can be utilized in phase detector to carry out phase demodulation, and identified result is averaged, to improve precision.

Claims (9)

1. be applicable to the carrier frequency estimating method of GNSS receiver, it is characterized in that:

Frequency domain sample is carried out to satellite intermediate frequency carrier signal, obtain the N frequency carrier wave frequency domain sampled value with equifrequent interval, N >=3, sinc function characteristic is met between described N frequency carrier wave frequency domain sampled value and carrier frequency, the a linear equation between carrier wave frequency domain sampled value and carrier frequency to be estimated is set up based on the trigonometric identity relation between the sampled point that N frequency carrier wave frequency domain sampled value is corresponding on sinc function curve, solve a linear equation and obtain estimating carrier frequencies formula, according to N frequency carrier wave frequency domain sampled value and estimating carrier frequencies formula estimating carrier frequency.

2. be applicable to the carrier frequency estimating method of GNSS receiver as claimed in claim 1, it is characterized in that:

Described N frequency carrier wave frequency domain sampled value obtains by correlator, fourier transform method (FT) or fast fourier transform method (FFT).

3. be applicable to the estimating carrier frequencies system of GNSS receiver, it is characterized in that, comprising:

Code stripper, is used for peeling off a yard information from satellite intermediate frequency signal;

Multifrequency point carrier wave frequency domain sampling system, be used for sampling at frequency domain to the carrier signal that code stripper exports, to obtain the N frequency carrier wave frequency domain sampled value with equifrequent interval, between described N frequency carrier wave frequency domain sampled value and carrier frequency, meet sinc function characteristic;

Frequency Estimation system, trigonometric identity relation between being used for based on the sampled point corresponding on sinc function curve of N frequency carrier wave frequency domain sampled value sets up a linear equation between carrier wave frequency domain sampled value and carrier frequency to be estimated, solve a linear equation and obtain estimating carrier frequencies formula, according to N frequency carrier wave frequency domain sampled value and estimating carrier frequencies formula estimating carrier frequency.

4. be applicable to the estimating carrier frequencies system of GNSS receiver as claimed in claim 3, it is characterized in that:

Described multifrequency point carrier wave frequency domain sampling system comprises N road parallel correlator.

5. be applicable to the estimating carrier frequencies system of GNSS receiver as claimed in claim 3, it is characterized in that:

Described multifrequency point carrier wave frequency domain sampling system comprises chronotron and the Fourier transform module of the serial of N road, and the chronotron of N road serial all connects Fourier transform module.

6. be applicable to the estimating carrier frequencies system of GNSS receiver as claimed in claim 3, it is characterized in that:

Described Frequency Estimation system comprises the parallel delivery module in N road, and the delivery module that N road walks abreast all connects frequency discriminator.

7. be applicable to the carrier phase estimation method of GNSS receiver, it is characterized in that:

The N frequency carrier wave frequency domain sampled value with equifrequent interval obtained according to claim 1 and estimating carrier frequencies value estimate carrier phase.

8. be applicable to the carrier phase estimation method of GNSS receiver as claimed in claim 7, it is characterized in that:

The described N frequency carrier wave frequency domain sampled value with equifrequent interval that obtains according to claim 1 and estimating carrier frequencies value estimate carrier phase, are specially:

According to the estimating carrier frequencies value that the frequency interval between N frequency carrier wave frequency domain sampled value and claim 1 obtain, arctan function is adopted to carry out phase demodulation, to obtain carrier phase estimated value to N frequency carrier wave frequency domain sampled value.

9. be applicable to the carrier phase estimating system of GNSS receiver, it is characterized in that, comprising:

Code stripper, is used for peeling off a yard information from satellite intermediate frequency signal;

Multifrequency point carrier wave frequency domain sampling system, be used for sampling at frequency domain to the carrier signal that code stripper exports, to obtain the N frequency carrier wave frequency domain sampled value with equifrequent interval, between described N frequency carrier wave frequency domain sampled value and carrier frequency, meet sinc function characteristic;

Frequency Estimation system, trigonometric identity relation between being used for based on the sampled point corresponding on sinc function curve of N frequency carrier wave frequency domain sampled value sets up a linear equation between carrier wave frequency domain sampled value and carrier frequency to be estimated, solve a linear equation and obtain estimating carrier frequencies formula, according to N frequency carrier wave frequency domain sampled value and estimating carrier frequencies formula estimating carrier frequency;

Phase estimating device, is used for carrying out carrier phase estimation according to the estimating carrier frequencies value that N frequency carrier wave frequency domain sampled value and the Frequency Estimation system of the output of multifrequency point carrier wave frequency domain sampling system export.