CN102508265B - Signal separation estimation theory-based satellite navigation signal multipath interference suppression method - Google Patents

Abstract

The invention discloses a signal separation estimation theory-based satellite navigation signal multipath interference suppression method, which mainly relates to a time delay estimation algorithm and a frequency estimation algorithm of a diameter signal and a multipath signal of a satellite navigation system. The method comprises the following steps of: estimating a satellite signal frequency which includes Doppler under the condition that a time delay is unknown, eliminating a fuzzy frequency according to the intermediate frequency value of the satellite signal and prior information in which a Doppler frequency shift range is known, and estimating the time delays of the diameter signal and the multipath signal respectively by using the signal separation estimation theory. By the signal separation estimation theory-based satellite navigation signal multipath interference suppression method, the time delay information and the frequency information of the diameter signal can be directly estimated and the aim of eliminating multipath signal influence can be fulfilled in a multipath environment.

Description

The satellite navigation signals multipath disturbance restraining method that separates estimation theory based on signal

Technical field

The invention belongs to satellite navigation positioning technical field, particularly relate to a kind of satellite navigation signals multipath disturbance restraining method that separates estimation theory based on signal.

Background technology

Since the satellite navigation positioning system occurs, obtained using very widely in every field, and become indispensable important foundation instrument in modern society's production, the life.Most of errors in the satellite navigation system all can be by complete or most of elimination the based on the differential technique of error relative theory in the certain limit, such as satellite ephemeris error and clocking error, ionosphere and tropospheric delay error etc.In actual measurement, receiver antenna also can receive the signal that other object reflects except receiving direct signal from satellite direction.Because diameter signal is different from the multipath signal path, thereby make the signal that receives produce distortion, the result causes occurring measuring error, forms multipath effect.

Although differential technique has greatly improved the bearing accuracy of navigational system, but because relevant position is not identical between reference station and user residing geographical environment position and satellite and receiver, therefore multipath signal amplitude, direction, quantity are not identical yet, the caused positioning error of satellite-signal multipath so differential system still can not be eliminated.

Cause that for multipath transmisstion the problem of error appears in the measurement of wireless signal time parameter, scholar both domestic and external is seeking the method that can effectively address this problem always, and present solution mainly is divided into based on the method for antenna and method two classes processed based on signal and data.

Wherein mainly comprise based on the method for antenna and adopt the specific type antenna, draw around the antenna multi-path environment figure and select the measures such as suitable place erects a television antenna.Can suppress multi-path influence from ground by Antenna Design, but the multipath signal from the antenna top is difficult to be suppressed by Antenna Design.

Signal and data processing technique method the most commonly used is to adopt the narrow correlation technology.The narrow correlation technology is the effective means a kind of commonly used that suppresses at present multipath and improve tracking accuracy, and correlator interval reduces the impact that multipath is followed the tracks of code phase by reducing sooner or later for it.In the narrow correlation algorithm, the correlator interval is less, can cause that the scope of multidiameter of multipath tracking error is just less.But narrow correlation technology hypothesis receiver signal passage is infinite bandwidth, and this condition can't be met in practice.The people such as Richard D.J. are verified, and when related interval during less than the bilateral bandwidth of passage equivalence reciprocal, the tracking error of delay lock loop will be tending towards a constant, can not reduce tracking error by the method that further reduces related interval.

Summary of the invention

In order to address the above problem, the object of the present invention is to provide that a kind of error is little, precision is high and treatment step simply separates the satellite navigation signals multipath disturbance restraining method of estimation theory based on signal.

In order to achieve the above object, the satellite navigation signals multipath disturbance restraining method that separates estimation theory based on signal provided by the invention comprises the following step that carries out in order:

(1) radiofrequency signal that satellite antenna is received down-converts to intermediate-freuqncy signal;

(2) analog if signal that above-mentioned down coversion is obtained carries out the A/D conversion, and is stored as digital medium-frequency signal;

(3) the unknown delay time signal that contains multipath that receives is carried out a square processing, to obtain satellite-signal actual frequency estimated value and corresponding fuzzy frequency estimation;

(4) remove the fuzzy frequency that obtains in step (3) estimation procedure, to obtain the satellite frequency estimated value;

(5) utilize the satellite frequency estimated value that obtains, according to separating the time delay that estimation theory estimates satellite-signal based on signal.

Down-convert to the intermediate-freuqncy signal operation in the described step (1) and adopt down conversion module to finish, down conversion module mainly is comprised of low noise radio frequency amplifier, frequency mixer and automatic gain control circuit.

The satellite navigation signals multipath disturbance restraining method based on signal separation estimation theory that the present invention proposes is in the situation of time delay the unknown, estimates first the frequency values of signal and the fuzzy frequency values of its correspondence; Then remove fuzzy frequency according to satellite-signal intermediate frequency and the known prior imformation of Doppler shift scope; Recycling is estimated to obtain frequency as known conditions, separates estimation theory by signal and estimates the time delay of diameter signal, thereby reach the purpose of erasure signal multi-path influence.This method has that error is little, precision is high and the advantage such as treatment step is simple.

Description of drawings

Fig. 1 is the satellite navigation signals multipath disturbance restraining method process flow diagram that separates estimation theory based on signal provided by the invention.

Fig. 2 is that the time delay evaluated error is with the signal to noise ratio (S/N ratio) change curve.

Fig. 3 is that estimated frequency error is with the signal to noise ratio (S/N ratio) change curve.

Fig. 4 is that the time delay evaluated error is with the change curve in relative time delay.

Embodiment

With specific embodiment the satellite navigation signals multipath disturbance restraining method that separates estimation theory based on signal provided by the invention is elaborated with reference to the accompanying drawings.

For the multipath performance evaluation that makes things convenient for satellite navigation signals and be without loss of generality, adopt the analytical model of single reflection path in the present embodiment.When having the multipath reflection path, method of the present invention is applicable equally.

As shown in Figure 1, the satellite navigation signals multipath disturbance restraining method based on signal separation estimation theory provided by the invention comprises the following step that carries out in order:

(1) radiofrequency signal that satellite antenna is received down-converts to intermediate-freuqncy signal;

The radiofrequency signal that satellite antenna is received is down-converted to intermediate-freuqncy signal by the down conversion module that is comprised of low noise radio frequency amplifier, frequency mixer and automatic gain control circuit etc., so that subsequent treatment.

(2) analog if signal that above-mentioned down coversion is obtained carries out the A/D conversion, and is stored as digital medium-frequency signal;

The model of signal can be expressed as:

$y\left(n\right)=\underset{p=1}{\overset{2}{\mathrm{\Σ}}}{\mathrm{\α}}_p{d}_p(n-{\mathrm{\τ}}_p)c(n-{\mathrm{\τ}}_p)e^{{\mathrm{j\ω}}_{\mathrm{dp}}(n-{\mathrm{\τ}}_p)}+e\left(n\right)---\left(1\right)$

Wherein, d (n) represents navigation message, is the C/A code of ± 1, c (n) expression satellite-signal in satellite navigation system, e (n) expression receiver thermonoise, α ₁, τ ₁, ω _D1The amplitude that represents respectively diameter signal, time delay and frequency.α ₂, τ ₂, ω _D2The amplitude that represents respectively multipath signal, time delay and frequency.In satellite navigation system, when multipath signal postpones greater than two chips, the error of generation on pseudo range measurement impact can ignore so our situation when only studying multipath less than two chips.Under this condition, the navigation message of diameter signal and multipath signal can be thought identical.Because receiver and reflecting surface close together, we can think that again receiver and reflecting surface are identical with respect to the motion of satellite, can think that namely direct signal and multipath signal Doppler shift equate that namely formula (1) can be reduced to:

$y\left(n\right)=\underset{p=1}{\overset{2}{\mathrm{\Σ}}}{\mathrm{\α}}_p{d}_p(n-{\mathrm{\τ}}_p)c(n-{\mathrm{\τ}}_p)e^{{\mathrm{j\ω}}_d(n-{\mathrm{\τ}}_p)}+e\left(n\right)---\left(2\right)$

(3) the unknown delay time signal that contains multipath that receives is carried out a square processing, to obtain satellite-signal actual frequency estimated value and corresponding fuzzy frequency estimation;

Formula (2) is carried out a square processing, can obtain:

$y^2\left(n\right)={\mathrm{\&alpha;}}_1^2{d}^2(n-{\mathrm{\&tau;}}_1)c^2(n-{\mathrm{\&tau;}}_1){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">e</figure-callout>}}^j+{\mathrm{\&alpha;}}_2^2{d}^2(n-{\mathrm{\&tau;}}_2)c^2(n-{\mathrm{\&tau;}}_2){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">e</figure-callout>}}^j$

$+2{\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_{2}d(n-{\mathrm{\&tau;}}_1)d(n-{\mathrm{\&tau;}}_2)c(n-{\mathrm{\&tau;}}_1)c(n-{\mathrm{\&tau;}}_2)e^{-j{\mathrm{\&omega;}}_d(2n-{\mathrm{\&tau;}}_1-{\mathrm{\&tau;}}_2)}$

$+2{\mathrm{\&alpha;}}_{1}d(n-{\mathrm{\&tau;}}_1)c(n-{\mathrm{\&tau;}}_1)e^{-j{\mathrm{\&omega;}}_d(n-{\mathrm{\&tau;}}_1)}e\left(n\right)+2{\mathrm{\&alpha;}}_{2}d(n-{\mathrm{\&tau;}}_2)c(n-{\mathrm{\&tau;}}_2)e^{-j{\mathrm{\&omega;}}_d(n-{\mathrm{\&tau;}}_2)}e\left(n\right)+e^2\left(n\right)$

$=\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_p^2{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">e</figure-callout>}}^j+e_1\left(n\right)---\left(3\right)$

Wherein, $e_1\left(n\right)=2{\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_{2}d(n-{\mathrm{\&tau;}}_1)d(n-{\mathrm{\&tau;}}_2)c(n-{\mathrm{\&tau;}}_1)c(n-{\mathrm{\&tau;}}_2)e^{-j{\mathrm{\&omega;}}_d(2n-{\mathrm{\&tau;}}_1-{\mathrm{\&tau;}}_2)}$

$+2{\mathrm{\&alpha;}}_{1}d(n-{\mathrm{\&tau;}}_1)c(n-{\mathrm{\&tau;}}_1)e^{-j{\mathrm{\&omega;}}_d(n-{\mathrm{\&tau;}}_1)}e\left(n\right)+2{\mathrm{\&alpha;}}_{2}d(n-{\mathrm{\&tau;}}_2)c(n-{\mathrm{\&tau;}}_2)e^{-j{\mathrm{\&omega;}}_d(n-{\mathrm{\&tau;}}_2)}e\left(n\right)+e^2\left(n\right)$

Because related coefficient is very not little simultaneously in time delay for the C/A code of same satellite-signal, signal and noise are incoherent, so the product term of the middle different delay satellite-signal C/A code of formula (3) and the Fourier analysis result of noise and signal times product term are close to zero.Therefore, frequency estimation

FFT that can through type (3) obtains:

${\widehat{\mathrm{\&omega;}}}_d=\arg \underset{{\mathrm{\&omega;}}_d}{\max }\frac{1}{N}{\left|\underset{n=-N/2}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{y}^2\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">j</figure-callout>}2{\mathrm{\&omega;}}_{d}n}\right|}^2---\left(4\right)$

(4) remove the fuzzy frequency that obtains in step (3) estimation procedure, to obtain the satellite frequency estimated value; Because the frequency range that calculates of FFT is between [0,2 π], thereby

The estimated value scope is between [0, π].Yet ω _dActual value between [0,2 π], this is just so that ω _dTrue estimated value may for

Perhaps

One in two frequencies is real frequency estimation, and another then is corresponding fuzzy frequency estimation.Therefore in the Frequency Estimation process, the frequency ambiguity problem of existence can cause miscount.Because the intermediate frequency after the satellite navigation signals down coversion is known, and the Doppler shift scope is generally ± 10kHz, therefore frequency error between actual frequency and the fuzzy frequency can utilize whether remove fuzzy frequency as criterion within the Doppler shift scope generally all greater than Doppler shift.

(5) utilize the satellite frequency estimated value that obtains, according to separating the time delay that estimation theory estimates satellite-signal based on signal.

Order $s\left(n\right)=d\left(n\right)c\left(n\right)e^{j{\mathrm{\&omega;}}_{d}n},$ Then formula (2) can be written as following form:

$y\left(n\right)=\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{p}s(n-{\mathrm{\&tau;}}_p)+e\left(n\right)---\left(5\right)$

Because satellite frequency estimated value

Obtain, utilize

Replace ω _dThen

$\hat{s}\left(n\right)=d\left(n\right)c\left(n\right)e^{j{\widehat{\mathrm{\&omega;}}}_{d}n}---\left(6\right)$

Formula (5) can further be rewritten as:

$y\left(n\right)=\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_p\hat{s}(n-{\mathrm{\&tau;}}_p)+e_2\left(n\right)---\left(7\right)$

Wherein, $e_2\left(n\right)=\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{p}s(n-{\mathrm{\&tau;}}_p)-\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_p\hat{s}(n-{\mathrm{\&tau;}}_p)+e\left(n\right)$

Formula (7) is carried out discrete Fourier transformation can be obtained:

$Y\left(k\right)=\hat{S}\left(k\right)\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_p{e}^{j{\mathrm{\&omega;}}_{p}k}+E_2\left(k\right)---\left(8\right)$

Y (k) wherein,

E ₂(k) be respectively y (n),

And e ₂(n) discrete Fourier transformation, ω _p=-2 π τ _pf _s/ N, f _sThe expression sampling rate.

Time delay and amplitude estimation value

With Can minimize to obtain by following non-linear least square cost function:

$Q\left({\{{\widehat{\mathrm{\&alpha;}}}_p,{\widehat{\mathrm{\&omega;}}}_p\}}_{p=1}^2\right)=\underset{k=-N/2}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{|Y\left(k\right)-\hat{S}\left(k\right)\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_p{e}^{j{\mathrm{\&omega;}}_{p}k}|}^2---\left(9\right)$

Order $a\left({\mathrm{\&omega;}}_p\right)={[e^{j{\mathrm{\&omega;}}_p(-N/2)},e^{j{\mathrm{\&omega;}}_p(-N/2+1)},...,e^{j{\mathrm{\&omega;}}_p(N/2-1)}]}^T$

Y＝[Y(-N/2)，Y(-N/2+1)，...，Y(N/2-1)] ^T， $\hat{S}=\mathrm{diag}\{\hat{S}(-N/2),\hat{S}(-N/2+1),...,\hat{S}(N/2-1)\}$

Formula (9) minimizes to be equivalent to following cost function is minimized so

$Q\left({\{{\widehat{\mathrm{\&alpha;}}}_p,{\widehat{\mathrm{\&omega;}}}_p\}}_{p=1}^2\right)={\left|\right|Y-\underset{p=1}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_p\hat{S}a\left({\mathrm{\&omega;}}_p\right)\left|\right|}^2---\left(10\right)$

Suppose ${\{{\widehat{\mathrm{\&alpha;}}}_q,{\widehat{\mathrm{\&omega;}}}_q\}}_{q=1,q\&NotEqual;\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">p</figure-callout>}}^2$ Known or estimated, then

$Y_p=Y-\underset{\underset{q\&NotEqual;\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">p</figure-callout>}}{q=1}}{\overset{2}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_q\left[\hat{S}a\left({\mathrm{\&omega;}}_q\right)\right]---\left(11\right)$

Following formula substitution formula (10) can be obtained:

$Q_1({\mathrm{\&alpha;}}_p,{\mathrm{\&omega;}}_p)={\left|\right|Y_p-{\mathrm{\&alpha;}}_p\hat{S}a\left({\mathrm{\&omega;}}_p\right)\left|\right|}^2---\left(12\right)$

To α _pAnd ω _pAsk to minimize, obtain respectively its estimated value and be

${\widehat{\mathrm{\&omega;}}}_p=\arg \underset{{\mathrm{\&omega;}}_p}{\max }{|a^H\left({\mathrm{\&omega;}}_p\right)\hat{S}*Y_p|}^2---\left(13\right)$

${\widehat{\mathrm{\&alpha;}}}_p=\frac{a^H\left({\mathrm{\&omega;}}_p\right)(\hat{S}*Y_p)}{{\left|\right|\hat{S}\left|\right|}_{\mathrm{<figure-callout\; id="2"\; label="F"\; filenames="HDA0000101890630000013.png"\; state="\{\{state\}\}">F</figure-callout>}}^2}{|}_{{\mathrm{\&omega;}}_p={\widehat{\mathrm{\&omega;}}}_p}---\left(14\right)$

${\{{\widehat{\mathrm{\&alpha;}}}_p,{\widehat{\mathrm{\&omega;}}}_p\}}_{p=1}^2$ Estimation procedure can realize by following two steps:

1) only there is diameter signal in hypothesis first, utilizes Y to estimate according to formula (13), (14)

2) usefulness obtains

Calculate Y according to formula (11) ₂, use again Y ₂Estimate

Then utilize

Reappraise Y ₁, then use Y ₁Estimate again

Convergence repeats above process until can be tried to achieve final

Emulation generates in the present embodiment satellite-signal and multipath signal frequency all are made as 1.25MHz, and sampling rate is 5MHz, and preliminary examination integral time is 1ms, DLL loop noise bandwidth 2Hz.

It is 700ns that Fig. 2 and Fig. 3 have provided respectively the extra time delay τ of multipath signal relative diameter signal, when narrow correlation device related interval d was 0.1 chip commonly using, the statistics root mean square of diameter signal time delay and frequency error was with the change curve of signal to noise ratio (S/N ratio) under the distinct methods.As can be seen from the figure along with the raising of signal to noise ratio (S/N ratio), three kinds of method time delays and frequency error all present and reduce trend.The result shows among Fig. 2, and conventional algorithm time delay evaluated error is larger, can not suppress well multipath, and narrow correlation algorithm and algorithm of the present invention can suppress multipath effectively to be disturbed, and Algorithm Error of the present invention is less than the narrow correlation algorithm.The estimated frequency error value of the presentation of results algorithm of the present invention that provides among Fig. 3 also is better than other algorithm.

Fig. 4 has provided at SNR, in the situation of the different extra time delays of multipath signal relative diameter signal, uses the time delay evaluated error of algorithm of the present invention and narrow correlation algorithm, conventional algorithm relatively.Along with related interval reduces, multipath error presents and reduces trend.When the bilateral bandwidth of equivalence was 10 times of code checks, related interval was less than 0.1 chip, and tracking error will be tending towards a constant, can not further improve performance by the method that reduces related interval.When 0.1chip＜τ＜1chip, the inventive method is better than the narrow correlation algorithm.

Claims (2)

1. one kind is separated the satellite navigation signals multipath disturbance restraining method of estimation theory based on signal, and it is characterized in that: described satellite navigation signals multipath disturbance restraining method comprises the following step that carries out in order:

(1) radiofrequency signal that satellite antenna is received down-converts to intermediate-freuqncy signal;

(2) analog if signal that above-mentioned down coversion is obtained carries out the A/D conversion, and is stored as digital medium-frequency signal;

(3) the unknown delay time signal that contains the multipath interference that receives is carried out a square processing, to obtain satellite-signal actual frequency estimated value and corresponding fuzzy frequency estimation;

(4) according to the intermediate frequency after the satellite navigation signals down coversion and the known prior imformation of Doppler shift scope, remove the fuzzy frequency that obtains in step (3) estimation procedure, to obtain the satellite frequency estimated value;

(5) utilize the satellite frequency estimated value that obtains, separate the time delay that estimation theory estimates satellite-signal according to signal; In this step, utilize and estimated the signal frequency estimated value that obtains in the step (4)

Simplify and obtain following signal model:

Wherein,

α ₁And τ ₁The amplitude and the time delay that represent respectively diameter signal, α ₂And τ ₂The amplitude and the time delay that represent respectively multipath signal, d (n) represents navigation message, the C/A code of c (n) expression satellite-signal, e (n) expression receiver thermonoise;

Following formula is carried out discrete Fourier transformation can be obtained:

Y (k) wherein, E ₂(k) be respectively y (n),

And e ₂(n) discrete Fourier transformation, ω _p=-2 π τ _pf _s/ N, f _sThe expression sampling rate;

Time delay and amplitude estimation value

With

Can minimize to obtain by following non-linear least square cost function:

Wherein,

Y＝[Y(-N/2)，Y(-N/2+1)，...，Y(N/2-1)] ^T，?

Suppose

Known or estimated, then

Following formula substitution formula (10) can be obtained:

To α _pAnd ω _pAsk to minimize, obtain respectively its estimated value and be

Estimation procedure can realize by following two steps:

1) only there is diameter signal in hypothesis first, utilizes Y to estimate according to formula (13), (14)

2) usefulness obtains

Calculate Y according to formula (11) ₂, use again Y ₂Estimate

Then utilize

Reappraise Y ₁, then use Y ₁Estimate again Convergence repeats above process until can be tried to achieve final

2. the satellite navigation signals multipath disturbance restraining method that separates estimation theory based on signal according to claim 1, it is characterized in that: the operation that down-converts to intermediate-freuqncy signal described in the step (1) adopts down conversion module to finish, and down conversion module mainly is comprised of low noise radio frequency amplifier, frequency mixer and automatic gain control circuit.

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