CN104880721A - Orthogonal decomposition method of satellite navigation anti-interference antenna digital signal - Google Patents

Abstract

The invention provides an orthogonal decomposition method of a satellite navigation anti-interference antenna digital signal. According to a normalized frequency point and an expected amplitude response vector, a K-order filter coefficient even symmetry FIR filter and a K-order filter coefficient odd symmetry FIR filter are designed by adopting a Parks-McClellan algorithm. A satellite navigation anti-interference antenna intermediate-frequency real digital signal is transmitted to the even symmetry FIR filter and odd symmetry FIR filter at the same time. The even symmetry FIR filter outputs an I-path signal same as the input digital signal, and the odd symmetry FIR filter outputs a Q-path signal orthogonal to the input digital signal. Compared with an orthogonal decomposition method based on the Fourier transform, the method is small in calculated amount, and is more suitable for orthogonal decomposition of the real digital signal after AD sampling of processing the satellite navigation anti-interference antenna signal.

Description

A kind of anti-interference antenna of satellite navigation digital signal Orthogonal Decomposition method

Technical field

The invention belongs to the anti-interference field of satellite navigation, is a kind of algorithm realizing anti-interference antenna of satellite navigation digital intermediate frequency signal Orthogonal Decomposition.

Background technology

In the signal processing of anti-interference antenna of satellite navigation, the first step that Orthogonal Decomposition is digital signal processing is carried out to the digital real signal after AD sampling.The amplitude of I, Q two ways of digital signals that digital signal Orthogonal Decomposition obtains and the balance of phase place affect anti-interference antenna of satellite navigation to one of key factor of interference rejection capability.Therefore, in order to complete the suppression to satellite navigation undesired signal better, prerequisite is a kind of digital signal Orthogonal Decomposition method that better can keep the Amplitude balance and phase balance of I, Q two ways of digital signals of design.

At present, have the main method that real signal carries out digital quadrature decomposition: the digital quadrature decomposition method based on Fourier transform, the digital quadrature decomposition method based on Hilbert transform, the digital quadrature decomposition method carried out with specific sample mode and the digital quadrature decomposition method utilizing digital mixing to carry out.Digital quadrature decomposition method based on Fourier transform utilizes the decomposition that twice Fourier transform completes I, Q road, can obtain ideal mirror image inhibition, but calculated amount is larger.Calculated amount based on the digital quadrature decomposition method of Hilbert transform is less, but owing to being limited wordlength to input signal sampling number, the unbalancedness on I, Q road obtained after causing it to decompose is larger.The digital quadrature decomposition method Project Realization of carrying out with specific sample mode is for convenience, better to the discomposing effect of narrow band signal, but for broadband signal, the unbalancedness on its I, Q road obtained after decomposing is larger.The sampling rate of the digital quadrature decomposition method utilizing digital mixing to carry out is not by the restriction of signal frequency, for narrow band signal, the digital quadrature decomposition method that its ratio of precision is carried out with specific sample mode is high, but the unbalancedness on I, Q road that it obtains after decomposing is still larger for broadband signal.

Suppress interfere signal for satellite navigation signals is generally the broadband signal covering whole satellite navigation signals frequency band range.Usually I, Q road adopting the digital quadrature decomposition method based on Fourier transform to complete digital signal in anti-interference antenna of satellite navigation process is decomposed.But, because anti-interference antenna of satellite navigation comprises multiple passage, the operand of Fourier transform and inverse Fourier transform is carried out very greatly to multiple passage simultaneously, needs to expend multipliers a large amount of in digital signal processor and memory resource.

Summary of the invention

In order to overcome the deficiencies in the prior art, the invention provides a kind of anti-interference antenna of satellite navigation digital signal Orthogonal Decomposition method, employing even symmetry FIR filter and odd symmetry FIR filter complete the Orthogonal Decomposition to intermediate frequency real digital signal after analog to digital conversion, are applicable to the Orthogonal Decomposition process to broadband signal, calculated amount is little and is easy to Project Realization.

The technical solution adopted for the present invention to solve the technical problems comprises the following steps:

The normalized frequency point of the first step, calculating FIR filter, comprises passband first frequency point passband second frequency point stopband first frequency point with stopband second frequency point wherein, f ₀be the centre frequency of anti-interference antenna of satellite navigation intermediate frequency work, B is the bandwidth of anti-interference antenna of satellite navigation intermediate frequency work, F _sbe the sample frequency of analog to digital converter, D is the transition band width between passband and stopband;

Second step, the design FIR filter expectation amplitude response vector within the scope of normalized frequency

a＝[a ₀,a _stop1,a _pass1,a _pass2,a _stop2,a ₁]

Wherein, a ₀represent the expectation amplitude response value on normalized frequency point 0; a _stop1represent at normalized frequency point f _stop1on expectation amplitude response value; a _pass1represent at normalized frequency point f _pass1on expectation amplitude response value; a _pass2represent at normalized frequency point f _pass2on expectation amplitude response value; a _stop2represent at normalized frequency point f _stop2on expectation amplitude response value; a ₁represent the expectation amplitude response value on normalized frequency point 1;

A ₀, a _stop1, a _pass1, a _pass2, a _stop2and a ₁span between 0 ~ 1.

3rd step, according to normalized frequency point with expect amplitude response vector, adopt the filter factor even symmetry FIR filter on Parks-McClellan algorithm design K rank and filter factor odd symmetry wave filter, obtain even symmetry FIR filter coefficient vector b respectively _evenwith odd symmetry FIR filter coefficient vector b _odd; Anti-interference antenna of satellite navigation intermediate frequency real digital signal is sent into even symmetry FIR filter and odd symmetry FIR filter simultaneously, even symmetry FIR filter exports the I road signal with supplied with digital signal homophase, and odd symmetry FIR filter exports the Q road signal orthogonal with supplied with digital signal.

The invention has the beneficial effects as follows: after the 128 rank even symmetry FIR adopting the inventive method to realize and odd symmetry FIR filter carry out Orthogonal Decomposition to intermediate frequency real digital signal after analog to digital conversion, to the inhibition of image frequency, image rejection performance that 8192 FFT computings obtain is suitable with adopting fourier transform method to carry out.But what the inventive method needed answer, and to take advantage of and be added with computing be 254 times altogether, and it is 53248 times altogether that 8192 FFT computings then need to take advantage of and be added with computing again.In addition, Fourier transform digital signal Orthogonal Decomposition method adopts the Orthogonal Decomposition of block processing mode realization to each data block, but the signal phase continuity between data block cannot ensure, as long as and namely the inventive method realizes, to the Orthogonal Decomposition of input digital intermediate frequency real signal, can ensureing the phase continuity of output orthogonal digital signal by streamline form after even symmetry FIR filter and odd symmetry FIR filter coefficient being determined.Therefore, the inventive method is less than the digital quadrature decomposition method calculated amount based on Fourier transform, is more suitable for the digital real signal after to AD sampling in anti-interference antenna of satellite navigation signal transacting and carries out Orthogonal Decomposition.

Accompanying drawing explanation

Fig. 1 expects amplitude response vector and normalized frequency point correspondence schematic diagram;

Fig. 2 is anti-interference antenna of satellite navigation digital signal Orthogonal Decomposition process schematic;

Fig. 3 is that FIR filter expects amplitude response schematic diagram;

Fig. 4 is even symmetry FIR filter coefficient and odd symmetry FIR filter coefficient schematic diagram, and wherein, (a) is even symmetry FIR filter coefficient, and (b) is odd symmetry FIR filter coefficient;

Fig. 5 is even symmetry FIR filter and odd symmetry FIR filter amplitude response schematic diagram, and wherein, (a) is even symmetry FIR filter amplitude response, and (b) is odd symmetry FIR filter amplitude response;

Fig. 6 is even symmetry FIR filter and odd symmetry FIR filter phase response.

Embodiment

Below in conjunction with drawings and Examples, the present invention is further described, the present invention includes but be not limited only to following embodiment.

The design performing step of even symmetry FIR filter of the present invention and odd symmetry FIR filter is as follows:

The first step: according to the centre frequency f of anti-interference antenna of satellite navigation intermediate frequency work ₀, bandwidth B, analog to digital converter sample frequency F _sand the transition band width D (usually getting 2MHz ~ 4MHz) between passband and stopband calculates FIR filter normalized passband first frequency point f _pass1, passband second frequency point f _pass2, stopband first frequency point f _stop1with stopband second frequency point f _stop2, calculation expression is as follows:

$f_{\mathrm{pass}1}=\frac{{2f}_0-B}{F_s}---\left(1\right)$

$f_{\mathrm{pass}2}=\frac{{2f}_0+B}{F_s}---\left(2\right)$

$f_{\mathrm{stop}1}=\frac{2f_0-B-2D}{F_s}---\left(3\right)$

$f_{\mathrm{stop}2}=\frac{{2f}_0+B+2D}{F_s}---\left(4\right)$

Second step: the expectation amplitude response vector a of design FIR filter within the scope of normalized frequency, expression formula is as follows:

a＝[a ₀,a _stop1,a _pass1,a _pass2,a _stop2,a ₁] (5)

Wherein, a ₀represent the expectation amplitude response value on normalized frequency point 0; a _stop1represent at normalized frequency point f _stop1on expectation amplitude response value; a _pass1represent at normalized frequency point f _pass1on expectation amplitude response value; a _pass2represent at normalized frequency point f _pass2on expectation amplitude response value; a _stop2represent at normalized frequency point f _stop2on expectation amplitude response value; a ₁represent the expectation amplitude response value on normalized frequency point 1.A ₀, a _stop1, a _pass1, a _pass2, a _stop2and a ₁span between 0 ~ 1.Figure 1 shows that the corresponding relation expecting amplitude response vector and normalized frequency point.

3rd step: the expectation amplitude response vector that the normalized frequency point calculated according to the first step and second step design obtain, employing Parks-McClellan algorithm design exponent number is filter factor even symmetry FIR filter and the filter factor odd symmetry wave filter on K rank, obtains even symmetry FIR filter coefficient vector b respectively _evenwith odd symmetry FIR filter coefficient vector b _odd.

It is b that anti-interference antenna of satellite navigation intermediate frequency real digital signal is sent into filter factor simultaneously _evenand b _oddfIR filter, filter factor is b _evenfIR filter export and the I road signal of supplied with digital signal homophase, filter factor is b _oddfIR filter export the Q road signal orthogonal with supplied with digital signal.

Anti-interference antenna of satellite navigation digital signal Orthogonal Decomposition process as shown in Figure 2.If receiving antenna array is made up of N number of identical antenna element.Down-converted by N element antenna array received to radiofrequency signal change analog intermediate frequency signal into.Analog-to-digital conversion process sends into the isometric even symmetry FIR filter of exponent number and odd symmetry FIR filter respectively after analog intermediate frequency signal being converted to intermediate frequency real number digital signal.Even symmetry FIR filter exports the digital signal with in-real digital signal homophase, i.e. I road signal; Odd symmetry FIR filter exports the digital signal orthogonal with in-real digital signal, i.e. Q road signal.

The present invention is applicable to the Orthogonal Decomposition process of GPS, BDS and GLONASS anti-interference antenna of satellite navigation digital intermediate frequency signal.The specific embodiment of the present invention is set forth for the Orthogonal Decomposition of BDS B3 frequency anti-interference antenna digital intermediate frequency signal:

Step 1: by BD2B3 frequency anti-interference antenna intermediate frequency center frequency f ₀=15.52MHz, sampling rate F _s=62MHz, bandwidth of operation B=20MHz and designed FIR filter transition band width D=1MHz parameter substitute into formula (1), formula (2), formula (3) and formula (4) and calculate FIR filter normalized passband first frequency point f respectively _pass1, passband second frequency point f _pass2, stopband first frequency point f _stop1with stopband second frequency point f _stop2:

$f_{\mathrm{pass}1}=\frac{{2f}_0-B}{F_s}=\frac{2\×15.52\mathrm{MHz}-20\mathrm{MHz}}{62\mathrm{MHz}}=0.1781---\left(6\right)$

$f_{\mathrm{pass}2}=\frac{{2f}_0+B}{F_s}=\frac{2\×15.52\mathrm{MHz}+20\mathrm{MHz}}{62\mathrm{MHz}}=0.8232---\left(7\right)$

$f_{\mathrm{stop}1}=\frac{{2f}_0-B-2D}{F_s}=\frac{2\×15.52\mathrm{MHz}-20\mathrm{MHz}-2\×1\mathrm{MHz}}{62\mathrm{MHz}}=0.1458---\left(8\right)$

$f_{\mathrm{stop}2}=\frac{{2f}_0+B+2D}{F_s}=\frac{2\×15.52\mathrm{MHz}+20\mathrm{MHz}+2\×1\mathrm{MHz}}{62\mathrm{MHz}}=0.8555---\left(9\right)$

Step 2: the expectation amplitude response vector a of design FIR filter within the scope of normalized frequency:

a＝[a ₀,a _stop1,a _pass1,a _pass2,a _stop2,a ₁]＝[0,0,1,1,0,0] (10)

Obtain FIR filter and expect amplitude response as shown in Figure 3.

Step 3: the expectation amplitude response vector a that the normalized frequency point calculated according to step 1 and step 2 design obtain, employing Parks-McClellan algorithm design exponent number is even symmetry FIR filter and the odd symmetry wave filter on 16 rank (K=15).Specific implementation adopts the firpm function in Matlab software SignalProcessing tool box to obtain filter coefficient vector b _evenand b _odd:

b _even＝firpm(K,f,a) (11)

b _odd＝firpm(K,f,a,’hilbert’) (12)

Wherein, f=[0,0.1458,0.1781,0.8232,0.8555,1] is normalized frequency vector, and a=[0,0,1,1,0,0] is the expectation amplitude response vector corresponding with normalized frequency vector.The even symmetry FIR filter coefficient obtained and odd symmetry FIR filter coefficient are respectively as shown in Fig. 4 (a) He Fig. 4 (b).Designed even symmetry FIR filter and the amplitude response of odd symmetry FIR filter are respectively as shown in Fig. 5 (a) He Fig. 5 (b).Fig. 6 is set even symmetry FIR filter and the phase response of odd symmetry FIR filter, and wherein solid line is the phase response of even symmetry FIR filter, and dotted line is the phase response of odd symmetry FIR filter.

BD2B3 frequency anti-interference antenna of satellite navigation if sampling signal is sent into simultaneously the even symmetry FIR filter obtained by step 3 and odd symmetry FIR filter to carry out filtering process and can obtain outputing signal with the I road of input signal homophase and the Q road orthogonal with input signal outputs signal.So far, the Orthogonal Decomposition process to BD2B3 frequency anti-interference antenna of satellite navigation digital intermediate frequency signal is completed.

Claims (2)

1. an anti-interference antenna of satellite navigation digital signal Orthogonal Decomposition method, is characterized in that comprising the steps:

The normalized frequency point of the first step, calculating FIR filter, comprises passband first frequency point passband second frequency point stopband first frequency point with stopband second frequency point wherein, f ₀be the centre frequency of anti-interference antenna of satellite navigation intermediate frequency work, B is the bandwidth of anti-interference antenna of satellite navigation intermediate frequency work, F _sbe the sample frequency of analog to digital converter, D is the transition band width between passband and stopband;

Second step, the design FIR filter expectation amplitude response vector within the scope of normalized frequency

a＝[a ₀,a _stop1,a _pass1,a _pass2,a _stop2,a ₁]

Wherein, a ₀represent the expectation amplitude response value on normalized frequency point 0; a _stop1represent at normalized frequency point f _stop1on expectation amplitude response value; a _pass1represent at normalized frequency point f _pass1on expectation amplitude response value; a _pass2represent at normalized frequency point f _pass2on expectation amplitude response value; a _stop2represent at normalized frequency point f _stop2on expectation amplitude response value; a ₁represent the expectation amplitude response value on normalized frequency point 1;

3rd step, according to normalized frequency point with expect amplitude response vector, adopt the filter factor even symmetry FIR filter on Parks-McClellan algorithm design K rank and filter factor odd symmetry wave filter, obtain even symmetry FIR filter coefficient vector b respectively _evenwith odd symmetry FIR filter coefficient vector b _odd; Anti-interference antenna of satellite navigation intermediate frequency real digital signal is sent into even symmetry FIR filter and odd symmetry FIR filter simultaneously, even symmetry FIR filter exports the I road signal with supplied with digital signal homophase, and odd symmetry FIR filter exports the Q road signal orthogonal with supplied with digital signal.

2. anti-interference antenna of satellite navigation digital signal Orthogonal Decomposition method according to claim 1, is characterized in that: a ₀, a _stop1, a _pass1, a _pass2, a _stop2and a ₁span between 0 ~ 1.