Summary of the invention
In order to solve the problems, such as that ZFFT exists, feedback function is had based on Chirp_z transformation the invention proposes a kind of
High-efficiency high-accuracy spectrum estimation and energy state postulate, in the big probable value of the frequency and bandwidth of knowing signal can quickly, it is high
Precision estimates signal frequency and signal energy, and consumption resource is less, since this method has feedback function, estimation
Precision is higher, and can track to the frequency of signal.
Be utilized in the present invention Chirp_z transformation, Chirp-z transformation be Lawrence Rabiner in 1975 to voice
Put forward when signal is analyzed, it the unit circle of z-plane can be become a helix gradually from unit origin to
In unit circle.Signal spectrum analysis can be realized on the helix on z-plane, may begin at any point, end at another
Arbitrary point.Therefore can to signal energy concentrate frequency band in spectral sample it is intensive, and sampled in other frequency bands it is sparse, and
The direct calculation method for carrying out Chirp_z transformation is converted into convolution form by the derivation of equation, so as to be carried out using FFT,
Greatly reduce calculation amount to achieve the purpose that further save resource, improve calculating speed.
Shown in the total formula such as formula (1) of Chirp_z transformation:
Wherein
A0Indicate the radius length of starting sample point, usual A0≤1;
θ0Indicate starting sample point Z0Phase angle, θ0=2 π f1/fs, wherein f1=fc- B/2 is the initial frequency point of refinement, fsFor
Signal sampling frequencies;
Indicate the sub-multiple angle between two consecutive pointsWherein f2=fc+B/2
For the end frequency point of refinement.
Due toIt can be transformed toWhereinTherefore Chirp_z transformation can be divided into the following steps realization:
1. selecting integer L one the smallest, it is set to meet L >=N+M-1, while meeting L=2m, wherein M is the point of refinement
Number;
2. the sequence for being N by length0 or arbitrary value are mended, is mended in present example(N≤n≤L-1) makes sequence length become L, therefore g (n) are as follows:
And the L point DFT of this sequence is sought using FFT method,
3. h (n) is asked according to formula,
The L point DFT of h (n) is sought with FFT method,
4. H (r) is multiplied with G (r), Q (r)=H (r) G (r) is obtained, Q (r) is L point frequency domain discrete series;
5. seeking the L point IDFT of Q (r) with FFT method, the circular convolution of h (n) He g (n) are obtained
In formula, preceding M value is equal to the linear convolution result [h (n) g (n)] of h (n) and g (n);
6. finally obtaining the transformed result X (z of Chirp_zk):
The technical solution of the present invention is as follows:
A kind of Frequency Estimation and energy state postulate with feedback function, which comprises the following steps:
A. input signal information is obtained, signal intermediate frequency f is included at least0With signal bandwidth B;Flag bit i is set simultaneously, and just
Beginningization i=0;
B. according to the signal intermediate frequency f of acquisition0The Chirp_z that refinement points are M is carried out to signal with signal bandwidth B to convert,
Flag bit adds 1 simultaneously;
C. the peak value Y of frequency spectrum is obtained according to the transformed result of Chirp_zmaxAnd the points V at peak value, and by as follows
Formula is updated signal intermediate frequency:
f0=f0-B/2+(V-1)·B/(M-1) (7)
That counts V at peak value Y and peak value asks method as follows:
(i) result X (Z transformed to Chirp_zK) every bit seek amplitude, due to X (Zk)=ak+bkI, 0≤k
≤M-1(ak,bkFor arbitrary constant, i is imaginary unit), therefore can be according to formulaTo seek amplitude;
(ii) enables Ymax=Y1, V=1, m=1, wherein m is digit;
(iii) judges whether m≤M is true, executes step (iiii) if setting up, if invalid end loop, exports peak
Count V at value Y and peak value;
(iiii) enables m=m+1 judge YmaxWith YmSize, if YmIt is big then enable Ymax=Ym, otherwise V=m returns to step
(iii);
D. judgement symbol position i >=it is 2 whether true, if so, calculating the energy Y of signal by following formulaenergy:
Yenergy=Ymax·ts (8)
Wherein ts=1/fs,fsFor the sample frequency of signal, f is exported0And YenergyReturn to step b;
If it is not, then entering step e;
E. level value is averaging to the result that Chirp_z in step b is converted and obtains the average level Z of noise;
F. according to the characteristic of the spectrum curve of FFT transform, it is assumed that
Ymax=Asinc (0) (9)
It enables
A (sinc (0)-sinc (x))=Z (10)
Wherein sinc (x)=sin (pi*x)/(pi*x) is sinc function, and pi is pi, and x is known variables, and A is normal
The value of number A can be found out by formula (9);
X can be found out according to formula (10) according to the A found out in the average level Z and (9) formula obtained in step e, according to public affairs
Formula (11) obtains frequency resolution S:
S=xB/ (M-1) (11)
New bandwidth, which is found out, further according to formula (12) replaces original signal bandwidth B:
B=S (M-1) (12)
Return to step b.
Beneficial effects of the present invention are that the method for the present invention is converted using Chirp_z, frequency in the frequency band concentrated to signal energy
Spectrum sampling is intensive, and sparse, to use in this way when reaching identical resolution ratio with common FFT resource is sampled in other frequency bands
Less;And the direct calculation method for carrying out Chirp_z transformation is converted to so as to use by convolution form by the derivation of equation
FFT is carried out, and greatly reduces calculation amount to achieve the purpose that further save resource, improve calculating speed;Make this hair in this way
Bright method is more efficient;The method of the present invention roughly estimates f using the mode fed back, the transformation of first time Chirp_z0It obtains new
Resolution ratio and bandwidth obtain new f according to obtained second of transformation of parameter progress is converted for the first time0And energy, with newly obtaining
F0Replace original f0, and in order to achieve the purpose that tracking the step will recycle down always, improve in this way Frequency Estimation and
The precision of energy estimation;And it can be to f0It is tracked;Therefore, the frequency of high-efficiency high-accuracy may be implemented in method of the invention
Estimate with energy.
Specific embodiment
With reference to the accompanying drawings and examples, the technical schemes of the invention are described in detail:
Since the method for the present invention can be applied in beacon detection, below by a method of the present invention in beacon detection
The example of application the specific implementation process of this method is illustrated.
Assuming that the expression formula of the beacon signal of input is x (n)=cos (2pifcT), signal intermediate frequency fc=
5.7MHz, bandwidth B=200KHz, sample frequency fs=200K, then satellite beacon receive process are as follows:
1) the step of x (n) being sampled, converted according to Chirp_z according to sample frequency carries out the signal after sampling
Chirp_z transformation, refinement points M=126;
2) peak value Ymax=1007.8 is obtained according to transformed result, at the 64th point, new f is obtained according to formula (7)0
For 5.7008MHz;
3) finding out noise average level is Z=95.9597;
4) obtaining x according to formula (9), formula (10) and formula (11) is 0.2442, and new resolution ratio S is 0.3907KHz;
New bandwidth B=48.8375 are obtained according to formula (12);
5) according to B and f0Chirp_z transformation is carried out to x (n), obtains new peak value Ymax=1029.3 at the 63rd point;
6) mould for calculating Y calculates the energy Yenergy=5.7181e-005 of signal further according to formula (8), by formula
(7) signal intermediate frequency f is obtained0=5.70006MHz exports Yenergy and f0;
5) and 6) 7) repeat.
The present invention, which essentially consists in, is applied to Chirp_z transformation in Frequency Estimation and energy estimation and in the process of estimation
In used feedback, to reach higher precision and frequency-tracking.