CN105182376A - GNSS signal mixer-free parallel code phase capturing method - Google Patents

Abstract

The invention discloses a GNSS signal mixer-free parallel code phase capturing method. The method conducts FFT on signals received at N points, the transformed sequence is recorded as y1<right arrow>, and N is a power of 2. The method then conducts FFT of local code signals at N points, obtains a conjugated sequence of the transformed sequence and records the obtained sequence as y2<right arrow>. The method rotates the y2<right arrow> right for m bit positions, multiplies the y2<right arrow> with corresponding points of the y1<right arrow> and obtains a sequence y3<right arrow>, conducts inverse FFT on the y3<right arrow>, and outputs a sequence y4<right arrow>. The y4<right arrow> is rotated left for m bit positions, and an output sequence Sm<right arrow> is a coherent integration result of N different code phases at the mth frequency point. The maximum value of the envelope of the Sm<right arrow> is compared with a threshold. If the maximum value exceeds the threshold, a signal is considered to exist, and a corresponding code phase and Doppler frequency are output. The method can complete Doppler frequency searching with no need of frequency conversion of the signal first. Besides, the search precision is high, the calculation is simple, and the method is easy for implementation.

Description

A kind of GNSS signal is exempted from mixing and to be walked abreast phase acquisition method

Technical field

The present invention relates to a kind of GNSS signal to exempt from mixing and to walk abreast phase acquisition method.

Background technology

Common GNSS signal catching method comprises: serial search methods, parallel frequency search method and parallel code phase search method.Serial search methods searches for different code phases and Doppler frequency successively, and implementation complexity is low, but the search time needed is longer; Parallel frequency search method, has walked abreast the search FFT of different frequency, is equivalent to utilize FFT to carry out spectrum analysis; Parallel code phase search method, has come the coherent integration operation convolution theorem of different code phase.Traditional code phase parallel search method needs first to carry out frequency conversion to signal, and to complete the search of Doppler frequency, computation complexity is high.

The process of parallel code phase search can represent as shown in Figure 1.For convenience of description, first do some hypothesis without loss of generality: suppose that coherent integration is counted as N (in order to carry out FFT computing, limiting N is the power of 2), coherent integration time NT _sfor the one-period of pseudo-random code; Note baseband signal is r _n, in corresponding coherent integration time, the baseband sampling signal phasor of input is the local pseudo-random code produced of note is c _n, corresponding local pseudo-random code vector is remember that the coherent integration results under different code phase is s _n, corresponding coherent integration results vector is represent the coherent integration results in N kind code phase situation respectively; Note is in coherent integration process, and the local carrier vector that the frequency of use is f is:

${\stackrel{\&RightArrow;}{p}}_f=\{1,e^{-j2{\mathrm{\&pi;fT}}_s},e^{-j2\mathrm{\&pi;}f2T_s},\mathrm{......},e^{-j2\mathrm{\&pi;}f(N-1)T_s}\}$

represent that frequency is the local carrier signal vector of f, be used for being multiplied with baseband signal, to eliminate Doppler frequency remaining in baseband signal, T _srepresent signal sampling interval, N represents that coherent integration is counted.

Summary of the invention

Technical matters to be solved by this invention is, not enough for prior art, provides a kind of GNSS signal to exempt from mixing and to walk abreast phase acquisition method.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of GNSS signal is exempted from mixing and to be walked abreast phase acquisition method, comprising:

1) carry out FFT conversion to N point Received signal strength, the sequence after conversion is designated as wherein N is the power of 2;

2) carry out FFT conversion to N point local code signal, get conjugation to the sequence after conversion, the sequence obtained is designated as

3) will behind ring shift right m position with corresponding point are multiplied, and obtain sequence right do FFT inverse transformation, the sequence of output is designated as

4) will ring shift left m position, the sequence of output be the coherent integration results of the different code phase of N kind under m frequency;

5) will envelope maximal value and thresholding contrast, if exceed thresholding, think that satellite navigation signals to be captured exists, and export corresponding code phase and Doppler frequency.

Described step 1) in, ${\stackrel{\&RightArrow;}{y}}_1=F_N{({\stackrel{\&RightArrow;}{p}}_m.*\stackrel{\&RightArrow;}{r})}^T={\mathrm{SHIFT}}_m\left({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T\right);$ Wherein, ${\stackrel{\&RightArrow;}{p}}_m=\{1,e^{-j2\mathrm{\&pi;}\frac{m}{N}},e^{-j2\mathrm{\&pi;}\frac{2m}{N}},\mathrm{......},e^{-j2\mathrm{\&pi;}\frac{(N-1)m}{N}}\},$ P _mfor the column permutation matrix of N × N dimension; T represents transposition; M=0,1 ..., N-1; SHIFT _mrepresent the m position that to be moved to left by sequence loops; F _nfor the matrix for calculating Fourier transform, $F_N=\left[\begin{array}{ccccc}1& 1& 1& ...& 1\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;1}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;1}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;1}\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;2}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;2}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;2}\\ .& .& .& .& .\\ .& .& .& .& .\\ .& .& .& .& .\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;(N-1)}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;(N-1)}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;(N-1)}\end{array}\right];$ for baseband signal.

wherein, conj represents and gets conjugation; for local pseudo-random code vector.

${\stackrel{\&RightArrow;}{s}}_m=F_N^{-1}\left({\mathrm{SHIFT}}_m\right(\left({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T\right).*SHIF{\underset{\&OverBar;}{T}}_m\left({\stackrel{\&RightArrow;}{y}}_2\right)\left)\right)=F_N^{-1}\left(\right({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T).*SHIF{\underset{\&OverBar;}{T}}_m({\stackrel{\&RightArrow;}{y}}_2\left)\right)P_m.$

Described step 5) in, thresholding wherein, σ _nfor noise mean square root, P _fafor single detects, (word detects and refers to: under a certain group of given pseudo-code phase and Doppler frequency, the satellite navigation signals of reception is reappeared signal with this locality and carries out related operation, the envelope value of operation result and the thresholding of setting contrast, if be greater than thresholding, think that satellite navigation signals to be captured exists, if be less than thresholding, think that signal does not exist) false-alarm probability, ln is for getting natural logarithm.

Compared with prior art, the beneficial effect that the present invention has is: method of the present invention is without the need to carrying out to signal wire the search that frequency conversion can complete Doppler frequency, and search precision is high, calculates simple, easily realizes.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of parallel code phase search;

Fig. 2 is embodiment of the present invention process flow diagram.

Embodiment

When catching, frequency search stepping is set to frequency f to be searched has N number of, can be expressed as:

m＝0,1,...,N-1；

Corresponding local carrier signal vector can be expressed as:

${\stackrel{\&RightArrow;}{p}}_m=\{1,e^{-j2\mathrm{\&pi;}\frac{m}{N}},e^{-j2\mathrm{\&pi;}\frac{2m}{N}},\mathrm{......},e^{-j2\mathrm{\&pi;}\frac{(N-1)m}{N}}\};$

According to the Shifting Property of discrete Fourier transform (DFT), can obtain Received signal strength be multiplied with local carrier signal vector after the Fourier transform of sequence be shown below

${\stackrel{\&RightArrow;}{y}}_1=F_N{({\stackrel{\&RightArrow;}{p}}_m.*\stackrel{\&RightArrow;}{r})}^T={\mathrm{SHIFT}}_m\left({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T\right);$

Wherein, SHIFT _mrepresent the m position that to be moved to left by sequence loops, subscript T represents transposition.F _nfor the matrix for calculating Fourier transform, its expression formula is as follows:

$F_N=\left[\begin{array}{ccccc}1& 1& 1& ...& 1\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;1}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;1}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;1}\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;2}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;2}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;2}\\ .& .& .& .& .\\ .& .& .& .& .\\ .& .& .& .& .\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;(N-1)}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;(N-1)}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;(N-1)}\end{array}\right];$

Local pseudo-random code vector fFT get conjugation after expression formula be:

${\stackrel{\&RightArrow;}{y}}_2=conj\left({\left(F_N{\stackrel{\&RightArrow;}{c}}^T\right)}^T\right);$

Wherein, conj represents and gets conjugation.

Will with after corresponding point are multiplied, then carrying out inverse Fourier transform, can to obtain the expression formula of coherent integration results as follows:

${\stackrel{\&RightArrow;}{s}}_m=F_N^{-1}{({\stackrel{\&RightArrow;}{y}}_1.*{\stackrel{\&RightArrow;}{y}}_2)}^T=F_N^{-1}{\left({\mathrm{SHIFT}}_m\right({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T).*{\stackrel{\&RightArrow;}{y}}_2)}^T;$

According to the character of discrete Fourier transformation, above formula can be written as following form:

${\stackrel{\&RightArrow;}{s}}_m=F_N^{-1}\left({\mathrm{SHIFT}}_m\right(\left({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T\right).*{\mathrm{SHIFT}}_{-m}\left({\stackrel{\&RightArrow;}{y}}_2\right)\left)\right)=F_N^{-1}\left(\right({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T).*{\mathrm{SHIFT}}_{-m}({\stackrel{\&RightArrow;}{y}}_2\left)\right)P_m$

Wherein, P _mfor the column permutation matrix (being obtained by every a line ring shift left m position of unit matrix) of N × N dimension, it makes every a line ring shift left m time of the vector of premultiplication with it or matrix.Can obtain exempting from mixing according to above formula to walk abreast phase acquisition structure.

As shown in Figure 2, job step of the present invention is as follows:

1) carry out FFT conversion to N point Received signal strength, N is the power of 2, and the sequence after conversion is designated as

2) carry out FFT conversion to N point local code signal, the sequence obtained after getting conjugation to the sequence after conversion is designated as

3) will behind ring shift right m position with corresponding point are multiplied, and obtain sequence right do FFT inverse transformation, the sequence of output is designated as

4) will ring shift left m position, the sequence of output be the coherent integration results of the different code phase of N kind under m frequency.

Calculate by above-mentioned steps after, will envelope maximal value and thresholding contrast, if exceed thresholding, think that signal exists, and export corresponding code phase and Doppler frequency.

Claims (5)

1. GNSS signal is exempted from mixing and to be walked abreast a phase acquisition method, it is characterized in that, comprising:

1) carry out FFT conversion to N point Received signal strength, the sequence after conversion is designated as wherein N is the power of 2;

2) carry out FFT conversion to N point local code signal, get conjugation to the sequence after conversion, the sequence obtained is designated as

3) will behind ring shift right m position with corresponding point are multiplied, and obtain sequence right do FFT inverse transformation, the sequence of output is designated as

4) will ring shift left m position, the sequence of output be the coherent integration results of the different code phase of N kind under m frequency;

5) will envelope maximal value and thresholding v _tcontrast, if exceed thresholding, thinks that satellite navigation signals to be captured exists, and exports corresponding code phase and Doppler frequency.

2. GNSS signal according to claim 1 is exempted from mixing and to be walked abreast phase acquisition method, it is characterized in that, described step 1) in, ${\stackrel{\&RightArrow;}{y}}_1=F_N{({\stackrel{\&RightArrow;}{p}}_m.*\stackrel{\&RightArrow;}{r})}^T={\mathrm{SHIFT}}_m\left({\left(F_N{\stackrel{\&RightArrow;}{r}}^T\right)}^T\right);$ Wherein, ${\stackrel{\&RightArrow;}{p}}_m=\{1,e^{-j2\mathrm{\&pi;}\frac{m}{N}},e^{-j2\mathrm{\&pi;}\frac{2m}{N}},......,e^{-j2\mathrm{\&pi;}\frac{(N-1)m}{N}}\},$ P _mfor the column permutation matrix of N × N dimension; T represents transposition; M=0,1 ..., N-1; SHIFT _mrepresent the m position that to be moved to left by sequence loops; F _nfor the matrix for calculating Fourier transform, $F_N=\left[\begin{array}{ccccc}1& 1& 1& ...& 1\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;1}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;1}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;1}\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;2}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;2}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;2}\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;& \&CenterDot;\\ 1& e^{-j\frac{2\mathrm{\&pi;}\&times;1}{N}\&times;(N-1)}& e^{-j\frac{2\mathrm{\&pi;}\&times;2}{N}\&times;(N-1)}& ...& e^{-j\frac{2\mathrm{\&pi;}\&times;(N-1)}{N}\&times;(N-1)}\end{array}\right];$ for baseband signal.

3. GNSS signal according to claim 2 is exempted from mixing and to be walked abreast phase acquisition method, it is characterized in that, described step 2) in, wherein, conj represents and gets conjugation; for local pseudo-random code vector.

4. GNSS signal according to claim 3 is exempted from mixing and to be walked abreast phase acquisition method, it is characterized in that, described step 4) in,

5. GNSS signal according to claim 4 is exempted from mixing and to be walked abreast phase acquisition method, it is characterized in that, described step 5) in, thresholding wherein, σ _nfor noise mean square root, P _fafor the false-alarm probability that single detects, ln is for getting natural logarithm.