CN105049081A - Long-code spread spectrum signal rapid capturing method adaptive to high dynamic environment - Google Patents

Abstract

The invention discloses a long-code spread spectrum signal rapid capturing method adaptive to a high dynamic environment. The method comprises the following steps: sampling spread spectrum signals by use of an analog-to-digital converter, and then obtaining complex baseband signals through a digital down converter; then in a first residence phase, realizing time frequency two-dimensional search by use of code phase compression and fast Fourier transform, and determining a substantial pseudo code phase compression interval and a frequency offset estimated value; and in a second residence phase, searching each code phase in a code phase compression phase interval one by one by use of a conventional coherent accumulation algorithm. According to the invention, the method has the following advantages: large-interval search is performed on a time domain by use of a code phase compression correlator and parallel search is carried out on a frequency domain by use of the fast Fourier transform so that large dynamic spread spectrum signals can be rapidly captured; and at the same time, the method is quite low in complexity and can save enormous hardware resources.

Description

A kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment

Technical field

The present invention relates to a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment in radio communication and navigation system.

Background technology

In Resistant DS Spread Spectrum System, acquiring pseudo code plays very important effect setting up in good communication link.Under high dynamic environment, there is larger speed of related movement in band spread receiver and transmitter, and consider that the factors such as anti-interference, Anti TBIgG usually use longer spreading code, therefore for receiver, the code phase will searched at acquisition phase and Doppler shift scope very large, capture time required when traditionally serial acquisition method is caught is very long, can not meet the requirement of fast Acquisition under high dynamic environment.

At present, under high current intelligence, spread-spectrum signal quick capturing method mainly contains three classes: (1) realizes pseudo-code phase with fast Fourier transform/Fast Fourier Transform Inverse and catches, the serial search of code phase is become parallel search, but Doppler frequency shift and symbol upset are on the impact of its acquisition performance very greatly, and this acquisition algorithm needs longer Fourier transform resource when catching long code.(2) carry out Doppler shift with fast Fourier transform to catch, multiple Partial-matched filter and fast Fourier transform are combined, acquisition speed is very fast, but along with the elongated of PN-code capture and the over-sampling to signal, will consume a large amount of hardware resources.(3) two dimensional compaction correlation capturing method, this acquisition algorithm is the fast Acquisition for the spread spectrum system in large frequency deviation, long code situation, the compression search of code phase and Doppler shift completes in unit residence time, and the method has saved at least time of half than conventional method.But this acquisition algorithm increases the demand to hardware resource in frequency compression process, and the resident acquisition bandwidth of single limits by frequency compression port number.

Summary of the invention

In view of the problem existing for above-mentioned prior art, the object of this invention is to provide a kind of based on the height dynamic long code spread-spectrum signal quick capturing method of code phase compression with fast Fourier transform.Its feature is: (1) uses code phase compression correlator to carry out large interval search in time domain, and frequency domain utilizes fast Fourier transform parallel search, and compared with two dimensional compaction correlation capturing method, this method can reduce capture time further; (2) by choose reasonable code phase compression correlator length, the high dynamic signal that can complete large Doppler shift is caught; (3) compared with the method for acquiring pseudo code based on matched filter or fast Fourier transform/Fast Fourier Transform Inverse, when long PN-code capture, the inventive method complexity is lower, can save great amount of hardware resources.

Object of the present invention is achieved through the following technical solutions:

Based on code phase compression and a long code spread-spectrum signal quick capturing method for fast Fourier transform, it is characterized in that, comprising:

A, utilize analog to digital converter to sample to the spread-spectrum signal that receiver receives, then utilize digital down converter to obtain complex base band signal;

B, utilize code phase to compress to realize time-frequency two-dimensional search for fast Fourier transform, determine the interval and frequency deviation interval of pseudo-code phase roughly, be designated as the first resident stage;

C, utilize traditional coherent accumulation algorithm to obtain first resident stage optimal compression code phase interval in phase point search for one by one, be designated as the second resident stage.

Described steps A comprises further:

A1, the sample frequency arranging digital to analog converter are f _s, its value is S times of pseudo-bit rate;

The spread spectrum that A2, receiver receive frequently signal obtains complex base band signal after analog to digital converter sampling and Digital Down Convert.

Described step B comprises further:

B1, set the code phase compressed coefficient as K, the code compressed sequence that the local pseudo-code of K road continuous phase is formed is carried out code phase to complex base band signal and compresses relevant, carry out quick, rough search to code phase is interval;

B2, to code phase compression correlator output carry out fast Fourier transform, realize the parallel capture to Doppler shift.

Described step B1 comprises further:

B11, a continuous K code phase to be defined as between a code phase compressional zone, if whole pseudo-code length can be divided between L code phase compressional zone.If between certain code phase compressional zone be [τ+iK, τ+iK+K-1], wherein i=0,1,2,3 ... L-1, namely i represents the fragment sequence number between this code phase compressional zone, and τ+iK represents the start-phase between this code phase compressional zone, and c (τ+iK) represents that phase place is the pseudo-code sequence of τ+iK.Then by suing for peace to the local pseudo-code of the bipolarity in this code phase compressional zone, obtain a yard compressed sequence

$C_c\left(i\right)=\underset{m=0}{\overset{K-1}{\mathrm{\Σ}}}c(\mathrm{\τ}+m)=c(\mathrm{\τ}+\mathrm{iK})+c(\mathrm{\τ}+\mathrm{iK}+1)+\·\·\·\·\·\·+c(\mathrm{\τ}+(i+1)K-1);$

B12, arrange code phase compression correlator the chip number M corresponding to the time of integration, corresponding sampling number SM;

B13, set the fragment sequence number of local pseudo-code as i=0, the code compressed sequence obtained and complex base band signal are carried out compression correlation intergal, obtain compression correlation.

Described step B2 comprises further:

B21, to arrange the threshold value in the first resident stage be T ₁;

B22, get the compression correlation of continuous P time, utilize P rank delay line to postpone compression correlation;

B23, each output of P rank delay line carried out to the fast Fourier transform that N (N > P) puts;

B24, determine the N point quick Fourier conversion maximum of modulus value of output valve and the channel number K corresponding to it _max;

If the maximum of the modulus value of B25 output valve is less than the threshold T pre-set ₁, then get i=i+1, arrange [τ+iK, τ+iK+K-1] between next compressed code phase region, then repeat the search step in the first resident stage, until the maximum of the modulus value of output valve is greater than the threshold value in the first resident stage;

If the maximum of the modulus value of B26 output valve is greater than the threshold T pre-set ₁, then optimal compression code phase interval [τ can be determined ₀, τ ₀+ K-1], and the start-phase τ in optimal compression code interval ₀, and channel number corresponding to the maximum of the modulus value of output valve can be utilized to estimate the approximation of Doppler shift for K _maxf _s/ (NSM), and by frequency feedback corresponding for this Doppler shift to digital down converter, suspend the search of the first resident stage code phase, entered for the second resident stage.

Described step C comprises further:

C1, to arrange the threshold value in the second resident stage be T ₂;

C2, optimal compression code phase interval [τ in local pseudo-code ₀, τ ₀+ K-1] in, first use code phase to be optimal compression code phase τ ₀local pseudo-code sequence and complex base band signal carry out correlation intergal;

C3, the correlation of correlation intergal;

If the correlation of C4 correlation intergal is less than the threshold T pre-set ₂, then the next code phase in optimal compression code phase interval is verified, until the search of whole optimal compression code phase interval is complete;

If C5 correlation is greater than threshold T ₂, then acquisition success is thought.

As can be seen from the technical scheme that the invention described above provides, the present invention uses code to compress correlator in time domain, frequency domain utilizes fast Fourier transform carry out parallel capture, further shorten capture time; And pass through the compression correlation length of choose reasonable code phase, catching large Doppler shift can be realized; This invention is simultaneously relative simple and flexible on hardware implementing, can save great amount of hardware resources.

Accompanying drawing explanation

Fig. 1 is system block diagram of the present invention

Fig. 2 is process chart of the present invention

Fig. 3 is the first resident module diagram of the present invention

Embodiment

The invention provides long code spread-spectrum signal quick capturing method under a kind of high dynamic environment.Core of the present invention is: set the start-phase of local pseudo-code as τ _,a continuous K code phase is defined as between a code phase compressional zone, local for bipolarity interior for the code phase compressional zone taking τ as start-phase pseudo-code is sued for peace, obtains a yard compressed sequence.The spread-spectrum signal that receiver receives obtains complex base band signal after analog to digital converter sampling and Digital Down Convert, then this complex base band signal and code compressed sequence is carried out compression correlation intergal, obtains compression correlation.Then compression correlation P rank delay line is postponed, and carry out N (N >=P) put complex fast Fourier conversion, then the maximum of the modulus value of fast Fourier transform output valve and threshold value is selected to compare, if be less than threshold value, just search between next compressed code phase region, then the search step in the first resident stage is repeated, until the maximum of the modulus value of output valve is greater than the threshold value in the first resident stage; If be greater than threshold value, the rough compression just completing code phase is caught, and obtains optimal compression code phase interval, enters for the second resident stage, complete and verify one by one the code phase in optimal compression code phase interval.

The system block diagram of the long code spread-spectrum signal quick capturing method based on code phase compression correlator and fast Fourier transform of the present invention as shown in Figure 1, comprising analog to digital converter, digital down converter, pseudo-code and Doppler shift pair resident trapping module:

Analog to digital converter and digital down converter: the spread-spectrum signal received by receiver by analog-to-digital conversion and Digital Down Convert process, thus obtains complex base band signal.

Pseudo-code and the two resident trapping module of Doppler shift: for completing the fast Acquisition combined with fast Fourier transform based on code phase compression correlator, be divided into two resident stages: (1) is in the first resident stage, a continuous K code phase is defined as between a code phase compressional zone, local for bipolarity in code phase compressional zone pseudo-code is sued for peace, obtains a yard compressed sequence.Then this yard of compressed sequence and complex base band signal are carried out correlation intergal, obtain compressing correlation.Then P rank delay line is utilized to postpone compression correlation, and to the output of P rank delay line carry out N (N >=P) put complex fast Fourier conversion, then the maximum of the modulus value of fast Fourier transform output valve and threshold value is selected to compare, if be less than threshold value, just search between next compressed code phase region, then the search step in the first resident stage is repeated, until the maximum of the modulus value of output valve is greater than the threshold value in the first resident stage; If be greater than threshold value, just suspend the code phase search in the first resident stage, obtain the approximation of optimal compression code phase interval and Doppler shift, and by frequency feedback corresponding for Doppler shift to digital down converter, entered for the second resident stage; (2) in the second resident stage, the phase point in the optimal compression code phase interval using traditional coherent Cumulate algorithm to catch in the first resident stage code phase is searched for one by one, realizes finally catching of pseudo-code.

Process chart of the present invention as shown in Figure 2, comprises the steps:

Step 201: the spread-spectrum signal that receiver receives is sampled.

Step 202: carry out Digital Down Convert process again to the spread-spectrum signal crossed through over-sampling, obtains the signal of complex baseband.

Step 203: set the code phase compressed coefficient as K, with local pseudo-code initial phase between the compressed code phase region of initial local pseudo-code.

Step 204: the initial phase in using local pseudo-code initial phase as compressed code phase region produces the local pseudo-code sequence of bipolarity that K road postpones a code phase successively.

Step 205: the local pseudo-code sequence summation of bipolarity K road being postponed successively to a code phase, obtains code compressed sequence.

Step 206: code compressed sequence and complex base band signal are carried out code and compresses correlation intergal, obtains compressing correlation.

Step 207: utilize P rank delay line to postpone to compression correlation.

Step 208: the conversion of N (N >=P) point quick Fourier is carried out to the output of P rank delay line.

Step 209: by the maximum of the modulus value of N point quick Fourier conversion output valve and the first threshold T ₁relatively.

Step 210: if export maximum to be less than the first threshold value, then continue between next compressed code phase region of search, and turn back to step 205.

Step 211: if export maximum to be greater than the first threshold value, then can estimate the approximation of Doppler shift, and this Doppler shift respective frequencies is fed back to digital down converter.

Step 212: determine that optimal compression code phase is interval, and first choose the local pseudo-code of first phase point in this interval.

Step 213: traditional coherent accumulation is carried out to the local pseudo-code being in this phase point.

Step 214: by the maximum of the modulus value of traditional coherent accumulation output valve and the second threshold T ₂relatively.

Step 215: if the maximum of the modulus value of output valve is less than the second threshold value, then search is in the local pseudo-code of the next phase point in optimal compression code phase interval, and turns back to step 213.

Step 216: if the maximum of the modulus value of output valve is greater than the first threshold value, then shown finally catching of pseudo-code.

Of the present invention based on code phase compression correlator and fast Fourier transform long code spread-spectrum signal quick capturing method the first resident module diagram as shown in Figure 3, comprising:

Whole pseudo-code length a continuous K code phase is defined as between a code phase compressional zone, if can be divided between L code phase compressional zone.If be [τ+iK between certain code phase compressional zone, τ+iK+K-1], wherein i=0,1,2,3, L-1, namely i represents the fragment sequence number between this code phase compressional zone, and τ+iK represents the start-phase between this code phase compressional zone, and c (τ+iK) represents that initial phase is the pseudo-code sequence of τ+iK.Then by suing for peace to the local pseudo-code of the bipolarity in this code phase compressional zone, obtain a yard compressed sequence

$C_c\left(i\right)=\underset{m=0}{\overset{K-1}{\mathrm{\Σ}}}c(\mathrm{\τ}+m)=c(\mathrm{\τ}+\mathrm{iK})+c(\mathrm{\τ}+\mathrm{iK}+1)+\·\·\·\·\·\·+c(\mathrm{\τ}+(i+1)K-1);$

Then code compressed sequence and complex base band signal are carried out code and compress correlation intergal, utilize P frequency divider the compression of whole PN-code capture to be correlated with simultaneously and be divided into Short Compression to be repeatedly correlated with.Then P rank delay line is utilized to postpone compression correlation, and to the output of P rank delay line carry out N (N>=P) put complex fast Fourier conversion, then the maximum of the modulus value of fast Fourier transform output valve and threshold value is selected to compare, if be less than threshold value, just search between next compressed code phase region, then the search step in the first resident stage is repeated, until the maximum of the modulus value of output valve is greater than the threshold value in the first resident stage; If be greater than threshold value, just suspend the code phase search in the first resident stage, determine that optimal compression code phase is interval, and calculate Doppler shift estimated value and be about K _maxf _s/ (NSM), by frequency feedback corresponding for Doppler shift in digital down converter, entered for the second resident stage simultaneously.

In sum, the invention provides a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment.

The above; be only the present invention's preferably specific implementation method, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (6)

1. adapt to a long code spread-spectrum signal quick capturing method for high dynamic environment, it is characterized in that, comprising:

A, utilize analog to digital converter to sample to the spread-spectrum signal that receiver receives, then utilize digital down converter to obtain complex base band signal;

B, utilize code phase to compress to realize time-frequency two-dimensional search for fast Fourier transform, determine the interval and frequency deviation interval of pseudo-code phase roughly, be designated as the first resident stage;

C, utilize traditional coherent accumulation algorithm to obtain first resident stage optimal compression code phase interval in phase point search for one by one, be designated as the second resident stage.

2. a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment according to claim 1, it is characterized in that, described steps A comprises further:

A1, the sample frequency arranging digital to analog converter are f _s, its value is S times of pseudo-bit rate;

The spread spectrum that A2, receiver receive frequently signal obtains complex base band signal after analog to digital converter sampling and Digital Down Convert.

3. a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment according to claim 1, it is characterized in that, described step B comprises further:

B1, set the code phase compressed coefficient as K, the code compressed sequence that the local pseudo-code of K road continuous phase is formed is carried out code phase to complex base band signal and compresses relevant, carry out quick, rough search to code phase is interval;

B2, to code phase compression correlator output carry out fast Fourier transform, realize the parallel capture to Doppler shift.

4. a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment according to claim 3, it is characterized in that, described step B1 comprises further:

B11, a continuous K code phase to be defined as between a code phase compressional zone, if whole pseudo-code length can be divided between L code phase compressional zone.If between certain code phase compressional zone be [τ+iK, τ+iK+K-1], wherein i=0,1,2,3 ... L-1, namely i represents the fragment sequence number between this code phase compressional zone, and τ+iK represents the start-phase between this code phase compressional zone, and c (τ+iK) represents that phase place is the pseudo-code sequence of τ+iK.Then by suing for peace to the local pseudo-code of the bipolarity in this code phase compressional zone, obtain a yard compressed sequence

$C_c\left(i\right)=\underset{m=0}{\overset{K-1}{\mathrm{\Σ}}}c(\mathrm{\τ}+m)=c(\mathrm{\τ}+\mathrm{iK})+c(\mathrm{\τ}+\mathrm{iK}+1)+\·\·\·\·\·\·+c(\mathrm{\τ}+(i+1)K-1);$

B12, arrange code phase compression correlator the chip number M corresponding to the time of integration, corresponding sampling number SM;

B13, set the fragment sequence number of local pseudo-code as i=0, the code compressed sequence obtained and complex base band signal are carried out compression correlation intergal, obtain compression correlation.

5. a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment according to claim 3, it is characterized in that, described step B2 comprises further:

B21, to arrange the threshold value in the first resident stage be T ₁;

B22, get the compression correlation of continuous P time, utilize P rank delay line to postpone compression correlation;

B23, each output of P rank delay line carried out to the fast Fourier transform that N (N > P) puts;

B24, determine the N point quick Fourier conversion maximum of modulus value of output valve and the channel number K corresponding to it _max;

If the maximum of the modulus value of B25 output valve is less than the threshold T pre-set ₁, then get i=i+1, arrange [τ+iK, τ+iK+K-1] between next compressed code phase region, then repeat the search step in the first resident stage, until the maximum of the modulus value of output valve is greater than the threshold value in the first resident stage;

If the maximum of the modulus value of B26 output valve is greater than the threshold T pre-set ₁, then optimal compression code phase interval [τ can be determined ₀, τ ₀+ K-1], and the start-phase τ in optimal compression code interval ₀, and channel number corresponding to the maximum of the modulus value of output valve can be utilized to estimate the approximation of Doppler shift for K _maxf _s/ (NSM), and by frequency feedback corresponding for this Doppler shift to digital down converter, suspend the search of the first resident stage code phase, entered for the second resident stage.

6. a kind of long code spread-spectrum signal quick capturing method adapting to high dynamic environment according to claim 1, it is characterized in that, described step C comprises further:

C1, to arrange the threshold value in the second resident stage be T ₂;

C2, optimal compression code phase interval [τ in local pseudo-code ₀, τ ₀+ K-1] in, first use code phase to be optimal compression code phase τ ₀local pseudo-code sequence and complex base band signal carry out correlation intergal;

C3, the correlation of correlation intergal;

If the correlation of C4 correlation intergal is less than the threshold T pre-set ₂, then the next code phase in optimal compression code phase interval is verified, until the search of whole optimal compression code phase interval is complete;

If C5 correlation is greater than threshold T ₂, then acquisition success is thought.