CN101022282A - Long-period spread spectrum code double-folding capture searching method - Google Patents

Abstract

A method for catch-searching spread spectrum code in long cycle includes carrying out fold on both received signal and local false code at receiving end, transforming folded signal to frequency domain and carrying out conjugate-multification on data two frequency domains, reverse- transforming multiplied data to time domain and carrying out calculation there to obtain maximum power value of each point, regulating local code phase to make researching if said maximum power value at largest point is less then threshold and simultaneously searching code phase of each point on generated local code phase by using available catch-searching method.

Description

The double-folding capture searching method of long-period spread spectrum code

Technical field

The present invention relates to use the system of long-period spread spectrum code communication, or use spreading code to do in the communication system of synchronous code the algorithm that a kind of spreading code is caught fast.

Background technology

Spread spectrum communication has lot of advantages, uses very wide.The adverse effect that spread-spectrum signal can resist or suppress to disturb, for example interference that other users cause in the channel; Spread-spectrum signal sends hidden signal with low-power, makes that signal is difficult to be detected by the listener-in; Can realize secure communication.Spread spectrum technic is widely used in military affairs, field such as civilian.

3 main standard WCDMA, TD-SCDMA of 3G (Third Generation) Moblie (3G) communication, CDMA-2000 are based on spread spectrum technic.Present most widely used satellite navigation system---global positioning system (GPS) is also based on spread spectrum technic.It then is the basic foundation of realizing spread spectrum communication that sign indicating number is caught.Only finished sign indicating number and caught and to set up synchronously at receiving terminal and transmitting terminal, could realize despreading, finished signal processing function at receiving terminal.More typical spread spectrum code acquisition algorithm has non-folding zero padding algorithm and expansion to duplicate overlapping acquisition search technology.

Non-folding zero padding algorithm is a kind of long-period spread spectrum code acquisition search algorithm relatively more commonly used in the world.Utilize relation relevant and convolution and convolution and discrete Fourier transform (DFT) (DFT), related operation can be realized with fast Fourier transform (FFT).If can realize relevant before to received signal (or local pseudo-code) carry out the zero padding operation, then can utilize FFT to reach the purpose of parallel search code phase.

Non-folding zero padding algorithm principle figure as shown in Figure 1.Carry out segmentation zero padding operation at first to the received signal, and carry out FFT computing (in this segment length of keeping the score is N, and the zero padding number is N/2).Local pseudorandom spread spectrum sign indicating number is carried out segmentation, FFT operation.Then the result behind their FFT is carried out conjugate multiplication and inverse fourier transform (IFFT).Result to IFFT carries out power detection, therefrom finds out maximum (or greater than setting the thresholding person) and follows the tracks of detection.Because the value of half is received signal and the value of local pseudo-code after being correlated with on N/2 the different code phases unit after among the IFFT gained result, so this method has reached the purpose of a parallel search N/2 code phase.

This method utilizes FFT to realize the parallel search of code phase, has improved search speed.But have following problem: the ability of (1) parallel search code phase a little less than, search speed is slower.With FFT length is N, and the zero padding number is that N/2 is an example, and this method at every turn can only a parallel search N/2 code phase.(2) the coherent integration time shorter, acquisition performance is relatively poor.Be N with FFT length equally, the zero padding number is that N/2 is an example, and this method pre-detection time of integration only is (N Δ t)/2, and wherein Δ t is the sampling period.

Expansion is duplicated overlapping acquisition search technology (XFAST, Extended replica Folding Acquisition SearchTechnique) and is meant signal is carried out segmentation earlier, and then corresponding addition, as shown in Figure 2.The XFAST schematic diagram as shown in Figure 3, its folding being meant folds local pseudo-code signal.Select the received signal of N point (N can get any positive integer, and for making things convenient for the FFT computing, General N is 2 inferior power) after front end analog-digital converter spare A/D sampling, and this signal is carried out FFT handle.As required, can to the FFT calculated result carry out again anti-interference, remove processing such as carrier doppler.According to the time uncertainty of received signal, determine code phase scope to be searched, and produce the local pseudo-code signal of dirt.The local pseudo-code signal that produces dirt folded (suppose that local pseudo-code signal folding times is 4, then need to select the local pseudo-code signal of 4N point to fold at every turn) and FFT, conjugation handle, then with received signal FFT (or removal Doppler) after the result multiply each other.Result after multiplying each other is carried out inverse fourier transform (IFFT) and power detection.If power detection finds have than the big person of thresholding, illustrate that then the code phase of received signal may drop in the local pseudo-code section.Should search for one by one 4 sections folding pseudo-codes of this locality this moment again, up to finding out that code phase that aligns with received signal---deblurring degree.If power detection is not found to occur than the big value of thresholding, then the mobile local code phase produces the local pseudo-code of another section and searches for once more, up to finding than the big person of thresholding, and then carries out the operation of deblurring degree.

XFAST can improve the code phase search ability of algorithm significantly.For example if every section block length is N, folding times is M, and then this algorithm once just can N code phase of parallel search (M-1), can only compare by a parallel search N/2 code phase with non-folding zero padding algorithm at every turn, and its speed is its 2 (M-1) times.M=4 for example, then its speed is 6 times of non-folding zero padding algorithm, and search speed is accelerated at double.

The outstanding advantage of this method is by local pseudo-code being folded, directly having reduced code phase unit number to be searched, thereby search speed is significantly improved.But the acquisition performance of this algorithm sharply descends with the increase of folding times.For example if local pseudo-code folding times is 2, then the ability of this algorithm parallel search code phase is 2 times of non-folding zero padding algorithm, the 3dB but acquisition performance has descended; If the local signal folding times is 20, then the ability of this algorithm parallel search code phase is 38 times of non-folding zero padding algorithm, the 13dB but acquisition performance has descended.Therefore this algorithm is only applicable to catch the higher long-period spread spectrum code signal of signal to noise ratio.

Summary of the invention

The invention is characterized in,, or use spreading code to do the communication system of synchronous code, make the twofold synchronization acquistion of spreading code at receiving terminal successively according to the following steps of a digital integrated circuit chip at the system that uses long-period spread spectrum code communication:

Step (1) is set in this spread spectrum communication in this digital integrated circuit, and the local spreading code of generation is C _i, single integration block length is N, and the spreading code folding times is M, and the received signal folding times is K, spread spectrum acquisition power threshold P _o, i=0 wherein, 1....

Step (2) is set and obtained sequence after receiver is sampled by analog to digital sampling device A/D is X _i,

Step (3) is to the sampled signal X of step (2) _iIntercepted length is the data that KN is ordered, and folds calculating, obtains sequence X ^p _i,

Step (4) is C to this locality generation spreading code of step (1) _iIntercepted length is the data that MN is ordered, and folds calculating, obtains sequence C ^p _i,

The folding sequence X that step (5) obtains step (3) ^p _iCarry out FFT and transform to frequency domain, obtain sequence Y ^p _i,

The folding sequence C that step (6) obtains step (4) ^p _iCarry out FFT and transform to frequency domain, obtain sequence D ^p _i,

The sequence Y that step (7) obtains step (5) and step (6) ^p _iAnd D ^p _iConjugate multiplication, and carry out IFFT processing conversion and return time domain, sequence E obtained ^p _i,

The sequence E that step (8) obtains step (7) ^p _iCarry out power detection, and therefrom find out power maximum P _Max,

Step (9) is if the power maximum P that step (8) calculates _MaxLess than power threshold P _o, then choose local spread spectrum codes C again ^p _i, and repeating step (4) is to (9), until utilizing the local spread spectrum codes C of choosing for the j time ^p _iThe P that the basis obtains _MaxMore than or equal to P _oTill,

The spread spectrum codes C that step (10) is being chosen for the j time ^p _iOn, catch with non-folding zero padding algorithm, the local pseudo-code phase of corresponding M N point is searched for, find out the local pseudo-code phase of aliging with received signal.

The present invention improves the acquisition performance of algorithm when the raising algorithm is to long-period spread spectrum code code phase unit parallel search ability, thereby reaches the purpose that improves the long-period spread spectrum code search speed.

Description of drawings

Fig. 1 is non-folding zero padding algorithm principle figure.

Fig. 2 is the folding schematic diagrames of handling of data.Wherein figure (a) is the schematic diagram data of original sampled signal; Figure (b) is the schematic diagram data that sampled signal is divided into groups, divides for 4 groups, and respectively with ' o ', ' △ ', ' x ', '+' mark; Figure (c) carries out schematic diagram data after the corresponding addition to four component group signals.

Fig. 3 is the schematic diagram that overlapping acquisition search algorithm (XFAST) is duplicated in expansion.

Fig. 4 is a double-folding capture searching algorithm schematic diagram.

Fig. 5 to Fig. 7 is the simulation performance comparison schematic diagram that overlapping acquisition search algorithm and double-folding capture searching algorithm are duplicated in non-folding zero padding algorithm, expansion.Wherein Fig. 5 (a) represents non-folding zero padding algorithm; Fig. 5 (b) represents respectively at k=2 to Fig. 5 (d), Fig. 6 (a) to Fig. 6 (d), the double-folding capture searching algorithm under 4,6,8,12,16,19 (M is 20) situation.It is 20 that Fig. 7 (a) represents M to Fig. 7 (d), and overlapping acquisition search algorithm is duplicated in the expansion that the noncoherent accumulation number of times is respectively under 2,4,6,8 situations.

Embodiment

Below in conjunction with accompanying drawing and example, effect of the present invention is done concrete the introduction:

In the present embodiment, choosing single integration block length is N=1024, and the spreading code folding times is M=20, and the received signal folding times is K=6, spread spectrum acquisition power threshold P _o, make the twofold synchronization acquistion of spreading code successively according to the following steps of a digital integrated circuit chip at receiving terminal:

Step (1) is set in this spread spectrum communication in this digital integrated circuit, and the local spreading code of generation is C _i,

Step (2) is set and obtained sequence after receiver is sampled by analog to digital sampling device A/D is X _i,

Step (3) is to the sampled signal X of step (2) _iIntercepted length is 6144 data, is divided into 6 groups, and every group 1024 point folds calculating, obtains sequence X ^p _i,

Step (4) is C to this locality generation spreading code of step (1) _iIntercepted length is 20480 data, is divided into 20 groups, and 1024 every group fold calculating, obtain sequence C ^p _i,

The folding sequence X that step (5) obtains step (3) ^p _iCarry out FFT and transform to frequency domain, obtain sequence Y ^p _i,

The folding sequence C that step (6) obtains step (4) ^p _iCarry out FFT and transform to frequency domain, obtain sequence D ^p _i,

The sequence Y that step (7) obtains step (5) and step (6) ^p _iAnd D ^p _iConjugate multiplication, and carry out IFFT processing conversion and return time domain, sequence E obtained ^p _i,

The sequence E that step (8) obtains step (7) ^p _iCarry out power detection, and therefrom find out power maximum P _Max,

Step (9) is if the power maximum P that step (8) calculates _MaxLess than power threshold P _o, then move 14336 local pseudo-codes and choose local spread spectrum codes C again ^p _i, and repeating step (4) is to (9), until utilizing the local spread spectrum codes C of choosing for the j time ^p _iThe P that the basis obtains _MaxMore than or equal to P _oTill,

The spread spectrum codes C that step (10) is being chosen for the j time ^p _iOn, catch with non-folding zero padding algorithm, corresponding 20480 local pseudo-code phase are searched for, find out the local pseudo-code phase of aliging with received signal.

Below by contrast double-folding capture algorithm and existing algorithm, invention effect of the present invention is described.

Set snr of received signal SNR=-12dB, carrier doppler is 100Hz, and code phase offset is 500 sampled points.In different received signal folding times K and non-coherent accumulation number of times situation, the acquisition performance that has not compared " non-folding zero padding algorithm ", " overlapping acquisition search algorithm is duplicated in expansion ", " double-folding capture searching algorithm " three kinds of algorithms.In order to compare " overlapping acquisition search algorithm is duplicated in expansion " and " double-folding capture searching algorithm ", local signal folding times M is 20.

Fig. 5 (a) represents " non-folding zero padding algorithm ", its non-coherent accumulation number of times is 1 (promptly not carrying out noncoherent accumulation), under this simulated conditions, " non-folding zero padding algorithm " is very outstanding the 500th relevant peaks of locating, and can find correct code phase location as we can see from the figure.Fig. 5 (b) is to Fig. 5 (d), and Fig. 6 (a) represents K=2 respectively to Fig. 6 (d), and 4,6,8,12,16,19, the noncoherent accumulation number of times is 1 o'clock " double-folding capture searching algorithm " simulation performance.Therefrom can see K 〉=6 o'clock, relevant peaks is very outstanding, can find correct code phase.Fig. 7 (a) is that M is 20 to Fig. 7 (c), and the non-coherent accumulation number of times is respectively 2,4, the simulation performance of " overlapping acquisition search algorithm is duplicated in expansion " under 6 situations, and therefrom relevant peaks has been submerged in the noise as can be seen, can not find correct code phase location; When the non-coherent accumulation number of times was 8, correlation peak was more outstanding, shown in Fig. 7 (d).

At this, if define search time

Then under the identical total said conditions of code phase to be searched, (remember that code phase to be searched adds up to A):

● " non-folding zero padding algorithm " is search time $T=\frac{\mathrm{<figure-callout\; id="512"\; label="A"\; filenames="A20071006468000111.png,A20071006468000121.png"\; state="\{\{state\}\}">A</figure-callout>}}{512};$

● " overlapping acquisition search algorithm is duplicated in expansion " is search time $T=\frac{A}{19\&times;1024}\&times;8=\frac{A}{2432};$

● " double-folding capture searching algorithm " is search time $T=\frac{A}{(20-6)\&times;1024}=\frac{A}{14336}.$

Therefore the search time of " double-folding capture searching algorithm " be " non-folding zero padding algorithm " 3.6%, be " overlapping acquisition search algorithm is duplicated in expansion " 17%, have the fastest search speed.

The above example is 1 embodiment of the present invention, and is not limited to this, is being no more than under the situation of spiritual scope of the present invention, and the many variations of being done is implemented, and all belongs to scope of the present invention.

Claims (4)

1, the double-folding capture searching method of long-period spread spectrum code, it is characterized in that, at the system that uses long-period spread spectrum code communication, or use spreading code to do the communication system of synchronous code, make the twofold synchronization acquistion of spreading code successively according to the following steps of a digital integrated circuit chip at receiving terminal:

Step (1) is set in this spread spectrum communication in this digital integrated circuit, and the local spreading code of generation is C _i, single integration block length is N, and the spreading code folding times is M, and the received signal folding times is K, spread spectrum acquisition power threshold P _o, i=0 wherein, 1...., detection threshold is set according to needed false alarm probability, acquisition probability.If P _FaThe false alarm probability of the single unit to be searched that expression is set, δ ²The expression noise variance, A is the received signal amplitude, then $P_o=\sqrt{-2\mathrm{KMN}({\mathrm{\&delta;}}^2+A^2)\ln P_{\mathrm{fa}}},$

Obtaining sequence after step (2) receiver is sampled to received signal by analog to digital sampling device A/D is X _i,

Step (3) is to the sampled signal X of step (2) _iIntercepted length is the data that KN is ordered, and folds calculating, obtains sequence X ^p _i, $X^{p_i}=\underset{l=0}{\overset{K-1}{\mathrm{\&Sigma;}}}{X}_{i+\mathrm{lN}},$

Step (4) is C to this locality generation spreading code of step (1) _iIntercepted length is the data that MN is ordered, and folds calculating, obtains sequence C ^p _i, $C^{p_i}=\underset{l=0}{\overset{M-1}{\mathrm{\&Sigma;}}}{C}_{i+\mathrm{lN}},$

The folding sequence X that step (5) obtains step (3) ^p _iCarry out FFT and transform to frequency domain, obtain sequence Y ^p _i, $Y^{P_i}=\underset{l=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}^{P_i}{e}^{-j\frac{2\mathrm{\&pi;}}{N}\mathrm{il}},$ $j=\sqrt{-1},$

The folding sequence C that step (6) obtains step (4) ^p _iCarry out FFT and transform to frequency domain, obtain sequence D ^p _i, $D^{P_i}=\underset{l=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{C}^{P_i}{e}^{-j\frac{2\mathrm{\&pi;}}{N}\mathrm{il}},$

The sequence Y that step (7) obtains step (5) and step (6) ^p _iAnd D ^p _iConjugate multiplication, and carry out IFFT processing conversion and return time domain, sequence E obtained ^p _i, $E^{P_i}=\frac{1}{N}\underset{l=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{F}^{P_i}{e}^{j\frac{2\mathrm{\&pi;}}{N}\mathrm{li}},$ Wherein $F^{P_i}=Y^{P_i}\&CenterDot;{\left(D^{P_i}\right)}^{*}$ Or $F^{P_i}={\left(Y^{P_i}\right)}^{*}\&CenterDot;D^{P_i},$ * complex conjugate is got in expression,

The sequence E that step (8) obtains step (7) ^p _iCarry out power detection, and therefrom find out power maximum P _Max, $P_{\max }=\underset{i}{\max }\left\{\right|\left|E^{P_i}\right|\left|\right\},$ " ‖ ‖ " represents delivery,

Step (9) is if the power maximum P that step (8) calculates _MaxLess than power threshold P _o, then move the local pseudo-code of (M-K) N point and choose local spread spectrum codes C again ^p _i, and repeating step (4) is to (9), until utilizing the local spread spectrum codes C of choosing for the f time ^p _iThe P that obtains for the basis _MaxMore than or equal to P _oOr search for till complete the space to be searched, parallel search code phase unit number is by the difference decision of M and K, and M is not less than K in this acquiescence,

The spread spectrum codes C that step (10) is being chosen for the f time ^p _iOn, search for non-folding zero padding algorithm, the local pseudo-code phase of corresponding M N point is searched for successively, find out the local pseudo-code phase of aliging with received signal.

2, the double-folding capture searching method of long-period spread spectrum code according to claim 1 is characterized in that, described local signal folding times M is more than or equal to received signal folding times K.

3, the double-folding capture searching method of long-period spread spectrum code according to claim 1 is characterized in that, described local signal folding times M is less than received signal folding times K.

4, the double-folding capture searching method of long-period spread spectrum code according to claim 1, it is characterized in that, the additional Doppler's circuit module of removing behind a FFT, utilize the mode of cyclic shift, result behind the FFT is carried out cyclic shift, remove received signal for the frequency shift (FS) influence that transmits.

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