CN101552621A - Method for capturing pseudo code sequence - Google Patents

Abstract

The invention relates to the technical field of direct sequence spread spectrum communication, in particular to a method for capturing pseudo code sequences. The method comprises the following steps: all different code phase sequences of local copy codes are divided into n groups uniformly, each group comprises m different code phase sequences, and the m different code sequences of each group are added, thus obtaining the compound code sequence of the group. The compound code sequences are firstly used for scoring with received satellite pseudo code sequences respectively, then compound code sequences that contain the satellite pseudo code sequences are searched; and then the satellite pseudo code sequences are searched in the m code phase sequences of the group corresponding to the compound code sequences. The method can be widely used in software receivers of GPS signals, Galileo signals and other communication signals, and direct sequence spread spectrum codes with different lengths can be captured flexibly.

Description

A kind of catching method of pseudo-code sequence

Technical field

The present invention relates to the direct sequence spread spectrum communication technical field, particularly a kind of catching method of pseudo-code sequence.

Background technology

The notion of software radio is meant with programmable microprocessor and replaces simulation or digital device to realize most of function of signal processing that software radio is closely linked the emulation of receiver and realization, has greater flexibility.After the notion of software radio occurs, since the eighties based on the digital radio power technology of hardware towards from now on more flexibly, advanced person's direction develops more.

The realization of software lock-on signal algorithm can make receiver adapt to different PN (pseudo noise) sequence, carrier frequency, phase change of different code length etc. more flexibly, also provides guarantee for receiver widely-used.1) flexible configuration of receiver provides possibility for receiver carries out the real-time Simulation processing to needed signal at any time.Can adopt different algorithms at different situations, data are gathered, analyzed and test.2) design of the software modularity of receiver also can be carried out visualizing monitor to the input and output signal of each module, therefore can assess the performance of each module after algorithms of different, so that use according to qualifications.3) software implementation of receiver can improve the utilization ratio of receiver greatly.The software implementation of receiver not only can receive processing flexibly from different Pseudo-Random Noise Codes, also can use different algorithms to come deal with data, analyze data etc. flexibly according to the residing environment of receiver, can improve the service efficiency of receiver like this.

Software receiver comprises the hardware and software design.Hardware designs mainly is the design of analog to digital converter (ADC) and digital signal processor (DSP), and software design comprises various Processing Algorithm, as related algorithm, location algorithm etc.

The research of the synchronization acquiring method appearance along with spread spectrum is begun, once adopted in early days and send reference sequences, send the certain synchronization sign indicating number, methods such as regularly unified and sequence state estimation realize sign indicating number synchronously, but these not very desirable.The technology of comparative maturity is exactly the relevant search technology, promptly adopts the local sequence and the receiving sequence of out of phase to carry out related calculation, and judges by the size of correlation whether sequence is synchronous.And these methods are at present all by using hardware to realize.

For now, mainly concentrate on aspect three of catching method, capture time, the detection judgment variables Distribution Statistics under various channels about the research of the synchronization acquiring method of receiver Pseudo-Random Noise Code.Usually in general receiver, for code phase synchronously, need search for all code phases, amount of calculation is big, search time is long.

Summary of the invention

Technical problem to be solved by this invention provides the catching method of the pseudo-code sequence that a kind of amount of calculation is little, search time is short.

Principle of the present invention is such: the correlation according to pseudo-random code sequence knows, has following character for the auto-correlation function of any one pseudo-random code sequence:

$R\left(\mathrm{\τ}\right)=\left\{\begin{array}{cc}[1-\frac{\left|\mathrm{\τ}\right|}{p{T}_c}(p+1)]& \left|\mathrm{\τ}\right|\≤T_c\\ -\frac{1}{p}& T_c\≤\left|\mathrm{\τ}\right|\≤(p-1)T_c\end{array}\right.---(1-1)$

Wherein p is the cycle of pseudo-random code sequence, i.e. code length; T _cBe the element duration of sequence, i.e. symbol width.If following formula that is to say the phase difference of understanding two pseudo-random code sequences in a code element, the correlated results of two sequence normalizations is bigger, otherwise two normalized correlated results of pseudo-random code sequence just

Expression for convenience, hypothesis receives the mixed sequence of two Pseudo-Random Noise Codes here, and only represents with its pseudocode form that then receiving code is:

X (t)=PN ₁(t+ τ ₁)+PN ₂(t+ τ ₂), PN wherein _iRepresent i pseudo random noise sequence code; τ _iThe pairing code phase of corresponding sign indicating number that expression receives.

Suppose that again this locality has reappeared the 1st pseudo random noise sequence code, local reproduction sign indicating number can be expressed as:

y(t)＝PN ₁(t+τ′ ₁)

(1-2)

PN wherein ₁Represent the 1st pseudo random noise sequence code; τ ' ₁The 1st the pairing code phase of pseudo random noise sequence code sequence of expression reproduction.

If the sign indicating number sequence that receives and the sign indicating number sequence of reproduction are carried out related calculation, then have:

R(t)＝x(t)·y(t)

＝[PN ₁(t+τ ₁)+PN ₂(t+τ ₂)]·PN ₁(t+τ′ ₁)

＝PN ₁(t+τ ₁)·PN ₁(t+τ′ ₁)+PN ₂(t+τ ₂)·PN ₁(t+τ′ ₁)

＝R1(τ ₁-τ′ ₁)+R2(t)

(1-3)

Correlated results in the following formula can have been regarded two parts as, wherein the R of first ₁(t) be the same yard relevant portion between two sign indicating number sequences in the family, second portion R ₂(t) be relevant portion between two sign indicating number sequences in the different sign indicating number families.Can know that from the character of pseudo-random code sequence the correlation between the sign indicating number sequence in two different sign indicating number families is 0 (ideally).Can find out that from explanation even have a plurality of pseudo random noise sequence codes to exist in the sign indicating number that receives, all belong to this part, its value all is 0 (in fact also being a value near 0) in theory to second portion.

The situation of first is described below again.Also can be divided into two kinds of situations about first:

1, when the sequence of sequence that receives and local reproduction was two sequences with the phase place in the family sequence different (referring to that phase difference is greater than a chip), according to formula (1-1), first can be write as:

$R1\left(t\right)={\mathrm{PN}}_1(t+{\mathrm{\τ}}_1)\·{\mathrm{PN}}_1(t+{\mathrm{\τ}}_1^{\′})$

$=R1({\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′})=-\frac{1}{p}---(1-4)$

Wherein, | τ ₁-τ ' ₁| 〉=T _c, T _cBe symbol width.The following formula explanation is along with the increase of p, and two such sequence correlations also are smaller.

2 sequences when the sequence that receives and local reproduction are with the phase place in the family sequence during near (referring to that phase difference is less than a chip) sequence of two, and according to formula (1-1), first can be write as equally:

$R1\left(t\right)={\mathrm{PN}}_1(t+{\mathrm{\τ}}_1)\·{\mathrm{PN}}_1(t+{\mathrm{\τ}}_1^{\′})$

$=R1({\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′})=1-\frac{|{\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′}|}{p{T}_c}(p+1)$

$=1-\frac{|{\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′}|}{T_c}\×\frac{(p+1)}{p}---(1-5)$

Wherein, | τ ₁-τ ' ₁|≤T _c, T _cBe symbol width.The following formula explanation is along with the phase difference of two sequences is more little, and its normalized correlation is big more, and the two presents a linear growth relation.

Can obtain by above-mentioned analysis: no matter whether the sequence of reproduction is of the same clan with receiving sequence, as long as the phasic difference mutually of reproduction sequence and receiving sequence is within a chip, the correlation drawn of its normalizing is exactly smaller so.

Utilize above-mentioned analysis result, can draw: if the sequence of a plurality of outs of phase of this locality reproduction is superimposed, with they with come relevantly with the receiving code sequence, whether a sequence just can judging in a plurality of out of phase sequences according to correlated results receiving sequence occurs.Utilize this analysis result, the algorithm of front is improved.

For this algorithm is described, further the sign indicating number sequence of hypothesis reception is

x(t)＝PN ₁(t+τ ₁)+PN ₂(t+τ ₂)，

The sign indicating number sequence of local reproduction can be expressed as: y (t)=PN ₁(t+ τ ' ₁)+PN ₁(t+ τ ' ₂), PN wherein ₁Represent the 1st kind of pseudo random noise sequence code; τ ' ₁The pairing code phase of first yard sequence of the 1st kind of pseudo random noise sequence code of expression reproduction; τ ' ₂Second pairing code phase of sign indicating number sequence of the 1st kind of pseudo random noise sequence code of expression reproduction, also will suppose here | τ ₁-τ ' ₁|≤T _cWith | τ ₁-τ ' ₂| 〉=T _c, the phase difference of the code phase of first sequence in the expression reproduction sequence and the code phase of receiving sequence is in a chip or code element, and the phase difference of second code phase that reappears code phase in the sequence and receiving sequence is greater than a code-element period.

If equally the sequence code that receives and the sequence code of reproduction are carried out related calculation, then have:

R(t)＝x(t)·y(t)

＝[PN ₁(t+τ ₁)+PN ₂(t+τ ₂)]·[PN ₁(t+τ′ ₁)+PN ₁(t+τ′ ₂)]

＝PN ₁(t+τ ₁)·PN ₁(t+τ′ ₁)+PN ₁(t+τ ₁)·PN ₁(t+τ′ ₂)

+[PN ₂(t+τ ₂)·PN ₁(t+τ′ ₁)+PN ₂(t+τ ₂)·PN ₁(t+τ′ ₂)]

(1-6)

One has three in the following formula, and wherein the 3rd also comprises and two parts be respectively:

PN ₂(t+τ ₂)·PN ₁(t+τ′ ₁)

With

PN ₂(t+τ ₂)·PN ₁(t+τ′ ₂)。

Know that according to preceding surface analysis these two all is that two sequences not of the same clan are carried out related operation, its normalized correlation is very little, and is negligible.

Second in the formula (1-6) is: PN ₁(t+ τ ₁) PN ₁(t+ τ ' ₂), expression be that the different sequence of two phase places of the same clan is carried out related operation.Owing to suppose | τ ₁-τ ' ₂| 〉=T _c, therefore the normalized correlated results of this item can directly obtain, and should be

First in the formula (1-6) is: PN ₁(t+ τ ₁) PN ₁(t+ τ ' ₁), expression be that the different sequence of two phase places of the same clan is carried out related operation.Owing to suppose | τ ₁-τ ' ₁|≤T _c, therefore the normalized correlated results of this item also can directly obtain from formula (1-5), should be $1-\frac{|{\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′}|}{T_c}\×\frac{(p+1)}{p}.$

Can obtain the receiving code sequence to this with the correlation that reappears the sign indicating number sequence is:

$R=1-\frac{|{\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′}|}{T_c}\×\frac{(p+1)}{p}+(-\frac{1}{p})---(1-7)$

Following formula is compared with formula (1-5), and is many one

Obviously, be because just make through summation and to have increased this item in the correlated results, can cause the result that certain decay is arranged.

Need supplementary notes a bit, but since top derivation supposed to have in the summation reproduction sign indicating number sequence and receiving sequence be phase difference of the same clan greater than a symbol width, if having m such sequence to appear at and item in, formula (1-7) need be write as following formula again:

$R=1-\frac{|{\mathrm{\τ}}_1-{\mathrm{\τ}}_1^{\′}|}{T_c}\×\frac{(p+1)}{p}+m\×(-\frac{1}{p})---(1-8)$

But wherein in the sequence that parameter m is represented to participate in suing for peace the phase difference of and receiving sequence code phase of the same clan with receiving sequence greater than the sequence number of a code element.

According to above-mentioned principle, technical scheme of the present invention is achieved in that a kind of catching method of pseudo-code sequence, it is characterized in that,

The first step, produce the local copy codes of the satellite pseudo-code sequence (satellite pseudo noise code) that is positioned at the receiver sky by pseudo-random code generator, all different code phase sequences of this local copy codes are divided into the n grouping uniformly, the per minute group comprises m different code phase sequences, with the m in the per minute group code phase sequences addition, obtain the compound key sequence of this grouping, be designated as P _i, i is a packet number, i=1,2,3 ... n;

Second step is with compound key sequence P _iCarry out correlation intergal with the satellite pseudo-code sequence that receives respectively, if compound key sequence P _iCorrelation integral value is greater than threshold value Th1, and then the satellite pseudo-code sequence of expression detection is included in the code phase sequences of this grouping; If compound key sequence P _iCorrelation integral value is then proceeded compound key sequence P less than threshold value Th1 _I+1The correlation intergal computing; If all compound key sequence P _iCorrelation integral value all is not more than threshold value Th1, then changes into each independent code phase sequences searching for, and promptly adopts conventional code phase sequence searching method;

The 3rd step is for above-mentioned compound key sequence P _iCorrelation integral value is greater than the respective packets of threshold value Th1, m in this a grouping code phase sequences is carried out correlation intergal with the satellite pseudo-code sequence that receives respectively again, if certain code phase sequences correlation integral value is greater than threshold value Th2, this code phase sequences just and the satellite pseudo-code sequence synchronous, promptly the satellite pseudo-code sequence is hunted down.

Described satellite pseudo-code sequence is a gps signal.

Described all different code phase sequences with this local copy codes are divided into the n grouping uniformly, and the per minute group comprises m different code phase sequences, and wherein m is 10～32, and n is 32～103.

Described all different code phase sequences with this local copy codes are divided into the n grouping uniformly, and the per minute group comprises m different code phase sequences, and wherein m is 32, and n is 32.

Described satellite pseudo-code sequence is a galileo signals.

The present invention divides into groups earlier to the code phase sequences that will search for, according to compare threshold, find out the grouping that comprises the satellite pseudo-code sequence, and then to the grouping in code phase sequences search for, find out and finally want synchronous code phase sequences, will reduce greatly volumes of searches and search time like this, improve the performance of receiver.

Work as m=1, during n=1023, be equivalent to code phase of per minute group, have 1023 groups, this situation is equal to nothing and divides into groups, and is the same with traditional code phase search method.

Work as m=1023, during n=1, be equivalent to have only a grouping, but in this grouping 1023 code phases are arranged, same with traditional method is the same.

Work as m=10, n=103, every group of 10 code phases, 103 groups altogether, last organizes 3 code phases, correlation intergal amount of calculation CQ ≈ 103+10=113.

Therefore, minimum correlation intergal amount of calculation should be min (n+1023/n), and n ∈ [1,1023] can obtain n ≈ 32, minimum correlation intergal amount of calculation CQ=32+31=63.And the correlation intergal amount of calculation that traditional code phase detection method needs is 1023.

Description of drawings

The present invention is described in further detail below in conjunction with description of drawings and concrete execution mode.

Fig. 1 is a flow chart of the present invention.

Fig. 2 is two normalized figures of sequence auto-correlation function, and abscissa is two code phase τ that sign indicating number of the same clan differs, and ordinate is the normalized autocorrelation functions value.

Be the normalization correlation, T _cBe symbol width.

Fig. 3 gps signal emulation module figure.

Fig. 4 is that signal to noise ratio is-situation during 10dB, and abscissa is some correlation time, and ordinate is the normalized autocorrelation functions value.

The delay sign indicating number sum that Fig. 4 a represents 12 reproduction sign indicating number sequences all with the phase alignment of receiving code sequence.

Fig. 4 b represents the delay sign indicating number sum of 12 reproduction sign indicating number sequences, and one of them reproduction sign indicating number sequence is identical with the receiving code sequence phase.

Fig. 4 c represents that 12 of local reproduction sign indicating number postpone not exist in the sign indicating number sign indicating number that aligns with receiving code.

Fig. 5 be signal to noise ratio be-situation of 20dB under, abscissa is some correlation time, ordinate is the normalized autocorrelation functions value.

The delay sign indicating number sum that Fig. 5 a represents 12 reproduction sign indicating number sequences all with the phase alignment of receiving code sequence.

Fig. 5 b represents the delay sign indicating number sum of 12 reproduction sign indicating number sequences, and one of them reproduction sign indicating number sequence is identical with the receiving code sequence phase.

Fig. 5 c represents that 12 of local reproduction sign indicating number postpone not exist in the sign indicating number sign indicating number that aligns with receiving code.

Fig. 6 is that signal to noise ratio is-situation of 30dB, and abscissa is some correlation time, and ordinate is the normalized autocorrelation functions value.

The delay sign indicating number sum that Fig. 6 a represents 12 reproduction sign indicating number sequences all with the phase alignment of receiving code sequence.

Fig. 6 b represents the delay sign indicating number sum of 12 reproduction sign indicating number sequences, and one of them reproduction sign indicating number sequence is identical with the receiving code sequence phase.

Fig. 6 c represents that 12 of local reproduction sign indicating number postpone not exist in the sign indicating number sign indicating number that aligns with receiving code.

Embodiment

Be illustrated in figure 1 as flow chart of the present invention:, produce this locality reproduction sign indicating number of the satellite pseudo-code sequence that is positioned at the receiver sky 1) at first by pseudo-random code generator.2) with all different code phase sequences of this locality reproduction sign indicating number, be divided into the n grouping uniformly, the per minute group comprises m code phase sequences.3) m in the per minute group code phase sequences addition obtained the compound key sequence.4) compound key sequence after the addition and the satellite pseudo-code sequence that receives are carried out correlation intergal, if greater than threshold value Th1, then the satellite pseudo-code sequence that detects of expression is included in this grouping.If be not more than threshold value Th1, then the compound key sequence of next grouping is carried out correlation intergal, up to the compound key sequence that finds greater than threshold value Th1.5) the compound key sequence to finding out is carried out correlation intergal again with each code phase sequences in its respective packets and satellite pseudo-code sequence, finds out wherein greater than that code phase sequences of threshold value Th2, so just can find out the specific code phase place of satellite pseudo-code sequence.

Embodiment: work as m=32, n=32,32 code phase sequences of per minute group, altogether 32 groupings, last 31 code phase sequences of dividing into groups because with 32 be more or less the same, can get same threshold as decision condition or get threshold value 31/32 as decision condition.To the code phase sequences summation of each grouping,, contain the satellite pseudo-random code sequence then, so just stop to carry out group searching if the correlation integral value of the 12nd grouping greater than threshold value 2dB, illustrates in this grouping again with satellite pseudo-random code sequence correlation intergal.In the 12nd grouping, carry out the concrete search of 32 code phase sequences subsequently, if after the 25th code phase sequences carried out correlation intergal, it was worth greater than 3dB, so just can judge and find the satellite pseudo-random code sequence.The ordering of this code phase sequences is 11 * 32+25=377, and the amount of calculation of correlation intergal is 12+25=37.

Further specify embodiments of the present invention below by the emulation of catching example to gps signal and galileo signals.The platform of emulation is Matlab6.5.

With reference to Fig. 2, be two normalized figures of sequence auto-correlation function, two sequences are the pseudo noise code of the same clan of different code phases, the code phase τ that abscissa differs for these two sign indicating numbers of the same clan, ordinate is the normalized autocorrelation functions value.As can be seen, in one-period, the code phase τ that differs is more little, and correlation is big more.

With reference to Fig. 3, because the length of pseudo-code is 1023 in the gps signal, each GPS random code is divided into 86 groupings, 12 code phase sequences of per minute group, different code phase sequences in the per minute group are carried out addition, carry out the correlation intergal computing with reception satellite pseudo-random code sequence then.Additive white Gaussian noise module (AWGN) among the figure, what promptly the input signal of correlation intergal computing is introduced is white Gaussian noise, and this noise is added in the input signal end.Gold Sequencegenerator module is a Ge Erde sign indicating number generator, produces pseudo noise code.Matrix multiply module is the module of correlation intergal.The Delay module is a time delay module, the code phase of delaying time.Also have a code phase sequences adder, carry out the addition of code phase sequences, be about to 12 code phase sequences and carry out addition.

Fig. 4, Fig. 5, Fig. 6 have provided the correlated results in three kinds of situations of different signal to noise ratios (ratio of gps signal and additive Gaussian noise) respectively.

From simulation result as can be seen:

Fig. 4 a, Fig. 5 a, Fig. 6 a can illustrate: if all the code phase with receiving code is identical for the code phase of 12 local reproduction sign indicating numbers, the peak value in the correlated results all is apparent in view.

Fig. 4 b, Fig. 5 b, Fig. 6 b can illustrate: if having the code phase of a sequence identical with the code phase of receiving code in 12 local reproduction sign indicating number sequences, though the peak value of its correlated results has obvious decline than the peak value of corresponding figures 4a, Fig. 5 a, Fig. 6 a, its peak value also is clearly.The reason that peak value descends is to have 11 sequences different with the code phase of receiving code to participate in summation, in fact is exactly because of second in the formula (1-8) in action.

Fig. 4 c, Fig. 5 c, Fig. 6 c can illustrate: if the neither one phase code is identical with the code phase of receiving code in the code phase of 12 sign indicating number sequences of local reproduction, then correlated results is littler.

The present invention also be can be used for catching in the Galileo system E1 frequency range clearing signal.For catching of galileo signals, with the main distinction of gps signal be exactly the sign indicating number length different, other steps are identical, can obtain consistent results.

Therefore, the The above results explanation can divide into groups to sue for peace to the code phase sequences of sign indicating number of the same clan earlier fully, after determining to divide into groups, determines concrete code phase sequences again.Can reduce the number of times of correlation intergal like this, reduce operand and operation time,, under the same clock cycle, can shorten the time of lock-on signal for receiver.

Claims (5)

1, a kind of catching method of pseudo-code sequence is characterized in that, may further comprise the steps:

The first step, produce the local copy codes of the satellite pseudo-code sequence that is positioned at the receiver sky by pseudo-random code generator, all different code phase sequences of this local copy codes are divided into the n grouping uniformly, the per minute group comprises m different code phase sequences, with the m in the per minute group code phase sequences addition, obtain the compound key sequence of this grouping, be designated as P _i, i is a packet number, i=1,2,3 ... n;

Second step is with compound key sequence P _iCarry out correlation intergal with the satellite pseudo-code sequence that receives respectively, if compound key sequence P _iCorrelation integral value is greater than threshold value Th1, and then the satellite pseudo-code sequence of expression detection is included in the code phase sequences of this grouping; If compound key sequence P _iCorrelation integral value is then proceeded compound key sequence P less than threshold value Th1 _I+1The correlation intergal computing; If all compound key sequence P _iCorrelation integral value all is not more than threshold value Th1, then changes into each independent code phase sequences searching for, and promptly adopts conventional code phase sequence searching method;

The 3rd step is for above-mentioned compound key sequence P _iCorrelation integral value is greater than the respective packets of threshold value Th1, m in this a grouping code phase sequences is carried out correlation intergal with the satellite pseudo-code sequence that receives respectively again, if certain code phase sequences correlation integral value is greater than threshold value Th2, this code phase sequences just and the satellite pseudo-code sequence synchronous, promptly the satellite pseudo-code sequence is hunted down.

2, the catching method of a kind of pseudo-code sequence according to claim 1 is characterized in that, described satellite pseudo-code sequence is a gps signal.

3, the catching method of a kind of pseudo-code sequence according to claim 2, it is characterized in that described all different code phase sequences with this local copy codes are divided into the n grouping uniformly, the per minute group comprises m different code phase sequences, wherein m is 10～32, and n is 32～103.

4, the catching method of a kind of pseudo-code sequence according to claim 3 is characterized in that, described m is 32, and n is 32.

5, the catching method of a kind of pseudo-code sequence according to claim 1 is characterized in that, described satellite pseudo-code sequence is a galileo signals.

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