CN101436877B - Method for capturing multi-path interference resistant PN code self-adapting threshold - Google Patents

Abstract

The invention discloses a method for capturing a self-adapting threshold of an anti-multichannel interference PN code in the technical field of communication, which comprises the following steps: firstly constructing a two-way parallel digital matched filter, achieving correlative operation of a spread-spectrum signal and a local PN code, then summing two-way correlative values after being squared, and obtaining synchronously verified decision statistic of the PN code after taking a square root. The method is characterized in that the statistic is added to a sequence converting circuit and an input end of a median filter simultaneously, the statistic output by the sequence converting circuit is processed by a two-way parallel form filter and then output values are summed, a mean value is taken to obtain a self-adapting judgment threshold, a judging device compares the judgment statistic with an input self-adapting judgment threshold till the judgment amount is larger than a threshold value, and capture of the PN code is decided to be successful at this moment. The method has the advantages that the method can adapt to a multichannel environment better, has excellent performance of anti-multichannel interference, has strong practicability, and can be applied to various mobile communication systems using direct sequence spread-spectrum technique.

Description

The PN code self-adapting threshold catching method that a kind of anti-multipath disturbs

Technical field:

The present invention relates to communication technical field, relate in particular under the multipath channel environment, realize that in direct sequence spread spectrum communication system (DSSS) the local code sequence is slightly synchronous with the sign indicating number sequence that receives, a kind of PN code capture method that anti-multipath disturbs.

Background technology:

The PN sign indicating number be the most basic most important problem in the direct sequence spread spectrum communication system (DSSS) synchronously.Synchronizing process generally comprises two parts: catch and follow the tracks of.Catching is coarse adjustment, can make the local code sequence slightly synchronous with the sign indicating number sequence that receives, and general phase error is in 1/2 chip lengths.Tracking is fine tuning, and sending and receiving end symbol phases error is further dwindled, and reaches synchronous accurately and in whole transmission course, keeps this synchronous.

Forefathers have carried out a large amount of research for catching of PN sign indicating number, but mainly concentrate on the catching method based on fixed threshold.In the GSM of reality; Because user's fast moving adds the influence of channel fading and dynamic disturbance, the power that causes receiving signal can change in great dynamic range; Traditional fixed threshold can not obtain good acquisition performance, can't adapt to actual applied environment.For this reason, people have proposed multiple adaptive threshold catching method.Document [1] [Kim, C.J., Lee; H.J., and Lee, H.S.; Adaptive acquisition of PN sequences for DSSS communications, IEEE Trans.Commun., 1998; 46 (8): 993-996] invariable false alerting in the Radar Signal Processing (CFAR) inspection technology is incorporated in the PN sign indicating number acquisition procedure, has proposed average statistics (MLAP) and two kinds of methods of sequencing statistical (OSAP), utilize a plurality of forward directions and back Background Noise Power to be estimated to observed quantity.Document [2] [Xue Wei, Xiang Jingcheng, Zhou Zhizhong; The threshold adaptive method of estimation that a kind of PN sign indicating number is caught; Electronic letters, vol, 2003,31 (12): 1870-1873] and MLAP, OSAP method in the document [1] all be to utilize the maximum likelihood (ML) of the sample equivalent Gaussian noise power of judgment variables to estimate.Improve estimated accuracy and must increase and handle window length, but under multi-path environment, the relevant peaks of multi-path signal-component possibly fall into handles window, cause the noise power estimated value higherly, detection probability significantly descends.Document [3] [Choi Kwonhue; Cheun Kyungwhoon; And Jung Taejin, Adaptive PN code acquisition using instantaneous power-scaled detection threshold under rayleigh fading and pulsed gaussian noise jamming, IEEE Trans.on Commun.; 2002; 50 (8): 1232-1235] proposed a kind of adaptive threshold scheme, exist under the situation of narrow band interference, thereby estimated value also can higherly cause decreased performance based on real-time Energy Estimation.

Summary of the invention:

The objective of the invention is to: provide a kind of and can adapt to multi-path environment, background noise is estimated in real time, the PN code self-adapting threshold catching method that anti-multipath disturbs.

The objective of the invention is to realize through the enforcement following technical proposals:

1, a kind of PN code self-adapting threshold catching method of anti-multipath interference, realize by following step:

A, at first make up the parallel digital matched filter F of two-way _I, F _Q, F is set according to the value of corresponding position in the local PN sign indicating number _IAnd F _QIn the weight coefficient of multiplier: the corresponding position of PN sign indicating number is 0, then weight coefficient get+1; The corresponding position of PN sign indicating number is 1, and then weight coefficient gets-1.

B, with the in-phase component r of the spread-spectrum signal that receives _IWith quadrature component r _QBe input to digital matched filter F respectively _IAnd F _QIn, the related operation between realization and the local PN sign indicating number.

C, to digital matched filter F _I, F _QHomophase and the quadrature two-way correlation of output carries out square asking mould, then the root of making even after two modulus additions obtained PN sign indicating number verification of synchronization decision statistic amount Z _n

It is characterized in that: d, the verification of synchronization decision statistic amount Z that is used to adjudicate _nBe added to the input of sequence change-over circuit and median filter simultaneously, the sequence change-over circuit is exported X according to median filter _nValue, to the Z of each input _nCarry out like the conversion that acts, with list entries Z _nConversion is output as a new sequence Y _nIf: Z _nValue greater than 5 times of X _n, then the sequence change-over circuit is exported Y _n=X _nOtherwise Y _n=Z _n

Median filter adopts shift register structure, and filter window length is 2N+1, and N is a positive integer here, and being located at i, to import the sampling point of sample sequence in filter window constantly be x _I-N... X _i..., x _I+N, this moment, filter was exported y so _i=med (x _I-N... X _i..., x _I+N), sample values all in the window of med () expression are here got the computing that it comes a middle value output by after the sequence arrangement from small to large.

E, the parallel morphological filter of structure two-way, the one tunnel is form open-close filter F _Oc, another road is that form is closed-Kai filter F _Co, with sequence Y _nBe added to F _OcAnd F _CoInput, it is carried out further smothing filtering.

The related definition of morphological filter is following:

If being respectively, f (n) and g (m) be defined in F={0,1 ...., N-1} and G={0,1 ...., the discrete function that M-1} is last, and N＞＞M.If f (n) is a list entries, g (m) is a structural element.F (n) is defined as respectively about corrosion and the expansion of g (m):

(n＝0，1，......，N-M)

$(f\⊕g)\left(n\right)=\underset{m=\mathrm{0,1},...,M-1}{\max }\{f(n-m)+g\left(m\right)\}---\left(2\right)$

(n＝0，1，......，N+M-2)

Where the symbols

and

denote erosion and dilation.

F (n) opens to close respectively with form about the form of g (m) and is defined as:

Symbol о and represent that respectively form opens and the form closed operation in the formula.

Oc (f (n)), co (f (n)) represent that respectively form open-close filter and form close-output of Kai filter, and form open-close filter and form close-the Kai filter adopts the cascade combining form of modal of morphological opening and closing operation, definition as follows:

oc(f(n))＝(fоg·g)(n)(5)

co(f(n))＝(f·gоg)(n)(6)

F, with morphological filter F _OcAnd F _CoThe addition of two-way output valve, get its mean value then and obtain self-adaptive decision threshold V _T

Because the anti-dilatancy of opening operation and the dilatancy of closed operation, there is the statistical bias phenomenon in the output of form OC and CO filter, uses separately somely can't obtain good effect.Therefore the present invention to open-close with close-output valve of Kai filter made average treatment.

G, the PN sign indicating number verification of synchronization decision statistic amount Z of decision device to importing _nSelf-adaptive decision threshold V with input _TRelatively big or small, as verification of synchronization decision statistic amount Z _nBe lower than threshold value V _TThe time, show local PN code phase and receive signal not synchronously that the decision statistic amount and the thresholding that then produce corresponding next phase place are made comparisons again, up to the corresponding verification of synchronization decision statistic amount Z of one of them phase place _nSurpass thresholding V _T, be judged to be acquisition success this moment, decision device output PN sign indicating number acquisition success index signal.

The invention has the advantages that: owing to used the estimator that is made up of sequence change-over circuit, median filter and morphological filter that background noise has been carried out real-time estimation, so the present invention can carry out the self adaptation adjustment according to the noise size by the detection threshold that is used for prize judgment that estimator obtains when catching carrying out the PN sign indicating number.Simultaneously, owing to carried out the sequence conversion to received signal, rejected the exceptional value in the sample; Eliminated the influence that possibly fall into the relevant peaks of handling the multi-path signal-component in the window, reduced the influence that multipath disturbs greatly, accomplished preliminary treatment data; Therefore; Adaptive threshold catching method proposed by the invention can be good at adapting to the multipath channel environment, and the anti-multipath jamming performance is excellent, can be applied to use the various GSMs of direct sequence spread spectrum skill.

Description of drawings

Fig. 1 catches the implementation method sketch map for PN sign indicating number of the present invention

Fig. 2 realizes receiving spread frequency signal and local PN sign indicating number for digital matched filter and carries out the sketch map of related operation

Fig. 3 is the false alarm probability P of system _FaBe respectively 0.01,0.001 and at 0.0001 o'clock, the graph of a relation of PN sign indicating number Acquisition Detection probability of the present invention and signal to noise ratio

Mark among the figure: r _IBe the in-phase component of the spread-spectrum signal that receives, r _QBe the quadrature component of the spread-spectrum signal that receives, F _IAnd F _QBe digital matched filter, () ²Be square operation, symbol

Be add operation, symbol

Be extracting operation, F _Oc, F _CoRepresent the form open-close respectively and close-the Kai filter, symbol 1/2 expression to input value divided by 2 computing, Expression is to Z _nAnd V _TCompare the computing of size, symbol The computing to a plurality of input variable summations is represented in expression multiplying, ∑.

Embodiment

In an embodiment of the present invention; Receiving signal is the Direct swquence spread spectrum signal; The modulation system of spread spectrum system adopts difference binary phase shift keying (DBPSK; Differential Binary Phase Shift Keying), the code length of spread spectrum PN sign indicating number is L=1023 (a m sequence), and spreading gain is about 30dB.Data rate is R _b=9.6kbit/s confirms that thus bit rate is R _c=9.6L=9820.8k chip/s, the about 20MH of required channel width _ZAdopt data bit and the synchronous mode of PN sign indicating number during spread spectrum, promptly the PN sign indicating number aligns with the transfer point of data bit, and each data bit width equals a PN sign indicating number cycle.

In an embodiment, digital matched filter F _I, F _QThe delay tap number be 1023, equal the code length of the PN sign indicating number that adopts, promptly digital matched filter will carry out related operation complete cycle to receiving the PN sign indicating number.Median filter sliding window length gets 9, the form open-close with close-the used structural element of Kai filter get g (m)=0,1,2,1,0}.So far, accomplished parameter setting to PN sign indicating number capture systems self-adaptive decision threshold.

The spread-spectrum signal that receives is divided into homophase (R through after the non-coherent demodulation _I) and quadrature (r _Q) two paths of signals, be input to digital matched filter F respectively _IAnd F _QIn, the related operation between realization and the local PN sign indicating number.

In order to overcome the influence of the phase deviation that the incoherent reception mode brings, to digital matched filter F _I, F _QHomophase and the quadrature two-way correlation of output carries out square asking mould, then the root of making even after two modulus additions obtained PN sign indicating number verification of synchronization decision statistic amount Z _n

The verification of synchronization decision statistic amount Z that is used to adjudicate _nBe added to the input of sequence change-over circuit and median filter simultaneously, the sequence change-over circuit is exported X according to median filter _nValue, to the Z of each input _nCarry out like the conversion that acts, with list entries Z _nConversion is output as a new sequence Y _nIf: Z _nValue greater than 5 times of X _n, then the sequence change-over circuit is exported Y _n=X _nOtherwise Y _n=Z _n

With sequence Y _nBe added to parallel form open-close filter F _OcClose with form-Kai filter F _CoInput, it is carried out further smothing filtering.With morphological filter F _OcAnd F _CoThe addition of two-way output valve, get its mean value then and obtain decision device test statistics is adjudicated required self-adaptive decision threshold V _T

Decision device is with the PN sign indicating number verification of synchronization decision statistic amount Z of input _nSelf-adaptive decision threshold V with input _TCompare, as verification of synchronization decision statistic amount Z _nBe lower than threshold value V _TThe time, show local PN code phase and receive signal not synchronously that the decision statistic amount and the thresholding that then produce corresponding next phase place are made comparisons again, up to the corresponding verification of synchronization decision statistic amount Z of one of them phase place _nSurpass thresholding V _T, be judged to be acquisition success this moment, decision device output PN sign indicating number acquisition success index signal.

In an embodiment, the PN sign indicating number is caught all and is realized by hardware.In practical application, the designer can select corresponding software realization mode as the case may be.

Fig. 3 has provided the false alarm probability P of system _FaBe respectively 0.01,0.001 and at 0.0001 o'clock, the PN sign indicating number Acquisition Detection probability of present embodiment and the relation of signal to noise ratio, along with signal to noise ratio increases, detection probability progressively increases, and has shown validity of the present invention.

Claims (1)

1. the PN code self-adapting threshold catching method that disturbs of an anti-multipath, realize by following step:

A, at first make up the parallel digital matched filter F of two-way _I, F _Q, F is set according to the value of corresponding position in the local PN sign indicating number _IAnd F _QIn the weight coefficient of multiplier: the corresponding position of PN sign indicating number is 0, then weight coefficient get+1; The corresponding position of PN sign indicating number is 1, and then weight coefficient gets-1;

B, with the in-phase component r of the spread-spectrum signal that receives _IWith quadrature component r _QBe input to digital matched filter F respectively _IAnd F _QIn, the related operation between realization and the local PN sign indicating number;

C, to digital matched filter F _I, F _QHomophase and the quadrature two-way correlation of output carries out square asking mould, then the root of making even after two modulus additions obtained PN sign indicating number verification of synchronization decision statistic amount Z _n

It is characterized in that: d, the verification of synchronization decision statistic amount Z that is used to adjudicate _nBe added to the input of sequence change-over circuit and median filter simultaneously, the sequence change-over circuit is exported X according to median filter _nValue, to the Z of each input _nCarry out like the conversion that acts, with list entries Z _nConversion is output as a new sequence Y _nIf: Z _nValue greater than 5 times of X _n, then the sequence change-over circuit is exported Y _n=X _nOtherwise Y _n=Z _n

E, the parallel morphological filter of structure two-way, the one tunnel is form open-close filter F _Oc, another road is that form is closed one and opened filter F _Co, with sequence Y _nBe added to F _OcAnd F _CoInput, it is carried out further smothing filtering;

F, to morphological filter F _OcAnd F _CoThe addition of two-way output valve, getting its mean value then is self-adaptive decision threshold V _T

G, the PN sign indicating number verification of synchronization decision statistic amount Z of decision device to importing _nSelf-adaptive decision threshold V with input _TRelatively big or small, as verification of synchronization decision statistic amount Z _nBe lower than threshold value V _TThe time, show local PN code phase and receive signal not synchronously that the decision statistic amount and the thresholding that then produce corresponding next phase place are made comparisons again, up to the corresponding verification of synchronization decision statistic amount Z of one of them phase place _nSurpass thresholding V _T, be judged to be acquisition success this moment, decision device output PN sign indicating number acquisition success index signal.

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