CN1206255A - Pesudo-random noise detector for signals having carrier frequency offset - Google Patents

Abstract

In the front end of a mobile phone receiver, detection of a carrier frequency offset in a received PN-modulated signal is performed by first correlating the received signal with a local replica of the PN codes generated within the receiver. The resulting despread signal is integrated over a fixed period, or dwell, of time, then run through a square-law envelope detector. The integration is divided into a plurality of sub-dwells, the values of which are each provided as an input to a Fast Fourier Transform (FFT) to generate a plurality of frequency bins. The magnitude for each FFT frequency bin is computed and a maximum value is selected. The maximum value and its corresponding bin number are saved in the signal processor's memory. The next PN code phase is tested and, depending on the search scheme, this sequence continues until the decision algorithm terminates the search.

Description

Puppet with carrier wave frequency deviation signal with

The machine noise detector

This invention relates generally to a kind of method and apparatus, and when having offset frequency in the carrier frequency, the utilization pseudo noise is modulated and detected direct sequence spread spectrum (DSSS) signal.

Based on the wireless communication system of direct sequence spread spectrum (DSSS) signal, comprise code division multiple access (CDMA), in a system, use common carrier frequency bandwidth and all base station communications.Carrier signal is to be modulated by pseudo-random noise (PN) signal that generator produced, and this generator provides the device that is different from this common frequency bandwidth.The PN spreading code that is included in second signal comprises a series of binary system chips, and each all has a chip period.The carrier wave and the PN signal of combination are to be modulated by the third signal that comprises digitized speech or data-signal.

For the third signal that uses in the receiving terminal conversion, after the carrier frequency demodulation, this piece PN generator must be synchronous with the PN sequence of input in the receiving terminal.The PN sign indicating number is used for initial captured signal and transmission data.By from the signal that receives, shifting out the PN sequence and, then can obtain the signal of despreading with symbol period of its integration.The despreading of received signal is to be finished by the local copy that produces the PN sign indicating number in the receiving terminal, and then local PN sign indicating number is synchronized to this PN sign indicating number, and this PN sign indicating number is superimposed upon on the reception ripple that is included in the received signal.The input signal that is brought by synchronous local PN sign indicating number copy multiplies each other or the despreading of modulation generation requirement again.

At acquisition phase, spread-spectrum signal is calibrated each other.Just this stage, receiver must be carried out some its most important function, promptly sets up chip regularly synchronously, correcting frequency offset.In case obtain synchronously, the interior closed loop tracking system of receiving terminal clock is regulating frequency and phase place constantly, to optimize the data-signal sampling of extracting from each received signal.

The process of this locality and reception PN signal is generally finished by two stages synchronously.At first, adjust roughly in two PN signals to little residue timing slip, catch to reach PN.In case capture, this PN sign indicating number must remain in the accurate synchronizing process that is called the PN tracking.In the direct sequence cdma system, the PN sign indicating number is very long usually.In order to reduce the complexity of receiving terminal hardware, require all PN sign indicating numbers relevant, and the relevant a part of cycle that reaches at the PN sign indicating number, promptly employed " time of staying " goes up relevant.

The DSSS input that is used to catch is normally used the reception that is similar to structure shown in Figure 1 to bring in and accomplished that this structure comprises: correlator 102 is used for the received signal plus noise is compared with copying from the PN code book ground of local PN generator 104; Integrator 106 is used for the wave detector output of a fixed dwell time is quadratured, to obtain whole integrated power; Square law envelope detector 108 and comparator 110 are used for this power and the comparison that sets in advance thresholding.When this power rank surpasses threshold value, then reached the rough adjustment of PN signal.Be used to determine to catch the optimum thresholding and the fixed value that whether have taken place and have nothing to do, but the function of signal to noise ratio (snr).As everyone knows, the SNR of communication channel will as a kind of function in time, the change of the speed of receiving terminal, position and changing.

A kind of simple model's capture technique, utilization has the maximum probability method of the single time of staying.The PN coded signal that this specification requirement receives is relevant with all possible phase position of local PN sign indicating number.Be somebody's turn to do relevant concurrent carrying out, and the output of corresponding wave detector is associated all with the same observation (stop) of received signal (plus noise).Correct PN calibration is decided by the comparator as local PN code phase location, and this phase position produces the maximum output from wave detector.Catch because of parallel work-flow and finish rapidly.Yet, the length code of being utilized for the CDMA signal and the big processing gain of requirement, the complexity of parallel computation can suppress.Other capture technique is known in the prior art.

By the No.5 of Chung et.al., 440,597 United States Patent (USP)s provide some concise and to the point descriptions of these technology, and one among the present inventor also is a partner of this research.The disclosure of ' 597 patent will be inserted in here, for your guidance.

When frequency error produces between transmission end and receiving terminal, perhaps because the oscillator drift that multi-path transmission (Rayleigh fading), temperature cause, Doppler effect, or the phenomenon that causes of other distortion, or the mutual combination of several persons, receiver/demodulator must at first determine frequency deviation before catching generation.The appearance of frequency deviation causes that the relative code phase place changes in time between PN sign indicating number reception and that this locality produces.The more important thing is the average speed of searching of offset frequency influence.

When detecting the signal that passes through additive white Gaussian noise (AWGN) channel, only be the function of noise variance detection time.Noise variance is big more, requires the relevant time long more, and this will cause long detection time.Because frequency deviation has also increased detection time, otherwise can cause the serious decay of acceptable geophone property experience in the frequency deviation that awgn channel exists.Coherent detection may be lost because of the existence of frequency deviation from the ability of the signal of awgn channel.

The conventional method that reduces the frequency deviation problem and handle long PN sign indicating number is to be separated into the whole time of integration many little part correlation times, or son stops (the observation cycle of received signal), with losing of causing of minimizing frequency time limit.Each son is stopped the calculating amplitude, and all sub-stop amplitudes are added up to obtain whole integration amplitude, this capture systems is called " uncorrelated adding method ", is a kind of Series P N capture systems that stops more.(see routine M.K.Simon, et.al, SpreadSpectrum Comm.Handbook (spread spectrum communication handbook), revised edition, 1994, McGraw-Hill, Inc.Part4, ch.1, " the quasi-noise code is caught in the direct sequence receiver " is hereby incorporated by).The whole amplitude time corresponding in this method reduces significantly, because son stops a part of only representing the time of staying, has only when existing little frequency deviation maybe might occur in the short time of integration, and this method is just more feasible.Another shortcoming of this method is to accomplish the detection of being correlated with.

The system of a suggestion of decision frequency deviation is disclosed in the United States Patent (USP) 5,556,202 of Lang, is hereby incorporated by.In this system, separation is correlated with and channel comprises a pair of shift LD character string, and the corresponding level of each character string is isometric.Received signal is divided at inter-stage.The inter-stage continuous in the shift LD character string provides phase rotation device, distributes the same-phase (I) of received signal and quadrature component (Q) to arrive corresponding shift LD character string.Each shift LD character tandem is relevant with the PN sequence of selection, with result summation and with set in advance relevant threshold value and compare.Suppose and to introduce wrong phase place rotation.And this system still uses uncorrelated adding method, has kept this shortcoming of this system.

Do not rely on irrelevant method, still need to keep the system of quick decision PN signal capture frequency deviation.System of the present invention has satisfied this needs.

The advantage of this invention provides a kind of method and system, with the frequency deviation that detects the detection time that reduces in the PN signal.

Another advantage of this invention is to provide a kind of utilization half-correlation detector, the method and system of enhancement PN signal capture.

Also having an advantage is that a kind of appraising frequency bias method and system with few additional treatments is provided.

In a model's embodiment, the front end of the mobile phone receiver of working in the network of utilization DSSS signal by at first the local copy with the PN sign indicating number that produces in received signal and the receiver is relevant, detects the frequency deviation in the PN modulation signal of reception.With result's one fixed cycle of despread signal integration, or the time of staying, square-law envelope detector passed through then.This integration is divided into one group of son stops, their each value is all imported as fast Fourier transform (FFT), to produce a class frequency sampling point.Calculate the amplitude of each FFT frequency sample point, and select maximum.This maximum and corresponding sampling point number are kept in the memory of signal processor.According to the plan of searching, detect next PN code phase, continue such step, stop the plan of searching up to the decision algorithm.In one embodiment by allowing data have the bank of filters of a filter, each sampling point of collecting and sampling is calculated its amplitude by each sampling point in frequency domain.Then, will be worth the thresholding comparison that sets in advance with by a kind of algorithm that determines.Alternatively, this sampling point is searched on serial or parallel ground, to be chosen in the maximum in the given integration.

Announcing coupling, and after termination searches, the sampling point index by average each high-amplitude that iterates obtains appraising frequency bias, and then does iterating of many search process at the PN code phase place that coupling has been found.Result's value is the frequency deviation that can be used for calculating the reception carrier frequency, and automatic frequency control (AFC) circuit that this information can be offered at receiving terminal comes the accurate adjustment receiver, to reach correct frequency.The performance of frequency estimator is the function of sampling number used in averaging process.

Detailed description to most preferred embodiment of the present invention will more help to understand the present invention in conjunction with the drawings, and label identical among the figure is represented identical parts, wherein:

Fig. 1 is the block diagram of the PN capture systems of prior art;

Fig. 2 is according to the block diagram with cell phone receiver front end of the present invention of other receiving function;

Fig. 3 is the flow chart of the testing process of expression frequency deviation;

Fig. 4 is the flow chart of the estimation procedure of expression frequency deviation;

Below optimum implementation describe the inventive method and device in detail and be applied to CDMA mobile phone receiver according to TIA/EIA IS-95 (the mobile radio station one base station compatible standard of dual mode wideband spread spectrum cellular system).It should be noted other wireless communication system that also method as described herein can be applied to equally adopt PN sign indicating number modulation signal based on DSSS.

Following detailed has been used the abbreviation that uses usually in many these fields, and first example of each abbreviation all at length provides definition, and for convenience, following table 1 has been listed abbreviation and their definition separately:

The abbreviation definition

A/D analog to digital (transducer)

The control of AFC automatic frequency

The control of AGC automatic gain

The ASIC application-specific integrated circuit (ASIC)

The AWGN additive white Gaussian noise

The BPF band pass filter

The CDMA code division multiple access

The DFT discrete fourier transform

The DS direct sequence

The DSSS direct sequence spread spectrum

The FFT fast fourier transform

The IF intermediate frequency

The IIR infinite impulse response

IS standard in transition period

The LNA low noise amplifier

The LO local oscillator

The LPF low pass filter

The MS mobile base station

The PN pseudo-random noise

The RF wireless frequency

The SAW surface acoustic wave

The SNR signal to noise ratio

Table 1

Fig. 2 realizes that the frequency deviation of inventing detects and the block diagram of the preferred plan of evaluation method.Receive the signal that transmits at antenna 201,,, consider the demodulation of receiving terminal, so have only from 869MHZ to 894MHZ through receive channel for cdma system by broadband band-pass filter 202.Broadband bandpass signal and low noise amplifier (LNA) are coupled, and output to frequency mixer/local oscillator (LO) 206, and the signal that receives is transformed into intermediate frequency (IF) signal downwards.The IF signal passes through band pass filter 208 filtering, and according to the control signal that automatic gain controller (AGC) 215 provides, is amplified by variable gain amplifier (VGA) 209.From VGA209 output, the IF signal is divided into I (homophase) and Q (quadrature component) in frequency mixer/LOs 210,211 place's phase places.Be coupled to analog/digital converter (A/D) 218 by low pass filter (LPF) 212,213 again.LPFs212,213 the most handy CDMA SAW filters, this is as can be known in this technology.Frequency synthesizer 214 generally includes the crystal oscillator and the phase detectors that are used for frequency standard, produces the control voltage signal and regulates the LOs frequency that is coupled with frequency mixer 207,210 and 211.The assembly of receiving terminal part comprises analog receiver.

Digitized IF signal comprises PN modulation signal plus noise.In digit receiver, digitized signal is coupled in automatic gain control (AGC) piece 215, PN search engine 217 and comprise RAKE demodulator 219, the digital data receiver of combiner 220 and channel-decoding piece 221.The one-sided bandwidth of CDMA signal is 0.6144MHZ, thus take a sample with the minimum data rate of 1.2288MHZ from the digital signal of A/Ds 218, to satisfy the requirement of sampling theory.

In the digital data receiver, RAKE demodulator 219 has 3 and line pointer, and each all comprises a local PN generator.The output of RAKE demodulator 219 pointers in colligator 220 places addition, and is delivered to channel-decoding piece 221 with maximum rate.From channel-decoding piece 221, data are delivered to digital signal processor (DSP) 230 with frame speed 50HZ.Easy in order to realize, and reduce whole mobile phone in size, AGC piece 215, search engine 217, ARKE demodulator 219, colligator 220 and channel decoder 221, the connection of various elements optimally is integrated among the ASIC (application-specific integrated circuit (ASIC)).

Search engine square 217, under DSP230 instructs, utilization and the corresponding to configuration lock-on signal of Fig. 1 PN capture systems.The search engine square also comprises the RAM of storage inside sample of signal.Interested frequency deviation detects and estimates that operation appears in search piece 217 and the DSP230.

With reference now to Fig. 3,, begin 217 transmission signal that receive, that change downwards from A/Ds 218 to the search engine square, sample of signal that receives and the signal correction of utilization from local PN generator (the 301st goes on foot), corresponding coherent signal is divided into Ns son and stops, each son stops a sub-time of staying of integration (Ts) (the 302nd step), and through square-law envelope detector (the 303rd step).Calculate the compound correlation of Ns according to equation (1): $R_n^{\left(0\right)}=\underset{m=0}{\overset{N_c-1}{\mathrm{\Σ}}}r(n-p{N}_c+m+t_0)\·a^{*}(n-p{N}_c+m)p=1,2,\…N_1--\left(1\right)$

Here n is relative PN code phase location;

Nc is the number that son stops relevant chips;

P is that son stops the index of correlation;

Ns is the number that son stops;

To is the actual value of initial time migration;

Rn, r and a ^*It all is plural number.

In the 304th step, the length of estimating associated vector Rx is to determine that whether it is 2 power, and promptly whether vector length is L=2 ⁿ(for example, L may be 4,8,16 ... 64 etc.).If L ≠ 2 ⁿ, then should increase by zero number, i.e. in " zero padding " (the 305th step), shown in equation (2), the length L that makes last vector is 2 power: $\stackrel{\‾}{R_n}=\[R_n^{\left(0\right)}{R}_n^{\left(1\right)}{R}_n^{\left(2\right)}---R_n^{(N-1)}00---0\]--\left(2\right)$ In order to describe, supposing has L available son to stop, and does not then require zero padding, i.e. Ns=L.

L son stops integrated value and is sent to DSP230, and DSP230 calculates L point DFT (discrete fourier transform) with fft algorithm, to provide L discrete sampling point in frequency spectrum (the 306th step).

Here Ts is the sampling rate that son stops;

W is corresponding rectangle window function.L may be little of 8 or 16, yet know that all the FFT value is big more, and performance is good more.Sampling point be centered close to X (fs/N), X is an integer (L/2 〉=X 〉=L/2) here.Supposition above given: L is 2 power and does not use zero padding that equation (3) can be expressed as:

In the 307th step, the length computation of every L sampling point is $Y_n^{\left(k\right)}=\left|Y_l\left(k\right)\right|--\left(5\right)$ Be treated to according to the maximum length of equation (6) decision (the 308th step): $Z=\max \left(Y_n^{\left(k\right)}\right)--\left(6\right)$ Infinite impulse response (IIR) filter, or finite impulse response filter (FIR), both mention in this technology, may be exactly to be used for this purpose.(see, routine Marven and Ewers, " straightforward procedure of Digital Signal Processing ", 1996 Wiley Interscience, NewYork).

In the 309th step, maximum Z compares with detection threshold value:

Here t is optimum threshold value (based on search algorithm), when the PN sign indicating number is synchronous, and H ₁Be correct supposition, when the PN sign indicating number is not adjusted, H ₂Be correct, many distinct methods of decision optimum threshold value are spoken of in best techniques.In these methods some are test modifications for this reason.If maximum Z does not satisfy the threshold value criterion, search algorithm is just announced carrier wave frequency deviation (the 312nd step), selects a kind of new PN phase code (the 313rd step), and this process went on foot for 309 steps from 301 and repeats.

The sampling point index I (n) of maximum Z and its correspondence decision in 308 steps is stored in (the 310th step) in the memory DSP230.In case satisfy threshold criterion, search algorithm is announced to detect, and termination is searched (the 311st step).

Because FFT has stored signal energy with discrete frequency, can continue this process so that the estimation frequency deviation to be provided.Frequency accuracy is the function of FFT length and its sampling frequency.Can be on average a plurality of relevantly promptly test correct PN deviation frequency N time, so that the estimation of N received signal length and frequency to be provided.Average qualified frequency sample point is to provide frequency accuracy preferably.

Fig. 4 provides the order of decision relative frequency deviation, is the continuation that detects the Fig. 3 that has frequency deviation.Determine the maximum element of FFT output vector and the termination of search (the 311st step) below, correct skew is relevant with the number of times of N increase, at every turn according to the 301st to 309 step calculating amplitude, search, peak frequency element relatively, in the 401st step, intactly show.Lp the sampling point amplitude that surpasses thresholding in the 309th step, " qualified sampling point " and their corresponding sampling point indexes are all recovered (the 402nd step) from the memory space of DSP.The exponential average of qualified sampling point is (the 403rd step): $K=\frac{1}{L_p}\underset{n=1}{\overset{L_p}{\mathrm{\Σ}}}1\left(n\right)1\left(n\right)=\[0,1,\…,(L-1)\]--\left(8\right)$ Here I (n) is the index vector of qualified sampling point, and Lp is the number of qualified sampling point.

The formula of decision forward and reverse frequency deviation and calculated rate (the 404th step) as follows: if (K＜(L/2)): Here Tc is the PN chip period.

L/2 represents a kind of so fuzzy boundary line, if frequency deviation reaches L/2, for calculated rate requires additional logic, the accuracy of frequency estimator is the function of sampling point number Lp ', will increase with the number of sampling purpose.

The frequency of calculating offers frequency synthesis 214 (see figure 2)s or other frequency deviation mode of AFC circuit, with the Frequency Distribution carrier frequency (the 405th step) of regulating local oscillator.

The system and method that is used to detect and estimate carrier wave frequency deviation of invention has used the method for " half-link up ", although incoherent fully, the accuracy that provides is better than non-coherent method in the preferred version.Because essence and realization itself that FFT is discrete are the facts that disperses, coherent relevant obtains at the sampling center.Because FFT process image distortion influence has caused some extra losing.This least bit place that is lost between the sampling point center can be up to 3.96dB.During the utilization zero padding, FFT length is big more, and is good more by the performance of whole frequency, yet its realization will be a cost to increase complexity and processing time.

Detect and estimate that the equipment of carrier wave frequency deviation method realizes,, can be used in the mobile phone structure already present hardware element and finish if consider to realize expensive minimum.With more moderate FFT length (8 or 16 point), detect performance and will obviously improve, can detect the signal that in cdma system, finds usually based on IS-95, though exist a large amount of frequency deviations (＞6KHZ).These raisings have used identical son to stop, and all integration lengths of the used non-additional capture technique that links up also can obtain these and improve, and also have such advantage in optimization technique, and this detector can be used to estimate frequency deviation.

Clearly, various modifications and changes can realize in the system of this invention in the system, and need not break away from the essence or the scope of this invention.Therefore, as long as meet within additional claim and the similar claimed range, this invention is bound to comprise the modification and the change of this invention.

We apply for a patent:

Claims (26)

1. be used for detecting a kind of detector at the carrier wave frequency deviation of the signal of Pseudo-Random Noise Code modulation, this detector comprises:

The receiver that is used for received signal has the transducer that received signal is converted to digital signal;

Be used to detect the relevant apparatus of digital signal, it comprises a kind of pseudo noise code generator with frequency matching device, wherein the pseudo noise code generator produces the phase position sequence at local PN sign indicating number, with relevant with digital signal, wherein the phase position of sequence is corresponding to being used for the Pseudo-Random Noise Code of modulated received signal;

A kind of digital signal processor, be used for receiving from the phase position sequence, with the relevant detection signal of selecting of phase position, and therefrom extract sampling with the length of being predetermined, sampling is done discrete fourier transform to produce a class frequency value, each frequency values all has mark index and amplitude, Digital Signal Processing and further determine the high-amplitude of this class frequency value, and with this high-amplitude value and amplitude threshold value relatively, wherein digital signal processor comprises the memory of storing high-amplitude value and its corresponding identification index;

If high-amplitude surpasses the amplitude thresholding, just can obtain to modulate Pseudo-Random Noise Code and choose between the relevant position synchronously, if high-amplitude is lower than the amplitude thresholding, will there be carrier wave frequency deviation, this pseudo-random noise generator is selected a new phase position from sequence, and digital signal processor decision is corresponding to the mark index and the amplitude of each rate value of new phase position sampling, stores high-amplitude and corresponding identification index in memory, repeats this process up to obtaining synchronously.

2. according to the detector of claim 1 description, a described class frequency value comprises L the sampling point of DFT, and mark index is the sampling point number.

3. according to the detector in the claim 2, wherein each sampling point in L sampling point is by bank of filters filtering, and a filter is corresponding to a sampling point.

4. according to the detector in the claim 2, correlator wherein is the multiple correlation device, and the sampling of extracting from detection signal comprises the associated vector that one group of son stops.

5. according to the detector in the claim 4, one group of son wherein stops L the sampling point that is less than DFT, and associated vector is a zero padding, and the vector length that provides is L.

6. according to the detector in the claim 6, wherein L is 2 power.

7. according to the detector in the claim 6, wherein L is 8.

8. according to the detector in the claim 6, wherein L is 16.

9. according to the detector in the claim 1, digital signal processor utilization fast fourier transform wherein calculates discrete fourier transform.

10. according to the detector in the claim 1, digital signal processor wherein is also average from a plurality of sign definiteness numbers that a plurality of sampling point obtained, to determine frequency deviation.

11. according to the detector in the claim 1, digital signal processor wherein comprises one group of filter, filter of corresponding each frequency is to determine the highest amplitude.

12. in the Direct Sequence Spread Spectrum Signal with PN modulation, the method for detected carrier frequency deviation comprises the steps:

Receive the PN modulation signal;

With sampling interval the one group of sampling point of signal extraction that is predetermined from receiving;

By PN code phase location relevant that produces the PN sign indicating number with this locality of selecting, despreading received signal;

Stop this despread signal of upper integral at interval at one group of son;

At interval each of this group stop done discrete fourier transform, and produce a class frequency sampling point thus, each frequency sample point all has a sampling point exponential sum amplitude;

The amplitude of each frequency sample point group that relatively should group, and determine high-amplitude has the highest amplitude for the sampling index of this frequency sample point;

High-amplitude value is compared with amplitude thresholding standard,, announce then synchronously that if do not satisfy, then have frequency deviation, and repeat following steps: separate diffusion, integration is done discrete fourier transform if satisfy, the PN code phase location of relatively newer choosing, synchronous up to obtaining.

13. according to the method in the claim 12, the step of wherein doing discrete fourier transform comprises the calculating fast fourier transform.

14. according to the method in the claim 12, also comprise and judge that whether this group amount at interval that stops is 2 power, if not, carry out zero padding to comprising the associated vector that son stops spacing value, be the vector length of 2 power time to obtain.

15. according to the method in the claim 14, wherein this vector length equals the quantity of this class frequency sampling.

16. according to the method in the claim 15, wherein, the quantity of this class frequency sampling is 8.

17. according to the method in the claim 15, wherein the quantity of this class frequency sampling is 16.

18. according to the method in the claim 12, the step that wherein compares each frequency sample point amplitude comprises by one group of filter filters this amplitude.

19., also be included in and store high-amplitude and corresponding sampling point index in the memory according to the method in the claim 12.

20. according to the method in the claim 12, also be included in after the acquisition synchronously, the estimation carrier wave frequency deviation comprises the steps:

Be repeated below step for one group of iteration: to the extraction of one group of sampling, the signal that despreading receives, the signal of integration despreading is done repeatedly discrete fourier transform in acquisition sync bit utilization PN code phase location;

Storage and the corresponding sampling index of high-amplitude of each iteration in the memory block;

Calculate the average sample index of this group iteration.

21. in having the mobile phone receiver of PN detector and digital signal processor, in receiving PN sign indicating number modulation signal, a kind of method that detects and estimate carrier wave frequency deviation, this method comprises:

(a) receive the received signal of simulating;

(b) received signal with simulation converts digital signal to;

(c) extract the stop sampling with the sampling interval that is predetermined from this digital signal;

(d) in this PN detector, relevant this stop sampling at the PN code phase location place that chooses, despreading and integration should stop sampling, had the associated vector of one group of sub-stop value with generation;

(e) in this digital signal processor, to each fast fourier transform of this child stop group, to produce a class frequency value, each frequency values all has an amplitude and a sampling index;

(f) determine the high-amplitude in this class frequency value and the sampling index of its correspondence;

(g) this high-amplitude is compared with the thresholding standard;

(h) if high-amplitude has satisfied the thresholding standard, then synchronous;

(i) if high-amplitude does not satisfy the thresholding standard, frequency shift (FS) is then arranged, and in the PN wave detector, selects a different PN code phase location, repeat (d) and arrive (g) step, till the high-amplitude in this class frequency value satisfies the thresholding standard;

(j) announcing the synchronous PN code phase location of choosing, repeating step from (d) to (g) for one group of iteration;

(k) for this group iteration, the high-amplitude corresponding sampling points index of average and each iteration

22. according to the method in the claim 21, also comprise and judge that whether this amount of organizing sub-stop value is 2 power, if not, associated vector is carried out zero padding, up to vector length 2 power.

23. according to the method in the claim 22, wherein vector length equals the quantity of this class frequency sampling point.

24. according to the method in the claim 23, wherein the quantity of this class frequency sampling point is 8.

25. according to the method in the claim 23, wherein the quantity of this class frequency sampling point is 16.

26., also comprise described high-amplitude and its corresponding sampling index are stored in the memory according to the method in the claim 21.

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