CN108401581B - A kind of PN code quick capturing methods in satellite spectrum-spread communication system - Google Patents
A kind of PN code quick capturing methods in satellite spectrum-spread communication system Download PDFInfo
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Abstract
The invention discloses a kind of methods of PN code fast Acquisitions in satellite spectrum-spread communication system, including：S1：Determine frequency search step-length；S2：It compensates different step frequencies successively in local signal frequency and adds up；S3：It calculates the roads I and the roads Q mixed frequency signal and receives the total correlation value of signal；S4：Total correlation value is corresponding in complex field to be added, its modulus value is sought；S5：Maximum one of peak value judges that Doppler frequency shift is located in the frequency drift compensation module；S6：If frequency compensation step-length, which is more than predeterminated frequency, compensates thresholding, S7 is executed；Otherwise, frequency shift amount and phase pushing figure are obtained；S7：Compensation frequency is continued to divide, search stepping length is reduced, returns to S2.Frequency compensation is constantly segmented by the present invention, while gradually reducing search range, improves compensation precision, shorten capture time, maximum correlation peaks are obtained by the calculating of correlation again, code phase is made to be compensated, PN codes is realized and the two dimension of Doppler frequency shift captures.
Description
Technical field
The present invention relates to spread spectrum code acquisition technical fields in satellite mobile communication system, more particularly to
A kind of PN code quick capturing methods in satellite spectrum-spread communication system.
Background technology
Direct sequence spread spectrum communication system (Direct Sequence Spread Spectrum,
DSSS) have many advantages, such as anti-multipath fading, anti-interference, high-acruracy survey, it is logical in satellite movement
In order to improve the anti-interference and secrecy ability of signal in letter system, use satellite spread spectrum real
The spread processing of existing satellite-signal.Accurate spread spectrum code acquisition and synchronize be the embodiment of its superior function
Basic premise.The acquisition procedure of spreading code needs to complete the thick synchronization of spreading code, by sending and receiving
The phase difference of both ends spreading code is limited in a chip, it is the basis of spread and disposal plus,
It is the basis that spread-spectrum signal correctly detects, such as the despreading of spread-spectrum signal, carrier synchronization, periodically same
Step, RAKE are received with multi-path combing, channel estimation etc..For low orbit (LEO) satellite and work
For the spread spectrum link for making in the high bands such as Ka stationary orbit (GEO) satellite, due to satellite or
The movement of terminal so that receive the carrier wave Doppler frequency displacements of signal up to hundreds of kHz,
In the case of there are Doppler frequency shift, the expression formula for receiving signal is：
Wherein s, fc, θ is power, frequency and the first phase of carrier wave respectively, without loss of generality,
θ=O is assumed in following analysis；G (t) is the baseband raised-cosine pulse after chip matched filtering；
C (t) is spreading code；Δ f is that (including sending and receiving both ends shake for the Doppler frequency displacements at sending and receiving both ends
Swing the frequency drift in source)；Be carrier wave instantaneous phase (opposite BPSK,π)；N (t) is unilateral
Power spectral density is N0/ 2 additive white Gaussian noise.Its baseband signal (nothing after oversampling
Data modulate when) mathematic(al) representation be：
Wherein, UrSpeed of related movement between satellite and ground based terminal, c are the light velocity,
For carrier frequency shift, τ is unknown PN code phases, TsFor sample time Ts=Tc/ 2, L are
The length of PN codes.
Above-mentioned expression formula shows that two main influences are carrier frequency shift and code frequency
Offset.Doppler frequency shift shows as the main influence of capture：Make local pseudo-code and receives pseudo-code
It is uncorrelated for a long time；Increase mean acquisition time；Reduce detection probability；Search rate is set to become
At random.
Therefore, realize that the fast accurate capture of spreading code is to influence under Large Doppler shift environment
The key of for Satellite Spreading Spectrum System performance.In recent years, numerous scholar research institutions are more rapidly accurate
PN codes really are captured, the scheme of many PN codes fast Acquisitions is had studied, PN codes are caught at present
Obtain the method for being mainly the following：
1, single step-searching, this is most traditional searching method, also referred to as sequential search method.It
A phase stepping amount (a PN codes symbol) will be gradually moved, primary phase is once made in often movement
Judgement is closed, until two PN codes are synchronous.This method advantage is that circuit is simple, it is easy to accomplish,
The disadvantage is that capture time is long, it is not suitable for the long sequence PN codes of low signal-to-noise ratio.
2, slippage correlation acquisition algorithm, it makes local code generator with launch code generator
Clock rate has certain rate, to make two code sequences seem in phase from phase
To sliding, slides and stop when two sequences are consistent.This algorithm comparison is classical, and advantage is real
It is now simple, the disadvantage is that capture time is longer；
3, matching wave filter capture method, it is when signal is real function, and related and convolution is only
The reversion of poor time.When input is Direct Sequence Spread Spectrum Signal, a matched filter is designed,
It is the time reversal of PN codes to make its unit impulse response, and a PN is reached when spreading code inputs
When the code period, there are one maximal correlations to export, and enables the output to local PN code generators set,
Two PN codes are made to reach thick synchronization.Biggest advantage is that capture time is short, but is only suitable for shorter puppet
The capture and unreliable under low signal-to-noise ratio of code；
4, the prize law based on sequence estimation, this method are using to the n in PN code generators
It is a can preset shift register carry out set to realize the synchronization of PN codes.I.e. with the code after demodulation
(including PN codes and information code and noise) goes to the shift register of local PN code generators
Set number so that local PN code generators generate PN codes from this state.It is located at a PN
Information code not reindexing in code chip lengths, then only need n PN code symbol width when
Between two PN codes can be made synchronous.But consider noise thing, acquisition speed unlike single step into
Soon.This method can be only applied to signal-to-noise ratio it is higher in the case of, there is no much meanings to real system
Justice.This method can solve the problems, such as long Interference excision, but this method is in high dynamic, property
When making an uproar smaller and it is not suitable for；
5, the prize law based on FFT, this method are will to receive signal and local signal sampling sample
This is after FFT transform, in frequency domain by the way that the frequency-domain data sequence of two signals is multiplied, so
Multiplication result is obtained into a correlated results sequence by IFFT transformation afterwards, then the result sequence
Sample correspond to the correlation of a collection of pseudo-code phase, and then directly the result sequence is carried out related
Fast Acquisition can be realized in blob detection, its advantage is that capture Doppler shift range is big, fits
The environment of high dynamic is in for receiver；
6, the shortcomings that automatic adaptation threshold judgement method based on constant false alarm rate, this algorithm is low
Detection probability under signal-to-noise ratio is very low, and capture time is longer.
7, the spread spectrum code acquisition based on pilot signal (first carries out the estimation of Doppler frequency shift, frequency
Spread spectrum code acquisition is carried out again after moving compensation), during pilot signal transmitted, utilize Adaptive spectra
Line booster (ALE) handles with estimating Doppler frequency shift value partial matched filter output,
After frequency offset correction, spread spectrum code acquisition judgement is carried out using traditional full matching acquisition algorithm.It should
Method is avoided to Doppler frequency shift in the scanning process of frequency domain, can be effectively eliminated mostly general
The influence for strangling frequency displacement, quickly completes the capture of spreading code.But this scheme is by frequency and spread spectrum
Code, which separates, to be captured, and is compared more two-dimentional while Acquisition Scheme, be will produce compared with long time delay.
Invention content
(1) it to solve the problems, such as
The technical problem to be solved by the present invention is to：How fast and accurately to realize PN Code acquisitions with
And the compensation of Doppler frequency shift.
(2) technical solution
In order to solve the above technical problems, the present invention provides in a kind of satellite spectrum-spread communication system
PN code quick capturing methods, which is characterized in that the described method comprises the following steps：
S0：System initialization, setpoint frequency compensate frequency n=0；
S1：Maximum doppler frequency f according to satellite communication systemmax, determine that frequency search walks
Into length Δ f, wherein Δ f=fmax/ PX, P are to divide the cumulative hop count of more step frequencies, and X is
The Doppler shift step number for including in every section, PX are to be divided within the scope of Doppler frequency shift
Total step-length number；
S2：The roads I and the roads Q signal for receiving signal respectively and are advanced into the roads P Doppler frequency shift
Compensating module carry out multistep into frequency compensation, for the 1st road signal, respectively with
Δf/Pn, 2 Δ f/Pn..., X Δs f/PnFrequency compensation is carried out, similarly the roads p signal is respectively with frequency
[(p-1)XΔf+Δf]/Pn, [(p-1) X Δ f+2 Δs f]/Pn..., [(p-1) X Δ f+X Δs f]/PnInto line frequency
Rate compensates, and is then added the signal of X compensation frequency in every road, generates P local I
Road signal mixed frequency signal and the P roads Q signal mixed frequency signal；Wherein, 1≤p≤P；
S3：The mixed frequency signal and local signal on the roads I, the roads Q are produced in frequency domain using fft algorithm
The local PN codes sequence that raw module generates carries out total correlation operation one by one, obtains total correlation value
CIk、CQk, 1≤k≤P；
S4：The corresponding roads I are corresponded to the correlation that the roads Q export in complex field and are added
Ck=CIk+j*CQk, and calculate its modulus value, by the characteristics of total correlation it is found that CkLength etc.
In the number of chips of a PN-code capture；
S5：Correlation peak module compares maximum one of peak value in P correlation according to peak value,
Thus judge PN code phase offsets, and can determine whether that Doppler frequency shift is located at Doppler frequency shift benefit
It repays in module T；
S6：Determination frequency compensates step delta fn=XT Δs f/PnWith institute's predeterminated frequency compensation thresholding
ΔfmSize, if Δ fn＞ Δs fm, execute step S7；Otherwise, how general system be successfully acquired
Strangle frequency shift amount and code phase offset amount；
S7：Doppler shift compensation module is positioned at the module T in S5, it will be in module T
Compensation frequency continue to divide P sections into, enable n=n+1, reducing frequency search stepping length is
Δf/Pn, acquisition accuracy is improved, and return to S2, repeats step S2 to step S7, until catching
Until succeeding.
Wherein, in step S6, according to judging result to the Doppler shift acquisition precision into
Row adjustment, further comprises：
If Δ fn＞ Δs fm, then continue the compensation frequency in the module T locked in S5 to be divided into P
Section, it is Δ f/P to enable n=n+1, diminution frequency search progress lengthn；
If Δ fn≤Δfm, then system be successfully acquired Doppler frequency shift amount and code phase offset amount.
A kind of PN code rapid capture systems in satellite spectrum-spread communication system, which is characterized in that
The system comprises：Local signal generation module, is based on FFT at Doppler shift compensation module
Total correlation module, complex field correlation summation module, peak-peak selecting module, thresholding ratio
Compared with judging module, P point-score frequency compensation resolving cells；
The local signal generation module is for generating local carrier and local PN code sequences；
The Doppler shift compensation module is used to compensate upper different steppings to local frequency signal
Doppler frequency shift, generate the signal of different frequency, and by its segmentation mix at local mixing frequency
Rate signal；
The total correlation module be used for the signal on the roads I, the roads Q after Doppler shift compensation and
The local PN codes sequence that local signal generation module generates carries out total correlation operation one by one, uses
Fft algorithm realizes that correlation length is the number of chips that PN-code capture is equal to a PN-code capture；
The complex field correlation summation module is for existing the obtained correlation in the roads I and the roads Q
It is added in complex field, obtains P sequence of correlation values；
The peak-peak selecting module is used to position the peak value of arbitrary sequence of correlation values, determines code
Phase offset, and between more each sequence correlation peak size, it is preliminary to judge Doppler frequently
The range of shifting；
The threshold comparison decision module is used to judge whether to meet the frequency compensation of system requirements
Precision, and whether complete Doppler shift compensation and phase capturing；
The Doppler shift compensation range P that the P point-scores frequency compensation resolving cell is used to lock
Decile gradually reduces compensation range, to meet the compensation precision of Doppler frequency shift.
(3) it has the following advantages that compared with the background technology, the present invention：
The present invention gradually reduces Doppler frequency shift by being constantly segmented Doppler frequency compensation
While compensating search range, the precision of Doppler frequency compensation is greatly improved, is contracted
Short capture time, then maximum correlation peaks are obtained by the calculating of correlation, so that code phase is obtained
To compensation, and then realize two dimension capture of the PN codes with Doppler frequency shift.
Description of the drawings
Fig. 1 is Doppler shift compensation modular structure principle schematic；
Fig. 2 is the schematic diagram of full digital correlator structure；
Fig. 3 is the principle schematic of P point-score frequency compensation resolving cells；
Fig. 4 is that the PN codes in the satellite spectrum-spread communication system of one embodiment of the present invention are quick
The flow chart of capture systems.
Fig. 5 is that the PN codes in the satellite spectrum-spread communication system of one embodiment of the present invention are quick
The functional block diagram of capture systems.
Specific implementation mode
With reference to the accompanying drawings and examples, the specific implementation mode of the present invention is made further detailed
Description.Once embodiment is for illustrating the present invention, but is not limited to the scope of the present invention.
A kind of PN code quick capturing methods in satellite spectrum-spread communication system include the following steps：
S0：System initialization, setpoint frequency compensate frequency n=0；
S1：Maximum doppler frequency f according to satellite communication systemmax, determine that frequency search walks
Into length Δ f, wherein Δ f=fmax/ PX, P are to divide the cumulative hop count of more step frequencies, X
For the Doppler shift step number for including in every section, PX is division in Doppler frequency shift
's
Total step-length number；
S2：The roads I and the roads Q signal for receiving signal respectively and are advanced into the roads P Doppler frequency shift
Compensating module carry out multistep into frequency compensation, for the 1st road signal, respectively with
Δf/Pn, 2 Δ f/Pn..., X Δs f/PnFrequency compensation is carried out, similarly the roads p signal is respectively with frequency
[(p-1)XΔf+Δf]/Pn, [(p-1) X Δ f+2 Δs f]/Pn..., [(p-1) X Δ f+X Δs f]/PnInto line frequency
Rate compensates, and is then added the signal of X compensation frequency in every road, generates P local I
Road signal mixed frequency signal and the P roads Q signal mixed frequency signal；Wherein, 1≤p≤P；
IkLu Zhong is by the signal of Doppler frequency compensation：
S(t)j sin[2π(Xk+l)Δft] (1)
In formula, S (t) is the signal received, 0≤k≤P-1,1≤l≤X.To be each how general
It strangles X thermal compensation signal in compensating module to add up, has just obtained IkThe local mixing frequency on road
Rate.
In QkLu Zhong, local mixed frequency generates and IkGenerate it is similar, by Doppler frequency
Rate compensation signal be：
S(t)cos[2πτ(Xk+n)Δft] (4)
S3：The mixed frequency signal and local signal on the roads I, the roads Q are produced in frequency domain using fft algorithm
The local PN codes sequence that raw module generates carries out total correlation operation one by one, obtains total correlation value
CIk、CQk, 1≤k≤P；
It, can be the process of convolution in time domain to reduce capture time in order to reduce calculation amount
It transforms to and carries out multiplying on frequency domain, formula (5) can be expressed as：
Wherein s [fr] it is to receive signal, s [f+fmix] it is local frequency compounding signal, concrete principle
Figure is as shown in Fig. 2, receive signal with local frequency compounding signal after FFT transform, in frequency
Then multiplication result is passed through IFFT by domain by the way that the frequency-domain data sequence of 2 signals is multiplied
Transformation obtains a correlated results sequence.
S4：The corresponding roads I are corresponded to the correlation that the roads Q export in complex field and are added
Ck=CIk+j*CQk, and its modulus value is calculated, enter step S5 correlation peak determination modules.By
The characteristics of total correlation, is it is found that CkLength be equal to a PN-code capture number of chips；
S5：Correlation peak module compares maximum one of peak value in P correlation according to peak value,
Thus judge PN code phase offsets, and can determine whether that Doppler frequency shift is located at Doppler frequency shift benefit
It repays in module T；
S6：Determination frequency compensates step delta fn=XT Δs f/PnWith institute's predeterminated frequency compensation thresholding
ΔfmSize, if Δ fn＞ Δs fm, execute step S7；Otherwise, how general system be successfully acquired
Strangle frequency shift amount and code phase offset amount；
S7：Doppler shift compensation module is positioned at the module T in S5, it will be in module T
Compensation frequency continue to divide P sections into, enable n=n+1, reducing frequency search stepping length is
Δf/Pn, acquisition accuracy is improved, and return to S2, repeats step S2 to step S7, until catching
Until succeeding.
Wherein, in step S6, according to judging result to the Doppler shift acquisition precision into
Row adjustment, further comprises：
If Δ fn＞ Δs fm, then continue the compensation frequency in the module T locked in S5 to be divided into P
Section, it is Δ f/P to enable n=n+1, diminution frequency search progress lengthn；
If Δ fn≤Δfm, then system be successfully acquired Doppler frequency shift amount and code phase offset amount.
A kind of PN code rapid capture systems in satellite spectrum-spread communication system, which is characterized in that
The system comprises：Local signal generation module, is based on FFT at Doppler shift compensation module
Total correlation module, complex field correlation summation module, peak-peak selecting module, thresholding ratio
Compared with judging module, P point-score frequency compensation resolving cells；
The local signal generation module is for generating local carrier and local PN code sequences；
The Doppler shift compensation module is used to compensate upper different steppings to local frequency signal
Doppler frequency shift, generate the signal of different frequency, and by its segmentation mix at local mixing frequency
Rate signal；
The total correlation module be used for the signal on the roads I, the roads Q after Doppler shift compensation and
The local PN codes sequence that local signal generation module generates carries out total correlation operation one by one, uses
Fft algorithm realizes that correlation length is the number of chips that PN-code capture is equal to a PN-code capture；
The complex field correlation summation module is for existing the obtained correlation in the roads I and the roads Q
It is added in complex field, obtains P sequence of correlation values；
The peak-peak selecting module is used to position the peak value of arbitrary sequence of correlation values, determines code
Phase offset, and between more each sequence correlation peak size, it is preliminary to judge Doppler frequently
The range of shifting；
The threshold comparison decision module is used to judge whether to meet the frequency compensation of system requirements
Precision, and whether complete Doppler shift compensation and phase capturing；
The Doppler shift compensation model that the P point-scores frequency compensation resolving cell is used to lock
P deciles are enclosed, compensation range is gradually reduced, to meet the compensation precision of Doppler frequency shift.
Claims (2)
1. the PN code quick capturing methods in a kind of satellite spectrum-spread communication system, feature exist
In including the following steps：
S0：System initialization, setpoint frequency compensate frequency n=0；
S1：Maximum doppler frequency f according to satellite spectrum-spread communication systemmax, determine that frequency is searched
Suo Bujin length Δ f, wherein Δ f=fmax/ PX, P are to divide the cumulative hop count of more step frequencies,
X is the Doppler shift step number for including in every section, and PX is to be drawn within the scope of Doppler frequency shift
The total step-length number divided；
S2：The roads I and the roads Q signal for receiving signal respectively and are advanced into the roads P Doppler frequency shift
Compensating module carry out multistep into frequency compensation, for the 1st road signal, respectively with
Δf/Pn, 2 Δ f/Pn..., X Δs f/PnFrequency compensation is carried out, similarly the roads p signal is respectively with frequency
[(p-1)XΔf+Δf]/Pn, [(p-1) X Δ f+2 Δs f]/Pn..., [(p-1) X Δ f+X Δs f]/PnInto line frequency
Rate compensates, and is then added the signal of X compensation frequency in every road, generates P local I
Road signal mixed frequency signal and the P roads Q signal mixed frequency signal；Wherein, 1≤p≤P；
S3：Using fft algorithm in frequency domain to the letter on the roads I, the roads Q after Doppler shift compensation
Number and local signal generation module generate local PN codes sequence carry out total correlation operation one by one,
Respectively obtain respective total correlation value CIkOr CQk, 1≤k≤P；
S4：By the total correlation value on the roads I all the way on whole roads P and the corresponding roads Q all the way in plural number
It is corresponded in domain and is added Ck=CIk+j*CQkAfterwards, and its modulus value is calculated separately；Wherein, Ck's
Length is equal to the number of chips of a PN-code capture；
S5：It is maximum to compare modulus value in P correlation according to modulus value for peak-peak selecting module
One, thus judge PN code phase offsets, and can determine whether that Doppler frequency shift is located at and P phase
In the value of pass in the opposite Doppler shift compensation module T of maximum one of modulus value；
S6：Determination frequency compensates step delta fn=XT Δs f/PnWith institute's predeterminated frequency compensation thresholding
ΔfmSize, if Δ fn＞ Δs fm, execute step S7；Otherwise, how general system be successfully acquired
Strangle frequency shift amount and code phase offset amount；
S7：Compensation frequency in Doppler shift compensation module T is continued to divide P sections into, is enabled
N=n+1, diminution frequency search stepping length are Δ f/Pn, acquisition accuracy is improved, and return
S2 repeats step S2 to step S7, until acquisition success.
2. the PN in a kind of satellite spectrum-spread communication system for realizing claim 1 the method
Code rapid capture system, which is characterized in that the system comprises：Local signal generation module,
2P Doppler shift compensation module, the total correlation module based on FFT, complex field correlation
Summation module, peak-peak selecting module, threshold comparison decision module, P point-score frequency compensations
Resolving cell；P is to divide the cumulative hop count of more step frequencies；
The local signal generation module is for generating local carrier and local PN code sequences；
The Doppler shift compensation module is used to dock the roads I and the roads the Q signal compensation of the collection of letters number
The Doppler frequency shift of upper difference stepping, generates the signal of different frequency, and by its segmentation mix at
Local mixed frequency signal；
The total correlation module be used for the signal on the roads I, the roads Q after Doppler shift compensation and
The local PN codes sequence that local signal generation module generates carries out total correlation operation one by one, uses
Fft algorithm realizes that correlation length is equal to the number of chips of a PN-code capture；
The complex field correlation summation module is for existing the obtained correlation in the roads I and the roads Q
It is added in complex field, obtains P sequence of correlation values；
The peak-peak selecting module is used to position the peak value of arbitrary sequence of correlation values, determines code
Phase offset, and between more each sequence correlation peak size, it is preliminary to judge Doppler frequently
The range of shifting；
The threshold comparison decision module is used to judge whether to meet the frequency compensation of system requirements
Precision, and whether complete Doppler shift compensation and phase capturing；
The Doppler shift compensation model that the P point-scores frequency compensation resolving cell is used to lock
P deciles are enclosed, compensation range is gradually reduced, to meet the compensation precision of Doppler frequency shift.
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| CN109856650A (en) * | 2019-01-15 | 2019-06-07 | 中国科学院国家天文台 | Code phase measuring method based on phase fringes |
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