CN103338177A - Frame synchronization method capable of resisting single-frequency interference - Google Patents

Abstract

The invention relates to a frame synchronization method capable of resisting single-frequency interference. A sending end is used for adding frame synchronization sequence to a frame header of a physical layer frame, and a receiving end is used for setting a threshold value so as to judge whether a frame start position is detected. The method comprises the following steps: (1) passing a received signal through a low order normalized LMS (Least Mean Square) self-adapting filter; (2) subtracting the output of the low order normalized LMS self-adapting filter from the received signal, so as to obtain a corrected received signal; (3) performing mutual correlation computation of energy normalization to the corrected received signal and the local sequence, so as to obtain a correlation result of energy normalization; (4) comparing the obtained correlation result of energy normalization with the preset threshold value, so as to obtain the start position of the physical layer frame. The method can accurately estimate the start position of the physical layer frame in presence of great single-frequency interference. Therefore, the hardware resource cost is saved, and the system real-time performance is not affected.

Description

A kind of frame synchornization method of resisting the single-frequency interference

Technical field

The invention belongs to digital communication technology field, be specifically related to a kind of normalization LMS(Least Mean Square that adopts low order, least mean-square error) frame synchornization method of sef-adapting filter, this method still can estimate frame start position when existing big single-frequency to disturb exactly in receiving signal.

Background technology

In the burst type communication system, receiving terminal is in order accurately to obtain the transmission time of physical layer frame, needs to utilize the partial information that receives in the signal that the initial moment of the physical layer frame that receives is estimated that this process both had been the synchronizing process of physical layer frame.Adopting relevant method is the method for most of communication systems synchronously, its basic way is more additional specific sequences in the signal of transmission, at receiving terminal by these sequences are carried out related operation, obtain a series of correlations corresponding with the associated window position after being correlated with, form correlated series (associated window is generic term, refers to participate in the signal sampling point scope of related operation); By correlated series and pre-set threshold value are compared, can determine the original position of physical layer frame.

Relevant method is divided two kinds of auto-correlation and cross-correlation, carries out two parts sequence of related operation in the autocorrelative method and all takes from the reception signal, and what carry out related operation in the method for cross-correlation then is reception signal and local sequence.Adopt auto-correlation and cross-correlation to carry out synchronous method pluses and minuses are respectively arranged.Adopt the same footwork of auto-correlation, advantage is that interference such as carrier frequency offset are had stronger resistivity, and major defect be correlated series along with the variation of associated window position linear change, near the peak value correlated results causes evaluated error in that the very possible peak value that surpasses under the random noise situation is arranged; Adopt the same footwork of cross-correlation, advantage is that correlation peak is outstanding, and antagonism random noise ability is stronger, and a little less than major defect is that resistivity that carrier frequency offset etc. is disturbed.

Yet, in traditional communication system, no matter adopting auto-correlation still is the method for synchronous of cross-correlation, when in receiving signal, existing strong single-frequency to disturb, because the power that single-frequency is disturbed is much larger than useful signal, so useful signal is submerged in the interference, and the correlation difference of doing relevant resulting correlation peak and random noise to received signal is little, correlation peak can't reach normal preset threshold far away, thereby can't carry out synchronously.In multi-carrier communications systems, method commonly used is that the position that single-frequency is disturbed is detected, and before synchronization module, be FFT(Fast Fourier Transform to received signal, fast Fourier transform), being subjected to the carrier wave that single-frequency disturbs and adjacent carriers shields or notch, pass through IFFT(Inverse Fast Fourier Transform, inverse fast Fourier transform again) transform to time domain receiving signal, just carry out at last synchronously.This method needs extra FFT and IFFT expense, and can introduce bigger time delay.

Summary of the invention

The objective of the invention is to propose a kind of frame synchornization method that utilizes the normalization LMS sef-adapting filter of low order, this method still can estimate frame start position exactly under the situation that exists bigger single-frequency to disturb.

The technical scheme of frame synchornization method of the present invention is as follows:

A kind of frame synchornization method of resisting the single-frequency interference, its step comprises:

(1) forms complete transmission signal at the physical layer frame head insertion frame synchronization sequence of data symbol stream and send to receiving terminal, and set a threshold value at described receiving terminal;

(2) receiving terminal obtains revised reception signal with the output that the input of primary reception signal deducts lower order filter;

(3) described revised reception signal and local sequence are done normalized crosscorrelation calculating, obtain the normalization correlated results;

(4) described normalization correlated results and described setting threshold are compared, find out the original position of frame, finish frame synchronization.

Further, described lower order filter is low order normalization sef-adapting filter, and the output of described filter is that the primary reception signal obtains by a low order normalization LMS sef-adapting filter.

Further, normalization LMS sef-adapting filter satisfies following condition:

The target response scalar is exported the poor of scalar with reality during the n time iteration:

Wherein,

Filter coefficient vector when representing the n time iteration,

Input vector when representing the n time iteration, the target response scalar during the n time iteration of d (n) expression, oeprator ^HThe expression conjugate transpose.

Further, the filter coefficient vector during the n+1 time iteration of normalization LMS sef-adapting filter satisfies the recurrence expression formula and is:

Wherein,

Be a positive real number factor, || || expression Euclidean norm, * represents complex conjugate.

Further, described low order normalization LMS sef-adapting filter exponent number be 3.

Further, normalized crosscorrelation is calculated as the mutual calculating of energy normalized:

(1) the local sequence S of receiving terminal storage _t={ s _t(1), s _t(2) ..., s _t(L) }, L is sequence length, and then the correlation window length of receiving terminal also is L, and signal sampling point sequence is R in the receiving terminal associated window _t={ r _t(1), r _t(2) ..., r _t(L) };

(2) calculate according to following formula by the energy normalized cross-correlation:

$\mathrm{corr}=\frac{|\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{r}_t\left(i\right)\·s_t*\left(i\right)|}{\sqrt{\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{\left|r_t\left(i\right)\right|}^2\·\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{\left|s_t\left(i\right)\right|}^2}},$ Wherein, i=1,2 ... L.

Further, described r _t(i) value changes along with the movement of associated window, described s _t(i) value with

Value immobilize and be stored in receiving terminal in advance.

Further, if the normalization correlated results surpasses preset threshold, then the original position of associated window deducts (exponent number-1 of normalization LMS sef-adapting filter) at this moment, obtains the original position of physical layer frame; Otherwise the slip associated window continues to seek the associated window position that surpasses threshold value.

Further, described frame synchronization sequence is selected from a kind of in M sequence, the ZC sequence arbitrarily.

Further, described local sequence is frame synchronization sequence.

Advantage of the present invention and technique effect are:

Propose a kind of frame synchornization method that adopts the normalization LMS sef-adapting filter of low order, when existing bigger single-frequency to disturb, still can accurately estimate the original position of physical layer frame.Utilize normalization LMS sef-adapting filter that frame synchornization method is improved, the feasible characteristic that has anti-single-frequency synchronously, and the exponent number of LMS sef-adapting filter is low order, compare with existing common method, this method only needs the filter of a low order, save the hardware resource expense, and can not influence the real-time of system.

Description of drawings

Fig. 1 is digital communication system schematic flow sheet in the prior art;

Fig. 2 is the synchronous schematic flow sheet of digital communication system in the prior art;

Fig. 3 is the synchronous schematic flow sheet that anti-single-frequency that the present invention proposes is disturbed;

Fig. 4 is the energy normalized peak Distribution schematic diagram that does not exist in the digital communication system in the prior art under the strong single-frequency disturbed condition;

Fig. 5 is the energy normalized peak Distribution schematic diagram that exists in the digital communication system in the prior art under the strong single-frequency disturbed condition;

Fig. 6 be the present invention propose do not have an energy normalized peak Distribution schematic diagram under the strong single-frequency disturbed condition;

Fig. 7 is the energy normalized peak Distribution schematic diagram under the strong single-frequency disturbed condition of the existence that proposes of the present invention.

Embodiment

Describe the frame synchornization method of employing normalization LMS sef-adapting filter of the present invention in detail below in conjunction with accompanying drawing, but be not construed as limiting the invention.

The flow chart of existing communication system as shown in Figure 1, workflow is as follows:

1. transmitting terminal, data source produces binary zero " 1 " bit data flow;

2. transmitting terminal, digital modulation module is modulated into data symbol stream d to binary data stream _s(n);

3. transmitting terminal, the frame synchronization sequence insert module is at data symbol stream d _s(n) preceding insertion frame synchronization sequence s _t(n), form complete transmission signal s (n);

4. receiving terminal, frame synchronization module receives signal r (n), utilizes s wherein _t(n) carry out related operation, draw the original position of physical layer frame, thereby obtain data symbol stream d _r(n);

5. receiving terminal, the digital demodulation module is to d _r(n) carry out demodulation, obtain the receiving terminal binary data stream.

Synchronization module workflow diagram in the existing system is as shown in Figure 2:

1. receive signal and local sequence and do the energy normalized cross-correlation, perhaps signal carries out auto-correlation, obtains correlated series;

2. correlated series and threshold ratio, find out the original position of frame.

The present invention proposes a kind of frame synchornization method that adopts the least mean-square error sef-adapting filter, the steps include:

(a) transmitting terminal, adding length at the frame head of physical layer frame is the frame synchronization sequence of N, and this sequence has good autocorrelation performance, and the peak value of relevant peaks is outstanding, and does the lower correlation of maintenance when relevant with other sequences or noise; Frame synchronization sequence can comprise pseudo random sequence such as the m sequence, or Zadoff ?Chu (ZC) sequence etc., good, outstanding relevant peaks that their characteristics have when relevant with do-it-yourself, and do the lower correlation peak of maintenance when relevant with other sequences.The effect that adds frame synchronization sequence is, receiver can be relevant by receiving sequence is done, obtain frame start position accurately by finding an outstanding sync peaks.

(b) receiving terminal is set a threshold value, is used for judging whether to detect frame start position; On time domain, relevant peaks can present the mountain peak shape of " rising-fall ", and the position at top then is sync bit accurately; For the correct sync bit that detects, then seek correlation peak greater than the point of threshold value, if greater than threshold value, then seek the maximum that satisfies in " greater than threshold value " these points again, corresponding time-domain position is sync bit; If less than threshold value, then think not to be sync bit.The setting of threshold value is decided by sequence length and correlation technique, and for example, under the non-normalized correlation technique situation, sequence is more long, and peak value is more big, and threshold value also can arrange more greatly.Appropriate threshold can draw by emulation or certain derivation.

(c) receiving terminal, with the signal that the receives normalization LMS sef-adapting filter by a low order, this filter will disturb rough estimate come out this single-frequency adaptively;

(d) receiving terminal will receive signal and deduct above-mentioned steps c) in the output of normalization LMS sef-adapting filter of low order, obtain revised reception signal;

(e) receiving terminal is with above-mentioned steps d) in revised reception signal and local sequence do the cross-correlation calculation of energy normalized, obtain the energy normalized correlated results;

(f) receiving terminal, with above-mentioned steps e) in resulting energy normalized correlated results and the step b) preset threshold compare: if the energy normalized correlated results surpasses preset threshold, then this moment associated window original position deduct the original position that (exponent number-1 of normalization LMS sef-adapting filter) is physical layer frame; Otherwise the slip associated window continues to seek the associated window position that surpasses threshold value.Above-mentioned steps e) mentions cross-correlation, and those skilled in the art understand that cross-correlation method is not unique, it is to consider that strong single-frequency interference can bring the energy instability that the present invention has chosen the relevant way of energy normalized, and normalization LMS sef-adapting filter estimate at a convergence process, it is big to cause non-normalized result to float in this process, be difficult to make threshold value, therefore used energy normalized, the codomain of correlation computations is grouped between 0 and 1.In step f), have a step " original position deduct (Jie Shuo ?1) " namely be owing to used that normalization LMS sef-adapting filter is extra to be introduced.

In an embodiment of the present invention, at above-mentioned steps c) in, the design of normalization LMS sef-adapting filter is as follows:

If the exponent number of normalization LMS filter is N, because this filter is not to disturb in order to remove single-frequency fully, but therefore assist in synchronization can get the lower-order number, as gets N=3 and get final product.With

Filter coefficient vector when representing the n time iteration,

Input vector when representing the n time iteration, the target response scalar during the n time iteration of d (n) expression, the target response scalar is exported the poor of scalar with reality during the n time iteration of e (n) expression, and following relation is then arranged:

In above-mentioned expression formula, oeprator H represents conjugate transpose; Order Be a positive real number factor, then normalization LMS adaptive filter coefficient recurrence expression formula is:

In above-mentioned expression formula, expression Euclidean norm, * represents complex conjugate; Vector

Each iteration is all once upgraded.In this method for synchronous, the input scalar u (n) during the n time iteration is as target response scalar d (n).The real number factor

Be a dimensionless number, its value is more little, and the filter coefficient convergence rate is more slow, and filter is also more stable simultaneously.Adjust

Size can control the convergence rate of filter.Above-mentioned formula can be with reference to " Adaptive Filter Theory " Fourth Edition, translation is " sef-adapting filter principle " the 4th edition, chapter 6 wherein " normalization minimum mean-square sef-adapting filter " first segment " normalization LMS filter is as the solution of constrained optimization problem ".Simon Haykin work, the Electronic Industry Press publishes.

In an embodiment of the present invention, at above-mentioned steps e) in, the cross-correlation method of carrying out energy normalized is as follows:

If the local sequence of receiving terminal storage (also being simultaneously the synchronizing sequence that transmitting terminal sends) is S _t={ s _t(1), s _t(2) ..., s _t(L) }, L is sequence length, and then the correlation window length of receiving terminal also is L.If signal sampling point sequence is R in the receiving terminal associated window _t={ r _t(1), r _t(2) ..., r _t(L) }, then the computational methods of energy normalized cross correlation results are:

$\mathrm{corr}=\frac{|\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{r}_t\left(i\right)\·s_t*\left(i\right)|}{\sqrt{\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{\left|r_t\left(i\right)\right|}^2\·\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{\left|s_t\left(i\right)\right|}^2}}---\left(3\right)$

By energy normalized, can overcome the non-normalized correlation that causes in the normalization LMS sef-adapting filter convergence process problem of acutely floating.In above-mentioned expression formula, r _tValue (i) (i=1,2 ... L) change along with the movement of associated window, and s _tValue (i) (i=1,2 ... L) with

Value be changeless, therefore can be stored in receiving terminal in advance, do not need double counting.The result of calculation of formula (3) will compare with threshold value, thereby judge whether current location is the original position of physical layer frame.

The present invention improves synchronization module in the existing communication system, the anti-single-frequency synchronization module workflow diagram after the improvement as shown in Figure 3:

1. signal carries out filtering by normalization LMS sef-adapting filter;

2. receive the output that signal deducts normalization LMS sef-adapting filter, obtain revised reception signal;

3. revised reception signal and local sequence are carried out the energy normalized computing cross-correlation, perhaps carry out auto-correlation computation;

4. the correlated series that obtains and threshold ratio, find out the original position of frame.

Below row for two example two the bigger single-frequency of explanation disturb influence to cross correlation results, and the present invention propose utilize normalization LMS sef-adapting filter cross-correlation method in the frame sync capability that exists under the big single-frequency disturbed condition.

Embodiment 1

If adopt frequency domain definition ZC sequence as synchronizing sequence, the ZC sequence definition is as follows:

When Nzc is odd number:

$a_q=\exp \&lsqb;-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003443205200021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;q}\frac{n(n+1)/2+\ln }{\mathrm{Nzc}}\&rsqb;$

When Nzc is even number:

$a_q=\exp \&lsqb;-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003443205200021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;<figure-callout\; id="2"\; label="q\; n"\; filenames="HDA00003443205200021.png"\; state="\{\{state\}\}">q</figure-callout>}\frac{n^{}}{}\frac{{}^2/2+\ln }{\mathrm{Nzc}}\&rsqb;$

Wherein, N _ZcThe length of expression ZC sequence, q is radical exponent, l can be arbitrary integer.In this example, N _ZcBe that 85, q is that 29, l gets 0.Sequence need transform to time domain in the frequency domain definition, and concrete grammar is: the both sides that these 85 points is arranged in order 0 frequency, and the 43rd point is set to 0, simultaneously mend 22 0 at negative frequency sideband place, mend 21 0 at positive frequency sideband place, the IFFT by 128 transforms to time domain then.

If the letter in the channel is made than being 13dB.When not existing single-frequency to disturb, the resulting synchronizing sequence peak Distribution of frame synchronization module shown in Figure 2 and noise sequence peak Distribution are as shown in Figure 4; Have that single-frequency is disturbed, interfering frequency at random and signal interference ratio during for-20dB, the resulting synchronizing sequence peak Distribution of frame synchronization module shown in Figure 2 and noise sequence peak Distribution are as shown in Figure 5.Two figure simulation times are 100,000.

Relevant peaks among Fig. 4 and Fig. 5 all is the statistics of carrying out after the normalization.The peak value of the cross-correlation curve among comparison diagram 4 and Fig. 5 as can be known, compare with the situation that does not exist strong single-frequency to disturb, exist signal interference ratio be-situation that the strong single-frequency of 20dB is disturbed under, the correlation peak aliasing of the correlation peak of synchronizing sequence and noise sequence together can't accurately be made the threshold value of sync peaks to realize frame synchronization accurately by existing cross-correlation method.

Embodiment 2

Connect example 1, use frame synchornization method as shown in Figure 3, wherein normalization LMS sef-adapting filter filtering is as follows:

y _k＝W _k ^HX _k-1

ε _k＝d _k-y _k

$W_{k+1}=W_k+\frac{{\mathrm{<figure-callout\; id="0"\; label="u"\; filenames="HDA00003443205200032.png"\; state="\{\{state\}\}">u</figure-callout>}}_0}{{\left|\right|X_{k-1}\left|\right|}^2}{{\mathrm{\&epsiv;}}_k}^{*}{X}_{k-1}$

Wherein, yk is the output of filter the k time, ε _kBe the k time output y _kWith idea output d _kResidual error, the filter coefficient vector when Wk is the k time.X _kRepresent the k time input, u ₀Be a constant coefficient, be set to 0.1.The exponent number of filter is 3.

When not existing single-frequency to disturb, the resulting synchronizing sequence peak Distribution of frame synchronization module shown in Figure 3 and noise sequence peak Distribution are as shown in Figure 6; The single-frequency of existence-20dB is disturbed, interfering frequency is at random the time, and the resulting synchronizing sequence peak Distribution of frame synchronization module shown in Figure 3 and noise sequence peak Distribution are as shown in Figure 7.Two figure simulation times are 100,000.

Comparison diagram 6 and Fig. 7, as seen the normalization LMS sef-adapting filter method of synchronization of band low order proposed by the invention is highly resistant to the influence of single-frequency, under the situation that no single-frequency disturbs and have strong single-frequency to disturb, still can make a sync peaks thresholding, as 0.5, can accurately estimate the initial position of frame.

Although disclose specific embodiments of the invention and accompanying drawing for the purpose of illustration, its purpose is to help to understand content of the present invention and implement according to this, but it will be appreciated by those skilled in the art that: without departing from the spirit and scope of the invention and the appended claims, various replacements, variation and modification all are possible.The present invention should not be limited to this specification most preferred embodiment and the disclosed content of accompanying drawing, and the scope of protection of present invention is as the criterion with the scope that claims define.

Claims (10)

1. resist the frame synchornization method that single-frequency is disturbed for one kind, its step comprises:

(1) forms complete transmission signal at the physical layer frame head insertion frame synchronization sequence of data symbol stream and send to receiving terminal, and set a threshold value at described receiving terminal;

(2) receiving terminal obtains revised reception signal with the output that the input of primary reception signal deducts lower order filter;

(3) described revised reception signal and local sequence are done normalized crosscorrelation calculating, obtain the normalization correlated results;

(4) described normalization correlated results and described setting threshold are compared, find out the original position of frame, finish frame synchronization.

2. the frame synchornization method that disturbs of opposing single-frequency as claimed in claim 1, it is characterized in that, described lower order filter is low order normalization sef-adapting filter, and the output of described filter is that the primary reception signal obtains by a low order normalization LMS sef-adapting filter.

3. the frame synchornization method that disturbs of opposing single-frequency as claimed in claim 2 is characterized in that normalization LMS sef-adapting filter satisfies following condition:

The target response scalar is exported the poor of scalar with reality during the n time iteration:

Wherein,

Filter coefficient vector when representing the n time iteration,

Input vector when representing the n time iteration, the target response scalar during the n time iteration of d (n) expression, oeprator ^HThe expression conjugate transpose.

4. the frame synchornization method that disturbs of opposing single-frequency as claimed in claim 3 is characterized in that the filter coefficient vector during the n+1 time iteration of normalization LMS sef-adapting filter satisfies the recurrence expression formula and is:

Wherein,

Be a positive real number factor, || || expression Euclidean norm, * represents complex conjugate.

5. the frame synchornization method that disturbs as claim 3 or 4 described opposing single-frequency is characterized in that, described low order normalization LMS sef-adapting filter exponent number be 3.

6. the frame synchornization method that disturbs of opposing single-frequency as claimed in claim 1 is characterized in that normalized crosscorrelation is calculated as the mutual calculating of energy normalized:

(1) the local sequence S of receiving terminal storage _t={ s _t(1), s _t(2) ..., s _t(L) }, L is sequence length, and then the correlation window length of receiving terminal also is L, and signal sampling point sequence is R in the receiving terminal associated window _t={ r _t(1), r _t(2) ..., r _t(L) };

(2) calculate according to following formula by the energy normalized cross-correlation:

$\mathrm{corr}=\frac{|\underset{i=1}{\overset{L}{\mathrm{\&Sigma;}}}{r}_t\left(i\right)\&CenterDot;s_t*\left(i\right)|}{\sqrt{\underset{i=1}{\overset{L}{\mathrm{\&Sigma;}}}{\left|r_t\left(i\right)\right|}^2\&CenterDot;\underset{i=1}{\overset{L}{\mathrm{\&Sigma;}}}{\left|s_t\left(i\right)\right|}^2}},$ Wherein, i=1,2 ... L.

7. the frame synchornization method of opposing single-frequency interference as claimed in claim 6 is characterized in that described r _t(i) value changes along with the movement of associated window, described s _t(i) value with Value immobilize and be stored in receiving terminal in advance.

8. the frame synchornization method that disturbs of opposing single-frequency as claimed in claim 1, it is characterized in that, if the normalization correlated results surpasses preset threshold, then the original position of associated window deducts (exponent number-1 of normalization LMS sef-adapting filter) at this moment, obtains the original position of physical layer frame; Otherwise the slip associated window continues to seek the associated window position that surpasses threshold value.

9. the frame synchornization method that disturbs of opposing single-frequency as claimed in claim 1 is characterized in that, described frame synchronization sequence is selected from a kind of in M sequence, the ZC sequence arbitrarily.

10. the frame synchornization method of opposing single-frequency interference as claimed in claim 1 is characterized in that described local sequence is frame synchronization sequence.

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