CN101924725A - Frame synchronization method and device for OFDM system - Google Patents

Abstract

The invention relates to a frame synchronization method for an OFDM system, which comprises the following steps: (a) carrying out self-correlation operation on a received signal sequence to obtain self-correlation results corr_auto (k); (b) selecting points at two sides of the peak value equal to a preset self-correlation decision threshold threshold_auto, respectively remarking the two points as k1 and k2, and finding the middle point k3 of the k1 and k2; (c) carrying out subsection cross-correlation operation on a signal sequence arranged between (k3-kfix) and (k3+kfix) and a local synchronous signal sequence, normalizing the result to obtain a normalized subsection cross-correlation result corr_cross(k), wherein the kfix is slightly larger than haft of the maximum multi-path time delay; and (d) taking the first peak point of subsection cross-correlation decision threshold threshold_cross in the subsection cross-correlation result corr_cross(k), adjusting the position of the received signal sequence according to the initial position of the frame, and outputting the received signal after synchronization. In the invention, the frame synchronization method not only can work in multi-path channel, but also can fight against larger carrier frequency offset.

Description

A kind of frame synchornization method of ofdm system and device

Technical field

The present invention relates to the communications field, relate in particular to the frame synchornization method and the device of a kind of OFDM (Orthogonal Frequency Division Multiplexing, OFDM) system.

Background technology

Frame synchronization is to make each pulsion phase at sending and receiving two ends in the communication system corresponding and be consistent channel time slot, thereby guarantees that each speech channel correctly transmits and receive unlikely confusion of receiving and dispatching between each road.

CMMB (China Mobile Media Broadcasting, China Mobile multimedia broadcasting) adopts OFDM (Orthogonal Frequency Division Multiplexing in the system, OFDM) technology, it is a kind of ofdm system, ofdm system has advantages such as availability of frequency spectrum height, anti-multipath interference performance be strong, but ofdm system is very high to the requirement of frame synchronization.The channel circumstance of CMMB system is abominable, and supports high-speed mobile, and system-frame is had higher requirement synchronously.

Existing frame synchornization method adopts related algorithm to realize usually, comprises auto-correlation algorithm and cross correlation algorithm two classes.Traditional cross correlation algorithm is relevant with the local signal sequence with the received signal sequence, has the outstanding advantage of correlation curve peak value, can resist the interference of Gaussian noise preferably, but the frame synchornization method that is based on traditional cross-correlation can not effectively resist carrier wave frequency deviation.In the CMMB system, require the system still can operate as normal when having bigger carrier wave frequency deviation, so can't directly utilize cross correlation algorithm.Usually utilize signal identical in the information sequence to be correlated with based on autocorrelative frame synchornization method, as Cyclic Prefix, pilot signal etc., with relevant after the received signal sequence delays certain time interval with oneself.This auto-correlation algorithm has stronger resistivity to interference such as carrier wave frequency deviations, but the received signal autocorrelator trace that adopts this method to obtain changes near peak value gently, be so-called plateau effect, make it be difficult under the bigger situation of Gaussian noise, accurately detect the original position of frame.

As seen, therefore the influence that the frame synchornization method in the ofdm system of existing employing related algorithm can not simultaneously effectively resist carrier wave frequency deviation and multipath channel can't be satisfied such as CMMB system etc. and adopt the requirement of the system of OFDM technology for frame synchronization.

Summary of the invention

Technical problem to be solved by this invention provides a kind of frame synchornization method of ofdm system, and the influence that can simultaneously effectively resist carrier wave frequency deviation and multipath channel is satisfied such as CMMB system etc. and adopted the requirement of the system of OFDM technology for frame synchronization.

For solving the problems of the technologies described above, the present invention proposes a kind of frame synchornization method of ofdm system, comprise the steps:

(a) sequence is carried out auto-correlation computation to received signal, obtains auto-correlation corr_auto (k) as a result;

(b) choose the point of the auto-correlation decision threshold threshold_auto that the peak value both sides equal to preset as a result among the corr_auto (k) in auto-correlation, be designated as k respectively ₁, k ₂, find k ₁, k ₂Mid point k ₃

(c) to being in k ₃-k _FixAnd k ₃+ k _FixBetween burst and local synchronous signal sequence carry out the sectional cross-correlation computing, and the result is carried out normalization, obtain normalized sectional cross-correlation corr_cross (k), wherein k as a result _FixBe slightly larger than half of maximum multipath time delay;

(d) get first peak point that sectional cross-correlation crosses sectional cross-correlation decision threshold threshold_cross among the corr_cross (k) as a result as frame start position, adjust the received signal sequence location according to this frame start position, the received signal after the output synchronously.

Further, said method also can have following characteristics, and in the step (a), described auto-correlation computation is with relevant with received signal sequence itself after the length N of a synchronizing signal of received signal sequence delays.

Further, said method also can have following characteristics, and when being applied to the CMMB system, in the step (b), described default auto-correlation decision threshold threshold_auto gets 0.25 in the bandwidth of CMMB system for 2M Hz.

Further, said method also can have following characteristics, and when being applied to the CMMB system, in the step (b), described default auto-correlation decision threshold threshold_auto gets 0.2 when the bandwidth of CMMB system is 6M/7M/8M Hz.

Further, said method also can have following characteristics, and in the step (c), the hop count of described segmentation is M, and M is a natural number, and when the relative frequency deviation of ofdm system existence was ε, M was determined by following formula:

corr_cros?s(k)≥δ，

Wherein δ is predefined numerical value, and the value of δ is between 0 to 1.

Further, said method also can have following characteristics, in the step (c), and k _FixBe 0.6 times of maximum multipath time delay.

Further, said method also can have following characteristics, and when being applied to the CMMB system, in the step (d), described sectional cross-correlation decision threshold threshold_cross gets 0.32 in the bandwidth of CMMB system for 2M Hz.

Further, said method also can have following characteristics, and when being applied to the CMMB system, in the step (d), described sectional cross-correlation decision threshold threshold_cross gets 0.08 when the bandwidth of CMMB system is 6M/7M/8M Hz.

For solving the problems of the technologies described above, the invention allows for a kind of frame-synchronizing device of ofdm system, comprise that successively the auto-correlation module, the peak value platform that link to each other choose module, sectional cross-correlation module, select module and adjusting module, wherein:

Described auto-correlation module is used for to received signal sequence and carries out auto-correlation computation, obtains auto-correlation corr_auto (k) as a result;

Described peak value platform is chosen module, be used for auto-correlation as a result corr_auto (k) choose the point that the peak value both sides equal default auto-correlation decision threshold threshold_aut o, be designated as k respectively ₁, k ₂, find k ₁, k ₂Mid point k ₃, choose and be in k ₃-k _FixAnd k ₃+ k _FixBetween burst, k wherein _FixBe slightly larger than half of maximum multipath time delay;

Described sectional cross-correlation module is used for being in k ₃-k _FixAnd k ₃+ k _FixBetween burst and local synchronous signal sequence carry out the sectional cross-correlation computing, and the result is carried out normalization, obtain normalized sectional cross-correlation corr_cross (k) as a result;

Described selection module, be used for getting sectional cross-correlation as a result corr_cross (k) cross first peak point of sectional cross-correlation decision threshold threshold_cross as frame start position;

Described adjusting module is used for adjusting the received signal sequence location according to this frame start position the received signal after the output synchronously.

Further, said method also can have following characteristics, k _FixBe 0.6 times of maximum multipath time delay.

Frame synchornization method of the present invention not only can be operated in multipath channel, and can resist bigger carrier wave frequency deviation, has improved the accuracy of frame synchronization, adapts to the bad working environment that the CMMB system exists high-speed mobile, multipath channel.Simultaneously, frame synchornization method of the present invention also can be generalized to other the ofdm system outside the CMMB system.

Description of drawings

Fig. 1 is the frame assumption diagram of CMMB system;

Fig. 2 is the frame synchronization flow chart of ofdm system in the embodiment of the invention;

Fig. 3 is a schematic diagram of seeking auto-correlation peak value platform in the embodiment of the invention;

Fig. 4 is a kind of particular flow sheet of sectional cross-correlation computing in the embodiment of the invention;

Fig. 5 is the frame-synchronizing device structure chart of ofdm system in the embodiment of the invention.

Embodiment

Main design of the present invention is, adopt the frame synchronization in the secondary related algorithm realization ofdm system, promptly sequence is carried out auto-correlation computation at first to received signal, in the auto-correlation result, find the peak value both sides to equal 2 points of default auto-correlation decision threshold, get this mid point of 2, again the burst in the certain limit of described mid point both sides is carried out sectional cross-correlation, get among the sectional cross-correlation result cross the sectional cross-correlation thresholding with a peak value as frame start position.The present invention at first utilizes auto-correlation algorithm to obtain the scope of frame start position, and then utilizes the sectional cross-correlation algorithm to obtain accurate frame start position.

Be example with the CMMB system below, by embodiment principle of the present invention and feature be described that institute gives an actual example and only is used to explain the present invention, is not to be used to limit scope of the present invention, the present invention is equally applicable to other ofdm systems.

The CMMB standard code in the broadcasting service frequency range, the frame structure of mobile multimedia broadcast system transmission signals, chnnel coding and modulation system.According to standard, the frame structure of CMMB system as shown in Figure 1.As can see from Figure 1, a frame of CMMB system is made up of 40 time slots, and total duration is 1s (1 second).Each time slot is made up of a beacon and 53 OFDM symbols.Each beacon comprises a sender unit identification TxID and two identical synchronous signal sequences, this synchronous signal sequence is by PN sequence (Pseudo-noise Sequence, pseudo noise sequence) variation obtains, the sub-carrier number of each synchronous signal sequence is 512 under the 2MHz pattern, and the sub-carrier number of each synchronous signal sequence is 2048 under the 8M pattern.

Fig. 2 is the frame synchronization flow chart of CMMB system in the embodiment of the invention, as shown in Figure 2, comprises the steps:

Step 210, sequence is carried out auto-correlation computation to received signal, obtains auto-correlation corr_auto (k) as a result;

Because each time slot all has two identical synchronous signal sequences, can be with relevant after the length N of a synchronizing signal of received signal sequence delays with oneself.Suppose that the burst that receives is designated as R={r _k, k ∈ [0 ,+∞) }, then autocorrelative mould value square is expressed as follows:

Not having frequency deviation in noiseless does not have under the perfect condition of multipath, when the associated window starting point (is established k=k this moment during just corresponding to the synchronizing signal original position ₀),

Peak value appears in the result of formula (1),

corr_auto(k ₀)＝N ²。

Autocorrelator trace changes near peak value gently, promptly so-called plateau effect, and relatively more difficult to the identification of signal peak, particularly under multipath channel, because the existence of multipath, it is longer that the peak value platform can become.Under multipath channel, the distance of establishing between each footpath is N ₁, N ₂... N _m, when associated window starting point during just corresponding to the synchronizing signal original position, autocorrelative mould value square can be expressed as under the multipath channel:

In the formula (2)

Value be not 1.

When the associated window starting point is positioned at multi-path location, can obtain the autocorrelative result of cotype (2),

Step 220 is chosen the point that the peak value both sides equal default auto-correlation decision threshold threshold_auto among the corr_auto (k) as a result in auto-correlation, is designated as k respectively ₁, k ₂, find k ₁, k ₂Mid point k ₃

Platform appears in auto-correlation result near frame start position, can't obtain accurate frame start position.If preestablish auto-correlation decision threshold threshold_auto, the peak value both sides are by the some k of auto-correlation decision threshold ₁, k ₂About peak value platform symmetry, get k ₁, k ₂Mid point k ₃, front and back translation k _FixIndividual, just can obtain auto-correlation peak value platform.The width of auto-correlation peak value flat-top is determined k by multidiameter delay _FixCan be set at half that is slightly larger than maximum multipath time delay, preferably, k _FixCan be 0.6 times of maximum multipath time delay.The principle of searching auto-correlation peak value platform as shown in Figure 3.

When the present invention was applied to the CMMB system, in the step 220, default auto-correlation decision threshold threshold_auto can get 0.25 in the bandwidth of CMMB system for 2M Hz, can get 0.2 when the bandwidth of CMMB system is 6M/7M/8M Hz.

This auto-correlation algorithm can obtain near the signal the frame start position, and gets rid of the signal of non-frame start position.Its shortcoming is that frame start position is accurate inadequately, and cross correlation algorithm has the sharp-pointed characteristic of peak value, and two kinds of algorithms can be complementary.But existing cross correlation algorithm can not resist bigger carrier wave frequency deviation, for this reason, has adopted the sectional cross-correlation algorithm in the step below the present invention, and this new algorithm not only can resist bigger carrier wave frequency deviation, and the sharp-pointed advantage of cross correlation algorithm peak value is arranged simultaneously.

Step 230 is to being in k ₃-k _FixAnd k ₃+ k _FixBetween burst and local synchronous signal sequence carry out the sectional cross-correlation computing, and the result is carried out normalization, obtain normalized sectional cross-correlation corr_cross (k), wherein k as a result _FixBe slightly larger than half of maximum multipath time delay, preferably, k _FixCan be 0.6 times of maximum multipath time delay;

Fig. 4 is a kind of particular flow sheet of sectional cross-correlation computing in the embodiment of the invention, and as shown in Figure 4, step 230 specifically can comprise:

(231), each synchronous signal sequence of establishing the transmitting terminal beacon is S={s ₁, s ₂..., s _N, wherein, N is a natural number, represents sequence length, and this sequence is simultaneously also as the local synchronous signal sequence of receiving terminal frame synchronization, and the received signal that receiving terminal obtains is R={r _k, k ∈ (∞ ,+∞) }, k is an integer, and the sequence in the associated window is divided into the M five equilibrium, and the width of associated window is N, and M, N are natural number, and then the length of each segmentation is N _m=N/M;

Here illustrate that associated window is exactly the burst that carries out sectional cross-correlation, the length of associated window is fixed, and is the length N of a synchronizing signal.

For increasing cross correlation value, can adopt the mould value square value of cross-correlation to represent.

(232) respectively received signal subsequence in each segmentation and local synchronizing signal subsequence are carried out cross-correlation, then the mould value of the cross correlation value of m segmentation square is

(233), obtain being used to detect the cross correlation results of frame synchronization with the cross correlation results addition of each segmentation:

(234) in order to make cross correlation results not be subjected to the influence of received signal power, cross correlation results is carried out energy normalized, promptly use the energy summation of correlated results divided by received signal in the associated window.The correlated results of energy normalized is expressed as:

The normalized crosscorrelation result's who calculates according to formula (4) numerical value and synchronizing sequence length and received signal power all do not have to be contacted directly, and its size thereby is convenient to set unified frame synchronization threshold value in [0,1] scope.Thereby carrying out peak value detects.

After the normalization, not having the sectional cross-correlation result under the perfect condition of frequency deviation is 1; When existing relative frequency deviation to be ε, the result of sectional cross-correlation is:

$\frac{{|1-e^{j2\mathrm{\π\ϵN}/M}|}^2}{{|1-e^{j2\mathrm{\π\ϵ}}|}^2}\·\frac{M^2}{N^2},$

If order:

$\frac{{|1-e^{j2\mathrm{\π\ϵN}/M}|}^2}{{|1-e^{j2\mathrm{\π\ϵ}}|}^2}\·\frac{M^2}{N^2}\≥\mathrm{\δ},$

Just can obtain making the result of sectional cross-correlation to remain on the value of the above suitable segments M of the δ of carrierfree frequency deviation.

The method of sectional cross-correlation makes the length of each sub-associated window much smaller than former correlation window length, has destroyed the orthogonality of original sequence, and makes the noise signal possibility increase similar to the local signal subsequence in each sub-associated window.Increase along with segments, the correlated results of other positions outside the frame start position increases gradually, the possibility that the correlated results of non-frame start position surpasses threshold value also increases gradually, therefore want the value of choose reasonable segments M, make that non-frame start position place correlated results numerical value can be not excessive and cause erroneous judgement.

Step 240 is got sectional cross-correlation and is crossed first peak point of sectional cross-correlation decision threshold threshold_cross as frame start position among the corr_cross (k) as a result;

Wherein, when the present invention was applied to the CMMB system, in the step 240, sectional cross-correlation decision threshold threshold_cross can get 0.32 in the bandwidth of CMMB system for 2M Hz, can get 0.08 when the bandwidth of CMMB system is 6M/7M/8M Hz.

Because the existence of multipath channel in the CMMB system, the sectional cross-correlation algorithm among the present invention is carrying out when peak value judges, choose the earliest the footpath but not maximum diameter as frame start position.

Step 250 is adjusted the received signal sequence location according to this frame start position, the received signal after the output synchronously.

Compared with prior art, the present invention adopts the sectional cross-correlation algorithm can resist bigger carrier shift, below how the present invention is realized that above-mentioned effect analyzes.

The mould value square expression of existing cross correlation algorithm is suc as formula (5):

When the associated window starting point (is established k=k this moment during just corresponding to the synchronizing signal original position ₀), this moment, the mould value square value of the cross correlation results that obtains was the peak value of slip correlated results mould value square.As if carrier wave frequency deviation is 0, then r _N+kS _n ^*=1, the peak value of the mould value of the cross correlation results of being obtained by formula (5) square is N ²When the relative carrier wave frequency deviation that exists in the system is ε, r _N+kS _n ^*=e ^{J2 π ε (n+k)}, the peak value of the mould value of cross correlation results square is:

(6)

In the formula (6), ε=Δ f/f _Band, Δ f is a carrier wave frequency deviation, f _BandBe signal bandwidth.The length of synchronizing sequence is fixed in the CMMB system, and promptly correlation window length N remains unchanged, the mould of cross-correlation square peak value can reduce along with the increase of relative carrier wave frequency deviation ε.When ε N=1, corr (k ₀)=0 adopts traditional cross correlation algorithm can't find frame head.Influence at this relative frequency deviation ε makes cross-correlation peak value put under the unidentified situation, according to formula (6),, can reduce the influence of frequency deviation to cross correlation results if can rationally change the size of associated window N, the value of raising formula (6), thus reach the purpose of frame synchronization.Based on this thought, the present invention proposes the sectional cross-correlation algorithm and be used for resisting carrier wave frequency deviation.After adopting the sectional cross-correlation algorithm, when having frequency deviation, the peak value of sectional cross-correlation result's mould value square is

$\mathrm{corr}\_\mathrm{cross}\left(k_0\right)=\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\left|\underset{n=1}{\overset{N_m}{\mathrm{\Σ}}}{e}^{j2\mathrm{\π\ϵ}(n+k_0+N_1+...+N_{m-1})}\right|}^2=\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\left|\underset{n=1}{\overset{N_m}{\mathrm{\Σ}}}{e}^{j2\mathrm{\π\ϵn}}\right|}^2$ (7)

$=\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\left|\frac{1-e^{j2\mathrm{\π\ϵ}{N}_m}}{1-e^{j2\mathrm{\π\ϵ}}}\right|}^2=\frac{1}{{|1-e^{j2\mathrm{\π\ϵ}}|}^2}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{|1-e^{j2\mathrm{\π\ϵN}/M}|}^2$

Comparison expression (6) and formula (7) can get, when having identical relative carrier wave frequency deviation ε, the segmentation associated window be N/M sectional cross-correlation mould square be the mould that obtains of traditional cross correlation algorithm square

$\frac{M{|1-e^{j2\mathrm{\π\ϵN}/M}|}^2}{{|1-e^{j2\mathrm{\π\ϵN}}|}^2},$

When having big carrier wave frequency deviation, the sectional cross-correlation algorithm is easier to detecting of peak value.When ε N=1, the result of sectional cross-correlation is

$\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{|1-e^{j2\mathrm{\π}/M}|}^2,$

Solved traditional cross correlation algorithm can't detect frame head because carrier wave frequency deviation is excessive problem.

Sectional cross-correlation algorithm after the improvement can resist bigger carrier wave frequency deviation, but the sectional cross-correlation algorithm still is subjected to the influence of multipath channel.The existence of multipath channel causes the sectional cross-correlation algorithm a plurality of peak values can occur near frame head, and this has brought certain difficulty for the identification of frame head.Though ofdm system can effectively resist multipath channel, this need be before finding frame head forwards time-domain signal to frequency-region signal and slides relevantly, and operand is excessive, is difficult to hardware and realizes, therefore needs to seek new algorithm.The algorithm that this paper adopts with auto-correlation and sectional cross-correlation algorithm in conjunction with having solved this problem.

Therefore frame synchornization method of the present invention not only can be operated in multipath channel, and can resist bigger carrier wave frequency deviation, has improved the accuracy of frame synchronization, adapts to the bad working environment that the CMMB system exists high-speed mobile, multipath channel.Simultaneously, frame synchornization method of the present invention also can be generalized to other the ofdm system outside the CMMB system.

The invention allows for a kind of frame-synchronizing device of ofdm system.Fig. 5 is the frame-synchronizing device structure chart of ofdm system in the embodiment of the invention, as shown in Figure 5, in the present embodiment, the frame-synchronizing device of ofdm system comprises that successively the auto-correlation module, the peak value platform that link to each other choose module, sectional cross-correlation module, select module and adjusting module, wherein:

The auto-correlation module is used for to received signal sequence and carries out auto-correlation computation, obtains auto-correlation corr_auto (k) as a result;

The peak value platform is chosen module, be used for auto-correlation as a result corr_auto (k) choose the point that the peak value both sides equal default auto-correlation decision threshold threshold_auto, be designated as k respectively ₁, k ₂, find k ₁, k ₂Mid point k ₃, choose and be in k ₃-k _FixAnd k ₃+ k _FixBetween burst, k wherein _FixBe slightly larger than half of maximum multipath time delay, preferably, k _FixCan be 0.6 times of maximum multipath time delay; When being applied to the CMMB system, default auto-correlation decision threshold threshold_auto can get 0.25 in the bandwidth of CMMB system for 2M Hz, can get 0.2 when the bandwidth of CMMB system is 6M/7M/8M Hz.

The sectional cross-correlation module is used for being in k ₃-k _FixAnd k ₃+ k _FixBetween burst and local synchronous signal sequence carry out the sectional cross-correlation computing, and the result is carried out normalization, obtain normalized sectional cross-correlation corr_cross (k) as a result;

Select module, be used for getting sectional cross-correlation as a result first peak point of corr_cross (k) mistake sectional cross-correlation decision threshold threshold_cross as frame start position; When being applied to the CMMB system, sectional cross-correlation decision threshold threshold_cross can get 0.32 in the bandwidth of CMMB system for 2M Hz, can get 0.08 when the bandwidth of CMMB system is 6M/7M/8M Hz.

Adjusting module is used for adjusting the received signal sequence location according to this frame start position the received signal after the output synchronously.

Wherein, the content of appropriate section is identical in the frame synchornization method of the course of work that auto-correlation module, peak value platform choose module, sectional cross-correlation module, select module and adjusting module various piece and principle and aforementioned ofdm system, repeats no more herein.

Frame-synchronizing device of the present invention not only can be operated in multipath channel, and can resist bigger carrier wave frequency deviation, has improved the accuracy of frame synchronization, adapts to the bad working environment that the CMMB system exists high-speed mobile, multipath channel.Simultaneously, frame synchornization method of the present invention also can be generalized to other the ofdm system outside the CMMB system.

The above only is preferred embodiment of the present invention, and is in order to restriction the present invention, within the spirit and principles in the present invention not all, any modification of being done, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. the frame synchornization method of an ofdm system is characterized in that, comprises the steps:

(a) sequence is carried out auto-correlation computation to received signal, obtains auto-correlation corr_auto (k) as a result;

(b) choose the point of the auto-correlation decision threshold threshold_auto that the peak value both sides equal to preset as a result among the corr_auto (k) in auto-correlation, be designated as k respectively ₁, k ₂, find k ₁, k ₂Mid point k ₃

(c) to being in k ₃-k _FixAnd k ₃+ k _FixBetween burst and local synchronous signal sequence carry out the sectional cross-correlation computing, and the result is carried out normalization, obtain normalized sectional cross-correlation corr_cross (k), wherein k as a result _FixBe slightly larger than half of maximum multipath time delay;

(d) get first peak point that sectional cross-correlation crosses sectional cross-correlation decision threshold threshold_cross among the corr_cross (k) as a result as frame start position, adjust the received signal sequence location according to this frame start position, the received signal after the output synchronously.

2. the frame synchornization method of CMMB according to claim 1 system is characterized in that in the step (a), described auto-correlation computation is with relevant with received signal sequence itself after the length N of a synchronizing signal of received signal sequence delays.

3. the frame synchornization method of CMMB according to claim 1 system is characterized in that when being applied to the CMMB system, in the step (b), described default auto-correlation decision threshold threshold_auto gets 0.25 in the bandwidth of CMMB system for 2M Hz.

4. the frame synchornization method of CMMB according to claim 1 system is characterized in that when being applied to the CMMB system, in the step (b), described default auto-correlation decision threshold threshold_auto gets 0.2 when the bandwidth of CMMB system is 6M/7M/8M Hz.

5. the frame synchornization method of CMMB according to claim 1 system is characterized in that in the step (c), the hop count of described segmentation is M, and M is a natural number, and when the relative frequency deviation that exists at ofdm system was ε, M was determined by following formula:

corr_cross(k)≥δ，

Wherein δ is predefined numerical value, and the value of δ is between 0 to 1.

6. the frame synchornization method of CMMB according to claim 1 system is characterized in that, in the step (c), and k _FixBe 0.6 times of maximum multipath time delay.

7. the frame synchornization method of CMMB according to claim 1 system is characterized in that when being applied to the CMMB system, in the step (d), described sectional cross-correlation decision threshold threshold_cross gets 0.32 in the bandwidth of CMMB system for 2M Hz.

8. the frame synchornization method of CMMB according to claim 1 system is characterized in that when being applied to the CMMB system, in the step (d), described sectional cross-correlation decision threshold threshold_cross gets 0.08 when the bandwidth of CMMB system is 6M/7M/8M Hz.

9. the frame-synchronizing device of an ofdm system is characterized in that, comprises that successively the auto-correlation module, the peak value platform that link to each other choose module, sectional cross-correlation module, select module and adjusting module, wherein:

Described auto-correlation module is used for to received signal sequence and carries out auto-correlation computation, obtains auto-correlation corr_auto (k) as a result;

Described peak value platform is chosen module, be used for auto-correlation as a result corr_auto (k) choose the point that the peak value both sides equal default auto-correlation decision threshold threshold_auto, be designated as k respectively ₁, k ₂, find k ₁, k ₂Mid point k ₃, choose and be in k ₃-k _FixAnd k ₃+ k _FixBetween burst, k wherein _FixBe slightly larger than half of maximum multipath time delay;

Described sectional cross-correlation module is used for being in k ₃-k _FixAnd k ₃+ k _FixBetween burst and local synchronous signal sequence carry out the sectional cross-correlation computing, and the result is carried out normalization, obtain normalized sectional cross-correlation corr_cross (k) as a result;

Described selection module, be used for getting sectional cross-correlation as a result corr_cross (k) cross first peak point of sectional cross-correlation decision threshold threshold_cross as frame start position;

Described adjusting module is used for adjusting the received signal sequence location according to this frame start position the received signal after the output synchronously.

10. the frame-synchronizing device of ofdm system according to claim 9 is characterized in that, k _FixBe 0.6 times of maximum multipath time delay.

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