CN103346990A - Method for correcting symbols regularly in DVB-T2 system - Google Patents

Abstract

The invention discloses a method for correcting symbols regularly in a DVB-T2 system. In symbol synchronization, PI symbols regenerated in a receiver are utilized to correlate to received signals to find initial positions of OFDM symbols; segmentation operation is conducted on correlation operations; P2 pilot frequency time domain signals locally generated are utilized to correlate to the received signals according to the initial positions of the symbols; weighted average is conducted on five-point sliding results, and then the corresponding GI mode and the position of the maximum are found out. The method greatly reduces operation amount and operation cost and improves mode detection accuracy.

Description

method for correcting symbol timing in DVB-T2 system

Technical Field

The invention relates to a method for symbol timing and mode detection in a DVB-T2 system.

Background

In a multi-carrier system, in order to maintain orthogonality of OFDM symbols and minimize mutual interference (ISI) between OFDM symbols, a Guard Interval (GI) is usually inserted between two OFDM symbols to achieve the above-mentioned object. I.e. copying a certain proportion of the tail part of the current OFDM symbol to the start position of the current OFDM symbol.

In a multi-carrier system, in order to adapt to different channel environment conditions, there are usually multiple choices of guard interval ratio modes, and in a receiver, the length of the guard interval selected by the current system must be determined to correctly determine the starting position of the OFDM symbol. In a multi-carrier system, in order to be able to correctly receive a signal, the receiver has to determine the start position of the OFDM symbol, i.e. the symbol timing.

The DVB-T2 system is a terrestrial digital television broadcasting system based on OFDM multicarrier technology, in which a baseband signal is divided into superframes, each superframe containing up to 255T 2 frames, each T2 frame starting with a P1 symbol bit followed by N P2 symbols, followed by a plurality of data symbols, wherein the P2 symbols and the data symbols have the same FFT length and Guard Interval (GI) length.

The P1 symbol has a fixed structure and a length of 2048, and as can be seen from fig. 2, part a is obtained by performing 1K IFFT after being encoded by signaling S1 and S2, and part C and part B are weighted copies of the first half and the second half of a, respectively, and the generation flow thereof is shown in fig. 3.

The P2 symbols are characterized by a dense pilot spacing of multiples of 3 or 6, depending on the FFT length and MISO type.

The symbol timing and mode detection method of the DVB-T2 system is generally a joint estimation [1], that is, a peak value is obtained by a sliding correlation method using the cyclic prefix characteristic of an OFDM symbol, and then the interval between the two peak values is determined, so as to determine the length of a transmission mode and a guard interval, and simultaneously complete symbol timing. The principle of the algorithm is as follows:

defining the autocorrelation function as:

$R_i\left(n\right)=\frac{1}{N_i}\underset{j=0}{\overset{\frac{N_i}{Q}-1}{\mathrm{\Σ}}}r(n-j)r^{*}(n-j-N_i)---\left(1\right)$

in the formula (1), the length of the N standard transmission mode FFT has two choices of 2K and 8K in DVB-T, and 5 choices of 1K, 2K, 4K, 8K, 16K, 32K and the like in DVB-T2. N/Q denotes the length of the GI, with Q having 4 values (4,8,16,32) in DVB-T and 7 values (4,8,16,32, 128, 128/19,256/19) in DVB-T2.

The corresponding autocorrelation function can be obtained as shown in fig. 6.

If Q is set correctly, the transmission mode can be determined by calculating the distance between the two peaks. From the above formula, we can easily see that if there are N choices for GI in the system, N-1 correlations as described above must be done to estimate the mode of GI. Since the length of the shortest GI is 1/128 in the DVB-T2 system, the correlation peak is small in this mode, and particularly, misjudgment easily occurs in the case of large channel interference.

In the DVB-T2 system, symbol timing is started after frame synchronization. After the frame synchronization is locked, two parameters S1 and S2 are provided, wherein S1 is a 3-bit parameter indicating whether the current system is in MISO mode or SISO mode, and T2-BASE or T2-LITE mode; s2 is a 4-bit parameter containing FFT SIZE and information of partial GI mode. Since the timing position of the frame synchronization has an error, more accurate symbol timing synchronization is required. The GI mode is also determined (the S2 parameter only tells the value range of the GI mode). It should be noted that in the DVB-T2 system, there are seven GI modes in total, i.e., 1/4, 1/8,1/16,1/32,1/128,19/128,19/256, and compared with DVB-T, the latter three modes, especially 1/128 mode, are shorter in length, and if the mode detection method of DVB-T is used, there is a high detection error.

If the symbol timing and pattern detection techniques in the existing DVB-T system are used, at least two OFDM symbols are needed to make the sliding correlation decision. And at least 6 times of the actions are needed when the sliding correlation is carried out. From equation (1), it can be seen that in 32K and 16K modes, because the sliding window is relatively large, the computation amount of this method is very large, which means that COST and POWER of the chip are relatively large. On the other hand, since the shortest GI length is only 64 points (1/128 GI in 8K mode or 1/32GI in 1K mode), the peak value after sliding correlation is small, and when a multipath channel occurs and the error of frequency offset is relatively large, the peak value is not obvious, so that a large probability of misjudgment occurs, that is, the performance of the chip is not guaranteed. The DVB-T symbol timing practice is clearly not applicable to the DVB-T2 system and needs to be improved.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method for correcting symbol timing in a DVB-T2 system, which reduces the computation amount and the capturing time of a symbol timing and mode detection method in the DVB-T system, and improves the accuracy of mode detection, aiming at the defects of the prior art.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a method for symbol timing correction in a DVB-T2 system, the method comprising:

1) generating a P1 symbol using two parameters S1 and S2 provided after DVB-T2 frame synchronization locking;

2) respectively taking sign bits from the two paths of I/Q of the P1 sign to obtain a sign synchronization related sequence ssc _ seq:

k=[0～1023]，

wherein $\mathrm{sign}\left[x\right]=\left\{\begin{array}{cc}+1,& x\&GreaterEqual;0\\ -1,& x<0\end{array}\right.,$

The representation takes the real part of P1,

the representation takes the imaginary part of P1;

3) and (3) carrying out segmented sliding correlation on the symbol synchronization correlation sequence ssc _ seq:

$\mathrm{corr}\_\mathrm{result}\left(l\right)=\underset{n=0}{\overset{\mathrm{seg}\_\mathrm{num}-1}{\mathrm{\&Sigma;}}}\left(\right|\underset{m=n*\mathrm{seg}\_\mathrm{len}}{\overset{(n+1)*\mathrm{seg}\_\mathrm{len}-1}{\mathrm{\&Sigma;}}}r(m+k)*\mathrm{ssc}\_\mathrm{seq}\left(m\right)\left|\right),$

wherein, corr _ result is a segment sliding correlation result, r (m) is a received signal after frame synchronization locking, seg _ num is the number of the segments of the sliding correlation, seg _ len is the length of each segment of the sliding correlation segments, seg _ len × seg _ num =1024, and l is more than or equal to-64 and less than or equal to 64;

4) determining the maximum value and the position of the segment sliding correlation result according to the segment sliding correlation expression in the step 3), and finding the first P2 symbol (including GI) r in the received signal_p2(s)；

5) Determining a pilot pattern of P2 according to S1 and S2, and generating a pattern detection sequence md _ seq0(w) according thereto;

6) setting an initial value GI = 1/4;

7) moving the part of the pattern detection sequence md _ seq0(w) with the tail length GI to the head, we get:

$\mathrm{md}\_\mathrm{seq}\left(w\right)=\left\{\begin{array}{cc}\mathrm{md}\_\mathrm{seq}0(N-N*\mathrm{GI}+w)& 0\&le;w<\mathrm{GI}*N\\ \mathrm{md}\_\mathrm{seq}0(w-\mathrm{GI}*N)& \mathrm{GI}*N\&le;w<N\end{array}\right.$

wherein w = [ 0-N-1 ], and N is the length of FFT;

8) for sequences md _ seq and r_p2Making subsection sliding correlation, wherein the sliding distance is 5:

$\mathrm{corr}\_\mathrm{result}\left(l\right)=\underset{n=0}{\overset{\mathrm{seg}\_\mathrm{num}-1}{\mathrm{\&Sigma;}}}\left(\right|\underset{m=n*\mathrm{seg}\_\mathrm{len}}{\overset{(n+1)*\mathrm{seg}\_\mathrm{len}-1}{\mathrm{\&Sigma;}}}{r}_{p2}(m+t)*\mathrm{md}\_\mathrm{seq}\left(m\right)\left|\right),$

wherein, $\mathrm{seg}\_\mathrm{len}*\mathrm{seg}\_\mathrm{num}=\left\{\begin{array}{cc}N& N\&le;8192\\ 8192& N>8192\end{array}\right.,$ t=[0,1,2,3,4,5]

9) summing the 5-point sliding correlation results obtained in the step 8) to obtain a correlation result of the current GI mode;

10) GI to other 6 patterns, i.e., GI =1/8,1/16,1/32,1/128,19/128,19/256, repeat 7) — 9), respectively), 7 correlation results are obtained;

11) comparing the maximum value of the 7 correlation results, wherein the corresponding GI mode is the result of mode detection;

12) in the above step 11), the maximum value is found from the result of the 5-point sliding correlation corresponding to the pattern detection result, and the position of the maximum value is the final result of correcting the symbol timing.

Compared with the prior art, the invention has the beneficial effects that: the invention fully utilizes the characteristics of the frame structure of the DVB-T2 system, the symbols P1 and P2 have very accurate correlation, and the accuracy of the detection result of the symbol timing position and the GI mode obtained by the method is obviously improved compared with the prior method; because the related operation only uses the sign bit of the sequence, the multiplication and accumulation operation is greatly simplified, and the cost is reduced; in symbol synchronization, since the P1 signal has a length of only 1024 points, the correlation operation requires only a sequence having a length of 1024 points for all FFT modes and GI modes. Since the symbol synchronization is started after the frame synchronization, the distance of the sliding correlation is related to the accuracy of the frame synchronization, which is [ -64,64] according to the characteristics of the P1 signal. Since only the sign bit of the P1 symbol is taken during the correlation process, multiplication is avoided and only addition is performed. Therefore, the number of operations required to complete symbol synchronization is 1024 × 128 complex addition operations, i.e., 262144 addition operations; also in the mode detection process, there are only addition operations, and the number of addition operations is: 8192 × 5 × 7 × 2= 573440; the method greatly reduces the operation amount and the operation cost and improves the mode detection accuracy.

Drawings

FIG. 1 is a DVB-T2 frame structure;

FIG. 2 is a DVB-T2P1 symbol structure;

FIG. 3 is a flow chart of generating P1 symbols for DVB-T2;

FIG. 4 is a pilot pattern (MISO pattern) of DVB-T2P 2 symbols;

FIG. 5 is a pilot pattern (SISO mode) of DVB-T2P 2 symbols;

FIG. 6 is a graph of an autocorrelation function obtained by a prior art method;

FIG. 7 is a schematic diagram of a PRBS generator for generating scrambling sequences;

FIG. 8 is a flow chart of symbol synchronization according to the present invention;

FIG. 9 is a schematic diagram of a PRBS sequence generator for generating a PRBS sequence;

FIG. 10 is a flow chart of the method of the present invention.

Detailed Description

In digital television systems such as DVB-T2, the synchronization module typically performs symbol synchronization and then performs mode detection and frequency offset estimation. The former is to find the exact position of the signal frame and symbol, and the latter is to complete further signal analysis and analysis, find the transmission mode and frequency offset of the system.

[a] Symbol synchronization

1) P1 symbols are generated using S1 and S2.

Since after frame synchronization locking, two parameters S1 and S2 are provided, which indicate the FFT mode and MISO mode adopted by the current system, and which determine the content and structure of the frame header P1 symbol of the DVB-T2 system.

TABLE 1S1 and S2 modulation modes

From the above table, it can be seen that S1 and S2 are parameters of 3bit and 4bit, respectively, corresponding to 8 and 16 possible sequences, respectively. Wherein the sequence length corresponding to S1 is 64 bits, and the sequence length corresponding to S2 is 256 bits. The generation of the P1 sequence is described in detail in reference [2 ].

First, the modulation sequence is selected according to S1 and S2:

{mss_seq₀…mss_seq₃₈₃}={css_S1,css_S2,css_S1}

={css_S1,0…css_S1,63,css_S2,0…css_S2,255,css_S1,0…css_S1,63}

wherein mss _ seq is a 384-bit length sequence, which is modulated to the corresponding 384 sub-carrier positions of 1K FFT after subsequent transformation. It is generated from the sequences S1 and S2. S1 is a 3-bit message with 8 options, corresponding to 64-bit messages css in each row of S1 in the above table_S1={css_S1,0…css_S1,63}. S2 is a 4-bit message with 16 options, corresponding to the 255-bit messages css in each row of S2 in the above table_S2={css_S2,0…css_S2,255}。

Secondly, carrying out DBPSK modulation on the modulation information:

mss_diff=DBPSK(mss_seq)

$\mathrm{mss}\_{\mathrm{diff}}_i=\left\{\begin{array}{cc}\mathrm{mss}\_{\mathrm{diff}}_{i-1}& ,\mathrm{mss}\_{\mathrm{seq}}_i=0\\ -\mathrm{mss}\_{\mathrm{diff}}_{i-1}& ,\mathrm{mss}\_{\mathrm{seq}}_i=1\end{array}\right.$

mss_diff_-1=+1

where mss _ diff is information of length 384 bits after mss _ seq is DBPSK modulated.

Third, the above sequence scrambling:

mss_scr=SCRAMBLING{mss_diff}

the scrambling sequence is generated by the PRBS generator shown in fig. 7, with a length of 384 bits, and the generator polynomial of the scrambling PRBS generator is: 1+ x¹⁴+x¹⁵(ii) a Where x is 0 or 1, the sequence after scrambling can be represented by the following formula:

mss_scr_i=mss_diff_i×(1-2PRBS_i)

wherein, PRBS_iIs whenThe bit (0 or 1) output by the previous time PRBS generator corresponds to the bit currently being scrambled in the DBPSK result, i = [0 ~ 383 ], []。

Fourthly, the above sequences are allocated to the subcarriers of the 1K mode at fixed positions.

Fifthly, IFFT is performed to obtain P1 symbols.

Sixthly, sign bits are respectively taken from the two paths of I/Q of the obtained P1 sign to obtain a sign synchronization correlation sequence required by the invention:

k=[0～1023]

wherein $\mathrm{sign}\left[x\right]=\left\{\begin{array}{cc}+1,& x\&GreaterEqual;0\\ -1,& x<0\end{array}\right.,$

The representation takes the real part of P1,

the imaginary part of P1.

The symbol synchronization flow diagram is shown in fig. 8.

2) Segmental sliding correlation

Because carrier synchronization is not completed when symbol synchronization is performed, a certain degree of frequency offset exists in the system, mismatching between a received signal and a symbol synchronization correlation sequence is caused, and at the moment, if sliding correlation is directly performed, a peak value cannot appear. Therefore, there is a need for an improvement in sliding correlation, i.e., piecewise sliding correlation.

$\mathrm{corr}\_\mathrm{result}\left(l\right)=\underset{n=0}{\overset{\mathrm{seg}\_\mathrm{num}-1}{\mathrm{\&Sigma;}}}\left(\right|\underset{m=n*\mathrm{seg}\_\mathrm{len}}{\overset{(n+1)*\mathrm{seg}\_\mathrm{len}-1}{\mathrm{\&Sigma;}}}r(m+k)*\mathrm{ssc}\_\mathrm{seq}\left(m\right)\left|\right)$

Where r (m) is the received signal after frame synchronization, seg _ num is the number of segments associated with sliding, and seg _ len is the length of each segment. seg _ len _ seg _ num =1024, -64 ≦ l ≦ 64.

3) Detecting peak values

Since the frame synchronization error is 1024 points at most, the length of the sliding correlation is 1024 at most. When the sliding correlation is finished, the maximum value and the position of the correlation result are obtained, and the position is the result of symbol synchronization.

[b] Pattern detection and symbol synchronization correction

Since in the DVB-T2 system, the beginning of each frame has P2 symbols, and P2 symbols are characterized by dense pilot, the pilot pattern is referred to fig. 4. we can use the time domain information of P2 symbols to perform pattern detection and symbol synchronization correction, and since the correlation of P2 signals is relatively good, we only need to take 8K length in 16K and 32K modes, that is, the longest sequence is 8K length in the pattern detection process. The method comprises the following specific steps:

1) pilot generation pattern detection sequence with P2 symbol:

a) by the PRBS sequence generator given in fig. 9, a PRBS sequence p2_ PRBS0(p) is generated, where p = [ 0. kmax-1 ]]Kmax is the number of effective subcarriers in the P2 symbol in the current transmission mode; the generator polynomial of the PRBS generator shown in fig. 9 is: x is the number of¹¹+x²+1, wherein x is 0 or 1;

b) determining the interval Dx of P2 symbol pilot frequency according to the current transmission mode, namely FFT or MISO mode;

c) setting the positions of the p2_ prbs1(p) sequence which are not integral multiples of Dx to zero;

p=[0～kmax-1]

d) cyclic shift of the sequence p2_ prbs1(p) gave the sequence p2_ prbs2(w)

$\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003338197700024.png"\; state="\{\{state\}\}">p</figure-callout>}2\_\mathrm{prbs}2\left(w\right)=\left\{\begin{array}{cc}\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003338197700024.png"\; state="\{\{state\}\}">p</figure-callout>}2\_\mathrm{prbs}1(w+\frac{k\max -1}{2}),& w\&le;\frac{k\max -1}{2}\\ 0,& \frac{k\max -1}{2}<w\&le;N-\frac{k\max -1}{2}\\ \mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003338197700024.png"\; state="\{\{state\}\}">p</figure-callout>}2\_\mathrm{prbs}1(w+\frac{k\max -1}{2}-N),& N-\frac{k\max -1}{2}<w\&le;N-1\end{array}\right.$

e) Performing IFFT on the sequence processed in the step d) to obtain a time domain sequence P2_ pilot3(w) of a P2 symbol pilot, wherein w = [ 0-N-1 ];

f) taking sign bit for p2_ pilot3(w) to get pattern detection sequence:

wherein w = [0 to N-1], and N is the length of FFT.

2) Pattern detection

Since the error of symbol synchronization is + -2, the window of sliding correlation is 5;

a) let GI = 1/4;

b) moving the part of the pattern detection sequence md _ seq0 with the tail length GI to the head, we get:

$\mathrm{md}\_\mathrm{seq}\left(w\right)=\left\{\begin{array}{cc}\mathrm{md}\_\mathrm{seq}0(N-N*\mathrm{GI}+w)& 0\&le;w<\mathrm{GI}*N\\ \mathrm{md}\_\mathrm{seq}0(w-\mathrm{GI}*N)& \mathrm{GI}*N\&le;w<N\end{array}\right.$

wherein w = [ 0-N-1 ], and N is the length of FFT;

c) performing subsection sliding correlation:

$\mathrm{corr}\_\mathrm{result}\left(l\right)=\underset{n=0}{\overset{\mathrm{seg}\_\mathrm{num}-1}{\mathrm{\&Sigma;}}}\left(\right|\underset{m=n*\mathrm{seg}\_\mathrm{len}}{\overset{(n+1)*\mathrm{seg}\_\mathrm{len}-1}{\mathrm{\&Sigma;}}}{r}_{p2}(m+t)*\mathrm{md}\_\mathrm{seq}\left(m\right)\left|\right),$

wherein, $\mathrm{seg}\_\mathrm{len}*\mathrm{seg}\_\mathrm{num}=\left\{\begin{array}{cc}N& N\&le;8192\\ 8192& N>8192\end{array}\right.,$ t=[0,1,2,3,4,5]

d) and summing the correlation results of the 5 points to obtain the correlation result of the current GI mode. Meanwhile, the original 5-point correlation result is reserved;

e) setting GI to other 6 patterns, respectively, repeating b), c), d), obtaining 7 correlation results;

f) comparing the maximum value of the 7 correlation results, the corresponding GI mode is the result of mode detection.

3) Symbol timing correction

In the result of the 5-point sliding correlation corresponding to the above pattern detection result, the maximum value is found, and its position is the final result of correcting the symbol timing that we need to obtain.

The flow chart of the method of the invention is shown in figure 10.

The symbol synchronization in the present invention is started on the basis of the frame synchronization. Although the frame synchronization of the DVB-T2 system can provide relatively accurate signaling S1 and S2, its positioning has a large error, especially under the environment with relatively severe channel conditions, and the positioning position of the frame synchronization usually has a relatively large deviation from the real window position with the largest FFT energy. Therefore, symbol synchronization is required for further corrective positioning.

The invention fully utilizes the characteristics of P1 symbols in a DVB-T2 system to assist in symbol synchronization. Since the snr threshold for the codec of P1 symbols is very low, the system can correctly resolve the signaling S1 and S2 as long as the frame synchronization can locate the P1 symbol position robustly. The invention uses the two parameters to reconstruct P1 symbol by using the generation method of P1 symbol of transmitter (see FIG. 3) at the receiving end. Then, the signal and the received signal after frame synchronization are performed with sliding correlation, because there is frequency offset in the received signal, the sliding correlation here needs to be performed with segmented correlation, and the position of the peak is found in the correlation result, thereby finding the starting position of the P2 symbol.

In the process of making the sliding correlation, in order to reduce the area, the regenerated P1 symbol can only take the sign bit, and the simplification does not affect the correlation of the P1 symbol.

The present invention generates a local sequence by IFFT calculation using the pilot of P2 symbol (see fig. 4), and this sequence can be stored in ROM in advance because the pilot pattern of P2 is known. To reduce hardware overhead, we also only take its sign bit. Since the P2 signal has relatively good correlation, we only need to take 8K length in 16K and 32K modes, that is, the longest sequence is 8K length in the mode detection process.

The P2 symbol and the received data are used for sliding correlation, and because frequency offset exists in the system, segmented sliding correlation is still needed. Because the timing error is + -2 in the symbol synchronization step, we need to do 5-point sliding correlation, transpose the P2 sequence separately for each GI mode and then do 5-point sliding correlation. Thus the total result obtained is a 5 x 7 array.

First, we perform weighted average on the 5-point sliding correlation result of each GI mode, and then find the maximum value among 7 values, and its corresponding GI is the GI that we need to estimate. Then, the maximum one is selected from the results of the 5-point sliding correlation of the corresponding GI, which is the timing position of the precise symbol synchronization.

By the method, the initial position of the OFDM symbol is accurately locked while accurate GI estimation is obtained.

References used in the present invention:

[1]Optimum receiver design for OFDM-based broadband transmission-part II,Michael Speth,IEEE2001；

[2]ETSI EN 302 755 V1.2.1,Digital Video Broadcasting(DVB);Frame structurechannel coding and modulation for a second generation digital terrestrial televisionbroadcasting system(DVB-T2)。

Claims (2)

1. A method for symbol timing correction in a DVB-T2 system, the method comprising:

1) generating a P1 symbol of the receiver in the current transmission mode by using two parameters S1 and S2 provided after the DVB-T2 frame synchronization is locked;

2) respectively taking sign bits from the two paths of I/Q of the P1 sign to obtain a sign synchronization related sequence ssc _ seq:

k=[0～1023]，

wherein $\mathrm{sign}\left[x\right]=\left\{\begin{array}{cc}+1,& x\&GreaterEqual;0\\ -1,& x<0\end{array}\right.,$

The representation takes the real part of P1,

the representation takes the imaginary part of P1;

3) and (3) carrying out segmented sliding correlation on the symbol synchronization correlation sequence ssc _ seq:

$\mathrm{corr}\_\mathrm{result}\left(l\right)=\underset{n=0}{\overset{\mathrm{seg}\_\mathrm{num}-1}{\mathrm{\&Sigma;}}}\left(\right|\underset{m=n*\mathrm{seg}\_\mathrm{len}}{\overset{(n+1)*\mathrm{seg}\_\mathrm{len}-1}{\mathrm{\&Sigma;}}}r(m+k)*\mathrm{ssc}\_\mathrm{seq}\left(m\right)\left|\right),$

wherein, corr _ result is a segment sliding correlation result, r (m) is a received signal after frame synchronization locking, seg _ num is the number of the segments of the sliding correlation, seg _ len is the length of each segment of the sliding correlation segments, seg _ len × seg _ num =1024, and l is more than or equal to-64 and less than or equal to 64;

4) determining the maximum value and the position of the segment sliding correlation result according to the segment sliding correlation expression in the step 3), and finding the P2 symbol r containing the GI part in the first received signal_p2(s)；

5) Determining a pilot pattern of P2 according to S1 and S2, and generating a pattern detection sequence md _ seq0(w) according thereto;

6) setting an initial value GI = 1/4;

7) moving the part of the pattern detection sequence md _ seq0(w) with the tail length GI to the head, we get:

$\mathrm{md}\_\mathrm{seq}\left(w\right)=\left\{\begin{array}{cc}\mathrm{md}\_\mathrm{seq}0(N-N*\mathrm{GI}+w)& 0\&le;w<\mathrm{GI}*N\\ \mathrm{md}\_\mathrm{seq}0(w-\mathrm{GI}*N)& \mathrm{GI}*N\&le;w<N\end{array}\right.$

wherein w = [ 0-N-1 ], and N is the length of FFT;

8) for sequences md _ seq and r_p2Making subsection sliding correlation, wherein the sliding distance is 5:

$\mathrm{corr}\_\mathrm{result}\left(l\right)=\underset{n=0}{\overset{\mathrm{seg}\_\mathrm{num}-1}{\mathrm{\&Sigma;}}}\left(\right|\underset{m=n*\mathrm{seg}\_\mathrm{len}}{\overset{(n+1)*\mathrm{seg}\_\mathrm{len}-1}{\mathrm{\&Sigma;}}}{r}_{p2}(m+t)*\mathrm{md}\_\mathrm{seq}\left(m\right)\left|\right),$

wherein, $\mathrm{seg}\_\mathrm{len}*\mathrm{seg}\_\mathrm{num}=\left\{\begin{array}{cc}N& N\&le;8192\\ 8192& N>8192\end{array}\right.,$ t=[0,1,2,3,4,5]

9) summing the 5-point sliding correlation results obtained in the step 8) to obtain a correlation result of the current GI mode;

10) GI to other 6 patterns, i.e., GI =1/8,1/16,1/32,1/128,19/128,19/256, repeat 7) — 9), respectively), 7 correlation results are obtained;

11) comparing the maximum value of the 7 correlation results, wherein the corresponding GI mode is the result of mode detection;

12) in the above step 11), the maximum value is found from the result of the 5-point sliding correlation corresponding to the pattern detection result, and the position of the maximum value is the final result of correcting the symbol timing.

2. The method for symbol timing correction in DVB-T2 system according to claim 1, wherein the step 5) of generating the pattern detection sequence md _ seq0 by using P2 symbol pilot comprises:

1) the PRBS sequence p2_ PRBS0(p) is generated by the PRBS sequence generator given on spec of DVB-T2, where p = [ 0. kmax-1]Kmax is the number of effective subcarriers in the P2 symbol in the current transmission mode; the generator polynomial of the PRBS sequence generator is: x is the number of¹¹+x²+ 1; wherein x is 0 or 1;

2) determining the interval Dx of P2 symbol pilot frequency according to the current transmission mode, namely FFT or MISO mode;

3) setting the positions of the p2_ prbs1(p) sequence which are not integral multiples of Dx to zero;

p=[0～kmax-1]

4) cyclic shift of the sequence p2_ prbs1(p) gave the sequence p2_ prbs2(w)

$p2\_\mathrm{prbs}2\left(w\right)=\left\{\begin{array}{cc}p2\_\mathrm{prbs}1(w+\frac{k\max -1}{2}),& w\&le;\frac{k\max -1}{2}\\ 0,& \frac{k\max -1}{2}<w\&le;N-\frac{k\max -1}{2}\\ p2\_\mathrm{prbs}1(w+\frac{k\max -1}{2}-N),& N-\frac{k\max -1}{2}<w\&le;N-1\end{array}\right.$

5) Performing IFFT on the sequence processed in the step 4) to obtain a time domain sequence P2_ pilot3(w) of a P2 symbol pilot, wherein w = [ 0-N-1 ];

6) taking sign bit for p2_ pilot3(w) to get pattern detection sequence:

wherein w = [0 to N-1], and N is the length of FFT.

Images