CN101588333A - Synchronization method suitable for terrestrial broadcasting national standard of Chinese digital televisions - Google Patents

Abstract

The invention provides a synchronization method suitable for the terrestrial broadcasting national standard of Chinese digital televisions. The synchronization method directly synchronizes signals according to the favorable self-correlation characteristic and the cyclic prefix resembling structural characteristic of a signal frame head PN sequence in the standard, does not need to locally generate a PN sequence on a receiving television and estimates frequency offset by utilizing the characteristic that PN sequence sections with fixed interval lengths have fixed phase offset so as to rightly correct integral frequency offset and decimal frequency offset by one step and realize frequency synchronization. The synchronization method suitable for the terrestrial broadcasting national standard of the Chinese digital televisions enables synchronization modules at the receiving terminals of digital television systems to accurately position signal start positions, have low complexity and simple operation and keep favorable reliability under the conditions of poor channels and low signal to noise ratios.

Description

A kind of method for synchronous that is applicable to the China Digital TV terrestrial broadcasting national standard

Technical field

The present invention relates to a kind of method for synchronous of Digital Television Terrestrial Broadcasting, particularly a kind of method for synchronous that is applicable to the China Digital TV terrestrial broadcasting national standard.

Background technology

China Digital TV terrestrial broadcasting national standard (hereinafter to be referred as the DTTB national standard) was formally issued in August, 2006.This standard has independent intellectual property right, has profound significance for the development that promotes China's Digital Television industry.In this standard, China Digital TV terrestrial broadcast system frame structure, chnnel coding and modulation system have been stipulated.These mandatory provisions are just at transmitting terminal, and the design of receiving terminal is wide-open.

At receiving terminal, at first the work that will finish is exactly synchronously, promptly finds the frame start position of signal frame, carries out channel estimating to extract frame head, and the frame data are sent into subsequently processing module.Being very important link in digital communication system synchronously, is the basis of all processing of receiving terminal, the synchronous whether accurate channel estimating subsequently that directly determined, and can equilibrium and channel-decoding normally carry out.

In the DTTB national standard, two kinds of relatively independently signal transfer modes have been stipulated, i.e. multicarrier (adopting the OFDM technology) pattern and single carrier mode.Wherein multi-carrier mode has mainly adopted the OFDM technology, and can the orthogonal property of OFDM be guaranteed and determine the quality of whole system performance to a great extent, and the quality of receiving-transmitting sides sign synchronization has very big influence to the orthogonality of system.

Before the present invention, a lot of based on the simultaneous techniques that adopts ofdm system, as maximal possibility estimation, Robust detection and pmoose method or the like, but these methods are to utilize insertion pilot tone and Cyclic Prefix to carry out synchronous detecting mostly, are similar to the frame structure of DVB.Because the DTTB national standard adopted brand-new frame structure, in frame head, Cyclic Prefix (CP) and pilot signal in the DVB standard have been replaced, so above-mentioned method for synchronous is not suitable for the DTTB national standard with the PN sequence.

Summary of the invention

Purpose of the present invention just is to address the deficiencies of the prior art, and design, research are applicable to the method for synchronous of China Digital TV terrestrial broadcasting national standard.

Technical scheme of the present invention is:

A kind of method for synchronous that is applicable to the China Digital TV terrestrial broadcasting national standard is characterized in that may further comprise the steps:

(1) sign synchronization:

PN head in the frame structure of initialization system transmission adopts is frame head mode 1 in the China Digital TV terrestrial broadcasting GB; In the PN sequence that 165 of receiving terminal buffer memorys receive, it is relevant to utilize it and 165 PN sequences of 255 beginnings of being separated by to do, as (formula 1):

$P\left(d\right)=\underset{n=0}{\overset{165}{\mathrm{\Σ}}}{x}^{*}(d+n)x(d+n+255)$ (formula 1)

Wherein d is the time, and x (n) is the symbolic information of corresponding time;

Calculate the average power R (d) of PN head then, P (d) is obtained M (d) divided by R (d), be i.e. M (d)=P (d)/R (d); Find the maximum moment corresponding of M (d) to be symbol head T_syn, shown in (formula 2):

T_syn=arg (Max[M (d)]) (formula 2)

(2) Frequency Synchronization:

After definite symbol head, on 255 the information bit of being separated by, there is the phase deviation of one 2 π * Δ w*255/N; For the sequence PN_front (n) of 165 of prefixes and 165 point sequence PN_end (n) of afterbody, following relation is arranged:

$\mathrm{PN}\_\mathrm{front}\left(n\right)*\exp (j*\frac{2\mathrm{\π}}{N}*\mathrm{\Δw}*255)=\mathrm{PN}\_\mathrm{end}\left(n\right)$ N=1,2 ..., 165 (formulas 3)

On this basis, obtain sign synchronization corresponding correlation peak P_syn constantly, as (formula 4):

$P\_\mathrm{syn}=\underset{n=1}{\overset{165}{\mathrm{\Σ}}}\mathrm{PN}\_f{\mathrm{ront}}^{*}\left(n\right)*\mathrm{PN}\_\mathrm{end}\left(n\right)=165*{\left|x\right|}^2*\exp (j*\frac{2\mathrm{\π}}{N}*\mathrm{\Δw}*255)$ (formula 4)

Then P_syn is asked phase angle Angle (P_syn), can estimate frequency deviation Δ w, as (formula 5):

$\mathrm{\&Delta;w}=\frac{\mathrm{Angle}(P\_\mathrm{syn})\&times;\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="A2008100249690007H2.png,A2008100249690007H3.png"\; state="\{\{state\}\}">N</figure-callout>}}{2\mathrm{\&pi;}\&times;255}$ (formula 5)

Because correlation window length is 255 in this method, and signal frame frame length is 3780, is-7.4～7.4 so this method can be estimated frequency deviation region.

Advantage of the present invention and effect are:

1. in the symbol synchronization process, do not need to produce local PN sequence at receiving terminal, but utilize a similar circulating prefix structure of the PN sequence inside that receives to estimate, reduced the complexity of system, and, can locate the original position of the OFDM piece that receives exactly by detecting the position of PN sequence relevant peaks.

2. only utilize the be separated by phase relation of 255 points of PN sequence in the frame, accurately estimate frequency shift (FS).Frequency offset estimation range can reach about ± 7.4, thereby corrected integer frequency bias and decimal frequency bias with settling at one go, and directly utilized the result in the symbol synchronization process, expense is little, computing is simple, can keep good reliability under abominable channel and low signal-to-noise ratio condition.

Other advantages of the present invention and effect will continue to describe below.

Description of drawings

Fig. 1---signal frame structure figure.

Fig. 2---frame head PN420 sequential structure figure.

Fig. 3---slip associated window schematic diagram.

Fig. 4---sign synchronization design sketch.

Fig. 5---the planisphere when having frequency deviation.

Fig. 6---the planisphere after the correction frequency deviation.

Fig. 7---symbol is the mean square error design sketch regularly.

Fig. 8---frequency offset estimating mean square error design sketch.

Embodiment

Below in conjunction with drawings and Examples, technical solutions according to the invention are further elaborated.

In the DTTB national standard, Frame is a kind of four layers multi-frame structure, is divided into a day frame, divides frame, superframe and signal frame.Wherein, a basic frame is called signal frame, and signal frame is made up of frame head and frame two parts, as shown in Figure 1.Signal frame is the elementary cell of system frame structure, the baseband signalling rate identical (7.56Msps) of frame head and frame signal.The frame head part is made of the PN sequence, and frame head length has three kinds of patterns.Frame partly comprises the system information of 36 symbols and the data of 3744 symbols, the OFDM piece of totally 3780 symbols.

According to frame head mode 1, this PN sequence definition is 8 rank m sequences of cyclic extensions.Can realize that reaching " 1 " through " 0 " to+1 value is the binary character of non-return-to-zero to the mapping transformation of-1 value by Fibonacci molded lines feedback shift register.Its frame head length is 420 symbols (PN420), as shown in Figure 2.By observing the PN420 sequence, we can find that it is by 8 rank PN sequences transformations of 255 symbols in fact, copies to afterbody by 83 symbols of head with this sequence then, again 82 symbols of afterbody are copied to head, thereby constituted the PN420 sequence head of 420 symbols.This shows, 165 symbols of this PN420 sequence header and 165 symbols of afterbody have identical information, promptly has the structure of a similar Cyclic Prefix (CP) in this PN sequence inside, the symbol sebolic addressing of head and afterbody is defined as PN_front (n) and PN_end (n) respectively, n ∈ [1,165].Because these two sections sequences are in full accord in transmitting terminal information, so even have frequency deviation at receiving terminal, also just bring a phase deviation, do not influence the detection and the judgement of sign synchronization.

(1) sign synchronization

Utilize in the above-described PN420 sequence the similarly structure of Cyclic Prefix (CP), in 165 receiving sequences of receiving terminal buffer memory, and it is relevant to utilize it and 165 PN sequences of 255 sign-ons of being separated by to do, as (formula 1):

$P\left(d\right)=\underset{n=0}{\overset{165}{\mathrm{\&Sigma;}}}{x}^{*}(d+n)x(d+n+255)$ (formula 1)

Wherein d is the time, and x (n) is the symbolic information of corresponding time.(formula 1) be equivalent to two be separated by 255, length is 165 slip associated window, as shown in Figure 3.Because the PN sequence has sharp-pointed autocorrelation performance, on the synchronous points of corresponding symbol head sharp-pointed peak value can appear.So under certain timing measurement criterion, when the correlation in (formula 1) reaches maximum, can judge the original position of this maximum time corresponding point,, can finish sign synchronization by obtaining this time point for the received signal frame.

The timing tolerance that here adopts is M (d)=P (d)/R (d), and wherein R (d) is the average power of PN255 sequence.Because the PN255 sequence is a receiving-transmitting sides all known information in advance, so can calculate R (d) earlier, can obtain M (d).At last, find the maximum moment corresponding of M (d) to be symbol head T_syn, shown in (formula 2):

T_syn=arg (Max[M (d)]) (formula 2)

(2) Frequency Synchronization

On the basis of sign synchronization, realize Frequency Synchronization, owing to there is frequency deviation Δ w, cause the orthogonal property of OFDM piece destroyed, according to the principle of vector addition, and then can cause the disperse and the rotation of planisphere.

According to the repeating data maximal possibility estimation principle of PN sequence, after definite symbol head, on 255 the information bit of being separated by, there is the phase deviation of one 2 π * Δ w*255/N.So, for by 165 symbol PN_front of head (n) of the PN420 sequence decided after the symbol synchronization process and 165 symbol PN_end (n) of afterbody, following relation is arranged:

$\mathrm{PN}\_\mathrm{front}\left(n\right)*\exp (j*\frac{2\mathrm{\&pi;}}{N}*\mathrm{\&Delta;w}*255)=\mathrm{PN}\_\mathrm{end}\left(n\right)$ N=1,2 ..., 165 (formulas 3)

On this basis, to the correlation peak P_syn of synchronization point T_syn correspondence, shown in (formula 4):

$P\_\mathrm{syn}=\underset{n=1}{\overset{165}{\mathrm{\&Sigma;}}}\mathrm{PN}\_f{\mathrm{ront}}^{*}\left(n\right)*\mathrm{PN}\_\mathrm{end}\left(n\right)=165*{\left|x\right|}^2*\exp (j*\frac{2\mathrm{\&pi;}}{N}*\mathrm{\&Delta;w}*255)$ (formula 4)

Then P_syn is asked phase angle Angle (P_syn), promptly can estimate frequency deviation Δ w, shown in (formula 5):

$\mathrm{\&Delta;w}=\frac{\mathrm{Angle}(P\_\mathrm{syn})\&times;\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="A2008100249690007H2.png,A2008100249690007H3.png"\; state="\{\{state\}\}">N</figure-callout>}}{2\mathrm{\&pi;}\&times;255}$ (formula 5)

Thereby be used for compensating the frequency shift (FS) of transmission course frame, recover the orthogonality between each subcarrier of OFDM piece.

Because associated window 255 symbols of only being separated by in the above process, and the length of frame OFDM piece is 3780 symbols, thereby its frequency offset estimation range can reach approximately ± 7.4, thus the correction that settles at one go integer frequency bias and decimal frequency bias.

In order to estimate the performance of this method for synchronous, 4 frame signals that receive are carried out sign synchronization, the as a result figure of Fig. 4 for being correlated with after suing for peace, can find, there are 4 tangible peak points, in the initial moment of 4 frame signals of these peak point correspondences, promptly symbol synchronization point has been verified by symbol synchronization process and can have been realized timing synchronization exactly.

Fig. 5 is for proofreading and correct the planisphere of the received signal before the frequency deviation, because the frequency deviation Δ w that abominable channel circumstance brings causes the orthogonal property of OFDM piece destroyed, according to the principle of vector addition, and then can cause the disperse and the rotation of planisphere, as shown in Figure 5.Fig. 6 can find for proofreading and correct the planisphere of the received signal after the frequency deviation, estimates frequency deviation Δ w and each sub-carrier frequencies of frame OFDM piece is compensated by this process, makes planisphere return to the state of signal when sending.

Fig. 7 and Fig. 8 be symbol timing mean square error and all square design sketch of frequency offset estimating respectively.Two curves on every figure represent under the additive white Gaussian noise channel (AWGN) respectively and multipath channel (being the U1 multipath channel herein) under mean square error.Even can find under the condition of low signal-to-noise ratio,, also can obtain lower symbol timing and frequency offset estimating deviation, thereby realize sign synchronization and Frequency Synchronization effectively by this method for synchronous.

Claims (1)

1. method for synchronous that is applicable to the China Digital TV terrestrial broadcasting national standard is characterized in that may further comprise the steps:

(1) sign synchronization:

PN head in the frame structure of initialization system transmission adopts is frame head mode 1 in the China Digital TV terrestrial broadcasting GB; In the PN sequence that 165 of receiving terminal buffer memorys receive, it is relevant to utilize it and 165 PN sequences of 255 beginnings of being separated by to do, as (formula 1):

$P\left(d\right)=\underset{n=0}{\overset{165}{\mathrm{\&Sigma;}}}{x}^{*}(d+n)x(d+n+255)$ (formula 1)

Wherein d is the time, and x (n) is the symbolic information of corresponding time;

Calculate the average power R (d) of PN head then, P (d) is obtained M (d) divided by R (d), be i.e. M (d)=P (d)/R (d); Find the maximum moment corresponding of M (d) to be symbol head T_syn, shown in (formula 2):

T_syn=arg (Max[M (d)]) (formula 2)

(2) Frequency Synchronization:

After definite symbol head, on 255 the information bit of being separated by, there is the phase deviation of one 2 π * Δ w*255/N; For the sequence PN_front (n) of 165 of prefixes and 165 point sequence PN_end (n) of afterbody, following relation is arranged: $\mathrm{PN}\_\mathrm{front}\left(n\right)*\exp (j*\frac{2\mathrm{\&pi;}}{N}*\mathrm{\&Delta;w}*255)=\mathrm{PN}\_\mathrm{end}\left(n\right)$ N=1,2 ..., 165 (formulas 3)

On this basis, obtain sign synchronization corresponding correlation peak P_syn constantly, as (formula 4):

$P\_\mathrm{syn}=\underset{n=1}{\overset{165}{\mathrm{\&Sigma;}}}\mathrm{PN}\_\mathrm{fron}{t}^{*}\left(n\right)*\mathrm{PN}\_\mathrm{end}\left(n\right)=165*{\left|x\right|}^2*\exp (j*\frac{2\mathrm{\&pi;}}{N}*\mathrm{\&Delta;w}*255)$ (formula 4)

Then P_syn is asked phase angle Angle (P_syn), can estimate frequency deviation Δ w, as (formula 5):

$\mathrm{\&Delta;w}=\frac{\mathrm{Angle}(P\_\mathrm{syn})\&times;N}{2\mathrm{\&pi;}\&times;255}$ (formula 5)

Because correlation window length is 255 in this method, and signal frame frame length is 3780, is-7.4～7.4 so this method can be estimated frequency deviation region.

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