CN1976331B - Symbol timing synchronization method and device using the method - Google Patents

Abstract

A codeword timing synchronization method, firstly, calculates the correlation between a sampling sequence and a delayed sampling sequence of a delay length N thereof to generate a correlation sequence, wherein N is the useful data length of a codeword in the sampling sequence. Next, a moving average is taken on the correlation sequence to generate a cross-correlation sequence, and then a difference operation is performed on the cross-correlation sequence to generate a differenced sequence. Then, a moving average is taken on the differenced sequence to generate a moving averaged sequence, and the peak position of the moving averaged sequence is detected to obtain the correct codeword timing.

Description

Symbol timing synchronization method and device using the method

technical field

The present invention relates to a symbol timing synchronization (symbol timing synchronization), and in particular to a method and device for symbol timing synchronization of a receiver in an orthogonal frequency division multiplexing (OFDM) system .

Background technique

In an OFDM communication system, the receiver must detect the starting position of each symbol to correctly reply to the information transmitted from the transmitter. This operation is called symbol timing synchronization. For some OFDM systems, such as wireless local area network (WLAN) or digital audio broadcasting (DAB) system, the transmitter will transmit some preamble or training sequence for the receiver to use as symbols Timed synchronization. However, for some other OFDM systems, such as terrestrial video broadcasting (DVB-T) systems, the transmitter does not transmit these preamble data or training sequences. These systems typically exploit the guard interval property to detect symbol timing.

FIG. 1 is a schematic diagram of a known OFDM system using a guard interval to detect symbol timing in an additive white Gaussian noise (AWGN) channel. Referring to FIG. 1, r[n] represents the sampling sequence of the received OFDM signal after analog-to-digital conversion, and r[n-N] represents the sequence that delays the sampling sequence r[n] by N sampling points. The sampling sequence r[n] is composed of a plurality of symbols, such as symbols 110 and 120 . Each code element is made up of a guard interval whose length is Ng (or has Ng sampling points) and useful data whose length is N (or has N sampling points), wherein the guard interval is placed at the front end of the useful data, and is copied from the tail portion of the useful data.

For example, the guard interval 111 of the symbol 110 is copied from the tail portion 112 of its useful data, and the symbol 110 is delayed by N samples, namely the symbol 110'. It can be known that the data in the guard interval 111' is the same as the data in 111 (the only difference between the two is a delay), and the guard interval 111 is copied from the end part 112, so the data in the guard interval 111' and the end part 112 are the same .

There is some correlation between the sequences r[n] and r[n-N] because there is a repeated structure within each symbol (eg guard interval 111 replicated from tail part 112). For example, by taking one of the sequences r[n] and r[n-N] as a conjugated complex number and multiplying it with another sequence that does not take a conjugated complex number (hereinafter referred to as the correlation function), that is (r *[n]×r[n-N]) or (r[n]×r*[n-N]), the correlation sequence j[n] can be generated. In the correlation sequence j[n], the interval 113 indicates that the sequence r[n] and r[n-N] have a high correlation in this interval. Finally, take a moving average of the correlation sequence j[n] to generate a cross-correlation sequence c[n], and then detect the position of its peak value 114 to obtain the correct starting position of the next symbol (such as symbol 120).

In addition, in US Pat. No. 6,088,406, the correlation sequence of multiple symbols is accumulated to make the peak of the cross-correlation sequence more obvious, thereby improving the reliability of detecting the peak position. However, for time-dispersive channels, the above symbol timing detection methods are not reliable enough. Especially for time-dispersed channels with long echo delay (long echo delay), such as single frequency network (single frequency network, SFN) channels often used in broadcasting systems, the reliability is still not enough. This is due to the fact that the peaks of the cross-correlation sequences are less pronounced in the SFN channel than in the AWGN channel.

Figure 2 is a schematic diagram of applying the symbol timing synchronization method shown in Figure 1 to an SFN channel with two paths, wherein the two paths have the same gain and the path difference is Ng, so when the OFDM signal passes through the SFN channel, the receiving The machine obtains the sampling sequence r ₁ [n] from one path and obtains the sampling sequence r ₂ [n] from the other path, that is, the sampling sequence r[n] is composed of the sequences r ₁ [n] and r ₂ [n].

Taking the symbol 210 in the sampling sequence r ₁ [n] as an example, the symbol 220 in the sampling sequence r ₂ [n] that is the same as the data in the symbol 210 is delayed by Ng sampling points from the symbol 210 . When the sequences r ₁ [n] and r ₂ [n] undergo correlation function and moving average respectively, they generate sequences c ₁ [n] and c ₂ [n] respectively. Therefore, the cross-correlation sequence c[n] can be regarded as a combination of sequences c ₁ [n] and c ₂ [n]. Compared with the cross-correlation sequence c[n] in the AWGN channel shown in Figure 1, the cross-correlation sequence c[n] in the SFN channel shown in Figure 2 no longer has an obvious peak, but a peak area instead, And ideally, the values of the sampling points in this area are all the same and are the maximum values. Unfortunately, the detection of the correct symbol position 214 is more difficult when the sample point values in the peak region are not the same due to the influence of noise and interference signals.

In order to overcome the above-mentioned symbol timing synchronization method, which has the disadvantage that the symbol position is not easy to detect in a time-dispersed channel such as an SFN channel, another method is disclosed in U.S. Patent No. 6,421,401, which uses two correlators to correlate function, thus providing a distinct peak. However, this method obviously requires an additional correlator, which means that more multipliers and storage devices are required to make the structure more complex. In addition, in the paper "Enhanced symbol synchronization method for OFDM system in SFN channels" presented by A.Palin and J.Rinne at the IEEE Globecom conference in 1998, it was proposed that the symbol timing can be determined by judging the cross-correlation sequence The amplitude of the sampling point is gradually increased to evaluate whether it exceeds a preset critical value. However, different types of time-dispersed channels will result in different amplitude ranges of sampling points in the cross-correlation sequence, so it is difficult to select an appropriate critical value to meet all types of time-dispersed channels.

Contents of the invention

The purpose of the present invention is to provide a symbol timing detection method and a device using the method that can be used in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, which has low complexity and high reliability, and is applicable to all type of channel, especially for time-dispersed channels with long echo delays.

The present invention proposes a symbol timing synchronization method, which is suitable for receivers of communication systems such as Orthogonal Frequency Division Multiplexing (OFDM), and is suitable for all types of channels, especially for times with long echo delays Distributed channels. This symbol timing synchronization method first calculates the correlation between the sampling sequence and the delay sampling sequence to generate a correlation sequence, wherein the delay sampling sequence is that the sampling sequence is delayed by N sampling points, where N is the number of useful data of symbols in the sampling sequence The number of sampling points. Then, take the moving average of the correlation sequence to generate the cross-correlation sequence, and then perform difference operation on the cross-correlation sequence to generate the sequence after difference. Then, a moving average is taken on the differential post-sequence to generate a post-moving average sequence, and a peak position of the post-moving average sequence is detected, wherein the peak position is used to obtain correct symbol timing synchronization.

In an embodiment, the above symbol timing synchronization method further includes averaging or accumulating M symbols on the cross-correlation sequence before performing a differential operation on the cross-correlation sequence to generate the differential sequence, where M is a positive integer. Furthermore, the above symbol timing synchronization method also includes providing an index, which is the peak value (ie, the maximum value) of the sequence after the moving average minus the minimum value of the sequence after the moving average, wherein the index is used for comparison with a preset critical value to determine Whether there is a symbol in the sample sequence.

The present invention proposes a symbol timing synchronization device, which in one embodiment includes a correlator, a differentiator, a moving average and a peak detector. In this embodiment, the correlator is used to receive the sampling sequence, calculate the correlation between the sampling sequence and the delayed sampling sequence with the sampling sequence delayed by N sampling points to generate a correlation sequence, and take a moving average on the correlation sequence to generate Cross-correlation sequence, where N is the number of sampling points of the useful data of the symbol in the sampling sequence. The differentiator is coupled to the correlator, and is used for performing difference operation on the cross-correlation sequence to generate a differenced sequence. The moving average unit is coupled to the differentiator, and is used for taking a moving average of the sequence after difference to generate a sequence after moving average. The peak detector is coupled to the moving averager for detecting the peak position of the sequence after moving average, wherein the peak position is used to obtain correct symbol timing synchronization.

In an embodiment, the above-mentioned device for synchronizing symbol timing further includes a symbol-taking averager (or a symbol-taking accumulator). This symbol averager (or symbol accumulator) is coupled between the correlator and the differentiator, and is used to average (or accumulate) M symbols for the cross-correlation sequence to generate the symbol average (or The cross-correlation sequence after accumulation), where M is a positive integer. Furthermore, the peak detector in the above-mentioned symbol timing synchronization device also generates an index, which is the peak value of the sequence after moving average minus the minimum value of the sequence after moving average, wherein the index is used to compare with the preset critical value to determine the sampling Whether there are code elements in the sequence.

Because the present invention performs difference operation on the cross-correlation sequence and then takes the moving average, even the OFDM signal can produce obvious peak value through the time dispersion channel with long echo delay, so it has high reliability symbol timing detection.

In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of a known OFDM system using a guard interval to detect symbol timing under an AWGN channel.

FIG. 2 is a schematic diagram of applying the symbol timing synchronization method shown in FIG. 1 to an SFN channel with two paths, where the two paths have the same gain and the path difference is Ng.

FIG. 3A and FIG. 3B are flowcharts of a symbol timing synchronization method according to an embodiment of the present invention.

4A and 4B are schematic diagrams and simulation diagrams of signals related to a symbol timing synchronization method according to an embodiment of the present invention, respectively.

FIGS. 5A and 5B are block diagrams of a symbol timing synchronization device according to an embodiment of the present invention, which respectively correspond to the symbol timing synchronization method shown in FIGS. 3A and 3B .

6A and 6B are block diagrams of a correlator in a symbol timing synchronization device according to an embodiment of the present invention.

FIG. 7 is a block diagram of a moving average in a symbol timing synchronization device according to an embodiment of the present invention.

8A and 8B are block diagrams of a symbol-fetching averager and a symbol-fetching accumulator in a symbol timing synchronization device according to an embodiment of the present invention, respectively.

[Description of main component labels]

S311-S315: Flow steps of a symbol timing synchronization method according to an embodiment of the present invention

S351-S356: Flow steps of the symbol timing synchronization method shown according to another embodiment of the present invention

r[n], r ₁ [n], r ₂ [n], r[nN]: Sampling sequence

j[n]: correlation sequence

c[n], c ₁ [n], c ₂ [n]: cross-correlation sequences

c’[n]: cross-correlation sequence after symbol average

110, 110’, 120, 120’, 210, 220: code elements

111, 111': protection interval

112, 112': end part

113: Interval (which represents a high degree of correlation)

114, 214, 414, 424: peak value (i.e. maximum value)

425: minimum value

500, 505: symbol timing synchronization device

510: Get correlator

520: Get symbol averager

530: Differential

550: Take moving average

570: Peak Detector

590: Phase Getter

610, 615: delayer

630, 635: Take the conjugate complex number device

650, 655: multiplier

670, 675: Take the moving average unit

710, 740: delayer

720: Adder

730: Subtractor

810: Divider

820: Adder

830: Delay

Ng: the length of the guard interval of the symbol (or the number of sampling points)

N: The effective data length of the symbol (or the number of sampling points)

N+Ng: symbol length (or number of sampling points)

Detailed ways

For the convenience of description of the embodiment, the communication system below takes an Orthogonal Frequency Division Multiplexing (OFDM) system using a guard interval to detect symbol timing as an example. The receiver of the OFDM system generates the sampling sequence r[n] after the received OFDM signal undergoes analog-to-digital conversion. At this time, the starting position of each symbol in the sampling sequence r[n] must be detected to correctly reply This operation is called symbol timing synchronization for the information transmitted from the transmitter.

FIG. 3A is a flowchart of a symbol timing synchronization method according to an embodiment of the present invention, and FIG. 4A is a schematic diagram of signals related to the symbol timing synchronization method shown in FIG. 3A . Please refer to FIG. 3A and FIG. 4A at the same time. In step S311, first calculate the correlation between the sampling sequence r[n] and its delayed sampling sequence r[n-N] delayed by N sampling points to generate a correlation sequence j[n ], where N is the number of sampling points of the useful data of the symbol in the sampling sequence r[n]. Here, the correlation sequence j[n] is, for example, (r*[n]×r[n-N]) or (r[n]×r*[n-N]), and even the multiplication can be replaced by subtraction, or Replace the multiplication with power subtraction. Next, in step S312, a moving average is taken on the correlation sequence j[n] to generate a cross-correlation sequence c[n]. Obviously, the process of steps S311 to S312 is the same as that shown in FIG. 1 or FIG. 2 , so the relevant description of generating the cross-correlation sequence c[n] shown in FIG. 4A through steps S311 to S312 will not be further described here.

Next, in step S313, a difference operation is performed on the cross-correlation sequence c[n] to generate a difference sequence d[n], wherein the difference operation can be realized in many ways, such as d[n]=c[n]-c[n -1] or d[n]=c[n]-c[n+1] is to realize the difference by subtraction. Then, in step S314, a moving average is taken for the sequence d[n] after the difference to generate the sequence e[n] after moving average, and the peak 414 position of the sequence e[n] after the moving average is detected in step S315, wherein the peak 414 position is used to obtain correct symbol timing synchronization.

FIG. 3B is a flow chart of a symbol timing synchronization method according to another embodiment of the present invention, and FIG. 4B is a signal related signal when the symbol timing synchronization method shown in FIG. 3B is applied to an SFN channel with two paths Simulation diagram. Please refer to FIG. 3B and FIG. 4B at the same time. In fact, steps S351 , S352 , S354 , S355 and S356 in FIG. 3B are the same as steps S311 , S312 , S313 , S314 and S315 in FIG. 3A . Therefore, the difference between the method shown in FIG. 3B and that in FIG. 3A is after taking the moving average of the correlation sequence j[n] to generate the cross-correlation sequence c[n] (ie step S312 or S352), and after the cross-correlation sequence c[ n] before carrying out the difference operation to produce the sequence d[n] after the difference (i.e. step S313 or S354), the cross-correlation sequence c[n] is earlier carried out to M symbol averaging or accumulation (i.e. step S353), wherein M is positive integer.

It can be seen from Figure 4B that the cross-correlation sequence c'[n] generated after the cross-correlation sequence c[n] is averaged by symbols has a lower noise level and produces a more obvious peak area. The resulting sequence e[n] has a distinct peak 424 position instead of a plateau. Furthermore, the difference between the peak value (ie the maximum value) 424 and the minimum value 425 of the sequence e[n] can be used to provide an index. When the value of this index is greater than the preset threshold value, it means that the received signal most likely contains OFDM signal symbols, so this index can be applied, for example, to speed up channel scanning.

5A and 5B are block diagrams of a symbol timing synchronization device according to an embodiment of the present invention, which respectively correspond to the symbol timing synchronization method shown in FIGS. 3A and 3B . Referring to FIG. 5A , the symbol timing synchronization device 500 includes a correlator 510 , a differentiator 530 , a moving average 550 , a peak detector 570 and a phase acquirer 590 . The correlator 510 is used to receive the sampling sequence r[n], calculate the correlation between the sampling sequence r[n] and the delayed sampling sequence r[n-N] delayed by N sampling points to generate a correlation sequence, and perform correlation Take the moving average of the characteristic sequence to generate the cross-correlation sequence c[n], where N is the number of sampling points of the useful data of the symbol in the sampling sequence r[n]. The differentiator 530 is coupled to the correlator 510, and is used for performing a difference operation on the cross-correlation sequence c[n] to generate a differenced sequence d[n]. The moving average unit 550 is coupled to the differentiator 530, and is used for taking a moving average of the sequence d[n] after difference to generate a sequence e[n] after moving average.

The peak detector 570 is coupled to the moving averager 550, and is used to detect the peak position of the sequence e[n] after the moving average, wherein the peak position is used to provide N-point discrete Fourier transform (N-point DFT) in the OFDM system processor or Fast Fourier Transform (FFT) processor to achieve correct symbol timing synchronization. Furthermore, the peak detector 570 can also provide an indicator, such as the difference between the peak value (ie, the maximum value (peak)) and the minimum value of the sequence e[n]. When the value of this index is greater than the preset threshold value, it means that the received signal most likely contains OFDM signal symbols, so this index can be applied, for example, to speed up channel scanning. In addition, the phase obtainer 590 is coupled to the output of the correlator 510 and the peak detector 570, and is used to obtain the phase of the cross-correlation sequence c[n], wherein this phase can be used for the carrier frequency between the transmitter and the receiver Offset correction.

Please refer to Fig. 5B, symbol timing synchronizing device 505 is similar to symbol timing synchronizing device 500, and the difference between the two is that symbol timing synchronizing device 505 also includes device 520, and device 520 can be to take symbol equalizer, also can be code fetch Meta accumulator. A symbol averager (or a symbol accumulator) 520 is coupled between the correlator 510 and the differencer 530, and is used to average (or accumulate) M symbols for the cross-correlation sequence c[n] to generate Take the cross-correlation sequence c'[n] after symbol averaging (or accumulation), where M is a positive integer. At this time, the phase acquirer 590 is coupled to the output of the symbol averager (or symbol accumulator) 520 , the input of the differentiator 530 and the output of the peak detector 570 .

6A and 6B are block diagrams of a correlator in a symbol timing synchronization device according to an embodiment of the present invention. Referring to FIG. 6A , the correlator 510 includes a delayer 610 , a conjugate complex 630 , a multiplier 650 and a moving average unit 670 . The delayer 610 receives the sample sequence r[n] and delays it by N sample points to generate the sequence r[n-N]. The complex conjugate unit 630 receives the sample sequence r[n] and takes the complex conjugate thereof to generate a sequence r*[n]. The multiplier 650 is coupled to the delay 610 and the output of the conjugate complex 630 , and multiplies the received sequence r[n−N] by r*[n] to generate a correlation sequence j[n]. The moving average unit 670 is coupled to the output of the multiplier 650 and takes a moving average of the correlation sequence j[n] to generate a cross-correlation sequence c[n].

Another implementation method of the correlator 510 is shown in FIG. 6B . The correlator 510 includes a delayer 615 , a conjugate complex number taker 635 , a multiplier 655 and a moving average unit 675 . The delayer 615 receives the sample sequence r[n] and delays it by N samples to generate the sequence r[n-N]. The conjugate complex numberer 635 is coupled to the output of the delayer 615 and takes the complex conjugate of the sequence r[n-N] to generate the sequence r*[n-N]. The multiplier 655 is coupled to the output of the complex conjugater 635 and multiplies the received sequence r[n] by r*[n−N] to generate a correlation sequence j[n]. The moving average unit 675 is coupled to the output of the multiplier 655 and takes a moving average of the correlation sequence j[n] to generate a cross-correlation sequence c[n].

FIG. 7 is a block diagram of a moving average in a symbol timing synchronization device according to an embodiment of the present invention. Referring to FIG. 7 , the moving average unit 550 includes a first delay unit 710 , a second delay unit 740 , an adder 720 and a subtractor 730 . The input end of the delayer 710 receives the post-difference sequence d[n], and delays the post-difference sequence d[n] by Ng sampling points and then sends it out from the output end of the delayer 710, where Ng is the code in the sampling sequence r[n] The number of sampling points in the protection interval of the element. The adder 720 adds the signal at its first input terminal to its second input terminal signal and then sends it out from its output terminal, wherein the first input terminal of the adder 720 receives the sequence d[n] after the difference, and the second input terminal of the adder 720 The input terminal is coupled to the output terminal of the delayer 740 . The delayer 740 is used to delay the signal at its input terminal by one sampling point and then send it out from its output terminal, wherein the input terminal of the delayer 740 is coupled to the output terminal of the adder 720, and the output terminal of the delayer 740 is coupled to the adder 720's second input. The subtracter 730 subtracts the signal at its first input terminal from the signal at its second input terminal (that is, generates the sequence e[n] after moving average) and sends it out from its output terminal, wherein the first input terminal of the subtractor 730 is coupled to the addition The output terminal of the subtractor 720, and the second input terminal of the subtractor 730 is coupled to the output terminal of the delayer 710.

8A and 8B are block diagrams of a symbol-fetching averager and a symbol-fetching accumulator in a symbol timing synchronization device according to an embodiment of the present invention, respectively. Referring to FIG. 8A , the symbol averager 520 includes a divider 810 , an adder 820 and a delay 830 . The input terminal of the divider 810 receives the cross-correlation sequence c[n], and divides the cross-correlation sequence c[n] by M and sends it out from the output terminal of the divider 810, where M is the number of symbols to be averaged. The adder 820 adds its first input terminal signal to its second input terminal signal to generate the cross-correlation sequence c'[n] after symbol averaging, and sends it out from the output terminal of the adder 820, wherein the first input terminal of the adder 820 An input terminal is coupled to the output terminal of the divider 810 , and a second input terminal of the adder 820 is coupled to the output terminal of the delayer 830 . The delayer 830 is used to delay the signal at its input terminal for (N+Ng) sampling points and then send it out from its output terminal, wherein the input terminal of the delayer 830 is coupled to the output terminal of the adder 820, and the output terminal of the delayer 830 coupled to the second input end of the adder 820 .

The device 520 shown in FIG. 5B can be the symbol-taking averager 520 as shown in FIG. 8A , or the symbol-taking accumulator 520 as shown in FIG. 8B . Please refer to FIG. 8B , the symbol accumulator 520 actually removes the divider 810 in the symbol averager 520 shown in FIG. 8A , that is, the first input terminal of the adder 820 directly receives the cross-correlation sequence c[ n].

In summary, the symbol timing synchronization method of the present invention and the device using the method perform differential calculation on the cross-correlation sequence c[n] and then take the moving average, even if the OFDM signal passes through a time-dispersed channel with long echo delay Significant peaks can also be generated, thus having high reliability symbol timing detection. Of course, the method and device of the present invention are also applicable to other types of channels, such as AWGN, Rayleigh or SFN channels.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, this The scope of protection of the invention should be defined by the appended claims.

Claims (20)

1. A symbol timing synchronization method is applicable to a receiver of a communication system, and the symbol timing synchronization method comprises: Computing a correlation of both the sampled sequence and the delayed sampled sequence to generate a correlation sequence; Taking a moving average of the correlation series to produce a cross-correlation series; performing a difference operation on the cross-correlation sequence to generate a differenced sequence; taking a moving average of the differenced series to produce a moving averaged series; and Detecting the peak position of the sequence after the moving average, wherein the peak position is used to obtain correct symbol timing synchronization; Wherein, the delayed sampling sequence is delayed by N sampling points for the sampling sequence, and N is the number of sampling points of useful data of symbols in the sampling sequence. 2. The symbol timing synchronization method according to claim 1, further comprising carrying out M symbol average or accumulation calculations to the cross-correlation sequence before the differential operation is carried out to generate the differential sequence to the cross-correlation sequence, Where M is a positive integer. 3. The symbol timing synchronization method according to claim 1, further comprising providing an index, which is compared with a preset critical value to determine whether there is a symbol in the sampling sequence, wherein the index is the peak value of the sequence after the moving average and its minimum value. 4. The symbol timing synchronization method according to claim 1, wherein the communication system comprises an OFDM system. 5. The symbol timing synchronization method according to claim 1, wherein the correlation sequence is obtained by multiplying the sample sequence obtained by taking a conjugated complex number and the delayed sample sequence. 6. The symbol timing synchronization method according to claim 1, wherein the correlation sequence is the multiplication of the sample sequence and the delayed sample sequence after taking a conjugated complex number. 7. The symbol timing synchronization method according to claim 1, wherein the correlation sequence is the subtraction or power subtraction of the sampling sequence and the delayed sampling sequence. 8. The symbol timing synchronization method according to claim 1, wherein the post-difference sequence is the cross-correlation sequence minus the cross-correlation sequence delayed by one sampling point. 9. A symbol timing synchronization device, suitable for a receiver of a communication system, the symbol timing synchronization device comprising: A correlator for receiving a sampling sequence, calculating the sampling sequence and delaying the correlation of the sampling sequence to generate a correlation sequence, and taking a moving average of the correlation sequence to generate a cross-correlation sequence; A differentiator, coupled to the correlator, the differentiator is used to perform a differential operation on the cross-correlation sequence to generate a differenced sequence; A moving average is coupled to the differentiator, and the moving average is used to obtain a moving average of the sequence after the difference to generate a sequence after the moving average; and a peak detector, coupled to the moving averager, the peak detector is used to detect the peak position of the sequence after the moving average, wherein the peak position is used to obtain correct symbol timing synchronization; Wherein, the delayed sampling sequence is delayed by N sampling points for the sampling sequence, and N is the number of sampling points of useful data of symbols in the sampling sequence. 10. The symbol timing synchronization device according to claim 9, further comprising a phase acquirer coupled to the output of the correlator and the peak detector, the phase acquirer is used to acquire the phase of the cross-correlation sequence. 11. The symbol timing synchronization device according to claim 9, further comprising a symbol averager, coupled between the correlator and the differentiator, the symbol averager is used to perform the cross-correlation sequence M symbols are averaged to generate the cross-correlation sequence after symbol averaging, where M is a positive integer. 12. The symbol timing synchronization device according to claim 9, further comprising a symbol accumulator, coupled between the correlator and the differentiator, the symbol accumulator is used to perform the cross-correlation sequence M symbols are accumulated to generate the cross-correlation sequence after symbol accumulation, where M is a positive integer. 13. The symbol timing synchronization device according to claim 11 or 12, further comprising a phase acquirer, coupled between the input of the differentiator and the output of the peak detector, the phase acquirer is used to acquire the symbol The phase of this cross-correlation sequence after averaging or summing. 14. The symbol timing synchronization device according to claim 9, wherein the peak detector also provides an index, which is compared with a preset critical value to determine whether there is a symbol in the sampling sequence, wherein the index is the moving average The difference between the peak value of the subsequent series and its minimum value. 15. The symbol timing synchronization device according to claim 9, wherein the communication system comprises an OFDM system. 16. The symbol timing synchronization device according to claim 9, wherein the correlator comprises: a delayer, configured to receive the sampling sequence and generate a delayed sampling sequence that delays the sampling sequence by N sampling points; A conjugate complex number device is used to receive the sampling sequence and generate a conjugate complex sampling sequence that takes a conjugate complex number of the sampling sequence; a multiplier, coupled to the delayer and the complex conjugater, the multiplier is used to multiply the sequence of delayed samples and the sequence of conjugated complex samples to generate the correlation sequence; and A moving average unit is coupled to the multiplier, and the moving average unit is used to take a moving average of the correlation sequence to generate the cross-correlation sequence. 17. The symbol timing synchronization device according to claim 9, wherein the correlator comprises: a delayer, configured to receive the sampling sequence and generate a delayed sampling sequence that delays the sampling sequence by N sampling points; A conjugate complex numberer is coupled to the delayer, and the conjugated complex numberer is used to take a conjugate complex number of the delayed sample sequence to generate a conjugate complex delayed sample sequence; a multiplier, coupled to the sequence of samples and the complex conjugater, for multiplying the sequence of conjugate complex delayed samples and the sequence of samples to generate the correlation sequence; and A moving average unit is coupled to the multiplier, and the moving average unit is used to take a moving average of the correlation sequence to generate the cross-correlation sequence. 18. The symbol timing synchronization device according to claim 9, wherein the moving average device comprises: The first delayer has an input end to receive the differential post-sequence and an output end, and the first delayer is used to delay the differential post-sequence by Ng sampling points and send it out from the output end of the first delayer, wherein Ng is the sampling point The number of sampling points in the guard interval of the symbol in the sequence; The adder has a first input terminal receiving the differential sequence, a second input terminal and an output terminal, the adder adds the first input terminal signal of the adder to the second input terminal signal of the adder, and the The output of the adder is sent out; The second delayer has an input end coupled to the output end of the adder and an output end coupled to the second input end of the adder, and the second delayer is used to delay a signal at the input end of the second delayer by one The sampling point is sent out from the output end of the second delayer; and A subtracter, having a first input terminal coupled to the output terminal of the adder, a second input terminal coupled to the output terminal of the first delayer and an output terminal, the subtractor will signal the first input terminal of the subtractor Subtracting the signal from the second input terminal of the subtractor to generate the post-moving average sequence, and sending the post-moving average sequence from the output terminal of the subtractor. 19. The symbol timing synchronization device according to claim 11, wherein the symbol averager comprises: A divider has an input end and an output end for receiving the cross-correlation sequence, and the divider is used to divide the cross-correlation sequence by M and send it out from the output end of the divider; An adder has a first input terminal coupled to the output terminal of the divider, a second input terminal and an output terminal, and the adder combines the signal of the first input terminal of the adder with the signal of the second input terminal of the adder generating the cross-correlation sequence after taking the symbol average, and sending the cross-correlation sequence after taking the symbol average from the output end of the adder; and a delayer having an input end coupled to the output end of the adder and an output end coupled to the second input end of the adder, the delayer being used to delay the input signal of the delayer by (N+Ng) samples After the point, it is sent out from the output end of the delayer, where (N+Ng) is a symbol length. 20. The symbol timing synchronization device according to claim 12, wherein the symbol accumulator fetching comprises: An adder having a first input terminal receiving a cross-correlation sequence, a second input terminal and an output terminal, the adder adding the signal at the first input terminal of the adder to the signal at the second input terminal of the adder to generate a symbol The cross-correlation sequence after accumulation, and the cross-correlation sequence after symbol accumulation is sent from the output terminal of the adder; and a delayer having an input end coupled to the output end of the adder and an output end coupled to the second input end of the adder, the delayer being used to delay the input signal of the delayer by (N+Ng) samples After the point, it is sent out from the output end of the delayer, where (N+Ng) is a symbol length.

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