TWI377808B - Method for fine symbol timing synchronization in ofdm system - Google Patents

Description

1377808 IX. Invention: [Technical field of invention] - Orthogonal frequency division complex (four), system + fine symbol sequence synchronization method is: in the upper line of multipath channel, after fast catching Fourier transform: Fu Hubu' uses the discrete pilots inserted to perform channel estimation. [Prior Art] Orthogonal Frequency Division Multiplexing (0RDM) applies multi-carrier modulation (Multi-Carrier Modulation) in the field of digital communication, mainly to divide the channel into several orthogonal sub-channels. The signal (4) is parallelized into low-speed sub-data streams and modulated to transmit on each sub-channel. The orthogonal signals can be separated by using relevant techniques at the receiving end, which can reduce mutual interference between sub-channels (ICI). 'The signal bandwidth on each subchannel is less than the associated bandwidth of the channel, so intersymbol interference can be reduced or eliminated. The advantage of OFDM system is that it can effectively resist multi-path time-delay spread and high spectrum utilization, but it also has the disadvantage of being sensitive to synchronization error. The synchronization error mainly includes carrier frequency deviation and sampling time. Sampling clock deviation and symbol synchronization deviation, where symbol synchronization deviation may cause inter-symbol interference (ISI) and inter-subcarrier interference (ICI), which has a serious impact on the demodulation system. And this orthogonal frequency division multiplexing technology is widely used in digital broadcasting systems. Taking the DVB-T system as an example, please refer to the modulation and demodulation flowchart of the dvB-T system shown in the first figure. In the transmission history, after the symbol input in the frequency domain (symbol) is input (10), the pilot and transmission parameter information (Transmission Parameter Signaling, TPS) (11) are inserted, and the protection is added. After the sideband (zero-band complementary to the band) (12), it is modulated onto the mutually orthogonal subcarriers by inverse fast Fourier transform (IFFT) (13), and a cyclic prefix is added before the output signal ( 14), through a digital analog conversion circuit for a conversion (15), transported to the transmitting front end (16), to obtain the transmission data in the time domain (time domain), and send data on the channel (17). Next, the corresponding receiver portion (18) first converts the data passing through the channel (17) by analog-to-digital conversion (19), followed by down-conversion and anti-aliasing filtering (20). Then, the synchronized sampling signal is received by the interpolator (21), and the frequency offset phase correction (22) is synchronized with the coarse symbol (23), and then the cyclic prefix (24) is removed to perform a fast Fourier transform (FFT) solution. After adjusting (25), the transmission parameter message (26) is demodulated, and finally the modulated data is obtained by channel estimation and equalization (27). It can be used to perform the synchronization procedure of the OFDM system before or after the FFT (25), as shown in the synchronization means, including carrier synchronization (29), sampling (Sampling clock) synchronization (30) and fine symbols. (Symbol Timing) Synchronous (28) means. Among them, the Fine Symbol Timing synchronization (28) is used to select the correct FFT window position when the cyclic prefix is removed. In order to effectively solve the complex multipath effect, the OFDM system uses the addition of the cyclic prefix, that is, the data after the symbol is copied to the front end to be used as a guard interval (Guard Interval), so as to avoid the signal factor. Interference caused by multi-path arrival. In the FFT coffee d, the first and third graphs show the position of the self-port under the multipath channel, and the non-synchronous situation occurs in the position of the ρ & Second, in order to remove the loop vocabulary when selecting the correct FFT window so many pinch channels, the correct window position refers to the first two. In the case of the multipath channel, the first path 201 1 - 02 ' is displayed in this example, and the conventional technique uses the window position 21 of the first path 201 as the window position of the =, and does not consider the second path 2附2 attached window: Moreover, the slashed part of the figure includes the cyclic prefix 203, 204 added before the output signal. Symbol synchronization is generally divided into two phases: 1) Fine symbol synchronization, executed after FFT, detecting the remaining symbols with the same y deviation, and locking the starting position of the FFT window to the first path. 2) The coarse symbol synchronization is performed before the FFT, and the correlation of the prefix of the Leilai ring determines the starting position of the paying number. When the signal noise is low, the precision of the coarse symbol synchronization is also low. As shown in the third figure, the first path 3〇1 and the second path 302, in the case of multipath fading, the coarse symbol synchronization will set the window position to the maximum diameter, in this case the second path 3〇2 The window position 31 is the FFT window position, not the position of the first path 3〇1, which is disadvantageous for subsequent channel estimation and equalization, and the reception performance is degraded. As shown in the fourth figure, the conventional technique finds the correct FFT window through the channel impact at the receiving end. As can be seen from the figure, the signal is input into a FDM system (401) to perform a fast Fourier transform (405) on the cyclic prefix (403) added to the transmitting end before removing each signal. In this example, the scatter pilots (407) are extracted from the signal, and the channel frequency domain is determined, and i=fu=conversion (409)' is obtained to obtain the channel impact or the second response. The first one exceeds the threshold value (4U). And as the starting position of the paying position to adjust the FFT window in the channel: = _ port for symbol synchronization, to overcome the above interference = Wei 1 _ step error caused by interference, 4 1 interference (ISI) and inter-subcarrier interference (ICI) The problem. SUMMARY OF THE INVENTION The interference is eliminated between the symbols, mainly in the pass: in the case of = month, this stably detects the correct symbol synchronization position. In the qFDm (10) symbol synchronization method of the present invention, the Mengdan speed Fourier transform module first reads the discrete pilots in the channel through the channel, and obtains the inner symbol 'by the linear interpolation by the linear interpolation to obtain a larger The allowable range of delay, Zeng Wei frequency domain response. ^ Through the zero-padding, the inverse impulse Fourier transform is used to obtain the channel impulse response, which gives the number of exit paths, the position and energy of each path, and the path 卩i The delay is then followed by the noise power estimation module according to the position and number of the check, the diameter is taken as the first path, and the FFT window position is adjusted accordingly, and the noise power corresponding to the window position is calculated successively, and finally the noise power is used. The smallest, set to the correct first path, the corresponding window position is the best FFT window, that is, the exact symbol start position.

Preferably, the method includes: at the beginning, the signal enters the OFDM 1377808 system, and the coarse symbol synchronization at the receiving end removes the cyclic prefix from the data of the channel, and then performs fast Fourier transform, and extracts the discrete guide in each symbol. After the frequency, the following linear interpolation is performed to obtain a discrete pilot with a small interval within the symbol, which is used to calculate the frequency domain response of the channel. After zero-padding, the inverse fast Fourier transform is performed to obtain the channel impulse response. Then, first set a threshold value, find and record the position and quantity of the multipath in the channel impulse response according to the threshold value, and then try to place each path as the first path according to the position and number of multipaths. The starting position of the window is respectively adjusted by the corresponding FFT window, and then the channel impulse response is obtained by extracting the discrete pilot, calculating the frequency domain response of the channel, calculating the channel impulse response, and then calculating the channel corresponding to the FFT window at each different position. The noise power of the impulse response. Finally, the corresponding path is the correct first path position, that is, the optimal symbol start position, when the noise power of the channel impulse response is minimum. [Complete Mode] The present invention provides a fine symbol timing synchronization method in an OFDM system. The main feature is that in the OFDM system, fine symbol synchronization is performed after fast Fourier transform (FFT) to find an optimal FFT window position and eliminate intersymbols. Interference (ISI) to achieve the best receiver performance, please refer to the DVB-T system's discrete pilot insertion structure shown in Figure 5. As shown in the figure, the insertion position of each pilot signal (pi 1 〇t ' with the center of the circle 'the circle' is not shown) has a certain regularity, in the frequency direction (horizontal arrangement), except for the beginning (Κπύη) and the end (K _ 〇 two subcarriers, within one symbol, every 12 subcarriers (carrying communication data, indicated by open circles) 10 1377808 will insert a discrete pilot 'in the time direction (column alignment), every 4 The symbols are cyclic (as the pilot positions of labels 1, 2, 3, 4 and 5, 6, 7, 8) 'repetitively repeat the position of each pilot. From the first symbol to the fourth symbol The starting position of the inserted discrete pilot will be 3 subcarriers in sequence, as shown in the figure _ pilots 501, 502, 503, 504 are separated by 3 subcarriers. Thus, every 4 symbols 'the discrete pilot position will Repeat once. Since the information of the scattered pilot is known to the receiving end and the insertion positions have equal intervals', the channel frequency domain response can be obtained from equation (1): Λ Η ,,

PP Lk - one (1) where = [drawing + 3 >< (/111 〇 £ 14) + 12 ^ ^ = 0, 1, 2 ... meaning -1, and, ± α · indicates the first The estimated frequency domain response on the kth subcarrier of the symbol, & represents the scattered pilot data on the kth subcarrier of the first symbol received after the fast Fourier transform, indicating the point ten, the known discrete Pilot data, * indicates conjugate (con juggeK indicates the number of discrete pilots within each symbol. p

Then the channel frequency domain response is followed by zero padding to form N/2 point data, and N r money reads the number of sub-bribes after the first fiscal position. 'System order, in 2K mode, N equals _, In the 8K mode, the nickname i1, 92' Μ is attached to the window length, that is, after the cycle prefix is removed, the zero padding is used to make the calculation point a power of 2, so that::^ The lobe transformation is used to calculate. After that, the channel impulse response is obtained by inverse fast Fourier transform: 11 1377808 hi, n =IFFT[^Lk) 5 n=;l, 2,..., N/2-1 ——-- -------------------------------(2) The channel impulse response shown by equation (2) reflects the number of time domain channels. Path information, including the number of paths, the position and energy of each path, and the channel delay. A schematic diagram of the channel impulse response of the multipath channel as shown in the sixth figure, which shows the number of the diameters entering the 0FDM system and the delay between the paths.

State, except for the path, is noise, such as a part close to zero energy. In the above discrete pilot insertion structure, the position interval of the discrete pilots in each symbol is 12 subcarriers. The channel frequency domain response calculated by them is equivalent to sampling the real channel frequency domain response by 1/12, reflecting ^ The 眭蜮 shock response is 1/12 of the true shock response. If the maximum channel delay exceeds Tu/12 (Tu is a symbol period), aliasing occurs. in

In the SPN (slngiefrequenCynetw〇rk) network, such a maximum delay is not enough. 奴 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 】 There are usually three methods: 1) Direct method: directly extract the four consecutive ## discrete pilots into a discrete pilot with a payout interval of 3. 2) 2 interpolation method: using a plurality of (such as 7) symbols ή C line linear interpolation before and after - a small interval (such as 3: graph monthly frequency, the specific process of linear interpolation is as follows, please see) The direction indicates the symbol 1, and the horizontal direction indicates that each fee is 12 2 M+3 corpse-~-(3), ~~(4) ^4,4+3^ =Γ^2,4+3ρ +i~Y6 Υ ^=4Υ^Ρ+^Υ1η3ρ For example, the equation (3) shows the position through the mark -2, k=4) and the number 7〇4 respectively (Bu 6, ^ position:: mark position (W, k= 4 = According to the center, the coefficient is 1/2; the equation point is calculated. The interpolation position of the label verification (1=4, k=7) is not the middle of the two points, and the county ancient film A and ' The number of waves 7〇2 is 3/4 and 1/4. By the number 7〇1 * 7{^2=plug, = the same system to reduce the interval between discrete pilots, and: the upper calculation is based on other relatives The calculation of the position will be applied. 3) Another method is to use the multiple of the (usually >7) symbols before and after. After FIR filtering, a discrete guide with a symbol interval of 3 can be used. Make the maximum delay

Tu/3,, the force is also incremented, and the preferred embodiment of the invention should = the interval between the less discrete pilots. The interpolation is reduced by the operation shown in the seventh figure above to obtain the discrete 1377808 pilot with interval 3. The channel impulse response is calculated by formulas (1) and (2), and the effective path is determined by setting the threshold value. The location and number of ). 2 mean _cir=—hln ( 5) ^ n=\ path _ threshold = kx mean _ cir (6) where i is the channel impulse response and the length is N/2. The mean of the magnitude of the channel impulse response. 6 is the scaling factor, which can be set according to the actual application settings and according to the statistical characteristics of the channel impulse response. For example, in the DVB-T system, it can be set to 5. Through the formulas (5) and (6), the threshold value can be proportional to the mean value of the channel impulse response, and the effective value is exceeded when the threshold value is exceeded. Otherwise, it is noise. After the fine symbol synchronization is completed, the delay corresponding to the path with the largest delay in the channel impulse response is the channel delay spread, so the calculation method provided by the present invention can obtain the correct window position. Can also get the maximum delay information and noise power. 'As described in the prior art, under the multipath channel, the coarse symbol synchronization will lock the symbol start position at the maximum path position. When the first path energy is smaller than the second path, the window position will be set near the second path. . At this time, if the path of the first threshold is used as the first path based on the obtained channel impulse response result, a misjudgment will occur. As shown in the eighth figure, when the first radial energy is smaller than the second diameter, the channel impulse response after the fine symbol synchronization is displayed as shown in the figure. As shown in the sixth and eighth diagrams, the points other than the path in the channel impulse response are all noise, such as the low-energy part near zero, and the power of the noise can be expressed as equation (7): W = WISI + WAWGN + W1CI --------------------(7) 14 13*77808 where ash/57 is the noise introduced by intersymbol interference' as the channel's Nans noise, %σ is the noise introduced by inter-subcarrier interference. In the time-invariant channel, the gray-scale is similar and remains basically unchanged. If the FFT window position is wrong, if the first path is outside the window, both gray m and gray/C/ will increase, resulting in total The noise power becomes larger. The present invention proposes a criterion for determining the noise power of the correct position based on the correct position, and obtains the optimum window position by comparing the noise power of each possible FFT window position. Under the time-variant channel, the %_ of continuous symbols will fluctuate with time, even if it is affected by the time-selective Fading characteristic of the channel. The FFT window is unchanged, and the noise power obtained by different symbols is also different. The corresponding noise power is calculated by adjusting the window position in different symbols, and the noise power at the correct position may be larger than the error position, thereby causing misjudgment. Therefore, the present invention further proposes that before calculating the noise power, a certain number (more than one symbol) of the time domain data (before the FFT) can be pre-stored, and then each time in the pre-stored time domain data, the window is moved, and only one symbol is obtained therefrom. The data is output to the fast Fourier transform module, ensuring that the noise power calculated by the fine symbol synchronization module is taken from the same symbol each time, eliminating the influence of fluctuations in time. To simplify the calculation, the value of the noise power W can be derived by summing the absolute values of the channel impulse response. The process for determining the correct first path by using the noise power is specifically as shown in the ninth figure, and the channel impulse response obtained by the above process is firstly passed through the set threshold value to obtain a plurality of paths ( Step S901); Next, moving the first path found to the left to the initial position of the channel impulse response 15 1377808, as shown in the left or right side of the channel impulse response pattern of the sixth or eighth figure, the present invention delays The FFT window realizes the left shifting action, such as delaying the start position of the FFT window in the time domain by the corresponding number of data (step S903), and calculating the FFT output of the new window position by extracting the discrete pilot with the interval of 12, and calculating The channel frequency domain response (step S905) is zero-padded to N/2, and then the channel impulse response is obtained by IFFT (step S907), and the first noise power result is obtained by finding the sum of the absolute values of the IFFT outputs (step S909). After that, the remaining paths found are moved to the left of the impact response in turn, and the corresponding number of data is delayed by the start position of the FFT window, and the remaining noise power results are calculated. The method proposed by the present invention does not need to move all the multiple paths, as long as the position of the first best path is judged after the comparison procedure (step S911), if the next noise power is larger than the previous one, the left shift process You can stop, indicating that the previous window position is the best during the left shift. If Mu goes to the last path (such as the first line) and does not appear to be larger than the previous noise power, then the third path is the best position during the left shift. After the process of shifting the left direction to the left is completed, the right shifting process is started, and the rightward shift from the last path to the start position of the impact response, and the process needs to advance the start position of the FFT window in the time domain. The corresponding number of pieces of data (step S913). The FF7 output of the advanced new window position is passed through the extracted discrete pilot, and then the channel frequency domain response is calculated (step S915), and the channel impulse response is obtained by zero padding and IFFT (step S917), and the absolute value of the IFFT output is obtained. And, the (estimated) noise power is obtained (step S919). Similarly, the position of the best path in the right shift direction is obtained (step 16 1377808 S921 )' and the condition of the end of the comparison is also that the next noise power is larger than the previous time, or moved to the first path (this example is At the beginning of the last path ^ ^, the minimum noise power appears. 〇^ After the sequel, compare the minimum squeaking work in the left and right directions, the smaller one is the correct first path and used in the present invention. Move the second party = step S923). ^

Referring again to the tenth figure, which shows a system diagram of the fine symbol synchronization different method used in the present invention, unlike the prior art (such as the first figure), the present invention first uses linear interpolation to obtain an interval of 3 or other complex numbers. The value of the = scattered pilot frequency, after calculating the frequency domain response and zero padding, and then the IFFT to obtain the channel impulse response, the FFT window position is adjusted by the synchronization process to estimate the noise power, and the first path is judged by comparing the noise power. Correct to the best m window starting position. ^ The system in the figure does not include the module to remove the cyclic prefix after receiving the signal, and 101 because the transmitting end is transmitting the signal, it will be avoided.

A signal interferes with the arrival of a symbol due to multipath delay, that is, after the output of the message is added to the pure prefix, and the receiver needs to remove it, other actions can be performed. Then, the signal is transmitted through the fast Fourier transform module 102, and then converted to go out. However, in order to avoid the signal interference caused by the multipath effect, it is necessary to obtain the correct FFT auto-symbol symbol, so the output signal will be The channel frequency domain response calculation module 103 first extracts the scattered pilots, and obtains the discrete pilots with small inter-symbol intervals (such as 3) by the above linear interpolation to obtain a larger time county®, and then the above equation (1) ) Calculate the channel frequency domain response. After (S) 17 1377808, the symbol is first padded to make the calculated number of points into a power of 2 (as in the DVB-T system, the number of points is N/2, N is the length of the FFT window, that is, the shift In addition to the symbol length after the beginning of the cycle prefix, the channel impulse response calculation module 106 calculates the channel impulse response through the inverse fast Fourier transform module 104, thereby obtaining the number of paths, the position and energy of each path, and the paths. The delay between. Then, the path information of the threshold value is transmitted to the noise power estimation module 105. The module 105 adjusts the FFT window position according to the position and number of the diameters, and takes each path as the first path and corresponds to the FFT window. Then, the modules 101, 102, 103, 104 and the like calculate the corresponding noise power according to the path data generated by the channel impulse response calculation module 106, and finally, the path with the minimum calculated noise power is set. For the correct first path, the best FFT window is obtained, which is the exact starting position of the symbol. After the starting position is found, the discrete pilot, IFf;T conversion is extracted again, and the channel impulse response is obtained. The position of the last path is found according to the threshold value, and the maximum delay of the channel is obtained, and the energy of each point below the threshold value is obtained. Calculate the average noise power. In the process of searching for the FFT window, in addition to performing noise power estimation in consecutive symbols, the data in the same symbol may be stored through another storage unit 107 to estimate the noise power in the same symbol, and the signal is eliminated in time. The effect of fluctuations on noise power judgment. According to the operation of each module of the fine symbol synchronization system described above, the flow of the preferred embodiment of the symbol synchronization method shown in Fig. 11 is organized. In step Sill, the signal enters the OFDM system, and the receiving end removes the cyclic prefix from the data of the channel, and then performs fast Fourier transform 18 1377808 (step S113), after which the inter-symbol interval is obtained after the linear interpolation. a smaller discrete pilot (step S115), and extracting discrete pilots in each symbol (step S117). In the preferred embodiment, a plurality of (eg, 7) discrete pilots are first extracted after FF7. Linear interpolation is performed to obtain a discrete pilot with a small inter-symbol interval (such as 3) to increase the allowable range of maximum delay. Next, in step S119, the channel frequency domain response is calculated. In the preferred embodiment, the channel frequency domain response is calculated by using equation (1), and after the channel frequency domain response is zero-padded, the inverse fast Fourier transform is performed to obtain the channel impulse response (step S121). ). Information such as the position and number of multipaths is found and recorded in the channel impulse response based on this threshold value (step S123). According to the position and the number of the multipaths, try to place each path as the first path at the start position of the window, and perform corresponding FFT window adjustments respectively (step S125), and the adjustment process may be performed in consecutive symbols, or may be performed. Store certain data in the same symbol. Then, a discrete pilot of one symbol is extracted from each window-adjusted FFT result, like the discrete pilot with a previous interval of 12, and the noise power of each corresponding FFT window is calculated (step S127). Then, steps 117, 119, 121, 123, 125, and 127 are repeated, including steps of repeatedly extracting discrete pilots, calculating a channel frequency domain response, performing an IFFT calculation channel impulse response, and the like (1, 119, 121). After the information of the track is recorded (step S123), the FFT window adjustment is performed (step S125), and the noise power of each corresponding FFT window is calculated (step S127). After repeating the above steps, finally, according to the comparison result of the noise power, 19 1377808 can obtain the correct first path position, that is, the optimum symbol start position with the smallest noise power (step S129). In summary, the present invention is a fine symbol timing synchronization method in an OFDM system, which mainly uses linear interpolation to obtain a discrete pilot with a small interval. After calculating the frequency domain response of the channel, after zero-padding, the channel impact is obtained through IFFT. In response, • and the step of determining the first path based on the minimum noise power estimation, thereby obtaining the correct starting position of the FFT window, that is, the step of synchronizing obtains the optimal symbol starting position in the 0FDM system. The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Therefore, equivalent structural changes in the description and the drawings of the present invention are equally included in the present invention. Within the scope of the agreement, Chen Ming. [Simple description of the diagram] The first figure shows the modulation and demodulation circuit of the DVB-T system of the prior art. φ The second figure shows one of the FFT window positions under the multipath channel. The second schematic diagram of the FFT window position under the multipath channel is shown; the fourth figure shows the circuit diagram of the conventional technique for performing symbol synchronization in the OFDM system. · The fifth figure shows the discrete guide of the DVB-T system. The frequency insertion structure; the sixth figure shows the channel impulse response under the multipath channel; the seventh figure shows the insertion structure of the interpolated discrete pilot; the eighth figure shows the channel impulse response under the multipath channel. 20 1377808 The ninth diagram is the flow of determining the first path using noise power according to the present invention; the tenth figure shows the system schematic circle of the fine symbol synchronous algorithm used in the present invention, and the eleventh figure shows the 0FDM system of the present invention; The flow of a preferred embodiment of the medium symbol synchronization method.

[Main component symbol description] Signal input 1〇Add protection sideband 12 plus loop word first 14 Remove loop prefix 24 Channel estimation and equalization 27 Digital analog conversion 15 Receive front end 18 Down conversion and anti-aliasing filter frequency offset phase correction 22 Transmission Parameter Message 26 Sampling Synchronization 30 First Path 201 Window Position 21 First Path 301 Window Position 31 Receive Signal 401 Fast Fourier Transform 405 Insert Pilot and TPS 11 IFFT 13 Channel 17 FFT 25 Carrier Synchronization 29 Transmit Front End 16 Analog Digit Conversion 19 20 Interpolator 21 coarse symbol synchronization 23 fine symbol synchronization 28 second path 202 cyclic prefix 203, 204 second path 302 removal of cyclic prefix 403 extraction of discrete pilot 407 21 1377808 inverse fast Fourier transform 409 find FFT window 411 pilot 5 (U, 502, 503, 504, 701, 702, 703, 704, 705, 706 removal cycle prefix module 101 fast Fourier transform module 102 channel frequency domain response calculation module 103 anti-fast Fourier transform module 104 noise Power estimation module 105 impulse response calculation module 106 storage unit 107

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Claims (1)

1377808 X. Patent application scope: 1. A fine symbol timing synchronization method in an orthogonal frequency division multiplexing system, comprising: receiving signals; performing a fast Fourier transform; performing a linear interpolation to obtain a discrete guide with a smaller interval Frequency; extracting the linearly interpolated discrete pilot; calculating the frequency domain response of the channel from the extracted discrete pilot; performing an inverse fast Fourier transform to calculate the threshold response of the channel and an effective path threshold, and the channel impulse response and the threshold Comparing the values, obtaining the information of the plurality of paths; according to the information of the plurality of paths, repeating the steps of adjusting the FFT window of the symbol pp · den, extracting the scattered pilot, calculating the frequency domain response of the channel, and calculating the channel impulse response, etc., obtaining one or more The channel impact response is calculated relative to the path, and the noise power is calculated; and based on the comparison of the one or more noise powers, the starting position of the symbol is obtained. 2. The fine symbol timing synchronization method in an orthogonal frequency division multiplexing system according to claim 1, wherein the linear interpolation performs the linear interpolation by using a discrete pilot of the plurality of symbols before and after the symbol to obtain a symbol interval. Smaller discrete pilots. 3. The fine symbol timing synchronization method in the orthogonal frequency division multiplexing system according to claim 1, wherein after calculating the frequency domain response of the channel, 23 1377808 the symbol is zero-padded to form a power of 2 The number of data of the party. 4. The fine symbol timing synchronization method in the orthogonal frequency division multiplexing system according to claim 1, wherein the time domain channel of the orthogonal frequency division multiplexing system is reflected by the impulse response calculation of the channel Multipath information, including the number of paths, the position and energy of each path, and the maximum delay of the channel. 5. The fine symbol timing synchronization method in the orthogonal frequency division multiplexing system according to claim 4, wherein each path is set as the first path of the orthogonal frequency division multiplexing system, and is set in the FFT window. Start position and adjust the corresponding FFT window of φ to calculate the relative noise power. 6. The fine symbol timing synchronization method in an orthogonal frequency division multiplexing system according to claim 5, wherein the position of the FFT window is determined by a path that is the smallest relative to the noise power. 7. The fine symbol timing synchronization method in an orthogonal frequency division multiplexing system according to claim 1, wherein the FFT window adjustment process is performed in consecutive symbols. 8. The fine φ symbol timing synchronization method in the orthogonal frequency division multiplexing system according to claim 1, wherein the FFT window adjustment process is performed in the same symbol. 9. The fine symbol timing synchronization method in the orthogonal frequency division multiplexing system described in claim 8 wherein the time domain data is stored for more than one symbol, and then the FFT window is moved each time. Obtain a symbol from it to ensure that the % portion of the noise power calculated each time is taken from the same symbol. 10. The fine symbol timing synchronization method in the orthogonal frequency division multiplexing system according to claim 1, wherein the noise power is obtained by summing the absolute values of the response of the channel impact 24 1377808. 11. The fine symbol timing synchronization method in an orthogonal frequency division multiplexing system according to claim 1, wherein a starting position of the symbol is relative to a first path of the orthogonal frequency division multiplexing system, the first The determining step of the path includes: • setting a threshold value, and the plurality of paths are obtained from the impact response of the channel; moving the plurality of paths to the left to the beginning of the impact response of the channel; # will be relative to the path The FFT wheel position of the FFT window is extracted by extracting the divergent pilot; calculating the frequency domain response of the channel relative to the path; zero-padding to the number of data having a power of 2, and obtaining the channel relative to the path through the inverse fast Fourier transform Impulse response, calculating the noise power relative to the path; determining the position of the optimal path by comparing the noise power with respect to the plurality of paths moving to the left; moving the plurality of paths to the right to the right The starting position of the FFT output relative to the FFT window position of the path by extracting the scattered pilot; calculating the frequency domain response of the channel relative to the path; zero-padding to the number of data having a power of 2 After the inverse fast Fourier transform, the channel impact response 25 to the path is obtained; = the noise power of the read path; the position relative to the plurality of good passages; and the noise power of the 夕 杈, the judgment is the most Shift left and shift to the right by two m 疋 The orthogonal frequency division multiplexing system takes the small noise power to determine the control direction and the moving direction. Symbol timing synchronization method, the number of data corresponding to the precise positional delay in the Orthogonal Frequency Division Multiplexing system of Dragon and ^; 3. If the patent application scope is the nth item... ... symbol timing synchronization method, the FFT window π start of the precision bit in the Orthogonal Frequency Division Multiplexing system and the corresponding resource in advance. 14 If the application is specifically touched, the action of the current (four) heart shift. The symbol timing synchronization method is obtained by summing the absolute values of the fine response in the sub-multiplexing system. (4) The rate is impacted by the channel. 15. Orthogonal frequency division multiplexing system sequence: orthogonal frequency division in a multipath channel The judgment of the second or second port of the multiplexing system results in the transmission of the symbols in the system, including: see the method of receiving the signal; removing the cyclic prefix from the signal passing through the channel; performing a fast Fourier transform; performing - linear interpolation Extracting the linear pilot value of the discrete pilot with a small interval of discrete pilots; 26, the frequency meter "" the frequency domain response; the number of data; the order to form a power of 2 Performing the conversion, calculating the channel impulse response and comparing with the H-impact response of the complex number ^ and extracting the discrete pilot, the #channel window according to the information of the plurality of paths; Two: f: should calculate the channel impulse response, and count (four) sound power; = for the # channel impact ratio of the upper noise power, relative to the noise power is the most = the position of the FFT window, get the Symbolic Starting position. 16·= j. The time-series synchronization method of the fine-paying number in the orthogonal frequency division multiplexing system described in Item 15, wherein the time domain of the orthogonal frequency division multiplexing system is reflected after the impulse response calculation of the channel The multipath of the channel includes the reading, the position and energy of each passage, and the maximum delay of the channel. 17. If the application is to reverse the orthogonal frequency division (4) in the range (4), the f-synchronization method is used, wherein each path is set as the first-path ' of the orthogonal frequency division multiplexing system in the FF window. Start position and adjust the corresponding FFT window to calculate the relative noise power. 18. The method of synchronizing the fine symbol timing in the orthogonal age complex as described in Item 15 of the application (4), wherein the FFT window adjustment process is performed in consecutive symbols. 19. The method of claim 4, wherein the FFT window adjustment process is performed in the same symbol as described in claim 15 of the patent application. 20. The fine symbol timing synchronization method in the orthogonal frequency division multiplexing system according to claim 19, wherein the time domain data greater than one symbol is prestored, and then the FFT window is only moved from each time. Get - A symbolic material to ensure that the noise power calculated each time is taken from the same symbol. 21. The fine symbol timing synchronization method in an Orthogonal Frequency Division Multiplexing system according to claim 15, wherein the noise power is obtained by summing the absolute values of the channel impulse responses. C S ) 28