TWI360974B - A synchronization method for ofdm systems - Google Patents

Description

1360974 IX. Description of the Invention: [Technical Field] The present invention relates to a signal synchronization method applied in a communication system, and more particularly to a signal synchronization method applied in an orthogonal frequency division multiplexing (OFDM) system. [Prior Art] Orthogonal Frequency Division Multiplexing (OFDM) is a high-efficiency multi-channel modulation and demodulation technology with strong suppression capability for multi-channel attenuation. Orthogonal Frequency Division Multiplexing (〇FDM) is currently used by many communication standards such as DVB-T, DAB, xDSL, 802.11X-based wireless local area network (WLAN), and 802_16x-based fixed or mobile The man system, the most recent mobile communication system with a trend of more than 3G, uses Orthogonal Frequency Division Multiplexing (OFDM) to transmit data. It divides the usable bandwidth into multiple narrow frequency bands, and the data can be Parallel transmission over these frequency bands, however, has the disadvantage of being prone to synchronization errors. "ML estimation of time and frequency offset in OFDM systems; 5 (IEEE Trans. Signal Process·, vol.45, no.7)' proposed by JJ van de Beek ' M. Sandell and P. 〇 _ Borjesson The element and frequency offset are simultaneously estimated by the delayed-correlation algorithm, which is the maximum likelihood estimate, but is better only in the environment of additive white Gaussian noise channel (AWGN). As with other communication systems, there are some synchronization issues to be considered in orthogonal frequency division multiplexing systems. First, the unknown signal delay will cause symbol time offset (STO). Synchronic symbol time (CST) and fine symbol time (FST) synchronization are required. 'There is also a carrier frequency offset between the transmitter and the receiver' so that the fractional carrier Frequency offset (fracti〇nalcarrjer 5 1360974 frequency offset, FCFO), integer carrier frequency offset carrjer g>eqUenCy offset, ICFO) and remaining carrier frequency offset (resjduai carrier fj*equenCy 〇ffset, - RCF 0) Must be eliminated; in addition, the sampling clock inconsistency between the analog-to-digital converter and the digital-to-analog converter will also cause sampling cl〇ck fyeqUency offset (SCFO). In Τ·M. Schmidl and D. C_ Cox's "Robust frequency and timing synchronization for OFDM," (IEEE Trans. Commun" vol. 45, no. 12), proposes a training symbol using time domain, which can be used in the static multipath method. But there are still some uncertain areas. "A robust timing and frequency synchronization for OFDM systems; 5 (IEEE Trans. Wireless Commun., vol_2, no. 4), proposed by H. Minn, V_K. Bhargava and KB Letaief, proposes a solution to the above disadvantages. However, the extra training symbols will waste system resources, and these methods will find the strongest multipath 'not the first multipath' and therefore not applicable to fme symb〇1 time estimation.

Although K. Ramasubramanian and K_Baum, the "An OFDM timing recovery scheme with inherent delay-spread estimation,, 5 (Proc. Φ IEEE GLOBECOM'Ol. vol. 5, pp. 3111-3115, Nov. 2001), Areas without inter-symbol interference (ISI) can be identified in the multipath fading channel, but too many symbols are required for accurate ST estimation. In M. Speth, S_Fechtel, G_Fock, and η. Meyer "Optimum receiver design for OFDM-based broadband transmission-part II: a case study, 5, (ffiEE Trans. Commun., vol.49, no.4, pp. 571-578, Apr. 2001)-

- The channel frequency response (CFR) must be predicted first, followed by the inverse fast Fourier transform (IFFT) to obtain the chaimd impulse response (CIR), which is then used to adjust the symbol boundary, which is fairly Complex D 6 [Embodiment] Symbol Time estimation is the first stage of the overall orthogonal frequency division multiplexing (〇FDM) synchronization process. It provides the estimated orthogonal frequency division symbol boundary of the subsequent stage. Value 'Please refer to Figure 1 for three consecutive symbol time-domain diagrams of the orthogonal frequency division multi-X communication system. Three consecutive symbols are (/_;)th Symb〇(/)th Symb 〇1 and (/+7) also

Symbd 'each symbol begins as a guard interval (GI). The estimated symbol time usually falls in one of the two defined areas, namely ST1, ST2 and ST3 in the figure, and the bad symbol time error area ST1. The good symbol time error region ST3 is within the guard interval (GI) of the orthogonal frequency division multiplex symbol, and the maximum delay of the channel is extended to Τί/. In (7)th Symbol, the pay element time error region ST3 has only channel effect without interaction symbol interference (isi) phenomenon, but the bad symbol time error region ST1 and the bad symbol time error region ST2 are respectively received (/_ Inter-symbol interference (ISI) of Symbol and (/+/)th Symbol. Therefore, after the coarse symbol time (CST) estimation is performed in the bad symbol time, the connection is continued. Fine symbol time (FST) estimation is used to fine tune the FDM symbol boundary to avoid inter-symbol interference (ISI) and signal-to-interference-and-noise ratio (Signal-to-Interference-and- Noise Ratio (SINR) is optimized. Fig. 2 is a schematic diagram showing the architecture of an orthogonal frequency division multiplexing (OFDM) communication system according to an embodiment of the present invention. In this embodiment, a baseband information bit stream (rate) For F=l/T) from the data source 20 through the signal mapper 21 to the N-point inverse fast Fourier transform 22 'serial-parallel conversion is sent to n sub-channels respectively, N-point reversal of the signals on the N sub-channels Fast Fourier Transform (IFFT) 22 processing to achieve quadrature modulation 'Converted into a continuous waveform by the digital analog converter 24, carried on the radio frequency (up-amplitude) to amplify and transmit, the RF center carrier frequency is /c, in order to eliminate the interference between the symbols, the insertion unit 23 is placed in the loop before the loop. The cyclic prefix (CP) is received by the receiving end via the channel 26. After the signal is moved from the radio frequency band to the base frequency signal, the radio frequency is sampled and quantized by the analog signal, and the analog digital bit = frequency „), and then The period τ signal, in the loop pre-removal, the 36 conversion to digital (PPT) 3 ^; / ^ ^ each sub-channel message stream _, correction and signal demapper 32 on the stream signal, the last transmission 2 The series conversion is the original serial number conversion ratio estimator 38, and the symbol of the analog-to-digital (OFDM) system t is selected in the positive-father frequency division multiplexing positive value, and the remaining ^ '..., the positive value and the carrier frequency The offset error dynamometer i correction value is respectively transmitted to the cyclic pre-removal unit 35 and in the above embodiment, where ^ is the frequency domain data of the Η Η 子 sub-band of the transmitting end, and 々 is the receiving end moxibustion The frequency domain data of the frequency band, the gas is the first / symbol The first time is sampled in the transmitted time domain, I is the size of the fast Fourier transform (FFT) that is included in the loop preamble ((8) of the receiver data, the number of the channel, printed) =#+% is 符17〇]^ The length of the symbol in the system, which includes the cyclic preamble (CP); the factory 8 is the sampling frequency, Λ is the carrier frequency, and tfy is the carrier frequency offset (CFO) through the subcarrier space. The resulting ^ Δ, Λ ^ / Λ « is the estimated maximum signal-to-interference plus noise ratio (MSINR) symbol time offset (STO) ' g / 靡 靡 is the estimated maximum signal to interference plus Signal ratio (MSINR) carrier frequency offset (CFO). In addition, the # complex data symbols in the transmitting end are modulated by the #点 inverse fast Fourier transform 22 to W subcarriers, and the inverse fast Fourier transform samples formed by the iVG of the last symbol are copied into the loop. Set (CP), which inserts the beginning of each OFDM symbol 'because of placing a loop preamble (cp) to form a guard interval (guardinterval)' to avoid inter-symbol interference (ISI) phenomena and to maintain inter-subcarriers In the orthogonal relationship, the received signal can be demodulated by the fast Fourier transform at the receiving end. 1360974 In Figure 1, the symbol time (ST) «Λ may fall within one of the three error regions of the OFDM symbol, and the range of the bad ST1 region is +1 'good ST3 region is -A/. +~+1<«△幺〇, another bad ST2 area range is S7V-1. The symbol time offset (STO) is regarded as the offset from the ideal symbol time. The ideal symbol time is recorded as the time coordinate 〇. In the figure, the 虚线 'dashed line' is at any point within the three symbol error regions. The received frequency domain data signal is not as shown in equation (1): X ,, k = ^!, k + .......................... ....... (1) Among them, no A is the correct data signal as shown in formula (2):

x{=YTwr^kxl<kw^^\^2) 1W w=〇 In addition, the kg* is the interference signal plus the additive white Gaussian noise channel (AWGN) signal v*, as shown in equation (3): It is 6_;2"/", and meaning=# + 乂 is the length including the loop preposition (CP). The inter-carrier interference (ICI) signal in equation (3) is equation (4):

N m*k n'=N~n& (4) The interference (ISI) signal between the symbols of equation (3) t is equation (5): Σ Knim-k+e/)Hmxl+^ (5) m "'=N~n& ' where K is the channel frequency response (CFR) of the mth subchannel. The power formed by the above 'correct data signal' is as shown in equation (6): (S) 10 m\xf Ν· Ίν7 £ Hk 2 - (6) -1 Ν nl =〇η2 =〇 and the power of the combined interference signal and the additive white Gaussian noise channel (awgn) signal is: σ1 ~ E Ν

Nk 111 ly2,km\Y\i __ Nl Nl ,, =Σ Σ ίχϋ—ε/) κ2 iV lm*kw, =0 «2=0 N-\ AM ( + Σ Σ %[,h^h Hk2 ( 7)

w, =//-wA n2=N^nA M~l yv-1 ( Λ + 2Σ Σ Σ W^~n^m-k+^ Hm2+a2 > m^k Wj =Α^-«δ n2~ N~nL V* where ' 'r=£[|xu| ]=♦—!], for transmitting data power, < for additivity white Shangsi noise channel (AWGN) power, SINR △, ~) The theoretical value is that the temperature depends on the symbol time offset (STO) and the carrier frequency offset (CFO). Please refer to FIG. 3, which illustrates a signal synchronization method flow (4) in an orthogonal frequency division multiplexing (〇FDM) communication system according to an embodiment of the present invention, including: step S1 receiving a frequency domain data signal in a channel, and analyzing frequency domain data. The signal is represented by 丨(1) and analyzes the frequency domain data power, interference power and AWGM power, as in equations (6) and (?). Step S2 calculates the average job-to-interference plus sinr of all subcarriers; using the envelopes of the second and fourth orders of motion embedded in the complex Gaussian noise, the SINR of the true value signal in the multipath attenuation can be obtained, (1) For the statistical operation, the equations (8), (9) and (10): > (9) 1360974

Q 厶

R ΓΣ ^ ΙΛ Ι + ΙΛ (10) Thus, the signal power & and interference function in the kth subcarrier can be expressed by equations (1) and (1)): ' (11)

Sk = (^l+Rk~Qk) / -5,, kk k'.............. (12) The estimated SINR at the kth subcarrier is Equation (13): = Sk / Ik. .............. (13) So the average Quanxuan New K gets the whole _ SINR, Wei q as the formula ((4) 1 ...... shows: η Κ (14) Can be === times average, so as to find == power "Guan Erbin, and interference signal ^~?Ιά;Ι.................. S: /: (16 )

The total power in equation (16) is the geometric mean of the power of the estimated SINR7/'s equation (7) using two Chiang & a ^ t / symbols, then IA '... ....two (1)): Then average all the Z symbols to get the simplified formula of the SINR of the formula ( ):

12 S (18) 1360974 The above estimation method only needs to receive the frequency domain f material without first knowing the channel and transmission data. The maximum value of equation (18) is obtained to obtain the symbol time offset (STO) and the carrier frequency offset (CF〇), as in equation (19): (^^, MS1NR 5 ^f.MSlNR ) ~ The two-dimensional search problem of Dou (9) is very complicated, no

Next, separate equation (9) to solve the independent symbol time offset (s = wave frequency offset (CFO) problem, as shown in equation (2〇): 戟

nAMSINR 8 fMSINR argmax{^K5 argC less f M SINR )} MSIhfR 5 )^ ε (20)

Please see Figure 4A for the SINR of a typical channel with 29 paths in the metropolitan area and the area of the interference (isi) between the sampled _ _ complement, its condition, and the 5 legs in the unsigned (·π Between 〇th) There is a flat area with a maximum value. The sampling display of the SINR estimation of the equation (18) is as shown in Fig. 4B, and the system implemented is the same as that of Fig. 4A. In Fig. 4B, it can be seen that equation (18) is not as good as equation U4. Accurate 'fine (10) is still clearly preserved, and the SINR of 4B B is in the bad ST1 area compared to 4A. The magnitude of the graph drop is more obvious. The estimation of equation (18) performs an average of all symbols, so that the SINR contour can be saved in the time-varying channel (time_variantchannei), as shown in Figure 5B, and the normalization of the map is The frequency (N_ahzed ϋ〇_Γ Frequency5 NDp) is 〇·ι. Further, if the result calculated by the 5-dirty estimation formula of the equation (14) is as shown in Fig. 5A, it can be understood that the equation (14) is not suitable for use in the time-varying channel. Fig. 6A and Fig. 6B show the SINIU ancient test of equations (14) and (18) in various CF values. The range of CF0 is _1/2 <^<1/2, The maximum value of CS ) 13 appears when CFO = 〇. The riding of the equations (14) and (18) in the time-varying channel is shown in Figures 7A and 7B, and the NDF condition is 0.1, and the 7B _ =) is estimated in the time-varying channel t. The measurement is _, which is better than the two points of the sampling symbol S3 in step S31 of the figure J3 and generates the interference of the two points plus the noise tb (szu); in order to reduce the search for the entire range (four) The calculation complexity ', the condition number is _Γ △ and the yuan " toilet + ' two points sampling, the time offset of the element boundary. In step S4, the two signals are subtracted from the interference plus noise ratio (SINR), and the error signal 'has the error signal close to zero; the symbol shown in FIG. 8 is the symbol of the present invention. Synchronous estimation, the structure is not intended, the formula 〇 8) in the above two points of the 5 dirty subtraction and filtering formed - error message m if the sampling of two points ^ _ Γ δ, qing Λ + γ λ are in the best ST The edge and the right side are equal to each other's distance. The i is the estimated time offset of the symbol time offset (ST0), the error signal heart (/), etc., 0 is the most 彳i; the ιυ(4) is in two In the case of the other, the error money center 0 is not equal to 0 ', and the error is made by the early/late gate (eai1y/late _, ELG). Where the 5 tigers approach the scales. Error signal eA(/) * The S curve of the error horn of the error signal equal to G is as shown in equation (21): eM) - Vi(nAMSm-r^sfMSINR)~^{n^Msm ^τΑ, ε/Μ5ΙΝΚ \... (21) The approximate line 彳峨 type is as shown in 帛9 mesh. The system adjusts the error value to 0 in the early/late idle loop. The sign indicates that the meaning is: F{z) KF loop filter gain; Κ1 clock detector essence gain κν voltage controlled oscillator gain; ΝΛζ) ζ conversion; Δ, Λ/Μν/?(7) Ζ conversion; 1360974 Εδ( ζ) Heart (/) ζ conversion; Κ (8) Filtered error message 4 (0 ζ conversion. In Figure 9 'range ηΔ signal (/) after ζ conversion (z-transf〇rm) produces \(z ) Input to the clock / [Time Detector 71], and output the Z signal of the _ error signal five Δ (ζ) to the loop filter (LoopFilter) 79, ' & thin circle filter 72 receives five △0) The signal generates five 1(2) signals, which is the Z-conversion of the filtered error number 4 (7). In the voltage controlled oscillator (VC0) 73, the symbol time (ST) will be expressed by the equation (22). )Adjustment:

^AMSINR (0 - ^AMSINR U ~ ^) + STS (22) Finally output the 0) signal, which is the Z conversion of the transport (/) signal. The loop system of Fig. 9 above can be expressed by the equation (23): L(z)=-_ 1 + ζ~ι(ΚΓ-2)+ζ~2(1-Κτα)........ (23) where 'espeech is the gain of the clock detector 71 itself; the ruler is the gain of the filter 72; A is the gain of the voltage controlled oscillator (VCO) 73; KT=KFKfKvNsTs .

This system is stable under the condition of equation (24): 〇 <a<\ and 0 << 4^+ β. (24) After the above adjustment, finally adjust the symbol time to the most in step S5. Good location. In another embodiment, the received frequency domain data gas number is multiplied by the smaller and larger frequency offset in each channel in step S32 in FIG. 3 to generate two signal-to-interference plus noise ratios. (SINR); and in step S4, the two signals are subtracted from the interference plus noise ratio (sinr), and an error signal is filtered to make the error signal approach zero; as shown in FIG. Schematic diagram of the carrier frequency (CF) synchronization estimation architecture, which differs from the figure 8 in the frequency offset f/ws/iw ~ in the early knives, and the frequency offset in the late branch 15 1360974 has f WS1NR VII f ' D is the estimated frequency offset of the carrier frequency offset (CFO), and the S curve of the frequency destroyer of the error signal is as shown in equation (25): 9 (') _ 6 (ΔΛ® only) ·, ^/mail/marriage-) - ^ «JWMW,+ ~ ). ( 25 ) • Finally, the carrier frequency offset is corrected in step S5. Please refer to Figures 11 to 14 and Figures 15 to 18 for comparison of the effectiveness of the present invention with other estimation methods under various conditions. The environmental parameters set are similar to those of the general metropolitan area. An OFDM system N=256 subchannels, guard interval Wg=AV8=32 and only consider data subchannels, quadrature phase shift keying (qpsk) modulation, • signal bandwidth 2.5 MHz and radio frequency 2.4 GHz, subcarrier range It is 8.68 kHz and the symbol period is 115.2 /^. The estimated maximum signal-to-interference plus noise ratio estimator is estimated using the mean-squared error (MSE). The parameters of the clock recovery loop are set as follows: = 0.9997, & = 〇.3, the normalized loop bandwidth is, where 5 is the loop bandwidth and is set to 0.05, and each simulation is 1 符 symbols. In the implementation of Fu Yuan's estimation, the present invention and A·J. AI-Dweik proposed minimum-interference ST estimation and [5] mentioned in the time domain without data-assisted symbol estimation The comparison of time-domain NDA ST estimation is shown in Fig. 11 and Fig. 12, respectively. Fig. 13 is a comparison of the performance of the symbol estimation of the present invention under various two-to-two ratio (SNR) conditions. Figure 14 is a comparison of the performance of the symbol estimates of the present invention in various positive normalized Doppler frequencies (NDF); in addition, in the implementation of carrier frequency offset estimation, the present invention and A_J. AI-Dweik The comparison of minimum-interference ST estimation is shown in Fig. 15 and Fig. 16, respectively, and Fig. 17 is the carrier frequency offset estimation of the present invention in various signal-to-noise ratio (SNR) conditions. The comparison of the performance below, the 18th figure is the performance comparison of the carrier frequency offset estimation of the present invention under various normalized normalized Doppler frequencies (NDF). In the above simulation comparison and analysis, the present invention compares with the minimum interference symbol estimation (mininrnm-imerferenceSTestimation) proposed by A·j. A!_Dweik, and 16 no respectively! 2 wave, partial (CF〇) case - complete comparison, the figure shows that whether it is the case of cutting, this turn can have better performance, and is less sensitive to the influence of carrier frequency offset (CFO) . Furthermore, the synchronization of the present invention will be directed toward the region of the interference between unsigned symbols ((5)) and the carrier frequency synchronization side will gather the most important _ _ _ _ _ _ In the case of low yue and ^ 〇 brother generation miscellaneous H, the county is also very strict

In summary, the present invention is directed to a method for arbitrarily step-by-step thief (maxi_SINR) in a quadrature frequency division multiplexing (〇FDM) system, where the _ 元 元 咖 位于 位于 位于 位于 位于 位于 位于 位于 位于 元 元 元 元 元 元 元 元 元 元 元 元The s leg value can solve the synchronization problem under the information of the wheelless data, so the invention is also a non-data-aided (NDA) algorithm. Moreover, the present invention can be used for multipath fading channels when time varying, and has high accuracy at low SNR, high CF threshold and high value. ’

The embodiments described above are merely illustrative of the technical spirit and the features of the present invention, and the objects of the present invention can be understood by those skilled in the art, and the scope of the present invention cannot be limited thereto. That is, the equivalent changes or modifications made by the spirit of the present invention are still within the scope of the invention. [Simplified description of the diagram] Field diagram Figure 1 shows the three consecutive symbol time intentions of the orthogonal frequency division multiplexing communication system. Fig. 2 is a diagram showing the twisting intention of the orthogonal frequency division multiplexing communication system according to an embodiment of the present invention. 11 'present architecture shows 17 (S) 1360974 Figure 3 "The invention - the method of signal compensation in the Orthogonal Guardian (〇fdm) communication system. Figure 4A and Figure 4B It is a map of each sampling index in various cases according to the present invention. Fig. 5 and Fig. 5 are diagrams showing the index of each sampling index in various cases in a time varying channel according to the present invention. Figure 6 is a diagram showing four samples of each sample index in the case of various cf values according to the present invention. Fig. 7A - Fig. 7B are diagrams showing the index of each sample index in the case of a Weidao towel in accordance with the present invention. ί 第 第 骑 骑 根据 根据 根据 第 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = The architecture shows off the other estimation methods in various ship conditions. She is exposed to the conditions of the species [main component symbol description] 20 data source 21 signal mapper 22 N-point inverse fast Fourier transform < S ) 18 1360974

23 Cycle pre-insertion unit 24 Digital analog converter 26 Channel 30 Data area 32 Signal demapper 33 Equalizer 34 N-point fast Fourier transform 35 Cycle pre-removal unit 36 Analog-to-digital converter 38 Maximum signal-to-interference plus miscellaneous Analog Estimator 71 Clock Detector 72 Loop Filter 73 Voltage Controlled Oscillator ST1, ST2, ST3 Symbol Time Error Region S1-S5 Flow Step 19

Claims (1)

1360974,. 一----- . September 23, 100 revised replacement page: X. Patent application scope: • L A signal synchronization method in orthogonal frequency division multiplexing communication system, including the following steps: Receive several Frequency domain data signals in the channel, analyzing the frequency domain data signals; and finding the maximum signal-to-interference plus noise ratio of the frequency domain data signals, the steps comprising: calculating the frequency domain data signals to generate an average signal pair Interference plus noise ratio; generating two signal-to-interference plus noise ratio (SINR); and subtracting the interference plus noise ratio (SINR) between the two signals, and transitioning an error signal and making the error The signal approaches zero. 2. The method for synchronizing signals in an orthogonal frequency division multiplexing communication system according to claim 1, wherein generating the two signals to interfere with the noise ratio is by sampling two points of each symbol in the channel Produced. 3. The method for synchronizing signals in an orthogonal frequency division multiplexing communication system as described in claim 1, wherein generating the two signals to interfere with the noise ratio is multiplied by each of the data signals in each channel Smaller and larger frequency offsets are generated. 4. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 1, wherein the frequency domain data signal comprises a data signal, an interference signal, and an additivity white Gaussian noise channel signal, the frequency domain The representation of the data signal is: heart = I 'where z △ is the correct data signal, t is the interference signal plus the additive white Gaussian noise channel (AWGN) signal. 5. The signal synchronization method in the positive-family crossover multiplex communication system according to claim 4, wherein the formula of the tribute signal is · 20 1360974 2丨~... is -Λ), wherein the order is «= 〇w is β - / 2 ; r / " ' is the channel frequency response of the Wth subchannel, X,,, is the frequency domain data of the female subband of the transmitting end. 6. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 4, wherein the interference apostrophe plus the additive white Gaussian noise channel signal is expressed by: m^kn = 〇 1 on, The external one is an add-on white Gaussian noise channel (AWGN) signal, and ^ is the channel frequency response of the first sub-channel, which is the frequency domain data of the w-th sub-band of the transmitting end, especially the inter-symbol interference (ISI) signal. It is also an interference signal between carriers. 7. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 6, wherein the expression of the interference signal between the carriers is: m φΙ( η '=Ν ~η^ The expression of the good signal between the symbols is: : and m ny~N~^^ 8. In the orthogonal frequency division multiplexing communication system described in claim 4 The signal synchronization method, wherein analyzing the frequency domain data signals further comprises converting the data signal and the interference signal plus the additivity white Gaussian noise channel signal into a power form, wherein the power of the data signal is: 21 1360974 σΗ = E where |V|2 △-1 "-Ή古Σ Rolling: ")" Ν Η ; and «I =0 «2=0 «• 玄 § §fl plus the plus The power of the white noise channel signal is σ 2 Ε Ν i,k NN 2 m2 Ν-ϊ N. Σ Σ Σ w less m^k /ij =0 w2 =〇//, + Σ Σ w: ηλ =M ~n& n2^Nn^ (w> ~η2)ε 2Σ Σ Yj H. + σ H\=N — rt& tt2=hi —η&", for transmitting data power, 'is additive white Gaussian The channel (regulation (10)) power 'heart and /^ are the channel frequency response of the mth and the & subchannel respectively. 9. The method of signal synchronization in an orthogonal frequency division multiple frequency system as claimed in claim i, wherein calculating the frequency domain data signals comprises: estimating a noise-to-interference plus noise ratio for each subcarrier; and averaging the The signal of the sub-news is the interference of the thief, the average cost of the production is less than the interference. 0. The signal synchronization method in the orthogonal frequency division multiplexing communication system described in claim 9, for each sub- The steps of the carrier estimation signal to the interference plus noise ratio are: SI = -ί— V jr γ * 7 Λ I , k Λ 1+1^ 22 丄湖974 And U. The signal synchronization method in the orthogonal frequency division multi-wei communication system according to claim 9, wherein the average of the sub-news city-to-interference plus noise ratio formula is: η, ^Σ";厶ι 12. The signal synchronization method in the orthogonal frequency division multi-wei communication system according to the fourth item, wherein the method further comprises: obtaining a maximum value to perform a symbol-offset and a wave frequency offset, wherein the maximum value is obtained. The expression is: ^amsinr = argmax {ηΊηΑ F , 1 J Ά, Α 5 6 fMSlNR ) / ^/msinr = arg max {η\ηκ 〇, 1. L n&,ef ^ V ^MSlNRi^f)&gt Where G is the carrier frequency offset (CF0) produced by the normalization of the sub-carrier space, which seems to be the symbol time. 13. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 12, wherein the error signal has a s curve of a time discriminator, and the expression is: ')-6 (3⁄4 plane - ; △, & 顺) - 伽 △ touch)). Is the time offset of the symbol boundary. Η. As requested! 2 The signal synchronization method in the orthogonal frequency division multiplexing communication system, wherein the error signal has an S curve of a frequency discriminator, and the expression is: '=gamma, Wr ")-gamma, heart The toilet,)· where ^ / is the frequency offset of the carrier frequency offset. (S) 23 1360974 15. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 1, wherein the error signal is brought close to zero by using a clock recovery loop. 16. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 15, wherein the clock recovery loop is an early/late gate clock recovery loop, and the expression is: Κτζ-\\-αζ ~ι) L{Z)= 1 + Ζ^(Κτ-2)+ζ-\ΐ-Κτα), the center of which is the total gain. twenty four