TW200937899A - A synchronization method for OFDM systems - Google Patents

Abstract

The present invention discloses a synchronization method for orthogonal frequency-division multiplexing (OFDM) systems based on signal-to-interference-and-noise-ratio (SINR) maximization. Due to the incurred losses from inter-symbol interference (ISI) and inter-carrier interference (ICI), the SINR of the received data drops drastically for synchronization errors. Owing to this characteristic, the synchronization errors are estimated, the symbol time offset (STO) and the carrier frequency offset (CFO), by maximizing the SINR. The invention proposes a SINR metric such that prior knowledge of the channel profiles and transmitted data are not required, thus the method is non-data-aided (NDA) and the transmission efficiency can be maximized.

Description

200937899 IX. Description of the invention: - [Technical field to which the invention pertains] The present invention relates to a signal synchronization method applied in a communication system, and in particular to a signal synchronization method applied in an orthogonal frequency division multiplexing (OFDM) system . [Prior Art] Orthogonal Frequency Division Multiplexing (O 〇 FDM) is a high-efficiency multi-channel modulation and demodulation technology with strong suppression capability for multi-channel attenuation. Orthogonal Frequency Division Multiplexing (OFDM) is currently used in many communication standards, such as DVB-T, DAB, xDSL, 802.11X-based wireless local area network (WLAN), and 802.16-inch fixed or Mobile MAN systems, the recent trend of mobile communication systems with more than 3G is almost all using Orthogonal Frequency Division Multiplexing (OFDM) to transmit data. The available bandwidth is divided into multiple narrow frequency f, and the data is It can be transmitted in parallel on these frequency bands, but its disadvantage is that it is easy to generate synchronization errors. ML O estimation of time and frequency offset in OFDM systems/5 (IEEE Trans.) published by J. J. van de Beek, M. Sandell and P. 〇 Borjess〇n

Signal Pro Prison, vol.45, n0.7), proposes the symbol and frequency offset to be estimated simultaneously using the delayed-correlation algorithm, which is the maximum approximation estimate but only available The white Gaussian noise channel (AWGN) has better performance in the environment. Just like other communication systems, there are some synchronization issues that need to be considered in orthogonal frequency division multiplexing systems. First, the unknown signal delay will cause the symbol time offset (STO) (coarse symbol time, CST) Λ fine symbol time (FST) synchronization, which is also in the transmitter and receiver. Shooting subtraction (10)f pick, subtraction · solution offset (threat (4) cWer 5 200937899 frequency offset, FCFO), integer carrier frequency offset (integrai caiTier frequency offset, ICFO) and residual carrier frequency offset (RCFO) Elimination; In addition, the sampling clock inconsistency between the analog-to-digital converter and the digital-to-analog converter also causes sampling cl〇ck frequenCy offset (SCFO). "R〇bust frequency and timing synchronization for OFDM; 5 (IEEE Trans. Commun., vol.45, no.12)", proposed by Τ·M. Schmidl and DC Cox, proposes a training symbol using time domain. The method of static multipath can be used, but there are still some uncertain regions. "A robust timing and frequency synchronization for OFDM systems," by H. Minn, VK Bhargava and Κ B. Letaief (IEEE Trans.

Wireless Commun., vol. 2, no. 4)' proposes a solution to the above shortcomings, but the extra training symbols will waste system resources, and these methods will find the strongest multipath, not the first multiple The path 'is not applicable to fine symb〇1 time estimation. Although K. Ramasubramanian and K. Baum, "An OFDM timing recovery scheme with inherent delay-spread estimation," (Proc. IEEE GLOBECOM'Ol. vol. 5, pp. 3111-3115, Nov. 2001), An area with no inter-symbol interference (ISI) can be identified in the multipath fading channel, but too many symbols are required for accurate ST estimation. 'Optimum receiver design for OFDM-based broadband transmission-part II: ει case study, (IEEE Trans. Commun., vol.49, no) by M. Speth, S. Fechtel, G. Fock, and H. Meyer .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 channel impulse response (CIR). ), which is used to adjust the symbol boundary, the processing is quite complicated. 6 200937899 SUMMARY OF THE INVENTION In order to solve the above problems, one of the objects of the present invention is to solve the problem of the same frequency of the orthogonal frequency division multiplexing (OFDM) system towel, and to correct the maximum SINR value (臓-) • Xiansui Guiyuan _ escaping element boundary = another object of the present invention (4) is the problem of carrier frequency offset in orthogonal frequency division multiplexing (〇fdm) system 'resolving - maximum 峨 interference plus noise · (__ Ο

SINR) H: 'The fine-grained Wei riding error correction seems to provide the correct down-clock calculation. 'The problem of signal synchronization can be obtained without knowing the channel contour and transmission. In order to achieve the above object, a method for synchronizing in an orthogonal frequency division multiplexing (OFDM) wanted system according to an embodiment of the present invention includes: receiving two domain data in a plurality of channels; Calculate the noise-to-noise ratio of the _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Subtracting and filtering out an error signal and bringing the error signal closer to zero. In order to achieve the above object, the orthogonal frequency division multiplexing (OF^VI) itw纟 towel data step-by-step method of the present invention includes: receiving two domain data subtraction in several channels, and analyzing the frequency spectrum view No. Calculate the ratio of the thief Weicheng production money to the dry noise ratio; the _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ; subtract two signals to the interference plus 4 ratio (SINR) and rhyme out _ county shout, and make the error signal close to 7

Inter-symbol interference (ISI). Therefore, 'after the coarse symbol time (CST) is estimated, the continuation of the symbol time (CST) is followed by the fine symbol time (fme 200937899 [Embodiment] Symbol Time estimate (SymbolTime) is the overall orthogonal score The first stage of the frequency multi-synchronization process, which provides the estimated orthogonal frequency division multiplex symbol of the subsequent stage 2, the three consecutive symbol time domain non-intentions of the L orthogonal orthogonal work track system, three The consecutive symbols are (4) h Symbd, ((10)Symb ^

Symb=per _ character is initially - protection off (GI), the estimated symbol time usually falls in one of the two defined areas, namely ST1, ST2 and ST3 in the figure, bad symbol time error The region sti and the good symbol time error region ST3 are within the guard interval (gi) of the orthogonal frequency division multi-symbol (ng), and the maximum delay spread of the channel is 〇. In (Square Symbol, the symbol time error region ST3 has only a channel effect without an intersymbol interference (isi) phenomenon, but the bad symbol time error region ST1 and the bad symbol time error region ST2 are respectively received (/ _7)th Symbol and (/+〇th Symbol's intersymbol interference symbol time, FST) estimation is used to fine tune the OFDM symbol boundary to avoid inter-symbol interference (ISI) and to add interference-to-noise ratio to the signal ( The signal-to-interference-and-noise ratio (SINR) is optimized. Figure 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. The baseband message bit stream (rate F=l/T) enters the N-point inverse fast Fourier transform 22 from the data source 20 through the signal mapper 21, and is respectively sent to the N sub-channels for N sub-channels after serial-parallel conversion. The signal is subjected to N-point inverse fast Fourier transform (IFFT) 22 processing to realize quadrature modulation, which is converted into a continuous waveform by the digital analog converter 24, and is transmitted on the radio frequency (up-amplification) to amplify and transmit, and the radio frequency center carrier frequency is Λ , to eliminate interference between symbols Therefore, the cyclic pre-insertion unit 23 is placed in a cyclic prefix (CP). 8 200937899 调, 5?=:: Channel 26 receives the RF signal and then performs RF solution == band (down frequency), then one The speed Ϊ ΪΓΓ removal unit 35 removes «pre-position, then N-point fast == JFFT) 34, equalizer 33 and signal demapping... each sub-streaming stream demodulation, decoding, data stream signal, Finally, pass ❹(4)H, change to the original string number 〇 lung ί L, 2 signal to interference plus noise ratio estimator 38, connect the analog digital receive digital signal 'and calculate the orthogonal frequency multiplex positive value last · The error value of the 70-time misreading of the i-time and the error of the carrier frequency shift are corrected to the cyclic pre-removal unit 35 and the 'sub-band of the moxibustion sub-band in the above embodiment Frequency domain data, / "Frequency domain data for the /: subband of the receiving end, '" is the "translated time domain sampling of the first symbol", and is the reception containing the cyclic preamble (cp) End data, , λγ is the number of subchannels, F(1) is the continuous time signal received, and # is fast Fourier transform (FFT) The size u+ horse is the symbol length in the 〇pDM Ο system, which includes the cyclic preamble (CP); is the sampling frequency, Λ is the carrier frequency, and is the carrier frequency offset (CF0) generated by the subcarrier space normalization. « is the maximum signal-to-interference plus noise ratio (MSINR) symbol time offset (STO) of f, which is the estimated maximum signal-to-interference plus noise ratio (MSINR) carrier frequency offset (CFO). In the transmitting end, w complex data symbols are modulated by the #点 inverse fast Fourier transform 22 to the tamping subcarrier, and the inverse fast Fourier transform sampling formed by the last symbol 会 is copied into the loop. Set (CP)' which inserts the beginning of each OFDM symbol, because a pre-loop (cp)' is placed to form a guard interval, which avoids cross-signal interference (ISI). • Phenomena and keep subcarriers The orthogonal relationship between the receivers can be used to demodulate the received signals at the receiving end using Fast Fourier Transform. 9 200937899, symbol 1 (ST) / 7 △ in Figure 1 may fall in one of the three error regions of the OFDM symbol, in the range of the bad ST1 region is -Is +1, good ST3 region range For another bad ST2 area, the range is 1<. The symbol time offset (STO) is regarded as the offset from the ideal symbol time. The ideal symbol time is recorded as 0, which is located in the figure AA, the dotted line, at any point within the three symbol error regions. The received frequency domain data signal is as shown in equation (1): 尤, =+ ............................... ..(1) Bean, X d 〇

The TU is the correct data signal as shown in equation (2): J·.· (2) w_ = 〇 another 'Additional white Gaussian noise channel (AWGN) signal for the interference signal is called '如式(3) Shown: ~Δ 1 .V-] T:k...w W Μ. p ~ / 2 Λ- / Λ/ Ν疋, and Ws=iV + are the lengths including the cyclic preposition (CP). The inter-carrier interference (ICI) signal in equation (3) is equation (4): Σ (4) n'~N-n^ The interference between symbols (ISI) in equation (3) is equation (5). ): 々诖Σ Σ k'h+~aA~1(5) m n'^Nn^ where is the channel frequency response (CFR) of the Wth subchannel. The power generated by the above-mentioned 'correct data signal' is as shown in equation (6): 200937899

E m

X l.k m2 N-nA—\ N2 w -(»1 -»2 )i (6)

N »1 =〇 »2=〇 and the combined interference signal and the power of the additive white Gaussian noise channel (AWGN) signal <= five

7«, |2 ΣΣΣ^1 -w2)(TO_々+£/) I is good|2 m^kn} =0 «2=〇N-\ N-\ / v + Σ Σ W-^h\H ? (7)

Wj =Α^-/3δ w2=A^-Wa N-\ N~\ / w Ί +2Σ Σ Σ K[n^2)[m~k+Ef) ΗΜ\σΛ m^k Wj =Λ^- «δ «2s^-wa * where '%rf=five[KJ]=five[I not+U| _ ' W|x| is the transmitted data power, σ: is the additive white Gaussian noise channel (AWGN) The theoretical value of power, SINR π(«Δ, ^·) is that South is dependent on symbol time offset (STO) and carrier frequency offset (CFO). ❹ Referring to FIG. 3 is a flowchart of a signal synchronization method in an orthogonal frequency division multiplexing (〇FDM) system according to an embodiment of the present invention, including: step S1, receiving a frequency domain data signal in a channel, and analyzing a frequency domain. The data signal is expressed by equations (1) to (5), and the frequency domain data power, the interference power, and the AWGM power are analyzed, as in equations (6) and (7). Step S2 calculates the average signal-to-interference plus noise ratio (SINR) of all subcarriers; using the envelope of the second and fourth order momentum embedded in the complex Gaussian noise to obtain the SINK of the true value signal in the multipath attenuation, Equation (1) is used for statistical operations to produce equations (8), (9), and (10): Μ ^ =^Σ |^/, aI ?................ ................ (8) 200937899

Q Δ

L

L Σ ΙΛ

>+\Λ (9) (10) = Signal power & and interference power at the kth subcarrier can be expressed by equation (1) and equation (η) (11) Ο 〇h =Mk -sk,... .......... (12) Estimation at the kth subcarrier 81]^ is the equation (13): Ik ~ Sk / Jk............... (13) So average all subcarriers [get the overall SINR, its value; 7 as shown in equation (14): .............. (14) In order to reduce the complexity, (8) and formula (9) ^=ι贝叫=〇, ^峨泰犹算<Correction; the first to find all subcarriers + - scoop 're-pair - the appropriate number of symbols for the second time ratio (SINR ), can reduce the division of the secret, the screaming of the interference plus the number of the work to /, reduce the number of divisions, the simplified signal power V and the interference gas on the power I _ as shown in equations (9) and (16), 卞摱. Hole S: 丨.............. (15) Κ (16) / character ===: the geometric mean of the power of the element, · //;. (17) again for all I symbol averaging_式(18) Simplified formula of all SINR.· 12 200937899 η,= τ^η; · (is) The above estimation only needs to receive the frequency domain data without first knowing the channel wheel. (channelp_e) and the data of the transmission. The maximum value is obtained by the equation (18), ς symbol time offset (sto) and carrier frequency offset (CF0), as in equation (19): ('μ面々μ面面) = arg = f,)} (The two-dimensional search problem of equation (19) is very complicated, and the equation (19) is separated to solve the independent symbol time offset (ST〇) wave frequency offset (CFO) without excessive performance loss. The problem, as shown in the formula (2〇): ^ ^^msinr = ^^{nnA,if MSJNR)} ......... (20) See Figure 4A for a typical example of the metropolitan area The SINR in the channel with 29 paths and the interference in the sampling towel, which is 256, the force = 32, s dirty in the unsigned (ie the area (H〇 also) has a flat area The maximum value of the simplified (18) SINR estimation sampling display is shown in Fig. 4B, and the system implemented is the same as Fig. 4A. The equation (18) versus 3 can be seen in the first crime map. The ship estimate is not as accurate as equation (14). However, the SINR profile produced by equation (18) is still clearly preserved, and the sikr of 4B ® is more pronounced in the bad ST1 region than in Figure 4A. 18) The estimate is averaged for all symbols. Action, so that the SINK contour can be saved in the time-varying channel (time_variantch (1), as shown in Figure 5b, 5 J-® t 113⁄43⁄4 Normalized Doppler Frequency, NDF) is 〇.1_. In addition, if it is evaluated by (3) The results calculated by the measurement are as shown in the first figure. It can be known that the equation (14) is not suitable for use in time-varying channels. Figures 6A and 6B show equations (14) and (18) in various The SINR estimate in the CF0 value, the range of CF0 is _1/2 <&< 1/2, the maximum value of the s job in the figure 13 200937899 appears when CF 〇 = = 0. Equation (14) and formula ( 18) Estimation of 3 in time-varying channels. As shown in Figures 7A and 7B, the SINR is estimated to be 0.1, and the SINR in the time-varying channel of Equation 7B is shown in Figure 7B. The test is robust and better than 7A (14). ^ ” Next, at step S31 in the third B1, the two points of the symbol are sampled, and the signal-to-interference plus noise ratio (SINR) of the two points is generated; Search for the entire range "counts generated by △", complexity /, pairing at heart △ and two time points, ~ is the time offset of the symbol boundary. ❹ Step S4 uses the signal interference of these two points The noise ratio (SINR) is subtracted, and an error signal is generated to make the error signal approach zero. FIG. 8 is a schematic diagram of the synchronization estimation architecture of the symbol 70 of the present invention. 51]^ subtracts and over^ forms an error signal 匕 (0, if the two points of the sample - T △ and " + τ Δ are respectively on the left and right sides of the best ST and the distance is equal to the opposite '' The time offset of the symbol time offset (STO), the error signal (/), etc., 0 'the best sampling point is in the middle of the two points; otherwise, in other cases the error is called (0 is not equal 0, the early/late gate (E(6) mode makes the error signal approach zero° error signal 匕 (0 is not equal to 〇, the S curve of the error signal's timing discriminator © is as shown in equation (21) : Δ ( ) Vl( ^AMSINR 5 ^fMSINR ) ~ ^/ i^AMSINR fMSINR )-...(21) The approximate linear model is shown in Figure 9. The error is used in the early/late gate recovery loop. The value is adjusted to 0, the sign of which means the meaning is: F{z) loop filter; KF loop filter gain; Κ1 f r" the essence of the clock detector; K'/ pressure-controlled vibrator benefit; '(') Z-conversion; ', MSWii(/) Z-conversion; 14 200937899 E^{z) e&(I) z-conversion; K(z) filtering The error message 4 (/) z conversion. In Fig. 9, the signal "Δ(/) of the range η △ is converted by z (z-transforn^ generates W Δ (4) input to the Time Detector 71, and outputs - the wrong signal ~ ( 0 Z conversion £ Δ (ζ) to loop filter (LoopFilter) factory 72), the ring filter 72 receives five △ (8) signal generation 圮 (8) signal, which is the filtered error 姨 4 (7) Z conversion. In the voltage controlled oscillator (VC0) 73, the symbol time (st) | is adjusted by equation (22):

^AMSINR (/) = ^A, MSINR (l-\) + KvNsTse'A(l).······ (22) Finally output element (z) signal, which is the Z conversion of 圮(/) signal . The loop system of Figure 9 above can be expressed by equation (23): l^(z) = -__Κτζ (1 -αζ i)_ 1 + ζ 1 {κτ -2^ + ζ~2{\~ Κτα). . . ....... (23) where the ruler/ is the gain of the clock detector 71 itself; ff is the gain of the filter 72; A is the voltage controlled oscillator (VCO) 73 Gain; k^KfKWs. This system is stable under the condition of equation (24): (24) 〇 <a<\ and 0<KT<^/ τ Λ + α: After the above adjustment, finally adjust the symbol time in step S5 Best 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 signals to interference plus impurity ratio ( SINR) 'and in step S4, the two signals are subtracted from the interference plus noise ratio (sj^), and an error signal is filtered to make the error signal approach zero; as shown in Fig. 1 is the present invention. Schematic diagram of the carrier frequency (CF) synchronization estimation architecture, which differs from the 8th figure in the frequency offset in the early branch, - τ^, and the frequency offset in the late branch 15 200937899 ^ fMSWR + T fy τ f The estimated frequency offset of the carrier frequency offset (CFO), the S curve of the frequency discriminator of the error signal is as shown in equation (25): ^/(0 = ^7/(^ A, MSINR 5 ^/MSINR —fy ) — 77/ (^\tMSINR , cloud f, MSINR +, ) (25) Finally, the carrier frequency offset is corrected in step S5. Please refer to Fig. 11 to Fig. 14 and Fig. 15 to Fig. 18 It shows the performance comparison between the invention and other estimation methods under various conditions. The environmental parameters set are similar to the general metropolitan area channel, and an OFDM system N=256 subchannels. Interval #G=AV8=32 and only consider the data subchannel, quadrature phase shift keying (QPSK) modulation, the signal bandwidth is 2.5 MHz and the radio frequency is 2.4 GHz, the subcarrier range is 8.68 kHz, and the symbol period is 115.2/ ^. The evaluation of the maximum signal-to-interference plus noise ratio estimator is based on the estimated mean-squared error (MSE). The parameters of the clock recovery loop are set as follows: β = 0.9997, normalized The loop bandwidth is 5AM, where 5 is the loop bandwidth and is set to 005, and each simulation is 1 unit. The minimum interference proposed by the present invention and AJ AI-Dweik is implemented during the implementation of the Fuyuan estimation. The comparison of the minimum-interference ST estimation and the time-domain M A ST estimation in [5] is shown in Figure 11 and Figure 12, respectively. Figure 13 is a comparison of the performance of the symbol estimation of the present invention in various signal-to-noise ratios (SNR), and Figure 14 is a diagram of the symbol estimation of the present invention in various normalized Doppler frequencies (NDF). The performance comparison; in addition, the implementation of the carrier frequency offset estimation, the present invention and AJ AI-Dweik The comparison of minimum-interference ST estimation is shown in the μ map and the 16th graph. The π map is the carrier frequency offset estimation of the present invention in various signal-to-noise ratios (snr) cases. Comparing the performance, Figure 18 is a comparison of the performance 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 comparison between the present invention and the minimum-interference ST estimation proposed by A. J_AI-Dweik, and 16 200937899 respectively, whether or not there is a load-biased bias (CFO) Situation-Complete comparison, the figure shows that regardless of whether there is carrier frequency offset (CF0), the performance of this method is better, and it is less sensitive to the influence of carrier frequency offset (CFO). Furthermore, the symbol synchronization of the present invention will be concentrated toward the region of the interference between unsigned symbols ((5)), and the carrier side synchronization side will face the carrier frequency offset (CF(1) aggregation, and most importantly, the symbol synchronization estimation and speech. Synchronous estimation _ mean square error (MSE) is minimally affected in the case of low prisoner and NDF, making the invention applicable in extremely severe situations.

In summary, the present invention is directed to the problem of symbol synchronization in an orthogonal frequency division multiplexing (〇FDM) system, and proposes a method of maximal sinr plus maximum sinr. The boundary has the largest value of 5, which can be used in the case of no information transmission, so the invention is also a non-data-aidec^NDA algorithm. And the present invention can be used for multipath fading channels with low SNR and high CF. Value and high _; have a local accuracy. The above-described embodiments are merely illustrative of the present invention, and are intended to enable those skilled in the art to understand the present invention; and = and to implement 'when the patent scope of the present invention cannot be limited thereto, g The equal change of the spirit revealed by π谷 reveals that Senna is still in the scope of patents that should be invented. In this [Simplified Description of the Drawings] Figure 1 shows three consecutive intents of the orthogonal frequency division multiplexing communication system.苻7 time time domain communication communication system architecture Fig. 2 is a diagram showing the orthogonal frequency division multi-intent according to an embodiment of the present invention. 17 200937899 Example - (._Communication diagram Figure 4β shows the sampling of each sample in various stupid situations according to the present invention ====^_娜树转种脉情==_Showing to turn her in the situation Sampling

G =:=r The present invention is a time-varying channel value. Figure 8 is a schematic diagram showing the symbol synchronization estimation architecture according to the present invention. = Shown as an early/late time clock recovery loop operation architecture = 0 according to an embodiment of the present invention is illustrated as a schematic diagram of the general frequency step side architecture according to the present invention - (4) The situation of the effect / Yulin (four) expected it fine conditions [main component symbol description] 2 〇 data source 21 signal mapper 22 反向 point reverse fast Fourier transform 18 200937899 23 loop pre-insertion unit 24 digital analog conversion 26 Channel 30 Data Area 32 Signal Demapper 33 Equalizer 34 N-point Fast Fourier Transform 35 Cycle Pre-Remove Unit 36 Analog-to-Digital Converter 38 Maximum Signal-to-Interference plus Noise Ratio Estimator 71 Clock Detection 72 72 loop filter 73 voltage controlled oscillator Q ST1, ST2, ST3 symbol time error region S1 ~ S5 process step 19

Claims (1)

200937899 X. Patent application scope: The signal synchronization method in the orthogonal frequency division h communication system includes the following steps: receiving frequency domain data signals in several channels, analyzing the frequency domain data signals; calculating the frequency domains The data signal produces an average signal-to-interference plus noise ratio; 'generates two signal-to-interference plus noise ratios (SINR); and subtracts the interference plus noise ratio (smR) between the two signals and overshoots - the error gas number and the error signal approaches zero. ° 2. The signal synchronization method in the orthogonal frequency division multiple secret message described in claim 1, wherein the two signals are generated by the interference and the shame is generated by taking two points of the symbol in the channel. . 3_ The method of juxtaposition of the orthogonal frequency division multiplexing communication secret towel as claimed in claim 1, wherein the generating two δ etiquette pair interference plus noise ratio is multiplied by each of the frequency domain data signals Smaller and larger frequency offsets within the channel are produced. 4. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 1, wherein the number includes a data signal, an interference domain, and an additivity white Gaussian noise channel signal, the representation of the frequency domain data signal. The formula is: , k U + ' where I Μ is the data signal of the positive disc, WA: is the interference signal plus the additive white Gaussian noise channel (AWGN) signal. 5' The signal synchronization method in the orthogonal frequency division multiplexing communication system according to item 4, wherein the data signal representation formula is: 200937899 ~ ¢ / A 1 W - w, -1 X /, wide VS ❼厂^), where 叭 is e~.12 π / Μ ' is the channel frequency response of the mth subchannel, which is the frequency domain data of the sub-band of the moxibustion at the transmitting end. The signal synchronization method in the orthogonal frequency division multiplexing communication system described in Item 4 of the present invention, wherein the expression of the haihe interference 峨 plus the additivity self-color Gaussian noise channel signal is: 乂二士51—如/}认^一△)+' -3⁄4+3⁄4 ' The externally is the additive white Gaussian noise channel (AWGN) signal, K is the channel frequency response of the mth subchannel, the U transmitting end The frequency domain data of the sub-bands is the inter-band interference (ISI) signal and the inter-carrier interference signal. 7. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to Item 6, wherein the expression of the interference signal between the carriers is: Ϊ % Example Into JV&, m^k The expression of the interference signal between the symbols is: -lNsef-kn^) : and Σ a)). m η'-Ή-η^ 8. The signal synchronization method in the orthogonal frequency division multiplexing communication system according to claim 4, wherein analyzing the frequency domain data signals further comprises adding the data signal and the interference signal The add-on white Gaussian noise channel signal is converted into a power form, and the power of the data signal is ·· 21 200937899 σ xf,k W Ν .(η1 _»2)6/ ; and the power of the interference city plus the Ligaic self-color high-subtraction reduction is: < = Ε[Ψ^Γ _ϋ y~l ΛΓ-1 Σ Σ Σ w:^~^){m-k+ef)\H m*k «1 =0 η2=〇I ' η —2 ”ι ="-»△ ” 2 = ;\Γ_„λ \α k 2 2 Hm + σν, where IX丨 is the transmitted data power, and the additivity white Gaussian noise channel (AWGN) power K and //* are the first lecture and the first moxibustion The channel frequency response of the subchannel. Ο 9. The method according to claim 1, wherein the calculating the frequency domain data signals comprises: estimating a signal pair for each subcarrier Interference plus noise ratio; and the average of these Ziyi's interference with the noise ratio, the average job-to-interference plus noise ratio. > 10. The orthogonal frequency division multiplexing yi as described in claim 9 The ten-way signal synchronization method of the system, wherein the step of estimating the noise-to-interference plus noise ratio for each sub-carrier is: S; 22 200937899 /; = s, goods VV k 八尤十/+u - \,; and n\ = s; //;. 0 in the orthogonal frequency division multiplexing communication system described in Dongxiang 9 Signal synchronization method, in which the average rider's gambling material is disturbed by Chengzhi shirt: η, = τ~Σ ° Lj I For the signal synchronization method in the orthogonal frequency division multiplexing communication system described in the monthly term 11, the method further includes obtaining a maximum value of 13⁄4 copper-symbol time offset and -micro age, and the formula for determining the maximum value For: ^msjNr = argmax ~, μ_ two argi^, pity 5/ is the carrier frequency offset (CFO) generated by subcarrier space normalization, the heart is 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 an S curve of a time discriminator, and the expression is: δ(0 ^l^'AMSINR ^ ^^^MSINR ^A^^fMSINR^· Its center is the time offset of the symbol boundary. 14. The signal synchronization method in the orthogonal frequency division multiplexing communication system described in claim 12, wherein the error signal The S curve with a frequency discriminator, the expression is: e a dad fMS brewing τ f, Qiao ^.hMSim, dad f) 4SINR seven τ f). Reality Γ / is the frequency offset of the carrier frequency offset. 23 200937899 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: KTz~{{\ Αζ~χ) {^Kj —2^+z 2(1 – Κγύ^ Its Chinese 7 is the total gain. twenty four