CN100518160C - Sample clock frequency deviation compensation method and device for OFDM receiver - Google Patents

Abstract

A method for compensating frequency deviation of sampling clock on OFDM receiver includes using FFT window controller to control FFT window position for picking up pilot phase deviation angle in current OFDM symbol to derive out offset amount crude estimation of current FFT window, using accumulated average of FFT window offset amount to estimate FFT window offset amount of OFDM symbol accurately, using this accurate offset amount to regulate each sub channel phase after current OFDM symbol is balanced and simultaneously using this accurate offset amount to judge whether FFT window of next OFDM symbol is displaced or not.

Description

The sample clock frequency deviation compensation method of OFDM receiver and device

Technical field

A kind of method and apparatus that is applied to the sample clock frequency deviation compensation of OFDM (OFDM) receiver.It belongs to digital communication technology field, method and the device thereof, particularly a class that relate to the sample clock frequency deviation compensation in OFDM (OFDM) communications field add the ofdm communication system sample clock frequency deviation compensation method and the device thereof of targeting signal (Preamble) and adding pilot tone (Pilots).

Background technology

OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology is the more superior technology of performance that high efficiency sends data on channel, this technology has used a plurality of sub-carrier frequencies in the channel width to send data.Simultaneously, ofdm system also has tolerance degree to multidiameter expansion and frequency selective fading, effectively frequency spectrum use and good characteristic such as anti-interference.At present at high-bit-rate digital subscriber line (HDSL), digital audio broadcasting (DAB), digital video broadcasting (DVB), wireless lan (wlan), wireless MAN fields such as (WMAN) obtains extensive use.

Usually the OFDM transmitting system adopts rapid fourier change (FFT) to send information through subcarrier, and adds the protection interval that Cyclic Prefix constitutes in the effective code element front portion, so that reduce multi-path influence.In a class OFDM block data transmission system is used, particularly the wireless data transmission occasion is (as WLAN (wireless local area network) IEEE802.11a, HiperLAN2, wireless MAN IEEE 802.16--OFDM pattern), add the steering signal (Preamble) that pseudo random sequence constitutes before each OFDM frame, it is synchronous to be used for frame head, Nonlinear Transformation in Frequency Offset Estimation, and channel estimating, as shown in Figure 2.

After Preamble handles, output at equalizer, receiver clock can be accurately synchronous with tranmitting data register, the not skew of FFT window this moment, but because there is frequency departure (generally within 50ppm) in the local receiver sampling clock with the transmission sampling clock, make to receive sampling clock offset launch clock gradually, cause that skew appears in the FFT window.The skew of FFT window will cause and occur the phase place rotation on current each subcarrier of OFDM symbol, and rotation amount is directly proportional with subcarrier number.

For correcting sampling frequency deviation and carrier frequency offset, the general equally distributed pilot channel (Pilots) that in the subchannel of OFDM, adds, the content receiver of pilot channel transmission can be known in advance.Accompanying drawing 4 has been described the sub-carrier phase rotation that causes the drift of FFT window to cause owing to frequency deviation of clock in the IEEE802.11a system.The each point abscissa is represented sub-carrier channels number among Fig. 4, and ordinate is represented the phase deviation amount.Wherein square dot is represented the phase deviation amount of pilot subchannel.

In demodulating process, the phase place rotation that needs this class of compensation to cause because of the skew of FFT window, as Maxime .B. Melissa Belote plucked instrument Koffsky, little Louis .R. Li Tewen is shown in the patent application 01102895.5.

In addition, when FFT window side-play amount arrives to a certain degree, just need keep synchronously, promptly move a sampled point forward or backward, also can be regarded as forward or mobile backward FFT window by the mode that changes synchronous points.Specifically, be higher than transmit clock, when the side-play amount of FFT window arrives to a certain degree, the FFT window moved a sampled point backward if receive sampling clock; Otherwise, the FFT window be moved forward a sampled point.See accompanying drawing 6.Just: if the side-play amount of the FFT window of current OFDM symbol surpasses a positive thresholding, then the FFT window moves forward once, and the side-play amount of FFT window increases a specific amount; Otherwise the side-play amount of the FFT window of current OFDM symbol is less than a negative thresholding, and window moves once backward, and FFT window side-play amount reduces by a specific amount.

By can obtain the estimation of FFT window side-play amount to the processing of pilot subchannel phase difference.Most method is to all being to come direct estimation FFT window side-play amount by the pilot signal phase difference of current OFDM symbol, noisy the time, the fluctuation of pilot signal phase difference causes the inaccurate of FFT window side-play amount estimation, causes the deterioration of overall system performance.

As shown in Figure 5, Jin Dongkui, device for carrying a tripots still all, Cui Jiongchen, Lee order and shine in patent 98104218.X, are that mould is obtained according to phase place with 2 π, adopt the phase difference zero passage to count and obtain the estimation of FFT window side-play amount.But this mode performance under low signal-to-noise ratio is bad, and estimates accurate inadequately to the phase place rotation of each subcarrier.

Jinhui's chastity, Li Xiankui is in patent application 00802091.4, formula (10) at its specification, (11) though in provided a kind of adding up and ask slope to estimate the method for side-play amount, but this method need be known the value of even number window side-play amount in advance, and big and calculation of complex of memory space and noise robustness are still good inadequately.

Summary of the invention:

There is this technical barrier of sampling frequency deviation in the present invention in order to solve in ofdm system, in the OFDM device, adopt the technical method of accurate estimating OFDM symbol FFT window side-play amount, can reduce noise to a great extent to the side-play amount estimation effect, also the just influence of compensated receiver sample clock frequency deviation more exactly.

The present invention uses the FFT window side-play amount of accurately estimating current OFDM symbol in the frame by all pilot signals that receive of current OFDM symbol.When receiving an OFDM symbol sometime, obtain FFT window side-play amount by the pilot signal phase deviation of calculating this symbol, the estimation of the side-play amount of such FFT window has big noise, directly use it to come correcting action can bring very big phase perturbation, influence the receiver overall system performance, the technology solution that the present invention proposes is to realize the side-play amount by current OFDM symbol in the same frame is added up by the calculation function device, be averaged again, obtain side-play amount poor of the FFT window between the two adjacent OFDM symbol, (because sample clock frequency deviation is stable, so can think that the difference of side-play amount of the FFT window between the two adjacent OFDM symbol is constant), the OFDM symbolic number that is received in difference by the FFT window side-play amount between the above-mentioned two adjacent OFDM symbol and the same frame like this can calculate the side-play amount of the FFT window of current OFDM symbol.As person skilled known to, the method by the sample that adds up can reduce the influence of noise to estimator, the present invention utilizes such principle to eliminate noise just, obtains the estimation of FFT window side-play amount more accurately.

Feature of the present invention in turn includes the following steps:

1. obtain channel equalizer coefficients and realize that receiver clock is just synchronous by the steering signal (Preamble) before the OFDM symbol, determine the accurate position of FFT window.

2. from the output subchannel of current OFDM symbol after, extract the pilot value of pilot channel by FFT and equilibrium, by with the comparison of predetermined pilot signal, ask phase angle deviation separately.

3. obtain average FFT window side-play amount according to following formula, be designated as shift_new (n);

$\mathrm{Shift}\_\mathrm{new}\left(n\right)=\frac{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="C20041008042000131.png,C20041008042000151.png"\; state="\{\{state\}\}">N</figure-callout>}}{2\mathrm{\&pi;}\&CenterDot;P}\&CenterDot;\underset{i=1}{\overset{P}{\mathrm{\&Sigma;}}}\frac{{\mathrm{\&theta;}}_i-\stackrel{\&OverBar;}{\mathrm{\&theta;}}}{p_i}$

Wherein:

N: n OFDM symbol of these frame data;

Shift_new (n): the FFT window side-play amount of utilizing the pilot signal of current OFDM symbol to obtain;

The number of N:OFDM system sub-carriers, promptly FFT's counts;

P: the number of an interior pilot signal of OFDM symbol,

θ _i: the phase deviation angle of i pilot signal,

The mean value of θ: P the pilot signal phase angle of deviation, $\stackrel{\&OverBar;}{\mathrm{\&theta;}}=\frac{1}{P}\underset{i=1}{\overset{P}{\mathrm{\&Sigma;}}}{\mathrm{\&theta;}}_i$

p _i: the channel number of i pilot signal

4. in same frame, will add up, add because the additional offset amount that mobile FFT window is brought is write as mathematical expression by the FFT window side-play amount that current OFDM symbol obtains:

sum_shift(n)＝sum_shift(n-1)+shift_new(n)+lack_overlap_counter(n)

Wherein, 1≤n≤M, M are total number of OFDM symbol in these frame data.

Sum_shift (n): the accumulated value of FFT window side-play amount, initial value are zero;

Shift_new (n): the FFT window side-play amount that the pilot signal of current OFDM symbol obtains;

Lack_overlap_counter (n): the number of times that the FFT window moves forward or backward, initial value are zero;

5. the computational methods of difference that obtain the FFT window side-play amount of average two adjacent OFDM symbol by the method that accumulated value is averaged are:

$\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n\&CenterDot;(n+1)}$

6. calculate the accurate estimation of side-play amount of the FFT window of current OFDM symbol, formula is as follows:

$\mathrm{est}\_\mathrm{shift}\left(n\right)=\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n+1}-\mathrm{lack}\_\mathrm{overlap}\_\mathrm{counter}\left(n\right)$

7. the FFT window side-play amount that obtains according to step 6 judges whether the FFT window of next OFDM symbol moves, and FFT window in the frame is moved time counting number.The condition of judging is: the side-play amount of the FFT window of current OFDM symbol is accurately estimated to surpass a positive thresholding, and then window moves forward once, and counter lack_overlap_counter adds 1; Otherwise the side-play amount of the FFT window of current OFDM symbol is less than a negative thresholding, and window moves once backward, and counter lack_overlap_counter subtracts 1.

8. the FFT window side-play amount that obtains according to step 6 is calculated each subchannel phase angle compensation amount, compensates the phase place rotation on each subchannel.Computing formula is as follows:

${\mathrm{\&theta;}}_k=-\frac{2\mathrm{\&pi;}\&CenterDot;\mathrm{est}\_\mathrm{shift}\left(n\right)\&CenterDot;k}{N}-\stackrel{\&OverBar;}{\mathrm{\&theta;}}$

Wherein k represents Sub-Channel Number, and θ represents the mean value of the current OFDM symbol pilot phase angle of deviation.

Description of drawings

Fig. 1 is a primary structure schematic diagram of the present invention.

Fig. 2 is a class OFDM transmission frame format figure, mainly is made of pilot signal (Preamble) and OFDM symbol two parts.

Fig. 3 is the demodulation method schematic diagram of the symbol of OFDM, removes Cyclic Prefix from each OFDM symbol, sends into the FFT module then.

Fig. 4 has described in the IEEE802.11a system because the sub-carrier phase that frequency deviation of clock causes rotation.

Fig. 5 is the structural representation of a referenced patent.

Fig. 6 is that the FFT window position moves schematic diagram.

Fig. 7 is the FFT window deviation rough estimate value sequence figure of each OFDM symbol, i.e. shift_new sequence chart.

Fig. 8 is the sequence chart that the FFT window deviation of each OFDM symbol is accurately estimated, i.e. est_shift sequence chart.

Fig. 9 is the concrete enforcement block diagram of pilot extraction and FFT window rough estimate module (6) among Fig. 1.

Figure 10 is that module among Fig. 1 (7) FFT window skew accumulation is specifically implemented block diagram with smart estimation module

Figure 11 is that concrete implementing procedure figure is judged in the adjustment of module among Fig. 1 (10) FFT window.

Embodiment

Based on embodiment of the present invention, the receiver clock frequency departure compensation in the WLAN (wireless local area network) of application IEEE 802.11a agreement with reference to accompanying drawing, provides concrete implementation step:

1. receiver is made carrier frequency synchronization after receiving steering signal (Preamble), clock synchronization and channel estimation works, and channel estimation coefficient passed to equalizer, and trigger the work of FFT window controller.

2. the each OFDM symbol that receives of receiver passes through FFT module and equalizer module by FFT window controller intercepting data division wherein.

3. accompanying drawing 9 is depicted as the concrete enforcement block diagram of (6) pilot extraction of module among Fig. 1 and the rough estimate of FFT window.Output obtains the-21 ,-7,7 and the pilot value of 21 channels in each subchannel after equilibrium, try to achieve four pilot signal phase angles by arc tan unit (40), again by phase angle difference computing unit (42), deduct the pilot value phase angle (0 or π) of precognition, obtain the phase deviation angle of four pilot tones.

4. after deducting average calculation unit (44) by phase angle difference, again by removing Sub-Channel Number computing unit (46), the phase angle difference straight slope that is calculated respectively, again by asking average calculation unit (48) to obtain the phase angle difference straight slope of current OFDM symbol, i.e. the rough estimate of FFT window skew.

5. accompanying drawing 10 is that module among Fig. 1 (7) FFT window skew accumulation is specifically implemented block diagram with smart estimation module.By the FFT window side-play amount unit (50) that adds up, the FFT window side-play amount that will obtain by current OFDM symbol in same frame adds up, by additional FFT window side-play amount unit (52), add the additional window side-play amount of being brought owing to mobile FFT window again, the following formula of specific implementation foundation:

sum_shift(n)＝sum_shift(n-1)+shift_new(n)+lack_overlap_counter(n)

Wherein, n represents n the OFDM symbol that begins from Signal;

Sum_shift (n) is the accumulated value of FFT window side-play amount, and initial value is zero;

Shift_new (n) is the FFT window side-play amount that the pilot signal of current OFDM symbol obtains;

Lack_overlap_counter (n) is the number of times that moves forward or backward by current OFDM symbol FFT window, and initial value is zero.

6. then by cumulant divider (54), and subtract additional FFT window side-play amount unit (56), obtain the accurate estimation of side-play amount of the FFT window of current OFDM symbol.This step computing formula is as follows:

$\mathrm{est}\_\mathrm{shift}\left(n\right)=\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n+1}-\mathrm{lack}\_\mathrm{overlap}\_\mathrm{counter}\left(n\right)$

Wherein:

Est_shift (n) represents the accurate estimation to current OFDM symbol FFT window side-play amount,

Sum_shift (n) is the accumulated value of FFT window offset amount, and initial value is zero;

N the OFDM symbol that the n representative begins from Signal;

Lack_overlap_counter (n) is the number of times that the FFT window moves forward or backward, and initial value is zero.

7. accompanying drawing 11 is concrete implementing procedure figure of module among Fig. 1 (10).Whether the accurate estimated value est_shift of side-play amount (n) that judges the FFT window of current OFDM symbol surpasses a positive thresholding (being taken as 0.6) (60), and then counter lack_overlap_counter adds 1 (62); Whether then judge est_shift (n) less than a negative thresholding-0.6 (64), if set up, counter lack_overlap_counter subtracts 1 (66).Then change and adjust FFT window position (68) according to the value of lack_overlap_counter.

8. adjust the phase place of each subchannel of current sign according to the FFT window side-play amount of accurate estimation, module is made of a multiplication unit and adder unit, and is as follows according to formula:

${\mathrm{\&theta;}}_k=-\frac{\mathrm{\&pi;}\&CenterDot;\mathrm{est}\_\mathrm{shift}\left(n\right)\&CenterDot;k}{32}-\stackrel{\&OverBar;}{\mathrm{\&theta;}},$ -26≤k≤-1，1≤k≤26

Wherein k represents Sub-Channel Number, θ from unit (44) in the accompanying drawing 9 calculate the mean value of four pilot phase angles of deviation.

Module described herein and unit both can adopt hardware to realize, also can adopt software to realize, or the compound mode of software and hardware realized.The technology of the present invention method is not limited to the foregoing description, and those skilled in the art are understood that the change that can make within the scope of the present invention on various forms and the details.Be that the present invention can be used for meeting the system of IEEE 802.11a standard, HiperLAN2 standard, IEEE 802.16 standards and the system of other employings OFDM; Great advantage of the present invention is the principle according to " asking average method can reduce the influence that noise is treated estimator by the sample that adds up ", the creationary introducing this technical process that " side-play amount by current OFDM symbol in the same frame added up; be averaged again; obtain side-play amount poor of the intersymbol FFT window of two adjacent OFDM " is estimated in order to the side-play amount that realizes accurate more current OFDM symbol FFT window.From the realization effect of this technology, be that measuring and calculating accuracy or system's antijamming capability general relatively " the sample clock frequency deviation compensation of receiver " method has all had large increase.

Claims (9)

1. method of proofreading and correct sample clock frequency deviation in the orthogonal frequency division multiplex OFDM receiver, this method comprises the following steps:

By processing, obtain the coefficient of equalizer and realize the first synchronous of sampling clock the aiming symbol preamble before the OFDM symbol;

From through extracting the pilot signal Pilots that inserts at interval with rule the current OFDM symbol after the equilibrium, obtain the pilot phase angle of deviation according to current OFDM symbol pilot signal, obtain the rough estimate of FFT window side-play amount;

These frame data are added up by the rough estimate of the FFT of current OFDM sign computation window side-play amount, to current OFDM symbol, by adding up by the rough estimate of each OFDM symbol FFT of current OFDM symbol window side-play amount in the same frame, obtain the FFT window side-play amount rough estimate of accumulative total, formula is as follows:

sum_shift(n)＝sum_shift(n-1)+shift_new(n)+lack_overlap_counter(n) (1)

1≤n≤M, M are total number of OFDM symbol in these frame data, when adding up, and for the rough estimate of current OFDM symbol FFT window side-play amount, the influence that brought of FFT window adjustment before also need adding, i.e. numerical value among the lack_overlap_counter, wherein:

Shift_new (n): the FFT window side-play amount rough estimate that obtains according to the pilot signal of current OFDM symbol;

Sum_shift (n): the accumulated value of FFT window side-play amount rough estimate, initial value are zero;

Lack_overlap_counter (n): the number of times that the FFT window moves forward or backward, initial value are zero;

Employing asks average method to calculate the mean value of difference of the FFT window side-play amount rough estimate of adjacent OFDM symbol, and the mean value calculation method of the difference of the FFT window side-play amount rough estimate of adjacent OFDM symbol is:

$\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n\&CenterDot;(n+1)}---\left(2\right)$

Then the FFT window side-play amount of current OFDM symbol is accurately estimated, after the mean value of difference that calculates the FFT window side-play amount rough estimate of average adjacent OFDM symbol multiply by the OFDM symbolic number of current reception, again

$\mathrm{est}\_\mathrm{shift}\left(n\right)=\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n+1}-\mathrm{lack}\_\mathrm{overlap}\_\mathrm{counter}\left(n\right)---\left(3\right)$

Deduct this before because the number of times that the FFT window moves forward or backward just obtains the accurate estimation of the FFT window side-play amount of current OFDM symbol, as shown in Equation (3):

Wherein: est_shift (n): to the accurate estimation of current OFDM symbol FFT window side-play amount;

Phase place rotation according to current each subcarrier of OFDM symbol after the accurate estimation compensation equilibrium of the FFT window side-play amount that obtains;

Simultaneously adjust next OFDM symbol FFT window position according to the accurate estimation of FFT window side-play amount.

2. method according to claim 1, be characterised in that: pilot signal is through extracting the specific subcarrier after balanced from FFT output, relatively obtain its phase deviation angle from the pilot signal of extraction and the pilot value of precognition, the FFT window side-play amount rough estimate of single OFDM symbol is that the slope by phase deviation angle sequence calculates, as shown in Equation (4):

$\mathrm{shift}\_\mathrm{new}\left(n\right)=\frac{N}{2\mathrm{\&pi;}\&CenterDot;P}\&CenterDot;\underset{i=1}{\overset{P}{\mathrm{\&Sigma;}}}\frac{{\mathrm{\&theta;}}_i-\stackrel{\&OverBar;}{\mathrm{\&theta;}}}{p_i}---\left(4\right)$

Wherein:

N: n OFDM symbol of these frame data;

Shift_new (n): the FFT window side-play amount rough estimate that obtains according to the pilot signal of current OFDM symbol;

The number of N:OFDM system sub-carriers, promptly FFT's counts;

P: the number of an interior pilot signal Pilots of OFDM symbol;

θ _i: the phase deviation angle of i pilot signal, unit is a radian;

p _i: the subcarrier number of i pilot signal;

The mean value of θ: P the pilot signal phase angle of deviation;

$\stackrel{\&OverBar;}{\mathrm{\&theta;}}=\frac{1}{P}\underset{i=1}{\overset{P}{\mathrm{\&Sigma;}}}{\mathrm{\&theta;}}_i.$

3. according to the method for claim 1, be characterised in that: if the accurate estimation of current sign FFT window side-play amount surpasses a positive thresholding, then next OFDM symbol FFT window moves forward once, and lack_overlap_counter adds 1; If the accurate estimation of current FFT window side-play amount is less than a negative thresholding, then next OFDM symbol FFT window moves once backward, and the lack_overlap_counter value subtracts 1.

4. according to the method for claim 1, be characterised in that: the accurate estimation of FFT window side-play amount according to the current OFDM symbol that calculates can be tried to achieve sampling clock deviation.

5. one kind is used to proofread and correct because the device of the side-play amount of the FFT window of the OFDM symbol that sampling frequency deviation brought in the orthogonal frequency division multiplex OFDM receiver, and its feature comprises:

Be used for going out the module of its FFT window side-play amount rough estimate from the single OFDM sign computation that receives, each FFT window side-play amount rough estimate by current OFDM symbol in the same frame is added up, obtain the FFT window side-play amount rough estimate of accumulative total, adopt the described method of formula (5) to calculate:

Sum_shift (n)=sum_shift (n-1)+shift_new (n)+lack_overlap_counter (n) (5) 1≤n≤M, M is total number of OFDM symbol in these frame data, when adding up, for the rough estimate of current OFDM symbol FFT window side-play amount, the influence that the adjustment of FFT window is brought before also need adding, be the numerical value among the lack_overlap_counter, wherein:

Shift_new (n): the FFT window side-play amount rough estimate that obtains according to the pilot signal of current OFDM symbol;

Sum_shift (n): the accumulated value of FFT window side-play amount rough estimate, initial value are zero;

Lack_overlap_counter (n): the number of times that the FFT window moves forward or backward, initial value are zero;

Be used for the FFT window side-play amount rough estimate cumulative mean of the OFDM symbol in the frame of all receptions is calculated the accurate estimation module of current OFDM symbol FFT window side-play amount, calculate poor that the FFT window side-play amount of adjacent OFDM symbol accurately estimates by the method that accumulated value is averaged, adopt the described method of formula (6) to calculate:

$\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n\&CenterDot;(n+1)}---\left(6\right)$

$\mathrm{est}\_\mathrm{shift}\left(n\right)=\frac{2\&CenterDot;\mathrm{sum}\_\mathrm{shift}\left(n\right)}{n+1}-\mathrm{lack}\_\mathrm{overlap}\_\mathrm{counter}\left(n\right)---\left(7\right)$

With the module that this OFDM symbol is proofreaied and correct in the accurate estimation of current OFDM symbol FFT window side-play amount, the accurate estimation of adopting the described method of formula (7) to calculate the FFT window side-play amount of current OFDM symbol:

Wherein: est_shift (n): to the accurate estimation of current OFDM symbol FFT window side-play amount;

And judge the module whether next OFDM symbol FFT window is shifted with the accurate estimation of current sign FFT window side-play amount.

6. according to the device of claim 5, be characterised in that: described being used for goes out the module of its FFT window side-play amount rough estimate from the single OFDM sign computation that receives, be from the single OFDM symbol that is received, to extract pilot signal, and calculate the module of FFT window side-play amount rough estimate thus.

7. according to the device of claim 5, be characterised in that: the described accurate estimation module that is used for the FFT window side-play amount rough estimate cumulative mean of the OFDM symbol in the frame of all receptions is calculated current OFDM symbol FFT window side-play amount, be to add up by the current OFDM symbol FFT window side-play amount rough estimate that receives in the frame, comprise also that wherein this module adopts the described method in formula (5) and (7) to calculate because the FFT window moves the mobile forward or backward number of times of FFT window that is brought.

8. according to the device of claim 5, be characterised in that: the effect of proofreading and correct the module of this OFDM symbol with the accurate estimation of current OFDM symbol FFT window side-play amount is, accurate estimation according to the FFT window side-play amount that is calculated compensates current OFDM symbol by the data on each subcarrier behind the equalizer, to eliminate the phase place rotation that the skew of FFT window brings, so also just eliminated the error that sampling clock deviation brought.

9. according to the device of claim 5, be characterised in that:, judge whether next OFDM symbol FFT window needs to be shifted forward or backward with the accurate estimation of the FFT window side-play amount of current OFDM symbol.

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