CN100499622C - OFDM time and frequency synchronization method - Google Patents

Abstract

This invention provides OFDM time frequency synchronous method, which contains making slide correlation to receiver signal and making time synchronism by circulation prefix in OFDM symbol to obtain the synchronous peak value phase information, the time synchronism can be obtained without adding leading cell in transmitter end, which raises spectrum efficiency and avoiding synchronism blooming, greatly reducing calculation and synchronism time delay, said invention has relative stable correlation time calculation quantity without influence to synchronism performance.

Description

A kind of method of OFDM Time and Frequency Synchronization

Technical field

The present invention relates to the technical field of data transmission in the mobile communication technology, be meant the method for a kind of OFDM (OFDM) Time and Frequency Synchronization especially.

Background technology

OFDM (OFDM, Orthogonal Frequency Division Multiplexing) is to utilize parallel transmission to improve a kind of mobile communication technology of communication data transmission rate.The basic thought of this technology is in frequency domain given channel to be divided into many orthogonal sub-channels, uses a subcarrier to modulate on each subchannel, and each subcarrier parallel transmission.Like this, although total channel be non-flat forms, have frequency selectivity, but each subchannel is a relatively flat, what carry out on each subchannel is narrow band transmission, and signal bandwidth is less than the respective bandwidth of channel, so the interference between the erasure signal waveform greatly.OFDM is that its allows subcarrier spectrum to overlap with respect to the difference of general multi-carrier transmission, as long as satisfy between subcarrier mutually orthogonally, just can isolate data-signal from the subcarrier of aliasing.

Because allowing subcarrier spectrum to mix, OFDM falls, its spectrum efficiency improves greatly, simultaneously, this technology also has the anti-multipath interference and intersymbol interference, channel estimating and equilibrium realize many advantages such as easy, that system's implementation complexity is low, thereby is a kind of modulation system efficiently.And this technology is easy to combine with various multiple access technologies, thereby generally believed it is indispensable core technology in the 4th third-generation mobile communication system.This technology is widely used in digital audio broadcasting (DAB), digital video broadcasting (DVB), ADSL (Asymmetric Digital Subscriber Line) (ADSL), wireless lan (wlan), wireless MAN (WMAN), Wireless Personal Network (WPAN), the unauthorized metropolitan area network of wireless high-speed many data communication systems such as (WHUMAN) at present, and 802.20 mobile wide-band wire-less accessing systems that Institute of Electrical and Electric Engineers (IEEE) standardization body is being discussed at present also will adopt this modulation technique.

The OFDM technology has above-mentioned numerous advantage, but it is to Time and Frequency Synchronization, and especially the requirement of Frequency Synchronization is very high, otherwise just causes disturbing between intersymbol interference (ISI) and subcarrier (ICI) easily.With IEEE 802.16a wireless MAN is example, require the residual frequency departure must be less than 2% of subcarrier spacing, therefore, the carrier frequency synchronization in the ofdm system, promptly compensating local carrier and the frequency offset of launching intercarrier, is important key technology in this system.

In ofdm system,, before each OFDM symbol Cyclic Prefix is arranged all for fear of intersymbol interference (ISI).The OFDM symbol is made of subcarrier in frequency domain, and the number of subcarrier has determined counting of time-frequency conversion (FFT).Subcarrier has three types, and it is respectively data subcarrier, pilot sub-carrier and virtual subnet carrier wave.Wherein, data subcarrier is used for transfer of data; Pilot sub-carrier is used for eliminating residual differing at first, and along with the development of technology, the effect of pilot sub-carrier further enlarges, and can be used to carry out Frequency Synchronization and channel estimating.The virtual subnet carrier wave is meant the carrier wave that does not send any data, and ofdm system is introduced the interference of adjacent band in order to reduce.

The even pectination interleaved plan of the general employing of pilot sub-carrier in the ofdm system equally spaced is distributed on the subcarrier, and the value on each pilot sub-carrier is produced by known pseudorandom number generator.The frequency-region signal structure of each symbol as shown in Figure 1 in the ofdm system.Among Fig. 1,

Represent the virtual subnet carrier wave;

The representative data subcarrier;

Represent pilot sub-carrier.Be spaced apart fixed value d between each pilot sub-carrier.

United States Patent (USP) 5,732,113 disclose the method for a kind of OFDM time and Frequency Synchronization.This method is inserted the leading cell that structure is special at transmitting terminal, utilizes this leading cell to realize Time and Frequency Synchronization.This leading cell is made of two OFDM symbol (symbol) SYN_A and SYN_B, and wherein front and back two parts of SYN_A are identical, and receiving terminal utilizes this cell to finish the time synchronized and the mark frequency offset estimating of ofdm system in time domain.Then the mark compensate of frequency deviation that estimates is fallen, and SYN_A and SYN_B are transformed to frequency domain, utilize the correlation of SYN_A and SYN_B on the frequency domain to finish the estimation of integer frequency bias.This method can realize Time and Frequency Synchronization fast, and has rational computation complexity.

After the OFDM time-frequency synchronization method that this patent is announced, many scholars optimize it and improve.Such as leading cell is reduced to a part, is changed the structure of leading cell etc. by two parts.Thus, the overall procedure block diagram of existing OFDM Time and Frequency Synchronization as shown in Figure 2.

Step 201, time synchronized.It is that targeting sequencing (preamble) carries out Time and Frequency Synchronization that ofdm system adopts leading cell to the received signal, promptly obtains time synchronized by the two sections identical data in front and back are correlated with, thereby obtains the sync peaks phase information of received signal.

Step 202, mark frequency deviation (FFO) is estimated.The sync peaks phase information of utilizing time synchronized to obtain is carried out the mark frequency offset estimating.

Step 203 is gone the mark frequency deviation.Revise according to the signal that the mark frequency offset estimating information butt joint that estimates is received, make only to have integer frequency bias in the revised received signal.

Step 204, time-frequency conversion (FFT).This received signal is transformed into frequency domain to be estimated to carry out integer frequency bias.

Step 205, integer frequency bias (IFO) is estimated.According to integer multiple frequency biasing formula, utilize the pilot tone mobile phase to close and carry out the integer frequency bias estimation, realize Time and Frequency Synchronization.

At the structure chart of OFDM symbol shown in Figure 1 in frequency domain, its integer multiple frequency is setovered formula as the formula (1):

${\mathrm{\ϵ}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\Σ}}{(Y_{n+1}\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}\right|---\left(1\right)$

Wherein, ε _IThe biasing of expression integer multiple frequency,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p _i+ g mould N _FFTAfter value, * represents to get complex conjugate.

The defective of said method is: no matter be the described method of United States Patent (USP), still the method after improving, all need increase a leading cell at the front end of emission's information, by leading cell is that targeting sequencing (preamble) carries out Time and Frequency Synchronization and channel estimating, certainly will bring extra expense to system like this, cause the spectrum efficiency of system to descend.More in short-term, this shortcoming is particularly evident in data to be transmitted.And, when ofdm system is used for mobile environment, need carry out channel estimating in real time, only carry out channel estimating and can not satisfy system requirements with targeting sequencing.

In addition, utilize pilot tone to move to be correlated with that to carry out the operand that integer frequency bias estimates very big, and synchronization delayed time is increased.With IEEE 802.16a OFDM (OFDMA) pattern is example, is spaced apart 11 subcarriers between the adjacent pilot frequencies, like this under worst case, need carry out that 11 times move is relevant just to obtain required peak value.Simultaneously, it can also be seen that, when this method is setovered greater than pilot interval in integer frequency, can occur bluring synchronously, promptly can't obtain correct Frequency Synchronization, thereby cause system normally to move by formula (1).

Summary of the invention

In view of this, the invention provides a kind of method of OFDM Time and Frequency Synchronization, an one purpose is in the communication system based on the OFDM modulation technique, need not add leading cell at transmitting terminal and can realize Time and Frequency Synchronization, thereby reduce the overhead of system, improve spectrum efficiency; Another object of the present invention is to avoid Frequency Synchronization fuzzy, the amount of calculation when reducing Frequency Synchronization.

For achieving the above object, technical scheme of the present invention is achieved in that

A kind of method of OFDM Time and Frequency Synchronization, this method may further comprise the steps:

A, carry out time synchronized to the received signal, obtain the sync peaks phase information of received signal;

B, carry out the mark frequency offset estimating according to the described sync peaks phase information of step a, and revise according to the signal that this mark frequency offset estimating information butt joint is received, make only to have integer frequency bias in the revised received signal, then, this received signal is transformed into frequency domain;

C, determine the actual virtual subnet carrier wave original position of this frequency-region signal that receives by the moving average or the summation of sliding, and obtain the poor of the desirable virtual subnet carrier wave original position of the frequency-region signal that receives and described actual virtual subnet carrier wave original position, then, value with the difference of this position is the center again, carries out integer frequency bias and estimates.

Preferably, the described method of carrying out time synchronized to the received signal of step a is: utilize the time window that equates with circulating prefix-length, it is relevant to slide to the received signal, relies on the Cyclic Prefix in the orthogonal frequency division multiplex OFDM symbol to carry out time synchronized.

Preferably, circulating prefix-length during more than or equal to system applies the time delay expansion and signal to noise ratio is determined when counting, described step a adopts a time window that equates with circulating prefix-length; Circulating prefix-length during less than system applies the time delay expansion and signal to noise ratio is determined when counting, described step a adopts the time window that equates with circulating prefix-length more than, and is the interval with the OFDM symbol lengths between each time window.

Preferably, the described method of obtaining the actual virtual subnet carrier wave original position of the frequency-region signal that receives of step c is: the actual virtual subnet carrier wave original position of obtaining this frequency-region signal by the moving average or the summation of sliding.

Preferably, described when the frequency-region signal that receives is carried out moving average or slides summation, the maximum frequency deviation position that allows from system begins to carry out smoothly.

Preferably, when the information of carrying on each pilot sub-carrier on the constant and adjacent OFDM symbol of pilot frequency locations between, adjacent OFDM symbol identical when pilot frequency information between adjacent OFDM symbol is identical, the described integer frequency bias that carries out is estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}\right|$ Determine integer multiple frequency biasing ε _IWherein,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p ^I+gMould N _FFTAfter value, ^*Complex conjugate is got in expression.

Preferably, when pilot frequency locations between adjacent OFDM symbol on constant and n+1 OFDM symbol and n the OFDM symbol ratio of the value on i pilot sub-carrier be C _n(i) time, the described integer frequency bias that carries out is estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}{C}_n{\left(i\right)}^{*}\right|$ Determine integer multiple frequency biasing ε _IWherein, Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p ^I+gMould T _FFTAfter value, ^*Complex conjugate is got in expression.

Preferably, when the position of i pilot sub-carrier differed the individual subcarrier of d (i) between identical and adjacent OFDM symbol when pilot frequency information between adjacent OFDM symbol, the described integer frequency bias that carries out was estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+d\left(i\right)+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}\right|$ Determine integer multiple frequency biasing ε I; Wherein,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p ^I+gMould N _FFTAfter value, ^*Complex conjugate is got in expression.

Preferably, the ratio of the value on i pilot sub-carrier on n+1 OFDM symbol and n the OFDM symbol is C _nWhen the position of i pilot sub-carrier differed the individual subcarrier of d (i) (i) and between adjacent OFDM symbol, the described integer frequency bias that carries out was estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+d\left(i\right)+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}{C}_n{\left(i\right)}^{*}\right|$ Determine integer multiple frequency biasing ε _IWherein,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p _i+ g] N _FFTExpression p _i+ g mould N _FFTAfter value, ^*Complex conjugate is got in expression.

The time window that utilization of the present invention equates with circulating prefix-length, it is relevant to slide to the received signal, rely on the Cyclic Prefix in the OFDM symbol to carry out time synchronized, obtain the sync peaks phase information of received signal, make in communication system based on the OFDM modulation technique, need not add leading cell and can realize time synchronized, thereby reduce the overhead of system, improve spectrum efficiency at transmitting terminal.Simultaneously, the characteristic of combined with virtual subcarrier of the present invention is carried out the integer frequency bias rough estimate, the synchronous blooming when having avoided integer frequency bias to estimate, and greatly reduce mobile relevant operand, thus reduced synchronization delayed time.For different frequency offsets, the method for the invention all has metastable associated numbers of times and amount of calculation, and the integer frequency bias estimation performance finally still guarantees by moving to be correlated with, thus to net synchronization capability without any influence.

Description of drawings

Figure 1 shows that the frequency-region signal structural representation of each OFDM symbol;

Figure 2 shows that prior OFDM system realizes the The general frame of Time and Frequency Synchronization;

Figure 3 shows that the The general frame of ofdm system realization Time and Frequency Synchronization of the present invention;

Figure 4 shows that a frequency-region signal example;

Figure 5 shows that the frequency-region signal among Fig. 4 carries out moving average figure afterwards.

Embodiment

For making technical scheme of the present invention clearer, the present invention is described further again below in conjunction with accompanying drawing.

Thinking of the present invention as shown in Figure 3, Fig. 3 is the The general frame that ofdm system of the present invention is realized Time and Frequency Synchronization.

Step 301, time synchronized.Utilize the time window that equates with circulating prefix-length, it is relevant to slide to received signal, relies on the Cyclic Prefix in the OFDM symbol to carry out time synchronized.

Step 302, mark frequency deviation (FFO) is estimated.The phase information of the sync peaks that obtains when utilizing time synchronized is carried out the mark frequency offset estimating.

Step 303 is gone the mark frequency deviation.The mark frequency deviation information that utilization estimates is revised to received signal, makes only to have integer frequency bias in the revised received signal.

Step 304, time-frequency conversion (FFT).Received signal is transformed into frequency domain to be estimated to carry out integer frequency bias.

Step 305, integer frequency bias (IFO) rough estimate.Utilizing virtual subnet carrier transmission data is zero characteristic, and integer frequency bias is carried out preliminary estimation, obtains general sync bit.

Step 306, integer frequency bias is smart to be estimated.Utilize the certainty of the pilot sub-carrier information on former and later two adjacent OFDM symbol to carry out the smart estimation of integer frequency bias, realize Time and Frequency Synchronization.

In the OFDM Time and Frequency Synchronization scheme proposed by the invention, step 302 is consistent with traditional OFDM time-frequency synchronization method to step 304, below emphasis the implementation method of step 301, step 305 and step 306 is described in detail.

In step 301, utilize the time window that equates with circulating prefix-length, it is relevant to slide to received signal, relies on the Cyclic Prefix in the OFDM symbol to carry out time synchronized.For example, in the long ofdm system of Cyclic Prefix such as IEEE802.16aOFDMA pattern, the length of Cyclic Prefix during more than or equal to system applies the time delay expansion and signal to noise ratio is determined counts, during as 64, adopt a time window that equates with circulating prefix-length can obtain good time synchronized performance.Cyclic Prefix in ofdm system is shorter, time delay expansion as the length of Cyclic Prefix during and signal to noise ratio is determined counts less than system applies, during as 64, adopt more than one and to slide relevant to receiving data with the isometric time window of Cyclic Prefix, be the interval with the OFDM symbol lengths between these time windows, can obtain good time synchronized performance equally.

Figure 4 shows that a frequency-region signal example.In the illustrated embodiment, it is 2048 points that FFT counts, and signal to noise ratio is 8dB, the frequency-region signal when integer frequency bias is 30 subcarrier spacings.Its abscissa is the position of subcarrier, and ordinate is an amplitude.Because the virtual subnet carrier wave is the amplitude of not transmitting any information in ofdm system is 0 subcarrier, and its effect is to reduce the interference of ofdm system to nearby frequency bands.Except DC component, remaining all is distributed in the both sides of frequency band, and under nothing was made an uproar environment, amplitude was zero on the cross-talk carrier wave of data in the middle of carrying out showing as behind the FFT to receiving.Therefore pass through multipath channel and add after the Gaussian noise that the signal strength signal intensity relative data subcarrier on the virtual subnet carrier wave is still very low.

The implementation method of the described integer frequency bias rough estimate of step 305 is utilized the above-mentioned characteristic of virtual subnet carrier wave just, the mould value of frequency-region signal (absolute value of real part or imaginary part also can) is carried out moving average, like this, a minimum value will appear in the original position at virtual carrier.This minimum value is actual virtual subnet carrier wave original position, and then obtains position poor of the minimum value that desirable virtual subnet carrier wave original position and actual virtual subnet carrier wave original position promptly smoothly obtain.The difference of this position is integer frequency bias rough estimate evaluation.For further reducing computation complexity, can begin to carry out smoothly from the maximum frequency deviation position that system allows.

Fig. 5 has provided the frequency-region signal among Fig. 4 and has carried out moving average figure afterwards.After smoothing processing, in virtual subnet carrier wave original position, a very sharp-pointed minimum has appearred as can be seen from the figure.Because this minimizing position is actual virtual subnet carrier wave original position, thereby can obtain integer frequency bias rough estimate evaluation at an easy rate.

The smart implementation method of estimating of the described integer frequency bias of step 306 is: the integer frequency bias rough estimate evaluation that obtains during with the integer frequency bias rough estimate is the center, application formula (1), calculate maximum by the value that changes g, carry out the smart estimation of integer frequency bias, thereby realize Time and Frequency Synchronization.

When carrying out the integer frequency bias rough estimate, can obtain the frequency deviation position comparatively accurately, because the rough estimate error is much smaller than pilot sub-carrier at interval, therefore when next carrying out the smart estimation of integer frequency bias, can not occur fuzzy synchronously.In addition, tentatively determined frequency offset during owing to rough estimate, therefore when carrying out the smart estimation of integer frequency bias, can reduce significantly and move the number of times of being correlated with.This method adopts smooth operation when the integer frequency bias rough estimate, smoothly only need addition and subtraction at every turn, and complexity is very low.For different frequency offsets, this method all has metastable associated numbers of times and amount of calculation, and the integer frequency bias estimation performance finally still guarantees by moving to be correlated with, thus to net synchronization capability without any influence.

Certainly, above-mentioned integer frequency bias rough estimate is not limited to use the method for moving average, can also utilize slip summation or other possible method to realize.

Above-described integer frequency bias is smart estimates to be based on that formula (1) carries out, and formula (1) is that pilot frequency information is identical between adjacent OFDM symbol, pilot frequency locations is constant between adjacent OFDM symbol, and draw under the identical prerequisite of the information of carrying on each pilot sub-carrier on the adjacent OFDM symbol.

If pilot frequency information is not simultaneously between adjacent OFDM symbol, can utilize the certainty of pilot frequency information on the adjacent OFDM symbol equally, adopt the method for the invention to carry out Frequency Synchronization, only need that formula (1) is done change slightly and get final product.The ratio of supposing on n+1 OFDM symbol and n the OFDM symbol value on i the pilot sub-carrier is C _n(i), then between the adjacent OFDM symbol value on i pilot sub-carrier have following relation:

X _n+1(P _i)＝X _n(P _i)C _n(i) (2)

Wherein, X _n(P _i) transmit X on n OFDM symbol of expression on i pilot sub-carrier _N+1(P _i) transmitting on i pilot sub-carrier on n+1 OFDM symbol of expression, then formula (1) will be replaced by following formula

${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}{C}_n{\left(i\right)}^{*}\right|---\left(3\right)$

Like this, when between adjacent OFDM symbol, using method of the present invention under the different situation of pilot frequency information, only need to calculate and get final product carrying out using when integer frequency bias is smart to be estimated formula shown in the formula (3).

If pilot frequency locations is variable between adjacent OFDM symbol, suppose that then the position of i pilot sub-carrier between adjacent OFDM symbol differs the individual subcarrier of d (i),

When the information of carrying on each pilot sub-carrier on adjacent OFDM symbol is identical, only need to change formula (1) into following form

${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+d\left(i\right)+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}\right|---\left(4\right)$

The information of carrying on each pilot sub-carrier on the adjacent OFDM symbol supposes that it satisfies the described relation of formula (2), then changes formula (1) into following form not simultaneously

${\mathrm{\&epsiv;}}_I=\underset{g}{\max }\left|\underset{i}{\mathrm{\&Sigma;}}{(Y_{n+1}\left({[P_i+d\left(i\right)+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)}^{*}{C}_n{\left(i\right)}^{*}\right|---\left(5\right)$

Under the variable situation of pilot frequency locations between adjacent OFDM symbol, when using method of the present invention, only need to calculate and get final product carrying out using when integer frequency bias is smart to be estimated formula shown in formula (4) or the formula (5).

The above only is preferred embodiment of the present invention, and is in order to restriction the present invention, within the spirit and principles in the present invention not all, any modification of being done, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (8)

1, a kind of method of OFDM Time and Frequency Synchronization is characterized in that, this method may further comprise the steps:

A, carry out time synchronized to the received signal, obtain the sync peaks phase information of received signal;

B, carry out the mark frequency offset estimating according to the described sync peaks phase information of step a, and revise according to the signal that this mark frequency offset estimating information butt joint is received, make only to have integer frequency bias in the revised received signal, then, this received signal is transformed into frequency domain;

C, determine the actual virtual subnet carrier wave original position of this frequency-region signal that receives by the moving average or the summation of sliding, and obtain the poor of the desirable virtual subnet carrier wave original position of the frequency-region signal that receives and described actual virtual subnet carrier wave original position, value with the difference of this position is the center again, carries out integer frequency bias and estimates.

2, method according to claim 1, it is characterized in that, the described method of carrying out time synchronized to the received signal of step a is: utilize the time window that equates with circulating prefix-length, it is relevant to slide to the received signal, relies on the Cyclic Prefix in the orthogonal frequency division multiplex OFDM symbol to carry out time synchronized.

3, method according to claim 2 is characterized in that, circulating prefix-length during more than or equal to system applies the time delay expansion and signal to noise ratio is determined when counting, described step a adopts a time window that equates with circulating prefix-length; Circulating prefix-length during less than system applies the time delay expansion and signal to noise ratio is determined when counting, described step a adopts the time window that equates with circulating prefix-length more than, and is the interval with the OFDM symbol lengths between each time window.

4, method according to claim 1 is characterized in that, described when the frequency-region signal that receives is carried out moving average or slides summation, the maximum frequency deviation position that allows from system begins to carry out smoothly.

5, according to arbitrary described method in the claim 1 to 4, it is characterized in that, when the information of carrying on each pilot sub-carrier on the constant and adjacent OFDM symbol of pilot frequency locations between, adjacent OFDM symbol identical when pilot frequency information between adjacent OFDM symbol is identical, the described integer frequency bias that carries out is estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }|\underset{i}{\mathrm{\&Sigma;}}(Y_{n+1}\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)*|$ Determine integer multiple frequency biasing ε _IWherein,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p _i+ g mould N _FFTAfter value, ^*Complex conjugate is got in expression.

According to arbitrary described method in the claim 1 to 4, it is characterized in that 6, the ratio of the value on i pilot sub-carrier is C on constant and n+1 OFDM symbol and n the OFDM symbol when pilot frequency locations between adjacent OFDM symbol _n(i) time, the described integer frequency bias that carries out is estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }|\underset{i}{\mathrm{\&Sigma;}}(Y_{n+1}\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)*C_n\left(i\right)*|$ Determine integer multiple frequency biasing ε _IWherein,

Represent n the received signal on the subcarrier, Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts,

Expression p _i+ g mould N _FFTAfter value, ^*Complex conjugate is got in expression.

7, according to arbitrary described method in the claim 1 to 4, it is characterized in that, when the position of i pilot sub-carrier differs the individual subcarrier of d (i) between identical and adjacent OFDM symbol when pilot frequency information between adjacent OFDM symbol, the described integer frequency bias that carries out is estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }|\underset{i}{\mathrm{\&Sigma;}}(Y_{n+1}\left({[P_i+d\left(i\right)+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)*|$ Determine integer multiple frequency biasing ε _IWherein,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts, Expression p _i+ g mould N _FFTAfter value, ^*Complex conjugate is got in expression.

According to arbitrary described method in the claim 1 to 4, it is characterized in that 8, the ratio of the value on i pilot sub-carrier on n+1 OFDM symbol and n the OFDM symbol is C _nWhen the position of i pilot sub-carrier differed the individual subcarrier of d (i) (i) and between adjacent OFDM symbol, the described integer frequency bias that carries out was estimated as: the value with the difference of described position is the center, according to ${\mathrm{\&epsiv;}}_I=\underset{g}{\max }|\underset{i}{\mathrm{\&Sigma;}}(Y_{n+1}\left({[P_i+d\left(i\right)+g]}_{N_{\mathrm{FFT}}}\right)Y_n\left({[P_i+g]}_{N_{\mathrm{FFT}}}\right)*C_n\left(i\right)*|$ Determine integer multiple frequency biasing ε _IWherein,

Represent n the received signal on the subcarrier,

Represent n+1 the received signal on the subcarrier, P _iThe position of representing i pilot sub-carrier, g is for satisfying $-\frac{d}{2}<g\&le;\frac{d}{2}$ Integer, d represents the interval between the pilot sub-carrier, N _FFTExpression FFT counts, Expression p _i+ g mould N _FFTAfter value, ^*Complex conjugate is got in expression.

Images