CN101299737A - Synchronous estimation method and system for orthogonal frequency division multiplexing technique - Google Patents

Abstract

The invention provides an in-phase estimation method and a system of the orthogonal frequency division multiplexing (OFDM) technology, wherein the method includes: obtaining the sub-channels which satisfy the given transmission quality in the OFDM symbols; computing the phase offset between the data on the obtained sub-channels and the data on the sub-channels with the same position in the adjacent OFDM symbols; estimating the residual carrier frequency shift and the sampling clock shift of the current OFDM symbols. The method and the system estimates the residual carrier frequency shift and the sampling clock shift through the mutual correlation data on the sub-channels which satisfy the given transmission quality, overcomes the effect of the sub-channel with bad quality to generate the error code, advances the precision of the in-phase estimation to a great extent.

Description

The synchronous estimation method of orthogonal frequency division multiplexi and system

Technical field

The present invention relates to OFDM (OFDM) technology, particularly a kind of synchronous estimation method of OFDM technology and system.

Background technology

OFDM is a kind of frequency multiplexing technique with transmission of high-rate data service ability, its band efficiency height, the anti-multipath interference performance is strong, therefore, OFDM is subjected to concern and attention more and more widely, and be considered to one of one preferred technique of following radio multimedium mobile communication, and application in the digital audio broadcasting standard (DAB) in the physical layer series standard of WLAN (wireless local area network), Europe and digital time-frequency standard (DVB).

Though formulated a plurality of technical standards for the OFDM transmission technology at present, still existed many difficult problems in the OFDM technology.Be one of technical barrier that exists during the OFDM transmission standard is formulated synchronously, ofdm system is very responsive to synchronous error, and very little synchronous error all may cause the serious decline of systematic function.In ofdm system, generally comprise two processes synchronously: the first step is synchronization acquistion, promptly transfer of data begin to set up synchronously; Second step was the estimation of residue simultaneous bias.

Wherein, in data transmission procedure, because the influence of Doppler frequency shift, the carrier frequency stability of receiving-transmitting sides is limited, and the unsteadiness of receiving-transmitting sides sampling clock oscillator, caused the existence of residue carrier frequency shift and sampling clock offset,, can cause the signal amplitude on the subchannel to reduce though the numerical value of these synchronous errors is less, destroy the orthogonality between subchannel, and introduce inter-carrier interference (ICI, Inter-Carrier Interference), error rate of system is increased.At the stationary problem during the transfer of data, the synchronous estimation method of existing at present two kinds of ofdm systems, first kind is that auxiliary (second kind is the auxiliary synchronous estimation method of non-pilot tone to pilot tone for PTA, synchronous estimation method PilotTone-Aided).

Before introducing two kinds of methods of prior art, be necessary the structure of OFDM symbol and the synchronizing signal model of ofdm system are carried out brief description.At first the structure to the OFDM symbol describes, and comprises Cyclic Prefix part and data division in the OFDM symbol, and wherein, data division comprises: pilot data and signal data, as shown in Figure 1, c _m(k) k signal data of m OFDM symbol of expression, p _m(k) k pilot data of m OFDM symbol of expression.M and m+1 represent m and m+1 OFDM symbol, p _m(k) and p _M+1(k) be two pilot datas in the OFDM symbol respectively, pilot data generally is used for extracting channel information and carries out channel estimating.Comprise N in the OFDM symbol _gIndividual Cyclic Prefix, N subchannel is divided into pilot subchannel and signal subspace channel, carries pilot data on the pilot subchannel, carrying signal data on the signal subspace channel.

Synchronizing signal model to ofdm system describes below.In the OFDM transmission system,, promptly comprise N data in an OFDM symbol if N point discrete Fourier inverse transformation (IDFT, Inverse DiscreteFourier Transform) is adopted in the ofdm system modulation; Ofdm system adopts K+1 sub-channel transmission information, wherein, and K＜N; The ofdm system sampling clock cycle is T; An OFDM symbol comprises two parts on time domain: data division and Cyclic Prefix part, wherein the time of Cyclic Prefix is N _gT is in order to overcome the interference between signals that is caused by multipath; An OFDM symbol comprises N _sIndividual sampled point, N _s=N+N _g

At this moment, the complex baseband signal x of m OFDM symbol of transmitting terminal transmission _m(t) can be expressed as:

$x_m\left(t\right)=\frac{1}{\sqrt{N}}\underset{k=-K/2}{\overset{K/2}{\mathrm{\&Sigma;}}}{c}_{m,k}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">e</figure-callout>}}^j---\left(1\right)$

(1) c in the formula _{M, k}It is the modulated complex certificate on k subchannel of m OFDM symbol of transmitting terminal.

In the OFDM transmission system, the discrete time impulse response h of the transmission channel of m OFDM symbol _m(k) can be expressed as:

$h_m\left(k\right)=\underset{k=0}{\overset{S-1}{\mathrm{\&Sigma;}}}{h}_{m,k}\mathrm{\&delta;}(k-{\mathrm{\&tau;}}_k)---\left(2\right)$

(2) δ (k) expression impulse function in the formula, { h _{M, k}K=0 ..., S-1} is a k path complex gain during m OFDM symbol, { τ _kBe the path delay of time in k path, and being taken as the integral multiple in sampling time usually, S is the total number of paths in the wireless channel.

The timing of putative signal has reached synchronously, and finishes with compensation in the Carrier frequency offset estimation of initial synchronisation acquisition phase, will carry out the synchronous estimation in the data transmission procedure below.In this process, need carry out the residue carrier frequency shift and the sampling clock offset of OFDM synchronous phase and estimate.

If the complex baseband signal of transmitting terminal is through after this transmission channel, be f ' in the carrier frequency of receiving terminal, the sampling clock cycle is T ', and hypothesis is when m=0, and system is a strict synchronism, and at this moment, the residue synchronous error can be respectively:

Residue carrier frequency error Δ f is: Δ f=f-f ';

Sampling clock error β is: β=(T-T ')/T.(3)

At receiving terminal, adopting the clock cycle is that the complex baseband signal of m OFDM symbol was sampled and can be expressed as after the sampling clock of T ' was sampled and removed Cyclic Prefix:

r _m，n＝r(t _n)，0≤n≤N-1，t _n＝(mN _s+N _g)T′+nT′； (4)

The N of a m symbol sampled data is by after the Fourier transform demodulation, and the data on each subchannel can be expressed as:

$Z_m\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{r}_{m,n}{e}^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;kn}}{N}}---\left(5\right)$

$={\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">e</figure-callout>}}^j{H}_m\left(k\right)c_m\left(k\right){\mathrm{\&alpha;}}_{m,k}+n_m\left(k\right)+I_m\left(k\right)$

(5) in the formula $H_m\left(k\right)=\underset{l=0}{\overset{K-1}{\mathrm{\&Sigma;}}}{h}_m\left(l\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{\mathrm{\&tau;}}_{l}k/T_u},$ Wherein, T _u=NT, n _m(k) be the Gaussian noise on k subchannel during m the OFDM symbol, I _m(k) be interference signal between subchannel, because the residue synchronous error is smaller, the interference signal between subchannel equivalence usually is a white Gaussian noise, α _{M, k}Be the attenuation coefficient of signal on k the subchannel causing of synchronous error, because the residue synchronous error is less, thereby α _{M, k}Become in 1.

Introduce the first method of prior art below: the PTA synchronous estimation method.This method is after receiving terminal carries out Fourier transform to signal, extracts the pilot data on all pilot subchannel in the OFDM symbol, calculates the phase place of the pilot data that extracts; Phase place according to described pilot data is carried out cross-correlation calculation to adjacent OFDM symbol, promptly calculates the phase difference of the data on the same pilot frequency locations of adjacent OFDM symbol; Utilize resulting phase difference estimation residue carrier frequency shift of this cross-correlation calculation and sampling clock offset.

The PTA synchronous estimation method simply is easy to realization, but in this method, the number N of pilot tone in the OFDM symbol _pDirectly influence the precision that remains carrier frequency shift and sampling clock estimation in the system with the transmission quality of pilot subchannel, and in existing OFDM transmission technology, the data of pilot tone are less, and, the influence of wireless channel self transmission quality has limited the precision of PTA synchronous estimation method.

Introduce the second method of prior art below: direct data (DD, Dicision-directed) synchronous estimation method.This method mainly comprises: utilize known channel estimating parameter that the data of receiving terminal OFDM symbol are compensated; Data in the OFDM symbol after the described compensation are carried out hard decision; After compensating, the data in the adjacent OFDM symbol after the compensation are carried out cross-correlation calculation through the data of hard decision; Estimate to remain carrier frequency shift and sampling clock offset according to the result after the cross-correlation calculation.

This method need not be extracted pilot tone, and still, the subchannel of channel transmission quality difference can produce error code in hard decision, and the error code of generation can be introduced in estimating synchronously and disturb, and influences the precision of synchronous estimation method.

By above description as can be seen, synchronous estimation method of the prior art all can be subjected to the influence of the subchannel of poor transmission, reduces the precision of estimating synchronously.

Summary of the invention

In view of this, the embodiment of the invention provides a kind of synchronous estimation method and system of ofdm system, so that improve the precision of estimating synchronously.

The embodiment of the invention provides a kind of synchronous estimation method of ofdm system, and this method comprises:

Obtain and satisfy the subchannel of setting transmission quality requirements in the current OFDM symbol; Calculate the phase difference between the data on the subchannel that data on the subchannel that obtains in the current OFDM symbol are adjacent same position in the OFDM symbol; Utilize the phase difference that is calculated, estimate the residue carrier frequency shift and the sampling clock offset of described current OFDM symbol.

The embodiment of the invention also provides a kind of synchronous estimating system of ofdm system, and this system comprises: channel selected cell, phase difference calculating unit and estimation unit;

The channel selected cell is used for obtaining current OFDM symbol and satisfies the subchannel of setting transmission quality requirements;

The phase difference calculating unit is used for calculating the phase difference between the data on the subchannel that data on the subchannel that current OFDM symbol obtains are adjacent same position in the OFDM symbol, and the phase difference that calculates is offered estimation unit;

The phase difference that utilizes the phase difference calculating unit to provide is provided estimation unit, estimates the residue carrier frequency shift and the sampling clock offset of described current OFDM symbol.

By as can be seen above, the synchronous estimation method and the system of the OFDM technology that the embodiment of the invention provides, cross-correlation data on the subchannel of the satisfied setting transmission quality requirements of obtaining by utilization, residue carrier frequency shift and sampling clock offset are estimated, avoid producing in the subchannel of poor transmission the influence of error code, improved the precision of synchronous estimation to a great extent.

Description of drawings

Fig. 1 is the structural representation of OFDM symbol;

The flow chart of the synchronous estimation method of the ofdm system that Fig. 2 provides for the embodiment of the invention;

Another flow chart of the synchronous estimation method of the ofdm system that Fig. 3 provides for the embodiment of the invention;

The structure chart of the synchronous estimating system that Fig. 4 .a provides for the embodiment of the invention;

The structure chart of the channel selected cell that Fig. 4 .b provides for the embodiment of the invention;

Form structure chart for first kind of the phase difference calculating unit that Fig. 4 .c provides for the embodiment of the invention;

Form structure chart for second kind of the phase difference calculating unit that Fig. 4 .d provides for the embodiment of the invention;

Fig. 5 when adopting different thresholding, mean square error (MSE) curve chart of the frequency offset residue (RCFO) of method that the embodiment of the invention provides and PTA method;

Fig. 6 when adopting different thresholding, the mean square error MSE curve chart of the sampling clock offset (SFO) of method that the embodiment of the invention provides and PTA method;

Fig. 7 is under identical sampling clock offset normalized value and different residue carrier frequency shift normalized values, the estimated performance curve of the inventive method and PTA method;

Fig. 8 is under identical residue carrier frequency shift normalized value and different sampling clock offset normalized values, the estimated performance curve of the inventive method and PTA method;

Fig. 9 is the residue carrier frequency shift aircraft pursuit course of the inventive method and PTA method under the same conditions;

Figure 10 is the sampling clock offset aircraft pursuit course of the inventive method and PTA method under the same conditions.

Embodiment

In order to make technique scheme, purpose and advantage more clear, the present invention is described in detail below in conjunction with specific embodiment.

The synchronous estimation method of the ofdm system that the embodiment of the invention provides mainly comprises: obtain and satisfy the subchannel of setting transmission quality requirements in the current OFDM symbol; Calculate the phase difference between the data on the subchannel that data on the subchannel that obtains in the current OFDM symbol are adjacent same position in the OFDM symbol; Utilize the phase difference that is calculated, estimate the residue carrier frequency shift and the sampling clock offset of described current OFDM symbol.

At this, the OFDM symbol that will use in the time of will carrying out channel estimating is as current OFDM symbol.

Wherein, satisfying the subchannel of setting transmission quality requirements in the described OFDM symbol that obtains can all be to satisfy the signal subspace channel of setting transmission quality requirements; Also can comprise the subchannel that satisfies the pilot data of setting transmission quality requirements and satisfy the signal subspace channel of setting transmission quality requirements.

When satisfying the subchannel of setting transmission quality requirements in the OFDM symbol that obtains all is that this method can also comprise: pick out the pilot subchannel in the OFDM symbol when satisfying the signal subspace channel of setting transmission quality requirements.

Wherein, calculate that the phase difference between the data can have following dual mode on the subchannel that data on the subchannel that obtains in the current OFDM symbol are adjacent same position in the OFDM symbol:

First kind of mode: the data on the subchannel that obtains in the current OFDM symbol are adjacent on the subchannel of same position in the OFDM symbol data and carry out obtaining the cross-correlation data after the cross-correlation calculation, signal cross-correlation data on the subchannel that obtains are carried out hard decision, and the phase difference of the sub-channel data of obtaining in the judgement data computation adjacent OFDM symbol that obtains according to hard decision.

The second way: at first the data on the subchannel that obtains are carried out hard decision, then, result according to hard decision, data on the subchannel that obtains in the current OFDM symbol are adjacent on the subchannel of same position in the OFDM symbol data and carry out cross-correlation calculation, draw the phase difference of the sub-channel data of obtaining in the adjacent OFDM symbol.

Be example in first kind of mode below, the synchronous estimation of ofdm system is described in detail.The flow chart of the synchronous estimation method of the ofdm system that Fig. 2 provides for the embodiment of the invention, as shown in Figure 2, this method mainly may further comprise the steps:

Step 201: in current OFDM symbol, pick out and satisfy the signal subspace channel of setting transmission quality requirements, and pick out all pilot subchannel.

Except this mode, this step can also have other mode, promptly picks out and satisfies the signal subspace channel of setting transmission quality requirements, and pick out and satisfy the subchannel of setting transmission quality requirements in the pilot subchannel.

Select in the OFDM symbol satisfy set transmission quality requirements the signal subspace channel can for: pick out the signal subspace channel that transmission quality in the OFDM symbol is higher than quality threshold.

Because there are corresponding relation in the transmission quality of channel and signal to noise ratio,, select the high subchannel of transmission quality so can adopt system of selection based on the subchannel signal to noise ratio.At this moment, described quality threshold is a signal-noise ratio threshold.This selection can be expressed as:

ζ＝{l|SNR _m(l)≥SNR _th} (6)

(6) in the formula: SNR _m(l) be signal to noise ratio on l the subchannel of m symbol, SNR _ThBe that signal to noise ratio selects thresholding, ζ is the set of the subchannel coefficient that obtains.

When selecting signal-noise ratio threshold, if the signal-noise ratio threshold of selecting is too low, the sub-channel data of obtaining is more, but when signal to noise ratio is low, the quality of data on the subchannel of selecting can be lower, and the data on these subchannels can produce error code, the precision that influence is estimated synchronously; If the signal-noise ratio threshold of selecting is too high, will reduce the number of selected subchannel, also can influence the precision of synchronous estimation.Select signal-noise ratio threshold to adopt and on the theory function basis, utilize method of emulation to determine.

In addition, this step also can adopt the system of selection of the noise ordering of subchannel.Size according to the snr value on each subchannel sorts, and at last according to the number of the high-quality sub-channels of system's initial setting, selects the subchannel of setting number according to from big to small order.

In addition, this step also can adopt the system of selection based on minimum judgement distance.Calculate in each subchannel the distance between each corresponding data in the data and planisphere respectively, select the subchannel that distance satisfies the distance threshold condition, this system of selection can be expressed as:

ζ＝{l|d _m(l)≤d _th}

Wherein, d _m(l) be the distance between the corresponding data in data and the planisphere in m the subchannel, d _ThBe the distance threshold of setting.

In addition, this step can also adopt the system of selection based on minimum phase.Calculate in each subchannel the phase pushing figure between each corresponding data in the data and planisphere respectively, select the subchannel that phase pushing figure satisfies the phase deviation threshold condition, this system of selection can be expressed as:

ζ＝{l|ρ _m(l)≤ρ _th}

Wherein, ρ _m(l) be the phase pushing figure between the corresponding data in data and the planisphere in m the subchannel, ρ _ThBe the phase deviation thresholding of setting.

Step 202: current OFDM symbol is adjacent signal data and pilot data on the OFDM intersymbol same position by signal data on the selected signal subspace channel of step 201 and the pilot data on the pilot subchannel, carries out cross-correlation calculation respectively.

Signal data in the next OFDM symbol that in this step the signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent on the signal subspace channel of same position carries out cross-correlation calculation, is the conjugation that the signal data on a certain sub-channel positions of selecting of next OFDM symbol be multiply by the signal data on the same sub-channel positions of previous OFDM symbol.Equally also can adopt the mode of other cross-correlation calculation.

In addition, the OFDM symbol adjacent with current OFDM symbol that embodiment among the present invention adopts is its adjacent next OFDM symbol, in addition, when channel quiet or change when slow, also can adopt a last OFDM symbol that is adjacent.

The pilot data that in this step the pilot data on the pilot subchannel of obtaining in the current OFDM symbol is adjacent on the pilot subchannel of same position in the next OFDM symbol carries out cross-correlation calculation, is the conjugation that the pilot data on a certain pilot frequency locations of a back OFDM symbol be multiply by the pilot data on the same pilot frequency locations of previous OFDM symbol.

Data to subchannel between adjacent OFDM symbol are carried out cross-correlation calculation, are reflected on the phase place phase difference of the data that are exactly the adjacent OFDM symbol sub-channels.

Adopt the cross-correlation calculation between adjacent OFDM symbol in this step, be because the phase deviation meeting that residue carrier frequency shift and sampling clock offset cause increases along with the increase of OFDM symbol, cause the data in the OFDM symbol to be displaced to another quadrant from a quadrant at last, the accumulation of a plurality of like this OFDM symbols makes adopts simple hard decision can't obtain correct court verdict in the step below.

Because supposing the decline of channel usually is slowly to change, promptly during m OFDM symbol and M+1 OFDM symbol, can think that subchannel upper signal channel coefficient is identical, that is: H _m(k) ≈ H _M+1(k), can obtain by (5) formula in the synchronizing signal model:

Receiving terminal, the data of k subchannel of m and m+1 OFDM symbol are respectively:

$Z_m\left(k\right)=$

$\exp (\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;\&epsiv;}\frac{(m{N}_s+N_g)}{N}(1+\mathrm{\&beta;})+\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\frac{(m{N}_s+N_g)}{N}\mathrm{k\&beta;})\&CenterDot;H_m\left(k\right)\&CenterDot;c_m\left(k\right)+n_m\left(k\right)---\left(7\right)$

$Z_{m+1}\left(k\right)=$

$\exp \left({\mathrm{j\&phi;}}_k\right)\&CenterDot;\exp (\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;\&epsiv;}\frac{(m{N}_s+N_g)}{N}(1+\mathrm{\&beta;})+\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20071010716000392.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\frac{(m{N}_s+N_g)}{N}\mathrm{k\&beta;})\&CenterDot;H_{m+1}\left(k\right)\&CenterDot;c_{m+1}\left(k\right)$

$+n_{m+1}\left(k\right)---\left(8\right)$

Wherein, φ _k≈ 2 π (1+N _g/ N) (ε+k β) (9)

ε is residue carrier wave frequency deviation normalized value, ε=Δ fNT.

Can obtain the cross-correlation data R on l the signal subspace channel of m and m+1 OFDM symbol by (7) formula, (8) formula _m(l) be:

$R_m\left(l\right)=Z_{m+1}\left(l\right)\&CenterDot;Z_m^{*}\left(l\right)=\exp \left(j{\mathrm{\&phi;}}_l\right)\&CenterDot;{\left|H_m\left(l\right)\right|}^2\&CenterDot;c_{m+1}\left(l\right)\&CenterDot;c_m^{*}\left(l\right)+{\tilde{n}}_m\left(l\right),l\&Element;\mathrm{\&zeta;}---\left(10\right)$

Wherein, ζ is the set of subchannel coefficient of the signal subspace channel correspondence of selected satisfied setting transmission quality requirements.

Equally, can obtain the cross-correlation data Q on l the pilot subchannel of m and m+1 OFDM symbol by (7) formula, (8) formula _m(l) be:

$Q_m\left(l\right)=Z_{m+1}\left(l\right)\&CenterDot;Z_m^{*}\left(l\right)=\exp \left(j{\mathrm{\&phi;}}_l\right)\&CenterDot;{\left|H_m\left(l\right)\right|}^2\&CenterDot;p_{m+1}\left(l\right)\&CenterDot;p_m^{*}\left(l\right)+{\tilde{n}}_m\left(l\right),l\&Element;\mathrm{\&gamma;}---\left(11\right)$

Wherein, γ is the set of the subchannel coefficient of pilot subchannel correspondence.

Step 203: the cross-correlation data on the signal subspace channel of the satisfied setting transmission quality requirements selected are carried out hard decision.

It is in order to obtain the influence to the cross-correlation data of data that transmitting terminal sends, can to eliminate the synchronous estimation of the error effect transmitting terminal data remain to(for) receiving terminal according to the hard decision result that this step is carried out hard decision to the cross-correlation data on the signal subspace channel that satisfy to set transmission quality requirements.

The described hard decision that carries out is: according to the distance of each the cross-correlation data point in the goal set of the cross-correlation data on the selected signal subspace channel, will be apart from the cross-correlation data point in the nearest goal set of the cross-correlation data on the described signal subspace channel of selecting as described cross-correlation data, i.e. hard decision data.This hard decision result

(l) can be expressed as:

${\hat{F}}_m\left(l\right)=\underset{E_t\&Element;\mathrm{\&Omega;}}{\arg \min }\left\{{|R_m\left(l\right)-E_t|}^2\right\},$ l∈ζ (12)

Wherein, $\mathrm{\&Omega;}=\left\{E_t\right|E_t=e_u\&CenterDot;e_v^{*},e_u,e_v\&Element;\mathrm{\&Pi;},t=\mathrm{1,2},...,M\},$ Ω is goal set, and ∏ is the set of the data on the data constellation figure on the subchannel, the cross-correlation data point E among the goal set Ω _tBe by the formed set of cross-correlation calculation by data among the ∏.

Step 204: utilize the hard decision result that the cross-correlation data that satisfy the signal subspace channel of setting transmission quality requirements are compensated; And the pilot tone cross-correlation data of utilizing known transmitting terminal pilot tone cross-correlation data that step 203 is calculated compensate.

This step obtains carrying on the receiving terminal subchannel cross-correlation data of phase deviation by compensation.At receiving terminal, the cross-correlation data of carrying phase deviation are to obtain by the influence with the cross-correlation data of receiving terminal data.Described compensation comprises: satisfying on the signal subspace channel of setting transmission quality requirements, replace the cross-correlation data of transmitting terminal given data with court verdict; On pilot subchannel, eliminate self influence to receiving terminal cross-correlation data with the known pilot tone cross-correlation data of making a start.

(12) formula of utilization compensates and can obtain (10) formula, carries the cross-correlation function X of phase deviation on l the signal subspace channel of m OFDM symbol _m(l) be:

$X_m\left(l\right)=R_m\left(l\right)\&CenterDot;F_m^{*}\left(l\right)=\exp \left(j{\mathrm{\&phi;}}_l\right)\&CenterDot;{\left|H_m\left(l\right)\right|}^2+{\hat{w}}_m\left(l\right),l\&Element;\mathrm{\&zeta;}---\left(13\right)$

Because the pilot tone cross-correlation function D of known transmitting terminal _m(l) be:

$D_m\left(l\right)=p_{m+1}\left(l\right)\&CenterDot;p_m^{*}\left(l\right),l\&Element;\mathrm{\&gamma;}---\left(14\right)$

(14) formula of utilization compensates and can obtain (11) formula, carries the cross-correlation function X of phase deviation on l the pilot subchannel of m OFDM symbol _m(l) be:

$X_m\left(l\right)=Q_m\left(l\right)\&CenterDot;D_m^{*}\left(l\right),l\&Element;\mathrm{\&gamma;}---\left(15\right)$

Therefore, be used in m OFDM symbol to remain that the cross-correlation data are on the subchannel that carrier frequency shift and sampling clock offset estimate:

$X_m\left(l\right)=\left\{\begin{array}{cc}{R}_m\left(l\right)\&CenterDot;F_m^{*}\left(l\right),& l\&Element;\mathrm{\&zeta;}\\ Q_m\left(l\right)\&CenterDot;D_m^{*}\left(l\right),& l\&Element;\mathrm{\&gamma;}\end{array}\right.---\left(16\right)$

Step 205: utilize the current OFDM symbol of cross-correlation data computation after the compensation to be adjacent the phase difference of the sub-channel data that the OFDM intersymbol obtains.

In this step, can calculate the phase difference that the cross-correlation data computation of utilizing after the compensation goes out signal data on the signal subspace channel that obtains in the adjacent OFDM symbol respectively, and the phase difference of pilot data on the pilot subchannel of obtaining; Also the ensemble average that the signal subspace channel that obtains and pilot subchannel can be constituted is divided into two subclass, then the phase place of the cross-correlation data of two subclass is subtracted each other the phase difference of the sub-channel data that obtains obtaining.

(16) phase of data on the selected subchannel in compensation back in the formula _lFor:

φ _l≈2π(1+N _g/N)(ε+l·β)，l∈χ (17)

Wherein, χ is the set of the subchannel coefficient of pilot subchannel and high-quality sub-channels correspondence, that is: χ=ζ+γ.

Can be at first in this step with all the subchannel coefficients among the set χ according to from small to large rank order, will gather χ then and be divided into two equal subclass χ of subchannel number ₁And χ ₂Subclass χ ₁And χ ₂The phase place of the cross-correlation data on two subchannels of middle correspondence is respectively φ _{L '}And φ _{L "}:

φ _l′≈2π(1+N _g/N)(ε+l′·β)，l′∈χ ₁ (18)

φ _l″≈2π(1+N _g/N)(ε+l″·β)，l″∈χ ₂ (19)

Then, the cross-correlation data phase that differs subchannel coefficient corresponding in two set bigger subtracts each other, and can balance out the phase deviation that the residue carrier frequency shift causes like this.The phase difference that obtains after subtracting each other _vFor:

φ _v＝φ _l′-φl _″≈2π(1+N _g/N)(v·β)，v∈χ ₃ (20)

Wherein, set χ ₃Expression set χ ₁And χ ₂The set that the phase difference of data constitutes on the son-channel of middle correspondence.

This χ that will gather is divided into two subclass χ that the subchannel number equates ₁And χ ₂Ask the mode of phase difference, can more can improve estimation performance so that corresponding subchannel coefficient differs greatly in two set.

In addition, when the high subchannel of the quality of being selected all is the signal subspace channel, also can adopt said method to carry out the calculating of phase difference, the ensemble average that the subchannel that the quality of soon being selected is high constitutes is divided into the subclass of being separated by, then the phase place of data on two subclass sub-channels is subtracted each other, obtain the phase difference of being asked.

Step 206: utilize the phase difference that calculates, estimate residue carrier frequency shift and sampling clock offset.

Sampling clock offset can be estimated by utilizing phase difference to be weighted average method in this step, can draw sampling clock offset

For:

$\widehat{\mathrm{\&beta;}}=\frac{1}{2\mathrm{\&pi;}(1+N_g/N)}\&CenterDot;\frac{1}{L}\underset{m=1}{\overset{L}{\mathrm{\&Sigma;}}}\left(\frac{\underset{v\&Element;{\mathrm{\&zeta;}}_3}{\mathrm{\&Sigma;}}v\&CenterDot;{\mathrm{\&phi;}}_v}{\underset{v\&Element;{\mathrm{\&zeta;}}_3}{\mathrm{\&Sigma;}}{v}^2}\right),v\&Element;{\mathrm{\&chi;}}_3---\left(21\right)$

Wherein, L represents to estimate synchronously the number of the OFDM symbol of employing.

Estimate the residue carrier frequency shift can for: with the phase of data on the selected subchannel in sampling clock offset substitution compensation back of trying to achieve _l, be about to (21) substitution (17) formula, the residue carrier frequency shift that obtains

For:

$\widehat{\mathrm{\&epsiv;}}=\frac{1}{2\mathrm{\&pi;}(1+N_g/N)}\&CenterDot;\frac{1}{N_c}\&CenterDot;\underset{l\&Element;\mathrm{\&chi;}}{\mathrm{\&Sigma;}}({\mathrm{\&phi;}}_l-2\mathrm{\&pi;}(1+N_g/N)(l\&CenterDot;\widehat{\mathrm{\&beta;}})),l\&Element;\mathrm{\&chi;}---\left(22\right)$

Wherein, N _cSatisfy the subchannel of setting transmission quality requirements and total number of pilot subchannel among the expression set χ.

Step 207: residual frequency carrier shift that utilization estimates and sampling clock offset compensate the data on the OFDM symbol next to be estimated.Repeat above-mentioned steps, finish up to OFDM sign estimation that will be to be estimated.

In addition, this step also can adopt the mode of closed loop feedback compensation.At first frequency offset residue and the sampling clock offset that estimates carried out the processing of single order closed loop feedback filter, the result after obtaining handling is:

${\widehat{\mathrm{\&epsiv;}}}_m={\widehat{\mathrm{\&epsiv;}}}_{m-1}+{\mathrm{\&gamma;}}_{\mathrm{\&epsiv;}}\&CenterDot;\widehat{\mathrm{\&epsiv;}}---\left(23\right)$

${\widehat{\mathrm{\&beta;}}}_m={\widehat{\mathrm{\&beta;}}}_{m-1}+{\mathrm{\&gamma;}}_{\mathrm{\&beta;}}\&CenterDot;\widehat{\mathrm{\&beta;}}---\left(24\right)$

Wherein, γ _εAnd γ _βIt is the Control Parameter of closed loop feedback filter.

Estimated value after will handling then compensates residue carrier frequency and sample frequency in time domain and frequency domain respectively, the data of next OFDM symbol is estimated again.

Above-mentioned is the detailed process of first kind of mode, and when using the second way, its process mainly may further comprise the steps as shown in Figure 3:

Step 301: in current OFDM symbol, obtain and satisfy the signal subspace channel of setting transmission quality requirements, and obtain pilot subchannel.

The subchannel of the satisfied setting transmission quality requirements of obtaining equally, in this step all is the signal subspace channel.Except this mode, can also obtain the subchannel of the satisfied setting transmission quality requirements in the pilot subchannel.

Step 302: the signal data on the signal subspace channel of the satisfied setting transmission quality requirements obtained is carried out hard decision.

In this step, signal data on the signal subspace channel that satisfy to set transmission quality requirements is carried out hard decision is: according to the distance of each the coordinate points data in the planisphere of the signal data on the selected signal subspace channel, and will be apart from the nearest coordinate points data of the signal data on the described signal subspace channel of selecting as described judgement data.

Step 303: according to the hard decision result signal data that satisfies on the signal subspace channel of setting transmission quality requirements is compensated, and utilize known pilot data skew that the pilot data on the pilot subchannel is compensated.

Step 304: the signal data that the signal data after the compensation on the signal subspace channel that obtains in the current OFDM symbol is adjacent after the compensation on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, and the pilot data after the compensation of the pilot subchannel obtained is carried out cross-correlation calculation.

The signal data that in this step the signal data after the compensation on the signal subspace channel that obtains in the current OFDM symbol is adjacent after the compensation on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, is the conjugation that the signal data after the compensation on a certain sub-channel positions of selecting of a back OFDM symbol be multiply by the signal data after the compensation on the same sub-channel positions of previous OFDM symbol.

In this step the pilot data on the pilot subchannel selected in the adjacent OFDM symbol being carried out correlation computations, is the conjugation that the pilot data on a certain pilot frequency locations of a back OFDM symbol be multiply by the pilot data on the same pilot frequency locations of previous OFDM symbol.

Step 305: the result according to cross-correlation calculation in the step 304 obtains calculating the phase difference that current OFDM symbol is adjacent the sub-channel data of obtaining in the OFDM symbol.

Step 306: utilize the phase difference that calculates, estimate residue carrier frequency shift and sampling clock offset.

Step 307: residual frequency carrier shift that utilization estimates and sampling clock offset compensate the data on the OFDM symbol next to be estimated.Repeat above-mentioned steps, finish up to OFDM sign estimation that will be to be estimated.

Synchronous estimating system to the OFDM technology describes in detail below.The structure chart of the synchronous estimating system that Fig. 4 .a provides for the embodiment of the invention, shown in Fig. 4 .a, this system mainly comprises: channel selected cell 400, phase difference calculating unit 410 and estimation unit 420.

Channel selected cell 400 is used for obtaining current OFDM symbol and satisfies the subchannel of setting transmission quality requirements;

Phase difference calculating unit 410, be used for calculating the phase difference between the data on the subchannel that data on the subchannel that current OFDM symbol obtains by channel selected cell 400 are adjacent same position in the OFDM symbol, and the phase difference that calculates is offered estimation unit 420;

The phase difference that utilizes phase difference calculating unit 410 to provide is provided estimation unit 420, estimates the residue carrier frequency shift and the sampling clock offset of current OFDM symbol.

Described estimation unit 420 can adopt the method described in the step 206 among Fig. 2, carries out the residue carrier frequency shift of described OFDM symbol and the estimation of sampling clock offset.

Wherein, the structure of described channel selected cell 400 is shown in Fig. 4 .b, and channel selected cell 400 can comprise: quality detection module 401 and signal subspace channel are selected module 402;

Quality detection module 401 is used for detecting the transmission quality of current each subchannel of OFDM symbol, and testing result is sent to the signal subspace channel selects module 402;

Described quality detection module 401 can be carried out quality testing by the signal to noise ratio to each subchannel; Also can carry out quality testing by calculating in the OFDM symbol in each sub-channel data and planisphere the distance between the corresponding data respectively; Can also the phase pushing figure between the corresponding data detects in each sub-channel data and planisphere by calculating respectively in the OFDM symbol.

The signal subspace channel is selected module 402, is used for the testing result according to quality detection module 401 transmissions, selects to satisfy in this OFDM symbol the signal subspace channel of setting transmission quality requirements.

When quality detection module 401 when the signal to noise ratio of each subchannel is carried out quality testing, the signal subspace channel selects module 402 to select signal to noise ratio to be higher than the subchannel of signal-noise ratio threshold by setting signal-noise ratio threshold; Also can be by subchannel be sorted according to signal to noise ratio, according to from selecting the subchannel of setting data to the order in school greatly.When quality detection module 401 when calculating respectively that the distance between the corresponding data is carried out quality testing in each sub-channel data and planisphere in the OFDM symbol, channel selects module 402 can pass through the setpoint distance thresholding, selects described distance to satisfy the subchannel of distance threshold condition.When quality detection module 401 when calculating respectively that the phase pushing figure between the corresponding data detects in each sub-channel data and planisphere in the OFDM symbol, channel selects module 402 to select described phase deviation to satisfy the subchannel of phase deviation threshold condition by setting the phase deviation thresholding.

In addition, this channel selected cell 400 can also comprise: pilot subchannel is selected module 403, be used for selecting all pilot subchannel of this OFDM symbol, perhaps, according to the testing result that quality-monitoring module 401 sends, select to satisfy in this OFDM symbol the pilot subchannel of setting transmission quality requirements;

Described quality-monitoring module 401 also is used for detecting the transmission quality of current OFDM symbol pilot subchannel, and concurrent censorship is surveyed the result and selected module 403 to pilot subchannel.

Structure can be formed, mode one and mode two in the difference corresponding method by two kinds in phase difference calculating unit 410.Fig. 4 .c is that first kind of phase difference calculating unit formed structure chart, and shown in Fig. 4 .c, this phase difference calculating unit mainly comprises: the first cross-correlation calculation module 411, hard decision module 412, first compensating module 413 and phase difference calculating module 414.

The first cross-correlation calculation module 411, channel subchannel in the current OFDM symbol is selected the signal data on the signal subspace channel of same position in the next OFDM symbol that the signal data on the signal subspace channel that module 402 obtains is adjacent carry out cross-correlation calculation, and the cross-correlation data that obtain are offered the hard decision module 412 and first compensating module 413.

Hard decision module 412 is used for the cross-correlation data that receive are carried out hard decision, and the judgement data that obtain behind the hard decision is offered first compensating module 413.

Described hard decision module 412 can adopt among Fig. 2 the method described in the step 203 to carry out hard decision.

First compensating module 413, be used to receive the judgement data of hard decision module 412 transmissions and the cross-correlation data that the first cross-correlation calculation module 411 sends, and utilize described judgement data that described cross-correlation data are compensated, and the cross-correlation data after will compensating send to phase difference calculating module 414.

Described first compensating module 413 can adopt that the method described in the step 204 compensates among Fig. 2.

Phase difference calculating module 414, be used to receive the cross-correlation data after the compensation that first compensating module 413 sends, calculate the phase place of the cross-correlation data after the compensation, the signal data on the signal subspace channel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol.

Described phase difference calculating module 414 can adopt among Fig. 2 the method described in the step 205 to carry out the calculating of phase difference.

Further, select module at the pilot subchannel that can comprise in the channel selected cell 400, described phase difference calculating unit 410 can also comprise: the second cross-correlation calculation module 415 and second compensating module 416.

The second cross-correlation calculation module 415, be used for the pilot data that current OFDM symbol channel selects pilot data on the pilot subchannel that module 400 obtains to be adjacent on the pilot subchannel of same position in the next OFDM symbol is carried out cross-correlation calculation, and the cross-correlation data that obtain are offered second compensating module 416.

Second compensating module 416 is used to utilize known transmitting terminal pilot tone cross-correlation data, and the cross-correlation data that the second cross-correlation calculation module 415 is sent compensate, and the cross-correlation data that obtain after will compensating offer phase difference calculating module 414.

Described phase difference calculating module 414, also be used to receive the cross-correlation data after the compensation that second compensating module 416 sends, calculate the phase place of the cross-correlation data after the compensation, the pilot data on the pilot subchannel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the pilot data on the pilot subchannel of same position in the next OFDM symbol.

Wherein, the described first cross-correlation calculation module 411 and the second cross-correlation calculation module 415 also can be arranged in the equipment; Described first compensating module 413 and second compensating module 416 also can be arranged in the equipment.

Fig. 4 .d is that second kind of phase difference calculating unit formed structure chart, and shown in Fig. 4 .c, this phase difference calculating unit mainly comprises: hard decision module 417, compensating module 418, the first cross-correlation calculation module 419 and phase difference calculating module 420.

Hard decision module 417, the signal data that is used on the signal subspace channel of satisfied setting transmission quality requirements that channel selected cell 400 is obtained carries out hard decision, and the judgement data that obtain behind the hard decision are offered compensating module 418.

Described hard decision module 417 can adopt the step 302 described in Fig. 3 to carry out the method for hard decision.

Compensating module 418, be used to receive the judgement data that hard decision module 417 provides, and utilize described judgement data, the signal data on the signal subspace channel of the satisfied setting transmission quality requirements obtained is compensated, and the signal data after will compensating sends to the first cross-correlation calculation module 419.

The method that described compensating module 418 can adopt the step 303 described in Fig. 3 to compensate.

The first cross-correlation calculation module 419, the signal data that signal data after the compensation on the signal subspace channel that is used for current OFDM symbol is obtained is adjacent after the compensation on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, and the signal cross-correlation data that obtain are offered phase difference calculating module 420.

The described first cross-correlation calculation module 419 can adopt the step 304 described in Fig. 3 to carry out the method for cross-correlation calculation.

Phase difference calculating module 4110, receive the signal cross-correlation data that the first cross-correlation calculation module 419 provides, calculate the phase place of described signal cross-correlation data, the signal data on the signal subspace channel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol.

Further, select module at the pilot subchannel that can comprise in the channel selected cell 400, described phase difference calculating unit 410 can also comprise: the second cross-correlation calculation module 4111.

The second cross-correlation calculation module 4111, the pilot data that pilot data on the pilot subchannel that is used for current OFDM symbol channel selected cell 400 is obtained is adjacent on the pilot subchannel of same position in the next OFDM symbol carries out cross-correlation calculation, and the pilot tone cross-correlation data that obtain are offered phase difference calculating module 4110.

Phase difference calculating module 4110, also be used to receive the pilot tone cross-correlation data that the second cross-correlation calculation module 4111 provides, calculate the phase place of described pilot tone cross-correlation data, the pilot data on the pilot subchannel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the pilot data on the pilot subchannel of same position in the next OFDM symbol.

In order to verify the performance of the synchronous estimation method that the embodiment of the invention provides, utilize simulation result to describe below.The condition of below carrying out emulation is: the sample frequency of ofdm system is 20MHZ; Subchannel number N=256 promptly adopts 256 IFFT, wherein, cyclic prefix CP=64, useful number of subchannels are 200, and pilot channel is included in 200 subchannels, the number of pilot channel is 8, lays respectively on the sub-channel positions of [13 38 63 88 113 138 163 188]; The maximum doppler frequency that system exists is 50HZ.

Fig. 5 when adopting different thresholding, mean square error (MSE) curve chart of the frequency offset residue (RCFO) of method that the embodiment of the invention provides and PTA method.MSE can reflect the error precision of estimated frequency shift.Emulation shown in this Fig be residue carrier frequency shift normalized value be 0.04 and the sampling clock offset normalized value be to make under 0.00002 the condition.Three threshold values are respectively according to from small to large order among the figure: thresholding one, thresholding two, thresholding three.As seen from Figure 5, select when higher when thresholding in the method provided by the invention, as thresholding three, its frequency offset estimating performance and PTA method performance basically identical, this mainly be because high threshold value make the subchannel that satisfies condition selected data seldom.When thresholding was selected to hang down, as thresholding one, the data of the subchannel of the condition that satisfies were many, but when threshold value was low, the transmission quality of selected subchannel was low, occurs error code easily, also can influence the performance of system.Three threshold values are compared, and thresholding two is an optimum thresholding for frequency offset residue is estimated.

Fig. 6 when adopting different thresholding, the mean square error MSE curve chart of the sampling clock offset (SFO) of method that the embodiment of the invention provides and PTA method.MSE can reflect the error precision of the sampling clock offset of estimation.Emulation shown in this Fig be residue carrier frequency shift normalized value be 0.04 and the sampling clock offset normalized value be to make under 0.00002 the condition.Three threshold values are respectively according to from small to large order among the figure: thresholding one, thresholding two, thresholding three.As seen from Figure 6, thresholding is more little, and the estimated performance of sampling clock offset is high more, and this is owing to adopting antithetical phrase interchannel phase change rule to be weighted estimation in sampling clock is estimated, and is insensitive to the error code of each channel.

Fig. 7 is under identical sampling clock offset normalized value and different residue carrier frequency shift normalized values, the estimated performance curve of the inventive method and PTA method.The sampling clock normalized value that adopts is 0.00002, and residue carrier frequency shift normalized value is respectively 0.06,0.04 and 0.02.The PTA method is along with the reducing of frequency offset residue as shown in Figure 7, and the MSE of its frequency offset residue slightly reduces; Estimated performance in the inventive method is under three kinds of situations, performance all is better than the PTA method, but when frequency offset residue is big, its performance becomes in the PTA method, along with reducing of frequency offset residue, the MSE of frequency offset residue descends rapidly, and this is because reducing along with frequency offset residue, high-quality subchannel increases thereupon, and therefore the performance of method of the present invention is significantly improved.

Fig. 8 is under identical residue carrier frequency shift normalized value and different sampling clock offset normalized values, the estimated performance curve of the inventive method and PTA method.The residue carrier frequency shift normalized value that adopts is 0.04, and the sampling clock offset normalized value of employing is respectively 0.00004,0.00002 and 0.000005.As seen from Figure 8, the PTA method is along with sampling clock offset reduces, and the MSE of its sampling clock offset slightly reduces; Performance in the inventive method all is better than the PTA method under three kinds of situations, and along with the reducing of sampling clock offset, the MSE of sampling clock offset descends rapidly.This is because along with the reducing of sampling clock, high-quality subchannel increases thereupon.But because the numerical value of sampling clock offset is generally less, compare with the variation of residue carrier frequency shift, the influence of its antithetical phrase channel transmission quality is little.

Fig. 9 is for being 15dB at average signal-to-noise ratio, and residue carrier frequency shift normalized value is 0.05, and the sampling clock offset normalized value is under 0.0004 the condition, the residue carrier frequency shift aircraft pursuit course of the inventive method and PTA method.As shown in Figure 9, the convergence rate of the inventive method and PTA method is all very fast, but the fluctuation range of PTA method is bigger in tracking, and the fluctuation range of the inventive method is smaller, can draw in tracing process by calculating, the variance of the residue carrier frequency tracking of PTA method is 1.8457e-004, and the variance of the residue carrier frequency tracking of the inventive method is 2.6659e-005, with respect to the PTA method, the performance of the inventive method has improved 5.9 times.

Figure 10 is for being 15dB at average signal-to-noise ratio, and residue carrier frequency shift normalized value is 0.05, and sampling clock offset is under 0.0004 the condition, the sampling clock offset aircraft pursuit course of the inventive method and PTA method.As seen from Figure 10, in the tracking, the fluctuation range of PTA method is big, the fluctuation range of the inventive method is little, can obtain in tracing process by calculating, the variance that the sampling clock offset of PTA method is followed the tracks of is 8.2279e-009, and the variance that the sampling clock offset of the inventive method is followed the tracks of is 2.1542e-009, has improved 2.8 times with respect to PTA method performance.

By above description as can be seen, the synchronous estimation method and the system of the OFDM technology that the embodiment of the invention provides, cross-correlation data on the subchannel of the satisfied setting transmission quality requirements of obtaining by utilization, residue carrier frequency shift and sampling clock offset are estimated, overcome the influence of the error code that produces in the subchannel of poor transmission, improved the precision of synchronous estimation.

Further, the method and system that the embodiment of the invention provides, the subchannel of the satisfied setting transmission quality requirements of being obtained is the signal subspace channel, can also comprise the satisfied pilot subchannel of transmission quality requirements or the whole pilot subchannel set, increased the sub-channel data that adopts, overcome in the PTA method, the precision of estimating is because the few and limited shortcoming of pilot subchannel data synchronously.

Further, hard decision method of the present invention does not need channel estimating, just can compensate,, overcome the dependence of synchronous estimation method channel estimating to obtain the data that transmitting terminal may send to data on the receiving terminal subchannel or cross-correlation data.

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 made, is equal to replacement, improvement etc., all should be included within the scope of protection of the invention.

Claims (26)

1, a kind of synchronous estimation method of orthogonal frequency division multiplex OFDM technology is characterized in that, this method comprises:

Obtain and satisfy the subchannel of setting transmission quality requirements in the current OFDM symbol; Calculate the phase difference between the data on the subchannel that data on the subchannel that obtains in the current OFDM symbol are adjacent same position in the OFDM symbol; Utilize the phase difference that is calculated, estimate the residue carrier frequency shift and the sampling clock offset of described current OFDM symbol.

2, method according to claim 1, it is characterized in that, the described subchannel that satisfies the setting transmission quality requirements in the current OFDM symbol that obtains comprises: according to the signal to noise ratio of current OFDM symbol sub-channels, obtain to satisfy in the current OFDM symbol and set the subchannel that signal to noise ratio requires.

3, method according to claim 1, it is characterized in that, described obtain in the current OFDM symbol satisfied the subchannel of setting transmission quality requirements and comprised: according to the relation between the corresponding data in each sub-channel data and the planisphere in the current OFDM symbol, obtain satisfy in the current OFDM symbol with planisphere in corresponding data set the subchannel of relation requirement.

4, method according to claim 1 is characterized in that, the subchannel of described satisfied setting transmission quality requirements comprises: satisfy the signal subspace channel of setting transmission quality requirements in the current OFDM symbol.

5, method according to claim 1, it is characterized in that the subchannel of described satisfied setting transmission quality requirements comprises: satisfy to set the signal subspace channel of transmission quality requirements in the current OFDM symbol and satisfy set transmission quality requirements pilot subchannel; Perhaps,

Satisfy the signal subspace channel of setting transmission quality requirements and all pilot subchannel in the current OFDM symbol.

6, method according to claim 4 is characterized in that, the data on the subchannel that obtains in the current OFDM symbol of described calculating are adjacent that the phase difference between the data comprises on the subchannel of same position in the OFDM symbol:

Signal data on the signal subspace channel that obtains in the current OFDM symbol is carried out hard decision obtain hard decision data; According to described hard decision data, signal data in the next OFDM symbol that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent on the signal subspace channel of same position carries out cross-correlation calculation, draws the phase difference between the signal data on the signal subspace channel that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent same position in the next OFDM symbol.

7, method according to claim 4 is characterized in that, the data on the subchannel that obtains in the current OFDM symbol of described calculating are adjacent that the phase difference between the data comprises on the subchannel of same position in the OFDM symbol:

The signal data that data on the signal subspace channel that obtains in the current OFDM symbol is adjacent on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, obtains signal cross-correlation data; Then described signal cross-correlation data are carried out hard decision and obtain hard decision data; And utilize described hard decision data, calculate the phase difference between the signal data on the signal subspace channel that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent same position in the next OFDM symbol.

8, method according to claim 5 is characterized in that, the data on the subchannel that obtains in the current OFDM symbol of described calculating are adjacent that the phase difference between the data comprises on the subchannel of same position in the OFDM symbol:

Signal data on the signal subspace channel that obtains in the current OFDM symbol is carried out hard decision obtain hard decision data; According to described hard decision data, the signal data that data on the signal subspace channel that obtains in the current OFDM symbol is adjacent on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, draws the phase difference between the signal data on the signal subspace channel that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent same position in the next OFDM symbol; And the pilot data that the pilot data on the pilot subchannel of obtaining in the current OFDM symbol is adjacent on the pilot subchannel of same position in the next OFDM symbol carries out cross-correlation calculation, draws the phase difference between the pilot data on the pilot subchannel that pilot data on the pilot subchannel of obtaining in the current OFDM symbol is adjacent same position in the next OFDM symbol.

9, method according to claim 5 is characterized in that, the data on the subchannel that obtains in the current OFDM symbol of described calculating are adjacent that the phase difference between the data comprises on the subchannel of same position in the OFDM symbol:

Signal data in the next OFDM symbol that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent on the signal subspace channel of same position carries out cross-correlation calculation, obtain signal cross-correlation data, and the pilot data on the pilot subchannel of same position carries out cross-correlation calculation in the next OFDM symbol that the pilot data on the pilot subchannel of obtaining in the current OFDM symbol is adjacent, and obtains pilot tone cross-correlation data; Described signal cross-correlation data are carried out hard decision obtain described hard decision data, and utilize described hard decision data and described pilot tone cross-correlation data, calculate the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol that the signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent, and the phase difference between the pilot data on the pilot subchannel of same position in the next OFDM symbol that is adjacent of the pilot data on the pilot subchannel of obtaining in the current OFDM symbol.

10, according to claim 6 or 8 described methods, it is characterized in that, describedly signal data on the signal subspace channel that obtains in the current OFDM symbol is carried out hard decision obtain hard decision data and comprise:

Calculate the distance of signal data each data point in the planisphere on the signal subspace channel that obtains in the current OFDM symbol, the data point on the planisphere that described distance is minimum is as hard decision data.

11, according to claim 6 or 8 described methods, it is characterized in that, described according to described hard decision data, the signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent signal data on the signal subspace channel of same position in the next OFDM symbol and carries out cross-correlation calculation and comprise:

The hard decision data of utilizing hard decision to obtain compensates the signal data on the signal subspace channel that obtains in the current OFDM symbol, signal data in the next OFDM symbol that will be adjacent with current OFDM symbol on the signal subspace channel of same position multiply by the conjugation of the signal data after the compensation of the signal subspace channel that obtains in the current OFDM symbol, the cross-correlation data on the signal subspace channel that obtains obtaining.

12, according to claim 7 or 9 described methods, it is characterized in that, described signal cross-correlation data carried out hard decision comprise:

The distance of each the cross-correlation data in the goal set of the cross-correlation data on the signal subspace channel that calculating is obtained, the cross-correlation data point in the goal set that described distance is minimum is as hard decision data; Wherein,

Described goal set is: the data that the data on the constellation figure of data institute on current each subchannel of OFDM symbol are adjacent on the data constellation figure on the OFDM symbol same position subchannel are carried out the cross-correlation data acquisition system that cross-correlation calculation obtains.

13, according to claim 7 or 9 described methods, it is characterized in that the signal data in the described next OFDM symbol that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent on the signal subspace channel of same position carries out cross-correlation calculation and comprises:

The conjugation of the signal data on the signal subspace channel that obtains in the current OFDM symbol be multiply by the signal data on the signal subspace channel of same position in the next OFDM symbol that is adjacent.

14, according to Claim 8 or 9 described methods, it is characterized in that the pilot data in the described next OFDM symbol that pilot data on the pilot subchannel of obtaining in the current OFDM symbol is adjacent on the pilot subchannel of same position carries out cross-correlation calculation and comprises:

The conjugation of the pilot data on the pilot subchannel of obtaining in the current OFDM symbol be multiply by the pilot data on the same position in the next OFDM symbol that is adjacent.

15, method according to claim 7, it is characterized in that, utilize described hard decision data, calculate that the phase difference between the signal data comprises on the signal subspace channel that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent same position in the next OFDM symbol:

Utilize described judgement data that described cross-correlation data are compensated, calculate the phase place of the cross-correlation data after the compensation, the signal data on the signal subspace channel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol.

16, method according to claim 9, it is characterized in that, described described hard decision data and the described pilot tone cross-correlation data utilized, calculate the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol that the signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent, and the phase difference between the pilot data on the pilot subchannel of same position comprises in the next OFDM symbol that is adjacent of the pilot data on the pilot subchannel of obtaining in the current OFDM symbol:

Utilize described judgement data that the cross-correlation data on the described signal subspace channel are compensated, calculate the phase place of the described cross-correlation data after compensating, the phase difference between the signal data in the next OFDM symbol that the signal data on the signal subspace channel that obtains obtaining in the current OFDM symbol is adjacent on the signal subspace channel of same position; Utilize known transmitting terminal pilot tone cross-correlation data that the cross-correlation data on the described pilot subchannel are compensated, calculate the phase place of the cross-correlation data on the pilot subchannel after compensating, the phase difference between the pilot data in the next OFDM symbol that the pilot data on the pilot subchannel that obtains obtaining in the current OFDM symbol is adjacent on the pilot subchannel of same position.

According to claim 15 or 16 described methods, it is characterized in that 17, the phase difference that described utilization calculated estimates that the sampling clock offset of described current OFDM symbol comprises:

Each phase difference that calculates is weighted on average, draws the sampling clock offset of described current OFDM symbol.

18, method according to claim 17, it is characterized in that, the residue carrier frequency shift of estimating described current OFDM symbol comprises: according to the relation between the sampling clock offset of the described described current OFDM symbol that compensates the phase place of the cross-correlation data on signals selected subchannel in back and the pilot subchannel and draw, obtain the residue carrier frequency shift of current OFDM symbol.

19, method according to claim 1 is characterized in that, this method further comprises: utilize the residue carrier frequency shift of described estimation and sampling clock offset that the data on each subchannel on the next OFDM symbol are compensated.

20, a kind of synchronous estimating system of OFDM technology is characterized in that, this system comprises: channel selected cell, phase difference calculating unit and estimation unit;

The channel selected cell is used for obtaining current OFDM symbol and satisfies the subchannel of setting transmission quality requirements;

The phase difference calculating unit is used for calculating the phase difference between the data on the subchannel that data on the subchannel that current OFDM symbol obtains by the channel selected cell are adjacent same position in the OFDM symbol, and the phase difference that calculates is offered estimation unit;

The phase difference that utilizes the phase difference calculating unit to provide is provided estimation unit, estimates the residue carrier frequency shift and the sampling clock offset of described current OFDM symbol.

21, system according to claim 20 is characterized in that, described channel selected cell comprises: quality detection module and signal subspace channel are selected module;

Quality detection module is used for detecting the transmission quality of current OFDM symbol signal subspace channel, and concurrent censorship is surveyed the result and selected module for the signal subspace channel;

The signal subspace channel is selected module, is used for the testing result that quality of reception detection module sends, and according to described testing result, selects to satisfy in the current OFDM symbol signal subspace channel of setting transmission quality requirements.

22, system according to claim 21, it is characterized in that, described channel selected cell also comprises: the pilot subchannel selected cell, be used for selecting all pilot subchannel of current OFDM symbol, perhaps, the testing result that quality of reception detection module sends, and, select to satisfy in the current OFDM symbol pilot subchannel of setting transmission quality requirements according to described testing result;

Described quality-monitoring module also is used for detecting the transmission quality of current OFDM symbol pilot subchannel, and concurrent censorship is surveyed the result and selected module to pilot subchannel.

23, system according to claim 21 is characterized in that, described phase difference calculating unit comprises: the first cross-correlation calculation module, hard decision module, first compensating module and phase difference calculating module;

The first cross-correlation calculation module, signal data in the next OFDM symbol that signal data on the signal subspace channel that is used for current OFDM symbol is obtained is adjacent on the signal subspace channel of same position carries out cross-correlation calculation, and the signal cross-correlation data that obtain are offered the hard decision module and first compensating module;

The hard decision module is used for to the received signal the cross-correlation data and carries out hard decision, and the judgement data that obtain behind the hard decision are offered first compensating module;

First compensating module, be used to receive the judgement data of hard decision module transmission and the signal cross-correlation data that the first cross-correlation calculation module sends, and utilize described judgement data that described signal cross-correlation data are compensated, and the signal cross-correlation data after will compensating send to the phase difference calculating module;

The phase difference calculating module, be used to receive the signal cross-correlation data after the described compensation, calculate the phase place of described signal cross-correlation data, the signal data on the signal subspace channel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol.

24, system according to claim 22, it is characterized in that described phase difference calculating unit comprises: the first cross-correlation calculation module, hard decision module, first compensating module, phase difference calculating module, the second cross-correlation calculation module and second compensating module;

The first cross-correlation calculation module, signal data in the next OFDM symbol that signal data on the signal subspace channel that is used for current OFDM symbol is obtained is adjacent on the signal subspace channel of same position carries out cross-correlation calculation, and the signal cross-correlation data that obtain are offered the hard decision module and first compensating module;

The hard decision module is used for to the received signal the cross-correlation data and carries out hard decision, and the judgement data that obtain behind the hard decision are offered first compensating module;

First compensating module, be used to receive the judgement data of hard decision module transmission and the signal cross-correlation data that the first cross-correlation calculation module sends, and utilize described judgement data that described signal cross-correlation data are compensated, and the signal cross-correlation data after will compensating send to the phase difference calculating module;

The second cross-correlation calculation module, the pilot data that pilot data on the pilot subchannel that is used for current OFDM symbol is obtained is adjacent on the pilot subchannel of same position in the next OFDM symbol carries out cross-correlation calculation, and the pilot tone cross-correlation data that obtain are offered second compensating module;

Second compensating module is used to utilize known transmitting terminal pilot tone cross-correlation data, and the pilot tone cross-correlation data that the second cross-correlation calculation module is sent compensate, and the pilot tone cross-correlation data that obtain after will compensating offer the phase difference calculating module;

The phase difference calculating module, be used to receive the cross-correlation data of the signal data after the described compensation, calculate the phase place of the signal cross-correlation data after the described compensation, the signal data on the signal subspace channel that obtains obtaining in the described current OFDM symbol is adjacent the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol; Be used to receive the pilot tone cross-correlation data after the compensation, calculate the phase place of the pilot tone cross-correlation data after the compensation, the pilot data on the pilot subchannel that obtains obtaining in the described current OFDM symbol is adjacent the phase difference between the pilot data on the pilot subchannel of same position in the next OFDM symbol.

25, system according to claim 21 is characterized in that, described phase difference calculating unit comprises: hard decision module, compensating module, the first cross-correlation calculation module and phase difference calculating module;

The hard decision module, the signal data on the signal subspace channel that is used for signal subspace channel selection module is obtained carries out hard decision, and the judgement data that obtain behind the hard decision are offered compensating module;

Compensating module is used to receive the judgement data that the hard decision module provides, and utilizes described judgement data, the signal data on the signal subspace channel that obtains is compensated, and the signal data after will compensating sends to the first cross-correlation calculation module;

The first cross-correlation calculation module, the signal data that signal data after the compensation on the signal subspace channel that is used for current OFDM symbol is obtained is adjacent after the compensation on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, and the signal cross-correlation data that obtain are offered the phase difference calculating module;

The phase difference calculating module, receive the signal cross-correlation data that the first cross-correlation calculation module provides, calculate the phase place of described signal cross-correlation data, the signal data on the signal subspace channel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the signal data on the signal subspace channel of same position in the next OFDM symbol.

26, system according to claim 22 is characterized in that, described phase difference calculating unit comprises: hard decision module, compensating module, the first cross-correlation calculation module, the second cross-correlation calculation module and phase difference calculating module;

The hard decision module, the signal data on the signal subspace channel that is used for signal subspace channel selection module is obtained carries out hard decision, and the judgement data that obtain behind the hard decision are offered compensating module;

Compensating module is used to receive the judgement data that the hard decision module provides, and utilizes described judgement data, the signal data on the signal subspace channel that obtains is compensated, and the signal data after will compensating sends to the first cross-correlation calculation module;

The first cross-correlation calculation module, the signal data that signal data after the compensation on the signal subspace channel that is used for current OFDM symbol is obtained is adjacent after the compensation on the signal subspace channel of same position in the next OFDM symbol carries out cross-correlation calculation, and the signal cross-correlation data that obtain are offered the phase difference calculating module;

The second cross-correlation calculation module, the pilot data that pilot data on the pilot subchannel that is used for current OFDM symbol is obtained is adjacent on the pilot subchannel of same position in the next OFDM symbol carries out cross-correlation calculation, and the pilot tone cross-correlation data that obtain are offered the phase difference calculating module;

The phase difference calculating module, receive the signal cross-correlation data that the first cross-correlation calculation module provides, calculate the phase place of described signal cross-correlation data, draw the phase difference between the signal data on the signal subspace channel that signal data on the signal subspace channel that obtains in the current OFDM symbol is adjacent same position in the next OFDM symbol; The pilot tone cross-correlation data that provide according to the second cross-correlation calculation module, calculate the phase place of described pilot tone cross-correlation data, the pilot data on the pilot subchannel that obtains obtaining in the current OFDM symbol is adjacent the phase difference between the pilot data on the pilot subchannel of same position in the next OFDM symbol.

Images