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

Synchronization estimation method and system of orthogonal frequency division multiplexing technology

Technical Field

The present invention relates to Orthogonal Frequency Division Multiplexing (OFDM) technologies, and in particular, to a synchronization estimation method and system for OFDM technologies.

Background

OFDM is a frequency division multiplexing technology capable of transmitting high-speed data services, and has high frequency band utilization rate and strong anti-multipath interference capability, so that OFDM receives increasing attention and attention, is considered to be one of the preferred technologies for future wireless multimedia mobile communication, and has been applied to the physical layer series standard of wireless local area networks, the digital audio broadcasting standard (DAB) in europe, and the digital time-frequency standard (DVB).

Although a number of technical standards have been established for OFDM transmission technology, there are still a number of challenges in OFDM technology. Synchronization is one of the technical problems existing in the establishment of the OFDM transmission standard, an OFDM system is very sensitive to synchronization errors, and the very small synchronization errors can cause the serious reduction of the system performance. In OFDM systems, synchronization generally involves two processes: the first step is synchronous capture, namely synchronization established at the beginning of data transmission; the second step is the estimation of the remaining synchronization offset.

In the data transmission process, due to the influence of doppler shift, the Carrier frequency stability of both the transmitting and receiving parties is limited, and the instability of the sampling clock oscillators of both the transmitting and receiving parties causes the existence of residual Carrier frequency offset and sampling clock offset, although the numerical values of the synchronization errors are small, the signal amplitude on the sub-channels is reduced, the orthogonality among the sub-channels is damaged, and Inter-Carrier Interference (ICI) is introduced, so that the system error rate is increased. For the synchronization problem during data transmission, there are two synchronization estimation methods of the OFDM system, the first is pilot tone-Aided (PTA) synchronization estimation method, and the second is non-pilot-Aided synchronization estimation method.

Before describing the two methods of the prior art, it is necessary to briefly describe the structure of the OFDM symbol and the synchronization signal model of the OFDM system. First, a structure of an OFDM symbol is explained, where the OFDM symbol includes a cyclic prefix portion and a data portion, where the data portion includes: pilot data and signal data, as shown in fig. 1, c_m(k) K-th signal data, p, representing the m-th OFDM symbol_m(k) Indicating the kth pilot data of the mth OFDM symbol. m and m +1 denote the m and m +1 th OFDM symbols, p_m(k) And p_m+1(k) Which are the pilot data in two OFDM symbols, respectively, that are typically used to extract channel information and perform channel estimation. One OFDM symbol includes N_gThe N sub-channels are divided into pilot sub-channels and signal sub-channels, the pilot sub-channels bear pilot data, and the signal sub-channels bear signal data.

The following describes a synchronization signal model of an OFDM system. In an OFDM transmission system, if an OFDM system modulation uses an Inverse Discrete Fourier Transform (IDFT), that is, one OFDM symbol contains N data; the OFDM system adopts K +1 sub-channels to transmit information, wherein K is less than N; the sampling clock period of the OFDM system is T; one OFDM symbol includes two in time domainThe method comprises the following steps: a data portion and a cyclic prefix portion, wherein the cyclic prefix is N in time_gT to overcome interference between signals caused by multipath; one OFDM symbol contains N_sA sampling point, N_s＝N+N_g。

At this time, the complex baseband signal x of the mth OFDM symbol transmitted by the transmitting end_m(t) can be expressed as:

<math> <mrow> <msub> <mi>x</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <msqrt> <mi>N</mi> </msqrt> </mfrac> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mo>-</mo> <mi>K</mi> <mo>/</mo> <mn>2</mn> </mrow> <mrow> <mi>K</mi> <mo>/</mo> <mn>2</mn> </mrow> </munderover> <msub> <mi>c</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <msup> <mi>e</mi> <mrow> <mi>j</mi> <mn>2</mn> <mi>&pi;k</mi> <mo>[</mo> <mi>t</mi> <mo>-</mo> <mrow> <mo>(</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>+</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>)</mo> </mrow> <mi>T</mi> <mo>]</mo> <mo>/</mo> <mrow> <mo>(</mo> <mi>NT</mi> <mo>)</mo> </mrow> </mrow> </msup> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

(1) in the formula c_m，kIs the modulated complex data on the kth sub-channel of the mth OFDM symbol of the transmitting end.

Discrete-time impulse response h of transmission channel of mth OFDM symbol in OFDM transmission system_m(k) Can be expressed as:

<math> <mrow> <msub> <mi>h</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>S</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msub> <mi>h</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mi>&delta;</mi> <mrow> <mo>(</mo> <mi>k</mi> <mo>-</mo> <msub> <mi>&tau;</mi> <mi>k</mi> </msub> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

(2) where δ (k) denotes an impulse function, { h {_m，k k 0.., S-1 is the k-th path complex gain during the m-th OFDM symbol, { τ_kThe "is the path delay of the kth path, which is usually taken as an integer multiple of the sampling time, and S is the total number of paths in the radio channel.

Assuming that the timing of the signal has reached synchronization and carrier frequency offset estimation and compensation in the initial synchronization acquisition phase has been completed, synchronization estimation in the data transmission process will be performed below. In this process, the remaining carrier frequency offset and sampling clock offset estimation of the OFDM synchronization phase needs to be performed.

After the complex baseband signal at the transmitting end is transmitted through the transmission channel, the carrier frequency at the receiving end is f ', the sampling clock period is T', and it is assumed that when m is equal to 0, the system is strictly synchronous, and at this time, the remaining synchronization errors may be:

the residual carrier frequency error Δ f is: Δ f ═ f-f';

the sampling clock error β is: β ═ T-T')/T. (3)

At the receiving end, after sampling and cyclic prefix removal are performed by using a sampling clock with a clock period T', the complex baseband signal sample of the mth OFDM symbol may be represented as:

r_m，n＝r(t_n)，0≤n≤N-1，t_n＝(mN_s+N_g)T′+nT′； (4)

after the N sampled data of the mth symbol is demodulated by fourier transform, the data on each subchannel can be represented as:

<math> <mrow> <msub> <mi>Z</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>N</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msub> <mi>r</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>j</mi> <mfrac> <mrow> <mn>2</mn> <mi>&pi;kn</mi> </mrow> <mi>N</mi> </mfrac> </mrow> </msup> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <mo>=</mo> <msup> <mi>e</mi> <mrow> <mi>j</mi> <mn>2</mn> <mi>&pi;&Delta;f</mi> <mrow> <mo>(</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mi>&beta;</mi> <mo>)</mo> </mrow> <mi>T</mi> </mrow> </msup> <mo>&CenterDot;</mo> <msup> <mi>e</mi> <mrow> <mi>j</mi> <mfrac> <mrow> <mn>2</mn> <mi>&pi;k</mi> </mrow> <mi>N</mi> </mfrac> <mrow> <mo>(</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>&beta;</mi> </mrow> </msup> <msub> <mi>H</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <msub> <mi>c</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <msub> <mi>&alpha;</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>n</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>I</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </mrow> </math>

(5) in the formula <math> <mrow> <msub> <mi>H</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>l</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>K</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msub> <mi>h</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>&tau;</mi> <mi>l</mi> </msub> <mi>k</mi> <mo>/</mo> <msub> <mi>T</mi> <mi>u</mi> </msub> </mrow> </msup> <mo>,</mo> </mrow> </math> Wherein, T_u＝NT，n_m(k) Is the Gaussian noise, I, on the k-th sub-channel during the m-th OFDM symbol_m(k) Is an interference signal between sub-channels, and because the residual synchronization error is relatively small, the interference signal between sub-channels is usually equivalent to white gaussian noise, alpha_m，kIs the attenuation coefficient of the signal on the k-th sub-channel caused by the synchronization error, and alpha is the attenuation coefficient of the signal on the k-th sub-channel due to the small residual synchronization error_m，kThe process proceeds to 1.

The first method of the prior art is described below: PTA synchronization estimation method. After Fourier transformation is carried out on signals at a receiving end, pilot frequency data on all pilot frequency sub-channels in an OFDM symbol are extracted, and the phase of the extracted pilot frequency data is calculated; performing cross-correlation calculation on adjacent OFDM symbols according to the phase of the pilot data, namely calculating the phase difference of data on the same pilot position of the adjacent OFDM symbols; the phase difference resulting from the cross-correlation calculation is used to estimate the remaining carrier frequency offset and the sampling clock offset.

The PTA synchronous estimation method is simple and easy to implement, but in the method, the pilot frequency in OFDM symbolNumber N_pAnd the transmission quality of the pilot subchannel directly influences the estimation precision of the residual carrier frequency offset and the sampling clock in the system, while in the existing OFDM transmission technology, the data of the pilot is less, and the influence of the transmission quality of the wireless channel limits the precision of the PTA synchronous estimation method.

The second method of the prior art is described below: a data-directed (DD) synchronization estimation method. The method mainly comprises the following steps: compensating the data of the OFDM symbol of the receiving end by using the known channel estimation parameters; carrying out hard decision on the data in the OFDM symbol after compensation; after compensating the data subjected to hard decision, performing cross-correlation calculation on the data in the adjacent compensated OFDM symbols; and estimating the residual carrier frequency offset and the sampling clock offset according to the result of the cross-correlation calculation.

The method does not need to extract pilot frequency, but the sub-channel with poor channel transmission quality can generate error codes in hard decision, and the generated error codes can introduce interference in synchronous estimation to influence the precision of the synchronous estimation method.

As can be seen from the above description, the synchronization estimation methods in the prior art are all affected by the sub-channel with poor transmission quality, and the accuracy of synchronization estimation is reduced.

Disclosure of Invention

In view of this, embodiments of the present invention provide a synchronization estimation method and system for an OFDM system, so as to improve accuracy of synchronization estimation.

The embodiment of the invention provides a synchronous estimation method of an OFDM system, which comprises the following steps:

acquiring a subchannel which meets the set transmission quality requirement in the current OFDM symbol; calculating the phase difference between the data on the sub-channel acquired in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol; estimating a remaining carrier frequency offset and a sampling clock offset of the current OFDM symbol using the calculated phase difference.

The embodiment of the invention also provides a synchronous estimation system of the OFDM system, which comprises: a channel selection unit, a phase difference calculation unit, and an estimation unit;

the channel selection unit is used for acquiring a sub-channel which meets the set transmission quality requirement in the current OFDM symbol;

the phase difference calculation unit is used for calculating the phase difference between the data on the sub-channel acquired from the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol, and providing the calculated phase difference to the estimation unit;

and the estimation unit is used for estimating the residual carrier frequency offset and the sampling clock offset of the current OFDM symbol by using the phase difference provided by the phase difference calculation unit.

It can be seen from the above that, in the synchronization estimation method and system of the OFDM technology provided in the embodiments of the present invention, the remaining carrier frequency offset and the sampling clock offset are estimated by using the acquired cross-correlation data on the sub-channel that meets the set transmission quality requirement, so that the influence of error code generated in the sub-channel with poor transmission quality is avoided, and the accuracy of synchronization estimation is improved to a great extent.

Drawings

Fig. 1 is a schematic diagram of an OFDM symbol structure;

fig. 2 is a flowchart of a synchronization estimation method of an OFDM system according to an embodiment of the present invention;

fig. 3 is another flowchart of a synchronization estimation method of an OFDM system according to an embodiment of the present invention;

FIG. 4.a is a block diagram of a synchronization estimation system according to an embodiment of the present invention;

fig. 4.b is a structural diagram of a channel selection unit according to an embodiment of the present invention;

fig. 4 c is a first structural diagram of a phase difference calculating unit according to an embodiment of the present invention;

fig. 4 d is a second structural diagram of a phase difference calculating unit according to an embodiment of the present invention;

FIG. 5 is a plot of the Mean Square Error (MSE) of the residual frequency offset (RCFO) for the method and PTA method provided by embodiments of the present invention, when different thresholds are used;

FIG. 6 is a MSE (mean square error) plot of sample clock offset (SFO) for the method and PTA method provided by the embodiments of the present invention when different thresholds are used;

FIG. 7 is a graph of estimated performance for the method of the present invention and the PTA method at the same sample clock offset normalization value and different remaining carrier frequency offset normalization values;

FIG. 8 is a graph of estimated performance for the method of the present invention and the PTA method at the same remaining carrier frequency offset normalization value and different sampling clock offset normalization values;

fig. 9 is a plot of residual carrier frequency offset tracking for the inventive process and PTA process under the same conditions;

fig. 10 is a sample clock offset tracking curve for the inventive process and the PTA process under the same conditions.

Detailed Description

In order to make the technical solution, objects and advantages described above more apparent, the present invention will be described in detail with reference to specific embodiments.

The synchronization estimation method of the OFDM system provided by the embodiment of the invention mainly comprises the following steps: acquiring a subchannel which meets the set transmission quality requirement in the current OFDM symbol; calculating the phase difference between the data on the sub-channel acquired in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol; estimating a remaining carrier frequency offset and a sampling clock offset of the current OFDM symbol using the calculated phase difference.

Here, the OFDM symbol used in channel estimation is used as the current OFDM symbol.

Wherein, all the sub-channels meeting the set transmission quality requirement in the obtained OFDM symbols may be signal sub-channels meeting the set transmission quality requirement; it may also include a subchannel for pilot data that meets the set transmission quality requirement and a signal subchannel for a signal that meets the set transmission quality requirement.

When all the sub-channels satisfying the set transmission quality requirement in the obtained OFDM symbol are signal sub-channels satisfying the set transmission quality requirement, the method may further include: and picking out the pilot frequency sub-channel in the OFDM symbol.

The following two ways may be used to calculate the phase difference between the data on the sub-channel obtained from the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol:

the first mode is as follows: and performing cross-correlation calculation on data on a subchannel acquired from the current OFDM symbol and data on a subchannel at the same position in the adjacent OFDM symbol to obtain cross-correlation data, performing hard decision on the acquired signal cross-correlation data on the subchannel, and calculating the phase difference of the subchannel data acquired from the adjacent OFDM symbol according to the decision data obtained by the hard decision.

The second mode is as follows: firstly, hard decision is carried out on the data on the obtained sub-channel, then, according to the result of the hard decision, the data on the sub-channel obtained in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol are subjected to cross-correlation calculation, and the phase difference of the data on the sub-channel obtained in the adjacent OFDM symbol is obtained.

The first method is taken as an example to describe the synchronization estimation of the OFDM system in detail. Fig. 2 is a flowchart of a synchronization estimation method of an OFDM system according to an embodiment of the present invention, and as shown in fig. 2, the method mainly includes the following steps:

step 201: and in the current OFDM symbol, selecting a signal sub-channel which meets the set transmission quality requirement, and selecting all pilot frequency sub-channels.

In addition to this, there may be another way to select the signal sub-channels that satisfy the set transmission quality requirement, and select the sub-channels that satisfy the set transmission quality requirement in the pilot sub-channels.

The selection of the signal sub-channel satisfying the set transmission quality requirement in the OFDM symbol may be: and selecting the signal sub-channels with the transmission quality higher than the quality threshold in the OFDM symbols.

Because the transmission quality of the channel has a corresponding relation with the signal-to-noise ratio, a selection method based on the signal-to-noise ratio of the sub-channel can be adopted to select the sub-channel with high transmission quality. At this time, the quality threshold is a signal-to-noise ratio threshold. This selection can be expressed as:

ζ＝{l|SNR_m(l)≥SNR_th} (6)

(6) in the formula: SNR_m(l) Signal-to-noise ratio, SNR, on the l sub-channel for the m symbol_thA threshold is selected for the signal-to-noise ratio and ζ is the set of acquired subchannel coefficients.

When the SNR threshold is selected, if the selected SNR threshold is too low, more sub-channel data are acquired, but when the SNR is low, the quality of data on the selected sub-channel is low, and the data on the sub-channels generate error codes to influence the precision of synchronous estimation; if the selected snr threshold is too high, the number of selected sub-channels is reduced and the accuracy of the synchronization estimation is also affected. The selected SNR threshold can be determined by simulation based on theoretical function.

In addition, the step can also adopt a selection method of the signal-to-noise ratio sequencing of the sub-channels. Sorting according to the magnitude of the signal-to-noise ratio of each sub-channel, and finally selecting the sub-channels with the set number from the sub-channels according to the number of the high-quality sub-channels initially set by the system from the large sub-channels to the small sub-channels.

In addition, the step may also adopt a selection method based on the minimum decision distance. Respectively calculating the distance between the data in each sub-channel and each corresponding data in the constellation diagram, and selecting the sub-channel with the distance satisfying the distance threshold condition, wherein the selection method can be represented as:

ζ＝{l|d_m(l)≤d_th}

wherein d is_m(l) Is the distance, d, between the data in the mth subchannel and the corresponding data in the constellation diagram_thIs a set distance threshold.

In addition, the step can also adopt a selection method based on the minimum phase. Respectively calculating phase deviation values between data in each sub-channel and corresponding data in a constellation diagram, and selecting the sub-channel with the phase deviation value meeting the phase deviation threshold condition, wherein the selection method can be expressed as:

ζ＝{l|ρ_m(l)≤ρ_th}

where ρ is_m(l) Is the phase offset value, rho, between the data in the mth subchannel and the corresponding data in the constellation diagram_thIs a set phase shift threshold.

Step 202: the signal data on the signal subchannel and the pilot data on the pilot subchannel selected in step 201 in the current OFDM symbol and the signal data and the pilot data at the same positions between the adjacent OFDM symbols in the current OFDM symbol are respectively subjected to cross-correlation calculation.

In this step, the cross-correlation calculation is performed between the signal data on the signal sub-channel obtained in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol, and is performed by multiplying the signal data on a selected sub-channel position of the next OFDM symbol by the conjugate of the signal data on the same sub-channel position of the previous OFDM symbol. Other ways of cross-correlation calculation may also be used.

In addition, the OFDM symbol adjacent to the current OFDM symbol used in the embodiment of the present invention is the next OFDM symbol adjacent to the current OFDM symbol, and in addition, when the channel is static or changes slowly, the previous OFDM symbol adjacent to the current OFDM symbol may also be used.

In this step, the cross-correlation calculation is performed between the pilot data on the pilot subchannel acquired in the current OFDM symbol and the pilot data on the pilot subchannel at the same position in the next adjacent OFDM symbol, and the pilot data at a certain pilot position of the next OFDM symbol is multiplied by the conjugate of the pilot data at the same pilot position of the previous OFDM symbol.

And performing cross-correlation calculation on the data of the sub-channels between the adjacent OFDM symbols, wherein the reflected phase is the phase difference of the data of the sub-channels in the adjacent OFDM symbols.

In this step, the cross-correlation calculation between adjacent OFDM symbols is adopted because the phase offset caused by the remaining carrier frequency offset and the sampling clock offset increases with the increase of OFDM symbols, and finally, the data in the OFDM symbols shifts from one quadrant to another quadrant, so that the accumulation of multiple OFDM symbols makes it impossible to obtain a correct decision result by using simple hard decision in the following steps.

Since it is generally assumed that the fading of the channel is slowly varying, i.e. the channel coefficients on the sub-channel can be considered to be the same during the mth OFDM symbol and the M +1 OFDM symbol, i.e.: h_m(k)≈H_m+1(k) From equation (5) in the synchronization signal model, we can obtain:

at the receiving end, the data of the kth sub-channel of the m-th and m + 1-th OFDM symbols are respectively:

$Z_m\left(k\right)=$

<math> <mrow> <mi>exp</mi> <mrow> <mo>(</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;&epsiv;</mi> <mfrac> <mrow> <mo>(</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>N</mi> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mi>&beta;</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;</mi> <mfrac> <mrow> <mo>(</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>N</mi> </mfrac> <mi>k&beta;</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msub> <mi>H</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msub> <mi>c</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>n</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>7</mn> <mo>)</mo> </mrow> </mrow> </math>

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

<math> <mrow> <mi>exp</mi> <mrow> <mo>(</mo> <msub> <mi>j&phi;</mi> <mi>k</mi> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;&epsiv;</mi> <mfrac> <mrow> <mo>(</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>N</mi> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mi>&beta;</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>j</mi> <mn>2</mn> <mi>&pi;</mi> <mfrac> <mrow> <mo>(</mo> <mi>m</mi> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>)</mo> </mrow> <mi>N</mi> </mfrac> <mi>k&beta;</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msub> <mi>H</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msub> <mi>c</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </mrow> </math>

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

wherein phi is_k≈2π(1+N_g/N)(ε+k·β) (9)

And epsilon is a residual carrier frequency offset normalization value, and epsilon is delta fNT.

The cross-correlation data R on the ith signal subchannel of the mth and (m + 1) th OFDM symbols can be obtained from the equations (7) and (8)_m(l) Comprises the following steps:

<math> <mrow> <msub> <mi>R</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>Z</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>Z</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mi>j</mi> <msub> <mi>&phi;</mi> <mi>l</mi> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msup> <mrow> <mo>|</mo> <msub> <mi>H</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>&CenterDot;</mo> <msub> <mi>c</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>c</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mover> <mi>n</mi> <mo>~</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> <mi>l</mi> <mo>&Element;</mo> <mi>&zeta;</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>10</mn> <mo>)</mo> </mrow> </mrow> </math>

where, ζ is a set of subchannel coefficients corresponding to the selected signal subchannels satisfying the set transmission quality requirement.

Similarly, the cross-correlation data Q on the l pilot subchannel of the m-th and m + 1-th OFDM symbols can be obtained from the equations (7) and (8)_m(l) Comprises the following steps:

<math> <mrow> <msub> <mi>Q</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>Z</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>Z</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mi>j</mi> <msub> <mi>&phi;</mi> <mi>l</mi> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msup> <mrow> <mo>|</mo> <msub> <mi>H</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>&CenterDot;</mo> <msub> <mi>p</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>p</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mover> <mi>n</mi> <mo>~</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> <mi>l</mi> <mo>&Element;</mo> <mi>&gamma;</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>11</mn> <mo>)</mo> </mrow> </mrow> </math>

where γ is a set of subchannel coefficients corresponding to the pilot subchannel.

Step 203: and carrying out hard decision on the cross-correlation data on the selected signal sub-channels meeting the set transmission quality requirement.

The hard decision of the cross-correlation data on the signal sub-channel meeting the set transmission quality requirement is to obtain the influence of the data sent by the sending end on the cross-correlation data, and the error influence of the data of the sending end on the residual synchronous estimation of the receiving end can be eliminated according to the hard decision result.

The making of the hard decision is: correlating the data on the selected signal sub-channels to respective ones of the target setAnd (4) distance of related data points, namely, taking the cross-correlation data points in a target set closest to the cross-correlation data on the selected signal subchannel as the cross-correlation data, namely, hard decision data. The hard decision result

(l) Can be expressed as:

<math> <mrow> <msub> <mover> <mi>F</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <munder> <mrow> <mi>arg</mi> <mi>min</mi> </mrow> <mrow> <msub> <mi>E</mi> <mi>t</mi> </msub> <mo>&Element;</mo> <mi>&Omega;</mi> </mrow> </munder> <mo>{</mo> <msup> <mrow> <mo>|</mo> <msub> <mi>R</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>E</mi> <mi>t</mi> </msub> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>}</mo> <mo>,</mo> </mrow> </math> l∈ζ (12)

wherein, <math> <mrow> <mi>&Omega;</mi> <mo>=</mo> <mo>{</mo> <msub> <mi>E</mi> <mi>t</mi> </msub> <mo>|</mo> <msub> <mi>E</mi> <mi>t</mi> </msub> <mo>=</mo> <msub> <mi>e</mi> <mi>u</mi> </msub> <mo>&CenterDot;</mo> <msubsup> <mi>e</mi> <mi>v</mi> <mo>*</mo> </msubsup> <mo>,</mo> <msub> <mi>e</mi> <mi>u</mi> </msub> <mo>,</mo> <msub> <mi>e</mi> <mi>v</mi> </msub> <mo>&Element;</mo> <mi>&Pi;</mi> <mo>,</mo> <mi>t</mi> <mo>=</mo> <mn>1,2</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <mi>M</mi> <mo>}</mo> <mo>,</mo> </mrow> </math> omega is a target set, pi is a set of data on a corresponding constellation diagram of the data on the sub-channel, and a cross-correlation data point E in the target set omega_tIs a set formed by the cross-correlation calculation of the data in ii.

Step 204: compensating the cross-correlation data of the signal sub-channels meeting the set transmission quality requirement by using the hard decision result; and compensates the pilot cross-correlation data calculated in step 203 using the known transmit-side pilot cross-correlation data.

This step obtains cross-correlation data carrying a phase offset on the receive terminal channel by compensation. At the receiving end, the cross-correlation data carrying the phase offset is obtained by taking the influence of the cross-correlation data of the receiving end data. The compensation comprises the following steps: on a signal sub-channel meeting the set transmission quality requirement, replacing the cross-correlation data of the known data of the sending end by the judgment result; on the pilot subchannel, the known sending-end pilot cross-correlation data is used for eliminating the influence of the sending-end pilot cross-correlation data on the receiving-end cross-correlation data.

The compensation of the equation (10) by the equation (12) can obtain the cross-correlation function X carrying the phase offset on the ith signal subchannel of the mth OFDM symbol_m(l) Comprises the following steps:

<math> <mrow> <msub> <mi>X</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>R</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>F</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>exp</mi> <mrow> <mo>(</mo> <mi>j</mi> <msub> <mi>&phi;</mi> <mi>l</mi> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msup> <mrow> <mo>|</mo> <msub> <mi>H</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msub> <mover> <mi>w</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> <mi>l</mi> <mo>&Element;</mo> <mi>&zeta;</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>13</mn> <mo>)</mo> </mrow> </mrow> </math>

due to the known pilot cross-correlation function D of the transmitting end_m(l) Comprises the following steps:

<math> <mrow> <msub> <mi>D</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>p</mi> <mrow> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>p</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> <mi>l</mi> <mo>&Element;</mo> <mi>&gamma;</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>14</mn> <mo>)</mo> </mrow> </mrow> </math>

the compensation of equation (11) by equation (14) can obtain the cross-correlation function X carrying the phase offset on the l pilot subchannel of the m-th OFDM symbol_m(l) Comprises the following steps:

<math> <mrow> <msub> <mi>X</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>Q</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>D</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> <mi>l</mi> <mo>&Element;</mo> <mi>&gamma;</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>15</mn> <mo>)</mo> </mrow> </mrow> </math>

therefore, the cross-correlation data on the sub-channel for the remaining carrier frequency offset and sampling clock offset estimation in the mth OFDM symbol is:

<math> <mrow> <msub> <mi>X</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <msub> <mi>R</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>F</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> </mtd> <mtd> <mi>l</mi> <mo>&Element;</mo> <mi>&zeta;</mi> </mtd> </mtr> <mtr> <mtd> <msub> <mi>Q</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msubsup> <mi>D</mi> <mi>m</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>,</mo> </mtd> <mtd> <mi>l</mi> <mo>&Element;</mo> <mi>&gamma;</mi> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>16</mn> <mo>)</mo> </mrow> </mrow> </math>

step 205: and calculating the phase difference of the subchannel data acquired between the current OFDM symbol and the adjacent OFDM symbol by using the compensated cross-correlation data.

In this step, the phase difference of the signal data on the signal sub-channel obtained in the adjacent OFDM symbol and the phase difference of the pilot data on the pilot sub-channel obtained by using the compensated cross-correlation data may be calculated respectively; or, the set formed by the acquired signal sub-channel and the pilot sub-channel may be averagely divided into two subsets, and then the phase difference of the acquired sub-channel data is obtained by subtracting the phases of the cross-correlation data of the two subsets.

(16) Where the phase phi of the data on the selected sub-channel after compensation_lComprises the following steps:

φ_l≈2π(1+N_g/N)(ε+l·β)，l∈χ (17)

wherein χ is a set of subchannel coefficients corresponding to the pilot subchannel and the high-quality subchannel, that is: ζ + γ.

In this step, all the subchannel coefficients in the set χ may be sorted in the order from small to large, and then the set χ is divided into two subsets χ with equal number of subchannels₁Hexix-₂. Subset χ₁Hexix-₂The phases of the cross-correlation data on the two corresponding sub-channels are respectively phi_l′And phi_l″：

φ_l′≈2π(1+N_g/N)(ε+l′·β)，l′∈χ₁ (18)

φ_l″≈2π(1+N_g/N)(ε+l″·β)，l″∈χ₂ (19)

Then, the phases of the cross-correlation data with larger difference of the corresponding subchannel coefficients in the two sets are subtracted, so that the phase offset caused by the residual carrier frequency offset can be cancelled. Phase difference phi obtained after subtraction_vComprises the following steps:

φ_v＝φ_l′-φl_″≈2π(1+N_g/N)(v·β)，v∈χ₃ (20)

wherein, the set χ₃Set of representations χ₁Hexix-₂The phase difference of the data on the corresponding sub-channel.

This divides the set χ into two subsets χ of equal number of subchannels₁Hexix-₂The method of calculating the phase difference can make the difference between the sub-channel coefficients corresponding to the two sets large, and can further improve the estimation performance.

When all the selected sub-channels with high quality are signal sub-channels, the phase difference may be calculated by dividing the set of the selected sub-channels with high quality into two sub-sets with different phases, and subtracting the phases of the data on the sub-channels in the two sub-sets to obtain the phase difference.

Step 206: using the calculated phase difference, a residual carrier frequency offset and a sampling clock offset are estimated.

The sampling clock offset in the step can be estimated by using a phase difference to carry out weighted average, and the sampling clock offset can be obtained

Comprises the following steps:

<math> <mrow> <mover> <mi>&beta;</mi> <mo>^</mo> </mover> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>&CenterDot;</mo> <mfrac> <mn>1</mn> <mi>L</mi> </mfrac> <munderover> <mi>&Sigma;</mi> <mrow> <mi>m</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>L</mi> </munderover> <mrow> <mo>(</mo> <mfrac> <mrow> <munder> <mi>&Sigma;</mi> <mrow> <mi>v</mi> <mo>&Element;</mo> <msub> <mi>&zeta;</mi> <mn>3</mn> </msub> </mrow> </munder> <mi>v</mi> <mo>&CenterDot;</mo> <msub> <mi>&phi;</mi> <mi>v</mi> </msub> </mrow> <mrow> <munder> <mi>&Sigma;</mi> <mrow> <mi>v</mi> <mo>&Element;</mo> <msub> <mi>&zeta;</mi> <mn>3</mn> </msub> </mrow> </munder> <msup> <mi>v</mi> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>,</mo> <mi>v</mi> <mo>&Element;</mo> <msub> <mi>&chi;</mi> <mn>3</mn> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>21</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein L represents the number of OFDM symbols used for synchronization estimation.

The estimated remaining carrier frequency offset may be: substituting the obtained sampling clock offset into the compensated phase phi of the data on the selected sub-channel_lThat is, the residual carrier frequency offset obtained by substituting (21) into the formula (17)

Comprises the following steps:

<math> <mrow> <mover> <mi>&epsiv;</mi> <mo>^</mo> </mover> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>&CenterDot;</mo> <mfrac> <mn>1</mn> <msub> <mi>N</mi> <mi>c</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <munder> <mi>&Sigma;</mi> <mrow> <mi>l</mi> <mo>&Element;</mo> <mi>&chi;</mi> </mrow> </munder> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mi>l</mi> </msub> <mo>-</mo> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msub> <mi>N</mi> <mi>g</mi> </msub> <mo>/</mo> <mi>N</mi> <mo>)</mo> </mrow> <mrow> <mo>(</mo> <mi>l</mi> <mo>&CenterDot;</mo> <mover> <mi>&beta;</mi> <mo>^</mo> </mover> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>,</mo> <mi>l</mi> <mo>&Element;</mo> <mi>&chi;</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>22</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein N is_cAnd the total number of the subchannels and the pilot subchannels which meet the set transmission quality requirement in the set χ is represented.

Step 207: and compensating data on the next OFDM symbol to be estimated by using the estimated residual frequency carrier offset and the sampling clock offset. And repeating the steps until the OFDM symbol to be estimated is estimated.

In addition, this step may also adopt a closed loop feedback compensation mode. Firstly, the estimated residual frequency offset and sampling clock offset are processed by a first-order closed-loop feedback filter, and the processed result is as follows:

<math> <mrow> <msub> <mover> <mi>&epsiv;</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mo>=</mo> <msub> <mover> <mi>&epsiv;</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>+</mo> <msub> <mi>&gamma;</mi> <mi>&epsiv;</mi> </msub> <mo>&CenterDot;</mo> <mover> <mi>&epsiv;</mi> <mo>^</mo> </mover> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>23</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mover> <mi>&beta;</mi> <mo>^</mo> </mover> <mi>m</mi> </msub> <mo>=</mo> <msub> <mover> <mi>&beta;</mi> <mo>^</mo> </mover> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>+</mo> <msub> <mi>&gamma;</mi> <mi>&beta;</mi> </msub> <mo>&CenterDot;</mo> <mover> <mi>&beta;</mi> <mo>^</mo> </mover> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>24</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein, γ_εAnd gamma_βIs a control parameter of the closed loop feedback filter.

And then compensating the residual carrier frequency and the sampling frequency of the processed estimated value in a time domain and a frequency domain respectively, and estimating the data of the next OFDM symbol.

The above is a detailed procedure of the first mode, and when the second mode is used, the procedure is as shown in fig. 3, and mainly includes the following steps:

step 301: and in the current OFDM symbol, acquiring a signal sub-channel meeting the set transmission quality requirement, and acquiring a pilot frequency sub-channel.

Similarly, all the subchannels meeting the set transmission quality requirement acquired in this step are signal subchannels. In addition to this, a subchannel satisfying a set transmission quality requirement among pilot subchannels can be acquired.

Step 302: and carrying out hard decision on the acquired signal data on the signal sub-channel meeting the set transmission quality requirement.

In this step, the hard decision of the signal data on the signal sub-channel that meets the requirement of the set transmission quality is: and according to the distance from the signal data on the selected signal sub-channel to each coordinate point data in the constellation diagram, using the coordinate point data closest to the signal data on the selected signal sub-channel as the judgment data.

Step 303: and compensating the signal data on the signal sub-channel meeting the set transmission quality requirement according to the hard decision result, and compensating the pilot data on the pilot sub-channel by using the known pilot data offset.

Step 304: and performing cross-correlation calculation on the compensated signal data on the signal sub-channel acquired from the current OFDM symbol and the compensated signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol, and performing cross-correlation calculation on the compensated pilot data of the acquired pilot sub-channel.

In this step, the cross-correlation calculation is performed between the compensated signal data on the signal sub-channel obtained from the current OFDM symbol and the compensated signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol, and is performed by multiplying the compensated signal data on a selected sub-channel position of the next OFDM symbol by the conjugate of the compensated signal data on the same sub-channel position of the previous OFDM symbol.

In this step, the correlation calculation is performed on the pilot data on the pilot subchannel selected in the adjacent OFDM symbol, and the pilot data on a certain pilot position of the next OFDM symbol is multiplied by the conjugate of the pilot data on the same pilot position of the previous OFDM symbol.

Step 305: and obtaining the phase difference of the sub-channel data obtained from the current OFDM symbol and the adjacent OFDM symbol according to the result of the cross-correlation calculation in step 304.

Step 306: using the calculated phase difference, a residual carrier frequency offset and a sampling clock offset are estimated.

Step 307: and compensating data on the next OFDM symbol to be estimated by using the estimated residual frequency carrier offset and the sampling clock offset. And repeating the steps until the OFDM symbol to be estimated is estimated.

The synchronization estimation system of the OFDM technique is described in detail below. Fig. 4.a is a structural diagram of a synchronization estimation system according to an embodiment of the present invention, and as shown in fig. 4.a, the system mainly includes: channel selection unit 400, phase difference calculation unit 410, and estimation unit 420.

A channel selection unit 400, configured to obtain a sub-channel that meets a set transmission quality requirement in a current OFDM symbol;

a phase difference calculation unit 410, configured to calculate a phase difference between data on a subchannel acquired by the channel selection unit 400 in the current OFDM symbol and data on a subchannel at the same position in an adjacent OFDM symbol thereof, and provide the calculated phase difference to the estimation unit 420;

and an estimating unit 420, configured to estimate a remaining carrier frequency offset and a sampling clock offset of the current OFDM symbol by using the phase difference provided by the phase difference calculating unit 410.

The estimation unit 420 may perform estimation of the remaining carrier frequency offset and the sampling clock offset of the OFDM symbol using the method described in step 206 of fig. 2.

The structure of the channel selecting unit 400 is shown in fig. 4.b, and the channel selecting unit 400 may include: a quality detection module 401 and a signal subchannel selection module 402;

a quality detection module 401, configured to detect transmission quality of each subchannel in a current OFDM symbol, and send a detection result to a signal subchannel selection module 402;

the quality detection module 401 may perform quality detection by performing signal-to-noise ratio on each sub-channel; the quality detection can also be carried out by respectively calculating the distance between each sub-channel data in the OFDM symbols and the corresponding data in the constellation diagram; detection can also be performed by calculating the phase offset value between each sub-channel data in the OFDM symbol and the corresponding data in the constellation diagram.

A signal sub-channel selecting module 402, configured to select a signal sub-channel that meets the requirement of the set transmission quality in the OFDM symbol according to the detection result sent by the quality detecting module 401.

When the quality detection module 401 performs quality detection on the signal-to-noise ratio of each sub-channel, the signal sub-channel selection module 402 may select a sub-channel having a signal-to-noise ratio higher than the signal-to-noise ratio threshold by setting the signal-to-noise ratio threshold; the sub-channels of the setting data can be selected according to the sequence from big to big by sorting the sub-channels according to the signal-to-noise ratio. When the quality detection module 401 performs quality detection by calculating the distance between each subchannel data in the OFDM symbol and the corresponding data in the constellation diagram, the channel selection module 402 may select a subchannel whose distance satisfies the distance threshold condition by setting a distance threshold. When the quality detection module 401 detects by calculating the phase offset value between each subchannel data in the OFDM symbol and the corresponding data in the constellation diagram, the channel selection module 402 may select the subchannel whose phase offset satisfies the phase offset threshold condition by setting a phase offset threshold.

In addition, the channel selecting unit 400 may further include: a pilot subchannel selection module 403, configured to select all pilot subchannels in the OFDM symbol, or select a pilot subchannel that meets a set transmission quality requirement in the OFDM symbol according to a detection result sent by the quality monitoring module 401;

the quality monitoring module 401 is further configured to detect the transmission quality of the pilot subchannel in the current OFDM symbol, and send the detection result to the pilot subchannel selecting module 403.

The phase difference calculating unit 410 may have two constituent structures, which correspond to the first and second ways of the method, respectively. Fig. 4.c is a first composition structural diagram of the phase difference calculating unit, and as shown in fig. 4.c, the phase difference calculating unit mainly includes: a first cross-correlation calculation module 411, a hard decision module 412, a first compensation module 413, and a phase difference calculation module 414.

The first cross-correlation calculation module 411 performs cross-correlation calculation on the signal data on the signal subchannel acquired by the channel subchannel selection module 402 in the current OFDM symbol and the signal data on the signal subchannel at the same position in the next adjacent OFDM symbol, and provides the obtained cross-correlation data to the hard decision module 412 and the first compensation module 413.

A hard decision module 412, configured to perform a hard decision on the received cross-correlation data, and provide decision data obtained after the hard decision to the first compensation module 413.

The hard decision module 412 may use the method described in step 203 of fig. 2 to make a hard decision.

The first compensation module 413 is configured to receive the decision data sent by the hard decision module 412 and the cross-correlation data sent by the first cross-correlation calculation module 411, compensate the cross-correlation data by using the decision data, and send the compensated cross-correlation data to the phase difference calculation module 414.

The first compensation module 413 may perform compensation by using the method described in step 204 of fig. 2.

And a phase difference calculating module 414, configured to receive the compensated cross-correlation data sent by the first compensating module 413, calculate a phase of the compensated cross-correlation data, and obtain a phase difference between signal data on a signal subchannel acquired in the current OFDM symbol and signal data on a signal subchannel at the same position in the next adjacent OFDM symbol.

The phase difference calculation module 414 may perform the phase difference calculation using the method described in step 205 of fig. 2.

Still further, for the pilot subchannel selection module that may be included in the channel selection unit 400, the phase difference calculation unit 410 may further include: a second cross-correlation calculation module 415, and a second compensation module 416.

A second cross-correlation calculation module 415, configured to perform cross-correlation calculation on the pilot data on the pilot sub-channel acquired by the channel selection module 400 in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol, and provide the obtained cross-correlation data to the second compensation module 416.

A second compensation module 416, configured to compensate the cross-correlation data sent by the second cross-correlation calculation module 415 by using known pilot cross-correlation data at the sending end, and provide the cross-correlation data obtained after compensation to the phase difference calculation module 414.

The phase difference calculating module 414 is further configured to receive the compensated cross-correlation data sent by the second compensating module 416, calculate a phase of the compensated cross-correlation data, and obtain a phase difference between pilot data on a pilot subchannel acquired in the current OFDM symbol and pilot data on a pilot subchannel at the same position in the next adjacent OFDM symbol.

The first cross-correlation calculation module 411 and the second cross-correlation calculation module 415 may also be disposed in one device; the first compensation module 413 and the second compensation module 416 may also be provided in one device.

Fig. 4.d is a second structural diagram of the phase difference calculating unit, as shown in fig. 4.c, the phase difference calculating unit mainly includes: a hard decision module 417, a compensation module 418, a first cross-correlation calculation module 419, and a phase difference calculation module 420.

A hard decision module 417, configured to perform hard decision on the signal data on the signal sub-channel that meets the set transmission quality requirement and is acquired by the channel selection unit 400, and provide decision data obtained after the hard decision to the compensation module 418.

The hard decision module 417 may adopt the method of making a hard decision in step 302 described in fig. 3.

The compensation module 418 is configured to receive the decision data provided by the hard decision module 417, compensate the acquired signal data on the signal sub-channel meeting the set transmission quality requirement by using the decision data, and send the compensated signal data to the first cross-correlation calculation module 419.

The compensation module 418 may use the method of compensating in step 303 described in fig. 3.

The first cross-correlation calculation module 419 is configured to perform cross-correlation calculation on the compensated signal data on the signal subchannel acquired in the current OFDM symbol and the compensated signal data on the signal subchannel at the same position in the next adjacent OFDM symbol, and provide the obtained signal cross-correlation data to the phase difference calculation module 420.

The first cross-correlation calculation module 419 may adopt the method of performing the cross-correlation calculation in step 304 illustrated in fig. 3.

The phase difference calculating module 4110 receives the signal cross-correlation data provided by the first cross-correlation calculating module 419, calculates a phase of the signal cross-correlation data, and obtains a phase difference between signal data on a signal subchannel acquired in the current OFDM symbol and signal data on a signal subchannel at the same position in the next adjacent OFDM symbol.

Still further, for the pilot subchannel selection module that may be included in the channel selection unit 400, the phase difference calculation unit 410 may further include: a second cross-correlation calculation module 4111.

A second cross-correlation calculating module 4111, configured to perform cross-correlation calculation on the pilot data on the pilot sub-channel acquired by the channel selecting unit 400 in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol, and provide the obtained pilot cross-correlation data to the phase difference calculating module 4110.

The phase difference calculating module 4110 is further configured to receive the pilot cross-correlation data provided by the second cross-correlation calculating module 4111, calculate a phase of the pilot cross-correlation data, and obtain a phase difference between pilot data on a pilot subchannel acquired in the current OFDM symbol and pilot data on a pilot subchannel at the same position in the next adjacent OFDM symbol.

In order to verify the performance of the synchronization estimation method provided by the embodiment of the present invention, a simulation result is used for description. The following simulation conditions were: the sampling frequency of the OFDM system is 20 MHZ; 256 subchannels, that is, 256-point IFFT is adopted, where cyclic prefix CP is 64, the number of useful subchannels is 200, the number of pilot channels is contained in 200 subchannels, and the number of pilot channels is 8, and each of the pilot channels is located at a subchannel position of [ 13386388113138163188 ]; the maximum doppler shift present in the system is 50 HZ.

Fig. 5 is a plot of the Mean Square Error (MSE) of the residual frequency offset (RCFO) for the method and PTA method provided by embodiments of the present invention when different thresholds are used. The MSE can reflect the error accuracy of the estimated frequency offset. The simulations shown in this figure were made with a remaining carrier frequency offset normalization value of 0.04 and a sampling clock offset normalization value of 0.00002. The three threshold values in the figure are respectively as follows according to the sequence from small to big: threshold one, threshold two, threshold three. As can be seen from fig. 5, in the method provided by the present invention, when the threshold is selected to be higher, such as threshold three, the frequency offset estimation performance is substantially consistent with the performance of the PTA method, mainly because the data of the selected sub-channels satisfying the condition is very little due to the high threshold value. When the threshold is selected to be lower, for example, the threshold one, the data of the sub-channel satisfying the condition is large, but when the threshold is lower, the transmission quality of the selected sub-channel is low, and errors are likely to occur, which also affects the performance of the system. Three threshold values are compared and threshold two is the best threshold for the remaining frequency offset estimation.

Fig. 6 is a diagram illustrating mean square error MSE curves of sampling clock offset (SFO) of the method and PTA method provided by the embodiments of the present invention when different thresholds are used. The MSE can reflect the error accuracy of the estimated sampling clock offset. The simulations shown in this figure were made with a remaining carrier frequency offset normalization value of 0.04 and a sampling clock offset normalization value of 0.00002. The three threshold values in the figure are respectively as follows according to the sequence from small to big: threshold one, threshold two, threshold three. As can be seen from fig. 6, the smaller the threshold, the higher the estimation performance of the sampling clock offset, which is because the sampling clock estimation adopts the weighted estimation of the phase change law between the sub-channels, and is insensitive to the bit error of each channel.

Fig. 7 is a graph of estimated performance for the method of the present invention and the PTA method under the same sample clock offset normalization and different remaining carrier frequency offset normalization. The sampling clock normalization value used was 0.00002 and the remaining carrier frequency offset normalization values were 0.06, 0.04, and 0.02, respectively. From fig. 7, it can be known that the MSE of the residual frequency offset of the PTA method is slightly decreased as the residual frequency offset is decreased; the performance of the estimation performance in the method of the invention is better than that of the PTA method under three conditions, but when the residual frequency offset is larger, the performance of the method is closer to that of the PTA method, and the MSE of the residual frequency offset is rapidly reduced along with the reduction of the residual frequency offset, because the number of high-quality sub-channels is increased along with the reduction of the residual frequency offset, the performance of the method of the invention is obviously improved.

Fig. 8 is a graph of estimated performance for the method of the present invention and the PTA method under the same residual carrier frequency offset normalization and different sample clock offset normalization. The remaining carrier frequency offset normalization values used were 0.04 and the sampling clock offset normalization values used were 0.00004, 0.00002, and 0.000005, respectively. As can be seen from fig. 8, the MSE of the PTA method is slightly decreased as the sampling clock skew is decreased; the performance of the method of the invention is better than that of the PTA method under three conditions, and the MSE of the sampling clock skew is rapidly reduced along with the reduction of the sampling clock skew. This is due to the fact that as the sampling clock is reduced, so is the number of high quality sub-channels. But since the value of the sampling clock offset is generally small, its impact on the sub-channel transmission quality is small compared to the variation of the remaining carrier frequency offset.

Fig. 9 is a graph of the residual carrier frequency offset tracking curves for the inventive method and PTA method under the conditions of an average signal-to-noise ratio of 15dB, a residual carrier frequency offset normalization of 0.05, and a sampling clock offset normalization of 0.0004. As shown in fig. 9, the convergence rate of the method of the present invention and the PTA method is fast, but the fluctuation range of the PTA method in tracking is large, but the fluctuation range of the method of the present invention is small, and it can be calculated that the variance of the residual carrier frequency tracking of the PTA method is 1.8457e-004 in the tracking process, and the variance of the residual carrier frequency tracking of the method of the present invention is 2.6659e-005, compared with the PTA method, the performance of the method of the present invention is improved by 5.9 times.

Fig. 10 is a sample clock offset tracking curve for the inventive method and PTA method under conditions of an average signal-to-noise ratio of 15dB, a residual carrier frequency offset normalization of 0.05, and a sample clock offset of 0.0004. As can be seen from fig. 10, the fluctuation range of the PTA method is large in tracking, the fluctuation range of the method of the present invention is small, and it can be calculated that the variance of the sampling clock offset tracking of the PTA method is 8.2279e-009 during tracking, while the variance of the sampling clock offset tracking of the method of the present invention is 2.1542e-009, which improves the performance by 2.8 times compared with the PTA method.

As can be seen from the above description, the synchronization estimation method and system of the OFDM technology according to the embodiments of the present invention estimate the remaining carrier frequency offset and the sampling clock offset by using the acquired cross-correlation data on the sub-channel that meets the set transmission quality requirement, overcome the influence of the error code generated in the sub-channel with poor transmission quality, and improve the accuracy of synchronization estimation.

Furthermore, in the method and system provided in the embodiments of the present invention, the obtained sub-channels meeting the set transmission quality requirement are signal sub-channels, and may further include pilot sub-channels meeting the set transmission quality requirement or all pilot sub-channels, so that the adopted sub-channel data is increased, and the disadvantage that the accuracy of synchronization estimation is limited due to less pilot sub-channel data in the PTA method is overcome.

Furthermore, the hard decision method adopted by the invention can compensate the data or the cross-correlation data on the sub-channel of the receiving terminal without estimating the channel so as to obtain the data possibly sent by the sending terminal, thereby overcoming the dependence of a synchronous estimation method on the channel estimation.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (26)

1. A synchronization estimation method of OFDM technique is characterized in that the method includes:

acquiring a subchannel which meets the set transmission quality requirement in the current OFDM symbol; calculating the phase difference between the data on the sub-channel acquired in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol; estimating a remaining carrier frequency offset and a sampling clock offset of the current OFDM symbol using the calculated phase difference.

2. The method of claim 1, wherein obtaining the sub-channels satisfying the set transmission quality requirement in the current OFDM symbol comprises: and obtaining the sub-channel which meets the requirement of the set signal-to-noise ratio in the current OFDM symbol according to the signal-to-noise ratio of the sub-channel in the current OFDM symbol.

3. The method of claim 1, wherein obtaining the sub-channels satisfying the set transmission quality requirement in the current OFDM symbol comprises: and acquiring the sub-channel meeting the requirement of setting the relation with the corresponding data in the constellation map in the current OFDM symbol according to the relation between the data of each sub-channel in the current OFDM symbol and the corresponding data in the constellation map.

4. The method of claim 1, wherein the sub-channels satisfying the set transmission quality requirement comprise: and the signal sub-channel which meets the set transmission quality requirement in the current OFDM symbol.

5. The method of claim 1, wherein the sub-channels satisfying the set transmission quality requirement comprise: the OFDM signal transmission method comprises the following steps that a signal sub-channel which meets a set transmission quality requirement and a pilot frequency sub-channel which meets the set transmission quality requirement are contained in a current OFDM symbol; or,

the signal sub-channel satisfying the set transmission quality requirement in the current OFDM symbol and all the pilot sub-channels.

6. The method of claim 4, wherein calculating the phase difference between the data on the sub-channel obtained in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol comprises:

performing hard decision on signal data on a signal sub-channel acquired from a current OFDM symbol to obtain hard decision data; and performing cross-correlation calculation on the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol according to the hard decision data to obtain the phase difference between the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol.

7. The method of claim 4, wherein calculating the phase difference between the data on the sub-channel obtained in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol comprises:

performing cross-correlation calculation on data on a signal sub-channel acquired in the current OFDM symbol and signal data on a signal sub-channel at the same position in the next adjacent OFDM symbol to obtain signal cross-correlation data; then, carrying out hard decision on the signal cross-correlation data to obtain hard decision data; and calculating the phase difference between the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol by using the hard decision data.

8. The method of claim 5, wherein calculating the phase difference between the data on the sub-channel obtained in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol comprises:

performing hard decision on signal data on a signal sub-channel acquired from a current OFDM symbol to obtain hard decision data; according to the hard decision data, performing cross-correlation calculation on the data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol to obtain the phase difference between the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol; and performing cross-correlation calculation on the pilot data on the pilot sub-channel acquired in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol to obtain the phase difference between the pilot data on the pilot sub-channel acquired in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol.

9. The method of claim 5, wherein calculating the phase difference between the data on the sub-channel obtained in the current OFDM symbol and the data on the sub-channel at the same position in the adjacent OFDM symbol comprises:

performing cross-correlation calculation on signal data on a signal sub-channel acquired in a current OFDM symbol and signal data on a signal sub-channel at the same position in an adjacent next OFDM symbol to obtain signal cross-correlation data, and performing cross-correlation calculation on pilot frequency data on a pilot frequency sub-channel acquired in the current OFDM symbol and pilot frequency data on a pilot frequency sub-channel at the same position in the adjacent next OFDM symbol to obtain pilot frequency cross-correlation data; and calculating the phase difference between the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol and the phase difference between the pilot data on the pilot sub-channel acquired in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol by using the hard decision data and the pilot cross-correlation data.

10. The method according to claim 6 or 8, wherein the hard-decision of the signal data on the signal sub-channel obtained in the current OFDM symbol to obtain hard-decision data comprises:

and calculating the distance from the signal data on the signal sub-channel acquired in the current OFDM symbol to each data point in the constellation diagram, and taking the data point on the constellation diagram with the minimum distance as hard decision data.

11. The method according to claim 6 or 8, wherein the performing, according to the hard decision data, cross-correlation calculation on signal data on a signal subchannel acquired in a current OFDM symbol and signal data on a signal subchannel at the same position in a next OFDM symbol adjacent to the current OFDM symbol comprises:

and compensating the signal data on the signal sub-channel acquired in the current OFDM symbol by using the hard decision data obtained by hard decision, and multiplying the signal data on the signal sub-channel at the same position in the next OFDM symbol adjacent to the current OFDM symbol by the conjugate of the compensated signal data of the signal sub-channel acquired in the current OFDM symbol to obtain the cross-correlation data on the acquired signal sub-channel.

12. The method of claim 7 or 9, wherein hard-deciding the signal cross-correlation data comprises:

calculating the distance from the cross-correlation data on the acquired signal sub-channel to each cross-correlation data in a target set, and taking the cross-correlation data point in the target set with the minimum distance as hard decision data; wherein,

the target set is: and performing cross-correlation calculation on data on a constellation diagram corresponding to the data on each subchannel of the current OFDM symbol and data on a constellation diagram corresponding to the data on the subchannel at the same position as the adjacent OFDM symbol to obtain a cross-correlation data set.

13. The method according to claim 7 or 9, wherein the performing cross-correlation calculation on the signal data on the signal sub-channel obtained in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next OFDM symbol adjacent to the current OFDM symbol comprises:

and multiplying the conjugate of the signal data on the signal sub-channel acquired in the current OFDM symbol by the signal data on the signal sub-channel at the same position in the next OFDM symbol adjacent to the conjugate.

14. The method according to claim 8 or 9, wherein the performing cross-correlation calculation on the pilot data on the pilot subchannel acquired in the current OFDM symbol and the pilot data on the pilot subchannel at the same position in the next OFDM symbol adjacent to the current OFDM symbol comprises:

and multiplying the conjugate of the pilot data on the pilot subchannel acquired in the current OFDM symbol by the pilot data at the same position in the next OFDM symbol adjacent to the conjugate.

15. The method of claim 7, wherein using the hard decision data to calculate a phase difference between signal data on a signal subchannel acquired in a current OFDM symbol and signal data on a signal subchannel co-located in a next OFDM symbol adjacent thereto comprises:

and compensating the cross-correlation data by using the judgment data, and calculating the phase of the compensated cross-correlation data to obtain the phase difference between the signal data on the signal sub-channel acquired from the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol.

16. The method of claim 9, wherein the calculating, using the hard decision data and the pilot cross-correlation data, a phase difference between signal data on a signal subchannel acquired in a current OFDM symbol and signal data on a signal subchannel at a same position in a next OFDM symbol adjacent thereto, and a phase difference between pilot data on a pilot subchannel acquired in the current OFDM symbol and pilot data on a pilot subchannel at a same position in a next OFDM symbol adjacent thereto comprises:

compensating the cross-correlation data on the signal sub-channel by using the decision data, and calculating the phase of the compensated cross-correlation data to obtain the phase difference between the signal data on the signal sub-channel acquired from the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol; and compensating the cross-correlation data on the pilot sub-channel by using the known pilot cross-correlation data of the sending end, calculating the phase of the cross-correlation data on the compensated pilot sub-channel, and obtaining the phase difference between the pilot data on the pilot sub-channel acquired from the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol.

17. The method of claim 15 or 16, wherein estimating the sampling clock offset of the current OFDM symbol using the calculated phase difference comprises:

and carrying out weighted average on the calculated phase differences to obtain the sampling clock offset of the current OFDM symbol.

18. The method of claim 17, wherein estimating the remaining carrier frequency offset for the current OFDM symbol comprises: and obtaining the residual carrier frequency offset of the current OFDM symbol according to the phase of the cross-correlation data on the compensated selected signal sub-channel and the pilot sub-channel and the obtained relation between the sampling clock offsets of the current OFDM symbol.

19. The method of claim 1, further comprising: and compensating data on each sub-channel on the next OFDM symbol by using the estimated residual carrier frequency offset and the sampling clock offset.

20. A synchronization estimation system for OFDM techniques, the system comprising: a channel selection unit, a phase difference calculation unit, and an estimation unit;

the channel selection unit is used for acquiring a sub-channel which meets the set transmission quality requirement in the current OFDM symbol;

a phase difference calculation unit, configured to calculate a phase difference between data on a subchannel acquired by the channel selection unit in the current OFDM symbol and data on a subchannel at the same position in an adjacent OFDM symbol, and provide the calculated phase difference to the estimation unit;

and the estimation unit is used for estimating the residual carrier frequency offset and the sampling clock offset of the current OFDM symbol by using the phase difference provided by the phase difference calculation unit.

21. The system of claim 20, wherein the channel selection unit comprises: the device comprises a quality detection module and a signal sub-channel selection module;

the quality detection module is used for detecting the transmission quality of the signal sub-channel in the current OFDM symbol and sending the detection result to the signal sub-channel selection module;

and the signal sub-channel selection module is used for receiving the detection result sent by the quality detection module and selecting the signal sub-channel which meets the set transmission quality requirement in the current OFDM symbol according to the detection result.

22. The system of claim 21, wherein the channel selection unit further comprises: the pilot subchannel selection unit is used for selecting all pilot subchannels in the current OFDM symbol, or receiving a detection result sent by the quality detection module, and selecting the pilot subchannels meeting the set transmission quality requirement in the current OFDM symbol according to the detection result;

the quality monitoring module is further configured to detect the transmission quality of the pilot subchannel in the current OFDM symbol, and send the detection result to the pilot subchannel selection module.

23. The system according to claim 21, wherein the phase difference calculation unit comprises: the device comprises a first cross-correlation calculation module, a hard decision module, a first compensation module and a phase difference calculation module;

the first cross-correlation calculation module is used for performing cross-correlation calculation on signal data on a signal sub-channel acquired in the current OFDM symbol and signal data on a signal sub-channel at the same position in the next adjacent OFDM symbol, and providing the obtained signal cross-correlation data to the hard decision module and the first compensation module;

the hard decision module is used for carrying out hard decision on the received signal cross-correlation data and providing decision data obtained after the hard decision to the first compensation module;

the first compensation module is used for receiving the judgment data sent by the hard judgment module and the signal cross-correlation data sent by the first cross-correlation calculation module, compensating the signal cross-correlation data by using the judgment data and sending the compensated signal cross-correlation data to the phase difference calculation module;

and the phase difference calculation module is used for receiving the compensated signal cross-correlation data, calculating the phase of the signal cross-correlation data and obtaining the phase difference between the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol.

24. The system according to claim 22, wherein the phase difference calculation unit comprises: the device comprises a first cross-correlation calculation module, a hard decision module, a first compensation module, a phase difference calculation module, a second cross-correlation calculation module and a second compensation module;

the first cross-correlation calculation module is used for performing cross-correlation calculation on signal data on a signal sub-channel acquired in the current OFDM symbol and signal data on a signal sub-channel at the same position in the next adjacent OFDM symbol, and providing the obtained signal cross-correlation data to the hard decision module and the first compensation module;

the hard decision module is used for carrying out hard decision on the received signal cross-correlation data and providing decision data obtained after the hard decision to the first compensation module;

the first compensation module is used for receiving the judgment data sent by the hard judgment module and the signal cross-correlation data sent by the first cross-correlation calculation module, compensating the signal cross-correlation data by using the judgment data and sending the compensated signal cross-correlation data to the phase difference calculation module;

the second cross-correlation calculation module is used for performing cross-correlation calculation on pilot data on a pilot subchannel acquired in the current OFDM symbol and pilot data on a pilot subchannel at the same position in the next adjacent OFDM symbol, and providing the acquired pilot cross-correlation data to the second compensation module;

the second compensation module is used for compensating the pilot frequency cross-correlation data sent by the second cross-correlation calculation module by using the known pilot frequency cross-correlation data of the sending end and providing the pilot frequency cross-correlation data obtained after compensation to the phase difference calculation module;

a phase difference calculation module, configured to receive the cross-correlation data of the compensated signal data, calculate a phase of the compensated signal cross-correlation data, and obtain a phase difference between signal data on a signal subchannel acquired in the current OFDM symbol and signal data on a signal subchannel at the same position in an adjacent next OFDM symbol; and the phase difference acquisition module is used for receiving the compensated pilot frequency cross-correlation data, calculating the phase of the compensated pilot frequency cross-correlation data, and acquiring the phase difference between the pilot frequency data on the pilot frequency sub-channel acquired in the current OFDM symbol and the pilot frequency data on the pilot frequency sub-channel at the same position in the next adjacent OFDM symbol.

25. The system according to claim 21, wherein the phase difference calculation unit comprises: the device comprises a hard decision module, a compensation module, a first cross-correlation calculation module and a phase difference calculation module;

the hard decision module is used for carrying out hard decision on the signal data on the signal sub-channel acquired by the signal sub-channel selection module and providing decision data obtained after the hard decision to the compensation module;

the compensation module is used for receiving the judgment data provided by the hard judgment module, compensating the signal data on the acquired signal sub-channel by using the judgment data and sending the compensated signal data to the first cross-correlation calculation module;

the first cross-correlation calculation module is used for performing cross-correlation calculation on the compensated signal data on the signal sub-channel acquired from the current OFDM symbol and the compensated signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol, and providing the acquired signal cross-correlation data to the phase difference calculation module;

and the phase difference calculation module is used for receiving the signal cross-correlation data provided by the first cross-correlation calculation module, calculating the phase of the signal cross-correlation data and obtaining the phase difference between the signal data on the signal sub-channel acquired in the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol.

26. The system according to claim 22, wherein the phase difference calculation unit comprises: the device comprises a hard decision module, a compensation module, a first cross-correlation calculation module, a second cross-correlation calculation module and a phase difference calculation module;

the hard decision module is used for carrying out hard decision on the signal data on the signal sub-channel acquired by the signal sub-channel selection module and providing decision data obtained after the hard decision to the compensation module;

the compensation module is used for receiving the judgment data provided by the hard judgment module, compensating the signal data on the acquired signal sub-channel by using the judgment data and sending the compensated signal data to the first cross-correlation calculation module;

the first cross-correlation calculation module is used for performing cross-correlation calculation on the compensated signal data on the signal sub-channel acquired from the current OFDM symbol and the compensated signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol, and providing the acquired signal cross-correlation data to the phase difference calculation module;

the second cross-correlation calculation module is used for performing cross-correlation calculation on pilot data on a pilot subchannel acquired in the current OFDM symbol and pilot data on a pilot subchannel at the same position in the next adjacent OFDM symbol, and providing the acquired pilot cross-correlation data to the phase difference calculation module;

the phase difference calculation module is used for receiving the signal cross-correlation data provided by the first cross-correlation calculation module, calculating the phase of the signal cross-correlation data and obtaining the phase difference between the signal data on the signal sub-channel acquired from the current OFDM symbol and the signal data on the signal sub-channel at the same position in the next adjacent OFDM symbol; and calculating the phase of the pilot cross-correlation data according to the pilot cross-correlation data provided by the second cross-correlation calculation module to obtain the phase difference between the pilot data on the pilot subchannel acquired in the current OFDM symbol and the pilot data on the pilot subchannel at the same position in the next adjacent OFDM symbol.

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