CN101299737B - Synchronous estimation method and system for orthogonal frequency division multiplexing technique - Google Patents

Abstract

The present invention provides a method and system for synchronous estimation of Orthogonal Frequency Division Multiplexing (OFDM) technology, wherein the method includes: obtaining sub-channels in the current OFDM symbol that meet the set transmission quality requirements; calculating the sub-channels obtained in the current OFDM symbol The phase difference between the data on the subchannel and the data on the subchannel at the same position in its adjacent OFDM symbol; using the calculated phase difference, estimate the remaining carrier frequency offset and sampling clock offset of the current OFDM symbol. The method and system estimate the remaining carrier frequency offset and sampling clock offset by using the obtained cross-correlation data on sub-channels that meet the transmission quality requirements, and overcome the influence of bit errors in sub-channels with poor transmission quality, The accuracy of synchronization estimation is greatly improved.

Description

Synchronization Estimation Method and System of Orthogonal Frequency Division Multiplexing Technology

technical field

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

Background technique

OFDM is a frequency division multiplexing technology capable of transmitting high-speed data services. It has high frequency band utilization and strong anti-multipath interference ability. Therefore, OFDM has received more and more attention and attention, and is considered to be the future wireless It is one of the preferred technologies for multimedia mobile communication, and has been applied in the physical layer series standards of wireless local area network, European digital audio broadcasting standard (DAB) and digital time-frequency standard (DVB).

Although a number of technical standards have been formulated for the OFDM transmission technology at present, there are still many difficult problems in the OFDM technology. Synchronization is one of the technical problems in the formulation of OFDM transmission standards. OFDM systems are very sensitive to synchronization errors, and very small synchronization errors may cause serious degradation of system performance. In an OFDM system, synchronization generally includes two processes: the first step is synchronization acquisition, that is, the synchronization established at the beginning of data transmission; the second step is the estimation of the remaining synchronization offset.

Among them, in the process of data transmission, due to the influence of Doppler frequency shift, the stability of the carrier frequency of both parties is limited, and the instability of the sampling clock oscillator of both parties causes the remaining carrier frequency deviation and sampling clock deviation. Although the value of these synchronization errors is small, it will cause the signal amplitude on the sub-channel to decrease, destroy the orthogonality between sub-channels, and introduce Inter-Carrier Interference (ICI, Inter-Carrier Interference), which will cause system errors. The code rate increases. For the synchronization problem during data transmission, there are currently two synchronization estimation methods for OFDM systems. The first is the synchronization estimation method of pilot-assisted (PTA, PilotTone-Aided), and the second is the non-pilot-assisted synchronization estimation method. .

Before introducing the two methods in 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, the structure of the OFDM symbol is described. The OFDM symbol includes a cyclic prefix part and a data part, wherein the data part includes: pilot data and signal data, as shown in Figure 1, c _m (k) represents the mth OFDM symbol The k-th signal data of , p _m (k) represents the k-th pilot data of the m-th OFDM symbol. m and m+1 represent the m and m+1 OFDM symbols, p _m (k) and p _m+1 (k) are the pilot data in the two OFDM symbols respectively, and the pilot data is generally used to extract channel information and perform channel estimation. An OFDM symbol includes N _g cyclic prefixes, and the N subchannels are divided into pilot subchannels and signal subchannels, the pilot subchannels carry pilot data, and the signal subchannels carry signal data.

The synchronous signal model of the OFDM system will be described below. In the OFDM transmission system, if the OFDM system modulation uses N-point Inverse Discrete Fourier Transform (IDFT, Inverse DiscreteFourier Transform), that is, one OFDM symbol contains N data; the OFDM system uses K+1 sub-channels to transmit information, where K<N; the OFDM system sampling clock period is T; an OFDM symbol includes two parts in the time domain: the data part and the cyclic prefix part, where the time of the cyclic prefix is N _g T to overcome the signal gap caused by multipath interference; one OFDM symbol includes N _s sampling points, N _s =N+N _g .

At this time, the complex baseband signal x _m (t) of the mth OFDM symbol sent by the transmitter can be expressed as:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\overset{\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="e\; j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">e</figure-callout></span><figure-callout\; id="2"\; label="e\; j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">\; </figure-callout>}}^{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

c _{m, k} in formula (1) is the modulated complex data on the kth subchannel of the mth OFDM symbol at the transmitting end.

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

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

(2) where δ(k) represents the impulse function, {h _{m, k} , k=0,..., S-1} is the k-th path complex gain during the m-th OFDM symbol, {τ _k } is the path delay of the kth path, usually taken as an integer multiple of the sampling time, and S is the total number of paths in the wireless channel.

Assuming that the timing of the signal has reached synchronization, and the carrier frequency offset estimation and compensation in the initial synchronization acquisition stage have been completed, the synchronization estimation during the data transmission process will be performed below. During this process, it is necessary to estimate the remaining carrier frequency offset and sampling clock offset in the OFDM synchronization phase.

Assuming that the complex baseband signal at the transmitting end is transmitted through the transmission channel, the carrier frequency at the receiving end is f', and the sampling clock period is T', and it is assumed that the system is strictly synchronous when m=0. At this time, the remaining synchronization error can be They are:

The remaining carrier frequency error Δf is: Δf=f-f';

The sampling clock error β is: β=(T-T′)/T. (3)

At the receiving end, after sampling and removing the cyclic prefix using a sampling clock with a clock period of T′, the complex baseband signal sampling of the mth OFDM symbol can be expressed as:

r _{m, n} = r(t _n ), 0≤n≤N-1, t _n =(mN _s +N _g )T'+nT'; (4)

After the N sampling data of the m-th symbol are demodulated by Fourier transform, the data on each sub-channel can be expressed as:

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">j</figure-callout></span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;kn</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="e\; j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">e</figure-callout></span><figure-callout\; id="2"\; label="e\; j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">\; </figure-callout>}}^{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="e\; j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">e</figure-callout></span><figure-callout\; id="2"\; label="e\; j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">\; </figure-callout>}}^{\mathrm{<span\; class="notranslate">\; </span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>$

其中，T_u＝NT，n_m(k)是第m个OFDM符号期间在第k个子信道上的高斯噪声，I_m(k)是子信道间的干扰信号，由于剩余同步误差比较小，子信道间的干扰信号通常等效为高斯白噪声，α_m，k是同步误差引起的第k个子信道上信号的衰减系数，由于剩余同步误差较小，因而α_m，k趋进于1。(5) where

Among them, T _u =NT, n _m (k) is the Gaussian noise on the kth sub-channel during the mth OFDM symbol, I _m (k) is the interference signal between sub-channels, since the remaining synchronization error is relatively small, the sub-channel The interference signal between channels is usually equivalent to Gaussian white noise. α _m,k is the attenuation coefficient of the signal on the kth sub-channel caused by the synchronization error. Since the remaining synchronization error is small, α _m,k tends to be 1.

The first method in the prior art is introduced below: the PTA synchronization estimation method. The method is to extract the pilot data on all pilot sub-channels in the OFDM symbol after performing Fourier transform on the signal at the receiving end, and calculate the phase of the extracted pilot data; Carry out cross-correlation calculation, that is, calculate the phase difference of the data at the same pilot position of adjacent OFDM symbols; use the phase difference obtained by the cross-correlation calculation to estimate the remaining carrier frequency offset and sampling clock offset.

The PTA synchronization estimation method is simple and easy to implement, but in this method, the number N _p of pilots in OFDM symbols and the transmission quality of pilot sub-channels directly affect the accuracy of residual carrier frequency offset and sampling clock estimation in the system, while in the existing In the traditional OFDM transmission technology, the pilot data is less, and the influence of the transmission quality of the wireless channel itself limits the accuracy of the PTA synchronization estimation method.

The second method in the prior art is introduced below: a data-oriented (DD, Dicision-directed) synchronization estimation method. The method mainly includes: using known channel estimation parameters to compensate the data of the OFDM symbol at the receiving end; performing hard judgment on the data in the OFDM symbol after the compensation; Perform cross-correlation calculations on the data in adjacent OFDM symbols; estimate the remaining carrier frequency offset and sampling clock offset according to the results of the cross-correlation calculations.

This method does not need to extract the pilot frequency, but the sub-channel with poor channel transmission quality will generate bit errors in the hard decision, and the generated bit errors will introduce interference in the synchronization estimation and affect the accuracy of the synchronization estimation method.

It can be seen from the above description that the synchronization estimation methods in the prior art are all affected by sub-channels with poor transmission quality, which reduces the accuracy of synchronization estimation.

Contents of the invention

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

An embodiment of the present invention provides a method for synchronous estimation of an OFDM system, the method comprising:

Obtain the sub-channel that meets the set transmission quality requirements in the current OFDM symbol; calculate 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; use the calculated and estimate the remaining carrier frequency offset and sampling clock offset of the current OFDM symbol.

The embodiment of the present invention also provides a synchronization estimation system of an OFDM system, the system includes: a channel selection unit, a phase difference calculation unit, and an estimation unit;

A channel selection unit, configured to obtain subchannels that meet the set transmission quality requirements in the current OFDM symbol;

A phase difference calculation unit, used to calculate the phase difference between the data on the subchannel obtained in the current OFDM symbol and the data on the subchannel at the same position in its adjacent OFDM symbol, and provide the calculated phase difference to the estimation unit;

An estimating unit, configured to use the phase difference provided by the phase difference calculating unit to estimate the remaining carrier frequency offset and sampling clock offset of the current OFDM symbol.

It can be seen from the above that the OFDM synchronization estimation method and system provided by the embodiments of the present invention use the cross-correlation data on the sub-channels that meet the set transmission quality requirements to calculate the remaining carrier frequency offset and sampling clock offset. It avoids the impact of bit errors in sub-channels with poor transmission quality, and improves the accuracy of synchronization estimation to a large extent.

Description of drawings

FIG. 1 is a schematic structural diagram of an OFDM symbol;

FIG. 2 is a flowchart of a synchronization estimation method for an OFDM system provided by an embodiment of the present invention;

Fig. 3 is another flow chart of the synchronization estimation method of the OFDM system provided by the embodiment of the present invention;

Figure 4.a is a structural diagram of the synchronization estimation system provided by the embodiment of the present invention;

Figure 4.b is a structural diagram of a channel selection unit provided by an embodiment of the present invention;

Figure 4.c is the first composition structure diagram of the phase difference calculation unit provided by the embodiment of the present invention;

Figure 4.d is a second composition structure diagram of the phase difference calculation unit provided by the embodiment of the present invention;

FIG. 5 is a curve diagram of the mean square error (MSE) of the residual frequency offset (RCFO) of the method provided by the embodiment of the present invention and the PTA method when different thresholds are used;

FIG. 6 is a curve diagram of the mean square error (MSE) of the sampling clock offset (SFO) of the method provided by the embodiment of the present invention and the PTA method when different thresholds are used;

Figure 7 is the estimated performance curves of the method of the present invention and the PTA method under the same sampling clock offset normalization value and different residual carrier frequency offset normalization values;

Figure 8 is the estimated performance curves of the method of the present invention and the PTA method under the same residual carrier frequency offset normalization value and different sampling clock offset normalization values;

Fig. 9 is the residual carrier frequency offset tracking curve of the inventive method and the PTA method under the same conditions;

Fig. 10 is the sampling clock offset tracking curves of the method of the present invention and the PTA method under the same conditions.

Detailed ways

In order to make the above technical solutions, objectives and advantages clearer, the present invention will be described in detail below in conjunction with specific embodiments.

The synchronization estimation method of the OFDM system provided by the embodiment of the present invention mainly includes: acquiring the subchannel meeting the set transmission quality requirements in the current OFDM symbol; The phase difference between the data on the sub-channel; using the calculated phase difference, estimate the remaining carrier frequency offset and sampling clock offset of the current OFDM symbol.

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

Wherein, the subchannels meeting the set transmission quality requirements in the obtained OFDM symbols may all be signal subchannels meeting the set transmission quality requirements; may also include subchannels meeting the set transmission quality requirements and pilot data subchannels meeting the set transmission quality requirements. Set the signal sub-channel for transmission quality requirements.

When the obtained subchannels meeting the set transmission quality requirements in the OFDM symbols are all signal subchannels meeting the set transmission quality requirements, the method may further include: selecting pilot subchannels in the OFDM symbols.

Wherein, calculating the phase difference between the data on the subchannel obtained in the current OFDM symbol and the data on the subchannel at the same position in its adjacent OFDM symbol can have the following two ways:

The first method: 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 cross-correlation calculated to obtain the cross-correlation data, and the signal cross-correlation data on the obtained sub-channel A hard decision is made, and a phase difference between subchannel data acquired in adjacent OFDM symbols is calculated according to the decision data obtained by the hard decision.

The second method: first make a hard decision on the data on the obtained sub-channel, and 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 The cross-correlation calculation is performed to obtain the phase difference of the sub-channel data acquired in adjacent OFDM symbols.

Taking the first way as an example, the synchronization estimation of the OFDM system will be described in detail below. Fig. 2 is the flowchart of the synchronous estimation method of OFDM system that the embodiment of the present invention provides, as shown in Fig. 2, this method mainly comprises the following steps:

Step 201: In the current OFDM symbol, select signal subchannels that meet the set transmission quality requirements, and select all pilot subchannels.

In addition to this method, there may be another method in this step, that is, selecting signal subchannels that meet the set transmission quality requirements, and selecting subchannels that meet the set transmission quality requirements from the pilot subchannels.

Selecting signal subchannels in OFDM symbols that meet the set transmission quality requirements may be: selecting signal subchannels in OFDM symbols with transmission quality higher than a quality threshold.

Because there is a corresponding relationship between channel transmission quality and signal-to-noise ratio, a selection method based on sub-channel signal-to-noise ratio can be used to select a sub-channel with high transmission quality. In this case, the quality threshold is a signal-to-noise ratio threshold. This choice can be expressed as:

ζ={l|SNR _m (l)≥SNR _th } (6)

(6) where: SNR _m (l) is the signal-to-noise ratio on the l-th sub-channel of the m-th symbol, SNR _th is the SNR selection threshold, and ζ is the set of acquired sub-channel coefficients.

When selecting the SNR threshold, if the selected SNR threshold is too low, more sub-channel data will be obtained, but when the SNR is low, the data quality on the selected sub-channel will be low. The data on the channel will generate bit errors, which will affect the accuracy of synchronization estimation; if the selected SNR threshold is too high, the number of selected sub-channels will be reduced, and the accuracy of synchronization estimation will also be affected. The selection of the SNR threshold can be determined by using a simulation method based on a theoretical function.

In addition, this step may also adopt a selection method of sorting the signal-to-noise ratio of the sub-channels. Sorting is performed according to the SNR value of each sub-channel, and finally, according to the number of high-quality sub-channels initially set by the system, a set number of sub-channels is selected in descending order.

In addition, this step may also adopt a selection method based on the minimum decision distance. Calculate the distance between the data in each sub-channel and the corresponding data in the constellation diagram respectively, and select the sub-channel whose distance satisfies the distance threshold condition. The selection method can be expressed as:

ζ＝{l|d _m (l)≤d _th }

Wherein, d _m (l) is the distance between the data in the mth sub-channel and the corresponding data in the constellation diagram, and d _th is the set distance threshold.

In addition, this step may also adopt a selection method based on the minimum phase. Calculate the phase offset value between the data in each subchannel and the corresponding data in the constellation diagram respectively, and select the subchannel whose phase offset value satisfies the phase offset threshold condition. The selection method can be expressed as:

ζ＝{l|ρ _m (l)≤ρ _th }

Wherein, ρ _m (l) is the phase offset value between the data in the mth subchannel and the corresponding data in the constellation diagram, and ρ _th is the set phase offset threshold.

Step 202: For the current OFDM symbol, the signal data on the signal subchannel selected in step 201 and the pilot data on the pilot subchannel and the signal data and pilot data at the same position between its adjacent OFDM symbols are respectively carried out Cross-correlation calculations.

In this step, the cross-correlation calculation is performed 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 OFDM symbol adjacent to it. The signal data at the selected sub-channel position is multiplied by the conjugate of the signal data at the same sub-channel position of the previous OFDM symbol. Similarly, other cross-correlation calculation methods may also be used.

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

In this step, the cross-correlation calculation is performed on the pilot data on the pilot sub-channel obtained in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol, which is to calculate the cross-correlation of the next OFDM symbol The pilot data at a certain pilot position is multiplied by the conjugate of the pilot data at the same pilot position of the previous OFDM symbol.

The cross-correlation calculation is performed on the data of the sub-channels between adjacent OFDM symbols, which is reflected in the phase as the phase difference of the data of the sub-channels in adjacent OFDM symbols.

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

Because it is usually assumed that the fading of the channel changes slowly, that is, the channel coefficients on the sub-channels can be considered to be the same during the m-th OFDM symbol and the M+1-th OFDM symbol, that is: H _m (k)≈H _m+1 (k), from formula (5) in the synchronous signal model can be obtained:

At the receiving end, the data of the kth subchannel of the mth and m+1 OFDM symbols are respectively:

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>$

$\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&epsiv;</span>}\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; k\&beta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>$

$\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&epsiv;</span>}\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="S071A7160620070518E000082.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; k\&beta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

in, ${\mathrm{\&phi;}}_k\&ap;2\mathrm{\&pi;}(1+N_g/N)(\mathrm{\&epsiv;}+k\&CenterDot;\mathrm{\&beta;})---\left(9\right)$

ε is the normalized value of the remaining carrier frequency offset, ε=ΔfNT.

From formulas (7) and (8), it can be obtained that the cross-correlation data R _m (l) on the lth signal subchannel of the mth and m+1th OFDM symbols is:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Wherein, ζ is a set of subchannel coefficients corresponding to the selected signal subchannels that meet the set transmission quality requirements.

Similarly, from equations (7) and (8), it can be obtained that the cross-correlation data Q _m (l) on the lth pilot subchannel of the mth and m+1th OFDM symbols is:

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

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

Step 203: Perform a hard decision on the cross-correlation data on the selected signal sub-channels that meet the set transmission quality requirements.

In this step, the purpose of making a hard decision on the cross-correlation data on the signal sub-channels that meet the set transmission quality requirements is to obtain the influence of the data sent by the sender on the cross-correlation data. The error impact of the synchrony estimate.

可以表示为：The hard decision is: according to the distance from the cross-correlation data on the selected signal sub-channel to each cross-correlation data point in the target set, the target closest to the cross-correlation data on the selected signal sub-channel is selected The cross-correlation data points in the set are used as the cross-correlation data, that is, hard decision data. the hard verdict

It can be expressed as:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}{\mathrm{<span\; class="notranslate">\; arg</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; \{</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

in, $\mathrm{\&Omega;}=\left\{{\mathrm{E.}}_t\right|{\mathrm{E.}}_t=e_u\&Center\; Dot;e_v^{*},e_u,e_v\&Element;\mathrm{\&Pi;},t=\mathrm{1,2},...,m\},$ Ω is the target set, Π is the set of data on the sub-channel corresponding to the data on the constellation diagram, and the cross-correlation data point E _t in the target set Ω is a set formed by cross-correlation calculation of the data in Π.

Step 204: use the hard decision result to compensate the cross-correlation data of the signal sub-channels that meet the set transmission quality requirements; and use the known pilot cross-correlation data at the sending end to compensate the pilot cross-correlation data calculated in step 203.

In this step, the cross-correlation data carrying the phase offset on the receiving sub-channel is obtained through compensation. At the receiving end, the cross-correlation data carrying the phase offset is obtained by combining the cross-correlation data of the receiving end data. The compensation includes: on the signal sub-channel that meets the set transmission quality requirements, using the judgment result to replace the cross-correlation data of the known data at the sending end; on the pilot sub-channel, using the known cross-correlation data of the sending end pilot The influence of itself on the cross-correlation data at the receiving end.

Using formula (12) to compensate formula (10), it can be obtained that the cross-correlation function X _m (l) carrying the phase offset on the l-th signal sub-channel of the m-th OFDM symbol is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; j\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; w</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

Since the known pilot cross-correlation function D _m (l) of the transmitting end is:

${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

Using formula (14) to compensate formula (11), it can be obtained that the cross-correlation function X _m (l) carrying the phase offset on the l-th pilot sub-channel of the m-th OFDM symbol is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

Therefore, the cross-correlation data on sub-channels used for estimation of residual carrier frequency offset and sampling clock offset in the mth OFDM symbol is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

Step 205: Using the compensated cross-correlation data, calculate the phase difference between the current OFDM symbol and the sub-channel data acquired between its adjacent OFDM symbols.

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

In formula (16), the phase φ _l of the data on the selected sub-channel after compensation is:

φ _l ≈ 2π(1+N _g /N)(ε+l·β), l∈χ (17)

Wherein, χ is a set of sub-channel coefficients corresponding to the pilot sub-channel and the high-quality sub-channel, that is: χ=ζ+γ.

In this step, all sub-channel coefficients in the set χ can be sorted in ascending order, and then the set χ is divided into two sub-sets χ ₁ and χ ₂ with equal numbers of sub-channels. The phases of the cross-correlation data on the corresponding two sub-channels in the subsets χ ₁ and χ ₂ are φ _l′ and φ _l″ respectively:

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 phases of the cross-correlation data whose corresponding sub-channel coefficients in the two sets differ greatly are subtracted, so that the phase offset caused by the remaining carrier frequency offset can be canceled out. The phase difference φ _v obtained after subtraction is:

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

Wherein, the set χ ₃ represents a set formed by the phase differences of the data on the corresponding sub-channels in the sets χ ₁ and χ ₂ .

This method of dividing the set χ into two sub-sets _χ1 and _χ2 with the same number of sub-channels to calculate the phase difference can make the corresponding sub-channel coefficients in the two sets have a large difference, and can improve the estimation performance.

In addition, when the selected high-quality sub-channels are all signal sub-channels, the above method can also be used to calculate the phase difference, that is, the set composed of the selected high-quality sub-channels is equally divided into separated sub-sets, and then the two sub-channels The phases of the data on the sub-channels in the set are subtracted to obtain the desired phase difference.

Step 206: Using the calculated phase difference, estimate the remaining carrier frequency offset and sampling clock offset.

In this step, the sampling clock offset can be estimated by using the weighted average method of the phase difference, and the sampling clock offset can be obtained for:

$\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; \&zeta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}}{\underset{\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; \&zeta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; \&chi;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; one</span>}<span\; class="notranslate">\; )</span>$

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

为：Estimating the remaining carrier frequency offset can be as follows: substituting the obtained sampling clock offset into the phase φ _l of the data on the selected sub-channel after compensation, that is, substituting (21) into (17), and obtaining the remaining carrier frequency offset

for:

$\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&chi;</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&CenterDot;</span>\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; \&Element;</span>\mathrm{<span\; class="notranslate">\; \&chi;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; two</span>}<span\; class="notranslate">\; )</span>$

Among them, N _c represents the total number of sub-channels and pilot sub-channels in the set χ that meet the set transmission quality requirements.

Step 207: Use the estimated remaining frequency carrier offset and sampling clock offset to compensate data on the next OFDM symbol to be estimated. The above steps are repeated until the OFDM symbols to be estimated are estimated.

In addition, this step may also adopt a closed-loop feedback compensation method. 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:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; three</span>}<span\; class="notranslate">\; )</span>$

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}<span\; class="notranslate">\; )</span>$

Among them, γ _ε and γ _β are the control parameters of the closed-loop feedback filter.

Then, the processed estimated value is compensated for the remaining carrier frequency and sampling frequency in the time domain and the frequency domain, respectively, and then the data of the next OFDM symbol is estimated.

The above is the detailed process of the first method. When using the second method, the process is shown in Figure 3, which mainly includes the following steps:

Step 301: In the current OFDM symbol, obtain signal subchannels that meet the set transmission quality requirements, and obtain pilot subchannels.

Likewise, the subchannels obtained in this step that meet the set transmission quality requirements are all signal subchannels. In addition to this method, sub-channels that meet the set transmission quality requirements among the pilot sub-channels can also be obtained.

Step 302: Perform a hard decision on the acquired signal data on the signal sub-channel meeting the set transmission quality requirement.

In this step, the hard decision on the signal data on the signal sub-channel that meets the set transmission quality requirements is: according to the distance from the signal data on the selected signal sub-channel to the data of each coordinate point in the constellation diagram, the distance The nearest coordinate point data of the signal data on the selected signal sub-channel is used as the decision data.

Step 303: Compensate the signal data on the signal sub-channels that meet the set transmission quality requirements according to the hard decision result, and compensate the pilot data on the pilot sub-channels by using the known pilot data offset.

Step 304: Perform cross-correlation calculation on the compensated signal data on the signal sub-channel acquired in 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 calculate the obtained The compensated pilot data of the pilot sub-channel is subjected to cross-correlation calculation.

In this step, the cross-correlation calculation is performed on the compensated signal data on the signal sub-channel obtained in the current OFDM symbol and the compensated signal data on the signal sub-channel at the same position in the next OFDM symbol, which is the latter The conjugate of the compensated signal data at a selected sub-channel position of the OFDM symbol multiplied by the compensated signal data at 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, which is to multiply the pilot data on a certain pilot position of the latter OFDM symbol by the same value of the previous OFDM symbol. The conjugate of the pilot data at the pilot position.

Step 305: According to the result of cross-correlation calculation in step 304, calculate the phase difference between the current OFDM symbol and the sub-channel data obtained in its adjacent OFDM symbols.

Step 306: Using the calculated phase difference, estimate the remaining carrier frequency offset and sampling clock offset.

Step 307: Use the estimated remaining frequency carrier offset and sampling clock offset to compensate the data on the next OFDM symbol to be estimated. The above steps are repeated until the OFDM symbols to be estimated are estimated.

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

A channel selection unit 400, configured to obtain subchannels in the current OFDM symbol that meet the set transmission quality requirements;

Phase difference calculation unit 410, used to calculate the phase difference between the data on the sub-channel obtained by the channel selection unit 400 in the current OFDM symbol and the data on the sub-channel at the same position in its adjacent OFDM symbol, and calculate the phase difference The difference is provided to the estimation unit 420;

The estimation unit 420 is configured to use the phase difference provided by the phase difference calculation unit 410 to estimate the remaining carrier frequency offset and sampling clock offset of the current OFDM symbol.

The estimating unit 420 may use the method described in step 206 in FIG. 2 to estimate the remaining carrier frequency offset and sampling clock offset of the OFDM symbol.

Wherein, the structure of the channel selection unit 400 is shown in Figure 4.b, the channel selection unit 400 may include: a quality detection module 401, and a signal sub-channel selection module 402;

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

The quality detection module 401 can perform quality detection by the signal-to-noise ratio of each sub-channel; it can also perform quality detection by calculating the distance between each sub-channel data in the OFDM symbol and the corresponding data in the constellation diagram; The phase offset values between each sub-channel data in the OFDM symbol and the corresponding data in the constellation diagram are respectively calculated for detection.

The signal subchannel selection module 402 is configured to select a signal subchannel in the OFDM symbol that meets the set transmission quality requirement according to the detection result sent by the quality detection 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 can select a sub-channel whose signal-to-noise ratio is higher than the signal-to-noise ratio threshold by setting the signal-to-noise ratio threshold; By sorting the sub-channels according to the signal-to-noise ratio, the sub-channels for setting data are selected according to the order from large to small. 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 can select the distance to meet the distance threshold condition by setting the distance threshold sub-channel. When the quality detection module 401 performs detection 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 can select the phase offset value by setting the phase offset threshold. Shift the sub-channels that meet the phase offset threshold condition.

In addition, the channel selection unit 400 may also include: a pilot subchannel selection module 403, configured to select all pilot subchannels in the OFDM symbol, or, according to the detection result sent by the quality detection module 401, select the pilot subchannel in the OFDM symbol Pilot sub-channels that meet the set transmission quality requirements;

The quality detection module 401 is further configured to detect the transmission quality of the pilot sub-channel in the current OFDM symbol, and send the detection result to the pilot sub-channel selection module 403 .

The phase difference calculation unit 410 may have two structures, which respectively correspond to mode 1 and mode 2 in the method. Figure 4.c is the first composition structure diagram of the phase difference calculation unit, as shown in Figure 4.c, the phase difference calculation 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 sub-channel acquired by the channel sub-channel selection module 402 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 provide the obtained cross-correlation data to the hard decision module 412 and the first compensation module 413 .

The hard decision module 412 is configured to make a hard decision on the received cross-correlation data, and provide the 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 in 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, and use the decision data to compensate the cross-correlation data, and make the compensated The cross-correlation data of is sent to the phase difference calculation module 414.

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

The phase difference calculation module 414 is used to receive the compensated cross-correlation data sent by the first compensation module 413, calculate the phase of the compensated cross-correlation data, and obtain the signal data on the signal sub-channel acquired in the current OFDM symbol and its adjacent Phase difference between signal data on signal subchannels at the same position in the next OFDM symbol.

The phase difference calculation module 414 may use the method described in step 205 in FIG. 2 to calculate the phase difference.

Furthermore, 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 .

The second cross-correlation calculation module 415 is used to calculate the pilot data on the pilot subchannel obtained by the channel selection module 400 in the current OFDM symbol and the pilot data on the pilot subchannel at the same position in the next OFDM symbol adjacent to it Cross-correlation calculations are performed, and the obtained cross-correlation data is provided to the second compensation module 416 .

The second compensation module 416 is configured to use the known pilot cross-correlation data at the transmitting end to compensate the cross-correlation data sent by the second cross-correlation calculation module 415, and provide the cross-correlation data obtained after compensation to the phase difference calculation Module 414.

The phase difference calculation module 414 is also used to receive the compensated cross-correlation data sent by the second compensation module 416, calculate the phase of the compensated cross-correlation data, and obtain the pilot sub-channel obtained in the current OFDM symbol. The phase difference between the frequency data and the pilot data on the pilot sub-channel at the same position in the next adjacent OFDM symbol.

Wherein, the first cross-correlation calculation module 411 and the second cross-correlation calculation module 415 may also be set in one device; the first compensation module 413 and the second compensation module 416 may also be set in one device.

Figure 4.d is a second composition structure diagram of the phase difference calculation unit, as shown in Figure 4.c, the phase difference calculation 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 .

The hard decision module 417 is configured to make a hard decision on the signal data on the signal sub-channels obtained by the channel selection unit 400 that meet the set transmission quality requirements, and provide the decision data obtained after the hard decision to the compensation module 418 .

The hard decision module 417 may adopt the method of hard decision in step 302 in FIG. 3 .

The compensation module 418 is configured to receive the decision data provided by the hard decision module 417, and use the decision data to compensate the acquired signal data on the signal sub-channels that meet the set transmission quality requirements, and convert the compensated signal data Send to the first cross-correlation calculation module 419.

The compensation module 418 may use the compensation method described in step 303 in FIG. 3 .

The first cross-correlation calculation module 419 is used to perform cross-correlation between the compensated signal data on the signal sub-channel acquired in the current OFDM symbol and the compensated signal data on the signal sub-channel at the same position in the next OFDM symbol adjacent to it. Correlation calculation, and the obtained signal cross-correlation data is provided to the phase difference calculation module 420.

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

The phase difference calculation module 4110 receives the signal cross-correlation data provided by the first cross-correlation calculation module 419, calculates the phase of the signal cross-correlation data, and obtains the signal data on the signal sub-channel acquired in the current OFDM symbol and its adjacent next The phase difference between signal data on signal subchannels at the same position in an OFDM symbol.

Furthermore, 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 .

The second cross-correlation calculation module 4111 is used to calculate the pilot data on the pilot sub-channel acquired by the channel selection unit 400 in the current OFDM symbol and the pilot data on the pilot sub-channel at the same position in the next OFDM symbol adjacent to it Perform cross-correlation calculation, and provide the obtained pilot cross-correlation data to the phase difference calculation module 4110 .

The phase difference calculation module 4110 is also used to receive the pilot cross-correlation data provided by the second cross-correlation calculation module 4111, calculate the phase of the pilot cross-correlation data, and obtain the pilot on the pilot sub-channel obtained in the current OFDM symbol The phase difference between the frequency data and the pilot data on the pilot sub-channel 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, the simulation results are used for description below. The following conditions for simulation are: the sampling frequency of the OFDM system is 20MHZ; the number of sub-channels N=256, that is, the IFFT of 256 points is adopted, wherein the cyclic prefix CP=64, the number of useful sub-channels is 200, and the pilot channel is included in Among the 200 sub-channels, the number of pilot channels is 8, which are respectively located at the sub-channel positions of [13 38 63 88 113 138 163 188]; the maximum Doppler frequency shift of the system is 50HZ.

Fig. 5 is a curve diagram of mean square error (MSE) of the residual frequency offset (RCFO) of the method provided by the embodiment of the present invention and the PTA method when different thresholds are used. The MSE can reflect the error accuracy of the estimated frequency offset. The simulation shown in this figure was done with a residual carrier frequency offset normalized to 0.04 and a sample clock offset normalized to 0.00002. The three thresholds in the figure are in descending order: threshold one, threshold two, and threshold three. It can be seen from Fig. 5 that when the threshold is selected higher in the method provided by the present invention, such as threshold three, its frequency offset estimation performance is basically consistent with the performance of the PTA method, mainly because the high threshold makes the selection satisfy the condition The subchannels have very little data. When the threshold is selected to be low, such as threshold 1, there are many subchannels that meet the conditions. However, when the threshold is low, the transmission quality of the selected subchannel is low, and bit errors are prone to occur, which will also affect the performance of the system. . Compared with the three thresholds, the second threshold is the best threshold for residual frequency offset estimation.

FIG. 6 is a curve diagram of the mean square error (MSE) of the sampling clock offset (SFO) of the method provided by the embodiment of the present invention and the PTA method when different thresholds are used. The MSE can reflect the error accuracy of the estimated sampling clock offset. The simulation shown in this figure was done with a residual carrier frequency offset normalized to 0.04 and a sample clock offset normalized to 0.00002. The three thresholds in the figure are in descending order: threshold one, threshold two, and threshold three. It can be seen from Figure 6 that the smaller the threshold, the higher the estimation performance of the sampling clock offset. This is because the weighted estimation of the phase variation between sub-channels is used in the sampling clock estimation, which is not sensitive to the bit error of each channel.

Fig. 7 is the estimated performance curves of the method of the present invention and the PTA method under the same normalized value of sampling clock offset and different normalized value of residual carrier frequency offset. The normalized value of the sampling clock used is 0.00002, and the normalized values of the remaining carrier frequency offset are 0.06, 0.04 and 0.02, respectively. It can be seen from Fig. 7 that the MSE of the residual frequency offset of the PTA method decreases slightly with the reduction of the residual frequency offset; the estimation performance in the method of the present invention is better than that of the PTA method in three cases, but in When the residual frequency offset is large, its performance tends to be that of the PTA method. As the residual frequency offset decreases, the MSE of the residual frequency offset decreases rapidly. This is because the high-quality The number of sub-channels increases accordingly, so the performance of the method of the present invention is obviously improved.

Fig. 8 is an estimated performance curve of the method of the present invention and the PTA method under the same normalized value of residual carrier frequency offset and different normalized value of sampling clock offset. The adopted normalized value of residual carrier frequency offset is 0.04, and the adopted normalized values of sampling clock offset are 0.00004, 0.00002 and 0.000005 respectively. As can be seen from Fig. 8, the MSE of the sampling clock offset of the PTA method decreases slightly with the decrease of the sampling clock offset; the performance in the method of the present invention is better than that of the PTA method in three cases, and with As the sampling clock skew decreases, the MSE of the sampling clock skew drops rapidly. This is due to the increase in high-quality sub-channels as the sampling clock decreases. However, since the value of the sampling clock offset is generally small, compared with the change of the remaining carrier frequency offset, its impact on the sub-channel transmission quality is small.

Fig. 9 is under the condition that the average signal-to-noise ratio is 15dB, the normalized value of residual carrier frequency offset is 0.05, and the normalized value of sampling clock offset is 0.0004, the residual carrier frequency offset of the method of the present invention and the PTA method Trace the curve. As shown in Figure 9, the convergence speeds of the method of the present invention and the PTA method are very fast, but the fluctuation range of the PTA method is relatively large in tracking, while the fluctuation range of the method of the present invention is relatively small, and it can be concluded that in the tracking process , the variance of the residual carrier frequency tracking of the PTA method is 1.8457e-004, while 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 the sampling clock offset tracking curves of the method of the present invention and the PTA method under the conditions that the average signal-to-noise ratio is 15dB, the normalized value of the remaining carrier frequency offset is 0.05, and the sampling clock offset is 0.0004. It can be seen from Fig. 10 that during tracking, the fluctuation range of the PTA method is large, and the fluctuation range of the method of the present invention is small. Through calculation, it can be obtained that in the tracking process, the variance of the sampling clock offset tracking of the PTA method is 8.2279e-009, while this The variance of the sampling clock offset tracking of the inventive method is 2.1542e-009, and the performance is improved by 2.8 times compared with the PTA method.

It can be seen from the above description that the synchronization estimation method and system of the OFDM technology provided by the embodiments of the present invention use the cross-correlation data obtained on the sub-channels that meet the set transmission quality requirements to calculate the remaining carrier frequency offset and sampling clock The offset is estimated, which overcomes the influence of bit errors generated in sub-channels with poor transmission quality, and improves the accuracy of synchronization estimation.

Furthermore, in the method and system provided by the embodiments of the present invention, the obtained subchannels that meet the set transmission quality requirements are signal subchannels, and may also include pilot subchannels or all pilot subchannels that meet the set transmission quality requirements. The sub-channel increases the sub-channel data used, and overcomes the disadvantage of the PTA method that the accuracy of synchronization estimation is limited due to the lack of pilot sub-channel data.

Furthermore, the hard decision method adopted in the present invention does not need to estimate the channel, and can compensate the data or cross-correlation data on the channel of the receiving terminal to obtain the data that the transmitting terminal may send, which overcomes the channel estimation method of the synchronous estimation method. Estimated dependencies.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection.

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 signal cross-correlation data by using the hard decision data, and calculating the phase of the compensated signal 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 hard 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 module is used for selecting all pilot subchannels in the current OFDM symbol, or receiving the 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 detection 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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