CN101808071A - Synchronizing method of OFDM (Orthogonal Frequency Division Multiplexing) system - Google Patents

Abstract

The invention relates to a synchronizing method of an OFDM (Orthogonal Frequency Division Multiplexing) system, belonging to the technical field of communication and comprising the following steps of: carrying out timing and synchronizing estimation process on received data and determining a first OFDM sign to obtain the position and related peak value of the starting sampling point of an ith OFDM sign and obtain the frequency deviation of the ith OFDM sign and the corrected frequency deviation of an (i+1)th OFDM sign so as to further obtain the starting sampling point and the frequency deviation of the whole OFDM system, wherein i is not less than 2 and not more than T+1, and T is synchronizing iterations. The invention can reduce the synchronizing time when the channel performance is good and enhance the accuracy and the stability of the timing synchronizing and frequency deviation estimating through iteration.

Description

Synchronization Method of OFDM System

technical field

The present invention relates to a method in the technical field of communication, in particular to a synchronization method for an OFDM (Orthogonal Frequency Division Multiplexing, Orthogonal Frequency Division Multiplexing) system.

Background technique

OFDM is a high-speed transmission technology in a wireless environment. Due to the complexity of the wireless channel, the channel conditions are more complicated, and the frequency response of the channel is mostly non-flat. In view of this feature, the main technical point of OFDM technology is to convert the frequency domain The channel is divided into multiple orthogonal sub-channels, and each sub-channel modulates a sub-carrier. In this way, although the frequency selectivity is reflected on the entire channel, for each sub-channel, its frequency response is flat, and for each sub-channel, the bandwidth of the signal is smaller than the coherent bandwidth of the channel, so the interference between signal waveforms can be greatly suppressed . In the OFDM system, at the same time, due to the mutual orthogonality between each subcarrier, a higher spectrum utilization rate can be achieved.

OFDM has obvious advantages for wireless systems, so it has been widely used, such as IEEE802.11a/b/g/n wireless local area network (Wi-Fi), IEEE802.16 wireless metropolitan area network (Wi-MAX), digital audio broadcasting (DAB), digital television broadcasting (DVB), and 3GPP's long-term evolution plan (LTE) and LTE_Advanced. At the same time, the combination of OFDM technology and MIMO technology has become a key technology for next-generation mobile communications. OFDM technology will be used in future communication systems play a more important role.

However, OFDM technology also has its defects and shortcomings, that is, the orthogonality between subcarriers of OFDM system is an important basis for its work, and good synchronization technology is necessary to ensure that each subcarrier in the system has good orthogonality. Then for the OFDM system, it is necessary to provide more accurate synchronization performance. The synchronization of the OFDM system mainly includes two aspects: one is the symbol timing estimation (hereinafter referred to as timing synchronization), if the timing synchronization is inconsistent with the actual position, it will bring a phase shift in the frequency domain and aggravate the inter-symbol interference (ISI); two It is the estimation of carrier frequency offset (hereinafter referred to as carrier synchronization). The main reason for carrier offset is that the frequency of the crystal oscillator between the transmitting end (TX) and the receiving end (RX) does not match, and the deviation between the local carrier frequencies of the transceiver equipment , channel Doppler shift, etc. Since the OFDM system requires the orthogonality between subcarriers, the frequency offset will destroy the orthogonality between subcarriers, so its existence causes inter-subcarrier interference (ICI).

So far, a large number of OFDM system synchronization methods have been proposed, including the use of training sequences and cyclic prefixes (CP). When training sequences, a known sequence is sent before data transmission. Generally, it has good autocorrelation and can Used for timing synchronization and carrier synchronization. Synchronization can be performed by using a cyclic prefix, but generally speaking, its performance is not as good as using a training sequence, but it does not require an additional training sequence, so higher spectrum utilization can be obtained.

After searching the existing literature, it is found that the Chinese patent application number is: 200510040501.3, and the name is: a cyclic prefix OFDM system synchronization method. This technology proposes to use only the cyclic prefix of OFDM symbols for timing and frequency offset estimation. However, this technology only uses the maximum cyclic prefix energy for timing judgment during timing synchronization, and fails to normalize the data, which is not conducive to the setting of the judgment threshold. In the timing synchronization frequency offset estimation process, only the frequency of the current OFDM symbol is used. The offset estimate is used as the result of frequency offset estimation, without cyclic iteration and combination, which will affect the stability and accuracy of the estimation when the signal-to-noise ratio is low; the influence of channel conditions is not considered, resulting in a longer synchronization time.

Contents of the invention

The object of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a synchronization method for an OFDM system. The invention reduces the time of synchronization under the condition of good channel performance; at the same time, it improves the accuracy and stability of timing synchronization and frequency offset estimation through iteration.

The present invention is achieved through the following technical solutions, and the present invention comprises the following steps:

The first step is to perform timing synchronization estimation processing on the received data, obtain the starting sample point of the first OFDM symbol is the θ _1st sample point, and extract the correlation peak value of the θ _1st sample point in the first OFDM symbol _P1 .

The timing synchronization estimation process includes the following steps:

1) Obtain the correlation value of each sample point in each OFDM symbol of the received data, specifically:

${\mathrm{<span\; class="notranslate">\; Cor</span>}}_{\mathrm{<span\; class="notranslate">\; i</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>\frac{\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; B</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</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">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; B</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</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">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>$

Among them: Cor _i (k) is the correlation value of the k-th sample point in the i-th OFDM symbol, _ri (k) is the received data of the k-th sample point in the i-th OFDM symbol, and N is each OFDM symbol The FFT length of , B represents the back-off length in estimation, ^* represents the conjugate, 1≤i.

2) Normalize the correlation value of each sample point, specifically:

M_i＝2n+1，n∈N⁺，

M _i =2n+1, n∈N ⁺ ,

为第i个OFDM符号中第k个样点的归一化相关值，M_i为第i个OFDM符号平滑窗的长度，Cor_i(k+l)是第i个OFDM符号中第(k+l)个样点的相关值。in:

is the normalized correlation value of the kth sample point in the ith OFDM symbol, M _i is the length of the smoothing window of the ith OFDM symbol, Cor _i (k+l) is the (k+l) of the ith OFDM symbol l) Correlation value of sample points.

3) When the largest normalized correlation value in the earliest OFDM symbol in the received data is greater than the decision threshold Thr, the OFDM symbol is the first OFDM symbol, and the sample point corresponding to the largest normalized correlation value in the OFDM symbol is the starting sample point of the OFDM symbol.

In the second step, frequency offset estimation processing is performed on the first OFDM symbol to obtain the frequency offset f ₁ of the first OFDM symbol.

The frequency offset estimation process is specifically:

f _i =ε _i □Δ,

in: ${\mathrm{\&epsiv;}}_i=\frac{1}{2\mathrm{\&pi;}}\&angle;(\underset{k={\mathrm{\&theta;}}_i}{\overset{{\mathrm{\&theta;}}_i+L-1}{\mathrm{\&Sigma;}}}{r}_i\left(k\right)\&Center\; Dot;r_i^{*}(k+N)),$

f _i is the frequency deviation of the i-th OFDM symbol, ΔF is the subcarrier spacing of the OFDM system, N is the FFT (Fast Fourier Transform) length of the OFDM symbol, L is the length of the cyclic prefix of the OFDM symbol, and θ _i is the i-th The position of the starting sample point of each OFDM symbol, ε _i is the normalized deviation of the i-th OFDM symbol, 1≤i, when i=1, r ₁ (k) is the k-th sample point of the first OFDM symbol When i>1, r _i (k) is the corrected data of the kth sample point of the ith OFDM symbol.

In the third step, according to the size of the correlation peak value _P1 of the initial sample point in the first OFDM symbol, the number of synchronization iterations T and the frequency offset correction parameter K of the OFDM system are set by looking up the table, and the second OFDM symbol is performed For frequency offset correction, the corrected data of each sample point in the second OFDM symbol and the corrected frequency offset of the second OFDM symbol are obtained.

The frequency offset correction is specifically:

f' _i =f' _i-1 +Kf _i-1 , 3≤i≤T,

Where: f′ ₂ =f ₁ ,

r′ _j (k) is the corrected data of the k-th sample point in the j-th OFDM symbol, r _j (k) is the data before correction of the k-th sample point in the j-th OFDM symbol, θ _j-1 is The position of the starting sample point of the j-1th OFDM symbol, N is the FFT length of the OFDM symbol, B is the number of samples returned during correction, f′ _i is the corrected frequency deviation of the i-th OFDM symbol, f′ _i-1 is the corrected frequency deviation of the i-1th OFDM symbol, f _i-1 is the frequency deviation of the i-1th OFDM symbol, f′ ₂ is the corrected frequency deviation of the second OFDM symbol, f ₁ is the frequency offset of the first OFDM symbol, K is the frequency offset correction parameter, 2≤j≤T.

In the fourth step, using the method of the first three steps, the corrected starting sample point of the ith OFDM symbol is θ _i , and the correlation peak value P _i of the θ _i sample point in the ith OFDM symbol is extracted to obtain the first The frequency offset f _i of i OFDM symbols, and the corrected frequency offset f′ _i +1 of the i+1th OFDM symbol is obtained, 2≤i≤T+1, where T is the number of synchronization iterations.

In the fifth step, the initial sampling point and frequency deviation of the first to T+1th OFDM symbols are combined to obtain the initial sampling point of the entire OFDM system is θ, and the frequency deviation of the system is f.

The merge process is:

f=f' _T+1 ,

Among them: f′ _j+1 =f′ _j +Kf _j , 2≤j≤T,

f' ₂ =f ₁ ,

P _i is the correlation peak value of the starting sample point of the ith OFDM symbol, N is the FFT length of the OFDM symbol, θ _i is the starting position of the ith OFDM symbol, f′ _T+1 is the T+1th OFDM symbol The corrected frequency deviation, f′ _j+1 is the corrected frequency deviation of the j+1th OFDM symbol, f′ _j is the corrected frequency deviation of the jth OFDM symbol, and f _j is the frequency of the jth OFDM symbol deviation, f′ ₂ is the corrected frequency deviation of the second OFDM symbol, f ₁ is the frequency deviation of the first OFDM symbol, K is the frequency deviation correction parameter, and T is the number of synchronization iterations.

Compared with the prior art, the beneficial effect of the present invention is: the data is normalized before the timing decision, which is convenient to set a stable decision threshold Thr under various channel and signal-to-noise ratio conditions, and can improve timing synchronization and The performance results of frequency offset estimation; compared with a single OFDM symbol, the results of multiple symbols are used for comprehensive estimation, and combined with channel conditions (reflected as the size of the correlation peak), the stability and accuracy of the estimation are greatly improved; The method is simple, only using the OFDM symbol and its cyclic prefix, no redundant information is required, and the time consumption of synchronization can be reduced without changing the synchronization performance. Improve channel utilization.

Description of drawings

FIG. 1 is a schematic diagram of comparison of frequency offset estimation stability obtained by using the prior art and the method of the embodiment respectively;

Fig. 2 is a schematic diagram of frequency offset estimation performance comparison obtained by using the prior art and the method of the embodiment respectively.

Detailed ways

Below in conjunction with accompanying drawing, the method of the present invention is further described: present embodiment is carried out under the premise of technical solution of the present invention, has provided detailed implementation and specific operation process, but protection scope of the present invention is not limited to following Example.

Example

The channel condition of the OFDM system in the present embodiment is SCM (subcarrier modulation) channel, and SNR is 5dB, and the length of the cyclic prefix of each OFDM symbol is 72, and the length of FFT is 1024, and the subcarrier spacing of OFDM system is 15kHz, the normalized deviation is 0.3, which specifically includes the following steps:

The first step is to perform timing synchronization estimation processing on the received data, and obtain that the starting sample point of the first OFDM symbol is the θ _1st sample point, and extract the correlation peak value of the θ _1st sample point in the first OFDM symbol _P1 .

The timing synchronization estimation process includes the following steps:

1) Obtain the correlation value of each sample point in each OFDM symbol of the received data, specifically:

${\mathrm{<span\; class="notranslate">\; Cor</span>}}_{\mathrm{<span\; class="notranslate">\; i</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>\frac{\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; B</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</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">\; i</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">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; B</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</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">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>$

Among them: Cor _i (k) is the correlation value of the k-th sample point in the i-th OFDM symbol, _ri (k) is the received data of the k-th sample point in the i-th OFDM symbol, and N is each OFDM symbol The FFT length of , B represents the back-off length in estimation, ^* represents the conjugate, 1≤i.

2) Normalize the correlation value of each sample point, specifically:

M _i =2n+1, n∈N ⁺ ,

为第i个OFDM符号中第k个样点的归一化相关值，M_i为第i个OFDM符号平滑窗的长度，Cor_i(k+l)是第i个OFDM符号中第(k+l)个样点的相关值。in:

is the normalized correlation value of the kth sample point in the ith OFDM symbol, M _i is the length of the smoothing window of the ith OFDM symbol, Cor _i (k+l) is the (k+l) of the ith OFDM symbol l) Correlation value of sample points.

3) When the largest normalized correlation value in the earliest OFDM symbol in the received data is greater than the decision threshold Thr, the OFDM symbol is the first OFDM symbol, and the sample point corresponding to the largest normalized correlation value in the OFDM symbol is the starting sample point of the OFDM symbol.

In this embodiment, the decision threshold Thr is 0.55.

In the second step, frequency offset estimation processing is performed on the first OFDM symbol to obtain the frequency offset f ₁ of the first OFDM symbol.

The frequency offset estimation process is specifically:

f _i =ε _i □ΔF,

in: ${\mathrm{\&epsiv;}}_i=\frac{1}{2\mathrm{\&pi;}}\&angle;(\underset{k={\mathrm{\&theta;}}_i}{\overset{{\mathrm{\&theta;}}_i+L-1}{\mathrm{\&Sigma;}}}{r}_i\left(k\right)\&Center\; Dot;r_i^{*}(k+N)),$

f _i is the frequency deviation of the ith OFDM symbol, ΔF is the subcarrier spacing of the OFDM system, N is the FFT length of the OFDM symbol, L is the length of the cyclic prefix of the OFDM symbol, θ _i is the initial sample of the ith OFDM symbol The position of the point, ε _i is the normalized deviation of the i-th OFDM symbol, 1≤i, when i=1, r ₁ (k) is the data of the k-th sample point of the first OFDM symbol, when i>1 r _i (k) is the corrected data of the kth sample point of the ith OFDM symbol.

In the third step, according to the size of the correlation peak value _P1 of the initial sample point in the first OFDM symbol, the number of synchronization iterations T and the frequency offset correction parameter K of the OFDM system are set by looking up the table, and the second OFDM symbol is performed For frequency offset correction, the corrected data of each sample point in the second OFDM symbol and the corrected frequency offset of the second OFDM symbol are obtained.

Table 1 shows the relationship between the correlation peak value P ₁ , the number of synchronization iterations T and the frequency offset correction parameter K selected in this embodiment.

Table 1

Correlation peak P ₁ The number of synchronization iterations T Frequency offset correction parameter K 0.35□0.65 12 0.4 0.65～0.8 8 0.2 0.8□1 4 0.05

The frequency offset correction is specifically:

f' _i =f' _i-1 +Kf _i-1 , 3≤i≤T,

Where: f′ ₂ =f ₁ ,

r′ _j (k) is the corrected data of the k-th sample point in the j-th OFDM symbol, r _j (k) is the data before correction of the k-th sample point in the j-th OFDM symbol, θ _j-1 is The position of the starting sample point of the j-1th OFDM symbol, N is the FFT length of the OFDM symbol, B is the number of samples returned during correction, f′ _i is the corrected frequency deviation of the i-th OFDM symbol, f′ _i-1 is the corrected frequency deviation of the i-1th OFDM symbol, f _i-1 is the frequency deviation of the i-1th OFDM symbol, f′ ₂ is the corrected frequency deviation of the second OFDM symbol, f ₁ is the frequency offset of the first OFDM symbol, K is the frequency offset correction parameter, 2≤j≤T.

In the fourth step, using the method of the first three steps, the corrected starting sample point of the ith OFDM symbol is θ _i , and the correlation peak value P _i of the θ _i sample point in the ith OFDM symbol is extracted to obtain the first The frequency offset f _i of i OFDM symbols, and the corrected frequency offset f′ _i +1 of the i+1th OFDM symbol is obtained, 2≤i≤T+1, where T is the number of synchronization iterations.

In the fifth step, the initial sampling point and frequency deviation of the first to T+1th OFDM symbols are combined to obtain the initial sampling point of the entire OFDM system is θ, and the frequency deviation of the system is f.

The merge process is:

f=f' _T+1 ,

Among them: f′ _j+1 =f′ _j +Kf _j , 2≤j≤T,

f' ₂ =f ₁ ,

P _i is the correlation peak value of the starting sample point of the ith OFDM symbol, N is the FFT length of the OFDM symbol, θ _i is the starting position of the ith OFDM symbol, f′ _T+1 is the T+1th OFDM symbol The corrected frequency deviation, f′ _j+1 is the corrected frequency deviation of the j+1th OFDM symbol, f′ _j is the corrected frequency deviation of the jth OFDM symbol, and f _j is the frequency of the jth OFDM symbol deviation, f′ ₂ is the corrected frequency deviation of the second OFDM symbol, f ₁ is the frequency deviation of the first OFDM symbol, K is the frequency deviation correction parameter, and T is the number of synchronization iterations.

The frequency estimation stability obtained by adopting the method of the prior art and the method of this embodiment respectively is shown in Fig. 1, and its abscissa is the number of OFDM symbols, and the ordinate is the residual frequency offset. It can be seen from the figure that the present embodiment is due to The cyclic iterative frequency offset estimation method is adopted, and the frequency offset estimation value is more stable than the existing method.

The frequency offset estimation performance comparison obtained by adopting the prior art method and the method of this embodiment respectively is shown in Fig. 2, and its abscissa is SNR (signal-to-noise ratio), and the ordinate is frequency offset estimation. As can be seen from this figure, this The method of the embodiment has more ideal frequency offset estimation performance.

Claims (5)

1. a synchronous method of OFDM system, is characterized in that, comprises the following steps: The first step is to perform timing synchronization estimation processing on the received data, and obtain that the starting sample point of the first OFDM symbol is the θ _1st sample point, and extract the correlation peak value of the θ _1st sample point in the first OFDM symbol _P1 ; The second step is to perform frequency offset estimation processing on the first OFDM symbol to obtain the frequency offset f ₁ of the first OFDM symbol; In the third step, according to the size of the correlation peak value _P1 of the initial sample point in the first OFDM symbol, the number of synchronization iterations T and the frequency offset correction parameter K of the OFDM system are set by looking up the table, and the second OFDM symbol is performed Frequency offset correction, obtaining the data of each sample point in the corrected second OFDM symbol and the corrected frequency offset of the second OFDM symbol; In the fourth step, using the method of the first three steps, the corrected starting sample point of the ith OFDM symbol is θ _i , and the correlation peak value P _i of the θ _i sample point in the ith OFDM symbol is extracted to obtain the first The frequency deviation f _i of the i OFDM symbol, and the corrected frequency deviation f' i+1 of the i ₊ 1 OFDM symbol, 2≤i≤T+1, T is the number of synchronization iterations; In the fifth step, the initial sampling point and frequency deviation of the first to T+1th OFDM symbols are combined to obtain the initial sampling point of the entire OFDM system is θ, and the frequency deviation of the system is f. 2. the synchronous method of OFDM system according to claim 1 is characterized in that, described timing synchronization estimation process, comprises the following steps: 1) Obtain the correlation value of each sample point in each OFDM symbol of the received data, specifically: ${\mathrm{<span\; class="notranslate">\; Cor</span>}}_{\mathrm{<span\; class="notranslate">\; i</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>\frac{\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; B</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</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">\; i</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">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; B</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</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">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>$ Among them: Cor _i (k) is the correlation value of the k-th sample point in the i-th OFDM symbol, _ri (k) is the received data of the k-th sample point in the i-th OFDM symbol, and N is each OFDM symbol The FFT length of , B represents the regression length when estimating, ^* represents the conjugate, 1≤i; 2) Normalize the correlation value of each sample point, specifically:

in:

is the normalized correlation value of the kth sample point in the ith OFDM symbol, M _i is the length of the smoothing window of the ith OFDM symbol, Cor _i (k+l) is the (k+l) of the ith OFDM symbol l) the correlation value of each sampling point; 3) When the largest normalized correlation value in the earliest OFDM symbol in the received data is greater than the decision threshold Thr, the OFDM symbol is the first OFDM symbol, and the sample point corresponding to the largest normalized correlation value in the OFDM symbol is the starting sample point of the OFDM symbol. 3. the synchronous method of OFDM system according to claim 1 is characterized in that, described frequency offset estimation process is:

in: ${\mathrm{\&epsiv;}}_i=\frac{1}{2\mathrm{\&pi;}}\&angle;(\underset{k={\mathrm{\&theta;}}_i}{\overset{{\mathrm{\&theta;}}_i+L-1}{\mathrm{\&Sigma;}}}{r}_i\left(k\right)\&CenterDot;r_i^{*}(k+N)),$ f _{i is} the frequency deviation of the ith OFDM symbol, ΔF is the subcarrier spacing of the OFDM system, N is the FFT length of the OFDM symbol, L is the length of the cyclic prefix of the OFDM symbol, θ _i is the starting sample point of the ith OFDM symbol ε _i is the normalized deviation of the i-th OFDM symbol, 1≤i, when i=1, r ₁ (k) is the data of the k-th sample point of the first OFDM symbol, when i>1, r _i (k) is the corrected data of the kth sample point of the ith OFDM symbol. 4. the synchronous method of OFDM system according to claim 1 is characterized in that, described frequency offset correction refers to:

(θ _j-1 +NB)<k<(θ _j-1 +N+N), f' _i =f' _i-1 +Kf _i-1 , 3≤i≤T, Where: f′ ₂ =f ₁ , r′ _j (k) is the corrected data of the k-th sample point in the j-th OFDM symbol, r _j (k) is the data before correction of the k-th sample point in the j-th OFDM symbol, θ _j-1 is The position of the starting sample point of the j-1th OFDM symbol, N is the FFT length of the OFDM symbol, B is the number of samples returned during correction, f′ _i is the corrected frequency deviation of the i-th OFDM symbol, f′ _i-1 is the corrected frequency deviation of the i-1th OFDM symbol, f _i-1 is the frequency deviation of the i-1th OFDM symbol, f′ ₂ is the corrected frequency deviation of the second OFDM symbol, f ₁ is the frequency offset of the first OFDM symbol, K is the frequency offset correction parameter, 2≤j≤T. 5. the synchronous method of OFDM system according to claim 1 is characterized in that, described merging process is:

f=f' _T+1 , Among them: f′ _j+1 =f′ _j +Kf _j , 2≤j≤T, f' ₂ =f ₁ , P _i is the correlation peak value of the starting sample point of the ith OFDM symbol, N is the FFT length of the OFDM symbol, θ _i is the starting position of the ith OFDM symbol, f′ _T+1 is the T+1th OFDM symbol The corrected frequency deviation, f′ _j+1 is the corrected frequency deviation of the j+1th OFDM symbol, f′ _j is the corrected frequency deviation of the jth OFDM symbol, and f _j is the frequency of the jth OFDM symbol deviation, f′ ₂ is the corrected frequency deviation of the second OFDM symbol, f ₁ is the frequency deviation of the first OFDM symbol, K is the frequency deviation correction parameter, and T is the number of synchronization iterations.

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