CN102480452A

CN102480452A - A carrier frequency synchronization circuit and method for an OFDM system

Info

Publication number: CN102480452A
Application number: CN2010102587996A
Authority: CN
Inventors: 乔树山; 黑勇
Original assignee: Institute of Microelectronics of CAS
Current assignee: Beijing Thinking Semiconductor Technology Co ltd
Priority date: 2010-11-26
Filing date: 2010-11-26
Publication date: 2012-05-30
Anticipated expiration: 2030-11-26
Also published as: CN102480452B

Abstract

The invention discloses a carrier frequency synchronization circuit and a method of an OFDM system, which comprises circuits such as decimal frequency offset estimation, decimal frequency offset compensation, integer frequency offset estimation, integer frequency offset compensation and the like; correspondingly, the method comprises the steps of fractional frequency offset estimation, fractional frequency offset compensation, integer frequency offset estimation and integer frequency offset compensation; performing normalization processing on cross-correlation values of two under-sampled synchronous sequences adjacent to a frequency domain to obtain an estimated value of fractional frequency offset, and performing fractional frequency offset compensation correction on the estimated value; then, carrying out autocorrelation operation on the high-energy carrier sign bit of each OFDM symbol after Fast Fourier Transform (FFT) processing, carrying out summation operation on the autocorrelation of a plurality of OFDM symbols to obtain an integer frequency offset estimation value, and then carrying out integer frequency offset compensation according to the integer frequency offset estimation value. By adopting the synchronous circuit and the method, the operation amount can be reduced, the influence of noise on frequency offset estimation can be reduced, and the design and the realization of low-power consumption equipment are facilitated.

Description

Carrier frequency synchronization circuit and method of OFDM system

Technical Field

The present invention relates to communication signal modulation technologies, and in particular, to a carrier frequency synchronization circuit and method for an Orthogonal Frequency Division Multiplexing (OFDM) system.

Background

The OFDM technology is widely applied to various high-speed data access systems, such as wireless local area networks, high-speed digital subscriber loops, asymmetric digital subscriber loops, digital audio broadcasting, digital video broadcasting, high-definition digital televisions, and the like, due to the capability of resisting multipath interference and frequency selective fading. Many international and domestic standards now use OFDM as a transmission means for the physical layer.

Since the OFDM technology can better solve the problems of multipath interference and broadband transmission in a high-speed communication system, the technology has become a candidate for a fourth-generation mobile communication technology (B3G/4G). At present, the standards of satellite broadcasting, digital mobile television broadcasting, digital terrestrial broadcasting and the like all adopt an OFDM technology as a core technology. But there is a problem: since OFDM technology relies on frequency orthogonality, once its orthogonality is destroyed, the error rate of its system will increase sharply, which is also a major drawback in the application of OFDM technology. The frequency offset is mainly generated due to the fact that the central frequencies of receiving and sending sections of a radio frequency circuit are mismatched; another reason is that both the transceiver and the receiver have doppler shifts with high relative velocity.

In an OFDM system, when a carrier frequency deviation occurs, a frequency deviation portion larger than a subcarrier spacing is called an integer frequency deviation Δ f_IThe integer frequency offset only shifts the output of Fast Fourier Transform (FFT) in the receiver, and does not destroy the orthogonality among the subcarriers, but will cause the demodulation result to be completely wrong; the portion of the frequency offset less than the subcarrier spacing is referred to as the fractional frequency offset Δ f_fIt destroys the orthogonality of the sub-carriers, causing sub-carrier interference, resulting in a rise in systematic error. Usually, the fractional frequency offset estimation and compensation are first performed in the time domain to eliminate the fractional frequency offsetAnd after the inter-subcarrier interference, performing integer frequency offset estimation and compensation in a frequency domain.

In a broadcast television system, the bandwidth of the system is generally narrow because the spectrum resources are very precious. In addition, because the channel environment for long-distance transmission is very bad, the system must resist a large delay spread, so the number of system subcarriers is generally large, and the interval of each subcarrier is small. Therefore, the carrier frequency deviation of the system receiver is generally larger than the subcarrier interval, and the system needs to be divided into integer carrier frequency deviation and decimal carrier frequency deviation for estimation respectively. Wherein:

for fractional frequency offset, estimation is mainly performed by using correlation characteristics, such as a preamble sequence-based delay correlation method and the like, the method has the main problems of large computation amount and high power consumption, and portable terminal equipment is very sensitive to power consumption, so that the design requirement on low-power-consumption equipment is high and the difficulty is high.

For integer frequency offset, the integer frequency offset Δ f may be performed using a scattered pilot or a continuous pilot inserted in the frequency domain_IEstimation, integer frequency offset estimation is actually based on maximum likelihood theory. Since the fractional frequency offset is corrected, the interference between subcarriers is substantially eliminated. The original k 'th sub-carrier is already shifted to k' th + delta f after FFT demodulation processing due to integer frequency offset_I. Setting continuous pilot frequency c in system_k′The sub-carrier position k' belongs to C, then the received demodulated continuous pilot frequency moves to k belongs to C + delta f_I. Conjugate correlation is carried out on two continuous OFDM symbols l-1, l, and the position of the maximum peak point offset from the ideal point, namely the integer frequency offset, is obtained. However, the above method has a disadvantage that the estimation process is greatly affected by interference such as noise and multipath fading. Especially, the continuous pilot is generally transmitted with burst energy, so that the relevant peak point is more obvious, for example, Speth, m; fechtel, s.; fock, g.; equation 12 in Meyr, H., optimal receiver design for OFDM-based broadband and transmission.II.A. channels, IEEE Transactions on Communications, Vol.49, Apr.2001, PP 571-578 (i.e., equation 12 in Apr.2001)Wherein x_kConjugate correlation value of continuous pilot of two adjacent OFDM symbols, C is subcarrier position of continuous pilot, and m is range of sliding left and right of continuous pilot).

In addition, integer carrier frequency offset estimation based on the inserted guard segment can be adopted. In an OFDM system, the sum of the data subcarriers and the pilot carriers is generally smaller than the FFT length N, and the remaining part is implemented by filling in virtual subcarriers. This corresponds to a guard band at both ends of the spectrum to reduce interference with adjacent bands. Here, a fixed subcarrier in each OFDM symbol carries no information, and its transmission power is 0, and this virtual subcarrier is called a guard segment. Based on the maximum likelihood theory, when the data and the pilot frequency subcarrier are not in the pre-designed sliding window, the energy in the sliding window reaches the minimum value, and the distance between the sliding window and the ideal position is the size of the integer frequency offset. The algorithm is highly affected by sliding window width and deep fading, and a trade-off needs to be made between the complexity and performance caused by the sliding window width.

Besides the above method, an integer carrier frequency offset estimation method based on preamble sequence in chinese patent with patent number 03100300.1, entitled "method for synchronization using time domain spread spectrum beacon in digital video broadcasting" can be adopted, that is, the preamble sequence received after time synchronization is used, corrected by fractional frequency offset, and then multiplied by [ -k ] successively_max，k_max-1]And (3) carrying out frequency offset of the integer carrier within the range, and then respectively carrying out cross-correlation operation by using ideal leader sequences, so that i, which is the maximum value obtained by the correlation value, is the integer frequency offset.

In summary, the fractional and integer frequency offset estimation method in the carrier frequency synchronization method of the existing OFDM system has the defects that the estimation process is greatly affected by the interference of noise, multipath fading phenomenon and the like, or the calculation amount is large, and the method is not suitable for being applied to equipment requiring low-complexity calculation.

Disclosure of Invention

The invention mainly aims to provide a carrier frequency synchronization circuit and a carrier frequency synchronization method of an OFDM system.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a carrier frequency synchronization circuit of an Orthogonal Frequency Division Multiplexing (OFDM) system comprises a decimal frequency offset estimation circuit, a decimal frequency offset compensation circuit, an integer frequency offset estimation circuit and an integer frequency offset compensation circuit; wherein,

the decimal frequency offset estimation circuit is used for carrying out normalization processing on the cross-correlation values of two under-sampling synchronous sequences adjacent to the frequency domain to obtain a decimal frequency offset estimation value;

the decimal frequency offset compensation circuit is used for inputting the decimal frequency offset estimation value into a numerical control oscillator to carry out decimal frequency offset compensation so as to correct the carrier frequency of the OFDM system;

the integer frequency offset estimation circuit is used for performing autocorrelation operation on the high-energy carrier sign bit of each OFDM symbol after Fast Fourier Transform (FFT) processing, and performing summation operation on autocorrelation values of a plurality of OFDM symbols to obtain an integer frequency offset estimation value;

the integer frequency offset compensation circuit is used for performing integer frequency offset compensation on the numerically controlled oscillator according to the integer frequency offset estimation value so as to correct the carrier frequency of the OFDM system.

A carrier frequency synchronization method of OFDM system, after the said OFDM system time synchronization, through normalizing the autocorrelation value of the adjacent synchronization sequence, ask the phase angle of the peak point, obtain the estimated value of decimal frequency offset, and carry on the decimal frequency offset compensation to the carrier frequency of OFDM system; and then, after the data after the decimal frequency offset compensation is further processed by Fast Fourier Transform (FFT), carrying out autocorrelation operation on the high-energy carrier sign bit of each OFDM symbol, carrying out summation operation on the autocorrelation of a plurality of OFDM symbols to carry out integer frequency offset estimation to obtain an integer frequency offset estimation value, and finally, compensating according to the integer frequency offset estimation value to correct the carrier frequency of the OFDM system.

Wherein the fractional frequency offset estimation comprises:

A. calculating the cross-correlation value of two adjacent synchronous sequences with the undersampling rate of alpha:

<math> <mrow> <msub> <mi>P</mi> <mi>xcorr</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>N</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msub> <mi>r</mi> <mrow> <mi>n</mi> <mo>+</mo> <mi>αk</mi> </mrow> </msub> <mi>conj</mi> <mrow> <mo>(</mo> <msub> <mi>r</mi> <mrow> <mi>n</mi> <mo>+</mo> <mi>αk</mi> <mo>+</mo> <mi>N</mi> </mrow> </msub> <mo>)</mo> </mrow> </mrow> </math>

where α is the undersampled value, r_nFor the nth sample value received, N is the sync sequence length, and conj (.) is the conjugate operation.

B. Calculating the autocorrelation values of two adjacent synchronous sequences with the undersampling rate of alpha:

C. Calculating a peak point phase angle of the normalized cross-correlation value, namely a decimal frequency offset estimation value:

<math> <mrow> <mi>Δ</mi> <msub> <mi>f</mi> <mi>f</mi> </msub> <mo>=</mo> <mfrac> <msub> <mi>f</mi> <mi>s</mi> </msub> <mrow> <mn>2</mn> <mi>πN</mi> </mrow> </mfrac> <mi>arg</mi> <mrow> <mo>(</mo> <mi>max</mi> <mrow> <mo>(</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mi>xcorr</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>P</mi> <mi>auto</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>)</mo> </mrow> </mrow> </math>

wherein fs is the sampling frequency, N is the length of the synchronization sequence, max (.) is the operation of solving the maximum value, and arg (.) is the operation of solving the complex phase angle.

The integer frequency offset estimation process comprises the following steps:

D. carrying out autocorrelation operation on the high-energy carrier sign bit of each OFDM sign in the frequency domain:

z_l，k+i＝sign(real(Z_l，k+i))+j*sign(imag(Z_l，k+i))

wherein,

for the operation of the sign bit of the high-energy carrier, a represents the sign bit of the high-energy carrier, and Th is a dynamically adjustable threshold; z_l，k+iA frequency domain data subcarrier;

E. summing the autocorrelation values of a plurality of OFDM symbols, and solving the minimum value, namely an integer frequency offset value:

wherein k is_minAnd k_maxRespectively, the sequence numbers of the first and last virtual sub-carriers in each OFDM symbol.

The frequency offset compensation process is to send the decimal frequency offset and the integer frequency offset obtained by the calculation in the step C or the step E into a frequency offset compensation module for compensation:

wherein r is the result of the received data after frequency offset compensation, r_nFor the nth sample value received, fs is the sampling frequency.

The carrier frequency synchronization circuit and method of the OFDM system provided by the invention have the following advantages:

by undersampling two adjacent synchronous sequences in the frequency domain and then carrying out normalization processing on the cross-correlation values, the estimated value of the fractional frequency offset is obtained, and the calculated amount of the fractional frequency offset estimation is reduced to a great extent. The method comprises the steps of carrying out autocorrelation operation on a high-energy carrier sign bit of each OFDM sign after Fast Fourier Transform (FFT) processing to obtain the offset between the minimum value and an ideal value, and further obtaining an integer frequency offset estimation value to reduce hardware overhead. By carrying out summation operation on the autocorrelation of a plurality of OFDM symbols, the influence of channel estimation errors on integral frequency offset estimation is reduced. In addition, the threshold value of the high-energy carrier is selected according to different working environments of the system, and the adaptive adjustment can be carried out to reduce the influence of system noise on the system performance.

Drawings

FIG. 1 is a schematic diagram of a carrier frequency synchronization circuit according to the present invention;

fig. 2 is a flowchart of a carrier frequency synchronization method of the OFDM system according to the present invention.

Detailed Description

The method of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments of the invention.

Fig. 1 is a schematic structural diagram of a carrier frequency synchronization circuit of the present invention, as shown in fig. 1, including a fractional frequency offset estimation circuit, a fractional frequency offset compensation circuit, an integer frequency offset estimation circuit, and an integer frequency offset compensation circuit, wherein the fractional frequency offset compensation circuit and the integer frequency offset compensation circuit are also called frequency compensation modules.

The invention uses the carrier frequency synchronous circuit, firstly, the cross-correlation value of two under-sampling synchronous sequences adjacent to the frequency domain needs to be normalized, the phase angle of the peak point is solved, namely, the decimal frequency offset estimation is carried out, and the estimated value of the decimal frequency offset is obtained; and inputting the decimal frequency offset estimation value into a Numerically Controlled Oscillator (NCO) to perform decimal frequency offset compensation so as to correct the carrier frequency of the OFDM system and keep the OFDM system synchronous. Then, carrying out autocorrelation operation on the high-energy carrier sign bit of each OFDM symbol after Fast Fourier Transform (FFT), namely carrying out integer frequency offset estimation, and then carrying out summation operation on autocorrelation values of a plurality of OFDM symbols to obtain an integer frequency offset estimation value; and finally, sending the integer frequency offset estimation value to a frequency offset compensation module to correct the carrier frequency of the OFDM system.

As a preferred embodiment, in a wireless broadcast system with a signal bandwidth of 10M, the number of subcarriers is 4096, the maximum frequency in the spectrum segment of the OFDM system is 2.6GHz, and the subcarrier spacing is 2.44 KHz/10 MHz. The frequency offset that is required to be maximally tolerated for the sender and receiver is also 20ppm, so the frequency offset estimation range of the frequency synchronizer should be 40 ppm. The frequency offset is 2.6GHz × 40 ppm-104 KHz, which corresponds to 104KHz/2.44 KHz-42.6 subcarrier spacing.

It can be seen from this that since the subcarrier spacing in the system is very small, the shift caused by the frequency offset is very large, with a maximum possible shift of approximately 43 subcarriers. The frequency offset needs to be divided into decimal and integer times subcarrier spacing for estimation separately.

Fig. 2 is a flowchart of a carrier frequency synchronization method of an OFDM system according to the present invention, and as shown in fig. 2, the carrier frequency synchronization method includes the following steps:

step 201, calculating a decimal frequency offset estimation value. The method comprises the following specific steps:

firstly, the cross-correlation value P of two adjacent synchronous sequences with the undersampling rate alpha is calculated by using the formula (1)_xcorr(n)：

<math> <mrow> <msub> <mi>P</mi> <mi>xcorr</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>N</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msub> <mi>r</mi> <mrow> <mi>n</mi> <mo>+</mo> <mi>αk</mi> </mrow> </msub> <mi>conj</mi> <mrow> <mo>(</mo> <msub> <mi>r</mi> <mrow> <mi>n</mi> <mo>+</mo> <mi>αk</mi> <mo>+</mo> <mi>N</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

Wherein alpha is an undersampled value; r is_nThe nth sampling value is received; k is an index after undersampling of the received signal, the value range of the index is 0, 1, the term, N-1, N is the length of the synchronization sequence, and conj (the term) is conjugate operation.

Then, the undersampling rate is calculated as alpha by formula (2)Autocorrelation value P of two adjacent synchronization sequences_auto(n)：

Finally, the formula (3) is used to calculate the peak point phase angle of the normalized cross-correlation value, i.e. the decimal frequency offset estimation value delta f_f：

<math> <mrow> <mi>Δ</mi> <msub> <mi>f</mi> <mi>f</mi> </msub> <mo>=</mo> <mfrac> <msub> <mi>f</mi> <mi>s</mi> </msub> <mrow> <mn>2</mn> <mi>πN</mi> </mrow> </mfrac> <mi>arg</mi> <mrow> <mo>(</mo> <mi>max</mi> <mrow> <mo>(</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mi>xcorr</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>P</mi> <mi>auto</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> </math>

Wherein f is_sIs the sampling frequency.

Step 202, performing fractional frequency offset compensation. The calculation is performed using equation (4):

wherein r represents the result after fractional frequency offset compensation; r is_nRepresenting the received nth sample value;

representing the ratio of the fractional frequency offset estimate to the sampling frequency.

In an OFDM system, when the delay correlation amplitude is maximized, the peak angular frequency is the fractional frequency offset. The input sampling points are subjected to undersampling with an undersampling rate alpha, so that the capacity of a memory (RAM) for performing summation can be reduced to 1/alpha, and the working frequency can also be reduced to 1/alpha.

In the fractional frequency offset synchronization method in this example, the undermining rate α is 4, that is, the ratio of the number of extracted points to all the points is 1/4, and the standard deviation of the fractional frequency offset estimation error is 0.022. In the method, the input sampling points are extracted once every 4 points, the RAM for summation can be reduced to 1/4, and the working frequency is also reduced to 1/4, so that the requirement on hardware is reduced, namely the complexity of hardware realization and the power consumption can be obviously reduced.

Step 203, performing integer frequency offset estimation, and performing autocorrelation operation on the high-energy carrier sign bit of each OFDM symbol in the frequency domain.

In the OFDM system, since the subcarrier spacing is relatively small, the integer frequency offset is relatively large, and the frequency offset can reach 42 subcarrier spacings. In this embodiment, the mapped data is shifted to the input of the Inverse Fast Fourier Transform (IFFT) by equation (5).

<math> <mrow> <mi>Z</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mi>Y</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> </mtd> <mtd> <mi>i</mi> <mo>&Element;</mo> <mo>[</mo> <mn>1,1538</mn> <mo>]</mo> </mtd> </mtr> <mtr> <mtd> <mi>Y</mi> <mrow> <mo>(</mo> <mi>i</mi> <mo>-</mo> <mn>1020</mn> <mo>)</mo> </mrow> </mtd> <mtd> <mi>i</mi> <mo>&Element;</mo> <mo>[</mo> <mn>2558,4095</mn> <mo>]</mo> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mi>i</mi> <mo>&Element;</mo> <mo>[</mo> <mn>1539,2557</mn> <mo>]</mo> <mo>,</mo> <mn>0</mn> </mtd> </mtr> </mtable> </mfenced> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> </math>

Wherein Z (i) and Y (i) represent the input of IFFT and the output of mapping, respectively.

It can be seen that 1019 subcarriers for subcarriers 1539 and 2557 are implemented by padding 0, and these subcarriers are referred to as virtual subcarriers.

Define the sign function sign () as:

<math> <mrow> <mi>sign</mi> <mrow> <mo>(</mo> <mi>a</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mn>1</mn> </mtd> <mtd> <mi>a</mi> <mo>&GreaterEqual;</mo> <mi>Th</mi> <mo>,</mo> </mtd> </mtr> <mtr> <mtd> <mo>-</mo> <mn>1</mn> </mtd> <mtd> <mi>a</mi> <mo>≤</mo> <mo>-</mo> <mi>Th</mi> <mo>,</mo> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mo>|</mo> <mi>a</mi> <mo>|</mo> <mo><</mo> <mi>Th</mi> <mo>,</mo> </mtd> </mtr> </mtable> </mfenced> </mrow> </math>

wherein, a represents a sign bit of a high-energy carrier, Th is a dynamic adjustable threshold value, and adjustment is carried out according to channel state information required by system soft decision;

definition of z_l，k+iComprises the following steps:

z_l，k+i＝sign(real(Z_l，k+i))+j*sign(imag(Z_l，k+i))

wherein Z is_l，k+iIs k + i subcarriers of the l-th OFDM symbol.

Then, the autocorrelation values of a plurality of OFDM symbols are summed, the minimum value is the integer frequency offset value, and the integer frequency offset value can be obtained by using a formula (6):

in the OFDM system of the present embodiment, each slot is composed of 53 OFDM symbols, i.e., N_s53. Wherein k is_minAnd k_maxIs the sequence number of the first and last virtual sub-carrier in each OFDM symbol.

And 204, performing integer frequency offset compensation on the synchronous carrier frequency of the OFDM system according to the integer frequency offset estimation value obtained in the step 203. The invention can use the formula (7) to calculate to obtain the integer frequency offset compensation result:

wherein, r represents the result after integer frequency offset compensation; r is_nRepresenting the received nth sample value;

the ratio of the integer frequency offset estimate to the sampling frequency.

In the integer frequency offset synchronization method in this example, compared with the integer carrier frequency offset estimation method related to chinese patent No. 03100300.1, the former synchronization method requires complex correlation operation, but only 1 bit (bit) correlation operation is required to apply the method of the present invention, and the operation complexity is greatly reduced, i.e., the carrier frequency offset estimation method based on the OFDM system of the present invention greatly reduces the operation amount and hardware implementation complexity.

In addition, the method provided by the invention can reduce the influence of channel estimation error on the overall frequency offset estimation. And the threshold selected for the high-energy carrier can be adaptively adjusted according to different working environments of the system to reduce the influence of system noise on the performance. The method can be widely applied to various wireless broadcast systems and communication fields.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.

Claims

1. A carrier frequency synchronization circuit of an Orthogonal Frequency Division Multiplexing (OFDM) system is characterized by comprising a decimal frequency offset estimation circuit, a decimal frequency offset compensation circuit, an integer frequency offset estimation circuit and an integer frequency offset compensation circuit; wherein,

2. A carrier frequency synchronization method of an OFDM system is characterized in that after the time synchronization of the OFDM system, normalization processing is carried out on autocorrelation values of adjacent synchronization sequences, a phase angle of a peak point is solved, a decimal frequency offset estimation value is obtained, and decimal frequency offset compensation is carried out on the carrier frequency of the OFDM system; and then, after the data after the decimal frequency offset compensation is further processed by Fast Fourier Transform (FFT), carrying out autocorrelation operation on the high-energy carrier sign bit of each OFDM symbol, carrying out summation operation on the autocorrelation of a plurality of OFDM symbols to carry out integer frequency offset estimation to obtain an integer frequency offset estimation value, and finally, compensating according to the integer frequency offset estimation value to correct the carrier frequency of the OFDM system.

3. The method for synchronizing carrier frequency of OFDM system of claim 1, wherein said fractional frequency offset estimation value is calculated by:

4. The method of claim 1, wherein the calculating the integer frequency offset estimate comprises:

z_l，k+i＝sign(real(Z_l，k+i))+j*sign(imag(Z_l，k+i))

wherein,

5. The method for synchronizing carrier frequency of OFDM system according to claim 3 or 4, wherein said frequency offset compensation process is to send the fractional frequency offset and the integer frequency offset calculated in step C or step E to the frequency offset compensation module for compensation: