KR20020086161A - Training symbol determining method and apparatus and method for estimating frequency offset in OFDM system - Google Patents

Abstract

PURPOSE: A method for determining a training symbol, and an apparatus and a method for estimating a frequency offset and synchronizing a frequency in an OFDM(Orthogonal Frequency Division Multiplexing) system are provided to newly determine the training symbol used for a symbol synchronization or a frequency synchronization in a receiver, and estimate an abbreviated and minute frequency offset using the determined training symbol and obtain the frequency synchronization of a received signal using the estimated frequency offset. CONSTITUTION: An A/D converter(410) converts a received analog training symbol signal with a baseband into a digital training symbol signal. A protection interval removing unit(420) removes a protection interval included in the digital training symbol signal using a detected symbol timing. An FFT(Fast Fourier Transform) unit(430) performs the FFT of the digital training symbol signal. An abbreviated estimating device(440) calculates a mean correlation value among phase difference information between the first training symbol data, phase difference information between the second training symbol, and phase difference information of predetermined training symbol data. The abbreviated estimating device(440) calculates each phase difference on the basis of the calculated mean correlation value, and estimates an abbreviated frequency offset on the basis of the calculated phase difference. A minute estimating device(450) estimates a minute frequency offset on the basis of the first training symbol data, the second training symbol data, and the first and second training symbol data corrected by the estimated abbreviated frequency offset. An adder(460) adds the outputs of the abbreviated estimating device(440) and the minute estimating device(450). A multiplier(470) multiplies the output of the adder(460) by the output of the A/D converter(410) for rotating a phase in a direction opposite with phase rotation by the frequency offset of the output of the A/D converter(410), and provides the multiplied value to the protection interval removing unit(420).

Description

Training symbol determination method and apparatus and method for frequency offset estimation and synchronization in orthogonal frequency division multiplexing system

The present invention relates to a method of determining a training symbol in an orthogonal frequency division multiplexing (OFDM) system, and an apparatus and method for frequency offset estimation and frequency synchronization using the same. More specifically, an OFDM system using N subcarriers A method for newly determining a training symbol transmitted from a transmitter of a transmitter and used for symbol synchronization and / or frequency synchronization at a receiver; and using the determined training symbol at an OFDM receiver, approximate and fine frequency offsets are estimated and the estimated frequency An apparatus and method for obtaining frequency synchronization of a received signal using an offset.

In general, since an OFDM signal is transmitted by converting parallel symbols in series, a symbol synchronization (or time synchronization) is required for capturing the starting point of a symbol in order to perform parallel conversion on a symbol-by-symbol basis from a serial signal transmitted from a receiver. . In addition, an OFDM signal requires a frequency offset estimator for accurately estimating and correcting a frequency offset because adjacent channel interference is introduced when there is a frequency offset between a carrier and a receiver oscillator.

That is, when the receiver of the OFDM system demodulates the received signal, the transmitter transmits a predetermined training symbol to capture the starting point of the OFDM symbol and to accurately synchronize the carrier frequency and the oscillator frequency of the receiver.

FIG. 1 illustrates a structure of a conventional training symbol, and as shown in the figure, in a transmitter of an OFDM system using N subcarriers, A _{1 to} A _N for N subcarriers during a first symbol period in a frequency domain. To configure the first training symbol (a) by allocating the data of each, and to assign the data of B _{1 to} B _N to the same N subcarriers as described above during the second symbol period to configure a second training symbol (b) The data A _{1 to} A _N of the first training symbol a and the data B _{1 to} B _N of the second training symbol b have a relationship of “B _k = A _k C _k , k = 1 to N”. It is configured to have.

Accordingly, the OFDM transmitter repeatedly transmits the same data for the same subcarrier for two symbol periods (if Ck = 1), or decides to have a relationship between the data (if Ck = 1), and then general data. The data X _{1 to} X _N of the symbol c are carried on each subcarrier and transmitted.

In a conventional OFDM receiver, symbol timing is restored using the first training symbol (a) and the second training symbol (b), and a frequency offset is estimated. As shown in FIG. An analog-to-digital (A / D) converter 210 for converting baseband analog signals to digital signals after demodulation; A symbol timing recovery unit 220 for detecting a start point of an OFDM symbol; A guard interval removal unit 230 for removing a guard interval included in an OFDM symbol by using the recovered symbol timing; Fast Fourier Transform (FFT) unit 240; A fine frequency offset estimator 250 estimating a frequency offset smaller than a subcarrier spacing; An integer multiple (or approximately) frequency offset estimator 260 for estimating an integer multiple offset of a subcarrier spacing; An adder 270 that calculates a total frequency offset by adding a fine frequency offset and an integer frequency offset; And a multiplier 280 that multiplies the output of the A / D converter 210 by converting the calculated frequency offset into a complex exponential function representing a change in phase.

The integer frequency offset estimator 260 may further include a symbol delay unit 261, a conjugate complex calculator 262, a correlation function calculator 263 and an integer frequency to calculate a correlation function using delayed and received symbols. An offset estimator 264.

Next, the operation of the conventional OFDM receiver configured as shown in FIG.

In the OFDM transmitter, if the training symbols (a) and (b) configured as shown in FIG. 1 are periodically or newly transmitted before the data symbol (c), the OFDM receiver of FIG. 2 transmits the signals transmitted from the OFDM transmitter. Receive the signal, demodulate the received signal into a baseband analog signal, convert the signal into a digital signal by the A / D converter 210, and first, the symbol timing recovery unit 220, to capture symbol synchronization. Enter it.

When the symbol timing recovery unit 220 detects a start point of a symbol, the guard period removal unit 230 removes the guard period included in the front part of the OFDM symbol using the FFT unit 240 for the remaining signals. Take an FFT at.

The output signal of the A / D converter 210 is input to the symbol timing recovery unit 220 and input to the fine frequency offset estimator 250 to estimate a frequency offset Δf1 equal to or less than a subcarrier spacing. The symbol synchronization acquisition by the symbol timing recovery unit 220 and the fine frequency offset estimation by the fine frequency offset estimator 250 utilize the repeated training symbols a or b.

The integer multiple frequency offset estimator 260 inputs the output signal of the FFT unit 240 to estimate the frequency offset of the integral multiple of the subcarrier spacing. The symbol delay unit 261 outputs the FFT unit 240 from the FFT unit 240. Delay the first training symbol (a) for a unit symbol period, conjugate the complex calculation unit 262 to conjugate the output signal of the symbol delay unit 261, and then transmit the resultant to the correlation function calculation unit 263. Enter it. The correlation function calculation unit 263 outputs the output signal of the conjugate multiple calculation unit 262, that is, the conjugate of the first training symbol a and the second training symbol b output from the FFT unit 240. Simultaneously input the data of these (a) and (b) in unit data sample unit to find the correlation function. The integer frequency offset estimator 264 obtains a position representing the maximum correlation value from the obtained correlation function and estimates the frequency offset Δf 2 of the integer multiple of the subcarrier spacing therefrom.

The frequency offsets obtained from the fine frequency offset estimator 250 and the integer frequency offset estimator 260 are added to each other through the adder 270, and the added offset value is added to the A / D by the multiplier 280. The output signal of the converter 210 is multiplied by a complex exponential function (e ^{-j2π (Δf1 + Δf2) n / N} ) in which the phase of the output signal is reversed, and the frequency offset between the carrier and the receiver oscillator generated during the demodulation process is multiplied. Correct it.

In conclusion, the conventional method of estimating the frequency offset between the oscillator and the carrier in the conventional OFDM receiver separately estimates the fine frequency offset and the integer frequency offset using two different circuits, and also estimates the integer frequency offset. Correlation functions are obtained by moving two consecutive OFDM training symbols (a) (b) one by one, as shown in Fig. 1, and the offset is estimated by calculating the frequency shift with the maximum correlation value among them. The technology had the following problems.

First, when estimating an integer frequency offset, an OFDM demodulator using an N-point FFT has to take up to N-1 correlations in order to calculate the interval at which the correlation is maximized. In this case, there is a large amount of computation, and as a result, a delay occurs in acquiring synchronization by the receiver. Second, complex circuits are needed to calculate correlation values by moving samples one by one to obtain a correlation function. Third, the accuracy is reduced in the case of time-varying channels because the correlation between two adjacent symbols is taken. Fourth, additional training symbols are needed for channel estimation.

That is, the problem of the conventional technique of estimating the frequency offset using the existing training symbols is that in the time domain method with a small amount of computation, the capture range of the frequency offset is limited by the ratio of the symbol length and the length of the guard interval. In the case of the unrestricted frequency domain method, since the correlation function must be obtained for all subcarrier spacings, the calculation amount becomes large, and since there is no countermeasure against the channel phase change according to the channel characteristics in the air, It cannot be estimated, and in order to solve this problem, a separate training symbol is required in addition to the first and second training symbols.

The present invention was created to solve the above problems, and an object thereof is to newly construct a training symbol to facilitate estimation of a frequency offset in an OFDM system, and to use the training symbol to adjust a frequency offset of a baseband OFDM signal. By significantly estimating the frequency offset estimation, the complexity of the circuit for calculating the correlation function can be reduced and the capture range of the offset can be expanded compared to the conventional method. Disclosure of the Invention It is an object of the present invention to provide a method for determining a training symbol of an orthogonal frequency division multiplexing system, a frequency offset estimation method, and a frequency synchronization method using the same.

In other words, an object of the present invention is to provide a method for configuring a training symbol in which data is allocated such that a correlation between OFDM subcarriers is proportional to a frequency offset, and to provide a simple method and apparatus for estimating a frequency offset using the same. By increasing the number of intervals up to 10 times, the computational amount is kept the same as the time domain method, and the channel phase error due to the deterioration of the multipath channel is estimated when the frequency offset is estimated.

1 is a view showing the structure of a conventional training symbol,

2 is a block diagram of a conventional OFDM receiver,

3 is a structural diagram of a new training symbol for explaining a training symbol determination method in an OFDM system according to an embodiment of the present invention,

4 is a block diagram of a frequency synchronizer by frequency offset estimation of an OFDM system receiver according to an embodiment of the present invention;

FIG. 5 shows a detailed block diagram of the coarse estimation device and the fine estimation device of FIG. 4.

※ Explanation of code for main part of drawing

410: analog-digital converter 420; Guard section removal unit

430: fast Fourier transform unit 440: approximate estimation device

441,451: delayer 442,452: conjugate complex conversion

443: difference signal storage unit 444,454,470: multiplier (part)

445,455: moving average calculation unit 446: approximately frequency offset estimation unit

450: fine estimation device 453: data correction unit

456: fine frequency offset estimator 460: adder

480: channel equalizer 490: channel gain estimator

In order to achieve the above object, a training symbol determination method of an orthogonal frequency division multiplexing (OFDM) system according to the present invention is performed by a transmitter for symbol synchronization and / or frequency synchronization in a receiver of an OFDM system using N subcarriers. In the method of determining a training symbol to be transmitted, one data is sequentially assigned to the N subcarriers in a frequency domain, and the first training symbol is determined to have correlation with each other between data values allocated to adjacent subcarriers. First step; And a second step of using the same data as the data of the first training symbols sequentially allocated to the N subcarriers, and assigning the corresponding data to the corresponding subcarriers so that the allocation order is reversed. Characterized in that configured.

In order to achieve the above object, an approximate frequency offset estimation method in an orthogonal frequency division multiplexing (OFDM) system according to the present invention includes a frequency in a receiver of an orthogonal frequency division multiplexing (OFDM) system using N subcarriers. In the frequency offset estimation method for synchronization, data values assigned to subcarriers adjacent to each other in a frequency domain are set to have a constant correlation with each other, and are allocated to the first training symbol and the subcarrier of the first training symbol transmitted. A first step of sequentially receiving second training symbols, each of which has been assigned data values in reverse order with respect to the order of each data value, for demodulation to baseband, digital conversion, and fast Fourier transform; A second step of delaying data of the first training symbol transformed to the Fourier transform during one sample data interval; Based on the delayed data of the first training symbol, subsequent free current transformed data, and phase difference information of the preset first training symbol, a correlation value is calculated between the delayed first training symbol and a constant corresponding to an integer multiple of the sample data interval. Calculating a mean correlation value during the interval as a first correlation value; The data of the second training symbol transformed to the Fourier transform is delayed for one sample data interval, and the data of the delayed second training symbol, followed by the Fourier transformed current data and the phase difference information of the preset second training symbol. A fourth step of calculating a correlation value therebetween and calculating an average correlation value for a predetermined period corresponding to an integer multiple of the sample data interval as a second correlation value; A fifth step of calculating a first phase difference based on the calculated first correlation value and calculating a second phase difference based on the calculated second correlation value; And a sixth step of calculating an approximately frequency offset based on the calculated first and second phase differences.

In order to achieve the above object, a fine frequency offset estimation method in an orthogonal frequency division multiplexing (OFDM) system according to the present invention includes a frequency in a receiver of an orthogonal frequency division multiplexing (OFDM) system using N subcarriers. In the frequency offset estimation method for synchronization, each data value assigned to subcarriers adjacent to each other in the frequency domain is set to have a mutually constant phase difference, and the first training symbol transmitted and the subcarriers of the first training symbol are respectively assigned. A first step of sequentially receiving second transmitted training symbols, each of which has been assigned data values in a reverse order to the order of the data values, for demodulation to baseband, digital conversion, and fast Fourier transform; Delaying the Fourier transformed first training symbol for one symbol period; And based on the data of the delayed first training symbol followed by the data of the second training symbol subsequently Fourier transformed and the data values of the first and second training symbols estimated by the calculation of the approximate frequency offset. And a third step of calculating the offset.

In order to achieve the above object, a frequency synchronization method by frequency offset estimation in an orthogonal frequency division multiplexing (OFDM) system according to the present invention includes a receiver of an orthogonal frequency division multiplexing (OFDM) system using N subcarriers. In the frequency synchronization method using the frequency offset estimation in the Equation, the data values assigned to the subcarriers adjacent to each other in the frequency domain are set to have a mutually constant phase difference to the first training symbol and the subcarrier of the first training symbol transmitted A first step of sequentially receiving a second training symbol in which data values are respectively assigned and transmitted in reverse order with respect to the order of each assigned data value, demodulating to baseband, digital conversion, and fast Fourier transform, and Delaying the data of the first transformed training symbol for one sample data interval And a correlation value between the delayed first training symbol and the subsequent data, which is subsequently transformed, and the phase difference information of the preset first training symbol. A third step of calculating an average correlation value corresponding to a predetermined interval corresponding to a first correlation value, and delaying the data of the second training symbol transformed after the four periods for one sample data interval, and the data of the delayed second training symbol And subsequent correlations are calculated based on the current data that has been transformed by the Fourier and the phase difference information of the preset second training symbol, wherein the average correlation value for a predetermined period corresponding to an integer multiple of the sample data interval is calculated. A fourth step of calculating a correlation value and a first phase difference based on the calculated first correlation value, A first step of estimating a coarse frequency offset, comprising a fifth step of calculating a second phase difference based on a second correlation value, and a sixth step of calculating a coarse frequency offset based on the calculated first and second phase differences ; A seventh step of delaying the first training symbol that has been transformed and output in the first step for one symbol period, and data of the delayed first training symbol and subsequently of the second training symbol that has been Fourier transformed; A second step of estimating a fine frequency offset, comprising an eighth step of calculating a fine frequency offset based on data and data values of the first and second training symbols estimated by the calculated approximate frequency offset; And a third process of acquiring frequency synchronization of the digitally converted data based on the approximate frequency offset value estimated in the first process and the fine frequency offset value estimated in the second process. do.

In order to achieve the above object, a frequency synchronization device by frequency offset estimation of an Orthogonal Frequency Division Multiplexing (OFDM) system according to the present invention is allocated to adjacent subcarriers in a frequency domain using N subcarriers, respectively. The second training symbol transmitted by assigning data values in the opposite order to the order of the first training symbol transmitted and set so that the data values have a mutually constant phase difference, and the respective data values assigned to the subcarriers of the first training symbol. In a receiving apparatus of an orthogonal frequency division multiplexing (OFDM) system using a signal as a received signal for frequency offset estimation and frequency synchronization, an analog / digital converting a received baseband analog training symbol signal into a digital training symbol signal. (A / D) conversion means; Guard interval removal means for removing a guard interval included in the digital training symbol signal using the detected symbol timing; Fast Fourier transform means for fast Fourier transform (FFT) of the removed training interval signal; Obtaining an average correlation value between them based on the phase difference between the data of the first training symbol and the phase difference between the data of the second training symbol and the corresponding phase difference information between the data of each preset training symbol corresponding thereto, Approximate estimation means for estimating each phase difference based on the calculated respective average correlation values, and then estimating a frequency offset approximately based on the calculated respective phase differences; Based on the data of the first training symbol transformed to the Fourier and subsequently the data of the second training symbol transformed to the Fourier transform and the data of the first and second training symbols estimated by the estimated coarse frequency offset. Fine estimation means for estimating fine frequency offset; Addition means for adding an output of the coarse estimation means and an output of the fine estimation means; And multiplying the output of the adding means and the output of the analog / digital converting means to rotate the phase in a direction opposite to the phase rotation caused by the frequency offset of the output of the analog / digital converting means. It consists of a multiplication means to provide as input.

Hereinafter, a training symbol structure of an orthogonal frequency division multiplexing (OFDM) system and a frequency synchronization device of an OFDM system receiver according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. Approximate frequency offset estimation method in orthogonal frequency division multiplexing (OFDM) system, fine frequency offset estimation method in orthogonal frequency division multiplexing (OFDM) system according to the present invention and orthogonal frequency division multiplexing (OFDM) according to the present invention An embodiment of a frequency synchronization method by frequency offset estimation in a system will be described in detail.

3 is a structural diagram of a new training symbol for explaining a training symbol determination method in an OFDM system according to an embodiment of the present invention.

First, the first training symbol (a) is configured by allocating N data of A _{0 to} A _N-1 to N subcarriers from _{0 to N-1} , respectively, and assigning each to subcarriers adjacent to each other in the frequency domain. The data values to be determined are determined to have a constant relationship with each other based on a relational expression of "A _{k + 1} = A _k C _k , 0≤k≤N-2".

The second training symbol (b) allocates N data of B _{0 to} B _N-1 to N subcarriers _{0 to N-1 in} the same frequency domain as the first training symbol (a). The data of B _{0 to} B _N-1 is configured such that the data of A _{0 to} A _N-1 is the same and the order of allocation is reversed (ie, B ₀ = A _N-1 , B ₁ = A _{N− 2} , ..., B _N-1 = A ₀ ), so that data values assigned to subcarriers adjacent to each other in the frequency domain are "B _{k + 1} = B _k C _k ^* , 0≤k≤N-2". It is decided to have a constant relationship with each other based on the relational expression of.

FIG. 4 is a block diagram of a frequency synchronization device based on frequency offset estimation of an OFDM system receiver according to an embodiment of the present invention. The first training symbol (a) and the second training symbol of the present invention configured as shown in FIG. The reception time of (b) will be described as an example.

4, an analog / digital (A / D) converter 410 for converting a received baseband analog training symbol signal into a digital training symbol signal; A guard interval eliminator 420 for removing a guard interval included in the digital training symbol signal using a symbol timing detected by a symbol synchronizer (not shown); A fast Fourier transform (FFT) unit 430 for transforming the guard interval-removed training symbol signal to a fast Fourier transform; The phase difference between the data of the first training symbol (a) transformed by the Fourier transform and the phase difference between the data of the second training symbol (b) and correspondingly, each training symbol before transmission set by the structure of the training symbol as shown in FIG. Based on the phase difference information (C _k , C _k ^* ) between the data, the average correlation values Q1 and Q2 are respectively obtained, and based on the calculated average correlation values Q1 and Q2, each phase difference Φ1 An approximate estimator 440 for estimating a frequency offset [Delta] f1 based on the calculated respective phase differences [phi] 1 and [phi] 2 after calculating [phi] 2; First and second data estimated by the Fourier transformed first training symbol (a) followed by data of the Fourier transformed second training symbol (b) and the estimated approximate frequency offset Δf1; A fine estimation device 450 which estimates a fine frequency offset [Delta] f2 based on the data of the second training symbol; An adder 460 that adds an output Δf1 of the coarse estimation device 440 and an output Δf2 of the fine estimation device 450; And multiply the output of the adder 460 by the output of the A / D converter 410 to rotate the phase in a direction opposite to the phase rotation caused by the frequency offset of the output of the A / D converter 410. And a multiplier 470 provided as an input of the guard interval remover 420.

In addition, a channel equalizer 480 is connected to an output terminal of the FFT unit 430, and the channel gain is estimated by using the output of the FFT unit 430 and the output of the coarse estimator 440. Thereafter, a channel gain estimator 490 provided as an input of the channel equalizer 480 is configured.

FIG. 5 illustrates a detailed block diagram of the coarse estimating apparatus 440 and the message estimating apparatus 450 of FIG. 4.

In FIG. 5, the coarse estimator 440 includes: a delayer 441 for delaying data of a training symbol signal that is Fourier transformed through the FFT unit 430 for one sample data (i.e., between subcarriers); A conjugate complex number conversion unit 442 for conjugating the data delayed by the delay unit 441; A difference signal storage unit 443 which stores preset phase difference data with respect to the first and second training symbols (a) and (b); A multiplier 444 that multiplies the output data of the conjugate complex conversion unit 442, the output data of the FFT unit 430, and the phase difference data provided from the difference signal storage unit 443 correspondingly, and obtains a correlation between them ); A moving average calculation unit 445 for calculating average correlation values Q1 and Q2 for a predetermined period with respect to the output of the multiplier 444; An approximately frequency offset based on the average correlation value Q1 for the first training symbol a and the average correlation value Q2 for the second training symbol b output from the moving average calculation unit 445. It consists of an approximate frequency offset estimator 446 for estimating [Delta] f1.

The fine estimation apparatus 450 may include: a delayer 451 for delaying data of a training symbol signal that is Fourier transformed through the FFT unit 430 for one symbol period; A conjugate complex number conversion unit 452 for conjugating the data delayed by the delay unit 451; The output data of the conjugate complex converter 452 and the FFT unit 430 based on the approximate frequency offset value Δf1 estimated by the coarse frequency offset estimator 446 of the coarse estimation device 440. A data estimator 453 for correcting output data to obtain a conjugate of the estimated data of the first training symbol and the estimated data of the second training symbol; Conjugation of output data of the conjugate complex conversion unit 452, output data of the FFT unit 430, correction data of the first training symbol and correction data of the second training symbol provided from the data correction unit 453. A multiplier 454 for multiplying and calculating correlation values between them; A moving average calculation unit 455 for calculating an average correlation value for one symbol period with respect to the output of the multiplier 454; A fine frequency offset estimator 456 estimates a fine frequency offset Δf2 based on the average correlation value output from the moving average calculator 455.

Subsequently, an approximate frequency offset estimation method in an orthogonal frequency division multiplexing (OFDM) system according to an embodiment of the present invention, a fine frequency offset estimation method in an orthogonal frequency division multiplexing (OFDM) system, and the present invention The frequency synchronization method by frequency offset estimation in an orthogonal frequency division multiplexing (OFDM) system according to the present invention will be described in detail, but will be described in parallel with the operation since it is applied to the OFDM receiver of the present invention.

In the receiver of the OFDM system of FIG. 4 using N subcarriers, the first training symbol a of FIG. 3 transmitted by a transmitter (not shown) for symbol synchronization and / or frequency synchronization is allocated to an adjacent subcarrier in the frequency domain. The data is determined to satisfy the following equation (1).

Here, the data A _k is complex data allocated to the k th subcarrier and can be expressed by Equation 2 below.

Here, M denotes that a phase modulation method having M signal points is applied as a subcarrier modulation method. The power of subcarriers This value is determined by the autocorrelation characteristics of the training symbols required in the time domain. C _k determines that the phase allocated to each subcarrier has a relationship as shown in Equation 3 below.

Where m _k is an integer between 0 and M-1. A _k and C _k is determined in advance to the data to know each other between OFDM transceiver, a memory, that is, the difference signal storage unit 443 of Figure 5 of the receiver, A _k, and a is a C _k conjugated C _k ^*, and A _k The inverse Fourier transform values 'a (n) and (0 ≦ n ≦ N-1)' are stored and used for symbol synchronization and / or frequency offset estimation.

In addition, the second training symbol (b) of FIG. 3 reverses the data order of the subcarriers of the first training symbol (a) in reverse order and has a relationship as shown in Equation 4 below.

In the OFDM receiver of the present invention configured as shown in FIG. 4, the baseband demodulated OFDM analog signal is converted into a digital signal through the A / D converter 410, and the guard interval eliminator 420 is included in an OFDM symbol. The guard interval is removed and the remaining part is input to the FFT unit 430. The FFT unit 430 receives N serial data, converts them in parallel, performs a discrete Fourier transform, and inputs the outputs to the coarse estimator 440 and the fine estimator 450.

The delay unit 441 of the coarse estimation device 440 shown in FIG. 5 delays the FFT output of the first training symbol a for one sample data period (i.e., the period of the subcarrier), and the conjugate complex number. After taking the conjugate through the conversion unit 442, the multiplier 444 converts the conjugate data value, the current FFT output data value, and the difference signal Ck * as the phase difference information stored and set in the difference signal storage unit 443. By taking cross-correlation through, the moving average calculation unit 425 obtains the average correlation value Q1 for the length of the P1 to P2 interval as shown in Equation 5 below.

Where R _k ¹ represents k-th data transformed after the first training symbol (a), P ₂ -P ₁ +1 is less than or equal to N, and P ₁ and P ₂ are values of frequency offset to be estimated. Determined by the range.

Further, the second training symbol (b) received after the first training symbol (a) is subjected to the average correlation with respect to the second training symbol (b) by the following equation (6) through the same process as described above. Find the value Q2.

Here, R _k ² represents the k-th data that is Fourier transformed of the second training symbol b.

Subsequently, the coarse frequency offset estimator 446 obtains the phase differences ΔΦ 1 and ΔΦ 2 based on Equations 7 and 8, respectively, using the two correlation values Q1 and Q2, and then calculates the phase differences with the calculated phase differences. Based on 9, approximately frequency offset Δf1 is obtained.

As such, when the frequency offset Δf1 is obtained based on Equation 9, subtraction is performed between the phase difference ΔΦ1 and ΔΦ2 between the same channels, and thus, the first and second training signals newly configured as shown in FIG. 3 according to the present invention. By this relationship, the channel phase difference due to deterioration of the channel characteristic is eventually deleted, leaving only 2XΔΦ. Therefore, the channel phase difference due to deterioration of the channel characteristics is removed in the process of obtaining the frequency offset Δf1.

In Equation 9, int [x] is an operation of selecting an integer close to x, and M represents the number of phase modulation signal points applied to the first and second training symbols (a) and (b).

The approximate frequency offset Δf1 thus obtained represents an integer multiple frequency offset portion with respect to the subcarrier spacing among all frequency offsets, and the integer is denoted as d for convenience of description below.

Using the training symbols (a) and (b) of the present invention as described above, and calculating the approximate frequency offset Δf1 through the coarse estimation device 440, the actual corresponding to R _k ¹ and R _k ² Estimates of Transmission Data Wow Are represented by Equations 10 and 11, respectively.

Next, a fine frequency offset estimation method will be described.

The delay unit 451 of the fine estimation apparatus 450 delays the data of the first training symbol a, which is after-transformed via the FFT unit 430, for one symbol period, and the delayed data is Conjugation is taken through the conjugate complex conversion unit 452.

The data correction unit 453 is subsequent to the data {R} `_ {k} ^ {1 *} and the first training symbol b of the first training symbol a delayed and conjugated. It receives data {R} `_ {k} ^ {2} of the second training symbol b, which has been transformed into a Fourier input, as an input, and also from the coarse frequency offset estimator 446 of the coarse estimation device 440. After receiving the estimated approximate frequency offset Δf1 (that is, d) as an input, based on the input data Δf1 (ie, d) and the equations (10) and (11), the first training symbol (a) Estimated Data for Data R _k ¹ And estimated data of the data R _k ² of the second training symbol (b). Conjugate Obtain

The multiplier 454 is {R} `_ {k} ^ {1 *} which is output data of the conjugate complex conversion unit 452, and {R}` _ {k} which is output data of the FFT unit 430. ^ {2}, which is correction data of the first training symbol provided from the data correction unit 453. And a conjugate of the correction data of the second training symbol Multiply by to find the correlation between them.

Subsequently, the moving average calculator 455 calculates an average correlation value for one symbol interval for the output of the multiplier 454. Finally, the fine frequency offset estimator 456 performs the moving average calculator 455. A fine frequency offset Δf 2 is obtained based on the average correlation value output from the equation, and is calculated based on Equation 12 below.

Here, Tu and Tg are valid symbol intervals and guard intervals, respectively, R _k ¹ and R _k ² are data of the k th first training symbol and the second training symbol, respectively, Wow Respectively represent data of the k th first and second training symbols estimated by the calculation of the coarse frequency offset.

Subsequently, the frequency synchronization according to the present invention is obtained by adding the approximate frequency offset and the fine frequency offset estimated by the adder 460 to the frequency offset through the multiplier 470 as shown in Equation 13 below. By converting the exponential function to rotate the phase in the opposite direction to the phase rotation by the multiplied by the output signal of the A / D converter 410 to obtain the frequency synchronization.

On the other hand, the estimation of the channel gain is calculated according to the following equation (14) and input to the channel equalizer 480.

here, Denotes the channel gain of the k-th subchannel.

As described in detail above, according to the method for determining a training symbol and an apparatus and method for frequency offset estimation and synchronization in an orthogonal frequency division multiplexing transmission system according to the present invention, the following effects are created.

First, since only up to three correlation values are needed to estimate the frequency offset, the time delay caused by the calculation time can be reduced. This property is applicable to realizing latency sensitive devices such as communication systems. Second, since only up to three correlations are needed to estimate the frequency offset, the complexity of the circuit can be reduced. Third, the acquisition range of the frequency offset can be extended up to 10 of the subcarrier spacing. Fourth, the frequency offset can be estimated without affecting the channel characteristics. Fifth, the training symbol used for frequency offset estimation can be used again for channel estimation, thereby reducing the overhead caused by additional training symbols.

Claims (18)

A method of determining a training symbol transmitted from a transmitter for symbol synchronization and / or frequency synchronization in a receiver of an OFDM system using N subcarriers, A first step of sequentially assigning one data to the N subcarriers in a frequency domain, and determining a first training symbol to correlate data values respectively allocated to adjacent subcarriers; And Using the same data as the data of the first training symbols sequentially allocated to the N subcarriers, and assigning the corresponding data to the corresponding subcarriers to determine the second training symbol so that the allocation order is reversed. A training symbol determination method of an orthogonal frequency division multiplex (OFDM) system, characterized in that configured. According to claim 1, Correlation between adjacent data values of the first training symbol is determined based on a relation of "A _{k + 1} = A _k C _k , 0≤k≤N-2", where A _k is a complex assigned to the kth subcarrier C _k is data and represents a phase difference as a difference signal between adjacent data values of the first training symbol. The method of claim 1, Correlation between adjacent data values of the second training symbol is determined based on a relationship of "B _{k + 1} = B _k C _k ^* , 0≤k≤N-2", where B _k is assigned to the kth subcarrier. C _k ^* denotes the conjugate of the C _k as a phase difference, which is a difference signal between adjacent data values of the second training symbol, wherein the training symbol determination method of an orthogonal frequency division multiplexing (OFDM) system. The method of claim 1, Determining a training symbol of an orthogonal frequency division multiplexing (OFDM) system, wherein each subcarrier of the first and second training symbols is allocated power according to an autocorrelation characteristic of a corresponding training symbol required in a time domain. Way. A frequency offset estimation method for frequency synchronization in a receiver of an orthogonal frequency division multiplexing (OFDM) system using N subcarriers, Data values allocated to subcarriers adjacent to each other in the frequency domain are set to have a mutually constant phase difference, so that data is transmitted in a reverse order with respect to the order of transmitted first training symbols and respective data values assigned to subcarriers of the first training symbol. A first step of sequentially receiving a second training symbol, each of which has been assigned a value, to be transmitted, demodulating to baseband, digitally converting, and fast Fourier transforming; A second step of delaying data of the first training symbol transformed to the Fourier transform during one sample data interval; Based on the delayed data of the first training symbol, subsequent free current transformed data, and phase difference information of the preset first training symbol, a correlation value is calculated between the delayed first training symbol and a constant corresponding to an integer multiple of the sample data interval. Calculating a mean correlation value during the interval as a first correlation value; The data of the second training symbol transformed to the Fourier transform is delayed for one sample data interval, and the data of the delayed second training symbol, followed by the Fourier transformed current data and the phase difference information of the preset second training symbol. A fourth step of calculating a correlation value therebetween and calculating an average correlation value for a predetermined period corresponding to an integer multiple of the sample data interval as a second correlation value; A fifth step of calculating a first phase difference based on the calculated first correlation value and calculating a second phase difference based on the calculated second correlation value; And And a sixth step of calculating an approximately frequency offset based on the calculated first and second phase differences. The method of claim 5, Correlation between adjacent data values of the first and second training symbols is "A _{k + 1} = A _k C _k , 0≤k≤N-2" and "B _{k + 1} = B _k C _k ^* , 0≤k Are respectively set based on the relation ≤ N-2 ", where A _k and B _k are complex data allocated to the k th subcarrier of the first and second training symbols, and C _k is the first training symbol. A phase difference between adjacent data values of C _k ^* denotes a phase difference between adjacent data values of the second training symbol as the conjugate of C _k , and approximately a frequency offset estimation method in an orthogonal frequency division multiplexing (OFDM) system. . The method of claim 5, In the third and fourth steps, the first and second correlation values Q1 and Q2 are respectively And Calculated based on Equation ² , wherein R ¹ and R ² represent the data that are Fourier-converted data of the first training symbol and the second training symbol, respectively, and C _k ^* and C _k are the first and second predetermined values, respectively. Orthogonal frequency division multiplexing characterized in that it represents phase difference information of a second training symbol, wherein P ₂ -P ₁ +1 is less than or equal to N and P ₁ and P ₂ are determined by a range of frequency offset to be estimated. Approximate frequency offset estimation method in a (OFDM) system. The method of claim 7, wherein In the fifth step, the first and second phase differences ΔΦ 1 and ΔΦ 2 are respectively. And And approximating a frequency offset in an orthogonal frequency division multiplexing (OFDM) system. The method of claim 8, In the sixth step, the approximately frequency offset Δf1 is Orthogonal frequency division multiplexing, characterized in that int [x] is an operation that takes an integer close to x, and M represents the number of phase modulation signal points applied to the training symbol. Approximate frequency offset estimation method in OFDM) system. A frequency offset estimation method for frequency synchronization in a receiver of an orthogonal frequency division multiplexing (OFDM) system using N subcarriers, Data values allocated to subcarriers adjacent to each other in the frequency domain are set to have a mutually constant phase difference, so that data is transmitted in a reverse order with respect to the order of transmitted first training symbols and respective data values assigned to subcarriers of the first training symbol. A first step of sequentially receiving a second training symbol, each of which has been assigned a value, to be transmitted, demodulating to baseband, digitally converting, and fast Fourier transforming; Delaying the Fourier transformed first training symbol for one symbol period; And A fine frequency offset, based on the data of the delayed first training symbol followed by the data of the second training symbol subsequently Fourier transformed and the data values of the first and second training symbols estimated by the calculation of the approximate frequency offset. Comprising a third step of calculating the fine frequency offset estimation method in an orthogonal frequency division multiplex (OFDM) system, characterized in that the configuration. The method of claim 10, In the third step, the fine frequency offset Δf2 is Calculated based on Equation 2, wherein Tu and Tg are valid symbol intervals and guard intervals, respectively, and R _k ¹ and R _k ² are data of the k th first training symbol and the second training symbol, respectively. Data for, Wow Are fine frequency offset estimation methods in an orthogonal frequency division multiplex (OFDM) system, wherein each represents data of the k th first and second training symbols estimated by the calculation of the coarse frequency offset. A frequency synchronization method using frequency offset estimation in a receiver of an orthogonal frequency division multiplexing (OFDM) system using N subcarriers, Data values allocated to subcarriers adjacent to each other in the frequency domain are set to have a mutually constant phase difference, so that data is transmitted in a reverse order with respect to the order of transmitted first training symbols and respective data values assigned to subcarriers of the first training symbol. A first step of sequentially receiving a second training symbol, each of which has been assigned a value, and sequentially transmitting and demodulating to baseband, digital conversion, and fast fast Fourier transform; Calculating a correlation value between the second step of delaying during the sample data interval, and based on the data of the delayed first training symbol followed by current data transformed after the Fourier and the phase difference information of the preset first training symbol. Calculating an average correlation value for a predetermined interval corresponding to an integer multiple of the sample data interval as a first correlation value; Step 3, delaying the data of the second training symbol that is transformed for one sample data interval, and the data of the delayed second training symbol, and subsequently the current data that is transformed to the Fourier transform and the preset second training. A fourth step of calculating a correlation value therebetween based on the phase difference information of the symbol, calculating an average correlation value for a predetermined period corresponding to an integer multiple of the sample data interval as a second correlation value, and calculating the correlation value to the calculated first correlation value. A fifth step of calculating a first phase difference based on the second correlation value, and a sixth step of calculating an approximately frequency offset based on the calculated first and second phase differences. A first step of estimating a coarse frequency offset with a step; A seventh step of delaying the first training symbol that has been transformed and output in the first step for one symbol period, and the data of the delayed first training symbol and subsequently of the second training symbol that has been Fourier transformed; A second step of estimating a fine frequency offset, comprising an eighth step of calculating a fine frequency offset based on data and data values of the first and second training symbols estimated by the calculated approximate frequency offset; And And a third process of acquiring frequency synchronization of the digitally converted data based on the approximate frequency offset value estimated in the first process and the fine frequency offset value estimated in the second process. Frequency Synchronization Method Using Frequency Offset Estimation in Orthogonal Frequency Division Multiplexing System. In the frequency domain using N subcarriers, data values assigned to adjacent subcarriers are set to have a mutually constant phase difference, and thus, each data value assigned to a first training symbol transmitted and a subcarrier of the first training symbol is transmitted. In a receiving apparatus of an orthogonal frequency division multiplexing (OFDM) system using second training symbols transmitted with data values assigned in reverse order with respect to the order, as a received signal for frequency offset estimation and frequency synchronization, Analog / digital (A / D) conversion means for converting the received baseband analog training symbol signal into a digital training symbol signal; Guard interval removal means for removing a guard interval included in the digital training symbol signal using the detected symbol timing; Fast Fourier transform means for fast Fourier transform (FFT) of the removed training interval signal; Obtaining an average correlation value between them based on the phase difference between the data of the first training symbol and the phase difference between the data of the second training symbol and the corresponding phase difference information between the data of each preset training symbol corresponding thereto, Approximate estimation means for estimating each phase difference based on the calculated respective average correlation values, and then estimating a frequency offset approximately based on the calculated respective phase differences; Based on the data of the Fourier transformed first training symbol and subsequently on the Fourier transformed data of the second training symbol and the data of the first and second training symbols corrected by the estimated coarse frequency offset. Fine estimation means for estimating fine frequency offset; Addition means for adding an output of the coarse estimation means and an output of the fine estimation means; And Multiplying the output of the adding means and the output of the analog / digital converting means to rotate the phase in a direction opposite to the phase rotation caused by the frequency offset of the output of the analog / digital converting means; A frequency synchronization device by frequency offset estimation in an orthogonal frequency division multiplexing (OFDM) system, comprising multiplication means for providing an input. The method of claim 13, The approximate estimating means, A first delayer for delaying data of the Fourier transformed training symbol signal for one sample data interval; A first conjugate complex converter which conjugates the data delayed by the first delayer; A difference signal storage unit configured to store preset phase difference data with respect to the first and second training symbols; A first multiplier for multiplying output data of the first conjugate complex conversion part, output data of the fast Fourier transform means, and corresponding phase difference data provided from the difference signal storage part correspondingly to obtain a correlation value therebetween; A first moving average calculator configured to calculate an average correlation value for a predetermined period with respect to the output of the first multiplier; And A coarse frequency offset estimator for estimating a coarse frequency offset based on a first mean correlation value for the first training symbol and a second mean correlation value for the second training symbol output from the first moving average calculator; And a frequency offset estimation of an orthogonal frequency division multiplexing (OFDM) system. The method of claim 14, The coarse frequency offset estimator calculates first and second phase differences based on first and second average correlation values, and estimates the coarse frequency offset based on the calculated difference between the first and second phase differences. A frequency synchronization device by frequency offset estimation of an orthogonal frequency division multiplexing (OFDM) system. The method of claim 15, The approximately frequency offset Δf1 is Calculated based on the following equation, where int [x] is an operation that takes an integer close to x, M denotes the number of phase modulation signal points applied to the training symbol, and Q1 and Q2 are the first and the second, respectively. A frequency synchronization device by frequency offset estimation of an Orthogonal Frequency Division Multiplexing (OFDM) system, characterized in that it represents a second mean correlation value. The method of claim 13, The fine estimation means, A second delayer for delaying the data of the Fourier transformed training symbol signal for one symbol period; A second conjugate complex conversion unit which conjugates the data delayed by the second delayer; The output data of the second conjugate complex conversion unit and the output data of the fast Fourier transform unit are corrected based on the approximate frequency offset value estimated by the coarse estimation unit to estimate the estimated data of the first training symbol and the second data. A data correction unit for calculating a conjugate of estimated data of a training symbol; Multiplying the conjugate data of the output data of the second conjugate complex conversion unit, the output data of the fast Fourier transform means, the correction data of the first training symbol, and the correction data of the second training symbol, and obtain a correlation value therebetween; Two multipliers; A second moving average calculator configured to calculate an average correlation value for one symbol period with respect to the output of the second multiplier; And A fine frequency offset estimator for estimating a fine frequency offset based on the average correlation value output from the second moving average calculation unit, the frequency offset estimation of an orthogonal frequency division multiplexing (OFDM) system Frequency synchronizer. The method of claim 17, The fine frequency offset Δf2, Calculated based on Equation 2, wherein Tu and Tg are valid symbol intervals and guard intervals, respectively, and R _k ¹ and R _k ² are data of the k th first training symbol and the second training symbol, respectively. Data for, Wow Denotes a conjugate of k-th correction data of the first training symbol, estimated data of the first training symbol of the second training symbol, and k-th estimation data of the second training symbol, respectively provided from the data correction unit. A frequency synchronization device based on frequency offset estimation of an orthogonal frequency division multiplex (OFDM) system.