KR20070117344A - Apparatus and method of channel estimation and channel compensation after symbol timing regulation in an orthogonal frequency division multiple system - Google Patents

Abstract

An apparatus and a method of channel estimation and channel compensation after symbol timing regulation in an orthogonal frequency division multiple system are provided to reflect a phase offset value for distorted phase to an OFDM symbol in order to obtain the distorted phase of a pilot symbol by performing channel estimation through two-dimensional interpolation of a time axis and a frequency axis. According to a method of channel estimation and channel compensation according to symbol timing regulation in an orthogonal frequency division multiple system, an analog signal received through an antenna is converted into a digital signal(310). A signal in a service band is filtered from the digital signal(315), and the signal in the service band is demodulated into pilot symbols and data symbols constituting one OFDM symbol by performing FFT(Fast Fourier Transform) according to a fixed window(320). Channel estimation values according to the pilot symbols are obtained. If symbol timing of the OFDM symbol is changed, a phase offset value according to the changed symbol timing is obtained. Channel estimation values by time interpolation and frequency interpolation are calculated by using the channel estimation values and channel estimation values obtained by prior OFDM symbols. Channel compensation for the data symbol is performed with the obtained channel estimation values(355). The channel-compensated data symbols are decoded(360).

Description

Apparatus and method of channel estimation and channel compensation after symbol timing regulation in an Orthogonal Frequency Division Multiple system

1 is a block diagram showing the configuration of a receiver capable of window adjustment and phase correction for symbol timing according to a preferred embodiment of the present invention.

2 is a diagram illustrating two-dimensional interpolation for channel estimation based on a time axis and a frequency axis according to a preferred embodiment of the present invention.

3 is a flowchart illustrating channel estimation and compensation after OFDM symbol reception according to an embodiment of the present invention.

4 is a detailed block diagram of a phase compensator and an interpolator in the receiver in accordance with a preferred embodiment of the present invention.

FIG. 5 is a diagram illustrating a structure of a memory storing a channel estimate value and a memory storing an increment value necessary to calculate a next channel value according to another embodiment of the present invention. FIG.

6 is a block diagram of channel estimation in accordance with another preferred embodiment of the present invention.

The present invention is directed to an orthogonal frequency division multiplexing system, and in particular, provides a method and apparatus for adjusting the window of a fast Fourier transform and performing channel estimation and compensation for the symbol to compensate for symbol timing error of the received symbol.

In the Orthogonal Frequency Division Multiplexing (OFDM) system, the discrete Fourier transform can be used to perform modulation / demodulation on all carriers in a batch so that a modulator / demodulator can be designed for each individual carrier. no need. Typically, there is one or more pilots with known complex values within one OFDM symbol.

In the OFDM symbol, modulation symbols that are the smallest unit of data exist, and the modulation symbols become the pilot or information symbols. The pilot is used as a reference value for demodulating the OFDM symbol by a Fast Fourier Transform (FFT), and is used for channel estimation. The channel estimation value at the time-frequency position where the pilot does not exist is obtained through interpolation of the time axis or the frequency axis.

In order to accurately estimate the channel in the OFDM system, a signal in the frequency domain of OFDM symbols after FFT demodulation is used so that pilots arranged on the time axis and the frequency axis can be used simultaneously.

At this time, the interval between the time axis pilot array and the frequency axis pilot array is observed to interpolate the axis having the shortest interval first, and then the axis having the shortest pilot interval is interpolated.

In order to not be affected by the symbol timing adjustment during the channel estimation process, frequency axis interpolation is used instead of time axis interpolation.

That is, in a normal channel state, time axis interpolation and frequency axis interpolation are performed, and frequency axis interpolation is performed for a portion of the channel estimation that is performed after the symbol timing is adjusted. As described above, performing both time axis interpolation and frequency axis interpolation is called two-dimensional interpolation, and performing only time axis or frequency axis interpolation is called one-dimensional interpolation.

In this case, a bit error rate (hereinafter, referred to as BER) may be lowered in the partial section than the normal channel state section in which the interpolation method considering the time axis and the frequency axis is performed.

As an example, when a terminal receives broadcast signals from different base stations in a broadcast system, since the channels experienced by the broadcast signals are different from each other, the screen state of the broadcast is changed in a corresponding section for performing 1D interpolation of some channels. It becomes bad. In addition, even in a communication system, there is a problem in that the reception sensitivity of the signal is reduced.

The present invention devised to solve this problem provides a method and apparatus for performing correct channel estimation of received symbols in an OFDM system.

In a preferred embodiment of the present invention, in a method for performing channel estimation and compensation according to symbol timing adjustment in an orthogonal frequency division multiplexing system,

Converting the analog signal received through the antenna (ANT) into a digital signal,

Filtering a signal of a service band from the digital signal, and demodulating the signal of the service band into pilot symbols and data symbols constituting an OFDM symbol by performing FFT (Fast Fourier Transform) conversion according to a predetermined window;

Obtaining channel estimation values according to the pilot symbols;

If the symbol timing of the OFDM symbol is changed, obtaining a phase offset value according to the changed symbol timing;

Calculating channel estimation values by time interpolation and frequency interpolation using the channel estimation values obtained by the channel estimation values and previous OFDM symbols while compensating the phase of the channel estimation values according to the pilot symbols according to the phase offset value; ,

Channel-compensating the data symbol with the obtained channel estimation values when all channel estimation values of corresponding time-frequency positions are obtained for the data symbols;

And decoding the channel compensated data symbols.

In the apparatus of the present invention, in the orthogonal frequency division multiplexing system in the apparatus for performing channel estimation and compensation according to the symbol timing adjustment,

An analog to digital converter (ADC) converter for converting analog signals received through an antenna (ANT) into digital signals;

A reception (Rx) filter for filtering a signal of a service band from the digital signal;

An FFT unit for demodulating the signal of the service band by fast fourier transform (FFT) according to a predetermined window and demodulating the pilot symbols and data symbols constituting one OFDM symbol;

A symbol timing checker for checking whether a symbol timing has been changed for the OFDM symbol, and calculating a phase offset value according to the changed symbol timing if the symbol timing has changed;

An FFT window controller for determining the position of the window according to the changed symbol timing and providing the window to the FFT unit;

A channel estimator for obtaining channel estimation values at corresponding time-frequency positions for the pilot symbols;

A phase compensator for compensating the phase of the channel estimation values according to the phase offset value;

An interpolator for calculating channel estimation values by time interpolation and frequency interpolation using the channel estimation values and channel estimation values obtained by previous OFDM symbols based on the phase compensated channel estimation values;

A channel compensator for channel compensating the data symbols with the obtained channel estimation values when all channel estimation values of corresponding time-frequency positions are obtained for the data symbols;

And a decoder for decoding the channel compensated data symbols.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that those skilled in the art may better understand the detailed description of the invention that follows.

Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. Those skilled in the art should recognize that the disclosed concepts and specific embodiments of the invention may be readily used as a basis for modifying or designing other structures for achieving the same purposes of the present invention. Those skilled in the art should also recognize that structures equivalent to the invention do not depart from the spirit and scope of the broadest form of the invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, detailed descriptions of well-known functions and configurations that may obscure the gist of the present invention will be omitted.

An important aspect of the present invention enables channel estimation through two-dimensional interpolation between the time axis and the frequency axis even when the symbol timing of the OFDM symbol received in the orthogonal frequency division multiplexing system is adjusted. Specifically, the present invention phase-compensates channel estimates before performing time interpolation, and phase recovers channel estimates before performing frequency interpolation.

1 is a block diagram showing the configuration of a receiver capable of symbol timing adjustment and phase correction according to a preferred embodiment of the present invention.

The device receives an analog signal through an antenna ANT and converts the analog signal into a digital signal in an analog-to-digital converter (hereinafter, referred to as an ADC) 100. The digital signal is filtered by only the signal of the service band in the reception filter 110, and the FFT unit 120 performs an FFT on an OFDM symbol of a unit determined by a window among the signals of the service band, thereby performing data symbols and pilot symbols. Demodulate by The demodulated data symbols are passed to the channel compensator 180.

The demodulated pilot symbols are passed to the symbol timing checker 130 and the channel estimator 150. The symbol timing checker 130 checks whether the symbol timing of the OFDM symbol is changed compared to the previous OFDM symbol according to the position at which the pilot symbols are detected, and if the symbol timing is changed, the FFT window adjuster 140 determines that the symbol timing is changed. The location of the window is determined and transmitted to the FFT unit 120 according to the changed symbol timing of the OFDM symbol. The detailed method of checking the symbol timing of the OFDM symbol is not highly related to the gist of the present invention, and thus detailed description thereof is omitted.

The symbol timing checker 130 transmits a phase offset value according to the change of the symbol timing to the phase compensator 160.

The channel estimator 150 obtains channel estimation values at corresponding time-frequency positions for the pilot symbols and transmits the channel estimation values to the interpolator 170.

The interpolator 170 calculates channel estimates of the entire OFDM frame through two-dimensional interpolation of the time axis and the frequency axis based on the channel estimates for the pilot symbols, wherein the channel estimates are calculated using the phase compensator ( In step 160, phase compensation is performed according to the phase offset value.

When the channel estimation values calculated by the two-dimensional interpolation are transferred to the channel compensator 180, the channel compensator 180 performs channel compensation on data symbols of the corresponding OFDM symbol by using the channel estimation values. The channel compensated data symbols are passed to the decoder 190. The decoder 190 decodes the data symbols into original information.

The interpolator 170 obtains channel estimation values for positions (ie, corresponding to pilot symbols) and remaining positions (ie, corresponding to data symbols) that are reference in the OFDM symbol with respect to the time axis and the frequency axis. At this time, the phase compensator is performed through the phase compensator 160.

For example, the phase is offset by α when the correct symbol is e ^jw = cosω + jsinω and the received symbol is e ^{jw + α} = cos (ω + α) + jsin (ω + α). The compensator 160 performs channel estimation through two-dimensional interpolation while compensating channel estimation values of the pilot symbols and channel estimation values stored in a channel estimator memory (not shown) according to the phase offset.

2 is a diagram illustrating two-dimensional interpolation for channel estimation based on a time axis and a frequency axis according to a preferred embodiment of the present invention.

Referring to FIG. 2, the horizontal axis is the frequency axis and the vertical axis is the time axis, and there are three time-frequency bins between the pilot (1) of OFDM symbol 4 and the pilot (2) of OFDM symbol 0 on the time axis. 210, and thus the pilot interval of the pilots 1 and 2 is three. Further, the pilot intervals (2, 3) of the OFDM symbol 0 on the frequency axis are longer than the pilot interval on the time axis. Therefore, channel estimation is first performed through interpolation in the time axis having a short pilot interval. Channel estimation through the interpolation is to determine how many data symbols are present between the pilot symbols (2, 3), and to obtain channel estimation values for each data symbol. The same applies to obtaining channel estimation values between the pilot symbols (2, 3) of the OFDM symbol 0 on the frequency axis.

3 is a flowchart illustrating channel estimation and compensation according to a preferred embodiment of the present invention.

Referring to FIG. 3, the OFDM receiver receives a signal analogized to an antenna ANT in step 305, and the analog signal is converted into a digital signal in step 310. In step 315, only the signal of the service band is filtered from the digital signal, and in step 320, the OFDM receiver demodulates the pilot symbols and data symbols by performing an FFT on the OFDM symbols of a predetermined window of the signal of the service band. do. The demodulated pilot symbols are used for two checks. First, in step 325, the OFDM receiver checks whether the symbol timing of the OFDM symbol is changed using the pilot symbols, and if so, adjusts the position of the window according to the changed symbol timing in step 330. After that, the process returns to step 320 to demodulate the next OFDM symbol.

In step 335, the OFDM receiver calculates a phase offset value for the OFDM symbol according to the changed symbol timing, and then proceeds to step 350.

If the symbol timing is not changed in step 325, the window is in the correct position, and the flow proceeds to step 350.

Secondly, in step 340, the OFDM receiver distinguishes whether each of the demodulated symbols is a pilot symbol or a data symbol. If the pilot symbol is a pilot symbol, the OFDM receiver proceeds to step 345 to determine a channel according to the pilot symbol. Obtain the estimated value and proceed to step 350 above. On the other hand, if it is a data symbol, the process proceeds to step 355 and the data symbol is stored in the channel estimator memory until a channel estimate of the corresponding time-frequency position is obtained.

In step 350, the OFDM receiver converts the channel estimation values according to the pilot symbols and the channel estimation values stored in the channel estimator memory according to the phase offset value, and converts the channel estimation values of the entire OFDM frame into a time axis and a frequency. Compute by two-dimensional interpolation of the axis. In step 355, the channel compensation value is multiplied by the channel estimation value of the corresponding time-frequency position with respect to the data symbol.

The channel compensated data symbol proceeds to step 360 to be used for decoding.

4 is a detailed structural diagram of the phase compensator 160 and the interpolator 170 in the receiver according to the preferred embodiment of the present invention.

The detailed structure diagram shows in more detail a configuration in which channel estimation values for data symbols are obtained by two-dimensional interpolation while applying a phase offset value, a symbol timing-adjusted value, to the channel estimation values for the pilot symbols and the obtained channel estimation values. will be.

The channel estimation part for obtaining the channel estimation value of the pilot symbol is excluded from FIG. 4 because the same applies regardless of whether the symbol timing is adjusted.

When the symbol timing is checked, a PC_CTRL_Value signal 410 indicating whether the symbol timing is adjusted is input to the first selector 400 as '0' or '1'.

When '0' is input as the PC_CTRL_Value signal 410, the symbol timing is not changed. Therefore, the first selector 400 provides a channel estimation value for the pilot symbol to the time interpolator 435. The time interpolator 435 stores the input channel estimate value in the memory 450 and interpolates the channel estimate values stored in the memory 450 on the basis of a time axis to obtain channel estimate values for data symbols. Obtained and stored in the corresponding location of the memory 450.

When the time interpolator 435 indicates that time axis interpolation is completed, the frequency interpolator 470 interpolates the channel estimate values stored in the memory 450 based on the frequency axis to perform the remaining data symbols. The channel estimates are obtained and stored in the corresponding location of the memory 450. Once the channel estimates for one OFDM symbol have been obtained, the channel estimates are passed from the frequency interpolator 470 to the second selector 480.

Meanwhile, when '1' is input as the PC_CTRL_Value signal 410, since the symbol timing is changed, the first selector 400 provides the input channel estimation value to the (+) phase compensator 420. The (+) phase compensator 420 receives a pilot position and a phase offset value indicating the position of a pilot symbol on an OFDM symbol, multiplies the channel estimate by the phase offset value, and compensates the phase, and a time interpolator 420. After storing the phase-compensated channel estimate at a corresponding position on the memory 450, interpolating the stored channel estimates based on a time axis, obtaining channel estimate values for data symbols, and then applying the corresponding channel estimates to the memory 450. Save to a location.

The negative phase compensator 440 receives the pilot position, multiplies the channel estimation values for the pilot symbols stored in the memory 450 by the inverse of the phase offset value, and restores the original phase. Store at the original location of 450. The frequency interpolator 460 performs interpolation based on the frequency axis among the channel estimation values stored in the memory 450 to obtain channel estimation values for the remaining data symbols and stores them in the corresponding positions of the memory 450. When all channel estimation values for one OFDM symbol are obtained as described above, the channel estimation values are transferred from the frequency interpolator 460 to the second selector 480.

The second selector 480 selects channel estimation values from the frequency interpolator 470 in the case of '0' according to the PC_CTRL_Value signal 410, and the channel estimate value from the frequency interpolator 460 in the case of '1'. Are selected and delivered to the channel compensator 490.

The channel compensator 470 performs channel compensation by applying the channel estimation values to data symbols. The reason for using the (+) phase compensator 420 and the (-) phase compensator 440 is to remove the influence of the adjustment of the symbol timing during the time interpolation.

The (+) phase compensator 420 performs compensation by multiplying a + jb which is a phase offset value, and the (-) phase compensator 440 performs compensation by multiplying a-jb which is an inverse of the phase offset value. Here, a and b are values determined according to the position of sub-carriers and the degree of symbol timing. As an example, a + jb = cos (2πx ((OFFSETx (i-nCarrierPerOFDM / 2))% Nfft) / Nfft) + jsin (2πx ((OFFSETx (i-nCarrierPerOFDM / 2))% Nfft) / Nfft) Determined by In this case, the OFFSET means the degree of the symbol timing is adjusted, i is the position of the sub-carrier (sub-carrier), n CarrierPerOFDM is the number of effective sub-carriers (sub-carrier), Nfft means the size of the demodulated OFDM symbol. . As such, the phases applied to the two phase compensators 420 and 440 have a conjugate relationship, and thus may be implemented as one phase compensator.

Meanwhile, as another embodiment of the present invention, a memory storing an increment value necessary for calculating the next channel value may be used instead of the memory 450 which stores channel measurements for a plurality of OFDM symbols and stores them. .

FIG. 5 is a diagram illustrating a structure of a memory storing a channel estimation value and a memory storing an increment value necessary to calculate a next channel value according to another embodiment of the present invention. In FIG. 5, the memory storing the channel estimation value y is referred to as “y memory 530.” The memory storing the increment value Δ: delta for calculating the next channel value is referred to as a “delta (delta) memory ( 510) ".

The channel estimation process using the memories 510 and 530 of FIG. 5 may be summarized as follows (1) to (4). In the following (2), the prime (') of y means information updated at the present time.

(1) The channel of the subcarrier carrying the pilot signal is estimated.

(2) The calculated channel estimation value is updated in the y memory 530 according to a to c in Equation 1 below.

a. y ₀ '= y ₀ + delta ₀ , (stored in multiples of 3)

b. y ₁ '= y ₂ + delta ₁ , (stored in positions where the remainder divided by 3 is 1)

c. y ₂ '= y ₃ + delta ₂ , (stored at position 2 divided by 3)

Here, the multiple of 3 means that when the order of subcarriers is from 0 to N, the position of the subcarrier on which the pilot is transmitted is a multiple of 3. In Equation 1, a is for updating a channel estimate value of a pilot, and b and c are for updating a channel estimate value corresponding to data. For convenience of explanation, the embodiment assumes a pilot structure in a digital video broadcasting-handheld (DVB-H) system, but the channel estimation process of the present invention is not limited to the DVB-H system.

(3) The calculated increment value is updated in the Δ memory 510 according to d to f in Equation 2 below.

d. delta ₀ = (channel estimate-y ₀ ) / 4, (pilot position of current OFDM symbol)

e. delta ₁ = (channel estimate- (y ₃ + delta ₃ ) / 3, (pilot position of current OFDM symbol + 1)

f. delta ₂ = (channel estimate- (y ₃ + delta ₃ ) / 3, (pilot position of current OFDM symbol + 2)

Subscript 3 in the above e. And f. Means (pilot position of the current OFDM symbol + 3).

In Equation 2, d is a part for calculating an increment value for time axis interpolation, and e and f are a part for calculating an increment value for diagonal interpolation considering both time axis and frequency axis. Referring to the operations of d to f, the interpolator calculates delta ₀ at the pilot position of the current OFDM symbol (d process), and calculates delta ₁ and delta ₂ at one or two subcarrier positions away from the position (e , f process). In this case, the channel estimation value of the y memory 530 and the increment value of the Δ memory 510 are stored in three subcarrier positions.

(4) Interpolation is performed on the frequency axis using the y memory 530.

In this case, a portion used for interpolation of the frequency axis in the y memory 530 is a portion that is a multiple of 3, a pilot position of a current OFDM symbol + 4 subcarriers, and a portion of a pilot position of a current OFDM symbol + 8 subcarriers. Thereafter, the receiver of FIG. 4 performs channel estimation according to the operations of (1) to (4), and then performs channel compensation using the result value interpolated on the frequency axis.

6 is a block diagram for channel estimation according to another preferred embodiment of the present invention. As the PC_CTRL_Value signal 630 indicating whether the symbol timing is adjusted, input paths of '0' or '1', which are symbol timing adjustments, are distinguished from each other.

If with reference to Figure 6 when the pilot symbols and data symbols for the FFT_OUT _K _i and FFT_OUT _K _Q which are demodulated symbols from the FFT unit 120 are input to the first selector 600, whether or not the pilot symbol deulinji The SC_LOC 605 signal, which is denoted as "0" or "1", is input to the first selector 600.

When '0' is input as the SC_LOC 605 signal, since the data symbols are input, the first selector 600 transmits the data symbols to the channel compensator 660.

Meanwhile, when '1' is input as the SC_LOC 605 signal, since the pilot symbols are input, the first selector 600 transfers the pilot symbols to the pilot channel estimator 610. The pilot channel estimator 610 obtains a channel estimation value for the pilot symbols and transfers the channel estimation value to the second selector 615 and the channel estimation value storage unit (y) 635.

When '1' is input as the PC_CTRL_Value signal 630, the channel estimation value is transmitted to the (+) phase compensator 620 by the second selector 615, and the (+) phase compensator 620 is the channel estimation value. Multiplying the phase offset value 625 by to compensate for the phase, and the channel increment storage unit (Δ) 650 calculates and stores an increment value for the phase compensated channel estimation value to calculate a next channel estimation value. .

When '0' is input as the PC_CTRL_Value signal 630, the channel estimation value is transmitted to the channel increment value storage unit Δ 650 without phase compensation.

Then, the channel increment storage unit (Δ) 650 calculates and stores an increment value of the channel estimation value which is not phase compensated. This process continues until the fourth symbol after the symbol timing is adjusted.

When the fifth OFDM symbol is input, the channel estimate storage unit (y) 635 is updated according to the above-described equation using the channel estimation value of the fifth OFDM symbol.

When '1' is input as the PC_CTRL_Value signal 630, the channel estimation value read from the channel estimation value storage unit y 635 is transmitted to the negative phase compensator 625 by the third selector 640. The (-) phase compensator 625 multiplies the channel estimation value by the inverse of the phase offset value to restore a phase, and the phase recovered channel estimation value stores the channel increment value storage unit (Δ) 650. While used to update, it is passed to a frequency interpolator.

 When '0' is input as the PC_CTRL_Value signal 630, the channel estimation value is used to update the channel increment value storage unit Δ 650 without phase compensation and is transmitted to the frequency interpolator.

The frequency interpolator 655 performs frequency interpolation using the channel values provided from the (-) phase compensator 625 or the third selector 640 to calculate a channel estimation value for one OFDM symbol and then a channel compensator. In operation 660, the channel compensator 660 performs channel compensation on the data symbols of the OFDM symbol by using the channel estimation value.

The position and sign of the phase compensator may vary depending on the application method, but applying the phase compensator to the estimated channel is the same.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

According to the present invention, when the symbol timing of an OFDM symbol received in an orthogonal frequency division multiplexing system is adjusted, channel estimation is performed through two-dimensional interpolation between the time axis and the frequency axis to obtain a distorted phase of the pilot symbol, which is then distorted in the OFDM symbol. It is characterized by reflecting the phase offset value with respect to the phase.

In the present invention, when the symbol timing is adjusted, the algorithm of channel estimation can be used in the same manner without phase lighting, and the performance can be maintained as if the symbol timing is not coarse. In addition, when the moving speed of the receiving terminal is fast, there is a superior advantage in the performance difference with the existing device.

Claims (8)

A method for performing channel estimation and compensation according to symbol timing in an orthogonal frequency division multiplexing system, Converting the analog signal received through the antenna (ANT) into a digital signal, Filtering a signal of a service band from the digital signal, and demodulating the signal of the service band into pilot symbols and data symbols constituting an OFDM symbol by performing FFT (Fast Fourier Transform) conversion according to a predetermined window; Obtaining channel estimation values according to the pilot symbols; If the symbol timing of the OFDM symbol is changed, obtaining a phase offset value according to the changed symbol timing; Calculating channel estimation values by time interpolation and frequency interpolation using the channel estimation values obtained by the channel estimation values and previous OFDM symbols while compensating the phase of the channel estimation values according to the pilot symbols according to the phase offset value; , Channel-compensating the data symbol with the obtained channel estimation values when all channel estimation values of corresponding time-frequency positions are obtained for the data symbols; And estimating the channel compensated data symbols. The method of claim 1, If the symbol timing has not changed, further comprising calculating channel estimates by time interpolation and frequency interpolation using the channel estimates and previous channel estimates without phase compensation of the channel estimates according to the pilot symbols. Channel estimation and compensation method. The method of claim 1, wherein the calculating of channel estimation values by the time interpolation and the frequency interpolation comprises Performing the time interpolation by multiplying the channel offset values according to the pilot symbols by the phase offset value according to the pilot position indicating the position of the pilot symbols on the OFDM symbol; Calculating all channel estimation values for the data symbols by performing the frequency interpolation by multiplying the phase compensated channel estimation values and the channel estimation values obtained by the time interpolation by the inverse of the phase offset value. Channel estimation and compensation method characterized in that. An apparatus for performing channel estimation and compensation according to symbol timing in an orthogonal frequency division multiplexing system, An analog to digital converter (ADC) converter for converting analog signals received through an antenna (ANT) into digital signals; A reception (Rx) filter for filtering a signal of a service band from the digital signal; An FFT unit for demodulating the signal of the service band by FFT (Fast Fourier Transform) conversion according to a predetermined window and demodulating the pilot symbols and data symbols constituting an OFDM symbol; A symbol timing checker for checking whether a symbol timing has been changed for the OFDM symbol, and calculating a phase offset value according to the changed symbol timing if the symbol timing has changed; An FFT window controller for determining the position of the window according to the changed symbol timing and providing the window to the FFT unit; A channel estimator for obtaining channel estimation values at corresponding time-frequency positions for the pilot symbols; A phase compensator for compensating the phase of the channel estimation values according to the phase offset value; An interpolator for calculating channel estimation values by time interpolation and frequency interpolation using the channel estimation values and channel estimation values obtained by previous OFDM symbols based on the phase compensated channel estimation values; A channel compensator for channel compensating the data symbols with the obtained channel estimation values when all channel estimation values of corresponding time-frequency positions are obtained for the data symbols; And a decoder for decoding the channel compensated data symbols. The method of claim 4, wherein if the symbol timing has not changed, The interpolator calculates channel estimation values by time interpolation and frequency interpolation using the channel estimation values and previous and subsequent channel estimation values without phase compensation of the channel estimation values according to the pilot symbols. . The method of claim 4, wherein the phase compensator, A first phase compensator for multiplying channel estimation values according to the pilot symbols with the phase offset value according to a pilot position indicating a position of the pilot symbols on the OFDM symbol; And a second phase compensator for reconstructing the phase by multiplying the phase offset values by the inverse of the phase offset values obtained by the phase compensated channel estimation values and the time interpolation. The method of claim 6, wherein the interpolator, A time interpolator which receives the phase compensated channel estimates from the first phase compensator and calculates channel estimates based on time interpolation using the previous channel estimates; And a frequency interpolator for calculating channel estimation values by frequency interpolation using the phase-recovered channel estimation values from the second phase compensator. The method of claim 7, wherein the time interpolator, A channel estimation value storing unit (y) for updating the previous channel estimation values stored in advance using channel estimation values; And a channel increment value storage unit (Δ) for calculating and storing an increment value for the phase compensated channel estimate value for calculating the next channel estimate value.

Images