KR20060066029A - Methods for tracking residual frequency, phase, timing offset and signal amplitude variation in ofdm systems, and methods thereof - Google Patents

Abstract

In the orthogonal frequency division multiplexing (OFDM) system, the present invention provides a residual frequency error, phase error, time error, and magnitude change tracking device for improving the performance and tracking speed of a phase and time error tracking method used in an existing OFDM system. It's about how. In accordance with an aspect of the present invention, a frequency error, phase error, time error, and magnitude change tracking device comprises: a frequency error compensator for compensating a tracking carrier error tracking value with an initial carrier frequency error estimate in a time domain; A magnitude tracking compensator configured to adjust a magnitude of a signal by multiplying an output value corresponding to a power calculation amount of a received pilot signal by a fast Fourier transform (FFT) input signal; A channel compensator for outputting a channel-compensated signal by multiplying a conjugate complex number of a frequency channel response of the received pilot signal by a received pilot signal; A carrier frequency error estimator for estimating a carrier frequency error parameter with a channel compensated pilot and providing a tracking carrier frequency error tracking value; A time error estimator for estimating a time error parameter with the channel compensated pilot; And a carrier phase error estimator for estimating a carrier phase error parameter with the channel compensated pilot.

Sync, OFDM, Frequency Error, Phase Error, Time Error, Magnitude Tracking

Description

Residual frequency error, phase error, time error, and magnitude change tracking device for OPDM system and method thereof {Methods for tracking Residual frequency, phase, timing offset and signal amplitude variation in OFDM systems, and methods}

1 is a diagram illustrating a frame structure of IEEE 802.11a according to an embodiment of the present invention.

2 is a diagram illustrating an OFDM subcarrier arrangement of IEEE 802.11a according to an embodiment of the present invention.

3 is a block diagram illustrating estimating a change in carrier phase using a pilot subcarrier according to an embodiment of the present invention.

4 is a block diagram illustrating estimating a time error using a pilot subcarrier according to an embodiment of the present invention.

5 is a block diagram illustrating estimating a carrier frequency error using a pilot subcarrier according to an embodiment of the present invention.

6 is a block diagram illustrating calculating a gain for compensating a signal size according to a change in signal size using a pilot subcarrier according to an exemplary embodiment of the present invention.

7 is a diagram illustrating a configuration of a loop filter to pass before compensating an estimate according to an embodiment of the present invention.

8 is a block diagram of an apparatus for tracking a residual frequency error, a phase error, a time error, and a magnitude change for an OFDM system according to an exemplary embodiment of the present invention.

9 is a BPSK constellation for showing tracking performance according to an embodiment of the present invention, and shows a constellation before tracking.

FIG. 10 is a BPSK constellation for showing tracking performance according to an embodiment of the present invention and is a diagram showing a constellation after tracking.

The present invention relates to an apparatus and method for tracking residual frequency error, phase error, time error, and magnitude change for an OFDM system, and more particularly, in an orthogonal frequency division multiplexing (OFDM) system, The present invention relates to a residual frequency error, phase error, time error, and magnitude change tracking device and method for improving the performance and tracking speed of a phase and time error tracking method used in a system.

According to IEEE 802.11a, which is a representative standard example of conventional OFDM packet communication, frequency and time synchronization is performed using an initial preamble. However, in order to overcome the system performance degradation caused by various factors such as residual frequency error due to initial frequency error estimation error, sampling frequency error and frequency shift, and signal size change in one frame, various synchronization tracking algorithms I need it.

In this OFDM scheme, first, the influence of the carrier frequency error is as follows.

이라는 송신 신호가

의 채널 주파수 응답을 갖는 채널을 통과하고,

만큼의 주파수 오차를 갖고 있을 때,

번째 부반송파의 수신 신호(

)가 다음의 수학식 1처럼 주어진다.In the case of the carrier frequency error, all subcarriers have a constant phase shift, and intercarrier interference (ICI) exists. Also,

Is a transmission signal

Passes through a channel with a channel frequency response of

When we have as much frequency error,

Received signal of the first subcarrier (

Is given by Equation 1 below.

는 부반송파간 간섭으로서, 다음의 수학식 2와 같이 주어진다.Here, N indicates the number of points of the fast Fourier transform (FFT), that is, the total number of subcarriers. Also, the

Is an inter-carrier interference, and is given by Equation 2 below.

Next, when there is a time error, the phase error increases in proportion to the index of the OFDM subcarrier, and the error and the slope are proportional to each other.

)와 오차가 없을 때의 주파수 영역 신호(

) 사이의 관계는 다음 수학식 3과 같다.Therefore, if one FFT section has an error of l = 0 and l ≠ k as a whole, the frequency domain signal having an error (

) And the frequency domain signal (without error)

) Is expressed by Equation 3 below.

이다. 따라서, 같은 시간 오차를 갖고 있더라도 DC 근처에 있는 낮은 주파수 성분들은 그 영향이 적지만, 높은 주파수 성분에서 그 영향이 커진다.here,

to be. Thus, even though they have the same time error, the low frequency components near DC have less effect, but the effect is higher at the high frequency component.

However, if the errors are not tracked and compensated for, there is little effect at the beginning of the frame, but the effects accumulate toward the end, resulting in severe performance degradation.

Therefore, a pilot symbol having a fixed pattern is used to estimate such errors.

As a conventional technique using the pilot symbols, a feedback scheme has been disclosed in which the average of the estimated phases and their slopes are passed through a loop filter and then compensated for the pilot symbols. The prior art using this feedback scheme achieves the desired system performance on the assumption that the residual carrier error is very small and the variation in time error is also very small.

Meanwhile, as a prior art, US Patent No. 6,122,24 (Registration Date: July 25, 199) discloses an invention named "Apparatus and Method for Clock Synchronization in a Multi-Point OFDM / DMT Digital Communications Systems". It is.

Specifically, the above-described invention is a method for estimating and tracking the difference between the frequency of the clock of the transmitter and the frequency of the receiver in the communication system using the OFDM scheme by using the signal information of the subchannel and the adjacent channel where the pilot is located. In order to provide, the receiver uses a method of estimating a frequency error based on a pilot signal, and also searches for a subsymbol containing a pilot signal at a receiver, and finds a phase of the selected pilot signal and an adjacent pilot signal. A method of obtaining a sampling frequency error based on this information by obtaining a difference is disclosed.

On the other hand, M. Luise et al., "Carrier Frequency Acquisition and Tracking for OFDM Systems," IEEE Transactions on Communications, vol. 44, no. 11, pp. 1590-1598, Nov. In 1996, we proposed a method of tracking the frequency error by looking at the phase difference between the demodulated symbol and the received symbol of subcarriers.

Baoguo Yang also describes "Timing recovery for OFDM transmission," IEEE Journal on Selected Areas in Communications, vol. 18, no. 11, pp. 2278-2291, Nov 2000, proposed a method for tracking symbol timing change due to clock frequency error using DLL (Delay-locked Loop) for frequency synchronization of sampling clock.

As described above, an OFDM packet communication system such as a wireless LAN acquires synchronization by using channel estimates and frequency error estimates obtained from a preamble at the beginning of a frame. Causes deterioration. In addition, the influence of the time error that increases or decreases constantly with time caused by the fixed frequency error and the sampling frequency error is estimated using the pilot symbols in the frequency domain and compensates for the effect. In addition, in the above Equations 1 and 2, a small amount of frequency error is represented by a constant phase error, and a time error is represented by a phase error having a slope.

The prior art can be applied in the case where the amount of error is small and there is almost no performance deterioration even if it is compensated by the feedback method. However, due to the influence of radio frequency (RF) circuit and analog circuit in addition to such error in actual situation, There may be a sudden frequency shift and phase shift, and also, there may be a change in signal size due to a gradual increase in the magnitude of the signal at the moment the transceiver amplifier is turned on, resulting in performance degradation of the OFDM system. .

An object of the present invention for solving the above problems, the residual frequency error, phase error, time error and magnitude change for the OFDM system that can improve the performance and tracking speed of the phase and time error tracking scheme used in the conventional OFDM system It is to provide a tracking device and a method thereof.

As a means for achieving the above object, the residual frequency error, phase error, time error and magnitude change tracking device for the OFDM system according to the present invention,

A residual frequency error, phase error, time error, and magnitude change tracking device for an orthogonal frequency division multiplexing (OFDM) system,

A frequency error compensator for compensating in the time domain by adding a tracking carrier error tracking value with an initial carrier frequency error estimate;

A magnitude tracking compensator configured to adjust a magnitude of a signal by multiplying an output value corresponding to a power calculation amount of a received pilot signal by a fast Fourier transform (FFT) input signal;

A channel compensator for outputting a channel-compensated signal by multiplying a conjugate complex number of a frequency channel response of the received pilot signal by the received pilot signal;

A carrier frequency error estimator for estimating a carrier frequency error parameter with the pilot compensated for by the channel and providing a tracking carrier frequency error tracking value;

A time error estimator for estimating a time error parameter with the pilot compensated for by the channel; And

Carrier phase error estimator for estimating a carrier phase error parameter with the channel compensated pilot

Characterized in that it comprises a.

In addition, as another means for achieving the above object, the residual frequency error, phase error, time error and magnitude change tracking method for the OFDM system according to the present invention,

In the residual frequency error, phase error, time error and magnitude change tracking method for an OFDM system,

a) estimating a carrier frequency error using the sum of the phases of the received pilot symbols;

b) estimating a time error by estimating the slope of the phase of the received pilot symbol;

c) if the residual frequency error is large or there is a momentary frequency phase shift, estimating a frequency error using the received pilot symbol and compensating for the entire time domain before the FFT;

d) compensating for the frequency error by adding an initial carrier frequency error to the tracking carrier error tracking value when the frequency error of step c) is large; And

e) estimating a magnitude error according to the magnitude of the signal using the pilot symbol

Characterized in that it comprises a.

Hereinafter, an apparatus and a method for tracking a residual frequency error, a phase error, a time error, and a magnitude change for an OFDM system according to an exemplary embodiment of the present invention will be described in detail.

Embodiments of the present invention provide an apparatus and method for tracking overall synchronization and amplitude by compensating for frequency and phase shifts and magnitude changes in a packet as well as compensation for residual carrier frequency errors and time errors in the prior art. Initiate.

In addition, the embodiment of the present invention is similar to the method used in the existing IEEE 802.11a single-antenna OFDM scheme, but it extends to a multi-antenna system and tracks frequency, phase, and time errors for each antenna. Each parameter is estimated using the pilot subcarriers allocated to each OFDM symbol, and then passed through a loop filter, and then a compensation method is performed in the OFDM symbol. However, in this case, since there may be a performance degradation due to an error between the parameter estimation time and the compensation time, by applying the feed forward method as well as the feedback method, the tracking performance and speed than the conventional method are applied. Will improve.

To this end, an embodiment of the present invention uses a Discrete Fourier Transform to first extract only the pilot subcarriers, and first estimates the tracking parameters using the pilot subcarriers obtained by using the discrete subcarriers, and then applies the data subcarriers of the OFDM symbols. This can be reflected immediately. In addition, in order to effectively cope with the frequency shift that may occur due to the effects of the RF analog circuit, the process of estimating and compensating the frequency shift and tracking the change of the received signal due to the characteristics of the power amplifier are also provided. By adding, the performance of the OFDM system is improved.

1 is a diagram illustrating a frame structure of IEEE 802.11a according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating an OFDM subcarrier arrangement of IEEE 802.11a according to an embodiment of the present invention. As in the example of IEEE 802.11a, it is assumed that the frame according to the embodiment of the present invention has the form as shown in FIG. 1, and the subcarrier arrangement of the OFDM symbol is as shown in FIG.

Referring to FIG. 1, the frame structure of IEEE 802.11a is given signal detection, AGC, interval for diversity selection, coarse frequency offset specification and timing synchronization interval, and channel and fine frequency offset measurement interval. It has a structure in which a guard interval is inserted.

On the other hand, there is a short preamble and a long preamble at the beginning of the frame, where the initial frequency error is estimated and the estimate compensates for the entire frame. In addition, the channel including the initial time error is estimated using the long preamble and compensated in units of OFDM symbols.

However, since there may be a residual error due to an initial estimation error and there may be other changes in time, a fixed pilot symbol is inserted into a fixed subcarrier in an OFDM symbol for tracking it. That is, in the IEEE 802.11a standard, pilots are inserted into -21, -7, 7, 21 subcarriers as shown in FIG.

Meanwhile, a method of estimating each parameter using the pilot symbol will be described below.

3 is a block diagram illustrating estimating a change in carrier phase using a pilot subcarrier according to an embodiment of the present invention.

The carrier frequency error can be estimated using the sum of the phases of the received pilots, as shown in Equation 4 below.

는

번째 OFDM 심벌에 대한 위상 추정치이고,

는

번째 OFDM 심벌에 수신 파일럿 심벌을 나타난다. 또한,

는 약속된 i번째 부반송파에 대한 송신 파일럿 심벌이다. 이때, 상기 P는 모든 파일럿 심벌의 인덱스로 이루어진 집합이다.here,

Is

Is a phase estimate for the first OFDM symbol,

Is

The received pilot symbol is shown in the first OFDM symbol. Also,

Is the transmit pilot symbol for the promised i-th subcarrier. In this case, P is a set consisting of indices of all pilot symbols.

)은 공액복소수 계산부(310)를 거쳐 곱셈기(320)를 통해 상기 수신 파일럿(

)과 곱해지고, 이후, 지연부(340)에서 지연된 양과 가산기(330)에 의해 더해진 후, 위상 추출부(350)에서 위상이 추출되어 반송파 위상 오차 추정치를 출력하게 된다. 즉, 반송파 주파수 오차는 수신 파일럿의 위상(

)의 합을 이용하여 추정하게 된다.Specifically, referring to FIG. 3, a transmission pilot (

) Through the multiplier 320 via the conjugate complex calculator 310 receives the received pilot (

), And then added by the adder 330 and the amount delayed by the delay unit 340, the phase is extracted by the phase extraction unit 350 to output a carrier phase error estimate. That is, the carrier frequency error is the phase of the received pilot (

Estimate using the sum of

4 is a block diagram illustrating estimating a time error using a pilot subcarrier according to an embodiment of the present invention.

번째 OFDM 심벌의 시간오차인

가 된다. Referring to FIG. 4, the time error estimator is configured as shown in Equation 5 below, which is a form of estimating a slope of a phase. That is, the phase difference between the first and third, second and fourth pilots divided by their index difference of 28

Time error of the first OFDM symbol

Becomes

번째 OFDM 심벌의 시간오차인

가 된다. 여기서, 도면부호 411, 413, 421, 423은 공액복소수 계산부, 미설명 도면부호 412, 414, 415, 422, 424, 425는 곱셈기를 나타내며, 도면부호 430은 가산기, 도면부호 440은 위상 추출부를 나타내며, 도면부호 450은 상기 인덱스 차이인 28로 나누기 위한 스케일링부를 나타낸다.Specifically, the first receive and transmit pilot is given by R _{-21, k} and S _-21 , the second receive and transmit pilot is given by R _{-7, k} and S _-7 , and the third receive and transmit pilot is Given R _{21, k} and S ₂₁ , and the fourth receive and transmit pilot is given by R _{7, k} and S ₇ , the phase difference between the first and third, second and fourth pilots is the index difference between them. Divided by 28

Time error of the first OFDM symbol

Becomes Here, reference numerals 411, 413, 421, and 423 denote conjugate conjugate calculation units, unexplained reference numerals 412, 414, 415, 422, 424 and 425 denote multipliers, reference numeral 430 denotes an adder, and reference numeral 440 denotes a phase extraction unit. Reference numeral 450 denotes a scaling unit for dividing by 28, which is the index difference.

On the other hand, there is a frequency error estimation part using a pilot symbol to estimate the case when the residual frequency error in the frame is large, or if there is an instantaneous frequency shift, and to compensate for this in the time domain before the fast Fourier transform (FFT). If such a frequency error is large, compensating it for a simple phase in the frequency domain after the fast Fourier transform (FFT) causes interference between subcarriers, resulting in performance degradation.

Accordingly, the embodiment of the present invention takes the form of compensating the frequency error after adding the portion to compensate the initial carrier frequency error.

5 is a block diagram illustrating estimating a carrier frequency error using a pilot subcarrier according to an embodiment of the present invention.

Referring to FIG. 5, the frequency error estimation method used takes the form of estimating the phase difference between the current OFDM symbol and the previous OFDM symbol and dividing it by 80 (for IEEE 802.11a), which is a sample interval of the OFDM symbol. Is given by Equation 6 below.

가 추정된 주파수 오차를 나타낸다. here

Denotes the estimated frequency error.

In detail, the reception pilot Ri _{and K pass} through the first delay unit 510, the conjugate complex calculator 520, and the multiplier 530, and then are added to the second delay unit 55 and the adder 540. After the phase is extracted by the phase extraction unit 56, the scaling unit 570 divides the phase by 80, the sample interval of the OFDM symbol, and then outputs a carrier frequency error estimate.

Finally, a gain estimation method for signal magnitude compensation is given as shown in FIG. 6.

6 is a block diagram illustrating calculating a gain for compensating a signal size according to a change in signal size using a pilot subcarrier according to an exemplary embodiment of the present invention.

Referring to FIG. 6, a signal size p_pwrk is calculated using the pilot of each OFDM symbol as shown in Equation 7 below.

At this time, prior to the gain calculation in the pilot power calculation unit 610, the reference power calculation unit 620 first determines the reference signal size (ref_pwr), a frame structure such as IEEE 802.11a corresponds to the position of the pilot in the long preamble The signal magnitude is determined in the manner as shown in Equation 7 with four symbols.

In addition, as shown in Equation 8 below, the error calculation unit 630 obtains a magnitude error of the signal, that is, a difference between the reference power and the received pilot power (ref_pwr-p_pwr), and compares the error with the reference power. Using the ratio, the signal magnitude compensation gain calculator 640 obtains a compensation gain value comp_gain of the signal magnitude and uses it as a loop input.

However, if the phase, time, and magnitude error estimates calculated immediately as shown in Figs. 4 to 6 are immediately compensated, the second loop can be appropriately adjusted while minimizing the effects on the estimation error. Pass through the filter, the structure is shown in FIG. Here, in the case of the carrier frequency error, as can be seen in the overall structure of FIG. 8 to be described later, the degree of compensation can be determined simply by using a first-order loop.

7 is a diagram illustrating a configuration of a loop filter to pass before compensating an estimate according to an embodiment of the present invention.

Referring to FIG. 7, a structure of a loop filter to pass before compensating an estimate according to an embodiment of the present invention is generally known and has two loop coefficients. The first loop coefficient is referred to as proportional gain. The second loop coefficient is referred to as an integral gain. Here, the first loop coefficient is multiplied by the loop input in the first multiplier 710, the second loop coefficient is multiplied by the loop input in the second multiplier 720, and then the first delay unit 740 and the first adder. After the addition by 730, the output of the first multiplier 710 and the output of the first adder 730 are added by the second adder 750, and then the output of the second adder 750 is The loop output is performed after being added with the second delay unit 770 and the third adder 770.

8 is a block diagram illustrating a residual frequency error, a phase error, a time error, and a size change tracking device for an OFDM system according to an exemplary embodiment of the present invention.

Referring to FIG. 8, the apparatus for tracking residual frequency error, phase error, time error, and magnitude change for an OFDM system according to an embodiment of the present invention has the overall structure as shown in FIG. 8. Will have

First, the frequency error compensator 801 has a sum 803 of an initial carrier frequency error estimate 802 and a tracking carrier error tracking value, and serves to compensate for a carrier error in a received signal. That is, the frequency error compensator 801 compensates in the time domain by adding the tracking carrier frequency error tracking value to the initial carrier frequency error estimate.

In addition, the FFT unit 804 converts a received signal in the time domain into a frequency domain signal. The frequency error compensator 801 and the FFT unit 804 are blocks for receiving an OFDM signal.

Next, the magnitude tracking compensation unit 805 passes the output of the pilot power calculation unit 907 through the loop filter 808 and then multiplies the output value by the input signal to adjust the magnitude of the signal. The size-compensated signal is output to the pilot subcarrier extractor 806 and the data subcarrier extractor 809.

The pilot data extractor 806 selects and outputs only pilot subcarriers among all subcarriers, and the data subcarrier extractor 809 selects and outputs only data subcarriers.

)를 수신 파일럿 신호(

)에 곱하여 출력하는 역할을 한다.In addition, the channel compensator 812 is a conjugate complex number of the frequency channel response of the pilot signal as shown in Equation 9 below.

) Receives a pilot signal (

Multiply by)

The carrier frequency error estimator 825, the carrier phase error estimator 814, and the time error estimator 815 estimate the respective parameters with the pilot compensated for by the channel. Here, the carrier phase error estimator 814 and the time error estimator 815 through which each parameter is estimated pass through loop filters 816 and 818.

Further, the output of the carrier frequency error estimator 825 is multiplied by a carrier frequency loop gain 826 and added to the delay unit 829, and then the carrier frequency is added together with an initial carrier frequency error estimate to give the frequency error. The compensation unit 801 is compensated.

In addition, the time error is multiplied by the multiplier 820 according to the characteristics of the pilot subcarrier is compensated by the phase compensation unit 813 of the pilot and data subcarriers.

Finally, the carrier phase error is compensated by adding the loop filter 816 output to the pilot subcarrier and adding the current phase estimate and the loop filter output to the data subcarrier. That is, when tracking and compensating the carrier phase, the pilot compensates only the loop filter output, and the data subcarrier compensates by adding the current estimate to the filter output.

In the case of such a phase change, it is estimated from the current symbol and has a form of compensating immediately from the symbol. That is, it has a feedforward property.

However, in order to have a feedforward property, it may be necessary to first extract the pilot symbols by having a Fourier transform unit for pilot symbols only. In this case, although the structure of FIG. 8 may be slightly changed, detailed description thereof will be omitted.

Therefore, the embodiment of the present invention has a form of tracking all errors such as frequency, phase, time, and magnitude through the above-described process.

Meanwhile, FIG. 9 is a BPSK constellation for showing tracking performance according to an embodiment of the present invention, and shows a constellation before tracking, and FIG. 10 is a BPSK constellation for showing tracking performance according to an embodiment of the present invention. The figure shows the constellation after tracking.

If such a circuit is provided for each reception path, the circuit can be applied to a multiple reception antenna system. When only the initial synchronization is used without the above tracking process, the constellation points of the BPSK are distorted as shown in FIG. 9, but the above-described tracking process enables restoration to a normal reception point as shown in FIG. 10. do.

While the invention has been shown and described in connection with specific embodiments thereof, it will be appreciated that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

According to the present invention, performance degradation due to these errors can be prevented by tracking various synchronization tracking and signal size changes that may occur due to an initial synchronization error and influence of radio frequency or analog circuit in an OFDM system in a wireless packet communication form. . In addition, according to the present invention, performance can be slightly degraded, but the system implementation cost can be reduced because relatively low radio frequency and analog devices can be compensated for.

Claims (11)

A residual frequency error, phase error, time error, and magnitude change tracking device for an orthogonal frequency division multiplexing (OFDM) system, A frequency error compensator for compensating in the time domain by adding a tracking carrier error tracking value with an initial carrier frequency error estimate; A magnitude tracking compensator configured to adjust a magnitude of a signal by multiplying an output value corresponding to a power calculation amount of a received pilot signal by a fast Fourier transform (FFT) input signal; A channel compensator for outputting a channel-compensated signal by multiplying a conjugate complex number of a frequency channel response of the received pilot signal by the received pilot signal; A carrier frequency error estimator for estimating a carrier frequency error parameter with the pilot compensated for by the channel and providing a tracking carrier frequency error tracking value; A time error estimator for estimating a time error parameter with the pilot compensated for by the channel; And Carrier phase error estimator for estimating a carrier phase error parameter with the channel compensated pilot Frequency error, phase error, time error and magnitude change tracking device comprising a. The method of claim 1, The carrier phase error estimator, the time error estimator, and the magnitude tracking compensator each include a second loop filter so as to appropriately adjust the compensation speed while minimizing the influence on the estimation error. Time error and size change tracking device. The method of claim 2, When the carrier phase error estimator tracks and compensates for the carrier phase, a pilot compensates only the loop filter output, and a data subcarrier compensates by adding a current estimate to the loop filter output. Time error and size change tracking device. The method of claim 2, The carrier phase error estimator estimates from the current symbol and has a feedforward form that compensates directly from the symbol. The method of claim 4, wherein The carrier phase error estimating unit includes a Fourier transform unit for pilot symbols only in order to have the feedforward shape, and extracts pilot symbols preferentially, wherein the frequency error, phase error, time error, and magnitude change tracking device. The method of claim 1, And the time error estimator is multiplied by a pilot subcarrier to compensate for the time error in the phase compensator of the pilot and data subcarriers. The method of claim 1, And the carrier frequency error estimator simply determines a degree of compensation using a first-order loop. The method of claim 7, wherein The output of the carrier frequency error estimator is multiplied by a carrier frequency loop gain, and then the carrier frequency is added together with the initial carrier frequency error estimate to compensate for the frequency error compensator. Error and size change tracking device. In the residual frequency error, phase error, time error and magnitude change tracking method for an OFDM system, a) estimating a carrier frequency error using the sum of the phases of the received pilot symbols; b) estimating a time error by estimating the slope of the phase of the received pilot symbol; c) if the residual frequency error is large or there is a momentary frequency phase shift, estimating a frequency error using the received pilot symbol and compensating for the entire time domain before the FFT; d) compensating for the frequency error by adding an initial carrier frequency error to the tracking carrier error tracking value when the frequency error of step c) is large; And e) estimating a magnitude error according to the magnitude of the signal using the pilot symbol Frequency error, phase error, time error and magnitude change tracking method comprising a. The method of claim 9, In the case of the carrier phase error, time error, and magnitude error, the frequency error, phase error, time error, and magnitude change are respectively passed through a second loop filter so as to properly adjust the compensation speed while minimizing the influence on the estimation error. Tracking method. The method of claim 9, In the step e), the power difference between the reference power and the received pilot symbol, which is a magnitude error according to the signal size, is calculated using the pilot symbol, and the compensation gain of the signal size is calculated using the ratio between the magnitude error and the reference power. A method for tracking frequency error, phase error, time error, and magnitude change, comprising determining a value.

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