WO2010134447A1

WO2010134447A1 - Offset compensating circuit and offset compensating method

Info

Publication number: WO2010134447A1
Application number: PCT/JP2010/057951
Authority: WO
Inventors: 祐司木村; 康之介山元
Original assignee: ミツミ電機株式会社
Priority date: 2009-05-19
Filing date: 2010-05-11
Publication date: 2010-11-25
Also published as: JP2010272901A; JP5387126B2

Abstract

An offset compensating circuit comprises: a DC offset estimating/compensating means that estimates the value of a DC offset included in an OFDM signal to compensate the DC offset; a frequency offset estimating/compensating means that estimates the value of a frequency offset included in the DC-offset compensated signal to compensate the frequency offset; an excessively compensated component calculating means that uses both the DC offset value estimated by the DC offset estimating/compensating means after the compensation by the frequency offset estimating/compensating means and the frequency offset value estimated by the frequency offset estimating/compensating means to calculate a component of a subcarrier excessively compensated in the DC offset compensating means; and an excessively compensated component removing means that removes, from the DC offset value estimated by the DC offset estimating/compensating means, the excessively compensated component calculated by the excessively compensated component calculating means to use the resultant in the DC offset compensation by the DC offset estimating/compensating means. Thus, the offset compensating circuit compensates the frequency offset of the signal as DC-offset compensated after the removal of the excessively compensated component and outputs the resultant.

Description

Offset compensation circuit and offset compensation method

The present invention relates to an offset compensation circuit and an offset compensation method for compensating an offset of an OFDM (Orthogonal Frequency Division Multiplexing) signal.

The OFDM scheme has a high transmission rate within a limited band and is resistant to multipath, and has recently been used for various wireless communications. For example, in the wireless LAN standard IEEE802.11a, g, an OFDM wireless signal is used.

Fig. 10 shows the OFDM baseband signal spectrum without DC offset and frequency offset. If the OFDM signal has no DC offset and no frequency offset, the subcarriers do not interfere with each other. Further, the center frequency of the DC subcarrier is 0 Hz.

FIG. 11 shows an OFDM baseband signal spectrum including a DC offset and a frequency offset. Since the presence of the DC offset and the frequency offset affects the demodulation process, it is necessary to compensate for the DC offset and the frequency offset.

Here, the DC offset and frequency offset of the OFDM signal will be described. The direct conversion OFDM receiver directly demodulates the RF (high frequency) signal received by the antenna to extract the I (in-phase) and Q (quadrature) components of the OFDM baseband signal, and then performs OFDM demodulation. Do.

However, in this direct conversion method, the frequency of the RF signal and the local oscillation signal are the same, but the level of the RF signal is not sufficient and the S / N is not good compared to the local oscillation signal. A DC offset occurs due to the wraparound of the component to the RF signal. However, in the OFDM system, the frequency intervals of all subcarriers are set so as to satisfy orthogonality, and the DC offset does not affect the demodulation process if it is originally. However, the oscillation frequency of the local oscillator does not completely coincide with the frequency of the RF signal and is slightly shifted, that is, it has a frequency offset. This frequency shift itself is a part of the frequency correction processing in the subsequent stage. However, if there is the above-described DC offset, the frequency error estimate is estimated larger or less than the actual one.

As a conventional offset compensation method for an OFDM signal, a first method (see, for example, Patent Document 1) that first compensates for a DC offset and then compensates for a frequency offset, and first compensates for a frequency offset and then compensates for a DC offset. Second method for compensation (see, for example, Patent Document 2), frequency offset candidate values are obtained by singular value decomposition of a system matrix, optimal frequency offset candidate values are searched, and optimal frequency offset candidates There is a third method for estimating the DC offset from the value (see, for example, Patent Document 3).

FIG. 12 shows a flowchart of an example of a conventional OFDM signal offset compensation method (first method). In FIG. 12, in step S1, a DC offset is estimated from the preamble of the OFDM signal, and the estimated DC offset is compensated. Thereafter, in step S2, the frequency offset is estimated, and the estimated frequency offset is compensated.

FIG. 13 is a flowchart showing an example of a conventional OFDM signal offset compensation method (second method). In FIG. 13, in step S3, the frequency offset is estimated from the preamble of the OFDM signal, and the preamble frequency offset is compensated. Thereafter, in step S4, a DC offset is estimated from the preamble compensated for the frequency offset, and in step S5, the DC offset is compensated for the OFDM signal data and the frequency offset is compensated.

FIG. 14 shows a flowchart of an example of a conventional OFDM signal offset compensation method (third method). In FIG. 14, a frequency offset candidate value is obtained by singular value decomposition of the system matrix, and the optimum frequency offset candidate value is searched by multiplying the received signal by the frequency offset candidate value in step S6. A DC offset is estimated from a candidate value of a large frequency offset. Next, the DC offset estimated in step S7 is compensated, and the estimated frequency offset is compensated.

Japanese Patent Laid-Open No. 2003-32216 JP 2004-304507 A JP 2008-135888 A

In the OFDM baseband signal spectrum of FIG. 11, the value observed as the DC offset value at the center frequency of 0 Hz includes the adjacent subcarrier component D ′. FIG. 15 shows an extracted subcarrier component D ′ adjacent thereto.

In the first method shown in FIG. 12, the component D ′ of the adjacent subcarrier is compensated in step S1, so that interference with the adjacent subcarrier is caused as shown in FIG. There was a problem of deterioration.

In the second method shown in FIG. 13, if the frequency offset is completely compensated in step S3, the DC offset can be accurately estimated in step S4. However, when the OFDM signal includes a DC offset and a frequency offset, if the frequency offset is estimated first, an error occurs in the estimated value of the frequency offset due to the influence of the DC offset. There was a problem that the reception performance deteriorated due to the error of the estimated value.

In the third method shown in FIG. 14, since the system matrix is subjected to singular value decomposition to obtain frequency offset candidate values, the circuit scale becomes large and the calculation takes time. Furthermore, there is a problem in that it takes a calculation time to search for an optimal frequency offset candidate value by multiplying the received signal by the frequency offset candidate value in step S6, and real-time offset compensation operation cannot be performed.

The present invention has been made in view of the above problems, and provides an offset compensation circuit and an offset compensation method for accurately estimating and compensating for a DC offset and a frequency offset at high speed without increasing the circuit scale. With the goal.

In order to solve the above problems, an offset compensation circuit according to the present invention is an offset compensation circuit that estimates and compensates for a DC offset and a frequency offset of an OFDM signal, and is included in a signal obtained by orthogonally demodulating the OFDM signal. DC offset estimation compensation means for estimating and compensating for an offset value, frequency offset estimation compensation means for estimating and compensating for a frequency offset value included in the signal compensated by the DC offset estimation compensation means, and the frequency offset estimation compensation Using the DC offset value estimated by the DC offset estimation compensation means and the frequency offset value estimated by the frequency offset estimation compensation means, the sub-carrier overcompensation component in the DC offset compensation means Overcompensation component calculating means for calculating An overcompensation component removing unit used for DC offset compensation in the DC offset estimation compensation unit by removing the overcompensation component calculated by the overcompensation component calculation unit from the DC offset value estimated by the offset estimation compensation unit; After removing the overcompensation component, the frequency offset estimation compensation means compensates the frequency offset for the signal compensated for the DC offset by the DC offset estimation compensation means, and outputs the signal.

In order to solve the above-described problem, an offset compensation method according to the present invention is an offset compensation method for estimating and compensating for a DC offset and a frequency offset of an OFDM signal, and is included in a signal obtained by orthogonally demodulating the OFDM signal. A first step for estimating and compensating for an offset value, a second step for estimating and compensating for a frequency offset value included in the signal compensated for in the first step, and a frequency offset compensated for in the second step The third step of estimating the DC offset value from the signal, the DC offset value estimated in the third step, and the frequency offset value estimated in the second step are used. A compensation component is calculated, and the overcompensation component is calculated from the DC offset value estimated in the first step. A fourth step of removing the overcompensation component in the fourth step, a fifth step of compensating the signal obtained by orthogonally demodulating the OFDM signal with the DC offset value, and a signal compensated in the fifth step. And a sixth step of compensating and outputting the included frequency offset value.

According to the offset compensation circuit and the offset compensation method according to the present invention, the DC offset and the frequency offset can be compensated at high speed and with high accuracy without increasing the circuit scale.

It is a block block diagram of one Embodiment of an OFDM receiver. It is a block block diagram of one Embodiment of an offset compensation circuit. It is a block diagram of an example of an OFDM radio frame. It is a wave form diagram of a symbol. It is a wave form diagram of a symbol. It is a figure which shows an OFDM baseband signal spectrum. It is a waveform diagram of a symbol for explaining the present invention. It is a waveform diagram of a symbol for explaining the present invention. It is a waveform diagram of a symbol for explaining the present invention. 6 is a flowchart of an embodiment of an offset compensation circuit operation. It is a flowchart in case offset compensation is performed in multiple times. It is a figure which shows a simulation result. It is a figure which shows the OFDM baseband signal spectrum without DC offset and frequency offset. It is a figure which shows the OFDM baseband signal spectrum containing DC offset and frequency offset. 5 is a flowchart of a conventional OFDM signal offset compensation method. 5 is a flowchart of a conventional OFDM signal offset compensation method. 5 is a flowchart of a conventional OFDM signal offset compensation method. It is a figure which shows the OFDM baseband signal spectrum for demonstrating the interference with respect to an adjacent subcarrier.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a block diagram of an embodiment of an OFDM receiver to which an offset compensation circuit of the present invention is applied. In FIG. 1, an RF signal received by an antenna 10 is amplified by a low noise amplifier (LNA) 11 and then supplied to

mixers

12 and 13, respectively.

The local oscillation signal output from the local oscillator 14 is directly supplied to the mixer 12, and is phase-shifted by π / 2 by the phase shifter 15 and supplied to the mixer 13. The

mixers

12 and 13, the local oscillator 14, and the phase shifter 15 constitute a direct conversion type quadrature demodulator. The mixer 12 multiplies the RF signal and the phase-shifted local oscillation signal to output an I (in-phase) signal of the OFDM baseband signal. The mixer 13 multiplies the RF signal and the local oscillation signal and outputs a Q (orthogonal) signal of the OFDM baseband signal.

The I signal output from the mixer 12 is amplified by an AGC (automatic gain control) amplifier 17, then unnecessary high frequency components are removed by a low-pass filter 18, digitized by an A / D converter 19, and sent to a digital compensation / demodulation unit 20. Supplied. The Q signal output from the mixer 13 is amplified by an AGC (automatic gain control) amplifier 21, then unnecessary high frequency components are removed by a low-pass filter 22, and digitized by an A / D converter 23 to be digitally compensated / demodulated. 20 is supplied.

The digital compensation / demodulation unit 20 estimates and compensates the DC offset and the frequency offset from the I and Q signals, and then performs demodulation. That is, offset compensation is executed in the digital compensation / demodulation unit 20.

<Offset compensation circuit>
FIG. 2 shows a block diagram of an embodiment of the offset compensation circuit of the present invention. In FIG. 2, the I and Q signals output from the A /

D converters

19 and 23 are supplied to the multiplier 31 after passing through various blocks. When a frequency offset value Δf is supplied from a frequency offset estimation unit 38, which will be described later, the multiplier 31 performs carrier recovery from the frequency offset Δf, performs frequency offset compensation by performing complex multiplication on each of the I and Q signals, and outputs the result. To do. The I and Q signals output from the multiplier 31 are supplied to a subtracter 32 and a DC offset estimation unit 33.

Here, FIG. 3 shows a configuration diagram of an embodiment of an OFDM radio frame in the wireless LAN standard IEEE802.11a. The OFDM radio frame has a PLCP preamble, a SIGNAL that is an OFDM header, and data in the data area. The PLCP preamble has a short training symbol that is a fixed pattern using short symbols and a long training symbol that is a fixed pattern using long symbols. The short training symbol has symbols S ₁ to S ₁₀ . The short training symbol and the long training symbol are used for synchronization, AGC, and offset estimation.

In this embodiment, the period of one symbol is sampled n times (for example, n = 16), and the I and Q signals are supplied from the A /

D converters

19 and 23, respectively.

The DC offset estimator 33 obtains a time average value of n samples of one symbol period for each of the short training symbols (eg, symbol S ₇ ) of the I and Q signals, and uses this time average value to estimate the DC offset of each of the I and Q signals. Value.

Specifically, assuming that a received signal (training symbol) without a DC offset is s (t) and a DC offset is D, a received signal r (t) having a DC offset is expressed as follows.

r (t) = s (t) + D
Here, since s (t), which is a training symbol, is a periodic signal having no DC component, the average value in one symbol section is zero. Therefore, if r (t) is averaged over one symbol interval (N samples), the DC offset can be obtained by the following equation.

When there is no DC offset and no frequency offset, the I and Q signals of each symbol have a time average value of 1 symbol period as shown in FIG. 4A. However, when there is a DC offset and a frequency offset, the I and Q signals of each symbol have values other than 0 for the time average value of one symbol period. The DC offset estimation unit 33 holds the DC offset value D ₀ estimated for each of the I and Q signals and supplies it to the selector 34 and the subtracter 35.

Incidentally, the control unit 40 the timing of the symbol _{S 7} in operation stable time (e.g. short training symbols for

AGC amplifier

17, 21 and other circuitry from the start of reception of the OFDM radio frame, Note that, for example, in the case of such _{S 5} and _{S 6} The DC offset estimation unit 33 is instructed to start the DC offset estimation operation. Further, the control unit 40 causes the selector 34 to select the DC offset value D ₀ output from the DC offset estimation unit 33 and supplies it to the subtracter 32.

The subtracter 32 supplies I, to the multiplier 37 and the frequency offset estimator 38 subtracts the DC offset value D ₀ for each Q signal output of the multiplier 31.

The frequency offset estimator 38 estimates the frequency offset using the 2n-sample I and Q signals that are the next two symbols (for example, the symbols S ₈ and S ₉ ) after the symbol (for example, the symbol S ₇ ) used for the DC offset estimation. Do. The frequency offset estimator 38 performs a complex correlation operation with the I and Q signals of n samples (one symbol period) before, and calculates a phase change amount with the I and Q signals n samples before, thereby calculating the frequency. Estimate the offset.

Specifically, assuming that a received signal (training symbol) without a frequency offset is s (t), the training symbol is a periodic signal, and the same data is repeated for each symbol interval Δt, and therefore is expressed by the following equation.

s (t) = s (t−Δt)
A signal r (t) having a frequency offset Δf is expressed by the following equation.

r (t) = s (t) exp (j2πΔft)
Since r (t) is a periodic signal, the following equation can be obtained by taking the autocorrelation for one symbol period. Note that s ^* represents a complex number conjugate with s.

r (t) s ^* (t−Δt) = | s (t) | ² exp (j2πΔfΔt)
The phase Δω in this equation is expressed by the following equation.

Δω = arg | s (t) | ² exp (j2πΔfΔt)
Therefore, the frequency offset Δf can be expressed as follows.

Δf = Δω / 2πΔt
If there is a frequency offset, the I and Q signals of each symbol have an apparent one symbol period as shown in FIG. 4B, and the correlation between the current sample and the sample one symbol period before becomes low. The frequency offset estimation unit 38 estimates the frequency offset value Δf and supplies it to the overcompensation component calculation unit 36 and the switch 39.

The control unit 40 switches the switch 39 so as to supply the multiplier 31 with the carrier regenerated from the frequency offset value Δf at the next symbol (for example, the symbol S ₁₀ ) for which the frequency offset has been estimated. As a result, the multiplier 31 outputs I and Q signals compensated for the frequency offset.

Here, as described above, in the OFDM signal including the DC offset and the frequency offset, as shown in FIGS. 11 and 15, the value D ₀ observed as the DC offset value at the center frequency 0 Hz is adjacent to the value D _0. A subcarrier component D ′ is also included. When the true value of the DC offset is D, the following relationship (1) is established.

_{D 0 = D + D '...} (1)
Therefore, as shown in FIG. 5, the OFDM baseband signal spectrum compensated for the DC offset and the frequency offset is DC offset compensated up to the adjacent subcarrier component D ′, and the adjacent subcarrier is interfered (overcompensated). It is in the state.

The DC offset estimator 33 obtains a time average value of n samples of one symbol period in the next symbol (for example, symbol S ₁₀ ) subjected to frequency offset estimation, and uses this time average value as the DC offset of each of the I and Q signals. The estimated value is d ′. As shown in FIG. 5, the DC offset estimated value d ′ in this case is a component caused by a component D ′ that is regarded as an offset of an adjacent subcarrier and is overcompensated. The control unit 40 controls the overcompensation component calculation unit 36 to supply the DC offset estimation values d ′ of the I and Q signals output from the DC offset estimation unit 33.

The overcompensation component calculation unit 36 calculates an overcompensation component D ′, which is a component of adjacent subcarriers, using the following equation (2) based on the DC offset estimation value d ′ of each of the I and Q signals. Here, f ₀ is the subcarrier spacing.

Here, as shown in FIG. 6A, a rectangular wave having a constant complex number A from time 0 to time T is expressed by the following equation (3).

The frequency spectrum obtained by Fourier transforming the rectangular wave represented by the above equation (3) can be represented by the following equation (4). Here, when T = 1 / _{f 0,} the frequency spectrum will become as shown in Figure 6B.

On the other hand, the complex DC offset added to the OFDM signal can also be considered in the same manner as the rectangular wave represented by the above equation (3). Therefore, the frequency spectrum of the DC offset is as shown in FIG. 6C.

Next, the above equation (4) is replaced with a DC offset calculation equation. Therefore, when T = 1 / f ₀ , AT = D ′, and f = Δf are substituted into the above equation (4), the following equation (5) is obtained.

When the above equation (5) is solved for D ′, the above equation (2) is obtained. The condition under which D ′ can be obtained using equation (2) is the case where d ′ is other than 0 because D ′ is calculated using the ratio to d ′. When d ′ is 0, the frequency offset Δf is Δf = ± f ₀ , ± 2f ₀ , ± 3f ₀ ,..., and such Δf = ± f ₀ , ± 2f ₀ , ± 3f _{In the} case of ₀ ,..., It is outside the range of the frequency offset that requires compensation in the wireless LAN standard IEEE802.11a, g.

Returning to FIG. 2, the overcompensation component calculation unit 36 supplies the overcompensation component D ′ of each of the I and Q signals to the subtractor 35. The subtracter 35 subtracts the overcompensation component D ′ from the DC offset value D ₀ held and output by the DC offset estimator 33 and supplies it to the selector 34. Selector 34 under the control of the controller 40, for example, supplied to the subtracter 32 selects the output of the subtracter 35 is at the reception timing of the symbol S ₁₀ and later. The switch 39 supplies the carrier 37 reproduced from the frequency offset value Δf to the multiplier 37 under the control of the control unit 40.

Thereby, the subtractor 32 subtracts the true value D of the DC offset from each of the I and Q signals that have passed through the multiplier 31, performs DC offset compensation, and supplies the result to the multiplier 37 and the frequency offset estimation unit 38. This DC offset compensation is not affected by the overcompensation component D '. The multiplier 37 performs frequency offset compensation by performing complex multiplication of the carrier reproduced from the frequency offset Δf on each of the I and Q signals, and outputs the result.

FIG. 7 is a flowchart for explaining the operation of the offset compensation circuit according to the embodiment of the present invention. In the flowchart of FIG. 7, DC offset estimator 33 in step S11, it estimates a DC offset value _{D 0.} In step S12, the subtractor 32 performs DC offset compensation of the I and Q signals.

Subsequently, in step S13, the frequency offset estimation unit 38 estimates the frequency offset value Δf. In step S14, the multiplier 31 performs frequency offset compensation of the I and Q signals.

Thereafter, in step S15, the DC offset estimation unit 33 estimates the DC offset estimated value d ′. In step S <b> 16, the overcompensation component calculation unit 36 calculates the overcompensation component D ′ using the DC offset estimation value d ′ supplied from the DC offset estimation unit 33. The subtractor 35 subtracts the calculated overcompensation component D ′ from the DC offset value D ₀ to obtain the DC offset D, and supplies the DC offset D to the subtractor 32.

Thereafter, in step S17, the subtractor 32 performs DC offset compensation of the I and Q signals using the DC offset D. In step S18, the multiplier 31 performs frequency offset compensation of the I and Q signals and outputs the result. After step S18 is executed, demodulation of the OFDM received signal is started.

By the way, after executing step S12 described above, steps S13 to S17 may be executed a plurality of times, then step S18 may be executed, and then demodulation of the OFDM received signal may be started. FIG. 8 shows a flowchart in this case. In the flowchart of FIG. 8, after executing step S12, steps S23 to S27 corresponding to steps S13 to S17 are repeated m times (m is an integer). That is, in step S23, the frequency offset estimation unit 38 estimates the frequency offset value Δf. In step S24, the multiplier 31 performs frequency offset compensation for the I and Q signals.

Thereafter, in step S25, the DC offset estimation unit 33 estimates the DC offset estimated value d ′. In step S <b> 26, the overcompensation component calculation unit 36 calculates the overcompensation component D ′ using the DC offset estimation value d ′ supplied from the DC offset estimation unit 33. The subtractor 35 subtracts the overcompensation component D ′ from the DC offset value D ₀ to obtain the DC offset D, and supplies the DC offset D to the subtractor 32. Thereafter, in step S27, the subtractor 32 performs DC offset compensation of the I and Q signals using the DC offset D. Finally, in step S28 corresponding to step S18, the multiplier 31 performs frequency offset compensation of the I and Q signals and outputs the result. After executing this step S28, demodulation of the OFDM received signal is started.

Thus, by executing a part of the processing in FIG. 7 a plurality of times as shown in FIG. 8, the offset estimation accuracy can be further improved.

FIG. 9 shows an EVM (Error Vector Magnitude) with respect to the frequency offset value when the DC offset and the frequency offset are compensated. This is a simulation result based on the wireless LAN standard IEEE802.11a. Here, the solid line indicates the result of compensation according to the prior art, and the one-dot chain line with a black circle indicates the result of compensation according to the present embodiment.

In the wireless LAN standard IEEE802.11a, the maximum frequency used is 5.805 GHz ± 232.2 kHz. As shown in FIG. 9, at a frequency offset of −232.2 kHz, the compensation result according to the present embodiment shows an improvement of about 25 dB relative to the compensation result according to the prior art. It turns out that it is suppressing.

In this embodiment, a time average is used for estimating the DC offset, a complex correlation operation is used for estimating the frequency offset, and the calculation of the above equation (2) is added, so that the DC offset and the frequency offset with high accuracy can be obtained. Compensation can be performed. Further, since the multiplier 31 and the overcompensation component calculator 36 may be added as compared with the conventional example (Patent Document 1), it is not necessary to add a particularly large block. For this reason, an increase in circuit scale can be suppressed. The time required for the estimation of the DC offset, the estimation of the frequency offset, and the calculation of the equation (2) is four symbol periods of the short training symbol, and the DC offset and the frequency offset can be compensated at high speed.

This embodiment has been described by taking the wireless LAN standard IEEE 802.11a, g as an example, but is not limited to the above embodiment. The present invention can be applied to the OFDM system adopted in the entire wireless LAN standard IEEE 802.11. Further, the present invention can be applied not only to a wireless LAN but also to general wireless communication using OFDM.

This international application claims priority based on Japanese Patent Application No. 2009-120484 filed on May 19, 2009. The entire contents of Japanese Patent Application No. 2009-120383 are incorporated herein by reference. Incorporate.

Claims

An offset compensation circuit that estimates and compensates for a DC offset and a frequency offset of an OFDM signal,
DC offset estimation compensation means for estimating and compensating for a DC offset value included in a signal obtained by orthogonal demodulation of the OFDM signal;
Frequency offset estimation compensation means for estimating and compensating for a frequency offset value included in the signal compensated by the DC offset estimation compensation means;
After the compensation by the frequency offset estimation compensation unit, the DC offset value estimated by the DC offset estimation compensation unit and the frequency offset value estimated by the frequency offset estimation compensation unit are used, and An overcompensation component calculating means for calculating an overcompensation component of the carrier;
An overcompensation component removing unit used for DC offset compensation in the DC offset estimation compensation unit by removing the overcompensation component calculated by the overcompensation component calculation unit from the DC offset value estimated by the DC offset estimation compensation unit;
Have
An offset compensation circuit, wherein after the overcompensation component is removed, the frequency offset is compensated by the frequency offset estimation compensation means for the signal compensated for the DC offset by the DC offset estimation compensation means.
The offset compensation circuit according to claim 1.
The overcompensation component calculation means sets the frequency offset value as Δf, the DC offset estimation value as d ′, the overcompensation component as D ′, and the subcarrier interval as f 0.

The overcompensation component is calculated according to the offset compensation circuit.
An offset compensation method for estimating and compensating for a DC offset and a frequency offset of an OFDM signal,
A first step of estimating and compensating for a DC offset value included in a signal obtained by orthogonal demodulation of the OFDM signal;
A second step of estimating and compensating for a frequency offset value included in the signal compensated in the first step;
A third step of estimating a DC offset value from the signal compensated for the frequency offset in the second step;
Using the DC offset value estimated in the third step and the frequency offset value estimated in the second step, a subcarrier overcompensation component in the first step is calculated, and is estimated in the first step. A fourth step of removing the overcompensation component from the obtained DC offset value;
A fifth step of compensating a signal obtained by orthogonally demodulating the OFDM signal with a DC offset value obtained by removing the overcompensation component in the fourth step;
A sixth step of compensating and outputting a frequency offset value included in the signal compensated in the fifth step;
An offset compensation method comprising:
The offset compensation method according to claim 3, wherein
An offset compensation method, wherein the second to fifth steps are repeated a plurality of times.