JP2001292123A - Demodulation device and demodulation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the carrier frequency error of an OFDM signal in short time and to shorten time, until a demodulation operation is stabilized from the start of an operation. SOLUTION: A difference frequency between the frequency of an IF signal and that of a carrier signal is preset in NCO 14 as an initial oscillation frequency. In NCO 14, an oscillation frequency is adjusted, so that the shift quantity of the center frequency of the OFDM signal after the carrier frequency error is corrected becomes zero. Since the frequency assumed as the carrier frequency error is previously outputted from NCO 14, when a reception operation is started, the pull-in operation of carrier frequency synchronism is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to orthogonal frequency division multiplexing transmission (OFDM).
The present invention relates to a demodulation device and a demodulation method applied to digital broadcasting by a multiplexing method.

[0002]

2. Description of the Related Art In recent years, as a system for transmitting digital signals, an orthogonal frequency division multiplexing system (OFDM) has been proposed.
A modulation method called "requency division multiplexing" has been proposed. In this OFDM system, a number of orthogonal subcarriers (subcarriers) are provided in a transmission band, data is allocated to the amplitude and phase of each subcarrier, and PSK (Phase Shift Keying) and QAM (Quadraturtu
This is a method of performing digital modulation by re-amplitude modulation.

In this OFDM system, since the transmission band is divided by a large number of subcarriers, the band per subcarrier wave becomes narrow and the modulation speed becomes slow, but the total transmission speed is different from that of the conventional modulation system. There is no feature. Further, the OFDM scheme has a feature that the symbol rate is reduced because a large number of subcarriers are transmitted in parallel. Therefore, in the OFDM system, the time length of the multipath relative to the time length of the symbol can be shortened, and multipath interference is reduced. Further, in the OFDM method, data is allocated to a plurality of subcarriers, so that IFFT (Inverse Fast Fourier Transform) that performs inverse Fourier transform during modulation is performed.
An er Transform operation circuit and an FFT (Fast Fourier Transform) operation circuit for performing a Fourier transform at the time of demodulation can be used to configure a transmission / reception circuit.

[0004] From the above characteristics, the OFDM system is widely studied for application to terrestrial digital broadcasting which is strongly affected by multipath interference. Such OF
As terrestrial digital broadcasting employing the DM system, for example, DVB-T (Digital Video Broadcasting-Terres
trial) and ISDB-T (Integrated Services Digital)
Broadcasting-Terrestrial) has been proposed.

[0005] A transmission signal according to the OFDM scheme is transmitted in a symbol unit called an OFDM symbol, as shown in FIG. This OFDM symbol is used as an IFF
An effective symbol, which is a signal period in which T is performed, and a guard interval in which a waveform of a part of the latter half of the effective symbol is copied as it is. This guard interval is provided in the first half of the OFDM symbol. For example, in the DVB-T standard (2K mode), 2048 subcarriers are included in an effective symbol, and the subcarrier interval is 4.14 Hz.
Becomes Also, data is modulated on 1705 subcarriers out of the 2048 subcarriers in the effective symbol. The guard interval is a signal having a time length of 1/4 or 1/8 of the effective symbol.

In such an OFDM digital television broadcast receiving apparatus (OFDM receiving apparatus),
A broadcast wave of a digital television broadcast broadcast from a broadcast station is received by an antenna and supplied to a tuner as an RF signal. The tuner uses the RF supplied from the antenna.
The signal is converted into an IF signal having a predetermined frequency (IF frequency f _IF ) using a local oscillator having a predetermined oscillation frequency. Then, this IF signal is converted into a digital signal by an analog / digital conversion circuit, and is then digitally orthogonally demodulated by a digital orthogonal demodulation circuit to be a baseband OFDM signal.

Here, the center frequency of the baseband OFDM signal after digital quadrature demodulation must be set to 0 as shown in FIG. Therefore, the carrier frequency fc used for the quadrature demodulation must match the IF frequency f _IF of the IF signal. Carrier frequency fc at the time of quadrature demodulation and IF frequency f _{IF of} IF signal
If they do not match, as shown in FIG. 5, there is an error in the center frequency after quadrature demodulation (carrier frequency error f _E ).
, And accurate digital quadrature demodulation cannot be performed.

As a means for eliminating such a carrier frequency error f _E , there is a method of operating the local oscillator of a tuner for converting an RF signal into an IF signal in synchronization with a local oscillator provided to a quadrature demodulation circuit. In general, the circuit configuration becomes complicated.

For this reason, generally, in an OFDM receiver,
The local oscillator of the tuner and the clock of the quadrature demodulation circuit are operated asynchronously, and the correction signal of the same oscillation frequency as the carrier frequency error f _E is complex-multiplied with the digital quadrature demodulation output, thereby obtaining the center of the digital quadrature demodulation output. I am adjusting the frequency.

A conventional O which corrects a carrier frequency error
The FDM receiver will be described with reference to FIG.

As shown in FIG. 6, a conventional OFDM receiver includes an antenna 102, a tuner 103, an A / D conversion circuit 104, a digital quadrature demodulation circuit 105, an fc
It has a correction circuit 106, an FFT operation circuit 107, an fc error detection circuit 108, and an NCO 109.

A broadcast wave of a digital television broadcast broadcast from a broadcast station is transmitted to an antenna 102 of an OFDM receiver.
And supplied to the tuner 103 as an RF signal. The RF signal received by the antenna 102 is
The frequency is converted to an IF signal by a tuner 103 including a local oscillator 103a and a multiplier 103b. The frequency-converted IF signal is digitized by an A / D conversion circuit 104 and supplied to a digital quadrature demodulation circuit 105.

The digital quadrature demodulation circuit 105 performs digital quadrature demodulation on the digitized IF signal using a carrier signal of a predetermined frequency (fc: carrier frequency).
Outputs a baseband OFDM signal. The carrier frequency fc of this carrier signal is asynchronous with the oscillation frequency of the local oscillator 103a of the tuner 102. As a result of digital orthogonal demodulation, the baseband OFDM signal becomes a complex signal including a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The baseband OFDM signal output from the digital quadrature demodulation circuit 105 is supplied to the fc correction circuit 106.

The fc correction circuit 106 includes a fc error correction signal output from the NCO 109 and a baseband OFDM signal.
The signal is subjected to complex multiplication to correct the carrier frequency error of the baseband OFDM signal after digital quadrature demodulation. fc
The baseband OFDM signal whose carrier frequency error has been corrected by the correction circuit 106 is
Supplied to

The fc error detection circuit 108 detects a shift amount of the center frequency of the baseband OFDM signal output from the fc correction circuit 106 based on the output signals from the fc correction circuit 106 and the FFT operation circuit 107. The fc error detection circuit 106 outputs the shift amount to the NCO 109 as an error component err.

The NCO 109 is a so-called numerically controlled oscillator, and generates an fc error correction signal whose oscillation frequency increases or decreases in accordance with the error component err detected by the fc error detection circuit 108. The NCO 109 reduces the oscillation frequency of the fc error correction signal being output if the supplied error component err is a positive value, and outputs the signal if the supplied error component err is a negative value. Control to increase the oscillation frequency of the fc error correction signal. By performing such control, the NCO 109 generates an fc error correction signal such that the oscillation frequency becomes constant when the error component err becomes zero.

As described above, the OFDM receiver corrects the carrier frequency error of the baseband OFDM signal by providing the fc correction circuit 106 at a stage subsequent to the digital quadrature demodulation circuit. That is, the fc error detection circuit 108 detects a deviation amount of the center frequency of the output signal of the fc correction circuit 106, and feeds back the deviation amount to the NCO 109 as an error component err. This NCO10
9 generates an fc error correction signal whose oscillation frequency fluctuates according to the error component err, and supplies it to the fc correction circuit 108. The fc correction circuit 108 corrects the carrier frequency error by complexly multiplying the baseband OFDM signal by the fc error correction signal.

[0018]

By the way, the oscillation frequency of the fc error correction signal by which the digital quadrature demodulation output is complex-multiplied has no error component err that is fed back immediately after the start of control (immediately after the start of operation). , And zero. Then, when orthogonal demodulation is performed on the initial data of the baseband OFDM signal, the carrier frequency error included in the initial data is fed back to the NCO 109 as an error component err as it is,
From the NCO 109, a digital quadrature demodulation output is complex-multiplied by a correction signal of an oscillation frequency corresponding to the error component err.

Therefore, the larger the carrier frequency error, the larger the initial response operation of the feedback control, and the longer it takes to converge the carrier frequency error to zero.

The present invention has been made in view of such circumstances, and has as its object to provide an OFDM signal demodulation apparatus and a demodulation method for shortening the time from the start of operation to the time when the demodulation operation is stabilized. .

[0021]

A demodulation apparatus according to the present invention is a demodulation apparatus for demodulating an orthogonal frequency division multiplexing (OFDM) signal. The demodulation apparatus converts the frequency-converted RF signal to an IF signal into the IFDM signal. An analog / digital conversion means for sampling by a sampling clock of a predetermined frequency which is asynchronous with the IF signal and converting the same to digital data, and the OFDM signal of the IF signal converted to digital data is synchronized with the sampling clock. Digital quadrature demodulation means for performing digital quadrature demodulation with a carrier signal to generate a baseband OFDM signal, and complex multiplication of the digital quadrature demodulated baseband OFDM signal by a correction signal to obtain a frequency of the IF signal Between the carrier and the frequency of the carrier signal (carrier frequency error) And Yaria frequency error correcting means detects the shift of the center frequency of the OFDM signal of the baseband from the output signal of the carrier frequency error correction means,
Correction signal generating means for generating the correction signal whose oscillation frequency is varied according to the shift amount of the center frequency,
The correction signal generating means sets a difference frequency between a frequency of the IF signal and a frequency of the carrier signal as an initial oscillation frequency of the correction signal.

In this demodulation device, the OFDM signal obtained by digital orthogonal demodulation of the IF signal is complex-multiplied by a correction signal, thereby correcting a carrier frequency error occurring during digital orthogonal demodulation of the IF signal. And
In this demodulator, the initial oscillation frequency of the correction signal is
The difference frequency between the frequency of the IF signal and the frequency of the carrier signal is used.

A demodulation method according to the present invention is a demodulation method for demodulating an orthogonal frequency division multiplex (OFDM) signal,
The OFDM frequency-converted from an RF signal to an IF signal
A signal is sampled with a sampling clock of a predetermined frequency which is asynchronous with the IF signal, converted into digital data, and the OFDM signal of the IF signal converted into digital data is converted into a carrier signal synchronized with the sampling clock. Performs a digital quadrature demodulation to generate a baseband OFDM signal, performs a complex multiplication of the digital quadrature demodulated baseband OFDM signal by a correction signal, and calculates a frequency of the IF signal and a frequency of the carrier signal. Of the baseband OFDM signal is detected from the signal in which the carrier frequency error is corrected, and the oscillation frequency is varied according to the center frequency deviation. To generate the correction signal, the frequency of the IF signal and the carrier signal. A difference frequency between the frequency, characterized in that the initial oscillation frequency of the correction signal.

In this demodulation method, the OFDM signal obtained by digital orthogonal demodulation of the IF signal is complex-multiplied by a correction signal, thereby correcting a carrier frequency error occurring at the time of digital orthogonal demodulation of the IF signal. And
In this demodulation method, the initial oscillation frequency of the correction signal is
The difference frequency between the frequency of the IF signal and the frequency of the carrier signal is used.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, as an embodiment of the present invention, a digital broadcast receiving apparatus (OFDM receiving apparatus) based on the OFDM system to which the present invention is applied will be described.

FIG. 1 shows a block diagram of an OFDM receiver to which the present invention is applied.

As shown in FIG. 1, the OFDM receiver 1 includes an antenna 2, a tuner 3, a local oscillator 4,
A / D conversion circuit 5, clock generation circuit 6, digital quadrature demodulation circuit 7, carrier generation circuit 8, fc correction circuit 9, FFT operation circuit 10, narrow-band fc error calculation circuit 11, wide-band fc Error calculation circuit 12 and addition circuit 1
3 and a numerical control oscillator (NCO) 14.

A broadcast wave of a digital television broadcast broadcast from a broadcasting station is received by an antenna 2 of an OFDM receiver 1 and supplied to a tuner 3 as an RF signal.

The tuner 3 multiplies the supplied RF signal by the local carrier generated by the local oscillator 4 to obtain R
The F signal is frequency-converted into an IF signal having a predetermined frequency (f _IF ). The IF signal whose frequency has been converted by the tuner 3 is supplied to the A / D conversion circuit 5.

The A / D conversion circuit 5 includes a clock generation circuit 6
Sampling clock (frequency f _CLK ) supplied from
By sampling the IF signal, the IF signal is digitized. The A / D conversion circuit 5 is, for example, a DVB
In the −T standard, a clock that enables the sampling number of effective symbols to be sampled at 2048 samples, that is, one OFDM symbol is 2560 (2048+
512) Sampling is performed with a clock that can be sampled.

Here, the frequency f _IF of the IF signal and the sampling clock f _C generated by the clock generation circuit 6
It is assumed that _LK has a relationship of, for example, 4f _CLK ≒ f _IF . However, the local oscillator 4 and the clock generation circuit 6 operate asynchronously, and the sampling clock generated by the clock generation circuit 6 and the IF signal are not synchronized.

The IF signal digitized by the A / D conversion circuit 5 is supplied to a digital quadrature demodulation circuit 7. The digital quadrature demodulation circuit 7 quadrature demodulates the digitized IF signal using a carrier signal of a predetermined frequency (fc: carrier frequency) generated from the carrier generation circuit 8 and outputs a baseband OFDM signal. . Since the carrier generation circuit 8 has a relationship of 4f _CLK ≒ f _IF , as shown in FIG.
Generate a digital carrier signal representing c). For example, one cycle is obtained when cosωt = 1, 0, −1, 0, and −
An orthogonal carrier signal having one cycle at sin ωt = 0, −1, 0, 1 is generated. In addition, the carrier frequency fc and the frequency f _{IF of the} IF signal do not completely match, and a certain frequency shift occurs. Here, the angular frequency ω is ω =
2πf _C ≒ 2πf _IF .

The baseband OFDM signal output from the digital quadrature demodulation circuit 7 is an FFT (Fast
Since the signal is a so-called time-domain signal before being subjected to Fourier Transfer (or Fourier Transferorm) calculation, it is hereinafter referred to as an OFDM time-domain signal. As a result of the orthogonal demodulation, the OFDM time domain signal is a complex signal including a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The OFDM time domain signal output from the digital orthogonal demodulation circuit 7 is supplied to the fc correction circuit 9.

The fc correction circuit 9 performs a complex multiplication of the fc error correction signal output from the NCO 14 and the OFDM time domain signal to correct the carrier frequency error of the OFDM time domain signal. The OFDM time domain signal whose carrier frequency error has been corrected by the fc correction circuit 9 is
And the narrowband fc error calculation circuit 11.

The FFT operation circuit 10 performs an FFT operation on the OFDM time domain signal, and extracts and outputs data modulated on each subcarrier. This FF
Since the signal output from the T operation circuit 10 is a signal in the so-called frequency domain after the FFT,
Called the FDM frequency domain signal.

The FFT operation circuit 10 performs an FFT operation on an effective symbol length range (a range of 2048 samples) obtained by removing a signal corresponding to the guard interval time length from the OFDM symbol.

As described above, the OFDM frequency domain signal output from the FFT operation circuit 10 is a complex composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal), like the OFDM time domain signal. Signal.
The OFDM frequency domain signal is converted to a wideband fc error calculation circuit 1
2 and a later-stage equalizer (not shown).

The narrow-band fc error calculation circuit 11 performs OFDM after digital quadrature demodulation by the digital quadrature demodulation circuit 7.
A narrow-band carrier frequency error component indicating a shift amount of the center frequency of the M time domain signal is calculated. Specifically, the narrow band f
The c error calculation circuit 11 calculates the deviation amount of the center frequency with an accuracy of ± 1/2 or less of the subcarrier frequency interval (for example, 4.14 Hz).

The narrow-band fc error calculation circuit 11 is an OFDM
For the time domain signal, the correlation between the waveform of the guard interval part and the waveform of the latter half part of the OFDM symbol (that is, the signal waveform of the guard interval copy source) is obtained,
A boundary portion of the OFDM symbol is obtained based on the correlation. The function indicating the obtained correlation is a complex signal, and the phase component at the boundary of the OFDM symbol in this function is information having an accuracy of ± 1/2 or less of the subcarrier frequency interval of the carrier frequency error component. ing. The narrow-band fc error correction circuit 11 obtains information with an accuracy of ± 1/2 or less of the subcarrier frequency interval as a narrow-band carrier frequency error component.

The narrow band carrier frequency error component obtained by the narrow band fc error calculating circuit 11 is supplied to the adding circuit 13.

The wideband fc error calculation circuit 12 performs OFDM after digital quadrature demodulation by the digital quadrature demodulation circuit 7.
Based on the M time domain signal, a wideband carrier frequency error component indicating a shift amount of the center frequency of the OFDM time domain signal is calculated. Specifically, the wideband fc error calculation circuit 12
The shift amount of the center frequency is calculated with subcarrier frequency (for example, 4.14 Hz) interval accuracy.

The principle of calculating the carrier frequency error component by the wideband fc error calculation circuit 12 will be described.

An OFDM signal generally has a CP (Contin
ual Pilots) signal. This CP signal is a signal that always indicates a specific phase and amplitude, and is inserted into subcarriers of a plurality of indexes in an effective symbol. The number of CP signals included in the effective symbol and the arrangement pattern of the insertion position are predetermined by standards. For example, DV
In the case of the BT standard (2K mode), 2048 subcarriers (0 to 2047) exist in one effective symbol, of which 45 subcarriers include a CP signal. In the DVB-T standard (2K mode), the allocation pattern of the CP signal is the index number of the subcarrier (170 in which the signal is modulated).
0, 48, 54, 87, 141, 1
56, 192, 201, 255, 279, 282, 33
3,432,450,483,525,531,61
8,636,714,759,765,780,80
4,873,888,918,939,942,96
9,984,1050,1101,1107,111
0, 1137, 1140, 1146, 1206, 126
9, 1323, 1377, 1491, 1683, 170
It is 4.

The wideband fc error calculation circuit 12 performs two-time differential demodulation on the OFDM frequency domain signal after the FFT operation between symbols that are temporally adjacent to each other.
By extracting the P signal and calculating how much the subcarrier position of the extracted CP signal is shifted from the original subcarrier position, the carrier frequency error component of the OFDM signal is calculated.

The wideband carrier frequency error component obtained by the wideband fc error calculation circuit 12 is supplied to the addition circuit 13.

The adder circuit 13 includes a narrow-band fc error component calculated by the narrow-band fc error
By adding the wideband fc error component calculated by the c error calculation circuit 12, the total center frequency shift amount of the baseband OFDM signal output from the fc correction circuit 9 is calculated. The adder circuit 13 outputs the calculated total deviation amount of the center frequency as an error component err. The error component err output from the addition circuit 13 is
Supplied to

The NCO 14 is a so-called numerically controlled oscillator, and generates an fc error correction signal that increases or decreases according to the error component err output from the addition circuit 13. This NCO
14 reduces the oscillation frequency of the fc error correction signal if the supplied error component err is a positive value,
If the supplied error component err is a negative value, fc
Control is performed to increase the oscillation frequency of the error correction signal. By controlling the NCO 14 in this way,
An fc error correction signal is generated such that the oscillation frequency becomes constant when the error component err becomes zero.

That is, the NCO 14 outputs an fc error correction signal having the carrier frequency error f _E between the oscillation frequency fc of the carrier frequency generated by the carrier generation circuit 8 and the frequency component f _IF of the IF signal as the oscillation frequency. You. Therefore, in the state of operating constantly,
The error component err output from the addition circuit 13 is set to 0, and the oscillation frequency of the fc error correction signal output from the NCO 14 matches the carrier frequency error. However, the carrier frequency error fluctuates with time depending on, for example, the reception state of the tuner 3.
The oscillation frequency is changed so as to follow this time change.

In the OFDM receiver 1 described above, the fc correction circuit 9 is provided at the subsequent stage of the digital quadrature demodulation circuit 7 to correct the carrier frequency error of the baseband OFDM signal. That is, the narrow band fc error detecting circuit 11 and the wide band fc error correcting circuit 12
An error component err indicating a deviation amount of the center frequency of the output signal of the correction circuit 9 is detected, and the error component err is detected by the NCO 14.
Feedback to The NCO 14 generates an fc error correction signal whose oscillation frequency fluctuates according to the error component err, and supplies the fc error correction signal to the fc correction circuit 9. The fc correction circuit 9 corrects the carrier frequency error by complexly multiplying the baseband OFDM signal by the fc error correction signal.

Here, the NCO 14 determines whether the oscillation frequency of the fc error correction signal output at the start of operation of the OFDM receiver 1 is the signal frequency f _IF of the IF signal and the carrier frequency generated by the carrier generation circuit 8. (Fc =
4f _CLK ) is preset to the difference frequency (f _C −f _IF ).

Although the signal frequency f _IF of the IF signal fluctuates to some extent depending on the reception state of the RF signal and the accuracy of the tuner 3, the theoretical frequency when these error components are not taken into account is the local oscillator 4 of the tuner 3. Is determined in advance according to the signal frequency output from. Also, the oscillation frequency fc of the carrier signal output from the carrier generation circuit 8 is
It is determined in advance by the clock frequency _fCLK of the sampling clock output from the clock generation circuit 6. Since the local oscillator 4 and the clock generation circuit 6 are not synchronized, there is a constant frequency shift between the frequencies of the IF signal and the carrier signal. NCO 14
This shift amount is preset, and at the start of operation, an fc error correction signal having an oscillation frequency corresponding to the shift amount is output.

By presetting the initial oscillation frequency of the NCO 14 in this manner, the error component err detected at the start of the operation is reduced, and the response until the deviation of the center frequency included after the fc correction is reduced to zero. And the time from the start of the operation to the stabilization of the demodulation operation is reduced.

[0053]

According to the demodulation device and the demodulation method of the present invention, the OFDM signal after digital orthogonal demodulation of the IF signal is complex-multiplied by the correction signal, so that the carrier frequency error generated at the time of digital orthogonal demodulation for the IF signal is obtained. Is corrected. In the demodulation device and the demodulation method according to the present invention, the initial oscillation frequency of the correction signal is set to IF
It is the difference frequency between the frequency of the signal and the frequency of the carrier signal.

Therefore, according to the present invention, the carrier frequency error can be corrected in a short time, and the time from the start of the operation to the stabilization of the demodulation operation can be shortened.

[Brief description of the drawings]

FIG. 1 is a block diagram of an OFDM receiver according to the present invention.

FIG. 2 is a diagram illustrating a carrier signal at the time of quadrature demodulation.

FIG. 3 is a diagram for explaining a guard interval of an OFDM signal.

FIG. 4 shows a baseband OFD when there is no frequency shift between a carrier frequency and an IF signal frequency during orthogonal demodulation.
FIG. 3 is a diagram illustrating frequency characteristics of an M signal.

FIG. 5 shows a baseband OFD when there is a frequency shift between a carrier frequency and an IF signal frequency during orthogonal demodulation.
FIG. 3 is a diagram illustrating frequency characteristics of an M signal.

FIG. 6 is a block diagram of a conventional OFDM receiver.

[Explanation of symbols]

1 OFDM receiver, 2 antennas, 3 tuners,
4 local oscillator, 5 A / D conversion circuit, 6 clock generation circuit, 7 digital quadrature demodulation circuit, 8 carrier generation circuit, 9 fc correction circuit, 10 FFT operation circuit, 11
Narrow band fc error calculation circuit, 12 Wide band fc error calculation circuit, 13 Addition circuit, 14 NCO

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Isao Matsumiya, Inventor F-term (reference) 5K004 AA05 AA08 FG02 FH08 JG01 JH05 5K022 DD01 DD13 DD19 DD33 DD43 5K047 within Sony Corporation 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo AA02 AA05 CC01 EE02 EE04 GG11 GG13 MM12 MM13

Claims (2)

[Claims] 1. A demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal, wherein the OFDM signal is frequency-converted from an RF signal to an IF signal.
Analog / digital conversion means for sampling a signal with a sampling clock of a predetermined frequency which is asynchronous with the IF signal and converting the signal into digital data; and sampling the OFDM signal of the IF signal converted into digital data by the sampling Digital quadrature demodulation means for performing digital quadrature demodulation with a carrier signal synchronized with a clock to generate a baseband OFDM signal; complex multiplying the digital quadrature demodulated baseband OFDM signal by a correction signal; Carrier frequency error correction means for correcting an error (carrier frequency error) between the frequency of the IF signal and the frequency of the carrier signal; and a deviation amount of a center frequency of the baseband OFDM signal from an output signal of the carrier frequency error correction means. Is detected, and according to the shift amount of the center frequency, Correction signal generation means for generating the correction signal whose oscillation frequency is variable, wherein the correction signal generation means calculates the difference frequency between the frequency of the IF signal and the frequency of the carrier signal by the initial oscillation of the correction signal. A demodulator characterized by using a frequency. 2. A demodulation method for demodulating an orthogonal frequency division multiplexing (OFDM) signal, wherein the OFDM signal is frequency-converted from an RF signal to an IF signal.
A signal is sampled with a sampling clock of a predetermined frequency which is asynchronous with the IF signal, converted into digital data, and the OFDM signal of the IF signal converted into digital data is converted into a carrier signal synchronized with the sampling clock. Generates a baseband OFDM signal by performing digital quadrature demodulation, and performs complex multiplication of the digital quadrature demodulated baseband OFDM signal by a correction signal, and calculates a frequency of the IF signal and a frequency of the carrier signal. The carrier frequency error is corrected, and the shift amount of the center frequency of the baseband OFDM signal is detected from the signal in which the carrier frequency error is corrected,
The correction signal is generated by varying the oscillation frequency according to the deviation amount of the center frequency, and the difference frequency between the frequency of the IF signal and the frequency of the carrier signal is set as the initial oscillation frequency of the correction signal. A demodulation method characterized by the above-mentioned.