JP2001127730A - Demodulation circuit for multi-carrier modulation - Google Patents

Abstract

(57) Abstract: In a demodulation circuit for a multi-carrier modulation system, a demodulation circuit that performs high-accuracy phase tracking with respect to a phase rotation caused by a residual carrier frequency error or phase noise is provided. SOLUTION: A pilot subcarrier extraction circuit (105)
The phase correction circuit (108) for correcting the residual frequency error and the phase rotation of the output of the sub-carrier is controlled by a phase rotation detection circuit (106) for the pilot subcarrier and a filter (107) for time-averaging the output. The filter (107) is a transversal filter, and controls the bandwidth of the filter (107) by controlling the number of taps and tap coefficients according to the subcarrier modulation scheme (107) of the received signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulation circuit for a multi-carrier modulation system for demodulating a multi-carrier signal using a different sub-carrier modulation system for each packet according to the state of a transmission line in a digital radio communication system. The present invention relates to a demodulation circuit including a phase tracking circuit for detecting and correcting a phase rotation caused by a residual carrier frequency error and phase noise inside the demodulation circuit.

[0002]

2. Description of the Related Art A multicarrier modulation / demodulation system is a system for transmitting information using a plurality of subcarriers. The input data signal is 16QAM (Quadrature amplitude) for each subcarrier.
modulation). Among the multicarrier modulation schemes, the orthogonal multicarrier modulation scheme in which the frequencies of the subcarriers are in an orthogonal relationship is orthogonal frequency division multiplexing (OF
DM: Orthogonal frequency division multiplexing, also known as the modulation method, the OFDM modulated signal is inverse discrete Fourier transformed
(Inverse discrete Fourier transform) circuit. This signal is frequency-converted to a carrier wave band and transmitted from a transmitting antenna. The receiver converts the frequency of the received carrier signal into a baseband signal. Then AD
The signal is input to a converter (Analog to digital converter), output as a digital baseband signal, and subjected to processing such as OFDM demodulation.

In automatic frequency control (AFC) in a demodulator, a carrier frequency error caused by an error of a local oscillator between a transmitter and a receiver can be suppressed to a certain required range. Occurs. Furthermore, phase noise is added to the received signal during the frequency conversion operation in the transceiver. In the method using M-ary QAM such as 16QAM, which is suitable for increasing the transmission rate, for subcarrier modulation, the received symbol data is determined based on the absolute phase during demodulation. The rotation leads to a deterioration of the error rate. As a correction circuit for these phase rotations, it is common to use a phase tracking circuit that transmits a known pilot subcarrier signal and detects and corrects the amount of phase rotation of the pilot subcarrier at a receiver.

FIG. 7 shows a block diagram of a demodulation circuit including a conventional phase tracking circuit. In a conventional demodulation circuit,
Phase tracking is performed on the subcarrier signal after channel equalization using pilot subcarriers. The operation of this demodulation circuit will be described below. Reception O in AFC circuit 1
The carrier frequency error of the FDM signal is corrected. After that, the time domain OFDM reception signal s1 is input to the FFT circuit 2 and
FDM batch demodulation is performed. Each subcarrier signal s2 subjected to OFDM demodulation is input to a channel equalization circuit 3, which estimates a transfer function of each channel generated in a multipath transmission path and performs channel equalization for each subcarrier. Further, the channel transfer function for each subcarrier detected by the channel equalization circuit 3 can be used for weighting operation of each pilot subcarrier signal when detecting the amount of phase rotation. The channel equalization signal s3 is input to the subcarrier modulation scheme demodulation circuit, and the subcarrier modulation scheme of the data section is determined based on the subcarrier modulation scheme information signal transmitted to the head of the packet, and outputs a determination signal s4. The channel equalized signal s3 is divided by a pilot subcarrier extraction circuit 5 into a pilot subcarrier signal s5 and an information subcarrier signal s6 other than the pilot subcarrier signal. In the phase rotation amount detection circuit 6, the pilot subcarrier signal s5
, A phase rotation amount s7 per OFDM symbol is detected using a known pilot data signal. Filter 7
In, the influence of thermal noise is suppressed by performing an averaging operation in the time direction over a plurality of OFDM symbols, and a phase rotation amount s8 due to a residual carrier frequency error and phase noise is extracted. Thereafter, the phase correction circuit 8 corrects the phase rotation amount of the information subcarrier signal s6 using the extracted phase rotation amount s8, and outputs a phase correction signal s9. The determination circuit 9 determines data based on the determination signal s4 determined by the subcarrier modulation scheme demodulation circuit 4, and outputs data s10.

As described above, the conventional demodulation circuit shown in FIG. 7 detects and corrects phase rotation caused by residual carrier frequency and phase noise. By detecting and correcting the phase rotation, it becomes possible to use the M-ary OFDM modulation method, which is largely degraded by the phase rotation, as the modulation method of the subcarrier.

[0006]

In order to use the M-value QAM modulation scheme that realizes a high transmission rate as a subcarrier modulation scheme of the OFDM modulation scheme, data determination is performed based on a residual carrier frequency error and phase rotation caused by phase noise. Since the signal determination point at the time rotates, a phase rotation detection and correction circuit is required in the demodulation circuit. 16QAM, 64QAM, and the like can be considered as the subcarrier modulation scheme used for the M-value QAM-OFDM modulation scheme. The selection of these subcarrier modulation methods is performed according to the transmission path environment for transmitting and receiving data. Specifically, it is as follows. After transmitting the data, the modulation scheme is decreased or increased according to the acknowledgment information of the acknowledgment (ACK: Positive acknowledgment) or the negative acknowledgment (NACK: Negative acknowledgment) from the receiving side. However, in the conventional demodulation circuit, the circuit configuration and parameters of the demodulation circuit are not changed according to the case where the multi-level number of the modulation scheme is reduced or increased.

For example, a modulation method having a large number of levels, such as 64QAM, is selected on a transmission line having a good communication environment with a large signal-to-noise power ratio. However, a filter used for averaging to extract the amount of phase rotation from thermal noise Is desirably small. This is because performing an averaging operation over a plurality of OFDM symbols in an environment with little thermal noise increases the effect of adding a phase rotation of unnecessary OFDM symbols before and after to a desired OFDM symbol. In addition, a modulation method such as 16QAM with a reduced multi-level number is selected for a transmission line having a small signal-to-noise power ratio.In this case, a filter having a large tap coefficient is used to suppress thermal noise. Can correctly extract the amount of phase rotation.

However, in the prior art, the tap coefficient of the filter is fixed. If the tap coefficient is fixed at a small value, the effect of the thermal noise cannot be sufficiently suppressed when used in a transmission line with a large amount of thermal noise, and the phase rotation amount cannot be extracted with high accuracy. On the other hand, when the tap coefficient is fixed to a large value, filtering is performed when used in a transmission line with low thermal noise, and the phase rotation between adjacent OFDM symbols is affected. Can not do it. As described above, since the tap coefficient of the average filter of the demodulation circuit is fixed, the phase rotation amount cannot be detected with high accuracy, and the packet error rate increases.

The present invention solves this problem and adaptively selects the tap coefficient of the average filter of the demodulation circuit according to the transmission path environment according to the subcarrier modulation scheme determined by the subcarrier modulation scheme determination unit. It is another object of the present invention to provide a demodulation circuit that performs phase tracking with high accuracy for phase rotation caused by a residual carrier frequency error and phase noise.

[0010]

According to the first, second and third aspects of the present invention, a filter means used for smoothing has a variable characteristic, and a subcarrier modulation method which is an output signal of a modulation method determination means. The characteristic of the filter means is adaptively selected according to the result of the determination of the information signal.

In the configuration of the conventional demodulation circuit, since the tap coefficient of the average filter of the demodulation circuit is fixed according to the modulation method used for information transmission, the amount of phase rotation according to the transmission path can be detected with high accuracy. There was a problem that the characteristics could be degraded because of the failure.

In the case of switching the modulation scheme according to the transmission path environment in the packet radio communication, it is necessary to inform the receiving side of the modulation scheme used for the data part. As a means for informing the receiving side, as shown in FIG. 4, after a synchronization preamble signal of a demodulator, a subcarrier modulation scheme information signal indicating a modulation scheme used for subcarrier modulation of a data portion is transmitted and demodulated. It is common to make a judgment.

According to the present invention, a signal indicating the modulation scheme used for the subcarrier modulation is demodulated, and at the time of data demodulation, the tap coefficient of the average filter of the demodulation circuit is adaptively adjusted for each packet in accordance with the modulation scheme. Change. The modulation scheme used for the transmission packet is adaptively selected and transmitted according to the state of the transmission path. Specifically, when there is a lot of noise, 16
Transmits a modulation method that transmits less data per symbol, such as QAM, but has excellent noise immunity. If the noise is low, the degradation is large with respect to noise, but the number of data that can be transmitted per symbol Is big 64
The signal is controlled and transmitted to use a modulation method such as QAM. In the demodulation circuit for a multi-carrier modulation system of the present invention,
The fact that the selected subcarrier modulation scheme reflects the state of the transmission path is used. When it is determined that the data is modulated using 16QAM, it can be determined that the region has a large amount of thermal noise, and by increasing the tap coefficient of the filter, the extraction accuracy of the amount of phase rotation can be improved. Also, conversely
When it is determined that the data is modulated by 64QAM, it can be determined that the area is low in thermal noise, and the accuracy of extracting the phase rotation amount can be improved by reducing the tap coefficient of the filter.

When a packet is received, it is determined by a subcarrier modulation signal determination unit. The modulated signal used in the data part of the received packet is m. Where 16QAM, 64QA
When M is selectively transmitted, m = 1 when it is determined as 16QAM, and m = 2 when it is determined as 64QAM.
And Assuming that the average number of symbols of the filter for suppressing the thermal noise and extracting the amount of phase rotation is n, the average number of symbols of the filter is selected as in equation (1).

[0015]

(Equation 1) Assuming that the filter input signal is x _i , the filter output signal y can be expressed as Expression (2).

[0016]

(Equation 2) Here, x _i and y are complex numbers. Here, for simplification, a moving average filter in which all tap coefficients of the filter are 1 is used. Actually, both the average number of symbols and the tap coefficient are selected according to the subcarrier modulation method according to the determination value m.

According to the present invention, the above-described processing is performed, and the tap coefficient of the average filter of the demodulation circuit is adaptively selected according to the subcarrier modulation scheme determined by the modulation scheme determining means. Is fixed, so that the problem of the prior art that the phase rotation amount cannot be detected with high accuracy is solved. By using the present invention, it is possible to perform high-quality transmission adaptively to a transmission environment without deteriorating characteristics according to the magnitude of thermal noise.

[0018]

FIG. 1 shows an embodiment of a multicarrier demodulation circuit according to the present invention. In this embodiment, the amount of phase rotation is detected using pilot subcarriers inserted for each OFDM symbol, as shown in the transmission spectrum model diagram shown in FIG.

The operation of the embodiment is as follows. For the received OFDM signal, the AFC circuit 101 corrects the carrier frequency error of the received signal. After that, the time-domain OFDM reception signal s101 is input to the FFT circuit 102, where OFDM demodulation is performed. Each subcarrier signal s102 subjected to OFDM demodulation is input to a channel equalization circuit 103, and channel equalization is performed using the estimated channel transfer function for each subcarrier. Here, the channel transfer function for each subcarrier detected by the channel equalization circuit can be used for weighting operation of each pilot subcarrier signal when detecting the amount of phase rotation. Subcarrier modulation demodulation circuit 104
Detects and determines the subcarrier modulation scheme from the channel equalized signal s103 and outputs it as a determination signal s104.

The pilot subcarrier extraction circuit 105 extracts pilot subcarriers from the channel equalized signal s103, and outputs pilot subcarrier signals s105.
And the information subcarrier signal s106 are output separately. In the phase rotation detection circuit 106, the pilot subcarrier signal s1
From 05, a phase rotation signal s107 per OFDM symbol is detected. At that time, it is also possible to perform weighting using the channel transfer function for each subcarrier estimated by the channel equalization circuit. This detected phase rotation signal s
The smoothing of 107 is performed over several OFDM symbols by the filter 107 to suppress the influence of thermal noise and extract the amount of phase rotation.
This filter changes the tap coefficient according to Equations (1) and (2) from the determination signal s104, performs filtering according to the thermal noise, and extracts the phase rotation amount s108 added to the data part.

This filter 107 is a feature of the demodulation circuit for a multicarrier modulation system of the present invention, and corresponds to the filter means of the present invention.

Further, using the phase rotation amount s108, the phase correction circuit 108 corrects the phase rotation amount and outputs a phase correction signal s109. The determination circuit 109 determines the data according to the distance from the threshold of the modulation signal indicated by the determination signal s104, and outputs data s110.

FIG. 2 shows an embodiment of the multi-carrier demodulation circuit according to the second aspect. In the present embodiment, the amount of phase rotation is detected using pilot subcarriers inserted for each OFDM symbol as shown in the transmission spectrum model diagram shown in FIG. The operation of the embodiment is as follows. For the received OFDM signal, the AFC circuit 201 corrects the carrier frequency error of the received signal. After that, the time-domain OFDM reception signal s201 is input to the FFT circuit 202, where the OFDM demodulation is performed. Each subcarrier signal s202 subjected to OFDM demodulation is input to a channel equalization circuit 203, and channel equalization is performed using the estimated channel transfer function for each subcarrier. Here, the channel transfer function for each subcarrier detected by the channel equalization circuit can be used for weighting operation of each pilot subcarrier signal when detecting the amount of phase rotation. Pilot subcarrier extraction circuit 20
In step 4, the pilot subcarrier signal s204 is extracted from the channel equalized signal, and an operation of separating the pilot subcarrier signal s204 and the information subcarrier signal s205 is performed. The phase rotation detection circuit 205 detects a phase rotation signal s206 per OFDM symbol from the pilot subcarrier signal s204. At that time, it is also possible to perform weighting using the channel transfer function for each subcarrier estimated by the channel equalization circuit. The filter 206 averages the detected phase rotation signal s206 over several OFDM symbols, suppresses the influence of thermal noise, and extracts the amount of phase rotation. When extracting the phase rotation amount of the subcarrier modulation scheme information signal s209 in which the information of the modulation signal of the data part transmitted at the head of the packet is described, this filter has a tap coefficient suitable for an environment with much thermal noise. It is effective to use The phase correction circuit 207 to which the phase rotation amount s207 and the information subcarrier signal are input corrects the phase rotation amount and outputs a phase correction signal s208. The switching circuit 208 divides the signal into a subcarrier modulation scheme information signal s209 transmitted at the head of the received signal and a data signal s210 which is a signal of the data part. The subcarrier modulation scheme demodulation circuit outputs the subcarrier modulation scheme information signal s.
From 209, the subcarrier modulation scheme is determined and a determination signal s211
Output as The filter 206 changes the tap coefficient according to the equations (1) and (2) and performs filtering according to the thermal noise to extract the phase rotation amount s207 added to the data part.

This filter 206 is a feature of the phase tracking circuit for a multicarrier modulation system of the present invention, and corresponds to the filter means of the present invention. The determination circuit 212 determines data according to the distance from the threshold of the modulation signal indicated by the determination signal s211 and outputs data s212.

FIG. 3 shows an embodiment of the multi-carrier demodulation circuit according to the third aspect. In the present embodiment, the amount of phase rotation is detected using pilot subcarriers inserted for each OFDM symbol as shown in the transmission spectrum model diagram shown in FIG. The third embodiment shows a case where the phase rotation caused by the residual carrier frequency error and the phase rotation caused by the phase noise are individually corrected.

The operation of the embodiment is as follows. For the received OFDM signal, the AFC circuit 301 corrects the carrier frequency error of the received signal. Thereafter, the time-domain OFDM reception signal s301 is input to the FFT circuit 302, where OFDM demodulation is performed. Each subcarrier signal s302 subjected to OFDM demodulation is input to a channel equalization circuit 303, and channel equalization is performed using the estimated channel transfer function for each subcarrier. Here, the channel transfer function for each subcarrier detected by the channel equalization circuit can be used for weighting operation of each pilot subcarrier signal when detecting the amount of phase rotation. Pilot subcarrier selection circuit 30
In 4, the pilot subcarrier signal s304 is extracted from the channel equalized signal s303. The stationary phase rotation detection circuit 305 detects the stationary phase rotation signal s305 from the pilot subcarrier signal s304. At that time, it is also possible to perform weighting using the channel transfer function for each subcarrier estimated by the channel equalization circuit. The detected phase rotation signal s305 and the channel equalization signal are input to the phase correction circuit 306, which corrects the amount of steady phase rotation and outputs a steady phase rotation correction signal s306.

Next, the phase rotation due to the phase noise is corrected. The pilot subcarrier extraction circuit 307 includes a pilot subcarrier signal s308 and an information subcarrier signal s307.
Is performed. The phase rotation detection circuit 308 detects a phase rotation amount s309 per OFDM symbol from the pilot subcarrier signal s308. At that time, it is also possible to perform weighting using the channel transfer function for each subcarrier estimated by the channel equalization circuit. filter
In 309, the phase noise amount s310 averaged over several OFDM symbols is extracted by suppressing the thermal noise. This filter is a subcarrier modulation scheme information signal s in which information of a modulation signal of a data portion transmitted at the head of the packet is described.
When extracting the phase rotation amount of 312, it is effective to use tap coefficients suitable for an environment with a lot of thermal noise. The phase correction circuit 310 and the information subcarrier signal s
307 is input, and phase correction is performed using the phase rotation amount s310. In the switching circuit 311, the subcarrier modulation scheme information signal s3
12 and a data signal s313 which is a signal of the data part. The subcarrier modulation scheme demodulation circuit 312 detects the subcarrier modulation scheme from the data signal information signal s312,
It is determined and output as a determination signal s314. Expression in filter
(1) Filtering is performed according to the identified subcarrier modulation scheme by changing the tap coefficient according to equation (2) to extract the phase rotation amount s310.

This filter 309 is a feature of the multicarrier phase tracking circuit of the present invention.
This corresponds to the filter means described in claim 3.

The determination circuit 314 determines the data in accordance with the distance from the threshold of the modulation signal indicated by the determination signal s313, and outputs data s314.

FIG. 6 shows the effect of the embodiment of the demodulation circuit according to the present invention by computer simulation.
The figure shows the packet error rate (PER) characteristics when the residual carrier frequency error and the phase noise are present. Table 1 shows the simulation conditions.

[0031]

[Table 1] F _BW is the PLL bandwidth as a condition of the phase noise, and? ² _rms
Indicates the signal power ratio of the phase noise. For comparison, the characteristics in the case where there is no residual carrier frequency error and no phase noise are also shown. In this case, the AFC and the phase tracking circuit are not used. The characteristics when the average number in the filter is 1 OFDM symbol and 2 OFDM symbols using the conventional phase tracking circuit are shown. Assuming that the identification of the subcarrier modulation signal is ideally performed, in the case of using the present invention, two symbols are averaged in 16QAM, and one symbol is averaged in 64QAM. On the other hand, in the conventional technology, the PER characteristic of one symbol average or two symbol average is shown. Therefore, when the effect of the present invention is compared with the conventional technology at PER = 0.01, when the required Eb / N0 is 64QAM, about
In the case of 1.7dB and 16QAM, an improvement of about 0.3dB will be obtained.

As described above, by using the present invention, it is possible to extract the phase rotation suitable for the subcarrier modulation method, and to obtain PER
It can be seen that the deterioration of is suppressed and the characteristics are improved.

[0033]

As described above, the multicarrier demodulation circuit of the present invention adaptively selects the tap coefficient of the average filter of the demodulation circuit based on the information determined by the subcarrier modulation scheme determination unit. The present invention provides a demodulation circuit capable of extracting a phase rotation amount according to a modulation method, and performing high-accuracy phase tracking even when phase rotation caused by a residual carrier frequency error or phase noise is added to a received signal. It is possible.

[Brief description of the drawings]

FIG. 1 is an example of a block diagram of an embodiment of the present invention.

FIG. 2 is another example of a block diagram of an embodiment of the present invention.

FIG. 3 is still another example of the block diagram of the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a transmission packet using the OFDM modulation scheme.

FIG. 5 is an explanatory diagram of a transmission spectrum model used in the embodiment of the present invention.

FIG. 6 is a diagram showing a result of a simulation.

FIG. 7 is a block diagram showing a conventional configuration.

[Explanation of symbols]

 101 AFC circuit 102 FFT circuit 103 Channel equivalent circuit 104 Subcarrier modulation scheme demodulation circuit 105 Pilot subcarrier extraction circuit 106 Phase rotation detection circuit 107 Filter 108 Phase correction circuit 109 Judgment circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Morikura 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 5K004 AA08 JA03 JA09 JB01 JG01 JH02 JJ05 JJ12 5K022 DD01 DD18 DD33 DD34 DD42 DD43

Claims (4)

[Claims] 1. An automatic frequency control means for receiving a wireless packet multi-carrier signal including a subcarrier modulation scheme information signal at the beginning of a packet and correcting a carrier frequency error, and a carrier frequency error output from the automatic frequency control means Multi-carrier demodulation means for performing multi-carrier demodulation of the multi-carrier signal subjected to the correction and outputting a sub-carrier signal; detection means for detecting a sub-carrier signal which is an output signal of the multi-carrier demodulation means; Means for judging the subcarrier modulation method from the subcarrier modulation method information signal output at the head of the packet from the means; and extracting the pilot subcarrier signal from the output signal of the detection means, Output carrier signal and information subcarrier signal separately Output means, a pilot subcarrier signal obtained by the extracting means, a phase rotation detecting means for detecting a phase rotation of the pilot subcarrier, and an output signal of the phase rotation detecting means, Filter means for smoothing the output signal of the detection means over a plurality of symbols; an information subcarrier signal which is an output signal of the extraction means and an output signal of the filter means are input; Phase correction means for outputting a subcarrier signal subjected to phase rotation correction by giving a phase rotation for correcting the phase rotation indicated by the output signal; and an output signal of the phase correction means is input and determined by the modulation scheme determination means A multi-carrier modulation scheme recovery unit configured by a determination unit for determining data based on the modulation scheme performed. In the circuit, the characteristics of the filter unit are variable, and the characteristics of the filter unit are adaptively selected according to a subcarrier modulation scheme that is a determination result of a subcarrier modulation scheme information signal that is an output signal of the modulation scheme determination unit. A demodulation circuit for a multi-carrier modulation method. 2. An automatic frequency control means for receiving a wireless packet multi-carrier signal including a subcarrier modulation scheme information signal at the beginning of a packet and correcting a carrier frequency error, and a carrier as an output signal of the automatic frequency control means A multi-carrier demodulation unit that demodulates a multi-carrier signal of a received signal having a corrected frequency error and outputs a sub-carrier signal; and a detection unit that detects the sub-carrier signal that is an output signal of the multi-carrier demodulation unit. Extracting means for extracting a pilot subcarrier signal from an output signal of the detection means to output a pilot subcarrier signal and an information subcarrier signal separately, and inputting the pilot subcarrier signal obtained by the extracting means, Phase rotation detecting means for detecting phase rotation of pilot subcarrier Filter means for receiving an output signal of the phase rotation detecting means and smoothing the output signal of the phase rotation detecting means over a plurality of symbols; an information subcarrier signal which is an output signal of the extracting means; and the filter means Phase correction means for inputting the output signal of the above, and outputting a subcarrier signal subjected to phase rotation correction by giving the information subcarrier signal a phase rotation for correcting the phase rotation indicated by the output signal of the filter means, A switching unit that switches and outputs a subcarrier modulation scheme information signal and a data signal output from the phase correction unit; and determines a subcarrier modulation scheme of a data part from a subcarrier modulation scheme information signal that is an output signal of the switching unit. A modulation scheme determining unit that performs the determination by the modulation scheme determining unit from a data signal that is an output signal of the switching unit. A demodulation circuit for a multi-carrier modulation system, comprising: a decision unit that decides data on the basis of a modulation scheme. The filter unit has a variable characteristic, and is a subcarrier modulation output signal of the modulation scheme decision unit. A demodulation circuit for a multicarrier modulation system, wherein a characteristic of the filter means is adaptively selected according to a subcarrier modulation system which is a determination result of a system information signal. 3. An automatic frequency control means for receiving a wireless packet multi-carrier signal including a subcarrier modulation scheme information signal at the beginning of a packet and correcting a carrier frequency error, and an output signal of the automatic frequency control means. Multi-carrier demodulation means for performing multi-carrier demodulation of a received signal having a corrected carrier frequency error and outputting a sub-carrier signal; and detection means for detecting the sub-carrier signal which is an output signal of the multi-carrier demodulation means. A selecting means for selecting and outputting only a pilot subcarrier signal from an output signal of the detecting means, and a stationary phase for inputting a pilot subcarrier signal obtained by the selecting means and detecting a stationary phase rotation of the pilot subcarrier. Rotation detection means, an output signal of the detection means and the stationary phase rotation detection The subcarrier signal subjected to the steady phase rotation correction by inputting the output signal of the means and giving the output signal of the detection means a phase rotation for correcting the steady phase rotation indicated by the output signal of the steady phase rotation detection means. First phase correction means for outputting, extraction means for extracting a pilot subcarrier signal from an output signal of the first phase correction means and separating and outputting the pilot subcarrier signal and the information subcarrier signal; Phase rotation detection means for detecting the phase rotation of the pilot subcarrier, inputting the output signal of the phase rotation detection means, and providing a plurality of output signals of the phase rotation detection means. Filter means for smoothing over the symbol; the information subcarrier signal which is an output signal of the extraction means; A second phase correction for inputting an output signal of a filter means and outputting a subcarrier signal for performing a phase rotation correction by giving the information subcarrier signal a phase rotation for correcting a phase rotation indicated by the output signal of the filter means. Means, a switching means for switching and outputting a subcarrier modulation scheme information signal and a data signal output from the second phase correction means, and a data section of a subcarrier modulation scheme information signal which is an output signal of the switching means. A modulation scheme determining unit that determines a subcarrier modulation scheme; and a determining unit that determines data based on a modulation scheme determined by the modulation scheme determining unit from a data signal that is an output signal of the switching unit. In the demodulation circuit for a multi-carrier modulation system, the characteristics of the filter unit are variable, and the output signal of the modulation system determination unit is Subcarrier modulation scheme, characterized in that adaptively selects the characteristics of the filter means in accordance with the sub-carrier modulation scheme is a determination result of the information signal, the multicarrier modulation scheme for demodulation circuit is. 4. The filter means is constituted by a transversal filter, and the bandwidth of the filter can be adjusted by adjusting the number of taps and tap coefficients.
Or the demodulation circuit for a multicarrier modulation method according to 3.