JPH1075228A - OFDM demodulator - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a stable OF without being affected by phase noise.
Demodulate the DM signal. SOLUTION: A quadrature detection circuit 31 obtains a complex vector of an input OFDM signal based on a local oscillation signal from a local oscillation circuit 32, and performs a Fourier transform in a symbol unit by a Fourier transform circuit 34 via a phase rotation circuit 33. After obtaining the demodulated vector, the data identification circuit 35 identifies the demodulated data based on the reference vector corresponding to the specified area, and the reception status monitoring circuit 36 monitors the error status. Further, the phase rotation calculation circuit 37 calculates the phase rotation amount from the phase difference between the demodulation vector and the reference vector, and outputs a predetermined phase offset to the phase offset generation circuit 40 according to the monitoring output. By adding to the amount of rotation and performing smoothing processing by the loop filter 39, the signal is applied to the phase rotation circuit 33 so that the phase rotation is automatically corrected even if the phase rotation reaches a pseudo stable position due to the symmetry of the signal. I made it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM demodulator for demodulating a modulation vector in an effective symbol period from an OFDM signal, and more particularly to a technique for correcting an error phase of a local oscillation signal.

[0002]

2. Description of the Related Art In recent years, transmission schemes using OFDM (orthogonal frequency division multiplexing) technology have attracted attention in digital audio broadcasting for mobile objects and terrestrial digital television broadcasting. This OFDM transmission system is a type of multi-carrier modulation system, in which coded data (information symbols) that have been serial-parallel converted into a number of subcarriers orthogonal to each other between adjacent ones
, Respectively, after converting them into digital modulation waves by inverse Fourier transform (converting the frequency domain into the time domain), add each to generate an OFDM signal, and perform the reverse processing after transmission to perform the original encoding. The data was obtained. This method has a characteristic that the period of each information symbol divided into subcarriers is long, so that it is hardly affected by a delay wave such as a multipath.

FIG. 7 shows a basic block configuration of an OFDM modulator that generates an OFDM signal on the transmitting station side. In FIG. 7, an inverse Fourier transform circuit 11 receives a plurality of modulation vectors (information symbols), and orthogonally inter-modulates each modulation vector in symbol units according to a symbol timing signal generated by a timing generation circuit (not shown). And a frequency domain signal is converted to a time domain signal by performing an inverse Fourier transform, thereby obtaining a signal in an effective symbol period. This signal is supplied to the guard period adding circuit 12.

The guard period adding circuit 12 sequentially takes in the signal of the effective symbol period from the inverse Fourier transform circuit 11 according to the symbol timing signal, and precedes the effective symbol period with the guard period for each symbol.
Further, the signal at the end of the effective symbol period output from the inverse Fourier transform circuit 11 is copied in the guard period to form a baseband OFDM signal. FIG. 8 shows the format of the baseband OFDM signal obtained by the guard period adding circuit 12. This OFDM signal is transmitted to the quadrature modulation circuit 1
3 is supplied.

The quadrature modulation circuit 13 performs quadrature modulation on the baseband OFDM signal obtained by the guard period adding circuit 12 using a local oscillation signal generated by a local oscillation circuit 14, and outputs an intermediate frequency band or a radio frequency band. , And output as an OFDM signal.

FIG. 9 shows a basic block configuration of an OFDM demodulator for demodulating an OFDM signal on the receiving station side. In FIG. 9, a quadrature demodulation circuit 15 receives an OFDM signal from the transmitting station and performs quadrature demodulation by a local oscillation signal (detection frequency signal) generated by a local oscillation circuit 16 to obtain an intermediate frequency band or a radio frequency band. Is converted to a baseband OFDM signal. This OFDM signal is supplied to a guard period removing circuit 17.
Supplied to

The guard period removing circuit 17 removes the guard period from the OFDM signal converted into the base band by the quadrature demodulating circuit 15 and extracts the signal of the effective symbol period.
The signal in the effective symbol period is supplied to the Fourier transform circuit 18.

The Fourier transform circuit 18 performs a Fourier transform on the signal in the effective symbol period to convert a signal in the time domain into a signal in the frequency domain, thereby obtaining a plurality of demodulated vectors (information symbols).

However, in the OFDM demodulator having the above configuration, an error occurs in the phase of the output of the local oscillation circuit 16 or the demodulation vector obtained by the Fourier transform circuit 18 due to phase noise generated inside the tuner for performing frequency conversion. There is a problem that mutual interference between subcarriers occurs.

Therefore, conventionally, the OFDM signal has been demodulated by synchronizing the frequency of the local oscillation signal.
As a method of synchronizing the frequency of an OFDM signal, a method of performing the frequency of a local oscillation signal is disclosed in Japanese Patent Laid-Open No. 7-143096. Hereinafter, the conventional O disclosed in the above publication will be described.
The FDM demodulator will be described with reference to FIG.

FIG. 11 shows a block diagram of the system.
The quadrature detection circuit 21 receives the OFDM signal, and outputs a complex detection signal obtained by quadrature detection using a locally generated local oscillation signal for each sampling clock. This complex detection signal is supplied to a Fourier transform circuit 22 and a symbol timing determination circuit 23.

The symbol timing determination circuit 23
Utilizing the fact that the signal at the end of the effective symbol period is copied in the guard period in the DM signal, the symbol timing is obtained by calculating the correlation between the complex detection signal delayed by the effective symbol period and the directly input complex detection signal. The determination is made, and the Fourier transform circuit 22 is notified of the effective symbol period.

The Fourier transform circuit 22 extracts a complex detection signal in an effective symbol period for each symbol, performs a Fourier transform, and outputs the result as a demodulated vector. The demodulated vector thus obtained is also supplied to the constellation analysis circuit 24.

This constellation analysis circuit 24
A demodulation vector is extracted from subcarriers of two or more different frequencies, a frequency error of a local oscillation signal for quadrature detection is obtained from a phase rotation of the constellation, and a detection frequency error signal is generated. The detection frequency error signal is supplied to the detection frequency control circuit 25.

The detection frequency control circuit 25 controls the frequency of the local oscillation signal for quadrature detection generated inside the quadrature detection circuit 21 based on the detection frequency error signal from the constellation analysis circuit 24.

The operation of the OFDM demodulator having the above configuration will be described below. The above-mentioned Japanese Patent Application Laid-Open No. 7-143096
As disclosed in the above publication, the conventional OFDM demodulator uses a constellation analysis circuit 24 to analyze each phase rotation of a constellation obtained from demodulated vectors on two or more different frequency subcarriers,
The frequency error of the local oscillation signal is detected.

This is because the Fourier transform circuit 22 uses OFDM.
It utilizes the fact that the phase rotation of a demodulated vector obtained by Fourier-transforming a signal is given by a detection frequency error.

[0018]

However, in the conventional OFDM demodulator disclosed in the above-mentioned publication, the frequency and the frequency of the local oscillation signal for quadrature detection are shifted and the Fourier transform is performed. In some cases, mutual interference between subcarriers occurs, and an accurate demodulation vector cannot be obtained, and the phase error of the local oscillation signal cannot be accurately obtained by the constellation analysis circuit.

Further, the modulation of each subcarrier is, for example, Q
In the case of multi-level modulation such as PSK or 64QAM,
Due to the symmetry of the constellation, a value in which the error phase difference is offset by, for example, 90 degrees is obtained, and an accurate phase difference cannot be obtained.

Further, the AFC system having the above configuration is configured to perform frequency control by observing for a long time and to stabilize at a predetermined frequency determined on average, and cannot remove a phase noise component generated by a tuner or the like.

The conventional automatic frequency control method has the above-mentioned problem with respect to the elimination of the phase noise which gives the frequency error the phase rotation. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problem and remove OFS orthogonal oscillation detection local oscillation signals and phase noise generated by a tuner to stably demodulate an OFD signal.
An M demodulator is provided.

[0022]

Means for Solving the Problems To solve the above problems, the present invention is configured as follows. (1) An OFDM demodulator that receives as input an OFDM signal that is an orthogonal frequency division multiplexed signal in which a plurality of carriers are frequency-multiplexed at fixed frequency intervals and each carrier is orthogonal in an effective symbol time period determined by a reciprocal of the frequency interval. A quadrature detector that receives the OFDM signal as input and obtains a complex detection vector of the OFDM signal based on a local oscillation signal; a local oscillator that generates a local oscillation signal to be supplied to the quadrature detector; Phase rotation means for receiving the output of the detection means as an input and rotating the phase of the input signal in accordance with a phase control signal, and OFD which is the output of the phase rotation means
Fourier transforming a complex detection vector of the M signal for each symbol, and a Fourier transforming means for obtaining a demodulation vector including modulation data of each of the plurality of carriers, and a demodulation vector which is an output of the Fourier transforming means as an input to a specified area. A data identification unit that allocates a corresponding reference vector to each demodulation vector, a reception status monitoring unit that monitors an error status of demodulated data by using an output of the data identification unit as an input, and outputs the demodulation vector and an output of the data identification unit. A phase rotation calculating means for obtaining a phase difference between a demodulation vector and a reference vector corresponding to each demodulation vector as an input; and a phase offset generating means for outputting a predetermined phase offset according to an output of the reception status monitoring means. Means, and an output of the phase rotation means as a first input, the phase offset generating means Adding means for adding outputs of both the output as a second input to smooth the output of the adding means as an input, and comprises a smoothing means for outputting a phase control signal to said phase line means.

(2) An OFDM signal, which is an orthogonal frequency division multiplexed signal, in which a plurality of carriers are frequency-multiplexed at fixed frequency intervals and each carrier is orthogonal in an effective symbol time period determined by the reciprocal of the frequency interval, is input. An OFDM demodulator, comprising: an orthogonal detection means for receiving the OFDM signal as input and obtaining a complex detection vector of the OFDM signal based on a local oscillation signal; and frequency control for generating a frequency control signal based on an output of the orthogonal detection means. A signal generator, a local oscillator for generating a local oscillation signal to be supplied to the quadrature detector, a local oscillator for varying the frequency based on a frequency control signal generated by the frequency control signal generator, and the quadrature detector. A complex vector of an output OFDM signal is Fourier-transformed for each symbol, and modulated data of each of a plurality of carriers is converted. Fourier transforming means for obtaining a demodulated vector, data identifying means for receiving a demodulated vector output from the Fourier transforming means as an input, and outputting a reference vector corresponding to a prescribed region in correspondence with each demodulated vector, Receiving status monitoring means for monitoring the error status of demodulated data with the output of the means as an input, and receiving the demodulated vector and the output of the data identifying means as inputs, and calculating a vector between the demodulated vector and a reference vector corresponding to each demodulated vector. Phase rotation calculating means for obtaining a phase difference;
A phase offset generating means for outputting a predetermined phase offset in accordance with an output of the reception status monitoring means, an output of the phase rotation amount calculating means as a first input, and an output of the phase offset generating means as a second input A first adding means for adding and outputting the two, a smoothing means for smoothing the output of the first adding means as an input, and a frequency control signal supplied to the local oscillating means from the output of the smoothing means. And a second adding means for adding an output to the data.

(3) An OFDM signal, which is an orthogonal frequency division multiplexed signal, in which a plurality of carriers are frequency-multiplexed at a constant frequency interval and each carrier is orthogonal in an effective symbol time period determined by a reciprocal of the frequency interval, is converted to a first signal. A tuner section for selecting from a received signal based on a local oscillation signal of
And a first local oscillation means for generating a local oscillation signal and varying its frequency based on the frequency control signal.
A quadrature detection means for use in a DM receiver, which receives the OFDM signal selected by the tuner section as an input, and obtains a complex detection vector of the OFDM signal based on a second local oscillation signal; and Frequency control signal generating means for generating a frequency control signal to be supplied to the first local oscillation means, local oscillation means for generating a second local oscillation signal to be supplied to the quadrature detection means, Fourier transforming a complex vector of an output OFDM signal for each symbol to obtain a demodulation vector including modulation data of each of a plurality of carriers, and a demodulation vector which is an output of the Fourier transformation means as an input. Data identification means for outputting a reference vector corresponding to the region corresponding to each demodulation vector,
A reception status monitoring unit that monitors an error status of demodulated data by using an output of the data identification unit as an input, and an output of the demodulation vector and the data identification unit, and a demodulation vector and a reference vector corresponding to each demodulation vector. Phase rotation calculating means for calculating the phase difference of the vector, a phase offset generating means for outputting a predetermined phase offset according to the output of the reception status monitoring means, and an output of the phase rotation amount calculating means as a first input. A first adding means for adding the output of the phase offset generating means as a second input and adding the two, and a smoothing means for smoothing the output of the first adding means as an input; A second adding means for adding an output to a frequency control signal supplied to the first local oscillation means is provided.

(4) In any one of the constitutions (1) to (3), the phase rotation amount calculating means calculates a phase rotation amount for a predetermined carrier wave among a plurality of carrier waves.

(5) In any one of the constitutions (1) to (3), the phase rotation amount calculating means calculates a phase difference between a demodulated vector and a reference vector corresponding to each demodulated vector. , And averaged and output in symbol units.

(6) In the configuration of any one of (1) to (3), the reception status monitoring means uses a correction status of an error correction code in a result of decoding digital data transmitted from the reference vector. And

[0028] (7) In any one of the constitutions (1) to (3), the reception status monitoring means may determine a state of a metric value used for Viterbi decoding for decoding digital data transmitted from a reference vector. The configuration is used.

(8) In any one of the constitutions (1) to (3), the reception status monitoring means uses a synchronization state of a data frame configuration as a result of decoding digital data transmitted from a reference vector. Configuration.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. (First Embodiment) FIG. 1 shows a block configuration of an OFDM demodulator according to a first embodiment of the present invention.

In FIG. 1, a quadrature detection circuit 31 obtains a complex detection signal by performing quadrature detection on an input OFDM signal based on a local oscillation signal generated from a local oscillation circuit 32. This complex detection signal is input to the phase rotation circuit 33, and a predetermined rotation is applied based on the phase control signal. The output is supplied to the Fourier transform circuit 34 for each symbol.

The Fourier transform circuit 34 extracts a complex detection signal in an effective symbol period, performs a Fourier transform to convert the time domain to the frequency domain, and thereby obtains a demodulation vector (information symbol).

The demodulated vectors are respectively assigned to specified reference vectors determined by the subcarrier modulation method by the data identification circuit 35. The demodulation vector and the reference vector are input to the phase rotation calculation circuit 37, and the phase difference between the reference vector and the demodulation vector is obtained as a corresponding subcarrier phase error signal. The reference vector obtained from the demodulated vector is input to the reception status monitoring circuit 36, and as a result of performing internal code decoding, outputs a reception status signal indicating a reception status lower than a predetermined quality.

The phase error signal obtained by the phase rotation calculation circuit 37 is input to a loop filter via an addition circuit 38, and after being smoothed, input to a phase rotation circuit 33, where the phase error of the input signal is Is removed.

When the reception quality signal is lower than the predetermined quality, the offset phase is output by the phase offset generation circuit and added to the phase error signal by the addition circuit 38.

Hereinafter, the operation of the first embodiment will be described assuming that the OFDM signal includes a component of the phase noise φ. Assuming that the complex detection signal in the low-band equivalent band of the OFDM signal to be modulated is S and the frequency of the output of the local oscillation circuit 32 is f, the input OFDM signal y (t) can be described as follows. y (t) = S · exp (j · (2πft + φ)) Then, a complex detection signal 101 output from the quadrature detection circuit is obtained.
Is: D (t) = S ・ exp (j ・ φ) where S is a composite signal of a plurality of subcarriers, and the modulation vectors C0 to Cn determined by the modulation method of each subcarrier.
Then, assuming that the detuning frequency is Δf, S is given by S = ΣCk · exp (j2πΔf · kt) exp (j ·
φ).

The complex detection signal is supplied to a phase rotation circuit 33.
And rotated according to the control signal. For simplicity, the following operation will be described with the initial rotation amount set to 0. Therefore, this complex detection signal is converted to a Fourier transform circuit 34.
, The output is Y (n): Y (n) = 1 / T∫S∫exp (−jn2πΔft) dt.

The demodulation vector of the n-th carrier is 1 / T１ ／ exp (jφ) ΣCkexp (j2πΔfkt) ·
exp (−j2πΔfnt) dt.

Exp (jφ) can be expanded as follows when φ is small. exp (jφ) = 1 + jφ By substituting this expression into the above expression, 1 / T∫ΣCk exp ｛j2πΔf (kn) t｝ + jφ
Ck exp ｛j2πΔf (kn) t｝ dt

As for the noise component, if two items are written as N (n), the demodulation vector obtains Y (n) = Cn + N (n).

This demodulated vector is supplied to the data identification circuit 35.
, And is assigned to the nearest reference vector Cn ′, and Cn ′ is output to the output of the data identification circuit 35.

The reference vector Cn 'and the demodulation vector Y
(N) is input to the phase rotation calculation circuit 37, respectively.
The phase shift of the demodulated vector from the reference vector is obtained as a phase rotation amount.

The phase rotation amount thus obtained is smoothed by the loop filter 39 via the addition circuit 38 and supplied to the phase rotation circuit 33. That is, the phase amount of the phase rotation circuit 33 is controlled according to the smoothed phase rotation amount. Note that the phase rotation calculation circuit 37 may include a configuration for averaging in symbol units.

The reference vector assigned from the demodulated vector is input to the reception state monitoring circuit 36. For monitoring the reception state, as a result of decoding digital data transmitted from the reference vector, for example, information such as a correction state of an error correction code, a state of a metric value used for Viterbi decoding, and a synchronization state of a data frame configuration can be used. .

The output signal of the reception state monitoring circuit 36 is
If a desired quality is not obtained in the reception state, the phase offset is output to the phase offset generation circuit 40 and a predetermined (1/2 or more of the interval of the stable point) phase offset is output. The signal is input to the terminal and is added to the above-described signal of the amount of phase rotation.

The modulation scheme of each carrier is 90, such as QAM.
In the case of degree rotation symmetry, the required phase rotation amount is limited within 90 degrees, the phase rotation of the demodulation vector is not restored,
At a position shifted by 90 degrees, the loop settles in a stable state. In such a situation, the basic state to be demodulated is such that the reception state monitoring signal becomes active when the phase is rotated by 90 degrees, the phase offset is forcibly added to the addition circuit 38, and a new stable point is obtained in the next state. Stable in

The phase offset generating circuit 40 outputs a phase offset when the reception state signal becomes active. The demodulated vector to which this signal is added is added by the output of the phase rotation calculating circuit 37. In the phase offset generation circuit 37, after the phase offset is generated, the generation of a new phase offset may be prohibited during the time when the phase rotation is corrected by the phase rotation error signal.

FIG. 2 shows basic vectors in the case of 16QAM. Each point indicates the position of the basic vector corresponding to the modulation data. FIG. 3 shows a state where the demodulation vector includes N (i) and phase rotation has occurred. FIG. 4 shows how the phase rotation of the demodulation vector is modified in response to the phase error.

Here, FIG. 4A shows that the phase rotation amount φ is 4
If it exceeds 5 degrees, it indicates a constellation of the demodulated vector. In this case, as shown in FIG. 4B, the correction of the phase rotation is sequentially performed in the direction of the arrow, and the phase is corrected so as to be rotated by 90 degrees. FIG. 4C shows a state in which a phase offset exceeding 45 degrees has been added from the phase offset generation circuit 40, in which the correction is started in the direction of the arrow and the phase is corrected to the position of the normal basic vector. Show.

Therefore, in the OFDM demodulator having the above configuration, even if phase noise is generated in a tuner or the like, the amount of phase rotation between the demodulation vector and the reference vector is obtained, and the phase detection is given to the complex detection signal. , The amount of phase rotation of the demodulation vector can be corrected. As a result, a demodulated vector without phase rotation can be obtained without being affected by phase noise.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 5, the same parts as those in FIG. 1 are indicated by the same reference numerals.

In FIG. 5, a quadrature detection circuit 31 obtains a complex detection signal by performing quadrature detection on an input OFDM signal based on a local oscillation signal generated by a local oscillation circuit 32. The output frequency of the local oscillation signal is controlled by the frequency control signal of the automatic frequency control signal generation circuit 42.

The automatic frequency control signal generation circuit 42 generates a frequency control signal so that the center frequency of the detection output of the quadrature detection circuit 31 becomes the center frequency of the OFDM signal, and outputs the signal to the local oscillation circuit 32 via the addition circuit 41. I do. Thereby, an AFC (automatic frequency control) loop is formed.

The complex detection signal is supplied to the Fourier transform circuit 34 for each symbol. This Fourier transform circuit 3
Reference numeral 4 extracts a complex detection signal in an effective symbol period, performs a Fourier transform to convert the time domain to the frequency domain, and thereby obtains a demodulation vector (information symbol). The demodulation vectors are respectively assigned to prescribed reference vectors determined by the subcarrier modulation method by the data identification circuit 35.

The demodulation vector and the reference vector are input to the phase rotation calculation circuit 37, and the phase difference between the reference vector and the demodulation vector is obtained as a corresponding subcarrier phase error signal. The reference vector obtained from the demodulated vector is input to the reception status monitoring circuit 36, and as a result of performing internal code decoding, outputs a reception status signal indicating a reception status lower than a predetermined quality.

The phase error signal obtained by the phase rotation calculation circuit 37 is input to a loop filter 39 via an addition circuit 38, and is smoothed. As a result, the addition circuit 41 outputs the signal of the automatic frequency control signal generation circuit 42. The signal is added to the output signal and input to the local oscillation circuit 32.

If the reception status signal indicates that the reception quality is lower than the predetermined quality, the phase offset generation circuit 4
The offset phase is output by "0" and added to the phase error signal by the adding circuit 38.

As can be understood from the above description, even in the OFDM demodulator having the above configuration, the phase rotation error signal obtained from the demodulation vector and the reference vector is added to the control signal of the automatic frequency control, and the phase rotation amount of the demodulation vector is reduced. The reception status monitoring circuit 36 corrects the data to a pseudo stable point.
The phase offset signal is added to the phase rotation amount in accordance with the output signal of the first embodiment, so that the same effect as in the first embodiment can be obtained.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. In FIG. 6, the same parts as those in FIGS. 1 and 5 are denoted by the same reference numerals.

In FIG. 6, a tuner 51 fetches a received signal from an antenna (not shown), and
The baseband OFDM signal is extracted based on the local oscillation signal for channel selection generated from.

The OFDM signal obtained here is supplied to a quadrature detection circuit 31, where it is subjected to quadrature detection based on a fixed local oscillation signal generated from a local oscillation circuit 32 to become a complex detection signal. The complex detection signal is supplied to the Fourier transform circuit 34 for each symbol.

The complex detection signal is supplied to an automatic frequency control signal generation circuit 52. The automatic frequency control signal generation circuit 52 generates a frequency control signal so that the center frequency of the OFDM detection output of the tuner 50 becomes the center frequency of the OFDM signal, and outputs the signal to the local oscillation circuit 51 via the addition circuit 53. Thereby, an AFC (automatic frequency control) loop is formed.

The Fourier transform circuit 34 extracts a complex detection signal in an effective symbol period, performs a Fourier transform to convert from the time domain to the frequency domain, and thereby obtains a demodulation vector (information symbol). The demodulation vectors are respectively assigned to prescribed reference vectors determined by the subcarrier modulation method by the data identification circuit 35.

The demodulation vector and the reference vector are input to the phase rotation calculation circuit 37, and the phase difference between the reference vector and the demodulation vector is obtained as a corresponding subcarrier phase error signal. The reference vector obtained from the demodulated vector is input to the reception status monitoring circuit 36, and as a result of performing internal code decoding, outputs a reception status signal indicating a reception status lower than a predetermined quality.

The phase error signal obtained by the phase rotation calculation circuit 37 is input to a loop filter 39 via an addition circuit 38 and smoothed. As a result, the addition circuit 53 outputs the signal from the automatic frequency control signal generation circuit 52. The signal is added to the output frequency control signal and input to the local oscillation circuit 51.

If the reception status signal indicates that the reception quality is lower than the predetermined quality, the phase offset generation circuit 4
The offset phase is output by "0" and added to the phase error signal by the adding circuit 38.

As can be seen from the above description, even in the OFDM demodulator having the above configuration, the phase rotation error signal obtained from the demodulation vector and the reference vector is added to the control signal for automatic frequency control for the tuner 50, and the phase of the demodulation vector is adjusted. Even if the rotation amount is corrected and a pseudo stable point is reached, the phase offset signal is added to the phase rotation amount in accordance with the signal output from the reception status monitoring circuit 36. The same effect as that of the embodiment can be obtained.

In some cases, a vector determined from decoded data after error correction is used as the reference vector signal. Further, the phase rotation amount calculation circuit 37 may calculate the phase rotation amount for a predetermined carrier wave among a plurality of carrier waves.

The loop filter 39 averages the output of the adder circuit 38 as described in each of the above embodiments. However, by using a digital filter or the like, a technique such as linear prediction can be used. Can be used. Further, in order to stabilize the loop operation, it is desirable to correct the phase error after the completion of the AFC pull-in operation.

[0070]

As described above, according to the present invention, OFDM
It is possible to provide an OFDM demodulator capable of performing more accurate demodulation by rotating and correcting the phase of a complex detection signal even in a state where there is phase noise generated by a tuner or the like in demodulation.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram illustrating a configuration of an OFDM demodulator according to a first embodiment of the present invention.

FIG. 2 is a vector plan view showing reference vectors according to modulation data of an OFDM signal in the embodiment.

FIG. 3 is a vector plan view showing an example of phase rotation of a demodulation vector in the embodiment.

FIG. 4 is a vector plan view showing an example of phase rotation of a demodulation vector and an example of correction of the phase rotation in the embodiment.

FIG. 5 is a block circuit diagram illustrating a configuration of an OFDM demodulator according to a second embodiment of the present invention.

FIG. 6 is a block circuit diagram illustrating a configuration of an OFDM demodulator according to a third embodiment of the present invention.

FIG. 7 is a block circuit diagram showing a basic configuration of an OFDM modulator on the transmitting station side.

8 is a signal configuration diagram showing a format of an OFDM signal in a base band for explaining the operation of the OFDM modulation device shown in FIG. 7;

FIG. 9 is a block circuit diagram showing a basic configuration of an OFDM demodulator on the receiving station side.

FIG. 10 is a timing chart showing a pattern of an OFDM signal into which null symbols and reference symbols are inserted.

FIG. 11 shows a conventional O which synchronizes a detection frequency and a sampling clock frequency without using a null symbol and a reference symbol.
FIG. 3 is a block circuit diagram illustrating a configuration of an FDM demodulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Inverse Fourier transform circuit 12 ... Guard period addition circuit 13 ... Quadrature modulation circuit 14 ... Local oscillation circuit 15 ... Quadrature demodulation circuit 16 ... Local oscillation circuit 17 ... Guard period removal circuit 18 ... Fourier transform circuit 21 ... Quadrature detection circuit 22 ... Fourier transform circuit 23 ... symbol timing determination circuit 24 ... constellation analysis circuit 25 ... detection frequency control circuit 31 ... quadrature detection circuit 32 ... local oscillation circuit 33 ... phase rotation circuit 34 ... Fourier transform circuit 35 ... data identification circuit 36 ... reception situation Monitoring circuit 37 ... Phase rotation calculation circuit 38 ... Addition circuit 39 ... Loop filter 40 ... Phase offset generation circuit 41 ... Addition circuit 42 ... Automatic frequency control signal generation circuit 50 ... Tuner 51 ... Local oscillation circuit 52 ... Automatic frequency control signal generation circuit 53 ... Addition circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomohiro Kimura 5-2-8 Akasaka, Minato-ku, Tokyo Inside the Next Generation Digital Television Broadcasting System Research Laboratories (72) Inventor Sadaji Kageyama 5 Akasaka, Minato-ku, Tokyo No. 2-8, Next Generation Digital Television Broadcasting System Laboratory Co., Ltd. (72) Inventor Akira Kisoda 5-2-8, Akasaka, Minato-ku, Tokyo Next Generation Digital Television Broadcasting System Co., Ltd. Laboratory (72) Invention Ken Kenichiro Hayashi 5-2-8 Akasaka, Minato-ku, Tokyo Inside the Next Generation Digital Television Broadcasting System Research Laboratories Co., Ltd. (72) Inventor Hitoshi Mori 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. An OFDM signal comprising an OFDM signal, which is an orthogonal frequency division multiplexed signal, in which a plurality of carriers are frequency-multiplexed at a fixed frequency interval and each carrier is orthogonal in an effective symbol time period determined by a reciprocal of the frequency interval. A demodulation device, which receives the OFDM signal as input, orthogonal detection means for obtaining a complex detection vector of the OFDM signal based on the local oscillation signal, and local oscillation means for generating a local oscillation signal to be supplied to the orthogonal detection means; A phase rotation unit that receives an output of the quadrature detection unit as an input and rotates the phase of an input signal according to a phase control signal, and performs a Fourier transform for each symbol on a complex detection vector of the OFDM signal that is an output of the phase rotation unit. Fourier transform means for obtaining a demodulated vector including each of the modulated data of Data identification means for assigning a reference vector corresponding to a specified area to each demodulation vector as a demodulation vector as input, reception status monitoring means for monitoring an error status of demodulation data as an input of the output of the data identification means, The demodulation vector and the output of the data identification means as input,
Phase rotation calculating means for calculating a phase difference between a demodulation vector and a reference vector corresponding to each demodulation vector, and a phase offset generating means for outputting a predetermined phase offset according to an output of the reception status monitoring means, Adding means for adding and outputting the output of the phase rotation means as a first input and the output of the phase offset generating means as a second input; smoothing the output of the adding means as an input; An OFDM demodulator comprising: a smoothing means for outputting a phase control signal. 2. An OFDM system comprising an input OFDM signal, which is an orthogonal frequency division multiplexed signal, in which a plurality of carriers are frequency-multiplexed at a constant frequency interval, and each carrier is orthogonal in an effective symbol time period determined by a reciprocal of the frequency interval. A demodulation device, comprising: a quadrature detection unit that receives the OFDM signal as input and obtains a complex detection vector of the OFDM signal based on a local oscillation signal; and a frequency control signal that generates a frequency control signal based on an output of the quadrature detection unit. Generating means, a local oscillation means for generating a local oscillation signal to be supplied to the quadrature detection means, and varying its frequency based on a frequency control signal generated by the frequency control signal generation means, and an output of the quadrature detection means Is a Fourier transform of a complex number vector of the OFDM signal for each symbol, and includes modulation data of each of a plurality of carriers. Fourier transforming means for obtaining a demodulated vector, data discriminating means for receiving a demodulated vector as an output of the Fourier transforming means as input, and outputting a reference vector corresponding to a prescribed area in correspondence with each demodulated vector, and the data discriminating means Receiving status monitoring means for monitoring the error status of demodulated data with the output of the input as input, and the output of the demodulation vector and data identification means as input,
Phase rotation calculating means for calculating a phase difference between a demodulation vector and a reference vector corresponding to each demodulation vector, and a phase offset generating means for outputting a predetermined phase offset according to an output of the reception status monitoring means, A first adder that outputs the output of the phase rotation amount calculator as a first input, adds the output of the phase offset generator to a second input, and adds and outputs both the outputs; An OFDM demodulator comprising: smoothing means for smoothing; and second adding means for adding an output of the smoothing means to a frequency control signal supplied to the local oscillation means. 3. An OFDM signal which is an orthogonal frequency division multiplexed signal in which a plurality of carriers are frequency-multiplexed at a fixed frequency interval and each carrier is orthogonal in an effective symbol time period determined by a reciprocal of the frequency interval. An OFDM receiving apparatus comprising: a tuner unit that selects from a received signal based on a local oscillation signal; and a first local oscillation unit that generates the first local oscillation signal and varies the frequency based on a frequency control signal. The OFDM signal selected by the tuner unit is used as an input,
Orthogonal detection means for obtaining a complex detection vector of an OFDM signal based on a second local oscillation signal; and a frequency control signal for generating a frequency control signal to be supplied to the first local oscillation means based on an output of the orthogonal detection means Generating means; a local oscillation means for generating a second local oscillation signal to be supplied to the quadrature detection means; a Fourier transform for each symbol of a complex vector of an OFDM signal output from the quadrature detection means; Fourier transforming means for obtaining a demodulated vector including each modulated data, and data identifying means for outputting a reference vector corresponding to a specified area with a demodulated vector output from the Fourier transforming means as an input, corresponding to each demodulated vector. And receiving status monitoring means for monitoring the error status of demodulated data with the output of the data identification means as input, Serial inputs the output of the demodulation vectors and data identifying means,
Phase rotation calculating means for calculating a phase difference between a demodulation vector and a reference vector corresponding to each demodulation vector, and a phase offset generating means for outputting a predetermined phase offset according to an output of the reception status monitoring means, A first adder that outputs the output of the phase rotation amount calculator as a first input, adds the output of the phase offset generator to a second input, and adds and outputs both the outputs; An OFDM demodulator comprising: smoothing means for smoothing; and second adding means for adding an output of the smoothing means to a frequency control signal supplied to the first local oscillation means. . 4. The OFDM apparatus according to claim 1, wherein said phase rotation amount calculation means calculates a phase rotation amount for a predetermined carrier among a plurality of carriers.
Demodulator. 5. The phase rotation amount calculating means calculates a phase difference between a demodulation vector and a reference vector corresponding to each demodulation vector, and then averages and outputs a symbol unit. Item 4. The OFDM demodulator according to any one of Items 1, 2, and 3. 6. The apparatus according to claim 1, wherein said reception status monitoring means uses a correction status of an error correction code in a result obtained by decoding digital data transmitted from a reference vector. OFDM demodulator. 7. The reception status monitoring means according to claim 1, wherein a state of a metric value used for Viterbi decoding for decoding digital data transmitted from a reference vector is used. Or the OFDM demodulator according to any one of the above. 8. The apparatus according to claim 1, wherein said reception status monitoring means uses a synchronization state of a data frame structure as a result of decoding digital data transmitted from a reference vector. OFDM demodulator.