JP2002290371A - Orthogonal frequency division multiplex transmission signal receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OFDM receiver, in which the performance of frequency synchronization and phase fluctuation elimination of a received signal can be enhanced even when a disturbing wave exists. SOLUTION: The OFDM receiver includes a demodulation circuit 14 that converts an OFDM signal comprising an effective period and a guard period into a demodulation signal on a frequency axis, a delay circuit 19 that delays the demodulation signal for the effective period, a correlation detection circuit 18 that obtains the correlation between a demodulation signal before delay and a demodulation signal after delay to output a correlation signal, a deviation detection circuit 21 that detects a deviation of the correlation signal from a reference value for other periods than the guard period, a correction circuit 22 that corrects the correlation signal for the guard period by using the deviation, an error detection circuit 23 that uses the corrected correlation signal to detect a frequency error of the demodulation signal, and a control circuit 24 that smoothes the signal denoting the frequency error and feeding back the result to the demodulation circuit 14 to control the detection in the demodulation circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an orthogonal frequency division multiplex (OFDM).
iplex) The present invention relates to frequency synchronization and phase noise removal in a transmission signal receiving apparatus.

[0002]

2. Description of the Related Art In recent years, digital transmission systems using OFDM transmission signals have been put to practical use, particularly in the field of terrestrial digital broadcasting. The OFDM transmission method is a method of transmitting transmission data by distributing it to a plurality of carriers, and is known as a method resistant to multipath interference because one symbol period is longer than that of single carrier transmission. Also, OF
In the DM transmission method, generally, a redundant period called a guard period is provided before an effective period in which data is actually transmitted, so that the influence of a multipath delay wave can be further reduced. .

As a method of detecting a frequency error in an OFDM receiver, a method using the guard period is known. Hereinafter, a method of detecting a frequency error using the guard period will be described.

FIG. 6 is a block diagram showing a configuration of a conventional OFDM receiver. This OFDM receiver is described in Japanese Patent No. 3074103.

In FIG. 6, an OFDM signal received by an antenna 101 is input to a tuner 102, which selects an OFDM signal of a predetermined channel and converts it into an IF (intermediate frequency) band. The output of the tuner 102 is an analog / digital converter (hereinafter, A
/ D converter) 103, and the A / D converter 10
3 to be converted into a digital signal.

The output of the A / D converter 103 is supplied to an IQ demodulation circuit 104. Here, the IQ demodulation circuit 1
A quadrature detection circuit is used as 04, and the output of the A / D converter 103 is quasi-synchronous quadrature detection and converted into a complex baseband signal by the quadrature detection circuit.

[0007] The complex baseband signal output from the IQ demodulation circuit 104 is converted to an FFT (Fast Fourier Transfer:
(Fast Fourier Transform) circuit 105. The FFT circuit 105 converts the complex baseband signal from data on the time axis to data on the frequency axis by an FFT (Fast Fourier Transform) operation. The output of the FFT circuit 105 is supplied to a demodulation circuit 106. The demodulation circuit 106
The data of each carrier is demodulated. The output of the demodulation circuit 106 is supplied to an error correction circuit 107, which decodes the error correction, that is, corrects an error occurring during transmission and decodes the received data.

The signal output from the IQ demodulation circuit 104 is branched and supplied to a correlation detection circuit 108 and a valid period delay circuit 109, respectively. The signal delayed by the valid period delay circuit 109 is supplied to the correlation detection circuit 108.

The correlation detection circuit 108 detects the correlation between these two signals during the guard period. FIG. 7A shows the correlation detection operation in the correlation detection circuit 108.
This will be described in detail with reference to FIG.

FIG. 7A shows a complex baseband signal output from the IQ demodulation circuit 104, and FIG. 7B shows a valid period delay signal output from the valid period delay circuit 109. Note that the complex baseband signal output from the IQ demodulation circuit 104 is hereinafter referred to as an IQ demodulated signal. FIG.
One symbol period of the IQ demodulated signal shown in (a) is composed of a guard period and an effective period for transmitting data.
In the guard period, the signal in the part after the valid period is copied. Therefore, when the correlation of the complex conjugate between the IQ demodulated signal and the effective period delay signal is obtained, a large correlation appears in a portion where the two coincide, as shown in FIG. 7C. In the figure, only the I component of the correlation signal is shown.

Further, when the correlation signal shown in FIG. 7 (c) is moving averaged with a guard period width, as shown in FIG. 7 (d),
A correlation signal having a peak at the beginning of the valid period is obtained. When there is no frequency error in the received OFDM signal, the peak of the correlation signal in the guard period appears only in the I component, and the Q component is almost zero. The signal shown in FIG. 7D is the output of the correlation detection circuit 108.

The output of the correlation detection circuit 108 is supplied to a timing detection circuit 110,
The timing indicating the beginning of the valid period is detected by 0. The output of the timing detection circuit 110 is the FFT circuit 1
05. The FFT circuit 105 finds a valid period using the detection signal output from the timing detecting circuit 110, and performs FFT on the IQ demodulated signal in the valid period.

The output of the correlation detection circuit 108 is ta
It is supplied to the n- ¹ circuit 111. tan ^-1 circuit 111
Finds a guard period using a detection signal output from the timing detection circuit 110, and calculates a phase angle tan ⁻¹ (Q /
Find I). When there is no frequency error in the received OFDM signal, the signal in the latter half of the valid period of the IQ demodulated signal matches the signal in the guard period of the valid period delayed signal, and therefore, FIG. 7A to FIG. As shown, the phase angle of the correlation signal becomes zero. That is, the output of the tan ^-1 circuit 111 is 0.

On the other hand, when there is a frequency error in the received OFDM signal, a phase corresponding to the frequency error exists between the signal in the latter half of the valid period of the IQ demodulated signal and the signal in the guard period of the valid period delay signal. , The magnitude of the phase angle of the correlation signal becomes a value proportional to the frequency error. Therefore, the output of the tan ^-1 circuit 111 becomes an error signal proportional to the frequency error.

The error signal output from the tan ^-1 circuit 111 is supplied to a frequency control circuit 112. The frequency control circuit 112 multiplies the supplied error signal by a gain coefficient and integrates the signal to generate a control signal for controlling the detection frequency of the IQ demodulation circuit 104. The control signal output from the frequency control circuit 112 is supplied to the IQ demodulation circuit 104. The IQ demodulation circuit 104 controls a detection frequency according to the control signal so that frequency synchronization can be achieved. Thereby, frequency synchronization in the received OFDM signal is achieved.

The prior art for performing frequency synchronization using the correlation signal in the guard period has been described above.
Using the correlation signal in the guard period, the received OF
A technique for removing a phase variation of a DM signal (received signal) is also known.

FIG. 8 is a block diagram showing the configuration of another conventional OFDM receiver. This OFDM receiver is
It is described in Japanese Patent No. 2907804. FIG.
In FIG. 6, the description of the same parts as those shown in FIG. 6 will be omitted, and only different parts will be described.

In FIG. 6, the output of the tan ^-1 circuit 111 is, as described above, the phase shift between the signal in the latter half of the valid period of the IQ demodulated signal and the signal in the guard period of the valid period delay signal. (Amount of phase fluctuation). The phase fluctuation estimating circuit 112 includes a tan ^-1 circuit 11
The amount of phase fluctuation at each sample point within one symbol period is estimated using the amount of phase fluctuation supplied from 1. The output of the phase fluctuation estimation circuit 112 is supplied to a phase correction circuit 114. The phase correction circuit 114 is a valid period delay circuit 1
13 to correct the amount of phase variation for the signal output from
Output to the FFT circuit 105.

As described above, it is possible to remove the phase noise of the tuner oscillator and the phase fluctuation of the received signal caused by the fading at the time of the mobile reception, and it is possible to suppress the deterioration of the transmission characteristic due to the phase noise.

[0020]

The conventional technique using the correlation signal in the guard period has been described above. However, the conventional technique has the following problems.

When there is strong interference such as CW (Continuous Wave) interference, the output of the correlation detection circuit 108 is a signal obtained by synthesizing a correlation signal in the absence of an interference wave and a correlation signal due to the interference wave. Becomes Therefore, even when the frequency error and the phase variation of the received OFDM signal are 0, the phase angle between the I component and the Q component of the correlation signal does not become 0, and the correct frequency error and the phase variation are detected. become unable.

Accordingly, the present invention has been made in view of the above problems, and provides an OFDM receiver capable of improving the performance of frequency synchronization and phase fluctuation removal of a received signal even when an interfering wave exists. The purpose is to:

[0023]

In order to achieve the above object, a first orthogonal frequency division multiplex transmission signal receiving apparatus according to the present invention comprises a valid period during which a data signal is transmitted, and a redundant period. A quadrature frequency division multiplex transmission signal comprising a guard period in which a data signal of the latter half of the valid period is copied is received, and the quadrature frequency division multiplex transmission signal is detected according to a set detection frequency to demodulate a demodulated signal. A demodulation circuit for outputting, a delay circuit for delaying the demodulation signal output from the demodulation circuit by the valid period, a demodulation signal before being delayed by the delay circuit, and a demodulation signal after being delayed by the delay circuit A correlation detection circuit that obtains a correlation with the correlation signal and outputs a correlation signal; and the correlation signal output from the correlation detection circuit with respect to the correlation signal in a period other than the guard period. A deviation detection circuit that detects an amount of deviation from a reference value of the signal, a correction circuit that corrects the correlation signal in the guard period using the deviation amount detected by the deviation detection circuit, and a correction circuit that corrects the correlation signal. An error detection circuit that detects a frequency error of the demodulated signal output from the demodulation circuit using the correlation signal thus obtained, and demodulates the signal that is output from the error detection circuit and that indicates the frequency error. A control circuit for controlling the setting of the detection frequency in the demodulation circuit by feeding back to the circuit.

In order to achieve the above object, a second orthogonal frequency division multiplexing transmission signal receiving apparatus according to the present invention comprises a valid period during which a data signal is transmitted and a redundant period, which is a second half of the valid period. A demodulation circuit that receives an orthogonal frequency division multiplex transmission signal composed of a guard period in which a data signal is copied and detects the orthogonal frequency division multiplex transmission signal according to a set detection frequency and outputs a demodulated signal; A delay circuit that delays the demodulated signal output from the demodulation circuit by the valid period, a demodulated signal before being delayed by the delay circuit, and a correlation between the demodulated signal after being delayed by the delay circuit. A correlation detection circuit that outputs a correlation signal, and, for the correlation signal output from the correlation detection circuit, a reference value of the correlation signal in a period other than the guard period. A displacement detecting circuit for detecting a shift amount,
A correction circuit that corrects the correlation signal in the guard period using the deviation amount detected by the deviation detection circuit, and an output from the demodulation circuit using the correlation signal corrected by the correction circuit A phase variation detection circuit for detecting a phase variation amount for each valid period of the demodulated signal;
A phase fluctuation estimating circuit for estimating a phase fluctuation amount within one symbol of the demodulated signal using a phase fluctuation amount output from the phase fluctuation detecting circuit, and a phase fluctuation amount estimated by the phase fluctuation estimating circuit; A phase correction circuit for correcting a phase variation of the demodulated signal output from the delay circuit.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an example in which frequency synchronization is performed using a correlation signal in a guard period provided in an OFDM transmission system according to the first and third embodiments of the present invention. In the second and fourth embodiments, an example in which phase noise is removed using a correlation signal in a guard period will be described. In explaining, over all the figures,
Common parts are denoted by common reference symbols.

[First Embodiment] First, in the OFDM transmission system, an OFDM signal has a plurality of symbol periods,
Further, one symbol period is divided into a valid period (data period) and a guard period, which is a redundant period provided before the valid period. In the first embodiment, a method of performing frequency synchronization using a correlation signal in a guard period will be described below.

FIG. 1 is a block diagram showing a first embodiment of the present invention.
FIG. 3 is a block diagram illustrating a configuration of an FDM receiver. FIG.
2A to 2E show OFDs of the first embodiment.
It is a figure which shows the operation | movement of the interference wave detection and correction | amendment in M receiver.

In FIG. 1, an OFDM signal received by an antenna 11 is input to a tuner 12, where the OFDM signal of a predetermined channel is selected and converted into an IF (intermediate frequency) band. The output of the tuner 12 is supplied to an analog / digital converter (hereinafter, A / D converter) 13 and is converted into a digital signal by the A / D converter 13.

The output of the A / D converter 13 is supplied to an IQ demodulation circuit 14. Here, the IQ demodulation circuit 14
The output of the A / D converter 13 is subjected to quasi-synchronous quadrature detection and converted to a complex baseband signal by the quadrature detection circuit. That is, I
The Q demodulation circuit 14 controls the A / A according to the set detection frequency.
The output of the D converter 13 is detected.

A complex baseband signal (hereinafter, referred to as an IQ demodulated signal) output from the IQ demodulation circuit 14 is
The signal is supplied to an FT (Fast Fourier Transfer) circuit 15. The FFT circuit 15 converts the IQ demodulated signal from data on the time axis to data on the frequency axis by FFT (Fast Fourier Transform) operation.

The output of the FFT circuit 15 is
6. The demodulation circuit 16 demodulates data of each carrier. The output of the demodulation circuit 16 is
The error correction circuit 17 decodes the received data by decoding the error correction, that is, by correcting the error that occurred during transmission.

The IQ demodulated signal output from the IQ demodulation circuit 14 is branched and supplied to a correlation detection circuit 18 and a valid period delay circuit 19, respectively. The signal delayed by the valid period delay circuit 19 is supplied to the correlation detection circuit 18.

The correlation detection circuit 18 detects the correlation between the IQ demodulated signal and the valid period delay signal, and obtains a correlation signal that has a peak at the beginning of the valid period. FIGS. 2A to 2D show the operation of correlation detection in the correlation detection circuit 18.
This will be described in detail with reference to FIG.

The IQ output from the IQ demodulation circuit 14
FIG. 2A shows the demodulated signal, and FIG. 2B shows the valid period delay signal output from the valid period delay circuit 19. FIG.
As shown in (a), one symbol period of the IQ demodulated signal is composed of a guard period and an effective period for transmitting data. In the guard period, the signal in the part after the valid period is copied. For this reason, I shown in FIG.
When the complex conjugate correlation between the Q demodulated signal and the effective period delay signal shown in FIG. 2B is obtained, as shown in FIG.
A large correlation appears in the part where both coincide. In this correlation detection, complex multiplication is performed on the IQ demodulated signal and the valid period delay signal to obtain a correlation signal as shown in FIG. Although FIG. 2C shows only the I component of the correlation signal, the same processing is performed on the Q component.

Further, when the correlation signal shown in FIG. 2 (c) is moving averaged with a guard period width, as shown in FIG. 2 (d),
A correlation signal having a peak at the beginning of the valid period is obtained. If there is no frequency error in the received OFDM signal, the correlation peak in the guard period appears only in the I component, and the Q component becomes almost zero. The signal shown in FIG. 2D is the output of the correlation detection circuit 18.

The output of the correlation detecting circuit 18 (FIG. 2D)
Are supplied to the timing detection circuit 20. The timing detection circuit 20 detects the timing indicating the beginning of the effective period from the signal shown in FIG. 2D and outputs the detection signal to the FFT circuit 15. FFT circuit 15
Finds a valid period using a detection signal output from the timing detection circuit 20, and performs FFT on the IQ demodulated signal in the valid period.

The output of the correlation detecting circuit 18 is branched and supplied to an offset detecting circuit 21. The operation of the offset detection circuit 21 will be described with reference to FIGS.
This will be described in detail with reference to FIG. When an interfering wave such as CW interference exists, the correlation signal between the IQ demodulated signal and the valid period delay signal is obtained by adding the interfering wave correlation component to the correlation component when no interfering wave exists, for example, as shown in FIG. ), The entire signal is a signal shifted by a certain amount from “0”. In other words, the correlation signal in the effective period when no interfering wave exists is "0", but when the interfering wave exists, a signal corresponding to the magnitude of the interfering wave is added to the entire correlation signal, and FIG. c) and FIG. 2 (d),
The signal is shifted from the “0” by a certain amount. The shift at this time is called an offset. The offset amount is
Indicates a shift amount caused by an interference wave, and refers to a difference between correlation signals when no interference wave exists and when there is an interference wave.

According to the timing signal shown in FIG. 2E supplied from the timing detection circuit 20, the offset detection circuit 21 applies the I component and the Q component of the correlation signal to each other except for the guard period. Validity period)
The average value of the correlation signal in the predetermined period T is calculated. When there is no interference, the average value of the correlation signal during the predetermined period T is almost 0. Therefore, the average value of the correlation signal is equal to the I component and the Q component (offset amount) of the correlation signal generated by the interference wave Is shown.

The output of the offset detection circuit 21 (FIG. 2)
(F) is supplied to the correction circuit 22. The correction circuit 22 corrects the offset amount for each of the I component and the Q component of the correlation signal in the guard period using the signal shown in FIG. In the correction of the offset amount, the amplitude of the signal shown in FIG. 2F in the guard period is subtracted from the I component of the correlation signal in the guard period at the timing of the signal shown in FIG. , The displacement caused by the interference wave is removed. Similar processing is performed on the Q component.

By repeating the above operation for each symbol, the influence of the interference wave is removed. If the time variation of the interference wave is slow, a correlation signal in a predetermined period other than the guard period may be obtained over a plurality of symbols, and the average value thereof may be obtained.

Next, the output of the correction circuit 22 is tan
^-1The signal is supplied to the circuit 23. tan ^-1The circuit 23
In accordance with the signal output from the
Phase angle from the I and Q components of the correlation signal during the
tan^-1(Q / I) is obtained. Received OFDM signal
If there is no frequency error, after the validity period of the IQ demodulated signal
In the guard period of the signal in the half and the valid period delay signal
The phase angle of the correlation signal becomes 0
You. That is, tan^-1The output of the circuit 23 becomes zero.
You.

On the other hand, when there is a frequency error in the received OFDM signal, a phase corresponding to the frequency error is provided between the signal in the latter half of the valid period of the IQ demodulated signal and the signal in the guard period of the valid period delay signal. , The magnitude of the phase angle of the correlation signal becomes a value proportional to the frequency error. Therefore, the output of the tan ^-1 circuit 23 becomes an error signal proportional to the frequency error.

The error signal output from the tan ^-1 circuit 23 is supplied to a frequency control circuit 24. The frequency control circuit 24 multiplies the supplied error signal by a gain coefficient and integrates the signal to generate a control signal for controlling the detection frequency of the IQ demodulation circuit 14. The control signal output from the frequency control circuit 24 is supplied to the IQ demodulation circuit 14. The IQ demodulation circuit 14 controls a detection frequency according to the control signal so as to achieve frequency synchronization. Thereby, frequency synchronization in the received OFDM signal is achieved.

With the above configuration, the O of the first embodiment is
The FDM receiver can accurately detect a frequency error with respect to a received OFDM signal even when a shift (offset) occurs in a correlation signal due to an interference wave, and can improve frequency synchronization performance when an interference wave exists. Can be improved.

[Second Embodiment] In a second embodiment of the present invention, a method for removing phase noise using a correlation signal in a guard period will be described.

FIG. 3 is a block diagram showing a configuration of the OFDM receiver according to the second embodiment. The OFDM receiver according to the second embodiment has a configuration similar to that of the first embodiment shown in FIG.
5, an effective period delay circuit 31 and a phase correction circuit 32 are arranged, and a phase fluctuation estimation circuit 33 is disposed in place of the frequency control circuit 24. The output of the phase fluctuation estimation circuit 33 is output to the phase correction circuit 32. Supply. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different components will be described below.

In FIG. 3, the output of the IQ demodulation circuit 14 is supplied to a valid period delay circuit 31, and the output of the valid period delay circuit 31 is supplied to a phase correction circuit 32.

As in the first embodiment, the correction circuit 22 removes the offset amount from the correlation signal in the guard period, and the tan ^-1 circuit 23 outputs the I signal of the correlation signal from which the offset amount has been removed. The phase angle is obtained using the component and the Q component. The output of the tan ^-1 circuit 23 indicates the amount of phase change between the signal in the latter half of the valid period of the IQ demodulated signal and the signal in the guard period of the valid period delayed signal.

The phase fluctuation estimating circuit 33 calculates tan ^-1
Using the amount of phase fluctuation output from the circuit 23, the amount of phase fluctuation at each sample point within one symbol period is estimated. The signal indicating the estimation result of the amount of phase fluctuation output from the phase fluctuation estimating circuit 33 is supplied to the phase correcting circuit 32. The phase correction circuit 32 corrects the phase fluctuation of the IQ demodulated signal output from the valid period delay circuit 31 according to the signal indicating the estimation result. As a result, the received OFD
The phase fluctuation of the M signal is removed.

With the above configuration, the O of the second embodiment is
The FDM receiver can accurately detect the phase fluctuation of the OFDM reception signal caused by the phase noise of the tuner oscillator or the fading at the time of the mobile reception even when the interference wave exists, and can detect the phase when the interference wave exists. Noise removal performance can be improved.

[Third Embodiment] In a third embodiment of the present invention, a method of performing frequency synchronization using a correlation signal in a guard period will be described.

FIG. 4 is a block diagram showing the configuration of the OFDM receiver according to the third embodiment. The OFDM receiver according to the third embodiment has a configuration in which a determination circuit 41 is provided between the offset detection circuit 21 and the frequency control circuit 24 in addition to the configuration of the first embodiment shown in FIG. It is.

In FIG. 4, the output of the offset detection circuit 21 is supplied to a correction circuit 22 and a judgment circuit 4
1 is supplied. The determination circuit 41 determines the absolute values of the offset amounts of the I component and the Q component of the correlation signal output from the offset detection circuit 21 and compares the larger absolute value with a predetermined value to determine the magnitude of the interference wave. . For example, the judgment circuit 4
1 outputs “0” when the offset amount is equal to or smaller than a predetermined value, and outputs “1” when the offset amount is larger than the predetermined value.

The output of the judgment circuit 41 is supplied to the frequency control circuit 24. The frequency control circuit 24
^{-1 The} error signal output from the circuit 23 is multiplied by a gain coefficient and integrated. When the output of the determination circuit 41 is "1", the error signal is higher than when the output of the determination circuit 41 is "0". Decrease the gain coefficient.

It is conceivable that the higher the level of the interference wave, the greater the variation of the frequency error signal due to the detection error of the offset detection circuit 21. Even in such a case, the level of the interfering wave is determined by using the above-described configuration, and when the level of the interfering wave is high, the gain of the integrator in the frequency control circuit 24 is reduced. However, frequency synchronization can be performed stably, and frequency synchronization performance can be improved.

[Fourth Embodiment] In a fourth embodiment of the present invention, a method for removing phase noise using a correlation signal in a guard period will be described.

FIG. 5 is a block diagram showing a configuration of the OFDM receiver according to the fourth embodiment. In the OFDM receiver according to the fourth embodiment, in addition to the configuration of the second embodiment shown in FIG. 3, a determination circuit 51 is provided between the offset detection circuit 21 and the phase fluctuation estimation circuit 33. Things.

In FIG. 5, the output of the offset detection circuit 21 is supplied to the correction circuit 22 and the output of the offset detection circuit 21 is determined.
1 is supplied. The determination circuit 51 determines the absolute value of the offset amount of the I component and the Q component of the correlation signal output from the offset detection circuit 21 and compares the larger absolute value with a predetermined value to determine the magnitude of the interference wave. . For example, the judgment circuit 5
1 outputs “0” when the offset amount is equal to or smaller than a predetermined value, and outputs “1” when the offset amount is larger than the predetermined value.

The output of the judgment circuit 51 is supplied to a phase fluctuation estimating circuit 33. The phase fluctuation estimating circuit 33 calculates ta
Using the phase variation output from the n- ¹ circuit 23, 1
The phase variation at each sample point in the symbol period is estimated. When the output of the determination circuit 51 is “1”, the estimation of the phase variation in the symbol is stopped. When the phase fluctuation estimation circuit 33 stops estimating the amount of phase fluctuation, the phase correction by the phase correction circuit 32 is also stopped.

It is conceivable that the larger the level of the interference wave, the larger the estimation error at the time of detecting the phase fluctuation due to the detection error of the offset detection circuit 21. Even in such a case, the level of the interfering wave is determined using the above configuration, and when the interfering wave is large, the estimation of the amount of phase fluctuation and the correction of the phase are stopped, that is, the operation of removing the phase noise is stopped. Accordingly, it is possible to suppress the deterioration of the transmission characteristics due to the malfunction of the phase noise removing circuit (the phase fluctuation estimating circuit 33 and the phase correcting circuit 32).

In the first to fourth embodiments,
Although an example has been described in which the symbol timing of the OFDM signal is detected using the correlation signal in the guard period, the present invention is not limited to this configuration. For example, when a transmission signal includes a reference signal, timing detection can be performed using the reference signal.

In the above embodiment, the case where frequency synchronization is performed using the correlation signal in the guard period and the case where phase noise removal is performed have been described. However, both may be combined.

Furthermore, each of the embodiments described above includes various stages of the invention, and various stages of the invention can be extracted by appropriately combining a plurality of constituent elements disclosed in each embodiment. Is also possible.

[0064]

As described above, according to the present invention, it is possible to realize an OFDM receiver that can improve the performance of frequency synchronization and phase fluctuation removal of a received signal even when an interference wave exists.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an operation in the OFDM receiver according to the first embodiment.

FIG. 3 is a block diagram illustrating a configuration of an OFDM receiver according to a second embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an OFDM receiver according to a third embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of an OFDM receiver according to a fourth embodiment of the present invention.

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

FIG. 7 is a diagram showing an operation in the conventional OFDM receiver.

FIG. 8 is a block diagram showing a configuration of another conventional OFDM receiver.

[Explanation of symbols]

Reference Signs List 11 antenna 12 tuner 13 analog / digital converter (A / D converter) 14 IQ demodulation circuit 15 FFT (Fast Fourier Transfer) circuit 16 demodulation circuit 17 error correction circuit 18 correlation Detection circuit 19: valid period delay circuit 20: timing detection circuit 21: offset detection circuit 22: correction circuit 23: tan- ¹ circuit 24: frequency control circuit 31: valid period delay circuit 32: phase correction circuit 33: phase fluctuation estimation circuit 41: judgment circuit 51: judgment circuit

Continued on the front page F term (reference) 5K022 DD01 DD13 DD33 DD44 5K052 AA01 AA11 BB02 BB15 CC06 DD03 EE38 FF32 GG42

Claims (10)

[Claims] 1. An orthogonal frequency division multiplex transmission signal comprising a valid period in which a data signal is transmitted, and a guard period in which a data signal in a second half of the valid period is copied. A demodulation circuit that detects the orthogonal frequency division multiplexing transmission signal according to a set detection frequency and outputs a demodulated signal; a delay circuit that delays the demodulated signal output from the demodulation circuit by the effective period; and the delay circuit A correlation detection circuit that obtains a correlation between the demodulated signal before being delayed and the demodulated signal delayed by the delay circuit and outputs a correlation signal, for the correlation signal output from the correlation detection circuit,
A shift detection circuit that detects a shift amount of the correlation signal from a reference value in a period other than the guard period, and corrects the correlation signal in the guard period using the shift amount detected by the shift detection circuit. A correction circuit, using the correlation signal corrected by the correction circuit,
An error detection circuit that detects a frequency error of a demodulated signal output from the demodulation circuit; and a demodulation circuit that smoothes a signal indicating the frequency error output from the error detection circuit and feeds back the signal to the demodulation circuit. An orthogonal frequency division multiplex transmission signal receiving apparatus, comprising: a control circuit that controls setting of a detection frequency in a circuit. 2. A method of determining the magnitude of an interference wave included in the orthogonal frequency division multiplex transmission signal using the amount of deviation detected by the deviation detection circuit, and outputting a result of the determination to the control circuit. The orthogonal frequency division multiplex transmission signal reception according to claim 1, further comprising a circuit, wherein the control circuit switches a gain for the demodulation circuit according to the determination result output from the determination circuit. apparatus. 3. The control circuit according to claim 2, wherein the gain is reduced when the determination circuit determines that the interference wave is large as compared to when the determination is that the interference wave is small. 5. The orthogonal frequency division multiplex transmission signal receiving device according to item 1. 4. The correlation detection circuit according to claim 1, wherein the correlation detection circuit obtains the correlation signal by multiplying the demodulated signal before the delay and the demodulated signal after the delay.
4. The orthogonal frequency division multiplexing transmission signal receiving apparatus according to any one of claims 3 to 3. 5. The correlation signal comprises an I component and a Q component, and the error detection circuit detects the frequency error by obtaining a phase angle using the I component and the Q component. The orthogonal frequency division multiplex transmission signal receiving apparatus according to any one of claims 1 to 4. 6. An orthogonal frequency division multiplex transmission signal comprising a valid period in which a data signal is transmitted, and a guard period in which a data signal in a second half of the valid period is copied in a redundant period. A demodulation circuit that detects the orthogonal frequency division multiplexing transmission signal according to a set detection frequency and outputs a demodulated signal; a delay circuit that delays the demodulated signal output from the demodulation circuit by the effective period; and the delay circuit A correlation detection circuit that obtains a correlation between the demodulated signal before being delayed and the demodulated signal delayed by the delay circuit and outputs a correlation signal, for the correlation signal output from the correlation detection circuit,
A shift detection circuit that detects a shift amount of the correlation signal from a reference value in a period other than the guard period, and corrects the correlation signal in the guard period using the shift amount detected by the shift detection circuit. A correction circuit, using the correlation signal corrected by the correction circuit,
A phase variation detection circuit for detecting a phase variation amount for each effective period of the demodulated signal output from the demodulation circuit; and using the phase variation amount output from the phase variation detection circuit, within one symbol of the demodulated signal. A phase fluctuation estimating circuit for estimating a phase fluctuation amount, and a phase correction circuit for correcting a phase fluctuation of a demodulated signal output from the delay circuit using the phase fluctuation amount estimated by the phase fluctuation estimating circuit. An orthogonal frequency division multiplex transmission signal receiving apparatus, comprising: 7. A magnitude of an interfering wave included in the orthogonal frequency division multiplex transmission signal is determined using the deviation amount detected by the deviation detection circuit, and a result of the determination is output to the phase fluctuation estimation circuit. The phase variation estimating circuit switches between performing and stopping the estimation of the phase variation amount according to the determination result output from the determining circuit. The orthogonal frequency division multiplex transmission signal receiving apparatus according to claim 6. 8. The phase fluctuation estimating circuit stops estimating the phase fluctuation amount when the determination circuit determines that the interference wave is large, and the phase fluctuation estimation circuit when determining that the interference wave is small. The orthogonal frequency division multiplex transmission signal receiving apparatus according to claim 6 or 7, wherein the estimation is performed. 9. The correlation detection circuit according to claim 6, wherein the correlation detection circuit multiplies the demodulated signal before being delayed and the demodulated signal after being delayed to obtain the correlation signal.
9. The orthogonal frequency division multiplexing transmission signal receiving apparatus according to any one of claims 8 to 8. 10. The correlation signal is composed of an I component and a Q component, and the phase variation detection circuit detects the phase variation amount by obtaining a phase angle using the I component and the Q component. The orthogonal frequency division multiplexing transmission signal receiving device according to claim 6, wherein: