JP2003229832A - Diversity receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diversity receiver capable of substantially selecting an antenna and stably performing reception. <P>SOLUTION: In this diversity receiver provided with a plurality of antennas for receiving a signal subjected to OFDM (orthogonal frequency division multiplexing) modulation, variable attenuators 9 to 12 attenuate received signals from the antennas 1 to 4 respectively, the respective attenuation outputs are synthesized, a guard correlator 20 detects a correlation between baseband I and Q signals obtained by orthogonally detecting a synthesized output in a guard interval period, and the attenuation quantity of the variable attenuators in a period corresponding to a guard interval section under the control of a diversity control circuit 22 is controlled on the basis of whether or not the peak level of a correlation output in the guard interval period increases so that an automatic frequency correction signal outputted from an AFC circuit 24 may be maintained to be a value just before a sudden change in predetermined period attenuation period when attenuation quantity is suddenly changed to a maximum value or zero. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver that receives a broadcast signal modulated (OFDM modulated) by an orthogonal frequency division multiplexing system.

[0002]

2. Description of the Related Art 1OFD of OFDM modulated broadcast signal
The M transmission symbol period includes an effective symbol section and a guard interval section. The effective symbol period is a signal period required for data transmission. The guard interval is for preventing intersymbol interference such as multipath, and is a cyclic copy of the last predetermined period length portion of the effective symbol section to the beginning of the effective symbol section.

Diversity receivers for receiving OFDM modulated broadcast signals such as digital terrestrial television broadcast signals are known. A conventional diversity receiver of this type is proposed by the applicant (Japanese Patent Application No. 2000-38005).

This diversity receiver detects the received signal level in a diversity receiver in which received signals from a plurality of antennas are attenuated by variable attenuators, the attenuated outputs are combined, and the combined output is demodulated into a baseband signal. , When the attenuation amount of one variable attenuator in the variable attenuator is switched during the period corresponding to the guard interval section based on the detected reception signal level and the reception signal level rises by switching the attenuation amount, the guard interval section The attenuation amount of the one variable attenuator is changed stepwise at a timing corresponding to the period corresponding to.

[0005]

However, even if the attenuation amount of the variable attenuator is controlled as described above, since the received signal level also includes a noise component, the received signal level is low and the C / N ratio is low. In a bad reception condition, when the received signal level of the OFDM modulation signal is low and there is an antenna whose output of the low noise amplifier is almost only a noise component, the attenuation amount of the variable attenuator of the system is set to 0 and other When the signal from the antenna is combined with the signal amplified by the low noise amplifier, the power of the noise component is added, the received signal level increases, and the diversity control circuit determines that the receiving condition is good. Actually, there was a problem that C / N became worse.

On the other hand, there is also a problem that the frequency correction of the baseband signal, which is the detection output, cannot be performed correctly for a certain period by controlling the attenuation amount of the variable attenuator.

An object of the present invention is to provide a stable diversity receiver by improving the reliability of substantial selection of antennas.

[0008]

A diversity receiver of the present invention is a diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol section and a guard interval section. Therefore, the variable attenuating means for attenuating the received signals from the plurality of antennas, the demodulating means for synthesizing the outputs from the variable attenuating means and demodulating the synthesized output, and the baseband signal obtained by the demodulating means Attenuation amount control means for changing the attenuation amount of the variable attenuating means in the period corresponding to the guard interval section, and when the attenuation amount of the variable attenuating means is suddenly changed from the maximum value to the minimum value, or from the minimum value to the maximum value. Received OFDM by receiving correlation output when suddenly changing to
Automatic frequency control means for holding the automatic frequency correction signal for correcting the deviation between the frequency of the modulation wave and the frequency of the transmission OFDM modulation wave at a value immediately before the sudden change of the attenuation amount for a predetermined period. Characterize.

The diversity receiver of the present invention is a diversity receiver including a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol section and a guard interval section. Corresponding to the guard interval section of the baseband signal obtained by the demodulating means, and the variable attenuating means for respectively attenuating the received signals from the Correlation detecting means for detecting the correlation of the period, and whether or not the peak level of the correlation output in the period corresponding to the guard interval section is increased, the attenuation amount of the variable attenuating means is set in the period corresponding to the guard interval section. The damping amount control means to be changed and the damping amount of the variable damping means are suddenly changed from the maximum value to the minimum value. Time, or when the value is suddenly changed from the minimum value to the maximum value, the automatic frequency correction signal for receiving the correlation output and correcting the difference between the frequency of the reception OFDM modulated wave and the frequency of the transmission OFDM modulated wave is set for a predetermined period. , Automatic frequency control means for holding the value immediately before the sudden change of the attenuation amount,
It is characterized by having.

The diversity receiver of the present invention is a diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol section and a guard interval section. Corresponding to the guard interval section of the baseband signal obtained by the demodulating means, and the variable attenuating means for respectively attenuating the received signals from the Correlation detection means for detecting the correlation of the period, the power detection means for detecting the power of the period corresponding to the guard interval section of the baseband signal obtained by the demodulation means, the power output of the period corresponding to the guard interval section The period corresponding to the guard interval interval based on whether the peak level has increased When the attenuation amount control means for changing the attenuation amount of the variable attenuation means and the attenuation amount of the variable attenuation means are suddenly changed from the maximum value to the minimum value or when the attenuation value is suddenly changed from the minimum value to the maximum value, the correlation output is A predetermined period of automatic frequency correction signal for receiving and correcting the difference between the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave,
Automatic frequency control means for holding the value immediately before the sudden change of the attenuation amount.

According to the diversity receiver of the present invention,
Since the automatic frequency correction signal is held at the value immediately before the sudden change in the attenuation amount for a predetermined period, stable diversity control can be performed without adversely affecting the automatic frequency control.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A diversity receiver according to the present invention will be described below with reference to an embodiment.

A diversity receiver A according to an embodiment of the present invention is constructed as shown in FIG.

In the diversity receiver A, the RF signals received by the antennas 1, 2, 3, 4 are amplified by the low noise amplifiers 5, 6, 7, 8 respectively, and then the variable attenuators 9, 10, 11, respectively. After being attenuated at 12, the mixture is input to the mixer 13 for synthesis, and the output of the mixer 13 is supplied to the tuner 14.

The tuner 14, which has received the combined output from the mixer 13, amplifies the combined output, frequency-converts it, and limits the band to convert it into an intermediate-frequency signal. The intermediate frequency signal output from the tuner 14 is an AD converter 15
To a digital signal, and the converted digital signal is supplied to the quadrature detector 16 for quadrature detection,
Convert to baseband I and Q signals.

The baseband I and Q signals output from the quadrature detector 16 are supplied to the effective symbol extraction circuit 17, and based on the timing signal (FFT-WINDOW) indicating the effective symbol section output from the timing reproduction circuit 21, In the effective symbol extraction circuit 17, only the signal in the period corresponding to the effective symbol is fetched from the baseband I and Q signals, and the signal in the period corresponding to the effective symbol section is F.
The data is supplied to the FT circuit 18, FFT processing is performed in the FFT circuit 18 to demodulate the OFDM modulated signal to separate into information for each carrier, and the information is supplied to the demapper circuit 19 to be demapped and transmitted as demodulated data.

On the other hand, the baseband I and Q signals output from the quadrature detector 16 are supplied to the guard correlator 20, and the input baseband I and Q signals of the guard correlator 20 and the baseband I and Q signals are effective. The product of the delayed baseband I and Q signals delayed by the time width of the symbol period is integrated over the time width of the guard interval period, and the integration is sequentially performed for each sample period for A / D conversion in the A / D converter 15. The correlation output is obtained by performing the shift, the correlation output is supplied to the timing reproduction circuit 21, the timing of the OFDM symbol is obtained from the peak position of the correlation output, and the timing signal (FFT-WINDOW) is sent to the effective symbol extraction circuit 17. .

Further, the correlation output CORR output from the guard correlator 20 and the timing signal (FFT-WINDOW
W) is supplied to the diversity control circuit 22, and an attenuation amount control signal for controlling the attenuation amount of the variable attenuators 9, 10, 11, 12 from the diversity control circuit 22 based on the correlation output CORR and the timing signal (FFT-WINDOW). CONT1, CONT2, CONT3, and CONT4 are sent to the variable attenuators 9, 10, 11, and 12, respectively,
The variable attenuators 9, 10, 11, 1 so that the output level of the mixer 13, that is, the combined reception signal level becomes high.
Control the amount of attenuation of 2.

In this way, the variable attenuators 9, 10, 1 are maintained with the attenuation amount of one or more variable attenuators maintained at 0.
The attenuation amounts of 1 and 12 are sequentially controlled to control the signal level input to the tuner 14 to be maximum.

The correlation output CORR is also supplied to an automatic frequency control circuit (AFC circuit) 24 which operates as an integral filter, and the correlation output CORR is filtered by the integral filter to output the output from the AFC circuit 24 based on the correlation output CORR. The oscillation frequency control signal is supplied to the numerically controlled oscillator of the quadrature detector 16 to correct the deviation between the frequency of the reception OFDM modulated wave and the frequency of the transmission OFDM modulated wave.

In the AFC circuit 24, the phase of the peak of the correlation output output from the guard correlator 20 is received OF.
The fact that it corresponds to the difference between the frequency of the DM modulation wave and the frequency of the transmission OFDM modulation wave is used.

The AFC circuit 24 has an amplifier 26 for determining a loop gain, an adder 25 for adding the output of the amplifier 26 and the correlation output CORR, a switch means 29 for selectively turning on / off the addition output, and an output of the switch means 29. Is delayed by one symbol period to output a delayed output to the amplifier 26, and an integrating filter composed of a switch means 30 for selectively turning on and off the input end and the output end of the delay device 27. The input is sent to the quadrature detector 16 as an oscillation frequency control signal.

The switch means 29 controls the switch means 29 to be in the OFF state for two symbol periods after the control signal for rapidly changing the attenuation amount of the variable attenuator from the diversity control circuit 22 to the minimum or maximum is output, and the switch means 30. Is turned on to hold the output from the 2-symbol period integration filter.

First, the operation of the diversity control circuit 22 will be described with reference to the timing charts shown in FIG. 2, FIG. 3, FIG. 4 and FIG. 5, taking the attenuation control signal CONT1 as an example.

In the diversity receiver A, the timing signal (FFT-WINDOW) indicates the period corresponding to the effective symbol section when the potential is high, and the period corresponding to the guard interval section when the potential is low. The attenuation amount control signal CONT1 is a signal for controlling the attenuation amount of the variable attenuator 9, and when the level of the attenuation amount control signal CONT1 is the maximum, the attenuation amount is controlled to 0, and the attenuation amount control signal CONT.
The amount of attenuation is maximum when the level of 1 is minimum. Also in the case of the attenuation amount control signals CONT2, 3, 4, the attenuation amount control signal C
This is similar to the case of ONT1.

Here, the diversity control circuit 22 uses the correlation output CORR to judge whether or not the reception condition is improved. In the diversity control circuit 22, the attenuation amount of the variable attenuators 9, 10, 11, 12 is changed during the period when the timing signal (FFT-WINDOW) is low potential, that is, during the period corresponding to the interval of the guard interval.

In FIG. 2, in order to prevent the input of the mixer 13 from disappearing, at least one of the variable attenuators 10, 11 and 12 is set to 0 and the initial state is set to 0. The level of the control signal CONT1 is minimum, that is, the attenuation amount of the variable attenuator 9 is maximum. Here, in order to evaluate the signal received by the antenna 1,
In the section where the timing signal (FFT-WINDOW) is at a low potential (see FIG. 2A), the attenuation control signal CONT1
Of the variable attenuator 9 (see FIG. 2B).
The attenuation of is set to 0.

As a result, the signal received by the antenna 1 is also combined by the mixer 13 and input to the tuner 14. At this time, in FIG. 2, the peak level of the correlation output CORR is higher than that of the previous correlation output CORR. The figure also shows the case where the temperature also rises (see FIG. 2 (c)).
In this case, if the mixer 13 combines the signals received by the antenna 1 and combines them, the output level of the mixer 13 increases, and it is determined that the reception condition is improved. In order to avoid the change, the level of the attenuation control signal CONT1 is temporarily returned to the minimum at the timing when the timing signal (FFT-WINDOW) becomes high potential, and thereafter, as shown by the arrow in FIG. The level of the attenuation amount control signal CONT1 is increased stepwise until the maximum level in a section where FFT-WINDOW) is at a low potential.

In the case of FIG. 3, the initial state of the receiver is shown in FIG.
However, the timing signal (FFT-WI
In the section where NDOW) becomes low potential (see FIG. 3A),
Maximize the level of the attenuation control signal CONT1 (see FIG.
FIG. 3B shows a case where the level of the correlation output CORR is lowered by setting the attenuation amount of the variable attenuator 13 to 0 (see FIG. 3C).

In this case, it is considered that the level of the output signal of the mixer 13 is lowered by combining the signals received by the antenna 1 in the mixer 13, and the peak level of the correlation output CORR is lowered, Since it is determined that the reception conditions have deteriorated, the timing signal (FF
The level of the attenuation amount control signal CONT1 is returned to the minimum at the timing when (T-WINDOW) becomes high potential (FIG. 3 (b)).
reference).

When the attenuation amount of the variable attenuator 9 is set to 0 during the period corresponding to the guard interval section in the state where the attenuation amount of the variable attenuator 9 is maximum as in the case shown in FIG. When the peak level of the correlation output CORR in the period corresponding to the next guard interval section is higher than the peak level of the correlation output in the period corresponding to the preceding guard interval section, it corresponds to the next guard interval section. The maximum amount of attenuation of the variable attenuator 9 is achieved during the period corresponding to the guard interval section following that period, that is, the original amount is restored, and the attenuation amount of the variable attenuator 9 is sequentially reduced to 0 during the period corresponding to the subsequent guard interval section. It will be reduced stepwise.
This makes it possible to set the amount of attenuation that can be stably received.

Further, as in the case shown in FIG. 3, the attenuation amount of the variable attenuator 9 is set to 0 in the period corresponding to the guard interval section in the state where the attenuation amount of the variable attenuator 9 is maximum. At this time, when the peak level of the correlation output CORR during the next guard interval period is lower than the peak level of the correlation output during the period corresponding to the preceding guard interval section, the variable attenuator 9
The attenuation amount of the variable attenuator 9 is maximized from the period corresponding to the subsequent guard interval section when the attenuation amount of 0 is set to 0, that is, the original amount is restored. This makes it possible to set the amount of attenuation that can be stably received.

In the case of FIG. 4 as well, the variable attenuators 10, 11, 1 are used.
Among the two, at least one or more have the attenuation amount of 0, and the level of the attenuation amount control signal CONT1 is maximum, that is, the attenuation amount of the variable attenuator 9 is 0 in the initial state. Here, in order to evaluate the signal received by the antenna 1, the attenuation control signal C is applied in a section where the timing signal (FFT-WINDOW) has a low potential (see FIG. 4A).
The level of ONT1 is minimized (see FIG. 4B), and the attenuation amount of the variable attenuator 9 is maximized.

As a result, the signals received by the antenna 1 are attenuated, combined by the mixer 13 and input to the tuner 14. As a result, in FIG. 4, the correlation output C
It shows a case where the peak level of the ORR is increased (see FIG. 4 (c)). In this case, if the signal received by the antenna 1 is attenuated, it is determined that the level of the correlation output CORR rises and the reception condition is improved, and then the timing signal (FFT-WINDOW) becomes high potential once. The level of the attenuation amount control signal CONT1 is returned to the maximum level (see FIG. 4B), and thereafter, as shown by the arrow in FIG. 4, the timing signal (FFT-WINDOW) of the attenuation amount control signal CONT1 is in the low potential section. The level is changed stepwise until the level becomes minimum (see FIG. 4B).

In the case of FIG. 5, the initial state is the same as that of FIG. 4, but the timing signal (FFT-WINDOW
By setting the level of the attenuation amount control signal CONT1 to the minimum level (see FIG. 5B) and the attenuation amount of the variable attenuator 9 to the maximum level in the section where W) becomes a low potential (see FIG. 5A). This shows a case where the peak level of the correlation output CORR has decreased (see FIG. 5 (c)). In this case, it is considered that the level of the output signal of the mixer 13 is decreased by combining the signals received by the antenna 1 in the mixer 13, and the peak level of the correlation output CORR is decreased, and the reception condition is Since it is determined that the timing signal (FFT-WINDOW) becomes high potential, the level of the attenuation amount control signal CONT1 is returned to the maximum (FIG. 5).
(See (b)).

As shown in FIG. 4, when the attenuation amount of the variable attenuator 9 is maximized in the period corresponding to the guard interval section in the state where the attenuation amount of the variable attenuator 9 is 0, When the peak level of the correlation output CORR in the next guard interval period is higher than the peak level of the correlation output in the period corresponding to the preceding guard interval section, the peak level of the correlation output CORR follows the period corresponding to the next guard interval section. The attenuation amount of the variable attenuator 9 is set to 0 in the period corresponding to the guard interval section,
That is, the variable amount is restored to the original value, and the attenuation amount of the variable attenuator 9 is increased stepwise to the maximum in the period corresponding to the subsequent guard interval section. This makes it possible to set the amount of attenuation that can be stably received.

Further, as in the case shown in FIG. 5, the attenuation amount of the variable attenuator 9 is maximized in the period corresponding to the guard interval section when the attenuation amount of the variable attenuator 9 is 0. At this time, when the peak level of the correlation output CORR in the period corresponding to the next guard interval section is lower than the peak level of the correlation output in the period corresponding to the preceding guard interval section, the attenuation of the variable attenuator 9 is reduced. The attenuation amount of the variable attenuator 9 is set to 0 from the period corresponding to the guard interval section that follows when the amount is maximized, that is, the original amount is restored. This makes it possible to set the amount of attenuation that can be stably received.

In this way, the variable attenuators 9, 10, 1 are maintained with the attenuation amount of one or more variable attenuators maintained at 0.
The attenuation amounts of 1 and 12 are sequentially controlled to control the signal level input to the tuner 14 to be maximum.

As described above, since the attenuation amount of the variable attenuator is controlled so that the peak level of the correlation output CORR is referred to detect the signal level, the influence of the noise component is reduced and stable diversity reception is achieved. Can be done.

Next, the operation of the AFC circuit 24 will be described with reference to FIG.
It will be described based on the timing chart of FIG. FIG. 6A shows a timing signal (FFT-WINDOW), where the low potential section shows a period corresponding to the guard interval section, and the high potential section shows a period corresponding to the effective symbol section.

In the example of FIG. 6, the diversity control circuit 22
Under the control of, the attenuation amount in the variable attenuator 9 is controlled from the maximum value to 0 in the n-th guard interval section (see FIG. 6B), and the attenuation amount in the variable attenuator 10 is 0 in the illustrated section. (See FIG. 6 (c)), the attenuation amounts in the variable attenuators 11 and 12 are maintained at the maximum in the illustrated section (see FIG. 6 (d) and FIG. 6 (e)), 1 or more. Set the attenuation of the variable attenuator to 0
It has been maintained at.

FIG. 6F schematically shows the baseband I and Q signals output from the quadrature detector 16, and FIG.
In FIG. 6F, the solid line and the broken line are shown in FIG.
This corresponds to the guard interval section shown in (a).
FIG. 6 (g) schematically shows the baseband I and Q signals delayed by the effective symbol period in order to obtain the guard correlation in the guard correlator 20, and in FIG. 6 (g), the solid line hatched portion and the broken line hatched portion. Corresponds to the guard interval section, and the solid diagonal line corresponds to the solid diagonal line portion in FIG. However, since the correlation output CORR output from the guard correlator 20 is a guard interval by copying the last predetermined length portion of the effective symbol period to the beginning of the effective symbol period, as shown in FIG. 6 (h). Become.

As is clear from FIG. 6 (h), the correlation output CORR is also in the period in which the time width in which the attenuation amount of the variable attenuator 9 is controlled from the maximum value to 0 is included in the time width to be integrated by the guard correlator 20. Be adversely affected. If AFC is performed based on the peak of the correlation output CORR that has been adversely affected,
The FC is also adversely affected and the accuracy of the AFC is reduced.

The period in which the AFC is adversely affected is, when the attenuation amount of the variable attenuator 9 is controlled from the maximum value to 0 in the nth guard interval period, near the beginning of the nth symbol section and the (n + 1) th symbol interval. It is a period including the vicinity of the beginning of the symbol section, that is, the period in which the attenuation amount of the variable attenuator 9 is controlled from the maximum value to 0, in the time width to be integrated by the guard correlator 20, which is the section a in FIG. And a section indicated by section b.

Therefore, the diversity control circuit 22
From the generation of the signal for changing the attenuation amount of the variable attenuator 9 output from the maximum value to 0, until the influence of changing the attenuation amount of the variable attenuator 9 from the maximum value to 0 disappears, that is, the variable attenuator. The period from when the attenuation amount of 9 is set to 0 from the maximum value to the end of the 2 OFDM transmission symbol period (see FIG.
During the period c) in (h), the switch means 29 is turned off and the switch means 30 is turned on by the output from the diversity control circuit 22.

As a result, during this period, the guard correlator 2
The added output of the correlation output CORR output from 0 and the output of the amplifier 26 is not used for AFC, and the output delayed by the delay device 27, that is, when the attenuation amount of the variable attenuator 9 is set to 0 from the maximum value. AFC is performed by the output held in the correlation output CORR.
It is possible to avoid adverse effects such as deterioration of the accuracy of.

Although the case where the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 is illustrated, the attenuation amount of the variable attenuator 9 is set to 0.
The same applies to the case where the variable attenuator 10,
The same applies to cases 11 and 12. Further, when the attenuation amount is controlled in a stepwise manner as shown in FIGS. 2 and 4,
Since the change in the attenuation amount corresponding to the step of each stair is small, the control signal for controlling the switch means 29 and 30 is not output from the diversity control circuit 22 to the AFC circuit 24.

As described above, when the diversity receiver A is used, the variable attenuator 9 has a maximum value of 0 until the influence of the variable attenuator 9 becomes zero. From 0 to 2 OFD
During the period until the end of the M transmission symbol period, the automatic frequency correction signal for receiving the correlation output and correcting the deviation between the frequency of the reception OFDM modulated wave and the frequency of the transmission OFDM modulated wave is set to the value immediately before the sudden change of the attenuation amount. Because I tried to keep it
It is possible to perform stable diversity reception without adversely affecting the AFC operation.

In the above description, the switch means 29 is in the off state and the switch means 30 is in the on state during the period from when the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 to the end of the 2 OFDM transmission symbol period. Although the case of controlling by the output from the diversity control circuit 22 has been described, the period from when the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 to the end of one OFDM transmission symbol period,
Even if the switch means 29 is turned off and the switch means 30 is turned on by the output from the diversity control circuit 22, the above-mentioned adverse effects are almost alleviated.

In the diversity receiver A,
The control of the AFC circuit 24 by the correlation output CORR from the correlation detector 20 and the output from the diversity control circuit 22 is left unchanged, and the baseband I and Q signals output from the quadrature detector 16 are received to guard the baseband signal. A power detector is newly provided to detect the power in the period corresponding to the interval section, and the power signal RX-POWER detected by the power detector is supplied from the diversity control circuit 22 in place of the correlation output CORR, and the power is supplied. Signal R
Attenuation control signal CONT1 based on X-POWER,
2, 3 and 4 may be generated, and even in this case, the same effect as in the case of the diversity receiver A can be obtained.

[0051]

As described above, according to the diversity receiver of the present invention, the reliability of antenna selection is substantially improved and stable diversity reception is achieved without adversely affecting the AFC operation. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a diversity receiver according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the diversity receiver according to the embodiment of the present invention.

FIG. 3 is a timing chart for explaining the operation of the diversity receiver according to the embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the diversity receiver according to the embodiment of the present invention.

FIG. 5 is a timing diagram for explaining the operation of the diversity receiver according to the embodiment of the present invention.

FIG. 6 is a timing chart for explaining the operation of the diversity receiver according to the embodiment of the present invention.

[Explanation of symbols]

A diversity receiver 9-12 Variable attenuator 13 Mixer 14 Tuner 15 AD converter 16 Quadrature detector 17 Effective symbol extraction circuit 18 FFT circuit 20 Guard correlator 21 Timing recovery circuit 22 Diversity control circuit 24 AFC circuit 25 adder 27 delay device 29 and 30 switch means

[Procedure amendment]

[Submission date] April 3, 2002 (2002.4.3)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

Diversity receivers for receiving OFDM modulated broadcast signals such as digital terrestrial television broadcast signals are known. There is a conventional diversity receiver of this type proposed by the applicant (Japanese Patent Application No. 2000-3800005 ).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhide Okuhata             1-14-6 Dogenzaka, Shibuya-ku, Tokyo Stocks             Company Kenwood F-term (reference) 5K022 DD01 DD13 DD23 DD33                 5K059 BB01 CC03 DD02 EE00                 5K067 AA02 AA24 BB04 CC02 CC24                       EE02 EE10

Claims (5)

[Claims] 1. A diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol section and a guard interval section, each receiving signal from each of the plurality of antennas. Variable attenuating means for attenuating, demodulating means for synthesizing outputs from the variable attenuating means, demodulating and outputting the synthesized output, and variable attenuating means for a period corresponding to the guard interval section of the baseband signal obtained by the demodulating means Attenuation control means for changing the attenuation amount of the and the attenuation value of the variable attenuation means when the attenuation value is suddenly changed from the maximum value to the minimum value or when the attenuation value is suddenly changed from the minimum value to the maximum value. An automatic frequency correction signal for correcting the difference between the frequency of the OFDM modulated wave and the frequency of the transmitted OFDM modulated wave is used for a predetermined period of time in which the amount of attenuation is sharp. A diversity receiver, comprising: an automatic frequency control means for holding the value immediately before the change. 2. A diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal, one symbol period of which includes an effective symbol section and a guard interval section, each receiving signal from each of the plurality of antennas. The variable attenuating means for attenuating, the demodulating means for synthesizing the outputs from the variable attenuating means, demodulating and outputting the synthesized output, and the correlation of the period corresponding to the guard interval section of the baseband signal obtained by the demodulating means are detected. And a damping amount control means for changing the damping amount of the variable damping means in the period corresponding to the guard interval section based on whether or not the peak level of the correlation output in the period corresponding to the guard interval section has increased. And when the attenuation of the variable damping means is suddenly changed from the maximum value to the minimum value, or from the minimum value to the maximum value. When a sudden change is made to, the automatic frequency correction signal for receiving the correlation output and correcting the difference between the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave is the value immediately before the sudden change of the attenuation amount for a predetermined period. A diversity receiver, comprising: an automatic frequency control means held in. 3. A diversity receiver comprising a plurality of antennas for receiving an OFDM-modulated signal, one symbol period of which comprises an effective symbol section and a guard interval section, each receiving signal from the plurality of antennas. The variable attenuating means for attenuating, the demodulating means for synthesizing the outputs from the variable attenuating means, demodulating and outputting the synthesized output, and the correlation of the period corresponding to the guard interval section of the baseband signal obtained by the demodulating means are detected Correlation detection means, power detection means for detecting the power in the period corresponding to the guard interval section of the baseband signal obtained by the demodulation means, and whether the peak level of the power output during the period corresponding to the guard interval section has increased Change the attenuation amount of the variable attenuator during the period corresponding to the guard interval section based on whether or not When the attenuation amount of the attenuation control means and the attenuation amount of the variable attenuation means are suddenly changed from the maximum value to the minimum value or when the attenuation value is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave is received by receiving the correlation output. And an automatic frequency control means for holding the automatic frequency correction signal for correcting the deviation between the frequency of the transmitted OFDM modulated wave and the value immediately before the sudden change of the attenuation amount for a predetermined period. Receiving machine. 4. The diversity receiver according to claim 1, 2 or 3, wherein the automatic frequency control means is an integral filter having a correlation output as an input. 5. The diversity receiver according to claim 1, 2 or 3, wherein the attenuation amount is suddenly changed during a period in which the automatic frequency correction output is held at a value immediately before the sudden change of the attenuation amount. A diversity receiver characterized in that it is at least one symbol period from time to time.